The EU funded H2020 SOLARSCO2OL project aims to demonstrate a 2 MW supercritical CO2 (sCO2) cycle with heat provided by molten salts in a relevant industrial operational environment at the premises of an existing solar complex in Spain, composed of a 50 MW Concentrating Solar Power (CSP) plant and a 6.1 MW dual-axis tracking PV plant. The new pilot plant will consist of a purposely designed molten-salt storage system including a molten salt electric heater, a storage tank, and the salt-to-sCO2 primary heater connected to the sCO2 cycle. In specific relation to the turbomachinery, the project aims to demonstrate the reliability and the technical performance of all key components present in a simple Brayton sCO2 cycle, including the balance of plant and control systems. Ultimately, the overarching goal of the project is to serve as a stepping-stone towards hybrid sCO2 based CSP and PV plants able to provide cost-efficient, flexible, modular, scalable, and dispatchable solar power. Besides the specific demonstration objectives, and related component development and verification, the project aims to investigate the techno-economic performance of advanced hybrid CSP-PV layouts combining electric heaters and sCO2 cycles at higher temperatures, as well as the social and environmental acceptability of the proposed solutions. The project started in October 2020 and will span for a period of 4 years, with three clear phases: design optimization (up to months 18-24); manufacturing, prototype tests, detailed engineering, procurement, and installation (up to month 36); and operational experience, analysis and conclusive recommendations during the last year. The anticipated budget for the project is 15.5 M€, and it has received a grant of 10M€ from the European Commission. The SOLARSCO2OL consortium is formed by 15 partners from industry and academia with complementary expertise in the fields of CSP and turbomachinery. In this paper, an overview of the project objectives, deliverables, and time plan is presented together with a condensed first-year summary including preliminary results from the conceptualization and design phases for the demonstration plant and its components.

In recent years, large installations of renewable power generators have contributed to reduce emissions from fossil sources. Nevertheless, the main features of renewable sources are the unpredictability and the non-dispatchability, exacerbating problems of power balancing for the electrical grid. In such a context, it is essential to investigate innovative energy storage systems, both at small and large scale, to maintain the high quality level of current electrical infrastructure and to guarantee spinning-reserve capability, thus ensuring grid stability. Closed-loop systems for thermo-mechanical energy storage based on rotating machinery could be a solution to achieve this goal. Basing on the state of the art and growing knowledge of CO2 cycles for power production, this paper aims to analyze innovative energy storage solutions involving closed cycles, employing different working fluids in subcritical or supercritical conditions, including CO2, N2O and SF6. Moreover, also H2O was treated as an evolving fluid for benchmark. Such various plant configurations have been sized for a net power level of 10 MWe during charging phase, considering the same charging (compression mode) and discharging (expansion mode) phase duration of 4 h. Their techno-economic features have been compared: Round Trip Efficiency (RTE) greater than 70% is achieved, demonstrating the potential of such plants as utility scale energy storage. Among the different working fluids considered, CO2 in supercritical conditions achieves the best RTE performance.

Multidisk bladeless turbines, also known as Tesla turbines, are promising in the field of small-scale power generation and energy harvesting due to their low sensitivity to down[1]scaling effects, retaining high rotor efficiency. However, low (less than 40%) overall isentropic efficiency has been recorded in the experimental literature. This article aims for the first time to a systematic experimental characterization of loss mechanisms in a 3 kW Tesla expander using compressed air as working fluid and producing electrical power through a high-speed generator (40 krpm). The sources of losses discussed are stator losses, stator–rotor peripheral viscous losses, end-wall ventilation losses, and leakage losses. After description of experimental prototype, methodology, and assessment of measurement accuracy, the article discusses such losses aiming at separating the effects that each loss has on the overall performance. Once effects are separated, their individual impact on the overall efficiency curves is presented. This experimental investigation, for the first time, gives the insight into the actual reasons of low performance of Tesla tur[1]bines, highlighting critical areas of improvement, and paving the way to next-generation Tesla turbines, competitive with state-of-the-art bladed expanders.

This paper presents a techno-economic feasibility analysis related to a heat pump installation in a poly-generative energy district to convert the overproduction of electricity into thermal power, easy to be stored in thermal storage tanks. The heat pump technology is already used for thermal/cooling energy production in different areas although application in energy districts in a power-to-heat modality to improve management of electrical/ thermal energy demands is still limited.

In this research, the installation of a heat pump in the poly-generative smart grid located at the University of Genoa Campus is presented. A time dependent one-year techno-economic analysis of the energy district is performed, throughout a model built with a software developed by the authors. The integration of the heat pump in the energy district is analysed, comparing the energetic, environmental and economic performance to the present configuration of the poly-generative energy district. The results show that the heat pump introduction grants several advantages, such as a reduction in gas consumption (24 ton/year, ? 15%) and an increase in the annual energy efficiency of cogenerative prime movers which can work for a higher number of hours (+23%) close to the design point.

This work aims to present the development and testing of an innovative tool for surge prevention in advanced gas turbine cycles. The presence of additional components, such as a saturator in humid cycles, a heat exchanger for an external combustor, a solar receiver or fuel cell stack in a hybrid system, implies the presence of larger size volumes between compressor outlet and recuperator or expander inlet. This large volume increases the risk of incurring in surge instability, especially during dynamic operations. For these reasons, at the University of Genoa, the Thermochemical Power Group (TPG) has implemented four surge precursors in a new diagnostic real-time software which can recognise a surge incipience condition comparing the precursor values with a set of moving thresholds. The most innovative aspects of this work are: (i) operational range extension and safer management of advanced gas turbine systems for energy generation, (ii) positive impact in energy efficiency due to this range extension of high efficiency systems, (iii) development of a new diagnostic tool for surge prevention using standard probes, (iv) small impact of this tool on the control and sensor costs, (v) software flexibility for adaptation to different conditions and machines. This very important final aspect is obtained with thresholds able to change automatically to adapt themselves to the plant and machine operational regime. From the cost point of view, the utilization of standard measurements is an essential requirement to equip commercial machines without significant impact on the capital costs. The software performance has been demonstrated using experimental data from a test rig composed of a T100 microturbine connected with a modular vessel, which permits to generate the effect of additional components (especially from the volume size point of view). Vibro-acoustic data, collected during machine transients from a stable operative condition to surge, were used to tune all the software parameters and to obtain a good surge predictivity.

In this paper, green hydrogen produced via water electrolysis and its conversion into three alternative fuels, such as methane, methanol, and ammonia, are considered. The four different Power-to-Fuel solutions are investigated and compared from both the technical and economic points of view aiming at providing a comprehensive overview of the Power-to-Fuel feasibility. At first, the global process efficiency, the storage capacity, the annual costs, and the production cost of the different fuels (in terms of mass, energy, and hydrogen content) are calculated for a reference scenario. Then, a sensitivity analysis is carried out analyzing the influence of many parameters (i.e. electricity cost, electrolyser CAPEX, operating hours, etc) on the economic viability of all the processes. Finally, map plots are developed reporting the fuel production cost for considering different renewable energy sources and their availability. They can be considered as a useful tool for pre-feasibility analysis of power to fuel processes enabling to analyze and compare the different solutions in different scenarios. It is found that the highest efficient process is the Power-to-Hydrogen (about 61.5%) followed by the methanol and ammonia processes and in the end the methane processes. In terms of energy storage and energy density by volume, the methanol resulted in the most suitable solution, while the ammonia resulted in the best H2 storage medium in terms of kg of H2 per m3 of storage (108 kgH2/m3). From the economic perspective, the annual cost breakdown showed that, in all the cases, the major expenditures are related to the electrical energy purchase and CAPEX and OPEX of the electrolyzer (around 90% of total costs), and a 50% reduction in electricity cost and electrolyzer CAPEX could lead to a reduction of about 30% and 18% on fuel production cost, respectively. The cheapest fuel in terms of mass and energy content are methanol (1.02 €/kg) and Hydrogen (0.16€/kWh), respectively. The ammonia production cost in terms of hydrogen content in mass resulted almost comparable with the Hydrogen one (5.76€/kgH2 and 5.31€/€/kgH2, respectively). The contribution of the co-produced oxygen sale has been estimated in around a 15% reduction of fuel production cost in all the cases.

This work shows the results of the experimental assessment of the HI-SEA joint laboratory between Fincantieri, the main Italian shipbuilder, and the University of Genova. The HI[1]SEA system is a 240 kW real-scale test rig complete of auxiliaries, made up of 8 Proton Exchange Membrane Fuel Cell stacks installed on two parallel branches, which can operate independently or in parallel by means of two dedicated DC/DC converters. The experimental assessment is performed by considering: (i) Stationary performance; (ii) dynamic performance; (iii) a maritime operative profile defined together with Fincantieri. The experimental results obtained in this work demonstrated that the system can successfully respond to static, dynamic, and typical maritime operative load profiles. It was also assessed the ability of the system to work simultaneously with two parallel branches, by means of two DC/DC converters, which represents a clear advantage in terms of load sharing and redundance onboard for security issues. Furthermore, the present study gives important advice and criteria for the design, construction, and control of similar Fuel Cell complete systems for maritime applications, which is particularly relevant considering that experimental studies on complete Fuel Cell systems is still limited.

The cost-effectiveness of turbomachinery is a key aspect within the small-size compressor market. For this reason, Tesla turbomachinery, invented by Nikola Tesla in 1913, could be a good solution, particularly for low volumetric flow applications, where volumetric compressors are usually used. It consists of a bladeless rotor which stands out for its ease of construction and its ability to maintain almost the same performance as size decreases. One of its advantages is that it can run either as a turbine or as a compressor with minor modifications at the stator. The objective of this paper is to investigate a 3kW Tesla compressor, which design was derived from an analogous Tesla expander prototype (59% isentropic efficiency from the numerical study), by conducting a computational fluid dynamic analysis for different disk gaps and diffuser configurations.

The potential of the Tesla compressor is shown to be quite promising, with a peak isentropic efficiency estimated at 53%. Although bladeless compressor is a simple turbomachinery device, different parts i.e., diffuser, tip clearance, and volute need to be optimized. Utilizing computational fluid dynamics algorithms, different disk gaps and different diffusers are simulated in order to increase the overall performance of the compressor and understand the flow dynamic behavior behind this technology. The dimensionless Ekman number is used to express the optimum disk space of the compressor rotor. Thus, the overall performance of the Tesla compressor is improved by 5-10% points compared to the initial model. Simultaneously, diffuser optimization strategies are applied and proved that there is a direct impact on the optimum design conditions, improving the pressure ratio at high mass flow rates.

High-efficient supercritical CO₂ (sCO₂) power blocks and the hybridization with solar photovoltaic (PV) plants have been identified as two viable solutions to enhance the economic competitiveness of Concentrating Solar Power (CSP) plants. This work introduces an innovative hybrid PV-CSP system layout with molten salt thermal energy storage and a sCO₂ power block. An active hybridization has been proposed employing a molten salt electric heater that allows storing the excess PV production as thermal energy. The scalability of the plant has been investigated using size-dependent cost functions and introducing a novel methodology for scaling the sCO₂ turbomachinery efficiencies. The conducted techno-economic optimizations show that the proposed hybrid PV-CSP plants can be cost-competitive. For a European solar resource location – 1900 kWh/(m²yr) – Levelized Cost of Electricity (LCOE) values lower than 66 EUR/MWh and capacity factors higher than 70 % can be achieved at 100 MWe. For a high-irradiance location – 3400 kWh/(m²yr) – a capacity factor of 85 % and a LCOE of 46 EUR/MWh have been found for the same scale. The selection of the sCO₂ power cycle has a marginal impact on these results so that a simple recuperated cycle can yield similar LCOEs as the recompressed, reheated, and intercooled layouts. For smaller scales, systems with large gaps between the PV and CSP capacities are preferred, laying the optimal conditions for the electric heater integration with utilization factors up to 21 %.

The aim of this study is to analyze the effect of fuel composition change on the performance and dynamic behavior of a T100 micro gas turbine. Fuel flexibility is a key asset of micro gas turbines and can support the energy transition when alternative fuels obtained from renewable energy sources are used. While the current research is mainly focusing on improving combustor performance, it is also required to investigate the effects of different fuel blends on the overall system. During transient operation, the use of fuels with a low LHV requires an increased fuel mass flow that can potentially reduce the compressor surge margin. Conversely, sudden composition changes of high LHV fuel can cause temperature peaks, detrimental for the turbine and recuperator life.

In this paper, a validated transient model for the T100 machine has been used to simulate the injection of different fuels in the natural gas line (feeding the burner). Injection of hydrogen and ammonia, two promising carbon-free fuels, have been tested. A transient analysis was performed with this tool to monitor the main performance parameters with the aim to (i) verify compressor safe operations during different working conditions and (ii) to identify appropriate fuel composition change schedules to ensure Turbine Outlet Temperature values within an acceptable range, while keeping the original fuel control system.

The main task of the present paper is the development and the implementation of a suitable analytical model to correctly capture rolling bearing radial stiffness, particularly nearby the critical speeds of the investigated rotor-bearings system. In this paper, such bearing non-linear stiffness model is applied to air bladeless turbines (or Tesla turbines) high speed rotors, in order to assess their global rotordynamic behavior when they are mounted on hybrid ball bearings.

In order to properly investigate all the issues related to critical speeds identification, an adequate number of tests was performed by exploiting an experimental air Tesla turbine prototype located at TPG experimental facility of the University of Genoa. The correlation between experimentally detected flexural critical speeds and their numerical predictions is markedly conditioned by the correct identification of ball bearings dynamic characteristics; in particular, bearings stiffness effect may play a significant role in terms of rotor bearings system natural frequencies and therefore it must be accurately assessed. Indeed, Tesla turbine rotor FE model previously employed for numerical modal analysis relies on rigid bearings assumption and therefore it does not account for bearings stiffness overall contribution, which may become crucial in case of “hard mounting” of rotor-bearings systems. Subsequently, high-speed air Tesla rotor is investigated by means of an enhanced FE model for numerical modal analysis within Ansys® environment, where ball bearings are modelled as springs whose stiffness is expressed according to non-linear analytic model implemented in Matlab®.

The obtained results in terms of rotor-bearings system modal analysis exhibit an improvement in experimental numerical results correlation by relying on such ball bearing stiffness model; moreover, beam-based FE model critical speeds predictions are coherent with experimental evidence and with respect to the previously employed FE model based on solid elements it is characterized by lower computational time and it is more easily interpretable. Thus, such experimentally validated numerical model represents a reliable and easily adaptable tool for high-speed rotating machinery critical speeds prediction in practical industrial application cases.

Dynamic compressors operating region is mainly constrained by fluid-dynamic instabilities occurring at low mass flow rate conditions, such as surge and rotating stall. This work presents a vibro-acoustic experimental investigation on a centrifugal compressor of an automotive turbocharger aimed to identify and confirm some surge precursor values in correspondence of its inception conditions. The experimental campaign was carried out at the University of Genoa and developed on a vaneless diffuser turbocharger exploited for the pressurization of an innovative solid oxide fuel cell (SOFC) emulator. The investigated turbocharger is coupled with a pressure vessel for a former emulation activity on a pressurized SOFC. In this kind of plants, the joint effect of large volume size downstream of the compressor makes more complex the dynamic behavior of the whole system during transients, thus significantly increasing surge onset risk.

The activity The main goal is to obtain a suitable quantitative indicator capable to detect in advance surge inception by relying only on vibrational and acoustic system response. Several transient operations starting from a compressor stable condition to surge instability onset were performed at different initial rotating speeds by progressively closing specific valves in the air line. When moving close to the surge line, vibro acoustic signals were acquired at a high sampling rate to detect variations in compressor blade passage phenomena due to possible interactions with rotating stall inception. Meanwhile, the trend of pressures, temperatures and mass flow rates measured in specific plant sections were acquired at a lower sampling rate to obtain a link between the compressor vibro-acoustic and performance behavior. Cyclostationary analysis and Several post-processing methods in time, angle and frequency domains were performed on microphone and accelerometer acquired signals to provide innovative diagnostic and predictive solutions (precursors) able to warn the incoming of surge compressor instability with cheap and not intrusive sensors like microphones and accelerometers.

SOFC-GT hybrid systems can be a good solution for small-medium size applications of distributed generation thanks to their high efficiency and their high fuel flexibility. Fueling these systems with raw biogas coming from biomass gasification makes them also completely renewable, but it introduces a high variability of performance due to the syngas composition fluctuations. For this reason, this work pursues the aim of realizing a robust system optimization, necessary to obtain the best design and ensure high efficiency combined with low variability. To do this, a co-flow, planar, anode supported SOFC Simulink model was used. Moreover, a related surrogate model was created to decrease the computational time and increase exponentially the number of simulations. To calculate the robust optimum design, the Monte Carlo method was used, simulating the syngas composition distribution with 2000 points and to the operating envelope with 5000 input combinations. Mean value and standard deviation in system efficiency were used to select a Pareto front. The robust points turned out to be those with low electric load, small-medium pressure, and high temperature, while maximum efficiency points were characterized by higher pressure levels. The smaller standard deviation at lower pressure was shown to be linked to the bottoming cycle operation and in particular to the gas turbine off-design condition. This difference between the two design conditions (robust optimum and efficiency optimum) confirmed the importance of this optimization process and the influence of fuel composition on system performance.

Natural gas turbine combined cycles (GTCCs) are playing a fundamental role in the current energy transition phase towards sustainable power generation. The competitiveness of a GTCC in future electrical networks will thus be firmly related to its capability of successfully compensating the discontinuous power demands. This can be made possible by enhancing power generation flexibility and extending the operative range of the plant.

To achieve this goal, a test rig to investigate gas turbine inlet conditioning techniques was developed at the TPG laboratory of the University of Genoa, Italy. The plant is composed of three key hardware components: a micro gas turbine, a butane-based heat pump, and a phase-change material cold thermal energy storage system. The physical test-rig is virtually scaled up through a cyber-physical approach, to emulate a full scale integrated system. The day-ahead schedule of the plant is determined by a high-level controller referring to the Italian energy market, considering fluctuations in power demands.

By using HP and TES, it is possible to control the mGT inlet air temperature and thus enhance the operational range of the plant optimizing the management of energy flows.

This article (Part 1) introduces the new experimental facility, the real-time bottoming cycle dynamic model, and the four-level control system that regulates the operation of the whole cyber-physical plant. The experimental campaign and the analysis of the system performance are presented in the Part 2.

In the current energy scenario, gas turbine combined cycles (GTCCs) are considered key drivers for the transition towards fossil-free energy production. However, to meet this goal, they must be able to cope with rapid changes of power request, and to extend their operating range beyond the limits imposed by the environmental conditions in which they operate.

The European H2020 project PUMPHEAT [1] aims at achieving this goal thanks to the integration of the GTCC with a heat pump (HP) and a thermal energy storage (TES). Both HP and TES are used to condition the air flow at the gas turbine compressor inlet, thus modifying the whole GTCC power output and extending its operative range. To study this setup, a dedicated cyber-physical facility was built at the University of Genova laboratories, Italy.

The plant includes physical hardware, such as a 100kWel micro gas turbine, (mGT), a 10 kWel HP and a 180 kWh change phase material-based TES. These real devices are up-scaled thanks to performance maps and real-time dynamic models to emulate a full-scale heavy duty 400 MW GTCC with a cyber-physical approach. The three real key components (mGT, HP and TES) are run in the laboratory. Data collected by various sensors is monitored in real-time and used to feed both the simulated GTCC bottoming cycle model and the four-level control system. The control system determines the optimal configuration of the whole plant and the operative point of the real devices to minimize the mismatch with a real electric power demand curve.

With the aim of analyzing the performance of the facility and to assess the potential of the proposed GTCC range enhancer, different operative configurations are tested: one for reducing the power production of the plant below the minimum environmental load (MEL) and two for augmenting the plant maximum power at certain ambient conditions.

From the analysis of these tests it is possible to verify the effectiveness of the proposed concept and to characterize the transient behavior of the real components.

Bladeless or Tesla turbines consist of several flat parallel disks mounted on a shaft with a narrow gap between them. The analytical solution of Navier-Stokes equations for the flow between disks has been extensively studied in the past. However, there is a significant impact of the stator exit-flow conditions on the performance and flow behavior inside the rotor of the Tesla turbine. There has been limited research on flow characterization and performance evaluation of stator-rotor interaction of the Tesla expander using 3D numerical simulation. The challenge arises due to a very high aspect ratio of the Tesla rotor (diameter to gap ratio > 1000). In order to accurately evaluate the torque on the disks due to shear forces, a very fine resolution mesh is necessary. 3D numerical modeling with a hexahedral mesh of the nozzle/stator with the commercial software is presented. A steady-state solution is obtained using a density-based solver for solution stability. The simulation is performed for a wide range of inlet pressures and rotational speeds. The numerical solution does not consider the effects of ventilation losses, end-disk leakages, exit kinetic energy and bearing losses. This work focuses on the stator performance, the stator-rotor interaction, the rotor entry losses due to disk tip, the rotor tip velocity ratio and the degree of reaction on the performance of the Tesla expander. Challenges in modelling and key fluid dynamic features are extensively discussed. The peak efficiency of 58% is predicted for 3 bar inlet pressure and a rotational speed of 30000 rpm for a 3 kW machine with air as a working fluid. The 3D numerical analysis provides insights on flow characterization, mainly stator-rotor interaction and flow between disks at different mass flows, with the aim to contribute to the fundamental knowledge towards further improvement of the Tesla turbine performance. Numerical results are also compared with experimented test results performed on a 100-W and a 3-kW air expander.

The integration of a Heat Pump (HP) with a Combined Cycle Gas Turbine (CCGT) to control the inlet air temperature has been previously investigated turning out to be a promising technology to meet the requirements imposed by the current electricity generation systems in terms of efficiency and flexibility. If the HP is coupled with a Thermal Energy Storage (TES) in an Inlet Conditioning Unit (ICU), it can be exploited in different modes to enhance the off-design CCGT’s efficiency or to boost the power output at full load. Furthermore, fuel-saving would be reflected in avoided emissions. The optimal sizing of the ICU, as well as an accurate estimation of the benefits, is a complex problem influenced by several factors such as the local climate and electricity market prices. The paper aims to systematically investigate, by means of a Mixed Integer Linear Programming model for optimal dispatch, the feasibility of an ICU integration in different scenarios (EU and US), providing general rules for assessing the concept application in new sites all around the globe. Different electricity markets have been analyzed and classified according to the parameters describing the average and variability of prices, the interdependency with the gas market, the ambient temperature, or the local carbon pricing policy. The most favorable conditions are identified and the dependency of the optimal ICU sizing on the climate and the electricity market is highlighted. The concept appears to be highly profitable in the hot regions with high price variability with an NPV of around 60 M€. Additionally, even in less profitable conditions (i.e., stable low prices in a cold climate), the system is able to increase the operating hours and reduce the economic losses. The performances enhancement described does not imply any environmental cost in terms of CO2 emissions.

Power-to-X solutions are getting year by year more and more market interest in the present and future Renewable (RES) driven energy market scenario. Their potential coupling with Combined Cycles Gas Turbine (CCGT), which have to be present together with RES as back-bone to guarantee grid resilience and stability, is currently under investigation also in order to enhance CCGT flexibility as short-/middle-term storage solutions.

The H2020 EU Funded PUMP-HEAT and FLEXnCONFU projects1study two different types of Power-to-X solutions: the former a power-to-heat concept by heat pump coupling and the latter a power-to-hydrogen/ammonia system via Electrolyser coupling), both targeting flexibility enhancement and emissions reduction. This paper presents and compares the market potential of Power-to-X solutions proposed in the two projects presenting guidelines for the upscale of the proposed Power-to-X solutions derived from a techno-economic assessment of the two Power-to-X solutions

These guidelines will bring to a preliminary assessment of the flexibility and electric market potential of Power-to-X solutions coupled with CCGTs, presenting specific features per both of them such as the most techno-economic viable sizes or market characteristics to leverage Power-to-X potential. Furthermore, the market potential is presented by analysing bottlenecks and drivers (in current and future EU scenarios) that could facilitate or hamper the widespread of the proposed technologies.

High efficiency, flexibility and competitive capital costs make supercritical CO2 (sCO2) systems a promising technology for renewable power generation in a low carbon energy scenario. Recently, innovative supercritical systems have been studied in the literature and proposed by DOE-NETL (STEP project) and a few projects in the EU Horizon 2020 program aiming to demonstrate supercritical CO2 Brayton power plants, promising superior techno-economic features than steam cycles particularly at high temperatures.

The H2020 SOLARSCO2OL project1, which started in 2020, is building the first European MW-scale sCO2 demonstration plant and has been specifically tailored for Concentrating Solar Power (CSP) applications. This paper presents the first off-design analysis of such a demonstrator, which is based on a simply recuperated sCO2 cycle. The part-load analysis ranged from 50% of nominal up to a 105% peak load, discussing the impact on compressor and turbine operating conditions. The whole system dynamic model has been developed in TRANSEO MATLAB® environment. Full operational envelop has been determined considering cycle main constraints, such as maximum turbine inlet temperature and minimum pressure at compressor inlet.

The off-design performance analysis highlights the most relevant relationships among the main part-load regulating parameters, namely mass flow rate, total mass in the loop, and available heat source. The results show specific features of different control approaches, discussing the pros and cons of each solution, considering also its upscale towards commercial applications. In particular, the analysis shows that at 51% of load an efficiency decrease of 20% is expected.

Supercritical carbon dioxide plants are attracting strong interest, particularly for distributed power generation, thanks to the high-power density, allowing high compactness and efficiencies due to the particular features of the fluid conditions near the critical point. In the present work, the feasibility of innovative turboexpanders is evaluated for the first European demonstrator of MW size, coupling small volumetric flows with technological simplicity, typical of these types of plants. In particular, the possibility of replacing conventional turbines with bladeless expanders is studied, proposing a design in line with those achievable by small radial and axial turbomachines. The bladeless expanders consist of flat parallel disks mounted on a shaft, separated by spacers to maintain small gaps between them. The laminar flow inside the rotor makes it highly efficient: however, rotor-stator interaction losses reduce the overall performance. Such bladeless expanders maintain high interest for their capability to tackle low volumetric flows, their relatively simple design and ease of manufacturability.

The design case presented in this paper is the feasibility study of a single modular bladeless expander using the existing conventional design (axial and radial stages) as the reference design. 3D numerical analysis is carried out using commercial computational fluid dynamic software. The results show ~55% total static efficiency of the bladeless expander at 37000 rpm for approximately 1.25MW output power. The impact on performance at different nozzle throat cross-sections and rotor disks diameter has been discussed. The overall performance of the expander is presented by evaluating the losses and improvement strategies that are discussed.

Supercritical CO2 (sCO2) is taking a growing interest in both industry and academic communities as a promising technology capable of high efficiency, flexibility, and competitive capital costs. Many possible applications are studied in the energy field, from nuclear power plants to CSP and waste heat recovery (WHR).

To evaluate the competitiveness of sCO2 cycles relative to other competing technologies, mainly steam and ORC, a specific techno-economic analysis is needed to fairly compare the different technologies for each application, in order to find the most appropriate market position of the innovative sCO2 plants, compared to the existing steam and ORC solutions.

In the present study, techno-economic analysis and optimization have been conducted focusing on WHR applications, for different sizes and cycle parameters operating conditions using an in-house simulation tool. The analyzed cycles were first optimized by aiming at maximizing the net electrical power and then aiming at minimizing the specific capital cost. As a result, compared to traditional plants, we obtained that in the first case, the more complex sCO2 cycle configuration shows competitive performance, while in the second case, the simpler sCO2 cycle configuration has a lower specific cost for the same electrical power produced (with a difference of approximately -130 €/kW compared to the steam cycle). In general, while traditional technologies confirmed a good trade-off between performance and cost, supercritical CO2 cycles show attractive characteristics for applications requiring simplicity and compactness, guaranteeing in the meantime other technical advantages such as water-free operation.

Recent developments in Pressure Gain Combustion (PGC) technology have demonstrated its ability to achieve higher thermal efficiencies and lower carbon emissions as compared to conventional gas turbine counterpart working in Brayton cycle. Ongoing studies suggest the possibility of implementing PGC in aircraft engines by replacing the high-pressure section (HP compressor, combustion chamber and HP turbine) with a PGC system. This, coupled with research on advanced materials and cooling solutions, offers the potential for higher overall gas turbine efficiency and fuel economy, contributing towards emission reduction of the aviation sector.

This paper aims at a comprehensive review of PGC technology solutions applied in the area of aero propulsion. Reported background covers the historic as well as ongoing research activities at the component level, the cycle level, and the propulsion application of Pulse Detonation Engine (PDE), Rotating Detonation Engine (RDE), Oblique Detonation Wave Engine (ODWE), Free Piston Composite Cycle Engine (FPCCE), and wave rotor engines. The analytical, numerical, and experimental research work is reviewed, providing also a comparison of PGC engine conceptual designs with existing gas turbine engines used in aerospace propulsion.

This study aims to investigate the reversible operation of a bladeless air expander prototype operated reversibly in compressor mode to understand the performance by numerical method and compare its results experimentally. A bladeless machine can reverse its operation by simply inverting the rotational speed. However, expander and compressor performance may differ significantly since losses are exacerbated in the compressor mode. The prototype was previously tested as an expander (experimental highest isentropic efficiency of 36.5%). In this work, the reverse mode is discussed, when the prototype is actuated as a compressor, with and without diffuser at variable rotational speeds. In compressor mode, the fluid enters through the center axially, passes radially outwards through disk gaps, and exits throughout the diffuser. The momentum transfer and pressure gain are carried out by the shear force produced on the surface of the rotating disk. An experimental/theoretical analysis focused on the pressure ratio, mass flow, and efficiency of bladeless compressor is conducted. High losses (main leakage across the rotor) were noticed during the experiments, affecting the overall Tesla compressor performance. Numerical calculations are carried out to estimate leakage losses by comparison with experimental results. It is shown that the original expander design would require specific modifications to reduce end disk leakages, which are higher in compressor mode than in expansion mode, significantly affecting the elaborated net mass flow. Improved diffuser, scroll, disk end gaps, and sealing mechanisms are discussed in order to augment overall performance of the bladeless prototype in compressor mode.

As International Maritime Organization set 2030 and 2050 targets to reduce CO2 emissions in maritime sector, the investigation of innovative clean solution as hydrogen fuel cells for clean energy generation onboard is gaining more and more value.

The present study investigates the thermal integration between PEM fuel cells and metal hydrides (for hydrogen storage) on board the first Italian zero-emissions ship with hydrogen and batteries propulsion, named ZEUS, built by Fincantieri Yard and launched in 2022. A model-based approach is developed to ensure the system’s control at different load demands for the vessel, including transient conditions. The study focuses on the most critical conditions for fuel cells during navigation, namely from maximum to minimum power and vice-versa. Load reduction does not imply particular issues, while load maximum increase may cause some problems in terms of stability, negatively affect fuel cell stacks lifetime. Three solutions are investigated and compared to solve the problem to achieve a safe and robust control system: (i) decrease the current ramp for fuel cells from 50 to 10 A/s; (ii) introduce an intermediate load step; (iii) adopt an advanced Model Predictive Control strategy.

Bladeless or Tesla turbines consist of several flat parallel disks mounted on a shaft with a narrow gap between them. The analytical solution of Navier-Stokes equations for the flow between disks has been extensively studied in the past. However, there is a significant impact of the stator exit-flow conditions on the performance and flow behaviour inside the rotor of the Tesla turbine. There is limited research on flow characterization and performance evaluation of stator-rotor interaction of the Tesla expander using 3D numerical simulation. The challenge arises due to a very high aspect ratio of the Tesla rotor (diameter to gap ratio > 1000). 3D numerical modelling with a hexahedral mesh of the nozzle/stator with the commercial software is presented. The simulation is performed for a wide range of inlet pressures and rotational speeds. This work focuses on the stator performance, the stator-rotor interaction, the rotor entry losses due to disk tip, the rotor tip velocity ratio and the degree of reaction on the performance of the Tesla expander. The peak efficiency of 58% is predicted for 3 bar inlet pressure and a rotational speed of 30000 rpm for a 3-kW machine with air as a working fluid. The 3D numerical analysis provides insights on flow characterization, mainly stator-rotor interaction and flow between disks at different mass flows. Numerical results are also compared with experimented test results performed on a 100-W and a 3-kW air expander.

Over the past decades, attention towards workplace safety has increased progressively, leading to a strong presence of automation and remote control on hazardous processes and devices. However, human intervention is sometimes necessary. Consequently, inadequate knowledge of equipment, poor maintenance of work tools and underestimation of possible risks can result into work accidents. Therefore, it is fundamental for each worker to be updated about necessary knowledge to run and maintain potentially dangerous work equipment. This knowledge is generally acquired through both theoretical studies and training on real devices, sometimes leading to the acquisition of a specific licence. However, this kind of training can test the ability to run the real system only during its standard behavior, but not during emergency situations or malfunctions. Moreover, the interaction of an unexperienced operator with a potentially hazardous system during the training process can lead to risky scenarios.

The goal of the PITSTOP project is to overcome the limits of traditional training and to reduce the possible risks of practical tests, thanks to an innovative integration of dynamic simulation models and a virtual reality environment. In this article, the case study of a small-scale steam generator for industrial applications is considered. However, the methodology proposed by the PITSTOP project could be easily extended to other hazardous systems.

A dynamic model of the system was developed in Matlab-Simulink, including all the main devices (i.e., water tank, pump, boiler), actuators (i.e., valves, buttons, switches, levers) and measuring equipment (i.e. temperature probes, pressure sensors, etc). The simulation of the steam generator relies on a mixed physics-based/data-driven approach, based on physical equations, semi-empirical correlations, performance maps and a thermophysical properties tool (Coolprop). The model was designed to simulate the normal operation of the system during stationary and transient scenarios, but also to recreate emergency situations and to show the effect of wrong or inconsistent actions by the operator. The control logics and emergency procedures of the steam generator were included in the model as well.

Operating the real system in various conditions, it was possible to collect experimental data characterizing its behavior, and to understand all the possible interactions of the operator with its actuators and their consequences. Experimental data were used to calibrate the Matlab-Simulink component models and to align the performance of the model with the real steam generator.

The virtual reality environment was developed in Unity, a graphics engine widely adopted by the videogame industry, using 3D CAD models of the steam generator and its surroundings. The user can access to this immersive system wearing an HTC VIVE headset. No other equipment must be worn, making the experience intuitive and easily accessible. In fact, the movement of the user in the environment is detected by two HTC VIVE cameras installed inside the testing room, while the interaction in the virtual reality environment is guaranteed by hand gestures that are captured and interpreted using Leap Motion controller.

Connecting the dynamic model with the virtual reality environment via UDP communication, it is possible to reproduce faithfully the interactions with the steam generator. The actions of the user on the actuators are used as inputs of the model. Simulating the system response over a time step, the outputs of the model (e.g., temperatures and pressures) are sent to the virtual reality environment, providing visual and audio feedbacks to the user.

Integration of thermal energy storage in energy systems provides flexibility in demand–supply management and in supporting novel operational schemes. In a combined heat and power cycle, it has been shown that integration of cold thermal energy storage is beneficial to fine-tune electric power and heating/cooling production profiles to better match the load demand. Latent heat storage systems have the advantage of compactness and low temperature swing, however storage performance analysis on large scale setup operating around the density inversion temperature is still limited. In this work, a shell & tube, latent heat based cold thermal energy storage was studied around the density inversion temperature of ice-water at 4 ?C and the performance was characterized. Sensitivity analyses on heat transfer fluid flow rate, flow direction and inlet temperature were performed. The results show 27% power increase with doubled mass flow and 18% shorter charge time with 2 ?C lower charge temperature. Contrary to general expectations during solidification, the cold thermal energy storage actually shows between 5% and 6% better thermal performance and reducing instant icing power jump of 36% due to supercooling with downwards cold heat transfer fluid flow in cooling charge cycle due to buoyancy change around density inversion temperature. This fact highlights the importance of accounting for the buoyancy effect due to density inversion when designing the operational schemes of large size cold thermal energy storage.

The increasing cost of energy consumption is one of the most common issues that is encountered by households. However, including more sources besides the power grid will help to reduce the total cost of energy consumption. In addition, including energy storage systems such are batteries will give the system more efficiency and high performance. The objective of the presented paper is to propose an optimal scheduling strategy for energy storage utilization in order to reduce the total energy consumption cost in homes supplied by several energy sources (solar and wind energy) besides the utility grid that is supposed to support the sale/purchase of energy. The results obtained by simulations proved the efficiency of the proposed scheduling strategy for the storage system, in optimizing the cost of consumed energy.

Ammonia is a promising energy vector and storage means for hydrogen. Power to ammonia (P2A) processes employ renewable energy to split water to provide the hydrogen for the Haber-Bosch ammonia synthesis. The fluctuating nature of the renewables requires a good dynamic behavior of these cycles.

Employing the software Aspen Plus Dynamics®, this paper investigates the dynamic behavior of a novel containerized P2A solution, which is going to be tested at the University of Genova in 2023.

The simulation results of the start-up, various load changes and the shutdown of the process suggest that the control architecture can handle all cases in a satisfactory way.

However, there seems to be room for improvement regarding the parameters of some controls.

The present paper aims to analyse the thermal coupling of PEM fuel cells fed by hydrogen, stored in metal hydride tanks for maritime applications, considering the first Italian zero emissions ship with hydrogen PEM fuel cells propulsion (ZEUS), launched in 2022. A dynamic model is developed, and the integrated propulsion system is analysed in different operative conditions, considering the transitory that can be experimented during navigation (i.e., from harbour to cruise speed). The behaviour of the fuel cells in dynamic conditions is investigated, considering two different control systems, based on PID and Model Predictive Control approaches.

This paper presents an algorithm to compare traditional and innovative energy systems for maritime applications, adopting a multi-criteria method. The algorithm includes a large and updated database of market solutions. Two case studies are investigated: (i) a sailing yacht (ii) and a large-size cruise ship. For case (i), Fuel Cells represent a competitive solution, in particular considering navigation in emission control areas; the installation of electrical batteries is also evaluated. For case study (ii) Internal Combustion Engines are the best solution: the evaluation of alternative fuels (LNG, ammonia, methanol) is performed, also in dual-fuel configuration.

In this paper, an optimization algorithm based on a Mixed-Integer Linear Programming (MILP) solver is proposed to find the optimal design of the energy generation system on a cruise ship. Both environmentally sustainable solutions (e.g., fuel cells and batteries) and traditional systems are considered. The performance of the energy systems is simulated on real load profiles of a cruise ship sailing in the Baltic Sea and taking into account all the operative and physical constraints. Two different objective functions are selected to test the algorithm, i.e. CO2 emissions and costs. In both cases the MILP determined the best technological mix.

In the current energy scenario, gas turbine combined cycles (GTCCs) are considered key drivers for the transition towards fossil-free energy production. However, to meet this goal, they must be able to cope with rapid changes in power request and extend their operating range beyond the limits imposed by the environmental conditions in which they operate. The European H2020 project PUMP-HEAT (Pump-Heat Project, 2021, D4. 6 – “Validation Results in Energy -Hub of MPC With Cold Thermal Storage,”) aims at achieving this goal thanks to the integration of the GTCC with a heat pump (HP) and a thermal energy storage (TES). To study this setup, a dedicated cyber-physical facility was built at the University of Genova laboratories, Italy. The plant includes physical hardware, such as a 100kWel micro gas turbine, (mGT), a 10 kWel HP and a 180 kWh change phase material-based TES. These real devices are up-scaled thanks to performance maps and real-time dynamic models to emulate a full-scale heavy-duty 400MW GTCC with a cyber-physical approach. The control system determines the optimal configuration of the whole plant and the operative point of the real devices to minimize the mismatch with a real electric power demand curve. Different operative configurations are tested: one for reducing the power production of the plant below the minimum environmental load (MEL) and two for augmenting the plant maximum power under certain ambient conditions. From the analysis of these tests, it is possible to verify the effectiveness of the proposed concept and characterize the transient behavior of the real components.

For small-medium heat pumps and small-scale energy storage (e.g., hydro) and other small-scale applications (up to 10kWe), an economical, reliable, durable, robust, and acceptable performing bladeless expander is an attractive technology. In this article, experiments are performed on a bladeless expander of 1kW design power with water as a working fluid. The complete expansion is in the subcooled liquid phase with an overall pressure drop across the expander in the 2-14 bar range. The water expander is designed as a similitude case study for a butane heat pump, where such a bladeless expander could replace the expansion valve recovering untapped energy from isenthalpic to isentropic expansion. Unlike conventional bladed expanders, the present bladeless expander consists of several co-rotating compact disks, closely spaced and parallelly mounted on the shaft which transmits torque using wall shear forces. The present expander design is an improved version resulting from the detailed loss characterization done on earlier air expanders.

The article begins with the definition of design conditions for water expander starting from the expected butane expansion in the heat pump, fully inside the liquid region. The rotor design of a bladeless expander is outlined using dimensionless parameters that dictate the performance features. The turbine is designed for 1kW of power output and 2kg/s mass flow with an overall pressure drop of 14 bar with a rotational speed of 8000 rpm. The resulting turbine rotor consists of an 80mm disk outer diameter, 120 disks and a 0.1mm gap between them. An experimental test rig employing water as a working fluid is described. Experiments are conducted for overall pressure drop ranging in the 2-14 bar interval, with a maximum rotational speed of 6500 rpm. The performance is recorded with two different stator configurations, having two different throat dimensions for varying mass flow at maximum inlet pressure. Peak total to static efficiency of 30% is obtained with a net power of 670 W at ~3000 rpm. An experimental ventilation loss (end wall viscous disk friction) is performed with both water and air as working fluids to estimate the power loss. It is found that ventilation loss is the major source of loss in the present turbine prototype with a power loss of 250W@3000 and 1100W@8000 rpm, varying quadratically with rotational speed. It is finally concluded that the expander performance is promising because ventilation losses can be potentially reduced with established strategies used in conventional expanders.

The Thermochemical Power Group (TPG) of the University of Genoa is investigating innovative solutions to increase the flexibility of gas turbine combined cycles (GTCC) and extend their operative range by integrating large size high performance heat pumps. Achieving this goal would make GTCCs more competitive in the future energy market, which will be characterized by a heavy presence of non-dispatchable renewable energy sources.

Within this framework, the authors designed and built a new experimental facility to emulate advanced GTCCs at laboratory scale, integrating a 100 kWel micro gas turbine (MGT), a 10 kWel heat pump (HP) and a 180 kWh cold thermal energy storage (TES), with scale-up equations and dynamic models, capable of hardware-in-the-loop tests.

The focus of this article is on the HP, which uses n-butane (R600) as working fluid and can be used both to heat and cool down the MGT compressor intake. The HP features one superheater and a 6-cylinder reciprocating compressor, which rotational speed can be continuously varied from 900rpm to 1800rpm.

A dynamic model of the HP was developed in TRANSEO, with dedicated Matlab-Simulink® models of all the main components. This model can be used to simulate the HP in various conditions, including part-load and transient operations, and to aid the design of the advanced GTCC control system. The evaporator and condenser models solve a system of non-linear equations to compute pressure, temperature, and distribution of the different phases of the working fluid along the heat exchangers. Such phase distribution is computed following a moving boundary approach.

An experimental campaign was carried out to collect data regarding the stationary performance of the HP. Values of COP and thermal power were analysed as a function of compressor speed and pressure at the condenser, keeping the conditions at the evaporator constant. Then, its transient behaviour was characterized, observing its response to step changes of both evaporator and condenser thermal loads. The model was then successfully calibrated and validated on both stationary and transient data, showing good accuracy and demonstrating its potential as digital twin of the real HP.

Current climate targets adopted worldwide pursue the decarbonization of all energy sectors. In power generation, the spread of RES has caused the shift of the Combined Cycle Gas Turbine (CCGT) power plants’ traditional role from providing constant baseload power to flexible operations providing services and backup capacity to the grid, as a consequence, the revenues opportunities on the traditional electricity markets (e.g, day-ahead, and intra-day markets) are no longer certain. At the same time is urgent to address a significant carbon intensity reduction in the heating sector, which is responsible for a large part of the current greenhouse gas emissions. Exploiting the low-exergy waste heat of CCGT’s water-cooled condenser as a thermal source for vapor compression heat pumps can meet two targets. On one hand, the revenues from heat production enhance the viability of the CCGT power plant, often essential for the security of the electrical supply. On the other hand, the heat delivered to the user represents a low-carbon alternative to traditional gas-fired boilers or even to air-sourced heat pumps characterized by lower efficiency. This work assesses the recovery of thermal energy from the sea cooling water at the bottoming cycle condenser of Tirreno Power 794 MWel CCGT in Vado Ligure through a high-temperature heat pump using R600 as a working fluid. Cooling water represents a privileged heat source and the integration into the power plant’s site allows running the HP at a lower cost than the electricity retail price. The case study takes into account the new Vado Ligure sports hall, to size the HP and explore the economic and environmental performances. The proposed layout is compared with the main solutions available: air source heat pump, gas, and electric boilers. The results show that on a lifespan of 20 years such integration of a heat pump with a CCGT could lead to consistent economical savings and emissions cuts.

Electrification is playing a major role in the industrial and energy sector, with heat pump (HP) market expected to grow significantly in the next future in accordance with the current energy transition phase, which aims to reduce the utilization of fossil fuels for heat production sector. It is therefore of crucial importance to find new ways to increase heat pump performance and reliability, containing maintenance costs. The use of dynamic compressors in HPs makes it possible to combine good performance with high compactness and silent operation, but unlike the volumetric compressor, this equipment could undergo dangerous instability during operation, which can occur in closed-cycle configuration, quite unusual for dynamic compressors. The aim of this paper is to present a new test-rig for stable and unstable performance analysis of dynamic compressors for innovative heat pumps. An in-depth description of the plant and instrumentation system is provided. The performance of the compressor is analyzed for different operating points, with a particular focus on near-surge operation. Experimental uncertainties and their reduction through data reconciliation techniques is thoroughly investigated.

Ship emissions reduction targets are pushing the maritime industry towards more sustainable and cleaner energy solutions. Marine fuels play a major role in this because of the emissions resulting from the combustion process associated with the prime mover(s), therefore, one of the technical solutions is to replace conventional marine fuels with cleaner fuels. Hence the aim of this study is to undertake environmental, technical, and economic analysis of alternative fuels to reduce the environmental footprint and lifetime costs of the long-distance shipping sector. As a case study, an ultra large container ship operating on the East-West trade route has been considered, and the analysis focus ed on natural gas and methanol as alternative fuels. This study adopted three approaches : environmental, technical, and economic methods to compare the alternative fuels with the conventional ones. The results showed that a dual-fuel engine operated by natural gas will reduce CO2, SOx, and NOx emissions by 28%, 98% and 85%, respectively , when compared with emission values for a diesel-powered engine. Furthermore, the reduction percentages reach 7%, 95% and 80% when using a dual-fuel engine operated by methanol, respectively. The proposed dual-fuel engines will improve the ship energy efficiency index by 26% and 7%, respectively. The study shows that methanol is the most economical alternative fuel for this container ship, replacing diesel with methanol, leads to a power system that is only 30% more expensive than the existing one. The analysis confirms that the cost of fuel has a major effect on the ship’s life cycle cost and that by reducing the fuel costs, the costs of the power system become more acceptable.

Proton exchange membrane fuel cells (PEMFCs) are considered among the most promising technologies for hydrogen utilization in both stationary and transport applications. Nevertheless, the cost of its components – especially the catalyst and the membrane – is still consistent and far from the cost predicted by the US Department of Energy. It is therefore essential to predict the effect of contaminants on PEMFC materials and to estimate their useful life. The literature on this topic is consistent, but the absence of standards for the experimental tests under contaminated flows makes it difficult to extrapolate the generic degradation trends and compare the results of different publications. This work aims to collect and interpret the results of the recent studies on catalyst contamination: the voltage degradation rate and reduction effect are defined via a data modeling work to understand and compare the effects of different contaminants, their concentrations, exposure times, and current densities. Thanks to the results of the present study, some conclusions are drawn regarding the impact of the different pollutants on cell voltage decay, with attention dedicated to establishing a correlation that takes into account also the different operating conditions.

Supercritical CO₂ (sCO₂) power cycles have been identified as technology enablers for increasing the cost-competitiveness of Concentrating Solar Power (CSP) plants. Compared to steam cycles, sCO₂ cycles have the advantage of allowing higher inlet turbine temperatures, while also deploying turbomachinery that can be a ten-fold more compact. Ongoing research in CSP focuses mainly in developing new receiver and storage concepts able to withstand such required higher temperatures, alongside new heat exchangers that enable coupling to a sCO₂ cycle. Meanwhile, advancements in sCO₂ turbomachinery have taken place in research projects aimed at investigating the technical feasibility of the cycle, including the optimized design of its individual components and new cycle configurations. Among these, only few focus in demonstrating a full-integrated system, including cycle control and dynamics, and only two worldwide have started plans for MW-scale pilots, none of them in Europe. The EU-funded SOLARSCO2OL project aims at demonstrating a first-of-a-kind 2 MW gross simple-recuperated sCO₂ Brayton cycle driven by heat provided by molten salts similar to those deployed in commercial CSP plants, which are able to operate at temperatures of up to 580°C. This paper introduces the project objectives and implementation plan, to then focus primarily on the results derived from the first year in specific relation to the conceptual design of each of 2 MW scale power cycle and its key components, including also the proposed integration and operational regimes, expected thermodynamic performance at nominal point, and up-scaling considerations.

The aim of this study is to analyse the off-design performance of an innovative turbocharged solid oxide fuel cell system, fed by biogas and designed to generate 30 kW during nominal operating conditions. The layout of such a plant combines the high efficiencies of the solid oxide fuel cell with a reduced-cost option for fuel cell pressurization: fuel cells are usually pressurized by a micro gas turbine, but the alternative use of a turbocharger, a mass-produced component widely used in the automotive field, could reduce significantly the capital cost of the system. This kind of layout has been rarely investigated in literature, and a detailed performance analysis of a turbocharged SOFC system would be a valuable source of information for both academia and industry. To perform this analysis, a steady-state model has been created using a modular tool developed in Matlab®- Simulink® that includes off-design models of the system components. The model has been used to compare different control strategies. The most suitable control strategy, based on wastegate and cold bypass valves, was adopted, obtaining compliance with the operative constraints and high system efficiency. Afterward, the system steady-state operation was simulated for various electric power loads and ambient temperatures. The performance analysis focused on the effect of these two variables on the system behaviour and has provided insight on the influence on the most significant system outputs, including global efficiency, temperatures and pressures. A system efficiency increase was observed at part load, with values growing from 50.8% to 57.3%. Higher values of ambient temperature resulted in a more significant pressurization of the fuel cell, affecting positively the system efficiency: from 50.5% at 0 ?C to 51.0% at 30 ?C. Great attention was paid to the system constraints, to verify that the plant could operate properly in all the considered conditions. The proposed control strategy was tested and proved to be effective at achieving this objective.

The availability of wildland fire propagation models with parameters estimated in an accurate way starting from measurements of fire fronts is crucial to predict the evolution of fire and allocate resources for firefighting. Thus, we propose an approach to estimate the parameters of a wildland fire propagation model combining an empirical rate of spread and level set methods to describe the evolution of the fire front over time and space. The estimation of parameters affecting the rate of spread is performed by using fire front shapes measured at different time instants as well as wind velocity and direction, landscape elevation, and vegetation distribution. Parameter estimation is done by solving an optimization problem, where the objective function to be minimized is the symmetric difference between predicted and measured fronts at different time instants. Numerical results obtained by the application of the proposed method are reported in two simulated scenarios and in a case study based on data originated by the 2002 Troy fire in Southern California. The obtained results showcase the effectiveness of the proposed approach both from qualitative and quantitative viewpoints.

The increase in energy demand, including peak power demand for electricity is one of the most important aspects to be considered in the electricity sector, as it has a negative impact on the flexibility of the power supply and the power balance in the electricity networks. Usually, some distribution system operators impose an additional cost on electricity consumption during peak hours, on other hand, they reducing the electricity price during off-peak periods to encourage householders to reschedule the use of electricity consumption. The work presented in this paper aims to propose an optimal strategy for scheduling energy consumption to help householders for reducing the cost of energy, as well as for saving energy in a residential house connected to a microgrid (Power grid system, PV, and battery storage system). The results presented are obtained using a particle swarm optimization algorithm (PSO) using Matlab. Two optimization scenarios are considered and compared to a base model to prove the efficiency and performance of the proposed optimization model. The results show that the scheduling strategy for energy consumption reduces the daily operating cost by 45% and that about 22% of energy is saved in the system.

The paper summarizes the main aspects of an experimental vibro-acoustic investigation developed by the authors on two violas da gamba (named in the following as viols).

The considered instruments show similar aesthetic and geometric characteristics, as one of them was made later adopting the other as a reference. However, they are characterized by non-negligible different construction solutions, such that is not possible to consider one a faithful replica of the other.

The instruments considered are a 16th century viol (hereinafter referred to as ancient viol) and a 21st century viol, inspired by the ancient instrument (hereinafter referred to as the modern viol). The ancient instrument has no bass bar and no sound post and has a rounded back. The modern one was deliberately made with a flat back, to follow the Italian school of construction of this type of instrument and, during this activity, it has been available in different configurations with and without bass bar and sound post. The availability of these two viols made it possible to evaluate how different construction solutions have a significant impact on both structural and acoustic response. Experimental modal analysis and operational vibro-acoustic response techniques have been extensively adopted for this aim. Considering its high intrinsic value, the measurements on the ancient viol have been reduced to the minimum necessary to obtain the suitable identification thereof. On the contrary, broad experimental activity on the modern viol has made its development possible, in analyzing its structural modification, related to the insertion of the bass bar and sound post, in order to verify the acoustic variations resulting from these variants.

The different behavior of the ancient viol, with respect to the modern one, has also been analyzed to underline how the sound itself changes from an antique to a contemporary conception of stringed musical instruments.

The growing need of dispatchable units, capable to balance the variable renewable energy electrical production leads to the development of strategies aimed at increasing power plants operational flexibility and global efficiency in part-load operation. A highly efficient heat pump (integrated in a conventional natural gas combined cycle is here proposed as a flexibility enhancement solution. Such concept, applied to power oriented combined cycle, allows to modify the compressor intake temperature with a consequent increase of the power production. While this operation for open cycle gas turbine is beneficial also to electric efficiency, combined cycles’ efficiency is less sensitive to the temperature variation and thus more influenced by the auxiliary consumption. The selection of the proper heat pump size for the proposed layout was based on an optimization process considering both combined cycle and heat pump off-design performance. After a statistical analysis of climatic data and their correlations with energy market condition for the six Italian price zones, the models developed were applied to assess the thermoeconomic potential of the proposed layout. This work highlights how a proper optimization process influences both revenues and size optimization and to highlight how such integrated system can be selected at its best considering typical market and climatic frames. The ratio between the air-cooled heat pump electrical consumption and the electrical combined cycle capacity that maximize power production increase was found to be 1/100. This finding can be extended to the others world Humid subtropical climate and Mediterranean hot summer climates zones. It is underlined how electrical market conditions could jeopardize the installation profits even under favourable climatic potential reducing the optimal economic heat pump size. Using off-design curves and optimization algorithm in performing coupling analysis appears to be more effective, with respect to simplified calculations under unfavourable economic and climate conditions.

The purpose of this paper regards the design and testing of control systems for a 30-kW turbocharged solid oxide fuel cell system fuelled with biogas. The adoption of a turbocharger, instead of a micro gas turbine, for the fuel cell stack pressurisation, is an innovative solution that is expected to decrease the capital cost of such systems and to facilitate their penetration into the energy market. However, not being connected to an electric generator, the turbocharger rotational speed, and thus the air mass flow, cannot be directly controlled as in microturbines. The control of turbocharged solid oxide fuel cell systems is a novel topic, characterised by many technical challenges that have not been addressed before. To regulate the stack temperature, a cold bypass valve is included, connecting the compressor outlet to the turbine inlet.

A dynamic model of this system was developed in Matlab-Simulink® to analyse the response of the turbocharged solid oxide fuel cell system to a cold bypass valve opening step change. System information obtained from this analysis was used to design and tune four controllers: a conventional proportional integral controller and three different cascade controllers. The controller performance was evaluated under two different scenarios, considering quite aggressive power ramps. The best results were obtained with a cascade controller, where the feedback loop was complemented by a feed-forward contribution based on power demand. This analysis demonstrated that such a control system effectively tracks the fuel cell maximum temperature target, complying with all the system operative constraints.

This paper aims to develop and test Bayesian belief network-based diagnosis methods, which can be used to predict the most likely degradation levels of turbine, compressor, and fuel cell (FC) in a hybrid system based on different sensors measurements. The capability of the diagnosis systems to understand if an abnormal measurement is caused by a component degradation or by a sensor fault is also investigated. The data used both to train and to test the networks are generated from a deterministic model and later modified to consider noise or bias in the sensors. The application of Bayesian belief networks (BBNs) to fuel cell—gas turbine hybrid systems is novel, thus the results obtained from this analysis could be a significant starting point to understand their potential. The diagnosis systems developed for this work provide essential information regarding levels of degradation and presence of faults in a gas turbine, fuel cell and sensors in a fuel cell—gas turbine hybrid system. The Bayesian belief networks proved to have a good level of accuracy for all the scenarios considered, regarding both steady-state and transient operations. This analysis also suggests that in the future a Bayesian belief network could be integrated with the control system to achieve safer and more efficient operations of these plants.

This paper shows control approaches for managing a pressurized solid oxide fuel cell (SOFC) system fuelled by biogas. This is an advanced solution to integrate the high efficiency benefits of a pressurized SOFC with a renewable source. The operative conditions of these analyses are based on the matching with an emulator rig including a T100 machine for tests in cyber-physical mode. So, this paper presents a real-time model including the fuel cell, the off-gas burner (OFB), and the recirculation lines. Although the microturbine components are planned to be evaluated with the hardware devices, the model includes also the T100 expander for machine control reasons. The simulations shown in this paper regard the assessment of an innovative control tool based on the model predictive control (MPC) technology. This controller and an additional tool based on the coupling of MPC and proportional integral derivative (PID) approaches were assessed against the application of PID controllers. The control targets consider both steady-state and dynamic aspects. Moreover, different control solutions are presented to operate the system during fuel cell degradation. The results include the system response to load variations, and SOFC voltage decrease. Considering the simulations including SOFC degradation, the MPC was able to decrease the thermal stress, but it was not able to compensate the degradation. On the other hand, the tool based on the coupling of the MPC and the PID approaches produced the best results in terms of set-point matching, and SOFC thermal stress containment.

Compressor response investigation in nearly unstable operating conditions, like rotating stall and incipient surge, is a challenging topic nowadays in the turbomachinery research field. Indeed, turbines connected with large-size volumes are affected by critical issues related to surge prevention, particularly during transient operations. Advanced signal-processing operations conducted on vibrational responses provide an insight into possible diagnostic and predictive solutions which can be derived from accelerometer measurements. Indeed, vibrational investigation is largely employed in rotating-machine diagnostics together with time-frequency analysis such as smoothed pseudo-Wigner Ville (SPWVD) time-frequency distribution (TFD) considered in this paper. It is characterized by excellent time and frequency resolutions and thus it is effectively employed in numerous applications in the condition monitoring of machinery. The aim and the innovation of this work regards SPWVD utilization to study turbomachinery behavior in detail in order to identify incipient surge conditions in the centrifugal compressor starting from operational vibrational responses measured at significant plant locations. The so developed investigation allows us to assess the reliability of this innovative technique with respect to conventional ones in this field of research, highlighting at the same time its qualities and drawbacks in detecting fluid machinery unstable behavior. To this aim, an experimental campaign has been conducted on a T100 microturbine connected with several volume sizes and this has allowed to assess diagnostic technique reliability in plant configurations with different dynamic properties. The results show that SPWVD is able to successfully identify system evolution toward an unstable condition, by recognizing different levels and features of the particular kind of instability that is going to take place within the plant. Instability phenomena regarding rolling bearings have also been identified and their interaction with surge onset has been investigated for diagnostic purposes.

In this paper an industrially established 1D model for two-phase nozzles design and analysis (Elliott, 1968) has been extended and validated with a wider range of experimental data, focusing on single component two-phase fluid expansion from initial quality in the 0%–25% range. The Authors focused on the correlations of the gas-liquid slip velocity and wall friction for two-flow regimes. The upgraded model has been tested on a converging nozzle showing accurate results under subcritical conditions (Ma<1). Furthermore, simulations have also been carried out on a convergent-divergent nozzle, concentrating on the diverging part at Ma><1, demonstrating that the new model obtained a significant reduction in error compared to the original Elliott model and to the well-known isentropic homogeneous approach (IHE). The extended model was also tested on a convergent-divergent nozzle produced by Carrier Corporation for the 19-XRT chiller, obtaining a satisfactory performance prediction. The validation process allowed to assess the limits of validity of the new model, which can be effectively used as design tool for subsonic or supersonic two-phase nozzles. In particular, the model capability to identify critical mass flow and critical expansion ratio has been investigated, showing good match for the critical expansion ratio, while margins of improvement remain for the critical mass flow prediction. [/av_toggle][/av_toggle_container] 2021P-TPG-11

M. Manzoni, A. Patti, S. Maccarini, A. Traverso, 2021

“Adiabatic Compressed CO2 Energy Storage”,  2021-sCO2.eu-118, The 4th European sCO2 Conference for Energy Systems, pp.1-9.

As the energy market is moving worldwide towards low-emission solutions, there is a growing interest in plants capable of storing non-dispatchable renewable power, contributing to maintain the high quality level of current electrical infrastructure and ensuring spinning-reserve capability, complementing the lack of frequency control by most of solar and wind technologies. CO2 cycles, including supercritical ones, could be a solution to achieve this goal. Most of current efforts on CO2 cycles are devoted to study the most promising configurations for power production, including supercritical CO2 plants for solar energy conversion. Basing on such extensive state of the art and growing knowledge, this paper aims to analyse innovative energy storage solutions involving closed cycles, employing different working fluids in sub-critical or supercritical conditions, including CO2. Different plant configurations and operating conditions at 10 MWe design point are compared in terms of Round Trip Efficiency (RTE) and preliminary costs, benchmarked against traditional large scale storage solution such as CAES. Subcritical CO2 cycles is shown to be a very promising solution with RTE>70% and attractive cost features, thus being a potential candidate for utility scale energy storage.

The aim of this work is to describe the design and the use of an innovative test rig for investigating the expansion of subcooled fluids inside a converging nozzle and the evolution of two-phase flows in Tesla-type turbines. The flow exiting the nozzle enters tangentially into a thin flat circular chamber and it finally is discharged in the center through a duct perpendicular to it. The experimental test rig has two nozzles placed in diametric position. This peculiar shape reproduces the geometry of a single gap between two discs of a Tesla turbine, a machine that potentially could replace the throttling valve in chillers and heat pumps to increase their COP. The study of a simple and static geometry is necessary in order to calibrate the CFD modeling of the phase change in nozzle and rotor chamber. The rig was designed and assembled by TPG of the University of Genoa in the framework of the Pump-Heat H2020 project.

Here it is used subcooled water and, in order to fully characterize the expansion conditions, the rig has been equipped with pressure sensors at the nozzle inlet and at the rig outlet. A Coriolis mass flow meter and a temperature sensor were also placed at nozzle inlet. High-resolution cameras provided and managed by Ansaldo Energia were used to look at the position and shape of the front of the fluid phase change along and around the nozzle as a function of varying pressure and temperature conditions. The tests were performed in the 2.1-5.1 barG pressure range and in the 132-155°C temperature range, feeding either one or both nozzles.

Future work involves the use of different nozzle profiles, such as a convergent/divergent in order to test both subsonic and supersonic flows, and experimental analysis of pressures in the rotor chamber, aimed to optimize the geometry of nozzles and Tesla turbines in two-phase applications.

Pressurized solid oxide fuel cell (SOFC) systems are one of the most promising technologies to achieve high energy conversion efficiencies and reduce pollutant emissions. The most common solution for pressurization is the integration with a micro gas turbine, a device capable of exploiting the residual energy of the exhaust gas to compress the fuel cell air intake and, at the same time, generating additional electrical power. The focus of this study is on an alternative layout, based on an automotive turbocharger, which has been more recently considered by the research community to improve cost effectiveness at small size (<100 kW), despite reducing slightly the top achievable performance. Such turbocharged SOFC system poses two main challenges. On one side, the absence of an electrical generator does not allow the direct control of the rotational speed, which is determined by the power balance between turbine and compressor. On the other side, the presence of a large volume between compressor and turbine, due to the fuel cell stack, alters the dynamic behavior of the turbocharger during transients, increasing the risk of compressor surge. The pressure oscillations associated with such event are particularly detrimental for the system, because they could easily damage the materials of the fuel cells. The aim of this paper is to investigate different techniques to drive the operative point of the compressor far from the surge condition when needed, reducing the risks related to transients and increasing its reliability. By means of a system dynamic model, developed using the TRANSEO simulation tool by TPG, the effect of different anti-surge solutions is simulated: (i) intake air conditioning, (ii) water spray at compressor inlet, (iii) air bleed and recirculation, and (iv) installation of an ejector at the compressor intake. The pressurized fuel cell system is simulated with two different control strategies, i.e. constant fuel mass flow and constant turbine inlet temperature. Different solutions are evaluated based on surge margin behavior, both in the short and long terms, but also monitoring other relevant physical quantities of the system, such as compressor pressure ratio and turbocharger rotational speed. [/av_toggle][/av_toggle_container] 2021P-TPG-14

A. Renuke, F. Reggio, A. Traverso, M. Pascenti, 2021

“Experimental Characterization of Losses in Bladeless turbine Prototype”,  ASME Paper GT2021-59328, ASME Turbo Expo 2021, virtual.

Multi-disk bladeless turbines, also known as Tesla turbines, are promising in the field of small-scale power generation and energy harvesting due to their low sensitivity to down-scaling effects, retaining high rotor efficiency. However, low (less than 40%) overall isentropic efficiency has been recorded in the experimental literature. This article aims for the first time to a systematic experimental characterization of loss mechanisms in a 3-kW Tesla expander using compressed air as working fluid and producing electrical power through a high speed generator (40krpm). The sources of losses discussed are: stator losses, stator-rotor peripheral viscous losses, end wall ventilation losses and leakage losses. After description of experimental prototype, methodology and assessment of measurement accuracy, the article discusses such losses aiming at separating the effects that each loss has on the overall performance. Once effects are separated, their individual impact on the overall efficiency curves is presented. This experimental investigation, for the first time, gives the insight into the actual reasons of low performance of Tesla turbines, highlighting critical areas of improvement, and paving the way to next generation Tesla turbines, competitive with state of the art bladed expanders.

The use of centrifugal compressors has been increasing tremendously in the last decade as they are a key component in the present energy scenario both in the modern internal combustion engine design and in advanced cycles and innovative plant layouts as fuel cell systems.

Instability phenomena limit the operating range of the whole compressor system, especially during fast transients. The target is therefore to extend the minimum flow limit in order to improve the operability of each unit, while avoiding compressor surge operation and guaranteeing safe operation. For this reason, it is necessary to develop a monitoring system capable of preventing surge and extending operating range of these machines, their performance, and reliability to allow the integration with the other plant components.

The experimental investigation, carried out at the University of Genoa turbocharger test facility and presented in this work, consists of steady state and transient measurements used to characterize and identify compressor behaviour in correspondence of surge inception conditions to determine different techniques which could represent surge precursors. The data analysis concentrates on pressure and vibro-acoustic signals by applying different signal processing techniques in time and frequency domain to classify compressor operation as stable or unstable. The cross correlation function and wavelet analysis have been identified as techniques to define a precursor able to detect incipient surge conditions. Through cross correlation function analysis, it has been possible to identify the presence of propagation phenomena in the system and to evaluate how these events become more significant near an unstable low-mass flow rate condition. At low mass flow rate condition, spikes of significant amplitude are well detectable in the cross correlation function indicating the rise of significant random content in the system responses associated to the rise of incipient surge condition.

Additionally, the continuous wavelet transform has been applied to operational signals to show how their time-dependent spectral structure responses can highlight the rise of unstable phenomena, not easily identifiable with traditional signal processing techniques. Exploiting its features in terms of good frequency and time resolution it allowed to identify different contents in system responses regarding phenomena which take place close to surge line and was able to detect their nature in conditions very close to deep surge ones (e.g. rotating stall with its intermitting characteristic nature).

Moreover, system response was studied in high frequency range and through a demodulation technique it was found how blade pass frequency energy content change interacting with rotating stall inception, moving close to surge line. The obtained results provide an interesting diagnostic and predictive solution to detect compressor instabilities at low mass flow rate operating conditions and to prevent compressor fails.

Combined Cycle Gas Turbines, CCGTs, are often considered as the bridging technology to a decarbonized energy system thanks to their high exploitation rate of the fuel energetic potential. At present time in most European countries, however, revenues from the electricity market on their own are insufficient to operate existing CCGTs profitably, also discouraging new investments and compromising the future of the technology. In addition to their high efficiency, CCGTs offer ancillary services in support of the operation of the grid such as spinning reserve and frequency control, thus any potential risk of plant decommissioning or reduced investments could translate into a risk for the well-functioning of the network. To ensure the reliability of the electricity system in a transition towards a higher share of renewables, the economic sustainability of CCGTs must be preserved, for which it becomes relevant to monetize properly the ancillary services provided. In this paper, an accurate statistical analysis was performed on the day-ahead, intra-day, ancillary service, and balancing markets for the whole Italian power-oriented CCGT fleet. The profitability of 45 real production units, spread among 6 market zones, was assessed on an hourly basis considering local temperature, specific plant layouts, and off-design performance. The assessment revealed that net income from the ancillary service market doubled, on average, the one from the day-ahead energy market. It was observed that to be competitive in the ancillary services market CCGTs are required to be more flexible in terms of ramp rates, minimum environmental loads, and partial load efficiencies. This paper explores how integrating a Heat Pump and a Thermal Energy Storage within a CCGT could allow improving its competitiveness in the ancillary services market, and thus its profitability, by means of implementing a model of optimal dispatch operating on the ancillary services market.

Electrical power production from CSP is worldwide still limited in its diffusion by a higher LCOE with respect to other renewable sources, nevertheless it offers some unique features such as the possibility of a reliable energy storage capability. Among the most interesting, emerging-to-industrial ready technologies, CO2 power cycles seem to have the potential to provide a major step toward the average plant efficiency and equipment cost levels needed to achieve the marketability. Today, in most cases, supercritical CO2 power loops are seen as an opportunity to achieve a major step in thermodynamic efficiencies if applied in supercritical condition and with a quite complicated cycle configurations (e.g. Recompressed and Re-Heated, or other combined solutions), with cycle maximum temperature above 650°C. Current cycle configurations are affected by a relative complexity of the power block, including non-negligible technological uncertainties with respect to simpler Brayton cycle solutions, possibly causing delay in the commercial application of the CO2 power block, at least for CSP applications. The aim of this article is to present some possible CO2 power closed cycle solutions, including supercritical as well as transcritical options, in order to propose cost-effective alternatives to current state-of-the-art steam power block of CSPs, highlighting that relatively simple CO2 cycle arrangements can enhance CSP competitiveness, representing a valid intermediate step towards next more advanced sCO2 cycles.

New policies and strict emission limits in the transports sector result in a gradual switch towards alternative fuels and hydrogen is getting attention: fuel cell systems are considered ideal energy converters of the next future. As the interest is rising in Proton Exchange Membrane Fuel Cells (PEMFC), there is a need for experimental research and dedicated laboratories on systems designed with Balance of Plant. In this context, the HI-SEA Laboratory (240-kW PEMFC by Nuvera FC, a joint between the University of Genoa-Fincantieri) was born. In this paper, the tuning of the laboratory to simulate a ship-likely environment is addressed, looking at the main problematics and resolutions, related to the cathodic line and the cooling control. Some guidelines are defined to install a PEMFC system onboard a ship exploiting the existing infrastructure. Thanks to the experimental campaign, a stack voltage model previously validated is employed to evaluate the performance of the system.

In this paper, the authors present an innovative approach to compare the most promising innovative technologies for energy production and storage for maritime applications. The developed algorithm, which include a large database built with market and literature data, compares several possible solutions, including innovative ones, from the environmental, economic and energetic standpoints. A detailed description of the functions implemented in the database is reported, explaining also in detail the algorithm developed to evaluate and compare the technologies. Then, the methodology is applied to two case studies to demonstrate the algorithm’s potential, the reliability of the wide range of data included in the database and the impact of the scenario on the final results. The investigated case studies are: (i) a small size passenger ship operating in urban areas (ii) a large size cruise ship. Analyzing the first case study, a focus on the impact of generation unit and fuel storage systems is developed for the most promising solutions, represented by fuel cells in comparison to standard solutions. The second case study shows that, as could be expected, the most promising solutions in this range of application is the use of MDO or LNG in Internal Combustion Engines. In order to evaluate the future potential of the different alternative fuels, a sensitivity analysis is performed to evaluate the impact of the increasing emissions’ importance: methanol, LNG, and ammonia are indicated as the most futurible fuels. It is worth noting that the presented approach has a general validity, thus it can be applied to other ships’ typologies; the modular structure also allows for including further emerging technologies.

As the interest in hydrogen and PEM fuel cells is growing, it is crucial to define the best technology for fuel storage, especially in the transportation field. Metal hydrides show different benefits, including the possibility of thermally coupling the hydrogen storage and utilization systems: fuel cells require heat subtraction for ensuring proper operation, while metal hydrides require heat to activate the hydrogen release reactions. This work describes the integration of PEMFCs and metal hydrides on board a zero-emissions ship, with a special focus on their thermal coupling; a model-based approach is developed to ensure the system’s feasibility at different load demands for the vessel, including transient conditions. The study is based on the real application of an innovative zero-emissions ship(ZEUS) financed by Fincantieri-Isotta Fraschini S.p.A, where the total power installation is set at 144 kW by PEMFC and 50 kg of hydrogen are stored by metal hydrides.

Polymer Electrolyte Membrane Fuel Cells are considered among the most promising technologies for hydrogen utilization in both stationary and automotive applications, thanks to high energy density and near zero emissions during the entire life cycle. Nevertheless, the cost of its components – especially the catalyst and the membrane – is still consistent and prevents from the expected cost decrease predicted by the US Department of Energy. It is therefore essential to predict the effect of contaminants on PEMFC’s materials and to estimate the useful life. This work aims to collect and interpretate the results of the recent studies on catalyst contamination: a voltage degradation rate is defined as mV lost per operative hour under stressing conditions, at different contaminant concentrations, and current densities. The literature on this topic is consistent, but the absence of standards for the experimental tests under contaminated flows – regarding in particular the boundary conditions and the exposure time – makes it difficult to extrapolate the generic degradation trends and to compare the results of different works. Thanks to the results of the present study, some test protocols for future activities are defined and the generic effects of specific contaminants – as reported in literature – are issued.

The increasing share of electricity produced from renewable energy sources (RES), with the consequent strong penetration in the current energy network, is causing a growing need of balancing power to compensate power supply from such fluctuating sources. For these reasons, nowadays the power plants are running more often at part-load providing ancillary services and sustaining the grid operability. Therefore, an increase in efficiency during part-load operation impacts positively the year-round efficiency. A possible solution, studied in the framework of PUMP-HEAT H2020 Project for flexibility enhancement, is characterized by the intake conditioning. Such concept, after a general introduction, is here applied to increase the temperature of the intake of power oriented combined cycle (PO-CCGT), mitigating the Gas Turbine off-design and resulting in an enhanced efficiency. In this work, a statistical analysis of actual PO-CCGT production profiles and climatic data is performed considering the Italian context, to assess the potential of this practice under the economic and environmental point of view.

Pressurized solid oxide fuel cell (SOFC) systems are one of the most promising technologies to achieve high energy conversion efficiencies and reduce pollutant emissions. The most common solution for pressurization is the integration with a micro gas turbine, a device capable of exploiting the residual energy of the exhaust gas to compress the fuel cell air intake and, at the same time, generating additional electrical power. The focus of this study is on an alternative layout, based on an automotive turbocharger, which has been more recently considered by the research community to improve cost effectiveness at a small size (<100 kW), despite reducing slightly the top achievable performance. Such a turbocharged SOFC system poses two main challenges. On one side, the absence of an electrical generator does not allow direct control of the rotational speed, which is determined by the power balance between turbine and compressor. On the other side, the presence of a large volume between compressor and turbine, due to the fuel cell stack, alters the dynamic behavior of the turbocharger during transients, increasing the risk of compressor surge. The pressure oscillations associated with such event are particularly detrimental for the system because they could easily damage the materials of the fuel cells. This paper aims is to investigate different techniques to drive the operative point of the compressor far from the surge condition when needed, reducing the risks related to transients and increasing its reliability. By means of a system dynamic model, developed using the TRANSEO simulation tool by Thermochemical Power Group (TPG), the effect of different antisurge solutions is simulated: (i) intake air conditioning, (ii) water spray at compressor inlet, (iii) air bleed and recirculation, and (iv) installation of an ejector at the compressor intake. The pressurized fuel cell system is simulated with two different control strategies, i.e., constant fuel mass flow and constant turbine inlet temperature. Different solutions are evaluated based on surge margin behavior, both in the short and long terms, but also monitoring other relevant physical quantities of the system, such as compressor pressure ratio and turbocharger rotational speed. [/av_toggle][/av_toggle_container] [/av_tab] [av_tab title='2020' icon_select='no' icon='ue800' font='entypo-fontello']

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A micro gas turbine (MGT) is a potential option for distributed energy systems driven by fuel and solar energy. The dynamic characteristics of a solar-hybrid microturbine system are essential to its control development and performance assessment. In this paper, a dynamic model is proposed, including an MGT (T100), a tubular air receiver and a sensible thermal energy storage system, which are experimentally validated well. Based on the developed model, the dynamic responses of a solar-hybrid microturbine system in stand-alone mode are studied considering load and Direct Normal Irradiance (DNI) changes. Results show that the fuel consumption is greatly reduced by integrating solar energy, which comes at the cost of system instability; if the investigated system experiences a significant load decrease, heliostats must be oriented away from the air receiver to ensure a stable operation, whereas the load must be increased incrementally to avoid a compressor surge in the case of a significant load increase. Compared to load change, DNI change will cause smaller overshoots of the MGT’s rotational speed and surge margin. The system is simulated with measured DNI and shows that the thermal energy storage can reduce the fluctuation of combustor inlet temperature from 130.8°C to 12.8°C.

In this manuscript, an automated framework dedicated to design space exploration and design optimization studies is presented. The framework integrates a set of numerical simulation, computer-aided design, numerical optimization, and data analytics tools using scripting capabilities. The tools used are open-source and freeware, and can be deployed on any platform. The main feature of the proposed methodology is the use of a cloud-based parametrical computer-aided design application, which allows the user to change any parametric variable defined in the solid model. We demonstrate the capabilities and flexibility of the framework using computational fluid dynamics applications; however, the same workflow can be used with any numerical simulation tool (e.g., a structural solver or a spread-sheet) that is able to interact via a command-line interface or using scripting languages. We conduct design space exploration and design optimization studies using quantitative and qualitative metrics, and, to reduce the high computing times and computational resources intrinsic to these kinds of studies, concurrent simulations and surrogate-based optimization are used.

The closing sound of a car door is objectively not related to the intrinsic quality of the vehicle but it is an important subjective parameter for vehicle evaluation. For automotive developers, it is very interesting to deepen this phenomenon and to define a methodology to understand the influence of several parameters on door-closing sound quality. The aim of this paper is to evaluate the possibility of analysing this phenomenon, called car-door slamming, using a numerical simulation approach. Simulation methods for vibro-acoustic analysis are sufficiently robust and predictive in the case of simple systems, as it emerges from a parallel investigation conducted on an elementary component like an annular disk. In simulating complex systems, as in the case of door slamming, where non-linearities may be significant, methods are not always reliable and sufficiently predictive. In the specific case, the main difficulty is to correctly identify the dynamic behaviour of a trimmed car door, which is a very complex system. The paper reports an analysis and a comparison between the experimental and simulation results of the car-door slamming phenomenon, highlighting the dependence of the quality of the numerical results on the particular simulation method adopted. The paper also reports an experimental and numerical vibro-acoustic analysis of a trimmed car door isolated from the vehicle with no constraints (free-free condition) to ascertain its dynamic behaviour in a simpler condition not coupled to the vehicle. The result shows a significant level of system complexity even in this case.

Micro gas turbine (MGT) engines in the range of 1–100 kW are playing a key role in distributed generation applications, due to the high reliability and quick load following that favor their integration with intermittent renewable sources. Micro-combined heat and power (CHP) systems based on gas turbine technology are obtaining a higher share in the market and are aiming at reducing the costs and increasing energy conversion efficiency. An effective control of system operating parameters during the whole engine life-time is essential to maintain desired performance and at the same time guarantee safe operations. Because of the necessity to reduce the costs, fewer sensors are usually avail-able than in standard industrial gas turbines, limiting the choice of control parameters. This aspect is aggravated by engine aging and deterioration phenomena that change operating performance from the expected one. In this situation, a control architecture designed for healthy operations may not be adequate anymore, because the relationship between measured parameters and unmeasured variables (e.g., turbine inlet temperature(TIT) or efficiency) varies depending on the level of engine deterioration. In this work, an adaptive control scheme is proposed to compensate the effects of engine degradation over the lifetime. Component degradation level is monitored by a diagnostic tool that estimates performance variations from the available measurements; then, the information on the gas turbine health condition is used by an observer-based model predictive controller to maintain the machine in a safe range of operation and limit the reduction in sys-tem efficiency.

In an increasingly decentralized energy market, micro gas turbines are seen with great potential due to their low emissions and fuel flexibility, which aligns with growing environmental concerns. Although presenting a relatively low efficiency, these machines could be improved by coupling it with an organic Rankine cycle. This manuscript covers the thermoeconomic design and optimization of such bottoming cycle for a 100 kWe micro gas turbine. The tool employed for such calculations is extensively described and was developed using solely open resources. The results shown that the saturation temperature at ambient pressure was an important variable when the minimum pressure is constrained above ambient and that a high degree of superheating was favored when the recuperated cycle is heated directly by the microturbine flue gases. Pentane was flagged as the best working fluid, generating 14.1 kWe of additional power and increasing the overall electric efficiency from 30 to 34.2%. The Authors show that at the current state of the art an efficiency of around 35% is the upper practical limit for such microturbine organic Rankine cycle combination.

Growing environmental concerns are driving the energy market toward the development of thermodynamic cycles to harness renewable energy and waste heat. This manuscript introduces the novel organic Rankine flash cycle, which combines the organic Rankine cycle with the trilateral cycle, merging their advantages in terms of high specific power output and low heat transfer irreversibility, respectively. By comparing the organic Rankine flash cycle to the organic flash cycle, it was found that the proposed architecture reaches a peak exergy efficiency at a more realistic value of two-phase expansion volume flow ratio, consistently achieves higher energy and exergy efficiencies, presents a lower cost, and is not constrained to operate close to the working fluid saturation temperature, promising easier operability. Considering pentane as working fluid, the exergy efficiency of the organic Rankine flash cycle is 18%p higher for a heat source temperature of 150 °C, 12%p for 175 °C, and 4%p for 200 °C. The attractive thermoeconomic performance of the proposed organic Rankine flash cycle highlights the potential of such a cycle as a new paradigm in the ORC panorama, encouraging further investigation towards practical demonstration.

The aim of the present work in this paper is to propose an optimized energy management strategy that allows enhancing the life cycle of batteries through the optimal scheduling of energy consumption in a house connected to a stand-alone energy system with an energy storage system (PV, wind turbine, diesel generator, and batteries). A rain flow counting algorithm is used to calculate the number of cycles of the battery, while the optimization problem was solved using a particle swarm optimization algorithm (PSO). The optimization aims to reduce the number of cycles in the whole day by managing the charging and discharging process in order to maximize the battery life cycle. The results obtained by the simulation prove the effectiveness of the proposed strategy in the optimization of the life cycle of the battery to more than 38%.

The expander is one of the key components of an ORC as the cycle efficiency strongly depends on the expander efficiency. This paper presents a method for design optimization of a radial inflow turbine (RIT) using a mean-line model. The novelty of this work lies in the equation-based formulation of the mathematical problem, which enables the use of an efficient gradient based method for optimization. This means that there is no distinction between real decision variables such as specific speed and velocity ratio, and parameters that are unknown a priori such as rotor outlet entropy and velocity. Constraints are imposed to ensure conservation of mass, and to ensure a feasible and consistent design, and the objective is to maximize the total-to-static efficiency. The main results showed an average CPU time less than one second and a success rate of 80% for converging to the global optimum when the independent variables were given random start values. We therefore recommend the proposed method for preliminary RIT-design or to be integrated into an ORC system design model enabling for instance working fluid screening with fluid-dependent expander efficiency.

Nowadays research in energy field is focused on conversion technologies which could achieve higher efficiencies and lower environmental impact. In such a context, fuel cells in general and pressurized solid oxide fuel cell (SOFC) hybrid systems are attractive for their high electric efficiency, potential for cogeneration applications, low carbon emissions and high performance at part-load. The aim of this work is to perform the design under uncertainty of an innovative turbocharged hybrid system, where a turbocharger is used to pressurize the fuel cell, featuring better cost effectiveness than a microturbine-based hybrid system at small scales (<100kWe). In this study, a response surface of the plant steady-state performance is developed considering the main operating parameters (fuel cell area, stack current density and recuperator exchange surface) as factors to create the metamodel, taking into account the uncertainties related to the turbocharger efficiency and to the ohmic losses of the fuel cell stack. The optimal economic design of such a turbocharged hybrid system is then analysed at off-design conditions, to preliminary assess the operating costs and profitability within the Italian market scenario considering the variability of fuel and electricity prices. Finally, the impact of uncertainties both on plant performance and economics are discussed, showing that both payback period and internal rate of return present a significant variability, mostly due to the uncertainties related to the prices, showing that a proper evaluation of the evolution of the prices along the years should be performed for a proper economic feasibility analysis.

This paper shows control approaches for managing a pressurized Solid Oxide Fuel Cell (SOFC) system fuelled by biogas. This is an advanced solution to integrate the high efficiency benefits of a pressurized SOFC with a renewable source. The operative conditions of these analyses are based on the matching with an emulator rig including a T100 machine for tests in cyber-physical mode (a real-time model including components emulated in the rig, operating in parallel with the experimental facility and used to manage some properties in the plant, such as the turbine outlet temperature set-point and the air flow injected in the anodic circuit). The T100 machine is a microturbine able to produce a nominal electric power output of 100 kW. So, the paper presents a real-time model including the fuel cell, the off-gas burner, and the recirculation lines. Although the microturbine components are planned to be evaluated with the hardware devices, the model includes also the T100 expander for machine control reasons, as detailed presented in the devoted section. The simulations shown in this paper regard the assessment of an innovative control tool based on the Model Predictive Control (MPC) technology. This controller and an additional tool based on the coupling of MPC and PID approaches were assessed against the application of Proportional Integral Derivative (PID) controllers. The control targets consider both steady-state (e.g. high efficiency solutions) and dynamic aspects (stress smoothing in the cell). Moreover, different control solutions are presented to operate the system during fuel cell degradation. The results include the system response to load variations, and SOFC voltage decrease. Special attention is devoted to the fuel cell system constraints, such as temperature and time-dependent thermal gradient. Considering the simulations including SOFC degradation, the MPC was able to decrease the thermal stress, but it was not able to compensate the degradation. On the other hand, the tool based on the coupling of the MPC and the PID approaches produced the best results in terms of set-point matching, and SOFC thermal stress containment.

Tesla bladeless turbomachines are recently being investigated due to many advantages such as its simple design and ease of manufacturing. If an efficient design is achieved, this will be a promising machine in the area of small-scale power generation and energy harvesting. This paper focuses on the experimental performance investigation of 3 kW (rated power) Tesla bladeless expander. The Tesla expander and electric generator are housed in a single casing making it first of its kind being tested with such configuration. The expander is fed with air and operated at high rotational speeds up to 40000 rpm. The test is carried out with different number of nozzles to understand its effect on the performance. Results show that the peak efficiency for two nozzles is better than one nozzle and four nozzle configurations for the same inlet pressure conditions. Experimental tests revealed that this turbine is most efficient Tesla turbine till now with air as a working fluid. Furthermore, one of the most important losses in Tesla turbomachines, nozzle loss, is experimentally characterized. Specific vibrational tests were carried out to obtain complete machine dynamical characterization. The vibrational response characterization of the turbine enabled us to recognize a disk mode family solicited by the air flow and to perform a proper machine maintenance and balancing aiming to reduce the energy of its operational vibration.

The present paper shows signal processing techniques applied to experimental data obtained from a T100 microturbine connected with different volume sizes. This experimental activity was conducted by means of the test rig developed at the University of Genoa for hybrid systems emulation. However, these results can be extended to all advanced cycles in which a microturbine is connected with additional external components which lead to an increase of the plant volume size. Since in this case a 100 kW microturbine was used, the volume was located between the heat recovery unit outlet and the combustor inlet like in the typical cases related to small size plants. A modular vessel was used to perform and to compare the tests with different volume sizes. The main results reported in this paper are related to rotating stall and surge operations. This analysis was carried out to extend the knowledge about these risk conditions: the systems equipped with large volume size connected to the machine present critical issues related to surge and stall prevention, especially during transient operations towards low mass flow rate working conditions. Investigations conducted on acoustic and vibrational measurements can provide interesting diagnostic and predictive solutions by means of suitable instability quantifiers which are extracted from microphone and accelerometer data signals. Hence different possible tools for rotating stall and incipient surge identification were developed through the use of different signal processing techniques, such as Wavelet analysis and Higher Order Statistics Analysis (HOSA) methods. Indeed, these advanced techniques are necessary to maximize all the information conveyed by acquired signals, particularly in those environments in which measured physical quantities are hidden by strong noise, including both broadband background one (i.e. typical random noise) but also uninteresting components associated to the signal of interest. For instance, in complex coupled physical systems like the one it is meant to be studied, which do not satisfy the hypothesis of linear and Gaussian processes inside them, it is reasonable to exploit these kinds of tools, instead of the classical Fast Fourier Transform (FFT) technique by itself, which is mainly adapt for linear systems periodic analysis. The proposed techniques led to the definition of a quantitative indicator, the sum of all auto-bispectrum components modulus in the subsynchronous range, which was proven to be reliable in predicting unstable operation. This can be used as an input for diagnostic systems for early surge detection. Furthermore, the presented methods will allow the definition of some new features complementary with the ones obtainable from conventional techniques, in order to improve control systems reliability and to avoid false positives.

Under new scenarios with high shares of variable renewable electricity, combined cycle gas turbines (CCGT) are required to improve their flexibility, in terms of ramping capabilities and part-load efficiency, to help balance the power system. Simultaneously, liberalization of electricity markets and the complexity of its hourly price dynamics are affecting the CCGT profitability, leading the need for optimizing its operation. Among the different possibilities to enhance the power plant performance, an inlet air conditioning unit (ICU) offers the benefit of power augmentation and “minimum environmental load” (MEL) reduction by controlling the gas turbine inlet temperature using cold thermal energy storage and a heat pump. Consequently, an evaluation of a CCGT integrated with this inlet conditioning unit including a day-ahead optimized operation strategy was developed in this study. To establish the hourly dispatch of the power plant and the operation mode of the inlet conditioning unit to either cool down or heat up the gas turbine inlet air, a mixed-integer linear optimization (MILP) was formulated using MATLAB, aiming to maximize the operational profit of the plant within a 24-hours horizon. To assess the impact of the proposed unit operating under this dispatch strategy, historical data of electricity and natural gas prices, as well as meteorological data and CO2 emission allowances price, have been used to perform annual simulations of a reference power plant located in Turin, Italy. Furthermore, different equipment capacities and parameters have been investigated to identify trends of the power plant performance. Lastly, a sensitivity analysis on market conditions to test the control strategy response was also considered. Results indicate that the inlet conditioning unit, together with the dispatch optimization, increases the power plant’s operational profit by achieving a wider operational range, particularly important during peak and off-peak periods. For the specific case study, it is estimated that the net present value of the CCGT integrated with the ICU is 0.5% higher than the power plant without the unit. In terms of technical performance, results show that the unit reduces the minimum environmental load by approximately 1.34% and can increase the net power output by 0.17% annually.

Model Predictive Control (MPC) is a well-known control architecture that has encountered an enormous variety of applications since the very beginning until current days. The pros and cons of such control technique are very well known and both of them rely on the embedded model, which is used to determine the control trajectory. Still, the discrepancy between embedded model and real operative conditions can affect the control response due to uncertainties in measurement chain, noise and so on. Still, it is hardly available in literature what would happen in case the plant is operating far from the design condition of the model. This is of particular interest once a linear MPC is governing a non-linear process where the linearization of the target plant must be processed to tune the MPC itself. This paper analyses experimental results from a fuel cell gas turbine hybrid system, namely SOFC/GT emulator test rig, where a linearized MPC was adopted to control stack inlet temperature. The test rig is constituted by a modified Turbec T100 micro gas turbine where a volume of 4 m3 is interposed between compressor and turbine. This emulates the impact of the SOFC on the GT. The system is connected in real-time mode to a model, which runs in parallel and reads what is going on the plant side and simulates the behavior of the associated SOFC stack. The MPC controller governs the plant according to the stack inlet temperature computed by the model in real-time mode. This MPC must be considered as a supervisor of the system, as the gas turbine was still equipped with its original control system. The plant was subject to an on-purpose strong degradation – operated via a constant venting of air from compressor to ambient. This operation strongly influenced the performance of the system, which were no longer able to operate at a level of temperature and power for which the controller was designed for. Still, a ramping down in power and back up was performed and the MPC showed performance which were in agreement with the design performance. Such surprisingly good result is explained with the complexity of the embedded model, which was derived from a completely physical model of the target system and constituted by more than 200 states.

Renewable energy penetration is growing, due to the target of greenhouse-gas-emission reduction, even though fossil fuel-based technologies are still necessary in the current energy market scenario to provide reliable back-up power to stabilize the grid. Nevertheless, currently, an investment in such a kind of power plant might not be profitable enough, since some energy policies have led to a general decrease of both the average price of electricity and its variability; moreover, in several countries negative prices are reached on some sunny or windy days. Within this context, Combined Heat and Power systems appear not just as a fuel-efficient way to fulfill local thermal demand, but also as a sustainable way to maintain installed capacity able to support electricity grid reliability. Innovative solutions to increase both the efficiency and flexibility of those power plants, as well as careful evaluations of the economic context, are essential to ensure the sustainability of the economic investment in a fast-paced changing energy field. This study aims to evaluate the economic viability and environmental impact of an integrated solution of a cogenerative combined cycle gas turbine power plant with a flue gas condensing heat pump. Considering capital expenditure, heat demand, electricity price and its fluctuations during the whole system life, the sustainability of the investment is evaluated taking into account the uncertainties of economic scenarios and benchmarked against the integration of a cogenerative combined cycle gas turbine power plant with a Heat-Only Boiler.

A Multi-point Approximation Method (MAM) coupled with adjoint is presented to increase the efficiency of a modern jet-engine fan blade. The study performed makes use of Rolls-Royce in-house suite of codes and its discrete adjoint capability. The adjoint gradient is used along with MAM to create a Design Of Experiment to enhance the optimization process. A generalized Free-Form Deformation (FFD) technique is used to parametrize the geometry, creating a design space of 180 parameters. The resulting optimum blade at design conditions is then evaluated at off-design conditions to produce the characteristic curve, which is compared with real test data. Finally, a preliminary Active Design Subspace (ADS) representing the fan efficiency is created to evaluate the robustness of the objective function in respect to the most significant design parameters. The ADS allows to collapse a large design space of the order of hundreds parameters to the few most important variables, measuring their contribution. This map is valuable in many respects to the fan designers and manufacture engineers to identify any ridges where the performance may deteriorate rapidly, hence a more robust part of the design space can easily be visualized and identified.

The present study presents a techno-economic analysis of a novel power plant layout developed to increase the dispatch flexibility of a Combined Cycle Gas Turbine (CCGT) coupled to a District Heating Network (DHN). The layout includes the incorporation of high temperature heat pumps (HP) and thermal energy storage (TES). A model for optimizing the short-term dispatch strategy of such system has been developed to maximize its operational profit. The constraints and boundary conditions considered in the study include hourly demand and price of electricity and heat, ambient conditions and CO2 emission allowances. To assess the techno-economic benefit of the new layout, a year of operation was simulated for a power plant in Turin, Italy. Furthermore, different layout configurations and critical size-related parameters were considered. Finally, a sensitivity analysis was made to assess the performance under different market scenarios. The results show that it is indeed beneficial, under the assumed market conditions, to integrate a HP in a CCGT plant coupled to a DHN, and that it remains profitable to do so under a variety of market scenarios. The best results for the assumed market conditions were found when integrating a 15 MWth capacity HP in the 400 MWel CCGT-CHP. For this case study, the investment in the HP would yield a net present value (NPV) of 1.22 M€ and an internal rate of return (IRR) of 3.04% for a lifetime of 20 years. An increase was shown also in operational flexibility with 0.14% of the electricity production shifted while meeting the same heating demand. Additionally, it was found that the TES makes the system even more flexible, but does not make up for the extra investment.

Pressurized solid oxide fuel cell systems are a particularly attractive conversion technology for their high electric efficiency, potential for cogeneration applications, low carbon emissions and high performance at part-load. In this work an innovative biofueled hybrid system is considered, where the fuel cell stack is pressurized with a turbocharger, resulting in a system with improved cost effectiveness than a microturbinebased one at small scales. In a previous work, a detailed steady state model of the system, featuring components validated with industrial data, was developed to simulate the system and analyze its behavior in different conditions. The results obtained from this model were used to create response surfaces capable of evaluating the impact of the main operating parameters (fuel cell area, stack current density and recuperator surface) on the performance and the profitability of the plant considering system uncertainties. In this paper, similar but extended response surfaces will be used to perform a multi-objective optimization of the system considering the capital costs of the plant and the net power produced as objectives (turbocharger is fixed in geometry). The impact of the energy market scenario on the optimal design of such a system will be investigated considering its installation in three different countries. Finally, the Pareto front produced by optimization will be used to evaluate the robustness of the top performance solutions.

During the last decades there has been a rise of awareness regarding the necessity to increase energy systems efficiency and reduce carbon emissions. These goals could be partially achieved through a greater use of gas turbine – solid oxide fuel cell hybrid systems to generate both electric power and heat. However, this kind of systems are known to be delicate, especially due to the fragility of the cell, which could be permanently damaged if its temperature and pressure levels exceed their operative limits. This could be caused by degradation of a component in the system (e.g. the turbomachinery), but also by some sensor fault which leads to a wrong control action. To be considered commercially competitive, these systems must guarantee high reliability and their maintenance costs must be minimized. Thus, it is necessary to integrate these plants with an automated diagnosis system capable to detect degradation levels of the many components (e.g. turbomachinery and fuel cell stack) in order to plan properly the maintenance operations, and also to recognize a sensor fault. This task can be very challenging due to the high complexity of the system and the interactions between its components. Another difficulty is related to the lack of sensors, which is common on commercial power plants, and makes harder the identification of faults in the system. This paper aims to develop and test Bayesian belief network based diagnosis methods, which can be used to predict the most likely degradation levels of turbine, compressor and fuel cell in a hybrid system on the basis of different sensors measurements. The capability of the diagnosis systems to understand if an abnormal measurement is caused by a component degradation or by a sensor fault is also investigated. The data used both to train and to test the networks is generated from a deterministic model and later modified to consider noise or bias in the sensors. The application of Bayesian belief networks to fuel cell – gas turbine hybrid systems is novel, thus the results obtained from this analysis could be a significant starting point to understand their potential. The diagnosis systems developed for this work provide essential information regarding levels of degradation and presence of faults in gas turbine, fuel cell and sensors in a fuel cell – gas turbine hybrid system. The Bayesian belief networks proved to have a good level of accuracy for all the scenarios considered, regarding both steady state and transient operations. This analysis also suggests that in the future a Bayesian belief network could be integrated with the control system to achieve safer and more efficient operations of these plants.

This paper aims to investigate the innovative design of a ducted horizontal-axis wind turbine and to compare its energy production with a traditional free turbine for energy harvesting, both at laboratory and on relevant environment scales. The ducted wind turbine was designed considering a convergent-divergent duct, with the turbine in the throat section, where the velocity is maximum. The first part of the present paper describes the test rig and the experimental activities at the University of Genoa (Italy) wind tunnel, aimed comparing between the ducted and the traditional wind turbine at laboratory scale, considering the same rotor and comparing the power production. The second part describes the pre-commercial prototype of the ducted turbine (1 m rotor diameter), installed in the harbor of Genoa and tested under real conditions. The two experimental campaigns have shown a power increase up to 2.5 from the same rotor, compared to the free turbine configuration. In both experimental campaigns, the influence of the angle between the wind direction and the duct was investigated to determine the maximum power output of the turbine, corresponding to a yaw angle of 20?. As a final step, a possible application of this kind of ducted wind turbines is presented, investigating the case study of highway tunnel illumination: in this case, the presence of a yaw angle allows for reducing the number of turbines for the same energy production.

The use of biogas to produce “green hydrogen” represents an interesting solution for assuring sustainability in the energy and mobility sectors with lower costs and a continuous production.

In this study, two hydrogen production plants using biogas as primary source, are studied and compared by applying the energy and exergy analyses for both the overall plant and components. The plants are designed as polygeneration systems able to produce high-pressure hydrogen, heat, and electricity for self-sustaining the energy consumption for purification, compression, and storage of the produced hydrogen. In this sense, these plants are proposed as on-site hydrogen production plants for the development of novel refueling stations.

The two proposed plants differ for the hydrogen production process: i) a biogas-to-hydrogen plant through steam reforming, ii) a biogas-to-hydrogen plant through autothermal reforming.

The results of the study have highlighted that the steam reforming-based configuration allows for achieving the best performance in terms of hydrogen production energy-based efficiency (59.8%) and hydrogen production exergy-based efficiency (59.4%). Moreover, the steam reforming-based configuration represents the best solution also considering the co-production of heat and hydrogen (energy-based efficiency 73.5% and exergy-based efficiency 64.4%), while the ATR-based layout, globally more exothermic, can be adopted when a larger local heat demand exists (energy-based efficiency 73.9% and exergy-based efficiency 54.8%).

This document describes an innovative wave energy converter for offshore applications. The Seaspoon device, designed as a large-size energy harvester, catches the kinetic energy of water orbital motions in ocean waves with promising conversion efficiency and robust technology, adaptable to different sea states. Most of the existing devices operate in on-shore condition. This makes the Seaspoon very adaptable and suitable for mobile installations. In addition, the localized energy production becomes very interesting for several research or commercial activities, in which the energy supply issue is a crucial aspect. Some prominent applications are meteorological or sea state monitoring, aquaculture activities, off-shore charging stations, power supply for different sensor types, etc. In the following paper, an initial overview of open-sea test facilities for wave energy conversion is presented, after that the paper treats Seaspoon technology: the design and installation phases of the first full scale prototype installed in the Gulf of Genoa, together with the monitored data from the open sea test campaign. Experimental results demonstrated the Seaspoon self-orienting behavior as well as its capability to efficiently harvest energy from sea states lower than the designed one.

This paper presents a data–driven model for the estimation of the performance of an air-cooled steam condenser (ACC) with the aim to develop an efficient online monitoring, summarized by the condenser pressure (or vacuum) as Key Performance Indicator. The estimation of the ACC performance model was based on different dataset from three different combined cycle power plants with a gross power of above 380 MWe each, focusing on stationary condition of the steam turbine. The datasets include both boundary (e.g. Ambient Temperature, Wind Speed) and operative parameters (e.g. steam mass flow rate, Steam turbine power, electrical load of the ACC fans) acquired from the power plants and some derived variable as the incondensable fraction, which calculation is here proposed as additional parameter. After a preliminary sensitivity analysis on data correlation, the paper focuses on the evaluation of different ACC Condenser models: Semi-Empirical model is described trough curves typically based on steam mass flow rate (or condenser load) and the ambient temperature as main parameters. Since monitoring based on ACC design curves Semi-Empirical models, provides biased poor results, with an error of about 15%, the curves parameters were estimated basing on training data set. Other two data driven models were presented, basing on a neural network modelling and multi linear regression technique and compared on the base of the reduced number of input at first and then including also the other process variables in the prediction of the condenser back pressure. Estimate the parameters of the Semi-Empirical model, results in a better prediction if just steam mass flow rate and ambient temperature are available, with an error of the 7%, thanks to the knowledge contained within the “curves shapes”, with respect to linear regression (8.3%) and Neural Network models (7.6%). Higher accuracy can be then obtained by considering a larger number of operative parameters and exploiting more complex data-driven model. With a higher number of features, the neural network model has proved a higher accuracy than the linear regression model. In fact, the mean percentage error of the NN model (2.6%), in all plant operating conditions, is slightly lower than the error of the linear regression model, but presents and much lower than the mean error of the Semi-Empirical model thanks to the additional data-based knowledge.

In the era of coal power station phase-out, natural gas fired combined cycle will drive the energy transition towards sustainable power generation. In a panorama of strong requirement for grid flexibility and non-dispatchable renewable penetration, the survival of a thermal power plant is strictly linked with operating successfully in compensating the renewable fluctuating production through flexible generation. The Italian case is taken as reference, considering that energy transition and renewable energy penetration may have similar effects also in different countries. In this direction, a test rig to investigate gas turbine compressor inlet conditioning techniques has been developed at the Tirreno Power laboratory of the University of Genoa, Italy. This is based on a Turbec T100 micro gas turbine (or microturbine), a Mayekawa heat pump and a phase-change material energy storage. The whole test-rig is virtually scaled up, through a cyber-physical system, to emulate a real 400MW combined cycle, with the heat pump governing the inlet conditions at the compressor. The microturbine is therefore used as the physical feedback for the system, whilst the steam bottoming cycle is simulated in real-time according to microturbine operation. The scope is to present the test rig and the procedure adopted to virtually scaleup a microturbine to a heavy-duty GT. the advantage of using microturbine for testing combined cycle flexibility options lays also on the possibility to make accelerated tests and to simulate multiple situations in compressed time windows.

In this paper, two different power-to-fuel solutions for sustainable fuel synthesis are investigated from the energetic, environmental, and economic standpoints. Both the solutions consider a pressurized PEM electrolysis section, fed by renewable sources, where high purity green Hydrogen is produced. Then, two separate processes are investigated for the synthesis of two distinct chemicals. In the first case, the hydrogen is mixed with CO2, sequestered by an industrial plant, and captured a carbon capture system (CCS): the two gases are sent to a pressurized reactor for methanol synthesis. In the second case, the hydrogen is mixed with N2, obtained from an industrial air separation unit (ASU), and sent to a reactor for ammonia synthesis. Both the synthesis processes are performed at high pressures and temperatures, thus a thermodynamic analysis is mandatory in order to calculate the overall efficiencies. In both cases, the power to fuel plants are investigated also in economic terms. Methanol synthesis presents a slightly higher efficiency compared to ammonia, while the two solutions are very similar from the economic standpoint. The sale of the co-produced oxygen allows for an improvement in economic terms for both cases and can be a key point in order to reach economic sustainability, together with the expected reduction in PEM electrolysers capital cost.

The paper focuses on the analysis of innovative energy systems onboard ships with the aim to evaluate, in a preliminary stage, which can be the most promising solution depending on the considered application. For this purpose, the dedicated tool HELM developed by the authors’ research group is employed. The tool uses maps reporting the main indicators (weight, volume, costs and emissions) for each component in relation to the installed power and the operational hours required (given by the user as an input), then it compares the results providing the best solution depending on the considered application. The maps have been built from a database developed throughout a wide analysis of the available market solutions in terms of energy generation devices (i.e. fuel cells, internal combustion engines), fuels (hydrogen, natural gas, diesel, methanol) and related storage technologies. The main strong point of HELM resides in its flexibility: it can be used for different typologies and sizes of ships (e.g. ferry boat, cruises, yachts); moreover, the database can be easily updated with more technologies. In this work, the focus is particularly on hydrogen application with PEM Fuel Cells and the use of innovative fuels (methanol, ammonia) in Internal Combustion Engines. Analysing different applications, it will be highlighted how the specific characteristics and priorities of the application affect the results of the best solutions. Furthermore, considering the regulation roadmap for the next years in the maritime context, promising technologies are highlighted also for future scenarios.

The exploitation of the biomethane as transport fuel is receiving increasing attention in many European countries. Technologies and processes for improving the Biogas-to-biomethane production with a lower energy consumption and lower costs are objective of several techno-economic studies.

In this paper two promising concepts for the biogas conversion are proposed and analyzed considering both technical and economic issues. The analysis regards the biogas upgrading by means of the chemical absorption with Hot Potassium Carbonate and the direct methanation of biogas by adding renewable hydrogen. In order to assess the feasibility of these technologies the numerical modelling has been applied for the plants designing. The energy results have then been used to assess the expected biomethane production price and a sensitivity analysis on the main parameters has been performed. Finally, economic performance of the options proposed will be evaluated under different market conditions.

The heating and cooling sector, responsible for a large fraction of greenhouse emissions, may have a large scale impact on the energy system evolution contributing to smart industrial and domestic electrification; at the same time the recent increase of renewable energy sources installation, posing a threat in terms of grid stability, makes available a considerable amount of clean and cheap electrical energy during peak hours production. Power to heat technologies constitute a promising solution to face both these issues reducing the electric demand variability and decarbonizing the heat production. Large vapor compression heat pumps are a reliable technology able to compete, under the economic point of view, with the heat-only-boilers in order to serve district heating networks. Performance and economic profitability of a compression cycle is strongly dependent on available thermal source and the temperature of water delivered to the network. The present work explores and compares performance and economic indicators under different installation conditions, considering compression heat pumps employing four different fluids: a traditional HCF (R134a) and three natural fluids, ammonia (R717), butane (R600), and propane (R290), often preferred nowadays to HCFs due to the lower global warming potential.

The Organic Rankine Cycle (ORC) is a thermodynamic cycle that can operate with a hot source over a wide range of temperatures, especially with low-grade heat (below 200°C). One of the main limitations for the success of small-scale ORC cycles (few to 100 kWe) is the relatively low isentropic efficiency of the typically used turbomachinery. Low turbine efficiency leads to low ORC cycle performance. To increase the performance of the cycle, the turbine efficiency must be increase, however, this significantly increases the cost of the machinery, making the cycle less profitable. In this work, the performance evaluation of low-temperature ORC cycles (100-150°C) with heat extraction along the expansion process is investigated, in an attempt to overcome this limitation. The studied cycle works in the same way as a conventional ORC, except that during the expansion process, heat is extracted. This heat is re-used later in the cycle, just before the hot source, allowing to reduce its load. The different cycles presented in this paper, using pentane as working fluid, are compared based on their exergetic and energetic efficiencies. The influence of three parameters on the cycle performance is studied: the regeneration ratio, the maximum temperature of the cycle and the turbine isentropic efficiency. In the case of a cycle using pentane with a maximum temperature of 150 °C and an turbine isentropic efficiency of 65%, the energy efficiency increases from 6.2% to 16.3% when going from no regeneration to full regeneration, and the exergy efficiency increases from 21.1 to 45.8%.. Secondly, the influence of the maximum temperature of the cycle is studied. Using pentane as the working fluid, the higher the maximum temperature is, the larger the benefits of heat extraction. However, this temperature cannot exceed the critical temperature of the organic fluid to stay in the case of a subcritical cycle. Finally, considering the turbine isentropic efficiency, it is possible to demonstrate that using a less efficient turbine, for example in small ORC systems, the performance of a cycle with an ideal turbine isentropic efficiency (100%) can be achieved compensating at cycle level the turbine losses with the heat extraction along the expansion process.

This paper shows signal processing techniques applied to experimental data obtained from a T100 microturbine connected with different volume sizes. This experimental activity was conducted by means of the test rig developed at the University of Genoa for hybrid systems emulation. However, these results can be extended to all advanced cycles in which a microturbine is connected with additional external components which lead to an increase of the plant volume size. Since in this case a 100 kW microturbine was used, the volume was located between the heat recovery unit outlet and the combustor inlet like in the typical cases related to small size plants. A modular vessel was used to perform and to compare the tests with different volume sizes. The main results reported in this paper are related to rotating stall and surge operations. This analysis was carried out to extend the knowledge about these risk conditions: the systems equipped with large volume size connected to the machine present critical issues related to surge and stall prevention, especially during transient operations toward low mass flowrate working conditions. Investigations conducted on acoustic and vibrational measurements can provide interesting diagnostic and predictive solutions by means of suitable instability quantifiers which are extracted from microphone and accelerometer data signals. Hence, different possible tools for rotating stall and incipient surge identification were developed through the use of different signal processing techniques, such as wavelet analysis and higher order statistics analysis (HOSA) methods. Indeed, these advanced techniques are necessary to maximize all the information conveyed by acquired signals, particularly in those environments in which measured physical quantities are hidden by strong noise, including both broadband background one (i.e., typical random noise) but also uninteresting components associated with the signal of interest. For instance, in complex coupled physical systems like the one it is meant to be studied, which do not satisfy the hypothesis of linear and Gaussian processes inside them, it is reasonable to exploit these kinds of tools, instead of the classical fast Fourier transform (FFT) technique by itself, which is mainly adapt for linear systems periodic analysis. The proposed techniques led to the definition of a quantitative indicator, the sum of all autobispectrum components modulus in the subsynchronous range, which was proven to be reliable in predicting unstable operation. This can be used as an input for diagnostic systems for early surge detection. Furthermore, the presented methods will allow the definition of some new features complementary with the ones obtainable from conventional techniques, in order to improve control systems reliability and to avoid false positives.

This manuscript presents a clean energy solution for marine applications, investigating both the choice of the most promising production and storage technologies and, in a second step, the best operational management in order to satisfy a ship’s energy demand. The case study subject of the analysis is a ferry, with a capacity up to 200 people, operating on the artificial lake of Itaipu hydroelectric plant (on the border between Brazil and Paraguay). In the framework of new international rules, aimed at clean and sustainable solutions, in particular in Emission Control Areas, PEM fuel cells are a promising technology for onboard power generation. In this paper a PEM fuel cell system is investigated in detail, analyzing the best operative strategy in terms of energy efficiency, CO2 emissions and costs, in comparison with the state-of-the-art solution for ships (fuel oil ICEs). The analysis is performed with two dedicated software tools, both developed at the University of Genoa: the first is a tool modeled to support the preliminary design and the choice of the most promising solutions for maritime applications; the second is a software program for thermo-economic analysis of energy systems in time-dependent conditions, aimed at determination of the best operative strategy, minimizing operative costs.

The proposed approach has general validity thus it can also be applied to different kinds of ships, even considering different technologies for energy generation and storage.

The sun is considered to be one of the most environmentally sound sources of clean and renewable energy. Nevertheless, new hybrid solar plants – combining solar power with another source of energy – have never been compared to traditional solar technologies. Therefore, the aim of this work is to compare the potential environmental impact of a 100 kWp photovoltaic plant (PV) with a 100 kW hybrid solar-gas turbine system (SHGT) using a life cycle assessment methodology. To the best of our knowledge, this type of comparison is the first of its kind. The analysis is performed considering three different scenarios for the SHGT. Additionally, a deep sensitivity analysis is undertaken, focusing on those parameters that mostly influence the outcomes. The results highlight that, using the currently available technology, PV resulted to be the best environmental choice, with greenhouse gas (GHG) emission of 0.043 kg CO_2eq/ kWh. SHGT plant emissions resulted to be higher, equal to 0.236 kg CO_2eq/kWh when running at nominal power 12 h/day, mainly due to the fuel contribution. However, improvements in receiver technology could make it possible to reach higher receiver outlet temperatures and consequently save fuel, reducing the overall environmental impact. Moreover, replacing the natural gas used as turbine running fuel with solar radiation leads to a reduction in GHG emissions, which become comparable to PV plant gases.

The dynamic modeling of energy systems can be used for different purposes, obtaining important information both for the design phase and control system strategies, increasing the confidence during experimental phase. Such analysis in dynamic conditions is generally performed considering fixed values for both geometrical and operational parameters such as volumes, orifices, but also initial temperatures, pressure. However, such characteristics are often subject to uncertainty, either because they are not known accurately or because they may depend on the operating conditions at the beginning of the relevant transient. With focus on a gas turbine fuel cell hybrid system (HS), compressor surge may or may not occur during transients, depending on the aforementioned cycle characteristics; hence, compressor surge events are affected by uncertainty. In this paper, a stochastic analysis was performed taking into account an emergency shut-down (ESD) in a fuel cell gas turbine HS, modeled with TRANSEO, a deterministic tool for the dynamic simulations. The aim of the paper is to identify the main parameters that impact on compressor surge margin. The stochastic analysis was performed through the response sensitivity analysis (RSA) method, a sensitivity-based approximation approach that overcomes the computational burden of sampling methods. The results show that the minimum surge margin occurs in two different ranges of rotational speed: a high-speed range and a low speed range. The temperature and geometrical characteristics of the pressure vessel, where the fuel cell is installed, are the two main parameters that affect the surge margin during an emergency shut down.

Economic dispatch for micro-grids and district energy systems presents a highly constrained non-linear, mixed-integer optimization problem that scales exponentially with the number of systems. Energy storage technologies compound the mixed-integer or unit-commitment problem by necessitating simultaneous optimization over the applicable time horizon of the energy storage. The dispatch problem must be solved repeatedly and reliably to effectively minimize costs in real-world operation. This paper outlines a method that greatly reduces, and under some conditions eliminates, the mixed-integer aspect of the problem using complementary convex quadratic optimizations. The generalized method applies to grid-connected or islanded district energy systems comprised of any variety of electric or combined heat and power generators, electric chillers, heaters, and all varieties of energy storage systems. It incorporates constraints for generator operating bounds, ramping limitations, and energy storage inefficiencies. An open-source platform, EAGERS, implements and investigates this optimization method. Results demonstrate a >99% reduction in computational effort when comparing the newly minted optimization strategy against a benchmark commercial mixed-integer solver applied to the same combined cooling, heating, and power problem.

This paper reports a review of an environmentally clean and efficient source of energy such as solid oxide fuel cell hybrid systems. Due to climate concerns, most nations are seeking alternative means of generating energy from a clean, efficient and environmental-friendly method. However, this has proven a big hurdle for both academic and industry researchers over many years. Currently, practical and technically feasible solution can be obtained via an integration of a microturbine and a fuel cell (hybrid systems). Combining the two distinct systems in a hybrid arrangement the efficiency of the microturbine increases from 25 to 30% to the 60-65% range. Hence, this paper outlines an engineering power generation solution towards the acute global population growth, the growing need, environmental concerns, intelligent use of energy with attendant environmental and hybrid system layouts concerning arising problems and tentative proposed solutions. Furthermore, advantages of a solid oxide fuel cell hybrid systems with respect to the other technologies are identified and discussed rationally. Special attention is devoted to modelling with software and emulator rigs and system prototypes. The paper also reviews the limitations and the benefits of these hybrid systems in relationship with energy, environment and sustainable development. Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are further discussed.

This paper describes a simplified framework to create dynamic models of SOFC/Gas Turbine Hybrid Systems. After some physical considerations on global SOFC/GT structure, the work focuses on the modelling approach. It embodies some empirical parameters, which can be derived from operating data or detailed simulation analysis. The framework results in a hybrid model – partly physics-based, partly data-driven – which covers a large range of working conditions. The resulting simplicity and robustness of the approach allows the potential adoption in different on-field applications such as fast response models for operators, control system development and validation, model-based controllers, as well as for dynamic performance evaluations. This last application is shown at the end of the paper, where the response of the model is compared with a real Cyber-Physical SOFC/Gas Turbine Emulator installed at the National Energy Technology Laboratory (NETL), Morgantown (West Virginia, USA).

The current study aims to perform a stochastic analysis on microturbine compact recuperators to evaluate the impact of uncertainties in design parameters on their cost and volume, by using two different probabilistic approaches: Monte Carlo (MC) and Response Sensitivity Analysis (RSA).

These two methods have been developed in Matlab® and then coupled with CHEOPE (Compact Heat Exchanger Optimisation and Performance Evaluation) software, which allows to analyze two different types of recuperators, used in microturbine applications: the furnace-brazed plate-fin type and the welded primary surface type. This paper focuses on an analysis of plate-fin type recuperators, for which the cost function adopted was tuned and verified in a previous study.

Three main parameters of the recuperator have been considered as uncertain: effectiveness, hot side and cold side pressure drops. The uncertainties associated with these three parameters are based on industrial knowledge. The aforementioned stochastic methods have been used to propagate such uncertainties on the relevant outputs, such as cost and volume, allowing us to evaluate the least expensive and the most compact recuperator among those analysed.

Thermal Energy Storage (TES) can play a critical role through provision of reliable energy supply and increase the market penetration of renewable energy sources. Thermochemical Energy Storage (TCES) based on reversible reactions offers distinguished advantages in comparison with sensible and latent heat storage: higher energy density, higher temperature range and possibility of seasonal storage. TCES systems based on the redox cycle of metallic oxides shows significant potential for integration with Concentrated Solar Power (CSP) plants using air as the heat transfer fluid, which also acts as a reactant for the redox reaction. A pilot scale thermochemical storage reactor designed for a CSP plant has been developed and tested in the framework of a collaborative European funded project “RESTRUCTURE” at the Solar Tower Julich (STJ). TCES system is proposed with the aim of achieving higher energy storage capacity and higher storage temperature. Numerical modeling of a TCES prototype presented in this study is a contribution towards this effort. The present work is focused on the innovative one-dimensional modeling of a TCES system based on the redox cycle of cobalt oxides (Co3O4/CoO), coated on the ceramics honeycomb structures. The numerical model for TCES involved the energy balance and reaction kinetics describing the redox reaction of cobalt oxides, to simulate the phenomena of thermochemical storage. The simulation results were presented as the temperature profiles at different positions inside the storage vessel and they were validated against experimental data published in literature by other groups. This validation proved that this model can simulate the overall thermochemical storage process with reasonable accuracy. The simulation tool was also used to perform the parametric analysis of the storage module, which provides guidance to optimize the performance of the storage system. Moreover, due to its good compromise between reliability and computational time, the established 1-D thermochemical storage model can be integrated with the CSP plant model for dynamic analysis of the whole system, which is the aim of this study.

This paper presents a Model Predictive Controller (MPC) operating an SOFC Gas Turbine hybrid plant at end-of-life performance condition. Its performance was assessed with experimental tests showing a comparison with a Proportional Integral Derivative (PID) control system. The hybrid system operates in grid-connected mode, i.e. at variable speed condition of the turbine. The control system faces a multivariable constrained problem, as it must operate the plant into safety conditions while pursuing its objectives. The goal is to test whether a linearized controller design for normal operating condition is able to govern a system which is affected by strong performance degradation. The control performance was demonstrated in a cyber-physical emulator test rig designed for experimental analyses on such hybrid systems. This laboratory facility is based on the coupling of a 100 kW recuperated microturbine with a fuel cell emulation system based on vessels for both anodic and cathodic sides. The components not physically present in the rig were studied with a real-time model running in parallel with the plant. Model output values were used as set-point data for obtaining in the rig (in real-time mode) the effect of the fuel cell system.

The result comparison of the MPC tool against a PID control system was carried out considering several plant properties and the related constraints. Both systems succeeded in managing the plant, still the MPC performed better in terms of smoothing temperature gradient and peaks.

Micro gas turbine engines in the range of 1-100 kW are playing a key role in distributed generation applications, due to the high reliability and quick load following that favor their integration with intermittent renewable sources. Micro-CHP systems based on gas turbine technology are obtaining a higher share in the market and are aiming at reducing the costs and increasing energy conversion efficiency. An effective control of system operating parameters during the whole engine lifetime is essential to maintain desired performance and at the same time guarantee safe operations. Because of the necessity to reduce the costs, fewer sensors are usually available than in standard industrial gas turbines, limiting the choice of control parameters. This aspect is aggravated by engine aging and deterioration phenomena that change operating performance from the expected one. In this situation, a control architecture designed for healthy operations may not be adequate anymore, because the relationship between measured parameters and unmeasured variables (e.g. turbine inlet temperature or efficiency) varies depending on the level of engine deterioration. In this work, an adaptive control scheme is proposed to compensate the effects of engine degradation over the lifetime. Component degradation level is monitored by a diagnostic tool that estimates performance variations from available measurements; then, the information on the gas turbine health condition is used by an observer-based model predictive controller to maintain the machine in a safe range of operation and limit the reduction in system efficiency.

In the pursuit of increasing their profitability, the design and operation of combined cycle power plants needs to be optimized for new liberalized markets with large penetration of renewables. A clear consequence of such renewable integration is the need for these plants for being more flexible in terms of ramping-up periods and higher part-load efficiencies. Flexibility becomes an even clearer need for combined heat and power plants to be more competitive, particularly when simultaneously following the market hourly price dynamics and varying demands for both the heat and the electricity markets. In this paper, three new plant layouts have been investigated by integrating different storage concepts and heat-pump units in key sections of a traditional plant layout. The study analyses the influence that market has on determining the optimum layouts for maximizing profits in energy-only markets (in terms of plant configuration, sizing and operation strategies). The study is performed for a given location nearby Turin, Italy, for which hourly electricity and heat prices, as well as meteorological data, have been gathered. A multi-parameter modeling approach was followed using KTH’s in house techno-economic modeling tool, which uses time-dependent market data, e.g. price and weather, to determine the trade-off curves between minimizing investment and maximizing profits when varying critical size-related power plant parameters e.g. installed power capacities and storage size, for pre-defined layouts and operating strategies. A comparative analysis between the best configurations found for each of the proposed layouts and the reference plant is presented in the discussion section of the results. For the specific case study set in northern Italy, it is shown that the integration of a pre-cooling loop into baseload-like power-oriented combined cycle plants is not justified, calling for investigating new markets and different operating strategies. Only the integration of a heat pump alone was shown to improve the profitability, but within the margin of error of the study. Alternatively, a layout where district heating supply water is preheated with a combination of a heat pump with hot thermal tank was able to increase the internal rate of return of the plant by up to 0.5%, absolute, yet within the error margin and thus not justifying the added complexity in operation and in investment costs. All in all, the analysis shows that even when considering energy-only market revenue streams (i.e. heat and electricity sells) the integration of heat pump and storage units could increase the profitability of plants by making them more flexible in terms of power output levels and load variations. The latter is shown true even when excluding other flexibility related revenue streams. It is therefore conclusively suggested to further investigate the proposed layouts in markets with larger heat and power price variations, as well as to investigate the impact of additional control logics and dispatch strategies.

Pressurised solid oxide fuel cell (SOFC) systems are a sustainable opportunity for improvement over conventional systems, featuring high electric efficiency, potential for cogeneration applications and low carbon emissions. Such systems are usually analyzed in deterministic conditions. However, it is widely demonstrated that such systems are affected significantly by uncertainties, both in component performance and operating parameters. This paper aims to study the propagation of uncertainties related both to the fuel cell (ohmic losses, anode ejector diameter and fuel gas composition) and the gas turbine cycle characteristics (compressor and turbine efficiencies, recuperator pressure losses). The analysis is carried out on an innovative hybrid system layout, where a turbocharger is used to pressurise the fuel cell, promising better cost effectiveness then a microturbine-based hybrid system, at small scales. Due to plant complexity and high computational effort required by uncertainty quantification methodologies, a response surface is created. To evaluate the impact of the aforementioned uncertainties on the relevant system outputs, such as overall efficiency and net electrical power, the Monte Carlo method is applied to the response surface. Particular attention is focused on the impact of uncertainties on the opening of the turbocharger wastegate valve, which is aimed at satisfying the fuel cell constraints at each operating condition.

Interest in small scale turbines is growing mainly for small scale power generation and energy harvesting. Conventional bladed turbines impose manufacturing limitations and higher cost, which hinder their implementation at small scale. This paper focuses on experimental and numerical performance investigation of Tesla type turbines for micro power generation. A flexible test rig for Tesla turbine fed with air as working fluid has been developed, of about 100W net mechanical power, with modular design of two convergent-divergent nozzles to get subsonic as well as supersonic flow at the exit. Seals are incorporated at the end disks to minimize leakage flow. Extensive experiments are done by varying design parameters such as disk thickness, gap between disks, radius ratio and outlet area of exhaust with speeds ranging from 10000 rpm to 40000 rpm. A quasi-1D model of the whole setup is created and tuned with experimental data to capture the overall performance. Major losses, ventilation losses at end disks, nozzle and exhaust losses are evaluated experimentally and numerically. Effect of design parameters on the performance of Tesla turbines is discussed.

The flexibility of power plants is a critical feature in energy production environments nowadays, due to the high share of non-dispatchable renewables. This fact dramatically increases the number of daily startups and load variations of power plants, pushing the current technologies to operate out of their optimal range. Furthermore, ambient conditions significantly influence the actual plant performance, creating deviations against the energy sold during the day-ahead and reducing the profit margins for the operators. A solution to reduce the impact of unpredicted ambient conditions, and to increase the flexibility margins of existing combined cycles, is represented by the possibility of dynamically controlling the temperature at compressor intake. At present, cooling down the compressor intake is a common practice to govern combined cycle performance in hot regions such as the Middle East and Africa, while heating up the compressor intake is commonly adopted to reduce the Minimum Environmental Load (MEL). However, such applications involve relatively slow regulation of air intake, mainly coping with extreme operating conditions. The use of continuously varying, at a relatively quick pace, the air temperature at compressor intake, to mitigate ambient condition fluctuations and to cope with electrical market requirements, involves proper modeling of the combined cycle dynamic behavior, including the short-term and long-term impacts of intake air temperature variations. This work presents a dynamic modeling framework for the whole combined cycle applied to one of IREN Energia’s Combined Cycle Units. The paper encloses the model validation against field data of the target power plant. The validated model is then used to show the potential in flexibility augmentation of properly adjusting the compressor intake temperature during operation.

The high share of non-dispatchable renewable energy source generators in the electrical grid has increased the need for flexibility of Gas Turbine Combined Cycles (GTCC) already installed. To maximize not only the maximum power produced, via Power Augmentation Technologies (PATs), but also to reduce the Minimum Environmental Load (MEL), both OEMs and GTCC owners have adopted several technical solutions. This kind of flexibility has become, year-by-year, ever more crucial to guarantee GTCC economical sustainability. Amongst the solutions which can be adapted to guarantee GTCC flexibility, the Inlet Conditioning System is a particularly interesting technical solution, which can be installed without restrictions related to the different GT design.

In this paper, an evaluation of the compressor inlet temperature effect over the Combined Cycle performance is presented, with a focus on the bottoming Cycle impact. Different Inlet Conditioning Strategies are then compared considering the energy, and the environmental impact on GTCC behavior. The performance of a layout including a Thermal Energy Storage (TES) and a Heat Pump (HP) is then evaluated and compared to other technical solutions.

A dynamic model is developed for a Micro Gas Turbine (MGT), characterized by an intrinsic free-spool configuration, coupled to large volumes. This is inspired by an experimental facility at the National Energy Technology Laboratory (NETL) called Hyper, which emulates a hybrid MGT and Fuel Cell system. The experiment and model can simulate stable and unstable operating conditions. The model is used to investigate the effects of different volumes on surge events, and to test possible strategies to safely avoid or recover from unstable compressor working conditions. The modelling approach started from the Greitzer lumped parameter approach, and it has been improved with integration of empirical methods and simulated components to better match the real Hyper plant layout and performance. Pressure, flow rate, and frequency plots are shown for the surge behavior comparing two different volume sizes, for cases where gas turbine shaft speed is uncontrolled (open loop) and controlled (closed loop). The ability to recover from a surge event is also demonstrated.

This paper focuses on rotor dynamic investigation of a bladeless turbine, or Tesla turbine, for application to innovative small scale cycles. Tesla rotor consists of a shaft with several co-rotating disks with small gaps between each other. The flow through the disks creates a momentum exchange by viscous effect, motoring the shaft. Thanks to its simplicity and low cost, the Tesla expander is attractive for energy harvesting and waste heat recovery from low/medium temperature in small and micro scale applications. Rotor assembly and its parts may present dynamic criticalities, due to their structural characteristics: to predict and ensure low vibrations during operations, numerical and experimental studies have been carried out on some prototypes. The activity started considering a non-rotating single Tesla disk both in free and real constrained configuration: an experimental modal analysis was performed, whose results were used to validate a disk numerical model. In this case, an analytical approach with a simplified geometry assumption was considered. All methods results were correlated each other and discrepancies have been identified and analysed. Furthermore, the investigation of a single disk rotor vibrational behaviour has been extended from static conditions to rotating conditions. Numerical analysis has been carried on taking into account the effect of gyroscopic couples and centrifugal field generated by disk rotation. In parallel, a corresponding experimental activity has been done using a dedicated test rig which allowed to perform vibrational operational measurement while the disk was in motion. Campbell diagram of the single rotating disk on the shaft has been obtained from numerical and experimental analysis allowing to identify system dynamic behaviour and to deepen aspects related to critical speeds. Finally, a whole rotor model has been developed, allowing the characterization of the dynamic behaviour of a fully assembled turbine rotor. The developed models, validated with experiments, are powerful tools that can predict the bladeless expander vibrational behaviour at the early phase of design.

In this paper, an analysis of the integration of a carbon capture unit and a power to fuel system for methanol synthesis with a coal power plant is presented from the energetic, environmental and economic standpoints. The study is carried out in three different sections. In the first part, the impact of the integration of a carbon capture system (CCS) and of a power to fuel plant (PtF) for methanol production is investigated in terms of plant average efficiency, fuel consumption, CO2 emissions. In the second part, the annual fixed and variable costs of the power plant, and the annual cost of electricity (COE) are assessed for different plant configurations. Additionally, future scenarios are analyzed considering the impact of European policies on the CO2 emission’s cost, defined by the European Emission Trading System (ETS). Finally, an economic feasibility analysis of the power to fuel plant is performed and the methanol production is evaluated. Moreover, a sensitivity analysis is carried out to evaluate the impact of the most affecting parameters (electrical energy cost, the methanol selling price and the capital cost of the electrolyzer) in terms of Internal Rate of Return (IRR).

Compressor behaviour analysis in critical working conditions, such as incipient surge, represents a significant aspect in the turbomachinery research field. Turbines connected with large-size volumes present critical issues related to surge prevention especially during transient operations. Investigations based on acoustic and vibrational measurements appear to provide an interesting diagnostic and predictive solution by adopting suitable quantifiers calculated from microphone and accelerometer signals. For this scope a wide experimental activity has been conducted on a T100 microturbine connected with different volume sizes. A machine dynamical characterisation has been useful for better interpretation of signals during its transient to the surge. Hence, different possible methods of incipient surge identification have been developed through the use of different signal processing techniques in time, frequency and angle domain. These results will be useful for control system development to prevent compressor failures.

Polygeneration systems, designed for providing multiple energy services like hydrogen, heat and electricity, represent a possible solution for the transition to sustainable lowcarbon energy systems, thanks to a substantial increase in the overall efficiency. A further step to reach zero-carbon energy systems can be done by using renewables as primary sources.

In this study a biogas-based polygeneration system for the combined hydrogen, heat and electricity production is designed and analyzed from energy and economic points of view.

The system consists of four sections: a biogas processing unit consisting in an autothermal reactor and a water gas shift reactor, an SOFC power unit, a hydrogen separation unit and a hydrogen compression/storage unit. The syngas generated in the autothermal reforming reactor is split in two fluxes: the first one is sent to the SOFC power unit for generating electricity and heat, the second one is sent to the water gas shift reactor to increase the hydrogen content. The hydrogen rich gas exiting the shifter, purified in the hydrogen separation unit (hydrogen quality is equal to 99.995%), is then compressed up to 820 bars and stored.

The system behavior and the energy performances have been investigated by using the numerical simulation based on thermo-electrochemical models. Four operating conditions, related to different SOFC loads (from 30% to 100%), have been analyzed. The evaluated overall efficiencies range from 68.5% to 72.3% and the energy saving, calculated with respect to the separate production of hydrogen, heat and electricity, ranges from about 8%to 26%.

The economic assessment, carried out by estimating the total capital investment and the plant profitability, has been performed by analyzing different management strategies (Base Load, Peaker, Ancillary Service and Mobility) and accounting for different technological development levels and market scenarios. Results show that the hydrogen production is the main contributor to the system economic sustainability thanks to the highest prices of hydrogen with respect to the electricity ones.

This study aims at investigating the economic viability, at the pre-feasibility level, of a 5MWelectrolyser base-methanol production plant, coupled with a PV power plant. The Authors investigated the impact of different parameters, such as the PV plant size, the electrical energy cost and the components capital costs on the methanol production cost and on the system economic viability. It was also analyzed the minimum recommended sale price of the methanol in order to assure an adequate time frame for the return of the investment, considering a different combination of the investigated parameters.

An economic sensitivity analysis, based on the RSM approach, was performed in order to define the most promising economic conditions under which the plant can be considered a profitable investment in terms of ARR. A guide for an economically viable plant design, allowing for the identification of the most suitable combination of the economic parameters, was proposed as a kind of “maps of existence”. For the reference case, the Methanol Production Cost (MPC) resulted around 324 V/ton and the minimum methanol sale price to achieve a PBP of 10 years. The sensitivity analysis identified the cost of electricity and the capital cost of the electrolyser as the most affecting parameters for the system economic viability. In terms of ARR, the methanol price represents the most significant factor. Considering a methanol sale price ranging between 400 and 1200 V/ton, the ARR varied from 5% (20 year of PBP) to 20% (5years of PBP). From the environmental point of view, it is worth underling that the methanol production plant here proposed allows to recycle about 5800 tons of CO2 per year and to avoid the consumption of about 5.2 MNm3 of NG per year (compared to the traditional production).

In this paper, an analysis of the integration of a carbon capture unit and a power to fuel system for methanol synthesis with a coal power plant is presented from the energetic, environmental and economic standpoints. The study is carried out in three different sections. In the first part, the impact of the integration of a carbon capture system (CCS) and of a power to fuel plant (PtF) for methanol production is investigated in terms of plant average efficiency, fuel consumption, CO2 emissions. In the second part, the annual fixed and variable costs of the power plant, and the annual cost of electricity (COE) are assessed for different plant configurations. Additionally, future scenarios are analyzed considering the impact of European policies on the CO2 emission’s cost, defined by the European Emission Trading System (ETS). Finally, an economic feasibility analysis of the power to fuel plant is performed and the methanol production is evaluated. Moreover, a sensitivity analysis is carried out to evaluate the impact of the most affecting parameters (electrical energy cost, the methanol selling price and the capital cost of the electrolyzer) in terms of Internal Rate of Return (IRR).

This work is devoted to an emulator test rig designed for experimental analysis on SOFC-based plants pressurised by a turbocharger. The utilization of a turbocharger for SOFC pressurization aims to reduce the machine costs, due to the large mass production of this component. This emulator rig is an essential plant to perform tests on the component integration, dynamic operations, control system development and prevention of risky operative conditions (e.g. surge). These are essential issues to be solved before developing expensive complete prototypes and the related commercialization. This experimental plant is based on a pressure vessel for emulating the thermal (combustor and inert ceramic material) and fluid dynamic (the volume) responses. The vessel pressurisation is obtained with a turbocharger, where the exhaust flow operating in the turbine powers the compressor. The plant is also equipped with a recuperator and with different valves for control and flexibility reasons (bleed, compressor/turbine bypass, and recuperator bypass). Preliminary experimental results are included in this work focusing attention on the turbocharger choice and on the component constraints. In details, these are the necessary experiments for choosing the suitable machine for the rig (with a good surge margin for this component coupling).

The aim of the present work is to retrace experimental, analytical and numerical analyses which deal with compressor instability phenomena, such as rotating stall and surge. While the first affects only the machine itself, the second involves the whole energy system. Surge onset is characterized by strong pressure and mass flow rate fluctuations which can even lead to reverse flow through the compressor. Experimental studies on prevention of axial compressor fluid dynamic instabilities, which can be propagated and eventually damage the solid structure, have been carried out by many authors. The first important studies on this topic tried to underline the main aspects of the complex detailed mechanism of surge, by replacing the compression system with an equivalent conceptual lumped parameter model. This is specially meant to capture the unsteady behaviour and the transient response of the compression system itself, particularly its dependence on variations in the volume of discharge downstream and in the settings of the throttle valve at its outlet (which simulates the actual load coupled to the compressor). Greitzer’s model is still regarded as the milestone for new investigations about active control and stabilization of surge and, more generally, about active suppression of aerodynamic instabilities in turbomachinery. During the last years, a lot of simulations and experimental studies about surge have been conducted on multistage centrifugal compressors with different architectures (e.g. equipped with vaneless or vaned diffusers). Moreover, further kinds of analysis try to extend the stable working zone of compressors, identifying stall and surge precursors extractable from information contained in the vibro-acoustical and rotodynamic response of the system.

The aim of the present work is to design a test rig suited to investigate the dynamic interaction between rotor and hydrodynamic journal bearings in micro gas turbines (microGT), i.e. with reference to small bearings (diameter in the order of ten millimeters). Particularly, the device is capable of measuring the journal location. Therefore, the journal motion due to rotor vibrations can be displayed, in order to assess performance as well as stiffness and damping of the bearings. The new test rig is based on Bently Nevada Rotor Kit (RK), but substantial modifications are carried out. Indeed, the relative radial clearance of the original RK bearings is about 2/100, while it is in the order of 1/1000 in industrial bearings. Therefore, the same RK bearings are employed in the new test rig, but a new shaft has been designed in order to reduce the original clearance. The new shaft enables us to study the bearing behaviour for different clearances, as it is equipped with interchangeable journals. The experimental data yielded by the new test rig are compared with numerical results. These are obtained by means of a suitable finite element (FEM) code developed by our research group. It allows the Thermo Elasto-HydroDynamic (TEHD) analysis of the bearing in static and dynamic conditions. In the present paper, bearing static performances are analysed in order to assess the reliability of the journal location predictions by comparing numerical and experimental results. Such comparisons are presented for both large and small clearance bearings of original and modified RK, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance equal to 8/1000). Nevertheless, rotor alignment is quite difficult with small clearance bearings and a completely new test rig is designed for future experiments.

This work is devoted to an emulator test rig based on a T100 microturbine (100 kW electric power) and designed for SOFC hybrid systems. Since this facility does not include a real fuel cell, it is mainly used for tests on the SOFC/T100 integration to analyse possible stress and risky operations (e.g. surge) especially in dynamic conditions. The tests performed with this rig range from component analysis, to experimental studies at dynamic conditions and surge risk analysis.

This paper aims to develop a tool for the performances comparison of innovative energy systems on board ships, both for concentrated and distributed generation applications. In the first part of the study, the tool database has been developed throughout a wide analysis of the available market solutions in terms of energy generation devices (i.e. fuel cells, internal combustion engines, micro gas turbines), fuels (hydrogen, natural gas, diesel) and related storage technologies. Many of these data have been collected also thanks to the laboratory experience of the authors’ research group on different innovative energy systems. From the database, a wide range of maps has been created, correlating costs, volumes, weights and emissions with the installed power and the operational hours required, given by the user as input. The tool highlights the best solution according to the different relevance chosen by the user for each key parameter (i.e. costs, volumes, emissions). In the second part, two different case studies are presented in order to underline how the installed power, the different ship typology and the user requirements affect the choice of the best solution. It is worth noting that the methodology has a general value, as the tool can be applied to both the design of new ships, and to the retrofit of already existing ships in order to respect new requirements (e.g. more and more stringent normative in terms of pollutant emissions in ports and restricted areas). Furthermore, the database can be easily extended to other generation and storage technologies.

The present work aims to suggest an innovative solution for seismic monitoring stations’ endurance. These stations are characterized by many different problems, such as lightning vulnerability, energy independence and noises disturbance. The suggested technology, for this type of application, is an improved bladeless turbo-expander patented by Nikola Tesla in the early 20th century, the Tesla turbine.

Wind turbine installation worldwide has increased at unrested pace, as it represents a 100% clean energy with zero CO2 and pollutant emissions. However, visual and acoustic impact of wind turbines is still a drawback, in particular in urban areas. This paper focuses on the performance evaluation of an innovative horizontal axis ducted wind turbine, installed in the harbour of Genova (Italy) in 2018: the turbine was designed in order to minimize visual and acoustic impacts and maximize electrical energy production, also during low wind speed periods. The preliminary study and experimental analyses, performed by the authors in a previous study, showed promising results in terms of energy production, compared to a traditional generator ( factor >2.5 on power output). In the present paper, the test campaign on a scaled-up prototype, installed in the urban area of Genova, is performed, with a twofold objective: (i) comparison of the ducted innovative turbine with a standard one, in order to verify the increase in energy production; (ii) analysis of the innovative turbine for different wind speeds and directions, evaluating the influence of ambient conditions on performance. Finally, based on the obtained results, an improved setup is proposed for the ducted wind turbine, in order to further increase energy production mitigating its visual impact.

A hybrid power plant combining a solid oxide fuel cell (SOFC) and a micro gas turbine (MGT) is a suitable technology solution for decentralized energy production utilizing natural gas and biogas. Despite having high electrical efficiency and low emissions, the dynamic interactions between components can lead to damages of the system if a comprehensive control strategy is not applied. Before building a coupled hybrid power plant demonstrator, the “hybrid system emulators” approach is followed to solve any integration issues. A test rig consisting of an MGT and emulated SOFC is developed. The dynamics of the SOFC are reproduced by a real time model. The created cyber-physical system provides an effective platform to validate and optimize the control concepts for the future hybrid demonstrator by adding the complexity of the hybrid plant to the MGT test rig. The ability to develop and test the control strategy on such a system dramatically reduces the technology risk and increases the chances of success for the demonstrator operation.

The need to enhance flexibility on current power plant is linked to the strong penetration of non-dispatchable sources in the current energy network, which causes a dramatic need for ancillary services to sustain the grid operability. A framework including a micro Gas Turbine (mGT), a Heat Pump (HP) and a PCM Storage is considered to enhance plant flexibility while facing grid and price fluctuations during day operations. The system so composed is devoted to electrical energy production only. A proper use of the HP allows, for instance, to heat up the compressor intake temperature whilst the system is operating at minimum load. The system can then produce a lower amount of energy in order to be more competitive in the infra-day energy market. At the same time, the cold storage is charged and the stored energy can be later used to power up the system during the peak hours by cooling the compressor intake. This work presents then the installation of the control system devoted to the management and the control of such complex system. The test-bed is defined to test different operating conditions and to validate the operating framework of the whole compound.

Nowadays the research in energy field is focused on conversion technologies which could achieve higher efficiencies and lower environmental impact. Among these, fuel cells are considered an extremely promising technology and pressurized solid oxide fuel cell (SOFC) systems are particularly attractive for their high electric efficiency, potential for cogeneration applications, low carbon emissions and high performance at part-load. This paper aims to perform a robust design of an innovative turbocharged hybrid system model, featuring components validated with industrial data, where a turbocharger is used to pressurize the fuel cell, promising better cost effectiveness than a microturbine-based hybrid system, at small scales. This study will evaluate the impact of the main operating parameters (fuel cell area, stack current density and recuperator surface) on the plant performance, considering uncertainties in the system and creating a response surface of the model to perform the study. Finally, a study of the operating costs of such plant is performed to evaluate its profitability in the Italian market scenario.

Flexibilization of Gas Turbine Combined Cycle (GTCC) is a key for plant operations in the present as well as in the near future. The increasing of non-dispatchable sources in the energy production environment causes strong fluctuations in energy price and energy production profiles. The opportunity to enhance flexibility of traditional GTCC is consequently welcomed. This work focuses on integration of a Heat Pump in a GTCC devoted to cogenerative purpose with the goal to integrate energy production, assist the power plant in normal operations and enriches the transient capability of the whole compound. This approach can be developed to be retro-fitted to existing power plant. In particular, a software-in-the-loop (SiL) application is here presented to test the developed control logics governing such power plant. The power plant model is developed and runs under Siemens AMESIM environment, whilst the control system is developed and integrated in Matlab/Simulink environment. The two systems are interfaced and exchange information with the goal to verify reliability of the control logics before going into the real field.

System simulation is used in many fields to help design, control or troubleshoot various industrial systems. Within the PUMP-HEAT H2020 project, it is applied to a combined cycles power plant, with innovative layouts that include heat pumps and thermal storage to un-tap combined cycle potential flexibility through low-CAPEX balance of plant innovations. Simcenter Amesim software is used to create dynamic models of all subsystems and their interactions and validate them from real life data for various purpose. Simple models of the Gas Turbine (GT), the Steam loop, the Heat Recovery Steam Generator (HRSG), the Heat Pump and the Thermal Energy storage with Phase Change material are created for Pre-Design and concept validation and then scaled to more precise design. Control software and hardware is validated by interfacing them with detailed models of the virtual plant by Model in the Loop (MiL), Software in the Loop (SiL) and Hardware in the Loop (HiL) technologies. Unforeseen steady state and transient behaviours of the power plant can be virtually captured, analysed, understood and solved. The purpose of this paper is to introduce the associated methodologies applied in the PUMP-HEAT H2020 project and their respective results.

Current energy conversion machines such as the micro gas turbine can be improved by harvesting the low-grade energy of the exhaust. A prominent option for such is the organic Rankine cycle due to its relatively efficient and reliable design. This manuscript presents a review on the subject and is the first step toward the design of an organic Rankine cycle bottoming a 100 kWe recuperated gas turbine. After introducing and covering the historical development of the technology, appropriate guidelines for defining the cycle arrangement and selecting the fluid are presented. At last, the viability of the cycle is assessed by assuming an appropriate efficiency value and general cost functions. The organic Rankine is expected to generate an additional 16.6 kWe of power, increasing the electrical efficiency from 30 to 35%. However, the capital cost increase was estimated in 48%.

The aim of this work is to explore the possibilities to find surge precursors from compressor vibro-acoustic analysis in a condition close to instability. For this purpose, a large campaign of data acquisition has been conducted by Thermochemical Power Group (TPG) of University of Genoa: T100 micro-turbine, equipped with three different volumes, has been sensorized with accelerometers and microphones and data acquired have been analysed with different methodologies in order to find surge precursors useful for the creation of an anti-surge control.

This paper presents a dynamic simulation of a heat pump using butane refrigerant for the purpose of integration with a combined cycle power system and thermal energy storage to enhance flexibility. A dynamic model of a heat pump system is developed using the Amesim software and the simulation result in the case of changing the heat source and heat sink conditions is shown to validate the simulation performance.

This paper presents a dynamic simulation of a heat pump using butane refrigerant for the purpose of integration with a combined cycle power system and thermal energy storage to enhance flexibility. A dynamic model of a heat pump system is developed using the Amesim software and the simulation result in the case of changing the heat source and heat sink conditions is shown to validate the simulation performance.

The increasing share of electricity produced from renewable energy sources (RES), with the consequent strong penetration in the current energy network, is causing a growing need of balancing power to compensate power supply from such fluctuating sources. For these reasons, nowadays the power plants are requested to improve their operational flexibility, together with their global efficiency in part-load operation, for ancillary services and to sustain the grid operability. A possible solution for flexibility enhancement is characterized by a highly efficient heat pump integrated in a conventional natural gas combined cycle (CC). Such concept can be applied both to power oriented combined cycle (POCC), to modify the compressor intake temperature with a consequent increase or decrease of the power production, and both to cogeneration CC in association with District Heating Network (DHN). In this work, a statistical analysis of climatic data and their correlations with energy market condition will be performed considering Italian context, to understand which the more suitable conditions for such integrated system are. The analysis will be performed on seasonal and daily basis. The final aim of this work is to identify how such integrated system can be operated at its best in the different Italian markets and climatic frames.

This paper aims to present a feasibility study for clean production, storage and distribution of large amounts of hydrogen, starting from low-cost available renewable electrical energy. Paraguay and Brazil own equally the binational company ITAIPU Hydroelectric Plant (14 GW, about 96,000 GWh/year of production). 50% of this energy corresponds to Paraguay: however, since its energy demand is quite low, a large amount of this energy is sold to Brazil, receiving a compensation of 10 $/MWh. In this context, seeking for ways of adding value to generated electricity, this paper assesses the potential of clean H2 production by water electrolysis, simulating the use of one generator unit of the mentioned company (700 MW) and discussing two alternatives for the produced hydrogen: a) using it for ammonia production as base for fertilizers; b) using it for passenger cars. A detailed thermo-economic analysis is performed using a dedicated software developed by the authors. The results show that production is economically feasible for both cases, moreover the process is completely clean and significant amounts of oxygen are produced, potentially representing an additional revenue for the process.

There are several small energy sources that can be exploited to provide useful energy: small temperature differences, mechanical vibrations, flow variations, latent exhausts are just some examples. The recovery of such common and small energy sources, usually wasted, for example with the conversion into useful amounts of electrical energy, is called energy harvesting. Energy harvesting allows low-power embedded devices to be powered from naturally-occurring or unwanted environmental energy (e.g. pressure or temperature difference). The main aim in the last years of researches in such field, was the increasing of the efficiency of such components, with a higher power output and a smaller size. At present, a wide range of systems incorporating energy harvesters are now available commercially, all of them specific to certain types of energy source. Energy harvesting from dissipation processes such as fluid lamination is a challenge for many different applications. In addition, control valves to dissipate overpressures are common usage of many plants and systems. This paper surveys the market opportunities of such harvesting systems, considering the trade-offs affecting their efficiency, their applicability, and ease of deployment. Particular attention will be devoted to small energy harvesters than can exploit small expansions, such as from lamination valves or to systems that can feed mini sensors from small pressure drops, promising compactness, efficiency and cost effectiveness.

The present research study aims at analysing technical and economic feasible solutions for heat pumps integration in energy districts for polygeneration purpose and particularly to store excess of electricity via Power-to-heat schemes considering that, from previous researchers’ works, thermal storage has been identified as the most remunerative and easy to handle storage technology to maximise self-consumption in polygeneration grids. This technology is already developed and currently employed for conditioning of residential, commercial and industrial buildings. However, studies regarding the analysis of heat pumps’ integration in energy districts for distributed generation are still limited. The potential advantages of its employment in this context are fuel savings, a lower emission level and the possibility to couple it with local renewable energy sources (i.e. solar panels, wind turbines) and traditional generators (i.e. engines, micro gas turbines) in order to increase flexibility in operational terms. In this paper, a performance analysis of the poly-generation energy district installed at the University of Genoa Campus, located in Savona, is analysed throughout a whole year: the model is implemented using a dedicated software tool, developed by Thermochemical Power Group. Different solutions for the integration of the heat pump, including size optimization, are investigated, considering the real data related to the University of Genoa Campus: the final aim of the analysis is to determinate the best operational strategy, minimizing variable costs (i.e. fuel) and evaluating the economic feasibility of heat pump installation in the energy district. This work has been also redacted as a preliminary analysis for solar-coupled HP integration (from a optimized management point of view) to be performed in the demonstration campaign of H2020 ENVISION Project*, where both RINA Consulting and University of Genova collaborate.

Paraguay has abundant hydroelectric energy (around 99%, in 2017 a generation reached 96,387 GWh) and it is currently exporting part of this energy. Some studies carried out by the National Electricity Administration indicate an increase in the demand for electric power where it is observed that the Reserve Generation Margin would be affected by the year 2025. To face this scenario, Paraguay is investigating alternative sources to diversify its energy production mix: this paper focuses on solar plants. Within the Electric System Master Plan, Paraguay aims to expand and improve the electric power supply system, mainly in the western part of the country in the central region of the Paraguayan Chaco. In this context and based on the experience of the Itaipu Technology Park in the installation and operation of the first two solar plants in the country, already in operation in the mentioned region, the aim of this paper is the evaluation of a future photovoltaic solar plant in the area of Loma Plata, which will be connected to the national interconnected grid system, with a power around of 10 MWp. For this purpose, a thermoeconomic analysis with a software tool is used to evaluate the viability of the proposal, evaluate different configurations and select the best option for the case study.

Fossil fuel power plants, as combined cycle plants (CCGT), will increasingly have to shift their role from providing base-load power to providing fluctuating back-up power to control and stabilize the grid, but they also have to be able to run at the highest possible efficiency. Combined Heat and Power generation could be a smart solution to overcome the flexibility required to a modern power plant, this work investigates different layout possibilities allowing to increase the overall efficiency through the heat recover from the hot flue gasses after the heat recovery steam generator (HRSG) of a CCGT. The flue gas (FG) cooling aims to recover not only the sensible heat but also the latent heat by condensing the water content. One possible solution couples a heat pump to the flue gas condenser in order to increase the temperature at which the recovered heat is supplied, moreover the evaluated layout has to comply with the requirement of a minimum temperature before entering the stack.

This work aims to understand the potential of an innovative technology for solar energy harvesting in a District Heating Network (DHN). The considered technology is aesthetic solar façade thermal panel. In order to guarantee the temperatures required by a 3rd generation DHN (around 75°C), a Heat Pump, using as cold source the heat from the panels, is necessary. It is worth noting that the coupling between façade panels and Heat Pump requires accurate evaluations. The optimum condition for the façade panels is to work at low temperatures (close to ambient or even below), while the Heat Pump reaches high Coefficient Of Performance (COP) when the temperature difference between hot and cold sources is minimized. In the first part of the study, a system model has been built using Matlab SIMULINK using results of tests on the panels already performed inside the H2020 ENVISION project. Different colours are considered. In the second part, a predictive mode-based strategy has been defined and tuned on the system in order to guarantee the best system performances in interaction with the DHN. This work will allow to understand whether this technology is feasible in the presented scenario and this layout can improve local energy exchange.

This paper presents the experimental campaign on Tesla turbo expanders carried out at Thermo-chemical Power group (TPG) of University of Genoa, Italy. An experiment system is established using compressed air as a working fluid. A 200 W turbine is tested with rotational speed up to 40000 rpm. Experimental analysis focused mainly on the efficiency features of this expander, showing the impact on performance of different disk gaps, disk thickness, discharge holes, exhaust geometry, as a function of speed and mass flow. An improved version of 3 kW air Tesla turboexpander is built. Preliminary experimental results are discussed along with the effect of number of nozzles on the performance of the turbine.

This paper summarizes the development of fully 3D Computational Fluid Dynamics (CFD) analysis for bladeless air micro expander for 200 W and 3 kW rated power. Modelling of nozzle along with rotor is done using structured mesh. This analysis, for the first time, demonstrates the interaction between nozzle and rotor using compressible flow density-based solver. The Shear Stress Transport (SST) turbulence model is employed to resolve wall effects on the rotor and to determine the shear stress accurately. The results illustrate the flow field inside stator and rotor along with complicated mixing zone between stator and rotor. The comparison of rotor-stator CFD simulation results is done with experiments to preliminary validate the model. The losses in the turbine are discussed with the help of experimental and numerical data.

The aim of this work is to describe the design of an innovative test rig for investigating the expansion of saturated fluids in the two-phase region. The experimental test rig was thought up and built by TPG of the University of Genoa. It will be equipped by probes and some optical accesses that permit high speed video recording and laser measurements. It will be useful for the study of the quality ratio, vapour and liquid droplet thermodynamic properties and their speed.

This paper focuses on a biofuel-based Multi-Energy System generating electricity, heat and hydrogen. The proposed system, that is conceived as refit option for an existing anaerobic digester plant in which the biomass is converted to biogas, consists of: i) a fuel processing unit, ii) a power production unit based on the SOFC (Solid Oxide Fuel Cell) technology, iii) a hydrogen separation, compression and storage unit. The aim of this study is to define the operating conditions that allow optimizing the plant performances by applying the exergy analysis that is an appropriate technique to assess and rank the irreversibility sources in energy processes. Thus, the exergy analysis has been performed for both the overall plant and main plant components and the main contributors to the overall losses have been evaluated. Moreover, the first principle efficiency and the second principle efficiency have been estimated. Results have highlighted that the fuel processor (the Auto-Thermal Reforming reactor) is the main contributor to the global exergy destruction (9.74% of the input biogas exergy). In terms of overall system performance the plant has an exergetic efficiency of 53.1% (it is equal to 37.7% for the H2 production).

Sea waves have a high energy potential [1], which justifies the efforts and research in this field. This abstract report the main results of the Sea-W.H.A.M. (Seaspoon Wave Harvesting by Air Microturbine) Project, whose aim was the development of a prototype of an autonomously-powered station for off-shore recharging of electric loads equipped with a WEC (wave energy converter). This project has been carried out within the Framework of the National Plan for Military Research (PNRM) by the Minister of Defense-Italian Navy and was undertaken by a Consortium composed of the University of Genoa and two companies, Techcom Srl and Advanced Microturbines Srl.

The core technology of the project is the Seaspoon, a device harvesting mechanical energy from sea waves developed at Università di Genova [2]. Such energy is used to actuate a piston to compress air in a reservoir. The compressed air in turn feeds the microturbine that charges a battery. Hence the recharging station was equipped with an energy storage system that utilized compressed air and a battery.

Thanks to this double pneumatic-electrochemical storage, the microturbine and a smart control algorithm, on-demand power was generated by forcing compressed air through the microturbine.

The integrated system developed is composed of:

• wave energy converter: a 5m diameter buoy connected to a hydraulic piston;
• hydro-pneumatic skid and compressed air storage: this component converts a bidirectional oil mass flow in a compressed air stream;
• microturbine and its control unit: it converts compressed air into electrical power.

Moreover, a wavemaker that could generate controllable waves on demand has been developed, in order to test the system and carry out future research activities in that area called Wave Lab. Such a wavemaker with 5m wave front and up to 0.5m wave height is a unique research infrastructure in Europe, being the only wavemaker operating in real sea water [3].

First the oil compressor system was sized: it consists of a hydraulic piston anchored to the seabed on one side and to a buoy on the other. Then the oil-pneumatic converter was integrated to feed the pneumatic storage with compressed air. Finally, the microturbine was installed downstream the reservoir. The energy produced by the microturbine charged a battery.

Ansaldo Energia is Italy’s largest supplier, installer and service provider for power generation plants and components, with the capabilities to build turnkey power plants on green field sites using its own technology and its own independent design, production, construction, commissioning and service resources.

Ansaldo Energia has an installed capacity of 218,000 MW in 90 countries, it has around 60 combined cycles (roughly 300 machines) under Long Time Service Agreement which required a continuous monitoring, data elaboration and maintenance.

Ansaldo Energia implemented central diagnostic infrastructure about 15 years ago to calculate and monitor on-line gas-turbine, steam-turbine efficiency KPIs, and to provide a condition based maintenance service to its customers.

Nowadays the infrastructure has been developed and improved for obtaining a global diagnostic center based in Genoa and Miami, now the data core can integrate and post elaborate data coming from all the worldwide assets.

In recent decades, the advances in technology of sensors, instrumentation and control, communication systems, have made available an increasing amount of data from systems, than need to be organized and specifically processed, to exploit the maximum available information.

In this presentation, the latest developments of Ansaldo Energia remote monitoring and diagnostic network are described. Starting from the acquisition systems (ADA) with vibration and combustion

integrated processing, to the database generation and sharing, until the introduction of predictive analysis systems (APEx).

ADA™ (Advanced Diagnostic Analysis) is the Ansaldo Energia suite for condition-based maintenance covering all the critical diagnostic needs for energy industry machinery, including: Steam and gas turbine performance monitoring, Gas turbine combustion monitoring, Vibration analysis, Generator diagnostics, Electrical transient and Fast event recorder.

Based on its modular design and leveraged by OSIsoft PI infrastructure, ADA allows for advanced monitoring of main equipment parameters like steam and gas turbine performances, gas turbine combustion, machinery vibrations, generator diagnostic, electrical transient and others. Computing modules, automatic report generation, alarms notification, large data storage capabilities are some of the key features of this state-of-the-art product in the field of remote monitoring and diagnostic.

Moreover, AEN developed a WEB portal used for sharing diagnostic data with all AEN departments involved on data analysis.

APEx (Ansaldo Predictive Expert) is Ansaldo Energia predictive tool used for predictive diagnostic and maintenance of combined cycle power plant component such as Gas Turbine, Steam Turbine, generator and BOP.

APEx make use of machine learning algorithms to build diagnostic model for real-time monitoring of many combined cycle power plant operating parameters.

The models are trained on historical normal behavior data using a large number of signals as input variables. After the training the model is released for the real-time monitoring to the diagnostic front-end. The system estimates an expected value of the monitored parameters comparing with the measured value. The deviations between the expected and measured values, called residuals, are used to detect incipient abnormal behavior or degradation of the machinery by the generation of Early Warnings. This procedure ensures high promptness level, minimizing false alarms.

The system also provides a calculation of time to fault to evaluate the severity of the degradation, estimating the residual operating time before the fault or the trip.

The developed APEx models are: combustion model, vibration model and performance model. Through those different models, Ansaldo Energia front-end is able to detect in advance abnormal behavior or underperformance of the machine under investigation such as: burners, compressor and air intake fouling, changes in combustion parameters (emissions and dynamic behavior), machine unbalancing, rotor rubbing, bearing issues, performance loss; in wider terms APEx helps to detect precursors of deviation from expected behavior in order to improve specialist analysis and plan the maintenance activities in advance.

In this presentation, case studies of APEx models online monitoring, generation of Early Warnings and time to fault or trip evaluation are described.

A major goal of politics, society, and industry is the reduction of carbon dioxide (CO2) emissions in order to prevent anthropogenic climate change and an increase in earth’s temperature. In addition, the expansion of renewable energies and the use of nuclear power, CO2 capturing (e.g. from exhaust gases), is regarded as a promising strategy to reduce global CO2 emissions. In this context, the Power-to-X technologies can provide an innovative energy storage concept by combining the main trends of energy systems aiming at high shares of renewable energies, reduction of CO2 emissions and sector coupling. A promising approach is the production of methanol as a chemical raw material or fuel. The goal of this paper is to present (i) an extensive thermodynamic analysis for the methanol production from carbon dioxide and hydrogen and (ii) an economic analysis for the process based on the thermodynamic studies. The thermodynamic analysis was carried out in the simulation tool Aspen Plus™ in order to investigate the impact of the operating temperature and pressure on the performance of the synthesis unit. Based on the thermodynamic results, an economic analysis has been performed in order to define the most feasible solution. For a defined optimal operating temperature, the fixed and operating costs and the methanol production cost were evaluated for different operating pressures. Finally, a sensitivity analysis has been performed in order to define the minimum methanol selling price that allows for a payback period of 10 years for different values of the electrical energy purchasing price.

The reduction of CO2 and, more generally, GHG (Green House Gases) emissions imposed by the European Commission (EC) and the Environmental Protection Agency (EPA) for passenger cars has driven the automotive industry to develop technological solutions to limit exhaust emissions and fuel consumption, without compromising vehicle performance and drivability. In a mid-term scenario, hybrid powertrain and Internal Combustion Engine (ICE) downsizing represent the present trend in vehicle technology to reduce fuel consumption and CO2 emissions. Concerning downsizing concept, to maintain a reasonable power level in small engines, the application of turbocharging is mandatory for both Spark Ignition (SI) and Diesel engines. Following this aspect, the possibility to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world. One method to recover exhaust gas energy from ICEs is the adoption of turbo-compounding technology to recover sensible energy left in the exhaust gas by-passed through the waste-gate valve. In the paper, an innovative option of advanced boosting system is investigated through a bladeless micro expander, promising attractive cost-competitiveness. The numerical activity was developed on the basis of experimental data measured on a waste-gated turbocharger for downsized SI automotive engines. To this aim, mass flow rate through the by-pass valve and the turbine impeller was measured for different waste-gate settings in steady-state conditions at the turbocharger test bench of the University of Genoa. The paper shows that significant electrical power can be harvested from the waste-gate gases, up to 94 % of compressor power, contributing to fuel consumption reduction.

Ocean Thermal Energy Conversion (OTEC) is a promising technology to provide sustainable and dispatchable energy supply to oceanic coastal areas and islands. It exploits the temperature difference between deep cold ocean water and warm tropical surface water in an Organic Rankine Cycle (ORC), guaranteeing a continuous and dispatchable electric production, overcoming one of the most critical issue of renewable generators such as PV or wind turbines. Despite the technological maturity of ORC application to OTEC systems, it still presents technical and economic barriers mainly related to their economic feasibility, large initial investments as well as heavy and time demanding civil installation works. To overcome such issues, multipurpose OTEC plants are proposed, producing electrical power as well as other products, such as useful thermal power (e.g. ambient cooling) and desalinated water. Since OTEC engineering is still at a low degree of maturity, there are no widespread and established tools to facilitate OTEC feasibility studies and to allow performance and cost optimization. Therefore, in this paper, a new tool for techno-economic analysis and optimization of multipurpose OTEC plants is presented. Starting from a detailed database of local water temperature and depth, the approach allows to provide a quantitative insight on the achievable performance, required investment, and expected economic returns, allowing for a preliminary but robust assessment of site potential as well as plant size. After the description of the techno-economic approach and related performance and cost functions, the tool is applied to an OTEC power plant case study in the range of 1 MW gross electrical power, including a preliminary assessment of scaling-up effects.

Climate change is driving the introduction of strict emission limits in the shipping sector favoring the introduction of alternative fuels, among which hydrogen. While the storage energy density of this energy vector is a key challenge that makes way to a variety of different solutions, from fossil fuel reformers to sodium borohydride systems, fuel cell systems are generally considered among the future ideal energy converters. Nevertheless very few fuel cell marine applications are available worldwide, none of them is related to a ship application, mainly because of the high power requirements. Fuel cells are relatively new in the shipping sector, up to now no civil industrial system has been commercialized yet while military applications rely only on the U212 submarine of the Italian and German Navy. The lack of favorable niche markets coupled with the strong conservative and traditional design principles held back the investment for optimized marine systems. For this reason, present and past projects made use of conveniently adapted automotive technologies into pilot demos, with particular focus on Proton Exchange Membrane Fuel Cell (PEMFC). However, ships requirements are largely different from automotive ones, not only for the power size that are in the range of MWs instead of kWs. On the other side, in order to take advantage of large scale production as well as of the modularity of fuel cell technology, the integrations of automotive or stationary based fuel cell subsystems, already available on the market, inside a dedicate modular marine system seems to be the solution pursued by many shipbuilders and contemplated by regulatory authorities. In hybrid system configurations, fuel cells are considered in combinations with batteries, another important technology under development, in order to take advantage of the superior energy performances of fuel cell systems and the highly power discharge dynamics of batteries. The need of fuel cell power systems for ships is pushing towards the creation of knowledge that requires laboratories able to challenge the abovementioned issues in order to give answers to shipbuilders and at a lower level also to rule makers.

This paper presents a Model Predictive Controller (MPC) operating an SOFC Gas Turbine hybrid plant at end-of-life performance condition. Its performance was assessed with experimental tests showing a comparison with a Proportional Integral Derivative (PID) control system. The hybrid system operates in grid-connected mode, i.e. at variable speed condition of the turbine. The control system faces a multivariable constrained problem, as it must operate the plant into safety conditions while pursuing its objectives. The goal is to test whether a linearized controller design for normal operating condition is able to govern a system which is affected by strong performance degradation. The control performance was demonstrated in a cyber-physical emulator test rig designed for experimental analyses on such hybrid systems. This laboratory facility is based on the coupling of a 100 kW recuperated microturbine with a fuel cell emulation system based on vessels for both anodic and cathodic sides. The components not physically present in the rig were studied with a real-time model running in parallel with the plant. Model output values were used as set-point data for obtaining in the rig (in real-time mode) the effect of the fuel cell system.

The result comparison of the MPC tool against a PID control system was carried out considering several plant properties and the related constraints. Both systems succeeded in managing the plant, still the MPC performed better in terms of smoothing temperature gradient and peaks.

The flexibility of power plants is a critical feature in energy production environments nowadays, due to the high share of nondispatchable renewables. This fact dramatically increases the number of daily startups and load variations of power plants, pushing the current technologies to operate out of their optimal range. Furthermore, ambient conditions significantly influence the actual plant performance, creating deviations against the energy sold during the day-ahead and reducing the profit margins for the operators. A solution to reduce the impact of unpredicted ambient conditions, and to increase the flexibility margins of existing combined cycles, is represented by the possibility of dynamically controlling the temperature at compressor intake. At present, cooling down the compressor intake is a common practice to govern combined cycle performance in hot regions such as the Middle East and Africa, while heating up the compressor intake is commonly adopted to reduce the minimum environmental load (MEL). However, such applications involve relatively slow regulation of air intake, mainly coping with extreme operating conditions. The use of continuously varying, at a relatively quick pace, the air temperature at compressor intake, to mitigate ambient condition fluctuations and to cope with electrical market requirements, involves proper modeling of the combined cycle dynamic behavior, including the short-term and long-term impacts of intake air temperature variations. This work presents a dynamic modeling framework for the whole combined cycle applied to one of IREN Energia’s Combined Cycle Units. The paper encloses the model validation against field data of the target power plant. The validated model is then used to show the potential in flexibility augmentation of properly adjusting the compressor intake temperature during operation.

Interest in small-scale turbines is growing mainly for small-scale power generation and energy harvesting. Conventional bladed turbines impose manufacturing limitations and higher cost, which hinder their implementation at small scale. This paper focuses on experimental and numerical performance investigation of Tesla type turbines for micro power generation. A flexible test rig for Tesla turbine fed with air as working fluid has been developed, of about 100W net mechanical power, with modular design of two convergent-divergent nozzles to get subsonic as well as supersonic flow at the exit. Seals are incorporated at the end disks to minimize leakage flow. Extensive experiments are done by varying design parameters such as disk thickness, gap between disks, radius ratio, and outlet area of exhaust with speeds ranging from 10,000 rpm to 40,000 rpm. A quasi-one-dimensional (1D) model of the whole setup is created and tuned with experimental data to capture the overall performance. Major losses, ventilation losses at end disks, and nozzle and exhaust losses are evaluated experimentally and numerically. Effect of design parameters on the performance of Tesla turbines is discussed.

The PUMP-HEAT (Performance Untapped Modulation for Power and Heat via Energy Accumulation Technologies) project aims to develop the concept of a new advanced energy system, which integrates Combined Cycle Gas Turbine (CCGT) plants and Combined Heat and Power (CHP) plants with fast-cycling highly efficient heat pumps and thermal energy storage for further enhancing the flexibility. The dynamic modeling and simulation tools are essential for investigation of a PUMP-HEAT conceptual design and for analysis of its dynamic characteristics in operation. It is also useful to implement a dynamic simulator as a built-in emulator in a real test facility to confirm the integration characteristics of each equipment and the entire control system.

In this study, a dynamic modeling of a real CCGT/CHP power plant, especially targeting a Heat Recovery Steam Generator (HRSG) and Steam Turbine (ST) system, is constructed based on the Modelica-based tool developed by Central Research Institute of Electric Power Industry (CRIEPI). The component models of this tool are developed based on mass and energy conservation equations for the dynamic analysis of thermal power generation systems. The validity of the model is evaluated comparing with operational data for both steady state and dynamic behavior, and the potential as a real-time simulator is also discussed from the viewpoint of simulation accuracy and calculation speed. In addition, the load following characteristics of ST power output by dynamic simulation are investigated.

Pressurised solid oxide fuel cell (SOFC) systems are a sustainable opportunity for improvement over conventional systems, featuring high electric efficiency, potential for cogeneration applications and low carbon emissions.

However, SOFC systems are largely affected by uncertainties in operational and geometrical parameters. Such uncertainties propagate through the whole system affecting the final outputs, causing performance variability and affecting system reliability as well. The aim of this work is to evaluate the impact of uncertainties on a 30kW pressurised SOFC gas turbine hybrid system fueled by biogas, through a stochastic analysis. Different sources of uncertainty have been considered and their influence over system performance has been evaluated thanks to the Response Sensitivity Analysis (RSA) probabilistic method, considering also their impact on economic parameters such as the pay-back period (PBP) and the internal rate of return (IRR).

Micro-turbines/expanders are growing in the fields of waste heat recovery, micro power generation and energy harvesting. Traditional turbines impose problems of complex nature of blades, balancing issues and high cost. The aim of this paper is to investigate feasibility of multiple disk Tesla air turbo expanders by extensively performing experimental and computational analysis. A flexible test rig of 200 W net mechanical power is developed with speed of rotation ranging from 10000 to 40000 rpm. The results of the experiments are presented and discussed by varying significant geometrical parameters of the prototype. A 3D computational fluid dynamic (CFD) analysis of rotor and stator with real fluid gas assumption is performed to characterize flow in the Tesla micro expander. Experimental turbine efficiencies found to be lower compared to the rotor efficiencies analyzed theoretically. The gap in the efficiency is discussed by analyzing CFD and experimental results.

This paper aims at investigating clean hydrogen production from the large size (14 GW) hydroelectric power plant of Itaipu, located on the border between Paraguay and Brazil, the two countries that own and manage the plant. The hydrogen, produced by a water electrolysis process, is converted into ammonia through the well-known Haber-Bosch process. Hydraulic energy is employed to produce H2 and N2, respectively, from a large-scale electrolysis system and an air separation unit. An economic feasibility analysis is performed considering the low electrical energy price in this specific scenario and that Paraguay has strong excess of renewable electrical energy but presents a low penetration of electricity. The proposal is an alternative to increase the use of electricity in the country. Different plant sizes were investigated and, for each of them, ammonia production costs were determined and considered as a term of comparison with traditional ammonia synthesis plants, where H2 is produced from methane steam reforming and then purified. The study was performed employing a software developed by the authors’ research group at the University of Genoa. Finally, an energetic, environmental, and economic comparison with the standard production method from methane is presented.

The paper presents and discusses modelling and simulation of a robotic vehicle called FURBOT, designed for last mile delivery of freights. The focus is on the design process through simulation to meet requirements typical of a robot as well as automotive performance as for a commercial van. It is introduced the original concept of vehicle self-adapting its configuration and speed to ensure stability and integrity of the load and to protect the chassis itself from overload and mechanical fatigue, making possible a leaner sizing of the chassis structures and so higher payload to overall mass. FURBOT is small, dexterous, thought to work in fleet, suitable for e-commerce market and endowed with a robotized system for loading/unloading the freight. A virtual prototype of the vehicle is implemented to predict with sufficient accuracy, yet from the first steps of the design process, the reaction and performance against typical driving conditions typical of vehicle development; control logics are consequently derived.

The University of Genoa hosts the HI-SEA (Hydrogen Initiative for Sustainable Energy Applications) joint laboratory with Fincantieri, to study the best design of a 240 kW PEMFC system for shipping. It is made up of 8 stacks (by Nuvera Fuel Cells) with BoP that come from a previous national project; stacks were left inactive for more than 2 years before being installed in the HI- SEA container. Inactivity leads to severe issues linked to the membrane’s water content, and for this reason during the study we focused on developing a performant recovery procedure for the stacks, based on thermal and humidity management. The implementation of the procedure will be described, showing its successful implementation. The 8 stacks were recovered, and their performance was restored, in comparison with polarization curves from factory tests and from the experimental campaign.

This paper presents an experimental assessment on the Fuel Cell System (FCS) performance tests conducted in the Hydrogen Initiative for Sustainable Energy Application (HI-SEA) Joint Laboratory of Fincantieri and University of Genova (UNIGE) [1]. The HI-SEA FCS plant is made up of 8 Fuel Cell (FC) stacks of 30 kW each for a total power of 240 kWe, originally designed for automotive applications, installed in two equal branches of 4 stacks in series. The two branches can be connected in parallel by means of two DC/DC converters together with an AC/DC converter that is able to simulate the presence of a 60 kW battery (BAT). The goal of the experimental campaign is to assess the performance and real behavior of the FCS when connected in parallel with and without DC/DCs, with or without the battery to assess the optimum BoP setup and the most feasible and efficient configuration for a ship application. The tests are conducted using typical ship power profiles. The results show that the operative profile could influence the FC performances if the BoP setup is not well optimized [2]. Stationary and dynamic performance of the system are evaluated in single branch and parallel branches configuration, with and without DC/DCs.

The study conclusion gives important indications on how to assemble, setup and control an FCS powerplant for marine application.

In 2018 the International Maritime Organization (IMO) addressed the difficult problem to reduce shipping GHGs emission, left apart since now from international Climate Change agreements [1]To challenge this problem the focus has been given to Alternative Fuels. Among all, Hydrogen represents one of the most interesting due to the possibility to combine it to Renewable Energy Source excess production issues [2]. For this reason, Fincantieri launched a Joint laboratory in collaboration with the University of Genoa, the HI-SEA Laboratory. The facility is made up of 8 PEMFC modules, supplied by Nuvera Fuel Cells, and it represents the world’s biggest PEMFC power plant specifically designed for the assessment of marine applications, with the goal to scale up the available PEM technology to MW size, addressing all the issues related to the installation and operation of this technology on-board a ship. This work concerns an experimental campaign aimed to assess the performance of the system under different operative conditions, with the goal to identify and quantify the influence of operational parameters. A comparative performance analysis is presented against the Factory Test data. The first step towards the validation of a simulation model for the prediction of system performance is carried out. This is the basis for a future work that will bring to a validate design tool for the scale up of fuel cell plant from kW to MW, specifically designed for marine application.

This paper shows experimental results obtained from a T100 microturbine connected with different volume sizes. The activity was carried out with the test rig developed at the University of Genoa for hybrid system emulation. However, these results apply to all the advanced cycles where a microturbine is connected with an additional external component responsible for volume size increase. Even if the tests were performed with a microturbine, similar analyses can be extended to large size turbines. A modular vessel was used to perform and to compare the tests with different volume sizes. To highlight the volume size effect, preliminary experimental results were carried out considering the transient response due to an on/off bleed valve operation. So, the main differences between system parameters obtained for a bleed line closing operation are compared considering three different volume sizes. The main results reported in this paper are related to surge operations. To produce surge conditions in this test rig, a valve operating in the main air path was closed to generate unstable behavior for the three different volume sizes. Particular focus was devoted to the operational curve plotted on the compressor map. The vibration frequency analysis showed significant amplitude increase not only during surge events but also close to the unstable condition. In details, possible surge precursor indicators were obtained to be used for the detection of risky machine operations. The experimental data collected during these tests are analyzed with the objective of designing control systems to prevent surge conditions.

Energy system reliability and operational cost depend highly on the performance degradation experienced by system components. In complex systems, degradation of each single component affects matching and interactions of different system parts. Gas turbine fuel cell hybrid systems combine two different technologies to produce power with an extremely high conversion efficiency. Severe performance decay over time currently limits high temperature fuel cells lifetime; although at a different rate, gas turbine engines also experience gradual deterioration phenomena such as erosion, corrosion, and creep. This work aims at evaluating, for the first time, the complex performance interaction between degrading components in a hybrid system. The effect of deterioration in gas turbine pressure ratio and efficiency on fuel cell performance was analyzed, and at the same time, the impact of the degrading fuel cell thermal output on turbine blade aging was modeled to estimate a remaining useful lifetime.

Integration of Thermal Energy Storage (TES) is one of the promising features of Concentrated Solar Power (CSP) technology which allows the Renewable Energy Sources (RES) to provide uninterrupted and dispatchable power supply, and thus facilitates the RES grid integration. Hybrid Solar Gas Turbine (HSGT) systems along with TES integration have gained great attention for the last decades. Numerical modelling and simulation tools are essential for the TES design optimization and analysis of its thermal behaviour during charging and discharging phases. This paper deals with the dynamic modelling and experimental validation of a TES at laboratory scale, which is part of the HSGT system. The TES is modelled with two different approaches: the CFD model using a commercial tool and a reduced-order model using the in-house transient simulation tool TRANSEO, which has been developed by Thermochemical Power Group (TPG) for the energy system dynamic analysis. The validation of both model results against the data obtained by the Authors through experimental investigation has highlighted that 2D discretization of the TES through the CFD model gives accurate representation of the thermal behaviour of the system, but it causes a significant computational expense. On the other side, 1D dynamic model reasonably predicts the time dependent thermal behaviour of TES, except some deviations from the experiments which are related to the simplified discretization scheme. However, due to its fast approach, the TRANSEO model can be effectively used to perform both TES initial design and sensitivity analysis, and also to develop or verify the control system at a later stage of HSGT system development.

This paper presents the development, implementation, and validation of a simplified dynamic modeling approach to describe solid oxide fuel cell gas turbine (SOFC/GT) hybrid systems (HSs) in three real emulator test rigs installed at University of Genoa (Italy), German Aerospace Center (DLR, Germany), and National Energy Technology Laboratory (NETL, USA), respectively. The proposed modeling approach is based on an experience-based simplification of the physical problem to reduce model computational efforts with minimal expense of accuracy. Traditional high fidelity dynamic modeling requires specialized skills and significant computational resources. This innovative approach, on the other hand, can be easily adapted to different plant configurations, predicting the most relevant dynamic phenomena with a reduced number of states: such a feature will allow, in the near future, the model deployment for monitoring purposes or advanced control scheme applications (e.g., model predictive control). The three target systems are briefly introduced and dynamic situations analyzed for model tuning, first, and validation, then. Relevance is given to peculiar transients where the model shows its reliability and its weakness. Assumptions introduced during model definition for the three different test rigs are discussed and compared. The model captured significant dynamic behavior in all analyzed systems (in particular those regarding the GT) and showed influence of signal noise on some of the SOFC computed outputs.

The use of model predictive control (MPC) in advanced power systems can be advantageous in controlling highly coupled variables and optimizing system operations. Solid oxide fuel cell/gas turbine (SOFC/GT) hybrids are an example where advanced control techniques can be effectively applied. For example, to manage load distribution among several identical generation units characterized by different temperature distributions due to different degradation paths of the fuel cell stacks. When implementing an MPC, a critical aspect is the trade-off between model accuracy and simplicity, the latter related to a fast computational time. In this work, a hybrid physical and numerical approach was used to reduce the number of states necessary to describe such complex target system. The reduced number of states in the model and the simple framework allow real-time performance and potential extension to a wide range of power plants for industrial application, at the expense of accuracy losses, discussed in the paper.

In the spectrum of current energy possibilities, hydrogen represents a solution of great interest toward a future sustainable energy system. No single technology can sustain the energy needs of the whole society, but integration and hybridization are two key strategic features for viable energy production based in hydrogen economy.

In the present work, a hydrogen energy model is analyzed. In this model hydrogen is produced through the electrolysis of water, taking advantage of the electrical energy produced by a renewable generator (photovoltaic panels). The produced hydrogen is chemically stored by the synthesis of sodium borohydride (NaBH4). NaBH4 promising features in terms of safety and high volumetric density are exploited for transportation to a remote site where hydrogen is released from NaBH4 hydrolysis and used for energy production.

This model is compared from an economic standpoint with the traditional hydrogen storage and transportation technology (compressed hydrogen in tanks).

This paper presents a thermodynamic and economic analysis of the process in order to determine its economic feasibility. Data employed for the realization of the model have been gathered from recent important progresses made on the subject.

The innovative plant including NaBH₄ synthesis and transportation is compared from an economic standpoint with the traditional hydrogen storage and transportation technology (compressed hydrogen in tanks). As a final point, the best technology and the components’ optimal sizes are evaluated for both cases in order to minimize production costs.

A modeling and control framework is proposed to describe the behavior of a water-ferrofluid two-phase 2D flow in the presence of a magnetic field and to devise proper optimal control actions. The dynamics of such a system descends from the cascade of magnetic field and Navier-Stokes equations. The former can be dealt with analytically, but this is not possible for the latter, which is usually treated numerically. The description of the motion of the interface between water and ferrofluid is accomplished by using level set methods. To overcome the computational difficulties when controlling such a system, a black-box model based on neural networks is constructed. Different kinds of neural networks are trained to account for the system behavior with an adequate precision in such a way to obtain a model that is well-suited for control. Optimal control is performed by using such black-box models with successful simulation results.

The recent trend of marine industry towards more efficient and versatile ships and lower emission has increased interest in hybrid solutions. However, the spread of this technology has been limited by several factors both economic and technical. Among these, a recurrent issue is the sizing of the Energy Storage System (ESS), which is strictly connected to the vessel typology, its operation and its control system. This paper presents an algorithm, developed within Wärtsilä Italia SpA, for the extraction of sequential operating modes from data recorded on board the vessel, in order to properly design a feasible ESS. The paper shows a technical economic analysis carried out on a small cruise vessel in order to identify competitive hybrid solutions compared to traditional configurations (engines running on conventional fuel or Liquid Natural Gas). Finally, the paper compares two case studies of a small vessel powered only by fuel cells (in place of conventional engines) and batteries, in order to prove the potential benefits derived from such innovative technologies with different operational profiles, also in hybrid mode.

This paper presents a steady-state model of an innovative turbocharged solid oxide fuel cell system fed by biofuel. The aim of this plant layout is the development of a reduced-cost solution, which involves the pressurization carried out with a mass production machine such as a turbocharger (instead of a microturbine). The turbocharger pressurizes the solid oxide fuel cell to increase the performance.

Following the experimental results to choose the suitable machine and for validating the turbocharger model, this tool was implemented to model the whole plant. It was used to calculate the operational conditions and to define the coupling aspects between the turbocharger, the recuperator and the solid oxide fuel cell system (comprising a fuel cell stack, an air preheater, a reformer, an off-gas burner and an anodic ejector).

The model permitted the component characterization and supported the design of an emulator test rig based on the coupling of a turbocharger and a pressure vessel. This facility was designed to conduct the experimental tests at system level on the matching between the machine and the fuel cell, especially for the dynamic and the control system aspects. To emulate the fuel cell, the rig was based on a specially designed pressure vessel equipped with a burner and inert ceramic materials. Moreover, the facility was designed to produce the turbine inlet conditions in terms of mass flow, temperature, pressure and gas composition (similitude conditions can be evaluated).

Electrical energy production by wind energy has assumed more and more relevance in the last years. This paper presents the design of a ducted horizontal axis wind turbine, in order to enhance the performance. The study compares the energy production of a ducted turbine to a traditional free turbine, highlighting the different features. In the first part of the work, different possible geometries have been investigated through a quasi-1D model, using correlations from literature to evaluate pressure, velocity and producible electrical power by the wind turbine. A 3D CFD model, in a set of configurations, has confirmed the preliminary results. The most promising geometries have been selected by combining the outputs of the two models. In order to confirm the results obtained by the numerical models, a test rig has been assembled at the wind tunnel of the Polytechnic School of the University of Genoa. Different possible configurations of the wind energy harvesting system have been tested: free turbine, horizontal duct, convergent duct and convergent-divergent ducts (with the turbine installed in the throat section). In particular, the convergent-divergent duct has shown the best results, with an increase factor close to 2.5 in terms of produced power, compared to the reference free turbine. Finally, the results obtained in the experimental campaign have been used to validate the two models (1D and 3D CFD). Considering the advantages in terms of energy production, this kind of configuration can be considered an interesting solution for many different situations, including energy harvesting.

Micro gas turbines (mGT) are emerging power sources for distributed generation facilities with promising features like environment friendliness, high fuel flexibility, cost effectiveness and efficient cogeneration of heat and power (CHP). However, curtailed heat demand during summers reduces the plant operating hours per year and negatively affects the overall economic feasibility of a CHP project. The micro Humid Air Turbine (mHAT) cycle is one of the novel cycles to increase the electrical efficiency of the gas turbine by utilizing the exhaust gas heat in periods of low heat demand, thus avoiding the system shutdown. However, the water injection system can introduce additional pressure losses in the mGT cycle, which may lead to compressor surge and it may also affect the recuperator performance in the long run due to corrosion. Hence, numerical simulation and diagnostic tools are essential for cycle optimization of mHAT and prediction of performance degradation.

This work is focused on the real time application of the AE-T100 model for the mHAT system located at the Vrije Universiteit Brussel (VUB), which is based on the T100 mGT equipped with a spray saturation tower. The AE-T100 model is a steady-state simulation tool for mGT cycles, which has been developed within a collaboration between the University of Genova (Unige) and Ansaldo Energia, and has been successfully applied at the Ansaldo Enegia test rig (AE-T100) for the diagnostic purpose. For this study, the basic AE-T100 model has been modified to simulate the humidified cycle according to the VUB plant configuration. The modified AET100 model has been validated against the experimental data obtained from the mHAT unit at nominal and part load.

Once the model was validated using real operating conditions, it has been used for monitoring the recuperator performance over large number of tests in dry mode, conducted over the past five years, as well as initial tests in wet mode, from the VUB-mHAT system. This work has proved the modeling capability of the AE-T100 tool to simulate the mHAT cycle with reasonable accuracy and first diagnostic application of the AE-T100 tool, in dry mode. However, the lack of data available at present in wet mode does not allow to provide a complete and robust diagnostics of this novel cycle under wet operation.

Hence, this preliminary analysis will provide basis for more detail diagnostics of the mHAT cycle using AE-T100 tool, over a longer time period under wet operation, in future.

The transient/dynamic modeling of energy systems can be used for different purposes. Important information can be obtained and used for the design phase. The control system and strategies can be safely tested on transient/dynamic models in simulation, increasing the confidence during experimental phase. Furthermore, these models can be used to acquire useful information for safety case. The analysis of energy systems in dynamic conditions is generally performed considering fixed values for both geometrical and operational parameters such as volumes, orifices, but also initial temperatures, pressure, etc. However, such characteristics are often subject to uncertainty, either because they are not known accurately or because they may depend on the operating conditions at the beginning of the relevant transient. With focus on a micro-gas turbine fuel cell hybrid system, compressor surge may or may not occur during transients, depending on the aforementioned cycle characteristics; hence compressor surge events are affected by uncertainty.

In this paper, a stochastic analysis was performed taking into account an emergency shut-down in a fuel cell gas turbine hybrid system, modelled with TRANSEO, a deterministic tool for the transient and dynamic simulations of energy systems. The aim of the paper is to identify the main parameters that impact on compressor surge margin. The stochastic analysis was performed through the RSA (Response Sensitivity Analysis) method, a sensitivity-based approximation approach that overcomes the computational burden of sampling methods such as MCS (Monte-Carlo Simulation). The results show that the minimum surge margin occurs in two different ranges of rotational speed: a high-speed range and a low-speed range, the latter being more sensitive for surge occurrence. The temperature and geometrical characteristic of the outer pressure vessel, where the fuel cell is installed, are the two main parameters that affect the surge margin during an emergency shut down.

Compressor surge is one of the main problem that may affect fuel cell gas turbine hybrid systems, because of the energy stored in the volume containing the high temperature pressurized fuel cell stack. The problem becomes even more crucial because in such kind of system, the fuel cell is the most sensitive and costly component that has to be preserved by abrupt pressure changes.

In order to determine the behavior of a dynamic compressor in its whole range of operating conditions, a calculation model was implemented in TRANSEO, a software tool for transient and dynamic analysis of microturbine and fuel cell based-cycles (based on Matlab-Simulink environment). The modeling procedure has been derived from the Greitzer’s 1976 nonlinear dynamic approach; the resulting T-RIG1 model predicts the transient response of a compression system and is able to simulate both normal and instable transient conditions. Several investigations have been done in order to characterize the impact of different parameters and configurations on the system response. The validation, in the frequency domain, was performed comparing calculations with experimental data measured from a dedicated test rig, where a small size turbocharger has been operated in stable and unstable conditions. In particular, the present work demonstrates the capability of the T-RIG1 model to simulate a free shaft turbocharger performance and instability, with the future purpose to develop feasible strategies for surge detection and recovery, applicable to turbocharger-based hybrid systems.

The aim of this work is the presentation of a new model for ejector performance calculation using a commercial tool. Due to the critical issues in recirculation performance, special attention is devoted to applications in hybrid systems based on high temperature fuel cells. The theoretical activity is supported by an experimental rig able to operate tests on ejectors at different operative conditions, with a layout similar to the fuel cell anodic recirculation. The model validation, operated considering experimental data obtained with this rig, is essential to evaluate the tool performance for design and off-design calculations. This aspect is particularly critical due to important limitations in the recirculation ratio (especially for the anodic side), to avoid unacceptable operative conditions in the fuel cells.

The results presented in this work were obtained with this validated model for an ejector applied on the anodic side of a Solid Oxide Fuel Cell (SOFC). A parametric analysis was carried out to show the effects of several parameters on the recirculation performance. The fully independent analysis of the influence of different properties (carried out with a specifically validated model) is an important innovative result for the application of such ejectors on high temperature fuel cells.

The coupling of a pressurized solid oxide fuel cell (SOFC) and a gas turbine has been proven to result in extremely high efficiency and reduced emissions. The presence of the gas turbine can improve system durability compared to a standalone SOFC, because the turbomachinery can supply additional power as the fuel cell degrades to meet the power request. Since performance degradation is an obstacles to SOFC systems commercialization, the optimization of the hybrid system to mitigate SOFC degradation effects is of great interest. In this work, an optimization approach was used to innovatively study the effect of gas turbine size on system durability for a 400 kW fuel cell stack. A larger turbine allowed a bigger reduction in SOFC power before replacing the stack, but increased the initial capital investment and decreased the initial turbine efficiency. Thus, the power ratio between SOFC and gas turbine significantly influenced system economic results.

The aim of this work is the demonstration of a surge prevention technique for advanced gas turbine cycles. There is significant surge risk in dynamic operation for turbines connected with large volume size additional components, such as a fuel cell stack, a saturator, a solar receiver or a heat exchanger for external combustion. In comparison with standard gas turbines, the volume size generates different behaviour during dynamic operations (with significant surge risk), especially considering that such additional components are including important dynamic constraints.

In order to prevent the surge events, a vibration analysis was carried out to develop precursors which are able to highlight the approach of this unstable operative zone. Since the sub-synchronous content of the measured vibrations is significantly increasing approaching the surge line, special attention was devoted to this parameter. The demonstration of a surge prevention system based on the sub-synchronous vibration content was carried out at the Innovative Energy Systems Laboratory of the University of Genoa. In this laboratory, a recuperated microturbine connected with a large size vessel was used. Starting from the stable operation, closing a valve in the main air line or increasing the compressor inlet temperature produced operative conditions with significant surge risk. The increase in sub-synchronous vibration content detected by the control system was used to perform an active operation (bleed valve opening) to avoid the approaching surge event.

The aim of this paper is the analysis of a turbocharged Solid Oxide Fuel Cell (SOFC) system considering the influence of fuel composition variation. This is an innovative system layout based on the coupling of an SOFC stack with a turbocharger. The SOFC pressurization carried out with a turbocharger instead of a microturbine is a solution to combine high efficiency with reduced-cost plant layout. Moreover, the fuel flexibility is an essential issue to operate the system with different fuel compositions ranging from natural gas to biogas (considering also the CO2 removal option).

This research activity started from the development of a steady-state system model using previously validated tools. The software was implemented in Matlab®-Simulink® environment considering the coupling of the different plant components. The analysis was started considering design conditions for a system fed by biogas (50% CH4 and 50% CO2 molar composition). Then, to reach fuel flexibility performance (as required for applications with renewable sources), the anodic ejector was re-designed to satisfy the related constraint for the Steam-to-Carbon ratio. The mentioned change in fuel composition involved also the control valves (bypass and/or bleed) to maintain the SOFC temperature at its set-point value, taking into account all the system constraints.

This paper aims to study the application of distributed generation technologies on a naval energy system, investigating the best operating strategy for energy management throughout an annual load profile. The thermo-economic analysis is performed considering electrical and thermal load demands referred to hotel and service loads of a cruise ship (around 6 MWel), both variable with the season and the period of the day, taking into accounttheoff-designcurvesandcostfunctionsforthedifferentgenerators. Four different solutionsareinvestigated,comparingtheoperativestrategiesintermsofenergyef?ciency, CO 2 emissions and annual costs.

The analysis is performed with dedicated software for the thermo-economic time-dependent analysis, developed by the University of Genoa. The thermo-economic approach has general validity, thus it can be also applied to different kinds of ships, even considering different technologies for energy generation and storage.

In the panorama of gas turbines for energy production, a great relevance is given to performance impact of the ambient conditions. Under the in?uence of ambient temperature, humidity and other factors, the engine performance is subject to consistent variations. This is true for large power plants as well as small engines. In Combined Cycle con?guration, variation in performance are mitigated by the HRSG and the bottoming steam cycle. In a small scale system, such as a micro gas turbine, the in?uence on the electric and thermal power productions is strong as well, and is not mitigated by a bottoming cycle. This work focuses on the Turbec T100 micro gas turbine and its performance through a series of operations with different ambient temperatures. The goal is to characterize the engine performance deriving simple correlations for the in?uence of ambient temperature on performance, at di?erent electrical loads. The newly obtained experimental data are compared with previous performance curves on a modi?ed machine, to capture the di?erences due to hardware degradation in time. An active management of the compressor inlet temperature may be developed in the future, basing on the analysis reported here.

The increase share of non-dispatchable renewables envisaged in the generation mix of Europe requires conventional plants to take on additional tasks. A higher flexibility of natural gas fired Combined Cycle (CC) power plants, which are currently the backbone of EU electrical grid, has become mandatory.

To increase the flexibility, and to further enhance turn-down ratio and power ramp capabilities of power-oriented CCs, an innovative concept based on the coupling of a highly efficient heat pump (HP) with CCs is proposed, featuring thermal storage and advanced control concept for smart scheduling.

A preliminary analysis of this integrated system is performed, evaluating the feasibility and the economic sustainability, along with the economic competitiveness with actual Combined Heat and Power plants, based on the analysis of the Energy Market trend.

The main objective of the PUMP-HEAT H2020 project is the Development of an integrated, flexibility-oriented Combined Cycle Balance of Plant concept, the PUMP-HEAT Combined Cycle (PHCC). This innovative plant layout is based on the integration of heat pumps and thermal energy storage, to un-tap combined cycle potential flexibility through low-CAPEX balance of plant innovations. In order to assess the added value of using thermal energy storage in the combined cycle, different layouts will be defined at the early stage of PUMP-HEAT. Some will include cold, warm or even hot thermal storage and some will include the latest phase change material (PCM) technologies. To manage this kind of plant, a control algorithm to achieve the best thermo-economic performances considering market requirements, plant efficiency, thermal storage level and operational constraints is mandatory. For this reason, project partners are investigating and developing different control algorithms for the PHCC integrated systems, focusing on flexibility enhancement and power grid operability. Within this framework, Model Predictive Control (MPC) algorithm for real-time supervision and management of the PHCC is being investigating and will be prototyped, virtually tested at simulation level, verified in hardware-in-the-loop and implemented in the demonstration site. The purpose of this paper is to introduce the global objectives of the project and to give details of control approaches, as well as to present the first results.

The effect of cathode airflow variation on the dynamics of a fuel cell gas turbine hybrid system was evaluated using a cyber-physical emulator. The coupling between cathode airflow and other parameters, such as turbine speed or pressure, was analyzed comparing the results at fixed and variable speed. In particular, attention was focused on fuel cell temperatures and gradients: cathode airflow, which is generally employed for thermal management of the stack, was varied by manipulating a cold-air bypass. A significant difference was observed in the two cases in terms of turbine inlet, exhaust gas, cathode inlet, and average cell temperatures. When the turbine speed was held constant, a change in cathode airflow resulted in a strong variation in cathode inlet temperature, while average cell temperature was not significantly affected. The opposite behavior was observed at variable speed. The system dynamics were analyzed in detail in order to explain this difference. Open-loop response was analyzed in this work for its essential role in system identification. However, a significant difference was observed between fixed and variable speed cases, because of the high coupling between turbine speed and cathode airflow. These results can give a helpful insight of system dynamics and control requirements. Cold-air valve bypass position also showed a strong effect on surge margin and pressure dynamics in both cases.

Solar energy has been considered as one of the promising solutions to replace the fossil fuels. To generate electricity beyond normal daylight hours, thermal energy storage systems (TES) play a vital role in concentrated solar power (CSP) plants. Thus, a significant focus has been given on the improvement of TES systems from the past few decades. In this study, a numerical model is developed to obtain the detailed heat transfer characteristics of lab-scale latent thermal energy storage system, which consists of molten salt encapsulated spherical capsules and air. The melting process and the corresponding temperature and velocity distributions in every capsule of the system are predicted. The enthalpy-porosity approach is used to model the phase change region. The model is validated with the reported experimental results. Influence of initial condition on the thermal performance of the TES system is predicted.

Micro gas turbines are a promising technology for distributed power generation because of their compact size, low emissions, low maintenance, low noise, high reliability and multi-fuel capability. Recuperators preheat compressed air by recovering heat from exhaust gas of turbines, thus reducing fuel consumption and improving the system efficiency, typically from 16–20% to _30%. A recuperator with high effectiveness and low pressure loss is mandatory for a good performance. This work aims to provide a comprehensive understanding about recuperators, covering fundamental principles (types, material selection and manufacturing), operating characteristics (heat transfer and pressure loss), optimization methods, as well as research hotspots and suggestions. It is revealed that primary-surface recuperator is prior to plate-fin and tubular ones. Ceramic recuperators outperform metallic recuperators in terms of high-temperature mechanical and corrosion properties, being expected to facilitate the overall efficiency approaching 40%. Heat transfer and pressure drop characteristics are crucial for designing a desired recuperator, and more experimental and simulation studies are necessary to obtain accurate empirical correlations for optimizing configurations of heat transfer surfaces with high ratios of Nusselt number to friction factor. Optimization methods are summarized and discussed, considering complicated relationships among pressure loss, heat transfer effectiveness, compactness and cost, and it is noted that multi-objective optimization methods are worthy of attention. Moreover, 3D printing and printed circuit heat exchanger technologies deserve more research on manufacturing of recuperators. Generally, a metallic costeffective primary-surface recuperator with high effectiveness and low pressure drop is a currently optimal option for a micro gas turbine of an efficiency of _30%, while a ceramic recuperator is suggested for a high efficiency micro gas turbine (e.g. 40%).

A solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system that uses such liquid fuels as ethanol is attractive for distributed power generation for applications in remote rural areas or as an auxiliary power unit. The SOFC system includes units that require and generate heat; thus, its energy management is important to improve its efficiency. In this study, a SOFC-GT integrated system with the external steam reforming of ethanol to produce hydrogen for the SOFC is proposed. Two SOFC-GT hybrid systems using a high-temperature heat exchanger and cathode exhaust gas recirculation are considered under isothermal conditions. The effects of key operating parameters, such as pressure, fuel use and turbomachinery efficiency, on the SOFC-GT hybrid system performance are discussed. The simulation results indicate that recycling the cathode exhaust gas from the SOFC-GT system requires less fresh air from the compressor, to maintain the SOFC stack temperature, and the heat recovered from the SOFC system is sufficient to supply both the fuel processor and air pre-heater. In contrast, an external heat is needed for the SOFC-GT system coupled to a recuperative heat exchanger.

The analysis of different energy systems has shown various sources of variability and uncertainty; hence the necessity to quantify and take these into account is becoming more and more important. In this paper, a steady state, off-design model of a solid oxide fuel cell and turbocharger hybrid system with recuperator has been developed. Performances of such stiff systems are affected significantly by uncertainties both in component performance and operating parameters. This work started with the application of Monte Carlo Simulation method, as a reference sampling method, and then compared it with two different approximated methods. The first one is the Response Sensitivity Analysis, based on Taylor series expansion, and the latter is the Polynomial Chaos, based on a linear combination of different polynomials. These are non-intrusive methods, thus the model is treated as a black-box, with the uncertainty propagation method staying at an upper level. The work is focused on the application on highly non-linear complex systems, such as the hybrid systems, without any optimization process included. Hence, only the uncertainty propagation is considered. Uncertainties in the fuel utilization, ohmic resistance of the fuel cell, and efficiency of the recuperator are taken into account. In particular, their effects on fuel cell lifetime and some simple economic parameters are evaluated. The analysis distinguishes the specific features of each approach and identifies the strongest influencing inputs to the monitored output. Both approximated methods allow an important reduction in the number of evaluations while maintaining a good accuracy compared to Monte Carlo Simulation.

In engineering design, uncertainty is inevitable and can cause a significant deviation in the performance of a system. Uncertainty in input parameters can be categorized into two groups: aleatory and epistemic uncertainty. The work presented here is focused on aleatory uncertainty, which can cause natural, unpredictable and uncontrollable variations in performance of the system under study. Such uncertainty can be quantified using statistical methods, but the main obstacle is often the computational cost, because the representative model is typically highly non-linear and complex. Therefore, it is necessary to have a robust tool that can perform the uncertainty propagation with as few evaluations as possible. In the last few years, different methodologies for uncertainty propagation and quantification have been proposed. The focus of this study is to evaluate four different methods to demonstrate strengths and weaknesses of each approach. The first method considered is Monte Carlo simulation, a sampling method that can give high accuracy but needs a relatively large computational effort. The second method is Polynomial Chaos, an approximated method where the probabilistic parameters of the response function are modelled with orthogonal polynomials. The third method considered is Mid-range Approximation Method. This approach is based on the assembly of multiple meta-models into one model to perform optimization under uncertainty. The fourth method is the application of the first two methods not directly to the model but to a response surface representing the model of the simulation, to decrease computational cost. All these methods have been applied to a set of analytical test functions and engineering test cases. Relevant aspects of the engineering design and analysis such as high number of stochastic variables and optimised design problem with and without stochastic design parameters were assessed. Polynomial Chaos emerges as the most promising methodology, and was then applied to a turbomachinery test case based on a thermal analysis of a high-pressure turbine disk.

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This paper shows experimental results obtained from a T100 microturbine connected with different volume sizes. The activity was carried out with the test rig developed at the University of Genoa for hybrid system emulation. However, these results apply to all the advanced cycles where a microturbine is connected with an additional external component responsible for volume size increase. Even if the tests were performed with a microturbine (for laboratory scale and for the related research interest in innovative cycles), similar analyses can be extended to on large size turbines. The main power systems including the effect of an additional volume connected with a turbine are: fuel cell based hybrid plants, humid cycles, externally fired layouts and innovative systems including high temperature thermal storage devices. Since in this case a 100 kW turbine was used, the volume was located between the recuperator outlet and the combustor inlet as in the typical cases related to small size plants. A modular vessel was used to perform and to compare the tests with different volume sizes.

To highlight the volume size effect, preliminary experimental results were carried out considering the transient response due to an on/off bleed valve operation. So, the main differences between system parameters obtained for a bleed line closing operation are compared considering three different volume sizes.

The main results reported in this paper are related to surge operations. This analysis was carried out to extend the knowledge about this risk condition: the systems equipped with large volume size connected with the machine present critical issues related to surge prevention especially during transient operations. For instance, if the T100 machine is operating with large volume components, the standard shutdown procedure can produce surge condition. This behavior is due to a slow depressurization rate in comparison with a standard microturbine. So, to produce surge conditions in this test rig, a valve operating in the main air path was closed to generate unstable behavior. It was possible to compare the effect of different volume sizes on main properties of the system using a modular vessel. Particular focus was devoted to the operational curve plotted on the compressor map. The system was equipped with different dynamic probes to measure the vibrations during normal and surge operations. The frequency analysis showed significant vibration increase not only during surge events but also close to the unstable condition. In details, possible surge precursor indicators were obtained to be used for the detection of risky machine operations. Since these surge precursors are considered important parameters for the control system point of view, an extensive experimental analysis was carried out considering the influence of volume size. These precursors were defined to produce control data (e.g. an on/off signal for a bleed valve) for surge prevention. The experimental data collected during these tests are analyzed with the objective of designing control systems to prevent surge conditions.

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This paper shows the Hardware-In-the-Loop (HIL) technique developed for the complete emulation of Solid Oxide Fuel Cell (SOFC) based hybrid systems. This approach is based on the coupling of an emulator test rig with a real-time software for components which are not included in the plant. The experimental facility is composed of a T100 microturbine (100 kW electrical power size) modified for the connection to an SOFC emulator device. This component is composed of both anodic and cathodic vessels including also the anodic recirculation system which is carried out with a single stage ejector, driven by an air flow in the primary duct. However, no real stack material was installed in the plant. For this reason, a real-time dynamic software was developed in the Matlab-Simulink environment including all the SOFC system components (the fuel cell stack with the calculation of the electrochemical aspects considering also the real losses, the reformer, and a cathodic recirculation based on a blower, etc.). This tool was coupled with the real system utilizing a User Datagram Protocol (UDP) data exchange approach (the model receives flow data from the plant at the inlet duct of the cathodic vessel, while it is able to operate on the turbine changing its set-point of electrical load or turbine outlet temperature). So, the software is operated to control plant properties to generate the effect of a real SOFC in the rig. In stand-alone mode the turbine load is changed with the objective of matching the measured Turbine Outlet Temperature (TOT) value with the calculated one by the model. In grid-connected mode the software/hardware matching is obtained through a direct manipulation of the TOT set-point.

This approach was essential to analyze the matching issues between the SOFC and the micro gas turbine devoting several tests on critical operations, such as start-up, shutdown and load changes. Special attention was focused on tests carried out to solve the control system issues for the entire real hybrid plant emulated with this HIL approach. Hence, the innovative control strategies were developed and successfully tested considering both the Proportional Integral Derivative and advanced approaches. Thanks to the experimental tests carried out with this HIL system, a comparison between different control strategies was performed including a statistic analysis on the results The positive performance obtainable with a Model Predictive Control based technique was shown and discussed. So, the HIL system presented in this paper was essential to perform the experimental tests successfully (for real hybrid system development) without the risks of destroying the stack in case of failures. Mainly surge (especially during transient operations, such as load changes) and other critical conditions (e.g. carbon deposition, high pressure difference between the fuel cell sides, high thermal gradients in the stack, excessive thermal stress in the SOFC system components, etc.) have to be carefully avoided in complete plants.

I

The use of model predictive control (MPC) in advanced power systems can be advantageous in controlling highly coupled variables and optimizing system operations. Solid oxide fuel cell/ gas turbine (SOFC/GT) hybrids are an example where advanced control techniques can be effectively applied. For example, to manage load distribution among several identical generation units characterized by different temperature distributions due to different degradation paths of the fuel cell stacks. When implementing a MPC, a critical aspect is the trade-off between model accuracy and simplicity, the latter related to a fast computational time. In this work, a hybrid physical and numerical approach was used to reduce the number of states necessary to describe such complex target system. The reduced number of states in the model and the simple framework allow real-time performance and potential extension to a wide range of power plants for industrial application, at the expense of accuracy losses, discussed in the paper.

I

This paper presents the development, implementation and validation of a simplified dynamic modeling approach to describe SOFC/GT hybrid systems in three real emulator test rigs installed at University of Genoa (UNIGE, Italy), German Aerospace Center (DLR, Germany) and National Energy Technology Laboratory (NETL, USA), respectively. The proposed modeling approach is based on an experience-based simplification of the physical problem to reduce model computational efforts with minimal expense of accuracy. Traditional high fidelity dynamic modelling requires specialized skills and significant computational resources. This innovative approach, on the other hand, can be easily adapted to different plant configurations, predicting the most relevant dynamic phenomena with a reduced number of states: such a feature will allow, in the near future, the model deployment for monitoring purposes or advanced control scheme applications (e.g. model predictive control). The three target systems are briefly introduced and dynamic situations analyzed for model tuning, first, and validation, then. Relevance is given to peculiar transients where the model shows its reliability and its weakness. Assumptions introduced during model definition for the three different test-rigs are discussed and compared. The model captured significant dynamic behavior in all analyzed systems (in particular those regarding the GT) and showed influence of signal noise on some of the SOFC computed outputs.

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Micro gas turbines (mGT) are emerging power sources for distributed generation facilities considering their environment friendliness, high fuel flexibility and efficient cogeneration of heat and power (CHP). Numerical simulation and diagnostic tools are essential for cycle optimization of mGT and prediction of performance degradation. This work is focused on fault diagnostics of T100 mGT through the application of AE-T100 model, a simulation tool, which has been developed within a collaboration between the University of Genoa (Unige) and Ansaldo Energia. This model has been developed for steady-state simulation of mGT in offdesign conditions. Leveraging on previous efforts for model development, tuning, first phase of validation through Ansaldo Enegia test rig (AE-T100) and diagnostic application of the model, the present work deals with further utilization of the diagnostic capability of the model for mGT cycles. For this purpose, it was used in real operating conditions through the AE-T100 test rig for the diagnostic aim of some unexpected machine behavior. The model results indicated high deviation from the actual field data in terms of fuel flow and efficiency, and so justified the diagnostic capability of the AE-T100 tool. Afterwards, based on the experimental observation of some bypass leakage from the burner in the same test rig, AE-T100 model was applied to model such leakage through the variation of AS ratio, leakage from the recuperator outlet to the ambient, combustor pressure drop and turbine section modification, and carried out the sensitivity analysis of these parameters. Sensitivity analysis has verified that the accurate impact of this leakage on overall mGT performance cannot be modeled with the help of AE-T100 tool in its current capacity. Therefore, some other investigations like analysis of compressor maps must be carried out to explain such a performance deviation in case of leakage. Afterwards, the analysis of compressor maps resulted from the operating conditions of the test conducted on the same machine after leakage repair, has highlighted the change in compressor operating point and thus, more efficient compressor functioning, which results in higher net power. Hence, this analysis has provided a more comprehensible explanation of this leakage impact on the mGT performance.

I

A control strategy to mitigate fuel cell degradation effects in a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid system was implemented on the Hybrid Performance facility at the National Energy Technology Laboratory. In this experiment, a cyber-physical approach was employed to emulate the SOFC component and to couple it to a physical recuperated gas turbine. An empirical degradation model simulated fuel cell performance decay over time depending on operating parameters. A combination of virtual and physical actuators was manipulated with the goal of ensuring safe fuel cell performance over time, maintaining constant voltage and minimizing thermal stresses as fuel cell power degraded. Three single-input single-output controllers were used for this purpose. In particular, a gain scheduling approach was used for voltage control to account for different degraded conditions of operation because stability could not be maintained with the initial controller gains. In addition, a bypass valve control was designed to maintain constant temperature difference across the cell, and turbine load was manipulated to keep constant speed.

This work presents the control design and implementation on the Hybrid Performance facility and illustrates the impact of fuel cell degradation on the entire system long-term performance. Controllers design was based on empirical transfer functions and stability analysis. Issues related to coupling phenomena between controlled variables are discussed. The results show the potential for an adequate control of the system to extend fuel cell operating lifetime.

I

In Solid Oxide Fuel Cell (SOFC) hybrid systems, anode recycle allows us to reach high stack fuel utilization without causing anode re-oxidation, which is detrimental for the fuel cell. In addition, anode recycle also helps the system to mitigate the risk of carbon deposition within the fuel cell when employing fuel with high methane/CO content. This work incorporated anode recycle within a pre-existing fuel manifold model which is embedded in a larger real-time SOFC model. To optimize system performance, we considered fuel manifold design and anode recycle concurrently. The pre-existing manifold model contained a fuel valve, mixing volume, and pipe system for pressure losses. Because increasing anode recycle percentage increased fuel mass flow, pressure losses in the system also increased. Therefore, a sensitivity analysis on manifold pipe diameter and fuel composition was conducted with parametric variation in anode recycle percentage. This enabled both minimization of pressure loss to avoid damage to the SOFC, and minimization of manifold residence time to maintain acceptable control response. The updated model allowed for further investigation of the effects of anode recycle within the fuel cell and ultimately the entire hybrid system.

I

The use of cyber-physical systems to simulate novel hybrid power cycles provides a cost-effective means to develop and test control strategies at the pilot scale. One of the primary challenges of implementing a cyber-physical power system component is the seamless coupling of a real-time model with hardware that interacts with its environment. A real-time solid oxide fuel cell model integrated with a physical recuperated turbine cycle results in significant capability in exploring the operational limits of a hybrid system. The creation of a model that can interact with hardware requires a delicate balancing act between fidelity, speed, and stability. In this case, the developed model makes use of both implicit and explicit methods for solving the differential equations associated with heat transfer and electrochemistry in a solid oxide fuel cell system. Stability and computational speed are evaluated over some transient simulations. The balance between implicit and explicit methodologies for solving the differential equations associated with heat transfer and the temperature profiles was examined. The method is particularly relevant during simulations involving localized degradation distributed along the cell. The results provide some quantification of the challenges faced in applying cyber-physical systems to hardware simulation of advanced power systems.

This book explores all technical aspects of solid oxide fuel cell (SOFC) hybrid systems and proposes solutions to a range of technical problems that can arise from component integration. Following a general introduction to the state-of-the-art in SOFC hybrid systems, the authors focus on fuel cell technology, including the components required to operate with standard fuels. Micro-gas turbine (mGT) technology for hybrid systems is discussed, with special attention given to issues related to the coupling of SOFCs with mGTs. Throughout the book emphasis is placed on dynamic issues, including control systems used to avoid risk conditions.

With an eye to mitigating the high costs and risks incurred with the building and use of prototype hybrid systems, the authors demonstrate a proven, economically feasible approach to obtaining important experimental results using simplified plants that simulate both generic and detailed system-level behaviour using emulators. Computational models and experimental plants are developed to support the analysis of SOFC hybrid systems, including models appropriate for design, development and performance analysis at both component and system levels.

Coupling a solid oxide fuel cell (SOFC) with a gas turbine provides a substantial increment in system efficiency compared to the separate technologies, which can potentially introduce economic benefits and favor an early market penetration of fuel cells. Currently, the economic viability of such systems is limited by fuel cell short lifetime due to a progressive performance degradation that leads to cell failure. Mitigating these phenomena would have a significant impact on system economic feasibility. In this study, the lifetime of a standalone, atmospheric SOFC system was compared to a pressurized SOFC gas turbine hybrid and an economic analysis was performed. In both cases, the power production was required to be constant over time, with significantly different results for the two systems in terms of fuel cell operating life, system efficiency, and economic return. In the hybrid system, an extended fuel cell lifetime is achieved while maintaining high system efficiency and improving economic performance. In this work, the optimal power density was determined for the standalone fuel cell in order to have the best economic performance. Nevertheless, the hybrid system showed better economic performance, and it was less affected by the stack cost.

In thermal grids and district heating, thermal storage devices play an important role to manage energy demand. Additionally, in smart polygeneration grids, thermal energy storage devices are essential to achieve high flexibility in energy demand management at relatively low cost. In this scenario, accurate evaluation of state of charge of storage vessels based on available measurements is critical.

The aim of this paper is to develop and compare three different models for state of charge estimation in stratified water tanks (discrete temperature measurements) and the related application in an experimental polygeneration grid with a real-time management tool. The first model is based on the empirical calculation of the state of charge considering the thermal power difference between generation and consumption, and afterwards correction based on measured temperatures. The second model is a mathematical approach considering a pre-defined temperature shape fitted with experimental data. The latter model is based on a 1-D physical approach using a multi-nodal method forced on the basis of the measured temperatures. The models were compared considering an experimental test performed in the polygeneration laboratory by the Thermochemical Power Group (TPG).

As a result of the comparative analysis, the first model was selected for applications in complex polygeneration grids, due to its good compromise between accuracy and computational effort. Several tests were carried out to demonstrate the performance of the empirical approach selected for the thermal storage model and the economic benefit related to the utilization of this vessel. The experimental plant, constituted by two different prime movers (a 100 kW microturbine and a 20 kW internal combustion engine) and a thermal storage tank, was able to demonstrate the performance of a real-time management tool. For this reason, special attention was devoted to the variable cost comparisons.

The novelty of this work lies in the development of the real-time management tool coupled with a thermal storage model by considering the simplified modelling approach. This is an essential requisite for complex polygeneration grids including hundreds or thousands of prime movers and thermal storage devices. Additionally, it is important to state that in such cases the required real-time performance could be difficult to obtain. The results, produced with the innovative and flexible experimental rig, demonstrate the positive impact of thermal storage as well as the effective management performance of this quite simple dispatching approach. Another important novel aspect regards this experimental assessment considering both specific 3-h tests and extended conditions typical of a possible real application.

This paper describes the recent developments of the innovative wave energy converter for off-shore applications named the Seaspoon. It is a wave energy converter (WEC) that harvests the energy content of oceans waves exploiting the circular motion of the water particles, perturbed at the free surface by the action of the wind.

The paper describes the recent test results on Seaspoon prototypes, the experimental validation of a CFD model, to be used to optimise the geometry of Seaspoon blades, enabling its future scale-up. The model has been successfully compared against literature data for wave motion and forces against a static body. Then, the model has been compared against experimental integral measurements from the Seaspoon test campaign. In particular, the flat blades tested in the laboratory-scale wave tank showed good agreement with the model predictions. Furthermore, experimental results on concave-type and convex-type blades are shown, demonstrating that the latter is the most promising shape: such blade type will be considered for the future development of the Seaspoon.

The test campaign and the simulation studies contributed to identify the best geometrical options to enhance the Seaspoon energy harvesting efficiency as well as adaptability to different sea-states.

The performance of a solid oxide fuel cell (SOFC) is subject to inherent uncertainty in operational and geometrical parameters, which can cause performance variability and affect system reliability. Operating conditions such as current demand, cell temperature and fuel utilization play an important role on the degradation mechanisms, which affect typical SOFCs. In previous work, a deterministic empirical degradation model of a SOFC was developed as a function of such operating conditions. By the nature of experimental data and regression fitting, this model was not deterministic. The aim of this work is to evaluate the impact of the uncertainties in the degradation model through a stochastic analysis. In particular, the Response Sensitivity Analysis (RSA), an approximate stochastic method based on Taylor series expansion, is applied to a standalone SOFC model and a fuel cell hybrid system model both subjected to cell degradation. The attention is principally focused on the impact on the fuel cell lifetime. To provide an indication of degradation effect and resulting lifetime uncertainty on economic performance, a cursory economic analysis is performed.

The coupling of a pressurized solid oxide fuel cell (SOFC) and a gas turbine has been proven to result in extremely high efficiency and reduced emissions. The presence of the gas turbine can improve system durability compared to a standalone SOFC, because the turbomachinery can supply additional power as the fuel cell degrades to meet the power request. Since performance degradation is an obstacles to SOFC systems commercialization, the optimization of the hybrid system to mitigate SOFC degradation effects is of great interest. In this work, an optimization approach was used to innovatively study the effect of gas turbine size on system durability for a 400 kW fuel cell stack. A larger turbine allowed a bigger reduction in SOFC power before replacing the stack, but increased the initial capital investment and decreased the initial turbine efficiency. Thus, the power ratio between SOFC and gas turbine significantly influenced system economic results.

This paper presents a design model of a turbocharged solid oxide fuel cell system fueled by biogas. The aim of this plant layout is the development of a low-cost solution considering the coupling of the solid oxide fuel cell (SOFC) with a low-cost machine such as a turbocharger (instead of a microturbine). The whole system model calculates the operational conditions and realizes the coupling between the turbocharger, the recuperator and the solid oxide fuel cell system (comprising SOFC, air pre-heater, fuel compressor and pre-heater, reformer, off-gas burner and anodic ejector). This model also supports the design of an emulator test rig in which a burner, located inside a thermal insulated vessel, replaces the solid oxide fuel cell system. The emulator test rig will be useful to study the matching between the turbocharger and the fuel cell to validate simulation models, design innovative solutions and test the control system of the whole plant.

This paper describes the recent development of the innovative wave energy converter for off-shore applications named the Seaspoon. It is a wave energy converter (WEC) that catches the energy content of oceans waves exploiting the circular motion of the water particles perturbed at the free surface by the action of the wind.

The paper describes the development and experimental validation of a CFD model, which will be used to optimise the geometry of Seaspoon blades, enabling its future scale-up. Such a model has been developed in the STAR-CCM+ environment. The model has been successfully compared against literature data for wave motion and forces against a static body. Then, the model has been compared against experimental measurements from the Seaspoon test campaign equipped with flat blades in a laboratory-scale wave tank, showing acceptable results in the prediction of the Seaspoon motion. Furthermore, experimental results on concave-type and convex-type blades are shown, demonstrating that the latter is the most promising shape: such blade type is currently object of CFD model validation and will be considered for the future development of the Seaspoon.

The test campaign and the simulation studies contributed to identify the geometrical options to enhance the Seaspoon energy harvesting efficiency as well as adaptability to different sea-states.

The main topic of this work is the development and validation of a simplified approach for the dynamic analysis of a Gas Turbine Combined Cycle (GTCC), with a particular focus on start-up procedure and associated mechanical stresses on the steam turbine (ST). The currently deregulated energy market led GTCC to undergo frequent startups, a condition often not considered during plant design. Moreover, the time required for the start-up is crucial under an economical viewpoint, though it is constrained by mechanical stresses imposed to thick components by thermal gradients. The framework proposed in this work aims to improve the accessibility to simulation software by applying commonly used office suite –Microsoft Excel/Visual Basic – with acceptable reduction in accuracy. Simplicity of model allow fast computation and its exploitation can be pursued by non-qualified plant operators. The obtained tool can be than adopted to support decision process during plant operations. The developed tool has been validated for a hot start-up against field measurements supplied by Tirreno Power S.p.A. Italy. Data are recorded through control and monitoring sensors of a 390 MW multi-shaft combined cycle based on the GT AEN94.3 A4 frame, but the results can be easily generalized to other layouts. Simulation result and stress evaluations around the steam turbine (ST) rotor show good agreement with experimental data.

This paper aims to present a feasibility study of the innovative plant for methanol synthesis from carbon dioxide sequestered by fossil fuel power plant and hydrogen, which is produced by water electrolyzer employing the over-production on the electrical grid. The thermo-economic analysis is performed in the framework of the MefCO₂ H2020 EU project and it is referred to the German economic scenario, properly taking into account the real market costs and cost functions for different components of the plant. Three different plant capacities for methanol production (4000 10,000 and 50,000 ton/year) have been investigated, assuming an average cost for electrical energy to feed electrolysers and analyzing the influence of the most significant parameters (oxygen selling option, methanol selling price and electrolysers’ capital cost) on the profitability of the plant.

The analysis has been performed in W-ECoMP, software for the thermo-economic analysis and plant optimization developed by the University of Genoa.

The hybridization of Solid Oxide Fuel Cell (SOFC) and gas turbine technologies provides an increase in system efficiency and economic performance. The latter aspect is significantly affected by fuel cell degradation, due to several mechanisms. However, hybrid systems allow different control strategies to minimize degradation effects on system performance and their impact on economic feasibility.

A real-time distributed model of a SOFC was used to simulate fuel cell degradation in the cases of a standalone stack and a hybrid configuration, in the latter of which the numerical model is normally coupled with the hybrid system hardware components of the National Energy Technology Laboratory (NETL) hyper facility. The results showed how in a hybrid system it is possible, with an appropriate strategy, to maintain constant voltage even if the cell is degrading, reducing degradation rate during time. At constant power demand, fuel cell life could be significantly extended using the operating strategies allowed by coupling with a turbine (an order of magnitude longer than a standalone fuel cell), maintaining high system efficiency despite fuel cell degradation.

This paper shows the performance curves obtained with an experimental campaign on the following different prime movers: a 100 kW microturbine, a 20 kW internal combustion engine, a 450 kW SOFC-based hybrid system and a 100 kW absorption chiller. While the size related to the microturbine and the engine are actual electrical power values, the hybrid system size is an electrical virtual power (an emulator rig was used for this plant) and the chiller value is a cooling thermal power. These experimental results were obtained with a smart polygeneration facility installed in the Innovative Energy Systems Laboratory by the Thermochemical Power Group of the University of Genoa. This facility was designed to perform tests on smart grids equipped with different generation technologies to develop and improve innovative control and optimization tools. The performance curves were obtained with two different approaches: tests on real prime movers (for the microturbine, the engine and the chiller) or measurements on an emulator rig (for the hybrid system). In this second case, the tests were carried out using an experimental facility based on the coupling of a second microturbine with a modular vessel. A real-time simulation software was used for components not physically present in the experimental plant. These results are a significant improvement in comparison with the available data, because experimental results are presented for different prime movers in different operative conditions (both design and part-load operations). Moreover, since both manufacturers and users are not usually able to control air inlet temperature, special attention was devoted to the ambient temperature impact on the 100 kW microturbine because this property has a strong influence on the performance of this machine. For this reason, empirical correlations on the ambient temperature effect were obtained from the experiments with the objective to perform an easy implementation of the optimization tools. Experimental performance curves (including several off-design conditions) are essential for smart grid management because (if they are implemented in optimization tools) they allow to find real optimal solutions (while tools based on linear or calculated correlations can obtain results affected by significant errors).

In recent years, many different concepts to manage smart distributed systems were proposed and solutions developed. Smart grids and the increasing influence of renewable sources on energy production lead to concerns about grid stability and load balance. Combined Heat and Power (CHP) generators coupled with solar or other renewable sources offer the opportunity to satisfy both electric and thermal power economically. Both electric and thermal demand and supply change continuously, and sources such as solar and wind are not dispatchable or accurately predictable. At the same time, it is essential to use the most efficient and cost effective sources to satisfy the demand. This problem has been studied at the University of Genoa (UNIGE), Italy, using different generators and energy storage device that can supply both electric and thermal energy to consumer buildings. Here the problem is formulated as a constrained Multi-Input Multi-Output (MIMO) problem with sometimes conflicting requests that must be satisfied. The results come from experiments carried out on the test rig located at the Innovative Energy System Laboratories (IESL) of the Thermochemical Power Group (TPG) of UNIGE. This paper compares three different control approaches to manage the distributed generation system: Simplified Management Control (SMC), Model Predictive Control (MPC), and Multi-Commodity Matcher (MCM). Control systems and their control actions are evaluated through economic and performance key indicators.

Fuel cell gas turbine hybrids present significant challenges in terms of system control because of the coupling of different time-scale phenomena. Hence, the importance of studying the integrated system dynamics is critical. With the aim of safe operability and efficiency optimization, the cold air bypass valve was considered an important actuator since it affects several key parameters and can be very effective in controlling compressor surge. Two different tests were conducted using a cyber-physical approach. The Hybrid Performance (HyPer) facility couples gas turbine equipment with a cyber physical solid oxide fuel cell in which the hardware is driven by a numerical fuel cell model operating in real time. The tests were performed moving the cold air valve from the nominal position of 40% with a step of 15% up and down, while the system was in open loop, i.e. no control on turbine speed or inlet temperature. The effect of the valve change on the system was analyzed and transfer functions were developed for several important variables such as cathode mass flow, total pressure drop and surge margin. Transfer functions can show the response time of different system variables, and are used to characterize the dynamic response of the integrated system. Opening the valve resulted in an immediate positive impact on pressure drop and surge margin. A valve change also significantly affected fuel cell temperature, demonstrating that the cold air bypass can be used for thermal management of the cell.

This paper aims to present a thermo-economic approach for methanol production comparing different renewable energy sources. In this study, the methanol is produced from the CO2 hydrogenation in a pressurized reactor; two different plant configurations are analyzed: in the first carbon dioxide is obtained from biogas upgrade, while in the second one CO2 is acquired from external sources. Carbon dioxide is mixed with hydrogen and then the gas is sent into the reactor for methanol synthesis. Hydrogen is produced by an alkaline pressurized electrolyzer (1 MW, 30 bar) fed by time-dependent electrical energy produced by renewable plants (hydroelectric, wind or photovoltaic), when available; in the remaining periods, electricity is purchased by the national grid.

Since the available electrical energy from the different renewable sources is not constant throughout the year, a time-dependent hierarchical thermo-economic analysis is performed in order to investigate the best plant configuration. The analyses are performed with the W-ECoMP simulation tool (developed by the authors’ research group) considering different costs of electricity and different methanol selling prices taking into account the future market forecast. The results for the two plant lay-outs are compared from energetic, economic and environmental point of view for the different renewable energy sources to evaluate the best solution in the Italian scenario.

This paper presents a thermo-economic analysis based on data from a real Smart polygeneration microgrid (SPM), designed to satisfy energy demands of the university campus of Savona (Italy). The plant is made up of different cogenerative generators (micro gas turbines and an internal combustion engine), renewable generators and two auxiliary boilers (one of them is off during the most of the time): the generators are “distributed” around the campus and coupled to electrical and thermal storages. Since several cogenerative units are included in the grid, the integration of the different storage systems is relevant in order to determine the best management strategy, following both thermal and electrical requests and taking into proper account the strong difference between the two energy demand profiles.

The thermo-economic analysis is performed exploiting the software W-ECoMP, developed by the authors’ research group, in order to find the best operational strategy, considering the importance of an appropriate storage system to manage the polygenerative energy district; attention is paid to the integration and combination of three different kinds of storage (hot and cold water tanks and electrical battery). Different scenarios are presented, combining the storages and showing their impact in terms of money savings and reduction of electrical energy purchasing from the National grid. Both the grid connected mode and island mode of operation of the SPM are considered.

The analysis is performed considering the time dependent nature of the energy demands throughout the whole year and implementing the experimental off-design curves of the real devices installed in the grid.

This paper presents a real smart polygenerative grid, designed to satisfy energy demands of the University of Genoa, Campus of Savona (Italy). The plant is made up by different generators: conventional boilers, combined heat and power (CHP) units, electrical and thermal storages and renewable generators.

The analysis of this polygenerative smart-grid is performed exploiting a software developed by the Authors’ research group, which allows for the time-dependent multi level thermo-economic optimization of polygenerative energy systems. In the models the experimental off-design curves of the real devices installed were used in order to increase the reliability of the simulation results and to allow model validation to be easily obtained. The gridwas simulated considering the time dependent nature of the demands throughout the whole year, finding best thermo-economic operational strategy.

Finally, attention is devoted to future lay-out modifications in order to reduce purchased electricity from the National grid in summer months, when, as the thermal request decreases, the CHP units are not currently properly exploited. Two different solutions are analyzed coupling the micro-gas turbine (mGT) CHP units with absorption chillers or with a small size organic Rankine cycle (ORC) turbine, and their thermo-economic performances are discussed in depth.

This entry deals with biomass as an energy source. Different types of biomass are described from the energy perspective, focusing on those more interesting for energy application. The main energy conversion technologies available are outlined, as well as the properties of their main products. Finally, an overview over the benefits that come from biomass exploitation for energy purposes is provided.

This paper proposes a time-dependent, thermo-economic hierarchical approach for the analysis of energy districts and smart poly-generation microgrids, in order to determine the optimal size of different prime movers, required to meet the energy demand of a generic user. This approach allows for determining the optimal size for each component of the energy district, as well as defining its most efficient operation management for the entire year, taking into proper account the time-dependent nature of the electrical, thermal and cooling demands, which are the main constraints of the optimisation problem. Additionally, the proposed method takes into consideration both energy performance and operation costs.

A specific case study is developed around the smart poly-generation microgrid at the University of Genoa, Savona Campus (Italy), which has been operational since 2013. In the original design, the microgrid includes different co-generative prime movers, renewable generators and a thermal storage system. In a second design an absorption chiller is included to supply the campus’ energy cooling demand.

Obtained results allowed identifying the best operation configuration, from a thermo-economic standpoint, for the considered scenario. The proposed method can be easily replicated in different applications and configurations of different smart poly-generative grids.

In this paper an approach for the determination of the optimal size and management of a plant for hydrogen production from renewable source (photovoltaic panels) is presented.

Hydrogen is produced by a pressurized alkaline electrolyser (42 kW) installed at the University Campus of Savona (Italy) in 2014 and fed by electrical energy produced by photovoltaic panels. Experimental tests have been carried out in order to analyze the performance curve of the electrolyser in different operative conditions, investigating the influence of the different parameters on the efficiency. The results have been implemented in a software tool in order to describe the behavior of the systems in off-design conditions.

Since the electrical energy produced by photovoltaic panels and used to feed the electrolyser is strongly variable because of the random nature of the solar irradiance, a time-dependent hierarchical thermoeconomic analysis is carried out to evaluate both the optimal size and the management approach related to the system, considering a fixed size of 1 MW for the photovoltaic panels. The thermo-economic analysis is performed with the software tool W-ECoMP, developed by the authors’ research group: the Italian energy scenario is considered, investigating the impact of electricity cost on the results as well.

The effect of cathode airflow variation on the dynamics of a fuel cell gas turbine hybrid system was evaluated using a cyber-physical emulator. The coupling between cathode airflow and other parameters, such as turbine speed or pressure, was analyzed comparing the results at fixed and variable speed. In particular, attention was focused on the fuel cell temperatures, since cathode airflow is generally employed for thermal management of the stack. A significant difference was observed in the two cases in terms of turbine inlet, exhaust gas, cathode inlet, and average cell temperatures. When the turbine speed was held constant, a change in cathode airflow resulted in a strong variation in cathode inlet temperature, while average cell temperature was not significantly affected. The opposite behavior was observed at variable speed. The system dynamics were analyzed in details in order to explain this difference. Open loop response was analyzed in this work for its essential role in control systems development. But, the significant difference shown in this work proved that some trends are not adequately captured with a standard system identification procedure, because of the high coupling between turbine speed and cathode airflow. Cold air valve bypass position also showed a strong impact on surge margin in both cases.

The liberalization of electricity market in Europe led to a growing competition between energy producers, making crucial the ability to optimize the management strategies of power plants. Combined Cycle Power Plants (CCPP) have to operate in a flexible way, with frequent and rapid variations of the power produced, in order to quickly adapt to the frequent changes in load imposed by the demand. Nowadays, they typically operate in cycling mode with daily start-up and shut-down. The components of the plant are subjected to great cyclical variations in temperature, which induce stresses on materials, especially during the start-up phases. The present activity concerns the assessment of life consumption -caused by these operations- on the rotor of the steam turbine of the CCPP (800 MW) inside the Tirreno Power thermal plant located in Vado Ligure, Italy. The aim is to draw a set of curves representing the percent life expended per cycle as a function of rate of steam temperature change and magnitude of the overall temperature increase. These curves are called Cyclic Life Expenditure curves (CLE). In the future, the developed methodology will be used to reduce the start-up times, keeping under control the life consumption of the rotor and optimizing the maneuvers that generate thermal transients.

The analysis and design of complex energy systems is generally performed starting from a single operating condition and assuming a series of design parameters as fixed values. However, many of the variables on which the design is based are subject to uncertainty because they are not determinable with an adequate precision. For advanced energy system and other processes, the uncertainties associated with model input parameters can affect both the performance and the cost. Methods for system design under uncertainty thus become essential. As uncertainty is a broad concept, it is possible, and often useful, to approach it in several ways. One rather general approach, which is applied to a wide variety of problems, is to assign a probability distribution to the various uncertain input parameters of the model. Many studies have faced optimization problems, but almost no one has considered the uncertainty as a factor to be taken into account. An off-design static model of a micro-turbine has been studied: it is built on the configuration of a Turbec T100 actually installed at the University research laboratory. Stochastic analysis has been treated implementing the approximated method Response Sensitivity Analysis (RSA) based on Taylor series expansion. RSA methods have been used on this system model to estimate its main performance and economic parameters under the influence of uncertainties related to various operating parameters of the turbo-machinery.

Despite the high efficiency and flexibility of fuel cells, which make them an attractive technology for the future energy generation, their economic competitiveness is still penalized by their short lifetime, due to multiple degradation phenomena. As a matter of fact, electrochemical performance of solid oxide fuel cells (SOFCs) is reduced because of different degradation mechanisms, which depend on operating conditions, fuel and air contaminants, impurities in materials, and others. In this work, a real-time, one dimensional (1D) model of a SOFC is used to simulate the effects of voltage degradation in the cell. Different mechanisms are summarized in a simple empirical expression that relates degradation rate to cell operating parameters (current density, fuel utilization and temperature), on a localized basis. Profile distributions of different variables during cell degradation are analyzed. In particular, the effect of degradation on current density, temperature, and total resistance of the cell are investigated. An analysis of localized degradation effects shows how different parts of the cell degrade at a different time rate, and how the various profiles are redistributed along the cell as consequence of different degradation rates.

In the present paper two operational strategies for the optimization of a cogenerative plant of 100kWe size are compared: the first one aims to maximize the primary energy saving, while the second aims to maximize the self-consumption of electrical energy in order to reduce the impact of the grid and system costs. The results of the two strategies are compared from both the energetic and economic standpoints.

It has long been recognized that the possibility for the integration of Thermal Energy Storage (TES) is one of the key advantages of CSP over other forms of renewable energy technology.

In this work, a high temperature ceramic storage test rig for gas turbine energy systems was presented with its innovative layout, which avoids the use of hot valves. Such experimental plant storage, developed by the University of Genoa, Italy, can be run with compressed air and it is ready for connection with the modified microturbine Turbec T100 onsite. The test rig represents a scaled-down version of a larger system designed for a hybridized solar gas turbine, where the solar input is emulated by an electrical heater.

Hybridized solar gas turbine cycles are attractive because of their high efficiency, potentially equal to combined cycle efficiency, and dispatchable power capability. The layout proposed here does not involve any hot air valve and does include a ceramic thermal storage. The plant dynamic model was developed using the original TRANSEO simulation tool. This paper presents the test rig experimental results and validation of dynamic model: eventually, design recommendations are drawn to improve the flexibility and the time response of such kind of CSP plants.

In this work, the National Energy Technology Laboratory (NETL) in collaboration with the Thermochemical Power Group (TPG) of the University of Genoa have developed a dynamic model of a 10 MW closed-loop supercritical CO2 (sCO2) recompression Brayton cycle plant in the MATLABSimulink environment. The sCO2 cycle modeled here is a closed cycle with an external thermal source used to heat the sCO2 working fluid before it is expanded in a turbine. The turbine exhaust heat is recuperated using high- and low temperature recuperators, with mixing of two compressor outlets between the recuperators (on the cold-side). About two thirds of the low-pressure sCO2 is compressed by a main compressor, after passing through a cooler, while the remaining working fluid flows directly through a bypass compressor. The reference fluid properties (REFPROP) method by the National Institute of Standards and Technology is used to provide the thermodynamic and transport properties for sCO2 over the cycle temperature and pressure range because the sCO2 behavior is highly non-ideal, especially at the inlet of the two compressors. Dynamic simulations have been carried out to assess the behavior of the plant during a typical process disturbance.

This work presents the dynamic behaviour of a new recuperated micro gas turbine (mGT) coupled with a large volume. Such system, called “emulator”, has been purposely designed for the future upgrade into a fuel cell mGT hybrid system. The tests, carried out by LG Fuel Cell Systems (LGFCS), aimed both at understanding the dynamic behaviour of the system and validating the dynamic simulation tool.

Within the wide experimental campaign, a subset of data has been selected to identify the key transient phenomena and characterise the dynamic behaviour of the system: in this respect, the focus is on start-up, warm-up and shutdown phases.

A dynamic model of the emulator was developed, based on the original software TRANSEO. The model was used to characterise the mGT performance and identify a performance gap in the expander. For this purpose, the machine was upgraded and substituted. Final results show that, after refinement of input data, the model is capable to predict accurately the overall system transient behaviour.

The growing environmental impacts and dwindling supply of conventional fuels have led to the development of more efficient and clean energy systems. Micro gas turbines (mGT) have emerged as energy conversion technology, which offer promising features like high fuel flexibility, low emissions level, and efficient cogeneration of heat and power (CHP). Numerical simulation is a vital tool to predict the off-design performance of mGT cycles, and it also helps in cycle optimization. Starting from a model available at Ansaldo Energia, for steady state simulation of mGT T100 cycles based on user requirements, within the cooperation between University of Genova (Unige) and Ansaldo Energia, a new more comprehensive simulation tool has been developed through the incorporation of additional components, features, and involving a more detailed mathematical approach. The most important upgrades involved a number of different air path flows and the power electronics, which takes into account the power consumption from auxiliary components as well as the generator and inverter efficiencies.

Once the model has been verified against the existing tools, it was used in real operating conditions at the Ansaldo Energia test rig. The mGT performance has been assessed for different power levels, starting from 100 kW (nominal power) to 60 kW and then back to 100 kW, with 10 kW steps. The two tests at 100 kW operating conditions have been carried out with two different ambient temperatures: 20°C and 25°C, respectively. Data have been acquired under stable operating conditions, considering the recuperator cold outlet temperature as the stability indicator.

Finally the new model AE-T100 has been used also for diagnosis of the whole mGT cycle. The model has been successfully applied to a special mGT equipped with an on-purpose damaged recuperator, identifying the causes of performance degradation.

The control of level sets generated by partial differential equations is still a challenge because of its complexity both from the theoretical and computational points of view. Specifically, we focus on the space-dependent optimal control problem of a moving front and search for an approximate solution method that is computationally feasible. We formulate the problem in an Eulerian setting and develop an efficient approximation scheme based on the extended Ritz method. Such a method consists in adopting a control law with fixed structure that depends nonlinearly from a number of parameters to be suitably chosen by using a gradient-based technique. Toward this end, we derive the adjoint equations for optimal control problems involving the normal and mean curvature flow partial differential equations. The adjoint equations allow to compute the gradient of the cost with respect to the vector of parameters of the control law. Numerical results are reported to show the effectiveness of the proposed approach in some 2D and 3D examples.

Solid oxide fuel cells are characterized by very high efficiency, low emissions level, and large fuel flexibility. Unfortunately, their elevated costs and relatively short lifetimes reduce the economic feasibility of these technologies at the present time. Several mechanisms contribute to degrade fuel cell performance during time, and the study of these degradation modes and potential mitigation actions is critical to ensure the durability of the fuel cell and their long-term stability. In this work, localized degradation of a solid oxide fuel cell is modeled in real-time and its effects on various cell parameters are analyzed. Profile distributions of overpotential, temperature, heat generation, and temperature gradients in the stack are investigated during degradation. Several causes of failure could occur in the fuel cell if no proper control actions are applied. A local analysis of critical parameters conducted shows where the issues are and how they could be mitigated in order to extend the life of the cell.

3% Ru/Al₂O₃catalyst is active in converting CO₂ into methane at atmospheric pressure. At 673 K and above the thermodynamic equilibrium is nearly attained. At 623 K CH₄ yield is above 85%. CO selectivity increases by decreasing reactants partial pressure apparently more than expected by thermodynamics. The reaction order for CO₂ partial pressure is confirmed to be zero, while that related to hydrogen pressure is near 0.38 and activation energy ranges 60–75 kJ/mol. Arrhenius plot demonstrates that only at reduced reactant partial pressure (3% CO₂) or high contact times, a contribution due to some diffusional  limitation is present. IR study shows that the H2—reduced catalyst has high-oxidation state Ru oxide species able to oxidize CO to CO2at 173–243 K, while after oxidation/reduction cycle the alumina surface acido-basic sites are freed and the catalyst surface contains both extended Ru metal particles and dispersed low valence Ru species. IR studies show that the formation of methane, both from CO and CO₂, occurs when both surface carbonyl species and surface formate species are observed. Starting from CO₂, methane is formed already in the low temperature range, i.e., 523–573 K, even when CO is not observed in the gas phase.

In this paper two different advanced control approaches for a pressurized SOFC hybrid system are investigated and compared against traditional proportional–integral–derivative (PID). Both advanced control methods use model predictive control (MPC): in the first case, the MPC has direct access to the plant manipulated variables, in the second case the MPC operates on the setpoints of PIDs which control the plant. In the second approach the idea is to use MPC at the highest level of the plant control system to optimize the performance of bottoming PIDs, retaining system stability and operator confidence. Two MIMO (multi-input multi-output) controllers were obtained: fuel cell power and cathode inlet temperature are the controlled variables; fuel cell by-pass flow, current and fuel mass flow rate (the utilization factor kept constant) are the manipulated variables.
The two advanced control methods were tested and compared against the conventional PID approach using a SOFC hybrid system model. Then, the MPC controller was implemented in the hybrid system emulator test rig developed by the Thermochemical Power Group (TPG) at the University of Genoa.
Experimental tests were carried out to compare MPC against classic PID method: load following tests were carried out. Ramping the fuel cell load from 100% to 80% and back, keeping constant the target of the cathode inlet temperature, the MPC controller was able to reduce the mismatch between the actual and the target values of the cathode inlet temperature from 7 K maximum of the PID controller to 3 K maximum, showing more stable behavior in general.

A pressure drop analysis for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle, implemented through the hybrid performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test, and evaluate the effects of different parameter on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide means of evaluating risk mitigation strategies. The cold-air bypass in the Hyper facility directs compressor discharge flow to the turbine inlet duct, bypassing the fuel cell, and exhaust gas recuperators in the system. This valve reduces turbine inlet temperature while reducing cathode airflow, but significantly improves compressor surge margin. Regardless of the reduced turbine inlet temperature as the valve opens, a peak in turbine efficiency is observed during characterization of the valve at the middle of the operating range. A detailed experimental analysis shows the unusual behavior during steady state and transient operation, which is considered a key point for future control strategies in terms of turbine
efficiency optimization and cathode airflow control.

Direct-fired fuel cell gas turbine hybrid power system responses to open-loop transients were evaluated using a hardware-based simulation of an integrated solid oxide fuel cell gas turbine (SOFC/GT) hybrid system, implemented through the Hybrid Performance (Hyper) facility at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). A disturbance in the cathode inlet air mass flow was performed by manipulating a hot-air bypass valve implemented in the hardware component. Two tests were performed; the fuel cell stack subsystem numerical simulation model was both decoupled and fully coupled with the gas turbine hardware component. The dynamic responses of the entire SOFC/GT hybrid system were studied in this paper. The reduction of cathode airflow resulted in a sharp decrease and partial recovery of the fuel cell thermal effluent in 10 s. In contrast, the turbine rotational speed did not exhibit a similar trend. The transfer functions of several important variables in the fuel cell stack subsystem and gas turbine subsystem were developed to be used in the future control method development. The importance of the cathode airflow regulation was quantified through transfer functions. The management of cathode airflow was also suggested to be a potential strategy to increase the life of fuel cells by reducing the thermal impact of operational transients on the fuel cell subsystem.

This paper aims to investigate a system for large size hydrogen production, storage and distribution to refueling stations for its employment in land transportation.

Hydrogen is produced by pressurized alkaline electrolysers, employing time-dependent renewable electricity produced by a large size hydroelectric plant (100 MW); the hydrogen is stored into pressurized tanks and delivered by trucks to the refueling stations. Since the technologies related to hydrogen vehicles still present high costs, an alternative solution is investigated: the hydrogen produced by water electrolysis is converted into Hydro-methane (a blend of methane and hydrogen, where H2 maximum volume content is 30%), which is easier to be stored and transported to the refueling stations, considering its higher energy content in volume terms.

Since electricity available from the hydroelectric plant varies widely throughout the year, a time-dependent hierarchical thermo-economic analysis is performed in order to investigate both the optimal size of the whole plant and the management of the alkaline electrolysers. The analysis is carried out for the H2 and Hydro-methane plant lay-outs, comparing the results from energetic, strategic and economic point of view in a typical European economic scenario (Italy).

For the different plant lay-outs, two energy scenarios are considered: (i) to feed the electrolysers only with renewable hydroelectricity during the year, keeping them off when it is not available; (ii) to purchase electricity from the national grid in shortage periods, in order to increase the utilization factor of the electrolysers and the production of H2 and Hydro-methane for the refueling stations.

This paper reports an entirely new simulation tool for a hybrid system emulator facility built by the Thermochemical Power Group (TPG) at the University of Genoa, Italy. This new software was developed with the following targets: realtime performance, good stability level and high calculation reliability. In details, to obtain real-time performance a new approach based on 0-D technique was chosen also for components usually analysed with 1-D or 2-D tools (e.g. the recuperator). These are essential key aspects to operate it in hardware-in-the-loop mode or to evaluate predictive results for long transient operations. This work was based on collaboration between the University of Manchester, UK and the University
of Genoa, Italy.
The activity was carried out with a test rig composed of the following technology: a microturbine package able to produce up to 100 kWe and modified for external connections, external pipes designed for several purposes (by-pass, measurement or bleed), and a high temperature modular vessel necessary to emulate the dimension of an SOFC stack. The real-time transient model of this facility was developed inside the Matlab-Simulink environment with the following modelling approach: a library of components allows to reach a high level of flexibility and an user-friendly approach. This model includes the machine control system as an essential device to analyse further layouts (new components in the rig) and hardware-in-the-loop operations.
The experimental data collected in the laboratory by TPG were used to validate the simulation tool. The results calculated with the model were satisfactory compared with experimental data considering both steady-state and transient operations. The most important innovative aspects of this work are related to this wide validation range (not only small power steps, but the whole operative range was considered)
obtaining real-time performance and considering microturbine conditions different from standard operations (additional pressure and temperature losses and unusual thermal capacitance). The modelling simplified approach used for such a complex system is an important innovative aspect, because usually the model reliability performance is obtained with more complex (and not real-time) tools. This work is based on an innovative modelling approach based on 0-D tools able to operate in real-time mode (as necessary for hardware-in-the-loop tests) with an accuracy level comparable with more complex and more time consuming software. This validated tool is an important base for future calculations to study innovative hybrid system layouts. For instance, TPG is planning to analyse the option of increasing fuel cell pressure
and performance with a booster system (e.g. a turbocharger).

This paper reports a new innovative re-compression technology for solid oxide fuel cell (SOFC) hybrid systems necessary to increase pressure at compressor outlet level (as required by fuel cell systems for managing cathodic recurculation and to increase SOFC efficiency). This work was based on a collaboration between the University of Manchester (United Kingdom) and the University of Genoa (Italy). The re-compression study will be performed with the hybrid system emulator rig by TPG. This device is composed of the following technology: a microturbine package able to produce up to 100 kWe which was modified for external connections, external pipes designed for several purposes (by-pass,
measurement or bleed), and a high temperature modular vessel necessary to emulate the dimension of an SOFC stack. For the purpose of re-compression, this test rig is planned to be equipped with a turbocharger capable of increasing pressure using part of recuperator outlet flow.
Theoretical activity was considered before carrying out the real experimental tests to avoid plant risky conditions. So, it was necessary to develop a transient model (Matlab-Simulink environment) to simulate the hybrid system emulator including the re-compression system. The results obtained with the model were carried out considering the start-up/shutdown phases of the turbocharger device.

Starting from a state of the art of CSP plants and the undergoing research in hybridization of Gas Turbine plants, the paper investigates alternative plant configurations particularly regarding the integration of CSP technology with mixed cycles because of their low water consumption and the possible use of current CSP components, assessed and compared with a through-life thermo-economic analysis.

This paper presents a real smart polygeneration grid, designed to satisfy energy demands of the University Campus of Savona (Italy). The plant is made up by different kind of generators: conventional boilers, CHP unit, electrical and thermal storage and renewable generators.
The analysis of this smart-grid is performed exploiting a software developed by the Author’s research group, which allows for the thermo-economic optimization of polygenerative energy systems. A model of the real plant was built and it was implemented in the software. The off-design curves of the real devices installed in the campus were used in order to increase the reliability of the simulation results. The grid was simulated considering the time dependent nature of the demands throughout the whole year. The model was used to simulate the smart grid behavior during the whole year, and find the best operational strategy.
Moreover a strong attention is given to future solution to the Smart grid Layout in order to reduce purchasing electricity from National grid in summer months, when, as the thermal request decreases, the CHP units are not exploited. Two possible implementations are analyzed coupling CHP units with absorption chillers or ORC turbine, comparing their techno-economic performances.

This paper shows a new advanced control approach for operations in hybrid systems equipped with solid oxide fuel cell technology. This new tool, which combines feed-forward and standard proportional–integral techniques, controls the system during load changes avoiding failures and stress conditions detrimental to component life. This approach was selected to combine simplicity and good control performance. Moreover, the new approach presented in this paper eliminates the need for mass flow rate meters and other expensive probes, as usually required for a commercial plant. Compared to previous works, better performance is achieved in controlling fuel cell temperature (maximum gradient significantly lower than 3 K/min), reducing the pressure gap between cathode and anode sides (at least a 30% decrease during transient operations), and generating a higher safe margin (at least a 10% increase) for the Steam-to-Carbon Ratio.
This new control system was developed and optimized using a hybrid system transient model implemented, validated and tested within previous works. The plant, comprising the coupling of a tubular solid oxide fuel cell stack with a microturbine, is equipped with a bypass valve able to connect the compressor outlet with the turbine inlet duct for rotational speed control. Following model development and tuning activities, several operative conditions were considered to show the new control system increased performance compared to previous tools (the same hybrid system model was used with the new control approach). Special attention was devoted to electrical load steps and ramps considering significant changes in ambient conditions.

The interest in off-shore multi-purpose platforms resides in the wide opportunities involved in it, for example considering the development of large marine infrastructure in the near future. An available off-shore site where testing marine energy converters (exploitation of wave, tidal and hydrokinetic energy, magnetohydrodynamic generator, linear converter) developing and implementing marine aquaculture, can short the gap to the next off-shore activities. Since near the city of Genova there is an abandoned but still well conserved and robust off-shore island it is interesting evaluate the cost and intervention to restore it making it an ideal site to explore the new frontier offered by living the oceans off-shore. This paper deals with the restoration study of an existing off-shore structure for oil discharging operations sited 1 miles off the port of Multedo, in the city of Genova, propsing different exploitation scenario.

The present paper proposes a study for the integration of a hybrid power system composed by rechargeable batteries and fuel cells with chemical gas storages for an Autonomous Underwater Vehicle (AUV) or Unmanned Undersea Vehicles (UUV). AUVs and UUVs are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time they are usually powered by lithium-ion secondary batteries, which have insufficient specific energy. In order to enhance the usage of these vehicles and to exploit their capabilities an increased endurance is required. Fuel Cell Energy Power Systems (FCEPS) have been identified as an effective means to achieve this endurance[1]. From literature it could be found that the present technology to power AUV is based on rechargeable batteries implemented with some form of battery management system. In order to improve the autonomy of the vehicles different technologies should be used. The state of the art is represented by the HUGIN AUV[2]. This vehicle is powered by a Alkaline Aluminium/Hydrogen peroxide semi-fuel cell. This paper will present an alternative power generation system based on a Proton Exchange Membrane (PEM) fuel cell fed by pure hydrogen and oxygen produced by a replaceable chemical storage for AUV. A technical sizing of the system has been done, supported by an analysis of the performance of the considered technologies. Standard AUV-UUV works on daily operational profile and thus have about 24h of autonomy. FCEPS for UUV requires particular characteristics of the vehicle to be installed and exploited. Starting from a statistical assessment of the existing UUVs for military and civil application an analysis of the most suitable dimensions, form and weight of the vehicle has been done together with an assessment of the requirements for different operative conditions in order to identify the most profitable target parameters for a future market development of this technology. The analysis of the application of an innovative hydrogen storage technology based on aluminium-water reaction is introduced for the first time. The study consider the performances of the system developed by the Technion Institute of Haifa (Israel), and present an evaluation of the theoretical achievable performance of the storage system and it’s exploitation for particular matching with the Fuel Cell System (FCS). An assessment of the performance of the FCEPS, that consider the combination of FCS and storage system, has been done through the procedure proposed by Davis and More[3] considering the best oxygen storage system and the best FCS. This procedure has been developed for the application of FCEPS on UUVs and gives the methodology to calculate key parameters that permit the comparison between different systems. Moreover this method has been also used by other researchers and today it’s available a wide database of systems performances available.

This work describes a system for off-shore power generation based on a Wave Energy Converter (WEC) called Seaspoon coupled to a microturbine. The paper reports the performance of the WEC under the action of regular sinusoidal waves investigated with numerical fluid dynamic simulation; such a converter can be coupled to an air microturbine-driven microgenerator into a system for off-shore energy generation. A description of the numerical results and of the microturbine technology is given together withan overview of the system, and its suitable applications.

This paper presents a statistical and techno-economic feasibility study for the exploitation of renewable energy generators and energy storage devices typically installed onboard pleasure boats to transform harbors and ports in energy districts able to exchange energy with the grid. In Europe about 48 million citizens regularly participate in recreational marine activities (36 million of whom are boaters), as well as countless numbers of tourists. Over 6 million boats are kept in European waters while 4,500 marinas provide 1.75 million berths both inland and in coastal areas [1]. Thanks to the proposed Smart Port concept, this scenario could be considered as an energy resource to improve renewable energy penetration and enlarge European grid storage capacity with negligible investments by exploiting existing facilities. Starting from statistics assessment of ports and boats present on the Mediterranean Shore [2] (particularly in Liguria region) and considering data related to the Italian national electric market (daily spread between minimum and maximum price of electricity, daily renewable energy production and their impact on the price [3]), different scenarios are analyzed according to different kind of generators (photovoltaics, wind) and storage technologies [4] (batteries, hydrogen) commonly used in the nautical sector in order to study the most profitable solutions. A case study in Italy is presented and the expected impacts in terms of yearly renewable deliverable energy, storage capacity, CO2 emission savings and money savings for boat owners and port managers is shown. This framework is analyzed at the present conditions and looking throughout future scenario that will include an increase of the number of electrical boats, a variable price of electricity and a decreasing price of batteries and hydrogen equipments as storage technologies. Considering the number of boats actually moored in the Italian marinas and equipped with renewable generators, relevant installation capital costs could be saved while the structural improvements that should be made to the ports are limited to the electrical connections and the smart control systems transforming it in an energy district able to interact with the electrical market through the national grid as a renewable generator or an energy buffer useful to the grid balance. The first required investment for the port will be the installation of bidirectional POD (point of delivery) and energy-meters, in order to make boats able to exchange energy with the grid while they are moored. It is important to underline that smart controls have to be investigated in order to guarantee a relevant state of charge of boats batteries. Suitable Business models enabling the exploitation of this new concept are shown. These models take into account the compensation rules to refund boat owners and other stakeholders, allowing sufficient profit margin to ports which would become actors in the energy market, interacting with the national grid as a RES producer, consumers and an electrical storages.

This paper investigates the integration of Concentrating Solar Power technology in air-steam Mixed Cycles for power production. Starting from a state of the art of CSP plants and the undergoing research in hybridization of Gas Turbine plants, the paper investigates alternative plant configurations particularly regarding the integration of CSP technology with mixed cycles, assessed and compared with a through-life thermo-economic analysis.
Solar heat collected by on the market CSP mirrors at moderate temperatures (300°C-500°C) can be employed to increase conventional steam-injection gas turbine power plants performances. Solar concentrating collectors for current steam solar power plants can be used for such an application can be simpler and less expensive than collectors supposed to be used for hybrid GT CSP Plants which need high temperature systems (collectors and receivers).
The solar hybridization of mixed cycles could be a good opportunity to combine gas turbine technology and CSP systems thus augmenting efficiency and achieving power dispatchability, but avoiding dedicated combustion chambers for hybrid CSP purposes (one of the big technologic problems to combine CSP and Gas Turbine technology). Moreover, the availability of commercial steam injected gas turbines at intermediate power range (10-100 MW) allows the realization of such hybrid mixed CSP power plants in their typical size, avoiding the need for very large solar fields and reducing the technological risk as well as the time to market.
Focus is on the design of the plant that was made analyzing different factor like solar share factor1, water consumption and reintegration and LCOE. A comparison of this innovative hybrid CSP-STIG plant with traditional STIG, Integrated Solar Combined Cycles (ISCC) and a traditional Combined Cycle was made. The mixed cycles CSP plants are analyzed using the original software WTEMP for the design point analysis, whose library was updated with dedicated modules.
The analysis shows that combining CSP technology with existing mixed cycles lets cost-competitive plant configurations with a relatively short time to market.

In this paper advanced control strategies based on Model Predictive Control (MPC) method are compared against a traditional PID controller in a Gas Turbine Pressurized SOFC hybrid system.
A model of the integrated mGT-SOFC hybrid system has been developed to analyze the impact of ambient temperature changes on system performance and dynamic behaviour. Four different MIMO controllers (multi input multi output) based on a linearized system model have been implemented in order to control fuel cell temperature and power with different ambient temperatures. Fuel cell temperature is regulated by manipulating the cell by-pass mass flow, while power is regulated by changing the fuel cell electrical current and fuel mass flow (the fuel utilization factor is kept constant). Load following simulations have been carried out as follows: the same load ramp from 100% to 80% of fuel cell power and back has been set and studied under three different ambient conditions, 263K, 288K and 313K (-10°C, 15°C and 40°C).
MPC demonstrated superior performance over the two distributed PID controls, thanks to the better setpoint tracking on the cell temperature, which is particularly evident when the ambient temperature deviates from the nominal condition. This is mainly explained by the capability of MPC in including the effects of non-linearities of the real system.

As distributed systems arise as the dominate approach in energy production, new and time-effective methods to study global configuration of small scale generation systems have to be discovered. This work proposes a comparison between two disparate approaches to microturbine modelling. The target system is a modified Turbec T100 microturbine coupled with an external vessel, which aims to simulate the dynamic global behavior of a fuel cell gas turbine hybrid system generator. The first model is based on first principles with ordinary differential equations to capture the dynamic performance of the turbine and it is developed with Matlab/Simulink environment. The second model is based on a simplified-physics time constant approach and it is developed with Excel/Visual Basic software, thus aiming at a viable tool for distributed applications, despite any lose in accuracy. Both models have been verified against the experimental data of the microturbine test rig, and compared in terms of computational efforts, modelling flexibility, prediction accuracy.

This paper proposes a dynamic simplified approach to model a Heat Recovery Steam Generator of a Gas Turbine Combined Cycle (GTCC) and its validation against field data. The adopted framework begins with some physical considerations on global HRSG structure, and then focuses on a specific application for a real plant, i.e. a 390 MW multi-shaft combined cycle based on the AEN94.3 A4 frame. Moreover the model embodies some parameters, which are easily derived from historical data to enhance the forecasting capabilities of the software, resulting in a hybrid model which covers a high range of working conditions. The whole model is designed to run in Excel/Visual Basic environment to allow for extended use by people who have limited experience in advanced modelling software. The model so created has been handled through a training process based on 10 days of experimental data, in order to create the basis for true system flexibility. Therefore, the feasibility of this approach has been verified using a Gas Turbine (GT) load profile accomplished in everyday working operations and validating the results against field data.

Micro Gas Turbines (mGTs) have arisen as a promising technology for Combined Heat and Power (CHP) thanks to their overall energy efficiencies of 80% (30% electrical + 50% thermal) and the advantages they offer with respect to internal combustion engines. The main limitation of mGTs lies in their rather low electrical efficiency: whenever there is no heat demand, the exhaust gases are directly blown off and the efficiency of the unit is reduced to 30%. Operation in such conditions is generally not economical and can eventually lead to shutdown of the machine. To address this issue, the mGT cycle can be modified so that in moments of low heat demand the heat in the exhaust gases is used to warm up water which is then re-injected in the cycle, thereby increasing the electrical efficiency. The introduction of a saturation tower allows for water injection in mGTs: the resulting cycle is known as a micro Humid Air Turbine (mHAT).
The static performance of the mGT Turbec T100 working as an mHAT has been characterised through previous numerical and experimental work at Vrije Universiteit Brussel (VUB). However, the dynamic behaviour of such a complex system is key to protect the components during transient operation. Thus, we have modelled the Turbec T100 mHAT with the TRANSEO tool in order to simulate how the cycle performs when the demanded power output fluctuates. Steady-state results showed that when operating with water injection, the electrical efficiency of the unit is incremented by 3:4% absolute. The transient analysis revealed that power increase ramps higher than 4:2 kW/s or power decrease ramps lower than 3:5 kW/s (absolute value) lead to oscillations which enter the unstable operation region of the compressor. Since power ramps in the controller of the Turbec T100 mGT are limited to 2 kW/s, it should be safe to vary the power output of the T100 mHAT when operating with water injection.

The theoretical efficiencies of gas turbine fuel cell hybrid systems make them an ideal technology for the future. Hybrid systems focus on maximizing the utilization of existing energy technologies by combining them. However, one pervasive limitation that prevents the commercialization of such systems is the relatively short lifetime of fuel cells, which is due in part to several degradation mechanisms. In order to improve the lifetime of hybrid systems and to examine long-term stability, a study was conducted to analyze the effects of electrochemical degradation in a solid oxide fuel cell (SOFC) model.
The SOFC model was developed for hardware-in-the-loop simulation with the constraint of real-time operation for coupling with turbomachinery and other system components. To minimize the computational burden, algebraic functions were fit to empirical relationships between degradation and key process variables: current density, fuel utilization, and temperature.
Previous simulations showed that the coupling of gas turbines and SOFCs could reduce the impact of degradation as a result of lower fuel utilization and more flexible current demands. To improve the analytical capability of the model, degradation was incorporated on a distributed basis to identify localized effects and more accurately assess potential failure mechanisms. For syngas fueled systems, the results showed that current density shifted to underutilized sections of the fuel cell as degradation progressed. Over-all, the time to failure was increased, but the temperature difference along cell was increased to unacceptable levels, which could not be determined from the previous approach.

This paper presents a novel machine start-up technique for SOFC hybrid system based on a re-compression approach. This approach shows the reality of operating the system without the manufacturer’s usual technique of using the standard control system. A hybrid system emulator rig located at Savona, Italy will be used for these research activities. The experimental test rig consists of an emulator that is based on a 100 kW microturbine connected to a modular vessel designed for fuel cell emulation. The microturbine pipes were carefully insulated and connected to a high temperature modular vessel necessary to emulate the dimension of an SOFC stack and lastly, for the purpose of re-compression, the test rig was modified to accommodate a turbocharger capable of increasing the fuel cell pressure (using part of recuperator outlet flow). This is necessary for operating at high efficiency conditions hybrid systems based on a cathodic recirculation driven by an ejector. For both economic reasons and to avoid system abnormal operations during the plant start-up conditions, a theoretical activity is very vital. A dynamic model of the solid oxide fuel cell gas turbine system was developed in Matlab®-Simulink® environment to investigate the transient behaviour during start-up phase. The results obtained shows reasonable values for several parameters, such as surge margin, turbine outlet temperature, and rotational speed. The results demonstrated the feasibility of this machine coupling (the microturbine with a turbocharger) avoiding risk operations during the start-up phase.

Starting from a state of the art of CSP plants and the undergoing research in hybridization of Gas Turbine plants, the paper investigates alternative plant configurations particularly regarding the integration of CSP technology with mixed cycles because of their low water consumption and the possible use of current CSP components, assessed and compared with a through-life thermo-economic analysis.

The present paper is examining the geometry optimization of a power production turbine, in the range of 100kWel, for a low enthalpy Organic Rankine cycle system (?100°C). In the last years, accelerated consumption of fossil fuels has caused many serious environmental problems such as global warming, ozone layer destruction and atmospheric pollution. It is this reason that a growing trend towards exploiting low-enthalpy content energy sources has commenced and led to a renewed interest in small-scale turbines for Organic Rankine Cycle applications. The design concept for such turbines can be quite different from either standard gas or steam turbine designs. The limited enthalpic content of many energy sources imposes the use of organic working media, with unusual properties for the turbine. A versatile cycle design and optimization requires the parameterization of the main turbine design. There are many potential applications of this power-generating turbine, including geothermal and concentrate solar thermal fields or waste heat of steam turbine exhausts. An integrated model of equations has been developed, thus creating a model to assess the performance of an organic cycle for various working fluids such as R134a and isobutane-isopentane mixture. The most appropriate working fluid has been chosen, taking its influence on both cycle efficiency and the specific volume ratio into consideration. This choice is of particular importance at turbine extreme operating conditions, which are strongly related to the turbine size. In order to assess the influence of various design parameters, a turbine design tool has been developed and applied to define the geometry of blades in a preliminary stage. Finally, as far as the working fluid is concerned, the mixture of 85% isopentane-15% isobutane has been chosen as the most suitable fluid for the low enthalpy ORC system, since its output net power is 10% higher compared to the output net power of R134a.

Distributed generation (DGs) and active distribution networks constitute an economic and technically viable alternative for reducing GHG emissions and increase the use of renewable energy sources in local distribution grids. These networks combine small and efficient prime movers (e.g. micro gas turbines and ICEs) with renewable power generators (e.g. small wind and solar) in order to supply both electricity and heat to low voltage and district heating networks. By replacing large generators, usually located far from the consumption loads, these active networks allow minimizing distribution losses considerably. Additionally, thermal and electric storage units can be included, in order to maximize selfconsumption and provide with additional load balancing, that compensates the power variability from renewable energy generators. However, designing and successfully controlling these complex networks, becomes a great engineering challenge; most computational modeling and simulation tools available for these systems are either focused on the individual generation components themselves, or the economic dispatch of multiple generators. Moreover, these tools often rely on commercial software with closed code that use manufacturers’ data for defining the parameters of the models’ components without providing enough flexibility to users, for further improve or adjust these parameters. This paper presents an object-oriented, component-based, open software library for simulating and optimizing the operation of active distribution networks, including multiple DGs and energy storage (both electric and thermal). All the models developed use the Modelica open-source modeling language, consequently, all the equations and parameters developed for each component, can be modified and adapted to model and simulate multiple configurations of different types of active distribution networks. The model components of the library have been validated with real operation data from the polygeneration microgrid lab of the University of Genoa, located in Savona, Italy.

The purpose of this paper is to present and discuss the performance of experimental curves related to the following prime movers for smart polygeneration grids: a microturbine (100 kW electrical power), an internal combustion engine (20 kW electrical power), a SOFC-based hybrid system (450 kW virtual electrical power) and an absorption chiller (100 kW cooling power). The experimental results reported here were obtained using a new facility developed by the Thermochemical Power Group: essential operations for distributed generation grids equipped with different types of technologies are possible, as well as test with different control and optimisation algorithms. Apart from the data on the hybrid system (obtained with an emulator rig based on the coupling of a microturbine, a modular vessel and a real-time simulation model for components not present in the rig), the performance curves of the other devices were obtained from measurements on real machines. Given the influence of ambient temperature on microturbine performance, correlations related to this parameter were developed from experiments for easy application in optimization tools.

The concept of energy support is heading more and more towards the idea of a distributed production, which points to a gradual replacement of the standard production concept centered on single large units. In this respect, for example, uncertainty associated to the energy demand of each unit of a district becomes a fundamental point to take in account: thus, a probabilistic approach to the analysis of distributed generation systems is highly recommended. In this sense, an off-design steady-state model of a micro-gas turbine (mGT) has been employed: it is built on the configuration of a Turbec T100 actually installed at the research laboratory of the Thermochemical Power Group. In particular, elements of uncertainty linked both to operating parameters of the machine and to the load demands during the year were present. Uncertainty analysis has been treated with two different methods. The first and most famous is Monte Carlo method, which, however, requires a large time consuming in order to achieve the necessary number of samples. It is clear that its application for analyze such complex systems would be computationally inefficient and expensive so, this paper proposes as alternative an approximated method called Response Sensitivity Analysis (RSA). It is based on Taylor series expansions and promises good accuracy still retaining acceptable computational time. This work has led to the following results:
1. estimations of probabilistic distributions for electrical power production at the outlet of generator, fuel consumption and net efficiency of the system during the entire working period; and in addition
2. an evaluation of the most probable return on investment time and the range within it could fall, depending on the requested interval of confidence based on the standard deviation of the output distribution probability.
3. Moreover, RSA has shown a wide compatibility with different types of problems, promising an easy applicability and scalability in different fields of study.

This paper presents simulation analysis based on data from a real Smart Polygeneration Microgrid (SPM), designed to satisfy energy demands of the University Campus of Savona (Italy). The plant is made up of different generators (conventional, cogenerative, renewable) which are “distributed” around the campus and they are coupled to electrical and thermal storages. Since the system is constituted by co-generative prime movers it can supply both electrical and thermal energy of the campus and the integration of storage is really important in order to follow both the requests, pursuing the best management strategy.
The analysis of this smart-grid is performed exploiting a software developed by the Author’s research group, which allows for the thermo-economic optimization of poly-generative energy systems. The software was used to find the best operational strategy showing the importance of an appropriate storage system to manage the grid taking into account its polygenerative features, analyzing the integration and the combination of three different kind of storage: hot water tank, cold water tank, electrical battery. Different scenarios are presented combining the three storages and showing the impact of them in terms of money savings and reduction of the purchasing of electricity from the National grid. These scenarios were analyzed both considering an interconnection with the national electrical grid and to operate the SPM in-island mode.

A tool for a time-dependent thermo-economic hierarchical approach for the investigation of energy systems, determining the optimal size and the best strategy of different prime movers in order to meet the energy (electrical, thermal, cooling) demands of a generic user is presented.
In particular, a specific case study was developed around the smart polygeneration grid at the University of Genoa, Savona Campus (Italy), operational since 2014. The simulation method considered the time-dependent energy load demands as problem constraints, and included the real off-design performance maps of the generators. This approach allows determining both the optimal size and the best management strategy for each component of the polygeneration grid, during the entire year, by optimising an economic function including capital and variable costs as well as maintenance costs of the system.

One of the issues of the greatest concern in integrated gasification (IGFC) systems is the high risk of composition changes in coal-derived syngas, which is strongly influenced by coal qualities and/or gasifier technologies.
The main goal of this work was to assess the impacts of syngas compositions resulting from different gasifier technologies on the fuel cell degradation rate. The solid oxide fuel cell (SOFC) response to various syngas compositions was investigated using a one-dimensional (1D) distributed fuel cell model that incorporates an empirical expression of localized SOFC degradation as a function of fuel cell solid temperature, current density, and fuel utilization. The process performance using four different syngas compositions was also compared to a humidified hydrogen operation as a baseline.
The results showed a correlation of degradation most significantly with the methane content of the fuels selected. At constant stack power production and constant global fuel utilization, the results demonstrated that increasing the methane content in coal-derived syngas shifted the peak of degradation rate from the inlet toward the center of the cell. Overall, the highest localized degradation rate with respect to voltage in all five cases was observed at 3.65%/1000 hr. The lowest overall rate of 1.89%/1000 hr was indicated in the case for humidified hydrogen. Increasing methane content to 17% in syngas increased the overall degradation rate to 3.05%/1000 hr.

This paper presents a new approach to increase compressor outlet pressure in SOFC based hybrid systems. Essential solution to ensure an increase in system performance (plants equipped with a cathodic re-circulation) or SOFC efficiency.
An emulator rig designed to perform tests on SOFC hybrid systems was considered to analyze three different configurations. This is an experimental plant based on the coupling of a microturbine with a modular vessel necessary to emulate the stack cathodic volume. Attention was focused on a re-compressor powered by a gas turbine (turbocharger) for simplicity and low cost performance.
In this paper attention is focused on the rig modifications necessary to operate tests on the turbocharger based configuration. Even if this is a worldwide innovative solution, results showed the coupling feasibility of these machines preventing surge risks. Special attention has to be devoted on the turbocharger start-up considering the dynamic different aspects of the two machines.

Thermal energy storage (TES) systems can effectively compensate for irregular solar irradiation and reduce the mismatch between solar supply and power demand in Concentrated Solar Power (CSP) plants. TES allows a solar resource to be dispatched, a high value proposition for power utilities which gives concentrating solar power (CSP) technology an edge over photovoltaic and wind power. Hence, TES is a key technology for solar thermal energy utilization.
This paper begins with an overview of hybrid CSP gas turbine plants, then introduces a new TES pilot plant based on a micro gas turbine system integrated with high temperature ceramic storage. Such a layout avoids the use of high temperature valves. The novel test plant uses an electric heater to simulate thermal input and is currently operated with compressed air in preparation for connection with a modified Turbec T100 microturbine. The test plant represents a scaled-down version of a larger hybridized solar gas turbine.
Results from cold test of pressure drop behaviour are used for validation of the plant pressure drop model. Flows exhibit Reynolds values between 3600 and 46000, thus being in a transitional mode between laminar and turbulent flow. Transitional flows are likely in real plants, balancing a compromise between heat transfer effectiveness and pressure drop.

The hybridization of solid oxide fuel cell (SOFC) and gas turbine technologies provides an increase in system efficiency and economic performance. The latter aspect is significantly affected by fuel cell degradation, due to several mechanisms. However, hybrid systems allow different control strategies to minimize degradation effects and impact on economic performance.

A real-time distributed model of a SOFC was used to simulate fuel cell degradation in the cases of a standalone cell and a hybrid configuration, where the numerical model would be normally coupled with the hardware components of a hybrid system. The results showed how in a hybrid system it is possible, with the appropriate controller, to maintain constant voltage even if the cell is degrading, reducing degradation rate during time. Fuel cell life could be significantly extended with the control strategies allowed by coupling with a turbine (an order of magnitude longer than a standalone fuel cell), maintaining high system efficiency despite fuel cell degradation.

Since compressor outlet pressure is an important property in an SOFC based hybrid plant, special attention is devoted to an innovative system able to increase this parameter with a commercial device. This in an essential approach to increase system performance (especially in case of an ejector based cathodic recirculation) using commercial (and low cost) technology. In details, to avoid the re-design of a completely new microturbine, the coupling of a commercial turbine with a turbocharger has been analyzed from experimental point of view.

This innovative plant layout has been studied with an emulator test rig for SOFC hybrid systems. It is an experimental facility based on the coupling of a commercial 100 kW gas turbine with a modular vessel to emulate the dimension of stack cathodic size. For these tests, a turbocharger has been included in the rig for a detailed analysis related to the coupling with the T100 machine. Special attention is focused on the rig modifications necessary to operate these tests and on the experimental results obtained with this facility. The performance obtained with this machine coupling has been demonstrated by the experimental data.

In order to avoid intermittent energy supply problems, thermal energy storage (TES) systems have been playing an important role in concentrated solar power (CSP) plants. Thus, a significant focus has been given on the improvement of TES systems from the past few decades. In this paper, a numerical model is developed to obtain the detailed heat transfer characteristics of lab-scale latent thermal energy storage system which consists of molten salt encapsulated spherical capsules and air. The melting process and the corresponding temperature and velocity distributions in every capsule of the system are predicted. The enthalpy-porosity approach is used to model the phase change region. The model is validated with the reported experimental results. The influence of initial condition on the thermal performance of the TES system is predicted.

In order to avoid intermittent energy supply problems, thermal energy storage (TES) systems have been playing an important role in concentrated solar power (CSP) plants. Thus, a significant focus has been given on the improvement of TES systems from the past few decades. In this paper, a numerical model is developed to obtain the detailed heat transfer characteristics of lab-scale latent thermal energy storage system which consists of molten salt encapsulated spherical capsules and air. The melting process and the corresponding temperature and velocity distributions in every capsule of the system are predicted. The enthalpy-porosity approach is used to model the phase change region. The model is validated with the reported experimental results. The influence of initial condition on the thermal performance of the TES system is predicted.

The methanation of carbon dioxide has been studied over 3% Ru/Al₂O₃ and 20% Ni/Al₂O₃ commercial catalysts. Experiments have been performed in diluted conditions in a flow catalytic reactor with a continuous IR detection of products. The data, reported here, confirm that 3% Ru/Al₂O₃ is an excellent catalyst for CO₂ methanation (96% methane yield with no CO coproduction at 573 K at 15,000 h^?1 GHSV in excess hydrogen). The performance is better than that of Ni/Al₂O₃ catalyst. The reaction orders over both catalysts with respect to both hydrogen and CO₂ were determined over conditioned catalysts. A conditioning of the Ru/Al₂O₃ catalyst by reactant gas stream was found to be needed and more effective than conditioning in hydrogen, possibly because water vapour formed during methanation reaction will react to remove chlorine impurities from catalyst surface Conditioned Ru/Al₂O₃ catalyst was found to retain stable high activity after different shut-down and start-up procedures, thus being possibly applicable in intermittent conditions.

This paper investigates hydrogen and methane generation from large hydraulic plant, using an original multilevel thermo-economic optimization approach developed by the authors.
Hydrogen is produced by water electrolysis employing time-dependent hydraulic energy related to the water which is not normally used by the plant, known as ‘‘spilled water electricity’’. Both the demand for
spilled energy and the electrical grid load vary widely by time of year, therefore a time-dependent hourby-hour one complete year analysis has been carried out, in order to define the optimal plant size. This time period analysis is necessary to take into account spilled energy and electrical load profiles variability during the year.
The hydrogen generation plant is based on 1 MWe water electrolysers fuelled with the ‘‘spilled water electricity’’, when available; in the remaining periods, in order to assure a regular H2 production, the energy is taken from the electrical grid, at higher cost. To perform the production plant size optimization, two hierarchical levels have been considered over a one year time period, in order to minimize capital and variable costs.
After the optimization of the hydrogen production plant size, a further analysis is carried out, with a view to converting the produced H2 into methane in a chemical reactor, starting from H2 and CO2 which is obtained with CCS plants and/or carried by ships. For this plant, the optimal electrolysers and chemical reactors system size is defined.
For both of the two solutions, thermo-economic optimization results are discussed and compared with particular emphasis to energy scenario, economic aspects, system size, capital costs and related investments. It is worth noting that the results reported here for this particular large H2 plant case represents a general methodology, since it can vary according to their different sizes, primary renewable energy, plant location, and different H2 utilization.

This paper summarizes key results of the analysis of different transport modes of hydro-methane, methanol, carbon dioxide and oxygen in Paraguay, Brazil and Argentina. Hydro-methane is produced in Paraguay and can be used to fuel natural gas vehicles, substituting gasoline and diesel which are at the moment imported from foreign countries. Methanol, also produced in Paraguay, is delivered to Brazil, which is one of the Countries with the highest demand. Oxygen is sold to Argentina for medical and industrial use. Carbon dioxide is delivered throughout Paraguay.
The aim of this study is to determine the best transportation technology from an economic and strategic point of view, minimizing costs associated to products distribution. Several scenarios are investigated; each scenario is associated with different delivery modes. A model is developed to estimate both capital and variable costs for different transportation technologies (pipeline, trucks, ships) in order to choose the lowest-cost delivery mode for each product, depending on distances and flow rates. Four different analysis are performed for each scenario, varying the number of vehicles which must be fueled by hydro-methane and considering its influence on the results.
The methodology presented here has a general value, thus it can be easily employed for the economic analysis of different fuels and distribution networks, also placed in different scenarios.

Optimization of power generation with smart grids is an important issue for extensive sustainable development of distributed generation. Since an experimental approach is essential for implementing validated optimization software, the TPG research team of the University of Genoa has installed a laboratory facility for carrying out studies on polygeneration grids. The facility consists of two co-generation prime movers based on conventional technology: a 100 kWe gas turbine (mGT) and a 20 kWe internal combustion engine (ICE). The rig high flexibility allows the possibility of integration with renewable-source based devices, such as biomass-fed boilers and solar panels.
Special attention was devoted to thermal distribution grid design. To ensure the possibility of application
in medium-large districts, composed of several buildings including energy users, generators or both, an innovative layout based on two ring pipes was examined. Thermal storage devices were also included in order to have a complete hardware platform suitable for assessing the performance of different management
tools.
The test presented in this paper was carried out with both the mGT and the ICE connected to this innovative thermal grid, while users were emulated by means of fan coolers controlled by inverters. During
this test the plant is controlled by a real-time model capable of calculating a machine performance ranking,
which is necessary in order to split power demands between the prime movers (marginal cost decrease objective). A complete optimization tool devised by TPG (ECoMP program) was also used in order to obtain theoretical results considering the same machines and load values. The data obtained with ECoMP were compared with the experimental results to obtain a broad validation of the optimization tool.

A thermo-economic analysis regarding large scale hydro-methane and methanol production from renewable sources (biomass and renewable electricity) is performed.
The study is carried out investigating hydrogen and oxygen generation by water electrolysis, mainly employing the hydraulic energy produced from the 14 GW Itaipu Binacional Plant, owned by Paraguay and Brazil. Oxygen is employed in biomass gasification to synthesize methanol; the significant amount of CO2 separated in the process is mixed with hydrogen produced by electrolysis in chemical reactors to produce hydro-methane.
Hydro-methane is employed to supply natural gas vehicles in Paraguay, methanol is sold to Brazil, that is the largest consumer in South America.
The analysis is performed employing time-dependent hydraulic energy related to the water that would normally not be used by the plant, named ‘‘spilled energy’’, when available; in the remaining periods,
electricity is acquired at higher cost by the national grid.
For the different plant lay-outs, a thermo-economic analysis has been performed employing two different software, one for the design point and one for the time-dependent one entire year optimization, since
spilled energy is strongly variable throughout the year.
Optimal sizes for the generation plants have been determined, investigating the influence of electricity cost, size and plant configuration.

Among renewable technologies, Concentrated Solar Power (CSP) plants are seen as an attractive option to reduce pollutants and the emission of greenhouses gases (e.g. CO2) not only for the United States regions of the Sun Belt (where CSP plants are in commercial use for more than 20 years [1]), but also for European Union, North Africa and Middle East.
CSP technologies are based on the concept of concentrating solar radiation to be used for electricity generation within conventional power cycles using steam turbines (most mature and common technology, gas turbines or Stirling engines).
CSP Solar tower plants can achieve high operating temperatures of over 1000 °C, enabling them to produce hot air for gas turbine operation. Solarized hybrid Gas Turbines can be used in combined cycles, composing a Solar Hybrid Combined Cycle yielding conversion efficiencies of more than 50 % (fig.1), this being a leap in performance for solar energy conversion.

This paper presents the development of a control approach for a smart polygeneration microgrid using the Model Predictive Control (MPC) paradigm. The importance of distributed generation systems has increased through recent years and questions of grid stability have emerged in the face of high concentrations of non-dispatchable power sources. Numerous proposals for “smart” distribution systems have emerged, including an architecture called the Energy Hub (E-Hub), which is a smart microgrid where both thermal and electrical power are supplied to customers by a mix of generator systems. The problem deals with a constrained Multi-Input Multi-Output (MIMO) optimization problem. This paper describes work underway on a real E-Hub located at the laboratories of the Thermochemical Power Group (TPG) of the University of Genoa (UNIGE), Italy. The TPG E-Hub is being integrated into a larger smart polygeneration grid under construction on the Savona campus of UNIGE as part of the European Union Resilient project. The proposed control approach aims to optimize the loading of various resources of the E-Hub in response to changing electrical and thermal demands from the campus-wide smart grid. This paper presents some of the results from initial testing of this approach to E-Hub control.

The aim of this work is the development of three different models to calculate the enthalpy content of a stratified water thermal storage tank from discrete temperature measurements. The difficulty related to enthalpy value evaluation comes from the discrete temperature measurement along the storage (often only 2 to 4 temperatures along the volume height are known): the actual temperature distribution between two subsequent probes is unknown. Three different models based on three different approaches were developed and compared, basing on experimental data. A first model calculates the enthalpy value considering the measured temperatures and the thermal power difference between generation and consumption. The second model uses a mathematical pre-defined temperature shape fitted considering real-time experimental data. The latter model is based on a 1-D physical approach using a multi-nodal method. All the models were validated against the experimental data obtained from the distributed generation laboratory installed in Savona, Italy.

This paper investigates a real Smart Polygeneration Microgrid, designed to satisfy energy demands of the University Campus of Savona (Italy). The plant is made up of (i) two auxiliary boilers (500kWth each), (ii) three micro gas turbines (30kWe, 65kWe and 100kWe), and (iii) an internal combustion engine fed by natural gas (20kWe). The system is also equipped with a thermal storage capacity of 12 m3 and PV panels for a total installed power of 77kWe. Generators are “distributed” around the campus. Since the system is made up of co-generative prime movers, it can supply both electrical and thermal energy to the campus.
The analysis of this smart-grid is performed exploiting original software for time-dependent thermo-economic optimization of poly-generative energy systems. A model of the real plant was built and implemented in the software. The off-design curves of the real devices installed on campus, based on experimental measurements, were used to increase the reliability of the simulation results. The grid was simulated considering the time dependent nature of energy demands throughout the year to identify the best operational strategy. Lastly, after analysing the data for each prime-mover, a modified plant layout was proposed to enhance thermo-economic performance and facilitate replication in other sites.

This paper presents a time-dependent thermo-economic hierarchical approach to the investigation of smart poly-generation grids determining the optimal size of different prime movers in order to meet the energy (electrical, thermal, cooling) demands of a generic user. A specific case study was developed around the smart poly-generation grid at the University of Genoa, Savona Campus (Italy), operational since 2013. In an initial configuration, the grid included different co-generative prime movers, renewable generators and a thermal storage system to manage the thermal load demand over the year. A second layout used a tri-generative plant including an absorption chiller to also meet campus cooling demand.
The simulation method considered the time-dependent energy load demands as problem constraints. This approach enabled both the optimal size and management for each component of the poly-generation grid to be determined for the entire year by giving due consideration to both energy and economic features.
The results enabled the identification of the best configuration from the thermo-economic standpoint for the considered scenario. The proposed method is easily replicated for different applications and configurations of smart poly-generation grids.

This paper investigates the integration of Concentrating Solar Power technology in Combined Cycles for power production. Starting from a state of the art of CSP plants, the paper investigates alternative plant configurations, assessed and compared with a through-life thermoeconomic analysis. Plant layouts include thermal storage to manage the load demand of the plant throughout the day, considering both variable solar input and variable power demand. Focus is on the impact of thermal storage devices on optimal layouts.
The hybrid combined CSP plants are analyzed using original software tools, WTEMP for the design point analysis and WECoMP for the time-dependent thermoeconomic optimization, to take into proper account the time-dependent nature of both the electrical load demand and the hour-by-hour irradiation during the year. The analysis shows that combining CSP technology with existing combined cycles a significant reduction of fuel consumption and greenhouse gas emissions is obtained, with an optimal solar share factor of about 20%, providing the grid with fully dispatchable power generation.

In this work the dynamic behaviour and the control strategy of a 12MWe size gas turbine hybridised with concentrated solar heat source has been investigated. Hybridised gas turbine cycles are attractive because of their high efficiency, potentially equal to combined cycle efficiency, and because of their dispatchable power capability. An existing gas turbine model has been modified into a hybrid layout to incorporate high temperature heat from a concentrated solar field, through a high pressure air-cooled receiver. The system does not involve any hot air valve and includes a ceramic thermal storage. The plant dynamic model was developed using the original TRANSEO simulation tool developed at the University of Genoa. Initially, plant steady-state performance is analysed, identifying potential issues. Then, the different dynamic operations (storage charging, discharging and bypass) are simulated, showing the feasibility of the control strategy proposed. Eventually, design recommendations are drawn to improve the flexibility and the time response of such kind of plants.

In this paper two different advanced control approaches for a pressurized SOFC hybrid system are investigated and compared against traditional proportional–integral–derivative (PID). Both advanced control methods use model predictive control (MPC): in the first case, the MPC has direct access to the plant manipulated variables, in the second case the MPC operates on the setpoints of PIDs which control the plant. In the second approach the idea is to use MPC at the highest level of the plant control system to optimize the performance of bottoming PIDs, retaining system stability and operator confidence. Two MIMO (multi-input multi-output) controllers were obtained: fuel cell power and cathode inlet temperature are the controlled variables; fuel cell by-pass flow, current and fuel mass flow rate (the utilization factor kept constant) are the manipulated variables.
The two advanced control methods were tested and compared against the conventional PID approach using a SOFC hybrid system model. Then, the MPC controller was implemented in the hybrid system emulator test rig developed by the Thermochemical Power Group (TPG) at the University of Genoa.
Experimental tests were carried out to compare MPC against classic PID method: load following tests were carried out. Ramping the fuel cell load from 100% to 80% and back, keeping constant the target of the cathode inlet temperature, the MPC controller was able to reduce the mismatch between the actual and the target values of the cathode inlet temperature from 7 K maximum of the PID controller to 3 K maximum, showing more stable behavior in general.

A data noise reduction model for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (HyPer) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. The system is controlled by an embedded real-time control platform provided by Woodward Industrial Control. Every sensor is monitored by the platform, and an overall strategy drives the system from start-up to shut-down. Fuel is regulated by a
valve which reacts based on the speed of the turbine. There are three optical encoder sensors which are used to monitor turbine speed, and the average of these three sensors is used as feedback for a PID controller, which works to regulate fuel consumption to the combustor. The turbine speed has demonstrated fluctuation in certain conditions, which may be a result of data noise combined with a systemic instability in the flow to the turbine. This research introduces the method of Double Exponential Smoothing as it is applied to data noise reduction in an embedded control platform. An experimental test was conducted to
evaluate the performance of the fuel valve speed control when filtered by a real-time Double Exponential Smoothing Algorithm. The results demonstrate, that when compared with traditional filtering techniques, Double Exponential Smoothing offers a significant improvement in both signal volatility and data latency.

A real-time dynamic model representing the pressurized fuel cell gas turbine hybrid system emulator test rig at Thermochemical Power Group (TPG) laboratories of the University of Genoa has been developed to study the fuel cell behavior during different critical operative situations like, for example, load changes (ramp and step), start-up and shut-down and, moreover, to implement an emergency shutdown strategy in order to avoid any damage to the fuel cell and to the whole system: focus has been on cathode/anode differential pressure, which model was validated against experimental data. The real emulator plant (located in Savona University campus) is composed of a 100 kW recuperated micro gas turbine, a modular cathodic vessel (4 modules of 0.8 m3 each) located between recuperator outlet and combustor inlet, and an anodic circuit (1 module of 0.8m3) based on the coupling of a single stage ejector with an anodic vessel.
Different simulation tests were carried out to assess the behavior of cathode-anode pressure difference, identifying the best control strategies to minimize the pressure stress on fuel cell stack.

Hardware-in-the-loop simulation (HiLS) is a specific technique designed in the experimental environment
for studying the coupling between different technologies, where simulated and hardware components interact to each other. Two different HiLS facilities used for educational and research purposes are examined in the paper: the Hybrid Performance (Hyper) project facility at the U.S. Department of Energy, National Energy Technology Laboratory (NETL), and the Hybrid system emulator at the Thermochemical Power Group (TPG) facility, run by the University of Genoa in Italy. Since one facility is at a national laboratory and the other one in a university environment, both facilities dedicate considerable resources to the education of students with a different perspective: industrial and experimental approach.
A description of the two configurations, the unique and overlapping attributes of each facility and the experimental results are reported and discussed to show different possibilities for students and researchers.
Undergraduates, Postgraduates and Ph.D. students have the opportunity to learn innovative configuration of energy power systems, innovative control strategies applied to hybrid configurations, how to design real hardware components, and how to implementation real-time simulation models. The strong impact of these two laboratories is to show to students the applicability about their knowledge studied during lectures.

A hardware-in-the-loop-simulation (HiLS) procedure for a direct-fired fuel cell turbine hybrid power system was evaluated for an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behaviour. It is possible to model, test and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and quantify risk mitigation strategies.
The previous implementation of emergency shut-down control strategies resulted in turbomachinery hardware failure. The primary linking event in these cases was compressor stall and surge resulting from the sudden loss of fuel during implementation of the standard double block and bleed strategy used during emergency failure. A new mitigation strategy involving automated ramps is proposed and described in detail to control the system from start-up to forced emergency shut-down.
The control architecture shows how the virtual fuel cell model can be coupled to the real gas turbine safely, in all of stage of operations. The paper includes improvements to the emergency shutdown procedure, failure analyses, and the comparison of experimental data with previous results.

Gross Error Detection (GED) is a technique used to identify possible systematic errors in measurements and validate data for a further diagnostic phase. It is always applied along with Data Reconciliation (DR), a technique to improve the accuracy of process data by adjusting the measured values to fit the process equations describing the physical phenomena. They have been applied for a long time to chemical plants with balance equations (mass and composition) and recently extended to industrial power plants. In this paper a wellknown GED technique based on serial elimination has been applied in a gas turbine plant operating in a combined cycle power plant. In a first analysis errors have been imposed manually in the field data to understand the minimum error amplitude avoiding the smearing effect: at the beginning a single gross error has been imposed on the fuel flow rate and on the compressor discharge temperature respectively, then multiple gross errors have been imposed simultaneously on the same measurements. The single gross error tests showed a high capacity of detection and localization, while the multiple gross error analysis highlighted the problems due to the smearing effect (the minimum error intensity to detect and locate errors increased with respect to the single error case). In a second analysis the GED technique has been used to detect and locate a gross error among the three sensors measuring the compressor discharge temperature. The main objective was to analyze the ineffectiveness in error detection and localization of using the mean for redundant measurements.

Long-term monitoring and diagnostic of power plants is a permanent issue for the energy companies. In particular with the increase of flexible operation (e.g. daily start-up and shutdown cycles, part load operations) the definition of proper diagnostic indicators becomes mandatory. Different monitoring strategies were developed, implemented and tested for the main components of a combined cycle power plant (e.g. Gas Turbine, Heat Recovery Steam Generator, Steam Turbine, Pumps) to prevent fault/failure or to plan/evaluate the maintenance activities.
This work focuses on the first principles health assessment of the Heat Recovery Steam Generator (HRSG). The impact of ambient conditions on the gas turbine outlet temperature and mass flow rate and thus on the HRSG behavior is presented referring to the control strategies of the Gas Turbine (GT). To validate the measurements a preprocessing phase basing on Data Reconciliation was performed, aimed at improving the
accuracy of the estimation of exhaust mass flow rate entering the HRSG. Gas Turbine and HRSG nergy balances are exploited to reduce the uncertainties of the results, eliminate the outlier data sets and obtain consistent data. Moreover an evaluation of the sensitivity of the indicator will be made basing on field measurements before and after a maintenance intervention.

The conversion of ocean wave power into sustainable electrical power represents a major opportunity to Nations endowed with such a kind of resource. At the present time the most of the technological innovations aiming at converting such resources are at early stage of development, with only a handful of devices close to be at the commercial demonstration stage. The Seaspoon device, thought as a large energy harvester, catches the kinetic energy of ocean waves with promising conversion efficiency, and robust technology, according to specific “wave-motion climate”. University of Genoa aims to develop a prototype to be deployed in medium average energy content seas (i.e. Mediterranean or Eastern Asia seas). This paper presents the first simulation and experimental results carried out on a reduced scale proof-of-concept model tested in the laboratory wave flume.

The experimental plant developed by TPG for studies on distributed generation systems was used for
tests on management improvement. The facility is based on two co-generation prime movers, a 100 kWe gas turbine (mGT) and a 20 kWe internal combustion engine (ICE) connected to an innovative thermal distribution grid. The piping layout was developed to obtain the highest flexibility level for connection with thermal energy storage devices. The resulting test rig constitutes an experimental hardware platform for assessing, on a real basis, the performance of different tools able to choose, in real-time mode, the ‘‘best’’ operative conditions. Therefore, a real-time software was developed to calculate marginal costs of plant operation and to improve the polygeneration grid management.
In the initial experimental campaign, only the individual generators were considered. Standard management (electrical load following thermal demand) and improved operation with thermal energy
storage approach were compared.
The main results are related to plant management tests using the real-time software. Both electrical and thermal demand values were considered for operation with the mGT, the ICE and the grid. A result comparison was performed for the grid operated at constant storage set-point value and with a constrained management approach.

The aim of this paper is to illustrate the operation of a real energy hub that can satisfy both thermal and electrical demands of a generic user. In particular, a specific case study developed around the smart grid of the University Campus of Savona (Italy), which just completed in 2014, is analysed. The grid includes different cogenerative prime movers and a storage system to manage the thermal load demand. Through a time-dependent thermo-economic hierarchical approach developed by the Authors, the work aims at optimizing the management strategy of the different prime movers to satisfy the energy demand, taking into proper account both the energetic and economic aspects. The analysis was carried out considering two different layouts, with and without a conventional stratified thermal storage, to evaluate the impact of this component in the management of the district.

In this paper, a system to harvest waste heat and convert it into electrical energy is presented; such a system is based on thermoelectric generators (TEG) modules exploiting the Seebeck Effect.
A technical and economic feasibility study of the system is presented, the most convenient applications of thermal energy residuals recovery in residential environment (detached house, condos, isolated off-the grid house) are evaluated according to the electrical supply of typical domestic low consumption devices (i.e. LED lighting); the total yearly production of thermoelectric generator is considered in different techno-economic scenarios.

Hybridized gas turbine cycles are attractive because of their high efficiency, potentially equal to combined cycle efficiency, and dispatchable power capability. TES technologies are important to accelerate market
penetration of CSP plants, overcoming the limitation due to the intermittence of the solar source.
In this work a high temperature ceramic storage Test rig for gas turbine energy systems was presented with its innovative layout, which avoids the use of hot valves. Such experimental plant storage is located at the University of Genoa, Savona Campus, Italy: it can be run with compressed air and it is ready for connection with the modified microturbine T100 onsite. The Test rig represents a scaled-down version of a larger system designed for an hybridized solar 12 MW gas turbine whose dynamics performance was presentedpreviously. This paper presents the dynamic analysis of such lab-scale mGT system, which provided the necessary requirements for the Test rig design.
The storage system proposed here does not involve any hot air valve and does include a short-term (30min equivalent) ceramic thermal storage. The plant dynamic model was developed using the original TRANSEO simulation tool. This paper investigates plant layout control strategy, showing the feasibility of the control procedure through dynamic simulation: eventually, design recommendations are drawn to improve plant flexibility and time response.

Long term monitoring and diagnostic of power plants is a permanent challenge for the energy companies. In particular with the increase of flexible exercise (e.g. daily start-up and shut-down cycles, part load operations) the definition of proper diagnostic indicators becomes mandatory. Different monitoring strategies were developed, implemented and tested for the main machineries of combined cycle power plants(e.g. Gas Turbine, Heat Recovery Steam Generator, Steam Turbine, Pumps) to prevent fault or failure or to plan/evaluate the maintenance activities.
This work focuses on the first principles health assessment of the Heat Recovery Steam Generator(HRSG). At first a brief analysis about the relationship between the global HRSG efficiency and the GT net power is presented. From an initial global study the attention has been addressed to a single component analysis focusing on the section that involves the first three heat exchangers in the HRSG gas path(named SH2, RH and SH1respectively). This choice has been done for two main reasons: firstly these heat exchangers are the most important in terms of quality of energy recovered (higher temperatures means higher exergy), secondly this section has the highest number of measurement points which allows redundancy in energy balances. This second point is the key for the implementation of an effective validation phase based on Data Reconciliation and Gross Error Detection in order to improve the accuracy of the results and show the effectiveness of such techniques in the power plant monitoring. Several input set of data have been preprocessed identifying steady-state conditions and then analyzed and compared to find the optimal subset of measurements giving the best accuracy of the results.

In this paper, a system to harvest waste heat and convert it into electrical energy is presented; such a system is based on thermoelectric generators (TEG) modules exploiting the Seebeck Effect.
A technical and economic feasibility study of the system is presented, the most convenient applications of thermal energy residuals recovery in residential environment (detached house, condos, isolated off-the grid house) are evaluated according to the electrical supply of typical domestic low consumption devices (i.e. LED lighting); the total yearly production of thermoelectric generator is considered in different techno-economic scenarios.

Sustainable distric development requires innovative energy use solutions. The aim of this paper is to illustrate the operation of a real energy hub that can satisfy both thermal and electrical demands of a generic user. In particular, a specific case study developed around the smart grid of the University Campus of Savona (Italy), which just completed in 2014, is analysed. The grid includes different cogenerative prime movers and a storage system to manage the thermal load demand. Through a time-dependent thermo-economic hierarchical approach developed by the Authors, the work aims at optimizing the management strategy of the different prime movers to satisfy the energy demand, taking into proper account both the energetic and economic aspects. The analysis was carried out considering two different layouts, with and without a conventional stratified thermal storage, to evaluate the impact of this component in the management of the district.

The aim of this work is the development of three different models to calculate the enthalpy content of a stratified water thermal storage tank from discrete temperature measurements. The difficulty related to enthalpy value evaluation comes from the discrete temperature measurement along the storage (often only 2 to 4 temperatures along the volume height are known): the actual temperature distribution between two subsequent probes is unknown. Three different models based on three different approaches were developed and compared, basing on experimental data. A first model calculates the enthalpy value considering the measured temperatures and the thermal power difference between generation and consumption. The second model uses a mathematical pre-defined temperature shape fitted considering real-time experimental data. The latter model is based on a 1-D physical approach using a multi-nodal method. All the models were validated against the experimental data obtained from the distributed generation laboratory installed in Savona, Italy.

In this paper, the impact of not controllable renewable energy generators (wind turbines and solar photovoltaic panels) on the thermo-economic optimum performance of poly-generation smart grids is investigated using an original time dependent hierarchical approach.
The grid used for the analysis is the one installed at the University of Genoa for research activities. It is based on different prime movers: (i) 100 kWe micro gas turbine, (ii) 20 kWe internal combustion engine powered by gases to produce both electrical and thermal (hot water) energy and (iii) a 100 kWth adsorption chiller to produce cooling (cold water) energy. The grid includes thermal storage tanks to manage the thermal demand load during the year. The plant under analysis is also equipped with two renewable noncontrollable generators: a small size wind turbine and photovoltaic solar panels.
The size and the management of the system studied in this work have been optimized, in order to minimize both capital and variable costs. A time-dependent thermo-economic hierarchical approach developed by the authors has been used, considering the time-dependent electrical, thermal and cooling load demands during the year as problem constraints.
The results are presented and discussed in depth and show the strong interaction between fossil and renewable resources, and the importance of an appropriate storage system to optimize the RES impact taking into account the multiproduct character of the grid under investigation.

This paper investigates large scale bio-methane generation from renewable sources, mixing hydrogen produced by water electrolysis and syngas obtained by pressurized oxygen blown biomass gasification.

Hydrogen is produced by water electrolysis employing time-dependent hydraulic energy related to the water which is not normally used by the plant, named “spilled water electricity”. The oxygen, also obtained in the electrolysis process, is employed for biomass gasification to produce syngas: after purification treatments, the syngas is mixed with hydrogen in a chemical reactor to obtain bio-methane.

The whole process is optimized here using two different thermo-economic approaches: (i) for the design point analysis of the chemical and thermodynamic significant parameters in electrolysis, gasification, syngas purification and methanation processes; (ii) for an entire one-year time-dependent analysis in order to define the optimal plant size, since the spilled energy and the electrical grid load vary widely throughout the day and the year. The hydrogen generation plant is based on 1 MWe water electrolysers using the “spilled water electricity”, when available; in the remaining periods, in order to assure a regular H2 production, the energy is taken from the electrical grid, but at a higher cost.

It is worth noting that the methane produced, named bio-methane, is totally “CO2free”, since it is produced from renewable sources only. Moreover, the optimization method presented here has a general value, thus it can be easily applied to different sizes, economic scenarios and plant locations.

Cathode–anode interaction, mainly based on cathode versus anode volume influence, recirculation performance, and turbomachinery integration, is an important issue for pressurised SOFC hybrid systems, and this aspect must be carefully considered to prevent fuel cell ceramic material failures through a reliable control system. Over the last 10 years, several theoretical analyses of this issue have been carried out at the University of Genoa. These interaction studies have been analysed and an experimental approach (for model validation, system development and prototype design activities) has been applied using emulator facilities or real plants. In particular, general hybrid system layouts based on the coupling of pressurized SOFC stacks of different geometries (planar, tubular, etc.) with a gas turbine bottoming cycle have been investigated using the hybrid system emulator facility of the University of Genoa. The experimental results are focused on the interaction between gas turbine and anodic circuit and on cathode–anode differential pressure behaviour for design, off-design and transient hybrid system operative conditions. The information obtained in these tests is essential to understand the main features of the variables that drive the phenomena and to design a suitable control system that can mitigate the differential pressure values during all plant operating conditions.

Among renewable energies sources, Ocean waves power, around the coasts worldwide, has been estimated to be in the order of 8,000-80,000TWh/y. The conversion of this resource into sustainable electrical power represents a major opportunity to nations endowed with such a kind of resource.
At the present time most technological innovations aimed at exploiting such resource are at early stage of development, with only a handful of devices close to be at the commercial demonstration stage. Very few of them, though, operates converting the wave energy contents at its very origin: the orbital motion of water particles right below the ocean surface.
The Seaspoon device catches the kinetic energy of ocean waves with promising efficiency conversion performance, according to specific “wave-motion climate”.

In this paper an innovative SOFC hybrid system is proposed, equipped with ejector-based cathodic recirculation. The cathodic flow is preheated by recirculating hot exhausts. However, this approach needs higher pressure values than those available with commercial micro gas turbines (mGT): a possible but expensive solution could be to design a completely new mGT. Another option could be to use a booster with the function of re-compressor installed between the mGT compressor and the ejector (in order to increase ejector inlet pressure). This choice allows the use of commercial machines with a substantial cost reduction by comparison with designing a new micro gas turbine. Moreover, this layout is able to separate the compressor ratio of the mGT from the ejector inlet pressure, generating more flexibility from the point of view of the control system. In this paper, a thermodynamic study of this machine coupling is carried out considering the hybrid system emulator developed by TPG at the University of Genoa. For this purpose, three different boosting approaches were examined with a steady-state model built in Matlab-Simulink environment. The results presented here were obtained to show emulator performance and flexibility. Available power and thermal aspects are discussed in detail.

The design of a turbine in a closed cycle setup of electrical power production constitutes the major challenge for the increase of system performance. The preliminary design of an electricity producing turbine, in the range of 100 kW, in a closed low enthalpy Organic Rankine Cycle, powered by either a geothermal and solar thermal field or exhaust emissions of PEM type fuel cells is presented in this paper. For this reason, an extended bibliographic review was performed; on the basis of its findings, an integrated model of equations was developed, aiming in the calculation of the thermodynamic parameters of a closed organic cycle for different working fluids, such as NH3, CO2 and R-134a. Moreover, another mathematical model was developed, in order to calculate the geometrical characteristics of the turbine, as well as the blade geometry, through velocity triangle. After comparison of results for the three working fluids, R-134a was chosen as the best solution, since the system performance index approached 10%. As it is already stated, the main purpose of the paper is the increase of an integrated system performance, which will make use of the wasted energy in the form of heat in order to produce electrical power: therefore, a subsequent study of all components of such a system ( the compressor, the evaporator, the condenser, the gearbox and the bearings) was carried out. Finally, it is worth noting that two versions of the turbine design were developed. In the first version, V2 turbine speed is explicitly subsonic, while in the second V2 turbine speed is equal to Mach, meaning that the flow is choked. Results show that, keeping the crucial parameters for the geometrical formation of the blade constant, turbine volume can be significantly decreased up to 90%.

Initial startup of a direct-fired fuel cell turbine power system with equivalence ratio control using cathode air bypass valves to minimize thermal shock to the fuel cell was evaluated using the Hybrid Performance (Hyper) project hardware-based simulation facility at the U.S. Department of Energy, National Energy Technology Laboratory. The turbine in the system was started with the minimum possible airflow through the fuel cell cathode from a cold condition using two bypass valves to mitigate thermal shock failure in the fuel cell. The limitation of bypass flow was set by air requirements to maintain a combustor equivalence ratio below 0.7 during turbine windup. A 1D distributed fuel cell model operating in real time was used to produce individual cell transient temperature profiles during the course of the turbine start. The results provide insight into the procedural requirements of starting a fully coupled hybrid system.

A new emergency shutdown procedure for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide means of quantifying risk mitigation strategies.
An open-loop system analysis regarding the dynamic effect of bleed air, cold air by-pass and load bank is presented in order to evaluate the combination of these three main actuators during emergency shut-down. In the previous Hybrid control system architecture, compressor failures were presented when the fuel and load bank were cut-off during emergency shut-down strategy. Improvements were implemented using a non-linear fuel valve ramp down when load bank was not operating. Experiments in load bank operation show compressor surge and stall after emergency shut-down activation. The difficulties in finding an optimal compressor and cathode mass flow for mitigation of surge and stall using these actuators are illustrated.

The aim of this study was to provide a characterization of non-symmetrical operation in two counter-flow primary surface exhaust gas recuperators installed in parallel flow loops. The hybrid system emulator test rig and facility designed and operated by the Department of Energy, National Energy Technology Laboratory located at the West Virginia (USA) campus was used for the study. Various tests from the past years often resulted in non-symmetrical operation, indicated by significantly variant temperature measurements at the outlets of the recuperators. Some specific tests have been carried out in order to identify the possible cause of this flow unbalance. The isolated effects of bleed air, cold air and hot air valve on the heat exchangers flow unbalance have been studied. Also, the impact of load bank changes on flow distribution has been considered in this study. Each test has been carried out in close loop fuel valve speed control. The influence of each independent variable in the study on parallel recuperator flow distribution has been quantitatively characterized using temperatures and a heat balance. Both the bleed and the cold air compressor bypass valves showed an appreciable impact on the heat exchangers flow unbalance, while hot air valve and load bank changes had minimal effect.

In this study the techniques of Data Reconciliation and Gross Error Detection have been applied to a microturbine-based test rig installed at the Thermochemical Power Group (TPG) laboratory of the University of Genoa, Italy. These techniques have been developed in the field of chemical engineering during the past 55 years with the purpose of reducing the effect of random errors and also eliminating systematic gross errors in the data by exploiting the relationships that are known to exist between different variables of a process (e.g. energy and mass balances). Two different applications of Data Reconciliation have been carried out: first the entire test rig was studied, generating a set of measurements affected just by random error; second, only the recuperator was taken into account using real measurements coming from a steady state test performed on the plant. The purpose of the former is to show the capability of Data Reconciliation in the adjustment of the measurements so that they can respect the constraints (balance equations). This application is somehow an “ideal application” of Data Reconciliation. Latter since gross errors are often present in the measurements coming from a real plant, a “real or experimental application” of Data Reconciliation was considered for a subsystem of the plant in which the actual measurements from plant probes were used. The objective was to understand if the measured values of temperature, pressure and mass flow rate at the inlet and outlet of the recuperator were physically compatible and reliable. Measured value affected by gross error was identified, focusing on its effect over all the other measurements during DR calculation.

This paper presents a thermo-economic study of a hydro-methane production plant. The aim is to determine the applicability and sustainability of the whole system in different economic scenarios.
The plant consists of three main parts: pressurized alkaline electrolyzers, an oxygen-blown biomass gasifier and Sabatier reactors for hydro-methane synthesis. Electrolyzers, supplied with electricity from the hydroelectric plant, produce hydrogen and oxygen; O2 is used as a gasification agent in the pressurized biomass gasifier to produce the syngas which, after being mixed with the hydrogen, is sent to the Sabatier reactors where the final product is achieved.
The system is completely renewable: the electrical energy needed for water electrolysis is produced by a hydroelectric plant, and the gasifier is supplied by biomass. Therefore, the fuel produced is “zero emission”. The hydro-methane produced in this way represents an optimal solution to reducing the amount of pollution caused by cars, as it avoids the use of fossil fuels.
The system is optimized through several economic and technological scenarios.
From a technological point of view, two different approaches are considered: (i) Obtaining carbon dioxide from an external source for use in the Sabatier reaction; (ii) employing the gasifier to produce a syngas rich in CO2, which, at the same time, allows the utilization of large amounts of oxygen generated through water electrolysis. On the economic side, a parametric analysis is used to compare several scenarios (i.e. Italy, South America) and investigate the influence of the cost of energy, the selling prices of hydro-methane and oxygen, and the purchasing cost of biomass and carbon dioxide on the system.

Fault detection methods are now being applied to a variety of systems in the field of chemical or mechanical engineering. Our study is focused on the application of fault detection techniques to fuel cells, in particular solid oxide fuel cells (SOFCs) systems.
Fault detection techniques are classified as (i) quantitative model-based methods; (ii) qualitative model-based methods, and (iii) process history based methods. In the previous two cases, the starting point for the fault detection is an extensive analysis of different types of faults, made through modelling results. Indeed, this is the subject of the present work, where we show the results of an extensive fault analysis carried out for different types of solid oxide fuel cells, through a quantitative model based on local mass and energy balances. The types of faults taken under consideration are (i) air leakage; (ii) fuel leakage; (iii) electrical connection deterioration or electrode degradation; iv) carbon deposition; v) crack in the electrolyte. For an analysis of the results, we define the residuals, i.e. the difference between the values of a physico-chemical parameter at the design point and under fault conditions. Residuals of voltage, solid and gas temperatures, pressure losses and fuel composition are taken into consideration.
Faults and residuals will provide the input classes and features, used in a subsequent work of fault detection through pattern recognition methods.

The experimental plant developed by TPG for studies on distributed generation systems was used for optimization tests. The facility is based on two co-generation prime movers, a 100 kWe gas turbine (mGT) and a 20 kWe internal combustion engine (ICE) connected to an innovative thermal distribution grid. The piping layout was developed to obtain the highest flexibility level for connection with thermal storage devices. The resulting test rig constitutes an experimental hardware platform for assessing, on a real basis, the performance of different optimization tools able to choose, in real-time mode, the “best” operative conditions. Therefore, a real-time software was developed to calculate marginal costs of plant operation and to optimize the polygeneration grid management.
In the initial experimental campaign only the individual generators were considered. Standard management (electrical load following thermal demand) and optimized operation with thermal storage approach were compared.
The main results are related to the optimization tests using the real-time software. Both electrical and thermal demand values were considered for operation with the mGT, the ICE and the grid. A result comparison was performed for the grid operated at constant storage set-point value and with a constrained optimization approach.

Data Reconciliation is a technique that improves the accuracy of process data by adjusting the measured values so that they satisfy the process equations describing the physical phenomena. Along with Gross Error Detection it can be used to identify possible systematic errors in measurements and validate data for a further diagnostic phase. These techniques have been applied for a long time only to chemical plants with balance equations (mass and composition) and then they have been extended to industrial gas turbine, including characteristic equations.
Usually all Data Reconciliation techniques are based on constrained minimization of an objective function which is the total weighted sum square of adjustments made to measurements to fulfill the constraints. The strategy proposed in this paper exploits least squares optimization to solve a system of non-linear equations, which represents the same Data Reconciliation problem in a more efficient way. The system of equations involves both the measurement adjustments weighted with measurement uncertainties, and the process equations characterized by an appropriate weight to maintain the error under expected limit, which allows to consider them fulfilled.
In this paper this novel approach to Data Reconciliation applied to industrial power plants has been studied and compared with classic Non Linear Data Reconciliation techniques, based on Sequential Quadratic Programming and Lagrange multiplier. Both linear and non-linear case studies have been developed to test the algorithms performance. Moreover a case study based on real field data has been carried out on the base of an Ansaldo Energia industrial gas turbine. To filter real data a Gross Error Detection technique based on serial elimination has been applied along with Data Reconciliation in order to identify the presence of some possible systematic errors in measurements.
The comparison between the several approaches has highlighted better performance in terms of implementation and calculation speed of the least square algorithm which provides the same accuracy both in reconciling measurements and in respecting the constraints.

This paper is based on the experimental Energy-Hub, developed by TPG (Thermochemical Power Group) of the University of Genoa . In the Savona campus, TPG set up an “E-Hub” laboratory where a real Energy District can be physically simulated, including renewable and energy storage.
In cooperation with the West Virgina University, a Model Predictive Control has been conceived and implemented to manage the generators to follow thermal and electrical demands of a representative group of buildings.
In the first stage of the work, a MPC was built in Matlab-Simulink, particularly focusing on thermal loads and building thermal requests. Models for each generators were built basing on experimental data.
Building consumptions are emulated through fan coolers and the electrical grid. Thermal storage is extensible used in the test rig: each user (building) is equipped with an independent stratified water storage; moreover large energy district energy storage is also available (5 + 5 m3 water tanks). Also meteorological conditions were considered as important and influent parameters on generator control.
After testing of the MPC on a simulation-only basis, the control algorithm was connected to the real Energy-Hub simulating the requests as a series of step change demands imposed on the electrical and thermal energy. The steps are constructed to test the ability of the MPC controller to pursue the best economic strategy for satisfying the energy demands. Two controllers were tested. The first one used a 1s sample time and a 100 sample-period prediction horizon, 6 sample-period control horizon. The second controller used a 10s sample time and a 100 sample-period prediction horizon, and 6-sample-period control horizon.
The paper presents the architecture of the MPC controller and discusses the experimental results obtained.

This work concerns the implementation of a new control system for hybrids with solid oxide fuel cell and microgasturbines. It is based on a complete hybrid system emulator test rig developed at the University of Genoa (Savona laboratory) by the Thermochemical Power Group (TPG). The plant is mainly composed of a 100 kW recuperated micro gas turbine coupled with both anodic and cathode vessels for high temperature fuel cell emulation and a complete real time model which purpose is to simulate the fuel cell and its electrochemical behavior. The model and the connected physical plant represent a full hardware-in-the-loop (HIL) facility.
Temperature, pressure and air mass flow rate at the recuperator outlet (downstream of the compressor) and rotational speed of the machine are inputs from the plant to the model. The turbine outlet temperature (TOT) calculated by the model is fed into the machine control system and the turbine electric load is moved to match the model TOT values.
A new revised stack inlet temperature controller has been extensively tested and showed to be very stable and robust. It is capable to contain temperature deviation against a fixed set point within a band of 3 °C when a fuel cell load ramp occurs. The controller is a standard PID (proportional-integral-derivative) plus a feed forward contribution. The PID is protected against wind up.

Solid Oxide Fuel Cells hold the greatest potential of any other fuel cell technology. Using low cost ceramic materials, they can achieve high electrical efficiencies without relying on CHP. Moreover, SOFCs operate at high temperature (typically above 800?C), which allows fuel flexibility. However, there are still significant technical challenges inhibiting the use of this promising new technology.
This paper examines the development of enabling technologies of SOFC/?GT Hybrid Systems for power generation. The positive characteristics and the drawbacks of solid oxide fuel cells are being introduced. Such an application includes a series of specifications and restrictions. The requirement of maintaining a 7 bar static pressure at the fuel cell inlet leads to the addition of a centrifugal compressor. This additional device is used as a booster with a desired pressure ratio of 1.5. The investigation of two alternative technical approaches for the driving of the booster is presented: an electrically driven compressor and a booster driven by a turbo-expander. The integration procedure carries on with the design of the cycle and its components. The present work is being concluded after the preliminary design of both the compressor and the expander. Results show a 5.79% higher total power output and a wider range of rotational speed for the turbocharger case. Hence, the radial turbine solution is proven to be the most appropriate one for the compressor driving.

Energy provision is the biggest issue to face for the world’s economy at any latitude. Nowadays the energy demand of developing Countries as well as that one of developed economies is huge and increasing at an unbearable pace. Considering the limited stocks of such an energy source, and the drawbacks related to the emissions associated to its utilization, the problem to find alternative energy sources and suitable conversion technologies must be solved in order to guarantee the growth and preserve the planet environment. Renewable energy sources are distributed and available all over the world in different forms and variable amounts. Among renewable energies sources, ocean waves power, around the coasts worldwide, has been estimated to be in the order of 1TW (1 TW/h 1012W). The conversion of this resource into sustainable electrical power represents a major opportunity to Nations endowed with such a kind of resource. At the present time most technological innovations aimed at exploiting such resources are at early stage of development, with only a handful of devices close to be at the commercial demonstration stage. None of them, though, operates converting the wave energy contents at its very origin: the orbital motion of water particles right below the ocean surface. The Seaspoon device catches the kinetic energy of ocean waves with promising conversion efficiency, according to specific “wavemotion climate”. University of Geoa aims to develop a prototype to be deployed in medium average energy content seas (i.e. Mediterranean or Eastern Asia seas) according to the interesting results of a first small scale proof-of-concept model tested in laboratory.

The present paper proposes an outline layout for the integration of Fuel Cells (FC) as Auxiliary Power Unit (APU) source for application on board a Mega Yacht. The assessment of the applicability of an on board Fuel Cell system has been carried on in order to identify the implications in terms of necessary space and therefore the suitable vessel size in which the system could be installed. The investigation has also focussed on the most profitable operational conditions in which the system onboard could be used. The study includes the assessment of different Fuel Cell technologies as well as of different Hydrogen Storage systems in order to find the best compromise that suit the requirements. A technical sizing of the FC system to be installed on-board the ship has been created together with the study of its dynamic performance using as a reference the Nuvera Proton Exchange Membrane (PEM) fuel cell data. The spaces for the installation of the FC system and the Hydrogen Storage system has been evaluated. Finally an assessment of the
installation technical impact on the ship has been made and a range of possible solutions found. The feasibility of the proposed design has been tested starting from Liquified Natural Gas (LNG) fuelled Mega Yacht concept provided by Fincantieri Shipyard.

Hydrogen energy technology allows to produce electricity from hydrogen and backwards to store large
amount of energy converting electricity into hydrogen, by means of a fuel cell, an electrolyser and a hydrogen storage system. The fuel cell market increased from 24,600 units in 2011 to 78,000 in 2012 offering components with improved converting performances; the expansion of this market and the
spread of hydrogen system applications is bringing down the industrial costs of such technology offering
new opportunities for commercial applications. This paper presents a technology assessment of an
hydrogen based energy system for sailboat up to 40 ft. in comparison to traditional electrical accumulators.
The object of this paper is to demonstrate the technical feasibility to install a hydrogen based Hybrid
Renewable Energy System (HRES) onboard sailboat in order to improve comfort and safety in a total
environmental friendly way by means of the analysis of an innovative system that integrates the renewable
energy produced by PV panels, wind generator and hydro generator together with a hydrogen hydrides
energy storage system, a water electrolyser, a fuel cell and a battery.
New regulation and the rising ecological sensibility in Europe need new clean technology to make green
the European nautical market, the biggest one in the world counting 1.4 yachting boat per 100 inhabitants
in Italy, and up to 2.2 in France.

This work is based on the hybrid system emulator plant developed by the Thermochemical Power Group (TPG) of the University of Genoa. This rig is composed of a 100 kW microturbine coupled with high temperature fuel cell emulation devices. A real-time model is used for components not physically present in the laboratory (solid oxide fuel cell (SOFC), reformer, anodic circuit, off-gas burner, cathode blower). It is necessary to evaluate thermodynamic and electrochemical performance related to SOFC systems. Using an
User Datagram Protocol (UDP) based connection with the control/acquisition software, it generates a hardware-in-the-loop (HIL) facility for hybrid system emulation. Temperature, pressure, and mass flow rate at the recuperator outlet and machine rotational speed are measured in the plant and used as inputs for the model. The turbine outlet temperature (TOT) calculated by the model is fed into the machine control system and the turbine electric load is changed to match the model TOT values (effective plant/model coupling to avoid modifications on microturbine controller). Different tests were carried out to analyze hybrid system technology through the interaction between an experimental plant and a real-time model. Double step and double ramp tests of current and fuel provided the system dynamic response.

This paper presents the steady state and transient model of a natural gas fuel processing system of a solid oxide fuel cell (SOFC) hybrid system, and its validation using data obtained through the use of a real plant. The model was developed by the Thermochemical Power Group of the University of Genoa, Italy, using the in-house tool TRANSEO working in the MATLAB/SIMULINK environment, whereas the real plant was designed and built by Rolls-Royce Fuel Cell Systems Limited (RRFCS) to feed a 250 kWe SOFC hybrid system with a methane stream undergoing requirements about composition, pressure, and temperature. The paper presents in detail the fuel processing system and, with particular emphasis, the selective catalytic sulphur oxidation (SCSO) and the catalytic partial oxidation (CPOx) subsystems. Thanks to the collaboration between the University and RRFCS, in the model the real physical properties of the different materials and geometry of the components have been carefully used. The transient model has been fully validated against experimental data obtained from long duration tests, which included the warm-up, part and full load operation, and cool-down phases of the external fuel processing system. In the validation process both gas and wall temperatures have been taken into account. The transient model has shown the ability to predict satisfactorily the plant behavior both at steady-state and transient conditions. The validated model is now under further development to be used for dynamic control system applications. [DOI: 10.1115/1.4005122]

A standard emergency shutdown procedure for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide means of quantifying risk mitigation strategies.
The previous implementation of facility emergency shutdown control strategies resulted in turbomachinery hardware failure, and would certainly have resulted in catastrophic failure of the fuel cell in the system. An analysis of system performance was completed to evaluate failure modes leading to the destruction of equipment. The primary linking event in these cases was compressor stall and surge resulting from the sudden loss of fuel during implementation of the standard double block and bleed strategy used in emergency shutdown. The implementation of this strategy and real-time communication is described in detail. Subsequently, a new mitigation strategy involving automated ramps is proposed for controlled emergency shutdown.

In this paper hydrogen generation and storage systems optimization, related to a very large size hydraulic plant (Itaipu, 14 GW) in South America, is investigated using an original multilevel thermo-economic optimization approach developed by the Authors. Hydrogen is produced by water electrolysis employing time-dependent hydraulic energy related to the water which is not normally used by the plant, named “spilled water”.
From a thermo-economic point of view, the two main aspects of the study are the optimal definition of the plant size and the whole system management. Both of them are strongly influenced by (i) spilled water energy variability related to its time-dependent distribution during the whole year, (ii) time-dependent electricity demand of Paraguay and Brazil (the owners of the Itaipu plant) electrical grids, and (iii) the hydrogen demand profile.
The system analyzed here consists of a very large size hydrogen generation plant (hundreds of MW) based on pressurised water electrolysers fed with the so called “spilled water electricity”, the related H2 storage, and the H2 demand profile for Paraguay transport sector utilization.
Since H2 plant optimal size is strongly correlated to optimal management and vice-versa, in this paper two hierarchical levels have been considered hour by hour on a complete year time period, in order to minimize capital and variable costs. This time period analysis is necessary to properly take into account spilled energy variability to find out H2 production system optimal size, optimal storage solution and best economical results.
For the optimal storage size, two different solutions have been carefully investigated: (i) classical long time H2 physical storage using pressurised tanks at 200 bar; (ii) hybrid one using reduced size physical storage (one day time demand) where the energy to feed electrolysers is taken from electrical grid when spilled water energy is not available [Rivarolo M, Bogarin J, Magistri L, Massardo AF. Hydrogen generation with large size renewable plants: the Itaipu 14 GW hydraulic plant case. In: 3rd international conference of applied energy (ICAE), 16–18 May 2011, Perugia; 2011.]. For both the two solutions, time-dependent results are presented and discussed with particular emphasis to economic aspects, system size, capital costs and related investments. It is worthy to note that the results reported here for this particular H2 large size plant case represent a general methodology, since it is applicable to different size, primary renewable energy, plant location, and different H2 utilization.

In this paper, sodium borohydride (NaBH4) is examined as a method of hydrogen storage and transport, and compared with hydrogen obtained from fossil sources. This chemical hydride has a very high storage density capability due to its large hydrogen content. Hydrogen is released as the main product of the reaction of NaBH4 with water, with sodium metaborate (NaBO2) as a by-product. The main disadvantage of the process is the production cost of the borohydride.
In this paper, an economic analysis is carried out of the production, storage and transport of hydrogen from NaBH4 and from fossil fuels.
Finally, a comparison is presented between various vehicles fuelled by petrol, hydrogen and sodium borohydride.

One of the main challenges in the perspective of a hydrogen economy is the development of a storage system both safe and with high weight capacity. Among the most promising systems are the storage in metals and chemical hydrides and the high pressure storage in tanks made of composite materials. Both these technologies allow volumetric densities equal or higher than that of liquid hydrogen.
The present work deals with the results obtained in a Italian national project, whose objectives have been the development of innovative technologies in specific applications: large scale energy storage, stationary applications in distributed generation, and automotive (with a particular attention to the fluvial and the sea transportation in protected areas).
The theoretical, modellistic and experimental activities have been oriented to the development of innovative high capacity metal hydrides, the study of a regeneration method for chemical hydrides, the integration of intermediate pressure electrolyzers with advanced compressors and, finally, the development of thermomechanical models for executive design of storage systems. A number of prototypes has been realised and installed in a test facility in the Fusina (Venezia) power plant. The activity has been completed with an executive feasibility evaluation, in the perspective of industrial applications.

This study aims at the development of a software tool for supply and demand matching of electrical and thermal energy in an urban district.
In particular, the tool has been developed for E-NERDD, the experimental district that TPG-DIMSET is going to build in Savona, Italy.
E-NERDD is an acronym for Energy and Efficiency Research Demonstration District. It is one of the districts that will be used within the project to demonstrate how different software tools and algorithms perform in thermodynamic, economic and environmental terms.
The software tool originally developed for and implemented in this work, called E-NERDD Control System, is targeted on enabling the operation of the hardware, when connected in a district mode.
Supply and demand are matched to reach a thermoeconomic optimum. An optimization algorithm is organized into two different levels of optimization: a first level that resolves a constrained minimization problem in planning power supply for each generator on the basis of day-before forecasting; and a second level that distributes among the different machines the gap between planned and real-time demand.
The algorithm developed is demonstrated in four test cases in order to test it in different working conditions.

This paper presents the development of a new experimental facility for analysis and optimization activities on smart polygeneration grids. The test rig is being designed and built in the framework of the European project “Energy-Hub for residential and commercial districts and transport” (E-HUB), which targets optimal energy management of residential and commercial districts.
The experimental rig, named “Energy aNd Efficiency Research Demonstration District” (E-NERDD), is located inside the University campus in Savona, and is based on four different prime movers able to produce both electrical and thermal energy: a 100 kWe micro gas turbine, a 20 kWe internal combustion engine, a 3 kWe Stirling engine, and a 450 kWe fuel cell/gas turbine hybrid system emulator based on the coupling of a micro gas turbine with a modular vessel.
While the electrical side is based on the connection with the campus grid (further developments are planned for a local electrical grid including storage units), thermal energy is managed through a dual ring-based water distribution system. The facility is also equipped with thermal storage tanks and fan cooler units to study and optimize different thermal management algorithms generating different thermal load demands. The facility also includes an absorption chiller for cold water generation. As a result, trigeneration operation is possible in a physically simulated urban district. Moreover, the rig is equipped with six photovoltaic panels (significant for the electrical aspects) and 10 kWp of thermal solar panels to be
integrated in the grid. Further technologies to be considered for the E-NERDD are power plants based on other renewable resource (e.g. with biomass fuel). These systems are planned to be analyzed through real plants (remote connection with the field) or through virtual models based on real-time dynamic approaches.
Experimental tests related to the performance of the micro gas turbine are reported and discussed in this paper. The focus here is on machine correction curves essential to evaluate factors for quantifying ambient temperature influence on machine performance. This analysis is essential for setting the thermal distribution grid and for future optimization tests.

This study is based on a complete hybrid system emulator test rig developed at the University of Genoa (Savona laboratory) by the Thermochemical Power Group (TPG). The plant is mainly composed of a 100 kW recuperated micro gas turbine coupled with both anodic and cathodic vessels for high temperature fuel cell emulation. The test rig was recently equipped with a real-time model for emulating components not physically present in the laboratory (SOFC block, reformer, anodic circuit, off-gas burner, cathodic blower). This model is used to fully evaluate thermodynamic and electrochemical performance related to solid oxide fuel cell systems. Using a UDP based connection with the test rig control and acquisition software, it generates a real-time hardware-in-the-loop (HIL) facility for hybrid system emulation. Temperature, pressure and air mass flow rate at the recuperator outlet (downstream of the compressor) and rotational speed of the machine are inputs from the plant to the model. The turbine outlet temperature (TOT) calculated by the model is fed into the machine control system and the turbine electric load is moved to match the model TOT values.
In this study various tests were carried out to characterize the interaction between the experimental plant and the real-time model; double step and double ramp tests of current and fuel provided the dynamic response of the system.
The control system proved to be fast, compared to the slow thermal response of the SOFC stack, and also reliable. The hybrid systems operated at 90% of nominal power with electrical efficiency of about 56% based on natural gas LHV.

This paper describes the development and testing of a new algorithm to identify faulty sensors, based on a statistical model using quantitative statistical process history. Two different mathematical models were used and the results were analyzed to highlight the impact of model approximation and random error. Furthermore, a case study was developed based on a real micro gas turbine facility, located at the University of Genoa. The diagnostic sensor algorithm aims at early detection of measurement errors such as drift, bias, and accuracy degradation (increase of noise). The process description is assured by a database containing the measurements selected under steady state condition and without faults during the operating life of the plant. Using an invertible statistical model and a combinatorial approach, the algorithm is able to identify sensor fault. This algorithm could be applied to plants in which historical data are available and quasi steady state conditions are common (e.g. Nuclear, Coal Fired, Combined Cycle).

In this paper, the impact of not controllable renewable energy generators (wind turbines or solar photovoltaic panels) on the thermo-economic optimum performance of poly-generation smart grids is investigated using an original time dependent hierarchical approach.
The grid used for the analysis is the one installed at the University of Genoa for research activities. It is based on different prime movers: (i) 100 kWe micro gas turbine, (ii) 20 kWe internal combustion engine powered by gases to produce both electrical and thermal (hot water) energy and (iii) a 100 kWth adsorption chiller to produce cooling (cold water) energy. The grid includes thermal storage tanks to manage the thermal demand load during the year and appropriate systems to model any kind of thermal and electrical load profiles. The system is also equipped with two renewable non-controllable generators: a small size wind turbine and photovoltaic solar panels.
The system optimization (size and management) including the renewable generators has been carried out using a time-dependent thermo-economic hierarchical approach developed by the authors, considering the time-dependent electrical, thermal and cooling load demands during the year as constraints, in order to minimize both grid capital and variable costs.
The results are presented and discussed in depth and show the strong interaction between fossil and renewable resources, and the importance of an appropriate storage system to optimize the RES impact taking into account the multiproduct character of the grid under investigation.

In this paper, the techniques of Data Reconciliation and Gross Error Detection have been applied to a MGT/HTFC (Micro Gas Turbine / High Temperature Fuel Cell) hybrid system emulator test rig installed and operated by N.E.T.L. (National Energy Technology Laboratory), West Virginia (USA). The plant includes two counter-flow heat exchangers working in parallel: theoretically, they should work in the same way, that is same mass flow rates and same temperature differences between hot and cold side; from various tests carried out on the plant, non-symmetrical operation has been often highlighted by measurements. The hardware redundancy of measurements and equations allowed the data reconciliation and gross error detection techniques to be employed. Gross Error Detection has been applied to identify the presence of some possible systematic gross errors in the data: no gross error has been found. Data Reconciliation allowed to significantly improve the accuracy of the estimation of the recuperator unbalance, mainly in terms of mass flow rate. The mass flow unbalance has been detected with sufficient level of confidence, and can now be used to better investigate such a phenomenon.

The core of this work is focused on the development of an experimental plant for wide optimization tests on distributed generation systems. The final objective regards the study of optimization techniques based on real-time software to be applied to general distributed generation systems. To demonstrate the software capability the experimental approach will be carried out through a laboratory plant composed of different types of cogeneration machines. This facility, named “Energy aNd Efficiency Research Demonstration District” (E-NERDD), is located inside the TPG’s laboratory at the University of Genoa (Savona site). All design, installation and test activities shown here were carried out in the framework of the European project “Energy-Hub for residential and commercial districts and transport” (E-HUB).
This test rig is composed of four different prime movers operating in combined heat and power mode: a 100 kWe micro gas turbine, a 20 kWe internal combustion engine, a 3 kWe Stirling engine, and a 450 kWe fuel cell/gas turbine hybrid system emulator. This final facility is based on the coupling of a second 100 kWe modified turbine with a fuel cell system emulator composed of a cathodic modular vessel and an anodic circuit (based on a single stage ejector and an anodic vessel). Furthermore, this emulator rig is
coupled with a real-time model for components not actually present in the facility, such as the fuel cell stack.
The sizes of these prime movers were chosen with the aim to cover typical sizes of distributed generators (from few kilowatts to 100 kW) and on the basis of existing technology already available in the laboratory (the 100 kW turbine for the hybrid system emulator). While on the electrical side the facility is based on a
direct connection with the campus grid, a new dual ring based water distribution system, equipped with water storage systems, was developed for heating thermal energy. The facility also includes an absorption chiller able to be coupled to the thermal grid for investigating trigeneration options. Moreover, the rig is equipped with 1.1 kWp photovoltaic panels and 10 kWp thermal solar panels to be integrated in the thermal grid. The second part of this work is focused on experimental tests related to the performance of prime movers. Particular attention is focused on micro gas turbine, internal combustion engine, and hybrid system emulator performance.

This paper investigates hydrogen and methane generation from large hydraulic plant, using an original multilevel thermo-economic optimization approach developed by the authors.
Hydrogen is produced by water electrolysis employing time-dependent hydraulic energy related to the water which is not normally used by the plant, known as “spilled water electricity”. Both the demand for spilled energy and the electrical grid load vary widely by time of year, therefore a time-dependent hour-by-hour one complete year analysis was carried out, in order to define the optimal plant size. This time period analysis is necessary to take into account spilled energy and electrical load profiles variability during the year.
The hydrogen generation plant is based on 1 MWe water electrolysers fuelled with the “spilled water electricity”, when available; in the remaining periods, in order to assure a regular H2 production, the energy is taken from the electrical grid, at higher cost. To perform the production plant size optimization, two hierarchical levels have been considered over a one year time period, in order to minimize capital and variable costs.
After the optimization of the hydrogen production plant size, a further analysis is carried out, with a view to converting the produced H2 into methane in a chemical reactor, starting from H2 and CO2 which is obtained with CCS plants and/or carried by ships. For this plant, the optimal electrolysers and chemical reactors system size is defined.
For both of the two solutions, thermo-economic optimization results are discussed and compared with particular emphasis to energy scenario, economic aspects, system size, capital costs and related investments. It is worth noting that the results reported here for this particular large H2 plant case represents a general methodology, since it can vary according to their different sizes, primary renewable energy, plant location, and different H2 utilization.

This entry deals with ocean waves as an energy source. Under the action of winds blowing over the ocean surface, energy content is transferred and carried by ocean waves up to the shoreline all over the world. Different types of devices are under development to conveniently convert this energy potential into electrical power. The opportunity of exploiting ocean waves as an energy source is presented here, and the economic and environmental impacts of different technical solutions are considered.

A newly developed integrated gasification fuel cell (IGFC) hybrid system concept has been tested using the Hybrid Performance (Hyper) project hardware-based simulation facility at the U.S. Department of Energy, National Energy Technology Laboratory. The cathode-loop hardware facility, previously connected to the real-time fuel cell model, was integrated with a real-time model of a gasifier of solid (biomass and fossil) fuel. The fuel cells are operated at the compressor delivery pressure, and they are fueled by an updraft atmospheric gasifier, through the syngas conditioning train for tar removal and syngas compression. The system was brought to steady state; then several perturbations in open loop (variable speed) and closed loop (constant speed) were performed in order to characterize the IGFC behavior. Coupled experiments and computations have shown the feasibility of relatively fast control of the plant as well as a possible mitigation strategy to reduce the thermal stress on the fuel cells as a consequence of load variation and change in gasifier operating conditions. Results also provided an insight into the different features of variable versus constant speed operation of the gas turbine section.

Energy provision is the biggest issue to face for the world’s economy at any latitude. Nowadays the energy demand of developing countries as well as that one of developed economies is huge and increasing at an unbearable pace. Considering the limited stocks of such an energy source, and the drawbacks related to the emissions associated to its utilization, the problem to find alternative energy sources and suitable conversion technologies must be solved in order to guarantee the growth and preserve the planet environment.
Among renewable energies sources, Ocean waves power, around the coasts worldwide, has been estimated to be in the order of 8,000-80,000TWh/y. The conversion of this resource into sustainable electrical power represents a major opportunity to nations endowed with such a kind of resource.
At the present time most technological innovations aimed at exploiting such resource are at early stage of development, with only a handful of devices close to be at the commercial demonstration stage. Very few of them, though, operates converting the wave energy contents at its very origin: the orbital motion of water particles right below the ocean surface.
The Seaspoon device catches the kinetic energy of ocean waves with promising efficiency conversion performance, according to specific “wave-motion climate”.
The performance of the device has been assessed through numerical model simulation performed in MATLAB environment. Defined an optimal geometry of the device for given wave parameters (H,T), a scale model will be tested with regular waves in a wave flume at the Department of Mechanical Engineering (DIME) of the University of Genova.

This work aims at the setup of an experimental district for distributed smart polygeneration. The district is controlled and its behaviour is optimized by a software tool for supply and demand matching of electrical and thermal energy in an urban district. In particular, the tool has been developed for ENERDD, the experimental district that TPG is going to build in Savona, Italy. E-NERDD is an acronym for Energy and Efficiency Research Demonstration District. The district will be used within the project to demonstrate how different software tools and algorithms perform in thermodynamic, economic and environmental terms. The software tool originally developed and implemented in this work, called ENERDD Control System, is targeted on enabling the operation of the hardware, when connected in a district mode. Supply and demand are matched to reach a thermo-economic optimum. An optimization algorithm is organized into two different levels of optimization: a first level that solves a constrained minimization problem in planning power supply for each generator on the basis of day-before forecasting; and a second level that distributes among the different machines the gap between planned and real-time demand. The algorithm developed is demonstrated in three test cases in order to test it in different working conditions.

The aim of this work is the chemical composition emulation of solid oxide fuel cell (SOFC) outlet flow, with the hybrid system emulator rig developed by TPG at the University of Genoa. To emulate this chemical composition studying its effects on a commercial machine, the layout of the test rig facility (T100 machine coupled with a modular vessel) was re-designed and expanded. This plant was equipped with a steam generator system to inject super-heated steam immediately upstream of the machine combustor.
Since it is not possible to re-generate the actual SOFC outlet composition with just steam injection (fuel cell outlet flow has higher percentage value of steam and CO2 than an expander inlet of a standard machine), this new system is essential to operate the test rig at specific chemical composition similitude condition. The objective of this new component is the developing of experimental data related to a commercial machine coupled with a fuel cell. In details, this paper deals with fuel cell outlet composition effects on main gas turbine properties because it is essential to know machine behaviour when it operates
inside a hybrid system (important aspect to prevent risks such as surge).
This new layout of the facility is essential to study the effect of steam rich mass flow rate on machine behaviour. For this reason, several tests at different operative conditions were carried out with the T100 machine operating in both electrical grid-connected and stand-alone modes.

This paper presents the development and testing of a new algorithm to identify and reconstruct faulty sensors, based on a statistical model using quantitative statistical process history. The process description is assured by a database containing the measurements selected under steady state condition and without faults during the operating life of the plant. An initial analysis of the historical data allows the algorithm to choose the most relevant signals to be used, through a variable selection process, optimizing the subsequent diagnostic phase. Multivariate regression models were used to perform a supervised feature selection and different state of the art selection criteria plus a new strategy were implemented and tested on experimental data comparing the different results. A statistical model of the system was then developed using Principal Component Analysis (PCA) and the impact of feature selection was estimated. Finally, a case study was developed based on a real micro gas turbine facility, at the University of Genoa, using historical data. The efficiency of the feature selection algorithm versus the knowledge of the experts in thermodynamics was evaluated.

This paper is focused on the performance of the 1 MW plant designed and developed by Rolls-Royce Fuel Cell Systems Limited. The system consists of a two stage turbogenerator coupled with pressure vessels containing the fuel cell stack, internal reformer, cathode ejector, anode ejector, and off-gas burner. While the overall scheme is relatively simple, due to the limited number of components, the interaction between the components is complex and the system behavior is determined by many parameters. In particular, two important subsystems such as the cathode and the anode recycle loops must be carefully analyzed also considering their interaction with and influence on the turbogenerator performance. The system performance model represents the whole, and each physical component is modeled in detail as a subsystem. The component models have been validated or are under verification. The model provides all the operating parameters in each characteristic point of the plant and a complete distribution of thermodynamics and chemical parameters inside the solid oxide fuel cell (SOFC) stack and reformer. In order to characterize the system behavior, its operating envelope has been calculated taking into account the effect of ambient temperature and pressure, as described in the paper. Given the complexity of the system, various constraints have to be considered in order to obtain a safe operating condition not only for the system as a whole but also for each of its parts. In particular each point calculated has to comply with several constraints such as stack temperature distribution, maximum and minimum temperatures, and high and low pressure spool maximum rotational speeds. The model developed and the results presented in the paper provide important information for the definition of an appropriate control strategy and a first step in the development of a robust and optimized control system.

The Thermochemical Power Group (TPG) of the University of Genoa designed and installed a complete hybrid system emulator test rig equipped with a 100 kW recuperated micro gas turbine, a modular cathodic vessel located between recuperator outlet and combustor inlet, and an anodic recirculation system based on the coupling of a single stage ejector with an anodic vessel. The layout of the system was carefully designed, considering the coupling between a planar SOFC stack and the 100 kW commercial machine installed at TPG laboratory. A particular pressurized hybrid system was studied to define the anodic side properties in terms of mass flow rates, pressures, and temperatures.
In this work, this experimental facility is used to analyze the anodic ejector performance from fluid dynamic and thermal points of view. The attention is mainly focused on the recirculation factor value in steady-state conditions. For this reason, a wide experimental campaign was carried out to measure the behavior of this property in different operative conditions with the objective to avoid carbon deposition in the anodic circuit, in the reformer, and in the fuel cell stack.

This paper presents and discusses the results of a complete thermoeconomic analysis of an integrated power plant for co-production of electricity and hydrogen via pyrolysis and gasification processes fed by various coals and mixture of coal and biomass, applied to an existing large steam power plant (ENEL Brindisi power plant – 660 MWe). Two different technologies for the syngas production section are considered: pyrolysis process and direct pressurized gasification. Moreover, the proximity of a hydrogen production and purification plants to an existing steam power plant favors the inter-exchange of energy streams, mainly in the form of hot water and steam, which reduces the costs of auxiliary equipment.
The high quality of the hydrogen would guarantee its usability for distributed generation and for public transport. The results were obtained using WTEMP thermoeconomic software, developed by the Thermochemical Power Group of the University of Genoa, and this project has been carried out within the framework of the FISR National project ‘‘Integrated systems for hydrogen production and utilization in distributed power generation’’.

La realizzazione di impianti per la produzione di energia da fonti rinnovabili, supportata in Italia da incentivi significativi, gode di un sistema di autorizzazione particolarmente favorevole denominato Autorizzazione Unica. Dal 2003 questo procedimento sostituisce ogni autorizzazione, nulla osta o atto di assenso che in precedenza veniva richiesto per iniziare la costruzione di un impianto.
Il D.Lgs. n. 387/2003, introduttivo della semplificazione, non aveva tuttavia fornito la disciplina attuativa prevista dall’articolo 12, comma 10; in assenza della norma di riferimento molte Regioni hanno provveduto autonomamente creando una situazione fortemente disomogenea sul territorio nazionale.
Finalmente, a distanza di sette anni, è giunto a compimento il decreto ministeriale 10 settembre 2010 contenente le linee guida nazionali per l’Autorizzazione Unica, attese da tutto il settore delle rinnovabili (che comprende fotovoltaico, solare a concentrazione, eolico, biomasse, idroelettrico, geotermia etc.).
Esse regolano tutti i nuovi procedimenti di autorizzazione e le Regioni e gli Enti Locali, cui oggi è affidata l’istruttoria di autorizzazione, hanno dovuto adeguare le disposizioni difformi eventualmente emanate.
Il volume svolge una analisi giuridica della situazione nazionale e regionale, un commentario del provvedimento e una descrizione delle disposizioni applicabili alle singole fonti rinnovabili.
Contenuti:
• Commento alle Linee guida (D.M. 10 settembre 2010) • Coordinamento con le discipline regionali • Coordinamento con il procedimento di VIA • Impatti su fotovoltaico, eolico, biomasse, idroelettrico • Appendice normativa.

In this study the techniques of Data Reconciliation and Gross Error Detection have been applied to a microturbine-based test rig installed at the Thermochemical Power Group (TPG) laboratory of the University of Genoa, Italy. These techniques have been developed in the field of chemical engineering during the past 55 years with the purpose of reducing the effect of random errors and also eliminating systematic gross errors in the data by exploiting the relationships that are known to exist between different variables of a process (e.g. energy and mass balances). Two different applications of Data Reconciliation have been carried out: first the entire test rig was studied, generating a set of measurements affected just by random error; second, only the recuperator was taken into account using real measurements coming from a steady state test performed on the plant. The purpose of the former is to show the capability of Data Reconciliation in the adjustment of the measurements so that they can respect the constraints (balance equations). This application is somehow an “ideal application” of Data Reconciliation. Latter since gross errors are often present in the measurements coming from a real plant, a “real or experimental application” of Data Reconciliation was considered for a subsystem of the plant in which the actual measurements from plant probes were used. The objective was to understand if the measured values of temperature, pressure and mass flow rate at the inlet and outlet of the recuperator were physically compatible and reliable. Measured value affected by gross error was identified, focusing on its effect over all the other measurements during DR calculation.

In this paper hydrogen generation from large size renewable power plants such as the ITAIPU hydraulic plant (14 GW power) in South America is investigated using an original thermo-economic approach developed by the Authors. The choice of Itaipu plant is related to the international agreement between “Parque Technologico de Itaipu” (PTI), Asuncion, Paraguay and “Sistemi Intelligenti Integrati” (SIIT) district based in Genoa, Italy.
In this analysis, only the hydraulic energy related to water which is not normally used by the plant named “spilled water”, and the particular electricity load profile during the different periods of the year (and of the day), are taken into account. In this way, the hydrogen generation does not affect the standard electricity production and consumption in Paraguay and Brazil, and it may be a very useful way to recover the otherwise lost hydraulic energy.
The analysed system consists of the hydrogen generation plant based on classical water electrolysers fed with “spilled water electricity”, the H2 storage system and H2 utilization sections. Since the spilled water power referred to H2 generation is in the “hundreds MW range” the definition of the optimal size of the plant, related capital costs, and optimal management is the key point of the problem. Therefore, different aspects of the problem have been carefully investigated such as: (i) atmospheric vs. pressurized electrolysers utilization; (ii) time dependent available hydraulic energy profile; (iii) time dependent H2 generation and storage plant optimum plant size and management; (iv) H2 consumption profile for different
applications.
The results of a preliminary investigation based on available data at PTI and the use of the original thermo-economic method are presented and discussed. It is worthy to note that the results for this particular H2 application also represent a general value, since the method is applicable for different size, primary energy, location plants, and different utilization of H2.

The aim of this work is the chemical composition emulation of solid oxide fuel cell (SOFC) outlet flow, with the hybrid system emulator rig developed by TPG at the University of Genoa. To emulate this chemical composition studying its effects on a commercial machine, the layout of the test rig facility (T100 machine coupled with a modular vessel) was re-designed and expanded. This plant was equipped with a steam generator system to inject super-heated steam immediately upstream of the machine combustor. Since it is not possible to re-generate the actual SOFC outlet composition with just steam injection, this new system is essential to operate the test rig at specific chemical composition similitude condition.
This new layout of the facility is essential to study the effect of steam rich mass flow rate on machine behaviour. For this reason, several tests at different operative conditions were carried out with the T100 machine operating in both electrical grid-connected and stand-alone modes.

The aim of this study is the development and testing of a control system for solid oxide fuel cell hybrid systems through dynamic simulations. Due to the complexity of these cycles, several parameters,
such as the turbine rotational speed, the temperatures within the fuel cell, the differential pressure between the anodic and the cathodic side and the Steam-To-Carbon Ratio need to be monitored and kept within safe limits. Furthermore, in stand-alone conditions the system response to load variations is required to meet the global plant power demand at any time, supporting global load variations and avoiding dangerous or unstable conditions. The plant component models and their integration were carried out in previous studies. This paper focuses on the control strategy required for managing the net electrical power from the system, avoiding malfunctions or damage. Once the control system was developed and tuned, its performance was evaluated by simulating the transient behave our of the whole hybrid cycle: the results for several operating conditions are presented and discussed.

The Thermochemical Power Group of the University of Genoa built a complete Hybrid System emulator test rig constituted by a 100 kW recuperated micro gas turbine, an anodic circuit (based on the coupling of a single stage ejector with a stainless steel vessel) and a cathodic modular volume (located between the recuperator outlet and combustor inlet).
The system is sized to consider the coupling of the commercial micro turbine, operated at 62 kW load, and a planar Solid Oxide Fuel Cell (SOFC) to reach the overall electrical power output of 450 kW. The emulator test rig has been recently linked with a real-time model of the SOFC block. The model is used to simulate the complete thermodynamic and electrochemical behavior of a high temperature fuel cell based on solid oxide technology. The test rig coupled with the model generates a real-time hardware-in-the-loop (HIL) facility for hybrid systems emulation. The model is constituted by a SOFC module, an anodic circuit with an ejector, a cathodic loop with a blower (for the recirculation) and a turbine module.
Temperature, pressure and air mass flow rate at recuperator outlet (downstream of the compressor) and rotational speed of the machine are inputs from the plant to the model. The turbine outlet temperature (TOT) calculated by the model is fed to the machine control system and the turbine electric load is moved to match the model TOT value. In this work different tests were carried out to characterize the interaction between the experimental plant and the real-time model; double step and double ramp tests of current and fuel characterized the dynamic response of the system. The mGT power control system proved to be fast enough, compared to the slow thermal response of the SOFC stack, and reliable. The hybrid systems was operated at 90% of nominal power with about 56% of electrical efficiency based on natural gas LHV.

Solid oxide fuel cell fuelled by methanol is an attractive option to limit the environmental impact of the marine sector. In this publication, a study on heat-recovery has been made for a 250 kW SOFC atmospheric system fuelled by methanol, to satisfy the auxiliary demand onboard of a commercial vessel. Feasible heat-recovery systems were investigated, taking into account efficiency, costs, and space requirements. The heat-recovery possibilities taken into account are electricity production using an Organic Rankine Cycle (ORC), steam/hot water production, air-conditioning obtained using an Absorption Chiller, and demineralised water recovery. The software WTEMP, developed by the TPG (Thermochemical Power Group) of the University of Genoa, was used for the analysis; models of bottoming cycle, desalination unit, and absorption chiller were developed for this work. The analysis has compared these different solutions to the conventional onboard systems.

During normal operation, compressor is mainly affected by fouling due to air pollution, which causes its performance to degrade over time. The main solutions to reduce compressor fouling are off-line compressor washing, on-line compressor washing, and advanced air filtration systems. Overall, the choice of the best recovery system for each gas turbine in the specific power plant is not trivial. The aim of this study is to provide a guide to identify the best washing or filter devices for a gas turbine (GT) in a specific power plant site, using literature information and GT users data.
Two procedures were conceived in order to have an user-friendly tool. ‘Best cleaning device’ was developed to help a GT user in the choice of the best devices for recovering compressor performance.Gathering information about GT performance and environmental conditions from
real applicatios and literatures, a value of recommendation for each technology is provided.
‘Best cleaning time’ is based on the thermoeconomics theory of ‘best maintenance time’ and it provides the user an estimation about the best time to perform a compressor off-line or on-line washing.
Both procedures have been proved on a few real cases, showing good results and indications to more in-depth development.

The availability of reliable simulation models can reduce the time required for commissioning test rigs as well as preventing components from suffering serious damage during testing. The aim of this study is to set up and validate, against experimental data, a real-time model referring to the Rolls-Royce Fuel Cell System Limited (RRFCS) based on hybrid system concept, composed by SOFCs. The dynamic model of the SOFC “block” has been developed, run in real-time, and successfully validated against experiments.
Initially, the dynamic evolution of the model is considered under constant inputs at steady-state and is compared against experimental data; in the second step, transient analysis is also considered. Step variations of the main air flow, main fuel flow, syngas flow and electrical current were performed.
The model can now be employed to carry out the following: performance analysis, design verification, development of control strategies, on-line analysis and integration with Human Machine Interface.

A newly developed Integrated Gasification Fuel Cell (IGFC) hybrid system concept has been tested using the Hybrid Performance (Hyper) project hardware-based simulation facility at the U.S. Department of Energy, National Energy Technology Laboratory. The cathode-loop hardware facility, previously connected to the real-time fuel cell model, was expanded by the inclusion of a real-time model of a gasifier of solid fuels, in this case biomass fuel. The fuel cell is operated at the compressor delivery pressure, and it is fuelled by an updraft atmospheric gasifier, through the syngas conditioning train for tar removal and syngas compression. The system was brought to steady-state; then, several perturbations in open loop (variable speed) and closed loop (constant speed) were performed in order to characterize the IGFC behavior. Experiments have shown the feasibility of relatively fast control of the plant as well as a possible mitigation strategy to reduce the thermal stress on the fuel cell as a consequence of load variation and change in gasifier operating conditions. Results also provided an insight into the different features of variable vs constant speed operation of the gas turbine section.

Compressor fouling in a Gas Turbine (GT) is an important issue which has to be studied to define compressor performance and GT reliability. Three main aspects have to be taken into account: the type of pollutants that could enter into the compressor, with their possible effects such as blade erosion and/or corrosion; the power and efficiency losses caused by fouling; the economic loss due to increase in fuel consumption and reduction in power output.
Two main solutions can be considered for reducing the fouling effect and restoring compressor performance: compressor washing and the High Efficiency Particulate Air filter (HEPA). The choice of the most effective devices for each power plant is not trivial, because of the great number of parameters to be taken into account. The aim of this study is to provide a guide to identifying and managing the best washing or filter devices for a GT in a specific power plant site, using information from the literature and GT user data from European Turbine Network (ETN) members. Two procedures were designed in order to have a user friendly tool:
“ Best Cleaning Devices” was developed to help GT users in the choice of the best devices for recovering compressor performance.
“Best Cleaning Time” is based on the “Best maintenance time” theory and it provides the user with an estimate about the best time to perform compressor off-line or on-line washing.
The procedures are explained in detail and tested on some real cases.

This work presents the re-engineering of the TRANSAT 1.0 code which was developed to perform offdesign and transient condition analysis of Saturators and Direct Contact Heat Exchangers. This model, now available in the 2.0 release, was originally implemented in FORTRAN language, has been updated to
C language, fully coded into MATLAB/Simulink environment and validated using the extensive set of data available from the MOSAT project, carried out by the Thermochemical Power Group of the University of Genoa. The rig consists of a fully instrumented modular vertical saturator, which is controlled and monitored with a LABVIEW computer interface. The simulation software showed fair stability in computation and in response to step variation of the main parameters driving the thermodynamic evolution of the air and water flows. Overall the model proved to be reliable and accurate for energy systems simulations.

In this paper a thermoeconomic analysis and optimization of micro gas turbines (MGT) up to 500 kWe is
presented. This analysis is strongly related to the need of minimizing specific capital cost, still high for MGT large market penetration, and optimizing MGT size to match market needs.
The analysis was carried out for both existing regenerative MGT cycles and new inter-cooled regenerative
cycles, using the Web-based ThermoEconomic Modular Program by the University of Genoa. The attention is mainly focused on the basis of thermodynamic, geometric and capital cost parameters of the main MGT devices (such as recuperator size, material and effectiveness, turbine inlet temperature, and compressor pressure ratio) and on economic scenario (fuel cost, cost of electricity, etc.) for different MGT size in the range 25–500 kWe.

The aim of this work is the experimental analysis of steady-state and transient behavior of a primary surface recuperator installed in a 100 kW commercial microgas Turbine (mGT). The machine is integrated in an innovative test rig for high temperature fuel cell hybrid system emulation. It was designed and installed by the Thermochemical Power Group (TPG), at the University of Genoa, within the framework
of the Felicitas and LARGE-SOFC European Integrated Projects. The high flexibility of the rig was exploited to perform tests on the recuperator operating in the standard cycle. Attention is mainly focused on its performance in transient conditions (start-up operations and load rejection tests). Start-up tests were
carried out in both electrical grid-connected and stand-alone conditions, operating with different control
strategies. Attention is focused on system response due to control strategy and on boundary temperature
variation because of its influence on component life consumption.

A hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC) has been implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL) in Morgantown, West Virginia, U.S.A. The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transients. It is possible to model, test and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide means of quantifying risk mitigation strategies.
Previous implementation of facility emergency shutdown in response to certain failures has resulted in hardware failure of both the turbomachinery and the simulated fuel cell.
An analysis of system performance was completed to evaluate failure modes leading to the destruction of equipment. The primary linking event in these cases was compressor stall and surge resulting from the sudden loss of fuel during implementation of the double block and bleed strategy used in emergency shutdown. A new mitigation strategy involving automated ramps was developed for controlled emergency shutdown. The implementation of this strategy is described in detail, and the efficacy is analytically compared with the results of previous failures.

This work is based on a complete hybrid system emulator test rig developed at the University of Genoa (Savona laboratory) by the Thermochemical Power Group (TPG). The plant is mainly composed of a 100 kW recuperated micro gas turbine coupled with both anodic and a cathodic vessels for high temperature fuel cell emulation. The test rig was recently equipped with a realtime model to emulate components not physically present in the laboratory (SOFC block, reformer, anodic circuit, off-gas burner, cathodic blower). This model is used to completely evaluate thermodynamic and electrochemical performance related to solid oxide fuel cell systems. It generates (through a UDP based connection with the test rig control and acquisition software) a real-time hardware-in-the-loop (HIL) facility for hybrid system emulation. Temperature, pressure and air mass flow rate at
recuperator outlet (downstream of the compressor) and rotational speed of the machine are inputs from the plant to the model. The turbine outlet temperature (TOT) calculated by the model is fed to the machine control system and the turbine electric load is moved to match the model TOT values.
In this work different tests were carried out to characterize the interaction between the experimental
plant and the real-time model; double step and double ramp tests of current and fuel provided the dynamic
response of the system. The control system proved to be fast, compared to the slow thermal response of the SOFC stack, and reliable. The hybrid systems operated at 90% of nominal power with about 56% of electrical efficiency based on natural gas LHV.

Since the model plays an important role in diagnosing solid oxide fuel cell (SOFC) system, this paper proposes a review of existing SOFC models for model-based diagnosis of SOFC stack and system. Three categories of modelling based on the white-, the black- and the grey-box approaches are introduced. The white-box model includes two types, i.e. physical model and equivalent circuit model based on EIS technique. The black-box model is based on artificial intelligence and its realisation relies mainly on experimental data. The greybox model is more flexible: it is a physical representation but with some parts being modelled empirically. Validation of models is discussed and a hierarchical modelling approach involving all of three modelling methods is briefly mentioned, which gives an overview of the design for implementing a generic diagnostic tool on SOFC system.

The aim of this work is the experimental analysis of a primary-surface recuperator operating in a 100 kW micro gas turbine, as in a standard recuperated cycle. These tests,performed in both steady-state and transient conditions, havebeen carried out using the micro gas turbine test rig developed by TPG at the University of Genoa, Italy. Even if this facility has mainly been designed for hybrid system emulations, it is
possible to exploit the plant for component tests, such as experimental studies on recuperators. The valves installed in the rig make it possible to operate the plant in the standard recuperated configuration, and the facility has been equipped with new probes essential for this kind of tests.
A wide-ranging analysis of the recuperator performance has been carried out with the machine operating in stand-alone configuration, or connected to the electrical grid, to test different control strategy influences. Particular attention has been given to tests performed at different electrical load values and with different mass flow rates through the recuperator ducts.
The final section of this paper reports the transient analysis carried out on this recuperator. The attention is mainly focused on thermal transient performance of the component, showing the effects of both temperature and flow steps.

The Thermochemical Power Group of the University of Genoa, Italy, has developed a new “Gas Turbine” laboratory to introduce undergraduate students to the Gas Turbines and Innovative Cycles course, and Ph.D.s to advanced experimental activities in the same field. In the laboratory a general-purpose experimental rig, based on a modified commercial 100 kW recuperated micro gas turbine, was installed and fully instrumented. One of the main objectives of the laboratory is to provide both students and researchers
with several experimental possibilities to obtain data related to the gas turbine steady-state, transient, and dynamic performance, including the effect of interaction between the turbomachines (especially the compressor), and more complex innovative gas turbine cycle configurations, such as recuperated, humid
air, and hybrid (with high temperature fuel cells). The facility was partially funded by two Integrated Projects of the EU VI Framework Program (Felicitas and LARGE-SOFC) and the Italian Government (PRIN project), and it was designed with a high flexibility approach including: flow control management, cogenerative and trigenerative applications, downstream compressor volume variation, grid-connected or stand-alone operations, recuperated or simple cycles, and room temperature control. The paper also shows, as an example of the possibilities offered by the rig, experimental data obtained by both Master and Ph.D. students. The tests presented here are essential for understanding commercial gas turbines and microturbine performance, control strategy development, and theoretical model validation.

The University of Genoa (TPG) has designed and developed an innovative test rig for high temperature fuel cell hybrid system physical emulation. It is based on the coupling of a modified commercial 100 kW recuperated micro gas turbine to a special modular volume designed for the experimental analysis of the interaction between different dimension fuel cell stacks and turbomachines. This new experimental approach that generates reliable results as a complete test rig also allows investigation of high risk situations with more flexibility without serious and expensive consequences to the equipment and at a very low cost compared with real hybrid configurations. The rig, developed with the support of the European Integrated Project “FELICITAS,” is under exploitation and improvement in the framework of the new European Integrated Project “LARGE-SOFC” started in January 2007. The layout of the system (connecting pipes, valves, and instrumentation) was carefully designed to minimize the pressure loss between compressor
outlet and turbine inlet to have the highest plant flexibility. Furthermore, the servocontrolled valves are useful for performing tests at different operative conditions (i.e., pressures, temperatures, and pressure losses), focusing the attention on surge and thermal stress prevention. This work shows the preliminary data obtained with the machine connected to the volume for the test rig safe management to avoid surge or excessive stress, especially during the critical operative phases (i.e., start-up and shutdown). Finally, the
attention is focused on the valve control system developed to emulate the start-up and shutdown phases for high temperature fuel cell hybrid systems. It is necessary to manage the flows in the connecting pipes, including an apt recuperator bypass, to perform a gradual heating up and cooling down as requested during these phases. It is an essential requirement to avoid thermal stress for the fuel cell stack. For this reason, during the start-up, the volume is gradually heated by the compressor outlet flow followed by a well managed recuperator outlet flow and vice versa for the shutdown. Furthermore, operating with a constant rotational speed control system, the machine load is used to reach higher temperature values typical of these kinds of systems.

This paper presents a research project carried out by TPG (Thermochemical Power Group) of University of Genoa to develop innovative monitoring and diagnostics procedures and software tools for software-aided maintenance and customer support. This work is concerned with preliminary outcomes regarding the thermo-economic monitoring of the bottoming cycle of a combined cycle power plant, using real historical data. The software is able to calculate functional exergy flows (y), their related costs (c) (using the plant functional diagram); after that non-dimensional parameters for the characteristic exergonomic indexes (?c, ?c*, ?k*) are determined.
Through a plant optimization (not described here) the reference conditions of the plant at each operating condition can be determined. Then, Non Dimensional Indexes related to each thermoeconomic parameter are defined, in order to depict a “cost degradation”, and thus a significant rise in the production cost of the main products of the Bottoming Cycle (steam and power).
The methodology developed has been successfully applied to historical logged data of an existing 400 MW power plant, showing the capabilities in estimating the “cost degradation” of the elements of the BC over the plant life, and trends in the thermoeconomic indexes.

In the humid air turbine cycle (HAT) cycle, the humidification of compressed air can be provided by a pressurised saturator (i.e.: humidification tower or saturation tower), this solution being known to offer several attractive features. This work is focused on an experimental study of a pressurised humidification tower, with structured packing. After a description of the test rig employed to carry out the measuring campaign, the results relating to the thermodynamic process are presented and discussed. The experimental campaign was carried out over 162 working points, covering a relatively wide range of possible operating conditions.
It is shown that the saturator behaviour, in terms of air outlet humidity and temperature, is primarily driven by, in decreasing order of relevance, the inlet water temperature, the inlet water over inlet dry air mass flow ratio and the inlet air temperature.
The exit relative humidity is consistently over 100%, which may be explained partially by measurement accuracy and droplet entrainment, and partially by the non-ideal behaviour of air-steam mixtures close to saturation.
Experimental results have been successfully correlated using a set of new non-dimensional groups: such a correlation is able to capture the air outlet temperature with a standard deviation sigma=2.8K.

High temperature fuel cells (MCFCs and SOFCs) can operate at atmospheric or pressurised conditions. In both cases, system performance can be significantly improved when the fuel cells are integrated with proper devices, which are designed to provide the necessary air inlet conditions and to recover the exhaust-gas energy.
This paper presents a review of modelling and design issues for the integration of turbomachinery with the fuel cell system, because turbomachinery is the most promising technology for coping with the high temperature fuel cell requirements. Since the gas turbine expander performance is significantly influenced by exhausts compositions, analytical approach is undertaken for properly modelling composition influence on expander performance, and results are presented to demonstrate the quantitative influence of the system parameters on the performance. The analysis covers the three main aspects of performance evaluation: the on-design, the off-design and, as a final mention, the control of the fuel cell hybrid systems.

Fuel cells own the potential for significant environmental improvements both in terms of air quality and climate protection. Through the use of renewable primary energies, local pollutant and greenhouse gas emissions can be significantly minimized over the full life cycle of the electricity generation process, so that marine industry accounts renewable energy as its future energy source. The aim of this paper is to evaluate the use of methanol in Solid Oxide Fuel Cells (SOFC), as auxiliary power systems for commercial vessels, through Life Cycle Assessment (LCA). The LCA methodology allows the assessment of the potential environmental impact along the whole life cycle of the process. The unit considered is a 20 kWel fuel cell system. In a first part of the study different fuel options have been compared (methanol, biomethanol, natural gas, hydrogen from cracking, electrolysis and reforming), then the operation of the cell fed with methanol has been compared with the traditional auxiliary power system, i.e. a diesel engine.
The environmental benefits of the use of fuel cells have been assessed considering different impact categories. The results of the analysis show that fuel production phase has a strong influence on the life cycle impacts and highlight that feeding with bio-methanol represents a highly attractive solution from a life
cycle point of view. The comparison with the conventional auxiliary power system shows extremely lower impacts for SOFCs.

In this paper the dynamic performance of a 1 MW hybrid system based on Molten Carbonate Fuel Cells technology is presented and carefully discussed. The cells are based on Ansaldo Fuel Cell Co. technology developed for external reforming and pressurised operation (up to 4-6 bars); the hybrid system is based on the coupling between the MCFC stack and micro gas turbine Turbec, the operation is analysed using both
natural gas and renewable gases such as hydrogen and other syngas. The hybrid system is modelled both from steady state (design and off-design) and from transient points of view. The problems of the integration between the micro gas turbine and the fuel cell stack fed with high hydrogen content syngas have been investigated. A suitable control system has been suggested for the startup phase and for the thermal management of the stack. The results are presented and discussed in depth.

The objective of this paper is to show the transient behaviour of a dynamic model representing a syngas generator processing pipeline natural gas for SOFC systems.
The plant was designed by Rolls-Royce Fuel Cell Systems (RRFCS), while the plant transient model was developed and tested by the Thermochemical Power Group (TPG) of the University of Genoa, using the in-house tool TRANSEO working in the Matlab/Simulink environment. The model represents a fuel processing unit from RRFCS, designed to feed an off-gas burner, part of a 250kWe fuel cell hybrid system, with a syngas stream undergoing precise requirements about composition, pressure and temperature.
This paper presents a simplified plant layout of the real system, however, in the model, physical properties of the real materials and geometry of components have been used; where no data were available, reasonable assumptions have been done.
The transient model has been validated against experimental data retrieved from two different duration tests including warm-up, part and full load operation and cool-down phases.
During the validation process both gas and wall temperatures have been considered and the transient model is shown to accurately simulate the plant thermal behaviour both at steady-state and transient conditions. The model is being further developed for control system applications.

The TPG research group of the University of Genoa designed and installed a complete hybrid system emulator test rig equipped with a 100 kW recuperated micro gas turbine, a modular cathodic vessel located between recuperator outlet and combustor inlet, and an anodic circuit based on the coupling of a single stage ejector with an anodic vessel. The layout of the system was carefully designed considering the coupling between a planar SOFC stack and the 100 kW commercial machine installed at TPG laboratory. A 450 kW direct-fired pressurized hybrid system was studied to define the anodic side properties in terms of mass flow rates, pressures, and temperatures. In this work, this experimental facility is used to analyze the cathodic/anodic side interaction from fluid dynamic and thermal point of view. Even if the tests carried out with this rig were produced with an ejector based anodic recirculation, results shown here for the cathode/anode interaction tests can be considered general not dependent on recirculation technology.
Attention is mainly focused on the cathode/anode differential pressure value in both design and off-design conditions. For this reason, a wide experimental campaign was carried out to measure the behavior of this property in different operative conditions with the objective to avoid pressure stress for the fuel cell stack. Furthermore, the interaction between the machine and the anodic circuit is studied and discussed in this
work.

High temperature fuel cells (MCFCs and SOFCs) can operate at atmospheric or pressurised conditions. In both cases, system performance can be significantly improved when the fuel cells are integrated with proper devices, which are designed to provide the necessary air inlet conditions and to recover the exhaust-gas energy.
This review reports about modelling and design issues in the integration of turbomachinery with the fuel cell system, since turbomachinery is the most promising technology for coping with the high temperature fuel cell requirements.
Analytical approach for properly modelling composition influence on expander performance is outlined. The analysis covers two main aspects of performance evaluation: the on-design and the off-design of fuel cell hybrid systems.

Keywords: high temperature fuel cell, gas turbine fuel cell hybrid system, similitude theory, radial turbomachinery

This work presents the re-engineering of the TRANSAT 1.0 code which was developed to perform off-design and transient condition analysis of Saturators and Direct Contact Heat Exchangers. This model, now available in the 2.0 release, was originally implemented in FORTRAN language, has been updated to C language, fully coded into MATLAB/Simulink® environment and validated using the extensive set of data available from the MOSAT project, carried out by the Thermochemical Power Group of the University of Genoa. The rig consists of a fully instrumented modular vertical saturator, which is controlled and monitored with a LABVIEW® computer interface. The simulation software showed fair stability in computation and in response to step variation of the main parameters driving the thermodynamic evolution of the air and water flows. Considering the actual mass flow rates, a geometric similitude was used to avoid calculation instability due to flows under 100 g/s. Overall the model proved to be reliable and accurate enough for energy system simulations.

The aim of this work is the experimental analysis of steady-state and transient behavior of a primary surface recuperator installed in a 100 kW commercial micro gas turbine. The machine is integrated in an innovative test rig for high temperature fuel cell hybrid system emulation. It was designed and installed by the Thermochemical Power Group (TPG), at the University of Genoa, within the framework of the Felicitas and LARGE-SOFC European Integrated Projects. The high flexibility of the rig was exploited to perform tests on the recuperator operating in the standard cycle. Attention is mainly focused on its performance in transient conditions (start-up operations and load rejection tests). Start-up tests were carried out in both electrical grid-connected and stand-alone conditions, operating with different control strategies. Attention is focused on system response due to control strategy and on boundary temperature variation because of its influence on component life consumption.
Further tests were carried out using the valves installed on the test rig to bypass the air side of the unit. Different operative conditions were analyzed to show the effect of different mass flow rates on recuperator behavior. Attention is mainly focused on recuperator performance when it operates in unbalanced flow rate conditions (i.e. different mass flow rate values in recuperator sides), as well as during advanced cycle start-up and shutdown operations.

The main aim of this paper is the thermoeconomic analysis of micro gas turbines in the range 25-500 kWe.
This thermoeconomic analysis is based on the Thermoeconomic Functional Analysis (TFA) approach developed by the Authors over the last twenty years and is strongly related to the need for minimizing of the specific capital cost which is still considered high, and for optimizing MGT size to match customers’ needs.
The investigation has been carried out using WTEMP code (Web-based ThermoEconomic Modular Program), developed by the Thermochemical Power Group of the University of Genoa [1][2][3]. The thermoeconomic analysis was performed on the basis of the thermodynamic, geometric and capital cost
parameters of the main MGT devices (i.e. recuperator effectiveness, turbine inlet temperature, compressor pressure ratio, etc.) and on the economic scenario (fuel costs, cost of electricity, etc.).
The subjects of the analysis were the existing Regenerative MGT (R-MGT) cycles [4][5] and new Inter-cooled Regenerative (ICR-MGT) cycles; for the sake of simplicity in this study, the economic value of heat in the case with CHP configuration was not considered.

In the distributed power generation market, Solid Oxide Fuel Cell–Gas Turbine (SOFC–GT) hybrids are an attractive option. Prototypes are being tested around the world with different types of fuel, but mainly natural gas. In this publication, a study of SOFC–GT hybrids for operation with liquid fuels is presented. Two liquid fuels were investigated, methanol and kerosene, in four layouts, taking into account different fuel processing strategies. A 500 kW class hybrid system (HS) was analysed. Web-based ThermoEconomic Modular Program (WTEMP) software, developed by the Thermochemical Power Group of the University of Genoa, was used for the thermodynamic and investment analysis. Performance was calculated based on zero-dimensional component models. The economic assessment was performed with a through-life cost analysis approach. The cost of the conventional components was calculated with WTEMP cost equations. As a final result, methanol-fuelled HSs are shown to stand out for both their thermodynamic and economic performance.

Considering the increased interest on the reduction of pollutant emissions, ENEL Produzione is pursuing the integration of an innovative hydrogen-fed gas turbine cycle into the existing coal-fired power station in Fusina (VE). The University of Genoa is collaborating on this project with ENEL regarding the study of the gas turbine blade cooling. This part presents the model used for simulations and comparison against experimental data.

Considering the increased interest on the reduction of pollutant emissions, ENEL Produzione is pursuing the integration of an innovative hydrogen-fed gas turbine cycle into the existing coal-fired power station in Fusina (VE). The University of Genoa is collaborating on this project with ENEL regarding the study of the gas turbine blade cooling. This part presents the assessment of the different impact that methane and hydrogen combustion has on blade cooling.

In the framework of the LARGE-SOFC European Integrated Project, an SOFC anodic circuit emulator has been designed to study the interaction between anodic and cathodic sides of the fuel cell stack. This new experimental facility has been designed to be coupled with the cathodic side emulator developed by TPG at the University of Genoa, Italy. This activity has been carried out in order to built a complete hybrid system emulator equipped with a 100 kW recuperated micro gas turbine, a cathodic vessel located between recuperator outlet and combustor inlet, and an anodic circuit based on the coupling of a single stage ejector with an anodic volume.
In order to design the anodic circuit test rig, a system analysis has been carried out considering the coupling between a planar SOFC stack and the 100 kW commercial microturbine installed at TPG laboratory. A new hybrid system has been studied and the anodic side properties have been defined in terms of fuel mass flow rate, recirculated mass flow rate, pressures, and temperatures. Starting from these calculations the ejector geometry has been designed and the anodic side volume has been defined.
A CFD analysis has been carried out to design the pipes necessary for the connection between the ejector and the anodic volume, and for the anodic side outlet. Particular attention has been devoted to the heat exchanger designed to emulate the anodic flow heating inside the stack. In fact, two original tubolar heat exchangers have been designed to be introduced inside the cathodic volume, in order to exploit the cathodic heat for the anodic side too.

Real-time (RT) modeling is a recognized approach to monitor advanced systems and to improve control capabilities. Applications of RT models are commonly used in the automotive and aerospace fields. Starting from existing components and models developed in TRANSEO, a new approach, called the multipurpose RT approach, is developed for the solid oxide fuel cell hybrid system application. Original C-based models have been reprogrammed into embedded MATLAB functions for direct use within MATLAB-SIMULINK.
Also, models in TRANSEO have been simplified to improve execution time. Using MATLAB?s Real-Time Workshop application, the system model is able to be translated into an autogenerated C-code, and run as an application specific RT executable.

The interest in solid oxide fuel cell systems comes from their capability of converting the chemical energy of traditional fuels into electricity, with high efficiency and low pollutant emissions. In this paper, a study of the design space of solid oxide fuel cell and gas turbine hybrids fed by methanol and kerosene is presented for stationary power generation in isolated areas (or transportation). A 500 kW class hybrid system was analysed using WTEMP original software developed by the Thermochemical Power Group of the University of Genoa. The choice of fuel-processing strategy and the influence of the main design parameters on the thermoeconomic characteristics of hybrid systems were investigated. The low capital and fuel cost of methanol systems make them the most attractive solutions among those investigated here.

In this work the thermoeconomic features of two different combined cycles using air ?open loop? and steam ?closed loop? cooled gas turbines are presented and compared in depth. In order to properly estimate both thermodynamic and thermoeconomic performance of the different combined cycles an analytical model of the blade cooling system has been developed in details and outlined in the paper. Internal Thermoeconomic functional analysis is not performed here, as only economic results are shown and discussed. The blade cooling detailed model, originally developed by TPG researchers, has been integrated into the web based modular code WTEMP, already validated for GT based cycles, developed in the last ten years by TPG. It is shown that the closed loop blade cooling configuration has the greatest potential in terms of thermodynamic efficiency and economic competitivity in the mid-term.

Received 11 August 2008;
revised 27 January 2009;
accepted 27 January 2009.
Available online 19 March 2009.

A new high temperature fuel cell-micro gas turbine physical emulator has been designed and installed in the framework of the European Integrated Project FELICITAS at the Thermochemical Power Group (TPG) laboratory located at Savona. The test rig is based on a commercial 100 kWe recuperated micro gas turbine (mGT) (Turbec T100 modified to be connected to a modular volume designed for physical emulation of fuel cell stack influence. The test rig has been developed starting with a complete theoretical analysis of the micro gas turbine design and off-design performance and with the definition of the more flexible layout to be used for different hybrid system(molten carbonate fuel cell or solid oxide fuel cell) emulation. The layout of the system (connecting pipes, valves, and instrumentation, in particular mass flow meter locations) has been carefully designed, and is presented in detail in this paper. Particular attention has been focused on the viscous pressure loss minimization: (i) to reduce the unbalance between compressor and expander, (ii) to maintain a high measurement precision, and (iii) to have an effective plant flexibility. Moreover, the volume used to emulate the cell stack has been designed to be strongly modular (different from a similar system developed by U.S. Department Of Energy-National Energy Technology Laboratory) to allow different volume size influence on the mGT rig to be easily tested. The modular high temperature volume has been designed using a computational fluid dynamics (CFD) commercial tool(FLUENT). The CFD analysis was used (i) to reach a high level of uniformity in the flow distribution inside the volume, (ii) to have a velocity field (m/s) similar to the one existing inside the emulated cell stack, and (iii) to minimize (as possible) the pressure losses. The volume insulation will also allow to consider a strong thermal capacity effect during the tests. This paper reports the experimental results of several tests carried out on the rig (using the mGT at electrical stand-alone conditions with the machine control system operating at constant rotational speed) at different load values and at both steady-state and transient conditions.

The authors present a study oriented on demonstrating how power plant diagnostics could be used in approaching condition based maintenance of several components of combined cycle power plants. In this paper two different performance parameters are considered: gas turbine performance and condenser performance. Gas turbine performance is evaluated through the correction of compressor pressure ratio and of gas turbine power, while condenser performance is evaluated through the calculation of the so-called terminal temperature difference.
After the description of the methodologies, a business case for both of them is presented, in order to show in terms of money savings the advantages of such analysis.

Abstract: This article presents a research project carried out by the Thermochemical Power Group of the University of Genoa and is concerned with the monitoring of a three pressure level heat recovery steam generator (HRSG).
The work consists of the development of an original computer code usingMatlab software that calculates the performanceof heat exchangers, at differentpower plant operating conditions.This
kind of software was developed with a twofold objective: to calculate the actual gas path inside the HRSG starting from the available measurements, thus obtaining the current effectiveness of
all the heat exchangers in the HRSG, and to estimate the expected performance of each heat exchanger to be compared with the actual ones. Once the actual effectiveness and the expected effectiveness of the heat exchanger are defined, non-dimensional performance parameters suitable for degradation assessment can be defined.
As a result of the sensitivity analysis, each performance parameter is coupled with an accuracy factor. The developed methodology has been successfully applied to historical logged data (3
years) of an existing large size (400MW) combined cycle, showing good capabilities in estimating the degradation of the HRSG throughout plant life.

Keywords: monitoring, combined cycle, heat exchangers, non-dimensional indexes, error propagation

This work reports about the latest application of a generic time-dependent real-time simulation tool, originally developed for fuel cell gas turbine hybrid systems, and now applied to an actual micro gas turbine test rig.
The real-time modeling is a recognized approach to monitor advanced systems and to improve control capabilities: applications of real-time models are commonly used in the automotive and aircraft fields. The overall objective is the improvement of calculation time of existing time-dependent simulation models, retaining acceptable accuracy of the results.
The real-time modeling approach already applied to fuel cell gas turbine system has been here validated against the experimental data of the micro gas turbine Turbec T100 test rig in Savona, Italy. The real-time model of the microturbine recuperator has been newly developed to fit such an application. Two representative transient operations have been selected for verification: the heating and cooling phases of the connected volume. Results show already an acceptable agreement with measurements, and they?ve contributed to a better insight in performance prediction of the entire plant.

This paper presents and discusses the results of a complete thermoeconomic analysis of an integrated power plant for co-production of electricity and hydrogen via pyrolysis and gasification processes, applied to an existing large steam power plant (ENEL Brindisi power plant-660 MWe).
The two considered technologies produce syngas with different characteristics in terms of temperature, pressure and composition, and this has a significant effect on the layouts of the complete systems proposed in the paper. Moreover, the proximity of a hydrogen production and purification plants to an existing steam power plant favour the inter-exchange of energy streams, mainly in the form of hot water and steam, which reduces the costs of auxiliary equipment.
Various coals (Ashland, South African and Sardinian Sulcis coal) and mixtures of South African coal and biomass (Poplar) are considered in this study, in order to explore the real potential of mixed fuels in terms of impact on plant economics and reducing CO2 emissions. Furthermore, the high quality of the hydrogen, produced through a Pressure Swing Adsorption unit or a dense Membrane unit, allows it to be used for distributed generation (e.g. by microturbine, Stirling engine, etc.) as well as public transport (using PEM fuel cells).
The results were obtained using WTEMP thermoeconomic software, developed by the TPG (Thermochemical Power Group) of the University of Genoa, and this project has been carried out within the framework of the FISR National project ?Integrated systems for hydrogen production and utilization in distributed power generation?.

This paper investigates options for highly efficient SOFC hybrid systems of different sizes. For this purpose different models of pressurised SOFC hybrids systems have been developed in the framework of the European Project ?LARGE SOFC – Towards a Large SOFC Power Plant. This project, coordinated by VTT Finland, counts numerous industrial partners such as Wartsila, Topsoe and Rolls-Royce FCS ltd.
Starting from the RRFCS Hybrid System [1], considered as the reference case, several plant modifications have been investigated in order to improve the thermodynamic efficiency. The main options considered are (i) the integration of a recuperated micro gas turbine and (ii) the replacement of the cathodic ejector with a blower.
The plant layouts are analysed in order to define the optimum solution in terms of operating parameters and thermodynamic performances.
The study of a large size power plant (around 110 MWe) fed by coal and incorporated with SOFC hybrid systems is also conducted. The aim of this study is to analyse the sustainability of an Integrated Gasification Hybrid System from the thermodynamic and economic point of view in the frame of future large sized power generation.
A complete thermoeconomic analysis of the most promising plants is carried out, taking into account variable and capital costs of the systems. The designed systems are compared from the thermodynamic and the thermoeconomic point of view with some of the common technologies used for distributed generation
(gas turbines and reciprocating engines) and large size power generation (combined cycles and IGCC).
The tool used for this analysis is WTEMP software, developed by the University of Genoa (DIMSET-TPG), able to carry out a detailed thermodynamic and thermoeconomic analysis of the whole plants.

This research is focused on the monitoring and diagnostic of the bottoming cycle (BC) of a large size combined cycle, composed by a three pressure level HRSG (Heat Recovery Steam Generator), a three expansion level steam turbine and auxiliary pumps. An original Matlab software was developed, which is composed by two parts: the first calculates HRSG performance, while the second is focused on the calculation of the steam turbines performance, at different power plant operating conditions.
In the first part a complete HRSG performance analysis is carried out: it consists of the calculation of each heat exchanger performance and health. The direct result of this analysis is the definition of Non Dimensional Performance Indexes (NDPI) for each heat exchanger, which define the instant degradation of each component, through the comparison between the ?actual? and the ?expected? effectiveness.
The second part calculates steam turbines performance. Two NDPIs are defined: one referred to the high pressure steam turbine and the other referred to the middle-low pressure steam turbine. The performance indexes are calculated comparing the actual expansion efficiency with the expected one. The NDPI previously defined will be used to monitor plant degradation, to support plant maintenance, and to assist on-line troubleshooting. Each performance parameter is coupled with an accuracy factor, which allows to determine the best parameters to be monitored and to define the related tolerance due to measurement errors.
The methodology developed has been successfully applied to historical logged data (2 years) of an existing large size (400 MW) combined cycle, demonstrating the capabilities in estimating the degradation of the BC performance throughout plant life.

Estimating the performance of all the components of a recuperated micro gas turbine cycle plays a determinant role in improving their reliability for distributed power generation and co-generation. The monitoring and diagnostic activity consists in continuously evaluating the productivity capacity and the efficiency of the plant, using the stream of data coming from the plant?s instrumentation. In this framework a diagnostic tool for the micro gas turbine installed at the TPG test rig (located in Savona, Italy) was developed, with the objective of monitoring the operating parameters of the turbomachine, the performance of the heat exchanger and, in general, the good operation of the plant.
Even though the commercial machine is equipped with the essential probes for control (rotational speed, TOT, intake temperature and eating water temperature meters) and diagnostic purposes (vibration sensor, filter differential pressure and other thermocouples), further instruments were introduced in the test rig to measure a larger number of properties and points. As result of this, a wide number of measurements is available and can be effectively used for the development of a diagnostic model. The diagnostic model presented in this paper is written in Matlab-Simulink? environment and, in its first version, provides information about compressor and turbine efficiency and heat exchanger effectiveness. The model was developed starting from the turbomachinery maps and the heat exchanger design performance. A validation of the code was performed using the measurements coming directly from the data acquisition system. Preliminary results coming from the model are presented, showing the different performance of each component of the plant in the various operating conditions.

The aim of this work is the experimental analysis of a primary-surface recuperator operating in a 100 kW micro gas turbine, as in a standard recuperated cycle. These tests,performed in both steady-state and transient conditions, havebeen carried out using the micro gas turbine test rig developed by TPG at the University of Genoa, Italy. Even if this facility has mainly been designed for hybrid system emulations, it is
possible to exploit the plant for component tests, such as experimental studies on recuperators. The valves installed in the rig make it possible to operate the plant in the standard recuperated configuration, and the facility has been equipped with new probes essential for this kind of tests.
A wide-ranging analysis of the recuperator performance has been carried out with the machine operating in stand-alone configuration, or connected to the electrical grid, to test different control strategy influences. Particular attention has been given to tests performed at different electrical load values and with different mass flow rates through the recuperator ducts.
The final section of this paper reports the transient analysis carried out on this recuperator. The attention is mainly focused on thermal transient performance of the component, showing the effects of both temperature and flow steps.

The Thermochemical Power Group (TPG) of the University of Genoa, Italy, has developed a new Gas Turbine laboratory to introduce undergraduate students to Gas Turbines and Innovative Cycles course, and Ph.D.s to advanced experimental activities in the same field.
In the laboratory a general-purpose experimental rig, based on a modified commercial 100 kW recuperated micro gas turbine, was installed and fully instrumented. One of the main objectives of the laboratory is to provide both students and researchers with several experimental possibilities to obtain data related to the gas turbine steady-state, transient and dynamic performance including the effect of interaction between the turbomachines (especially the compressor) and more complex innovative gas turbine cycle configurations, such as recuperated, humid air, and hybrid (with high temperature fuel cells).
The facility was partially funded by two Integrated Projects of the EU VI Framework Program (Felicitas and Large-SOFC) and the Italian Government (PRIN project) and it was designed with a high flexibility approach including: flow control management, co-generative and tri-generative applications, downstream compressor volume variation, grid-connected or stand-alone operations, recuperated or simple cycles, and roomtemperature control.
The layout of the whole system, including connection pipes, valves, and instrumentation (in particular mass flow meter locations) was carefully designed, for educational purposes, by a group of Ph.D. students using CFD tools (Fluent), and it is presented in detail in this paper. The paper also shows, as an example of the possibilities offered by the rig, experimental data obtained by both Master and Ph.D. students. The tests presented here are essential for understanding commercial microturbine performance, control strategy development, and theoretical model validation.

Il presente articolo presenta i risultati relativi ad uno studio di fattibilita’ per la realizzazione di una cella combustibile ad ossidi solidi a temperatura intermedia IT-SOFC e di una stazione sperimentale integrata per il collaudo e la verifica delle prestazioni delle celle a combustibile.
L?obiettivo dello studio di natura sperimentale e’ stato quello di giungere alla realizzazione di una IT-SOFC di tipo planare ad anodo supportato ed al progetto di dettaglio e alla realizzazione di un prototipo di una stazione sperimentale integrata per il collaudo della cella stessa.
Il lavoro e’ stato suddiviso in quattro fasi:
1. Realizzazione di celle singole planari;
2. Realizzazione di piccoli stack (3, 5 celle);
3. Realizzazione di una stazione di collaudo per il test di celle e stack;
4. Collaudo prototipo di cella/stack e dispositivo di prova.
Il lavoro ha complessivamente ottenuto buoni risultati. Le procedure di preparazione delle celle, pur avendo raggiunto risultati soddisfacenti, possono essere ulteriormente migliorate per migliorare le prestazioni. La realizzazione dello stack dal punto di vista della progettazione ha mostrato da subito un buon grado di praticit? nel montaggio delle celle e dell’applicazione del sigillante. La stazione sperimentale intesa nel senso piu’ ampio ha contribuito fortemente nel semplificare tutte le procedure di start-up, shut-down e di controllo dei parametri di processo e di misura. Mediante tale strumento la gestione delle misure e’ meno soggetta ad errori operativi consentendo di migliorare sia la ripetibilita’ dei test sia le condizioni di sicurezza, che anche su stack di dimensioni di laboratorio ? necessario tenere sotto controllo.

This paper describes the results of thermodynamic and economic modelling based on integrating an existing large size steam power plant with a hydrogen production and purification plants fed by coal or biomass mixed with coal.
The high quality of the hydrogen produced would guarantee its usability for distributed generation and for public transport. The proximity of a hydrogen production plant to a steam power plant could favour connections in terms of energy requirements exchange; systems proposed could represent an attractive approach to co-production of hydrogen and electricity. Two different technologies for the syngas production section are considered: pyrolysis process and direct pressurised gasification.

This paper is focused on the performance of the 1MW plant designed and developed by Rolls-Royce Fuel Cell Systems Limited. The system consists of a two stage turbogenerator coupled with pressure vessels containing the fuel cell stack, internal reformer, cathode ejector, anode ejector and off gas burner. While the overall scheme is relatively simple, due to the limited number of components, the interaction between the
components is complex and the system behaviour is determined by many parameters. In particular two important subsystems such as the cathode and the anode recycle loops must be carefully analyzed also considering their interaction with and influence on the turbogenerator performance. The system performance model represents the whole and each physical component is modelled in detail as a sub-system. The component models have been validated or are under verification. The model provides all the operating parameters in each characteristic point of the plant and a complete distribution of thermodynamics and chemical parameters inside the SOFC stack and reformer. In order to characterise the system behaviour, its operating envelope has been calculated taking into account the effect of ambient temperature and pressure as described in the paper. Given the complexity of the system various constraints have to be considered in order to obtain a safe operating condition not only for the system as a whole but also for each of its parts. In particular each point calculated has to comply with several constraints such as stack temperature distribution, maximum and minimum temperatures and high and low pressure spool maximum rotational speeds. The model developed and the results presented in the paper provide important information for the definition of an appropriate control strategy and a first step in the development of a robust and optimized control system.

Emission reduction is one of the challenges in the design of energy systems. This concern was already present in the aviation sector through the last decade, but now it is getting stronger as far as aviation is being included in the greenhouse gas trading system. In this sector, increasing fuel efficiency is considered the most effective mean of reducing emissions. Solid Oxide Fuel Cell hybridization with gas turbines was identified as a promising power generation system to substitute Auxiliary Power Units in airliners. The objective of this work is to present the physical, weight and cost models developed for simulating fuel cell and gas turbine hybrid systems for transportation applications. These models were implemented in WTEMP, original software developed by the Thermochemical Power Group of the University of Genoa. The analysis of two system layouts is conducted as case study. A promising system presented in literature is compared to a ?simple cycle? system, proposed in this work. Since it is characterised by a non-recuperated layout, its efficiency is lower, but this system has the advantage of being less expensive and more light-weighted than other systems being evaluated in open literature.

Considering the increasing interest on the reduction of pollutant emissions, ENEL Produzione is pursuing the integration of an innovative hydrogen-fed gas turbine cycle into the existing coal-fired power station in Fusina (VE). The purpose is to develop and demonstrate the first hydrogen-coal combined cycle in the world. The University of Genoa is collaborating on this project with ENEL regarding the study of the gas turbine blade cooling. An original flexible computational tool, proprietary to DIMSET, for the complete analysis (convective and film) of high-temperature gas-turbine stages was adapted to the specific geometry of Nuovo Pignone GE10 gas turbine. The model evaluates the mainstream gas flow conditions and the velocity at the mean stage diameter in a series of computational sections in the axial direction of the expander. The impact of hydrogen and steam on the thermal exchange with turbine blades have been evaluated. This work described the phenomena undergoing in the cooled expansion of steam rich mixtures, showing, in general, an increase in blade temperature due to the variation in steam content and velocity of the mainstream as far as hydrogen and steam are employed to replace natural gas fuel.

This paper presents a research project carried out by TPG (Thermochemical Power Group) of University of Genoa to develop innovative monitoring and diagnostics procedures and software tools for softwareaided maintenance and customer support. This work is concerned with preliminary outcomes regarding the thermoeconomic monitoring of the bottoming cycle of a combined cycle power plant, using real historical data. The software is able to calculate functional exergy flows (y), their related costs (c) (using
the plant functional diagram); after that non dimensional parameters for the characteristic exergonomic indexes (Dc, Dc*, Dk*) are determined. Through a plant optimization (not described here) the reference conditions of the plant at each operating condition can be determined. Then, non dimensional indexes related to each thermoeconomic parameter are defined, in order to depict a ??cost degradation??, and thus a significant rise in the production cost of the main products of the bottoming cycle (steam and power).
The methodology developed has been successfully applied to historical logged data of an existing 400 MW power plant, showing the capabilities in estimating the ??cost degradation?? of the elements of
the BC over the plant life, and trends in the thermoeconomic indexes.

Fuel processing is a fundamental step in any fuel cell system fuelled with hydrocarbons. This work focuses on the development of the model of one reactor of the Fuel Processor unit being developed by Rolls-Royce Fuel Cell Systems Limited: the SCSO (Selective Catalytic Sulphur Oxidation). The transient model has been validated against experimental data: attained results are shown to demonstrate both the accuracy of results and the validity of modelling approach.

The objective of this paper is to show the modelling and the transient behaviour of a natural gas desulphurising system.
The plant was designed and built by Rolls-Royce Fuel Cell Systems Limited, while the plant transient model was developed and tested by the Thermochemical Power Group (TPG) of the University of Genoa, using the in-house tool TRANSEO working in the Matlab/Simulink environment. The model represents a fuel processing unit from Rolls-Royce Fuel Cell Systems Limited, designed to feed a 250kWe fuel cell hybrid system with a methane stream undergoing requirements about composition, pressure and temperature.
This paper presents a simplified plant layout of the real system. In the model, physical properties of the materials and geometry of the components have been used; where no data were available, reasonable assumptions have been done.
The transient model has been validated against experimental data retrieved from a 120 hours test and including warm-up, part and full load operation and cool-down phases.
During the validation process both gas and wall temperatures have been considered and the transient model is shown to satisfactorily predict the plant behaviour both at steady-state and transient conditions.
The model is being further developed for control system application.

The aim of this work is the development of an optimization tool that could be a useful instrument in the evaluation of the designing, sizing and managing of the cogenerative plants. This tool is a software called ECoMP, the acronym for Economic Cogeneration Modular Program. In this name the two main characteristics of the software are integrated: the modular structure and the purpose, that is the economical optimization of the cogenerative plants.
In order to include innovative plant modules in the code, the fuel cell hybrid plants have been analyzed both from a static and dynamic point of view.
The hybrid plant analyzed is composed by a Molten Carbonate Fuel Cell (MCFC) coupled with a micro gas turbine. The basics of any module are the off design performances of a plant and to do this, it has been necessary to study in depth the behaviour of the fuel cell hybrid systems.
To develop a new ECoMP module it is necessary to include in the software the off design performance curves and to obtain these curves, a new model has needed.
The structure of ECoMP is time depending and it is necessary to know the dynamic behaviour of the hybrid plants and his time response to a load variation, to a startup or a shutdown operation, to include them in ECoMP. With this purpose, a transient model has been developed.

The aim of this work is the experimental analysis of steady-state and transient behavior of a primary surface recuperator installed in a 100 kW commercial micro gas turbine. The machine is integrated in an innovative test rig for high temperature fuel cell hybrid system emulation, designed and installed by Thermochemical Power Group at the University of Genoa in the framework of the Felicitas and LARGE-SOFC European Integrated Projects.
The high flexibility of the rig was exploited to perform tests on the recuperator operating in the standard cycle focusing the attention on its performance in transient condition. Start-up tests were carried out in both electrical grid-connected and stand-alone conditions operating with different control strategies. The attention is focused on system response due to control strategy and on boundary temperatures variation for its influence on component life consumption.
Further tests were carried out using the valves installed on the test rig to bypass the air side of the unit. Different operative conditions were analyzed to show the effect of different flow rates on recuperator behavior. The attention is mainly focused on recuperator performance when it operates in unbalanced flow rate conditions (i.e. different mass flow rate values in recuperator sides).

The TPG research group of the University of Genoa designed and installed a complete hybrid system emulator test rig equipped with a 100 kW recuperated micro gas turbine, a modular cathodic vessel located between recuperator outlet and combustor inlet, and an anodic recirculation system based on the coupling of a single stage ejector with an anodic vessel.
The layout of the system was carefully designed considering the coupling between a planar SOFC stack and
the 100 kW commercial machine installed at TPG laboratory.
A particular pressurized hybrid system was studied to define the anodic side properties in terms of mass
flow rates, pressures, and temperatures. In this work, this experimental facility is used to analyze
the anodic ejector performance from fluid dynamic and thermal point of view. The attention is mainly focused on the recirculation factor value in steady-state conditions. For this reason, a wide experimental campaign was carried out to measure the behavior of this property in different operative conditions with the objective to avoid carbon deposition in the anodic circuit, in the reformer, and in the fuel cell stack.

This paper reports about a feasibility study on the manufacturing and testing of laboratory-scale high temperature fuel cell stacks, namely IT-SOFC. The manufacturing procedure of planar anode-supported cells and the test facility were set up and successfully run. The work encompassed the set up of requirements, the design, the construction, the validation and the testing of a small ITSOFC stack within the newly developed test station.
Overall, results were in-lined with requirements, the test facility worked out well and the fuel cell stacks showed acceptable performance. Improvements are possible in the stack design and assembly, especially if larger size stacks are to be developed: the chosen design proved to be effective and practical for testing of the prototype; sealing deposition proved to work out properly. Fuel cell stack performance can be improved further by alternative designs and materials: this work focused on the first step, i.e. the feasibility of technology and the demonstration of the fully automated test station. Now, repeatability of measurements and safety of procedures have been achieved, and they constitute a valuable basis for further technology development and testing.

In this work an integrate system for generation, storage and transport of hydrogen using chemical hydride
has been studied. In particular, the sodium borohydride (NaBH4) has been considered, representing a good
energetic carrier with a very high storage density due to its high hydrogen contains. In this case, the hydrogen is released as main product of the reaction of NaBH4 with water, while the by-product is sodium metaborate (NaBO2). In the first part of the work, the simulation of the packed bed reactor has been developed, using MATLAB SIMULINK. To optimise the operating conditions, the influence of some variables has been analysed, such as NaBH4 concentration, reactor length, velocity of the flow, different types of catalyser, etc.. In parallel to the theoretical activity, an experimental test rig has been designed
with the aim of validating the code results and to support the choice of materials and operating parameters. The test rig is under development in the frame of a national Project sponsored by Regione Veneto and Ministry of Environment, and in collaboration with Enel Research Centre-Pisa.

This paper presents the study of a polymeric fuel cell stack for application in stratospheric long duration balloons (LDB). Such a particular application provides severe requirements in terms of external pressure (a few mbar) and temperature (remarkably below 0°C): Regarding this, the operating conditions of the fuel cell must be decoupled of the external environment. In this case, it is envisaged that feeding gases are pure hydrogen and pure oxygen. Fuel cell cathode and anode sides require the development of proper recirculation devices in order to avoid the release of exhausts into the atmosphere with risks of ice formation, loss of the weight of the nacelle and also a possible interference on the measurements
taken on board. The scope of this work consists of:
– Preliminary design and modelling of the polymeric fuel cell power module.
– Comparison of different hydrogen storage technologies in terms of weight and volume.

The paper describes the development of concepts and components for pressurised and non-pressurised SOFC power plants. The long term goal is to develop commercially competitive power and CHP plants in the range of hundreds of kW to 1 MW size.

A dynamic Solid Oxide Fuel Cell (SOFC) model was integrated with other system components (i.e.: reformer, anodic off-gas burner, anodic ejector) to build a system model that can simulate the time response of the anode side of an integrated 250 kW pressurized SOFC hybrid system. After model description and data on previous validation work, this paper describes the results obtained for the dynamic analysis of the anodic loop, taking into account two different conditions for the fuel flow input: in the first Case (I), the fuel flow follows with no delay the value provided by the control system, while in the second Case (II) the flow is delayed by a volume between the regulating valve and the anode ejector, this being a more realistic case.
The step analysis was used to obtain information about the time scales of the investigated phenomena: such characteristic times were successfully correlated to the results of the subsequent frequency analysis. This is expected to provide useful indications for designing robust anodic loop controllers.
In the frequency analysis, most phase values remained in the 0-180? range, thus showing the expected delay-dominated behavior in the anodic loop response to the input variations in the fuel and current. In Case I, a threshold frequency of 5Hz for the pressure and STCR, and a threshold frequency of 31Hz for the anodic flow were obtained. In the more realistic Case II, natural gas pipe delay dominates, and a threshold frequency of 1.2Hz was identified, after which property oscillations start to decrease towards null values.

In this paper the results of thermodynamic and economic models based on the integration of an existing large size steam power plant (ENEL?s Brindisi power plant-660 MWe) with hydrogen production and purification plants, are described and compared. The high quality of the hydrogen produced can guarantee its utilisation for distributed generation (micro gas turbine, stirling engine) and public transportation (PEM fuel cells) as well.
The proximity of an hydrogen production and purification plant to an existing steam power plant can favour connections in terms of energy requirements exchanges; the integrated system, proposed here, can represent an attractive approach to a flexible hydrogen-electricity co-production.
Two different technologies for syngas production section are considered: direct pressurised gasification and pyrolysis processes. The technologies produce syngas with different characteristics in terms of temperature, pressure and composition: this aspect affects deeply the layouts of the complete systems proposed in the paper. The pyrolysis process model is referred to an existing 800 kWt ENEL?s coal and biomass fed pyrolysis plant placed in Bastardo (Perugia, Italy): a detailed model of the plant has been realised.
Different coals (Ashland, South Africa, Sulcis) and a mixture of biomass (Poplar, Mischantus, Wood residuals, Husk) are considered in this study to explore the real potential of mixed-fuels in terms of thermodynamic performances and costs.
The results were obtained using WTEMP software, developed by the TPG of the University of Genoa, showing the performance attainable by integrating a real steam power plant with systems for hydrogen production and purification for a novel vision of clean distributed hydrogen generation.

Monitoring of all components of large size combined cycle power plants (gas turbine, HRSG, steam turbine, auxiliaries) plays a determinant role in improving plant availability, profitability and scheduling of maintenance.
This paper presents a research project carried out by TPG (Thermochemical Power Group) of University of Genoa in collaboration with Ansaldo Energia S.p.A. to improve existing monitoring and diagnostics procedures and to develop innovative software tools for software-aided maintenance and customer support: the first part of activities is concerned with the monitoring of a three pressure level HRSG (Heat Recovery Steam Generator), which is presented in this paper.
A procedure for estimating HRSG performance in large size combined cycle power plant is presented. The work consists in the development of an original Matlab code which calculates heat exchangers performance, at different power plant operating conditions. The Matlab code uses some parameters (areas of heat exchangers, heat transfer coefficient, heat loss, pressure drop) coming from a detailed on-design model necessary only for setting some parameters for the calculation. The original Matlab code was developed with a twofold objective: to calculate the actual gas path inside the HRSG starting from the available measurements, thus obtaining the current effectiveness of all the heat exchangers in the HRSG; to estimate the expected performance of each heat exchanger to be compared with the actual ones.
Once the actual efficiency and the expected efficiency of the heat exchanger are defined, non-dimensional performance parameters suitable for degradation assessment can be defined. Such parameters will be used to monitor plant degradation, to support plant maintenance, and to assist on-line troubleshooting. As a result of the sensitivity analysis, each performance parameter is coupled with an accuracy factor. The accuracy of each performance parameter is estimated through the sensitivity analysis, which allows to determine the best parameters to be monitored and to define the related tolerance due to measurement errors.
The methodology developed has been successfully applied to historical logged data (2 years) of a large size (400 MW) combined cycle in Italy, showing the good capabilities in estimating the degradation of the HRSG along plant life.

Solid oxide fuel cell hybridization with micro gas turbines is an attractive option for distributed power generation up to a few MW, allowing to obtain high efficiency and low pollutant emission. In this publication, a comparative thermoeconomic analysis of SOFC hybrid systems with methanol and kerosene fuel processors is presented. Methanol can be produced from renewable sources. Also, hybrid systems fuelled by methanol can achieve high efficiencies due to effective heat recovery from the exhaust gases in the low temperature reformer. Kerosene is representative of conventional liquid fossil fuels, and it is also a typical fuel for aerospace applications. A 500 kW class hybrid system was chosen for this analysis and the performance was calculated based on macroscopic component models. The results were obtained with WTEMP software, developed by the Thermochemical Power Group of the University of Genoa. The choice of the fuel processing strategy and the influence of the main design parameters on the thermoeconomic characteristics of hybrid systems were investigated.

The Multi-Purpose Model represents a new methodology for developing model based tools for control system design and verification. The Multi-Purpose Model, as described in this paper, simulates a SOFC hybrid system – a challenging and innovative application of dynamic modelling and control.
Real-time modelling is a recognised approach to monitor advanced systems and to improve control capabilities. Applications of Real-Time (RT) models are commonly used in the automotive and aerospace fields.
Starting from existing TRANSEO components and models, a new approach to fit hybrid system application has been developed. Original C-based models have been translated into embedded Matlab functions for direct use within Matlab-Simulink. The resulting models have then been used to auto-generate c-code with the Real-Time Workshop. The C-code has then been compiled to produce application specific executables.

This paper describes and compares the results of thermodynamic and economic modelling based on integrating an existing large size steam power plant (ENEL’s Brindisi power plant-660 MWe) with hydrogen production and purification plants. ENEL is one of the main Italian power utility. The high quality of the hydrogen produced would guarantee its usability for distributed generation (e.g. by micro gas turbine, Stirling engine, fuel cell, etc.) and also for public transport (using PEM fuel cells).
The proximity of a hydrogen production and purification plant to an existing steam power plant could favourite connections in terms of energy requirements exchange; moreover the complete systems proposed could represent an attractive approach to flexible co-production of hydrogen and electricity.
Two different technologies for the syngas production section are considered: the pyrolysis process and direct pressurised gasification. These technologies produce syngas with different characteristics in terms of temperature, pressure and composition: this has a profound effect on the layout of the complete systems proposed in this paper. The model for the pyrolysis process is based on an existing 800 kWt coal – and biomass – fed pyrolysis ENEL?s plant placed in Bastardo (Perugia, Italy): a detailed model of the plant was created.
Different coals (Ashland, South Africa, Sulcis) and biomass (poplar, mischantus, wood residuals, husks) are considered in this study in order to explore the real potential of mixed-fuel in terms of thermodynamic performances and costs.
The results were obtained using WTEMP software, developed by the Thermochemical Power Group of the University of Genoa, showing the performance attainable by supplementing an actual steam power plant with systems for hydrogen production and purification for a novel vision of clean distributed power generation and public transport.

One of the most interesting methods of water introduction in a gas turbine circuit is represented by the humid air turbine cycle (HAT). In the HAT cycle, the humidification can be provided by a pressurised saturator (i.e.: humidification tower or saturation tower), this solution being known to offer several attractive features. This work is focused on an experimental study of a pressurised humidification tower, with structured packing. After a description of the test rig employed to carry out the measuring campaign, the results relating to the thermodynamic process are presented and discussed. The experimental campaign was carried out over 162 working points, covering a relatively wide range of possible operating conditions.
It is shown that the saturator’s behaviour, in terms of air outlet humidity and temperature, is primarily driven by, in decreasing order of relevance, the inlet water temperature, the inlet water over inlet dry air mass flow ratio and the inlet air temperature.
The exit relative humidity is consistently over 100%, which may be explained partially by measurement accuracy and droplet entrainment, and partially by the non-ideal behaviour of air-steam mixtures close to saturation.
Experimental results have been correlated using a set of new non-dimensional groups: such a correlation is able to capture the air outlet temperature with a standard deviation ?=2.8K. The correlation is useful for describing the off-design behaviour of the pressurised saturation tower under investigation, and it is the first step towards a generalised representation of the behaviour of structured packing humidification towers for HAT application.

High temperature fuel cells (MCFCs and SOFCs) can operate at atmospheric or pressurised conditions. In both cases, system performance can be significantly improved when the fuel cells are integrated with proper devices, which are designed to provide the necessary air inlet conditions and to recover the exhaust-gas energy.
This paper presents a review of modelling and design issues for the integration of turbomachinery with the fuel cell system, because turbomachinery is the most promising technology for coping with the high temperature fuel cell requirements.
Analytical approach is undertaken for properly modelling composition influence on expander performance, and results are presented to demonstrate the quantitative influence of the system parameters on the performance. The analysis covers the three main aspects of performance evaluation: the on-design, the off-design and, as a final mention, the control of the fuel cell hybrid systems.

In the distributed power generation market, SOFC/GT hybrids are an attractive option. Prototypes are being tested around the world with different types of fuel, but mainly natural gas. In this publication, a study of SOFC/GT hybrids for operation with liquid fuels is presented. Two liquid fuels were investigated, methanol and kerosene, in four layouts, taking into account different fuel processing strategies. A 500 kW class hybrid system was analysed. WTEMP software, developed by the Thermochemical Power Group of the University of Genoa, was used for the thermodynamic and investment analysis. Performance was calculated based on zero-dimensional component models. The economic assessment was performed with a through life cost analysis approach. The cost of the conventional components was calculated with WTEMP cost equations. As a final result, methanol fuelled hybrid systems are demonstrated to distinguish for both their thermodynamic and economic performance.

Monitoring of all the components of large size combined cycle power plants (gas turbine, HRSG, steam turbine, auxiliaries) plays a determinant role in improving plant availability, profitability and maintenance scheduling. This paper presents a research project carried out by TPG (Thermochemical Power Group) of University of Genoa in collaboration with Ansaldo Energia S.p.A. to improve existing monitoring and diagnostics procedures and to develop innovative software tools for software-aided maintenance and customer support.
This work is concerned with the preliminary outcomes regarding the thermo-economic monitoring of the bottoming cycle (BC) of a combined cycle power plant, using real historical logged data. The software, developed in a Matlab environment, is able to calculate functional exergy flows (y) and their related costs (c), calculated on the basis of the whole plant functional diagram. Once the exergy flows costs has been defined, it is possible to determine non-dimensional parameters also for the characteristic exergonomic indexes (?c, ?c*, ?k*).
Through a plant optimization (not described in the paper) the reference conditions of the plant at each operating condition can be determined. Then, Non Dimensional Indexes (NDI) related to each thermoeconomic parameter are defined, in order to depict a ?cost degradation?, and thus a significant rise in the production cost of the main products of the Bottoming Cycle (i.e.: steam and power). The methodology developed has been successfully applied to historical logged data (2 years) of an existing large-sized (400 MW) combined cycle power plant, showing the capabilities in estimating the ?cost degradation? of the elements of the BC over the life of the plant, and the trends in the thermoeconomic indexes.