Fuel Cell Gas Turbine Systems Research Articles

A novel multi-generation energy harvesting system integrating photovoltaic and solid oxide fuel cell technologies

This paper designs a new multi-generation system based on solar tower power supply, integrating a solid oxide fuel cell-gas turbine system, a supercritical recompressed carbon dioxide cycle, a Rankine cycle, an organic Rankine cycle, a compressed air energy storage system and a liquefied natural gas system. The aim is to overcome the intermittent and unstable nature of the solar power supply and ensure continuous power generation throughout the day, as well as improving the energy efficiency of the solar power system and minimising exhaust emissions from the integrated system. The system is modelled and evaluated in terms of energy, exergy, environment and economy. The results show the solar system energy efficiency of 10.09%, the total system energy efficiency of 19.28%, a round-trip efficiency of 58.66% and an exergetic round-trip efficiency of 52.06%, preventing the emission of 2090 tons of CO2 (a total of $50175 in environmental fines) per year. Finally, the proposed system was applied to a case study in the Xixiangtang district of Nanning, China, where the system, combined with real data, produced 24.8 MWh of electricity on the day with the highest direct of normal irradiance. In addition, the results of the economic analysis show the dynamic payback period is 6.9 years.

Thermodynamic and economic analysis of a novel multi-generation system integrating solid oxide electrolysis cell and compressed air energy storage with SOFC-GT

Traditional gas-fired power plants are characterized by low efficiency and challenges in peak regulation. Even with the incorporation of compressed air energy storage, they still exhibit deficiencies in flexibility during peak load regulation. In this paper, we propose a novel hybrid power system based on gas-fired power plants, capable of producing electricity, heat, and hydrogen, while achieving flexible peak load regulation. The system is comprehensively evaluated using energy analysis, exergy analysis, and economic analysis. Results show that the total energy efficiency and exergy efficiency of this hybrid power system perform well, surpassing existing research on fuel cell-gas turbine systems. Among the subsystems, the fuel cell contributes the most to the total energy output of the hybrid system but also incurs the highest exergy losses, while the relative exergy losses of the water electrolysis and compressed air energy storage systems are relatively small. The configuration of dual energy storage systems enhances the flexibility in peak load regulation. Additionally, the proposed hybrid system exhibits low carbon emissions of 0.08 to 0.12 t/GJ. Considering factors such as discount rate, the initial investment cost can be recovered in 5.81 years, and the calculated net present value is 492,275.82 k$. Thus, the proposed scheme also possesses certain advantages in terms of economic feasibility.

Enhancing geothermal ORC power generation with SOFC: A comprehensive parametric study on thermodynamic performance

Geothermal energy is a promising renewable energy source due to its abundant global reserves. However, most geothermal resources are of low grade, severely restricting their power generation capacity and efficiency. In this study, the geothermal organic Rankine cycle power generation system is combined with a solid oxide fuel cell-gas turbine system to improve the overall power supply and heat utilization efficiency. The heat source and cycle temperature are upgraded using high-temperature solid oxide fuel cell waste gas, and the combined system’s efficiency is further improved through cascade heat utilization. Electrochemical-thermodynamic models are developed for the proposed system, and energy-exergy analysis is carried out. The effects of fuel cell current density, operating temperature and geothermal grade on the combined system’s performance are comprehensively analyzed. Compared to the standalone geothermal system, the energy efficiency and output power of the organic Rankine cycle increase by 8.11% and 7.95% respectively in the baseline case. Under the lowest geothermal temperature condition, the cycle output power is improved by 22.64%. The net power of the combined system can vary from 358 kW to 846 kW by adjusting the fuel cell current density from 1000 A m−2 to 8000 A m−2, demonstrating a flexible power supply capability. The optimal solid oxide fuel cell operating temperature is 1023.15 K, resulting in the highest system overall energy efficiency of 14.85%. The presented work provides essential guidelines for improving geothermal power generation performance and designing applicable combined systems.

Study of Trends in System Efficiency for a Biomass Integrated Gasification Fuel Cell Gas Turbine System when Carbon Dioxide Content is Enhanced

Study of Trends in System Efficiency for a Biomass Integrated Gasification Fuel Cell Gas Turbine System when Carbon Dioxide Content is Enhanced

Optimization of supercritical carbon dioxide based combined cycles for solid oxide fuel cell-gas turbine system: Energy, exergy, environmental and economic analyses

Among various supercritical carbon dioxide cycles, the supercritical recompression carbon dioxide cycle can well adapt to the high temperature of the exhaust gas of the solid oxide fuel cell-gas turbine system to augment power generation. Nevertheless, even after the recovery by the supercritical recompression carbon dioxide cycle, the exhaust gas still contains a large amount of unutilized waste energy. Few studies introduce low-temperature cycles to build cascade cycle systems, which are very likely to address this issue effectively. From the perspectives of energy, exergy, environmental and economic indexes, this article analyzes and compares the improvement potential of integrating four common low-temperature cycles, including organic Rankine cycle, transcritical carbon dioxide cycle, Kalina cycle, and organic flash cycle. Different key operating parameters are considered in-depth and optimized by a genetic algorithm. The results illustrate that in terms of efficiency, the introduction of the organic Rankine cycle is the most outstanding since it can reach the highest energy efficiency of 72.74–73.55% (exergy efficiency of 70.22–71.01%) across wide operation conditions. In terms of cost, the coupling of Kalina cycle is suggested due to the lowest capital cost of 19.94 $/h. The environmental penalty of the four systems all accounts for 14.73% of the total cost. As a consequence, the pros and cons of four common low-temperature cycles are fully demonstrated, which can provide references for the power plant planning.

Application analysis of a hybrid solid oxide fuel cell-gas turbine system for marine power plants

ABSTRACT The results of theoretical studies of the possibilities of using hybrid solid oxide fuel cell–gas turbine (SOFC-GT) systems for marine power plants are presented. A 500 kW auxiliary marine power plant scheme using stacks of SOFCs in combination with a regenerative gas turbine operating with over-expansion based on our recent patent application is proposed. The results of mathematical modelling showed the opportunity to obtain a hybrid scheme efficiency of about 55% with the optimal values of the gas turbine compression ratio 2.0–2.2 and the exhauster compressor ratio 1.3–1.4. The application of the considered hybrid SOFC-GT system gives an increase in electrical efficiency by 19% in comparison with a cycle without a gas turbine. The aerodynamic structure of chemically reacting flows in a combustor is determined, as well as the features of the formation of toxic components during the combustion of SOFC off-gas with very low heating value.

A solid oxide fuel cell- supercritical carbon dioxide Brayton cycle hybrid system

New technologies are being developed to produce electricity cleaner and more efficient. Promising technologies among these are the solid oxide fuel cell and the supercritical carbon dioxide Brayton cycle. This study investigates the potential of integrating both technologies.The solid oxide fuel cell is known as a potentially clean and highly efficient technology to convert chemical energy to electricity. The high operating temperatures (600–1000 °C) allow the possibility of a bottoming cycle to utilize the high quality excess heat and also facilitate reforming processes, making it possible to use higher hydrocarbons as fuel.The supercritical carbon dioxide Brayton cycle has received attention as a promising power cycle. It has already been identified as a suitable cycle for relatively low temperature, compared to traditional gas turbines, heat sources for several reasons.Firstly because of the high efficiency, around 40%–45% for the common simple recuperative cycle. Secondly, because the turbine inlet temperature of a supercritical carbon dioxide is around 700 °C is low, compared to well over 1000 °C for a common air Brayton cycle. This is especially of interest because solid oxide fuel cell developers are targeting lower operating temperatures to avoid the use of exotic and expensive materials. And thirdly, the cycle can operate entirely above the critical point. Therefore the temperature increases gradually with the energy added to the cycle. This is more suitable for waste heat because the exergy loss decreases and more low temperature heat can be utilized compared to a steam Rankine cycle where most of the heat is added above the relatively high boiling point of pressurized water.A thermodynamic model of the solid oxide fuel cell- supercritical carbon dioxide Brayton cycle hybrid system is developed to explore and analyze different concepts of integration.Several conclusions are drawn. Firstly it is found that recirculating cathodic air increases the efficiency of the system and decreases the size of the heat exchangers. Secondly, applying a pinch point optimization decreases the size of the heat exchangers but increases the complexity of the system while the efficiency is not much affected. Thirdly, applying the recompression cycle in stead of a simple recuperative supercritical carbon dioxide cycle increases the efficiency of the system but not as significantly when operating the supercritical carbon dioxide as a stand-alone system while the complexity of the system increases even more. And finally, compared to a directly coupled solid oxide fuel cell-gas turbine system the solid oxide fuel cell- supercritical carbon dioxide Brayton cycle hybrid system is more efficient but significantly more complex.

High efficiencies with low fuel utilization and thermally integrated fuel reforming in a hybrid solid oxide fuel cell gas turbine system

Solid oxide fuel cell (SOFC) - gas turbine (GT) systems have a potential to achieve 70% efficiency, which with high fuel flexibility and high part load efficiency, makes this hybrid a promising technology for the next power generation systems. To realize the high efficiency and reduce the capital cost, most studies focus on high fuel utilization SOFC stack design with internal fuel reforming configuration in SOFC-GT hybrids. None of them have considered low fuel utilization SOFC design in the hybrid system, which could extend the SOFC lifetime and also decrease the capital cost from fuel cells, accelerating the commercialization of fuel cell technologies. To fill this research gap, this work examined the system performance of a pressurized natural gas hybrid SOFC-GT system with a thermally integrated fuel reforming process. Specifically, system cycle analysis was performed in this work to explore the feasibility of achieving high efficiencies with low SOFC fuel utilizations. An equilibrium reformer model and a one-dimensional SOFC model were employed to represent the SOFC system, while balance of plant model was built in Ebsilon® to simulate the associated performance of recuperated gas turbine cycle. With the thermally integrated system configuration, 70% efficiency could be reached at 50% SOFC fuel utilization with a high fuel pre-reforming rate (only ~ 5 mol% CH4 at anode inlet). Low fuel utilization operations with high fuel pre-reforming rates provided higher design flexibility without violating any operational constraints while maintaining a high system efficiency as compared to on-anode reforming.

Design, modelling and techno-economic analysis of a solid oxide fuel cell-gas turbine system with CO2 capture fueled by gases from steel industry

The steel industry is one of the major sources of CO2 emissions that are released in the manufacture and process of steel as well as in related power production. Focused on reduction of CO2 emissions in the power production, this paper presents a novel solid oxide fuel cell-gas turbine combined heat and power system fed by coke oven gas. The solid oxide fuel cell-gas turbine system design consists of an adequate gas cleaning section for contaminants removal, solid oxide fuel cell as the main power producer and an anode offgas pressure swing adsorption based CO2 capture unit. This system is thermodynamically and techno-economically analyzed and compared with a reheat steam turbine. Furthermore, the reheat steam turbine is retrofitted with a CO2 capture unit. It is then compared to the solid oxide fuel cell-gas turbine system to analyse the difference in system efficiencies.The solid oxide fuel cell-gas turbine system yields an electrical efficiency of 64%, which is significantly higher than electrical efficiency achieved by both, a conventional reheat steam cycle (34.1%) and the retrofitted system (27.0%). Moreover, it depicts a combined heat and power efficiency of 73%. Results also reveal that the solid oxide fuel cell-gas turbine system can achieve a reduction of 50% in CO2 emissions for equal power production. Furthermore, techno-economic analysis lead to a payback period of 9 years, taking into account state-of-the-art taxes and variation in the cost of components over the lifetime, without taking into account the fuel cost.

Stall/surge dynamics of a multi-stage air compressor in response to a load transient of a hybrid solid oxide fuel cell-gas turbine system

A better understanding of turbulent unsteady flows in gas turbine systems is necessary to design and control compressors for hybrid fuel cell-gas turbine systems. Compressor stall/surge analysis for a 4 MW hybrid solid oxide fuel cell-gas turbine system for locomotive applications is performed based upon a 1.7 MW multi-stage air compressor. Control strategies are applied to prevent operation of the hybrid SOFC-GT beyond the stall/surge lines of the compressor. Computational fluid dynamics tools are used to simulate the flow distribution and instabilities near the stall/surge line. The results show that a 1.7 MW system compressor like that of a Kawasaki gas turbine is an appropriate choice among the industrial compressors to be used in a 4 MW locomotive SOFC-GT with topping cycle design. The multi-stage radial design of the compressor enhances the ability of the compressor to maintain air flow rate during transient step-load changes. These transient step-load changes are exhibited in many potential applications for SOFC/GT systems. The compressor provides sustained air flow rate during the mild stall/surge event that occurs due to the transient step-load change that is applied, indicating that this type of compressor is well-suited for this hybrid application.

Exergetic, economic, and environmental evaluations and multi-objective optimization of a combined molten carbonate fuel cell-gas turbine system

The principal goal in the present work is to model a molten carbonate fuel cell-gas turbine (MCFC-GT) hybrid plant from energetic, exergetic, economic and environmental standpoints and to optimize the system through a multi-objective optimization scheme. Two conflicting objectives including exergetic efficiency and total cost rate of the system are introduced for multi-objective optimization. TOPSIS decision-making method is employed to determine the system final optimum design, leading to an overall exergetic efficiency of 51.7% and the total cost of 0.324 million USD per year. Moreover, a sensitivity analysis of the Pareto frontier to fuel unit cost and effective interest rate has been performed to investigate the variation of objective functions with economic parameters. Finally, a sensitivity analysis on the optimization results was performed for some of the key parameters, revealing the fact that operating pressure of the system has the highest impact on the exergetic efficiency compared to the other operating parameters.

Hybrid Fuel Cell Gas Turbine System Design and Optimization

Ultrahigh efficiency, ultralow emission fuel cell gas turbine (FC/GT) hybrid technology represents a significant breakthrough in electric power generation. FC/GT hybrid designs are potentially fuel flexible, dynamically responsive, scalable, low-emission generators. The current work develops a library of dynamic component models and system design tools that are used to conceptualize and evaluate hybrid cycle configurations. The physical models developed for the design analysis are capable of off-design simulation, perturbation analysis, dispatch evaluation, and control development. A parametric variation of seven fundamental design parameters provides insights into design and development requirements of FC/GT hybrids. As the primary generator in most configurations, the FC design choices dominate the system performance, but the optimal design space may be substantially different from a stand-alone FC system. FC operating voltage, fuel utilization, and balance of plant component sizing has large impacts on cost, performance, and functionality. Analysis shows that hybridization of existing fuel cell and gas turbine technology can approach 75% fuel-to-electricity conversion efficiency.

Thermodynamic Analysis of Solid Oxide Fuel Cell Gas Turbine Systems Operating with Various Biofuels

AbstractSolid oxide fuel cell–gas turbine (SOFC‐GT) systems provide a thermodynamically high efficiency alternative for power generation from biofuels. In this study biofuels namely methane, ethanol, methanol, hydrogen, and ammonia are evaluated exergetically with respect to their performance at system level and in system components like heat exchangers, fuel cell, gas turbine, combustor, compressor, and the stack. Further, the fuel cell losses are investigated in detail with respect to their dependence on operating parameters such as fuel utilization, Nernst voltage, etc. as well as fuel specific parameters like heat effects. It is found that the heat effects play a major role in setting up the flows in the system and hence, power levels attained in individual components. The per pass fuel utilization dictates the efficiency of the fuel cell itself, but the system efficiency is not entirely dependent on fuel cell efficiency alone, but depends on the split between the fuel cell and gas turbine powers which in turn depends highly on the nature of the fuel and its chemistry. Counter intuitively it is found that with recycle, the fuel cell efficiency of methane is less than that of hydrogen but the system efficiency of methane is higher.

Experimental and theoretical evidence for control requirements in solid oxide fuel cell gas turbine hybrid systems

Hybrid fuel cell gas turbine sensitivity to ambient perturbations is analyzed using experimental and dynamic simulation results. Experimental data gathered from the world's first pressurized hybrid SOFC–GT system tested at the University of California, Irvine, capture performance variations due to diurnal temperature oscillations. A dynamic modeling methodology demonstrates accuracy, robustness, and clearly identifies critical system sensitivities that require additional control systems development. Simulation results compare favorably with dynamic experimental responses. Predictions of component temperatures, pressures, voltage and system power exhibited 5°C, 2kPa, 2mV, and 0.5% error respectively. Moderate ambient temperature fluctuations, 15°C, caused variations in stack temperature of 30°C, and system power of 5kW. Small to moderate changes in fuel composition produced 30°C shifts in stack temperature and 25% changes in system power. Simple control loops manipulating fuel cell air flow through SOFC bypass and inlet temperature through recuperator bypass are shown to effectively mitigate internal temperature transients at the expense of reduced system output. The observed temperature fluctuations resulting from typical environmental perturbations are of concern for performance loss and diminished longevity. Experiments and dynamic simulation results indicate the importance of integrated control systems development for hybrid fuel cell gas turbine systems.

Effects of operating and design parameters on the performance of a solid oxide fuel cell-gas turbine system

We present a steady-state thermodynamic model of a hybrid solid oxide fuel cell (SOFC)–gas turbine (GT) cycle developed using a commercial process simulation software, AspenPlus™. The hybrid cycle model incorporates a zero-dimensional macro-level SOFC model. A parametric study was carried out using the developed model to study the effects of system pressure, SOFC operating temperature, turbine inlet temperature, steam-to-carbon ratio, SOFC fuel utilization factor, and GT isentropic efficiency on the specific work output and efficiency of a generic hybrid cycle with and without anode recirculation. The results show that system pressure and SOFC operating temperature increase the cycle efficiency regardless of the presence of anode recirculation. On the other hand, the specific work decreases with operating temperature. Overall, the model can successfully capture the complex performance trends observed in hybrid cycles. Copyright © 2010 John Wiley & Sons, Ltd.

A comparison between conventional recuperative gas turbine and hybrid solid oxide fuel cell—gas turbine systems with direct/indirect integration

Conventional recuperative micro gas turbines have a 30 per cent low heating value (LHV) maximum efficiency at full load. Therefore, if they are to be used in a potential distributed energy scenario, solutions must be developed that increase efficiency. An innovative gas turbine-based technology is the fuel cell — gas turbine hybrid system. This work is aimed at studying how the basic performance of a conventional Brayton cycle changes when heat addition is done at a fuel cell. Two layouts are considered: a direct system where the compressor feeds the fuel cell directly and an indirect system where only heat is transferred between subsystems. Direct and indirect systems have been studied at full and part load, concluding that the efficiency versus pressure ratio curves of hybrid systems change substantially with respect to a traditional gas turbine; part-load efficiency hardly decreases. Maximum efficiency of hybrid systems doubles the efficiency of state of the art micro gas turbine and remains high at part load. Furthermore, the benefit of a certain increase in temperature is higher for hybrid systems than for conventional engines. Finally, a simple economic analysis shows that the total installation and operation/maintenance costs of hybrid systems make them competitive against conventional gas turbines.

Comparison between pressurized design and ambient pressure design of hybrid solid oxide fuel cell–gas turbine systems

Design performances of the hybrid solid oxide fuel cell (SOFC)–gas turbine (GT) system have been investigated. A pressurized system and an indirectly heated ambient pressure system were analyzed and their performances were compared. In the baseline layout, the basic performance characteristics of the two system configurations were analyzed, with the cell operation temperature and the pressure ratio as the main design parameters. The pressurized system exhibits a better efficiency owing to not only the higher cell voltage but also more effective utilization of gas turbine, i.e., a larger GT power contribution due to a higher turbine inlet temperature. Independent setting of the turbine inlet temperature was simulated by using the additional fuel supply as well as the air bypass. Increasing the pressure ratio of the gas turbine hardly improves the system efficiency, but the efficiency becomes less sensitive to the turbine inlet temperature. In the ambient pressure system, the available design parameter range is much reduced due to the limit on the recuperator temperature. In particular, design of the ambient pressure hybrid system with a gas turbine of a high pressure ratio does not seem quite feasible because the system efficiency that can be achieved at the possible design conditions is even lower than the efficiency of the SOFC only system.

The design of stationary and mobile solid oxide fuel cell–gas turbine systems

A general thermodynamic model has shown that combined fuel cell cycles may reach an electric-efficiency of more than 80%. This value is one of the targets of the Department of Energy (DOE) solid oxide fuel cell–gas turbine (SOFC–GT) program. The combination of a SOFC and GT connects the air flow of the heat engine and the cell cooling. The principle strategy in order to reach high electrical-efficiencies is to avoid a high excess air for the cell cooling and heat losses. Simple combined SOFC–GT cycles show an efficiency between 60 and 72%. The combination of the SOFC and the GT can be done by using an external cooling or by dividing the stack into multiple sub-stacks with a GT behind each sub-stack as the necessary heat sink. The heat exchangers (HEXs) of a system with an external cooling have the benefit of a pressurization on both sides and therefore, have a high heat exchange coefficient. The pressurization on both sides delivers a low stress to the HEX material. The combination of both principles leads to a reheat (RH)-SOFC–GT cycle that can be improved by a steam turbine (ST) cycle. The first results of a study of such a RH-SOFC–GT–ST cycle indicate that a cycle design with an efficiency of more than 80% is possible and confirm the predictions by the theoretical thermodynamic model mentioned above. The extremely short heat-up time of a thin tubular SOFC and the market entrance of the micro-turbines give the option of using these SOFC–GT designs for mobile applications. The possible use of hydrocarbons such as diesel oil is an important benefit of the SOFC. The micro-turbine and the SOFC stack will be matched depending on the start-up requirements of the mobile system. The minimization of the volume needed is a key issue. The efficiency of small GTs is lower than the efficiency of large GTs due to the influence of the leakage within the stages of GTs increasing with a decreasing size of the GT. Thus, the SOFC module pressure must be lower than in larger stationary SOFC–GT systems. This leads to an electrical-efficiency of 45% of a cycle used as a basis for a design study. The result of the design study is that the space available in a mid-class car allows the placement of such a system, including space reserves. A further improvement of the system might allow an electrical-efficiency of about 55%.