Solid Oxide Fuel Cell Gas Research Articles

Characteristic Investigation of a Novel Aircraft SOFC/GT Hybrid System under Varying Operational Parameters

In this study, the implementation of a solid oxide fuel cell–gas turbine hybrid engine for primary propulsion and electric power generation in aircraft is investigated. The following three parameters, which are crucial in attaining optimal performance at any point in the flight profile, were identified: the oxygen-to-carbon ratio of the catalytic partial oxidation reformer, the fuel utilization factor of the fuel cell, and the airflow split ratio at the outlet of the high-pressure compressor. The study assesses the impact of varying these parameters within specified ranges on the performance of the hybrid system. At the design point, the system yielded a total power output of 1.96 MW, with 102.5 kW of electric power coming from the fuel cell and 7.9 kN (1.86 MW) of thrust power coming from the gas turbine. The results indicate that varying the oxygen-to-carbon ratio affected the fuel cell’s fuel utilization and resulted in a slight decrease in gas turbine thrust. The fuel utilization factor primarily affected the power output of the fuel cell stack, with a minor impact on thrust. Notably, varying the airflow split ratio showed the most significant influence on the overall system performance. This analysis provides insights into the system’s sensitivities and contributes to the development of more sustainable aircraft energy systems.

Effect of steam reinjection mass flow rate on the SOFC–GT system with steam reinjection

A solid oxide fuel cell (SOFC) is regarded as the first choice of high-efficiency and clean power generation technology in the 21st century due to its characteristics of high power generation efficiency and low pollutant emission. In this paper, hydrogen is used as a fuel for SOFCs using the EBSILON platform. A sensitivity analysis of the solid oxide fuel cell–gas turbine (SOFC–GT) system with steam reinjection is carried out to investigate the effect of the steam reinjection mass flow rate on the improvement of the electrical efficiency of the system and on the values of the other parameters. The results show that the variation in the steam reinjection mass flow rate has an effect on other parameters. Changes in several parameters affect the electrical efficiency of the system, which reaches 74.11% at a pressure ratio of 10, SOFC inlet temperature of 783.15 K, turbine back pressure of 70 kPa, and steam reinjection mass flow rate of 6.16 kg/s. Future research can optimize the overall parameter selection of the system in terms of economy and other aspects.

Energy, Exergy, and Economic (3E) Analysis of SOFC-GT-ORC Hybrid Systems for Ammonia-Fueled Ships

A feasible solid oxide fuel cell–gas turbine–organic Rankine cycle (SOFC-GT-ORC) hybrid system for ammonia-fueled ships is presented in this study. To confirm the quantitative changes in thermodynamic performance and economics according to the system configuration, the system using ammonia fuel was simulated, and energy, exergy, and economic (3E) analyses were performed. As a result, the system economics generally had an inversely proportional relationship with the thermodynamic performance. System optimization was performed using a multi-objective genetic algorithm, setting the conflicting thermodynamic performance and economics as objective functions. The key results of this study obtained through optimization are as follows. With the introduction of the ORC, the SOFC-GT hybrid system thermal efficiency was increased by 2–6%, but the cost increased by 14–24%. In the SOFC-GT-ORC hybrid system, preferentially reducing the irreversibility of the SOFC, combustor, and ORC evaporator is advantageous in terms of performance. It is economical to use a moderate amount of SOFC fuel to achieve the target output; the cost of the ORC in the SOFC-GT-ORC hybrid system was approximately $23/h. This study is unique in that it systematically conducted a 3E analysis, which had not been previously well-performed for SOFC hybrid systems for ammonia-fueled ships.

Techno-Economic Optimization of SOC Design and Operating Conditions in a Solid Oxide Fuel Cell-Gas Turbine Hybrid System

In a circular economy, highly efficient energy conversion systems are paramount to maximize resource utilization and minimize waste production, including carbon dioxide emissions. Solid oxide fuel cell-gas turbine hybrid systems, which can reach efficiencies of greater than 75%-LHV, have demonstrated to be a promising technology on the way to cleaner power generation. During the energy transition period, solid oxide fuel cell-gas turbine hybrid systems are likely to be operated on natural gas, however, their scalability allows these systems to reach very high efficiencies even at small scales, enabling the use of distributed resources such as biogas. In this presentation the authors will discuss key performance and economic metrics of small-scale (10 MW) advanced solid oxide fuel cell-gas turbine hybrid systems and their relation to cell design and system design elements. Current challenges in solid oxide fuel cell development include thermal cell management and production cost. This presentation presents findings of how cell design parameters influence thermal gradients and specific solid oxide cell costs on a $/kW-basis under hybrid system operating conditions. Moreover, specific cell components are identified, and effects will be discussed that can synergistically reduce thermal stress and specific cell cost at the same time. Informed by this analysis, the optimized cell design is integrated into a solid oxide fuel cell-gas turbine hybrid system in order to provide a comprehensive analysis of system operating conditions under consideration of thermal cell gradients, and new insights into economics and levelized cost of electricity are provided. The presentation will discuss the impact of fuel utilization, operating voltage, and operating pressure upon the heat integration, system’s operating window, and power output. A discussion of economic parameters will highlight cost driving factors to inform research on the next generation of solid oxide cells.

Techno-Economic Analysis of Solid Oxide Fuel Cell-Gas Turbine Hybrid Systems for Stationary Power Applications Using Renewable Hydrogen

Solid oxide fuel cell (SOFC)–gas turbine (GT) hybrid systems can produce power at high electrical efficiencies while emitting virtually zero criteria pollutants (e.g., ozone, carbon monoxide, oxides of nitrogen and sulfur, and particulate matters). This study presents new insights into renewable hydrogen (RH2)-powered SOFC–GT hybrid systems with respect to their system configuration and techno-economic analysis motivated by the need for clean on-demand power. First, three system configurations are thermodynamically assessed: (I) a reference case with no SOFC off-gas recirculation, (II) a case with cathode off-gas recirculation, and (III) a case with anode off-gas recirculation. While these configurations have been studied in isolation, here we provide a detailed performance comparison. Moreover, a techno-economic analysis is conducted to study the economic competitiveness of RH2-fueled hybrid systems and the economies of scale by offering a comparison to natural gas (NG)-fueled systems. Results show that the case with anode off-gas recirculation, with 68.50%-lower heating value (LHV) at a 10 MW scale, has the highest efficiency among the studied scenarios. When moving from 10 MW to 50 MW, the efficiency increases to 70.22%-LHV. These high efficiency values make SOFC–GT hybrid systems highly attractive in the context of a circular economy as they outcompete most other power generation technologies. The cost-of-electricity (COE) is reduced by about 10% when moving from 10 MW to 50 MW, from USD 1976/kW to USD 1668/kW, respectively. Renewable H2 is expected to be economically competitive with NG by 2030, when the U.S. Department of Energy’s target of USD 1/kg RH2 is reached.

Techno-Economic Optimization of SOC Design and Operating Conditions in a Solid Oxide Fuel Cell-Gas Turbine Hybrid System

Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems can reach exceptionally high fuel-to-electricity conversion efficiencies while emitting virtually zero criteria pollutants. Due to these characteristics and their fuel-flexibility, SOFC-GT hybrid systems are seen as a key technology in sustainable power generation. In this work we explore SOFC cell design parameters that can synergistically reduce thermal stress and cost, as well as system-level design strategies to maximize economic performance. Results show that NG-fueled hybrid systems can reach efficiencies of 75%-LHV at a cost-of-electricity of 77.73 $/MWh. A similar biogas system with integrated anaerobic digester and biogas upgrading resulted in an efficiency of 53%-LHV and a cost-of-electricity of 137.19 $/MWh.

A novel comparison of energy-exergy, and sustainability analysis for biomass-fueled solid oxide fuel cell integrated gas turbine hybrid configuration

Conventional gas turbines (GT) are working with limited fuels and exhibit thermal efficiency between 30 and 40%. This restriction with the fuels and its efficiency range can be improved by adding an electrochemical fuel cell, i.e; a Solid Oxide Fuel Cell (SOFC). This paper proposes three different types of biomasses, including pine sawdust, poplar sawdust, and almond shell, which may all be used to power the novel biomass-fueled solid oxide fuel cell gas turbine (SOFC-GT) presented herein. MATLAB based simulation is used to validate the results of this fuel cell based hybrid cycle performance. Three performance parameters are considered namely, current density (id), turbine input temperature (TIT), and pressure ratio (rp) to evaluate the performance of the proposed system. For this, energy-exergy approaches based on the first and second law of thermodynamics are used to assess each cycle component as well as the entire system. The sustainability index and environmental impact factor of each component are evaluated using dimensionless modified exergy indicators. With all three of the suggested biomass fuels, the SOFC-GT hybrid system runs most effectively at pressure-ratio of 6 and TIT 1250 K. Pine sawdust (Case-1) exhibits the largest levels of exergy destruction (2653.14 kW), environmental effect (0.91), and the lowest sustainability index (2.09) but it also has the highest levels of thermal efficiency (63.12%).

Comparative analysis of the thermodynamic performances of solid oxide fuel cell–gas turbine integrated systems for marine vessels using ammonia and hydrogen as fuels

To mitigate environmental issues and implement energy management strategies, hydrogen is emerging as the most promising and sustainable energy source to help achieve decarbonization targets and meet world energy demands. However, hydrogen poses significant storage and transportation challenges due to its low volumetric and gravimetric density. Hence, ammonia is a potential candidate for a hydrogen storage medium because it contains 17.65% hydrogen by weight, and its volumetric hydrogen density is 45% higher than that of liquid hydrogen. In the maritime sector, these available fuels of ammonia and hydrogen are utilized via internal combustion engines, fuel cells, and gas turbines, which are employed on board ships. This study investigates the possibility of using ammonia and hydrogen as fuels for Solid Oxide Fuel Cells (SOFCs). A combined SOFC-Gas Turbine (GT) system was proposed to generate power for marine propulsion plants. This system was designed and modeled with support from Aspen HYSYS V.12.1. Thermodynamics performances of the proposed system were analyzed using the first and second laws of thermodynamics. The energy efficiencies of direct ammonia and hydrogen SOFCs were 60.96 and 64.46%, respectively. The energy efficiencies of the combined systems increased by 12.37 and 13.97% when using ammonia and hydrogen as fuels, respectively, compared with that of single SOFC systems. The exergy destruction of the primary components with each fuel was examined. Furthermore, a parametric study was performed to select the most suitable fuel utilization factor for the system. This analysis proved that ammonia has the potential as a hydrogen carrier and that waste heat recovery is an effective method to improve the thermodynamic performance of an SOFC system.

Evaluation of Tubular SOFC’s Performance at Elevated Pressure for Highly-Efficient Clean Power Generation

Growing global energy needs and demand over imminent reductions of harmful greenhouse gas emissions, call for development of highly efficient, clean and reliable power generation from both renewable and fossil resources. A hybrid solid oxide fuel cell gas turbine (SOFC-GT) system is a promising candidate for fulfilling such need of a low emission, highly efficient power generation. This system can be applied to stationary, transportation, aviation, and maritime power generation applications. This study focuses on understanding operational characteristics of the pressurized SOFC as a key component for the successful design and construction of a highly efficient SOFC-GT hybrid system.Pressurization of an SOFC can cause improvement on electrode kinetics, stack lifetime and round-trip efficiency by cell integration with downstream components such as gas turbines and catalytic reactors (for electrolysis) [1-4]. However, literature data from experimental studies on the electrochemical behavior of the SOFC as a function of operating pressure is relatively scarce. This is presumably due to the complexity involved in the construction and operation of pressurized system. To address such research challenge, a pressurized SOFC test rig as shown in Fig. 1 has been constructed and commissioned at Tennessee Technological University (TTU) to allow tubular SOFCs to be characterized under a maximum operating pressure of 60 psia (~4 bar) and maximum operating temperature of 825oC. A detailed system set-up shown in Fig. 2. The power generation capacity for the test rig can be scaled up to 2.4 kW. For this study, performance of single anode supported SOFC tubes with H2 and CH4 fuels were examined by varying pressure from 1 bara to 4 bara and temperature from 675oC to 775oC, with fuel utilization held constant at 50% and an oxygen-to-carbon ratio (O/C) of 0.6 for the methane operation. The testing cells were gratuitously supplied by Special Power Sources (SPS) LLC, USA, with cathode/electrolyte outside-layers supported on the anode inner-layer as a 14”-long tube. Silver ink and wires are used for cell current collection from active surface area of ⁓100 cm2 . The connection fixture can be seen in Fig. 1. V-I curves of tubular SOFCs in Fig. 3 measured from step-wise electronic load profile indicate total performance gain of 13% as H2 pressure increases from 1 bara to 4 bara, with highest peak power density obtained at 0.61 Wcm-2. As comparison Fig.4 and 5 demonstrate pressurization suppressed gas diffusion limit for tubular SOFC at higher current density in CH4 fuel, leading to 44 % increase of peak power density to 0.51 Wcm-2 at 4 bara.Electrochemical impedance spectroscopy (EIS) studies were performed using a Solartron 1260/PAR 263 electrochemical testing system in 4-point connection measurement to understand effects of pressurization on the SOFC performance. SOFC impedance spectra as Nyquist and Bode plots in Fig.6 (b) and (d) indicate the tubular SOFC performance is mainly limited by anode mass transports, which are greatly improved by pressurization. From non-linear, least-square cell impedance fitting and previous findings on impedance of similar larger cells, an equivalent-circuit model (ECM) in Fig. 6(a) has been identified to best represent impedance responses from the most rate-limiting processes of tubular SOFCs. The Warburg component (Ws) in the ECM with resonance frequency around 10Hz typically corresponds to gas diffusion in porous electrode of tubular SOFC [3-5], while paralleled R-CPE component at <1Hz resonance frequency can be attributed to gas-conversion impedance (GCI) due to gas phases concentration gradient along fuel-flow channel resulting from reactant conversion [5,6]. Experimentally observed changes of such impedances with fuel compositions, flow rates and tubular SOFC configuration are generally in agreement with theoretical assumptions and other reports [4-6]. Overall, results of this work demonstrate pressurization can effectively boost anode-supported SOFCs’ performance by overcoming fuel-side mass-transport limit associated with practical cell configuration and testing geometry. The experimental performance data collected can then be used to fit key constants and estimate parameters for numerical modeling of the SOFC system performance at elevated pressures.References can be seen in the figure document. Figure 1

Study on Model Evolution Method Based on the Hybrid Modeling Technology With Support Vector Machine for an SOFC-GT System

Abstract The mechanism models of solid oxide fuel cell–gas turbine (SOFC-GT) systems are very useful to analyze the thermodynamic performance details, including the internal complex transfers of mass, heat, and electrochemical processes. However, several physical-property parameters in the mechanism model are unmeasurable and difficult to accurately quantify from the operation data when the inevitable degradation occurs. As a result, it is difficult for the mechanism model to accurately capture the SOFC electrochemical characteristic during the full operating cycle. In this paper, a model evolution method based on hybrid modeling technology is proposed to address this problem. A hybrid modeling framework of a SOFC-GT system is designed by combining a least squares-support vector machine algorithm (LS-SVM) electrochemical model with our previous mechanism model. The electrochemical characteristic of SOFC is easily identified and evolved by re-training the LS-SVM model from operating data, no longer needing a mechanism electrochemical model. The validated full-mechanism model from our previous work is taken to simulate a physical SOFC-GT system to generate the operating data. Various LS-SVM models are trained by different data sets. The comparison results demonstrate that the LS-SVM model trained by large-size data set 3 performs the highest accuracy in predicting the local current density. The maximum absolute error of prediction is only about 1.379 A/m2, and the prediction mean square error of the normalized test data reaches 4.36 × 10−9. Then, the LS-SVM hybrid model is applied to evaluate the thermodynamic performance of a SOFC-GT system. The comparison results between the hybrid model and our previous full-mechanism model show that the hybrid model can accurately predict the SOFC-GT system performance. The maximum error is 1.97% at the design condition and 0.60% at off-design conditions. Therefore, the LS-SVM hybrid model is significant for accurately identifying the real electrochemical characteristic from operation data for a physical SOFC-GT system during the full operation cycle.

Soft computing investigation of stand-alone gas turbine and hybrid gas turbine–solid oxide fuel cell systems via artificial intelligence and multi-objective grey wolf optimizer

Despite of huge effort performed in the literature encompassing the concept of hybrid solid oxide fuel cell–gas turbine (SOFC-GT), the economic and environmental superiority of this hybrid system over a conventional gas turbine (GT) has not yet been clarified. In the present study, a proper scale of solid oxide fuel cell was integrated with a GT and a comprehensive comparison analysis based on energy, exergy, exergo-economic and environmental (4E) criteria were conducted between 10 MW GT and hybrid SOFC-GT systems. Three different scenarios were considered for the comparison analysis, encompassing baseline operation, parametric behavior and optimum conditions. An appropriate artificial neural network (ANN) was utilized to model the systems, and then, the obtained ANNs were introduced to Grey Wolf optimizer. Using grey wolf optimizer, a multi-objective optimization problem was solved considering exergy efficiency, CO2 emission and unit cost of product as the objectives. The hybrid SOFC-GT system had a better performance than the GT system in terms of environmental and exergo-economic performances as the results of all three scenarios showed. However, this integration slightly increased the investment cost of the system at the baseline scenario. After optimization, at best trade-off between the objectives, the SOFC-GT exergy efficiency, CO2 emission and unit product cost were obtained to be 68.5 %, 277.7 kg/MWh, and 22.7 $/GJ, however, these values for the GT were 32.38 %, 588.4 kg/MWh, and 26.9 $/GJ, respectively.

Coupling impacts of SOFC operating temperature and fuel utilization on system net efficiency in natural gas hybrid SOFC/GT system

The major design parameters of SOFC have great impacts on the net electrical efficiency of SOFC/GT hybrid systems. The influence of the SOFC operating temperature and fuel utilization on the net efficiency of a pressurized solid oxide fuel cell gas turbine hybrid system was studied in this paper. The system model was combined a 1D SOFC model, which included a lumped equilibrium steam methane reformer model in the Simulink, with a gas turbine recuperated cycle model in Ebsilon®. A system design point study was established to observe the coupling impacts of SOFC operating temperature and fuel utilization on the system performance. Thirty design cases of SOFC operating temperatures (635 °C–835 °C) over a range of SOFC fuel utilization(45%–90%) were evaluated. The optimal SOFC fuel utilization shifted from 65% to 55% when the SOFC operating temperature decreased from 835 °C to 635 °C. The maximal(minimal) system efficiency was 74%(49%) at 65%(90%) SOFC fuel utilization with operating SOFC at 835 °C(635 °C). The results show that high operating temperature leads to the high efficiency of the entire hybrid system, but high fuel utilization might cause a decrease in system efficiency.

Coordinated control approach for load following operation of SOFC-GT hybrid system

In order to achieve the fast load following and safe transient operation of Solid Oxide Fuel Cell-Gas Turbine hybrid system, a novel control approach by combining the multi control loops with the coordinated protection loops is proposed in this work. The coordinated protection loops can adjust the transient behavior of operation parameters on-line to avoid the undesired operation faults, such as compressor surge, reformer carbon deposition, fuel cell thermal crack and turbine blade overheat. Meanwhile, the fuzzy logic theory is introduced to self-tuning the control parameters to meet the control requirements of the nonlinear time varying system. The analysis in system transient behavior during load step changes operation indicates that the present work can realize parameters decoupling and eliminate the instability of SOFC-GT. The proposed control strategy can reduce the SOFC current overshoot by 10.8% during the load step-down operation, meanwhile, this reduces the transient maximum temperature changing rate by almost 47.7%. In addition, by changing the transient behavior of air and fuel flow, the proposed control strategy can reduce the temperature overshoot by 1.16% in load step-up operation. This leads to the transient maximum temperature gradient is decreased by 0.18K/cm.

Numerical analysis of transport phenomena in solid oxide fuel cell gas channels

The gas channel geometry in solid oxide fuel cells (SOFCs) influences the reacting thermo-fluid process and, thus, overall cell performance. This paper presents a dimensionless approach to the study of the transport phenomena in the gas channels of planar anode-supported proton-conducting SOFC. Out-of-scale modeling reduces the number of variables that should be investigated and offers generalized results, giving insight into similar fuel cells. A 2D numerical model for the multiphysics process in SOFC is developed. A dimensionless form of the governing equations is derived in order to identify the dimensionless quantities that characterize the transport phenomena in SOFC. Reynolds, Peclet, and Sherwood are the important parameter groupings of flow channels that influence mass and temperature distribution. The efficacy of the computational fluid dynamic model is confirmed by comparing simulated results with experimental data from the literature. The effect of fuel and air channels’ dimensionless parameters on cell performance is discussed. Similar changes in fuel and air channels exert various influences on SOFC electrical performance. It is found that reducing Pe in the fuel channel improves power generation. However, Sh and Re reduction effect neutralize the increase in power generation due to Pe reduction in the air channel.

Study on the performance comparison of three configurations of aviation fuel cell gas turbine hybrid power generation system

Developing aviation power generation methods with high efficiency is one of the important issues that need to be solved in aviation field, especially for More/All Electric aircraft. In this paper, the advanced solid oxide fuel cell gas turbine hybrid power generation system based on aviation kerosene is studied. And the performance of three configurations of hybrid system without/with SOFC exhaust recirculation are compared and evaluated, which are a basic hybrid system without exhaust recirculation (BHS), an anode exhaust recirculation hybrid system (ARHS), and an anode and cathode exhaust recirculation hybrid system (ACRHS). The results show that the power generation efficiency of the BHS is 59.3%, while the two hybrid systems with exhaust recirculation increase to around 70%: the efficiency of ARHS is 70.9%, and ACRHS is 69.7%. But the ACRHS shows greater potential in increasing the SOFC cathode inlet temperature. And the specific work of the hybrid system with exhaust recirculation can reach more than 760 kW (kg air)−1. In addition, the parameters such as pressure ratio, temperature ratio and fuel utilization have important influence on the performance. Due to the advantages of high power generation efficiency and specific work, hybrid system is a competitive power generation system in aviation field.

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.

Design and performance analysis of a de-coupled solid oxide fuel cell gas turbine hybrid

Hybrid solid oxide fuel cells (SOFC) cycles of varying complexity are widely studied for their potential efficiency, carbon recovery and co-production of chemicals. This study introduces an alternative de-coupled fuel cell-gas turbine hybrid arrangement that retains the high efficiency thermal integration of a topping cycle without the high temperature heat exchanger of a bottoming cycle. The system utilizes a solid-state oxygen transport membrane to divert 30%–50% of the oxygen from the turbine working fluid to the intermediate temperature SOFC. Thermodynamic modeling delineates design trade-offs and identifies a flexible operating regime with peak fuel-to-electric efficiency of 75%. Co-production of electricity and high purity hydrogen result in net energy conversion efficiencies greater than 80%. The potential to retrofit existing turbine systems, particularly micro-turbines and stand-by ‘peaker’ plants, with minimal impact to compressor stability or transient response is a promising pathway to hybrid fuel cell/turbine development that does not require turbomachinery modification.

An integrated solution to harvest the waste heat from a large marine solid oxide fuel cell

The substantial use of fossil fuels in marine transportation aggravates the problems of energy shortage and environmental pollution. The application of fuel cell and waste heat recovery technology in ships can effectively address this severe global issue. In this study, a novel combined system comprising a solid oxide fuel cell–gas turbine subsystem, supercritical-carbon dioxide recompression cycle, and Kalina cycle is introduced and analyzed. First, the feasibility of each model is verified by comparing the subsystems with results in the literature. Subsequently, zeotropic working fluids are used in the supercritical-carbon dioxide recompression cycle. Then, the optimum composition and ratio of working fluids in the bottoming cycles are determined by simulation. Finally, the thermodynamic and economic properties are simulated and analyzed. The results illustrate that the actual power output and thermal efficiency of this combined system can reach 286.41 kW and 71.37%, respectively. The latter is 38.65% higher than the efficiency of a solid oxide fuel cell. In addition, the maximum cost recovery time of the waste heat recovery system is 7.492 year, which completely satisfies the economic requirements. To summarize, the proposed novel system design exhibits characteristics of high efficiency and cleanliness and is a better option for marine power generation equipment.

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.

Performance analysis of a biogas-fueled SOFC/GT hybrid system integrated with anode-combustor exhaust gas recirculation loops

This paper proposed a solid oxide fuel cell–gas turbine (SOFC-GT) hybrid system combined with anode and combustor exhaust recirculation loops. The ejector technology is introduced to perform the recirculation loops. And the hybrid system is fueled by a typical farm biogas. Furthermore, the interaction between these two recirculation is discussed. Results show that the anode recycle loop can rise the electrical efficiency of hybrid system and drop the SOFC temperature gradient. Meanwhile, the anode exhaust recirculation is beneficial to avoid the carbon deposition in reformer and prevent the fuel cell thermal crack, and the combustor exhaust recirculation can allow the system safety operated over a wider temperature range. The optimal recirculation ratio of 0.4 and 0.425 are determined in anode and combustor exhaust respectively to obtain the maximum power generation efficiency and ensure the safety operation of SOFC. The design efficiency of described system can reach to 62.21%. In addition, a parametric analysis is carried out to evaluate the coupling effect among multiple working parameters on the performance of SOFC-GT. Results indicated that the reasonable air flow rate, fuel flow rate, fuel utilization and steam to carbon ratio are the necessary prerequisite to safeguard the healthy operation of SOFC-GT.