Solid Oxide Fuel Cell Gas Turbine Hybrid Research Articles

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.

Comparative study of fuel types on solid oxide fuel cell – gas turbine hybrid system for electric propulsion aircraft

As a novel aviation power generation system, the solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system has high electrical efficiency. Because aviation applications are sensitive to weight, the research of this system should not only consider thermodynamic performance but also focus on mass. Fuel is the energy source of the aircraft powered by SOFC-GT hybrid system, and the types not only affect the power generation performance and mass of the system but also determine the storage capacity. Therefore, the impact of fuel types on the SOFC-GT aircraft can be fully evaluated through the comprehensive analysis of the performance and mass. In this paper, the aircraft powered by SOFC-GT hybrid system fueled by hydrogen, ethanol and alkanes (n-decane, n-octane and liquid methane) are investigated. By establishing the thermodynamic model and mass model, the influence of fuel types on the performance of autothermal reforming, SOFC-GT hybrid system, and aircraft cruise is studied in sequence. The results show that in the reforming process, methane has the best hydrogen production performance and makes SOFC efficiency the highest. However, the performance of the SOFC-GT system is influenced by many factors. For non-hydrogen fuels, n-decane can achieve higher electrical efficiency, while methane has lower fuel consumption. The thermodynamic performance of the hydrogen-fueled system has absolute advantages, but it depends on the larger heat exchanger. Furthermore, for the electric regional aircraft powered by the SOFC-GT hybrid system, the range of aircraft fueled by hydrogen and ethanol is poor, and liquid hydrogen can only take advantage of its high energy density at lower payload due to the mass penalty of the cryogenic tanks, while n-decane and n-octane are superior. Meanwhile, CO2 emissions can still be significantly reduced by matching n-decane with the efficient SOFC-GT hybrid system.

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%).

Study on an adaptive multi-model predictive controller for the thermal management of a SOFC-GT hybrid system

A SOFC temperature control system based on adaptive multimodel predictive control (MMPC) method is designed for a solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system with anode and cathode ejectors. Two multi-input and multi-output MPCs (under 100% and 90% load) are designed to control the anode and cathode inlet temperatures. The accuracy of the identified linear models are both more than 95%. The control performance of the designed MMPC is compared with a single MPC and traditional PI. The comparison results demonstrate that the proposed MMPC is most effective and competitive in SOFC thermal management. During the load following, the controller overshoot is less than 1.19K. The settling time is about 2000s, and the integral of time-weighted absolute error is less than 472.

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

A novel control strategy with an anode variable geometry ejector for a SOFC-GT hybrid system

A novel control strategy was developed with an anode variable geometry ejector for a solid oxide fuel cell-gas turbine (SOFC-GT) system. The anode inlet temperature was controlled by combining two modes to achieve a greater controllable range: anode variable geometry ejector adjusting and after-burner fuel valve adjusting. Two tests were carried out under small-scale and large-scale load steps. The results indicate that all controlled variables can be effectively kept around set-point. Moreover, the critical parameters are kept within safe ranges, including steam-to-carbon ratio higher than 2.0, peak temperature gradient below 10 K/cm, peak time-dependent temperature gradient below 3 K/min, and surge margin higher than 15%. The developed novel control strategy can maintain almost constant SOFC spatial temperature. The spatial temperature variation is within 2.50 K under 5% load step, and within 14.30 K under 30% load step. Besides, the novel control strategy can keep the system efficiency at a high level (more than 63.21%) during the load tracking. Compared with the conventional control strategy with a fixed geometry ejector, the results demonstrated that the novel control strategy can significantly improve the system performance, especially the transient behaviors of after-burner fuel rate, turbine inlet temperature, and system efficiency.

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.

Rapid load transition for integrated solid oxide fuel cell – Gas turbine (SOFC-GT) energy systems: A demonstration of the potential for grid response

Rapid load transition is an essential requirement for integrated energy systems to maintain grid resilience as more renewable resources are added to the grid. Integrated solid oxide fuel cell – gas turbine (SOFC-GT) systems can provide high efficiency and low carbon emissions over a broad range of turndown. These hybrids also have the potential to enable rapid grid response. The challenge has been to demonstrate effective control strategies to manage load transitions. In the present study, a load transition of ∼50% was achieved in 10 s using a novel but simple strategy. Power demand on the SOFC and the GT were ramped down concurrently. During this transition, the SOFC anode fuel was manipulated to maintain SOFC fuel utilization while the cathode inlet air flow and temperature were also manipulated to thermally protect the SOFC. This study was conducted using the Hybrid Performance (Hyper) facility at the National Energy Technology Laboratory (NETL) in a co-simulation environment with the Idaho National Laboratory (INL)’s grid-simulation. The load ramping strategy was tested using a hardware-based cyber-physical simulation methodology. The results demonstrate a high-fidelity representation of SOFC-GT hybrid dynamics and validation of the control strategy. Thermal and electrochemical transients indicated that the SOFC was well protected during rapid load turndown without violating operability constraints. This demonstration revealed the non-linear nature of tightly coupled SOFC-GT system components, especially the non-linear response of SOFC cathode air flow and inlet temperature controls. These results highlight the needs and challenges in developing adaptive automatic controls for autonomous rapid load transitions. This work demonstrates that SOFC-GT hybrids are a viable option to provide the fast-ramping characteristics essential to accommodate high levels of variable renewable power while maintaining grid resilience, reliability, and environmental performance. The results also demonstrate the utility of co-simulation in advancing the tightly-coupled integrated energy systems needed to meet goals for zero-carbon power generation.

Comparison of different fuel cell temperature control systems in an anode and cathode ejector-based SOFC-GT hybrid system

Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems are facing challenges in terms of fuel cell temperature control due to its significant effect on safe and efficient operation. In this study, five different temperature control systems are designed according to different SOFC control strategies and control points in anode and cathode ejector-based SOFC-GT hybrid systems. Firstly, three SOFC temperature control strategies including only anode-side control, only cathode-side control, and two-side control are compared. The comparison results indicate that the cathode-side temperature control strategy can effectively maintain the system efficiency. In addition, the two-side control strategy is better than one-side control strategies considering the safe operation of the anode and cathode differential temperature. Then, three SOFC temperature control points including input temperature, output temperature, and average temperature are chosen in order to investigate the effect of control variables. The comparison results indicate that maintaining the average temperature is better than the other temperature control points. Therefore, the two-side average temperature control system of SOFC is more appropriate to guarantee efficient and safe operation. The temperature distribution in SOFC is more feasible, and the efficiency of SOFC and the whole hybrid system is most efficient at a part load condition.

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.

Performance characteristics of a solid oxide fuel cell hybrid jet engine under different operating modes

Solid oxide fuel cell (SOFC) technology is promising. Jet engines can be integrated with SOFCs (SOFC hybrid jet engine) for aircraft. The specific thrust of the engine is greatly improved by replacing turbines with SOFC systems. Four operating modes are designed for the engine to achieve about 50% ∼ 100% thrust variation. Mode 1: Regulating the fuel flow in the reformer under the constant air flow for the SOFC system. Mode 2: Regulating the fuel flow in the afterburner with zero fresh air for afterburners. Mode 3: Regulating the fuel and air flow for the SOFC. Mode 4: Regulating the fuel flow in the afterburner with constant air flow for afterburners. The performance and thermodynamic parameters of the engine under different operating modes are examined and compared according to the built mathematical models. The simulation results show that the effects of operating modes on the engine are remarkably different from that on the traditional SOFC gas turbine hybrid systems for electricity generation. All of the parameters of components change sharply in modes 1 and 3, and the thermal efficiency of the engine increases respectively from 0.577 to 0.687 and 0.491 to 0.687 with the increase of load. The component parameters of the engine are slightly changed in modes 2 and 4 except the parameters related to the afterburner. In mode 2, the thermal efficiency decreases from 0.577 to 0.454. It decreases from 0.491 to 0.434 in mode 4. In a nutshell, the performance of the engine can be varied in a wide range under the operating model 4 with increasing the afterburner temperature from 832 K to 2261 K. The operating mode 4 is the best.

Performance Evaluation of an SOFC-GT Hybrid System With Ejectors for the Anode and Cathode Recirculations

The ejectors used for the fuel cell recirculation are more reliable and low cost in maintenance than high-temperature blowers. In this paper, an anode and cathode recirculation scheme, equipped with ejectors, was designed in a solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system. The ejector model, SOFC model, and other component models and the validation were conducted to investigate the performance of the hybrid system with anode and cathode ejectors. The geometric parameters of the ejectors were designed to perform the anode and cathode recirculation loops according to the design conditions of the hybrid system with a blower-based recirculation loop. The cathode ejector geometries are much larger than the anode ejector. In addition, the sensitivity analysis of the primary fluid for the standalone anode and cathode ejectors is investigated. The results show that the ejector can recirculate more secondary fluid by reducing the ejector outlet pressure. Then, the anode and cathode ejectors were integrated into the SOFC-GT hybrid system. A blower gets involved downstream, and the compressor is necessary to avoid high expensive cost of redesigning compressor. The off-design and dynamic performance were characterized after integrating the anode and cathode ejectors into the hybrid system. The dynamic and off-design performances show that the designed ejectors are effectively integrated into the anode and cathode recirculation loops to replace the blower-based recirculation loops. The safety range of relative fuel flow rate is 0.62–1.22 in the fixed rotational speed strategy, and it is 0.53–1.1 in the variable rotational speed strategy. The variable rotational speed strategy can ensure higher system efficiency, which is more than 61% at a part-load condition.

Study on Fuel Utilization Dynamic model of a SOFC-GT Hybrid System Based on Deep Learning Technique

In order to perform operation management tasks, including state monitoring and control strategy optimization, of a solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system, a data-driven dynamic model based on deep learning technique of long short term memory (LSTM) network is developed to predict the behaviours of fuel utilization. In addition, a LSTM model with unsupervised deep auto-encoder (DAE) method was developed to extract the feature from input data. The comparison performance between the common LSTM model and DAE-LSTM model was investigated. The results show that the DAE-LSTM model can enhance the prediction performance. Moreover, the effect of data size was investigated. The results demonstrate that the unsupervised DAE-LSTM model trained by large data size can further improve the prediction performance. The maximum error is only 0.00529, and average error decreases to 0.00025. In conclusions, the unsupervised DAE-LSTM model is an effective approach to predict dynamic behaviours.

Experimental study of homogeneous charge compression ignition engine operation fuelled by emulated solid oxide fuel cell anode off-gas

A solid oxide fuel cell (SOFC) hybrid system is a system that combines an SOFC with an additional power generation device to increase the efficiency of the system. The SOFC–gas turbine hybrid system has been primarily investigated for SOFC hybrid systems. However, the current power generation capacity of an SOFC is less than several MWs; for this generation capacity, an internal combustion engine is generally more efficient and economical than a gas turbine. Focusing on this point, recently, the concept of an SOFC–internal combustion engine hybrid system was proposed. However, the operation of this system has not been experimentally studied yet. In this paper, as the first step in an experimental investigation of the hybrid system, an experimental study on the operation of an internal combustion engine fuelled by SOFC anode off-gas was conducted. To successfully combust the SOFC anode off-gas, which includes a large amount of diluents (H2O and CO2), the homogeneous charge compression ignition (HCCI) method was selected instead of spark ignition as the combustion strategy of the internal combustion engine in the hybrid system. For the HCCI engine experiments, a single-cylinder HCCI engine and experimental equipment for emulating SOFC anode off-gas were constructed. Various HCCI engine experiments were performed while varying several system control parameters, e.g., the fuel utilization factor of an SOFC, which primarily affects the composition and flow rate of the engine intake gas. The experiments indicated that, in general system operating condition, HCCI engine operation yields a significant amount of power (w/25–30% gross indicated efficiency) and produces significantly low NOx emissions (<5 ppm @ O2 15%) under stable HCCI combustion (<5% COV IMEPg, which is the coefficient of variance of the gross indicated mean effective pressure). Considering that the experiment was performed using a small single-cylinder engine, these experimental results reveal that the use of an HCCI engine as the bottoming cycle in an SOFC hybrid system is promising. In addition, it has been found how each system control parameter affects HCCI engine operation. It was confirmed that HCCI engine operation was not always stable in all system operating conditions. System operating conditions that induce an exceedingly low engine load (<1.8 bar IMEPg, which is the gross indicated mean effective pressure) should be avoided as it decreases the stability of engine operation. Additionally, system operating conditions that make an engine intake gas with excessive dilution (fuel molar fraction < 0.125) should be avoided to decrease the amount of unburned CO emission and maintain a CO combustion efficiency higher than 90%.

Thermo-environmental and economic comparison of three different arrangements of solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems

A comparative analysis is performed for three different layouts of SOFC-GT hybrid systems with internal reformer from the viewpoints of energy, exergy, environmental and economic. The three considered designs are distinguished by number of SOFC stack, as single SOFC stack is employed in one system, while two SOFC stacks (cell numbers halved) are used for the other designs. For the second system, two stacks are fed by fuel and air in parallel way; however, in the third case, two stacks are fed by fuel in parallel and air serially. A mathematical model is developed in EES software to simulate the performance of the cycles through a parametric study. In addition, exergy destruction rate of components of the plants are achieved to recognize the main sources of ireversibilities. The analyses demonstrated that two-stack SOFC-GT series type is more efficient, leading energy and exergy efficiencies to reach 63.22% and 60.81% correspondingly, which are about 20.3% and 8.89% higher than conventional SOFC-GT and parallel type, respectively. The highest source of exergy destruction amongst all system components belongs to after burner. Furthermore, it is observed that the highest total cost, 24.95 $/h, is attributed to conventional SOFC-GT hybrid system while the least amount corresponds to SOFC-GT series type, 18.5 $/h. The CO2 gas emission obtained for two-stack SOFC-GT hybrid system series type, 313.3 kg/MWh, obtained to be the lowest.

Study on control strategy for a SOFC-GT hybrid system with anode and cathode recirculation loops

The solid oxide fuel cell-gas turbine (SOFC-GT) hybrid power generation system offers a possible technology of high efficiency combined with low emissions. Due to its highly coupled system and complex dynamic characteristics, several vital parameters such as fuel cell temperature, thermal stress, steam-to-carbon, turbine inlet temperature, and compressor surge margin must be controlled and restricted to a feasible zone to guarantee the safe operation of the hybrid system. A novel control strategy was carried out for the SOFC-GT hybrid system with anode and cathode recirculation loops. In the SOFC thermal management system, two control loops were introduced to keep anode temperature and cathode temperature. The behaviors of the control system were compared with the control system without an anode temperature control loop during load following. The results reveal that the anode channel temperature and cathode channel temperature should both be controlled to avoid huge temperature differences and temperature gradient in SOFC. The designed control system 1 in this study for the hybrid system is feasible and effective.

Gas turbine advanced power systems to improve solid oxide fuel cell economic viability

Abstract 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.

Cycle analysis of solid oxide fuel cell-gas turbine hybrid systems integrated ethanol steam reformer: Energy management

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.

Estimation of operating parameters of a SOFC integrated combined power cycle using differential evolution based inverse method

Inverse analysis is an efficient method to estimate parameters that characterizes a given system. It offers lot of flexibility at the designer’s hand in selecting the most suitable combination of parameters satisfying a given set of objective functions. In this study, inverse analysis of a solid oxide fuel cell (SOFC)–gas turbine (GT)–steam turbine (ST) combined cycle (CC) power system is performed. The system’s net power, efficiencies (energy and exergy) and the total irreversibility at compressor pressure ratio (CPR) 6 and 14 are considered as objective functions for the inverse problem. A differential evolution (DE) based inverse algorithm is used for simultaneously estimating six operating parameters of the plant. It was seen that the inverse technique was very effective in estimating the operating parameters of a hybrid SOFC–GT–ST plant correctly within the prescribed lower and upper bound of the parameters. Multiple combinations of parameters are obtained from the study and all these combinations of parameters satisfy the given single objective function/set of objective functions. Any objective function value be set and then operating parameters be determined accordingly using the inverse method. The results offer plenty of scope for selection of suitable operating parameters for the plant.