Fuel Cell-gas Turbine Hybrid System Research Articles

Use of zero-dimensional modelling to predict performance and assess feasibility of solid oxide fuel cell-gas turbine hybrid system

This study looks at a steady state and a dynamic model of a solid oxide fuel cell-gas turbine (SOFC-GT) system. The steady state model is used to perform a sensitivity analysis of the system’s electrical efficiency to design parameters at design point, while the dynamic model is used to predict key performance indicators across the operating range of the system. Electrical efficiency at the design point was found to be most sensitive to gas turbine pressure ratio and SOFC temperature. Power output was increased from the baseline to peak on the dynamic model and peak electrical efficiency was found to be 0.61 at 58% load.

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.

Thermodynamic Analysis of Three Internal Reforming Protonic Ceramic Fuel Cell-Gas Turbine Hybrid Systems

Protonic ceramic fuel cells (PCFCs) offer direct and efficient conversion of hydrocarbon fuels into electricity. In this study, three internal-reforming (IR)-PCFC/gas turbine (GT) hybrid systems are proposed and analyzed to achieve higher system efficiency. High-quality heat from GT in system 1 and system 2 is supplied to anode and cathode preheaters, respectively, whereas in system 3, the heat is simultaneously split into both preheaters. Effects of air flow rate, fuel utilization factor (Uf), and steam to carbon ratio (S/C) are also investigated. It is found that the best system design can be achieved by effectively utilizing GT exhaust heat for both electrode preheaters, as indicated in system 3. The maximum energy system efficiency obtained among the hybrid systems analyzed in this study is 71% with total exergy destruction of 686.7 kW. When fueled by methane, the hybrid system can achieve energy and exergy efficiencies of 71% and 77%, respectively, with 0.85 Uf. On the other hand, propane-fueled systems can achieve energy and exergy efficiencies of 68% and 75%, respectively. As S/C increases from 2 to 7, system efficiency decreases from 71% to 50%. When system 3 is fueled with butane or propane, system efficiency is only 3% lower than that fueled by methane.

Fast and stable operation approach of ship solid oxide fuel cell-gas turbine hybrid system under uncertain factors

This work focuses on investigating the adaptability of solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system for ship application under uncertain factors. The effect of rapids, wind and waves on the performance of ship SOFC-GT is analyzed. In addition, a novel control system combining fuzzy logic theory, temperature feedforward and coordination factor on-line adjustment is proposed to address the problem of load disturbances caused by uncertain factors. The results show that the proposed operation strategy can shorten the thermal response time inside fuel cell stacks by almost 49.97%, meanwhile, reducing the maximum temperature changing rate at the electrochemically active tri-layer cell composed of anode, electrolyte, and cathode (PEN structure) by around 17.86%. Moreover, the reasonable matching between air flow and fuel flow is an essential prerequisite to ensure the safe and efficient operation of ship SOFC-GT. While the SOFC-GT is working at full load, the results indicate that the fuel to air ratio cannot exceed 2.56✕10−2 g/g. Finally, an application scenario of the 5000-ton river-to-sea cargo ship sails from Nanjing Port to Yangshan Port (Eastern China) is conducted to analyze the operation characteristics of ship SOFC-GT under uncertain factors. Two set of 1000 kW SOFC-GT systems with the electrical efficiency of 64.66% is designed for the target ship, the results conclude that the operation strategy of each SOFC-GT system supports 50% load is beneficial in reducing the power tracking time and SOFC temperature overshoot. The average electrical efficiency of 61.45% and 61.04% are achieved in winter and summer typical days respectively in the whole voyage.

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.

A Degradation Diagnosis Method for Gas Turbine—Fuel Cell Hybrid Systems Using Bayesian Networks

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

Energy and exergy analyses of solid oxide fuel cell-gas turbine hybrid systems fed by different renewable biofuels: A comparative study

In recent years, many studies have been conducted on hybrid solid oxide fuel cell and gas turbine which fed by renewable fuels to reach the high-efficiency power and the low pollution. In this paper, a thermodynamic study based on energy and exergy analyses of a hybrid solid oxide fuel cell and gas turbine hybrid system has been conducted in the presence of reforming with steam, in which the effects of using natural gas and other biofuels including Sewage biogas, Agricultural and Industrial waste biogas, Syngas, Biofuel and Gasified biomass, have been compared to this system. The purpose of this paper is to investigate the effect of each of the mentioned fuels on the performance of individual equipment and the entire system from the thermodynamic perspective. Initially, the modeling and energy balance of all components in the system were carried out in detail. Further, calculating the exergy destruction of all components of the system and the effects of applying different biofuels on the key parameters of the system, including total production power, operating pressure and temperature, compression ratio, the water-to-fuel ratio in the reforming, energy and exergy efficiency, and the amount of irreversibility of each component in the system have been analyzed. To compare more accurately between different fuels, an equal amount of each fuel is considered, and the effect of each fuel system on the hybrid system is analyzed by calculating the operating parameters of the system. By studying the results of modeling, it was determined that natural gas with 879.03 kW produced the highest production capacity and Gasified biomass with 45.44 kW has the least amount of power generation. By studying the thermodynamics of the system, if it is fed with Natural gas, the highest exergy destruction (687.45 kW) occurs and the lowest total exergy destruction rate is related to the system fed by gasified biomass (101.12 kW). Comparing the fuels, it was concluded that the electrical efficiency of the system fed with natural gas has the highest efficiency (72.71%) and Biofuel has the lowest total electrical efficiency (56.6%). Furthermore, by examining the exergy efficiency of the whole system, it was found that Natural gas with the highest efficiency of 61.29% and Gasified biomass with 46.06% the lowest exergy efficiency can be detected. Finally, the effect of the percentage combination of each fuel on the performance of all equipment from the perspective of energy and exergy has been studied.

Parametric analysis and optimization for exergoeconomic performance of a combined system based on solid oxide fuel cell-gas turbine and supercritical carbon dioxide Brayton cycle

Fuel cell-gas turbine hybrid system is a potential field of investigation. This study establishes a modeling and optimization framework for a novel hybrid system consisting of a solid oxide fuel cell, a gas turbine and a supercritical carbon dioxide Brayton cycle. Based on the proposed thermodynamical model, a parametric analysis is investigated to determine the impacts of several key parameters on the system exergoeconomic performance. Meanwhile, bi-objective optimization is conducted for maximizing the exergy efficiency and minimizing the levelized cost of electricity via the Epsilon-constraint approach. The Linear Programming Techniques for Multidimensional Analysis of Preference decision-making approach is further employed to select the Pareto optimum solution from Pareto frontiers. The results show that several extreme values for the exergy efficiency and the levelized cost of electricity exist in a series of sensitivity curves, respectively. The Pareto frontiers indicates that with the increase of the exergy efficiency, the levelized cost of electricity shows a moderately increasing trend at first and increases rapidly afterward. Overall, at the Pareto optimum solution, the combined system can achieve an optimal exergy efficiency and levelized cost of electricity by 68% and 0.0575 $ kWh−1, respectively.

Comparison between conventional design and cathode gas recirculation design of a direct-syngas solid oxide fuel cell–gas turbine hybrid systems part II: Effect of temperature difference at the fuel cell stack

This study focuses on the effect of the temperature difference at the fuel cell stack (ΔTcell) on the performances of the two types of SOFC–GT hybrid system configurations, with and without cathode gas recirculation system. In order to investigation the effect of matching between the SOFC temperature (TSOFC) and the turbine inlet temperature (TIT) on the hybrid system performance, we considered additional fuel supply to the combustor as well as cathode gas recirculation system after the air preheater. Simulation results show that the system with cathode gas recirculation gives better efficiency and power capacity for all design conditions than the system without cathode gas recirculation under the same constraints. As the temperature difference at the cell becomes smaller, the both systems performance generally degrade. However the system with cathode gas recirculation is less influenced by the constraint of the cell temperature difference. The model and simulation of the proposed SOFC–GT hybrid systems have been performed with Cycle-Tempo software.Article History: Received January 16th 2018; Received in revised form July 4th 2018; Accepted October 5th 2018; Available onlineHow to Cite This Article: Azami, V and Yari, M. (2018) Comparison Between Conventional Design and Cathode Gas Recirculation Design of a Direct-Syngas Solid Oxide Fuel Cell–Gas Turbine Hybrid Systems Part II: Effect of Temperature Difference at The Fuel Cell Stack. International Journal of Renewable Energy Development, 7(3), 263-267.http://dx.doi.org/10.14710/ijred.7.3.263-267

Compressor Instability Analysis Within a Hybrid System Subject to Cycle Uncertainties

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

Effect of different operating strategies for a SOFC-GT hybrid system equipped with anode and cathode ejectors

Ejector technology is introduced to perform the anode and cathode recirculation loops with low maintenance costs and high reliability. Four different operating strategies were designed for the novel solid oxide fuel cell-gas turbine hybrid system with anode and cathode ejectors to keep high efficiency and safety at a part-load operating condition. The part-load characteristics under different operating strategies were compared according to the simulation results. The comparison results show that the operating strategy has great effect on the part-load performance of the hybrid system with anode and cathode ejectors. Maintaining the SOFC operating temperature with variable speed operation has a great significance on the system efficiency. Moreover, fuel utilization, turbine inlet temperature, fuel cell temperature should be controlled and monitored to guarantee safely operating. Specifically, a concept of monitoring the temperature difference between anode and cathode channel is proposed. It can effectively avoid huge fuel cell temperature differences and compressor surge. Therefore, case 4 is an effective and appropriate operating strategy, which adjusts the primary fuel flow rate of SOFC, rotational speed, assistant fuel flow rate, compressor/turbine bypass flow rate to maintain turbine inlet temperature and temperature differences between anode and cathode.

Performance and availability of a marine generator-solid oxide fuel cell-gas turbine hybrid system in a very large ethane carrier

This study investigates the proper configuration of an electric propulsion system for a very large ethane carrier. The system consists of a dual-fuel diesel electric generator and a solid oxide fuel cell-gas turbine hybrid system to replace the mechanical propulsion system based on a marine diesel engine. When the ship navigates the open sea, the dual-fuel diesel electric generator and hybrid system run in parallel at a power rating of 16 MW. However, the hybrid system only operates during the berthing state for ship hoteling. The system efficiency, energy efficiency design index, and availability are considered to identify the optimal system configuration. When the dual-fuel diesel electric generator produces 10 MW, the hybrid system generates 6 MW. Because the electric propulsion system complies with international environmental regulations, it may be broadly acceptable for gas carriers in terms of eco-efficiency. The system achieves high availability by using fault tree analysis and minimal cut sets.

Control strategy design for a SOFC-GT hybrid system equipped with anode and cathode recirculation ejectors

The ejectors equipped for anode and cathode recirculation loops are more reliable and low-cost in maintenance than blowers in a solid oxide fuel cell-gas turbine hybrid system. However, an effective control system is one of the technical challenges associated with the development of the hybrid system. In present work, a novel control strategy was designed to restrict the hybrid system equipped with anode and cathode recirculation ejectors to a safe and feasible zone. Six control loops were carried out to control the vital parameters including power, rotation speed, fuel utilization, anode and cathode inlet temperature, and turbine inlet temperature. At the same time, the performance of another control system without anode inlet temperature control loop was also investigated. A comparison results of the two control systems reveal that both anode and cathode inlet temperature loops are necessary. If there is no anode inlet temperature control loop, the system efficiency decreases by 0.18%, the fuel cell inlet temperature differences between anode and cathode increases by 9 K and the compressor surge margin decreases by 1.8% at 95% system load. It not only causes a little reduction in efficiency but also may cause some latent dangers of the hybrid system at a part load condition. Consequently, the control system with all six control loops is effective and appropriate.

Comparison Between Conventional Design and Cathode Gas Recirculation Design of a Direct-Syngas Solid Oxide Fuel Cell–Gas Turbine Hybrid Systems Part I: Design Performance

In this paper, a conventional SOFC–GT hybrid system and a SOFC–GT hybrid system with cathode gas recirculation system fueled with syngas as the main source of energy were analyzed and their performances were compared. In the conventional SOFC–GT hybrid system, the incoming air to the cathode was heated at air recuperator and air preheater to meet the required cathode inlet temperature. In the SOFC–GT hybrid system with cathode gas recirculation, besides air recuperator and air preheater, the recirculation of the cathode exhaust gas was also used to meet the required cathode inlet temperature. The system performances have been analyzed by means of models developed with the computer program Cycle–Tempo. A complete model of the SOFC–GT hybrid system with these two configurations evaluated in terms of energy and exergy efficiencies and their performance characteristics were compared. Simulation results show that the electrical energy and exergy efficiencies achieved in the cathode gas recirculation plant (64.76% and 66.28%, respectively) are significantly higher than those obtained in the conventional plant (54.53% and 55.8%). Article History: Received Feb 23rd 2017; Received in revised form May 26th 2017; Accepted June 1st 2017; Available onlineHow to Cite This Article: Azami, V, and Yari, M. (2017) Comparison between conventional design and cathode gas recirculation design of a direct-syngas solid oxide fuel cell–gas turbine hybrid systems part I: Design performance. International Journal of Renewable Energy Development, 6(2), 127-136.https://doi.org/10.14710/ijred.6.2.127-136

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.

An optimal configuration for a solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system based on thermo-economic modelling

The aim of this research is to present an optimal configuration for solid oxide fuel cell-gas turbine hybrid systems based on thermo-economic modelling. To this end, four different designs of direct hybrid systems with pressurized and atmospheric fuel cells have been presented. In the first two designs, one stack fuel cells has been used in the hybrid system, and in the other designs, two stack fuel cells have been utilized. By examining four hybrid system, it was found that hybrid system with one pressurized fuel cell hybrid system is better than the other. The advantages of this system include its lower irreversibility rate, low purchase, low installation and startup costs, and the adequate price of its generated electricity. Results show that the hybrid system with one atmospheric fuel cell has a low electrical efficiency, high irreversibility rate; and also the price of its generated electricity is higher than that of the other proposed systems. Conversely, the hybrid systems with two fuel cells, in spite of enjoying a high efficiency, are not cost-effective and economical. The findings indicate that the total efficiency of 64% and electrical efficiency of 51% was achieved for optimal hybrid system. Also, the thermo-economic analyses show that the generated electricity price is about USD 11.6 cents/kWh based on the Lazareto's model and USD 18.5 cents/kWh based on the total revenue requirement model. The purchase, installation and startup cost of this hybrid system is about $1692/kW; which is almost twice the cost of a gas turbine unit.

Effects of SOFC Exhaust Gas Recirculation on Performance of Solid Oxide Fuel Cell-Gas Turbine Hybrid System Utilizing Renewable Fuels

A solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system run on renewable fuels, such as biogas and ethanol, is an interesting power generation technology due to its high efficiency. To avoid a carbon formation on the anode catalyst by the direct feed of hydrocarbon fuels to SOFC, a pre-reformer is needed to integrate with the SOFC system for hydrogen production. As the steam reformer and air preheater are units that require high external energy input, the efficient heat management of the SOFC system is necessary. Regarding the SOFC system, the anode and cathode recirculations are employed to recover high-quality waste heat for reformate gas and gas turbine cycle, affecting the electrical and thermal system efficiency. In this study, a steam reformer and SOFC-GT hybrid system with anode and cathode recirculations is investigated. The aim of this work is to analyze the effects of the anode and cathode recirculations on the performance of SOFC-GT systems. The mathematical model of SOFC, gas turbine, and auxiliary units based on mass and energy balances under steady-state operation is employed for this study. The parametric analysis of key operating parameters, such as fuel utilization, steam to carbon ratio and operating pressure, on the system performance is performed. The results indicate that the SOFC hybrid system with the anode recirculation can reduce the supplied heat for the external steam reformer; on the other hand, it degrades the gas turbine performance due to a decrease in the turbine inlet temperature. When considering the hybrid system with the cathode recirculation, it is found that the efficiency of the SOFC-GT system is higher. However, the turbine inlet temperature is extremely high, leading to the cooling problem of a micro turbine.

Effects of SOFC Exhaust Gas Recirculation on Performance of Solid Oxide Fuel Cell-Gas Turbine Hybrid System Utilizing Renewable Fuels

The use of biogas and ethanol as fuel for solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system needs of the external steam reformer. As the steam reformer and air preheater are units that require high external energy input, the efficient heat management of the SOFC system is necessary. Thus, the aim of this study is to analyze the recycling of the SOFC exhaust gas in the SOFC-GT hybrid system supplying fuels as ethanol and biogas. The effect of the recirculation ratio of the anode exhaust gas on the performance of SOFC-GT hybrid system, i.e., the SOFC efficiency, the turbine to SOFC power ratio, and the overall efficiency of hybrid system was firstly investigated. Additionally, the recirculation of both anode gas and cathode gas in the SOFC-GT hybrid system was studied.