SOFC-GT System Research Articles

Thermodynamic analysis and multi-objective optimization of different gas turbine configuration strategies for an atmospheric SOFC system

Solid oxide fuel cells (SOFCs) play a critical role as a key technological component in the utilization of hydrogen energy. Extensive research has been conducted on pressurized SOFC hybrid systems, focusing on performance enhancement and novel system configurations, etc. However, the planar SOFC suitable for commercial application exists limitations that confine its operation solely to atmospheric pressure. Moreover, SOFC exhaust contained considerable potential for energy recovery. In light of these limitations, two hybrid power generation systems of SOFC and GT have been proposed: direct and indirect utilization of SOFC cycle exhaust. Parameter and exergy analysis has been conducted to investigate the characteristic of SOFC-GT system. Multi-objective optimization is performed by setting exergy efficiency and output power as objective. The results reveal that the combustion process contributes significantly to system losses, with exergy efficiency reaching a maximum of 49.48% and 41.61%, respectively. Additionally, the system's maximum output power reaches 92 kW. Notably, the indirect SOFC-GT system demonstrates an 8% increase in exergy efficiency compared to the direct SOFC-GT system at the same output power. To improve the overall system fire efficiency, it is recommended to develop planar SOFCs suitable for high pressure and slow down the reaction process inside the combustion chamber.

Analysis of the thermodynamic performance of the SOFC-GT system integrated solar energy based on reverse Brayton cycle

Efficient power generation systems are an essential way to reduce carbon emissions. To avoid the complex effects of high-pressure conditions on the solid oxide fuel cell (SOFC) and gas turbine (GT) hybrid systems, while further improving energy efficiency. A SOFC-GT hybrid system based on the reverse Brayton cycle (RBC) is proposed, in which the SOFC operates at near atmospheric pressure conditions and GT expands below atmospheric pressure. Solar energy is integrated to further enhance system performance. Rigorous assessments of the novel system and the pressurized system are conducted utilizing energy, exergy and economic analysis. The sensitivity analysis of environmental parameters on the novel system's performance is performed. The results show that the novel system generates power and efficiency better than the conventional system when the GT compression ratio is 3 and 6, respectively. The power generation and exergy efficiency of the novel system at the design point is 60.47 % and 58.57 %, respectively. The largest exergy destruction occurred in the SOFC. The lowest exergy efficient components are the parabolic dish collector (PDC) and heat exchanger 2. The novel system is more cost-effective due to the higher lifetime of the SOFC, with the levelized cost of energy (LCOE) is 0.1418 $/kWh.

Thermodynamic performance analysis of direct methanol solid oxide fuel cell hybrid power system for ship application

Methanol is a fuel that can be directly supplied to solid oxide fuel cell (SOFC) without carbon deposition. This paper introduces the direct methanol SOFC-Internal combustion engine (ICE) hybrid power and SOFC-Gas turbine (GT) hybrid power systems. Thermodynamic performance analysis of the hybrid power systems and an investigation into the impact of various parameters were conducted. The results indicate that the electric efficiency of the SOFC-ICE system is 56.07 %, which is 3 percentage points higher than the SOFC-GT system but 3–4 percentage points lower than the SOFC-ICE system with pre-reforming. Increasing fuel utilization rate, operation temperature, and excess air ratio is beneficial to the performance of the SOFC, and raising current density helps improve the system's power density. Load-sharing strategy research demonstrates that in a scenario where the power ratio between SOFC and the ICE is 35:65, compared to a methanol engine, the efficiency of the SOFC-ICE hybrid power system increases by 4.3 %. Despite a 1.4-fold increase in weight and a 1.66-fold increase in cost, the fuel consumption rate and carbon emissions decrease by 8.8 %. Therefore, the strategy of combining a high-power engine with a low-power SOFC is currently a suitable load-sharing strategy for ship applications.

Techno-Economic and Environmental Analysis of a Hybrid Power System Formed From Solid Oxide Fuel Cell, Gas Turbine, and Organic Rankine Cycle

Abstract Distributed energy technology is an essential pathway for future advancements in the field of energy technology. In the present study, organic Rankine cycle (ORC) is integrated with solid oxide fuel cell (SOFC)-gas turbine (GT) hybrid power system. The conventional metrics employed for assessing the performance of SOFCs, gas turbines, and organic Rankine cycles, such as voltage and gross real efficiencies, have some limitations as indices of merit. Contemporary second law concepts and economic and environmental analysis have been used to enhance hybrid power system evaluation. R1233zd(E) has been selected as the ORC working fluid. The outcomes reveal that, under certain conditions, the present configuration may reach 55.67% energy efficiency and 53.55% exergy efficiency. Economic and environmental analysis shows that the hybrid system's total cost rate and Emissions of CO2 gas (EMI) under design conditions are 36.09 $/h and 355.8 kg/MWh, respectively. Thermodynamic evaluation of present SOFC-GT-ORC configuration shows 11.72% improvement in exergy efficiency compared to hybrid SOFC-GT cycle. Consequently, the hybrid SOFC-GT-ORC system is far better than the hybrid SOFC-GT system. In the future, other ORC fluids like R123, R601a, and R245fa can be used as ORC fluids.

Probabilistic analysis of solid oxide fuel-cell integrated with gas turbine

Abstract Solid Oxide Fuel Cell (SOFC) integrated with a Gas Turbine (GT) is a highly efficient way to convert chemical energy of hydro carbon fuel into electrical energy. SOFC-GT is a high temperature, high pressure system and features a fuel flexibility, which makes it easier to retrofit into the existing power plants. A lot of research had already taken place to make SOFC-GT more fuel efficient and cost effective as well. SOFC-GT is a complex thermodynamic electro-chemical system that has numerous input variables that affect the overall efficiency of the system. In order to further develop the SOFC-GT technology and future research, clear understanding is required to analyze relationship between the input and output parameters. One way to analyze the input/output relationship over the range of parameter variations is to conduct a probabilistic sensitivity analysis. A probabilistic sensitivity analysis of 19 input variables has been conducted to understand how each variable would affect the net power output and overall efficiency of a SOFC-GT system.

Investigation on combining multi-effect distillation and double-effect absorption refrigeration cycle to recover exhaust heat of SOFC-GT system

This study introduces the double-effect absorption refrigeration cycle (D-ARC) and multi-effect distillation with thermal vapor compression unit (MED-TVC) technologies to recover exhaust heat from the SOFC-GT system. This scheme can efficiently utilize waste heat at various temperature levels while enabling large-capacity cooling and freshwater production. The supercritical CO2 Brayton cycle is employed to facilitate the reliable operation of D-ARC and MED-TVC within their preferred temperature zones while enhancing the power output of the entire system. The techno-economic-environmental evaluation, comparative analysis and sensitivity analysis are performed to explore the feasibility of its engineering implementation. The proposed system obtains thermal, exergic and electrical efficiencies of 78.56 %, 65.41 % and 65.77 % with the total cost rate being 18.53 $/h and freshwater production 829.30 ton/year under design conditions, respectively. Exergy analysis indicates that SOFC and afterburner exhibit the highest irreversibility with values of 21.60 kW and 26.02 kW among all the components. Comparative analysis reveals that the system has exceptional thermal efficiency while exhibiting competitive advantages in electrical and exergic efficiencies compared to similar systems. Sensitivity analysis demonstrates that the electrical efficiency and net power output stabilize at their respective maximum values within the SOFC inlet temperature range of 514.3℃-528.6℃. Moreover, it is a promising option by increasing SOFC operating pressure and GT isentropic efficiency to enhance system efficiency and reduce CO2 emission. This work contributes to the development and waste heat recovery of the SOFC-GT system and other prime power units with similar exhaust gas temperature levels.

Design and energy efficiency analysis of hydrogen - fueled SOFC-‘GT+ST’ combined cycle system

In order to enhance electricity generation efficiency of hydrogen-fueled fuel cell gas turbine combined cycle system abbreviated as SOFC-GT system, a new combined system of fuel cell with turbine abbreviated as SOFC-GT+ST system is based on the feature of high concentration of water vapor in the anode of hydrogen fuel cell and the introduction of steam turbine, and a system model based on ebsilon software is built to compare the system under the same parameter conditions. The system model is built based on ebsilon software, and the system power, power generating efficiency, and the loss of the electricity is comparatively studied under the same parameters, and improved SOFC-GT+ST is proposed. Research results show the following: the second system, which utilizes the spent gas of cathode and anode separately, effectively utilizes the thermal energy of water vapor in the anode spent gas and improves the power generation efficiency of the system; the improved SOFC-′GT+ST The improved SOFC-‘GT+ST’ system further improves the power generation efficiency of the system by recycling the hydrogen in the SOFC that does not participate in the electrochemical reaction, which reaches 65.88%. The research in this paper provides a reference for improving.

Thermodynamic performance study of a novel cogeneration system combining solid oxide fuel cell, gas turbine, organic Rankine cycle with compressed air energy storage

Energy storage becomes increasingly significant for addressing imbalance of grid supply and demand. In this paper, a new cogeneration system based on combined compressed air energy storage (CAES), solid oxide fuel cell (SOFC), gas turbine (GT) and organic Rankine cycle (ORC) is proposed. SOFC-GT system replaces GT combustor of traditional CAES, and SOFC-GT can operate with high efficiency at peak time. At the same time, ORC is employed to recover the exhaust from GT. Especially, in the new system, the surplus electricity is utilized to compress air, thus eliminating power consumption of air compressor in conventional SOFC-GT. Additionally, the system can also provide heat and power for small-scale distributed generation application users. The combined system is simulated based on Aspen plus and embedded Fortran. The energy, exergy analysis and parametric sensitivity analysis are used to evaluate the system performance. The results revealed that the round-trip efficiency, exergetic round-trip efficiency and discharging electrical efficiency are 76.07%, 61.78% and 72.39%, respectively. Compared with an integrated SOFC-GT-ORC system without energy storage, the electrical efficiency of the new system increases by 17.07%. Overall, the combined system can achieve high efficiencies, which can provide important theoretical guidance for efficient energy utilization.

Thermodynamic and thermoeconomic analysis of a novel power and hydrogen cogeneration cycle based on solid SOFC

To enhance the performance of the thermodynamic systems, reduce the pollutants emission to the environment, and decline the fuel utilization, waste heat recovery methods are in high interest. In this paper, a new configuration of an integrated solid oxide fuel cell and gas turbine combined with a biogas reforming cycle is presented for the cogeneration of power and hydrogen. The thermal energy discharged from the SOFC-GT system is used to supply the energy required for the reforming reaction in the biogas reforming cycle for hydrogen production. Comprehensive thermodynamic and thermoeconomic modeling has been performed using EES software. Also, a parametric study has been performed to demonstrate the effect of different parameters on the main performance metrics of the devised system. The results revealed that the energy efficiency and exergy efficiency of the proposed combined system have increased compared to the SOFC-GT system by 23.31% and 28.19%, respectively. The net output power and hydrogen production rate are obtained by 2726 kW and 0.07453 kg/s, respectively. From the exergy viewpoint, the afterburner causes a considerable amount of exergy destruction for the system by approximately 26% of the total exergy destruction rate. Besides, the sensitivity analysis revealed that by increasing the inlet temperature of the fuel cell, the cell voltage reaches a maximum value at a temperature of 679 K and then decreases. Moreover, the total exergy destruction rate and SUCP of the cogeneration system is calculated by 1532 kW and 9400 $/GJ, respectively.

Development and exergoeconomic evaluation of a SOFC-GT driven multi-generation system to supply residential demands: Electricity, fresh water and hydrogen

In this study, a novel multi-generation system is proposed by integrating a solid oxide fuel cell (SOFC)-gas turbine (GT) with multi-effect desalination (MED), organic flash cycle (OFC) and polymer electrolyte membrane electrolyzer (PEME) for simultaneous production of electricity, fresh water and hydrogen. A comprehensive exergoeconomic analysis and optimization are conducted to find the best design parameters considering exergy efficiency and total unit cost of products as objective functions. The results show that the exergy efficiency and the total unit cost of products in the optimal condition are 59.4% and 23.6 $/GJ, respectively, which offers an increase of 2% compared to exergy efficiency of SOFC-GT system. Moreover, the system is capable of producing 2.5 MW of electricity by the SOFC-GT system, 5.6 m3/h of fresh water by MED unit, and 1.8 kg/h of hydrogen by the PEME. The associated cost for producing electricity, fresh water and hydrogen are 3.4 cent/kWh, 37.8 cent/m3, and 1.7 $/kg, respectively. A comparison between the results of the proposed system and those reported in other related papers are presented. The diagram of the exergy flow is also plotted for the exact determination of the exergy flow rate in each component, and also, location and value of exergy destruction. Finally, the capability of the proposed system for a case study of Iran is examined.

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.

A new direct ammonia solid oxide fuel cell and gas turbine based integrated system for electric rail transportation

Abstract A novel direct ammonia intermediate-temperature solid oxide fuel cell based integrated system is developed, analyzed and proposed for clean rail electric transportation. The present multigenerational system provides all the required energy demands of a passenger locomotive. This system is studied using a validated thermodynamic model to evaluate its energy and exergy efficiencies and power outputs. Parametric studies are performed to investigate the system in more depth, thermodynamically. Based on these, the integrated system can reach optimized energy and exergy efficiency values of 71.0% and 76.8%, respectively. The use of supercritical ammonia-organic Rankine cycle improves both energy and exergy efficiencies by 12.9% and 11.8%, respectively compared to an ammonia based SOFC-GT system. These values are comparable to typical methane-based systems and the use of ammonia eliminates CO2 emissions.

Comparative study of combined solid oxide fuel cell-gas turbine-Organic Rankine cycle for different working fluid in bottoming cycle

Worldwide efforts are being made for evolving viable electricity generation alternative to the traditional fossil fuel based power generation systems and also to enhance the efficiency of existing power generation systems. Studies have been made for integrating fuel cell with gas turbine cycle and Organic Rankine cycle, but there exist possibility of further investigation by incorporating the measures to increase effective energy utilization in the cycle along with consideration of different working fluids in Organic Rankine cycle. In the present paper, a combined cycle system consisting of technologies namely solid oxide fuel cell, gas turbine and Organic Rankine cycle is studied. The considered combined cycle system employs Heat Recovery Steam Generator followed by Organic Rankine cycle as bottoming cycle for recovering the waste heat coming out from hybrid SOFC-GT system through a Heat Recovery Vapour Generator. The considered SOFC-GT system has methane gas being used as fuel which is reformed by both external and internal reformers with anode gas recycling. Here three different working fluids namely R141b, R245fa and R236fa are used in bottoming Organic Rankine cycle for comparing their effects on the cycle performance of proposed SOFC-GT-ORC combined cycle system based on first law of the thermodynamics. Results have been obtained from the computer simulation based on thermodynamic modeling of SOFC-GT-ORC combined cycle and the effects of gas turbine inlet temperature, cycle pressure ratio, fuel utilization factor and ORC turbine inlet temperature are investigated on the cycle performance. The study indicates that the efficiency is increased about 8%-12% by recovering SOFC-GT waste heat through ORC and R236fa is found to be the best in terms of power generation capacity and efficiency of SOFC-GT-ORC system. Outcome from this paper gives insight to the power sector professionals and research community working for evolving efficient and robust power generation alternatives based on the combination of direct energy conversion system and indirect energy conversion system.

SOFC Stack Model for Integration Into a Hybrid System: Stack Response to Control Variables

Due to the tight coupling of physical processes inside solid oxide fuel cells (SOFCs), efficient control of these devices depends largely on the proper pairing of controlled and manipulated variables. The present study investigates the uncontrolled, dynamic behavior of an SOFC stack that is intended for use in a hybrid SOFC-gas turbine (GT) system. A numerical fuel cell model is developed based on charge, species mass, energy, and momentum balances, and an equivalent circuit is used to combine the fuel cell's irreversibilities. The model is then verified on electrochemical, mass, and thermal timescales. The open-loop response of the average positive electrode-electrolyte-negative electrode (PEN) temperature, fuel utilization, and SOFC power to step changes in the inlet fuel flow rate, current density, and inlet air flow rate is simulated on different timescales. Results indicate that manipulating the current density is the quickest and most efficient way to change the SOFC power. Meanwhile, manipulating the fuel flow is found to be the most efficient way to change the fuel utilization. In future work, it is recommended that such control strategies be further analyzed and compared in the context of a complete SOFC-GT system model.

Techno-economic assessment of high efficient energy production (SOFC-GT) for residential application from natural gas

Fuel cells, as alternatives for conventional energy conversion systems, have the prospect for exploiting fossil fuels (especially natural gas) more benignly and efficiently. High temperature Solid Oxide Fuel Cell (SOFC) with the ability of direct natural gas reforming is promised to be the most efficient device for a direct conversion of the fuel chemical energy into the electricity. Its efficiency can be further increased up to 70% when the SOFC is coupled with a Gas Turbine (GT) cycle. To provide the required energy for the household application, a kW range SOFC-GT (11–42.9 kWe) combined cycle is proposed in this article. Complete thermodynamic simulation of a SOFC-GT power system is done. Then a four floor building is introduced for energy consumption section. Each floor has the 100 m2 flat. After calculating the required electrical and thermal load of building, the size of proposed system is determined and the economic evaluation is considered. Four different climatic areas of Iran are selected for this study. The results show that among the selected cities, SOFC-GT is more economic in the hot and wet climate area (Ahvaz). The prime cost of electrical energy per kWh and the period of return is 0.0208 US$ and 8.3494 years respectively in Ahvaz.

Optimization methodology of turbomachines for hybrid SOFC–GT applications

The objective of this work is to suggest a method for optimizing the compressor and turbine components in hybrid SOFC–GT (Solid Oxide Fuel Cell – Gas Turbine) applications. The hybrid system evaluations are made on the basis of a typical SOFC generator scheme without any modifications. The method consists of two steps. A parametric study is conducted in order to assess the operating range of the hybrid SOFC–GT system and select the desired operating line for achieving the optimum system efficiency at various operating points. Based on that information, optimum compressor and turbine geometries are estimated using in-house turbomachinery design codes and an optimization procedure. The new components ensure the best performance not only in the design point but also during part-load operation. The results of the present analysis are useful for designing hybrid SOFC–GT systems based on a fixed SOFC generator design.

Analysis of a pressurized solid oxide fuel cell–gas turbine hybrid power system with cathode gas recirculation

A pressurized solid oxide fuel cell–gas turbine hybrid system (SOFC–GT system) has been received much attention for a distributed power generation due to its high efficiency. When considering an energy management of the system, it is found that a heat input is highly required to preheat air before being fed to the SOFC stack. The recirculation of a high-temperature cathode exhaust gas is probably an interesting option to reduce the requirement of an external heat for the SOFC–GT system. This study aims to analyze the pressurized SOFC–GT hybrid system fed by ethanol with the recycle of a cathode exhaust gas via a simulation study. Effect of important operating parameters on the electrical efficiency and heat management of the system is investigated. The results indicate that an increase in the operating pressure dramatically improves the system electrical efficiency. The suitable pressure is in a range of 4–6 bar, achieving the highest system electrical efficiency and the lowest recuperation energy from the waste heat of the GT exhaust gas. In addition, it is found that the waste heat obtained from the GT is higher than the heat required for the system, leading to a possibility of the SOFC–GT system to be operated at a self-sustainable condition. Under a high pressure operation, the SOFC–GT system requires a high recirculation of the cathode exhaust gas to maintain the system without supplying the external heat; however, the increased recirculation ratio of the cathode exhaust gas reduces the system electrical efficiency.

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

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

Solid oxide fuel cell/gas turbine trigeneration system for marine applications

Shipping contributes 4.5% to global CO2 emissions and is not covered by the Kyoto Agreement. One method of reducing CO2 emissions on land is combined cooling heating and power (CCHP) or trigeneration, with typical combined thermal efficiencies of over 80%. Large luxury yachts are seen as an ideal entry point to the off-shore market for this developing technology considering its current high cost.This paper investigates the feasibility of combining a SOFC-GT system and an absorption heat pump (AHP) in a trigeneration system to drive the heating ventilation and air conditioning (HVAC) and electrical base-load systems. A thermodynamic model is used to simulate the system, with various configurations and cooling loads. Measurement of actual yacht performance data forms the basis of this system simulation.It is found that for the optimum configuration using a double effect absorption chiller in Ship 1, the net electric power increases by 47% relative to the electrical power available for a conventional SOFC-GT-HVAC system. This is due to more air cooled to a lower temperature by absorption cooling; hence less electrical cooling by the conventional HVAC unit is required. The overall efficiency is 12.1% for the conventional system, 34.9% for the system with BROAD single effect absorption chiller, 43.2% for the system with double effect absorption chiller. This shows that the overall efficiency of a trigeneration system is far higher when waste heat recovery happens.The desiccant wheel hardly reduces moisture from the outdoor air due to a relative low mass flow rate of fuel cell exhaust available to dehumidify a very large mass flow rate of HVAC air, Hence, desiccant wheel is not recommended for this application.

Modelling of simple hybrid solid oxide fuel cell and gas turbine power plant

This paper presents the work on a simple, natural gas-fed, hybrid solid oxide fuel cell–gas turbine (SOFC–GT) power-generation system. The system consists of an internal-reforming SOFC (IRSOFC) stack, a combustor, a GT, two compressors and three recuperators. Two case studies are conducted with particular attention on the effects of operating pressure and fuel flow-rate on the performance of the components and overall system. Results show that an internal-reforming hybrid SOFC–GT system can achieve an electrical efficiency of more than 60% and a system efficiency (including waste heat recovery for co-generation) of more than 80%. It is also found that increasing the operating pressure will improve the system efficiency, whereas increasing the fuel flow-rate (while keeping the fuel utilisation rate unchanged) causes the system efficiency to decrease. In the latter case, the increase in system fuel consumption is relatively higher which removes the benefit of increase in SOFC stack and turbine power output.