Solid Oxide Fuel Cell Hybrid System Research Articles

Design and sensitivity analysis of a multistage solid oxide fuel cell hybrid system with an inter-cooled-recuperated gas turbine and organic Rankine cycle

A solid oxide fuel cell (SOFC) hybrid system with an inter-cooled-recuperated gas turbine(ICRGT) and organic Rankine cycle (ORC) was designed to address exergy destruction in the burner of a conventional SOFC and gas turbine (GT) system. In unfired mode of this system, SOFC acts as the GT heater and reheater instead of burners; burners are used only to aid load regulation in fired mode. In unfired mode, the system electrical efficiency is 69.86 % and the overall efficiency is 82.22 %. The total exergy destruction of the system is 21.93 % lower than that in fired mode by exergy analysis, which indicates the effectiveness of reducing afterburner exergy destruction, and the superior energy efficiency of this mode. For the design analysis, we analyzed the influence of different factors on the system, including the number of SOFC modules, turbine outlet temperature, burner exhaust into the turbine, oxidant utilization of SOFC cathode(OUC), and fuel utilization of SOFC anode(FUA) on the system. For the sensitivity analysis, we determined the variation rules of the components and system parameters for fuel proportions of 70–105 %. This work provides a reference for optimizing the design and operation of SOFC-GT and other SOFC hybrid systems.

Achieving near-zero emission and high-efficient combined cooling, heating and power based on biomass gasification coupled with SOFC hybrid system

Extensive studies on coupling biomass as a fuel to power systems for clean and efficient energy conversion provides a realistic path towards carbon neutrality. Therefore, a novel system was proposed, which featured biomass CO2 gasification, solid oxide fuel cell (SOFC) with carbon capture, and ammonia Rankine cycle. A thermodynamic model of the system process was developed and used to comprehensively assessment of the performance in terms of thermodynamic, CO2 reduction potential, and economic. The results indicate a net electrical efficiency of 50.41%, a net electrical output of 9124.5 kW, a CHP efficiency of 70.2%, and an exergy efficiency of 45.6%. The key sources of irreversibility identified through exergy analysis were found to be the gasifier, SOFC, and afterburner. Moreover, in this system, an impressive maximum CO2 capture rate of 99.9% was achieved, and a low CO2 specific emission of 0.64 kg/MWh was recorded, highlighting its emission reduction potential compared to conventional CCHP systems. Economic analysis further supports the feasibility of this system, revealing the levelized cost of electricity at 58.17 $/MWh and the swift initial investment recovery period of 4.34 years. This novel system signifies a promising pathway towards a sustainable and economically viable energy conversion.

Optimization and performance analysis of a near-zero emission SOFC hybrid system based on a supercritical CO2 cycle using solar energy

Renewable energy represented by solar energy has the characteristics of intermittency and fluctuation. To ensure that the grid can operate safely and stably after the large-scale grid connection of renewable energy power, a new hybrid system consisting of a solid oxide fuel cell (SOFC), a solar power tower plant, and a supercritical CO2 (S-CO2) Brayton cycle is proposed in this study from the perspective of energy, exergy, and economy. By utilizing the cold source loss of the S-CO2 cycle to provide part of the energy required for the alkaline electrolyzer, it can efficiently produce and store hydrogen, achieving zero greenhouse gas emissions while increasing efficiency. Meanwhile, the high-temperature exhaust gas from SOFC is recovered by the S-CO2 cycle. The system considers two operation modes, switching two types of S-CO2 cycle configurations to efficiently utilize solar energy according to the variation of solar radiation energy. The thermal efficiency of the proposed system is improved by 16.61% and 6.88% compared with the other two typical S-CO2 cycle power generation systems, and the net power output reaches 8.0 MW. A parameter study shows that increasing the split ratio is beneficial to improve the thermodynamic performance of the system. However, at a split ratio less than 0.76, it is beneficial to the total cost rate of the system. The results of multi-objective optimization show that the exergy efficiency of the combined system and the total system cost rate reach 56.86%, 513.10$/h and 56.45%, 481.59$/h for the system with an additional simple S-CO2 cycle and the system with an additional recompression S-CO2 cycle, respectively, and the optimum point is selected by the TOPSIS and LINMAP methods.

Analysis of solid oxide fuel cell hybrid power system in marine application for CO2 reduction

The usefulness of a solid oxide fuel cell (SOFC) for a large vessel is evaluated by estimating the amount of CO2 emitted by a crude oil tanker. Conventional and two SOFC hybrid power generation systems are proposed and analyzed. The traditional system consists of five generators and a steam boiler, whereas two SOFC hybrid systems are made up of five smaller generators with additional SOFC power and a steam boiler. The performance of the SOFC is calculated through a zero-dimensional model developed, including electrochemical stack model. The CO2 emission of the SOFC hybrid system is estimated depending on the SOFC capacity, 2.5 MW and 5.0 MW. CO2 emissions in the SOFC hybrid system are 5.4% ∼8.8% lower than in the traditional structure for one round trip sail. The reduction of CO2 comes from two factors; the high efficiency of SOFC and the operations of DF generators at a relatively high load rate. The SOFC hybrid system can be an eco-friendly technology to reduce the CO2 emissions of the large ships.

Design and energy analysis of solid oxide fuel cell and gas turbine hybrid systems with membrane reactor

ABSTRACT The methanol-reforming solid oxide fuel cell (SOFC) emits high concentration of CO2 from the anode outlet. To achieve the goal of clean and low-carbon power generation, a CO2 capture unit is integrated with SOFC. In this work, the CO2 capture unit were set at different places in the conventional SOFC and gas turbine (GT) hybrid system. One was to place the water-gas-shift membrane reactor (WGSMR) at the anode inlet (SOFC-MRpre) and the other at the anode outlet (SOFC-MRpost). The key parameters, including the anode off-gas recycling ratio (RR), steam-to-carbon ratio (S/C), and operating pressure, have been investigated. Besides, the effects of the parameters on the power production, electrical efficiency, system efficiency, and CO2 capture capacity of the two processes were analyzed. It was found that the electrical and system efficiencies reached 53.3% and 41.8% for the SOFC-MRpre process, while 62.0% and 60.4% for the SOFC-MRpost process, respectively. The results show that placing the membrane reactor at the anode outlet can significantly reduce the energy consumption of the vacuum and blower, thus increasing the system efficiency. Besides, near-zero carbon emissions with only a 7.3% energy penalty can be achieved by the SOFC-MRpost process. These results reveal that the SOFC-MRpost process has more advantages than the SOFC-MRpre process.

Achieving high-efficiency conversion and poly-generation of cooling, heating, and power based on biomass-fueled SOFC hybrid system: Performance assessment and multi-objective optimization

In order to develop clean and efficient energy conversion technology, a novel combined cooling, heating and power (CCHP) system using biomass as fuel is proposed in this work. The proposed CCHP system consists of biomass gasification unit, solid oxide fuel cell (SOFC), engine power generation unit and absorption refrigeration unit. Thermodynamic model of the CCHP system is developed for the parametric and exergy analyses to evaluate the performance. The parametric analysis shows that increasing the steam to biomass ratio or the SOFC fuel utilization factor helps to improve the electrical efficiency, while the increase of air equivalent ratio has a negative effect. The exergy analysis shows that the two units of biomass gasification and engine power generation have the largest exergy destruction ratio, which is 46.9% and 16.8% under the biomass flux of 500 kg·h−1. This is because these two units involve in high-temperature thermochemical reaction process, resulting in relatively large exergy destruction. Besides, the tradeoff between maximum exergy efficiency, CCHP efficiency and minimum total annual cost is conducted by multi-objective optimization. Through optimization, the system could reach the high CCHP efficiency of 75% and net electrical efficiency of 52%, as well as the low total annual cost of 410 k$ simultaneously. This work could provide the basic design idea, and high-efficiency and low-cost operation strategy for the practical application of the proposed novel biomass-fueled CCHP poly-generation system.

A novel ammonia solid oxide fuel cell-based powering system with on-board hydrogen production for clean locomotives

Due to the current limitations in hydrogen storage technologies in heavy-duty vehicles, on-board hydrogen production from alternative fuels comes as a viable solution. Ammonia is one type of fuel that can easily be produced and stored in these vehicles. For this reason, this paper aims at presenting a novel powering system that uses ammonia to produce power and hydrogen simultaneously to drive a passenger locomotive. The novelty of the on-board hydrogen production unit is the use of waste heat from a solid-oxide fuel cell hybrid system to disassociate the hydrogen from ammonia. A thermodynamic model based on energy and exergy analyses, which was developed and validated earlier, is used to assess the present novel system. The results of the thermodynamic assessment show that the overall energy and exergy efficiencies of this novel powering system are 61.2% and 66.3%, respectively. The ammonia disassociation and separation thermal processes have a relatively low exergy destruction rate of 1.05 kW. Also, the parametric studies are conducted in this work and the results show that producing more hydrogen enhances the overall energy and exergy efficiencies by only 0.28% and 0.24%, respectively.

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%.

Energy analysis and techno-economic assessment of a co-gasification of woody biomass and animal manure, solid oxide fuel cells and micro gas turbine hybrid system

Co-gasification of woody biomass and animal manure is an effective technology to utilize animal manure. In this work, the thermodynamic and economic analysis of an integration of co-gasification of woody biomass and animal manure with solid oxide fuel cell (SOFC) and micro gas turbine is carried out. The overall thermodynamic performance of this combined heat and power (CHP) system is investigated by a mathematics model consisting of simple zero-dimensional model of SOFC and one-dimensional model of downdraft biomass gasifier. The net present value (NPV) method is adopted to investigate the economic feasible of the CHP system.The gasifier model includes two parts. The pyrolysis-oxidation zone includes pyrolysis zone and combustion zone, and a lumped capacitance method and chemical equilibrium are used to simulate the species in pyrolysis-oxidation zone, while one-dimensional kinetic model is adopted to analyze the performance of reduction zone, which considering geometrical dimensions of downdraft gasifier and actual char conversion process.Effects of three operating parameters such as air flow rate in gasifier, moisture content of blended fuel and mass fraction of woody biomass in blended fuel on overall performance of CHP system are evaluated. The results show that decreased mass fraction of animal manure and increased mass flow rate of gasification air have positive effect on conversion of char owing to higher reaction temperature. Entire conversion of char in gasifier and electrical efficiency of the CHP power system above 45% can be achieved on the condition that mass fraction of animal manure is less than 0.4, moisture content is less than 0.4 and mass flow rate of gasification air is more than 47 kg h−1 as the total mass flow rate of blended fuel equal to 28 kg h−1.Economic analysis shows that more woody biomass rather than animal mature in blend fuel is more economically attractive despite of the low cost of animal mature. The particular high initial capital investment of SOFC is the main part of the whole CHP system. In this work, the payback time is less than eight years. If the target cost less than 3000 €/kW for SOFC in a future year will be reached and the optimized operating parameter is adopted, the investment of a co-gasification of woody biomass and animal manure, SOFC and MGT hybrid system will be more competitive for the user.

Thermodynamic analysis and performance optimization of solid oxide fuel cell and refrigerator hybrid system based on H2 and CO

A hybrid system consisting of solid oxide fuel cell (SOFC) and absorption refrigerator is established, where hydrogen and carbon monoxide are the reactant in electrochemical reactions of SOFC, and air conditioning is derived for the residence due to the utilization of waste heat from the SOFC. On the basis of electrochemistry and thermodynamics, the electric voltage and power of the SOFC, the cooling rate of refrigerator under given flow rate of high-temperature heat, and the equivalent energy conversion efficiency and power of the hybrid system are obtained. The effect of some of the key parameters including molar ratio of carbon monoxide to hydrogen consumed in the electrochemical reactions, the working temperature of the SOFC on the performance of the hybrid system is investigated. The optimal operation strategy is explored to achieve the high equivalent energy conversion efficiency of the hybrid system, for example, the molar ratio of carbon monoxide to hydrogen consumed in the electrochemical reactions is suggested 0.053 to attain the optimal equivalent energy conversion efficiency of the hybrid system. The maximum equivalent energy conversion efficiency of the SOFC and refrigerator hybrid system will reach 87%.

The Solid Oxide Fuel Cell (SOFC) and Gas Turbine (GT) Hybrid System Numerical Model

Fuel cells when combined with conventional turbine power plants offer high efficiencies. The feature of certain fuel cells (Solid Oxide Fuel Cell or SOFC, Molten Carbonate Fuel Cell or MCFC), which makes them suitable for hybrid or combined systems, is their high operating temperature. In this work, a detailed thermodynamic model of SOFC and gas turbine hybrid system is simulated in MATLAB. Few configurations of the combined or hybrid cycles are proposed and analyzed. A comparative study based upon performance parameters, such as SOFC power and turbine inlet temperature is used to select the better configuration. Simple thermodynamic models for the compressor and turbine are used during the configuration selection.

Optimal Operation Conditions for a Methane Fuelled SOFC and Microturbine Hybrid System

The study of a hybrid system obtained coupling a methane fuelled gas microturbine (MTG) and a solid oxide fuel cell (SOFC) was performed. The objective of this study is to evaluate the operation conditions as a function of the independent variables of the system, which are the current density and fuel utilization factor. Numerical simulations were carried out in developing a C++ computer code, in order to identify the preferable plant configuration and both the optimal methane flow and the current density. Operation conditions are able to ensure elasticity and the most suitable fuel utilization factor. To confirm the reliability of the models, results of the simulations were compared with reference results found in literature.

Re‐Compression Model for SOFC Hybrid Systems: Start‐up and Shutdown Test for an Emulator Rig

AbstractThis paper reports a new innovative re‐compression technology for solid oxide fuel cell (SOFC) hybrid systems necessary to increase pressure at compressor outlet level (as required by fuel cell systems for managing cathodic recurculation and to increase SOFC efficiency). This work was based on a collaboration between the University of Manchester (United Kingdom) and the University of Genoa (Italy). The re‐compression study will be performed with the hybrid system emulator rig by TPG. This device is composed of the following technology: a microturbine package able to produce up to 100 kWe which was modified for external connections, external pipes designed for several purposes (by‐pass, measurement or bleed), and a high temperature modular vessel necessary to emulate the dimension of an SOFC stack. For the purpose of re‐compression, this test rig is planned to be equipped with a turbocharger capable of increasing pressure using part of recuperator outlet flow. Theoretical activity was considered before carrying out the real experimental tests to avoid plant risky conditions. So, it was necessary to develop a transient model (Matlab®‐Simulink® environment) to simulate the hybrid system emulator including the re‐compression system. The results obtained with the model were carried out considering the start‐up/shutdown phases of the turbocharger device.

Pressurized SOFC Hybrid Systems: Control System Study and Experimental Verification

In this paper, two different advanced control approaches for a pressurized solid oxide fuel cell (SOFC) hybrid system are investigated and compared against traditional proportional integral derivative (PID). Both advanced control methods use model predictive control (MPC): in the first case, the MPC has direct access to the plant manipulated variables, in the second case, the MPC operates on the setpoints of PIDs which control the plant. In the second approach, the idea is to use MPC at the highest level of the plant control system to optimize the performance of bottoming PIDs, retaining system stability and operator confidence. Two MIMO (multi-input multi-output) controllers were obtained: fuel cell power and cathode inlet temperature are the controlled variables; fuel cell bypass flow, current and fuel mass flow rate (the utilization factor kept constant) are the manipulated variables. The two advanced control methods were tested and compared against the conventional PID approach using a SOFC hybrid system model. Then, the MPC controller was implemented in the hybrid system emulator test rig developed by the thermochemical power group (TPG) at the University of Genoa. Experimental tests were carried out to compare MPC against classic PID method: load following tests were carried out. Ramping the fuel cell load from 100% to 80% and back, keeping constant the target of the cathode inlet temperature, the MPC controller was able to reduce the mismatch between the actual and the target values of the cathode inlet temperature from 7 K maximum of the PID controller to 3 K maximum, showing more stable behavior in general.

Study on zero CO2emission atmospheric pressure SOFC hybrid power system integrated with OTM

SUMMARY In order to further reduce the energy consumption of CO2 capture from the traditional SOFC hybrid power system, based on the principle of energy cascade utilization and system integration, a zero CO2 emission atmospheric pressure solid oxide fuel cell (SOFC) hybrid power system integrated with oxygen ion transport membrane (OTM) is proposed. The oxygen is produced by the OTM for the oxy-fuel combustion afterburner of SOFC. With the Aspen-plus software, the models of the overall SOFC hybrid power systems with or without CO2 capture are developed. The thermal performance of new system is investigated and compared with other systems. The effects of the fuel utilization factor of SOFC and the pressure ratio between two sides of OTM membrane on the overall system performance are analyzed and optimized. The research results show that the efficiency of the zero CO2 emission atmospheric pressure SOFC hybrid power system integrated with OTM is around 58.36%, only 2.48% lower than that of the system without CO2 capture (60.84%) but 0.96% higher than that of the zero CO2 emission atmospheric pressure SOFC hybrid system integrated with the cryogenic air separation unit. Copyright © 2014 John Wiley & Sons, Ltd.

Emulator Rig for SOFC Hybrid Systems: Temperature and Power Control with a Real‐Time Software

AbstractThis work is based on the hybrid system emulator plant developed by the Thermochemical Power Group (TPG) of the University of Genoa. This rig is composed of a 100 kW microturbine coupled with high temperature fuel cell emulation devices. A real‐time model is used for components not physically present in the laboratory (solid oxide fuel cell (SOFC), reformer, anodic circuit, off‐gas burner, cathode blower). It is necessary to evaluate thermodynamic and electrochemical performance related to SOFC systems. Using an User Datagram Protocol (UDP) based connection with the control/acquisition software, it generates a hardware‐in‐the‐loop (HIL) facility for hybrid system emulation. Temperature, pressure, and mass flow rate at the recuperator outlet and machine rotational speed are measured in the plant and used as inputs for the model. The turbine outlet temperature (TOT) calculated by the model is fed into the machine control system and the turbine electric load is changed to match the model TOT values (effective plant/model coupling to avoid modifications on microturbine controller). Different tests were carried out to analyze hybrid system technology through the interaction between an experimental plant and a real‐time model. Double step and double ramp tests of current and fuel provided the system dynamic response.

Comparison study on different SOFC hybrid systems with zero-CO2 emission

Based on a traditional SOFC (solid oxide fuel cell) hybrid power system, three different SOFC hybrid power systems with zero-CO2 emission are proposed in this paper and their performances are analyzed and compared. The anode outlet gas of SOFC burns with the pure oxygen and the concentration of CO2 is greatly increased. In order to maintain the appropriate turbine inlet temperature, three different measures (steam injection, CO2 gas injection and heat exchange layout) are taken. Because the outlet flue gas of the afterburner mainly consists of CO2 and steam, the CO2 in the flue gas can be captured easily by the condensation method after the recovery of work and heat. With the exergy analysis method, this paper studies the exergy loss distributions of every unit of SOFC hybrid systems with CO2 capture and reveals the variation rules of exergy loss distributions. The effects of the main operating parameters on the overall performances of SOFC hybrid systems with CO2 capture are also investigated. The results show that the zero CO2 emission SOFC hybrid systems still have higher efficiencies, which only decrease about 3–4% compared with that of the basic SOFC hybrid system without CO2 capture.

Transient Model Validation of a Desulfurizer and a Syngas Generator for High Temperature Fuel Cells

This paper presents the steady state and transient model of a natural gas fuel processing system of a solid oxide fuel cell (SOFC) hybrid system, and its validation using data obtained through the use of a real plant. The model was developed by the Thermochemical Power Group of the University of Genoa, Italy, using the in-house tool TRANSEO working in the Matlab/Simulink environment, whereas the real plant was designed and built by Rolls-Royce Fuel Cell Systems Limited (RRFCS) to feed a 250 kWe SOFC hybrid system with a methane stream undergoing requirements about composition, pressure, and temperature. The paper presents in detail the fuel processing system and, with particular emphasis, the selective catalytic sulphur oxidation (SCSO) and the catalytic partial oxidation (CPOx) subsystems. Thanks to the collaboration between the University and RRFCS, in the model the real physical properties of the different materials and geometry of the components have been carefully used. The transient model has been fully validated against experimental data obtained from long duration tests, which included the warm-up, part and full load operation, and cool-down phases of the external fuel processing system. In the validation process both gas and wall temperatures have been taken into account. The transient model has shown the ability to predict satisfactorily the plant behavior both at steady-state and transient conditions. The validated model is now under further development to be used for dynamic control system applications.

Simulation of an atmospheric SOFC and gas turbine hybrid system using Aspen Plus software

SUMMARY Fuel cell is an energy conversion device that transforms the chemical energy of a fuel gas directly into electrical energy without direct combustion as an intermediate step. One type of fuel cell is the solid oxide fuel cell (SOFC) with the operation temperature of around 1273°K. The high operating temperature of the SOFC also provides excellent possibilities for feeding into a gas turbine (GT) to generate additional electricity. In this paper, an atmospheric SOFC and GT hybrid system have been simulated by application of Aspen Plus existing functions and unit operation modules. The study has shown that the system efficiency and voltage reduce continuously as the current density increases due to increase of Ohmic and concentration losses. However, the output power increases due to enhancement of the current density. Therefore, the system should operate at low current density if the goal is to generate power at higher efficiency. Moreover, if the goal is to produce more power, the system should operate at high current density. The simulation results indicate that the cycle can achieve high electrical generation efficiency (68.2%), which is very attractive compared to the ideal efficiency of combined cycle power plants around 50%. Moreover, a parametric analysis has been performed to assess the effects of the several operating condition variation on the system performance. Copyright © 2011 John Wiley & Sons, Ltd.

Temperature Control of a SOFC and MGT Hybrid System

Transients in a load have a significant impact on the performance and durability of a solid oxide fuel cell (SOFC) integrated into a micro gas turbine (MGT) hybrid power system. One of the main reasons is that the SOFC operating temperature and turbine inlet temperature change drastically due to the load change. Therefore, in order to guarantee the temperature to operate within a specified range, an adaptive proportional-integral-derivative (PID) decoupling control strategy based on a dynamic radial basis function (RBF) neural network is presented to control the temperature of a natural gas fueled, tubular SOFC/MGT hybrid with internal reforming in this paper. Using the self-learning ability of the dynamic RBF neural network, the proportional, integral, and differential factor of the PID controller are tuned on-line. The simulation results show that it is feasible to build the adaptive PID decoupling controller for temperature control of the SOFC/MGT hybrid system.