Thermodynamic Evaluation And Fuel Cell Performance Simulation Of Chemical Looping Gasification-SOFC Coupling System

Gasification technology plays an important role in energy conversion and utilization,whereas carbon emission problems are also brought out during conventional gasification process.Chemical looping gasification,as a new gasification method,can effectively improve the shortcomings of traditional gasification technology by introducing oxygen carriers to achieve internal separation of carbon dioxide.In recent years,the coupling system of solid oxide fuel cell（SOFC）and gasification process has also become a promising new method of energy conversion.In this paper,for the chemical looping gasification-SOFC coupling system,through the utilization of thermodynamic analysis and multi-physical field coupling simulation means,the system performance is evaluated and deeply explored,then the control of the system can be achieved.Based on the Gibbs free energy minimum principle,the thermodynamic analysis of the chemical looping gasification-SOFC coupling system is carried out.The effects of sorption enhancement on the system performance are compared.The influence of operating parameters on SOFC temperature and pressure,Ca O to carbon ratio,Fe₂O₃ to carbon ratio and water to carbon ratio on the gasification product composition and energy utilization of the system is analyzed.The results show that chemical looping technology can enhance the energy conversion efficiency and exergy efficiency of the system.The improvement of SOFC temperature and pressure is conducive to the energy conversion efficiency and exergy efficiency of the system.The increase of Ca O/C ratio is beneficial to the production of hydrogen in gasification products,whereas reducing the energy conversion efficiency and exergy efficiency of the system.The increase of H₂O/C ratio is conducive to the increase of the production of syngas and methane in gasification products,while an excessive increase of H₂O/C ratio can cause the conversion of other fuel gases to hydrogen.In addition,it is found that more carbon is deposited on the side wall,making the current density at the side wall less than that in the middle region.The carbon deposition at the end of channel is more serious,resulting in that the current density becomes lower than that using pure hydrogen as fuel.In order to clarify the performance of SOFC in chemical looping gasification-SOFC coupling system,the simulation study of SOFC is carried out based on the multi-physical field coupling model,considering the effect of carbon deposition on the reaction.It is found that carbon deposition affects the catalytic activity and inhibits the electrochemical reaction,resulting in the increase of hydrogen mole fraction.At the same time,the temperature of SOFC using gasification product as fuel is lower than that using pure hydrogen due to other endothermic reactions and carbon deposition preventing the release of heat from electrochemical reaction.In terms of polarization loss,the polarization loss of SOFC using gasification product as fuel is greater and more energy is required to break through the activation energy barrier of electrochemical reaction.The influence of operating conditions on SOFC performance is further analyzed.The results show that the anode and cathode fuel countercurrent mode can improve the performance of the SOFC to a certain extent and the increase of the H₂O/C ratio of the system can improve the current density output of the SOFC.Carbon deposition is effectively inhibited.Increasing the fuel reactor temperature can inhibit the carbon deposition of the SOFC in the system,but the hydrogen production of chemical looping gasification is weakened.Hence,an excessive temperature is not conducive to the output performance of the SOFC.