| Solid oxide fuel cell is widely used in stationary power generation as well as cogeneration with its high efficiency and fuel flexibility in the background of energy crisis and environmental protection.System performance in the field of cogeneration is a key factor for the further development of SOFC-CHP systems.System performance can be improved by reasonable thermal management measures,and AOGR and COGR are commonly used thermal management methods.In SOFC-CHP systems,there are more studies on the use of AOGR and COGR alone,while the simultaneous use of both,especially the interaction,is rare,so the performance of SOFC-CHP systems using both AOGR and COGR is studied with theoretical and engineering practical significance.In addition,the remaining major boundary conditions have obvious effects on the performance of the different systems,and it is necessary to study the effects of the remaining major boundary conditions on the system performance of the simultaneous use of AOGR and COGR.Therefore,in this paper,a 1 kW natural gas-fueled SOFC-CHP system model was developed using Matlab/Simulink software,and the effects of the main boundary conditions AOGR rate,COGR rate,STCR,reformer Uf and stack outlet temperature on the performance of the simultaneous AOGR and COGR systems were investigated,and the following conclusions were obtained:(1)Using AOGR alone improves net electrical efficiency and system fuel utilization,but reduces thermal efficiency.Changes in voltage and current density at high AOGR rates cause drastic changes in current that may adversely affect external appliances,while excessive AOGR rates cause a continuous reduction in system exhaust gas energy resulting in system failure.More heat recovery with COGR alone increases the system thermal efficiency,but the total system power consumption increases leading to a decrease in net electrical efficiency.Excessive COGR rate prevents the secondary air preheater from working properly resulting in system not operating properly.(2)The simultaneous use of AOGR and COGR is beneficial to the system,which allows a significant increase in thermal efficiency without much impact on net electrical efficiency.The interaction of AOGR and COGR causes the system input energy to increase with COGR,and the total power consumption decreases before increasing.Therefore the net electrical efficiency increases before decreasing.Compared to COGR alone,the system thermal efficiency improvement is more pronounced when AOGR and COGR are used together,but the total system heat recovery is reduced.In this study,it is concluded that the best system performance can be obtained with medium AOGR and COGR rates,and the best system performance is obtained with AOGR rate and COGR rate of 0.4 and 0.5,respectively,with net electrical efficiency,thermal efficiency and total system efficiency of 50.24%,24.27%and 74.51%,respectively.In addition,a suitable exhaust gas recirculation control strategy should be determined according to the demand in practical applications.(3)An increase in STCR causes the required input energy of the system to first decrease and then increase,while the total power consumption remains basically the same,so the net electrical efficiency of the system first increases and then decreases,but thermal and total efficiency keep decreasing.In this study,it is concluded that low STCR should be selected without carbon accumulation.Stack Uf increases the net system electrical efficiency but decreases the thermal efficiency,while increasing the stack outlet temperature improves the system thermal efficiency significantly,both of which guide the design and matching of the stack in practical application systems.(4)In this study,the main boundary conditions AOGR rate of 0.4,COGR rate of 0.5,STCR of 2,stack Uf of 0.75,and stack outlet temperature of 850℃ resulted in the best system performance with net electrical efficiency,thermal efficiency,and total efficiency of 50.47%,41.88%,and 92.35%,respectively. |
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