Performance analysis of a natural gas-fueled 1 kW solid oxide fuel cell-combined heat and power system with off-gas recirculation of anode and cathode

Both anode off-gas recirculation (AOGR) and cathode off-gas recirculation (COGR) can increase the performance of solid oxide fuel cell-combined heat and power (SOFC-CHP) systems on their own, however, they both have unavoidable drawbacks. Thus, the combined effect of both on the system is worth investigating. The essential challenge is to figure out what the best AOGR and COGR ratios are under the combined situation. In this paper, the effects of varied AOGR ratios and COGR ratios on the system performance were investigated. A model of a 1 kW natural gas-fueled SOFC-CHP system was constructed which uses Cycle-Tempo software. It is demonstrated that moderate AOGR can improve the net electrical efficiency, but too much AOGR will reduce the H₂ concentration at the anode inlet and prevent the stack from working properly; moderate COGR can improve the thermal efficiency, but too much COGR can lead to large changes in current density variation and cause drastic changes in current, which affects the system and external electrical equipment. While, combining AOGR with COGR can improve both the net electrical and thermal efficiency, which results in higher total efficiency. As a result, the combined configuration of an AOGR ratio of 0.4 and a COGR ratio of 0.4 is recommended. In this scenario, the net electrical efficiency of the system is 47.38%, the thermal efficiency is 28.98%, the total efficiency is 76.37%, and the actual fuel utilization rate is 0.834.