Optimal Method for the Anode Exhaust Gas Recycling of Atmospheric Solid Oxide Fuel Cell-Combined Heat and Power Systems

This study elucidates the effect of recirculation methods for anode exhaust gas recirculation on the performance of solid oxide fuel cell-combined heat and power systems in atmospheric operation. Thermodynamically feasible system layouts are designed and comparatively analyzed in the aspects of electrical efficiency and system operability by conducting numerical simulations. The results indicate that a recycle blower is more suitable than an ejector for anode exhaust gas recirculation of atmospheric solid oxide fuel cell-combined heat power systems to increase an electrical efficiency. The systems employing a recycle blower show a higher electrical efficiency than the systems employing an ejector, reducing the total parasitic power by 48-49%. Ejector-assisted anode exhaust gas recirculation is more vulnerable to pressure drop in the recirculation loop than the recycle blower-assisted option. Regarding system operability, the systems with an ejector should be concerned about the outlet tem-perature of a fuel compressor, and the systems employing a recycle blower should be concerned about the pinch point temperature difference of a recycle gas cooling heat exchanger. The system operability is inhibited by the pressure drop in the recirculation loop and the high entrainment ratio, and each factor is mainly influenced by current density and fuel utilization, respectively.