Thermal management of bypass valves for temperature difference elimination in a 5 kW multi-stack solid oxide fuel cell system

Large-scale solid oxide fuel cell (SOFC) stationary power generation systems require multi-stack SOFC integration. System consistency has a significant impact on stable, long-term operations. Investigations on the flow and temperature distributions of the system and effective thermal management are necessary to improve system consistency. In this study, a multi-stack SOFC system homogeneity thermal management method and its decision process are proposed based on the flow network method. The flow and thermal distributions and performance are investigated by considering air stoichiometries of 1.5, 2.0, and 2.5. A thermal management strategy using bypass valves is proposed to solve the maldistribution issue of the system. Both the flow characteristics calculated by the flow network and the electrothermal characteristics of the stack determine the bypass valve opening (or air mixing ratio). The results indicate that a maximum temperature difference of 60 K can be reduced to 0 K through the proposed thermal management strategy in a 5 kW multi-stack system. The application of the bypass valve enables the system to attain temperature consistency, and the thermal efficiency of the entire SOFC combined heat and power system can be increased by up to 50% at the set temperature.