Analysis of a Solid Oxide Fuel Cell System with Low Temperature Anode Off-Gas Recirculation

Abstract

At Forschungszentrum Jülich GmbH an SOFC system with anode off-gas recirculation loop operating at temperatures up to 160°C is simulated. To analyze the effect of anode off-gas recirculation, a dynamical system model was implemented in Matlab/Simulink. The results show, that the recirculation rate has a significant effect on the electrical efficiency. In principle, at constant current density high recirculation rates decrease the cell voltage and increase the power demand of the recirculation blower. Therefore, the highest electrical efficiency can be reached with high system fuel utilization, low recirculation rate and in consequence high stack fuel utilization. On the other hand less amount of steam is available for the reforming reaction at low recirculation rates. Therefore, the minimum recirculation rate is determined by the risk of carbon formation. An optimal operation range to avoid carbon formation and to ensure a high electrical efficiency requires recirculation rates between 65 and 70% and system fuel utilizations above 90%.