Process Analysis for Achieving Highly Enhanced Total Efficiency on Multi-Stage Fuel Supplied SOFC System

Solid oxide fuel cells have a promising potential to realize a highly efficient energy conversion from chemical energy into electrical power. The system modification should be necessary for practical SOFC system to enhance its performance. We investigated a multi-stage fuel supply SOFC system which has additional fuel supply inlets between each SOFC stack. The anode offgas from the first stack is supplied to the next stack as reformed fuel gas being mixed with additional fresh fuel. In this study, the effect of the additional fuel flow ratio was evaluated to improve the electricity and heat output. In a two-stage SOFC stack case, by increasing the additional fuel supply ratio to the 2nd stack, total electrical output was almost the same, while it increased in the 2nd stack and it decreased in the 1st stack in which the system maintained thermally self-sustained operation. On the other hand, total heat output increased because the amount of vaporized water supplied to the system was decreased. Considering the results of this analysis, the multi-stage fuel supplied SOFC system can achieve higher energy conversion efficiency.