Design and performance analysis of a cascade solid oxide fuel cell system for high electrical efficiency

Highlights: • Optimized design of the cascade solid oxide fuel cell system has been proposed. • Performance of cascade system has been compared other two types of systems. • Superiority of cascade system has been verified with various operating parameters. • Anode off-gas recirculation system has the highest stack electrical efficiency. • Cascade system has the highest system electrical efficiency except low external reforming ratio. To enhance the electrical efficiency of a solid oxide fuel cell system, a cascade system has been proposed. In the cascade system, two stacks are installed in series so that the second-stage stack utilizes the anode off-gas from the first-stage stack to increase the electrical efficiency of the system without an anode off-gas recirculation device. In this study, a mathematical model of the cascade system has been developed to achieve the system optimization. To confirm the superiority of the cascade system compared to the single-stage system and the anode off-gas recirculation system in terms of the system electrical efficiency, the effects of the operating parameters on the system efficiency has been analyzed, such as the current density, external reforming ratio, and steam-to-carbon ratio. The simulation results show that the cascade system has the highest system electrical efficiency among the three types systems, except for the low external reforming ratio of 30%. This study can provide the basic insight to establish the optimization for the cascade solid oxide fuel cell system.