Coupled CFD and Process Simulation of a Fuel Cell Auxiliary Power Unit

A high-temperature auxiliary power unit (APU) based on solid oxide fuel cell (SOFC) technology is analyzed in this study using coupled computational fluid dynamics (CFD) and process simulation. The tightly integrated process flowsheet consists of a reformer, desulfurizer, SOFC stack, combustor, and various heat exchange and rotating equipment items. A detailed three-dimensional CFD model is used to represent the cross-flow, planar SOFC. Process simulations are used to calculate the overall material and energy balances. Coupled CFD and process simulations are performed over a range of fuel cell currents to generate a voltage current curve and analyze the effect of current on fuel utilization, power density, and overall system efficiency. The fuel cell APU system considered here generated 4.3 kW of power and yielded a maximum fuel-to-electricity conversion efficiency of 45.4% at a current of 18 amperes. Integrated CFD and process simulations provide a better understanding of the fluid mechanics that drive overall performance and efficiency of fuel cell systems. In addition, the analysis of the fuel cell using CFD is not done in isolation but within the context of the whole APU process.