Numerical investigations to determine the optimal operating conditions for 1 kW-class flat-tubular solid oxide fuel cell stack

Abstract

In this study, a detailed three-dimensional numerical model is developed which simultaneously assimilates the transport processes, the electrochemical and chemical reactions to optimize the performance of 1 kW-class flat-tubular solid oxide fuel cell stack while operating on H2 and pre-reformed methane fuels. The unique feature of this CFD (computational fluid dynamic) model is that it encompasses the electrochemical oxidation of H2 and CO as well as internal steam reforming reactions including radiation heat transfer analysis in the full stack. A CFD model validated with the experiments performed in-house is utilized to explore the optimal operating conditions by investigating the effect of pre-reforming rate, air/fuel inlet temperatures, oxidant utilizations and radiative heat transfer effect on the temperature distributions. The numerical results elucidated that temperature and the current density distributions can be regulated by adjusting the methane conversion in the pre-reformer. It is also observed that neglecting the CO electro-oxidation in the modeling can underestimate the stack performance; whereas increasing the inlet temperature increases the stack performance. The oxidant utilization analysis established that higher oxidant utilization adversely affects the stack performance due to higher cathodic activation polarization losses. Radiation heat transfer analysis demonstrates that it curtails peak temperature and minimizes temperature gradients of the stack components.