Computational study of Pd-membrane CH4 steam reformer with fixed catalyst bed: Searching for a way to increase membrane efficiency

Abstract

This paper focuses on the feasibility of coupling a Pd-alloy composite membrane with specially structured catalytic bed for SMR at realistic operating and design conditions. The practical aim is computational design of a compact fuel processor, capable to produce 3–4 kg/h of high purity hydrogen (100–130 kW total power) for PEM FC applications. The research goal is searching for a way to increase membrane efficiency by facilitating hydrogen transport across the catalyst bed (suppressing concentration polarization phenomena) that greatly deteriorates fixed-bed membrane reactor (MR) performance. A pseudo-2D model is developed to analyze the operation of different MR types: tube-in-tube or sandwich-type, granular or structured catalyst with Ni or Rh as active component. In order to overcome mass and heat transport limitations a novel type of catalyst support, closed-cross-flow-structure (CCFS) was incorporated in the MR model. The significant increase of MR efficiency was predicted after replacement of 8%Ni/Al2O3 coating by 1%Rh/Al2O3 catalyst. The potential advantages of the suggested MR type are shown to be effectively realized in case of ultra-thin Pd membrane 4.5 μm with extremely high MR output productivity >4 kg(H2)/h/m2.