Elementary reaction modeling and experimental characterization on methane partial oxidation within a catalyst-enhanced porous media combustor

In this study, the fuel-rich combustion of methane in a two-layer porous media burner consisting of dense alumina pellets of different diameters was investigated experimentally and numerically. For a fixed inlet gas velocity of 0.15 m/s, methane-rich flames were stabilized near the interface of two layers for equivalence ratios from 1.4 to 1.6. It was found that 40% of the methane was converted to syngas at the equivalence ratio of 1.6 using a reforming efficiency based on low heating values. To further increase the hydrogen yield and make the burner more suitable for applications in fuel cells, a portion of the downstream layer was coated with 0.08 wt % Ni catalyst. The reforming efficiency of methane to hydrogen increased from 18.2% to 23.9% after the catalytic enhancement. A combined homogeneous and heterogeneous elementary reaction mechanism was developed for methane partial oxidation in the porous media burner with catalytic enhancement. A one-dimensional model was explored by coupling the combined mechanism with heat-transport and mass-transport processes within the burner. The modeled temperature profiles and gas compositions showed good agreement with the experimental results. The model is demonstrated to be a useful tool for understanding the reaction processes within the burner and for burner design optimization. The nickel catalyst mainly promoted the water-gas shift reaction, and the heterogeneous reactions were dominant in the region where the catalyst was loaded. The burner design was optimized by studying the effects of the pellet diameter, layer length, and catalyst loading on the reforming efficiencies.