Catalytically enhanced methane-rich combustion by porous media reactor

Syngas production by the partial oxidation reforming of methane is a promising technology with a simple setup and quick dynamic response, which has great potential for application in small-scale fuel cells and portable power units. In this study, a catalytically enhanced porous media combustor for partial oxidation reforming is designed and tested. In the combustor, fuel-rich combustion in porous media and catalytic partial oxidation are integrated, benefitting from the merits of both technologies. Without external heat source, the combustor is directly ignited with a stoichiometric gas mixture during the cold startup process, and then adjusted to the partial oxidation conditions. Three zones, a preheating zone, an oxidation zone involving exothermic reactions, and a reforming zone involving endothermic reactions, are observed, which significantly affect the temperature profile in the axial direction. Considering both the methane conversion and reforming efficiency, the optimal equivalence ratio range for self-sustained operation is found to be 2.0-2.4. At an equivalence ratio of 2.0, the effect of the gas velocity on the temperature profile and gas composition of products are studied experimentally. At an equivalence ratio of 2.4 and a gas velocity of 0.13 m/s, the reforming efficiencies of the reactor reach 61.5% and 64.8% when 0.5 wt% Pd and 0.5 wt% Rh, respectively, are introduced to the second layer of the porous media. The carbon deposition at different axial positions of the reactor is analyzed, and the results indicate that carbon deposition by methane pyrolysis in the high-temperature oxidation zone is the dominating cause of carbon deposition. A re-ignition process at stoichiometric condition is helpful for the elimination of carbon.