Hydrogen production by methane-rich combustion in a ceramic burner

The objective of this paper is to study the hydrogen production mechanism by fuel-rich combustion of a methane-air mixture in a ceramic burner. Experiments were carried out in a combustor with a silica-alumina porous ceramic plate of 20 mm thickness and 0.32 porosity set at the bottom of a combustion chamber. The premixed gas of methane and air passed through the porous ceramic plate and was ignited above the plate. The flammability limit was up to 2.5 in equivalence ratio for methane-air combustion in the ceramic burner. Then hydrogen yield in the combustion gas was about 10% in mote fraction. Setting a wire net at the downstream of the flame extended the flammability limit in the fuel-rich region. It was caused by combustion temperature elevation. These results imply the applicability of the ceramic burner to non-catalytic reforming of methane. The behavior of the partial oxidization and pyrolysis in this ceramic burner was analyzed numerically by a chemical kinetic model. The model takes account of 31 chemical species and 147 elementary reactions. The species include C-1 to C-3 hydrocarbons and radicals. A set of the ordinary differential equations for the reaction rates was integrated by the Gear's method. The model expressed the experimental results well in the equivalence ratio less than 2.0 in which no soot emission takes place. This model was also applied to analyze the yield mechanism of hydrogen molecule products in the fuel-rich combustion of the methane-air mixture. Hydrocarbons and radicals of CH3, CH2O and C2H6 were significant intermediates for the elementary reactions related to the hydrogen yield. The transient behaviors of hydrogen yield are influenced sensitively by the three major reactions. These results imply that the conversion of methane to hydrogen can be predicted by the limited sequential reactions.