Autothermic Reforming by Super-Adiacatic Combustion in Porous Media

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Autothermic reforming by super-adiabatic combustion in porous medium was investigated through numerical simulation and experiment. A mixture of methane, air and steam is introduced into a spongelike porous medium, where the flow direction is alternated at a regular interval. Both gas-phase combustion and reforming reaction occur around the middle of the porous medium which is made of a cordierite ceramics with a nickel catalyst layer for the reforming reaction. During the period when the product gases pass through the porous medium, the flowing gas enthalpy is stored by the porous medium. Upon reversal, the mixture is preheated before entering the reaction zone, as flowing through the porous medium. By using the reciprocating-flow system, the excess enthalpy combustion occurs ; as a result, the flammability limit is extended to the fuelrich side. Consequently, a part of the methane supplied is consumed for exothermic reaction, i.e., combustion reaction with oxygen, while the residual p … More art is converted into the hydrogen ; where the endothermic reaction for the production of hydrogen occurs.For the reciprocating-flow super-adiabatic combustion system, the flammability limit is extended to the equivalence ratio of about 5 by the heat recirculation. The most striking feature is that the methane conversion, i.e., the conversion ratio from methane to hydrogen, reaches the value above 90 % over a wide range of the equivalence ratio, and the exit temperature of the product gas is almost the same as that of the inlet temperalure. That is, the combustion reaction heat is effectively converted into the reaction heat for the production of hydrogen, and the flowing gas enthalpy is effectively recirculated to increase the temperature of the mixture. With increasing equivalence ratio, the methane conversion decreases because of the decrease in the temperature in the porous catalyst. In this case, to avoid the deposition of the carbon on the catalyst surface, the large amount of steam is supplied. For the ratio of the steam flow rate to the methane flow rate of 7, the mass of carbon is conserved within 5% between the inlet and outlet of the reformer. Furthermore, the reforming system proposed here has a much higher space velocity of 2600(/h)than that of 500(/h)for conventional tubular reformers. Consequently, the reforming system proposed here has a high potential to reduce the scale of the reformer and to produce some valuable species through the combustion process. Less