Mechanical Engineering Journal (Feb 2016)
Experimental study on a methanol auto-thermal reforming for compact reformer
Abstract
Performance of self-sustaining methanol auto-thermal reforming (ATR) was investigated experimentally in order to elucidate a reforming reaction mechanism and a condition required for high purity H2 production for compact reformer. The reformer consists of vaporizing and reforming sections in a single unit. The exothermic oxidation and endothermic steam reforming (STR) take place simultaneously in the reforming section. The reforming section is surrounded by the vaporizing section and then the heat for vaporization is supplied from the reforming section. Two types of exothermic oxidation reaction were investigated as the heat source for STR; one is a partial oxidation (POX) and the other is a total oxidation (TOX). CuO/ZnO/Al2O3 catalyst and Pt/Al2O3 catalyst were used for STR and POX, respectively. While, only CuO/ZnO/Al2O3 catalyst was needed for TOX because TOX took place when fuel and oxygen were supplied to the CuO/ZnO/Al2O3 catalyst. Experiments were investigated in the range of oxygen/carbon ratio (O/C ratio) 0.1-1.5, steam/carbon ratio (S/C ratio) 1.0-3.0 and N2 mole ratio 79-50 % in oxidizer. The results showed that the H2 formation reached maximum at around O/C=0.4 in both STR/POX and STR/TOX cases in the present study. When O/C ratio is decreased from 0.4, heat formation by the oxidation reactions decreases and is insufficient to reform residual CH3OH by STR. As a result, H2 formation and the methanol conversion ratio decrease. When O/C ratio is increased from 0.4, the H2 formation decreases, because methanol is consumed with the excess O2 by TOX and CH3OH for STR decreases. After all, O/C=0.4 gives an appropriate balance of heat supply and methanol for H2 production. These results elucidate that the reaction rate of oxidation reactions, POX and TOX, is much faster than that of STR. In other words, methanol is first consumed by the oxidation reaction and the residual methanol is used for STR. For S/C ratio, H2 formation is decreased in the higher S/C ratio. N2 mole ratio in oxidizer has few influence over the reforming gas. The chemical equilibrium calculations support the experimental results.
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