Thermal resistance effect on methanol-steam reforming performance in micro-scale reformers

摘要

We numerically investigate hydrogen production based on methanol-steam reforming (MSR) using a micro-scale cylindrical packed bed reformer. The reformer wall is included in the physical model. The heat required for the reforming reaction is supplied either internally using a heating rod placed along the center of the reformer or externally by a heat flux applied at the reformer outer wall. Our results show that the thermal resistance from the heat source to the reformer environment plays an important role in the reformer performance. This thermal resistance depends on the reformer geometry, wall material and heat transfer coefficients inside the catalyst bed and outside the reformer. Based on our numerical results, it is suggested that better methanol conversion and hydrogen yield can be obtained using reformer wall material with low thermal conductivity and thin thickness. For both internal and external heating under the same heat rate supply, no significant difference in reformer performance was found. A water gas shift (WGS) reaction model was included in the present numerical model. In the reformer low-temperature zone the forward WGS reaction was clearly demonstrated, resulting in a decrease in carbon monoxide (CO) selectivity. In the high temperature zone the backward WGS reaction was also clearly demonstrated in which CO selectivity increases with the increase in temperature. For both internal and external heating under the same heat rate supply, our results indicated that CO selectivity is about thirty times lower when the WGS reaction is neglected.