Effects of Stack Structure and Heat Loss on the Stability and Efficiency of Steam-Methanol Reforming Microreactors for Hydrogen Production

Abstract

The linear scale-out approximation ignores the influence of exterior heat loss and thus cannot address extinction issues. The present study is focused primarily upon the roles of stack structure and heat loss in the stability and efficiency of microreactors for hydrogen production by steam-methanol reforming. Computer simulations are performed to model the complex physicochemical processes in a variety of different heat loss situations. The effects of channel number, wall thermal conductivity, and surface-area-to-volume ratio are investigated to assess the importance of stack structure and heat loss in microreactor design. The results indicate that the total heat loss becomes increasingly significant for designing reactors with small stacks of channels. About half of heat released is lost if a global-type extinction occurs. The critical heat loss coefficient depends heavily upon the number of channels. The design with a large stack of channels more closely beneficially improves heat utilization and reduces heat loss. There is a significant linear relationship between energy efficiency and heat loss coefficient. Significant heat loss may cause extinction in edge channels while still permitting very high conversion in center channels. The wall thermal conductivity is of vital importance to ensure stability operation. Higher wall thermal conductivity provides stability benefits, but walls with very low thermal conductivity can be employed to reduce heat loss by sacrificing the thermal coupling capability.