Numerical modelling for design of microchannel reactors: Application to hydrogen production from methanol by steam reforming

Microchannel reactors involve chemical-reaction engineering problems in their design and operation, with heat and mass transfer considerations dominating their practicability and efficiency. Study of the fundamental transport phenomena necessitates their description in sophisticated mathematical form. The present study seeks to address this particular problem by investigating the effects of various factors on the transport processes in a heterogeneously catalysed microchannel steam reforming reactor. Numerical modelling for reactor design was performed using a model that accounted for complex catalyst dynamics. Dimensionless number analyses were conducted to understand the nature of the transport processes. The reactor performance was evaluated by means of various parameters, and design recommendations were made. Different operating limit lines were mapped out, and various definitions of energy efficiency were distinguished. The results indicated that the use of microchannel technology enables the achievement of unusually favourable conversion. While mass-transfer limitations are dominant, the reaction is practically feasible at millisecond contact times. A maximum output power in excess of 70 watts per channel can be reached, and energy efficiencies up to about 70 percent are available. The operating limit line can be changed as desirable to maintain the desired product yield throughout the range of conditions. While an optimum velocity for maximum efficiency exists, the flow rate and catalyst loading must be carefully adjusted to simultaneously control the conversion and maximum power within certain needed limits.