Simulation studies of autothermal reactor system for H-2 production from methanol steam reforming

Steam reforming of methanol is a principal route for the production of hydrogen. Owing to the high endothermicity of this reaction, attention must be directed at energy-saving measures to improve production economics. However, the novel concept involving the coupling of the oxidation of the methanol (a strongly exothermic step) to the steam reforming reaction is an intuitively attractive operation for energy minimisation. This paper reports the results of a mathematical investigation on the performance of a class of adiabatic dual-bed catalytic reactor systems with cylindrical and spherical geometries that may be used to promote internal heat exchange for the coupled reaction network. Analysis shows that, while the coaxial cylindrical system and the dual-bed single tubular reactor generally need optimal water-to-methanol feed ratios of about 3-4, the spherical arrangement always requires a ratio less than 1 for equivalent or even better performance. The spherical reactor system in which the oxidation catalyst was placed in the inner sphere with steam reforming in the annular space showed the most promising performance in terms of reactor efficiency (about 80%) and H-2 production (125 m(3) gas (m(3) reactor)(-1) s(-1)) while the coaxial reactors exhibited the poorest efficiency (less than 10%) for a H-2 production rate of 19.5 m(3) gas (m(3) reactor)(-1) s(-1). Thus the spherical reactor with an inner oxidation catalyst bed is the most attractive configuration for this autothermal process in terms of product maximization, feed and energy minimization.