(443c) The Development of Microchannel Reactors for Hydrogen Production: Experimentation and CFD Modelling

A microchannel reactor for hydrogen production from ammonia is simulated with a three-dimensional (3D) CFD model using Comsol Multiphysics, in order to obtain a mathematical framework to understand the reaction-coupled transport phenomena associated with the microchannel reactor. The catalysts used consisted of commercial Ni-Pt/Al₂O₃ and Ru/Al₂O₃ catalysts in the form of a porous wash-coat deposited on the walls of the micro channels. The transport processes and reactor performance are elucidated in terms of velocity, temperature, and species concentration distributions, as well as local reaction rate and ammonia conversion profiles. The baseline case is first investigated to determine the behaviour of the microchannel reactor, then microstructural design and operating parameters are methodically altered around the baseline conditions to explore the optimum values. The simulation results show that an optimum ammonia space velocity (GHSV) yields 99.1% ammonia conversion and a power density of 32 kW_e L^-1 at the highest operating temperature of 973 K for the Ni-Pt based catalyst. It is shown that a 40-μm-thick porous wash coat is most desirable at these optimum conditions. Also a small channel hydraulic diameter (225 µm) is observed to contribute to high ammonia conversion. It is reported that the Ru/Al₂O₃ gives a superior yield than the Ni-Pt/Al₂O₃ at optimal conditions and that experimental and model results agree very well. The results obtained confirm that a catalytic microchannel reactor can be most desirable for small scale hydrogen production from ammonia, required especially for the operation of fuel cells.