Integrated Steam Reforming/Catalytic Combustion Annular Microchannel Reactor for Hydrogen Production
MetadataShow full item record
The overall goal of this dissertation work is the development of an annular microchannel reactor (AMR) that couples methane steam reforming and catalytic combustion of methane to produce hydrogen and/or synthesis gas achieving breakthroughs in heat transfer rates and methane reforming capacities. This is accomplished through reaction engineering design analysis and CFD models, validated by experimental data provided by our industrial collaborator, Power+Energy, Inc. The initial goal was to produce a CFD model that could verify experimental results provided by Power+Energy, Inc enabling the rapid design of an AMR prototype. Once the CFD model was verified, a manufacturable design produced higher power densities than competitive planar technology and competitive overall thermal efficiencies. The next goal was to establish that catalytic combustion of methane is a viable means of providing the heat duty necessary to sustain isothermal operation of the AMR and to match AMR heat duty profiles, established previously. Catalytic combustion of methane will supply sufficient heat flux to the AMR, but there will be axial mismatch in the heat duty profiles resulting in temperature deviations, investigated later using a coupled geometry. The next goal was to investigate the potential of an unconventional catalyst design space wherein catalyst efficiency is maintained, while thermal efficiency is increased due to the thickening of the catalyst coating. 1-D analysis show that the catalyst coating could be thicker than the catalyst efficiency “rule of thumb,” while maintaining high thermal efficiencies for the methane steam reforming conditions used. For the 2-D analysis, the AMR geometry is used and shows that the catalyst coating could be increased as much as three fold with minimal losses to catalyst efficiency while maintaining high thermal efficiencies. The final goal was to couple the models presented previously using isolated geometries, while including a finite thermally conductive wall. The objective was to show the effects of heat flux mismatch and prove that the temperature deviations seen when comparing the AMR and combustion results, will be less severe than suggested by the 1-D conduction model indicates due to multi-directional heat conduction within the volume-separating wall. Temperature deviations occurring from the heat flux mismatches still occur; however, the previous performance prediction are proven incorrect. The separated models over predict the methane capacity needed for the combustion chamber, subsequently under predicting thermal efficiency and combustion heat utilization. Additionally, the temperature deviations present allow for higher hydrogen yield than originally predicted. An asymmetric design is introduced that attempts to better match the drastic heat flux in the begging of the steam reforming reaction. This asymmetric design allows for high heat flux into the AMR tube, but generates hotspots. These hotspots are then investigated with the intent of mitigation. The objective was to add catalyst to the inner tube of the AMR, which would then act as a reactive heat sink subsequently reducing the magnitude and size of the hotspot. Nine different catalyst additions are investigated in a case study surrounding the lowest flowrate indicates that any catalyst addition will reduce the hotspot to a manageable size and temperature.
Butcher, Holly A (2017). Integrated Steam Reforming/Catalytic Combustion Annular Microchannel Reactor for Hydrogen Production. Doctoral dissertation, Texas A & M University. Available electronically from