Biogas fixed-bed upgrading through catalytic shift–methanation: A numerical investigation and experimental validation

The numerical investigation of simultaneous methanation and water gas shift reactions (shift–methanation) for biogas upgrading in a fixed-bed reactor is conducted in this work. The catalyst bed was represented as a porous media model, and the reaction kinetics were coupled with heat and mass transfer in the whole simulation process in order to visualize the composition change and temperature profile in the reactor. The effect of reaction temperature, H2/CO ratio of feed gas, and initial CH4 content on the process was separately investigated. It was found that the biogas upgrading with highest CO conversion and CH4 mole fraction could be realized under a reaction temperature of 630 K. Larger H2/CO and initial CH4 content was beneficial to the biogas upgrading process but, in the meantime, lead to a higher temperature rise in the catalyst bed zone. The mass fraction of each component showed uniformity in the radial direction but presented an axial gradient due to the isotropy of porous media, while the temperature profile displayed both radial and axial gradients, which were caused by the temperature difference between the catalyst bed and the reactor wall. The results of experimental validation were in good accordance with the expected ones via numerical simulation.