Numerical simulation of carbon dioxide methanation reaction for synthetic natural gas production in fixed-bed reactors

Abstract

This study examines and elucidates the CO2 methanation reaction for synthetic natural gas (SNG) production. The reaction performance is characterized using CO2 conversion under various operating conditions. A fixed-bed tubular reactor is used as the physical model and axisymmetric non-isothermal governing equations for the gas flow, energy transfer and species transport are solved numerically. The reactant inlet temperature is used as the primary parameter. An optimum inlet temperature is determined at which the CO2 conversion has a maximum value. With inlet temperature higher than the optimum temperature, CO2 conversion decreases due to the reverse Sabatier reaction. The parametric study shows that CO2 conversion can be enhanced by increasing the reaction pressure, H2/CO2 ratio and reactor size and by decreasing the reactant feed rate and inert gas amount. Heat removal characterized by the heat transfer coefficient plays an important role in CO2 conversion. CO2 conversion may decrease significantly when heat removal is high and the reaction temperature is low. When the reactant inlet temperature is in the revere reaction regime, the heat removal has an insignificant effect on CO2 conversion. This study also shows that higher CO2 conversion results when Ru/Al2O3 catalyst is used as compared with Ni/Al2O3 catalyst.