Flow behaviors, reaction kinetics, and optimal design of fixed- and fluidized-beds for CO₂ methanation

The performances of three catalytic reactors for CO₂ methanation, i.e., single fixed-bed (1FxB), two-stage fixed-bed (2FxB), and bubbling fluidized-bed (BFB), were evaluated at a feed flow rate of 166.5 Nm³/h. A heterogeneous catalytic reaction model (HCRM) combining the one-dimensional plug-flow model on the reactor scale and the reaction–diffusion model on the particle scale was used for 1FxB and 2FxB. A two-phase reaction model (TPRM), including the mass transfer between the bubble and emulsion phases and axial dispersion, was proposed for the BFB. The results from HCRM and TPRM were in good agreement with experimental and modeling data. The 1FxB, 2FxB, and BFB were optimized via the parametric study considering the hot spot temperature, operating temperature and pressure, space velocity, flue gas recirculation ratio, and operational stability. The catalyst weights of 1FxB, 2FxB, and BFB required for a 90% CO₂ conversion were 191, 40, and 34 kg, respectively. The proposed models were able to identify the flow behaviors, mass transfer, and reaction kinetics of the fixed- and fluidized-beds, which are useful for the optimal design of CO₂ methanation reactors.