Computational fluid dynamics and discrete element method (CFD-DEM) integrated with a new localstructure-dependent (LSD) drag model and modified reaction kinetics are used to simulate the bubbling fluidized bed methanation process. The nonlinear Hertzian model is employed to describe the particleparticle collision process. An approximate image processing method (AIPM) is developed to investigate the bubble properties in the reactive gas-solid fluidized bed, by which the bubbles can be located, measured, and tracked from the CFD-DEM results. The results of the bubble properties and reaction behavior are in good agreement with the correlations in the literature and the experimental data, respectively. The sensitivity study of particles Young's modulus indicates that this parameter has a minor influence on the simulation results but the simulation efficiency can be significantly improved by reducing this parameter. The feasibility of the isothermal flow assumption is also validated for simulations of the fluidized bed methanation process by the CFD-DEM method. In addition, the comparison between CFD-DEM and the two-fluid model (TFM) results shows that both models gave similar results for the reactor performance but the TFM provides smaller bubble size. (C) 2019 Elsevier Ltd. All rights reserved.