This study presents detailed 3D unsteady CFD simulations, performed using NEPTUNE_CFD V1.08@Tlse code, of air-methane combustion in a dense fluidized bed containing inert particles. Predictions are compared with the experimental data reported in Dounit et al. (2001a, 2001b, 2008). In their study, the authors investigated the behavior of natural gas combustion process in dense fluidized bed and in the freeboard at temperatures lower than a critical value (< 850°C). The main outputs of the experiments are vertical profiles of gaseous-species concentrations and gas temperature. In CFD simulations, an Euler-Euler approach is used to compute separately gas and solid phases flows (primary variables for each phase are volume fraction, velocity, enthalpy, mass fraction), with detailed closure models to account for fluid-particle and particle-particle mass, momentum and energy transfers. Gaseous combustion is modeled by a two-step mechanism following Arrhenius-type equations (Dryer & Glassman, 1973, Westbrook and Dryer, 1981). The Eulerian modeling takes into account the energy exchange by radiation between the gas, the particles and the reactor walls as well. The 3D unsteady simulations are analyzed to characterize dynamic flow behavior, thermal spatial distribution and interphase equilibrium. Time-averaged quantities are computed to compare predictions with the available experimental measurements.