Fluidized-bed reactors (FBR) are found in a large variety of industrial processes ranging from coal gasification to water treatment. In reactive FBR processes, gas-solid mixing and interactions can be enhanced as well as the chemical reaction rate. These properties are particularly interesting to achieve low-temperature combustion with high conversion efficiency and low pollutant emissions such as nitrogen oxides. The objective of this study is to achieve simulations of a FBR at mesoscopic scale using a coupled CFD/DEM (Discrete Element Method) approach in order to gain insight into the physics of such processes and to extract information to be used in the modeling at macroscopic scale. The chosen configuration is a semi-industrial FBR fed with a mixture of natural gas and air containing 200M sand beads. Experimental data show a shift in the combustion regime above a critical temperature of 800°C. Large-Eddy Simulations (LES) are performed using the finite-volume code YALES2, a low-Mach number solver based on unstructured meshes. Its DEM solver has been designed to perform simulations in arbitrarily complex geometries and optimized for massively parallel computing: it features a dynamic collision detection grid for unstructured meshes, packing/unpacking of the halo data for non-blocking MPI exchanges and a dynamic load balancing algorithm.