The objective of this study is to simulate the motion and chemical conversion of solid fuels in a packed bed moving on a forward acting grate. The approach considers a packed bed to be composed of a large number of individual (currently spherical) particles, which have different properties and sizes. Each of these particles undergoes a sequence of processes such as heating, drying, pyrolysis and char combustion. Chemical species and energy are released from the solid phase mix and react in the cross flowing gas phase. This approach for the simulation of a reacting moving bed on a forward acting grate is coupled to the numerical simulation of the reacting flow in the combustion chamber above the grate. For the reacting granular flow the 2D-version of the discrete element code of the Department of Energy Plant Technology (LEAT) is used. For the reacting flow in the combustion chamber the 3D-CFD code ANSYS-CFX has been applied. The concept of discrete element modelling with special emphasis on the multi-physics coupling and the coupling of DEM with ANSYS-CFX is introduced, and the necessary framework is presented. Results are shown for the fluid flow in the combustion chamber and the solid flow on the grate. (C) 2009 Elsevier B.V. All rights reserved.