The objective of this study was to numerically investigate the particle dispersion mechanisms in the gas-solid two-phase jet for a fuel-rich/lean burner by means of coupling the discrete element method (DEM) with the computational fluid dynamics (CFD). The DEM was employed to deal with the particle-particle and the particle-wall interaction in the computation of solid flow; while gas flow was computed by CFD based on the commercial software package Fluent. The particles with various Stokes numbers equal to 0.1, 0.5, 1, 2 and 3 (corresponding to particle diameter 10.8, 24.17, 34.18, 48.38 and 59.21 mu m, respectively) in the gas-solid fuel-rich/lean jet were investigated in this study. The particle-particle collision was simulated and its effect on the fuel-rich/lean separating performance was evaluated. The results show that the particle-particle collision occurred more frequently with the increasing of Stokes numbers from 0.1 to 3. The particle dispersion became more uniform between the fuel-rich side and the fuel-lean side for particles with small Stokes number; while for particles at St > 1, a better fuel-rich/lean separating performance was achieved. The efficiency of the DEM-CFD coupling method was validated by the corresponding experiments, and a good agreement between the simulation and experiments was achieved as a result of the particle-particle collision. (C) 2010 Elsevier Ltd. All rights reserved.