As one of the most efficient and reliable entrained flow coal gasification technologies, the Opposed Multi-Burner (OMB) coal-water slurry gasification technology has been applied in 38 plants. The particle residence time in a commercial scale OMB gasifier is studied in this work by using a 3D numerical model. The Realizable k-epsilon model and discrete particle stochastic trajectory model are employed to solve the gas-solid two-phase flow. The model is validated with the particle residence distribution (RTD) obtained from the bench scale gasifier. The Direct Simulation Monte Carlo (DSMC) method and hard sphere model are used to calculate the gas-solid flow in gasifier impinging zone to consider the effects of the inter-particle collision. In order to reveal the intrinsic factors that dominate the particle residence time, the particle flow behavior is investigated and the mechanical analysis is conducted. A criterion is proposed and used to evaluate the dominant factor of particle flow in different flow regions of the OMB gasifier. The following results are obtained: The inter-particle collisions in Jet Zones and Impinging Zone of the OMB gasifier slightly reduce the particle residence time in these regions. In the regions close to the Impinging Zone, nearly all of the particles are completely controlled by the drag force, while the gravity is the dominant factor to most of the particles in the Outlet Zone. In the middle part of the down flow Impinging Flow Zone, the dominant factor of particle flow can be significantly affected by the particle diameter and inlet gas velocity. (C) 2015 Elsevier B.V. All rights reserved.