Abstract: In the coal-direct chemical looping combustion process, the separation of char and ash from oxygen carriers is essential for reducing the requirement of fresh oxygen carriers and avoiding the char into the air reactor. In this work, a three-dimensional simulation is conducted to investigate the solid-solid separation process in a fluidized bed reactor by means of the multi-fluid model, where the multi-scale drag model is implemented to describe the bubble effect in the bed. The elutriation process of fine particles from mixture is evaluated. The model prediction is compared with the experimental results. The results demonstrate that the dependence of the elutriation rate on fine particle diameter is not monotonous owing to the formation of agglomeration. Meanwhile, the increase of operating temperature promotes the non-uniform degree of interphase drag force and the elutriation rate of fine particles is reduced.