A drag model based on energy minimization multi-scale（EMMS)approach was used in the numerical simulation for fast fluidized bed（FFB)containing Geldart A particles.The Johnson and Jackson boundary conditions（BCs)were used for solids phase.Parametric studies of the specularity coefficient were performed to evaluate its impact on the predicted gas-solids two-phase flow characteristics in term of S-shaped axial voidage profile

outlet solids flux

local voidage radial profile and local particle axial velocity.The experimental conditions of Fan were simulated and compared with experimental data on the aforementioned characteristics.It were found that the wall boundary condition for solids phase played a much important role in simulating the S-shaped axial voidage profile

and directly affected the capability of capturing the heterogeneous flow structure.A “wall-core-annulus” heterogeneous flow structure

which was significantly different from the commonly known “core-annulus” two-zone structure

could be captured in the bottom of the riser when the free-slip wall condition and EMMS-based model were used together.