The solids circulation is crucial for sustaining biomass gasification within dual fluidized-bed gasification systems, because the heat utilization between the gasifier and combustor is mainly implemented through the circulation of bed material. In this work, a three-dimensional model was established to simulate the hydrodynamics of a dual fluidized-bed gasification system. The purpose of this work was to find effective ways to improve the solids circulation. In this CFD (computational fluid dynamics) model, the MP-PIC (multiphase particle-in-cell) method was applied to simulate the gas-solid flows in the dual fluidized bed system. This model simulated the hydrodynamics of the bubbling fluidized-bed gasifier, chute, pneumatic-riser combustor, cyclone separator, and loop-seal in the dual fluidized-bed system. Studies of grid resolution and numerical parcel were conducted to examine the model accuracy. A series of case studies were implemented to investigate the impact of operating parameters on the solids circulation rate, such as particle diameter, solid inventory, steam supply to gasifier, and air supplies to combustor. (C) 2016 Elsevier Ltd. All rights reserved.