Three dimensional full-loop CFD simulation of hydrodynamics in a pilot-scale dual fluidized bed system for biomass gasification

A three-dimensional CFD model was developed to simulate the hydrodynamics in a pilot-scale dual fluidized bed system for biomass gasification. The system includes a fast fluidized bed (FFB) for char combustion, a cyclone separator, two loop-seals, and a bubbling fluidized bed (BFB) for biomass gasification. A comparison of a hybrid EMMS drag model (i.e. the EMMS/matrix drag model for FFB, and the EMMS/bubbling drag model for BFB) proposed in this paper and the Gidaspow drag model was carried out at air and steam gasification conditions. The solid circulation rate, solid inventory distribution, and the pressure distribution predicted by the hybrid EMMS drag model were in better agreement with experimental data. The effect of solid inventory on hydrodynamics was evaluated by using the hybrid EMMS drag model. The results indicate that the solid circulation rate and its fluctuation increased with increasing solid inventory. In the simulated system, the operating stability was reduced when the solid inventory was increased to 200 kg due to “choking” phenomenon.