(686e) Hydrodynamics In a Semi-Dual Fluidized Bed Biomass Gasifier
The bed material circulation rate plays an important role in hydrodynamics and operation ability in dual fluidized-bed (DFB) gasifiers. The high circulation rate results in a high heat demand and a low heat transfer from riser to gasifier, which makes disadvantage in the DFB gasifier. In this study, a semi-dual fluidized bed (sDFB) biomass gasifier is proposed to reduce the solid circulation rate. A cold-rig sDFB (0.8 m × 0.2 m ×3.85 m height) was designed and installed to investigate hydrodynamics of the apparatus and the solids circulation. In order to calculate the amount of direct back-mixing particles through the gasifier–riser interconnection area, an Eulerian-Eulerian two fluids unsteady-state two-dimensional (2D) model incorporating with the granular flow kinetic theory was used. The packing limit of this CFD model was adjusted according to the experimental data for the solid circulation rate and the pressure drops. It was found from the simulation results that the amount of solids is directly back-mixed through the gasifier–riser interconnection area about 5-12% of solids circulation rate.