Hydrodynamics of cold-rig biomass gasifier using semi-dual fluidized-bed

This study reports a semi-dual fluidized-bed (sDFB) biomass gasifier, which is a novel design of dual fluidized-bed (DFB) with the internal mixing of solid particles between riser and gasifier to enhance the heat and mass transfer. A cold-rig experiment of sDFB (0.8m width×0.2m depth×3.85m height) was performed to investigate fluid hydrodynamics and solid circulations. Pressures were sampled at 43 points along the sDFB gasifier. An external circulation rate of sand was measured for 60s after 2min of the operating time. In order to estimate the amount of direct back-mixing particles through the gasifier–riser interconnection area, an Eulerian–Eulerian two-dimensional computational fluid dynamics (CFD) model was developed for the cold-rig sDFB. This CFD model included the kinetic theory of granular flow and the k–є dispersed turbulence model. The CFD simulation results were validated with the experiment data. About 17% back-mixing of particles through the gasifier–riser interconnection area were obtained from the CFD simulation. This indicates that the sDFB has a possibility of having higher heat and mass transfer than the conventional DFB. The CFD simulation demonstrates that the semi-dual fluidized-bed (sDFB) can improve heat and mass transfer due to internal solid circulation via the interconnecting hole between riser and gasifier. [Display omitted] ► A novel semi-dual fluidized-bed (sDFB) is proposed for biomass gasification. ► Cold-rig experiments were performed to measure external solid circulation rates. ► A CFD model was developed to estimate internal solid circulation rates. ► The sDFB can improve heat and mass transfer by 17% due to internal solid circulation.