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 (0.8 m width × 0.2 m depth × 3.85 m 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 60 s after 2 min 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.Figure optionsDownload as PowerPoint slideHighlights
► 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.