Particle-scale modeling of biomass gasification in the three-dimensional bubbling fluidized bed

Biomass gasification in a three-dimensional bubbling fluidized bed is numerically simulated via the computational fluid dynamics coupled with the discrete element method (CFD-DEM) incorporated with heat and mass transfer, and chemical reactions. The particle-scale investigation of the heterogeneous reaction rate of the biomass particles along with the essential aspects (including fluid force, collision force, dispersion) of the solid phase is presented. The results indicate that biomass particles behave with larger horizontal and vertical distance especially in the freeboard region than the sand particles. Strong backmixing of the solid material exists near the sidewall, and large fluid force on the particles appears in the lower bed. Similar trends of the particle-scale fluid force, velocity and dispersion can be observed for the biomass and sand particles, though the magnitudes are larger for the biomass. Chemical reactions result in the axial segregation of the biomass particles. Among all the heterogeneous chemical reactions, the char oxidation is fastest while the hydrogenating reaction is the slowest. Increasing the temperature, and steam-to-biomass ratio and equivalence ratio values all enhance the particle-scale behaviors of both the biomass and sand particles. Also, the temperature improves nearly all the reaction rates. The results obtained here provide essential understanding regarding the particle-scale behaviors of the biomass gasification process in the fluidized bed.