Numerical simulation and experimental verification for the sorting behaviors of mixed biomass particles in a novel Z-shaped fluidized bed

Abstract

Inclined gas–solid fluidized bed has excellent particle separation and purification performance. Hence, Z-shaped fluidized bed as a novel fluidization system is designed in this work. The effect of superficial gas velocity on the sorting behaviors of mixed biomass particles is investigated by using the computational fluid dynamics and discrete element method, and a high-speed fluidization image experiment platform is established. The density and elastic modulus of biomass particles are experimentally measured, and the shapes are characterized by sphericity. Detailed information (i.e., distribution behavior and flow velocity of particle and fluid, particle residence time, and particle force) are obtained and analyzed. Results show that particles and fluid phases are not uniformly distributed, and a core-annulus structure is observed. The mixed particles movement process is divided into rising, settling, resuspension, and separation. The predictions on the solid distribution and sorting behaviors in the fluidized bed agree well with the experimental findings. Given the different densities and sizes, clean products flow upward and impurities flow downwards when the inlet air velocity is 1.5 m/s. As the superficial gas velocity increases, the transport efficiency of mixed particles improves, but the separation degree decreases. Clean products and impurities are effectively separated under the optimal gas velocity of 1.5–2.5 m/s. Particles in the channel center have a good following performance, moving in a zigzag pattern with the fluid, but they tend to slide along the inclined wall. The dynamic forces of the mixed particles are influenced by the channel section area. These findings provide valuable insight into the development and optimization of particle purification appliances in multiphase reactors.