Improving biomass mixture separation efficiency in multiple inclined channels of gas–solid fluidized bed: CFD-DEM simulation and orthogonal experiment

In order to improve the separation efficiency of clean biomass products and waste, a Z-shaped fluidized bed with multiple inclined channels is developed and applied in industrial production. Particle motion characteristics are studied using the computational fluid dynamics and discrete element method and verified by imaging experiments. The influences of operating parameters on the separation of mixture with different densities are investigated. A L9(34) orthogonal array is proposed to identify the main and secondary factors, and the optimal combination working condition is determined. Results demonstrate that the mixtures collide and separate many times in the inclined fluidization channels. The superficial velocity is the core for the separation efficiency, followed by the aspect ratio, and the conveying speed has a minimum effect. The Z-shaped fluidization system has an optimal performance when the superficial velocity is 6 m/s, the aspect ratio is 15/2.5 mm, the conveying speed is 2 m/s, and the mass flow rate is 0.156/0.033 kg/s. Compared with the average of the orthogonal table, the collection rate of clean products and impurities in the optimal combination increases by 70.4% and 10%, respectively. Moreover, particles are mainly perpendicular to the airflow with a zigzag movement pattern. The core-annulus structure and reflux of particles and gas are observed. The predictions on the biomass distribution agree well with experimental results, and the angle error is less than 14%. These findings will provide helpful guidance on biomass recovery utilization and other cleaner production.