Effect of Coal Particles on Bed Characteristics and Their Motion Behavior in a Gas-Solid Separation Bed

Air-dense medium fluidized beds have attracted more attention due to their unique advantage of forming a density bed suitable for coal separation without water participation. However, the detailed effects of coal particles on separation fluidization are not yet fully understood. In this study, the effects of feeding particles on bed fluidization characteristics and bed voidage (including single emulsion phase and bubbling state), as well as their motion behavior, are investigated comprehensively. The results indicate that the initial critical fluidization velocity decreases when a middle- or high-density feeding particle layer is present. Moreover, it is found that the feeding particles exert compression and expansion effects on the emulsion phase or the bubbling fluidized bed with a lower fluidization number when the feeding particle volume is below and above a certain value, respectively, and that the expansion ratio can also be affected by the static bed height. Additionally, the fluidization number corresponding to the optimal settlement performance of high-density feeding particles presents an ascending trend with decreasing medium particle size and static bed height, and the influence of fluidization number on the settlement performance can be weakened and separation time can be shortened with increasing feeding particle size. The backmixing degree of low-density feeding particles is expected to decrease by reducing fluidization number and increasing medium particle size.