Separation performance of coal in an air dense medium fluidized bed at varying feeding positions

[Display omitted] •Coal separation in ADMFB at varying feeding positions was studied.•Bubble behavior during separation process were analyzed.•Effect of different parameters on separation process was investigated.•Ash separation degree was used to evaluate separation performance. Coal preparation is the basis and prerequisite for clean coal utilization. Air dense medium fluidized bed separation (ADMFB) technique demonstrated good separation performance for coal cleaning. Feeding position remarkably affects separation performance of ADMFB. In this work, we studied how feed height, separating time and gas velocity influence fluidization. Bubble behavior and separation process of the coal in ADMFB were investigated using pressure measuring system and image analysis. Ash separation degree (Sash) was used to evaluate separation performance of ADMFB. Research results showed that separation performance was satisfactory when the material was fed from the upper or middle position, and it was poor when the material was fed from the bottom position. Materials needed certain period of time to complete the sink-float process. Sash values increased and then stabilized as separation time increased. Sufficient loosening of the materials was the key factor for the highly efficient separation. Gas velocity increase helped materials to loosen, and it also destroyed bridging and smuggling. Thus, the overall separation performance improved, while, excessive gas speed was unfavorable. At h∗ = 0.75, t = 5 min and N = 1.8, ADMFB showed excellent separation performance, and its corresponding Sash value reached maximum value equal to 1.07.