A novel helical transport mechanism enabling continuous discharge in centrifugal fluidization separation for coal cleaning

Coal beneficiation is the source technology for coal cleaning, yet efficient separation of 0.25–1.00 mm coarse coal slime remains a major challenge. Although centrifugal fluidization concentrators exhibit superior performance in fine particle separation, their semi-continuous operation confines them to the recovery of trace dense minerals, limiting their applicability in coal cleaning. In this study, a novel helical transport mechanism was proposed to enable continuous discharge in centrifugal fluidization, and a separation bowl with a helical groove structure was designed. Computational fluid dynamics was employed to investigate the flow field characteristics, while particle transport and separation mechanisms were revealed through theoretical analysis and experiments. The results showed that the helical structure generates distinct flow field characteristics depending on the rotation direction. Under reverse rotation, the helical structure agitates the fluid, reducing its velocity and filling most of the separation bowl, thereby producing a relatively uniform velocity distribution. In contrast, under corotation, the helical structure guides the fluid upward along the groove, confining it within the channel and generating a distinct interlayer shear structure in the velocity field. The particle transport behavior is primarily governed by the helical groove radial inclination angle ( θ ) and the fluidizing water injection angle ( β ). Within the present experimental system, continuous discharge was achieved when θ ≥ 3.11° and β ≥ 60°. The separation performance of coarse coal slime is superior under corotation than under reverse rotation. The agitation effect under reverse rotation partially disrupts the stratified structure, hindering effective separation. By comparison, stable density-based stratification is achieved under corotation, with an Ep value of 0.12 g/cm 3 . This study presents a novel approach to achieving continuous discharge in centrifugal fluidization separation and provides a new method for coarse coal slime separation.