Abstract
An experimental study has been conducted to elucidate the mechanism of radial segregation in the bed of a rotary kiln and to determine the size and composition of the segregated core. Bed-behavior diagrams were obtained, and slumping and rolling characteristics were measured, for two sand mixtures and one limestone mixture containing fines. The fines resulted in significant changes in bed behavior, but no effects were observed on either static or dynamic angle of repose, shear angle, slumping frequency, or active-layer thickness. Therefore it was concluded that the fines do not segregate according to the differential flow of particles down the surface of the bed. Instead percolation, in which the fines pass through the voids in the coarser solids, appears to be the operative mechanism. The size of the segregated core was measured by sampling the bed of solids. Predictions of core width based on geometric considerations and a core composition having the minimum void fraction agreed reasonably well with measurements. A second region of segregation was found adjacent to the wall. The two zones of segregation can influence deleteriously kiln performance. Solids in the central core are not exposed to the hot freeboard gases and therefore may only partially react. The zone of fines at the kiln wall can reduce wall/bed friction to the extent that the bed slips against the wall.
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