The modeling of transverse solids motion in rotary kilns

Abstract

Mathematical models have been developed to predict the conditions giving rise to the different forms of transverse bed motion in a rotary cylinder: slumping, rolling, slipping, cascading, cataracting, and centrifuging. Model predictions of the boundaries between these modes of bed motion compare well with previously reported measurements, and can be represented conveniently on a Bed Behavior Diagram which is a plot of pct fill against Froude number (or bed depth vs rotational speed). The location of the boundaries is shown to depend on material variables which characterize frictional conditions in the bed. For the slumping/rolling boundary these are primarily the shear angle and the limiting wedge angle which defines the solids involved in a slump. For the slipping/slumping and slipping/rolling boundaries the governing material variables are the bed/wall friction angle and the upper angle of repose and dynamic angle of repose, respectively. Similarly, the location of the other boundaries related to cascading and cataracting is determined by the dynamic angle of repose. Complete Bed Behavior Diagrams have been calculated for solids having different particle size and particle shape rotated in cylinders having different diameters. © 1983 The Metallurgical of Society of AIME.