MODELING OF PARTICLE MIXING AND SEGREGATION IN THE TRANSVERSE PLANE OF A ROTARY KILN

Thorough mixing of particles in the transverse plane of a rotary kiln or drier is essential to the uniform heating or cooling of the charge and ultimately, to the generation of a homogeneous product. However, d ifferences in particle size and density result in a de-mixing process whereby smaller or denser particles segregate to form an inner core or kidney of segregated material which may never reach the bed surface t o be exposed to freeboard temperatures. A model has been developed to predict the preferential movement of particles in the shearing active layer. This model determines the extent of fine particle segregation a nd is based on the principle of percolation in the active layer, where by fines sift through the matrix of the bed to form the segregated cor e. Incorporating results of a granular flow model developed for this p urpose, it has been possible to establish the dimensions of the segreg ated core as well as fines (jetsam) concentration in the rest of the b ed cross-section. This result is necessary in assessing the effect of segregation on bed temperature nonuniformities in rotary kilns. Copyri ght (C) 1996 Elsevier Science Ltd