Particle motion and mixing in a rotary kiln

Abstract

The motion and mixing of solid materials within a rotary kiln was studied experimentally by visual observationof tagged particles in a laboratory kiln. Particle mixing rates were evaluated by the time required to achieve complete or randomized mixing of the kiln bed. Experiments were conducted to investigate the effects of particle type, kiln loading, and wall friction on mixing rates in the bed with the bed in either slipping mode or rolling mode. In slipping mode, the bed behaved as a relatively solid mass with little mixing of particles when compared to operation in rolling mode. In rolling mode the following effects were noted: Increasing kiln loading increased the time required to achieve complete mixing; e.g. in one experiment, a 500% increase in kiln loading resulted in a 67% increase in the time to achieve mixing. Particle type was shown to have an effect on mixing time and an empirical relationship was developed to predict kiln mixing times based on the ratio of the coefficient of particle/particle friction to the coefficient of particle/wall friction.