A simple dynamic model for solid transport in rotary dryers

The solid particle movement in a rotary drum plays an important role in dry ing processes. The solid distribution in the drum affects the amount of con tact surface between the solid and the gas. The retention time of solids in fluences the time particles can stay in contact with the gas in order to tr ansfer heat and mass. Any heat and mass transfer model for a solid particle dryer must be able to predict solid flowrate and solid hold-up. There have been several reports in the literature regarding the modelling aspects of solid transport in dryers. If the model is developed for model-based contro l, it must be simple and yet represent dynamics of the system accurately. T his paper addresses solid motion modelling and the effects of different var iables involved in solid transport phenomena. Sugar drying process is the c ase study in this work. A steady state semi-empirical model was modified to predict solid hold-up and flowrate in rotary dryers. This model was incorp orated into a heat and mass transfer model to predict solid moisture and te mperature for inferential and model-based control purposes. Results of seve ral experiments that have been used to investigate dynamics of the system i n terms of solid motion and to validate the model are also presented. The a pproach advocated in this paper is directly applicable to the transport of other solids in rotary drum equipment and can thus be regarded as a general ized model.