MATHEMATICAL-MODELING OF CONTINUOUS CROSS-FLOW DIFFUSION-CONTROLLED DRYERS

A mathematical model has been developed for continuous cross-dow dryer s operating in diffusion-controlled regime. In the model, a cross-dow dryer is treated as a series of gas-solid contact stages, each purged by a stream of drying gas while wet solids are passing through. By ana lyzing the gas-solid interactions in each stage, boundary conditions f or intra-particle diffusion were established and model equations obtai ned. The model correlates the amount of moisture removed to a number o f process variables (diffusivity, partition coefficient, particle size , residence time, total number of stages, solids loading, drying gas h umidity and purge rate) and allows effects of these variables on dryin g to be studied. For drying fine powders, the effect of reduced mass t ransfer efficiency due to particle agglomeration and gas channeling is taken into account in the model by factoring an efficiency parameter into the Fourier number. Model predictions of product moisture concent ration based on laboratory-measured partition coefficient, diffusivity , and efficiency factor were found to closely match data from a commer cial cross-dow HDPE powder dryer. Copyright (C) 1996 Elsevier Science Ltd