MATHEMATICAL-MODELING OF DIFFUSION-CONTROLLED PNEUMATIC-CONVEYING DRYERS

A mathematical model for a continuous pneumatic-conveying dryer has be en developed for removing internally bound moisture from solid particu lates. The dryer relies on a recirculating carrier gas stream for entr ainment. Drying is carried out by injecting into the gas loop a fresh stream of conditioned drying gas while an equal amount of wet gas is v ented out. Because pneumatic-conveying dryers usually employ huge gas velocities, the particulates are well dispersed in the gas. Therefore, For solids absent of surface moisture, the drying kinetics is control led by intraparticle diffusion. The model developed based on the diffu sion mechanism relates the moisture reduction in the solids to various process parameters (diffusivity, partition coefficient, particle size , residence time, solids loading, drying gas usage, and carrier gas re circulating rate), and is fully predictive. Therefore, it can be used to study the effects of these variables. The model was compared with t he plant data and found to match the data within +/-15%.