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%.