Drying equipment dispersion, dryers

Pneumatic dryers, also called flash dryers, are similar in their operating principle to spray dryers. The product to be dried is dispersed into an upward-flowing stream of hot gas by a suitable feeder. The equipment acts as a pneumatic conveyor and dryer. Contact times are short, and this limits the size of particle that can be dried. Pneumatic dryers are suitable for materials that are too fine to be dried in a fluidised bed dryer but which are heat sensitive and must be dried rapidly. The thermal efficiency of this type is generally low. 

Dust Explosions Dispersion dryers can be more hazardous than layer-type dryers if we are drying a solid combustible material which is then dispersed in air, particularly if the product is a fine particle size. If this finely dispersed product is then exposed to an ignition source, an explosion can result. The following conditions (van t Land, Industrial Drying Equipment, Marcel Dekker, New York, 1991) will be conducive to fire and explosion hazard ... 

Fabrics that cannot be finished with aqueous fluoropolymer dispersions can be finished by spray application of a fluoropolymer dispersed in a volatile solvent, such as stabilized trichloroethylene [150] or tetrachloroethylene [151]. After spraying, fabrics pass directly from the spray booth into a dryer heated at 38-66°C. The finish is cured for 60 s at 150°C or at a lower temperature if the fabric cannot tolerate heating at 150°C [150]. Equipment has been built for continuous pad-dry-heat application of fluoropolymers from a volatile solvent, which is recovered almost completely and recycled [151]. The use of volatile solvents has caused environmental concerns. 

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