OVERVIEW

The processes of the drying of solids and the evaporative cooling of process water with air have a common foundation in that both deal with interaction of water and air and involve simultaneous heat and mass transfer. Water cooling is accomplished primarily in packed towers and also in spray ponds or in vacuum spray chambers, the latter for exceptionally low temperatures. Although such equipment is comparatively simple in concept, it is usually large and expensive, so that efficiencies and other aspects are considered proprietary by the small number of manufacturers in this field.

In contrast, a great variety of equipment is used for the drying of solids. Thomas Register and Chemical Engineering Buyers' Guide (2003) list many manufacturers of drying equipment, classified according to the type of equipment or the nature of the material being dried. An indication of the difficulty of any process is the vast amount of equipment available, and drying is a good example. Dryers may perform additional tasks besides the handling and transporting of the product being dried. For example, perforated belt conveyors and pneumatic conveyors through which hot air is blown transport material, while other models have the ability to cool, react, heat treat, calcinate, humidify, agglomerate, sublime, or roast. These processes can be done separately or, if required, combined with each other. Solids being dried cover a range of sizes from micron-sized particles to large slabs and may have varied and distinctive drying behaviors. As in some other long-established industries, drying practices...