Rotary tray dryers

Figure 9.8. Rotary tray, through-circulation belt conveyor, and heated screw conveyor dryers, (a) Rotary tray dryer (Wyssmont Co.), (b) Action of a rotating tray and wiper assembly (Wyssmont Co.), (c) A single conveyor belt with air upflow in wet zone and downflow in dry (Proctor and Schwartz Inc.), (d) A two-stage straight-through belt conveyor dryer, (e) A three-belt conveyor dryer as the material becomes dryer, the loading becomes deeper and the belt longer (Proctor and Schwartz Inc.), (f) Screw conveyor dryer with heated hollow screw (Bepex Corp.).

The process of sublimation is analogous to the drying of solids so much the same kind of equipment is usable, including tray dryers (Fig. 9.6), rotary tray dryers (Fig. 9.8), drum dryers [Fig. 9.11(b)], pneumatic conveying dryers (Fig. 9.12), and fluidized beds (Fig. 9.13). The last of these requires the subliming material to be deposited on an inert carrier which is the fluidized material proper. 

Wyssmont Co. 1470 Bergen Blvd. Ft. Lee, NJ 07024 Continuous Rotary Tray Dryers... 

The turbo-tray dryer can handle materials from thick slurries [1 million (N s)/m (100,000 cP) and over] to fine powders. It is not suitable for fibrous materials which mat or for doughy or tacky materials. Thin slurries can often be handled by recycle of dry product. Filter-press cakes are granulated before feeding. Thixotropic materials are red directly from a rotary filter by scoring the cake as it leaves the drum. Pastes can be extruded onto the top shelf and subjected to a hot blast of air to make them firm and free-ffowing after one revolution. 

Use alternate drying method (ex. vacuum drying instead of atmospheric drying vacuum tray dryer, freeze drying, cryogenic CO2 drying, instead of vacuum rotary dryer) where material is subdivided in multiple locations... 

TABLE 9.8. Performance of Rotary Tray and Pan Dryers (a) Multitray Dryers at Atmospheric Pressure... 

Cost data for drum dryers, rotary dryers, tray dryers, and tumble dryers are presented in Figs. 16-29 through 16-32. The data available cover both atmospheric and pressure systems. 

Wentz and Thygeson, 1979 tray dryer from Perry, Chemical Engineers Handbook, 4th ed., p. 20-7 conveyor and spray dryers from Proctor and Schwartz, Inc. rotary, flash, and fluid bed dryers from Williams-Gardner, 1971, pp. 75,149, 168, 193). (Walas, 1988). 

Some product is sold in slurry which is a convenient form since it eliminates dust, saves energy, and lowers the cost. The industries which are frequent users of such product are paper and paints. Many other applications require material to be in a powder form, therefore the sluny is flocculated, concentrated (filter presses), and dried. Several dryer types are used such as rotary, tray, fluidized bed process or spray. The clay may be pulverized after some of these drying process depending requirements. Figure 2.34 shows the morphology of kaolin. A typical platy structure is clearly displayed on this photograph. 

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