Tumbling driers

Solid rinse additives are invariably encountered in the form of tumble drier sheets. The major problem here is one of avoiding premature firagrance loss and this is maybe one instance where some form of heat-triggered fragrance encapsulation is warranted this has been extensively patented by Procter and Gamble (Sec. II.D). Solid or powder rinse conditioners, although they are frequently a topic for the patent literature, have never been a real commercial success because of rather poor cold-water dispersability characteristics. Perfume problems would probably be primarily associated with fatty base odor coverage. 

Figure 9.4. Types of dryers cited in Tables 9.1 and 9.2. (a) Tray or compartment, (b) Vacuum tray, (c) Vertical agitated batch vacuum drier, (d) Continuous agitated tray vertical turbo, (e) Continuous through circulation, (f) Direct rotary, (g) Indirect rotary, (h) Agitated batch rotary (atmos or vacuum), (i) Horizontal agitated batch vacuum drier, (j) Tumble batch dryer, (k) Splash dryer. (I) Single drum, (m) Spray, (n) Fluidized bed dryer, (o) Pneumatic conveying (mostly after Nonhebel and Moss, 1971).

Dealing with powders, it is necessary to either (1) drop or blow substrates through the luminous gas phase or (2) contain powders in the bottom of reactor and tumble the reactor wall in a marmer similar to that of wet clothes in a drier. 

Conditions in which the solids move over a heated surface are employed in tumbling and agitated driers. Drying rates are higher than those obtained in static beds because fresh solids are continually exposed to the hot surface. The heat treatment received by the solid is more uniform. 

Agitated batch driers consist of a jacketed cylindrical vessel with agitator blades designed to scrape the bottom and walls. They may operate at atmospheric pressure or under vacuum. Pasty materials that could not be handled in tumbling or fluidized-bed driers, may be successfully dried at rates higher than can be achieved in an oven. 

A coated granule containing a solid (carbofuran) and a liquid (diazinon) insecticide is to be prepared. The solid inseeticide is ground to a fine powder the liquid inseeticide is sprayed onto an absorbent silica. A combination of two adhesives is used. Granular (0.4-0.8 mm) quartz is first sprayed with a liquid polyurethane while tumbling the quartz in a shell blender. Once the mass is wetted the inseetieide powders are added. After tumbling the mass to adhere the powders, an aqueous solution of polyvinyl alcohol is sprayed onto the surface. In order to set the adhesive the mass is transferred to a drier and heated to about 60°C. 

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