Belt dryer

Convection dryers Belt conveyer dryer Flash dryer Fluid bed dryer Rotary dryer Spray dryer Tray dryer (batch)... 

Pulse combustion dryer Conventional dryers Belt conveyor dryer Rash dryer Ruid bed dryer Rotary dryer Spray dryer... 

Among the contact drying processes in the paper industry are steam heated centrifugal dryers and disk dryers. The types of convection dryers used are drum dryers, belt dryers or rack dryers. 

PPS is used as a coating material on non-stick cookware in competition with Teflon, and in corrosion resistant coatings for industrial parts. PPS fibre is used for manufacture of filter bags, braided sleevings and dryer belts, in competition with fibreglass. 

Tunnel dryers are shown in Fig. 3.15a. Wet material on trays or a conveyor belt is passed through a tunnel, and drying takes place by hot air. The airflow can be countercurrent, cocurrent, or a mixture of both. This method is usually used when the product is not free flowing. 

To produce a spandex fiber by reaction spinning, a 1000—3500 molecular weight polyester or polyether glycol reacts with a diisocyanate at a molar ratio of about 1 2. The viscosity of this isocyanate-terrninated prepolymer may be adjusted by adding small amounts of an inert solvent, and then extmded into a coagulating bath that contains a diamine so that filament and polymer formation occur simultaneously. Reactions are completed as the filaments are cured and solvent evaporated on a belt dryer. After appHcation of a finish, the fibers are wound on tubes or bobbins and rewound if necessary to reduce interfiber cohesion. 

Reaction spinning equipment is quite similar to that of solution wet spinning. It differs principally in the use of fewer wash baths and in the use of belt-type dryers instead of heated cans. 

In the belt process, the mixture is cast onto the belt or conveyor (high temperature polyethylene (264)) where gelling occurs (261,265). The gel is removed from the surface before syneresis, cut into smaller particles, and passed to a holding or washing tank (Fig. 14). The Hquid is removed from the precipitate using common chemical deHquefying methods, and the resulting particles ate dried in a continuous dryer. 

Active Dry Yeast (ADY). The production of active dry yeast is very similar to the production of compressed yeast. However, a different strain of yeast is used and the nitrogen content is reduced to 7% of soHds compared with 8—9% for compressed yeast. The press cake made with the active dry yeast strain is extmded through a perforated plate in the form of thin strands with a diameter of 2—3 mm and a length of 3—10 mm. The strands are dried on endless belts of steel mesh in drying chambers (a continuous process) or in roto-louvre dryers (a batch process), with the temperature kept below 40°C. Drying time in drying chambers is 3—4 h and in roto-louvre dryers is 6 h or more. The final moisture level attained is 7.5—8%. 

Air Drying Equipment. Tunnel kiln dryers (70) are long furnaces comprised of several zones of different temperature, humidity, and air flow through which the ware travels on a moving car or belt. These kilns afford continuous processing. Periodic kiln cross-circulation dryers (70) are box furnaces in which ware is stacked on permanent racks or on a car that can be shuttled in and out of the furnace. Fans or jets are used to circulate heat uniformly through the ware. The process is not continuous, but production rates can be enhanced by shuttling multiple cars. 

Radiative Heat Transfer Heat-transfer equipment using the radiative mechanism for divided solids is constructed as a table which is stationary, as with trays, or moving, as with a belt, and/or agitated, as with a vibrated pan, to distribute and expose the burden in a plane parallel to (but not in contacl with) the plane of the radiant-heat sources. Presence of air is not necessary (see Sec. 12 for vacuum-shelf dryers and Sec. 22 for resubhmation). In fact, if air in the intervening space has a high humidity or CO9 content, it acts as an energy absorber, thereby depressing the performance. 

FIG. 12-34 Cross-flow of gas and solids in a cascade-type gravity dryer. (Link-Belt Co., Multi-Louvre piinciple.)... 

Continuous-tray dryers such os continuous metol belts, vibrating troys utilizing hot goses, vertical turbodryers... 

FIG. 12-73 Link-Belt Roto-Louvre dryer. (Material Handling Systems Division, FMC Corp.)... 

TABLE 12-25 Manufacturer s Performance Data for FMC Link-Belt Roto-Louvre Dryers ... 

Agitated/Monoplate Nutsche Filter/Dryer Horizontal Plate Filter/Dryer Continuous Equipment Rotary Drum Filter Centrifugal Filter Horizontal Belt Filter... 

Drying times range from a few seconds in spray dryers to 1 hr or less in rotary dryers and up to several hours or even several days in tunnel shelf or belt dryers. 

Continuous tray and belt dryers for granular material of natural size or pelleted to 3-15 mm have drying times in the range of 10-200 min. 

In this type, the solids are fed on to an endless, perforated, conveyor belt, through which hot air is forced. The belt is housed in a long rectangular cabinet, which is divided up into zones, so that the flow pattern and temperature of the drying air can be controlled. The relative movement through the dryer of the solids and drying air can be parallel or, more usually, counter-current. 

Coprecipitation of special cations such as antimony or cerium can improve lightfastness further [2.45]. After treatment in aqueous media, the pigments are washed on a rotary vacuum filter or a filter press until they are free of salt, and then dried using, e.g., belt, spray, or fluidized-bed dryers. 

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