Dryers screen-conveyor

Belt-conveyor and screen-conveyor (band) dryers are truly continuous in operation, carrying a layer of solids on an endless conveyor. 

Typical dryers for solids and pastes include tray and screen-conveyor dryers for materials that cannot be agitated and tower, rotary, screw-conveyor, fluid-bed, and flash dryers where agitation is permissible. In the following treatment these... 

Screen-conveyor dryers are typically 2 m (6 ft) wide and 4 to 50 m (12 to 150 ft) long, giving drying times of 5 to 120 min. The minimum screen size is about... 

Screen-conveyor dryers handle a variety of solids continuously and with a very gentle action their cost is reasonable, and their steam consumption is low, typically 2 kg of steam per kilogram of water evaporated. Air may be recirculated... 

Test facilities for agglomeration methods must also include some peripheral equipment, such as mixers, heaters or coolers, conveyors, crushers, dryers, screens, etc., although the variations that are available in these special areas from outside sources can not be offered. Therefore, additional tests for the evaluation and selection of the best peripheral equipment are often necessary at different facilities. 

While the pilot plant approach during project development must be investigated and decided upon on an individual basis, testing of equipment is always necessary. For that reason, essentially all manufacturers and/or vendors maintain sometimes rather elaborate facilities (Section 9.1 and [B.48, B.97]), which normally feature machines of different sizes, including, in some cases, large scale equipment, to avoid scale-up problems. These test facilities must also include some peripheral equipment, such as mixers, heaters or coolers, conveyors, crushers, dryers, screens, etc., although the variations that are available in these special areas from outside sources can not be offered. Therefore, additional tests for the evaluation and selection of the best peripheral equipment are often necessary at different facilities. 

Typically, the impingement air hits perpendicularly or near perpendicularly onto one or both of the product surfaces. If air impinges onto both surfaces, a tenter frame is often used to control the transverse dimension and to transport the product through the dryer. If air impinges onto only one product surface, the product is typically supported on a mesh screen, conveyor, or roller. 

Impregnation catalysts are dried in units, where solvent removal is possible without mixing of the solid support in order to avoid any damage, such as attrition or abrasion, that may cause a loss of the active metal. Typically, tray and screen-conveyor dryers are preferred. The use of rotary dryers is limited due to a high rate of attrition. 

Figure 9.2-2. Continuous tunnel dryers (a) tunnel dryer trucks with countercurrent air flow, (b) through-circulation screen conveyor dryer.

Steam-heated air is the usual heat-transfer medium employed in these dryers, although combustion gases may be used also. Temperatures above 600 K are not usually feasible because of the problems of lubricating the conveyor, chain, and roller drives. Recirculation of air is in the range of 60 to 90 percent. Conveyors may be made of wire-mesh screen or perforated-steel plate. The minimum practical screen opening size is about 30 mesh. 

Screen Printing Ink is applied to part through a finely woven screen. Screen is masked in areas that won t be painted. Economical means for decorating flat or curved surfaces, especially in relatively short runs. Screens, fixture, squeegee conveyorized press setup (for any kind of volume). Dryers Manual screen printing possible, for very low-volume items... 

Through-circulation Dryers. Material is supported on a conveying screen that moves continuously. Hoi gases from below or above conveyor pass through the material and pick up moisture. 

Conveying-screen dryers are fabricated with conveyor widths from 0.3- to 4.4-m sections 1.6 to 2.5 m long. Each section consists of a sheet-metal enclosure, insulated sidewalls and roof heating coils, a circulating fan, inlet-air distributor baffles, a fines catch pan under the... 

Conveying-screen dryers are fabricated with conveyor widths from 0.3- to 4.4-m sections 1.6 to 2.5 m long. Each section consists of a sheet-metal enclosure, insulated sidewalls and roof, heating coils, a circulating fan, inlet air distributor baffles, a fines catch pan under the conveyor, and a conveyor screen (Fig. 12-51). Table 12-23 gives approximate purchase costs for equipment with type 304 staimess-steel hinged conveyor screens and includes steam-coil heaters, fans, motors, and a variable-speed conveyor drive. Cabinet and auxiliary equipment fabrication is of aluminized steel or stainless-steel materials. Prices do not include temperature controllers, motor starters, preform equipment, or auxiliary feed and discharge conveyors. These may add 75,000 to 160,000 to the dryer purchase cost (2005 costs). 

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