Tray driers

Sodium Bicarbonate. Many soda ash plants convert a portion of their production to sodium bicarbonate [144-55-8], NaHCO. Soda ash is typically dissolved, carbonated, and cooled to crystallize sodium bicarbonate. The mother Hquor is heated and recycled. The soHd bicarbonate is dried in flash or tray driers, screened, and separated into various particle size ranges. Bicarbonate markets include food, pharmaceuticals, catde feed, and fire extinguishers. U.S. demand was approximately 320,000 t in 1989 world demand was estimated at one million metric tons. 

Polyethers such as monensin, lasalocid, salinomycin, and narasin are sold in many countries in crystalline or highly purified forms for incorporation into feeds or sustained-release bolus devices (see Controlled-RELEASE technology). There are also mycelial or biomass products, especially in the United States. The mycelial products are generally prepared by separation of the mycelium and then drying by azeotropic evaporation, fluid-bed driers, continuous tray driers, flash driers, and other types of commercial driers (163). In countries allowing biomass products, crystalline polyethers may be added to increase the potency of the product. 

Drying Rooms For drydng materials that cannot be agitated, the drying room, and tray drier (which there are many varieties) can be used. In the former, the material may be spread on pans and these stacked in a rack, which leaves a space between the trays for air circulation. The room has loosely fitted side walls of plaster board, or similar material, or even canvas, and contains a steam radiator. The natural circulation of the warm air removes the moisture the drying period is generally long, for example, one or two days. 

Tray, Truck, and Tunnel Driers In order to accelerate drying, the closet is factory-built with tight walls. It forms a box, and the air is passed by means of a fan over a radiator or over finned tubes and then over the trays. A portion of the air escapes at the discharge opening the remainder is reheated and recirculated. An amount of new air equivalent to the volume discharged is admitted at the fan. Secondary heating tubes are placed in the path of the air to restore their temperature and heat content. In the tray drier, shallow pans 2 ft by 3 ft by 2 in. deep, for example, are placed on a rack, forming part of the drier. In the truck drier, the rack is on wheels, and the whole may be wheeled in and out of the drier. There may be one or several trucks to each drier, and each truck may have twelve, sixteen or more levels for trays. 

The condensed reaction mixture is evaporated in film evaporator 16 under vacuum. The crude l-(2,6-dimethyl)-phenoxy-2-aminopropane hydrochloride is precipitated in tank 17 using HCl dissolved in organic solvent //, separated in centrifuge 18, and dried in tray drier 19. The final purification by crystallization from solvent III occurs in crystallizer M. Pure l-(2,6-dimethyI)-phenoxy-2-amino-propane hydrochloride is separated in centrifuge 21 and dried in tray drier 22. The plant is equipped with typical solvent recovery and storage facilities not shown in the figures. 

The volume of the closest standard stirred tanks are 1.6 and 2.5 m while a tray drier of 0.5 m can be assumed standard. The total volume of the equipment is 4.6 m . Since the bottleneck is in stage 1 two units in parallel out-of-phase operation may be considered. The cycle time then becomes ... 

A 100 kg batch of granular solids containing 30 per cent moisture is to be dried in a tray drier to 15.5 per cent of moisture by passing a current of air at 350 K tangentially across its surface at a velocity of 1.8 m/s. If the constant rate of drying under these conditions is 0.0007 kg/s m2 and the critical moisture content is 15 per cent, calculate the approximate drying time. Assume the drying surface to be 0.03 m2/kg dry mass. 

Favored Vacuum Drier units are of the closed type such as Rosenmund, the Conical drier, the vacuum tray drier, or the vacuum paddle drier type... 

Static solids bed Heated shelf tray drier... 

A more traditional means of drying is the tray drier. Hot air flows over a series of shelves on which the wet material is spread. Compared to the fluidized bed drier, fhe solid-air interface is smaller, and water molecules... 

Vacuum tray driers offer an alternative method for drying small quantities of material. When scaled up, construction becomes massive to withstand the applied vacuum and cost is further increased by the associated vacuum equipment. Vacuum tray driers are, therefore, only used when a definite advantage over the hot air oven is secured, such as low temperature drying of thermolabile materials or the recovery of solvents from the bed. The exclusion of oxygen may also be advantageous or necessary in some operations. 

Production of ZrCl4. Zirconium oxide from the hafnium-separation step was mixed with carbon black, dextrin, and water in proportions 142 Zr02, 142 C, 8 dextrin, and 8 water. The mixture was pressed into small briquettes (3.8 X 2.5 X 1.9 cm) and dried at 120°C in a tray drier. The oxide briquettes were charged to the reaction zone of a vertical-shaft chlorinator lined with silica brick. The charge was first heated by carbon resistance strips until it became conductive. During production, the bed temperature was maintained at 600 to 800 C by an electric current passed directly through the bed. After steady conditions were reached, a reactor 66 cm in diameter produced about 25 kg ZrCLt/h. The ZrCU was condensed from the reaction products in two cyclone-shaped aftercondensers in series, and the chlorine off-gas was removed in a water scrubbing tower. 

Washing and adsorption The belt filters are used for washing and dewatering of fine solids in the manufacture of catalysts, zeolites, alumina and other crystalline substances, and so on. The belt filter requires the associated equipment — several vacuum pumps and separation drums. Through-circulation tray driers and through-circulation rotary driers are used to dry solids. All these are continuous crosscurrent processes. These could be replaced with a moving-bed, Hildebrand (screw) conveyer or Kennedy extractor [18], each of which is a countercurrent process. Their potential for PI has not been explored. 

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