Tray Dryer

• Temp. Range : 50C to 250C
• Temp. Control : Thermostatic
• Inner Chamber : Mild Steel / Stainless Steel

Tray dryer is used for the drying of wet products of crude drugs, granules, powders, and chemicals etc. A cabinet with a heater, that is laboratory oven, is the simplex dryer form in this class. The value of these ovens is very little as there is no control of the humidity or heat transfer. Tray dryer with directed circulation form is the best type, in which the air is heated up, and oriented across the material in an effective flow. The material to be dried is dispersed on trays' tiers. The trays have perforated, wire mesh or solid bottoms. Screen tras lined with paper ensures that the air circulates across, and not through the drying material. Used as a disposable tray liner, the paper reduces cleaning time and prevent the contamination the product. In modern tray dryers a uniform air & temperature is maintained, by using a well-insulated cabinet with perfectly set fans & heating coils. They are designed for uniform air flow and potential heat of vaporization. Also, there is a good control of heat as well as humidity.

Principle

Hot air is continuously circulated in tray dryers. Forced convection heating is there to remove moister from solids. At the same time, the moist air is separated partially.

Construction

• Tray dryer construction comprises a rectangular chamber with insulated walls.
• Trays are set inner side of the heating chamber.
• Number of trays may differ with the size of dryer.
• Minimum three trays for laboratory size dryers, while industry size may contain over 20 trays.
• Each tray is rectangular / square, and approximately 1.2 to 2.4 meters square in area.
• Trays commonly loaded from 10-100 mm deep.
• Distance between bottom of upper tray and surface of the loaded substance in the consequent tray must be 40 mm.
• Alternatively the trays can be set in trucks on wheels, which can be rolled into / out of the chamber.
• Two such trucks can be placed inside the dryers.
• Electrically heated elements are given inside instead of outside, to heat the air steam.

Working

Wet solid is loaded on to the trays, and the trays are placed in the chamber. Fresh air is presented through inlet, which goes through the heaters and becomes heated. Then, hot air is distributed by means of fans at 2-5 meter per second. Turbulent flow lowers the limited vapor pressure in the atmosphere as well as reduces the depth of the air boundary layer. The air picked up the water; as the water vaporizes from the surface, it diffuses from interior of the solids through capillary action. These procedures follow in a single pass of air. The contact time is short and amount of water picked in a single pass is also small. Consequently, the discharged air to 80 to 90 % tune is dispersed back through the fans. Only 10 to 20% fresh air is bring together. Outlet is there to discharge the moist air. As a result, uniform air flow and constant temperature for the materials is maintained, and help in achieving uniform drying. At the end of drying, trays are pulled out of chamber and taken to a dumping station.

Pharmaceutical Applications

• Drying of sticky materials
• Drying of granular mass and crystalline material.
• Plastic substances can be dried with tray dryers.
• Wet mass preparations, pastes & precipitates .
• Crude drugs, chemicals, tablet granules, powders
• Some sorts of equipment are also dried in the tray dryers.

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