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It is an example of a Static bed dryer. In this process, there is no relative movement among the solid particles being dried. It is operated in a batch process. This type of dryer operates by passing hot air over the surface of a wet solid that spread over trays arranged in racks and due to forced convection moisture is removed.
Construction of Tray Dryer:
- It consists of a chamber whose wall is insulated by thick glass wool or suitable heat insulating material. Inside the chamber, there are various trays on which wet materials are placed. The number of trays depends on the size of the chamber. For laboratory purposes, a minimum of 3 trays is required. There should be an appropriate distance between the upper, middle, and lower tray. The dryer is also attached to the provision of free: air inlet and air outlet. The fan in the dryer is used to circulate air over the material placed in trays. The heater is also provided inside to facilitate uniform heating. The door of the heater is explosion-proof and is locked with the help of spring-loaded ball latches with suitable pressure. Door lips are having a Neoprene rubber gasket to prevent leakages.
Working of Tray Dryer:
- Wet material is spread into trays and placed into the chamber. The doors are closed. The air is introduced through an inlet and heater air heated up. Hot air is circulated by Tan over the tray. There should be uniform airflow otherwise proper drying will not be achieved. Even baffles are used to distribute the air uniformly over the trays. Some moist air is continuously vented through the outlet. The fresh air enters through the inlet. The water evaporates from the interior of the solid due to hot air. In the end, trays are removed from the chamber and dried material is collected.
Advantages of Tray Dryer:
- Tray Dryer is the most conventional dryer used very widely and still being used where the moisture content is more and where the product has to be dried at low temperature for long hours.
- It is a batch process and can also be used where the quantity of material is less.
- In the tray dryers, the handling of the materials can be done without losses.
- The batch sizes in the pharmaceutical industry are relatively small 250 kg or less per batch compared with the chemical industry 1000 kg or more per hour.
- Valuable products can also be handled effectively.
- Not suitable for oxidizable and thermolabile substances.
- The process takes a long time.
- The process is expensive to operate
- Tray dryer is used in the drying of the sticky materials.
- Tray dryers are used in the drying of the granular mass or crystalline materials,
- Plastic substances can be dried by tray dryers.
- Wet mass preparations, precipitates, and pastes can be dried in a tray dryer.
- In the tray dryers the crude drugs, chemicals, powders, and tablet granules are also dried and show free flowing of the materials by picking up the water.
- Some types of equipment can also be dried in the tray dryers.
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