Principle of Tray Dryer

A tray dryer is a convectional drying equipment with enclosed insulated chambers and trays placed on top of each other in a trolley. The driers are used in processes where drying and heating are a crucial part of the industrial manufacturing process such as in the food products, pharmaceutical, dye stuff, and chemicals manufacturing among others. The materials to be dried are either solid or wet and are placed on the trays.

The heat through the trays is transferred via hot air circulation by a stream in a radiator coil or electric heater. The transfer of heat, as well as the proper circulation of the heat, is facilitated by the installed blower fans. Additionally, the equipment has a control panel for temperature control as well as other parameters fixed outside the equipment and assist in its functioning.

The basic working principle of this incredible machine is the continuous circulation of hot air. In the tray dryer, moisture is removed from the solids that are placed in the tray by a forced convectional heating. The moist air is removal is conducted partially but in a simultaneous fashion.

Initially, the wet solids are loaded into the trays and the trays placed in the dryer chambers. There is then the introduction of fresh air through the inlet, the air passes through the heaters where it is heated up.

The objective of the heating is to ensure that the heated air reaches the wet solids on the tray, therefore, the fans in the tray dryer are used to circulate the hot air at a speed of two to five meters per second. The turbulent air flow reduces atmospheric partial vapor pressure and the thickness of the layers of the air boundary.

The heated air picks up water. During water evaporation from the surface, there is diffusion of the water from the interior of the solids by a capillary action. All the above-mentioned events happen in a single pass of air. There is a short contact time and only a small amount of water is picked in a single pass and as a result, the discharge air to the rate of 80 to 90 percent is circulated back through the fans and only a maximum of 20 percent of fresh air is introduced.

The moisture discharge occurs through the outlet. Therefore, uniform air flow and constant temperature over the solid materials can be maintained for achieving uniform drying. In the event the materials to be dried are wet granules such as in capsule or tablet drying, drying is continued until the desired moisture content is attained. At the completion of the drying process, the drying trucks or trays are pulled out of the chamber and taken to the tray dumping station.

In totality, the large working space, sturdy construction, controlled temperature, uniform air circulation are the basic principles for the functionality of the tray dryer. it is an equipment with an admirable and exquisite ability to assist in the drying of plastic and chemical powder, electrodes, bakery, food, among other equipment.

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