Tray dryer Construction and Working Principle and Advantages

Discover the construction and working principle of a tray dryer, explained in simple human language. Uncover how this essential device efficiently dries various materials for a wide range of applications.

Construction: It is the simplest of batch dryers and is also known as a cabinet Or compartment dryer. The tray dryer shown in the image is a batch-operated direct dryer. It consists of an enclosed insulated cabinet Or a large compartment into which the material to be dried is placed on a number of removable trays. The trays may either be fabricated from sheets or from screens. 

The trays may be stacked on racks or loaded on trucks. It is provided with inlet and outlet connections for air. A heating coil either electrical or steam-heating is incorporated into it. In these dryers, steam, gas, or electrically heated air is used as the drying medium. The air is circulated in the dryer over the trays by means of a fan fitted at the top. 

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Tray Dryer working

The material to be dried is spread over the trays and put into the cabinet and then it is closed. Steam is continuously passed through the coil and the fan is started. Air is heated by heating coils its relative humidity decreases and the hot air then passes over the trays. 

The moisture is evaporated from the wet feed, gets added to the air and finally, the air leaves the dryer through the outlet. The process is continued until the solids are dried. The cabinet is opened dried material is removed from the trays and a fresh batch is charged. 

For getting good drying the air after drying should be thrown out completely but in this way, a large portion of heat associated with the hot gas will be lost and the operation will become costly. To avoid this heat loss about 80-90% of the air is recirculated by adjusting a damper provided at the outlet, and the remaining portion is exhausted out and the same amount of fresh air is taken in through the inlet.

Tray dryer diagram

The overall rate of drying of such a dryer is 0.2 to 2.0 kg water/m3h material surface and the thermal efficiency is of the order of 20-25%. The trays are generally 600 mm wide, 900mm long, to 30to40 mm deep. They are made of mild steel, stainless steel, enameled iron, etc., and are fabricated from sheets of 3 mm to 6 mn thick. 

Tray Dryer Advantages

Relatively cheap and easy to construct/build.

Low space requirement. 

Ease in cleaning. 

Requires low maintenance (low maintenance cost) 

No loss of product during drying. 

Tray Drying Disadvantage

Expensive to operate due to high labor requirements for loading and unloading (high labor costs and heat economy). 

Long drying cycles (4 to 48 h per batch). 

Small quantities are handled. 

Tray dryer Applications

The tray dryer is well suited for small-scale production and drying of valuable materials like dyes and pharmaceuticals. It is especially useful for drying wet lumpy solids and wet filter cakes which must be spread over the trays. 

These dryers may be operated under a vacuum in many cases with indirect heating. In such dryers, all joints must be airtight. The trays may rest on hollow metal plates supplied with steam vapor from the wet solid is removed by a vacuum pump. Vacuum tray dryers are suited for heat-sensitive materials.

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