Tray Driers

Tray driers are widely used in food and agro based industries for drying of grainy food and dairy products like casein that can’t be spray or roller dried. This method of drying is employed for small to medium capacity requirement. The process of drying is relatively slow. The process of drying also requires more energy as compared to other improved techniques of drying.

The grainy product of uniform small grain size may be spread on trays by hand or mechanically, should be spread evenly and not more than 0.9 to 1.1 kg of grains should be placed on each standard tray of 75 by 75 cm. The bottom tray on each truck should be of finer mesh than the others, or should be covered with a cloth to catch fine particles that may sift through the other trays.

In cabinet and tunnel type tray driers, drying of loaded trays is carried out under different temperature conditions. The filtered air is supplied to air heaters and the heated air is blown over the wet material. Heating of air is carried out either by electrical heaters or steam coil heaters. Proper control of temperature and humidity of air coming in contact with the curd are the essentials of efficient drying of product.

A temperature of 52-57 °C for the air entering a tunnel drier is suitable for casein curd. Higher temperatures may be used for well-washed curd, but they are not recommended because of the risk of discolouring the casein and impairing its solubility.Especially during the early stages of drying, it is desirable to circulate a portion of the air so that the surface of the particle will not become fully dried while the interior is still moist. Care should be taken that the temperature in the drier does not rise above 57 °C towards the end of the drying when comparatively small amounts of water are being evaporated. Drying once started should not be interrupted, but should continue until the desired level of drying is complete.driers