Rotary Dryers and Coolers
Rotary dryers are used for drying wet powders or wet cakes which require long time to dry. Rotary dryer consists of a hollow drum fitted with staggered louvres internally. When this drum rotates, the louvres help in lifting the product and showering it from top. The wet product is fed at one end of the rotating drum. In co-current dryers the hot air comes in contact with the product at the feeding end. By the time the product travels up to the other end of the drum, it gets dried due to contact with hot air. The dry product is either collected at the bottom of the discharge end of rotary drum or conveyed to cyclone separator or bag filter. The air can be directly or indirectly heated using steam, thermic fluid, oil, gas or solid fuel and is handled by centrifugal fans. Rotary dryer used for high temperature calcination is known as rotary kiln. In this the rotary drum is lined with refractory internally and operates at temperature range of 600 0C to 1500 0 C.
Rotary coolers operate on the same principle as rotary dryers except that these handle either ambient or cold airs in order to cool the products.