Rotary Dryers

The Rotary Dryer is a volume dryer very commonly used in the industries. It is used for many different applications involving pastes and filters cakes that break up during the drying cycle. These are safe where the tumble dryers need to be avoided. They are of different types like direct rotary cascade dryers, indirect (steam) tube rotary dryers, multipass rotary dryers, rotary tube furnace dryers, and rotary louver dryers. Rotary dryers though quite flexible in their performance are nit suitable for wet and sticky products.

Process
The basic principle is that the wet feed is introduced at one end and the hot air at another. They mix well in the rotary drum. This produces the dry product and the wet gas is exhausted. The rotation is achieved by either a direct drive or chain drive. The drum normally is inclined down from feed to discharge at a slight angle. Rotary dryers can process extremely high volumes of product.

Direct rotary cascade dryers: It is the most common type. They have flights to lift the feed and drop it to the bottom in a curtain, cascading along the length of the dryer. Are so designed that they prevent cross-sectional asymmetry of the curtain. They are arranged in repeating patterns, in several rows.

Rotary Steam Tube Dryers: The functioning is similar to the cascade dryers except that heat source is indirect . the product here is transferred through the tubes heated internally by steamor any other kind of thermal transfer fluid.

Rotary Louver Dryers: Here the feed material is supported over the louvers mounted on external rotating drum. The hot gas is passed through the louver and the product bed and exhausted.

Rotary Tube Furnace Dryers: They consist of a muffle furnace with a steel drum and tumbling and rolling flights. The feed is exposed to the drum surface that is heated from outside. The tumbling action mixes the product so as to provide even heating.