Drum dryer operation

The drum dryer is a continuous contact dryer widely used in the food industry for drying products initially in liquid form.

It is highly flexible equipment consists of one or two horizontally mounted hollow cylinders made of high-grade casts iron or stainless steel, a supporting, a product feeding system, a scrapper and auxiliaries.

The variety of feed arrangements available ensures that solution, suspension and pastes with a wide range of viscosities can be dried.

In drum drying, a thick film of feedstock is applied to the external surface of a heated drum which rotates slowly about its horizontal axis.

The feed can be pre-concentrated and preheated to reduce the drying load but there is a limit to the feed concentration beyond which the sheet may not form well.

In operation steam at temperature up to 200 °C heats the inner surface do the drum. The moist material is uniformly applied in a thin layer (0.5 - 2mm) onto the outer drum surface.

The layer of material remains attached to the drum for about 80% of a revolution drum which time moisture evaporates and leaves behind a layer of solids, which is subsequently removed from the drum surface by a scrapper or doctor knife.

There are many types of drum dryer available:
*Atmospheric double drum dryers
*Atmospheric single drum dryers
*Atmospheric twin drum dryers
*Enclosed drum dryers
*Vacuum Double drum dryers

The single-drum comprises only one roll. A double drum dryer comprises two rolls, which rotate toward each other at the top.

By using the drum dryer, the products have a good porosity and hence good rehydration due to boiling evaporation.

Drum dryers also can dry viscous foods, such as pastes and gelatinized or cooked starch, which cannot be easily dried with other methods.
Drum dryer operation