Rotary dryer

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The rotary dryer, sometimes known as a rotary kiln, is a type of industrial dryer employed to reduce or minimise the moisture content of the material it's handling by bringing it into direct contact with heated gas. The dryer is made up of a large, rotating cylindrical tube, usually supported by concrete columns or steel beams. The dryer slopes slightly so that the discharge end is lower than the material feed end in order to convey the material through the dryer under gravity. Material to be dryed enters the higher end of the dryer, and as the dryer rotates, the material is lifted up by a series of internal fins lining the inner wall of the dryer. When the material gets high enough to roll back off the fins, it falls back down to the bottom of the dryer, passing through the hot air stream as it falls. This air stream can either be moving toward the discharge end from the feed end (known as a co-current rotary dryer), or toward the feed end from the discharge end (known as a counter-current rotary dryer). The air stream can be made up of a mixture of air and furnace exhaust fumes (known as a direct heated dryer) or simply hot air (known as an indirect-heated dryer, which generally carries a lesser risk of causing product contamination).

The rotary dryer is also capable of calcining the material, or mixing two or materials, and sometimes stimulating a reaction between two or more materials. The rotary kiln (as it is called when it is not being used to dry a material) is commonly used in the cement industry to cause a key reaction between two of it's major components.

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