Grain rotary dryers have the feed materials pass through a rotating cylinder together with a stream of hot gas. Internal lifters or flights elevate the feed and drop it in a curtain from the top to the bottom cascading along the length of the dryer.

Grain rotary dryers have the feed materials supported and moving over a set of louvers mounted to an external rotating drum. The hot gas is introduced into a tapered bustle below the feed ring. The air passes through the louvers and then the product before being exhausted from the dryer.