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. Flights need to be carefully designed to prevent asymmetry of the curtain. Material moves from one end of the dryer to the other by the motion of the material falling due to the angle of inclination of the drum. Some rotary dryers are double and triple pass units where each drum is nested inside the previous drum.
The rotation of the drum causes the material to roll and mix providing intimate contact with the drying gas. Material moves from one end of the dryer to the other by the motion of rolling, some fluidization and due to the angle of inclination of the drum.
Feed Characteristics Powders, granules, non friable agglomerates, large solid particles. Low to high feed rates
Heat Source Steam, coal, liquid fuels, or gas
Extraction Normally induced. Systems can have combustion, forced and induced draft fans for operation.
Dust Collection Cyclones, bag houses, scrubbers, Electrostatic precipitators. Systems require dust collection.
Control PLC, infrequently solid state controllers. System controls on discharge temperature. Can modulate energy and feed.
Benefits High throughput Forgiving Operation Robust Can handle variations in feed although the product may be inconsistent High temperature operation - can be refractory lined. Unit can have integral cooling section. (Optional)