In Steam Rotary Dryers steam is used as heating medium: steam is conveyed inside a series of tubes. The heat transfer occurs from the tubes wall to the product by radiation and conduction even if the temperature of metal surfaces is generally low, as a result of the saturation temperature of steam which depends on its inlet pressure.
Saturated steam is preferred type of medium, since heat is transferred to product by steam condensing and negligible effect is given by superheated steam.
Temperature of dried product cannot exceed steam saturation temperature, therefore Steam Rotary Dryers meet application when products sensible to heat have to be dried.
The interior of the cylinder contains concentric rows of steam tubes bayonet type. At product feed side the external tubes are closed with a cap and supported by spacers welded inside the shell. Along the length of the tubes, intermediate supports are provided.
At discharge side each tube is turned into a header. Each tube has a concentric steam distribution pipe.
To prevent that the wet product feed comes immediately in contact with the hot surfaces of the steam tubes a cylindrical plate is layed over the tube in the product feed zone.
Flight bars are welded to the cylinder adjacent to each tube to ensure intimate contact of product with the heat transfer surface.
Steam is introduced to the header by means of a rotary joint which provides also to evacuate condensate.
At discharge end some openings in the cylinder allow discharge of the product into the discharge breeching. The breeching encloses the cylinder and bottom part is hoppered and flanged. The breeching face encircling the cylinder will be equipped with a special friction type seal. The top of the breeching has a flanged opening for drying air inlet.
At the product feed side, the cylinder is provided with a feed inlet head equipped with screw conveyor feeder and flanged opening for air and vapour removal.
Steam Rotary Dryer is suitable for processing solvents and hazardous products using special sealing system.
Product that can be processed by Steam Rotary Dryers:
- Soya bean
- Powdered product