ANS:A - rotary

A rotary dryer is a type of industrial dryer used to remove moisture from a material through the application of heat. It consists of a rotating drum or cylinder that is inclined slightly to the horizontal. Here's how it works:

1. Drum: The main component of a rotary dryer is the cylindrical drum, which is typically made of steel and is mounted horizontally or slightly inclined. The drum is rotated slowly, usually by means of a motor and gears.
2. Material Feed: The material to be dried is fed into the rotary dryer at the upper end of the drum. The material can be in the form of a slurry, powder, granules, or other types, depending on the application.
3. Heat Source: Heat is supplied to the rotary dryer to evaporate the moisture from the material. This heat can be provided by various means, such as direct firing with a burner, indirect heating through hot gases or steam flowing through the drum, or by other methods.
4. Drying: As the drum rotates, the material is exposed to the heated air or gases inside the dryer. The moisture in the material evaporates due to the heat, and the resulting water vapor is carried away by the air or gas stream.
5. Discharge: Once the material has been sufficiently dried, it reaches the lower end of the drum, where it is discharged from the dryer. The dried material may be collected in a hopper, conveyor, or other equipment for further processing or storage.

Rotary dryers are commonly used in various industries for drying bulk materials such as minerals, ores, fertilizers, chemicals, biomass, and agricultural products. They offer advantages such as high throughput, continuous operation, versatility in handling different types of materials, and efficient heat transfer due to the large surface area exposed to the drying medium. Additionally, rotary dryers can be customized with features such as internal lifters or flights to improve mixing and drying efficiency.