ANS:C - rotary

A rotary dryer is a type of industrial dryer used for the drying of bulk solids, liquids, or pasty substances such as chemicals, minerals, fertilizers, and, as you mentioned, sugar. Here's how it works:

1. Rotating Drum or Cylinder: The core component of a rotary dryer is a cylindrical drum or shell that rotates around its axis. This drum is typically made of metal and is supported by wheels or rollers at each end.
2. Heat Source: Heat is supplied to the dryer to evaporate moisture from the material being dried. This heat can be provided by various means, including direct-fired burners, indirect heat exchangers, or steam coils located inside the drum.
3. Material Feed: The wet or moist material is fed into one end of the rotating drum through a feed chute or conveyor system. As the drum rotates, the material cascades through the heated air inside the drum.
4. Heat Transfer: The heated air inside the drum comes into direct contact with the material, transferring heat energy to it. This heat causes the moisture in the material to evaporate, effectively drying it.
5. Flight Lifter Design: To improve the drying efficiency and ensure thorough mixing of the material, flight lifters are often attached to the inner surface of the drum. These flight lifters lift and shower the material as the drum rotates, promoting better heat transfer and uniform drying.
6. Moisture Removal: The moisture-laden air exits the rotary dryer through exhaust ports or ducts. Depending on the dryer design, the moist air may pass through cyclones or other air pollution control devices to remove dust and particulate matter before being discharged into the atmosphere.
7. Discharge: Once the material reaches the desired moisture content, it is discharged from the dryer through an outlet chute or conveyor system located at the opposite end of the drum.

Rotary dryers offer several advantages for large-scale drying operations, including high throughput capacity, uniform drying, flexibility in operation and control, and the ability to handle a wide range of feed materials. They are widely used in industries such as agriculture, mining, food processing, and chemical manufacturing for drying various bulk solids and liquids.