ANS:A - rotary

Free-flowing granular materials are best dried in a rotary dryer. Rotary dryers are commonly used for drying granular materials due to their efficient and versatile design. Here's why they are suitable for drying free-flowing granular materials:

1. Continuous Drying: Rotary dryers operate continuously, allowing for a continuous feed of the granular material into the dryer and continuous discharge of dried material. This makes them well-suited for processing large quantities of granular material efficiently.
2. Uniform Drying: The rotating drum of a rotary dryer ensures that the granular material is continuously and uniformly exposed to the drying medium (usually hot air or gas). This promotes uniform drying throughout the material, preventing overdrying or underdrying.
3. Agitation and Mixing: The tumbling action of the drum inside a rotary dryer helps in agitating and mixing the granular material, ensuring that all particles come into contact with the drying medium. This enhances heat and mass transfer, leading to faster and more thorough drying.
4. Variable Residence Time: The residence time of the granular material inside the rotary dryer can be adjusted by controlling the drum rotation speed and the dryer inclination. This allows for optimization of the drying process to achieve the desired moisture content in the dried product.