Large scale drying of wheat is done in a __________ dryer.

ANS:B - spouted bed

A spouted bed is a type of fluidized bed reactor commonly used in the chemical and process industries for various operations such as drying, granulation, coating, and chemical reactions. It operates on the principle of fluidization, where a gas is passed through a bed of solid particles to create a fluid-like behavior. Here's how a spouted bed typically works:

1. Bed of Solid Particles: The spouted bed contains a bed of solid particles, such as granules or powder, which are typically placed in a cylindrical vessel. The bed is initially stationary.
2. Gas Injection: A gas (usually air or an inert gas) is introduced into the bottom of the bed through a distributor plate or nozzle. The gas flows upward through the bed of particles, causing them to become fluidized.
3. Formation of Spout: As the gas flow rate increases, a spout or fountain-like structure forms at the center of the bed. This spout consists of gas and particles that are continuously lifted and recirculated within the bed.
4. Particle Circulation: The gas flow creates a circulating motion within the bed, causing the particles to move upward along the spout, then outward near the top of the bed, and downward along the walls of the vessel. This circulation pattern enhances mixing and heat transfer within the bed.
5. Product Processing: Depending on the specific application, various operations can be carried out within the spouted bed, such as drying, granulation, coating, or chemical reactions. For example, in drying applications, wet material can be introduced into the spouted bed, where the hot gas flow removes moisture from the particles, resulting in dried product.

Spouted beds offer several advantages, including high heat and mass transfer rates, good mixing, and uniform drying or processing of particles. They are versatile and can be used for a wide range of applications in industries such as pharmaceuticals, food processing, chemicals, and environmental engineering. However, they require careful control of gas flow rates and operating conditions to maintain stable operation and prevent particle entrainment.