ANS:A - spray dryer

A spray dryer is a widely used industrial equipment designed to convert a liquid or slurry into a dried powder form. It operates on the principle of atomization, evaporation, and drying to achieve rapid and efficient drying of liquid feed materials. Here's how a spray dryer typically works:

1. Atomization: The liquid feed material, which could be a solution, suspension, or emulsion, is pumped into the top of the spray dryer. Inside the dryer, the liquid is atomized into small droplets. This atomization can be achieved using various methods such as rotary or nozzle atomizers, depending on the characteristics of the feed material and the desired particle size of the final product.
2. Contact with Hot Air: Simultaneously, hot air or gas is introduced into the drying chamber of the spray dryer. The hot air serves as the drying medium and is heated to temperatures suitable for rapid evaporation of moisture from the droplets.
3. Evaporation and Drying: As the atomized liquid droplets travel through the drying chamber, they come into contact with the hot air. The high temperature of the air causes rapid evaporation of the moisture contained within the droplets. This results in the formation of dried particles, leaving behind a fine powder.
4. Separation and Collection: The dried powder is then separated from the hot air stream using cyclones, bag filters, or other separation devices. The dried powder is collected at the bottom of the spray dryer, while the hot air, now laden with moisture, is typically vented or passed through a separate air handling system for further treatment.

Spray dryers offer several advantages for drying liquid materials:

• Rapid drying rates due to large surface area-to-volume ratio of atomized droplets.
• Production of fine, free-flowing powders with controlled particle size distribution.
• Capability to handle heat-sensitive materials, as the residence time in the drying chamber is relatively short.
• Continuous operation, allowing for high throughput and efficiency in industrial-scale production.

Spray dryers are extensively used in various industries such as food and beverage, pharmaceuticals, chemicals, ceramics, and detergents for the production of powdered products like milk powder, instant coffee, pharmaceutical powders, detergents, and more.