ANS:C - Fluidised bed drier

Among the options provided, the fluidized bed dryer is not typically considered a batch dryer. Fluidized bed dryers are usually continuous in operation, where a bed of solid particles is suspended and agitated by a stream of air or gas, allowing for efficient drying. In contrast, batch dryers, as the name suggests, operate in batches, where a finite quantity of material is loaded, dried, and then unloaded before the next batch begins. Truck dryers, agitated pan dryers, and vacuum shelf dryers are examples of batch dryers commonly used in various industries. A fluidized bed dryer is a type of dryer used in industrial processes to efficiently dry particulate materials by suspending them in a fluidized state. It operates on the principle of fluidization, where a stream of gas (usually air or nitrogen) is passed through a bed of solid particles, causing them to behave like a fluid. Here's how a fluidized bed dryer works:

1. Bed of Particles: The process begins with a bed of solid particles placed in a chamber or vessel. These particles can vary in size and shape depending on the application but are typically small enough to allow for effective fluidization.
2. Introduction of Gas: A stream of gas, often heated to the desired drying temperature, is introduced into the bottom of the bed. As the gas flows upward through the bed, it passes through the gaps between the particles.
3. Fluidization: As the gas velocity increases, it reaches a point where it overcomes the gravitational forces acting on the particles, causing them to become suspended in the gas stream. At this point, the bed of solid particles behaves like a fluid, with the particles constantly moving and circulating within the gas.
4. Heat and Drying: The heated gas not only fluidizes the particles but also transfers heat to them, facilitating the drying process. Moisture or other volatile components present in the particles evaporate into the gas stream and are carried away, leaving behind dried particles.
5. Control: The temperature, gas flow rate, and residence time of the particles in the fluidized bed can be controlled to optimize the drying process and ensure uniform drying of the material.

• High heat and mass transfer rates, leading to efficient drying.
• Uniform drying of particles due to constant mixing and circulation.
• Good control over drying parameters, allowing for precise control of the drying process.
• Flexibility to handle a wide range of materials, including those with varying particle sizes and shapes.