How Does a Fluid Bed Dryer Work?

Fluidized Beds

• When a finely-divided solid is introduced to fluid-like liquid or gas under the right conditions, it forms a mixture that has many properties of fluids. This type of mixture is called a fluidized bed. In a fluid bed dryer, the powdered material is shaken on a vibrating screen that's above an intake, which supplies air for the drying process.

Drying

• A stream of warm or hot air enters the dryer through the air intake. Particles of the bulk matter become suspended in the turbulent stream. They are then fluidize, meaning the mixture of air and particles begins to behave increasingly like a homogenous fluid. The warmth of the air promotes evaporation, helping to dry the solid more rapidly. To prevent the bulk matter from leaving the dryer with exhaust air, designs may incorporate a tapered exhaust to reduce air velocity in the exhaust port.

Features

• Many features of the fluid bed dryer depend on its design and application. Back-mix flow beds treat materials that become fluidizable after materials on their surfaces evaporate. By allowing the solids to mix back and forth, they preserve uniform conditions throughout the fluidized layers. By contrast, plug flow beds use baffles to keep solids from mixing along the horizontal plane, ensuring conditions vary uniformly. Other designs incorporate variations on these two broad themes.

Fluid Bed Processors

• Fluid bed processors rely on the same operating principles, but they may be used to dry, moisturize, cool and aggregate materials. A fluid bed dryer is basically just a subcategory of a fluid bed processor, which is a subcategory of a fluidized bed device. Many food products, detergents, drugs and polymers are treated in fluid bed dryers or other types of processors.