In fluidized bed dryers, a bed of material is fluidized through vibration or air flow. The powders are then dried by direct heating from hot air or combusted gas flow (direct) or through contact with heated surfaces (indirect).

In general, fluid bed dryers operate on a through-the-bed flow pattern with the gas passing through the product perpendicular to the direction of travel. In batch operation, a dose of feed is metered into the dryer bowl and processed until the desired final moisture has been attained. For continuous systems, wet feed is introduced by being metered into the drying section (zone) by means of a suitable feeder. The dry product is discharged from the same section.

In direct systems, hot gas is introduced into the dryer's wind box or plenum. The plenum is a "pressurized box" that distributes the gas evenly across the distributor or fluidizing plate that separates the product from the wind box. The fluidizing plate is a proprietarily designed perforated plate that has either non-directional or directional holes (nozzles), with or without caps, through which the gas passes. The process gas passes from the wind box into the drying chamber and interacts with the feed, lifting and maintaining the feed in a fluidized state termed a bed. The bed attains fluid-like properties, flowing and mixing in a similar fashion to a liquid. The fluidization provides intimate contact between each material particle and the gas stream, creating an efficient transfer device.