Fluid bed dryers are designed to dry powder particles, where the residual moisture content is higher than what is wanted in the final powder. Hot drying air is distributed through specially designed perforated plates, on which the powder particles/agglomerates are resting.
    The velocity of the drying air makes the powder ‘fluidize’, i.e. the particles get airborne; however, to the extent that only the finest/smallest particles leave the fluid bed with the air, while the bigger particles/agglomerates are conveyed/transported with the upward and forward directed flow of air (due to the perforation technique of the plate) into the subsequent section. Here cold and/or dehumidified is introduced to cool the powder to the wanted temperature.

A fluidized bed consists of fluid-solid mixture that exhibits fluid-like properties. As such, the upper surface of the bed is relatively horizontal, which is analogous to hydrostatic behavior. The bed can be considered to be an inhomogeneous mixture of fluid and solid that can be represented by a single bulk density.

In fluidized beds, the contact of the solid particles with the fluidization medium (a gas or a liquid) is greatly enhanced when compared to packed beds. This behavior in fluidized combustion beds enables good thermal transport inside the system and good heat transfer between the bed and its container. Similarly to the good heat transfer, which enables thermal uniformity analogous to that of a well mixed gas, the bed can have a significant heat-capacity whilst maintaining a homogeneous temperature field.
    Fluid bed drying is suited for powders, granules, agglomerates and pellets with an average particle size between 50 microns and 5 mm.