Understanding batch fluid-bed drying
Fluid bed technology is often used in bulk solids processing, particularly for drying. A fluid bed dryer can be continuous [in which material is continuously fed into the dryer -- typically a horizontal unit -- and discharged into the process line while the dryer operates] or batch [in which material is loaded into the dryer -- typically a vertical unit -- in batches, dried, and then unloaded]. This article concentrates on batch fluid bed dryers. After describing some drying and fluid bed processing basics, the article discusses how a batch fluid bed dryer works, how process variables affect fluid bed drying, and how to select and validate a batch fluid bed dryer.
A batch fluid bed dryer offers the benefits of both batch and fluid bed processing. Because the dryer operates in batches, it handles many different materials, permits rapid and frequent product changeovers and short production runs, and costs relatively little to install. Unlike other batch dryers with stationary beds [such as tray dryers], in which the particles form a static bed and only a few particles are directly exposed to the heat source, a batch fluid bed dryer fluidizes the particles. This fluid bed partially suspends the particles in an upward-flowing gas stream [typically air], forming a liquid-like bed that provides good mixing, gentle handling, and rapid heat and mass transfer.