ABSTRACT

Fluidized bed (FB) dryers have found widespread applications for drying of particulate or granular materials in the chemical, food, ceramic, pharmaceutical, polymer, and similar industries. More recently, they also found special applications in drying of suspensions, sludges, and soft pastes, which are atomized into an FB of already dry material (backmixing) or the bed of inert particles (Devahastin, 2000; Mujumdar, 2007). Among the advantages of the FB dryers, one may cite

High drying rates due to excellent gas-particle contact• Higher thermal effi ciency, especially if part of the thermal energy • for drying is supplied by internal heat exchangers Lower capital and maintenance costs compared to a rotary dryer • of similar drying capacity Easy to control•

The main limitations of the fl uidized bed dryers are as follows:

Depending on density, the particle size is limited to 2-5 mm to main-• tain a technically reasonable superfi cial velocity of fl uidizing air. Size distribution should be as narrow as possible to avoid exces-• sive carryover. Particles should be isometric as fl akes, strips, and fi bers cannot • be fl uidized. High power consumption due to the need to suspend the entire • bed in a gas stream leading to a high pressure drop. Low fl exibility and potential of defl uidization if the feed is too • wet.