It is used for several purposes including granulation, coating, drying, and pelletization.(Teunou and Poncelet; Yang et al.; Olsen "Batch Fluid-Bed Processing Equipment - a Design Overview: Part I,") In the food industry, fluidization is used in freezing and cooling, freeze drying, puffing, classification, blanching, and cooking.(Dewettinck and Huyghebaert) Essentially, fluidized bed coating entails the introduction of granules into a coating cell and fluidization by air flow. The coating substance is sprayed through a nozzle with the aim of achieving a homogenous layering of the coating material on the granule. The process may be done as a batch or continuous one. Current industry trends favor the use of the continuous process over the batch process, in order to optimize efficiency of operation, and consistency of product quality.(Teunou and Poncelet)
In the food industry, granule coating can be used to prepare encapsulated powders which separate reactive components in a mixture, mask unpleasant taste or flavor, protect unstable ingredients from degradation by environmental factors, reduce hygroscopicity, or provide controlled release.(Teunou and Poncelet) It also produces modified flow, compression, dust reduction and density properties in the coated products.(Teunou and Poncelet) The method has been used to encapsulate enzymes, labile proteins, yeast and aromas in polysaccharide matrices and for film coating of extruded products by lipids, resins, or proteins.(Teunou and Poncelet) Maa et al. reported the coating of lactose granules with recombinant human deoxyribonuclease using spray coating technologies.(Maa, Nguyen and Hsu) In food processing, The applications of fluidized bed coating in the food industry have been reviewed by a number of authors.(Dziezak; Arshady; Duxbury and Swientek) A recent review by Werner et al. looked at the current state of the art with respect to air-suspension particle coating in the food industry.(Werner et al.)
In the pharmaceutical industry, fluidized bed coating is utilized in the facilitation of delayed, sustained or controlled release; selective enteric release, masking of taste, stability to degradation, and pharmaceutical elegance.(Dewettinck and Huyghebaert)
Explanation of different spray location technologies
There are three classic geometries for spray coating location: the top spray, bottom spray (or "wurster" spray), and tangential (or side) spray with rotating disk(Olsen "Batch Fluid-Bed Processing Equipment - a Design Overview Part 2"; Yang et al.).
The oldest spray location technology is the top spray method, in which the spray nozzle is located atop the fluid bed chamber, and the sprayed droplets move countercurrently to the air flow.(Yang et al.) It was developed from the older fluidized bed dryers.(Dewettinck and Huyghebaert) It involves the acceleration of granules from a container past a nozzle which sprays the coating countercurrently on the fluidized particles.(Dewettinck