Wurster bottom-spray system

The Wurster bottom spray system has also been used successfully to coat particles as small as 100 microns. Attempting to coat smaller particles may result in the same difficulties as discussed in the previous segment. Batch capacities range from a few hundred grams to approximately 600 kg. Because fluidization quality is affected by batch size, at least 50% of the volume outside of the partition should be occupied by the uncoated product. Finished product batch size (for fine and intermediate particles) can be determined by the following equation . 

Bottom-spray film coating is accomplished by means of the Wurster system, originally developed by Dr. D.E. Wurster (Wurster 1959). A scheme of the bottom-spray fluid bed is given in Figure 16.4. 

Figure 372. Schematic representations of the product handling sections of three fluidized bed coaters. (a) Top spray, (b) tangential spray (rotary fluid bed coater), (c) bottom spray (Wurster coating system)...

Fig. 5.13 Sketch of the material processing section of a bottom spray fluidized bed coater (Wurster coating system) [B.71]...

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