Fluid-bed granulator-dryers

Effervescent granules were prepared in a fluid bed granulator / dryer. 

Fluid-bed granulator/dryer Fluid-bed granulator/dryer... 

Fig. 6.2-27 P ID of a batch vacuum top-spray fluid-bed granulator with solvent recovery (courtesy Glatt, Binzen, Germany) Fig. 6.2 -28 Comparison of the drying temperatures and times achieved in contact and vacuum fluid-bed dryers (courtesy Glatt, Binzen, Germany)...

Given that the introduction of solvent obviously produces wet granules, the wet granulation process includes a drying step. Drying typically occurs in a fluid bed dryer. But there are other options, such as microwave vacuum dryers. In 1994, White applied on-line NIRS to monitor moisture content and predict drying end point in two TK Fielder microwave dryers. The NIR spectral data were correlated to off-line Karl Fischer measurements which resulted in a standard error of prediction equal to 0.6% when the samples... 

Figure 15 Fluid bed dryer with integrated high-shear granulator and mills.

A fluidized bed is a granulator as well as a dryer. It therefore has operational limits that are defined by its ability to evaporate solvent being sprayed in. Often, the energy required to heat the granules is small compared to that required to evaporate the solvent. The exit gas and particles from the fluid-bed have the same temperature as the granules in the bed due to the intense mixing action of the bed. Hence, the mass energy balance limitations are quite evident ... 

Therefore, product temperature should be monitored closely to control the fluidized bed drying process. During fluid-bed drying, the product passes through three distinct temperature phases (Fig. 21). At the beginning of the drying process, the material heats up from the ambient temperature to approximately the wet-bulb temperature of the air in the dryer. This temperature is maintained until the granule moisture content is reduced to the critical level. At this point, the material holds no free surface water, and the temperature starts to rise further. 

Rotary granulator subclasses primarily are distinguished by their structural architecture. They have either open top architecture, such as a vertical centrifugal spheronizer, or closed top architecture, such as a closed top fluid bed dryer. 

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