Fluid bottom spray

Fig. 7.9. Batch fluid bed spray granulator used to produce tablet granulations in the pharmaceutical industry. Air-flow necessary for fluidization is generated by a suction-fan (2) mounted in the top portion of the unit, directly driven by an electric motor. The air being used is heated to the desired temperature by an air heater (5). Prefilters remove all impurities at the air inlet (6). The material to be processed has been loaded into the material container (1). The container bottom consists of a perforated plate above which a fine mesh stainless steel retaining screen is fitted. Exhaust filters (7) mounted above the product container retain fines and dust. The granulating liquid (3) is sprayed as a fine mist through a mechanical or pneumatically actuated nozzle (4) onto the finely dispersed, fluidized material to form the desired agglomerates. (Courtesy Aeromatic AG.)...

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. 

In a top-spray fluidised bed, air is introduced through a uniform air distribution plate. Compared to the particle motion in the bottom-spray fluidised bed, the fluidisation pattern is less controlled. Particular to the top-spray method, the nozzle is positioned above the particle bed, and coating liquid is sprayed coimtercurrently, or down, into the fluidising core particles. Compared to a Wurster fluid bed, it is more... 

FIG. 21-170 Niro Precision Granulation process. Agglomeration in bottom-spray draft tube fluid-bed granulation. Scale-up is accomplished by replicating draft tube geometry. Courtesy Niro Fharma Systems.)... 

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)...

Bottom spraying, sometimes referred to as the Wurster process, involves the spraying of the tablets at the bottom of the fluid bed. In this setup, there is a column introduced into the fluid bed chamber, which ensures that tablets in the centre of the chamber are directed upward. At the top of the column, the tablets descend the chamber at the edge of the chamber from where they will be redirected to the spraying region. 

Wurster (bottom spray) fluid bed coating Spouted bed coating Top spray granulation Tangential spray (rotary) granulation... 

FIGURE 47.8 Schematics of a fluid-bed coaler (a) top spray, (b) bottom spray, and (c) tangential spray. 

In a spray-coating process, an inert soluble core composed of sugars, salts, polymers, or a combination of these are flnidized within a fluid bed and an enzyme solution is sprayed on the core to make a continuous film on the surface. The process can be carried out either in a top spray mode, that is, where the spray nozzles are placed in the top of the fluid bed chamber or as a bottom spray... 

With the high demand for encapsulated materials in the global market, fluid-bed coaters have become more popular. They are used for encapsulating solid or porous particles with optimal heat exchange [105]. The Hquid coating is sprayed onto the particles and the rapid evaporation helps in the formation of an outer layer on the particles. The thickness and formulations of the coating can be obtained as desired. Different types of fluid-bed coaters include top spray, bottom spray, and tangential spray (Fig. 1.16). 

Like in batch oriented fluid bed processors the spray nozzles can be arranged either as top-spray or bottom-spray. For blends that can be hardly granulated, typically bottom-spray arrangements are preferred to take advantage of local overwettings. 

Some typical fluid bed granulation equipment and a few of their main characteristics are given in Fig. 1. The conventional fluid bed granulator (Fig. la) can be operated in either top (as shown) or bottom spray mode. The bed is usually tapered, as shown, to improve solid circulation. The spouted bed granulator (Fig. lb) is somewhat different in that it has no distributor and that there is a calibrated gap between the nozzle and the bottom of the spout that allows discharge of granulated material. It is common industrial practice to combine the two fluid beds presented so far... 

The fluid coking process accomplishes ihe coking operation in a continuous manner. Feed is sprayed into a fluid bed of hoi coke in a coking reactor. Steam introduced inio the bottom of the reactor provides the fluidization energy. The cracked products are quenched in an overhead scrubber and then go to Ihe fractionator. The coke is deposiled on Ihe particles in the reactor, which commute with a heater vessel in which a portion of the coke is burned to heal up the reluming coke particles to supply the energy for the coking reaction. 

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