Fluidized Spray Drying

Figure 5 Principle of an FSD set-up

FSD. Fluidized spray drying (FSD) produces granules from a liquid in a one-step process (Figure 5). One option is to produce the active in the primary production as granules, so that it only requires blending with excipients suitable for direct compression for secondary processing. This can only be done with actives that are tacky (in a wet state), otherwise the addition of a binder is necessary. Another possible use of FSD technology is to mix all the ingredients into a solution or suspension and to produce granules in a one-step operation. A principle drawing of an FSD set-up is shown in Figure 5.

During the FSD process, the liquid feed is atomized at the top of the tower in a cocurrent mode. After the liquid is evaporated, the particles generated leave the drying chamber together with the exhaust air. These particles are then separated in a cyclone or filter and reintroduced into the drying chamber where they come into contact with wet droplets and form agglomerates. After these agglomerates have reached a certain weight they cannot leave via the top of the tower with the exhaust air, but fall down into the integrated fluid bed at the bottom of the drying chamber. Here they are dried and cooled before being discharged.

However, this type of equipment is difficult to clean, particularly the external pipework, when changing to another product. Systems have, therefore, been developed where the external pipework does not come into contact with the product (Figure 6).

Figure 6 An FSD Spray Dryer With Internal Filters