• Fundamentals of Fluid Bed Drying             Back to GEA NIRO
• Fluid Bed Types
• Fluid Bed Designs
• Fluid Bed Process Systems
• Industry Applications

DRYING/COOLING
These are the most frequent applications of fluid beds. Different process systems are applied depending upon product, volatiles, operational safety and environmental requirements.

Open system
Featuring atmospheric air in a once-through system where water is to be removed. Normally a push-pull system is used to balance the pressure to be slightly negative in the free board of the fluid bed. Depending upon the product and available heat source, direct or indirect heating may be applied. The exhaust air is cleaned by e.g. bag filter, cyclone with or without wet scrubber.

In cases where products pose a dust explosion risk, open cycle systems feature pressure shock resistant components or alternatively semi-closed cycle, self-inertizing layouts can be considered.

Closed cycle system
Featuring drying in an inert gas atmosphere (usually nitrogen) recycling within the system. It must be used for drying feedstocks containing organic volatiles or where the product must not contact oxygen during drying. Closed cycle systems are gastight, and addition of inert gas is controlled by monitoring the oxygen content of the drying gas and the system pressure, which is kept positive. The evaporated volatiles are recovered in a condenser.

AGGLOMERATION/GRANULATION
Fluid bed processing requires that the solids are in particulate form prior to entering the fluid bed. In the special case of fluid bed spray granulation, particles are built up in the fluid bed by spraying a liquid into the fluidized layer particles.

Particulate solids ideal for fluid bed processing may be formed in an independent process step such as crystallization, coagulation, or polymerization, followed by mechanical dewatering. Particles may also be formed by spray drying.

In other cases dry or wet solid particles may have to undergo a degree of agglomeration or granulation prior to entering the fluid bed.

Rewet agglomeration system
In the rewet agglomeration system, a fine powder is conveyed to an agglomeration chamber where the powder is dispersed in air and contacted with a spray of liquid. Moist, porous agglomerates are formed and subsequently dried under lenient fluidization conditions in a Vibro-Fluidizer. After cooling, the powder is discharged, classified, and fines recycled for further agglomeration together with fines from the exhaust air dust collector. Rewet agglomeration systems are typically used for food products like coffee, cocoa-sugar, where instant properties and coarse particles are required.

Survey of agglomeration and granulation processes using fluid bed technology

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