Basic Fluid Bed Technology

What is a Fluidized Bed? A fluidized bed is formed when a quantity of a solid particulate substance (generally contained within some type of fluid bed processor) is conditioned to behave as a fluid. This is achieved by introducing process gas through the particulate medium. This results in the medium then taking on many characteristics of a fluid, enabling it to be processed in a variety of ways.

To get a better idea of how the fluidization process works, click on the buttons below to cycle the animation slides.

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Fluid Bed Drying Conditioned gas flows through a bed of material, separating the particles and causing the bed to behave like a fluid. The fluidized particles transfer moisture to the process gas quickly and efficiently. The evaporative effect keeps the particles cool during the process, permitting even temperature-sensitive products to be fluid bed dried.
fluid bed drying
Fluid Bed Granulation The fluid bed granulation process (also known as agglomeration) involves suspending particulates in an air stream and spraying a liquid from the top down onto the fluidized bed. Particles in the path of the spray get slightly wetted and become tacky. The tacky particles collide with other particles and adhere to them to form a granule.

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Dry-Stage Vs. Wet-Stage Granulation There are two different modes of fluid bed granulating: dry stage and wet stage. In dry-stage granulation, the particles only require a slight wetting to become tacky and stick to each other. The granulating solution is applied at a rate less than or equal to the evaporation rate. Thus the particles remain "dry" through the entire process. In wet-stage granulation, the particles require significant wetting before they become tacky enough to stick to each other. The granulating solution is applied at a rate higher than the evaporation rate until the particles build up enough moisture to granulate. The characteristics of the particles when wet and the type of granulating solution being used will determine which mode of granulating is most appropriate. While dry-stage is more common, wet-stage granulating allows for denser products.