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The fluidised bed process is widely used across a whole host of industries. Its application includes not only heat and material. transfer procedures that include cooling, drying and calcination, but also complex multi-phase processes, such as agglomeration, spray granulation and coating.

A static bulk of solid particles is fed in at sufficient speed by a stream of gas and broken up, causing individual particles to float: the solid particles seem to 'flow', giving the appearance of liquid. This process is thus referred to as fluidisation.

Agglomeration
A high percentage of fine dust and poor flowability often make powdered substances difficult to process when it comes to bottling, measuring and transport. The process of agglomeration changes the physical properties of these products.

A powder's fine particles are fused together using a binding agent to form larger groups of particles, which makes them easier to process. Equally, for many substances it is sometimes only possible to achieve good solubility by increasing particle porosity through agglomeration or instantisation. Substances created through agglomeration ensure a good flow of material and lower dust levels in the surrounding area.

Advantagesare:improves flowability, lowers risk of separation, reduces percentage of fine dust, improved tabletisation and instantisation.

The starting product (powder) is injected into the fluidised bed processor as a 'fluid', i.e. vigorously mixed in with a heated gas stream and held in a suspended state. Using specially designed two-substance nozzles, the particles are moistened with a suitable liquid. A liquid bridge forms between the individual particles. During the subsequent drying process, these bridges become solidified and thus stabilise the granulate. The blackberry-shaped structure is then dried to achieve the desired final moisture content.

Fluid bed coating

Fluidised beds are used to coat particles that are considerably finer than those treated inside coating drums. The process has been specially adapted for the application of protective films which are specifically used, e.g. to release active agents, to act as a gastro-resistant layer, to mask tastes, to improve the product's appearance or even to improve its shelf life and storage stability.Advantagesare:improves flowability, lowers risk of separation, reduces volume of particulate matter, increases bulk density and lowers hygroscopicity.

In this process hot air is evenly injected into the fluidised bed, keeping the product in a suspended state. Whilst suspended in air, the particles are covered with the coating fluid using a very fine spray which is applied using a two-substance nozzle. The injected air causes the fluid to evaporate and dries the layer of film. This allows several layers of the film to form, creating a homogeneous, stable coating around the separated particle.

(Spray) Granulation

Spray granulation refers to the drying of fluids which results in the simultaneous formation of granulate. In fluidised beds, this process is used to obtain compact and almost circular granulate with outstanding physical properties.Nuclei are subdivided into two groups: inherent nuclei, which form due to abrasion and fracture, and foreign nuclei, which are produced through the drying process. Compared to agglomeration, the granulate created here is harder and thicker. The continuous fluidised bed spray granulation process is suitable for all applications which require a homogeneous, dust-free granulate with a high bulk density.Advantagesare:taste masking, aesthetic appearance and application of functional coating such as gastro-resistant layers as well as protective layers against moisture and oxidisation.

The granulation nuclei are suspended by the force of the heated air flow. This separates the particles out from one another, which makes it possible to wet the entire surface area of each individual granulation nucleus with the sprayed liquid.The fluid comes into contact with the particle surface and begins to evaporate. As this happens, a solid layer begins to cover the granulation nucleus, forming a solid coating. The addition and solidification of further droplets adds layers to the granulate like an onion.Parameters such as high solid content, grain size and residual moisture can be very precisely regulated inside the fluidised bed during spray granulation, which means a wide variety of materials can be processed to granulate. As the granulate is simultaneously dried and shaped, the process is also referred to as continuous fluidised bed spray granulation. The top or bottom spray method (i.e. with or without a Wurster draft tube) can be used in spray granulation.