Variety of Processes through the Fluid Bed Technology

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Grain to Grain

The main elements of a fluidized bed apparatus are the inlet air chamber, the process chamber, the spray system and the filter. In the unit, the particles are fluidized continuously by an upward heated air flow. Fine particles can be returned to the process chamber for being agglomerated further by internal blow back filters. In this process, the volume flow rate is kept rather low in order to prevent a possible abrasion of the particles due to a high gas speed. As soon as the point of minimum fluidisation has been exceeded and an uniform and homogeneous fluidisation behaviour has been established, the spray of binding solution or suspension is started. During liquid spray the solvent evaporates in the air flow. The high frequent contacts, the particle to particle collisions and the wetting with liquid result in the creation of loose agglomerates. These particles are consolidated and grow further due to further collisions with powder or other agglomerates until they have reached the required particle size. Afterwards, the product with the improved properties can be discharged in batches or continuously.

From the Laboratory to the Mass Product

The fluidized bed plant can be realised in all sizes from laboratory scale to production scale. Among other things, guidelines of the EHEOG (European Hygienic Engineering & Design Group) are taken into account in order to guarantee a safe processing and good quality of the products in the pharmaceutical and food industries.

Two types of agglomeration process, which can be characterised by their form of injection, are distinguished. In almost every case, on or more spray nozzles spraying downwards onto the fluid bed from the top are used (top spray process). This counter current process enables overwetting of the process and thus enables the production of agglomerates with a larger grain structure.

By using spray nozzles spraying upwards into the fluid bed (bottom spray process), the possibility exists that, if the nozzle pressure and/or the temperature are to high, the spray droplets are sprayed through the fluidized bed and the powder particles are not hit. That process corresponds to the principle of spray drying; it results in the creation of fine dust and thus a smaller grain size. The choice of the spray option has a decisive influence on the product properties such as agglomerate hardness, agglomerate density and bulk weight.

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