Granulation is the process of forming grains or granules from a powdery or solid substance, producing a granular material. It is applied in several technological processes in the chemical and pharmaceutical industries. Typically, granulation involves agglomeration of fine particles into larger granules, typically of size range between 0.2 and 4.0 mm depending on their subsequent use. Less commonly, it involves shredding or grinding solid material into finer granules or pellets.
Granulation technics are basically of two types:
In wet granulation, granules are formed by the addition of a granulation liquid onto a powder bed which is under the influence of an impeller (in a high-shear granulator), screws (in a twin screw granulator) or air (in a fluidized bed granulator). The agitation resulting in the system along with the wetting of the components within the formulation results in the aggregation of the primary powder particles to produce wet granules. The granulation liquid (fluid) contains a solvent or carrier material which must be volatile so that it can be removed by drying, and depending on the intended application, be non-toxic. Typical liquids include water, ethanol and isopropanol either alone or in combination. The liquid solution can be either aqueous based or solvent-based. Aqueous solutions have the advantage of being safer to deal with than other solvents
The dry granulation process is used to form granules without a liquid solution because the product granulated may be sensitive to moisture and heat. Forming granules without moisture requires compacting and densifying the powders. In this process the primary powder particles are aggregated under high pressure. A swaying granulator or a roll compactor can be used for the dry granulation.
Granulation for solids
In plastic recycling, granulation is the process of shredding plastic objects to be recycled into flakes or pellets, suitable for later reuse in plastics extrusion