Granulation process uses a vertical granulator, available in various sizes to satisfy different needs of several possible applications.
Vertical granulator consist of a revolving shaft installed in the center of a cylindrical chamber. On the shaft are fixed some knives having a variable slope.
Flowing powdered raw materials and installed mixing knives guarantee turbulence condition.
During this condition, the liquid raw materials required for the process and for the aggregation are injected in the descending flow of solid raw materials.
Residence time in the mixing cylindrical chamber depends on two parameters: inclination of the knives and their speed of rotation. The average residence time is about 1 second and the product content in the chamber is about 5-10% of the total volume. This condition requires high accuracy of the solid and the liquid dosing systems. Atomized liquid raw materials are completely surrounded by the powder so to obtain dry and free-flowing products.
Mixing and granulation processes depend on the following parameters:
- Speed of the shaft
- Inclination of the knives
- Number of the used knives
- Percentage of liquid raw materials and pressure used for atomization
- Different kind of solid and liquid raw materials
During the mixing and granulation process, part of the product adheres to the internal surface of the cylindrical chamber so hampering the operation. This is why the chamber is made of a flexible material which allows its continuous deformation by means of rolls running with a vertical alternating movement along the external surface. This operation permits to detach the possible deposit stuck on the internal surface.