The three-stage dryer involves transfer of the second drying stage into the base of the spray drying chamber and having the final drying and cooling conducted in the third stage located outside the drying chamber. It consists of a main drying chamber, static integrated bed chamber and vibro fluidized bed chamber.
In the main chamber primary drying of the droplets takes place in the main chamber as they fall from the atomizer to the base of the chamber.
AThe second drying stage takes place as drying air is sucked through the powder layer. The moisture content of the powder falling on the Integrated bed is 12 – 20 % depending upon the type of product. This second drying stage reduces the moisture content to 8-10 %. The moisture content is very important to achieving the exact degree of agglomeration of the product and porosity of the powder layer.
The third and last drying stage for skimmilk and whole milk concentrates takes place in the vibro fluidized bed dryer where the moisture contents of the powder reduces to 2.8% to 3.5%. Fluidized bed chamber is supplied with heating and cooling section. Only a small amount of powder leaves the plant together with the drying and cooling air as fines. This powder is separated from the air in a cyclone. The powder is recirculated, either to the main chamber or to a point in the process appropriate to the type of product and the agglomeration required.