Conversion of liquids containing dissolved or suspended solids into powder form of required specifications, by evaporation of liquids, takes place in a spray dryer. Spray drying is a highly efficient drying method with possibility to have close control over the particle size, bulk density and moisture content of the dried powder. The spray drying process consists of atomisation of the liquid feed into fine droplets with the help of spray nozzle/s or rotating disc. These fine droplets are brought in contact with hot air in a suitably designed drying chamber. The liquid gets vaporised and the solid particles in dry form are collected at the bottom of the chamber. The fine particles which are carried by the air are separated either in cyclone separator or bag filter or wet scrubber.
Types of Spray Dryers
Spray dryers are broadly classified into two types based on the method of atomisation. These are :
Sub Types of Spray Dryers
There are various arrangements of the spray dryers depending upon the pattern of air flow, type of pollution control equipment used, type of air heating method used. Following are the sub types of spray dryers depending upon the air flow pattern.
Special types of Spray Dryerss
Spray Coolers
Spray coolers are used for obtaining powders from molten products like oils, fats, glycerine etc. In the process of spray cooling the products in molten form are sprayed through nozzle or rotating disc atomiser in a cooling chamber. This sprayed material is brought in contact with either ambient air or cooled air depending upon the melting point of the product. As the cooling takes place the cooled product in powder form is discharged from the bottom of the cooling chamber. Particle sizes up to 500 microns are possible by spray cooling.