Compressed Air can be dried by two methods -
Refrigeration
Sorption
Refrigeration:- When the temperature of the air is lowered, its ability to hold moisture is reduced. A refigeration dryer reduces the dewpoint of the air by reducing the temperature of the air, thus separating moisture.
Sorption:- The air stream passes over a bed of granular desiccant which in its active state has a vapour pressure below the vapour pressure of air stream to be dried and therefore physically removes the moisture from the air stream. Sorption can be classified into Absorption and Adsorption.
Absorption:- Absorption systems use a desiccant that dissolves with the absorbed moisture. The desiccant cannot be regenerated.
Absorption:- Adsorption dryers operate by passing compressed air through a bed of desiccant material, to which the water vapour is adsorbed.. These desiccants once saturated can be regenerated and reused.