The drying of compressed air is carried out by a variety of processes. Compressed air drying, working on the principle of cooling and condensation, makes use of refrigeration systems. Pressure dew points of down to 2°C are achieved by these methods. Pressure dewpoints below the limit value 0°C cannot be reached by the principle of condensation, as such systems freeze as soon as the condenser temperature drops below 0°C.
Compressed air dryers operating on the principle of adsorption can achieve pressure dewpoints below 0°C. Compressed air drying by adsorption for pressure dewpoints down to -110°C (state of the art) differ according to the mode of regeneration:
1) Heatless regeneration
2) Heat regeneration
Many of the compressed air dryers in use are refrigeration dryers. The physical principle of refrigeration drying consists of cooling the compressed air down to a few degrees above 0°C, then separating the condensate from the compressed air flow and disposing of it externally. Cooling is carried out almost exclusively by means of two heat exchangers, the first one of which is an air/air heat exchanger and the second one an air/refrigerant heat exchanger. The refrigerant, usually freon, is conducted through a closed refrigerant circuit. In principle, the cooling process is arranged in such a way that the cooling temperature in the air/refrigerant heat exchangers amounts to 1 - 3°C. At lower temperatures, the precipitated water would freeze, thus icing up the heat exchanger and integrated separator. Refrigeration dryers are capable of achieving pressure dewpoint temperatures between 2 - 10°C. The mode of operation of a refrigeration dryer falls under the generic heading of separators while being subject to thermodynamic concepts.
The purpose of the following text is an explanation of adsorptive compressed air drying. For this reason, other types of drying are intentionally not dealt with.
