The regeneration of the desiccant vessel can be during three different methods:

Desiccant Dryer with molecular sieve

Heatless “pressure-swing” drying which uses part of the dry compressed air coming from the other vessel to dry the desiccant in the vessel being generated at lower pressure.

Heated Dryer with molecular sieve, this can use a hot air blower, so there is no loss of compressed air.

Heat of compression. This can only be used with an oilfree compressor.

Membrane Dryer with molecular sieve

Membrane Dryer with molecular sieve refers to a dehumidication membrane that removes water vapor from compressed air. It is used in pneumatic components, air bearings, air spindles, medical equipment, air guns and pneumatic brakes for vehicles & trains.

The term “desiccant Dryer with molecular sieve” refers to a broad class of Dryer with molecular sieves. Other terms commonly used are regenerative Dryer with molecular sieve and twin tower Dryer with molecular sieve, and to a lesser extent adsorption Dryer with molecular sieve.

The compressed air is passed through a pressure vessel filled with an adsorbent media such as activated alumina, silica gel, molecular sieve or other desiccant material. The desiccant can bring the dewpoint of the air down to -40 degrees Celsius or below. This means that the air will not condense water until it is cooled to -40 degrees Celsius. In practice two cylinders with desiccant are used; one is drying the air, while the other vessel is being regenerated. The switching of the vessels and the regeneration sequence is typically done automatically via solenoid operated valves.