Fully automatic regenerative desiccant dryers working on the ‘Pressure Swing’ (heatless) method of regeneration, are a highly reliable and economical way to dry compressed air and other gases to dewpoints below -70°C measured at atmospheric pressure. The dryers continuously dry compressed air by using two identical adsorption vessels each filled with a desiccant to adsorb water vapour. While one vessel is on-stream drying the compressed air, the other is off-stream being regenerated. The vessels are alternated on and off-stream resulting in a continuous supply of dry air downstream.
The method of regeneration is by swinging the pressure in the adsorption vessel from the high system pressure to a low pressure just above ambient. The desiccant is unable to retain the water at the lower pressure and gives it up to the purge air which passes through the bed at low pressure in the opposite direction to the on-stream flow. The purge air, which is a small percentage of the system air, has already been dried at high pressure. Expansion of this air to the low pressure side through a factory set orifice causes it to become very dry. The very dry purge air regenerates the desiccant as it takes moisture away and carries it out of the dryer via the silencer.