Instrument air dryer is equipment for drying a compressed air to the required dryness over a regeneration cycle and usually part of the instrument air generator package.
In general, the heatless dryer is preferred by using an alumina silicate desiccant as a moisture absorbance. The compressed air is just simply streamed through a pile of the alumina silicate desiccant to absorb the moisture.
Instrument Air Dryer
In the initial state, the purge valve A is close and purge valve B is open. This configuration will make the tank A pressurized and tank B unpressurized. The inlet auto switch valve will close the line to the lower pressure side causing all compressed air goes to tank A.
This moist compressed air is then dried by the alumina silicate desiccant pile and produces the less moist air. After that, the less moist compressed air will go to instrument air distribution network through outlet auto switch valve.
A portion of this less air is also goes to tank B to desorbs moist from the alumina silicate desiccant pile (if any).
After some minutes, the alumina silicate desiccant pile in the tank A is in moist saturated condition and need to desorb by a less moist air. An instrument air dryer panel than open the purge valve A and close the purge valve B.
All moist compressed air now will go to tank B due to the inlet auto switch valve close the line to tank A (which is a low pressure side). The moist air will be dried by the alumina silicate desiccant pile in the tank B and produces the less moist air. This less moist air will go to instrument air distribution network through auto switch valve.
A portion of this less moist air will also go to tank A to desorb moist from the saturated moist alumina silicate desiccant pile. The cycle time or timing of this auto switch is controlled from the instrument air dryer control panel.