Pulse purge regenerative gas dryer

A gas drying apparatus having at least two desiccant-containing towers which alternately receive moisture-saturated air from an inlet to be dried during a drying phase, and then receive dry air during a regeneration phase to regenerate the desiccant which had previously adsorbed moisture from saturated air during the drying phase, the apparatus comprising:

• an inlet valve for each of the towers for introducing saturated air under pressure into the tower during the drying phase and passing the saturated air over the desiccant so that the dry air exits the tower and is delivered to an outlet;
• control means to alternately open and close each inlet valve so that only one of the towers receives the saturated air during predetermined drying phase;
• purge adjusting valve means to divert a portion of the dry air exiting a first tower in a drying phase and to direct the portion of the dryer to a second tower in the regeneration phase,
• the portion of the diverted dry air flowing along one of two flow paths including a first flow path having an isolation valve, a heater and a pulse purge regeneration control valve for selectively enabling delivery of heated dry air to the second tower, and a second flow path which bypasses the first flow path and includes a bypass valve for selectively permitting delivery of unheated dry air to the second tower so as to cool the desiccant therein;
• a temperature sensing arrangement associated with the second tower for monitoring internal temperature of heated dry air delivered into the second tower such that upon reaching a predetermined desired maximum temperature of the heated dry air into the second tower, the heater is selectively energized and de-energized to maintain that desired maximum temperature;
• and a purge outlet valve for each of the towers for releasing the air used for regeneration of the desiccant from the tower being regenerated, each purge outlet valve being kept open by the control means during the entire regeneration phase,
• whereby the control means operates in a first condition to close the bypass valve, open the isolation valve and alternately open and close the pulse purge regeneration valve so as to shoot incremental amounts of diverted, heated dry air into the second tower, and operates in a second condition to close the pulse purge regeneration valve and isolation valve and de-energize the heater, and open the bypass valve so as to permit cooling of the desiccant in the second tower.