A gas drying apparatus is provided 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 diverts a portion of dry air flowing along one of two flow paths including a first flow path having a heater and a pulse purge regeneration control valve for selectively enabling delivery of heated dry air to the tower being regenerated, 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 tower being generated so as to cool the desiccant therein. A temperature sensing arrangement is provided for monitoring and maintaining the internal temperature of heated dry air delivered into the tower being regenerated.
A heat of compression gas drying apparatus includes an air inlet fed by a source of compressed moisture laden air, an air outlet and first and second desiccant-containing towers for processing air flowing therethrough. A portion of cooled dried air delivered to the air outlet is selectively diverted to either a pathway having a heater so that heated dried air may be delivered to a tower having its desiccant regenerated, or to a separate pathway so that cooled dried air is delivered to the regenerating tower. In each case, a purge isolation valve is controlled to deliver and hold pressurized dried air in the regenerating tower after which the dried air in the regenerating tower is purged to atmosphere by pulsing an exhaust valve arrangement connected to the regenerating tower.
An improved control scheme is set forth for an adsorption process that removes water and carbon dioxide (CO.sub.2) from a feed gas using a hybrid of both temperature swing (i.e. TSA) and pressure swing (PSA) to regenerate the adsorbent. The control scheme comprises adjusting the quantity of heat to be provided by the regeneration gas as a function of temperature data taken within a strategic portion of the water selective adsorbent zone. The strategic portion corresponds to the location for the desired transition from regeneration by temperature swing, to regeneration by pressure swing. In a preferred embodiment of the present invention, said quantity of regeneration heat is also adjusted as a function of the water content of the feed gas.
