Heatless desiccant dryers are used to treat unheated compressed air to regenerate the desiccant bed. This dryer is the most expensive to operate because of the large amount of compressed air that's consumed for purging during the regeneration cycle. Heated desiccant dryers have the lowest energy operating cost of the three types. A heating element supplements the drying action of the purge air. The heater can be mounted internally to heat the desiccant bed directly or externally to heat the purge air that's blown through the bed. Internal heating elements shorten the life cycle of desiccant beds and may cause dew point spikes. However, the amount of air required is reduced because the heat supplements the air's drying action.
Heatless regenerative air dryer does not require any external heat source for regeneration. The system utilizes retained heat of adsorption generated from the previous adsorption cycle. It automatically delivers a standard -40F pressure dew point. The compressed air laded with moisture vapor enters the system through the right inlet valve and proceeds to enter the desiccant bed through the stainless steel diffuser screen. The air flows up from the bottom of the tank to the top allowing separated and condensed liquid to remain at the bottom of the vessel not contaminating the rest of the desiccant. A percentage of the dry air is direct-ed and metered to the left desiccant bed for regeneration. The adsorbent purge air enters the desiccant bed from the top and flows down collecting moisture from the desiccant. The now moisture laden purge air exits the system through the purge valve and muffler.
Heatless type dryer is the simplest type of air dryer with activated alumina/molecular sieves drying agent. In heatless dryer, two vessels filled with desiccant are provided, which cycle automatically, producing dry air continuously. In this unit, wet air enters the bottom of one vessel and passes upwards through the desiccant bed where the moisture is adsorbed. The dry air comes out from the top. This dryer's design is virtually maintenance free and fully automatic. It does not require any heating for re-generation and therefore is very simple in design and smooth in operation.