Wet compressed air must first be filtered to remove particles and oil aerosols before it can be directed to the dryer inlet port where this air, via a multi-directional valve, will be directed up through a bed of activated alumina desiccant where its dew point is significantly reduced (typically to -40°F) by the time it exits the on-line (drying) tower. A small portion of air is separated from the dry air stream by a proportioning valve and orifice and is directed to the off-line tower. The remaining dry air stream exits the dryer via another multi-directional valve. This dry air stream must be filtered for particulates before being directed to the end use.
The portion of dry air, called “purge” air, directed to the off-line tower is reduced to near atmospheric pressure before entering the tower and passing downward through the “wet” desiccant bed. The purge air, which becomes extremely dry by the reduction in pressure, readily drives adsorbed moisture off of the desiccant preparing it for another adsorption cycle. The moisture-laden purge air exhausts to atmosphere during the regeneration process. When regeneration is complete the off-line tower is gradually returned to line pressure and the multi-directional valves now bring the just regenerated desiccant tower on-line, routing wet compressed air up through its desiccant bed and directing dry purge air down through the desiccant bed of the now off-line tower to accomplish regeneration. This process of adsorption and desorption can be repeated more than hundred thousand times before the desiccant must be replaced.
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