Compare DESICCANT COMPRESSED AIR DRYERS. A desiccant compressed air dryer uses electric heat to regenerate the desiccant bed. The desiccant compressed air dryer is comprised of two towers that contain the desiccant and valves that shunt the compressed air from one tower to the other for drying.

The desiccant compressed air dryers come as: External Heated dryer and Internal Heated dryer. All systems have two columns with the drying air flowing upward through one column, while the other column is being regenerated

Externally heated purge air dryers draw a small amount of dry air from the system. The air is heated before flowing through the drying column stripping the adsorbed water from the desiccant. The desiccant air dryer uses about 7% of the compressed air in the system for regeneration and has a cycle time of four to eight hours.

External blower desiccant air dryers use outside heated air to regenerate the desiccant. After regeneration, this air is purged from the dryer. This type of dryer has a four hour cycle time, three hours with the heater on and one hour with the heater off so the desiccant can cool. There is a small dewpoint spike for a few minutes after the tower is switched to drying. Blower purge dryers are the most expensive to purchase, but they do not use any compressed air for regeneration

Internal heated regenerated dryers have heating elements mounted in each column. About 2 to 3% of the compressed air is drawn to the drying column where it is heated prior to flowing over the desiccant stripping away the adsorbed moisture. This type of dryer works on a 4 hour drying cycle. The internal heated dryers are used primarily for drying compressed gasses such a nitrogen and argon.

The capacity of the desiccant air dryer is measured in scfm at the input to the unit. The ratings are to standard CAGI ADF100. That is at 100 psig input pressure, 100 F input temp and 5 psi max pressure drop. The standard dryness, or dew point is -40 F. A lower dew point can be achieved with lower air flow and more purge air. Advantages of heated desiccant air dryers are less cost to operate and less compressed air is used in the regeneration of the desiccant compared to heatless dryers. Disadvantages are shorter desiccant lifespan and higher purchase cost compared to heatless dryers.

Coalescing oil filters are a must with desiccant compressed air dryers when drying air from an oil injected compressor. A particle filter is recommended for oil free compressed air.