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Sahara Air Products

Economics of Air Drying

Presented in a 10-part series, this informative article

takes a look at wet compressed air and

how various types of dryers function to dry the air.

 

 

Part 5: Heatless

 

 

By Charles Henderson, Vice President

Henderson Engineering Co., Inc.

 

The basic difference between the types of regenerative dryers is the method of regeneration.

 

One of the most common types of regenerative dryers is the heatless or pressure swing dryer. This dryer is normally used for air flows below 1000 SCFM. This dryer has the lowest initial cost of any regenerative dryer. We size a heatless dryer the same way we do the deliquescent, multiplying the inlet flow rate by a pressure modifier to calculate the corrected dryer size. Temperature is not a factor when sizing a heatless dryer, as long as the inlet air temperature is below 120°F. If the temperature is above 120°F, the desiccant loses its efficiency, which results in higher dew points.

 

The heatless dryer utilizes the pressure swing principle to regenerate the desiccant bed. Wet air enters the dryer and is diverted into the drying tower where all of the air is dried to a -40°F dew point. At the outlet of the dryer, 15% of this dried air is diverted into the regenerating tower where it is expanded to atmospheric pressure. This super dry air now comes into equilibrium with the desiccant and draws the moisture off the desiccant, regenerating it back to full capacity. The wet purge air is then blown out to atmosphere. See Illustration 4. The valves switch every few minutes automatically diverting air from one tower to the other.

 

Acrobat icon Get Adobe Reader T Series Heatless Flow Schematic

Illustration 4: T Series Heatless Flow Schematic

The heatless dryer is recommended for applications that don't use more than 1000 SCFM, or where electricity is not available. Because you are constantly losing 15% of your compressed air, the heatless dryer is the most expensive dryer to operate.

 

The Sahara T series heatless dryer is the simplest, most efficient heatless dryer available. Yet it still requires a 15% purge air loss. There are a variety of options available to try to reduce the average purge loss, however, when the dryer is faced with the worst case inlet conditions, when the dryer is operating at full capacity there is no purge savings. You’re looking at a 15% air loss all of the time.

 

Industry calculates that compressed air costs .25/1000 cubic feet. This cost accounts for the initial price of the compressor, maintenance, power used by the compressor, and so on.

 

The heatless dryer sized for 1000 SCFM would have a continual purge air loss of 150 SCFM (15% of the inlet flow). To calculate the annual operating cost, we would use the following formula:

 

 

 

 

 

 

 

 

 

 

 

 

The annual cost of purge air for the heatless dryer is $19,710. The heatless dryer also consumes a small amount of electricity to operate the timer and solenoid valves; this is generally less than 50 watts.

 

Learn more about Sahara's T Series Heatless Air Dryer.

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