DAS Technology Comparison with Conventional Systems

.

This page provides a detailed technical comparison between the performance of a conventional compressor system and one equipped with the DAS Technology.  This DAS Technology comparison looks at three stages of compressor operation:

  • Conditions within the compressors before startup.
  • During the initial pressurization of the systems.
  • With the compressors are under load.

Compressors before starting

Both compressor systems are off. Have been sitting overnight in the workshop and are at the same temperature. DAS Technology compressor was working the previous day and has a dry receiver. Conventional compressor was working the previous day and has some water in the receiver.

DAS Technology comparison: before compressor start-up.
©AGISEN Limited 2017

Conventional Compressor: OFF Condition

Water in the receiver makes the uncompressed air above it saturated, therefore, the air has a relative humidity of 100\%. This air has a dew point temperature of 25^{\circ}C.

DAS Compressor: OFF Condition

The DAS Technology receiver contains little or no water. The air in the receiver will have a dew point temperature a few degrees below 25^{\circ}C.

Compressors building up receiver pressure

DAS Technology comparison: building up pressure in the receiver.
©AGISEN Limited 2017

Conventional Compressor: Building up receiver pressure

The partial pressure of water vapour  in ambient air at 25^{\circ}C and 70\% RH is 22\, hPa.  Under these conditions, the ambient air has a saturated vapour pressure (SVP) of 31.7\, hPa and a dew point temperature of 19.2^{\circ}C. All the water is in the vapour phase.  The compressor pressurizes the ambient air to 2\, bar(g) increasing the vapour pressure of the water in the system from 31.7\, hPa to 65.7\, hPa.  The dew point temperature of the air in the receiver rises from 25^{\circ}C (ambient saturated condition) to 37.8^{\circ}C and the receiver starts to fill with water.  Approximately 51\% of the water vapour content of the ambient air is compressed into a liquid.  No liquid water is removed from the system at this point.

DAS Compressor: Building up receiver pressure

The DAS Technology module keeps the keeps the process pressure elevated above the receiver pressure.  The water vapour pressure in the DAS Technology module is about 219\,hPa resulting in a dew point temperature of  62^{\circ}C.  Maintaining the air at this pressure and cooling to ambient temperature results in the conversion of 86\% of the water content of the air into the liquid state. The receiver stores the air in a substantially dryer condition due to the removal of this water by the DAS Technology module. The stored compressed air is water-free (unsaturated).

Compressors operating under low load conditions

DAS Technology comparison: Under light load conditions.
©AGISEN Limited 2017

Conventional Compressor: Low Load Conditions

The compressed air in the receiver has a partial pressure of 173\,hPa and a temperature of 30^{\circ}C at 100\,psiThis temperature will rise with use forcing more water into the vapour phase. The saturated air in the receiver has a dew point temperature of 30^{\circ}C and an absolute humidity of 3.8\,gm^{-3}75\% of the total water content of the air is in liquid form and lies in the receiver and various system component.  As the temperature of the stored air increases the amount of water vapour that it can hold increasesAt 40^{\circ}C, 43\% of the water is now in the vapour phase. At 50^{\circ}C this increases to 78\%A pressure drop of 2 bar at this temperature will force all the water into the vapour phase.  This water vapour is therefor pumped throughout the whole system.

DAS Compressor: Low Load conditions

The compressed air processed by the DAS Technology module removes 85\% of the total water.  This leaves the compressed air with an absolute humidity of 2.4\,gm^{-3}. When moved to the receiver this air has a dew point temperature of 21^{\circ}C, 3^{\circ}C below ambient.  The stored air is dry and unsaturated and hence able to support more water in the vapour phase.  This allows a compressor system equipped with the DAS Technology to dry an otherwise wet compressor systemOne of the other main advantages of the DAS Technology is that the dryness of the air tracks with changes in the ambient temperatureA constant dew point temperature differential is hence maintained and dry gas consistently delivered.

See Also

Demistifying Compressed Air

Dry Air Supply (DAS) Technology

References

Dew Point in Compressed Air – Frequently Asked Questions, Vaisala Application Note, 2013. http://www.vaisala.com/Vaisala%20Documents/Application%20notes/Dew-point-compressed-air-Application-note-B210991EN-B-LOW-v1.pdf

Humidity Conversion Formulas, Calculations formulas for Humidity, Vaisala 2013. http://www.vaisala.com/Vaisala%20Documents/Application%20notes/Humidity_Conversion_Formulas_B210973EN-F.pdf

Sidebar