Compressed Air Fail: A poor dryer choice


compressed air failA grain sorting facility purchased a new, larger compressor to renew their compressed air system—as well as to prepare for future load additions. The previous compressor was a 50-hp size with a 200-cfm desiccant air dryer with dew point control. To prepare for future needs, a new 75-hp compressor was purchased with a new larger desiccant dryer. Because the budget was tight at the time of purchase, the dew point dependent switching option was not chosen for the new dryer, nor were efficient airless condensate drains.

An auditor was called in to assess the compressed air system as part of the customer’s efficiency efforts. Instruments were placed on the air compressor and dryer to measure pressure, power and flow. Special testing was done to determine the purge flow of the dryer as part of normal testing.

Upon analysis, the auditor found that the 300-cfm air dryer was consuming a constant 80 cfm of purge—far higher than the rated 45 cfm flow–because the purge flow is not adjusted to the correct setting. And because this dryer had no purge saving controls this excessive purge was being consumed constantly, even though the average plant load was only 20% of the rating of the air dryer. The air dryer was consuming most of the compressed air produced by the compressor.

Calculations found that retrofit of the air dryer and the use of airless drains could save 17% if applied to the existing compressor. Further to this, the use of a new VSD compressor could save 35% because the existing unit is running for significant periods of time in the unloaded condition.

In addition, this survey found that the compressed air is used in a heated building, therefore a desiccant dryer is not required. Readings also indicate that there was an excessive 20 psi pressure differential across the air dryer filters because they have never been changed. This pressure drop causes the air compressor to cycle excessively, greatly decreasing efficiency.

In all, system reconfiguration has the potential to reduce the electrical operating costs by 66%. This facility has significant energy incentives available to help them purchase the required upgrades.

Learn more about air compressors and dryers in our next Compressed Air Challenge seminar in your area. Visit for more information.




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