Many industrial sites measure their compressed air quality, or think they do. When asked to show the dew point of a system with refrigerated air dryers, the compressor operators will typically point to the air dryer display, not knowing that the reading is not really dew point, but the temperature within the air dryer itself. Quite a few things can affect the level of dryness besides the temperature of the air — for example, a condensate drain failure (Fig. 1).
The most challenging sites in which to monitor and detect air dryer failure are ones with multiple parallel air dryers. Installation of dryers in parallel has its benefits, the resulting pressure loss is usually lower, saving power, and the system more reliable, but when one unit of a multiple set of dryers fails it is often difficult to identify a problem and narrow down the exact one causing the problem.
A particular issue is the fact that the dew point reading from a transducer placed at the outlet of a compressor room will measure the average dew point. For example, on a system of five parallel dryers, with one failed unit in the mix, the reading on a main dew point meter will often only read slightly higher under normal conditions — even though one of the dryers has completely stopped functioning. Therefore, it pays to closely monitor and trend the output of the compressor room, and even place dew point monitors on each individual dryer, if air quality is critical.
This was the recent experience at a large industrial plant producing abrasives. The site had all refrigerated dryers in parallel, and each one showed normal dew point on the local control monitor. However, frequent complaints from production areas about water in the compressed air challenged the compressor room operators. Many checks of the dryers and associated condensate drains showed no problems. The problem wasn’t solved until the Facilities Superintendent arranged to purchase and use a dew point monitor.
The output of the main compressor room showed only slightly elevated levels; however, when the dew point readings of the individual dryer outputs were monitored, one-by-one, it became obvious that one dryer was the culprit. Further testing found an unexpected internal leak in the heat exchanger.
Many new, more accurate, and affordable air quality measurement instruments have been developed that can help monitor not only dew point, but lubricant content, hazardous gas contamination, air temperature, pressure, and even particulate size and volume.
Add these types of instruments to your monitoring system to know for sure our compressed air quality is to your specification.
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