FAQ: Lessons Learned of Dessicant Dryers

Desiccant dryers are a great option for removing moisture from compressed air.  If you already use a desiccant dryer or are looking at purchasing one, here are a few lessons learned after years of air dryer use.

1. Purge Rates

When it comes to purging rates, for a desiccant dryer, this is based on the nameplate rating.  Without moisture control, the air flow is unaffected by the drying air.  Desiccant dryers often run with lower purge rates than the nameplate specifies.  The air dryer could also continue to run, purging air even without air flow when there is no set dew point control.  In these instances, the dryer is inefficient, creating waste and using energy when you don’t need it to be running.

2. Regular Maintenance is Key!

To keep the dryer working for you with maximum efficiency, you can adjust the purge flow.  This is done manually, and the best practice is to test the dryer regularly.  The valves and gauges may need to be calibrated to keep the dryer running properly.  As part of the maintenance, you also need to ensure the check valves are functioning.  The dew point control sensors also need to be regularly checked for proper calibration.  When the dew point controls are set, the purge flows will stay at normal levels.  This prevents waste and allows the desiccant dryer to run efficiently.  The sensors need to be calibrated for the control system to function properly.

3. Purgeless is Misleading

Purgeless dryers still need air to cool the desiccant.  These dryers are set to a four-hour cycle, which does not allow enough time for the desiccant to naturally cool.  If the desiccant does not cool, it won’t dry the air as you need it to.  These dryers then need compressed air to cool the desiccant.  It’s true that purgeless dryers are not purging air, but instead, are still using compressed air as a coolant.  Air consumption is still occurring.

4. Inlet Air Temperature

The temperature of the air coming into the desiccant dryer affects the moisture levels.  If the temperature drops 20 degrees, the moisture content of the air cuts in half.  If it drops another 20 degrees, the same is true.  Heatless desiccant dryers do not benefit from the lower temperatures and lack of moisture, continuing to run as they would with air at higher temperatures and increased humidity levels.  The desiccant dryers with dew point controls will adjust purge flows based on temperatures and moisture levels.

5. Filter Differentials

Desiccant dryers usually have a series of filters to prevent contamination of the desiccant. These filters cause pressure differentials, requiring more compressed air to bypass the resistance they offer up.  The difference in pressures can affect controls set on the compressor and may be the cause of inefficient operations, using more energy and costing more money. Dual inlet filters can reduce the difference in pressures, causing the efficiency of the dryer to improve.