Does the dew point curve on the psychometric chart apply to compressed air?

by Al
(Cary, NC)

I have a screw type air compressor system that is having moisture problems with condensate dropping out in the particulate filters just upstream of the receiver tank as well as in the receiver.

We have no refrigerated dryer, but use desiccant dryers downstream of the receiver tank to drop the dew point to below -40F.

I don't believe the condensate is reaching the desiccant dryer, but the desiccant isn't lasting too long (about one year) and we recently had an event to where the dew point reached +65F!!!

Ambient/inlet conditions to compressor suction port are: 90F at 70% RH.

Compressor output is 100 psig at 100F. Why is there condensate?

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Bill says...

Hi Al. A few things off the top....

You want the receiver to be a sort of after cooler, and you want lots of water condensing in the receiver, to get it out of the air before that wet humid air gets into your air lines.

Make sure you drain the tank often (depending on your air use, at least once a day, or better yet, install an auto drain).

You would have a filter in the line upstream of the receiver to take out free water migrating out of the compressor itself.

The air going into the tank is hot, high in water vapor, and should be low in free water content.

You don't indicate what type of desiccant dryer you have (twin tower, regenerative..?) and I am surprised that you don't have a method to make sure the air entering the dryer is within tolerance.

Off hand, a year between desiccant charges doesn't seem to frequent to me.

Based on what you've said, I can only assume that your downstream demand is, periodically, much higher than the capacity of your desiccant dryer, and is overloading it. Then, water vapor is getting by the dryer, into the mains, and condensing there.

Cheers,

Bill