compressed air moisture

[Billgas]

hello -
I have a new ac system to operate that is old as them dar hills.

I have noticed that a seemingly large amount of water/moisture collect in a dischagre storage bottle.

The HP is 25 hp, so it is on hte medium size.

What features can I look at on reducing thee amount of moisture into the system?

Are there product to place on the suction side that can assist in drying the incoming air?

 

[quark]

It is not advised to put such a system on the suction side, even if it may exist. Firstly, you will create pressure drop and secondly you will waste energy.

Air can hold less moisture at high pressures and that is why it is easy to dry the air at higher pressures. If you see good amounts of condensate collected in the receiver, your air is becoming more dryer. Put a trap to the drain line so that you can remove the condensate. Get the CA analyzed for dryness. If your application requires more dryness, go for a dryer.

 

[dcasto]

The four things that make more water than you use to are:

The air outside has more humidity
You are moving more air
You are operating at a higher pressure
You are cooling the air after you compress it more.

The last two items are how you get as much water out as possible without a dryer.

 

[MikeHalloran]

Here in SoFla, it's traditional to put compressors outside, where the humidity averages about a thousand percent. The resulting product is compressed water with a little air in it.

I've wondered if it would help to let the compressor inhale from an air conditioned space. Would that be a code violation?



Mike Halloran
Pembroke Pines, FL, USA

 

[JayMaechtlen]

Don't know about codes, but the inside air will have less moisture in it.
It should certainly help.
I guess the flow from any ordinary air compressor shouldn't work the A/C system too hard.

Cheers
Jay


Jay Maechtlen

http://home.covad.net/~jmaechtlen/

 

[dcasto]

either you have to remove water before or after the compressor. air will hold about 7.5#/mmscf at 100% humity on a 100 dgree day. On a 70 degree day (that would be inside an AC building) the air holds 2.5#/mmscf. If you compress gas to 200 psig and cool it to 120 degrees, it holds about 1 #/mmscf. So the compression step removes 6.5 #'s water, the AC only removes 5#/mmscf. If you want to get all the water out before you compress and get the water down to 1#/mmscf, you would have to cool the room down to 40 degrees.

 

[evelrod]

Mike, as you may know, after I retired I worked for an industrial air compressor sales/repair facility for a few years. We tried your idea and, it did work...just not anywhere near as well as we expected, ie, NOT.

Billgas, old or new, they all 'make' water. It's pretty easy to install an electrical water drain on the reciever that will automatically drain the water at preset intervals. It's also relatively easy to install a water trap, even an automatic one, in the discharge line, preferably closest to the work station. Finally, the only really positive method is to use a refrigerated dryer. A 25hp ac will need a dryer commensurate with the airflow rate. You can even find rebuilt dryers if you look. Most pro paint shops have all these items installed. Google up some of the AC companies. Their sites have some very insightfull info.

Rod

 

[Billgas]

I think there is a desicant dryer in the flow. I'll check.

 

[evelrod]

Billgas, the only 'desicant' dryer/seperator I did was at a dental lab and they were small manual units installed at each work station in the system. A dryer of this type for a 25hp ac would need to be rather large(depending on your geographic location, for sure), expensive and, labor/service intensive. We did install 'dryers' with chemical 'desicants' to remove oil, etc. from medical/breathing air, but I did not personally service them.

Again, the only truly cost effective method of H₂O removal is the refrigerated dryer.

Rod

 

[MikeHalloran]

We had desiccant dryers in our engineering lab on the drops for general use. Even with a nominal daily air consumption near zero, the desiccant had to be changed every day.



Mike Halloran
Pembroke Pines, FL, USA

 

[dcasto]

psa desicant driers are quite normal in the process industry. They all automted and require little maintenance. I've installed units on 300 hp air compressors. As for cost, i believe they are lower than a refrigerated unit.

 

[Billgas]

what psa stand for?

 

[griffengm]

In a cubicle next to our 40 hp a/c, there stands a monument to dessicant driers. It has been bypassed for at least twelve years and contains a solid block of dessicant.
The story as best I can gather is that shortly after installation, in the midst of summer, someone forgot to maintain the system. Since its demise, we have used traps at outlets and drains anywhere we put a drop. Operators ar responsible for daily maintenance in their work area and checking supply when starting air fed machines that have been sitting more than a day or so. Not perfect but it works.
Moral: if you are going to use dessicant make certain you have the discipline needed during times of increased risk.
Just my 20 mils.

Griffy

 

[crjones]

Air out of a compressor at say 100 psig is saturated. As air flow through pipes or is held in a receiver its temperature goes down. So its saturation temperature goes down. The change in specific volume is the condensate. For most applications this is adequate. Refrigerant dryers will suppress the dew point further. Chemical drying or dessicant is really for the few applications that require extremely dry air. This kind of drying is best at point of application.

 

[NickE]

There are dessicant dryers that regenerate themselves. My links are at work, they are mostly used on oil-free small dental/laboratory units.

Werther International comes to mind.

 

[quark]

PSA is pressure swing adsorption and these dryers are quite reliable and are easy to operate and maintain. You have atleast 7% of compressed air wastage (for heated type) interms of regeneration. Heatless types have upto 15% wastage for regeneration.

Operational economy is with refrigerated types upto -25⁰C atmospheric dew point. Beyond that one should go for either alumina(generally -40) or zeolite molecular sieve(upto -70) PSA systems. Oil is detrimental to PSA systems. These systems come with a 5 micron filter to take care of the fines released into the air (if not default supply then it should be recommended)

 

[Ashereng]

We also use desicant dryers in our instrument air packages. Size of the compressor goes from 2 HP up. We also have systems where the desicant can be regenerated, as well as those where "Bobby" changes it out every so often when the "dot" goes pinkish.

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