Cooling water for an old Joy Recip Air Compressor...

[elektropl8r]

Hello,

I was on a job recently and ran into three (3) 150 HP Joy recip air compressors (2 stage). I was working on trying to figure out a good estimation for the pressure drop of cooling water through each compressor (the cooling water is plumbed in countercurrent fashion: aftercooler, innercooler, high pressure cylinder, low pressure cylinder, discharge)...and I have not had much luck. Does anyone have experience with such units or could offer any advice?

Thanks all,

Kyle.

 

[bobc]

kyle,
just what do you need the pressure drop figure for? i think this would be a very difficult calculation due to the casting internal finish and flow path. are you trying to determine cooling rate? i also do not understand the flow pattern, are not the inter cooler, the high and low cylinders all on separate circuits, each with it's own discharge line?
email me with particulars and i will attempt to assist.
bob creely
bcreely@yahoo.com

 

[elektropl8r]

Bob,

Thanks for writing. Basically, the customer was having difficulty cooling these units with tower water due to insufficient discharge pressure from the tower's distribution pumps. The heat load of each unit (with the tower water delta T) mandated a flow of approximately 80 GPM to each compressor. There were three (3) compressors. These were all fed from one (1) tower water feed manifold. When I arrived onsite, I saw this feed manifold was only 1.5" black iron. So, we have 240 GPM through a 1.5" line. There's the problem.

So, in writing up my recommendations, I thought it would be good if I had some general idea of the pressure drop throught these compressors. I anticipate it to be about 10 psi at 80 gpm (as you mention, bob, the flow pattern through the jackets themselves is very complex). But its just a guess...

Basically, from the feed manifold, each compressor is plumbed in parallel. However, the flow through the components of each compressor is in series...its feed, aftercooler, intercooler, high pressure cylinder, low pressure cylinder, discharge. As I mentioned, I anticipate this pressure drop to be in the neighborhood of 10 psi per compressor...Just an accurate estimate would suffice...When they do replumb the feed manifold, I have asked them to measure the pressure drop with a known flow...

Any help you can provide would be wonderful, Bob. I appreciate the response!

Take care,

Kyle.

 

[TBP]

According to a Spirax Sarco publication - "Compressed Air - Practical Study PS 12" (which is really just a booklet), they recommend for 2 stage machines that the water go first to the intercooler, then first and second stage cylinders. They further say that most compressor manfacturers recommend cooling water outlet temps of 95* - 120*F from the cylinders. I'm assuming that this is for lube oil considerations. Too hot, and the oil will thin out, too cold, and the oil won't flow properly and/or there will be condensation forming that will emulsify the oil. It doesn't talk about the aftercooler, so I'm assuming it has it's own circuit.

It gives water flows for 2 stage machines with aftercoolers as 5 Imperial gallons per minute (published in the U.K.) or 6 USGPM per 100 SCFM at with an air pressure of 100 PSIG.

"Hook Ups", also by Spirax Sarco says approx CFM is horsepower times 5, and that approx USGPM cooling water required for compressors is:

42.5 X horsepower / number of cylinders all divided by 8.33 X the delta-T of the cooling water.

There it is, for what it's worth. It's been a while since I worked with air compressors, and I don't recall actually using this information. However, I'm trying to remember the last time I got bogus advise from a Spirax Sarco publication, and I can't.