air compressor in hot ambient environment

[hockeydad1]

I work in an industrial facility, and we have a 400 scfm rotary screw air compressor in a very bad (hot) location, such that it runs hot in the summer and has tripped on high HP element discharge temp. Moving the compressor or cooling the local environment would be costly. My question - are there compressor types (in the 400-600 scfm range) that tolerate high ambient room temperatures better (run cooler, I guess) than others? e.g. reciprocating vs. rotary screw or lobe? Looking for any personal experience on this. Thanks in advance.

 

[minerk]

Have you considered ductwork and forced air ventilation for the compressor? Or how about water cooled rather than air cooled?

 

[MintJulep]

How about an oil cooler?

 

[hockeydad1]

Thanks for your replies. Yes, in fact, we did duct some forced, cooled air to the compressor. The compressor is air cooled, so we ran some duct from a nearby service water heat exchanger to blow cooled air into the machine air intake. We have also removed the side panels (acoustic panels) and that did drop the temp about 5 deg. F. Problem is, this time of year the heat sink temperature is in the 70's, so this cooling isn't doing much good. So, I was just looking for some thoughts on whether a different compressor type might be better at withstanding the environment.

 

[zdas04]

When you say "rotary screw" you are lacking a key piece of information--is it an oil-injected screw or a dry screw? Is it motor driven or engine driven? You didn't say what your discharge pressure is.

My guess from the problem you're having is that it is a dry screw running at nearly maximum compression ratios. You can almost almost always lower the discharge temp of a dry screw by putting something like a Roots blower in the suction piping. It only takes a few pounds of positive pressure to significantly change the discharge temp. You can also do the same thing by lowering the discharge pressure if you are running significantly higher pressure than you really need (often people will set their cycle points 50-100 psig higher than necessary to reduce the frequency of compressor running).

Discharge temps are a function of compression ratios and inlet temp (the discharge temp sensor is located upstream of the cooler). You can change the ratios or you can change the suction temp, but ratios will give you more bang for the buck, and changing suction pressure is the most economical way to change ratios.



David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[Newmanite]

Your air cooling is only as good as the ambient environment.
Ensure all guarding and cowling around the fan and cooler pack is in serviceable order.Is there a chance the air passing through the cooler (to lower the reciever oil temp)is being picked up by the intake of the compressor?
Can you extend the intake tubing higher or perhaps further away from actual intake of compressor?Could this reduce the temperature?In the compressor house is there a possibility of heat extraction within the room?

 

[hockeydad1]

David Simpson -

Thanks. It's a dry screw, motor driven, 120 psig discharge pressure. I like your idea of lowering the discharge pressure. It gives me something to think about. There is no suction piping - the compressor takes inlet from the surrounding environment (that, plus the forced cooled air we ducted to the intake area). Thanks

 

[sreid]

Possibly an evaporative cooler.

http://www.piec.com/default.htm

 

[zdas04]

You're doing 9.2 ratios (assuming sea level) so you have to be doing in in two stages (a single stage with 100F inlet would have almost 600F out).

Let's say you're pretty well balanced at a reasonable 3.1 ratios/stage.

- First stage suction 14 psia, 100F
- First stage discharge 44 psia, 317F
- Second stage suction 43 psia, 120F
- Second stage discharge, 134.7 psia, 344F (which gets you to the trip with a very small extra dP in the interstage cooler)

Now if you can fabricate an inlet plenum that can withstand 5 psig, then:

- Zeroth stage suction, 14.5 psia, 100F
- Zeroth Stage discharge, 19.7 psia, 148F
- First stage suction, 19.6 psia, 148F
- First stage discharge, 51.0, 338F
- Second stage suction, 50.0, 120F
- Second stage discharge, 134.7, 309F

35F for 5 psig is about what you would expect in the real world, and it may be the difference between working and not working.

David

 

[hockeydad1]

David -

Correct, it's a two stage compressor. And you're close on your temps. The HP hi disch temp trip is at 446 deg. F. Well done. Not sure how to duct an intake but I'll have to go take a closer look at the machine. It would seem to be a conceptually easy thing to do.

 

[ClicketyClack]

Hockeydad:

Sometimes removing the "acoustic enclosures" is a bad idea. Most compressors with enclosures are designed to run with the sides on. This channels the cooling air through the coolers. Removing the enclosure doors could be reducing the flow of cooling air through the coolers.

You need to improve ventilation. I have two 100 HP oil free air cooled compressors running in 100 degree ambient conditions with no problems. But you have to vent the heated air, keep the coolers clean and keep the inlet air fresh.