Rotary Vs. Reciprocating Compressors 4

[Bwilli02]

hello,

I am in the process of upgrading two reciprocating compressors. Each compressor has a cylinder bore of 7 inches, a stroke of 5 inches, a piston displacement of 148.4 c.f.m, and a capacity of 100 scfm at 100 psig. I have researched both type of compressors, (rotary screw & reciprocating) but haven't made a decision yet. Can anyone recommend some reputable companies who I should deal with, and what are you feelings on centrifugal compressors.

seeking knowledge

P.S. The two compressors are basically to maintain a constant pressure for a pair of accumlator tanks, but need to be continous duty for pneumatic tool operation.




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Professional Student
ME Co-op
Georgia-Tech Spring 05'
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[smckennz]

Atlas Copco and Ingersoll Rand are both good brands.
For your duty screw compressors will probably work out the best.
Centrifugals are OK, but part load operation needs special attention and they are precision machines because of the high speeds. They normally come into their own at much higher flow rates and continuous demand.

Cheers

Steve

 

[smckennz]

Atlas Copco and Ingersoll Rand are both good brands.
For your duty screw compressors will probably work out the best.
Centrifugals are OK, but part load operation needs special attention and they are precision machines because of the high speeds. They normally come into their own at much higher flow rates and continuous demand.

Cheers

Steve

 

[Bwilli02]

Steve,

Thanks for the reply. I have started looking at Atlas Copco and the Ingersoll Rand. I was a little unclear on the part load operation stipulation, but now I understand.
Thanks again.

Byron

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Professional Student
ME Co-op
Georgia-Tech Spring 05'
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[tkdhwjd]

For recip (both air and process), I would suggest Dresser-Rand. Not sure if Ingersoll-Rand still does a designing of a recip compressor. GE compression is also a reputable company. Hanover is also pretty good, although I rather go with Dresser Rand.

For rotary screw compressor, I can think of two companies. Kobe Compressor (Kobelco), which is the oldest compressor company in Japan. Good reputation. This company designs both oil-free and oil-flooded type compressors. Ariel Corp also designs a screw type, but they only design oil-flooded type.

As far as considering centrifugal, you will have to understand what type of gas you are dealing with, how much you are trying to compress, and the required discharge pressure. If MW swing is severe, you must not go with a centrifugal. If DP requirement is high, go with a recip. If the DP is relatively low and the required capacity is low, then a screw comp is the best bet.

Hope this helps.

 

[zdas04]

Bwilli02,
You might want to look at faq378-764 for some info on choosing recips vs. rotaries.

It sounds like you're starting with atmospheric air and boosting it to 100 psig at sea level which is at least 8 ratios (depending on any suction piping) - an easy hump for a flooded screw, but you shouldn't try it in one stage in a dry screw, recip, or centrifugal (heat of compression would be over 900F). Packagers are doing good things with coalescing filters these days and I'm generally OK recommending a flooded screw in air service.

All of the screws mentioned above are refrigeration derivatives. For air service, I'd go with a (cheeper and perfectly servicable) air derivative machine. Look at Gardner-Denver or Sullair.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

 

[Bwilli02]

David,

The FAQ you recommeded helped has helped me out a lot. Thank you for bringing it to my attention. We have purchased oil-flooded rotary screw compressors from sullair before for our turbine blow down machines (I work at a hydro-power plant) and the problem with the sullair machine we have been having is that the oil doesn't reach the temperature that it needs to be so it hasn't been getting filtered properly, we lose a lot of oil because of that. However, these compressors that I am replacing will get more use than those. Right now, our Recips that we are using are water cooled, but I wanted to get rid of that, and either use a refrigerant, or air. Do you think that air could suffice? Sorry to burden you with so many questions.

Byron Williams

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Professional Student
ME Co-op
Georgia-Tech Spring 05'
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[quark]

I have been using 100 cfm and 100 psi single stage non lube reciprocating compressors of Ingersoll Rand and Chicago Pneumatic make for past 7 years and they are running fine. You will have problems if you go above 100 cfm or 100 psi.

I never heard cooling the air by refrigerant and also it seems to be not a better option with respect to overall energy consumption and mechanical strength of the compressor body casting.

Air cooled compressors will be ok(not as good as water cooled) but then you can't cool the compressed air below the ambient temperature. I don't suggest them for multistage compressors. If you are using non lube compressors I strongly suggest you to go for water cooling otherwise you will have problems with frequent damage of guide and piston rings.

zdas!

Nice FAQ.

Regards,




Eng-Tips.com : Solving your problems before you get them.

 

[zdas04]

Bryan,
Getting the oil temp high enough to cook off the oil is critical to the longevity of the equipment. I like to make sure that I have 205-215F outlet temp (usually means 180F or so oil inlet temp).

You'll need a two-section cooler (air is the most common spec I use). The Oil section needs enough control to get the temp up (a thermostatically controlled cooler-bypass is essential). The air section is smaller since your gas will always be 205-215F. I don't know what your temp specs are, but usually if you get to 125F everything is ok (that can be tough in many desert countries and you have to design for your spec). If you have a spec that requires better than 15F approach to ambient, then water cooling is required.

Hope this helps.


David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

 

[ccfowler]

For the duty you have described, I would not seriously consider a centrifugal, dry screw, or "oil-free" reciprocating compressor. Depending on the details of the duty cycle, environmental conditions, maintenance & operating considerations, etc., I expect that the most practical choices will involve 2-stage reciprocating compressors or oil-flooded screw compresors.

I've known big, slow 2-stage, water-cooled reciprocating compressors to serve nearly trouble-free for decades in similar applications, and these can be expected to provide the best energy efficiency. If the flow requirements vary significantly in the duty cycle, such compressors (with suitable unloading systems) can handle very wide ranging flow requirements with minimal energy and operating & maintenance penalties. All of the manufacturers mentioned above are worthy of serious consideration.

I know that single stage reciprocating compressors have been used for similar applications, but it is unlikely that the initial cost savings will ultimately justify the greater operating and maintenance costs. Unless the expected service life is very short (a few months), I would not seriously consider a single stage compressor for these conditions.

I would be sure to provide the maximum practical moisture removal through aftercooling and then use coalescing filters to remove oil from the compressed air. I would only use additional drying (dessicant, etc.) if really necessary, and then I would consider use of refrigeration chilling first.