intercooling 3 stage air compressor 1

[lw9423]

Hello-
I was wondering if there is a curve which gives a rule of thumb amount of heat that needs to be rejected per psi compressed or cfm through a reciprocating compressor.

I have many 3 stage Bellis and Morcom intercooled compressors and am trying to determine the amount of cooling load they place on the Cooling Tower system.

Thanks-
Luke

 

[Montemayor]

Luke:

I know of now such "rule of thumb". I've done a lot of interstage coolers - both process design and fabrication and the way I've always done it - and what I recommend to you - is to do a simple heat balance around the intercooler. You know the air temperatures - in/out - as well as what you have as cooling water and what you would propose to heat it to. It's a simple heat balance that any engineer should do. This gives you the heat load the intercoolers put on your CW supply.

 

[NewfieEng]

I work for one of the larger compressor companies in the US and if there was such a rule of thumb I would love to know it.

As it stand we analyes in detail each compressor cooler individually using the Temperature out of the reciprocating compressor cylinders and the excact dimensions of the cooler. There are many variable that are taken into acount.

The energy balance suggested by Montemayor souds like a good approximation, but no substitute for indepth analysis.

 

[BigInch]

Hard to make a rule of thumb, since a specific gas being compressed has major effects on heating, as well one would have to be relatively good at estimating the approximately 1/7 root of the ratio of discharge pressure to suction pressure x the absolute inlet temperature. I'm not much for taking the 1/7th root out of my head, never mind off my thumb.

Next question is why do you want to? Its easy enough to program a spreadsheet to give you reasonably good answers with very little effort. Besides, this does not strike me as something anyone would need a rule of thumb for anyway. Does anyone design compressor interstage coolers using rules of thumb?

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[lw9423]

Thanks for all the suggestions!

I am not designing the intercooling nor the compressor, nor the cooling tower. However, I am trying to determine the aggregate load placed on the cooling tower throughout the year, the intercooling is a portion of that load. The big scheme is to recommend methods that this company can save on energy costs through more efficient use of their pumps, air compressors, chillers, lights, etc. If the pumps can be slowed because the cooling currently provided is too much, they will save $ and be happy.

That being said... the reason I thought there might be some "rule of thumb" when it comes to heat rejected per psi of compression would give me a "fairly accurate" estimatation - a co-worker suggested that I might find some information on it. anyways, It has been suggested to use a T-s diagram for each stage, assuming that the air is intercooled back to that ambient pressure each time, and knowing the cfm of the user of the air to obtain a theoretical "fairly accurate" estimation of the cooling.

Cheers,
luke

 

[BigInch]

If you're not adverse to making a quick calculation, accepting the possibility of a possibly wide error range, you can get an IDEA of compressed temperature with this,

T2 = T1 x (P2/P1)^(1/7)

T's & P's are absolute.

I would not use it for anything other than to find out if T2 is in or out of what could be a rather wide range.



Going the Big Inch!

http://virtualpipeline.spaces.msn.com