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Centrifugal Compressor Curve

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#1 hhamed

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Posted 11 January 2019 - 09:09 AM

Dears

 

Excuse me for my English.

 

I have a question about centrifugal compressor curves.  As you know, centrifugal compressor performance curves are supplied for specified Suction T & P and MW.  As far as I know, when suction condition of a centrifugal compressor such as MW or P or T changes, compressor curve changes.  I have a centrifugal compressor curve (with curve) in specified pressure and temperature and MW in (KJ/Kg ) versus Actual Volume flow and specified MW.  I want to use it in condition that pressure an gas composition changes, how can I drive new curve for it.  Is there any correlation or should a new curve should be asked from vendor?  Or Can I use this curve for new suction condition?

 

Best Regards


Edited by Art Montemayor, 11 January 2019 - 12:15 PM.


#2 Art Montemayor

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Posted 11 January 2019 - 12:37 PM

Hamed:

 

As moderator, I’ve taken the initiative to edit your post for punctuation, grammar, etc. - but no spelling.  For that, everyone has SpellCheck.  I did this to allow our members to understand your query better.

 

You are right; your English needs work on it - but so does your engineering.  Why do you give the units of MW (molecular weight) as (KJ/Kg)?  Isn’t the molecular weight given as kg/kg-mole or lb/lb-mole?

 

You state “how can I drive new curve for it”.  Do you mean “draw” instead of drive?

 

If you intend to change the gas service of your existing centrifugal compressor, I can tell you from personal experience with centrifugal compressors that you should consult with and request a new compressor performance curve from the manufacturer, citing all the conditions and properties of the proposed, different gas you intend to compress.  To redefine the new, proposed suction conditions on your machine and operate it as such is to take the total responsibility on your shoulders.  I assume that, like me, you have never designed - nor much less manufactured a centrifugal compressor.  Hardly anyone has.  The matter of generating a new performance curve (if that is a possibility) is best left in the hands of the experts who designed and fabricated the machine itself.  I have seen far too many mishaps with centrifugal machines in the past by persons who couldn’t interpret their performance curves and I would expect far more from those who generate their own performance curves.  Centrifugal machines are great - but they have a multitude of trade-offs.  This is just one of them.  They are very specific in their design.



#3 breizh

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Posted 12 January 2019 - 01:52 AM

Hi,

To add to Art's comments , please consider the document attached.

Hope this is helping you and others.

Breizh

Attached Files



#4 hhamed

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Posted 12 January 2019 - 02:13 AM

Dear Montemayor,

 

Thank you for your edit.

 

It is clear that the unit of MW is not (KJ/Kg).

 

It is because of my English. I Meant that the compressor curve is polytropic head in (KJ/Kg) versus actual volume flow.

 

Yes I am not designer but my question clearly is that I have a centrifugal compressor with performance curve in polytropic head versus actual volume flow at specified suction Pressure, temperature and molecular weight.  I want to use it for another different suction condition.  Can I use this performance curve? or I should ask vendor for new curve or I can modify and change this curve by correlations to draw new curve for new suction condition..



#5 Bobby Strain

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Posted 12 January 2019 - 10:11 AM

What are design and new conditions?



#6 hhamed

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Posted 13 January 2019 - 03:04 AM

What are design and new conditions?

 

Existing Design Conditions:

P(suction) =13.8 barg

T(suction) = 50 C

MW = 22

Head(polytropic) = 137 kj/kg

Flow = 1910 m3/h

 

New Operating conditions:

P(suction) = 4 barg

T(suction) = 40 oC

MW = 25

 

Fixed Speed.  Compressor has performance curve at the original, existing design conditions


Edited by Art Montemayor, 13 January 2019 - 11:16 AM.


#7 Bobby Strain

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Posted 13 January 2019 - 11:28 AM

It should work OK. But you will get only about 14.5 bar(g) discharge pressure.

 

Bobby



#8 breizh

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Posted 14 January 2019 - 12:03 AM

Hi,

To support your work  a calculator from internet.

 

https://www.elliott-...com/Compressors

 

a resource from Ankur :

 

http://www.cheresour...sor_preview.pdf

 

good luck.

 

Breizh






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