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# Centrifugal Compressor Polytropic Data Calculation

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### #1 Plant Production Engineer

Plant Production Engineer

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Posted 13 April 2010 - 11:41 AM

Dear Engrs,

If anybody want to know their respective industrial centrifugal compressors performance, just send me below data:

• Compressor inlet Temperature (ºC)
• Compressor outlet Temperature (before discharge cooler) ºC
• Compressor suction pressure (bara)
• Compressor discharge pressure (bara)
• Compressor flow (In MMscfd or SM³/hr)
• Gas composition (mol%) at inlet of compressor
• 100 % speed (rpm) of compressor.
• Current speed (rpm) of compressor

I will calculate the performance and give you the below results:

Total polytrophic data:
2. Efficiency %
3. Gas power (kW)

Attached excel sheet is for your info, but it'll give you only 95% accuracy in results.

You can send me e-mail.
farraz@hotmail.com

Soon I'll come back with Gas turbine axial compressor, Gas generator & power turbine efficiency calculations just for knowledge sharing.

Edited by Plant Production Engineer, 28 August 2011 - 08:58 PM.

### #2 ankur2061

ankur2061

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Posted 13 April 2010 - 02:36 PM

farraz,

1. By providing gas composition, the molecular weight should automatically be calculated

2. You can think of incorporating mass flow (remains unchanged irrespective of P&T) which gets converted to actual inlet volumetric flow at the inlet P&T.

3. Provision for computation of Z1 (inlet compressibility), Z2 (outlet compressibility) and Zavg (Z1+Z2/2) in the spreadsheet itself (Note: For compressor power & head calculations, always Zavg is used).

4. Provision for calculation for no. of wheels/impellers per stage/section could be provided.

5. Instead of N (rotational speed) given as an input it gets calculated from the spreadsheet itself.

6. You can think of providing shaft power based on mechanical losses by adding it to gas power.

Just some ideas for making a great spreadsheet into an excellent one.

Regards,
Ankur.

### #3 Plant Production Engineer

Plant Production Engineer

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Posted 16 April 2010 - 02:26 PM

Ankur

I have to work more on this sheet to make it 99% accurate & will consider your important points.

Will you please share some info regarding Gas turbine GG (Gas Generator) and PT (Power Turbine) performance?

Thanks & Regards,

Faraz

### #4 Zauberberg

Zauberberg

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Posted 17 April 2010 - 12:25 AM

Faraz, take a look into these materials:

http://www.gmrc.org/...entrifugals.pdf
http://www.psig.org/...s/1990/9806.pdf

One thing you can certainly do out there in the field is to monitor axial compressor efficiency by comparing actual vs. isentropic discharge temperature and see when is the time to do online or offline turbine wash. There should be a procedure in place for both of these.

I remember we had a spreadsheet generated by us and GE/Nuovo Pignone engineers that used to help us in turbine performance monitoring and troubleshooting. It's not a rocket science in any case, you can easily setup one of your own.

### #5 breizh

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Posted 17 April 2010 - 10:54 PM

Faraz ,

Attached an other book to support your study and suggestion from Ankur .

hope this helps

Breizh

### #6 breizh

breizh

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Posted 21 April 2010 - 06:55 AM

Hi ,
You may find some interest in theses spreadsheets (reference previous posts)
Regards

Breizh

### #7 Plant Production Engineer

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Posted 22 April 2010 - 10:56 PM

Thanks Zauberberg & breizh,

I have tried to calculate efficiency of Axial Compressor of SGT-200 Gas Turbine. Experts; plz check & validate, if it is correct.

Data
P1 atmosphere (bara) = 1
P2 Disch. (bara) = 6.73
K (Cp/Cv) = 1.36 (for Air)

(k-1)/k = (1.36-1)/1.36 = 0.2647

(n-1)/n =
Ln (T2 Absolute)/(T1 absolute)
Ln (P2 / P1)

(n-1)/n =
Ln (278+273.1)/(28+273.1) = 0.3170
Ln (6.73 / 1.001)

Polytropic Efficiency =
(k-1)/k = 0.2647 / 0.3170 = 0.83
(n-1)/n.

### #8 s nautiyal

s nautiyal

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Posted 23 April 2010 - 03:36 AM

Dear All,
I am interested in knowing the centrifugal compressor discharge temperature calculations for higher pressure ratios(Pout/Pin) , around 3 or more.

I was using the below formula, but its not useful for high pressure ratios.

TOUTLET = TINLET*{(PDISCHARGE/PINLET)^((n-1)/n)}

Kindly also help me understanding the limitation of above formula.

### #9 Plant Production Engineer

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Posted 29 March 2011 - 05:15 PM