GT axial flow compressor efficiencey 3

[k9ine]

Is there industry standard formulae to calculate the efficiencey of a GT axial flow compressor and do correction factors for ambient conditions need to be used.

As an example how do I calculate the efficiencey on a 17 stage axial flow GT compressor under the following conditions:

ambient inlet temp: 15 degrees C
compressor discharge temp: 400 degrees C
ambient inlet pressure: 1003mbar
compressor discharge pressure 15 bar absolute.

Will results be a true representation of compressor efficiencey?

Any help would be appreciated.

Thanks to all those who replied to my silica questions.

 

[ma2mw]

I don't know if this will help - it has an overview of GE gas turbine performance and factors that affect it

http://www.gepower.com/publications/en_us/pdf/GER3567h.pdf

 

[abeltio]

good tip by ma2mw.
the theoretical calculation of the axial compressor efficiency would be an approximation... there are many factors to be considered in the case of a gas turbine. and as the axial compressor never works without the gas turbine attached to it... Original Equipment Manufacturers (OEM's) never publish segregated efficiencies (i.e. compressor and turbine) but the overall efficiency.
The efficiency also considers the absolute pressure at the inlet bellmouth (not the atmospheric) and the absolute exhaust pressure after the last gas turbine stage.
In industry practice, the compressor discharge pressure is a reference to know if the unit is firing where expected, but is not considered for efficiency calculations.
There are flow factors and annulus factors that are only known to the OEM to calculate the flow thru the compressor... So, do not get too excited about a theoretical calculation on a GT axial compressor... your best bet are the procedures set forth by the OEM.
Cheers.
a.

 

[k9ine]

Thanks for replying. I was thinking more about compressor efficiencey when deciding if off-line washing is needed.

Cheers.

 

[abeltio]

Ohhhh... ok. That is a different story then... to determine the frequency of water wash there are some indications.
1. increase in compressor discharge temperature
2. decrease in compressor discharge pressure
3. decrease in GT output
4. increase in GT heat rate

All corrected for ambient conditions, per manufacturer's recommendations.
Depending on the WW conditions... e.g. need to reduce load for on-line ww, if required, or need to shutdown for off line ww you will be able to decide which is the acceptable power output loss / heat rate increment that gives you the maximum revenue for your plant considering the output/Heat Rate improvement.

Cheers.
a.

saludos.
a.

 

[k9ine]

Thanks again for the help abeltio. Do you have a formulae that I could use to get realistic results, an industry standard perhaps.

 

[abeltio]

Sorry, i've only used the OEM recommendations which seem to work pretty well.


saludos.
a.

 

[Adam01]

You will need to compare the heat-rate, output CPD and temp on the same basis. These need not be at STP. If you have data on the above factors after the unit was overhauled and or washed (and you recorded the ambient conditions at the time) then it would be possible to compare current performance factors against the recently overhauled/washed condition when the ambient conditions were the same. The relative effect of difference in ambient conditions on your turbine/compressor will vary from design to design. ie industrial type designs are less affected by ambient conditions than aero derivative designs. I say this because it is unlikely that you will be able to match the ambient and operational conditions exactly for an exact comparison. Some judgement is required. I get the impression that it is a GT in compressor service so is likely to be an aero derivative.

The alternative is to calculate the heatrate and output back to the same conditions, usually STP. For this you will need the manufacturers correction curves for the particular CT.

There are many other factors to look into when you make the comparison eg does your unit have IGV's and are they in the some position between comparisons, if you have inlet cooling is this in the same condition and efficiency, operational loadings etc.

Alternatively visual inspection of the compressor will tell you if you have anything to clean off. You will need to boroscope the latter stages aswell as the front end and most OEM wash systems don't effectively clean the latter stages stages of the compressor section. Compare the two ends and it will tell you if you have anything to clean off and also how effective you cleaning is.

good luck

 

[k9ine]

Thanks Adam01 for the advice.