GAs turbine performance calculation -Doubst, i need some help.

[ferchuvicente]

Dearl All,

I am trying to calculate the performance charactersitic of a LM 2500 gas turbine in our gas plants. But i have some doubts regarding to collect data, ( i ma taking data from MARK V, system control). For example the temperture T5.4 is valid to consider the combustion gases temperature???,
In my case we have a T5.4 = 744ºC (i think that is low)
Other doubts, i have T1(inlet compressor temperature=24.3ºC ambient) and at discharge compressor (16 stages) P2=13,2 and T2=413ºC, so if you use the theory to corroborate the date is not working.(T2=T1*Rc^(k-1/k))
Rc=Ratio compressor in this moment 13.2 and k (adiabtic coeficient)and our real temperature at discharge is 413ºC
so 413 is not equal to 24.3ºC*13.2^(1.4-1/1.4)

What is happening ,i know that i have to use n(politropic) but even in this way is very different the results.

Best regards

Fernando

 

[21121956]

Hello everybody:

T2=T1(p2/p1)^(n-1)/n

n = polytropic index, usually between 1,45 and 1,7.
T1 = Air inlet ABSOLUTE temperature (ºR or ºK)
T2 = Compressed air outlet ABSOLUTE temperature (ºR or ºK)
p1 = Air inlet ABSOLUTE pressure (PSIA or bara)
p2 = Compressed air outlet pressure (PSIA or bara)

Try once again !

 

[ferchuvicente]

Dear friend
thanks for your time, is working better using absolute values. But, how i know the real value of n(1,45-1,7) is a great difference. where i can get a good aproximation for n.
Best regards

 

[21121956]

Hello everybody:

The value of the polytropic index "n" has a strong relationship with the refrigeration of the compressed air. Usually, it is determined experimentally.

According to Emden´s equation, n = 1/(k-1).

If you do not have available information of your compressor, you could ask for the test run report, performed on the manufacturer´s workshop or, calculate "n" as a bench mark using the commissioning values obtained during the start up of your power plant.

 

[gtsim]

Also have a look at this thread

thread1036-173075

 

[AndreChE]

Find the reverse function of 21121956 thread.

If you have suction and discharge Temperature and Pressure, you calculate real "n" and you know "k" you calculate whatever you want...

 

[timbones]

If I recall correctly, the T5.4 temperature is not the temperature of the combustion gases, it is the temperature downstream of the HP turbine (which is why your calculation doesn't work). The temperature upstream of the HP turbine (TIT) is not measured (the temperature sensors just can't handle the heat). Combustion temperature is calculated, but I don't recall exactly how.

You might be able to do it using an energy balance around the combustor with the compressor discharge temperature/flow/pressure and the fuel heating value and flow as inputs and assuming an adiabatic combustor.