Hello experts;

I start to study the gas turbine components.

I have a confusion about axial compressor

If barometric pressure at the site is 14.5 PSIA and Inlet filter differential pressure is 3 inch of water column, then what is the inlet pressure of the axial compressor.

It is 11 stage axial compressor. The compressure discharge pressure is 118 PSIG.

I want to calculate the pressure ratio but how and where i measure the Inlet compressor pressure?

Thanking you i will remain

 

There must be inlet vacuum at compressor inlet IN INCH OF H20.if it is present then i can give u the answer

 

Samual,

How much accuracy does your calculation require? What are you using the compressor pressure ratio number for? The formula used by one OEM for calculating compressor pressure ration (CPR) for their heavy duty gas turbines is:

CPR = (CPD + Ambient)/Ambient
CPR = (118.0 psig + 14.5 psia)/14.5 psia
CPR = 132.5 psia / 14.5 psia = 9.138
<pre>
| | |
Ambient | Inlet | Axial | Axial
| Filter | Comp | Comp Disch
| | Inlet |
| | |
14.5 | 3.0 in | | 118.0 psig
psia | Water | | 132.5 psia
</pre>

But, if one looks at the table above, one could subtract the Inlet Filter drop from the ambient and consider the result as "ambient" which is what would be present at the inlet to the axial compressor in the area of the bellmouth.

I believe the OEM doesn't include the inlet filter differential pressure in the calculation is that there should always be a drop across the inlet filter because there should always be a filter on the inlet--but that's a scientific, wild-arsed guess as to why the inlet filter differential pressure drop is not included in the compressor pressure ratio calculation.

Also, the turbine is ultimately exhausting to atmosphere. Even if there is a small back-pressure on the exhaust, it will be very similar to the inlet filter pressure drop.

 

Hello experts
thanks for help. I came back from the site and i give you following data

1.Air inlet filter diffrential pressure is 1.8 " h20

2. Pressure at the compressure inlet by measuring diffrential pressure gauge 0 t0 10 "h2o, Connect low side of the gauge and note 3" H2o.

3. PCD is 119 Psig and Barometric pressure is 14.3Psia.

If the Inlet pressure which is 3" H2O if increase or decrease what effect on the axial compressor and how i calculate the PR of the compressor? Can i calculate the roughly flow in PPS?

Regards

 

Dear Samual,

You only need compressor Inlet pressure?

For that you have the data.

The gauge(or Pressure transmitter) which is showing compressor inlet vacuum is basically showing you the amount of vacuum present on compressor suction.

As your gauge reads 3 inch of water column so convert that into PSI.
3inches of H20= 0.10Psi
so
0.10Psi vacuum is present at compressor inlet and Inlet pressure (P1) is 14.50(atmospheric P)-0.10psi
=14.40 PSi

So you have the Compressor Inlet pressure=14.40Psia

For that you can calculate compressor Efficiency

You only have to tell me the Compressor inlet temperature and discharge temperature along with P1 and P2.

Thanks,
Hope it helped

 

Hello experts;
Good day.

1.The Compressor inlet temperature is 95 Deg F

2. P1=Compressor inlet pressure is calculated as
(Barometric pressure =14.3-(DP at inlet compressor 0.1 PSI)=14.2 PSI

3. P2 is 119 PSIG

4. T2 (Compressor discharge temperature is 590 Deg F)

Please guide me how i calculate the efficiency and if efficiency know can i calculate the Flow in PPS?

Regards

 

Formula for compressor efficiency;<pre>
[( P2C/P1C)^(k-1/k) - 1]
Eff= ___________________________

[( T2C/T1C) -1]

Where P2C = compressor discharge pressure
P1C = compressor inlet pressure
T2C = compressor discharge temperature
T1C = compressor inlet temperature
K = 1.4
Units of pressure should be 'psi'
Units of temperatures should be 'Rankins' (F+460)</pre>
Dear Samual:Are you sure that compressor inlet temperature is 95 degree F.where the inlet temperature RTD installed?
Please check compressor inlet temperature again

my second question is
what cooling method utilized for compressor inlet area cooling?
for example Evap system or fog etc

 

Hello Hafzal;

Good day. Yes the compressor inlet temperature is correct because evaporative cooling system is not running due to some reasons. When it operates the Inlet temperature come to near about 73 to 78 deg f.
After calculation the efficiency can i know the mass air flow?

Regards

 

Nup
You could not calculate mass flow from this.

Most of the turbines have in-build system to calculate mass flow but some does not.

Same is the case with our turbine too. although we have compressor inlet scroll differential pressure, but we have not exact orifice measurement at compressor inlet. (I am considering orifice as compressor suction typical shape which usually bends at suction)

You need compressor inlet area which is called Bell mouth and then to implement formula.

2nd as for your compressor efficiency is concerned your current data seems wrong. weather you collect data at turbine transient phase or some of your instrument show wrong value.

Please provide data at turbine base load (max load) at stable condition.

 

Samual... Is vibration frequency in sympathy with rotor-rpm or rated line-frequency, if the two are different?

Regards, Phil Corso

 

> You could not calculate mass flow from this.

Hello
Is The formula of efficiency correct? is k is not used in the denominator with temperatures?

regards

 

Formula for compressor efficiency;<pre>
[( P2C/P1C)^(k-1/k) - 1]
Eff= ___________________________

[( T2C/T1C) -1]

Where P2C = compressor discharge pressure
P1C = compressor inlet pressure
T2C = compressor discharge temperature
T1C = compressor inlet temperature
K = 1.4
Units of pressure should be 'psi'
Units of temperatures should be 'Rankins' (F+460)</pre>
Practicle data of our plant

T1=83F
T2=807F
P1=28.5 inch of Hg (13.99 PSIA)
P2=209 PSIA
INserting the values in above formula we have compressor efficiency of 87.2% almost.

 

Samual,

if you have your compressor map, by efficiency and pressure ratio, mass flow is determined.

 

Hello Hafzal;

Thanks for guide me on each step. I read your practical data which u post.
Where from you measure the P1?

I calculate as
p1= Barometric pressure- (air inlet filter differential pressure+ inlet differential pressure)

Is it correct?

>Formula for compressor
>efficiency;<pre>
> [( P2C/P1C)^(k-1/k) - 1]
>Eff= ___________________________
>
> [( T2C/T1C) -1]
>
>Where P2C = compressor discharge
>pressure
> P1C = compressor inlet pressure
> T2C = compressor discharge
>temperature
> T1C = compressor inlet temperature
> K = 1.4
> Units of pressure should be 'psi'
> Units of temperatures should be
>'Rankins' (F+460)</pre>
Second if i have the bell mouth area what is the formula to calculate the flow? also guide me which units i used to calculate the flow in PPS.

Thanking you i will remain

 

Dear,

For measurement of P1 (Compressor inlet pressure) we have installed Pressure transmitter which gives us direct reading of inlet manifold pressure (inlet pressure) in Inch of hg.

We also have the reading of Atmospheric pressure, inlet filter DP, and compressor inlet vacuum. by taking these values you can also calculate P1.
Here it is

P1 = Atmospheric pressure - Compressor inlet vacuum

(where as compressor inlet vacuum reading is already sum to inlet filter differential pressure)

2-
Each turbine inlet area is different so the formula is also different. Manufacturer can give you the formula for that. and secondly why are you focusing the values is PPS? just download Unit converter and interchange mass flow units.

thanks