MARK V Fuel Gas Flow Calculation

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gas_flow

Following are the instantaneous value inputs to the GAS_FLOW_CALC1 Block for the GE Frame 5 gas turbine.

Note: following are snapshot values.
FDG1 : 574 mmWc
FDG2 : 575mmWc
FPG3 : 17.30 Kg/Cm2
FQG : 1.17 Kg/S
FQKGDB : 76
FQKGG : 1.046
FQKGSG : 0.608
FQKGSL : 737
FTG : 53 Deg C

Orifice details available from performance guarantee test calculation sheet given at the commissioning time are as follows:

Diameter of Pipe @ 20 Deg C : D' = 0.154051 m
Diameter of Pipe during test : D = 0.154109842 m
Flowing Temp : FT = 54.95 Deg C
Beta : 0.582160533

Problem: the FQG calculated by Mark V is 1.17 Kg/s. using a Daniel's flow calculator for these values the gas flow reading is 1.46 Kg/s. (I'm not sure if the Daniel's flow calculator that I have is a licensed version.)

Given these facts, is there a reason to believe that Mark V's FQG may be wrong and needs some change of constants?

Thanks.
 
How long ago was the orifice plate and metering tube installed?

When was the last time the orifice plate dimension was inspected, for diameter and for the sharpness of the knife edge and for correct installation?

When was the last time the differential flow transducers were calculated?

1.17 kg/s is about half of rated flow-rate for a Frame 5 as I recall; what speed/load was this data taken at?

Usually when performance data is gathered from the meter tube/orifice assembly during commissioning, a water-tube manometer is used and the readings are manually recorded and used to calculate the flow-rate for performance characteristics.

As has been said before on control.com, the fuel flow monitoring instrumentation on the Mark V (or Mark IV or Mark VI) are not "revenue" quality. They can't be used as a check against some meter or flow totalizer which is being used to determine volume for billing purposes. That kind of accuracy is simply not required for GE-design heavy-duty gas turbine fuel flow-rate measurement. Most often, the flow-rate is only used for calculating Wet Low NOx injection flow-rates or Power Augmentation Injection flow-rates, neither of which require extremely high accuracy.
 
>How long ago was the orifice plate and
>metering tube installed?

The Orifice Plate, DP Transmitters were installed Five years ago

>When was the last time the orifice
>plate dimension was inspected, for
>diameter and for the sharpness of the
>knife edge and for correct
>installation?

Orifice Plate has never been inspected snce installation

>When was the last time the differential
>flow transducers were calculated?

Four months ago.

>1.17 kg/s is about half of rated
>flow-rate for a Frame 5 as I recall;
>what speed/load was this data taken
>at?

16MW - Preselect load
N - 5100RPM

Thanks
 
One of the things I've always done when this was raised as a problem is to use a water tube manometer (inexpensive or easily made) to measure the differential pressure across the orifice plate to confirm that value being transmitted by the transmitter is accurate. I've also used a calibrated gage or pressure instrument to measure the upstream pressure of the natural gas supply. It's usually discovered that there's something amiss with the calibration of the transmitters, or the condition of the orifice.

I'm not personally familiar with a "Daniels flow calculator" but presume that it may be programmed for the particular characteristics of Daniels flow-measuring equipment and may not be 100% compatible with the instrumentation at your site. This could also be part of the problem. Have you tried manually calculating the flow-rate using industry-standard equations to see if the flow-rate is satisfactory?

What is the fuel flow-rate measurement being used for in the Mark V Control Sequence Program? Wet Low NOx flow-rate calculation? Power Augmentation flow-rate calculation?
 
>One of the things I've always done when
>this was raised as a problem is to use a
>water tube manometer (inexpensive or
>easily made) to measure the
>differential pressure across the
>orifice plate to confirm that value
>being transmitted by the transmitter is
>accurate. I've also used a calibrated
>gage or pressure instrument to measure
>the upstream pressure of the natural
>gas supply. It's usually discovered
>that there's something amiss with the
>calibration of the transmitters, or the
>condition of the orifice. <

We did not suspect the transmitters 'til now because both of them were showing the same DP (excuse the 1mmWc difference), but it's true that the orifice has never been checked since installation. Secondly, even if the DP is wrong, with all other parameters constant, the flow calculation by Mark V and a flow calculator should app. match (if DP is wrong, then calculations will differ from the true value, but the wrong value should match).

>I'm not personally familiar with a
>"Daniels flow calculator" but presume
>that it may be programmed for the
>particular characteristics of Daniels
>flow-measuring equipment and may not be
>100% compatible with the instrumentation
>at your site. This could also be part of
>the problem. Have you tried manually
>calculating the flow-rate using
>industry-standard equations to see if
>the flow-rate is satisfactory? <

We calculated the flow using the same DP values using an AGA3 software again. Manual calculation is too mathematical, so didn't try it. Plus, I don't have a simpler equation. The performance test booklet talks of so many parameters viz., flowing temp, reference temp, flowing pressure, reference pressure, density at STP, density at flowing condition, orifice dia. at STP, Orifice dia. at flowing conditions, orifice expansion coefficients, etc. The complete equation is scary.

Another thing that I did not understand is that these parameters don't appear in Fuel_Gas_calc bbl as inputs. Can this explain the difference, because the flow calculators I am using (Daniel or AGA3) ask for all these parameters?

>What is the fuel flow-rate measurement
>being used for in the Mark V Control
>Sequence Program? Wet Low NOx flow-rate
>calculation? Power Augmentation
>flow-rate calculation? <

Yes sir, the FQG appears only in two rungs. seq_nox5 & seq_nox6. seq_nox5 is the Gas_flow_calc bbl and seq_nox6 is injection block. I am not aware of power augmentation part but FQG search did not result in any other rungs except those mentioned above.

If we get a flow metering party or a third party to validate the flow metering instrumentation and still observe the difference from Mark V calculation which constant can be changed to match it with the validated readings.

Thanks.
 
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