GT Frame 9E Mode Changeover Failure

There is an urgent issue at one of our gas turbine frame 9E. Due to drop in Gas Pressure at our site, GTs load dropped to almost 15 MWs. After gas pressure stability, GT-1 and GT-3 load increased and mode changeover was successful. But on GT-2, mode changeover failed on following alarms.<pre>
2019-05-25T13:38:51.124 2019-05-25T13:38:51.129 G2 PRC ALARMED G2.L28FSD_ALM SECONDARY FLAME DETECTOR TROUBLE ALARM
2019-05-25T13:39:51.724 2019-05-25T13:39:51.723 G2 Event ALARMED G2.L28FDE Flame Detector Channel #5 Flame Detector Channel #5 2 99 Boolean TRUE Good
2019-05-25T13:39:51.684 2019-05-25T13:39:51.692 G2 Event ALARMED G2.L28FDF Flame Detector Channel #6 Flame Detector Channel #6 2 99 Boolean TRUE Good
2019-05-25T13:39:51.244 2019-05-25T13:39:51.255 G2 Event NORMAL G2.L28FDE Flame Detector Channel #5 Flame Detector Channel #5 1 99 Boolean FALSE Good
2019-05-25T13:39:50.564 2019-05-25T13:39:50.567 G2 Event ALARMED G2.L28FDE Flame Detector Channel #5 Flame Detector Channel #5 2 99 Boolean TRUE Good
2019-05-25T13:39:50.444 2019-05-25T13:39:50.442 G2 PRC ALARMED G2.L83LLEXT_ALM EXTEND L-L MODE HIGH EMISSIONS - ALARM EXTEND L-L MODE HIGH EMISSIONS - ALARM 2 99 Boolean TRUE Good
2019-05-25T13:39:49.404 2019-05-25T13:39:49.411 G2 Event NORMAL G2.L28FDE Flame Detector Channel #5 Flame Detector Channel #5 1 99 Boolean FALSE Good
2019-05-25T13:39:47.844 2019-05-25T13:39:47.848 G2 Event ALARMED G2.L28FDE Flame Detector Channel #5 Flame Detector Channel #5 2 99 Boolean TRUE Good
2019-05-25T13:39:47.764 2019-05-25T13:39:47.770 G2 Event NORMAL G2.L28FDE Flame Detector Channel #5 Flame Detector Channel #5 1 99 Boolean FALSE Good
2019-05-25T13:39:47.484 2019-05-25T13:39:47.489 G2 Event ALARMED G2.L28FDE Flame Detector Channel #5 Flame Detector Channel #5 2 99 Boolean TRUE Good
2019-05-25T13:39:47.404 2019-05-25T13:39:47.411 G2 Event ALARMED G2.L28FDG Flame Detector Channel #7 Flame Detector Channel #7 2 99 Boolean TRUE Good</pre>
During mode changeover, when transfer valve open to 22% and primary valve closes to 7%, all secondary flame scanners start reading zero due to which mode changeover failed. Machine went into extended lean lean. However spread and exhaust thermocouples readings are normal and stable.

This issue arrived on Friday, and since then many attempts were taken but failed. Case is already put up with GE for their recommendations.

Kindly put your valuable suggestions on this issue, have you faced any such scenario.

Regards,
Waqas
 
Waqasbm,

This is odd, because when the primary gas control valve is closing and is at 7% most of the fuel is being directed to the secondary- and transfer nozzles. You didn't mention what the secondary gas control was doing during the Lean-Lean to Premix Transfer.?.?.?

What load are you attempting to transfer into Premix at?

If the unit has Inlet Bleed Heat is it enabled and working properly?

If the unit has IBH, can you disable it and try the transfer at higher load (fuel flow-rate)?

What is the gas fuel supply pressure doing during the transfer attempt?

What is the P2 pressure doing during the attempt?

What is load doing during the transfer attempts?

What is the hydraulic pressure doing during the attempt?

Is the ambient air more humid than normal?

If the unit has evaporative cooling is it enabled when you are attempting the transfer?

If the secondary flame sensors are water-cooled are they receiving too much cooling water flow (which could be causing moisture to condense on the sensor lonses)?

Specifically, what are the secondary flame detector intensities at the time of the initiation of the transfer? Is it always the same flame detectors which lose indication?

It is just odd that with most all of the fuel being directed to the secondary combustion zone that flame would be lost in the secondary combustion zone.... What alarms are active before the transfer attempts?

Please write back with the requested information, and let us know how you fare in resolving the issue!
 
Hi CSA,

Nice to interact with you on the above problem. We have been following you for many years.


Here are replies to your queries on behalf of <b>waqasbm</b> (we are colleagues):

What load are you attempting to transfer into Premix at?
- Around 50 to 60 MWs depending upon [email protected] 1970 degree C.

If the unit has Inlet Bleed Heat is it enabled and working properly?
- IBH is working fine as far as upstream / downstream pressure and feedback is concerned.

If the unit has IBH, can you disable it and try the transfer at higher load (fuel flow-rate)?

-We have attempted mode change over by isolating IBH valve at higher load around 80MWs but same phenomenon is happening.

What is the gas fuel supply pressure doing during the transfer attempt?

-P1 remains stable around 380 psig

What is the P2 pressure doing during the attempt?

-P2 remains same around 333 psig

What is the hydraulic pressure doing during the attempt?
- Transmitter is not avail on hydraulic header.

Is the ambient air more humid than normal?
- Humidity is 60 to 70% which is normal.

Specifically, what are the secondary flame detector intensities at the time of the initiation of the transfer? Is it always the same flame detectors which lose indication?
- All four flame scanners remained stable at the time of initiation of transfer until when VGC-1 reduced to 7% and VGC3 increased to 22%.

The only thing we have notices in addition to, is the increased plp_dp, pls_dp and pwp_dp. Current readings are 30,28,21 psig. But we had successful startup with similar pressures in the past.

Looking forward.

Muhammad Ahmed
 
Top