Hi,

Why when we try go to premix mode from lean lean mode, It is not done?
Why we haven't any alarm to describe what happen for system when we try go to premix mode and It is not done?
It is very bad for GE gas turbine company.

My system after the HGP doesn't go to premix mode.

 

abdi,

You very simply have NOT provided enough information for us to be of any help to you at all.

We can only presume that the turbine had DLN-I combustors, is firing on gas fuel, and that a HGPI was just completed.

We don't know if the unit has Inlet Bleed Heat, if the IBH system was active and working properly, what load you were trying to transfer from Lean-Lean into Premix at, what you did to try to attempt another transfer, and what troubleshooting you have done.

In order to transfer from Lean-Lean to Premix, it's necessary for the flame in the Primary Combustion Zone to be extinguished (that's one of the conditions, anyway). Does the flame in the Primary Combustion Zone go out for a few seconds during the Lean-Lean-to-Premix Transfer? If not, then the transfer won't be successful.

What other Process Alarms are active at the time you are trying to transition from Lean-Lean to Premix mode? What Process Alarms are annunciated during and after the failed transfer attempt?

What do you do to try another transfer from Lean-Lean to Premix--and what happens?

We just don't have enough information to be of any help. Does the unit have a Transfer Gas Fuel Valve, or is it "Transfer-less"? Are you certain the calibration/operation of the Gas Fuel Splitter Valve is correct? Are you sure the operation of the IBH Control Valve is correct (if so equipped)?

What load does the unit normally transfer from Lean-Lean to Premix at? What is the combustion reference temperature at that load--before the outage, and now after the outage?

It's not just bad for the GE Company--it's bad for the GE turbine! Did GE perform the HGPI? If so, what are they doing to try to help resolve the problem? If GE didn't do the outage, what is the company that did the outage doing to try to help resolve the problem?

If your system went into Premix Mode before the outage, then, unless there have been MAJOR changes to the hardware and software it should go into Premix mode after the outage. Are you sure all manual valves in the gas fuel piping and purge systems are in their proper positions? Is the air supply to all air-operated valves (purge valves, usually) turned on?

What have you done to try to troubleshoot the problem? What were the results?

 

Hi,

After check all of signal to active the premix unsuccessful. I find the primary zone detected the flame. Why?

 

abdi,

The usual reason is because the fuel to the primary combustion zone was NOT completely shut off. This typically happens when the LVDT calibration of the Gas Fuel Splitter Valve is not correct, or the valve has been refurbished and the stroke is not set correctly, or a combination of the two.

It's hard to extinguish the primary flame if fuel is still flowing into the primary combustion zone.

If the Gas Fuel Splitter Valve was either refurbished, or someone/some company performed a mechanical adjustment, or someone attempted to calibrate the LVDTs without actually physically observing and measuring the actual valve stem position during your HGPI this is the likely cause(s).

Another possible cause could be an incorrectly set null bias value for the servo-valve output, usually occurring when someone is attempting to calibrate LVDTs when they aren't sure of the process.

Lastly, if the servo-valve was replaced, did anyone verify the polarity of the servo currents being applied to the servo-valve coils? VERY important, and frequently overlooked.

Please write back to let us know what you find!

 

hi,

The flame in primary zone remove during transferring,but when GCV1 (after the flame remove in primary zone)go to opening and GCV2 go to close the transferring unsuccessful and the primary zone detect flame. Why?

thanks a lot.

 

abdi,

It's really not possible to say for sure without a LOT more information.

My first inclination would be that, if flame is being extinguished, then something is happening to cause the ignitors (spark plugs) to re-ignite the flame in the primary combustion zone. Again, you haven't told us what Process Alarms are being annunciated when the Speedtronic is trying to transfer to Premix, and that could help us help you understand what is--or isn't--happening.

Another possibility could be that there is something amiss with the reassembly of the combustion hardware, or that some manual valves are not in the correct position.

If there is a high exhaust temperature spread before or during the transfer that could be the problem--or contributing to the problem.

If it were possible for us to be able to say with any certainty what the problem at your site is being caused by with the information you have provided someone would have done so. In my experience, the majority of these failures to transfer after maintenance outages are the result of one of two things: either a problem with the combustion system hardware or the reassembly of the hardware (and the Mechanical Dept. <b>never</b> believes it's a mechanical or re-assembly issue, but it usually turns out to be the reason), or it's an LVDT "calibration" issue.

If the gas valves were refurbished or replaced (and, again, you haven't told us if they were or weren't), that could also be a problem. But the problem is <b>NOT</b> likely a Speedtronic control problem.

Finally, every hour of operation in Extended Lean-Lean mode is equivalent to <b>TEN</b> hours of Premix operation. DLN-I combustors are not intended nor designed to be operated in Extended Lean-Lean for more than a few hours during troubleshooting or in an emergency. Prolonged operation in Extended Lean-Lean is extremely hard on combustion liners.

Best of luck with your problem. Please write back to let us know what you find when you resolve the problem!

 

hi,

flame is being extinguished, then flame detection in primary combustion zone is happening,during the GCV1 going to open and GCV2 GOING TO CLOSING.

Extended lean lean mode high emission Alarm are being annunciated when the Speedtronic is trying to transfer to Premix,

there is a high exhaust temperature spread during the transfer but less than allowable spread for example allowable spread is 180 and spread #1, 2, 3 ARE around 100.

 

abdi,

The spreads seem very high for a machine just coming off a HGPI.

Since you seem convinced there is some relation to the opening/closing of the two gas control valves, have you compared the rates of opening/closing before the outage to those after the outage?

For the opening/closing rates to have changed, under normal outage conditions, it would be necessary for someone to have changed the servo gain(s) deliberately, or the valve actuators and/or the servo-valves to something other than original equipment. Dirty or incorrect servos could also be the culprit. As could incorrect wiring re-terminations and bad LVDT "calibration(s)."

In order to extinguish the flame in the primary combustion zone it's necessary to shut off the fuel flow to the primary fuel nozzles and re-direct all the fuel flow to the secondary combustion zone. Then, once flame has been extinguished for a few seconds fuel is re-admitted back into the primary fuel nozzles at the same time fuel flow to the secondary combustion zone is reduced. Without being able to see the P&IDs (piping schematics) for your turbine it's difficult to say what the two GCVs control on your machine.

But if it worked before the HGPI it should work after the HGPI--without any manual intervention. So, you must review all the work which was done to try to determine what might have changed which could be causing the problem. If the L.O. system and/or the hydraulic system was disturbed it's possible that some dirt was dislodged that has caused a servo-valve problem. If the servos were replaced, then they may not be the right servos, they may not be installed properly, they might not be wired correctly. If the gas control valves were refurbished they might not have the proper internals, they might not be assembled correctly, they might not have been adjusted properly, and/or the actuator may not have been installed or serviced correctly.

The combustion hardware may not have been correctly installed, or the fuel nozzles may not have the proper orifices. Again, in my experience <b>based on the scant information provided</b> most problems like this are mechanical (improper re-assembly; improper manual valve positions; improper combustion hardware and/or fuel nozzles). Occasionally improper LVDT calibration procedures cause similar problems after maintenance outages. Improper installation of substitution of servo-valves have also caused problems.

But unless someone has been deliberately making changes to Speedtronic parameters, or has not properly re-terminated wiring after the outage then the problem is most likely mechanical--no matter how much the Mechanical Dept. wants everyone to believe otherwise. It's someone's job at this point to review the work which was done in order to make a determination as to the most likely cause(s) of the problem and then methodically work through them until the actual cause is found and resolved.

There's virtually nothing we can do at this point <b>based on the information provided</b> to help you. There's no logic which can be forced--without the potential for catastrophic damage!!! No magic button to push. Just a recommendation for solid analysis and methodical troubleshooting.

And a request that you write back when the cause of the problem is found and resolved!

 

So Abdi, slowly we are learning more about your problem, as CSA has said the more information you can provide, the better we can try to help.

You indicate that the unit is attempting to transfer from Lean-lean to premix. Flame is being extinguished in the primary zone when the primary gas valve goes closed. But instead of flame staying only in the secondary zone, it is reestablishing itself in the primary zone as the primary gas valve starts to open again.

Again as CSA has indicated this type of problem after a CI or HGP inspection is typically related to a hardware issue.

My first question would be have you verified all the flame detectors? During startup when you are in primary mode are you indicating flame only on the primary channels? Since the leads for the primary and secondary flame detectors are close to each other I have seen them connected incorrectly before. This can cause flame to be indicated from the incorrect flame detector channel.

As far as hardware, who produced your hardware, nozzles, TP, liners, etc? Was it GE, or an aftermarket supplier? For flame to move from the secondary zone back into the primary zone could be caused by many issues. Leaking fuel nozzles for the secondary nozzle could allow a flame path that would allow the flame to travel back into the primary zone. A problem with the liner could change the required pressure drop across the liner venturi, allowing flame to travel back into the primary zone.

Any instrumentation issues that cause an incorrect reading of reference temperature (TTRF) can cause the unit to atttempt the transfer at an incorrect load where compressor airflows are not at correct values.

What temperature does the unit attempt to transfer? Is is around 1950 degf? At what megawatt load does this occur? Is this load consistent with what it did prior to the outage?

Are the exhaust spreads you are seeing now consistent with what they were prior to the outage? Assuming you did not have this issue then. Any large exhaust spread indicates poor combustion in at least one can. This can cause a pressure drop across two adjacent cans, which can allow flame to move back from the secondary zone to the primary zone. Do you notice an crossfire tubes indicating higher temperature than others, or possibly glowing?

Primary zone re-ignition is not an easy issue to diagnose, but we will continue to try and help, making suggestions that may lead to a discovery. Keep the information coming.

 

If the exhaust spread temperatures described by abdi are (as I suspect) in Celsius, they are <b>REALLY</b> high. One must remember there are fourteen combustors on a Frame 9E and only four of them have flame detectors in the primary combustion zone. The presumption is that if the four primary flame detectors all indicate the absence of flame then there is no flame in any of the other ten combustors. But, the high spreads--especially if they are in Celsius--indicate that flame may still be present in one or more combustors when it's not present in the four with the flame detectors. Or, if the fuel flows to all the secondary nozzles are not uniform then uneven pressures can exist in the combustors which could cause primary zone re-ignitions which prevent attainment of Premix mode.

Again, these symptoms are most likely the result of mechanical issues, which can include plugged ("choked") secondary fuel nozzle orifices, problems with combustion liners, problems with fuel control valves and/or the LVDT calibrations or fuel control valves, etc.

Based on the information provided, it continues to look like a mechanical issue (as such problems usually are).

Finally, during a Lean-Lean to Premix transfer the Speedtronic is usually automatically raising load, which automatically increases the allowable exhaust temperature spread to the maximum, and then when the load increase is complete the allowable exhaust temperature spread will start integrating down. The allowable exhaust temperature is usually a function of axial compressor discharge temperature, so if the thermocouples aren't working properly (as they frequently don't after many a maintenance outage) then the allowable exhaust temperature spread won't be correct, either.

Even if the spreads are in deg F they are still high for a machine just coming off an outage.

 

Have you checked the operation of the tertiary manifold gas purge valves VA13-3 and VA13-4. We encountered this problem once and it ended up been the timing of the above valves. From memory i think the requirement is 40seconds max to open. Also the switches 33PG5-6-7-8, and 63PG-2 should be checked also.

 

hi,

AT TIME 15:03:30:500 FLAME at primary zone extinguished,then at time 15:03:46:500 the flame detected in primary zone.during this time the spread# 1, 2, 3 goes up to 112, 107, 88
the temperature of exhaust are in Celsius:

TTXD-1:573
TTXD-10:618
TTXD-11:601
TTXD-12:597
TTXD-13:602
TTXD-14:603
TTXD-15:613
TTXD-16:590
TTXD-17:555
TTXD-18:547
TTXD-19:544
TTXD-2:545
TTXD-20:584
TTXD-21:585
TTXD-22:581
TTXD-23:576
TTXD-24:571
TTXD-3:529
TTXD-4:510
TTXD-5:504
TTXD-6:540
TTXD-7:559
TTXD-8:590
TTXD-9:617

WE have four flame detector in primary zone:
can#14,3,2,1
MW:84
TTRF1:1077 in Celsius GOES TO PREMIX
CPD:8.5 BAR

I THINK THE PRESSURE of discharge of compressor is low. AM I CORRECT?
you say check the calibration the LVDT OF gas control valve please say to me how you find the calibration of LVDT of valve may be cause the problem or which signal must be check to sure?

 

abdi,

Yes; CPD does seem low. Do all the CPD transmitters indicate the same pressure? How does that compare with the CPD Pressure Gauge on the Accessory Gauge Panel? How does it compare with operation before the HGPI?

If the ignitors are firing to re-ignite the primary flame detectors then it's probably because of the high spread(s), but I would expect a Combustion Trouble Alarm to occur also (that's a guess based on early Speedtronic DLN-I sequencing; GE Belfort have made a LOT of changes to what was once standard sequencing).

As for verifying LVDT calibrations, that has to be done off-line, while actually measuring valve position and comparing it to reference and calibrated LVDT feedback.

However, based on the delay between loss of primary flame and re-establishment of primary flame it continues to sound more and more like a mechanical problem with combustion hardware and/or combustion hardware re-assembly. Which, again, most of these problems are.

Are the witches' hat strainers installed in the gas fuel piping? If so, have then been checked for cleanliness? If the same spreads occur at the same exhaust thermocouples each time you try to transfer to Premix, then you need to start pulling primary and secondary fuel nozzles to check for blockages or something like that.

Again, we don't know what was done to the control system during the outage AND most of these kinds of problems after mechanical maintenance outages are mechanical/reassembly problems. If you purchased combustion hardware from someone other than the OEM, that's one place to suspect. I've seen incorrect dilution holes cause similar problems, and inabilities to maintain NOx and/or CO emissions even if Premix could be obtained.

Best of luck! Please do write back to let us know what you find. A lot of people are following this thread to learn how the problem was resolved.

 

hi,

YOU tell me the delay between loss of primary flame and re-establishment of primary flame it continues to sound more and more like a mechanical problem with combustion hardware and/or combustion hardware re-assembly. IT means that we must opening the hardware combustion chamber. I THINK IT'S DIFFICULT TO DO because the all of thing for combustion chamber now is new and opening this system is hard work and I am not sure exactly what problem in hardware combustion chamber exit, please guidance me.

before HGP FOR 5000hrs this unit work in premix mode after that this unit can't go to premix mode and for 881 hrs works in extended lean lean mode.

 

abdi,

The control system can only do so much. It cannot be used to make a mechanical issue like this go away.

GE publication GER-3620 says every hour of operation in Extendedean-Lean is the equivalent of TEN hours of operation in Premix mode.

When a DLN-I combustor is operated in Ext. Lean-Lean mode there is diffusion flame in both the primary and secondary combustion zones. And if the unit is being operated at or near Base Load then quite a lot of fuel is being combusted in a diffusion flame (hottest possible flame temperatures) and the diffusion flame impinges on the venturi between the primary and secondary combustion zones--weakening the venturi.

There have been other reports on various Web forums, including control.com, about serious and catastrophic failures of combustion hardware after prolonged operation at high load in Ext. Lean-Lean mode

I fully understand your frustration and the fact that you are asking why the unit won't transfer into Premix. The likely reason is that something was not reassembled correctly, or the wrong parts were used during reassembly, but the problem is not likely the control system. By confining to operate the unit in Extended Lean-Lean you are doing even more damage to the hot gas path components.

DLN-I systems are complex systems and if it were possible for someone to say, "Adjust [this or that] and you will be able to transfer into Premix mode," it would have been suggested already.

Using a qualified contractor/supervisor and parts supplier to perform HGPI and similar maintenance work is critical. Allowing a contractor/supervisor to leave site without the unit being able to return to normal operation is not typical. Having a qualified and knowledgeable controls person present during the re-start is good insurance against trouble like this.

Yes; it's hard, difficult, and extremely expensive to shut the unit down and take it apart again so soon after the HGPI but BASED ON THE INFORMATION PROVIDED IN RESPONSE TO QUESTIONS ASKED OF YOU that's what it's likely going to require to resolve your issue.

Here's a link to another thread on control.com about the damage caused by continued operation in Ext. Lean-Lean and another unit that didn't do regularly scheduled maintenance. They are both scary scenarios.

http://www.control.com/thread/1375449205

There is a Frame 9 Discussion Group on LinkedIn that also has a similar discussion at the same time (month/year) as the one above complaining about damage caused by prolonged operation in Ext. Lean-Lean mode when it was not possible to transfer to Premix.

In all these cases the exact cause of the inability to transfer to Premix was never determined--because of the extensive damage to the unit.

I'm trying to tell you to get the contractor/supervisor of the HGPI back to site to investigate and correct the inability to transfer to Premix, or the consequences may be catastrophic.

Please write back to let us know when you do finally take the combustion system apart what the combustion liners look like.

 

Hello Dear Friends

This is my experience with one of the DLN-1 frame 6 Ge Gas turbines at one of our sites. It also happened after the HGP inspection. The flame was getting extinguished in primary zone but was re established immediately when machine was getting transfered primary to secondary mode and gets transfered to extended lean lean mode, The reason later on we found out was the Spark plug.

The techinician fixed the insertion length of the sparkplug more into the combustion chamber which reignited the primary zone. Please check your sparkplugs insertion. or you may find the sparkplug is almost burnt half way?

Also there are software temperature switchs and conditions in the MKV software program which will allow transfer if the conditions are met. Please check if the constants and set values were not changed

Cheers

Mambo

 

Mambo,

I don't understand how ignitor insertion depth can have anything to do with failure to transfer from Lean-Lean to Premix. During a successful transfer, the ignitors should not be energized, so insertion depth should not have an effect.

The intent of extinguishing diffusion flame in the primary combustion zone is to then re-introduce gas fuel into the primary combustion zone without diffusion flame to create an extremely lean fuel/air mixture and reduce hot gas temperature which reduces the formation of NOx.

If the ignitors fire after flame is is extinguished in the primary combustion zone during or even after a Lean-Lean to Premix transfer it's because either diffusion flame was detected in one or more of the combustors with flame detectors, OR a high exhaust temperature spread was detected (which could be an indication of diffusion flame in one of the combustors WITHOUT flame detectors).

There is one other condition when the ignitors should be energized during Premix operation: when the unit is being unloaded and a transfer from Premix to Lean-Lean is being initiated.

I have had to adjust ignitor insertion depth because when the unit would trip because diffusion could not be re-established in the primary combustion zone during unloading/shutdown. Air flows are so high at higher loads that if the ignitor is not properly located in the combustor that the air flow will not allow the spark to re-ignite the fuel in the primary combustion zone, causing the unit to trip because of an inability to establish diffusion flame during unloading/shutdown.

So, if you could clarify or explain how ignitor insertion depth is a problem when the ignitors should not be energized that would help my understanding of your description.

The original poster has NOT provided any information about what changes may or may not have been made to the Control System or control system parameters. Usually, these kinds of things are not adjusted during any maintenance outage, because they never change. They are pretty universal settings for most machines with DLN-I combustion systems.

Hopefully we'll hear back from the original poster after he's taken the machine apart and discovered what the problem was and the unit then successfully transfers into Premix mode.

 

CSA,
I have seen excessive igniter insertion depth cause re-ignition of the primary shortly after transfer a number of times over the years. It's a glow plug.

 

mhwest,

This is an understandable explanation.

However, one one would think if the ignitor were getting hot enough to become a glow plug that the life IOC the ignitor would be significantly shortened--even after the depth was decreased. Also, since the ignitors are usually held in position by a Swaglock compression fitting that it would have to cut off extremely carefully to prevent damage to the ignitor body.

At any rate, thanks for the additional information. It's most helpful.

 

Hello everyone

the problem is not the ignitor position because we do not have any flame until the CGV1 reached 27% of opening (from Lean-Lean to premix). It means if we had glow on ignitor then immediately we should see the flame.

also we checked the re-ignation graph, always the state was 0. So the big question is, as soon as we have mixed air and fuel in primary combustion at 27% of opening of CGV1, we see the flame in primary without having any re-ignation??