DLN Tuning gas turbines

B

Thread Starter

Brian

Can anyone explain to me the meaning of "DLN system tuning"? Also I would like to know what parameters are observed and calibrated while tuning the DLN machine to optimize the NOX flow to minimum and at the same time have a good reliability and availability of the machine.
 
DLN tuning I think is different if you have DLN1 or DLN2. I have heard that DLN2 is normally carried out by a GE tuning specialist and you can damage hardware if you get it wrong. My only experience has been with DLN1 on a 9E.

DLN1 system tuning is moving the premix split around to achieve the optimum NOx levels against unit stability. If you increase the value of the split the NOx should decrease, but can also make the unit more likely to suffer from flashbacks/primary re-ignition.

FXKSP5 (max limit) and FXKSP6 (min Limit) are the constants that set a band for the premix split settings. Ours were originally set at 84 and 81 I think. Check the current split output, it is likely to be at one end of this band and adjust the other constant to match it. Now move the value of both constants in 0.5% steps up and down between about 79 and 86%, let the unit stablise after each change and monitor the NOx for a period. Record the data and at the end you should be able see were is the optimum point for your unit.

If you find afterwards that you are experiencing flashbacks you may need to reduce the values slightly.

I cannot find the write up I have for this at the moment so the split values I have quoted are from memory only. I will try and track down this document and I will post any updates.

Hope this helps.

Simon
 
I have found our write up now, and the settings for the split range from 77 - 85% and is in 1% increments. At each test point we record values of NOx, CO, O2, MW, and TTRF1.
 
The exact process of tuning a machine with DLN-I or DLN-2.n combustors is slightly different, but the main principles are to try to maintain emissions within compliance levels (usually both NOx and CO), maintain flame stability (since in Premix combustion mode the premix combustion air-fuel mixture is very, very lean), and keep dynamic pressure pulsations in the combustion system to a minimum. Sometimes, that's really difficult to do, and we are finding out that for many locations in the world that DLN tuning must be performed at least twice during the year, because of ambient temperature changes.

Dynamic pressure pulsations can take a couple of different forms and occur at a couple of different frequencies, but they can be very damaging to combustion components. They are internal pressure pulsations which can become quite high under the right circumstances and basically cause the combustion components to vibrate and shake, sometimes almost violently.

During tuning, as Simon has said, about the only "knob" there is for trying to adjust the fuel flow to the various nozzles and combustion zones is to vary the fuel flow-rate split between primary and secondary combustion zones (in DLN-I combustors) and between the various fuel nozzles (in DLN-2.n combustors). Hopefully, the various orifices on the combustion liners have been properly sized; sometimes, during DLN tuning it is necessary to remove the combustion liners and have the orifices re-sized and then begin the tuning process of adjusting fuel flow-rates to the combustion zones or nozzles to try to achieve the desired balance of emissions, flame stability, and dynamic pressure pulsations.

Some turbines require special sensors to monitor the dynamic pressures in each of the combustors during tuning; this used to be done for all DLN combustor-equipped gas turbines, but GE has since determined that with current combustion hardware designs it's not so critical for DLN-I combustor-equipped machines. However, GE has also determined that running DLN-I machines at the lowest possible NOx levels also results in the highest combustor dynamics, so while it's possible to get some fairly low NOx levels out of the machine by adjusting the fuel splits within acceptable limits, it's also possible to cause premature combustion hardware failure. So, they also say that it's not advisable to adjust fuel splits on DLN-I machines to the lowest levels possible without also doing some combustion dynamic monitoring. But, adjusting them to operate at or just slightly below guaranteed emissions levels without combustion dynamic monitoring is usually very safe for the combustion hardware.

During tuning, the combustor pressures and emissions levels are monitored while the fuel flow-rate splits are adjusted. There are proprietary matrices that are consulted and used in the tuning process to help with achieving the desired operation. A lot of DLN tuning is just experience; most of the engineers certified to be 'DLN tuners' have worked extensively with others to learn their craft, and have access to people who have lots of experience, also.

It's a very complicated process involving emissions levels (both NOx and CO, usually) and flame stability and combustion dynamics, which has been reduced to some relatively simple steps. However, when a problem is encountered it can be quite a long process to determine exactly what is occurring and how to deal with it.

An analogy is like an automobile from the middle of the twentieth century versus a new model. Back in the 1950s cars had a radio (AM), a heater, usually a manual transmission, manual windows and door locks, and a carburetor. They were fairly simple to work on, though they weren't very reliable. Today's automobiles have radios (AM, FM, satellite, HD, MP3, CD, DVD, etc.), heaters and air conditioners, electric windows and door locks, most now have automatic transmissions in many parts of the world, and multiple computers, one or two or three which control the fuel injection system. Not just anybody can work on them, but they are a lot more reliable and powerful than they used to be. They also have emissions control systems that are fairly complicated, not just anyone can work on them, and those that do need special equipment and training and access to knowledgeable people for support.
 
Thanks to everyone in the control room for their responses, I am just waiting for the next opportunity to do what we have discussed in the control room, will come back with the result of the tests.

Thank you very much to control.com for keeping the topic alive and vibrant, I hope there will be more comments and tips on the DLN1 tuning from everyone.

Brian
 
>Thanks to everyone in the control room for their responses,

---- snip ----

> Thank you very much to control.com for keeping the topic alive and
> vibrant, I hope there will be more comments and tips on the DLN1 tuning from everyone.

thanks for the comments. am an environmental coordinator in a gas to power plant. i usually take emission stack readings and CO has exceeded the allowable limits. the Gas turbine is GT10B1 a contractor has been hired to do tuning on GT10B1. What is a tuning?
 
Hello All ,

I am trying to get some instructions ( most essentials ) for DLN 2.6 tuning

I have seen some good old threads treating this subject.

Could anybody try to give me a better picture for DLN 2.6 tuning ?

Thanks for sharing your knowledges i appreciate that.

James
 
Hi

I have a question about the effect of tuning on premix steady state mode in below scenario?

Our turbine will only enter premix mode if the unit MW is carefully set to 81 MW. In this case we will have Premix Steady State for a few hours. (TTRF1 close to 1081-1091 centigrade degree).

As soon as the Load is increased, the flame returns to the primary and the turbine enters the mode EXTENDED-LEAN-LEAN.

Also, according to the following values, are these values correct?

FXKSP: 100

FXKSP1: 81

FXKSP2: 100

FXKSP3: 100

FXKSP4: 100

FXKSP5: 84

FXKSP6: 81


Turbine is GE-F9- DLN1 and installed at sea level(300m) and hot climate (10 centigrade in January).

HGPI:

We performed the HGPI successfully and filled every related forms. During this inspection, we saw the highly deformation on all combustion liners at dilution hole area then we change them.

Operation:

Turbine was started normally, and turbine give the load between 70-80 MW at lean-lean mode. The exhaust spreads between 18-25 Centigrade at this mode. Around the reference temperature (TTRF1=1087 C) the unit get to start to change to premix mode. During this operation and extinguishing the of the flame in the primary zone, the vibration at the No. 2 bearing is increasing from 2mm/s to 10mm/s (5 time higher). Flame extinguishes at primary zone successfully and as we estimate load is decrease. During the increase of load (as result of primary zone fuel injection), after second the flame detectors detect the flame at primary zone. Because of it, the spark plug energizes then we have flame at primary zone, and we could not have the stable premix operation.

We calibrate the spark plug and flame detectors. As I said the temperature spread is normal (20degree centigrade).

IBH (inlet blead heat) is disable.


about the load when the failure occurs. As temp=15 C and h=200m the load is between 80-85 MW.

About the active alarms: relays alarm, resignation alarm, high emission

We never tune the turbine for emission.
 
MBA,

Does the unit have IBH (Inlet Bleed Heating)? Is it in operation when it has trouble getting into and remaining in Premix Steady State?

What is the grid frequency--in other words, how stable is it when operating the unit and trying to get into and remain in Premix Steady State?

What are the exhaust temperature spreads? (TTXSP1, and possibly TTXSP2 and TTXSP3)?

What alarms are being annunciated prior to and when the unit automatically transfers to Extended Lean-Lean?

What is the value of TTRF (or TTRF1) when the unit is having trouble getting into and remaining in Premix Steady State?

Have you tried manually loading the unit up from Lean-Lean combustion mode and letting the Mark* complete the transition into Premix Steady State--and waiting to see what happens (WITHOUT enabling Pre-Selected Load Control!)? If so, what happens? (As the unit begins the Lean-Lean-to-Premix transfer the Mark* will start loading the machine. This is NORMAL and to be expected. It is done so as to prevent the unit from transferring into Premix Steady State and then trying to transfer back into Lean-Lean by loading the unit for a short period to ensure TTRF/TTRF1 stays high enough to remain in Premix Steady State.) A LOT of people DO NOT like this bit of loading because the load the unit usually ends up at is higher than the Pre-Selected Load Setpoint they want to operate the machine at which causes Pre-Selected Load Control to unload the unit and it transfers back into Lean-Lean and then starts loading again because the load is lower than the Pre-Selected setpoint/reference, and the vicious circle starts and continues--but it's standard and pretty much unavoidable. This isn't a problem with the Mark*--it's a problem with the operating practices. Using Pre-Selected Load Control for a setpoint/reference which is in the "zone" of loading/unloading because of TTRF/TTRF1 changing. But, no one ever listens about not using Pre-Selected Load Control, and the problems persist. "The definition of insanity is doing the same thing, and expecting different results." (That quote is usually attributed to Albert Einstein....)

It is very common practice to perform DLN tuning after any maintenance outage.

GE likes to say that DLN-I is a "mature" technology--meaning that it's been around for decades and is pretty stable. While it has been around for decades, the parameters in a turbine (fuel nozzles; combustion liners; transition pieces; side seals; nozzles; shrouds; etc.) change with each maintenance outage, even if just slightly it's enough some times to upset the mature technology known as DLN-I.

Further, as fuel changes (and it does!) over time, the emissions will also change.

Gas Fuel Control Valve (GCV; GSV; etc.) LVDT calibration can also play havoc with DLN tuning over time. If not done correctly small changes in feedback scaling can have large changes in combustion stability and emissions levels.

So, if it's been some time since the unit has been "tuned" for DLN emissions, it should seriously be considered. SERIOUSLY.

The damage you described is consistent with long-term operation in Extended Lean-Lean--where the diffusion flame balls are large and hot and can impinge on the combustion liner and cause loss of TBC (Thermal Barrier Coating) and even distortion (warpage). GE says one hour of operation in Extended Lean-Lean combustion mode is equivalent to TEN HOURS of operation in Premix Steady State. So, if your unit automatically transfers back to Extended Lean-Lean and then it is operated in Extended Lean-Lean for hours at a time (or longer) the combustion hardware is taking a beating. But if you MUST have the power you don't really have a choice--but you should be factoring in the Extended Lean-Lean fired hours to any maintenance outage planning, because the hardware is going to deteriorate faster the longer it is operated in Extended Lean-Lean mode.

Extended Lean-Lean combustion mode is meant to be a transitory combustion mode--for the most part. In the early days of DLN-I when the unit failed to stay in Premix Steady State and flame was detected in the Primary Combustion Zone the unit was tripped--meaning if power was required from the generator the unit had to be re-started and re-loaded to Premix Steady State and hope it would remain in Premix Steady State. So, the designers came up with Extended Lean-Lean mode--which was thought at the time to be not harmful to the equipment. By having combustion automatically switch to Extended Lean-Lean the unit could remain running while the operators and their supervision would decide what to do. They could unload the unit and the re-load it to get back into Premix Steady State--and hope it stayed there. Or they could shut the unit down while they decided on a course of action to troubleshoot and resolve the inability to stay in Premix Steady State. In an emergency--when power was absolutely required--it was felt it could be operated for a few hours in Extended Lean-Lean without harm to the combustion hardware.

So, Extended Lean-Lean is meant to be a temporary mode of operation that allows the unit to be unloaded/re-loaded back into Premix Steady State. If it won't stay in Premix Steady State, then something needs to be done. HINT, HINT: It's most likely NOT anything to do with the Mark*--it's something wrong with the combustion hardware (fuel nozzles; combustion liners; etc.) that's causing the inability to get into and remain in Premix Steady State. If gas fuel supply pressure is unstable, it could be the gas fuel supply pressure. If the grid frequency is unstable, it is mostly likely the varying turbine/axial compressor speed and air flows that are causing the inability to get into/remain in Premix Steady State. Plugged fuel nozzles could also be the problem--but these things are NOT under the control of or caused by the Mark* (contrary to (false) popular opinion).

Well, there has been LOTS of data over a couple of decades from damaged combustion liners due to long periods operation in Extended Lean-Lean, and GE has changed their recommendation about Extended Lean-Lean operation. When operations/ownership were told that it wasn't recommended to run long-term in Extended Lean-Lean their first reaction is always, "The Mark* didn't shut the unit down, or trip it, and it allowed the unit to continue to operate! It's not our fault the combustion hardware was damaged--it's that damned Mark*'s fault!"

My suggestions would be to schedule DLN tuning at the earliest possible convenience. The unit should be shut down prior to the DLN tuning, the emissions monitor system should be calibrated or its calibration should be verified, and the LVDTs of the gas fuel control valves and the IGVs should be checked for accuracy of calibration, and re-calibrated if necessary. If the servo currents of the valves/IGVs are not balanced during verification/calibration then the polarity of the servo currents should also be verified and corrected if necessary. (I would also recommend an off-line compressor water wash be performed at this time; can't hurt anything.) Hopefully the gas fuel is clean and there aren't any liquids entrained in the gas which are condensing in the fuel nozzles (because of the pressure/temperature drops across the valves and fuel nozzle orifices).

THEN the unit should be re-started and loaded to Premix Steady State, and tuned for operation throughout the range of possible operation. This can take as much as 4-8 hours, or as little as 2 hours. It all depends.

It's really impossible for us to just look at some values and say the unit is or isn't operating correctly. We would also need to know what the emissions (NOx and CO and O2) are doing when the unit IS in Premix Steady State. But, really, I think you should have the unit tuned before anything else. Because, the tuner is going to be able to spot issues and make recommendations based on what he/she sees while doing the tuning--things we can't see or know over the World Wide Web.

Hope this helps!

Please write back to let us know what you find and how you succeed in resolving the issue and getting the unit to reliably transfer into and remain in Premix Steady State.
 
MBA,

If the unit is transferring to Premix Steady State and the only thing that happens is flame is detected again in the primary combustion zone then it's highly likely that there is some kind of ignition source--other than the spark plugs--in the primary combustion zone. Impurities in the gas fuel can collect on fuel nozzle tips and get very, very hot, and will stay very hot during the Lean-Lean-to-Premix transfer. If the build-up is hot enough to ignite gas fuel when it is reintroduced to the primary combustion zone after diffusion flame has been extinguished during the combustion mode transfer then the Mark* will fire the plugs to try to establish flame in all the primary combustion zones--and annunciate Extended Lean-Lean is active (if the TTRF/TTRF1 is above the transfer temperature).

There have also been reports of the tips of high energy ignitors (the "spark plugs" used in DLN-I machines) not being set at the proper insertion into the combustion can (allowing them to protrude too far into the combustion can), causing the tips to be so hot that they will ignite fuel in the primary combustion zone when it is re-introduced during the combustion mode transfer.

If the spreads are low (as you say) and don't increase during the transfer, then it's pretty likely there's some kind of ignition source that's causing the fuel reintroduced to the primary combustion zone to ignite into a diffusion flame during the last stages of the Lean-Lean-to-Premix combustion mode transfer. The likely culprits are deposits on the tips of the primary fuel nozzles from impurities in the gas fuel (gas compressor lubricating oil; diesel; gasoline; natural gas liquids; silica--have ALL been found in natural gas these days because suppliers are NOT spending much if anything to make their gas clean because they feel like the price is too low already and they don't want to invest any more when their profit margin is "low").

I don't fully understand this statement: "...Flame extinguishes at primary zone successfully and as we estimate load is decrease. During the increase of load (as result of primary zone fuel injection), after second the flame detectors detect the flame at primary zone...." If everything is working correctly, there shouldn't be any appreciable drop in load as fuel is shifted from the primary combustion zone to the secondary combustion zone during a Lean-Lean-to-Premix transfer to extinguish the diffusion flame in the primary combustion zone. Neither should the load start to increase when fuel is re-introduced to the primary combustion zone during the late stages of the combustion mode transfer. If this is happening, then it would seem something is amiss with the gas fuel splitter valve, and/or the gas transfer valve, or the fuel nozzle orifices in the secondary (and/or transfer nozzle tips) are plugged ("choked"). If everything is working properly from a control standpoint AND the fuel nozzles are clean and clear then the fuel flow-rate from the primary combustion zone is just shifted to the secondary combustion zone--same fuel flow-rate, so same load!--and then a portion is shifted back to the primary combustion zone.

I would suspect if the secondary/transfer orifices were plugged that would also show up in emissions readings when in Premix Steady State.

And, if they are plugged, then it's likely there is some kind of blockage in the primary fuel nozzles orifices--which could be building-up on the tips of the primary fuel nozzles, getting hot, and igniting fuel when it is reintroduced into the primary combustion zone.

It's possible the Gas Splitter Valve LVDTs are not calibrated properly and this could be at least part of the reason for some of the issues you describe. If the Gas Fuel Skid has a Gas Transfer Valve and it's LVDTs are not calibrated properly, this could be part of the problem, too. (Some newer GE-design heavy duty gas turbines have what's called an Independent Gas Control Valve arrangement, with four gas valves, one serving as the SRV, one as the Primary Gas Control Valve, on as the Secondary Gas Control Valve, and one as the Gas Transfer Valve (if the unit is configured to have a gas transfer system. Older turbines had the combined SRV/GCV assembly and a Gas Splitter Valve to direct the output of the GCV to either the primary or the secondary fuel nozzles. And some of these older units came with a Gas Transfer Valve which redirected a portion of the secondary gas fuel flow to a set of transfer passages/orifices on the secondary fuel nozzles during a Lean-Lean-to-Premix transfer. It would be extremely helpful to know which gas fuel system is used on the turbine at your site.)

And, sorry for not seeing your entire post the first time I read it and responded. I am not always seeing entire Control.com posts sometimes, not always, but more often then it should be happening (which is never).

Finally, is there a reason you disable IBH?

Several of the things you describe are not normal; load swings during Lean-Lean-to-Premix combustion mode transfers should be almost imperceptible, if not very small. I don't understand the descriptions you used (" about the load when the failure occurs. As temp=15 C and h=200m the load is between 80-85 MW.")

IBH is required to have a larger band of Premix Steady State operation--meaning with IBH active, it should be possible to get into Premix Steady State earlier (at a lower load) than without IBH active. And, also, with IBH active it should be possible to remain in Premix Steady State longer (to a lower load) than without IBH active. In other words, and these are just example values, without IBH active the usual load range for Premix Steady State is around 80-100% of rated load--meaning the unit won't transfer into Premix Steady State until load is up around 80%, and will transfer out of Premix Steady State when unloading at slightly less than80% of rated load.

With IBH active, the unit might transfer into Premix Steady State at loads around 40% of rated, and should remain in Premix Steady State all the way up to Base Load. When unloading the unit it should stay in Premix Steady State until slightly below 40% of rate load with IBH active. This "widens" or enlarges the available band of operation while in Premix Steady State, from approximately 80-100% to approximately 40-100%--which is a large improvement in the range of low-emissions operation.

So, it would be interesting to know why IBH is not active and what would happen if it was active....

Anyway, hope this helps!
 
MBA,

Another thing--which may or may not be applicable, since we don't know very much about the equipment at your site--is that there were some GE-design heavy duty gas turbines which were sold without gas transfer valves or without the capability of transfer passages/orifices in the secondary fuel nozzle assemblies. Many times when these units transferred from Lean-Lean to Premix Steady State there was a very audible "roar" accompanied by a rise in the mid unit vibration levels. What was happening was there was a LOT of fuel being forced through the secondary fuel nozzle passages (because there was not transfer system/nozzle/orifices) and that caused some dynamic pressure pulsations in the combustors. When possible, GE tried to sell/install IBH on these units--because they would try to transfer into Premix Steady State at lower loads--meaning lower fuel flow-rates, meaning less fuel to force through the secondary fuel nozzles. In fact, on some of these units with IBH it was NOT possible to disable IBH without forcing it off (using logic forcing).

Based on the information provided, I have to believe there is something amiss with DLN tuning--and the possibilities for that are numerous and some have been described above. It also seems like there is some unnatural ignition source in the primary combustion zone which is igniting the gas fuel introduced to the primary combustion zone after primary diffusion flame has been extinguished. Again, this is based on the information provided. What you are describing is not normal operating behaviour, and it's not normal for machines with DLN combustors to be re-started after maintenance outages without some kind of DLN tuning.

And, another thing about units with DLN combustors is that if the site experiences high and low ambient temperatures (based on the nameplate rating of the gas turbine) then it's very common for sites to also have to re-tune when ambient temperatures start falling to near expected lows as well as when they rise again to near expected highs. This is because the amount of air flowing through the axial compressor will change with temperatures, so large temperature changes can mean higher or lower air flows which may affect emissions without re-tuning the DLN combustion system.

Hope this helps! Again, it is strongly suggested that you get a knowledgeable and experienced DLN tuner to site, or someone who has access to very good remote tuning expertise and assistance, and work with that individual to tackle the issues you have raised so as to restore reliable low-emissions operation over a normal range of operation (approximately 80-100% without IBH, and approximately 40-100% with IBH)--while maintaining emissions at proper levels and steady-state operation in Premix combustion mode. The liner damage you mentioned is highly indicative of prolonged operating time in Extended Lean-Lean combustion mode--something which is not recommended and which should be avoided to prevent damage to combustion liners such as you have already witnessed.

Hope this helps! Please write back to let us know how you succeed in your efforts to restore normal, reliable operation.
 
Hi CSA

Thank you for your reply and I apologize for the delay.

Does the unit have IBH (Inlet Bleed Heating)? Is it in operation when it has trouble getting into and remaining in Premix Steady State?

The Unit has IBH but it is not available, so it is not in service

What is the grid frequency--in other words, how stable is it when operating the unit and trying to get into and remain in Premix Steady State?


the grid frequency is stable


What are the exhaust temperature spreads? (TTXSP1, and possibly TTXSP2 and TTXSP3)?


22,18,17


What alarms are being annunciated prior to and when the unit automatically transfers to Extended Lean-Lean?

Normal combustion primary zone auto reignition

What is the value of TTRF (or TTRF1) when the unit is having trouble getting into and remaining in Premix Steady State?

1083

Have you tried manually loading the unit up from Lean-Lean combustion mode and letting the Mark* complete the transition into Premix Steady State--and waiting to see what happens (WITHOUT enabling Pre-Selected Load Control!)?

Yes, we load the unit manually, around 81 MW the unit get in to premix-steady state mode but after 1-2 hour it gets back into Extended lean-lean.
Further, as fuel changes (and it does!) over time, the emissions will also change.

Gas Fuel Control Valve (GCV; GSV; etc.) LVDT calibration can also play havoc with DLN tuning over time. If not done correctly small changes in feedback scaling can have large changes in combustion stability and emissions levels.

The unit has GCV 1,2,3 and SRV. all gas control valves are calibrated automatically.

  • The fuel nozzles (primary & Secondary) have been serviced.
The compressor washing has been done.
I don't fully understand this statement: "...Flame extinguishes at primary zone successfully and as we estimate load is decrease. During the increase of load (as result of primary zone fuel injection), after second the flame detectors detect the flame at primary zone...."

I mean that the premix process is done properly, and the flame is removed from the primary area after it is transferred to the secondary area. There is no problem. And the unit goes into premix steady state mode.

This condition occurs in the preselected mode and is about 81 MW. After this event, if even one megawatt is added to the unit load, the bearings 2 vibration (due to the combustion chambers vibration) increase, and the unit exits the premix.

Another thing--which may or may not be applicable, since we don't know very much about the equipment at your site--is that there were some GE-design heavy duty gas turbines which were sold without gas transfer valves or without the capability of transfer passages/orifices in the secondary fuel nozzle assemblies. Many times when these units transferred from Lean-Lean to Premix Steady State there was a very audible "roar" accompanied by a rise in the mid unit vibration levels. What was happening was there was a LOT of fuel being forced through the secondary fuel nozzle passages (because there was not transfer system/nozzle/orifices) and that caused some dynamic pressure pulsations in the combustors. When possible, GE tried to sell/install IBH on these units--because they would try to transfer into Premix Steady State at lower loads--meaning lower fuel flow-rates, meaning less fuel to force through the secondary fuel nozzles. In fact, on some of these units with IBH it was NOT possible to disable IBH without forcing it off (using logic forcing).



When we get out of the premix, we experienced this kind of roar in combustion chambers area plus increased vibration in the bearing no. 2, but in our turbine, there is transfer valve.

thanks a lot
 
MBA,

Most sites with DLN combustors have an emissions monitoring system (often called a CEMS--Continuous Emissions Monitoring System) which is used to ensure that emissions do not exceed guarantee (which can often result in civil and/or criminal penalties, including jail time in some parts of the world--yes, jail, as in prison). The emissions levels are very good indicators of the "health" of the DLN combustion system, and so they are very useful in picking up on problems, both subtle as well as obvious.

You have described damage to combustion liners caused by improper operation of the DLN combustion system--for whatever reason, but most probably (based on the information provided) because of extended operation in either Lean-Lean or Extended Lean-Lean combustion mode. Simply because the Mark* doesn't trip the unit and allows it to continue to run when there are problems with the combustion system DOES NOT MEAN the unit should continue to be operated until the next planned maintenance outage. The Mark* gets a bad reputation because of all the alarms (Process and Diagnostic) it annunciates and because of the trips and troubles it gets blamed for--most of which are NOT the fault of the Mark*; it is simply reacting to the information and status it is receiving. If the packagers of the Mark* made it so that it would not allow unit operation for even simple issues its reputation would be even worse than it is.

The packagers made a conscious decision to allow the unit to operate with some combustion problems primarily to allow for data-gathering and troubleshooting--but also for periods or situations where the electrical power was needed for an emergency. They trusted that conscious and experienced operators and their supervisors would recognize when the unit was not working properly and would take appropriate action to resolve the issue(s) to restore proper reliable operation.

DLN units require periodic tuning; always have, always will. Sometimes, there is no changes required--but still, it's prudent and good practice to check to make sure things are working properly. Your unit "dodged a bullet" because the damaged liners did not rupture and cause much worse damage--but they could have. And that should be the reason to take corrective action now, rather than later.

You say IBH is not available. If it were my unit I would do whatever is necessary to make it available, and I would enable it prior to a START and gather data as the unit is loaded and transfers combustion modes. Why? Because, if the unit doesn't have a gas transfer valve--or one of the GCVs is not being used as a gas transfer valve (to send fuel to the transfer passages/nozzles on the secondary fuel nozzle)--that means when the unit tries to transfer to Premix at higher loads there is a LOT of fuel that has to go through the secondary fuel nozzles. And, based on the information provided--specifically you say that when the unit is going through a Lean-Lean-to-Premix transfer the unit drops load and eventually recovers load--there is something seriously wrong with the set-up or configuration or assembly of the combustion system and/or the fuel delivery system. Using IBH to get into Premix sooner, at lower fuel flow-rates, would be a good test of the system and its ability to get into and remain in Premix Steady State.

I would REALLY like to know how this works out for you, and how it ultimately resolved. Get someone knowledgeable and trained and with access to support and assistance to site to help with the problems. Because, the next time, the liners may crack and fail and cause very serious damage to the turbine section before they are replaced. There is nothing more I can, or am willing to, do. The unit simply is not behaving properly. We don't know what the emissions are when it is operating in Premix combustion mode.

The Mark has two ways of detecting primary zone re-ignition. The first is by the flame detectors--of which there are only four in the fourteen combustion cans of a GE-design Frame 9E heavy duty gas turbine. SOOOO, if the flame is ignited in the primary combustion zone of any of the combustors WITHOUT a primary flame detector then the Mark* won't know about it. The flame should propagate (spread through) the cross-fire tubes from cans with primary flame to cans without primary flame--and when the flame is established in a can with a primary flame detector then the Mark* will fire the ignitors (spark plugs) and change the fuel split to the Extended Lean-Lean value and annunciate the alarms you have listed.

The OTHER way the Mark* can detect flame in one or more primary combustion cans WITHOUT primary flame detectors is by exhaust temperature spreads. When a diffusion flame is burning where a premix flame should be burning the hot combustion gases from that combustor will be higher than normal, resulting in an exhaust temperature spread. Sometimes, but not often, the flame will not propagate (spread through) the cross-fire tubes into adjacent combustors, and when that happens the Mark* will fire the ignitors to try to reignite flame in the primary combustion zones to reduce the exhaust temperature spread. But, you have not described an increase in exhaust temperature spreads during the reignition, and have not listed Combustion Trouble as one of the alarms which are annunciated when the unit switches to Extended Lean-Lean. So, this probably isn't a cause--but data would be helpful....

There is one more possible cause of combustion trouble in DLN combustion systems, and that is what's called a lean blow-out. I have not personally experienced this issue, and there isn't a lot written about it on the World Wide Web. But, DLN combustion is a very delicate balancing act, especially DLN-I, and there are multiple ways for premix flame to be lost. GE actually has a lot of charts and diagrams and troubleshooting methods which can be very useful.

Get someone to site to help with this problem--before it gets really, Really, REALLY expensive. And, I'm not just talking about parts and labor, I'm also talking about loss of revenue (from the sale electricity and/or steam) when the unit cannot run. Rebuilding a turbine after a catastrophic failure in the turbine section can take months and millions of dollars--and that DOES NOT include the lost revenue from power- and/or steam generation!

Best of luck! Please write back to let us know how this is ultimately resolved. Fix the problem(s), or they will soon become much bigger problems with long-lasting effects.
 
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