Dear CSA,
We have gas turbine frame 9. E
Fuel is light crude oil.
Our problem is during normal shutdowns and after the generator breaker opened and RPM is going down sometimes when the speed reaches 1600-1700 RPM, an alarm comes ( turbine trip by loss of flame ), as happened in the last two normal shutdowns not as before the flame had gone at 1200-1300 RPMS . And sometime normal shutdown is going smoothly.
please, could you help us.
Regards.

 

What other Process Alarms are active when the machine is going through a shutdown sequence? (List ALL Process Alarms, even if you think they might be relevant!) If the machine has a Mark* turbine control system, what Diagnostic Alarms are present when the machine is going through a shutdown sequence? Alarms ARE very important, contrary to popular (and false) belief. Sometimes the alarm text messages can be cryptic, but unless they are erroneous alarms (caused by bad sensors and/or wiring issues), but that doesn't make them any less meaningless.

Has the ambient temperature (the temperature of the air entering the axial compressor changed from when the shutdown was working correctly until now?

Have the exhaust temperature spread(s) increased both:

- while online and producing power
- during shutdown prior to the flame-out

How long has it been since the last maintenance inspection was completed? Immediately prior to this flameout problem starting? Or weeks or months prior?

The most likely cause--as will be shown clearly if exhaust temperature spreads increased recently, especially during shutdown--is liquid fuel nozzle passages/orifices being plugged, or one or more liquid fuel check valves are failing or have failed, or if the machine is a dual fuel (natural gas and distillate) one or more of the purge check valves are failed or failing. Another potential cause might be low liquid fuel forwarding pump pressure, or problems with high-pressure liquid fuel pump or the liquid fuel pump clutch or clutch coupling, though the latter is less likely if the machine runs fine at rated speed and on load.

You want help. We need answers. Liquid fuel problems are not as difficult to find and resolve as are gas fuel problems--because there are individual fuel lines supplying fuel from the liquid fuel flow divider to each combustor. (Gas fuel systems are supplied from a common manifold which makes individual problems much more difficult to find and resolve--especially problems with high exhaust temperature spreads.)

If the machine has a Mark* turbine control system it is recommended you set up a trend recording of individual exhaust temperatures as well as exhaust temperature spreads and start it just prior to breaker opening during a shutdown and let it run through the shutdown sequence until after flame has been lost--either normally or prematurely. There should also be a Trip History Display function on the operator interface which can provide some (limited) help with this kind of problem, but it's better than nothing. It would be VERY helpful to have this information (from both sources) to pinpoint the issue as best as possible.

Alarms.

Recent ambient temperature changes

Exhaust temperature spreads (during normal operation and during shutdown (a good shutdown AND a bad shutdown would be really helpful)

Time since last maintenance outage

Trend data during shutdown (normal AND problem shutdown data is REALLY good for you and for us)

Trip History Data

If you want to take photographs with your smartphone and post them to the thread, PLEASE BE SURE THE PHOTOGRAPHS ARE CLEAR AND READABLE.

Give us the above information and you will probably be very surprised at the quality of the response(s) you may receive. Give us ALL of the requested information, and you WILL be surprised. And, even if you don't give us much if any information you have the most common problems to investigate and eliminate.

Remember: Troubleshooting is VERY OFTEN a process of elimination--which means when you don't know what the problem is or might be you need to make a list of the possible causes and then in a logical manner check each and every possible cause, eliminating the ones that aren't causing the problem, until you find the one that is. And, also remember: Sometimes problems can be caused by more than one issue, too. I know, that can be a little deflating and intimidating--but it's never impossible.

Go forth and conquer.

 

Dear WTF,
Regarding to Trip History Trend,
as you know that atomizing booster compressor is started during shutdown at speed 60% ( about 1800 RPM ), and in our GT-2 normal shutdown, the atomizing pressure ratio AAPR was 1.2 before RPM reached 1900 - 1800 then after starting of atomizing booster compressor suddenly AAPR increased to 1.8 in 7 seconds then GT-2 tripped by loss of flame at 1700 RPM
and by comparing this status with with same normal shutdown of GT-1 ( another turbine ) atomizing booster compressor started at speed 60% AAPR was 1.2 then during 7 seconds AAPR increased only to 1.3 ( no loss of flame happened at 1700 RPM
only flame out happened at 1300 RPM as usually.
our question is : Is sudden increase of AAPR from 1.2 to 1.8 NORMAL?

 

To answer your question: It would seem that such a sudden increase in AAPR could blow the flame out, particularly since fuel flow is low and decreasing during shutdown.

Generally, the reason to start the AA Booster Compressor during shutdown is to try to prevent smoking (large plumes of white "smoke", which is really unburnt diesel fuel usually because of poor atomization). Usually there would be two or more combustors which flamed out (combustors without flame detectors) and the fuel would land on hot internal parts and vaporize instead of combusting, producing the billowy white plumes of "smoke").

I've never worked on a machine with pressure- or differential pressure transmitters to produce an Atomizing Air Pressure Ratio (AAPR). So, I have no actionable data of recorded pressures/ratios. But, I can tell you that an AAPR above approximately 1.3 while running at rated speed and some load was thought to be very high. I would have to look at the AA P&ID to understand how the AAPR could get so high.

This was a good catch. You're probably on to something. Use the AA P&ID to sort out how the AAPR could get so high. Although I would be VERY surprised if there was any information in the Operation & Maintenance Manual about AA pressure ratios at various speeds/loads, anything is possible. Another place to look is the NOTES section of the AA P&ID for some possible information about AA pressure ratios. Last, there might be something in the Control Specification for the machine provided with the Mark* turbine control system.

Please let us know what you find.

 

for your information, the normal AAPR of our gas turbine ( which working with light crude oil ) is 1.5 while normal running at rated speed ( 3000 RPM ) and loaded about 90 MW, and regarding to this ratio, in the atomizing system description there in only alarm in case AAPR reaches 1.8 but no trip ( during normal operation ), only trip if it is reached 1.05 ( very low AAPR ).
you can see the attached file ( atomizing P&ID ) as you would have to look at ( it will help )
we are waiting for your advise.
Thanks.

 

Thank you for at least one sheet of the AA P&ID....

I've reviewed and I don't see any obvious reason why the AAPR jumped to more than 1.5 (to 1.8, I think you wrote). All the GE machines I worked on with dual fuel (natural gas/distillate) had a bypass around the main AA Compressor to reduce AA pressure when running on natural gas. I only worked on one distillate/crude unit, and it was heavy (VERY heavy) crude. And it didn't have such sophisticated instrumentation as this P&ID indicates.

I would say that it was possibly an instrumentation error, BUT, the flame was lost (extinguished--by something, possible excess AA pressure/flow). I do see a 96VA-18 on VA18-1, along with a ZT. I'm unfamiliar with some of the new device numbering (what was wrong with the "old" device numbering which was used for 60+ decades, I ask?), but in my day a 96 device could be some kind of position transmitter (full stroke? open to close) and ZT was a limit switch (indicating one position (open or closed?)) so I'm not sure if VA18-1 is a "bang-bang" valve as it used to be (either open or closed) or is modulated with some signal from the Mark* VIe. I would guess VA18-1 is open when running on light crude, and closed when running on distillate, so flow would go through the orifice around VA18-1 only when running on distillate (because a lower AAPR is required for distillate than for light crude). VA22-1 is probably opened when the Booster AA Compressor is started and running during start-up, and is probably opened during shutdown when the Booster AA Compressor is used to reduce smoking.

I'm guessing--because I don't know what the state of VA18-1 is during shutdown (most likely closed because a normal shutdown happens on distillate)--that for some reason VA18-1 was closed and suddenly opened, and increased the AAPR when the Booster AA Compressor was started. That's just a SWAG (Scientific Wild-Arsed Guess). If you have data from 96VA18 and the ZT on VA18-1 that would help understand which might have happened.

But, everything else looks "normal" to me (other than the nomenclature being used for some of the devices).

Do you know what the state of VA18-1 is during shutdown, from 14HS drop-out? Is it open or closed, or does it close during at some point during deceleration? Does it change state at all during deceleration? The air pressure for the actuator most likely comes from CPD, and that is decreasing during deceleration. I think the "FO" designation on VA18-1 means "Fail Open, so if air pressure being used to keep VA18-1 closed dropped below what was required to keep it closed it would open (by spring pressure). This kind of suggests that the pressure regulator VPR18-1 might not be working properly. These small air pressure regulators almost NEVER get any attention, either to check the operation and setpoint or even just cleaning and replacement if necessary.

That's all I can see or suggest. VA18-1 suddenly opened and cause AAPR to jump and extinguish flame in a number of combustors--probably NOT because it was commanded to by the Mark* VIe, but possibly because of some problem with VPR18-1.

Please let us know what you discover.

 

Dear WTF,
Regarding to Trip History Trend,
as you know that atomizing booster compressor is started during shutdown at speed 60% ( about 1800 RPM ), and in our GT-2 normal shutdown, the atomizing pressure ratio AAPR was 1.2 before RPM reached 1900 - 1800 then after starting of atomizing booster compressor suddenly AAPR increased to 1.8 in 7 seconds then GT-2 tripped by loss of flame at 1700 RPM
and by comparing this status with with same normal shutdown of GT-1 ( another turbine ) atomizing booster compressor started at speed 60% AAPR was 1.2 then during 7 seconds AAPR increased only to 1.3 ( no loss of flame happened at 1700 RPM
only flame out happened at 1300 RPM as usually.
our question is : Is sudden increase of AAPR from 1.2 to 1.8 NORMAL?
Any update? After viewing your post, I started searching for the top online essay writing services to help me finish my essay writing assignment. While doing so, I came across this https://envirocitizen.org/ website which makes it easy for me to finish my essay writing assignment so that I can turn it in on time.

Any update?