GT Losing power Frame 6B from 33MW to 22MW at Base Load

M

Thread Starter

Mambo

Hello Fiends,

I have come to a Gas Turbine side where I am told that the output of turbine has gone down from 32 MW at Base to 23 MW Base load.

I need suggestion for improvement. One thing I am also told that the BTU of Gas is at present 650BTU earlier it was over 1500BTU. Does this make any difference on GT Load?

Thanks
Mambo
 
The reduction in heating value of the gas fuel most definitely makes a difference! If this is a "permanent" change, you will need to contact the turbine supplier to find out what is required - likely new fuel nozzles and SRV and GCV trim, along with revised control settings. You may also be risking damage to the combustion liners since the control valves are likely wide open and you are getting a higher delta-P across the fuel nozzles than they were designed for.
 
MAMBO,

Where you brought to site to help with the performance problem?

Yes; a drop in BTU content would definitely cause a drop in performance. BTU is a measurement of the amount of energy contained in a material. However, it's surprising that the turbine could be started (reliably and without a lot of "tweaking" and effort) with such a drop in energy content. Getting a unit to start and run on low BTU content fuel can even cause internal damage to the hot gas path components (nozzles, liners, transition pieces, turbine nozzles and -buckets, and exhaust components).

If the unit is running at Base Load (BASE LOAD selected and enabled) and the unit is running on low BTU gas fuel at the required supply pressure and P2 pressure then it's likely the GCV is at, near or above 100% open as the Speedtronic (you didn't say which turbine control the unit has) will be trying to put as much fuel into the unit as possible to try to make the actual exhaust temperature equal to the exhaust temperature control reference and because the energy content of the gas is low, then the actual exhaust temperature won't be near the reference.

If the Mark is a digital version (IV, V, VI or VIe) then you should be able to look at the exhaust temperature reference and actual exhaust temperature and see if the two are the same or different when Base Load is selected.

Without a LOT more information, we can't be of much help. There are MANY things which can cause a loss of performance (and they have been covered in MANY previous posts on control.com, available using the 'Search' feature of control.com). But, certainly, low BTU content is one of them. You likely won't be able to remedy low BTU content unless there is some kind of gas treatment system (which wouldn't likely be a part of the typical gas turbine control system) present that isn't working properly. The fuel nozzles and control valves are sized for a fuel with a particular energy content (range) and the type of change you are referring to is pretty certain to be outside of the range of normal operation.

Best of luck with your problem!
 
Dear CSA and Otised,

Thanks for your valuable answer to my question.

I am here to solve this problem.
I have noticed following parameters

Base Load selected

TTRXP = 585 DEG c
TTRXS = 511 DEG C
TTRX = 509 DEG C
TTXM = 502 DEG C
CTIM = 34 DEG C
FSR = 72
CTD = 355 DEG C
FPRGOUT = 242 PSI

Please verify what Mr. OTISED mentioned in his reply, yes gas valve are 100 %fully open; and if changing trim of valve will help solve this problems or kindly suggest best solution. bringing in super seeded fuel nozzle will help?

Unit has MK V Speedtronics

Thanks once again for your valuable information.
Mambo
 
Dear Otised,

Thanks for your valuable opinion on this situation. What are the settings to be changed, we will get new fuel nozzles and GCV/SRV trims, but what factors we will take care about?

Kindly advice more about settings and changes.

This is a frame 6 Machine with MKV speedtronic
I can provide more data as required.
Thanks once again for valuable info sharing

Mambo
 
MAMBO,

The data you have provided shows that while Base Load is selected, the Secondary Exhaust Temperature Control Reference (TTRXS) is lower than the Primary Exhaust Temperature Control Reference (TTRXP). This is probably because the BTU content of the fuel is much lower than expected (for the fuel valve internals and fuel nozzle construction) and the GCV is wide open.

Also, from the data the actual exhaust temperature (TTXM) is less than the exhaust temperature reference, likely also a result of the low BTU content of the fuel.

The kind of information you are asking for is usually part of a paid engineering study provided by a knowledgeable firm with considerable engineering resources able to determine fuel valve internals ("trim") and fuel nozzle orifice area. Some very low BTU gas fuels require a second "set" of nozzles and a valve to port flow to the second set of nozzles.

But, it's not likely you're going to get the information you seek from a free Internet forum. And, if you did, it would likely be questionable, anyway. You would need to spend some time verifying any information provided to be safe when it comes to operating the turbine long-term with no ill effects.

Best of luck with your project!
 
Mambo,

The settings likely to change are those for the SRV P2 control and the various FSR constants (minimum, maximum, and others).

I cannot tell you what the new settings will be - you will need to get them from GE, after you have provided a current fuel analysis. They will feed the pertinent data into a computer and it will define what hardware (valve trim, fuel nozzles, etc.) and software changes are required, along with a price for all this. (You may not like the price!)

This is not a minor change. Based on the heating values you provided in the initial question, you will need to get more than twice the flow of the new fuel as compared to the original fuel for the same power output.
 
Dear Otised,
Thanks a lot for your valuable reply and I hope the things mentioned will be followed and taken up by higher management.

I will keep posting/updating on this link until we bring up this unit back to normal.

Thanks
Mambo
 
Dear CSA,

Thanks a lot for your valuable information. The points you have mentioned will be reviewed by upper management and will be actioned in proper way. I will keep posting/updating this link until we bring this unit back on line to normal.

Best Regards,
Mambo
 
Dear CSA and all friends..

This is to inform that...

Finally all the issue on this Fr 6B turbine are solved and the unit was commissioned couple of days ago.

It took long time for us. Work was delayed mainly due to unavailable of right spare parts

We had the Gas valve trims replaced - specially for SRV. Raised P2 pressure FPKGNG constant and P2 is higher then before ie, 20 bars, also adjusted Temperature curves. New Fuel nozzles were specially designed with bigger holes by renowned engineering company, running parameters - TTXM=550, TTRXP=551,TTRXS=570, TTRX=550 Deg C, FSR=74.5%, Dwatt = 32 MW, CTIF = 32 Deg C

Thanks to all persons who commented and provided reply to my questions.

Best Regards
Mambo
 
Mambo,

Many thanks for the information--and congratulation for resolving the issue! I'm sure the Customer is extremely happy.

That was quite a large change in heat content, and if the Customer is going to be experiencing changes in heat rate over time, it might be good to look into a scheme that can automatically adjust P2 pressure reference and to a certain extent exhaust temperature control to optimize turbine performance without endangering the machine. GE calls these two options "sliding P2 pressure control" and "wide Wobbe Index control." It's not cheap, but it sure does make handling different fuels over time a lot easier.

Again, thanks and congratulations!!!

 
Mambo,

Wow, good to know your problem is solved.

Thanks for your feedback to know everybody what you have done (this is more important in this forum)

TTXM=550, TTRXP=551, TTRXS=570, so primary cure is matching with reference temperature.

Thanks again and good update.

Take care
G.Rajesh
 
Dear CSA,

Thanks for the info, these questions were asked by customer and I have asked back to the Engineering firm who supplied the modification.

Cheers
Mambo
 
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