Good Morning All,

I work for a CCGT operator in Europe, we have recently had GE undertake a DLN tuning procedure in line with some recent changes to control hardware.

We have GE 9FA+e with DLN 2.6+ combustion system

From the tuning report we have GE have highlighted that Peak 1 dynamics were a little high, in the order of 2-2.5 psi and 3 psi at certain load values (current ambient average approx 6 deg C). In order to bring those values back in line they have altered certain control constants - this is where my knowledge falls down. I have the constants they altered but would like to translate into some real meaning (i.e. english - bleed valve positions etc etc).

I previously worked for an OEM myself and would occasionally look at combustion dynamics issues but the combustors, whilst of the Dry low emissions configuration, were vastly different from these. For a start these are multi-fuel injectors and those previously worked on were single fuel injectors. As such I'm conscious that they may have different drivers/root cause.

So my questions is firstly, what are the following constants, or at least what do they relate to (i.e. bleed valves, firing temperature settings, fuel splits, etc, etc)

- FXKSG2_M_'x' ('x' being 0-4)

- TG2_SS_'y' ('y' being 0-5)

- PG2_SS_'z' ('z' being 0-5)

Secondly, is there anybody out there that has any experience on these combustor types that can tell me what mechanism is likely to drive peak 1 dynamics on these units. I appreciate what I'm asking here given that I have some experience in the area but I'm trying to narrow my search in some way, even just to be left with many other options. I can analyse the rest from there.

Thanks
TurboPower

 

TurboPower,

Understanding DLN Tuning (heavy emphasis on the 'tuning' term) means one really needs to understand the fuel nozzles, fuel nozzle passages (fuel flows out of more than one set of orifices in a DLN 2.6+ fuel nozzle, as well as from pegs around the body of the combustion can (the Quaternary "pegs"/nozzles), and combustion zones of the particular DLN system in use on the turbine. Tuning is the "fine" adjustment to the "coarse" adjustment which is the nozzle orifice sizing, the dilution hole sizing, the combustion liner head-end orifice sizing--none of which can be changed when the turbine is operating but all of which can have a large impact on dynamic pressures, dynamic pressure oscillations and emissions.

The Control Constants you listed are arrays, and arrays are usually used to define "curves" for defining how much fuel is to go to this set of fuel nozzles or that set of fuel nozzles (Primary, Secondary, Tertiary, Quaternary). By controlling how much fuel goes into each set of fuel nozzles the dynamic pressures and dynamic pressure oscillations (vibrations) can be affected to limit them to some extent.

But, assembly procedures, if not closely followed, and component tolerances (fuel nozzle orifice sizes; dilution hole sizes; etc.) can also have a large impact on operation and emissions, and changing Control Constants is only like a "fine" adjustment and can't be used to prevent or reduce pressures/pressure oscillations or control emissions in every case. Sometimes, it's just necessary to change combustion hardware and start the tuning process all over again (of adjusting the "fine" Control Constants to tweak pressures and/or emissions).

DLN combustors are very finicky and touchy systems.

I would expect that there is some kind of "longname" description of each Control Constant array in the application code (the .m6B file) or in the Control Specification for the unit(s). You should be able to use these, along with the 'Help' feature of Toolbox or ToolboxST (depending on which one your site uses) to understand which fuel splits are being affected and how. Without being able to see the application running in the turbine control panel at your site it's virtually impossible to say for certain what each array is doing.

As for "Peak 1" dynamics, I would also suspect that GE has some documents which you can obtain from them to help with understanding this week's flavour of combustion explanations. Just ask your CPM.

Hope this helps!

 

Dear TurboPower,

I attempted to search the control constants you provided in your post, with some controller files I have and did not come up with anything. I suspect your unit to be something of a newer vintage, possibly with more bells and whistles as far as the DLN2.6.

I wish I could provide more information, but GE is constantly changing their methods, and doesn't share or explain the information very well. But as CSA says the idea of the tuning is typically to move the split of fuel between certain nozzles to control the different dynamics. There may also be some tweaking done to control firing temperature to improve emissions. But the emphasis is usually always to control dynamics and prevent lean blow outs.
And lastly as you know this "tuning" is usually impacted most by changes in hardware and ambient temperatures.

 

Thank you for that gents,

Most informative as always!

My concerns primarily related to potential build issues since the HGPI, upon rebuild. I appreciate that variance in manufacturing and build tolerances, engine to engine, will obviously yield diffirng values of dynamics/emissions values - to what degree/magnitude I'm uncertain as my experience with this burner type/combustion system is limited. As the values sat at 3 psi up from a nominal ~1psi reading post HGPI, pre latest DLN tuning, I was concerned that simply 'tuning' may be hiding the root cause for these oscillations.

A difficult one to judge as being in the position of the OEM I have made such alterations based on experience and judgment but more difficult to assess without the proper specific experience - I'm back to asking questions based on first principles I'm afraid.

A GE controls engineer confirmed the control constants later yesterday and I have a call with the tuning engineer later next week. I'm not suggesting there is anything untoward I would simply like to establish a better understanding of both the equipment, combustor types and associated intricacies.

I think I have some 'bed time reading' to be doing on the combustion system, if I can obtain some decent material that is.

Thanks again gents!

 

FSX/MIKEVI,

I have been on a couple of root-cause analyses lately of DLN-I units with combustion issues and I have been very surprised at the forthcoming attitude of GE when asked for more information about tuning and failure modes; I have to say, it was rather refreshing though surprising. They provided some "canned" PowerPoint presentations about failure modes, and when asked for clarification and further information they were quick to respond, though it was mostly spoken (conference calls) and email--not much in the way of GEHs or GERs or GEIs one could refer to or study or give to others to refer to or study. (Some things don't change, it seems.)

Hopefully, FSX, you can get some good information from your discussion with the tuner, and possibly some failure mode PowerPoint presentations. (I caution you about the .ppts, though, that they can be superficial and make a lot of assumptions about the reader's knowledge and understanding of DLN principles and combustor design and construction. At least in my recent experience, though, when pressed for clarification and more information GE did respond in a timely manner, but with not much more.

 

Sorry; I meant to be addressing TurboPower, not FSX, in this thread....

 

CSA,

Managed to get a quick phone call from the tuning engineer late on yesterday. A very generic conversation to begin with with graduating levels of more helpful information as the discussion continued. It was agreed that he would look into the situation further for a compare and contrast, pre and post outage, of two identical units. I appreciate there will always be differences it's a basic cross reference to see where we sit - an order of magnitude of sorts.

I had made an informal inquiry as to some documentation and information on such issues and/or diagnostics reference but his reply was that he was unaware of any such information - I was kind of expecting that reply in all honesty. Would you happen to know what may be the best department/facility to contact so as I may be able to prompt our GE on site rep to pursue? Is there a title for this presentation that I may reference?

As always your help and advise is appreciated.

TurboPower

 

TurboPower,

The presentations I viewed were for DLN-I problems; I am only presuming there is something similar for DLN 2.6e systems. The presentations I saw were breakdowns of Fishbone diagrams for explaining various DLN-I problems--cause and effect explanations.

I would have to believe your CPM has access to the vaunted GE PAC and their database of problems and resolutions as relates to DLN 2.6e systems.

I'm not presently aware of any specific publications (it's well known that GE doesn't document things very well) and was only hoping that something similar to what I'd seen for DLN-I systems had been done for DLN 2.6e systems.

Ask your CPM if he can obtain anything from the PAC or the Remote Tuning Center regarding Fishbone diagrams or cause and effect explanations for DLN 2.6e combustion dynamics.

Sorry I couldn't be more help, but the litigious nature of OEMs these days prevents outside parties for retaining Corporate documents without NDAs (Non-Disclosure Agreeements) so I can't retain anything I'm allowed to see without fear of reprisal.

 

CSA,

Sorry for the delay in the reply, I've been waylaid.

Not to worry, appreciate a point in the right direction nonetheless. I'll prompt my CPM and revert to conclude the post if and when I receive something.

Regards
TurboPower