Flame Detector Thresholds in Combined Cycle IO Configurator

B

Thread Starter

bil07

HI

In the IO configurator the flame detector thresholds are defined as values for each detector level A and Level B. The diagram in the CSP (Flamepri) shows the switch for L28FDm as being between FD_n_HI and FD_n_LO.
Are the values of FD_n_HI and LO the count thresholds defined by Level A and B in the IO Configurator?
<<< Rung Number 55 >>>
the values of FD_n_HI and LO?????

<b>Moderator's Note:</b> PG9171E is a combined cycle gas turbine
 
bil07,

Yes; there was a lot of inconsistency in terminology between sequencing and the I/O Configurator, but, if I understand the question correctly Level A and Level B correspond to FD_n_LO and FD_n_HI, respectively (if I remember that version of PROMs correctly).

The two levels were primarily used to prevent false flame indications during Premix operation, when some combustion hardware arrangements caused the Primary Flame Detectors to "see" flame when there was none, resulting in nuisance combustion mode switches from Premix to Extended Lean-Lean.

HOWEVER, several sites have improperly used these settings to prevent combustion mode switches where there <b>WAS</b> actual primary zone re-ignitions. This resulted in more than a couple severe combustion liner failures because the unit actually had flame in the primary zone with ~80% of fuel in the primary and continued to remain in Premix combustion mode, which caused the liners to collapse.

So, if the unit has been running without problems and suddenly seems to be experiencing primary zone re-ignitions and the proposed fix is to change the flame detector intensity levels--be absolutely certain that the primary zone flame indications are false, and not the result of primary zone re-ignitions. If there is a true primary zone re-ignition, it will be accompanied by high exhaust temperature spreads. In fact, because there are only four combustors with flame detectors but primary flame can be established in any of the other six combustors before it propagates to a combustor with a flame detector the sequencing in the Mark V will switch combustion modes from Premix to Extended Lean-Lean on a high exhaust temperature spread, in an attempt to protect those combustors without flame detectors.

If the problems started after a maintenance outage, it's probably likely there is some issue with the flame detector mounting or positioning. It's possible to improperly screw the flame detector on the mounting tube, cross-threading the connection, and resulting in a slight misalignment of the flame detector. Also, it has been reported that immediately after replacement of fuel nozzles and some combustion liners that reflectivity in the liner is very high, and if the primary fuel split in Premix mode is lower than normal then the primary flame detectors will erroneously detect flame. The only "fix" for this is to run the unit for some period of time (usually on the order of a hundred hours or so...).

Hope this helps! If you're suddenly having flame detection issues on a machine that was previously running without any problems, please describe them here and we'll try to help. But, changing sensitivities is highly discouraged as a method of problem resolution, unless it is certain this is the proper fix (such as when new flame detectors with very high sensitivities are installed, such as when UV (Honeywell) flame detectors are replaced with Reuter-Stokes Flame Trakkers, or some other type of flame detector).
 
Perfect!!

Thanks CSA....I needed that conformation.

? What's your recommendation in replacing liners that has coating that is NON GE specific.

Right on!!!!!!
 
My recommendation would be to be as diligent as possible in making the salesperson provide as much information as possible about the coating--how it compares to the TBC provided by GE, why it's better than GE's TBC, what the benefits are versus GE's TBC, what the life expectancy/fired hour expectation is--and what the guarantee is versus GE's TBC. Just being less expensive isn't all you want to know (it may be all the sourcing and/or the owner want to know, but if you're the maintenance guy who has to take things apart when they fail prematurely you have other criteria to base your decision on).

I'd also be asking about references to see what others have experienced with the same or similar equipment and coatings. A lot to people find it very difficult to ask for and call/contact reference; until after there are failures/problems and then they learn about other similar problems. Ask for and contact references for things like this; it's also a great way to meet other people and share other experiences and best practices and such. Don't wait until after there's a problem.

Hope this helps. There are a lot of reputable suppliers out there who don't have the overhead or profit margins GE have, and can sell the thing cheaper--but it's the after-sales service and reputation you're most interested in when deciding to change vendors once you have confidence the item is comparable and will meet your needs.
 
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