Frame-V Gas Turbine Flame Detector Bypassed


Thread Starter


frame-V gas turbine, running in NG fuel with HSD stand by. there is HRSg also with supplementary firing on need basis (on average daily 3-4 hrs). The flame detection signal L28FDA is bypassed/forced.
my question is

1. what may happen if actual flame gets out?

2. what may be the worst effect before turbine tripped in secondary protection like reverse power?

3. My another question is, say when there is supplementary firing ON in HRSG side and actual flame gets out, and NG gets into turbine and exhaust path without burnt. When released NG reaches supplementary firing flame area, flame will come back up to turbine blades and explosion may occur. Am I thinking realistic?

may please be enlightened.
This is probably one of the stupidest posts on the forum for a long time. Most of the big disasters on gas turbines that killed people were caused by Protection being jumpered. I'm not even going to start the analysis of what could happen (I'll leave it for CSA to jump in and do it). Work it out for yourself of what could happen if you get a flameout, you are just waiting for the big bang!

I, personally, have never seen a GE-design heavy duty gas turbine with a single flame detector--but I haven't seen every perversion of GE-design heavy duty gas turbine ever made, either.

So, this is predicated on there being two flame detectors--redundant flame detectors, so that a unit can run with only one working flame detector. Even if the non-working flame detector is intermittent ("flickering").

And, it's also an especially bad idea if there are high exhaust temperature spreads at the same time. Because, there are only two flame detectors in two of the ten combustors. And, high exhaust temperature spreads can mean the flame in one or more combustors is already questionable--and if the combustor experiencing the problem is the one with the intermittent flame detector signal then things are bad to begin with because the flickering could mean the flame in that combustor is already unstable and 10% of the fuel flowing into the turbine is already flowing into that combustor and into the exhaust. And, if it's another combustor with flame instability that's got problems--one without a flame detector--then that's still seriously bad.

However, forcing a non-working (flickering or failed) flame detector of a redundant pair to a logic "1" is <b>SERIOUSLY</b> begging for trouble. If the other flame detector were to fail and there truly was a loss of flame the turbine control panel would NOT shut off the flow of fuel. And especially if there is auxiliary firing in the HRSG.

And when I say "begging for trouble" I mean that one is just ASKING for a catastrophic failure. Especially under the conditions suggested.

To answer the specific questions:

1) Presuming that a loss of fuel flow was not the cause for the loss of flame, fuel will not be shut off, because one flame detector is forced to a logic "1" and the turbine control system can't distinguish between a true logic "1" and a forced logic "1". About the only reason flame could be lost in all the combustors without a loss of fuel flow is excessive NOx or Power Augmentation Steam Injection flow-rate, or some non-detected bobble in IGV angle or some serious restriction of fuel flow-rate that didn't actually shut off all the fuel flow but reduced it so far that flame was lost but fuel was still flowing.

2) It will take some time (a fraction of a second at best, and a second or two at worst) on actual loss of flame for the reverse power relay to operate and open the generator breaker. And, reverse power relay operation <b>DOES NOT</b> trip the turbine, so fuel will continue to be flowing into the turbine and exhaust even if the generator breaker opens on reverse power.

3) There's going to be a pretty big explosion, and not just in the turbine--but also in the exhaust/HRSG. And, fuel will continue to flow into the turbine and exhaust until the turbine control system detects an exhaust overtemperature, or a high "vibration" or something similar.

The post itself isn't so bad, but if this is a real situation--that is stupid. And the supervision that made this decision should be demoted, or worse. This just speaks volumes about the lack of training for operators and operators who become supervisors and managers. And it ain't good speak, either.

Again, if there are two flame detectors the turbine can run with only one--and it's a really, Really, REALLY, <b>REALLY BAD idea</b> to force a non-working flame detector--even if it's flickering. Seriously bad idea. <b>SERIOUSLY BAD IDEA.</b> As in, you don't want to be anywhere near the unit and HRSG when it's running.

Everyone reading this hopes this is just a hypothetical question. We REALLY hope it's just a hypothetical post.
Dear CSA, glenmorangie and Dear All,

I <b>really do hope</b> that it's just a hypothetical question and I <b>really do hope</b> it's not a true situation.

Dear All,

Thank you for your valuable guidance. The situation is actual. It is not in my scope to comment on the higher management's decision.

Regarding stupidity, nuclear fusion & fission, dynamite, High voltage electricity, don't you think these are also responsible for several catastrophic outcomes?

Are all of them really stupid? If yes then we are also stupid no doubt.
What I mean is, time and situation is the key controller.
It may not within your scope to comment on higher management's decisions but I still think that you should at least make them aware of the serious risks that they are taking. I'm sorry if using the word stupid was offensive to you. But to jumper major protection, especially Flame Detectors, is really very dangerous and is indeed stupid of higher management to force someone to do this!
Barindra75... you must advise someone in authority about what you have observed!

You, your fellow workers (including management) visitors, people in surrounding communities, etc, are in a very, very, very precarious situation!

I suggest you search Archives for flame-detectors, flame-eyes, and the like. Specifically:

o http://www.Control.Com/thread/1026148686

o http://www.Control.Com/thread/1307045968

o http://www.Control.Com/thread/1366228921

o http://www.Control.Com/thread/1434478016

Phil Corso