One of the GE 6FA+e gas turbines has a problem of combustion humming caused by fuel pressure fluctuations during start up and unit trips from exhaust over temperature or sometimes flame out.Sometimes the fluctuations of fuel pressure are lower and unit reaches full speed no load without any problem.

we reduced the sensitivity of the fuel control servo valve from 2.7 to 1.95 and was ok for one start, but after a second start next day the same occurred with lower pressure fluctuations and without tripping of the unit.

Fuel and air filters are new. We've checked the IGVs and are constant, also the atomising air pressure is constant.

Any ideas? would it be a problem with the hydraulic fuel control valve?

frixos

 

Frixos,

My watch works sometimes and it doesn't work others. Sometimes it works for two minutes; sometimes it works for two hours; sometimes it works for two days. You can't see my watch.

What could be the problem?

How would you respond to my request for help? Would you begin by asking if the watch was a mechanical watch with a spring that must be manually wound, or it it was an electronic watch with a battery? Would you then ask if it was an analog watch (with a dial and hands) or if it was a digital watch with an LED display? Would you then ask if the watch had been wound recently, or if the battery had been recently replaced?

The point is: You would have to ask several questions in order to get enough information to be able to offer an opinion or some help. I provided very little information that was of help in my original request.

That's the situation with your request: You haven't told us what fuel you are trying to start the unit with (natural gas; distillate (liquid fuel); or?).

You haven't told us if the fuel supply pressure is stable or unstable.

You say the "filters" are clean, but you haven't said which "filters" (many people refer to the y-strainer upstream of the gas fuel control valves as a filter; it's not).

You haven't told us, for example, if you normally run the unit on gas fuel and are now trying to start the unit on liquid fuel, and it hasn't been started or run on liquid fuel for weeks or months or years.

You haven't told us how long since the last maintenance outage on the unit with the problem.

You haven't told us when this problem started--which is just about the single most important question when troubleshooting.

So, when you post to a forum like this for help you have to provide as much information as possible in your original post if you want a quick and concise response. Otherwise, you are going to be asked several questions about the problem you are experiencing just to get enough information to be able to offer a suggestion or a solution.

Try to anticipate the questions you might be asked. Remember the people you are asking know nothing about the plant where you work.

Also, you have mentioned that one of the 6FA+e turbines at your site is experiencing a problem. What is different about this unit from the other turbines? Or the way it's being operated?

Finally, one of the things that makes control.com so useful for so many people is that when a problem is resolved or a question is satisfactorily answered the original poster usually responds to let others reading the post the problem was solved or the question was answered--and if the information provided was useful or not. In the future when people use the 'Search' feature of control.com to search for problems similar to theirs they can find complete threads with indications as to what worked and what didn't work, making one person's question help MANY people. "Feedback is the most important contribution!"(c) here at control.com--and feedback comes primarily from the original poster.

Please write back with answers to the above questions and we can try to provide some helpful answers.