Frame 6b Fuel Control Problem

D

Thread Starter

davidmcc

Hi all,

maybe someone has experienced this before and can advise. After short outage, compressor wash, boroscope, liquid fuel filter change. At FSNL machine started pulsating (accelerating/decelerating) and there was lots if white smoke. this was after firing and when beginning to accelerate so manually stopped. Next test was up to fire stage, everything stable, switching to auto, same thing happened. Tried adjusting FSR settings, made no difference. Any suggestions what to check?

Thanks n advance for any advice offered,
Dave
 
davidmcc,

How often does this machine start and run on liquid fuel?

Was the unit running on liquid fuel prior to the filter change?

White smoke coming from the exhaust of a gas turbine running on liquid fuel is the result of unburned fuel getting into the exhaust area and partially combusting. This happens when the flame in one or combustors is lost but fuel continues to flow into that or those combustors.

The most common cause for liquid fuel control valve instability is pockets of in the liquid fuel system piping--including the filter vessels if not properly vented after filter replacement. During firing and FIRE mode, the fuel flow reference is fixed, and it's likely that the flow isn't high enough to cause the air pockets to compress and expand repeatedly. But, when AUTO mode is selected the fuel flow rate increases as a function of turbine acceleration rate and the air pockets get into a resonant condition where they are uncontrollably contracting and expanding and causing great instability in both liquid fuel supply pressure AND flow and the liquid fuel control valve is trying to respond--and it's a big mess, resulting in the loss of flame in one or more combustors and white smoke.

Most GE-design heavy duty gas turbines with liquid fuel capability have liquid fuel forwarding skids with liquid fuel pressure regulators. They can exacerbate the problem of air pockets in the piping/filter vessels if not properly adjusted.

Some liquid fuel supply systems have high-point vents in the highest points in the piping and are pitched to allow venting of air. Many, unfortunately, do not. But if all that was done was to change liquid fuel filters then it's most likely air was introduced into the liquid fuel system and needs to be vented out. If the low-pressure filters were changed and not properly vented prior to starting, the air can move to the high-pressure filter vessel, where it needs to be vented. Start the forwarding pump, vent the low-pressure filter(s), then open the liquid fuel stop valve (as long as the supply pressure is less than approximately 60 psig (approximately 4.1barg)--which is kiss than the liquid fuel check valve cracking pressure) and then vent the high-pressure filter.

But, it's most likely NOT a control system or servo-valve problem. Most likely not; depends on oil cleanliness, servo-valve age/condition. It's most likely not a liquid fuel flow divider speed feedback problem, either, if everything was working properly before.

Please write back to let us know how you fare in resolving the issue and what you discover!
 
Hi CSA,

Thanks for your comprehensive reply. We found the problem to be a ruptured bladder in the fuel forwarding skid accumulator so there was no dampening when the fuel rate increased and the flow/pressure went into a wobble and we tripped the machine on the stop button as it sounded bad, the turbine and diesel starting engine sounded like they were accelerating and decelerating drastically. We replaced the bladder and everything went back to normal.

We have two of these machines so when the second one came out the following week, we checked the pressure in the bladder and it seemed ok. when the second machine was coming back it exhibited the exact same problem. Only problem is we only had one spare and we're getting quotes of 12 weeks.

Have you any info on a vendor that might have a stock of these? we think our spare came from Ansaldo Thomassen, we don't have a GE part number but the packaging had OLAER brand name on it.

Thanks again for your help.
 
davidmcc,

Thanks for letting us know what you found!!!

I am finding more and more that some hydraulic service suppliers have excellent capabilities when it comes to supplying parts or equipment that meet or exceed OEM spec's--and can even fabricate components (possibly such as bladders). Check with your local preferred provider of hydraulic parts and services; even if they can't help you directly they may be able to refer you to a company who can.

Let us know how you fare.
 
Hi CSA,

Thanks for your advice. We have a couple of problems with a local non-oem solution. We don't have a spec/dimensions etc. We would have to go through our management of change which might take longer than the OEM delivery time of 12 weeks! Anyone who could advise where I could find a spec, that would be much appreciated.

Thanks,
David
 
Top