After a trip on "compressor operating limit max control error". unit is not starting up on liquid fuel and trip each time on loss of flame.
Activities performed: checked pressure upstream liquid fuel stop valve ok at 50psi. checked pressure on atomizing air booster line around 6 to 7 psi at startup, replaced flow divider, liquid fuel check valves and finally liquid fuel bypass is responding. despite all this during startup unit still tripping on loss of flame. can anybody advise on the issue unit is now running on gas fuel.

 

Okay; it's tripping on loss of flame.

<b>When is it tripping on loss of flame???</b>

After warm-up is complete? During acceleration?

We also don't know what kind of Speedtronic you have and what kind of data-gathering capabilities you may have.

Are you saying you never had problems starting on liquid fuel before the trip event?

Tell us exactly what is happening during firing, warm-up, and acceleration. When, exactly, is the loss of flame trip occurring? At what speed? What is FSR at the time the flame goes out?

Have you looked at the Tell-tale Leak-off to see if any of the Liquid Fuel Purge Air check valves are leaking?

Have you tried switching to liquid fuel at FSNL?
If you have, have you shut down on liquid fuel and tried re-starting on liquid fuel?

What were the individual fuel pressures as read from the Manual Selector Valve during firing and warm-up? They should be within approximately 10% of each other. If not, then something is wrong.

But you haven't given us enough information.

 

CSA,
Here are some additional information

> Okay; it's tripping on loss of flame.
> <b> When is it tripping on loss of flame???</b>

Tripping on loss of flame just 30s after ignition FD_INTENSE 1 max at 140 and FD_INTENS 2 at 40 max then dropped before the trip and O on FD_INTENS 3,4.

> After warm-up is complete? During acceleration?

before warmup

> We also don't know what kind of Speedtronic you have and what kind of
> data-gathering capabilities you may have.

Speedtronic Mark V. B type

> Are you saying you never had problems starting on liquid fuel before the trip
> event?

No problem on liquid fuel before this one

> Tell us exactly what is happening during firing, warm-up, and
> acceleration. When, exactly, is the loss of flame trip occurring? At what speed?
> What is FSR at the time the flame goes out?

FSR is at 12.68% before trip. our firing FSR is 17.5%

> Have you looked at the Tell-tale Leak-off to see if any of the Liquid
> Fuel Purge Air check valves are leaking?

We did not check

> Have you tried switching to liquid fuel at FSNL?

Not wet but we are planning for a fuel mix.

> If you have, have you shut down on liquid fuel and tried re-starting on
> liquid fuel?

Initial shutdown was from gas.

> What were the individual fuel pressures as read from the Manual Selector Valve
> during firing and warm-up? They should be within approximately 10% of each
> other. If not, then something is wrong.

Reading is around 9-10 bar except can#9 at 7 bar.

 

Abdou,

<b>From the information provided</b> it's very difficult to determine exactly what might be the cause of inability to ignite and maintain flame on liquid fuel after the trip event. By the way you didn't say if the trip occurred when running on liquid fuel or on gas fuel...?

It would seem that flame is not being established at all in cans 3 & -4 (zero intensity). It's very likely there was white smoke coming from the exhaust shortly after the turbine tripped on loss of flame. (Unburned distillate fuel usually partially combusts in the exhaust and causes white smoke.)

The low pressure at can 9 suggests a problem with either the liquid fuel check valve or the purge air check valve. Though not very likely, it could also be a problem with the fuel nozzle.

Shortly after flame is detected during firing (17.54%)--usually two seconds after flame is detected in two or more cans--and then FSR is cut back to warm-up (the 12.68% value) for 60 seconds. That's a pretty significant reduction in FSR--almost one-third. In my experience, that's pretty much on the border of reliable starting. If a machine has any other problems (such as check valve problems, etc) cutting the fuel back this much can result in difficult start-ups, including high spreads and smoking during warm-up and acceleration, and even loss of flame trips.

The reason for reducing the fuel after firing is to try to reduce thermal stress on the machine. But, if fuel is cut back too much then flame will be lost--and that is a form of thermal stress in itself. Again, a unit may never experience a problem with a particular set of firing/warm-up values--until there is another problem or problems and then start-up can be difficult. The trick is to establish flame relatively quickly during firing and then reduce fuel yest maintain flame. This can be tricky, and, again may work fine for many years--until some other problem or problems make for difficulty establishing or maintaining flame.

During previous liquid fuel start-ups, what were the exhaust temperature spreads during warm-up and acceleration?

It will be very interesting to hear the results of your fuel transfer. If you have high spreads during liquid fuel operation, it's a pretty safe bet there is some check valve or fuel nozzle problem. Monitor the Tell-tale Leak-off during the transfer to see if any of the Purge Air Check Valves are leaking. If you see liquid fuel coming out of the Tell-Tale Leak-off, the low pressure(s) from the Manual Selector Valve gauge will usually lead you to the leaking purge check valve.

If there is no fuel in the Leak-off, but there are low pressure readings from the Manual Selector Valve gauge readings that usually indicates problematic liquid fuel check valve(s).

Last, when posting for help with a problem the more information you can provide in the original post the more concise the response will usually be. Provide all the information you have and the results of any troubleshooting in the original post, and the initial responses will usually be more helpful.

Please write back to let us know what you find.

 

Abdou,

There's still another possibility, though remote, that should still be looked into. Spark plugs do deteriorate over time, and it's also not uncommon for the ceramic insulators inside them to break.

Firing on liquid fuel requires a pretty good spark. If the liquid fuel wets the end of the spark plug(s) it can cause a weak spark to be non-existent, so a strong spark is required especially for liquid fuel machines.

So, it's not too difficult to remove the spark plugs and examine them to see if they are in good condition and intact. The electrodes also wear and if the gap gets too large the spark will also become weak. There are rebuild kits available for the spark plugs, with new electrodes and ceramic insulators.

Also, don't forget to examine the spark plug connectors--where the high-voltage cable connects the plug. Quite often the spring-loaded contacts can become loose; there's just a small "nail" holding the high voltage lead to the spring contact and it can very easily be lost. Lack of a good contact at the connector can also cause a weak spark.

A lot of time when an issue like this occurs, it's the result of several problems--not a single one. Troubleshooting and resolution requires a logical and methodical approach, eliminating all possible problems for the most trouble-free and reliable operation.

Again, write back to let us know the results of the troubleshooting.

 

CSA,

Unit is now back running on gas.
We're still waiting for an opportunity to test a transfer to diesel when load demand will be acceptable to allow further troubleshooting on the unit. I will get back with the outcomes and one more time thanks for the response and the additional checks suggested.

 

We face the same problem but it was more stranger.

if you want to start the unit in fuel oil, it will fail but if you start the unit with fuel gas it will success.

so we do the following, start on Gas then at FSNL we make change over then synch.

the plan was success but after that we try to fix the problem.

after long time with troubleshooting we do the following.

we remove the spark plug and we put a glass to cover that place and a camera over the glass and we initiate the turbine. we found that the oil coming out like droplets not atomized but we check the atomizing air pressure it was OK.

so we check the nozzles we found the problem it was there. change the nozzles every thing fine.

i hope this help
moayad daghles

 

An update on this issue. last time we attempted a mix fuel operation 50/50 gas/diesel. Combustion system Allowable and Spreads temperature were all normal. A diesel leak was noticed this leak was coming from VR27 (liquid fuel inlet relief valve). We fixed the leak now turbine is operating normally on fuel mix but no attempt on full transfer to diesel has been done yet. A major inspection is plan in few months. fuel nozzles will be replaced a this time if it is the factors then it will be fixed. anyway thanks one more time for all the answers.

 

Abdou,

Many thanks for the update!