High Exhaust Temperature Spread


Thread Starter


Good morning,

Our 30MW gas turbine, frame 6, mark 6E, when running on gas trips on high exhaust temperature spread, but we don't experience such when on liquid fuel firing mode. It's been suggested we clean the nozzles. But I was thinking since we don't experience it in the liquid fuel firing mode, clogged nozzle is unlikely to be the cause. And again we can't start the turbine on liquid fuel firing mode, so we usually start on gas firing and switches to liquid firing before the spread issues come out.

Pls anyone with useful info on the likely causes and possible solution.
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There are usually separate passages for liquid fuel and gas fuel in "the" fuel nozzles, so the suggestion to clean them (specifically the gas fuel portions of the fuel nozzles) is correct.
Thanks for your response, we will examine and clean the nozzles tomorrow. Pls do you have idea why the turbine cannot start on liquid fuel firing, but can run on it after starting it in gas firing mode.

Thanks once again

Yes; I have lots of ideas BUT I'm not going to guess and speculate and try to explain every one of them--because you aren't telling what alarms are occurring when the unit "doesn't start" on liquid fuel.

Does it fire and then lose flame during acceleration?

Does it not fire at all?

Can you see white smoke during firing and acceleration when starting on liquid fuel?

Does the exhaust temperature increase when firing on liquid fuel?

Does the unit have conventional combustors or DLN-I combustors?

What is the liquid fuel supply pressure when you are starting on liquid fuel--is it stable or is it oscillating?

If you start on gas fuel, transfer to liquid fuel when you get to FSNL (Full Speed-No Load), shut down on liquid fuel, and then try starting on liquid fuel--what happens? Does the unit start on liquid fuel or what? And WHAT ALARMS--PROCESS & DIAGNOSTIC--are annunciated when you try to start on liquid fuel?

Is the Booster Atomizing Air Compressor running when starting on liquid fuel?

What is the Atomizing Air Compressor Inlet Air Temperature when running on liquid fuel?

What is the axial compressor discharge pressure and the Atomizing Air pressure when running at rated speed on liquid fuel?

What is the axial compressor discharge pressure and the Atomizing Air pressure when running at rated speed on gas fuel?

Every previous thread and response on control.com can be searched and read using the 'Search' feature at the far right corner of the Menu bar of every control.com webpage. The subject of failures to start GE-design heavy duty gas turbines on liquid fuel have been covered MANY times before on control.com, and can be searched and found using the 'Search' feature of control.com.

If you want more assistance, you will need to provide the answers to the above questions (even if you don't think one or more are relevant). If you will provide the list of Alarms (Process and Diagnostic) at a minimum that occur when you are trying to start on liquid fuel, we can probably help you troubleshoot and resolve the problem(s). But, we need more information. Information that only you can provide. And, you can also use the 'Search' feature to look up previous threads and responses--there are a LOT of them.