Dear experts of GE frame 9e,
Your immediate assistance is humbly needed to solve an issue.

After modifying our GE 9E gas turbine from natural gas to diesel oil with the installation of a dual fuel nozzle, the natural gas line was purged, and the liquid fuel line was flushed. However, during start-up, it was noticed that liquid fuel was coming out of the false start drain. What could be the cause?

 

Look at your Liquid Fuel P&ID (Piping & Instrumentation Diagram). There may also be a Liquid Fuel Purge system P&ID.

We PRESUME you were starting and/or running on liquid fuel when this occured.

How much fuel came out of the false start drains?

Did the flow of liquid fuel out of the false start drain valve stop after a fashion?

Was it a false start drain valve from the turbine compartment or the exhaust duct?

Was there a large amount of white smoke in the gas turbine exhaust when liquid fuel was observed to be coming out of a false start drain valve?

It's not unusual for some liquid fuel to collect in the bottom of a combustor (and quite often in the bottom (lowest) combustors and flow out of the false start drain valves during initial firing and operation. And, one of the functions of the false start drains valves is to drain any uncombusted liquid fuel to the gas turbine drains tank--to prevent it from suddenly igniting during starting and acceleration.

For many GE-design Frame 9E heavy duty gas turbines there is a normally open valve in the false start drain line that is closed when axial compressor discharge pressure (CPD) gets above a certain value and this prevents hot combustion gases from flowing through the false start drain lines into the gas turbine drains tanks--after any uncombusted liquid fuel has has a change to drain (or be blown) out of the area where the unburnt liquid fuel collected (the lower combustors, or the exhaust duct beneath the exhaust diffuser).

Again, someone needs to use the (hopefully) provided P&IDs with the new liquid fuel system and liquid fuel purge system to look at what and where the valves are AND to make sure that at some point during the acceleration up to FSNL the valves close (I think some machines now use solenoid-operated shut-off valves instead of CPD-operated valves--but the P&IDs will show what type of valve(s) are being used).

And, again, it's not uncommon for some unburnt (uncombusted) liquid fuel to collect in the lower combustors or the combustion wrapper or the exhaust compartment (especially when there is a failure to establish flame during starting on liquid fuel). It's even common to see a small amount of liquid fuel flowing out of the false start drain lines during a START if flame doesn't happen within 10-15 seconds of firing--the unburnt liquid fuel has to be drained somewhere.

If, however, there is flow out of the false start drain valves during normal operation--THAT is NOT good and the machine should be shut down and the cause investigated and corrected before re-starting. Even liquid fuel draining from the Tell-Tale Leak-off--which OFTEN gets misidentified as a false start drain line--during normal operation at rated speed IS NOT normal and should be investigated and corrected (that cause is usually a malfunctioning or failed liquid fuel purge check valve, again which should be found on a P&ID).

So, you have several things to clarify for us if you want more help. And, you need to have people be sure they have identified false start drain lines properly and are familiar with P&IDs AND the location of the devices shown on the P&IDs and how they operate and when they should be opened or closed, and how they are opened or closed.

Neglect the P&IDs at your own peril. They ARE NOT difficult to learn or understand AND they should be committed to memory by properly trained and experience personnel. They are critical to understanding proper operation and troubleshooting. AND, most HMI graphics DO NOT show the entirety of ANY system on the display, so knowing and understanding the entire system is the best way to become familiar with the equipment and how it operates--and the purpose of the P&IDs is to provide the means to learn and understand each system and the components of each system. The turbine control is surprisingly reliant on a lock of devices it does not control for proper operation. Knowing the P&ID of each system--and knowing where each device on every P&ID is located--is really important when trying to troubleshoot and understand how the machine works and if it's working properly and what the problem(s) might be.