Hi I did post it wrong it is a frame 5 gas turbine with mark6 speedtronics. The GT was off and wasn’t on ratchet . When it was switched off it was checked and checked the following day the oil level was ok. After about 10 days there was probably about a ton of diesel in the oil sump the fuel pump has been checked and seems ok.I corrected my hasty reply mistakes in the response above.... SORRY FOR ANY CONFUSION!!! A Frame 5 can be controlled by a Mark V (the Frame series uses the "Arabic" numerals, and the Mark* turbine controls use the Roman numerals).
Thank you for getting back to us with some answers.
The P&IDs really hold the information you need, but I'll try to summarize here.
But, first, I have a question: Did the Mark VI annunciate an alarm "L.O. LEVEL HIGH"? (or something to that effect)
Most sites have some diesel storage tanks where the liquid fuel for the turbine is stored. There is usually a small skid with two pumps which draw fuel from the storage tanks, through a strainer, and pump it to the turbine Accessory Compartment. On the fuel forwarding skid there is usually a solenoid-operated stop valve, 20FD-1, and a pressure regulator to limit the pressure downstream of the skid and upstream of the turbine Accessory Compartment. That pressure regulator is usually set for approximately 55-60 psig. (Some AEs (Architect-Engineers) or EPCs (Engineering Procurement Companies) provide their own skid for forwarding fuel from the storage tanks to the turbine, and sometimes there is a pressure regulator and sometimes there is not.
The fuel, on its way to the turbine Accessory Compartment, usually passes through one low pressure liquid fuel filter. Sometimes, on newer units there is a second low-pressure liquid fuel filter in the Accessory Compartment. The fuel, at a pressure of around 55-60 psig then goes to the Liquid Fuel Stop Valve, I think the device number is VS1-1, which is controlled by a solenoid-operated valve, 20FL-1. This liquid fuel stop valves requires hydraulic oil pressure to open the stop valve, and there is a limit switch to indicate when the valve is closed (it has to be closed in order to be able to START the turbine initially). And, usually there are alarms to say if the valve is open when it should NOT be open, too, but not always.
After the liquid fuel leaves the stop valve is then passes through the high pressure liquid fuel pump, which is driven by an output shaft of the Accessory Gear through and electric clutch. So, in order for the high-pressure liquid fuel pump to rotate the turbine shaft has to be turning AND the electric fuel pump clutch has to be energized.
Depending on the age of the turbine there is usually a liquid fuel bypass valve around the high pressure liquid fuel pump, and by controlling the opening and closing of this bypass valve the fuel flow-rate to the turbine is controlled. The bypass valve is usually OPEN when the unit is at rest, so there is a path for fuel to flow AROUND the high pressure liquid fuel pump and towards the fuel nozzles/combustors.
After the fuel flows through the high pressure liquid fuel pump it then passes through the liquid fuel flow divider, whose function is to equally divide the fuel flowing out of the high pressure liquid fuel pump into ten equal flows to each of the 10 fuel nozzles/combustors. There is a gauge and a manual selector valve which can be used to check the liquid fuel pressures to each of the 10 fuel nozzles/combustors, as well as the output pressure of the high pressure liquid fuel pump and the inlet pressure to the high pressure liquid fuel pump.
After the fuel leaves the flow divider in 10 individual tubes it then has to flow through a check valve which requires 100 psig oc pressure (sometimes it's only 90 psig)--but the check valve cracking pressure is supposed to be at least 50% or so higher than the liquid fuel pressure from the forwarding pumps at the fuel storage tanks. This should prevent flow which might get through the liquid fuel stop valve and around the high pressure liquid fuel pump (through the open liquid fuel bypass valve) from getting into the fuel nozzles and combustors.
I was at one site in the late 1980s where the AE used 300 psig pumps to send the fuel from the storage tanks to the turbine Accessory Compartment--without any pressure regulator. When the turbine tripped due to high exhaust temperature the 300 psig fuel pressure would not let the liquid fuel stop valve close--and fuel flow to the turbine fuel nozzles and combustors did NOT stop. We had to close the manual isolation valve at the edge of the turbine Accessory Compartment to shut off the flow of fuel to the turbine and prevent an overspeed and worse....
There is another check valve which the liquid fuel has to get past on it's way to the fuel nozzle, and that's the liquid fuel purge check valve. These have been known to leak and allow liquid fuel to flow in the reverse direction (back towards the Atomizing Air Compressor), but there is a three-way valve which should direct any leakage to the gas turbine drains tank through what's identified on the Liquid Fuel Purge P&ID as the 'Tell-Tale Leakoff'--so named because any flow out of this drain would be an indication that at least one of the 10 atomizing air check valves was leaking in the reverse direction.
So, under typical conditions and a typical design, even if the liquid fuel forwarding pumps were started by the Mark* AND the liquid fuel forwarding stop valve, 20FD-1 was energized to open the valve, liquid fuel would flow towards the turbine Accessory Compartment up to the liquid fuel stop valve (VS1-1). To open the liquid fuel stop valve, there would have to be L.O. pressure and hydraulic pressure--from either the Aux. Hyd. Pump (if present) OR the unit would have to be spinning (from the diesel starting means). IF the liquid fuel stop valve was open liquid fuel could flow around the high-pressure liquid fuel pump to the flow divider and to the 10 liquid fuel check valves at each of the fuel nozzles/combustors. BUT, the liquid fuel pressure would have to be greater than 90-100 psig in order to open the liquid fuel check valves and allow the liquid fuel to flow into the fuel nozzles and combustors. With no flame or no air flow (I'm presuming the unit was NOT spinning), the fuel would puddle in the bottom of the combustion wrapper, and the lower combustors and would flow out of the normally open false start drain valves and into the gas turbine drains tank.
The Frame 5 is a two-bearing machine, so I don't know how liquid fuel would get from the combustion wrapper and into the L.O. reservoir--there's no path I'm aware of for that to occur. The bearings are basically "sealed" (covered) so the turbine would have to "fill up" with liquid fuel to even get into the bearing enclosures past the labyrinth seals to get into the bearing drains and make its way back into the L.O. reservoir.
On all of the GE-design heavy duty gas turbines I've seen all of the liquid fuel piping is OUTSIDE of the L.O. reservoir, to prevent any leaks from getting into the L.O. reservoir.
What I have also heard of (I wasn't at the site where this occurred) was that the diesel fuel supplier who provides the diesel fuel for the diesel fuel starting motor was new and no one was around when he arrived to fill the diesel starting motor fuel tank in the turbine Accessory Compartment. He mistook the L.O. reservoir fill line for the diesel starting motor fuel tank fill line and pumped a whole bunch of liquid fuel into the L.O. reservoir before someone realized the L.O. LEVEL HIGH alarm had been annunciated and went out to investigate. A little bit of paint would have saved a LOT of oil and work (two different colors for the two different fill lines, which are sometimes located close to each other and look an awful lot alike).
I simply can't imagine any other way for fuel to get into the L.O. reservoir--with the exception of the diesel starting motor fuel tank (which, again, is usually under the diesel motor and above the L.O. reservoir) having a leak. Again, if enough fuel leaked into the L.O. reservoir there should have been a L.O. LEVEL HIGH alarm. And, the level in the diesel starting motor fuel tank would be very low. The diesel starting motor has it's own "forwarding" pump from its own fuel storage tank, and it has its own high-pressure fuel pump for the injector--all outside of the L.O. reservoir, though directly above it.
If the fuel did in fact get all the way to the fuel nozzles/combustors and then through the false start drain valves and into the gas turbine drains tank, there's usually an alarm to warn of a high gas turbine drains tank level (either on the gas turbine control system, or the plant DCS or balance-of-plant control system). But, it's not clear to me how liquid fuel would get from the combustion wrapper and lower combustion cans into the L.O. reservoir.
So, it would be VERY MUCH APPRECIATED if you would keep us posted on what you find!!! Because this is pretty strange. And a LOT people read these threads, and will for many years, so you would be helping a lot of people avoid a similar problem.
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by Seth Price
by Seth Price
by Seth Price