The GT starts up with liquid fuel (diesel) up to a speed of 95%, at this exact moment the magnetic pickups (77FD1 and 77FD2) start to show values that vary very quickly, between 20% and 5%, before reaching 95% of the speed they show stable values at 20%. When the GT presents this unstable behavior at 95% speed it trips. The alarm displayed after triggering is "FD1-1 feedback trip" and "VC3 does not follow reference". "L3LFBFB_ALM" the recommendation is to check the flow divider, but how could there be a problem if it worked well until almost reaching full speed at load (95%)? Regarding the "L3LFBA_ALM" alarm, the recommendation is to calibrate the VC3 bypass valve, how do I do it?
Is there a possibility that the problem originated from the liquid fuel pump clutch when reaching maximum no-load speed?
Can anyone who has experienced this experience tell me how to resolve the problem?

Note: GT has not worked with liquid fuel for almost 4 years, only with fuel gas, but before that time i worked with gas and liquid fuel without any problems

 

@JULIÃO NGAIE,

Note: GT has not worked with liquid fuel for almost 4 years, only with fuel gas, but before that time i worked with gas and liquid fuel without any problems

If you did nothing to try to ready the liquid fuel system for operation after four years and simply just tried to START the machine on liquid fuel, you were just asking for the problem(s) presented to you.

If a dual-fuel (gas/distillate) machine runs "regularly" on liquid fuel the liquid fuel system is kept clear of air and bacteria (yes--distillate left undisturbed in pipes and vessels for very long periods of time can develop bacteria which can cause issues with liquid fuel components--in particular control valves and high-pressure liquid fuel pumps, as well as in piping and fuel filter vessels).

Liquid fuel check valves leak. Full stop. Period. They also require periodic testing and replacement--even when liquid fuel is used regularly.

As the machine approaches FSNL (particularly around 95% TNH) the fuel flow increases as the compressor discharge pressure increases as speed approaches rated, the IGVs are opened AND the compressor bleed valves close. All of these things tend to increase the fuel flow rate to maintain speed and acceleration rate. And, when fuel flow increases then trapped air in piping and fuel filter vessels moves along through the high-pressure liquid fuel pump and liquid fuel bypass valve and into/through the flow divider.

Yes; the liquid fuel pump clutch has to transmit more torque to the pump when the flow increases so this might be a problem, and it shouldn't be overlooked when troubleshooting, but it's not likely the cause--unless you have some reason to believe the liquid fuel pump clutch has been damaged or has been sitting/rotating in a lot of oil, possibly from a leaky seal.

GE recommends periodically and frequently (their recommendation is usually once per week) operating the liquid fuel system to keep it exercised and so problems can be recognized and resolved. This could be just switching from natural gas to liquid fuel for 10 or 20 minutes and then switching back to gas fuel. At rated speed, and even under load.

My recommendation is to start the machine on gas fuel, let it get to FSNL and warm up for about 15-30 minutes or so at FSNL, then initiate a transfer from natural gas to distillate fuel. Yes; there's still a chance the machine will trip if you do nothing before attempting this start (like bleeding the air out of the liquid fuel filters and any high points in the liquid fuel supply piping all the way up to the high-pressure liquid fuel filter). But, you may get lucky and the majority of air and contaminants may just blow out during the initial part of the transfer and the machine may have a small drop in speed and then go to 100% liquid fuel. If it does that, you should be letting the machine run for 15 minutes or so, and then shutting down while running on liquid fuel, then STARTing again on liquid fuel and observing the start-up.

When the machine is running on liquid fuel you should have someone stationed near the liquid fuel tell-tale leak-off looking for any liquid fuel flow--there shouldn't be any, and if there's any appreciable amount the cause should be troubleshot and resolved (it's most likely a leaking liquid fuel purge check valve).

You should also be monitoring exhaust temperature spreads to see how they behave during operating, as well as during STARTing on liquid fuel.

But, simply expecting a machine that ran "well" on liquid fuel four years ago to just start up the first, second or even third time on liquid fuel with no preparation to start and go to FSNL and be synched and loaded is not reasonable. It could happen, but it's not really likely.

When liquid fuel flow divider feedback is suddenly erratic, especially at low liquid fuel flows, its usually the result of air trapped in the liquid fuel supply piping and vessels that hasn't been properly blown out OR a problem with the liquid fuel forwarding pump/pressure regulator (if the machine is equipped with a liquid fuel forwarding pump pressure regulator) or some blockage in the liquid fuel supply piping that is restricting fuel flow (such as a dirty liquid fuel forwarding pump suction strainer or liquid fuel filters that have been contaminated with crap and crud which has formed in the liquid fuel lines when the system hasn't been run for a long time. It could also be liquid fuel check valves acting up, or liquid fuel purge check valves leaking.

There are a LOT of liquid fuel system components that are controlled or monitored by the Mark* turbine control system which all have to be working properly with clean fuel which is free from air in order for the machine to start and run reliably on liquid fuel.

 

@JULIÃO NGAIE,

Note: GT has not worked with liquid fuel for almost 4 years, only with fuel gas, but before that time i worked with gas and liquid fuel without any problems

If you did nothing to try to ready the liquid fuel system for operation after four years and simply just tried to START the machine on liquid fuel, you were just asking for the problem(s) presented to you.

If a dual-fuel (gas/distillate) machine runs "regularly" on liquid fuel the liquid fuel system is kept clear of air and bacteria (yes--distillate left undisturbed in pipes and vessels for very long periods of time can develop bacteria which can cause issues with liquid fuel components--in particular control valves and high-pressure liquid fuel pumps, as well as in piping and fuel filter vessels).

Liquid fuel check valves leak. Full stop. Period. They also require periodic testing and replacement--even when liquid fuel is used regularly.

As the machine approaches FSNL (particularly around 95% TNH) the fuel flow increases as the compressor discharge pressure increases as speed approaches rated, the IGVs are opened AND the compressor bleed valves close. All of these things tend to increase the fuel flow rate to maintain speed and acceleration rate. And, when fuel flow increases then trapped air in piping and fuel filter vessels moves along through the high-pressure liquid fuel pump and liquid fuel bypass valve and into/through the flow divider.

Yes; the liquid fuel pump clutch has to transmit more torque to the pump when the flow increases so this might be a problem, and it shouldn't be overlooked when troubleshooting, but it's not likely the cause--unless you have some reason to believe the liquid fuel pump clutch has been damaged or has been sitting/rotating in a lot of oil, possibly from a leaky seal.

GE recommends periodically and frequently (their recommendation is usually once per week) operating the liquid fuel system to keep it exercised and so problems can be recognized and resolved. This could be just switching from natural gas to liquid fuel for 10 or 20 minutes and then switching back to gas fuel. At rated speed, and even under load.

My recommendation is to start the machine on gas fuel, let it get to FSNL and warm up for about 15-30 minutes or so at FSNL, then initiate a transfer from natural gas to distillate fuel. Yes; there's still a chance the machine will trip if you do nothing before attempting this start (like bleeding the air out of the liquid fuel filters and any high points in the liquid fuel supply piping all the way up to the high-pressure liquid fuel filter). But, you may get lucky and the majority of air and contaminants may just blow out during the initial part of the transfer and the machine may have a small drop in speed and then go to 100% liquid fuel. If it does that, you should be letting the machine run for 15 minutes or so, and then shutting down while running on liquid fuel, then STARTing again on liquid fuel and observing the start-up.

When the machine is running on liquid fuel you should have someone stationed near the liquid fuel tell-tale leak-off looking for any liquid fuel flow--there shouldn't be any, and if there's any appreciable amount the cause should be troubleshot and resolved (it's most likely a leaking liquid fuel purge check valve).

You should also be monitoring exhaust temperature spreads to see how they behave during operating, as well as during STARTing on liquid fuel.

But, simply expecting a machine that ran "well" on liquid fuel four years ago to just start up the first, second or even third time on liquid fuel with no preparation to start and go to FSNL and be synched and loaded is not reasonable. It could happen, but it's not really likely.

When liquid fuel flow divider feedback is suddenly erratic, especially at low liquid fuel flows, its usually the result of air trapped in the liquid fuel supply piping and vessels that hasn't been properly blown out OR a problem with the liquid fuel forwarding pump/pressure regulator (if the machine is equipped with a liquid fuel forwarding pump pressure regulator) or some blockage in the liquid fuel supply piping that is restricting fuel flow (such as a dirty liquid fuel forwarding pump suction strainer or liquid fuel filters that have been contaminated with crap and crud which has formed in the liquid fuel lines when the system hasn't been run for a long time. It could also be liquid fuel check valves acting up, or liquid fuel purge check valves leaking.

There are a LOT of liquid fuel system components that are controlled or monitored by the Mark* turbine control system which all have to be working properly with clean fuel which is free from air in order for the machine to start and run reliably on liquid fuel.

Sorry, I forgot to mention, before the start up we did some preparation. We remove the liquid fuel from the circuit, replace the check valves, replace the high pressure filters and the filters on the filtering skid. Then we performed fuel recirculation, so we decided to start up the GT.
I must also emphasize that the GT's behavior during the starting process was normal, the VC3 and the Magnetic Pickup were unstable when it reached 95% speed, before 95% speed they were still at normal values.