Hi,

Recently we have faced a unit trip while Auto Changeover got initiated by Coalescing filter Condensate level switch malfunction.
This is a Frame 9E unit running with Mark Vie Control system in TMR configuration.
Before unit trip, it was running on Base load and with Fuel Gas. We have low BTU gas with BTU value of 470 BTU/SCF.

During investigation it has been observed that Unit load increased during fuel change over and caused shifting of Temperature control from CPD to FSR temperature and eventually unit tripped on high exhaust temperature.

Following indications appeared before trip:

1-FSR Temperature Reference Active
2-Exhaust Temperature High
3-Exhaust Overtemperature Trip

I believe FSR should have been reduced and control system should have limited the load which did not happen in this case.

Kindly provide your suggestions/analysis for the event. I am attaching the events summary and log for reference.

Regards,

 

@asifamin,

It’s probably possible to tune the Mark* VIe to survive an automatic gas-to-distillate fuel transfer at Base Load, but without testing and tuning your expectation that the FSR should have been reduced before the transfer was initiated is unrealistic—unless the turbine control was specifically commissioned to do so with very different fuels.

The typical sequence for any fuel transfer is to attempt to control the FSR DURING the transfer (as FSR on the running fuel is reduced and FSR on the fuel being transferred to is being increased) all the while monitoring CPD- or CPR bias AND exhaust temperature. This is a very challenging situation even when not running at Base Load. If the two FSRs at Base Load are not similar when the fuel transfer is initiated then the transfer sequence is even more challenging. The typical time to ramp one FSR to zero and the other to the required value is usually 30 seconds, which is really a short time for loads above 100 MW AND running at Base Load.

if the two FSRs are not even closely similar when running at Base Load then the “balancing act” of maintaining load—ANY load—is made even more difficult and if it’s occurring while running at Base Load it’s even more challenging.

Usually, during commissioning a tuning procedure called “fuel matching“ is or should be done to try to match the two FSRs at the load which is anticipated fuel transfers will be performed. And if the machine has DLN-I combustors that is very difficult to do, especially at Base Load. There are certain nozzle flow-rates and pressures which must be maintained when fuel matching is being tuned. And it’s much easier with conventional combustion systems than with DLN combustion systems.

You failed to mention how often fuel transfers are attempted on this machine (the OEM recommends once per week if successful transfers are critical…!).

I can’t properly view the data you provided on my phone and I’m not near my computer for a few days. But it certainly doesn’t appear your expectations for a typically-configured Mark* VIe are reasonable and we don’t know if fuel matching was performed or properly performed or if the gas fuel make-up has changed since commissioning and if it has if another fuel matching process was properly performed. And we don’t know what kind of combustion system the machine has. All of these are important factors—as well as if regular fuel transfers (at any load) are performed.

It is suggested to hire a knowledgeable, experienced engineer to analyze and assist with achieving realistic goals given the machine and site conditions and configurations.

Blessed day.

 

@asifamin,

It’s probably possible to tune the Mark* VIe to survive an automatic gas-to-distillate fuel transfer at Base Load, but without testing and tuning your expectation that the FSR should have been reduced before the transfer was initiated is unrealistic—unless the turbine control was specifically commissioned to do so with very different fuels.

The typical sequence for any fuel transfer is to attempt to control the FSR DURING the transfer (as FSR on the running fuel is reduced and FSR on the fuel being transferred to is being increased) all the while monitoring CPD- or CPR bias AND exhaust temperature. This is a very challenging situation even when not running at Base Load. If the two FSRs at Base Load are not similar when the fuel transfer is initiated then the transfer sequence is even more challenging. The typical time to ramp one FSR to zero and the other to the required value is usually 30 seconds, which is really a short time for loads above 100 MW AND running at Base Load.

if the two FSRs are not even closely similar when running at Base Load then the “balancing act” of maintaining load—ANY load—is made even more difficult and if it’s occurring while running at Base Load it’s even more challenging.

Usually, during commissioning a tuning procedure called “fuel matching“ is or should be done to try to match the two FSRs at the load which is anticipated fuel transfers will be performed. And if the machine has DLN-I combustors that is very difficult to do, especially at Base Load. There are certain nozzle flow-rates and pressures which must be maintained when fuel matching is being tuned. And it’s much easier with conventional combustion systems than with DLN combustion systems.

You failed to mention how often fuel transfers are attempted on this machine (the OEM recommends once per week if successful transfers are critical…!).

I can’t properly view the data you provided on my phone and I’m not near my computer for a few days. But it certainly doesn’t appear your expectations for a typically-configured Mark* VIe are reasonable and we don’t know if fuel matching was performed or properly performed or if the gas fuel make-up has changed since commissioning and if it has if another fuel matching process was properly performed. And we don’t know what kind of combustion system the machine has. All of these are important factors—as well as if regular fuel transfers (at any load) are performed.

It is suggested to hire a knowledgeable, experienced engineer to analyze and assist with achieving realistic goals given the machine and site conditions and configurations.

Blessed day.

@WTF?

Thank you for your response.

Just to answer your questions, Unit is non DLN and fuel matching is performed properly as the issue is never faced during fuel change overs at part load.
I am not saying that FSR should have reduced prior to start of fuel change over procedure but to limit the load or control the load during fuel change over.
Also, we are not performing any fuel change over periodically. Units start on HSD and then are converted to Gas Fuel and remain on Gas Fuel until unit is being shut down and converted back to HSD during shut down. These conversions always remain smooth and no issues have been observed.

A second event of units trip again occurred few days back on both of our Gas Turbines as Fuel Gas Pressure reduced significantly from suppliers end and units converted to HSD. This time first change over to Liquid fuel was successful for both units and operator changed the fuel back to Gas as he thought pressure is stabilized. But just after fuel change over to Gas, again pressure dropped and this time fuel change over was not successful and units tripped on Exhaust Overtemperature Trip.
During investigation it was observed that Load on both Units increased sharply from 120 MW to 180 MW (Base Load is 120 MW). Data is being shared with OEM, however event is copy of first event where load increased significantly and unit tripped on Exhaust Overtemperature Trip.
I would also like to highlight that there is a some difference of CV value between both fuels:
HSD: 19600 BTU/LB
Gas: 470 BTU/SCF
However i am not sure if this can contribute to the issue.

Would like to get your/experts thoughts on it.

Thanks