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from the Mark V department...
About Liquid Fuel
Continuous process industries, DCS questions. topic
Posted by Zihni on 27 December, 2012 - 2:58 am
Dear Experts..

We have two GT which F9E and MS9001E. We want to pass from gas fuel to liquid fuel. But we haven't worked with liquid fuel since a long time.Therefore, we don't know that the system is normal. That why, whether work normal the system for understand;

How we can test while on-line?
What we can do? (To liquid fuel from gas fuel for to pass.)
I wait to your advice..


Posted by CSA on 27 December, 2012 - 1:54 pm
Dear Zihni,

Do you know if it's possible to transfer fuels automatically on the two units? Not every dual fuel unit has the capability, or has the capability enabled.

Presuming the capability is present and is enabled, all that's required is to select the fuel you wish to transfer to by clicking on the button on the HMI and confirming the choice. The Speedtronic will take care of all the rest. It is recommended the unit be lightly loaded (about 10-20% of rated load), and that Pre-Selected Load Control NOT be selected.

If the unit uses water or steam injection for NOx emissions reduction, I would greatly suggest you turn it off during any fuel transfer.

If the units have DLN combustors, I heartily recommend you attempt the gas-to-liquid fuel transfer in Primary Combustion mode.

When transferring from Gas to Liquid fuel, there is a period when the Forwarding pumps are started, the forwarding pump stop valve is opened, and then the Liquid Fuel Stop Valve is opened and the liquid fuel pump clutch is energized and the Atomizing Air Bypass Valve is closed--all of this before the LFBV starts to close to increase the liquid fuel flow-rate while decreasing the gas fuel flow-rate. Once the actual ramping-up of liquid fuel flow and ramping-down of gas fuel flow starts the typical time for the ramping is about 30 seconds. So, when selecting Liquid Fuel while running on Gas Fuel, there will be about 30 seconds or so when it seems like "nothing" is happening (but there is!) and then when the Speedtronic actually starts decreasing gas fuel and increasing liquid fuel that takes about 30 seconds or so. Shortly after the fuel transfer is complete, the Gas Fuel Purge Valves are sequenced to start purging the gas fuel nozzle passages.

I would highly suggest that if you are transferring to liquid fuel from gas fuel after a long time of not operating on liquid fuel that you vent all of the air from the liquid fuel supply piping and filter canisters before attempting a transfer. To do this, you would need to start a liquid fuel forwarding pump, and force open the Liquid Fuel Forwarding Stop Valve, usually device 20FD-1. That will pressurize the piping all the way to the liquid fuel stop valve, 20FL-1. You can then vent the high-points of the piping and the filter canisters (upstream of 20FL-1) using forwarding pump pressure.

If it's been a long time since you've operated on liquid fuel, I would also suggest you locate the Tell-tale Leak Off drain piping outside of the turbine compartment and post someone at that location when you attempt the gas-to-liquid fuel transfer. If any of the Purge Air Check Valves leak (and they are prone to leak!), there will be a visible flow through the Tell-tale Leak Off drain. And, if you have someone posted there to see the flow, you will know that at least one of the Purge Air Check Valves is leaking. You want to know if there is any liquid fuel flowing in the Tell-Tale Leak Off during or after the transfer attempt, and the ONLY way to know if there is flow out of the Tell-Tale Leak Off is to have some stationed there during and after the transfer.

You should also have one, preferably two, people posted at the manual selector valve downstream of the Liquid Fuel Flow Divider. Once the gas-to-liquid fuel transfer starts you should have one person slowly rotating the manual selector valve through the 16+ detents while the second person records the pressures at each detent. The "rule of thumb" is: Once the transfer has completed, all of the 14 fuel nozzle pressures should be within 10% of each other. Any pressure that is 10% more or 10% less than the average of all the pressures is suspect, and if there are high exhaust temperature spreads then the high/low pressure(s) will correspond to the fuel nozzle or Liquid Fuel Check Valve or Purge Air Check Valve that is causing the higher-than-normal exhaust temperature spread.

You should also know that a successful gas-to-liquid fuel transfer after a long period of gas fuel-only operation is probably not going to happen, unless you are VERY lucky (and most people are NOT so lucky). There will likely be high exhaust temperature spreads, and/or a trip (most likely because of air in the line, or failed check valves, or plugged fuel nozzles or check valves). If the unit is loaded when you are attempting the transfer, it's very likely that load will swing during the transfer prior to the trip. If, somehow, the unit does not trip during the transfer attempt then it's very likely there will be high exhaust temperature spreads and/or the load after the transfer is complete will be more or less than when the transfer is started. If Pre-Selected Load Control is enabled and active when attempting the transfer and the inevitable load swings occur then Pre-Selected Load Control will exacerbate (make worse) the load swings by causing the fuel flow to swing even more than it already is. So, don't use Pre-Selected Load Control when transferring fuels. Ever. (This is another good reason among many others NOT to use Pre-Selected Load Control. Ever.)

Also, prior to the transfers you want to set up some data-gathering using whatever tools you have available on the HMI(s). Look at liquid fuel flow feedback (usually signal name FQL or FQL1 or FQLM), and liquid fuel flow-rate reference (FQR and FQROUT). If the LFBV has LVDTs, monitor those also (usual FSL). Also, monitor load (DWATT) and SRV position (FSGR) and GCV position (FSG) and P2 pressure (FPG2) and P2 pressure reference (FPRG) and gas fuel flow (if available; usually FQG). You can also put the servo currents into the list of data points, but if you have Mark Vs, the data won't be updated very quickly. Record the data while attempting the transfer. You can also put exhaust temperature (TTXM) and exhaust temperature spreads (TTXSP1, TTXSP2, & TTXSP3). CPD is also a good one to monitor, as is IGV angle (CSGV).

If you are prepared for the transfer and have people stationed at the various locations monitoring the parameters as noted above and you are collecting the data suggested using the HMI, then you will be best able to understand any difficulties and be able to take appropriate and meaningful action in the event the transfer is unsuccessful, or results in high exhaust temperature spreads.

If by some miracle the transfer is successful and exhaust temperature spreads are not abnormally high, then you can decide whether or not to increase load. If the unit is running on liquid fuel, that means the liquid fuel system is likely free of air and can actually be started on liquid fuel without too much trouble at this point. (Trying to start a unit on liquid fuel when it's been operated on gas fuel only for a long period of time is usually difficult if not impossible. It's always best to transfer from gas to liquid, then shut down, and start on liquid fuel--once the liquid fuel system has been purged of air and is "primed" and ready for a start attempt).

Other problems which can occur during a gas-to-liquid fuel transfer include problems with the atomizing air bypass valve not operating properly to increase the atomizing air flow/pressure; and problems with the purge air pre-cooler not being able to maintain temperature properly. So, monitor the AA Pressure during and after the transfer attempt. Sometimes, the Gas Fuel Purge valves won't work properly and the unit will be tripped because of leaking valves, or will automatically be transferred back to gas fuel because the valves didn't sequence properly. It's probably not a bad idea to monitor the pressure switch between the double-block-and-bleed gas fuel purge valves, as well as the purge valve limit switches, during the transfer, using the HMI data-gathering method.

Pay attention to any Process Alarms, as well as Diagnostic Alarms, during the transfer attempt and resolve them as soon as possible.

Preparation and planning is key to being able to formulate a plan in the likely event the transfer is not successful. Without information and data, you will likely re-start the unit a couple of times and trip it a couple of times before deciding to just start pulling fuel nozzles and check valves. Worse, you will try re-starting on liquid fuel after a trip during a gas-to-liquid fuel transfer, and it will not be successful the third, fourth or sixth attempt. And then you will start on gas fuel fuel, successfully, and you will be writing back for help and direction. Don't do this.

Plan in advance. Review the P&IDs for the Liquid Fuel System, and the Atomizing Air System, and the Fuel Purge System (Gas- and Liquid Fuel Purge). Find the Tell-Tale Leak Off and monitor it. Understand the liquid fuel flow divider manual selector valve positions and record the data during and after the transfer. Moving the valve handle during the transfer WILL NOT affect the liquid fuel flows to the fuel nozzles.

Hope this helps! It's a lot to do, but when you have problems (and there is an excellent chance you WILL have problems!) you will have information to be able to formulate a meaningful approach to resolving the problems. By bleeding air out of the liquid fuel supply piping and filter canisters before attempting the transfer you will have a much better chance of success. Be forewarned: The Liquid Fuel- and Purge Air Check Valves provided with most dual fuel GE-design heavy duty gas turbines fail. And, they usually exhibit signs of failure only when attempting to transfer to liquid fuel after long periods of gas fuel-only operation.

Write back to let us know how you fare.


Posted by G.Rajesh on 30 December, 2012 - 12:30 am
Please follow the CSA instructions.

We are regularly testing availability on liquid fuel for our all machines (6B-3, 9E-2).

Though it regular (monthly) we had trip on transfer and suspecting air in the line. Now we are planning to place automatic vent valve in the liquid fuel line in two places for each machine.

Normally it'll take 30 sec's to transfer, if LFBV not closed (allowing fuel to nozzle) after 20 sec's we'll return back to gas to avoid trip.

You can bleed air from stop valve to final filter by keeping slight open the final filter vent valve during start-up (close once air free liquid observed in the outlet).

take care
G.Rajesh


Posted by Zihni on 13 January, 2013 - 12:49 pm
Hi My Friend..
Thank you for your reply..

We firstly began with forwarding station for works. The station was prepared for normally work then L20FL1X valve by force we opened stop valve. We wanted to open by-pass valve but Servo valve didn't work and replaced it. We tested for new servo valve therefore for each processor outputs was connected 9V battery and was given open on the command. During test the machine had worked on the gas. Then we passed to fuel system. The machine was normal.


Posted by CSA on 13 January, 2013 - 7:40 pm
Zihni,

Thanks for the feedback!

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