On startup we faced the following issue with our GE frame9 gas turbine.

Our gas turbine starts on liquid fuel and after reaching the load of 37.5MW, it gets ready for fuel changeover. On reaching 60 MW, we gave fuel changeover command i.e. from liquid to gas. The changeover sequence starts to initiate. Liquid fuel valves starts to get close and at the same time gas fuel valve i.e. SRV starts to get open. At 60 MW load, GCV position was 24% and liquid fuel valve was almost close. At this instant when liquid fuel valve was completely close, GCV was rapidly change from 24% to 29% and then back from 29% to 22%. Consequently load varied from 60MW to 92MW and then back from 92MW to 29MW. As load drops down to 29MW (below 37.5MW) so fuel was changed back to liquid and we experienced unsuccessful fuel changeover to gas. Further attempts were made and then finally in the fourth attempt we got successful. In the fourth attempt fuel changeover command was given at 65MW load.

Still in the successful fuel changeover sequence we are experiencing rapid changes in GCV position as well as load dipping.

 

All questions are relevant; they all need to be answered for a reply.

How often do you transfer fuels? Every start? Once per week? Once per month?

How often does the unit start and stop? Every day? Once per week? Once per month? How long does the unit run once it's started? Half a day? A day? A week?

Have you ever had successful fuel transfers? Meaning, ones without some kind of load swing (the usual term for load increasing/decreasing/increasing/decreasing/increasing, etc.) during the transfer? Please describe the successful fuel transfers, noting any load swings (the maximum and minimum loads experienced during the transfer).

Do you have to transfer fuels during a normal shutdown?

If so, what are those transfers like (from gas back to distillate)? Does the unit experience load swings during these transfers? If so, how much?

What is the gas fuel that is being burned? (It's kind of unusual for a unit not to be able to be started on gas fuel, unless the fuel has a high hydrogen content or a high BTU content, higher than natural gas, for example.)

The concept of "matching fuels" during a fuel transfer can be very difficult, especially if the fuels have a large difference in energy content. You mentioned that the FSR at 60 MW for the gas fuel is only about 24%. What is the liquid fuel FSR at 60 MW?

These problems can be very difficult to troubleshoot and understand without being on site to witness the running conditions. Does the gas fuel pressure come from a compressor on site (reciprocating or centrifugal)? Is the compressor control able to control pressure/flow during the initial portion of the fuel transfer from liquid to gas, and during the last portion of the transfer from gas to liquid?

Also, during transfers, the liquid fuel supply pressure (upstream of the Liquid Fuel Stop Valve) must remain stable. And the Speedtronic doesn't usually control that pressure, or the pressure from any gas fuel compressor output, or gas fuel supply source. But, stable pressure at low flow-rates is very important.

Lastly, it sounds like you are using Pre-selected Load Control during fuel transfers. Not recommended. It can exacerbate any other problems and make the load swings worse.

I can pretty much <b>GUARANTEE</b> that the problem(s) you are experiencing during fuel transfers are <b>NOT</b> caused by the Mark V, and that the Mark V is reacting to external issues/stimuli. The fuel splitter algorithm in the Mark V is pretty good, presuming that a good job of fuel-matching has been done.

For the typical "universal fuel splitter" algorithm (which we don't know is in use in the Mark V or not), it works by virtue of the fact that for a particular load if the energy of the two fuel flow-rates is equal that when as one fuel flow-rate is ramped down and the other is ramped up (both at the same rates) that the power produced by the turbine (and generator) will remain constant during the transfer and will end up at the same output after the transfer.

That's easier said than done, because it involves some field tuning, and usually during commissioning there is little time or patience for field tuning (sad but true). And, if the one of the fuels, as I suspect, is significantly different from the other then fuel matching can be even more difficult--not impossible, but more difficult. For example, if the FSR for one fuel is 45% at 60 MW and the FSR for the other fuel is 24% at 60 MW, then fuel-matching is going to be more difficult.

I don't really think we can help too much with this problem in this forum, especially if the gas fuel is not similar to natural gas in composition and energy content. There are just too many variables and too many things we can't know without being able to see the Piping Schematics (P&IDs) and the CSP and witness the operation and see some trends (VIEW2, etc.).

I'd still like to know the answers to the questions, though--all of them. We could point to some areas that a field service person could concentrate on, or eliminate, while trying to help smooth the fuel transfers at your site. Which is what I recommend: Get someone to site who's knowledgeable and has some technical support from "engineering" (wherever that may be) to help you diagnose and resolve the problem.

Again, I doubt very seriously that the problems being exhibited by the Mark V are caused by the Mark V. While there may be some tuning parameters which might be adjusted to help with the load swings, it much more likely that there are external issues/stimuli which are affecting the Mark V. And, as has been said many times on control.com: The liquid fuel system of GE-design heavy duty gas turbines has a lot of components, most of them are not controlled or even monitored by the Speedtronic, and all which must work properly and together in order to have a successful fuel transfer or a successful start. (Those of you with liquid fuel only units are probably scratching your heads, saying, "What is the big deal?!?!?" because you don't have the same issues as people with dual fuel units. And you should just consider yourselves very lucky, because if you suddenly found yourself working at a plant with dual fuel units which were expected to start reliably on either fuel, or transfer on a moment's notice reliably to either fuel, would find out quickly about how hard this can be!)

 

As insane as this sounds, check to see that your gas company is supplying you with "the good stuff".

We had a similar problem with a burner that was running fine until it shut down for no reason. We made several attempts to relight it, and when I finally checked the potency of the gas from a line tap, it wouldn't even light off.

We reported the problem to the gas company, who told us politely that we were crazy, but finally sent a service guy out with a sniffer to test the gas (when it became apparent that we weren't going to use any more NG until the problem was resolved).

Initially the readings on his tester came in at 18% and eventually rose to 100% once we bled the line enough.

The gas line in question is a high pressure line (~60 PSI) so there was no chance of air getting into the line (which was what the tech tried to have me believe at first).