NFinch,
",... one [operator] mentioned they had reignited a flame-out [of a Frame 6B unit] in the past. ..." That's a pretty wide open statement. Did the re-ignition occur while the unit was at or near rated speed? How did they do that, exactly? Was it intentional? If so, it probably required a good bit of logic forcing and a super-size amount of bravado and luck. Did they accomplish it by clicking on the START button on the HMI (or twisting the START switch handle on the old control panel? What speed was it that the unit re-ignited at?
GE-design Frame 6B heavy duty gas turbines are pretty robust machines. They can take a licking and keep on ticking--usually. The fuel flow-rate of a Frame 6B at FSNL (Full Speed-No Load) is usually around 20% of rated, sometimes a little higher, sometimes a little lower. I would agree that one could calculate the electrical load based on fuel flow-rate and heat content of the fuel being burned.
Some heavy duty gas turbines are purged before ignition at a higher rotational speed because the purging time is shorter than it would be if the unit purged at or near "firing speed." When this happens, the speed is allowed to decrease after the purge time is complete before the ignitors are energized and the fuel is admitted to the combustors. This is to lessen the thermal stress on the combustors and hot gas path hardware versus having to put extra fuel into the machine when it's rotating faster--which would be required to establish flame and would result in a higher spike in internal and exhaust temperatures, which reduces parts life and reliability.
If the unit being discussed flamed-out while at rated speed and suddenly re-ignited (because of some ignition source in the combustor OTHER THAN an ignitor) that would mean that fuel was still flowing after the loss of flame (BAD!!!), and if the ignition occurred in the exhaust, THAT would be even worse and harder on the exhaust plenum, exhaust duct and stack, and the flame would have to travel in reverse through the turbine section and back into the combustor.
So, there's a LOT we don't know about this "incident" and even more important what the effect on the hot gas path and exhaust was.
I didn't quite understand the previous reference to OCGT (Open Cycle Gas Turbine???), but if it referred to a gas turbine that was not exhausting into an HRSG (Heat Recovery Steam Generator (a "boiler")) that's often referred to as Simple Cycle (as opposed to Combined Cycle--when the GT exhaust heat produces steam in an HRSG). Why do the units in your idea have to be re-started at synchronous speed? Do the units at your site(s) run that often, or are they necessary evils when solar production goes down in the evening until other generator can be brought on line?
I think this idea/concept is a short-term solution to a problem that is, or possibly should be, solved by storage. It could be pumped storage, or it could be compressed air storage, or it could be batteries.
There are many Combined Cycle power plants which have sea containers filled with batteries that are being used for energy storage and grid frequency control, right now today. Excess generation is used to "top up" the batteries, and when the batteries aren't being used for grid frequency control the output of the turbine-generators is simply reduced. I realize this isn't exactly the same as the problem you're trying to solve, but by storing and releasing the energy in response to solar cycles this seems to be a possible solution.
Does it make sense to try this idea/concept and invest money into research and a control system and possibly incur some unintended and possibly catastrophic damage to what you admit is old equipment (which might be somewhat "expendable")? (Peaking generation is pretty valuable right now, though.) Or to invest in storage capability, which can be used for many years, and is the way the world has to go with the increased reliance on renewal generation which has it's ups and downs--which can't be matched with load at times? (Remember the Texas scenario where wind generators were being paid to shut down a couple of years ago?)
It's an interesting, and innovative, idea/concept. It has risk, which storage technology also has but not as much. But, eventually, isn't storage going to be the way to solve the problem of excess generation and/or low demand/load?
I haven't mentioned this is not a very green solution to a real problem. About the same thing cold be accomplished by using large grids of reinforcing bars (rebar) welded together and submerged in brine. Applying electrical current to the rebar would result in boiling the water. But, this, too, is wasteful; the water usually evaporates into the atmosphere and has to be replaced with "new" water (but we are experiencing sea level rise for some strange reason.... but not climate change according to many non-scientists). (There could be a recuperative aspect to this, though.) This is a very low risk solution, and not really expensive to construct or operate or maintain.
",... one [operator] mentioned they had reignited a flame-out [of a Frame 6B unit] in the past. ..." That's a pretty wide open statement. Did the re-ignition occur while the unit was at or near rated speed? How did they do that, exactly? Was it intentional? If so, it probably required a good bit of logic forcing and a super-size amount of bravado and luck. Did they accomplish it by clicking on the START button on the HMI (or twisting the START switch handle on the old control panel? What speed was it that the unit re-ignited at?
GE-design Frame 6B heavy duty gas turbines are pretty robust machines. They can take a licking and keep on ticking--usually. The fuel flow-rate of a Frame 6B at FSNL (Full Speed-No Load) is usually around 20% of rated, sometimes a little higher, sometimes a little lower. I would agree that one could calculate the electrical load based on fuel flow-rate and heat content of the fuel being burned.
Some heavy duty gas turbines are purged before ignition at a higher rotational speed because the purging time is shorter than it would be if the unit purged at or near "firing speed." When this happens, the speed is allowed to decrease after the purge time is complete before the ignitors are energized and the fuel is admitted to the combustors. This is to lessen the thermal stress on the combustors and hot gas path hardware versus having to put extra fuel into the machine when it's rotating faster--which would be required to establish flame and would result in a higher spike in internal and exhaust temperatures, which reduces parts life and reliability.
If the unit being discussed flamed-out while at rated speed and suddenly re-ignited (because of some ignition source in the combustor OTHER THAN an ignitor) that would mean that fuel was still flowing after the loss of flame (BAD!!!), and if the ignition occurred in the exhaust, THAT would be even worse and harder on the exhaust plenum, exhaust duct and stack, and the flame would have to travel in reverse through the turbine section and back into the combustor.
So, there's a LOT we don't know about this "incident" and even more important what the effect on the hot gas path and exhaust was.
I didn't quite understand the previous reference to OCGT (Open Cycle Gas Turbine???), but if it referred to a gas turbine that was not exhausting into an HRSG (Heat Recovery Steam Generator (a "boiler")) that's often referred to as Simple Cycle (as opposed to Combined Cycle--when the GT exhaust heat produces steam in an HRSG). Why do the units in your idea have to be re-started at synchronous speed? Do the units at your site(s) run that often, or are they necessary evils when solar production goes down in the evening until other generator can be brought on line?
I think this idea/concept is a short-term solution to a problem that is, or possibly should be, solved by storage. It could be pumped storage, or it could be compressed air storage, or it could be batteries.
There are many Combined Cycle power plants which have sea containers filled with batteries that are being used for energy storage and grid frequency control, right now today. Excess generation is used to "top up" the batteries, and when the batteries aren't being used for grid frequency control the output of the turbine-generators is simply reduced. I realize this isn't exactly the same as the problem you're trying to solve, but by storing and releasing the energy in response to solar cycles this seems to be a possible solution.
Does it make sense to try this idea/concept and invest money into research and a control system and possibly incur some unintended and possibly catastrophic damage to what you admit is old equipment (which might be somewhat "expendable")? (Peaking generation is pretty valuable right now, though.) Or to invest in storage capability, which can be used for many years, and is the way the world has to go with the increased reliance on renewal generation which has it's ups and downs--which can't be matched with load at times? (Remember the Texas scenario where wind generators were being paid to shut down a couple of years ago?)
It's an interesting, and innovative, idea/concept. It has risk, which storage technology also has but not as much. But, eventually, isn't storage going to be the way to solve the problem of excess generation and/or low demand/load?
I haven't mentioned this is not a very green solution to a real problem. About the same thing cold be accomplished by using large grids of reinforcing bars (rebar) welded together and submerged in brine. Applying electrical current to the rebar would result in boiling the water. But, this, too, is wasteful; the water usually evaporates into the atmosphere and has to be replaced with "new" water (but we are experiencing sea level rise for some strange reason.... but not climate change according to many non-scientists). (There could be a recuperative aspect to this, though.) This is a very low risk solution, and not really expensive to construct or operate or maintain.