Changing the Fuel in GTG GE Frame 9E


Thread Starter


At the time of fuel changes from gas to diesel and vice versa.
There are sudden changes to the load during fuel switching (about 50 megawatts).
So please help to find a problem.

If your load is falling when you switch to diesel, check your diesel LP supply pressure. That is usually the problem. Try to increase by 0.5 - 1.0 Bar and try the changeover again. If it helps, you should be able to figure out by how much you need change the pressure to get a smooth transfer.
Thanks for your answer. Given that there is a decrease in load during the change of fuel from gas to gasoline, please provide guidance on how to increase the load of about 50 megawatts when changing fuel from gas to gas-oil.

I told you already on my previous Email. Increase the Liquid Fuel LP supply pressure by 0.5 - 1.0 Bar and try again. There should be a PCV for this in your off base skid.
Considering that during the change of fuel from liquid to gas, there is also an increase in the load of 50 megawatts.
What is the cause?


What kind of combustion system is in use on the GE-design Frame 9E at your site?

How often do you transfer fuels?

Are fuel transfers initiated manually, or automatically (such as when gas fuel supply pressure drops too low; or when liquid fuel supply pressure drops too low)? If it's automatically occurring when fuel supply pressure is dropping, how fast is the supply pressure dropping? Because it may be difficult, if not impossible, to catch or maintain load if the fuel supply pressure has dropped too low. In that case, it might be best to increase the pressures at which low fuel supply pressure is alarmed, and when a fuel transfer is initiated. And, it might also be necessary to start reducing load, also, in order to try to keep supply pressure from dropping too fast.

The most common cause of load swings during fuel transfers from gas to liquid is air in the liquid fuel supply piping, including the filter vessels. The second most common cause of load swings during gas-to-liquid fuel transfers is low and unstable liquid fuel supply pressure (as glenmorangie has suggested).

When a dual-fuel unit is commissioned there is a procedure which must be done called "fuel matching" to try to match FSRs on gas and liquid so that when fuel transfers are performed there won't be large load swings. Usually, fuel matching isn't done very well, if at all. So, let's say when the unit is running on liquid fuel at 100 MW the FSR is 67.9%, and when it's running on gas fuel at 100 MW the FSR is at 73.4%. Fuel matching would try to make the FSR for both fuels the same at 100 MW, or as close as possible. But, it takes time and effort and usually at that point in commissioning the job is behind schedule and all the Customer wants to do is generator MW and get paid for the MW they generate.

Another thing which REALLY hampers fuel transfer is if Pre-Selected Load Control is enabled and active during the fuel transfer (whether from gas-to-liquid or liquid-to-gas). If you are intentionally performing a fuel transfer, TURN OFF Pre-Selected Load Control. If it's active and there are load swings it will make them worse. (Pre-Selected Load Control is a very poor way to operate a GE-design heavy duty gas turbine anyway; it shouldn't be used except for load changes, and as soon as the desired load is achieved it should be disabled (by clicking or either RAISE- or LOWER SPEED/LOAD.)

So, that's about it. If you can provide more actionable data. That's things like what load are you trying to transfer fuels at; what is the FSR and load of the fuel that is being burned before the transfer is initiated, and what is the FSR and load of the fuel being transferred to when the transfer is complete; is Pre-Selected Load Control enabled and active during the fuel transfer; what is the liquid fuel supply pressure during the transfer (both from gas-to-liquid, and from liquid-to-gas), and what should it be (from the Device Summary and/or Control Specification); was all the air bled from the liquid fuel supply piping (from the high-point vents and filter vessels) before the transfer from gas to liquid was initiated; what was the gas fuel supply pressure during the transfer (both from gas-to-liquid, and from liquid-to-gas), and what should it be (from the Device Summary and/or Control Specification); <b>what Process- and Diagnostic Alarms are annunciated during the fuel transfers</b> (this is <b>VERY</b> important to know); etc. All of these things impact the stability of fuel transfers--<b>ALL</b> of them. Some more than others, but they ALL do. And, it could be a combination of things, too (it often is).

And, if you want to troubleshoot and resolve the issue you have to provide the data--actionable data which is numbers and values. Not anectodal data (it's unstable, and it shouldn't be). These are complex, multi-million Euro machines which have a lot of parameters and factors which can affect the unit operation and stability. "If you don't have data, then you're just another person with an opinion." (That's basically a quote from W. Edwards Deming--look him up; he was right about that, and a LOT of other things!). It takes data to make good decisions, and troubleshooting involves making decisions.

Remember--USUALLY the Mark* doesn't control fuel supply pressures, not the liquid fuel supply pressure or the gas fuel supply pressure. So, operation will be impacted if either pressure is not what it should be (particularly liquid fuel), or is unstable, during the transfer. Sometimes fuel pressures are very unstable when the flow of a fuel is very low, such as then liquid fuel starts flowing during a gas-to-liquid transfer, or when gas fuel stop flowing during a gas-to-liquid fuel transfer. Both can cause load swings.

It should be clear--without actionable data which helps us to understand the situation and conditions at your site (because every site is NOT the same--contrary to popular (and false) belief) and to try to help pinpoint the issue(s) there's not too much can be done. Yes; the equipment may be similar and it may have the same name (Frame 9E), but site conditions are almost NEVER exactly the same.

Complex, multi-million Euro machines these are. There usually isn't one answer--hence all of the verbiage above. Get us actionable data, and we'll get you a better answer.

What is the hydraulic pressure before and during the fuel transfers?

I forgot to ask about the hydraulic accumulator; is it properly charged and are the valves in the proper position?