We operate a CCGT GE 9FA and are required by our system opearator to be capable of operating on both gas and liquid fuel. We are able to switch from gas to liquid fuel seamlessly but have been informed by GE that we are required to reduce load to circa 35MW in order to charge from liquid fuel back to gas. The system operator has asked us to investigate how we may be able to switch back to gas at higher loads. Would anyone be able to explain to me why we are required to reduce load to change back from distillate to gas and if there is any technical fix that can be employed to improve this?

 

When a unit is transferring from gas to liquid, there isn't any combustion mode transfers for liquid fuel operation, to speak of. It goes very quickly from gas fuel premix mode to liquid fuel diffusion mode.

When you're transferring from liquid to gas, the turbine needs to go through the various combustion mode transfers while loading the machine to get to full load in the lowest emissions mode.

There's no way to just go from liquid fuel operation (which is predominantly diffusion flame) to gas fuel premix mode easily.

Does that answer your question?

 

I also operate a dual fueled 9FA and have the same limitation on gas to LF transfers.

Out of interest how often does your system operator require your site to demonstrate liquid fuel compliance?

Also you state that you get seamless transfers from gas to LF. What is your liquid fuel pre-fill timer set to - the default is 30 seconds.