Due to a new restriction on our plant steam turbine, we are looking to regain lost plant output by increasing the maximum IGV angle on our 7FA units from 87 to 89 degrees.

Has anyone else done this and if so, what sort of MW gains did you experience?

Were there any negative side effects caused by this?

 

You should work with the packager/manufacturer of the gas turbine to analyze the hot gas path components and axial compressor configuration, first, to determine if this is feasible from a hardware standpoint.

Second, they will also likely calculate a new CPR-biased exhaust temperature control curve, and possibly a new IGV exhaust temperature control curve.

Third, the tuning of the DLN combustors will likely have to be re-done.

It's not as simple as changing the max IGV angle.

Of course, you can always do that without consulting the packager/manufacturer and tell us the results in a year or two after a CI, HGPI or Major. Or after a possible forced outage due to unforeseen consequences.

If you own the machine (meaning it's not under warranty or some kind of service- or maintenance agreement with implied warranties of some sort) you are free to operate your machine however you want. Just be willing to accept the consequences of your actions.

 

I am looking to get info from other users experiences. I would like to know what gains I can expect from the slight increase in airflow.

 

The 7F Users Group is probably one of the better users groups; it is (or at least it was; I haven't been to the site in about two years) very well used with some very knowledgeable users who are very quick to share their experiences and opinions.

There are MANY 7F users (including FA, FA+ and FA+e and FB) users there, far more than here, and quite a lot of them have experience with most of the various conversion, modifications and updates.

 

Effect of increase in IGV angle

well, if you see that chara graphs, you will know that there will not be much increase in the air flow. The IGv opening from 56 to 85 % only contributes to a 10-12 % increase in the air flow. Thus from 85 to 90 deg you may perhaps increase the air flow by another 2-3% at max.

this was done in a gulf refinery in a frame 6 machine (31.2MW), at the site condition the frame 6 air flow at 85 deg was around 490t/hr when it was increased to 90 (the iGV went only till 89.2 or something) the air flow increased to 495-496 tonnes. the power output increased by 0.3MW. seeing that there was not much increase in the power output the iGV max angle was reverted back.

you will face a similar situation in your frame 7 machine. the reason i believe is the limitation of the compressor design , it is designed to operate at a particular flow , just opening the IGV more is not going to increase the compressor to perform more. As far as i know there will be no other consequences , you can do it as a experiment but do not see this as a permanent solution to your problem.