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IGV on Temperature Control
Running Frame 7EA IGV on temperature control

We have F7EA with Mark Vie control. It is NON-DLN with HRSG. Due to market condition we would like to run IGV on temperature control so that steam production can be increased. We never tried before. I went through this forum using search engine, and found that once on base load IGV can not be control (remains full open). Here are the questions:

Can we use manual button on IGV page on HMI to close IGV, if yes how far load has to drop?

I think if controlling FSR is FSRT then IGV can not be controlled, controlling FSR should FSRN to close IGV?

Being a median select IGV can not be closed under 57 ( in 57 and max is 84).

If we bring it down what should we look CPD, MW or any other parameter?

I don't know what else could be look into it? I appreciate if CSA answers? Any member using IGV control or manipulating IGV for steam make on regular basis or occasionally? Please share your experience with forum.

Thanks

2 out of 2 members thought this post was helpful...

IGV Exhaust Temperature Control can only be used when the unit is NOT operating at Base Load. (One of the definitions--the main one, actually--of Base Load is that the IGVs are at maximum operating angle.)

If you select IGV Exhaust Temperature Control ON when the unit is at Base Load, nothing will happen--until you start to lower load. As load begins to drop and exhaust temperature begins to drop (barely begins to drop, that is), the IGVs will start closing--which will keep the exhaust temperature, TTXM, close to the exhaust temperature reference, TTRX.

As load is reduced, the IGVs will continue to close to try to maximize the exhaust temperature--meaning to try to maintain it as close as possible to TTRX, until such time as the IGVs are at minimum operating angle (57 DGA), and they can't be closed any further. At this point, as load is reduced the exhaust temperature will also begin to drop faster.

Recall the exhaust temperature reference curve has a negative slope, up to the Isothermal temperature--which is a flat line (usually at approximately 1100 deg F for most B/E class machines). So, exhaust temperature will rise slowly as the unit is unloaded from Base Load with IGV Exhaust Temperature Control ON, until it reaches the Isothermal temperature and it will level off at that temperature for awhile, and will eventually start to drop from that value, too, until such time as the IGVs are at the minimum operating angle, and then as load is reduced further the exhaust temperature will fall "faster."

If you start the unit with IGV Exhaust Temperature Control ON, the IGVs will remain closed as the unit is loaded, until the exhaust temperature, TTXM, reaches TTRX. At this point if fuel were increased (to increase load) the exhaust temperature would tend to increase--but the IGVs will open to maintain exhaust temperature as close as possible to TTRX as the unit is loaded, until finally, when the IGVs are at maximum operating angle the unit will be at Base Load.

There is probably a Manual IGV control button on some HMI display--but it can ONLY be used to open the IGVs above the reference angle. It CANNOT be used to close the IGVs below the reference angle. Ever.

IGV Exhaust Temperature Control is intended to maximize exhaust temperature to maximize steam production/temperature when the unit is below Base Load (that is, when the IGVs are NOT at maximum operating angle and the unit is on CPD-biased exhaust temperature control). Again, IGV Exhaust Temperature Control will only modulate IGV angle when the unit is NOT operating at Base Load. And it will do so by closing the IGVs to maximize exhaust temperature (during unloading), and by keeping the IGVs closed longer (during loading).

You should know that when IGV Exhaust Temperature Control is ON and modulating the IGVs that the gas turbine heat rate increases--which means the amount of fuel required to produce the same load as when IGV Exhaust Temperature Control is OFF is higher. HOWEVER, the overall thermal efficiency of the unit (the gas turbine and HRSG) is higher. So, there is a little trade-off, and that trade-off is what helps to maximize steam production/temperature at the expense of GT heat rate. But, again, the overall thermal efficiency of the unit (gas turbine and HRSG) is higher, so it's a net win for the plant.

There is nothing else you need to be concerned with. The Mark VIe will take care of everything--that's it's job. As long as all the inputs are calibrated and scaled correctly it will protect the unit and help to maximize exhaust temperature and steam temperature/production at part load.

Hope this helps!

2 out of 2 members thought this post was helpful...

sardar108,

I don't think you will increase steam production over base load condition. The IGV temperature control line is below the base load temperature control line. While you may be able to close the IGV's using manual IGV control, this will not increase steam production. You might increase the steam temperature a little, but you will reduce the airflow, and hence also reduce the exhaust gas flow, which will actually reduce steam production.

The way to increase steam production above the base load limit is to add supplemental firing to the HRSG.

Additional steam production requires additional energy input to the GT/HRSG system, which means additional fuel flow. You can't put more fuel into the gas turbine without exceeding its base load firing temperature limit. Therefore the additional fuel would have to go after the gas turbine, which means supplemental firing. This would not be a low cost field modification! (Unless the unit was initially purchased with provisions for future addition of supplemental firing.)

1 out of 1 members thought this post was helpful...

otised is correct--it's not possible to increase steam production over that which occurs at Base Load without auxiliary firing of the HRSG.

IGV Exhaust Temperature Control can be used to increase steam production over that which would be available without using IGV Exhaust Temperature Control--but that's all. Air flow is down because the IGVs are being closed to increase exhaust temperature. Exhaust temperature increase will help to make steam temperature higher and to slightly increase steam production--but only above what would be possible at any Part Load condition without IGV Exhaust Temperature Control.

Auxiliary ("Duct") firing is the only way to increase steam production significantly, and the only way to increase steam production above Base Load operation.

Thank you, otised, for the clarification. I was not very clear about "increased steam production," and it could have been interpreted to mean above Base Load production levels.

Thanks Otised and CSA, as always I am enjoying reading your explanation.

I think we will try to do IGV control sometime in October during HGPI, I will keep posting our findings. You may tell me what other parameters we should be looking? Besides, there are many common variables we will make note of those. I am still looking in this forum if they use IGV temp control.

Thanks for valuable info.

1 out of 1 members thought this post was helpful...

sardar108,

MANY plants use IGV Exhaust Temperature Control. In fact, most units with DLN combustors use IGV Exhaust Temperature Control whether or not they exhaust into an HRSG, and they can't disable it--it's always on.

It's proven technology that's been around for decades. It looks at the CPD-biased exhaust temperature reference, TTRX, and the actual exhaust temperature, TTXM, and adjusts the IGVs to try to keep the actual exhaust temperature as close to TTRX as possible while loading by keeping the IGVs closed as much as possible. As long as the CPD transmitters are working correctly and calibrated and scaled correctly there's really nothing additional to watch. You can look in the ToolboxST file to find the IGV control section and once you find that you can work backwards to the IGV Exhaust Temperature Control section and see what signal names there are to monitor. TXGVERR is one that comes to mind (I don't have any application code or sequencing to look at at this time).

Again, it's pretty tried-and-true, tested, proven logic. If you have some past Trends you can look at from start-up/loading, you can see how the IGVs work without IGV Exhaust Temperature Control enabled. What I think you'll find is that the IGVs stay closed until the exhaust temperature reaches approximately 700- or 900 deg F (I can never remember which temperature that is...). And then as the unit is loaded and the exhaust temperature would tend to increase the IGVs are opened to maintain the 700- or 900 deg F setpoint. Once the IGVs reach their maximum operating angle (typically 84 DGA for most older 7EA units), as load is increased the exhaust temperature will then start to rise--until it reaches TTRX, at which time the unit will be on CPD-biased Exhaust Temperature Control, or, Base Load.

With IGV Exhaust Temperature Control ON, as the unit is loaded the IGVs will stay closed much longer--until the exhaust temperature gets very close to TTRX. Then, as the unit is loaded and the exhaust temperature would tend to increase the IGVs are opened to maintain TTXM very close to TTRX. (Older units used to have a slight offset between TTRX and TTXM at Part Load, approximately 10 deg F; but newer control schemes have done away with the offset.) Once the IGVs reach their maximum operating angle, and TTXM is equal to TTRX, the unit will be at Base Load.

It's as simple as that. Find some recent start-up/loading Trends, or create one the next time the unit is started. You only need to monitor TTRX, TTXM, CPD, FSRN, FSRT, TNH, DW and CSGV. (And you don't even really need the FSRs or TNH--but it might be helpful when you compare the Trends of IGV Exh Temp Control OFF to IGV Exh Temp Control ON--which you should do when you are first trying IGV Exhaust Temperature Control so everyone can see the differences in exhaust temperature versus load.)

Thanks, I got it. It is easy to start the unit on IGV temp control from start up. What I am looking here how to go on IGV control, if you are already on BASE LOAD? Following steps are logical to start with (and correct me if I am wrong).

Reduce the load (about 10%) or till controlling FSR is FSRN. I will use governor as compared to preselect. I want to keep speed droop active in case grid sees any major upset. Hopefully at this time by selecting IGV temp control "ON" GT will have smooth ramp down (closing) on IGV to reach TTRX, which is new TTRX (TTRXGV).

Next week I will study the IGV temp reference block along with TTRXGVB. One question comes in mind: if one can not go below IGV reference angle, then what is the use of manual IGV button (open or close) on HMI? Or when this is used? Can we use after dropping the load? If so, then how the IGV reference is changed? Nothing was done except dropping the load. I think, I will get most of these questions answered if I go and study the related function blocks. Meantime any suggestions, please keep posting.

Thanks

sardar108,

Typically, you are overthinking this. You can turn on IGV exhaust temperature control while the unit is at Base Load--nothing will happen (because the IGVs are at maximum operating angle and IIXM equals TTRX). I think if you look at TTRXGV while the unit is at Base Load you will see it probably equal to or very close to TTRX--it, along with TTRX, is being calculated ALL the time, even when the unit isn't running. It's just not active until IGV exhaust temp control is enabled and the unit is at Part Load.

As you lower TNR and the unit goes back on Droop Speed Control the exhaust temperature, TTXM, will (would) begin to drop--but IGV exhaust temp control will start closing the IGVs to keep TTXM equal to TTRX.

And, really? You're going to worry about grid frequency control in Southern California??? Shouldn't be a problem unless there is a big heat wave when you're attempting this, and then, should you be reducing load anyway.?.?.? And aren't there new units in Long Beach--BIG ones?

IIXM should have been TTXM....

Gotta love splcjeqrs.

Sometimes.

NOT.