As I heard, in the past the IGV of gas turbine was working as on / off (when the turbine is in shutdown mode the IGV is 42 DAG and when the turbine is in full speed and loaded, the IGV are completely openend till 82 DAG.

Now the IGV are controlled and opened by dependence of load.

Thanks a lot

 

You heard correctly. Many of the early GE-design heavy duty gas turbines had IGVs that were either open or closed; there was no intermediate or modulated position. (They were affectionately referred to as "bang-bang" IGVs.) The IGVs were (and are) usually kept closed during starting and shutdown to prevent surge and stall conditions, and to make starting easier as well.

Newer compressor designs required a means of controlling (reducing) air flows at lower loads and so IGVs were modulated to provide axial compressor protection.

Additionally, it was found that by modulating the IGVs that the exhaust temperature could be increased at part load, thereby allowing more exhaust heat when the exhaust of the turbine is used to heat water and/or make steam. So, as combustion turbines became more commonly used to produce steam via a waste heat recovery "boiler" (or a Heat Recovery Steam Generator, HRSG), modulated IGVs became even more commonplace. (This actually slightly reduces the combustion turbine "efficiency", but increases the overall "combined cycle" thermal efficiency because it allows more steam to be produced for the same fuel flow-rate.)

Now, in newer units, the IGVs are used to control (limit) air flow in DLN (Dry Low NOx) combustor-equipped machines to allow them to remain in low emissions mode at lower loads (providing more "turn-down").

And, in some large machines the IGVs are also used to provide axial compressor protection in very cold ambients when operating at high power outputs.

So, there may be many reasons for modulating the IGVs, or not, depending on the age of the machine and the application.

And, IGVs are not modulated as a function of load; it only appears that way. They are modulated in relation to the maximum allowable exhaust temperature based on the exhaust temperature control reference (which is usually a function of CPD on GE-design heavy duty gas turbines).

 

Are there any references for this upgrade? Like GER's etc? I have referenced GER3571H. It mentions this type of upgrade for a MS5001 Models A through M and R (FT3F) and MS5002A (FT2E). I have a customer who has a Hitatchi 6001 and has the "bang - bang" style and is considering installing the modulated IGV system. I know with the frame 5's a new style of bell mouth inlet casing is installed and some other things.

Best Regards,
Jason Hampton

 

i have a single shaft gas turbine (GE10) where the IGV positioner is an electrical motor with a special driver card. i have noticed that the IGV goes to fully close position when the turbine trip on load.

my question is
when the turbine trip, the IGV should rapidly or slowly close?
and why to protect the compressor or reduce the air flow to the turbine?

 

IGV should go fully closed on a trip, usually within 2 seconds to fully closed. This is to prevent a shut-down surge or choke.

 

Well explained Mr.CSA & Mr.Johnston.

Take care
G.Rajesh

 

My question, IGVs are modulated on exhaust temp reference and that is a function of CPD? Can you please clear this bias on CPD, what happens if CPD transmitter fails? Mine is F7EA and Mark VIe. I always get confused on this matter since CPD will depend on IGV's opening.

Thanks

 

sardar9,

Yes; when operating in IGV Exhaust Temperature Control mode the IGVs are modulated based on the CPD-biased exhaust temperature reference.

Your question about a failure of the CPD transmitter is a little unclear. Do you mean a complete loss of CPD feedback, or a higher-than-actual CPD feedback?<pre>
* Isothermal Exhaust
*------------------- <--Temperature Limit
* \
* \
* \
TTRX * \ <-CPD-biased Exhaust
* \ Temperature "Curve"
* \
* \
*
*
*
* * * * * * * * * * * * * * * *
CPD</pre>
Looking at the graph of CPD-Biased Exhaust Temperature Control, where TTRX (TTXM) is on the vertical axis, and CPD is on the horizontal axis, until CPD reaches a certain level the exhaust temperature reference is a flat line--called the Isothermal Limit. So, if CPD feedback was lower than actual or completely missing (for a unit with conventional combustors) the exhaust temperature reference will not be higher than the Isothermal Limit. And, the IGVs will be modulated to that point.

Which is true when the CPD transmitter is working properly, too. Since <b>rated</b> power (Base Load) occurs at some point on the (negatively) sloped line below the Isothermal Limit, the IGVs when in IGV Exhaust Temp Control are controlling to the Isothermal Limit value, which is the "maximum" allowable exhaust temperature.

If CPD feedback were lower than actual CPD then the exhaust temperature reference would be lower than usual, which would mean the IGVs would probably be open more than if CPD feedback were equal to actual CPD.

Units equipped with multiple CPD transmitters should not experience a "failure" (which I interpret as a complete loss of CPD feedback).

By the way, Base Load is defined to occur when the IGVs are "full open" (maximum operating angle). So, your conditions are only applicable when the unit is operating at Part Load, and this means the CPD will usually only be slightly less the value at which the (negatively) sloped exhaust temperature reference "begins"--which is usually very near Base Load, and "full" CPD.

This was a difficult question to answer. Yes; CPD is a function of IGV angle, but when operating at Part Load the exhaust temperature reference is usually equal to the Isothermal Limit, especially if the ambient is warm and humid.

 

There is a secondary backup reference known as ttrxs. This is based on megawatts or FSR for stag machines. When correctly set it is usually 20-30f above the primary ttrxp. When all is well with no faults ttrx = ttrxp

 

The isothermal limit setting doesn't change if the backup (secondary) exhaust temperature reference becomes active. The differential shifts the (negatively) sloped portion of the curve to the right (if the Control Constants are calculated correctly). This would extend the isothermal limit to the right, also.

 

Yep, TTK_I is used for calculation of both the primary ttrxp and secondary ttrxs curves. These are two control curves not a single curve shifted to the left. End result is in a correctly configured system there is a few degrees between them. Nevertheless the question I was responding to is what happens on a CPD signal failure. I was making the point that there is a separately calculated independent backup control protection curve.

 

Can you please tell more about backup control protection curve?

Thanks