Dear All,

i am working with Frame 6 machine having Mark VIe control system.
I want to know is there any problem or it is OK.
machine is on part load(AUTO) with following data

CPD - 141 psi
IGV opening - 72 Deg
Exhaust temperature - 1041 Deg F
load - 31 MW (max capacity 36 MW)
IGV temperature control reference - 1056 Deg F
IGV temperature control curve Isothermal - 1069 (TTKGVI-constant)
Exhaust temperature control curve Isothermal - 1080 (Constant)
IGV minimum opening - 56 deg
IGV Max opening - 86 Deg

We have HRSG connected to GT and IGV temperature control mode is ON.

I understand that as per IGV algorithm, based on CPD value temperature control reference TTRXGV is calculating 1056 Deg F.

Now my question is IGV opening is normal. As i feel at this point, to increase the exhaust temperature(For HRSG) IGV should get close to minimum position, until the IGV temperature control reference reaches to 1069 Deg F.

Does IGV modulated differently in Part, Preselect and Base load?
Hope my question is clear.

Simply i want to know, why IGV is not getting close more to increase exhaust temperature, and what parameter decides the opening of IGV.

 

There is something a little strange. Basically with IGV temp. Control on, the IGVs should hold the Exhaust Temp. at the IGV Temp reference (1056 Deg)as you load and keep opening until full open as you load the machine. When the IGVs are full open and the machine keeps loading, the Exhaust temp will reach Exhaust temp. Control and you are then at Base Load.

IGVs should control Exhaust Temp by progressively opening as you load the machine.

If you want to send me your Email address, I can send you a write up from GE on IGV temp. Control.

[email protected]

 

thank you sir.

Actually my mistake, IGV temperature reference and exhaust temperature are matching that is 1056 Deg F in my above post, mistakenly i wrote it as 1041 Deg F.

But my question is, does IGV also modulate CPD? Then it should get close to minimum position, so that exhaust temperature increases to 1069 Deg F?
Thanks.

 

Of course, IGV angle modulates CPD, that's how you make the exhaust temp. higher at lower load by reducing the CPD and hence the cooling air flows.

 

That's what i have asked in first post.

If there is margin for closing the IGV and make exhaust temperature higher up to (TTKGVI=1069 Deg F) then why it is held at lower temperature.

 

There is one possibility I wish to share. I have come across the problem that IGV failed to modulate TET. It was about 10 Celsius colder. Fuel flow had yet reached the maximum.

My finding - Compressor inlet temperature measurement was 2-3 Celsius hotter than it should due to measurement error.

It turned out to be that the IGV control logic sensed that gas temperature at compressor inlet was higher by a few degree Celsius (1.5-2 C). The controller responded by limiting the maximum fuel flow. This is logical since the air density is lesser at higher temperature. Therefore air mass flow rate was also reduced. As a result, maximum firing was restricted. The GT lost 2-3MW of its capacity.

 

Let me try....

If it senses compressor inlet temperature is higher than normal, and control bias is an open loop control.