Hi everyone,

I am a new user of this information sea and also a new operation engineer in a CCPP with two 9FA GE gas turbines (255 MW) and 270 MW steam turbine. I want to ask a question about the openness of IGV at gas turbines. Why is its minimum openness 27 DGA? And is it changable or what is its effect? Or in the other mean why has it minimum openness? Thanks your answers already...

 

Welcome! And congratulations on your new position.

This author has a feeling about why you might be asking this question; can you tell us why you think the IGVs (Inlet Guide Vanes) should be more open or more closed?

This author has wondered about this question, also. It is believed that there is a minimum opening which must be maintained in the event of a unit trip (emergency shutdown) and/or a catastrophic failure of the IGV actuator to maintain a minimum flow through the compressor. In other words, if the IGVs were allowed to fully close during operation or a shutdown it would probably damage the compressor. So, a mechanical limit has been set to protect the compressor as much as possible.

Further, if the IGVs were to fully close when the compressor was at or near rated speed, they would probably be sucked into the compressor, causing even more damage.

The angle should NOT be changed. There is a mechanical limit on the actuator travel to prevent them from closing much further. And, opening them more during a start-up would cause problems during firing and acceleration. It would also require more torque from the starting means.

Again, can you tell us why you think the IGVs should be at some angle other than 27 DGA (DeGrees Angle) during start-up or shutdown?

Does your site cycle during the day? Starting and shutting down fairly frequently? Does the HRSG (Heat Recovery Steam Generator) cool down excessively during shutdown periods, so you or someone thinks that by closing the IGVs during shutdown the heat can be retained in the HRSG longer?

This problem has occurred at several sites. One solution has been to used a rolling (roll-up) door in the inlet duct; closing the door during shutdown reduces the draft through the unit and "bottles up" the heat in the HRSG. There have been other similar solutions, but closing the IGVs is not one of them. Again, there is a minium mechanical stop, and usually the actuator cannot travel much beyond that point, anyway.

Feedback from posters is critical to this forum. If you get your question answered here or find a solution to your problem, or even if the replies are a complete miss, it helps others who search the forum to know if the information provided was helpful or not. If you've searched the forum and found feedback, you already know what we're talking about. So, welcome--but don't forget to let us know if you find what you're looking for when you originate a thread.

markvguy

 

hi markvguy!

I'm sorry to reply too late...

I think my last question wasn't clear. I want to ask whether the openness of IGV is a site specific parameter or this value is a design value for 9FA gas turbine. Does this mean that in 9FA gas turbines this value is always 27 DGA?

Also the function of this minimum openness is to prevent the compressor to damage. At this point in our plant we have compressor bleed off valves to prevent from surge effects! Can you explain the function of this system? And also another question... in normal operation of CTG (means base load or part load) if one of these valves opens what will unit do (trip or anything else)?

Thank you again already.

Also one of your questions' answer is our plant's planned outage time for a year is app. 10...

 

The minimum IGV angle specified for a particular unit in the Control Specification is the minimum IGV angle for that unit for that site for that application.

There are some other 9FA users who monitor this site. If any one of them is reading this, can you tell us what the minimum IGV angle is for your unit(s)?

Compressor bleed valves serve to divert a portion of the compressor flow at stages downstream of the inlet. This author has never heard of a GE-design heavy-duty gas turbine without compressor bleed valves--they are crucial to protecting the axial compressor during starting and shutdown. They are required regardless of the IGV angle. In fact, the IGVs of most units modulate further open during acceleration while the compressor bleed valves remain open.

For most F/FA-class units, if a(the) compressor bleed valve(s) open during on-line operation the unit will trip.

There's another thread in progress on this site about compressor bleed valves; check that for more information.

It would be helpful to understand why you're asking the question about miminum IGV angle.

markvguy

 

Thank you for your information, markvguy!

 

if there is a minimum IGV angle required to protect the compressor, does increasing IGV during turbine operation yield any improvement?
im asking this because according to one of my operator, the IGV of my plant was increased from 84 to 86 previously and it caused some improvement on the GT load.

thx
sridaran

 

Hi to you all
I am new on the platform, and a gas turbine mechanical maintenance engineer maintaining GE frame 9E gas turbines. Recently a unit tripped on IGV control trouble (IGV not opening). The operating pressure of the auxilliary hydraulic pump is 1500psi but inspection it was 27psi. So we suspected the pump, carried out inspection and discovered minimal bearing damage and was changed and the pump brought back to service, while the main hydraulic pump was inspected for failed teflon gear which was still okay. After these intervention, low pressure still persisted and IGV control system could not be actuated to open IGV. What could be the issue?

 

Check the operation of IGV dump valve 20TV-1