We have two GE PG5371 gas turbine at fertilizer complex in Pakistan. each having ISO rating capacity of 26.3Mw. controlling system is MARK V & both turbine are operate on synchronized state with combine cycle ON mode. at combine cycle ON IGVs opening reduced to 56% & becomes fixed by default. total plant load active power demand is 20Mw . each gas turbine shared the 10Mw With exhaust temp 405 & 420C respectively at 56% IGVs opening , 10Mw load.

Now our aim is to review & increase the exhaust temp to 10 to 15C more by reducing further IGVs opening from 56% angle to 52% so that in HRSG steam generation can be increased. Now what you suggest new opening & how we can make it safe for max exhaust temp increasing. Especially is there any chance to of compressor stall & surging if we go to reduce 4% more IGVs opening . If it is, then how by which mean we can find out new safe opening.

Exhaust tripping temp is 570C that is far away from normal operated value. Our gas turbine IGVs range is 42 to 85 degree.

Plz respond also of the other GE Frame 5 machine about the IGVs opening & exhaust temp in combine cycle On mode.

Thank you

 

ZEESHAN,

You have identified the possible pitfalls of closing the IGVs below 56 DGA: surge/stall.

Please contact the manufacturer or packager of the turbines at your site for assistance with this issue.

If you want more exhaust temperature, then increase the load. You are operating at low GT loads, which is not very efficient--not for the GTs nor even for the total GT & HRSG.

There is also the possibility of adding auxiliary duct burners to the HRSG, though you seem to be searching for the low-cost, easy solution. Good luck, and let us know if you find one!

 

Also note that increasing the exhaust temperature may not produce more steam, only steam at a higher temperature. In fact, the mass flow may be reduced.

Closing the IGV's, while it increases exhaust temperature also reduces exhaust gas flow. If you want more energy out, you have to put more energy in. That means increasing the fuel flow, either into the gas turbine or into a supplemental burner. We still haven't figured out how to break the law of conservation of energy.

 

thanks CSA for your reply, we have duct burner in HRSG. however our objective is to make steam generation from HRSG more economical by recovery of max heat recovery from GT flue gases by adjusting the appropriate opening of IGVs where air flow drop should be negligible..

 

Well, as has been said before: When you own the machine and "the warranty" you can do whatever you want--as long as you're willing to pay for any consequences.

As otised says, you may (likely) not achieve the desired result along with possibly causing untold damage to the turbine.

Best to talk to the turbine manufacturer or packager before proceeding.

 

Thanks for the reply & interesting closing sentence. its our general experienced that when Gas turbine combine cycle mode is ON IGVs reduced from 85 to 56deg angle & as a result steam generation in HRSG increased that support us to reduce firing in duct burner. more over in night timing at 04oo hrs GTs exhaust temp comes down almost 25 deg C & fuel flow in duct burner increased to 2500NMC/hr even though in night gas turbine mass flow rate of compressor has increased & in case of high ambient temp at 1500 hrs fuel gas flow in HRSG duct burner increased to 3300 nmc/hr for the same steam generation 92ton/hr.

That some how is a practical experience to figured out energy conservation law momentary