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Forcing IBH OFF 9E
DLN (Dry Low NOx) combustors 9E to force IBH OFF 85MW

Hi,

why if the turbine you are working on has DLN (Dry Low NOx) combustors 9E, IGV exhaust temperature control I THINK always on. then we decided to force IBH OFF. WITH 85MW
Is corrected or not? MY SYSTEM IS FRAME 9E AND MARK VIE GE AND DRY LOW NOX-1.
thank you for reply

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

bil07,

What are you trying to achieve by forcing IBH (Inlet Bleed Heating) OFF?

What is the significance of 85 MW?

Yes, IGV Exhaust Temperature Control is always ON with DLN-I combustion systems. It's necessary to keep the air-fuel mixtures and dynamic pressures in normal, controllable regions to maintain stable combustion and emissions.

Without IBH, operation in Premix Steady-Tate combustion mode (the lowest NOx emissions mode) below approximately 80% of rated load is. generally not possible--which restricts operation to a narrow load range to maintain low NOx emissions.

By using IBH, it's generally possible to get into Premix Steady-State combustion mode (lowest NOx emissions mode) sooner (sometimes as low as 40% of rated Load)--which means a wider load range of low NOx emissions operation is possible. Or said another way, the unit can remain in Premix Steady-State combustion mode below approximately 80% of rated load, and to loads as low as approximately 40% of rated load. This means the possible low NOx emissions operating range can be reached at lower loads -as low as approximately 40% of rated load) during starting, and if the unit needs to remain in low NOx emissions mode while in operation below approximately 80% of rated load it can--down to approximately 40% of rated load.

If IBH is turned OFF, the load range of low NOx emissions operation is reduced to 20% of rated load, and only above 80% of rated load. That's a pretty narrow band of operation in lox NOx emissions mode.

With IBH ON, the load range of low NOx emissions operation is expanded to approximately 60% of rated load, from approximately 40% of rated load to Base Load.

So, unless the unit only operates at or very near Base Load the majority of the time it's running, shutting off IBH is going to restrict low NOx emissions operation to approximately 80-100% of rated load.

If the unit exhausts into an HRSG ("boiler") to produce steam for some process or for a combined cycle power plant (CCPP), there may be an issue with steam temperature or flow-rate that someone is trying to control or limit or expand by changing the way the gas turbine operates. Or, the HRSG has some design characteristic (flaw) that someone is trying to use the gas turbine to compensate for either to protect the HRSG or to produce more steam. These kinds of schemes are usually very complicated, can be very difficult to operate in reliably while maintaining low NOx emissions AND maintaining optimal gas turbine parts life and longevity, and allowing for plant operating flexibility over s wider load range.

Without understanding what you are trying to achieve, and what the knock-on effects of forcing IBH OFF are on other aspects of plant operation and reliability we can't be of much help. The concepts of DLN-I combustion and IBH have been covered many times in the past on control.com, and when people ask these types of questions it's usually always when trying to find some kind of "work-around" scheme for either a plant design issue or because of issues related to improper combustion hardware or some other limitation that has cropped up that is not normal. This is how some extremely complicated--and restrictive--control schemes get started that are never fully documented or understood, and when the originator (perpetrator) leaves the plant the scheme becomes a real problem with no explanation and no resolution.

"We've always operated that way! But we don't have any idea why we've always operated that way, and we want to change the way we operate but because we've always operated that way and we don't know why, we're afraid to change. Mr. Expert, tell us in 20 minutes, or less, why we've always operated that way, and make it possible for us to change how we operate overnight with 100% confidence and a 100% guarantee that the plant will never be damaged and will be more efficient and profitable!"

So, think LONG and HARD about the problem you have not explained that you seem to be trying to solve, because the "solution" can cripple the plant now and for years. It might seem simple to you now--but if you leave the plant it will likely be a not-so-great legacy. The better solution might be an attemporator, or auxiliary burners, or a material change for some section of the HRSG. Using control schemes to overcome design issues can be very problematic. Sometimes it works, often it doesn't, and sometimes it can get very expensive and complicated.

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

bil07,

I should have also said that IBH should only be on when the IGVs are below approximately 62 DGA on a GE-design Frame 9E heavy duty gas turbine with DLN-I combustors . When the IGVS are above approximately 62 DGA the IBH Control Valve should be closed. So, if there is some need to force the IBH Control Valve closed when the IGVs are above approximately 62 DGA then it would seem there is some problem with the IBH Control Valve, and/or the IBH Control Valve actuator. (And, there is usually a manual IBH isolation valve which could be manually closed to ensure there is no flow through the IBH Control Valve when there shouldn't be flow through the IBH Control Valve.)

IBH (despite it's poorly chosen name) serves to protect the axial compressor from stall/surge at rated speed when the IGVs are closed below approximately 57 DGA--which they will be if IBH is ON during starting and initial loading, and during shutdown when the unit is still in Premix Steady-State combustion mode and below approximately 80% of rated load. (The IGVs are closed below approximately 57 DGA to reduce the air flow into the combustors to protect against dynamic pressure oscillations and to maintain Premix air-fuel ratios as Load is reduced below approximately 80% of rated. NOTE: Air/fuel mixtures are NOT monitored nor are they calculated by the Mark* Speedtronic turbine control system. All of that is done during the design of the combustion parts and the fuel nozzles.)

There is approximately 5 DGA of hysteresis ("deadband") as the IGVs open above 57 DGA (to 62 DGA)during loading, and as they begin to close below 62 DGA during unloading.

But, when the IGVs are above approximately 62 DGA the IBH control valve should be fully closed on a typical GE-design Frame 9E heavy duty gas turbine with DLN-I combustors.

There should be no need to force any logic to stop IBH.

I want to also mention that some DLN-I units do not a Transfer Gas Valve, and some of the turbine control systems for those units were programmed to not allow an operator to select IBH OFF or ON. This is because the fuel flow-rates through the secondary fuel nozzle passages are so high when trying to switch from Lean-Lean combustion mode to Premix Steady-State combustion mode at loads around 80% of rated that very high combustion dynamics occur which can affect the mechanical wear-rates of hot gas path parts as well as the stability of combustion (which could result in trips from 80% of rated load--with all the wear and tear and accelerated factored fired hour accumulations). So, forcing IBH OFF for units without Gas Transfer Valves and without buttons on the HMI to select IBH OFF & ON should not be done so as to protect the unit and maximize parts life.)

Before IBH, it was NOT possible to get into Premix Steady-State below approximately 80% of rated load nor to stay in Premix Steady-State below approximately 80% of rated load. This severely limited the low NOx emissions operating range of those units. When IBH was developed and applied to DLN-I units it allowed the units to get into Premix earlier during loading (at approximately 40% of rated load) and to remain in Premix longer during operation (below approximately 89% of rated load to approximately 40% of rated loaf--which expands the low NOx emissions operating range greatly.)

Then in an effort to simplify the DLN-I gas fuel system it was decided to eliminate the Gas Transfer valve--and to do that without causing harm to the unit it was necessary to add IBH to permit Lean-Lean-to-Premix transfers at lower fuel flow-rates (lower loads). And the ability to select IBH OFF and ON was removed from the turbine control system.

But, then it was decided not to offer the Transfer-less gas fuel system, and IBH could generally be selected ON or OFF by the operator.

Isn't this fun?!?!?!

Hope this helps!

dear csa,

thanks ok