Function of IBH in liquid fuel (diesel) operation?

Dear all
We have a 9FA dual GT with DLN 2.6+, mark VI by
the readings in this valuable forum I already know that one of the main function of IBH is to protect the axial compressor from surge conditions (we also have some valves to avoid that surge conditions 20CB-1, 20CB-2, wich discharg from extraction 9 and 13 to the exhaust) and to extend the premix combustion mode (we have mode 3-6.2-6.3 or mode N-B-C) and that way to achieve the low NOX emision in a wide range of load.
the compressor need the IBH and the 20CB valves?? is not enough with de IBH (in the former DLN the IBH never was used at all)

I also know that the changes of combution modes are given by the CA_CRT factor (before this was done with the TTRF1)
what is exactly the CA_CRT? why use that and not the TTRF?

but my main question is ...with liquid fuel the behaivor of the IBH is complete different to in natural gas but the changes in combustion modes are given in the same CA_CRT , and the reduction in nox emission is because the water inyection so wich is the function of IBH with liquid fuel? its also extend the combustion mode? in liquid or gas the combustion modes are the same?

 
Dear all
We have a 9FA dual GT with DLN 2.6+, mark VI by
the readings in this valuable forum I already know that one of the main function of IBH is to protect the axial compressor from surge conditions (we also have some valves to avoid that surge conditions 20CB-1, 20CB-2, wich discharg from extraction 9 and 13 to the exhaust) and to extend the premix combustion mode (we have mode 3-6.2-6.3 or mode N-B-C) and that way to achieve the low NOX emision in a wide range of load.
the compressor need the IBH and the 20CB valves?? is not enough with de IBH (in the former DLN the IBH never was used at all)

I also know that the changes of combution modes are given by the CA_CRT factor (before this was done with the TTRF1)
what is exactly the CA_CRT? why use that and not the TTRF?

but my main question is ...with liquid fuel the behaivor of the IBH is complete different to in natural gas but the changes in combustion modes are given in the same CA_CRT , and the reduction in nox emission is because the water inyection so wich is the function of IBH with liquid fuel? its also extend the combustion mode? in liquid or gas the combustion modes are the same?

changes of combustion modes in gas and liquid fuel

1595792882983.png
 
ratm,

I know I sound like a broken record, but GE Belfort--who has "responsibility" for the programming and functionality of GE-design Frame 9 heavy duty gas turbines (E- and F- and FA-class, and all the perversions of F-class--as well as the HA-class machines)--has a habit of twisting and changing lots of established sequencing in ways one can never imagine, making it more complicated than it need be and failing to document the changes.

Anyway, I can't really think of a reason why IBH would really be necessary for liquid fuel operation--because it's not DLN (Dry Low NOx). I CAN tell you that F-class machines use a different IBH control valve than B/E-class machines; it is normally open as opposed to normally closed (on the B/E-class machines). My understanding is that on F-class machines the IGVs are held closed during starting and initial rated speed operation. This requires axial compressor protection during starting and initial rated speed operation to protect the compressor. I also believe that IBH is left active (cannot be disabled) during liquid fuel operation so that operation is similar on either fuel.

That's about all I can add or offer. IBH on F-class machines is slightly different than on B/E-class machines; so it's necessary during starting and initial rated speed operation. B/E-class machines can usually be operated without IBH (as long as they aren't transferless) and on many machines equipped with IBH it is operator-selectable (though most operators and their Operations Managers and I&C tech's don't know this).

Hope this helps! (If not, maybe someone else can offer a different view.)
 
thanks a lot again CSA for your response about the IBH
in another subject do you know why the factor CA_CRT is used instead the TTRF1?
 
CA_ don't know what that means.

CRT probably means Combustion Reference Temperature.

I imagine the combined CA_CRT comes from the ARES function, and replaces the TTRF1. I imagine--because GE deems ARES to be extremely proprietary--that CA_CRT is a realtime calculated Combustion Reference Temperature which uses multiple inputs from measured parameters (including, but not limited to, exhaust temperature, compressor discharge temperature, compressor inlet temperature, compressor discharge pressure, exhaust duct back pressure, and on, and on, and on, and on, and on ....) to calculate a firing temperature that will yield the highest output when operating at Base Load and the best performance. That's just a SWAG (Scientific Wild-Arsed Guess). I have read a total of 1-1/2 pages of nebulous information GE included in a manual for an FA-class machine with ARES. There are a number of similar brief and nebulous documents, all written in an effort to deflect questions about ARES, what it does, and how it works. I would imagine there would be some useful information in the GE Control Specification provided with the Mark VIe, and maybe GE Belfort put something more in the manuals they provide--but that's my best guess.
 
Dear SCA
I have one more question about the IBH.
Im gonna make a suposition and i would like to see if it seems logic to you, there is the thing:
In the former DLN wich was DLN 2.0 for a 9FA gas turbine in a combined cycle, the IBH was never used, in fact was in disconected mode, the IGV minimun openning was 54° and the max 90°
now we have a DLN2.6+ and now the IBH cannot be disconected anymore and the IGV minimun openning drop to 42° and max 88°
so my best guess is because now the IGV is below the minimun design point (with the danger of surge conditions to apear) it was necesary to modulate the air flow with the IBH to avoid surge ..its seem correct to you?
another doubt....I know that the low nox is achieve in a lean premix combustion mode wich means less air than the
stoichiometric, so (have in mind my poor knowledgde in combustion) its not better more air? (more IGV openning)

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best regards

RATM
 
RATM,

I would agree with you, mostly. In DLN-I and DLN 2.6 the only way to control air flow into the combustor is through modulating the IGVs. For low-load operation in premix combustion mode it's necessary to reduce air flow so much in order not to lean out the premix flame to the point that it is extinguished that it's necessary to close the IGVs a lot below the design minimum IGV angle at low load while at rated speed. That's what IBH does--it recirculates a portion of the compressor discharge air flow back to the axial compressor inlet; this reduces back-pressure on the axial compressor and the slight increase in axial compressor inlet air temperature causes the temperature of air entering the axial compressor to be less dense, which also improves the compressor operating limit protection. So, instead of just venting some of the CPD to atmosphere, or to the gas turbine exhaust (where it will cool the exhaust temperature that enters the HRSG (since most F/FA-class machines exhaust to an HRSG--Heat Recovery Steam Generator ("boiler")), they direct it back to the axial compressor inlet and take advantage of the fact that the hot air will slightly raise the axial compressor inlet air temperature which will reduce the temperature which will reduce the air density which will reduce the tendency of the compressor to exceed it's design limits (and possibly go into stall/surge and cause damage to the axial compressor).

Since DLN 2.6 is always burning in premix mode (with a slight "pilot" diffusion flame) it is probably necessary to reduce the air entering the combustor as much as possible to maintain the premix flame without extinguishing it because of excess air, so that's one reason the IGVs are closed so much during acceleration and initial loaded operation. Again, the only "knob" to adjust air flow is the IGVs--and if you have to close the IGVs so much that you can cause the axial compressor to exceed it's operating limits and damage itself, well then you have to do something to try to mitigate the situation--and IBH is one of those things. (In DLN-I, the IBH is used to allow the unit to get into premix combustion mode sooner than would otherwise be possible, and that "extends" the range of operation in premix combustion mode. Said another way, the unit can operate at lower loads in premix steady state with DLN-I combustors when using IBH (again, to protect the axial compressor from damage caused by closing the IGVs below the design minimum operating angle). And, again, slightly heating the axial compressor inlet air helps to reduce the density of the inlet air which helps to protect the compressor, as well as reducing "back-pressure" by recirculating a portion of the compressor discharge air).

That's about all I know and can explain. As a commissioning engineer, it was my job to ensure the parameters programmed into the turbine control system were all met and not exceeded and that was my assurance, so to speak, that the axial compressor was adequately protected. At a few sites in the world where extremely unusual cold ambient temperatures were experienced, the axial compressors were still occasionally subject to damage and/or failure because the ambients were so much colder than anticipated which means the air density was so much higher than anticipated. After the damage was caused, the control and protection schemes were modified to reduce load (which was NOT popular for plant owners and accountants--but was necessary to keep generating at least "some" power rather than experiencing forced outages caused by axial compressor failures which last a long time and cost a lot of money to repair and result in lots of lost revenue because the unit isn't running at all).

Hope this helps!

Again, I'm not sure why IBH is used when operating on liquid fuel--other than it kind of "standardizes" unit operating on both fuels. I'm sure there's some combustion-related reason OR the combustion system was designed to have lower air flows while operating on liquid fuel, possibly helping to reduce emissions a little and reducing the need for water- or steam injection a little (that treated, boiler-quality water is lost and gone to the atmosphere when it's injected into the turbine and can't ever be recovered--so the money spent to make the boiler-quality water is also lost and gone forever (except that when there's no gas fuel the unit can continue to run and produce revenue running on liquid fuel).

That's all I got for this thread!
 
Dear SCA
Once again you help me to understand this subject
your contributions are always very appreciated.
thank you for your time, i know you earn nothing (money) helping people here.
best regards
 
RATM,

I learn something from nearly every response I make, and from many of the posts others make, too. Money is important, yes; but it's not everything. Wealth comes in a lot of forms, not just monetary, and some days I am the wealthiest person in the world. And, as long as we remain healthy and dodging this COVID-19 thing we are all wealthy and lucky at the same time. (A former colleague said something I'll always remember: "The harder I work, the luckier I get." And, I've found that to be oh so very true over time.)

Thank you for the kind words; those are also part of my wealth.
 
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