IGV for DLN Type Without IBH

A

Thread Starter

ABDI

hi,

why if the turbine you are working on has DLN (Dry Low NOx) combustors, IGV exhaust temperature control is not operator-selectable; it's always on?

I THINK IGV always on, because need for IBH. but in my system IBH can't work, then we decided to force IGV OFF.

Is corrected or not? MY SYSTEM IS FRAME 9E AND MARK V GE AND DRY LOW NOX-1.

thank you for reply
 
I do not understand what do you mean by IGV OFF. When IGV is not moving, you will not be able to increase/ decrease the air flow going into your combustor, and hence you will not be able to burn more/less fuel.

DLN is a type of combustor to burn more efficiently and produce less NOx. I donot think that is any way related to IGV exhaust temperature control.

So you always need IGV to be controlled if you want to burn more/less fuel and hence change load supplied.
 
Killz has it almost correct, in that the IGVs are used to control the air flow into the combustors--and for DLN combustors it's very important, critical, really, for the IGVs to control air flow since premix operation is borderline unstable to begin with. The design of DLN-I combustors is to force almost all of the compressor discharge air into the "head end" of the combustor (where the primary fuel nozzles are located) so as to lean the air-fuel mixture as much as possible--without causing unstable combustion, which is very difficult when the air-fuel mixture is so lean.

DLN-I turbines operate with IGV temperature control always enabled--that's why there's no buttons to allow it to be selected OFF. The combustion and control system is designed and programmed to use the IGVs in this mode to help prevent lean blow-outs and maintain stable combustion.

So, it's not correct to force IGV temperature control OFF for a DLN-I unit--whether or not IBH is enabled, working or not working. IBH is simply a method for protecting the axial compressor when the IGVs are closed below 57 DGA in order to allow Premix operation to lower loads than would otherwise be possible. So, the IGVs are being used to reduce air flow as fuel is being reduced while in Premix steady-state so as not to lean out the air-fuel mixture in the primary combustion zone too much, resulting in a primary zone re-ignition or trip.

IGV exhaust temperature control for non-DLN units is used to maximize exhaust temperature when the gas turbine is exhausting into a boiler or some other process where heat is required. It reduces turbine efficiency (heat rate) but improves the overall plant efficiency. But, for DLN machines, IGV exhaust temp control is required for proper operation of the combustion system and should NOT be forced OFF.
 
I want to know what happen in combustion DLN-1 type if the IGV MODE IS OFF AND THE IBH system doesn't in service (because there isn't any control loop for IBH system).

THANK YOU FOR REPLY
 
Hi CSA,

If the IGV mode in DLN TYPE frame 9E mark V should not force to IGV off mode, why there is the logic exhaust temperature control?

There isn't selectable bottom to IGV ON AND IGV OFF mode for operator but we can select the IGV temperature control logic.
 
abdi,

We want to know how you think IGV Exhaust Temperature Control and IBH are related--because they are not. [NOTE: IGV position and IBH are related, but IGV Exhaust Temperature Control and IBH <b>are not</b> related.] It's not clear what you mean by "no control loop for IBH"--do you mean the unit doesn't have IBH?

Regardless of the answer of whether your unit has IBH or not, or if it's not working for some reason, all DLN-I combustor-equipped units are designed to operate with IGV Exhaust Temperature Control ON at all times. As you noted--there is no button on the HMI to disable it.

IBH is a really bad name for the function it provides--which is to protect the compressor when the IGVs are closed below 57 DGA at rated speed.

And the reason IGVs might be closed below 57 DGA at rated speed is to reduce the air flow into the combustor (by reducing the air flow into the axial compressor) to maintain the desired air-fuel mixture as the unit is unloaded (units are unloaded by reducing fuel)--which allows the unit to remain in Premix Steady State at loads much lower than would otherwise be possible if the air flow into the combustor couldn't be reduced as fuel was reduced as the unit was unloaded. This is called "turndown"--the ability to operate at lower loads while remaining in Premix Steady State, the lowest emissions mode. And increased turndown (the ability to operate at lower loads while remaining in Premix Steady State) is only possible if the air flow into the combustor can be reduced as fuel is being reduced to maintain combustion stability and reduce combustion dynamics.

So, if the fuel were to continue to be reduced when the IGVs reached 57 DGA nut the IGVs couldn't close any more to reduce the air flow into the combustor, then the unit would likely lose flame because of combustion instability and/or dynamic pressure pulsations.

IGV exhaust temperature control keeps the IGVs closed longer than otherwise in order to reduce the air flow through the unit which increases exhaust temperature. This reduces the air flow into the combustors--and on a machine with conventional combustors there is so much excess air flowing into the combustion zone it doesn't really affect flame stability or combustion dynamics very much. It does increase heat rate (which decreases gas turbine efficiency) BUT it increases overall plant ("combined cycle") efficiency--which means the plant is more efficient even if the gas turbine is marginally less efficient. Again, for a machine with conventional combustors, this is perfectly acceptable to be able to switch between "simple cycle mode" (IGV Exhaust Temperature Control OFF) and "combined cycle mode" (IGV Exhaust Temperature Control ON).

On a machine equipped with DLN-I combustors, most of the axial compressor discharge air enters the primary combustion zone at all times when the unit is running. There is no "damper" that can change how much air enters the primary combustion zone versus the secondary combustion zone--in other words, there's no method for splitting the axial compressor discharge between the primary- and secondary combustion zones that can be used to increase the air flow into one while decreasing the air flow into the other. The only "knob" that can be used to control the total air flow into both combustion zones is the IGVs. That's it; there's nothing else.

The DLN-I combustion system is designed to operate as efficiently as possible--and for maximum combustion stability--when the IGVs are operating in Exhaust Temperature Control mode. The fuel splits to the two combustion zones for the various combustion modes are designed with air flows that are known to exist when IGV Exhaust Temperature Control is active, and there is <b>NO</b> mechanism in the Speedtronic that will change fuel flows if the IGVs <b>ARE NOT</b> in Exhaust Temperature Control mode on a machine equipped with DLN-I combustors.

Again, the air/fuel mixtures of a DLN-I combustor-equipped machine are designed with air flows known to exist when IGV Exhaust Temperature Control is active. That means that combustion stability is maximized and combustion dynamics (the vibrations which naturally occur when fuel is combusted) are minimized when IGV Exhaust Temperature Control is active on a unit equipped with DLN-I combustors.

On a DLN-I combustor-equipped machine if IGV Exhaust Temperature Control were forced OFF (when it should ALWAYS be <b>ON</b>) that means that too much air will be entering the combustor for the amount of fuel that is being burned. This means the air-fuel mixture will be even leaner than normal, which can lead to combustion instability (in diffusion flame- (Primary- and Lean-Lean) <b>and</b> Premix Steady State combustion modes!) and increased combustion dynamics. Combustion dynamics are the vibrations that cause increased wear on combustion liner hula seals, liner/fuel nozzle interfaces, transition pieces, bull-horns, side seals, etc. They can also cause combustion gas flow pulsations that can lead to loss of flame trips.

Again, there is <b>NO</b> recalculation of fuel splits when IGV Exhaust Temperature Control mode is selected OFF on a DLN-I combustor-equipped machine. This means if someone forces IGV Exhaust Temperature Control Mode OFF that air flows into the combustors primary- and secondary combustion zones will be higher than normal, and air-fuel mixtures will be leaner than normal--both of which can lead to combustion instability (turbine trips) and increased combustion dynamics (which can cause increased wear on the combustion hardware and loss of flame trips).

IBH and IGV Exhaust Temperature control are not related. DLN-I combustor-equipped turbines are designed to operate with IGV Exhaust Temperature Control enabled and active--that's why there's no operator button to enable/disable IGV Exhaust Temperature Control: It's not supposed to be disabled on DLN-I combustor-equipped machines. Disabling it by forcing it off can lead to combustion instability (which can lead to turbine trips) and it can also lead to increase combustion dynamics which will accelerate wear on combustion components.

AND, most importantly (in some places in the world, anyway) forcing IGV Exhaust Temperature Control OFF will likely lead to increased CO emissions at a minimum, and maybe even increased NOx emissions under certain circumstances.

DLN-I combustor-equipped units are designed to operate with IGV Exhaust Temperature Control active (ON) at all times.

IBH and IGV Exhaust Temperature Control are, for all intents and purposes, mutually exclusive. DLN-I combustor-equipped units with IBH--and units without IBH--b>DO <NOT</b> have buttons to enable/disable IGV Exhaust Temperature Control. IGV Exhaust Temperature Control is supposed to be active at all times on a DLN-I combustor-equipped unit. (At least they shouldn't! GE HMIs can be horribly configured at times, and the application code for DLN-I combustor-equipped units should not allow IGV Exhaust Temperature Control to be selected OFF even if the buttons were on the HMI.)

Now--which you <b>HAVEN'T SAID</b>--if the turbine is operating <i>at Base Load AND you are forcing IGV Exhaust Temperature Control OFF</i> then nothing untoward will happen as a result of that decision. Because the <b>definition</b> of Base Load begins with the IGVs at maximum operating position which means the IGVs are at their full open position and IGV Exhaust Temperature Control is disabled so forcing it OFF won't have any affect. <b>BUT</b> if the unit is unloaded from Base Load--either automatically or by the operators--with IGV Exhaust Temperature forced OFF, then not so good things will most likely happen. If the unit doesn't lose flame then the increased combustion dynamics will cause increased wear on the combustion hardware. I could even envision a scenario where one or more combustion liners might collapse while the turbine was operating because of the increased combustion dynamics (they are very powerful), which would lead to a long and very costly shutdown to repair the resulting damage.

Hope this helps!
 
abdi,

As many manufacturers do, they use logic/sequencing in many different applications.

Simply because the logic exists does not mean it should be forced ON or OFF. The fact there is no operator-selectable ON/OFF capability should speak volumes for the intent of the operation of the unit.

Further, I'll wager there is a LFALSE or LTRUE (or false or true) contact in the logic that prevents operator selection of ON or OFF--which is why it had to be forced OFF.

Again, to answer this specific question: In an effort to use similar logic/sequencing in multiple applications, and to prevent the need to "re-invent the wheel" to write IGV Exhaust Temperature Control specific to DLN-I machines GE or the packager of the turbine decided to use existing logic/sequencing and most likely to prevent operator enabling/disabling by placing blocking logic (using LFALSE or LTRUE or false or true contacts) in the enabling rung.

And, to the larger point of the this thread: There is NO relation between IGV Exhaust Temperature Control and IBH. If a DLN-I combustor-equipped unit has IBH--or even if it doesn't--the Speedtronic will still use, and the system requires, the IGVs to be positioned using IGV Exhaust Temperature Control at all times under all operating conditions. Except when Base Load is selected, active <b>AND</b> the unit is operating at Base Load (when the IGVs are at their maximum operating position and IGV Exhaust Temperature Control is not active even though it is enabled).

Period.

Full stop.
 
> IBH is a really bad name for the function it provides--which is to
> protect the compressor when the IGVs are closed below 57 DGA at rated speed.

The reason for the name is that, piping-wise, this system was originally designed for turbines located in extremely cold climates (north slope of Alaska), to prevent icing in the inlet ducting and filters. This was in the good old days before DLN and "F" class gas turbines.
 
hi CSA,

When you say increased air flow in combustion chamber (change IGV MODE From ON to OFF) in DLN-1 TYPE can cause increase combustion dynamic, I want to know why? or what happen in combustion exactly?
please refer me a Article or Paper about it?

because we can't go to premixed mode (the best mode) we decided work in primary mode.

in primary mode with IGV on we have low load. but with IGV off, we have high load at primary mode.

and another reason for selected IGV OFF is: reduce combustion temperature to increase life of combustion chamber.

please hint me exactly to explain for my boss.

THANK YOU VERY MUCH FOR REPLY
 
abdi,

There is no written documentation that details what you are looking for. What I know I've learned from working on these units for a couple of decades, working with combustion- and design engineers, observing the evolution of DLN-I technology over the years, understanding how turbines operate and how the combustion system operates, and writing and correcting DLN-I sequencing/logic.

Further, you are not being forthcoming in your description of how the unit is being operated and why. You are just looking for validation of flawed thinking and so are not providing all the details.

Primary and Lean-Lean combustion modes are--<b>again</b>--transitory modes; that is, they are modes through which the unit must transition in order to get to Premix Steady State. Extended Lean-Lean is a temporary mode for troubleshooting and is only intended to be operated in for short periods of time while attempting to get back into Premix Steady State.

Premix Steady State is the design, long-term operation mode for DLN-I combustor-equipped units. Not Primary mode; not Lean-Lean mode; not Extended Lean-Lean mode. But, you're going to find that out soon enough.

GE considers DLN-I technology to be proprietary technology, and so they publish very little about the details of how it works. I'm only covering the high-level details here, and not exposing any proprietary information or trade secrets. If anyone would take the time to look at and analyze the combustion system components and some of the sequencing/logic, all of what I've tried to explain could be learned and confirmed first-hand.

And you're going to get to see first-hand what the combustion system components look like--when they have to be replaced. Which is going to happen sooner rather than later at your site. I know of a Frame 9E in South America that burned down to the ground when being commissioned because the start-up T.A forced it to remain in Primary Combustion Mode all the way to Base Load. We are talking about cast steel and metal burning.

The good news about that site was that no one was injured or killed when that happened. It took months to rebuild the unit--and in that time it produced zero electricity. None. Zilch. Zero. Nada. Nothing. And, it cost a great deal (millions of US Dollars) to rebuild.

I fervently hope that no one at your site is injured or killed. DLN-I combustor-equipped units are not like units with conventional, diffusion flame combustors. DLN-I units can't be operated at high loads and for extended periods of time in any other mode than Premix Steady State without serious damage, eventually catastrophic damage. I venture the combustors in your unit are damaged beyond repair at this point and are dangerously close to collapse. When that happens, gas fuel can make it's way into the compressor discharge casing and then either a fire or an explosion is going to occur.

Best of luck--again, I sincerely hope that no one gets injured or killed when the unit "crashes." Because if it continues to be operated as you are describing, it's going to crash.

I think you've already been told this, but get yourself a copy of GEH-3920. It details the effects of operation in combustion modes other than Premix Steady State. It doesn't have the information you are looking for (again, that's proprietary for the most part) and it's not going to tell you that if you can't get into and remain in Premix Steady State you need to shut the unit down and investigate and resolve the issue. But that's what needs to happen. Odds are that the problem is mechanical--I'd estimate the odds are 9:1 that the problem is mechanical. If it wasn't mechanical when this problem started, it is now--that much I can <b>guarantee.</b>

I would really like to see the pictures of the combustion hardware that's removed from the unit. But, I have a very good imagination, and I've just recently seen some pictures of a Frame 9E in North Africa that was operated in Extended Lean-Lean for some time, repaired, and then operated again in Extended Lean-Lean for a long period of time. I think the total repair bill for the two outages and hardware was in excess of USD 3 million. And, the operators were told what the cause was after the first outage (liquids in the gas fuel), and they refused to believe it and continued to operate the unit just as before--and then refused to believe it even when a gas analysis proved the existence of the liquids. I'm NOT saying that's what happened in your case--but the results are going to be the same: Damaged liners and nozzles and hot gas path hardware. If any parts break off and go into the turbine section, the damage can even be worse--and more costly, and take longer to repair.

Best of luck. I'm finished with this thread. And this issue. Free advice is worth what you paid for it: Nothing. I'm learning that paid advice, correct or incorrect, is more often followed and heeded than free advice that's correct and helpful. This is just one more validation of that painful fact. Get someone to site that can answer your questions and help you resolve your problems.

Before someone gets hurt or killed.
 
Actually, I'm <b>not</b> done with this thread. This issue started back in December of 2013 with this thread:

http://www.control.com/thread/1386045425

And then it became this thread:

http://www.control.com/thread/1400902483

And, now it's morphed into this present thread.

So, since December of 2013 this unit has been operated in modes other than Premix Steady State, and continues to be operated in modes other than Premix Steady State. Now, the IGVs are being forced into Simple Cycle mode to get more load because it seems the unit can't be operated in even Lean-Lean mode any longer. Which is just further evidence that the combustion liners are damaged and in danger of catastrophic failure. One can only imagine how many trips this unit has suffered, and as we all know, trips are injurious in their own right.

And, yet, still, because the unit will start and run in Primary Mode, or Lean-Lean Mode, the supervisors continue to direct the operators to run the unit--even after being repeatedly told that Primary- and Lean-Lean Modes are transitory modes and NOT to be used for extended operation. And, now they want validation of their "logic" to force the IGVs into Simple Cycle Mode to increase load in Primary Mode.

So, this is the history of this problem: Some firm was allowed to come in and perform a Hot Gas Path inspection. We don't know the origin of the parts used in the HGP. But we do know that the company was "allowed" to leave site before the unit was confirmed to operate properly in Premix Steady State Mode--which it apparently was prior to the HGP. So, something done (or not done, or not done properly) during the HGP was most likely the cause of the inability to remain in Premix Steady State. Most sites would hold the firm doing the mechanical work responsible to return and rectify the problem.

And, despite being told repeatedly that Premix Steady State is the design mode of operation, the site continues to insist that just because the turbine runs in Primary- and Lean-Lean (and Extended Lean-Lean) modes that it's okay to continue to run the unit in modes other than Premix Steady State. And, now that they can't get anywhere near rated load (which is, again, further evidence of real problems) they are forcing logic to get more load in Primary Mode.

These are the facts as we know them. Based on what little information has been provided. The names have not been changed to protect the innocent, nor the guilty. Unfortunately, we'll never hear another peep from this site. But, it's a small world in the power generation industry. Turbine crashes like the one this unit is headed for usually get talked about. The facts of how it came to be are not going to be known, and GE will get the blame, as usual. Not the operators or their supervisors who are making the decisions to continue to run the turbine regardless of (free, worthless) advice.

I can hear it now, "The Speedtronic didn't prevent us from operating in Primary- or Lean-Lean or Extended Lean-Lean Modes! It's the Speedtronic's fault! The Speedtronic allowed us to force the IGVs into Simple Cycle Mode on a DLN-I combustor-equipped machine! It's the Speedtronic's fault!"

Yep; the finger-pointing will start immediately after the crash. And no one at the site will ever say, "We had some advice from control.com not to run the unit like this. Was that good advice or not?" Nope. "The Speedtronic let us do that--it's the Speedtronic's fault!"

This just further proves the need for training for operators and supervisors. Sure, anyone can click on a target with a mouse and claim to be an operator or a supervisor. But, it's correctly making these kinds of decisions (showing good judgement) that define a true operator or supervisor. Operating a turbine requires knowledge and experience. Knowledge comes from training, and experience, well.... There's a saying that goes:

"Good judgement comes from experience.

Experience comes from poor judgement."

There's going to be a lot of "experience" at this site real soon. Hopefully, the bad judgement that led to it will turn into good judgement in the future.
 
Hi CSA,

I totally believe you about your discussion that the IGV MODE FOR DLN TYPE must be ON. BUT in my site want to know what happen for thermal- acoustic when we work in IGV:OFF because increase the temperature in combustion hardware is very bad for life of combustion component?

please define me about the different between dynamic pressure, instability flame with thermal- acoustic?
in my document: higher firing temperature reduces hot gas path parts lives, while lower firing temperature increase parts lives.

Thank you very much to reply me.
 
abdi,

There's nothing I can add to change your supervisors minds. I would just like to see the photos of the liners when the next outage happens.

And get just 1% of the cost of the outage to repair the damage.
 
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