DLN1 MODES DURING OPERATING IBH of gas turbine fram 6b

There are four (4) basic modes of combustion on a GE-design DLN-I combustion system:

1) Primary
2) Lean-Lean
3) Premix Steady State
4) Extended Lean-Lean

During starting and loading of the unit to Base Load, or near Base Load, the unit starts in Primary combustion mode, then transitions to Lean-Lean combustion mode and then transitions to Premix Steady State combustion mode--which is the combustion mode which yields the lowest NOx emissions possible.

The benefit of using IBH (Inlet Bleed Heat) is that during starting and loading the unit can transition into Lean-Lean and Premix Steady State sooner than would otherwise be possible. Without IBH the unit would transition into Premix Steady State at approximately 80% of rated turbine load. With IBH in operation and working properly the unit can transition into Premix Steady State at approximately 40% of rated load. (Again, the unit still has to transition from Primary to Lean-Lean before it can transition to Premix Steady State with IBH enabled and working properly; that just occurs at a lower load than would be possible without IBH.)

When unloading from Premix Steady State without IBH the unit can only unload down to approximately 80% of rated turbine load before it has to transition back to Lean-Lean combustion mode from Premix Steady State. With IBH in operation and working properly the unit can remain in Premix Steady State combustion down to approximately 40% of rated turbine load. As the unit is unloaded further, it transitions back to Primary combustion mode, and remains there during shutdown to flame-out.

It should be evident that with IBH enabled and working properly the load range for Premix Steady State (the lowest NOx emissions mode) is "extended." In other words, WITHOUT IBH a GE_design DLN-I combustion system can only operated in Premix Steady State combustion mode from approximately 80% of rated turbine load to 100% of rated turbine load. WITH IBH working properly and enabled a GE-design DLN-I combustion system can be operated from approximately 40% of rated turbine load to 100% of rated turbine load--and increase of approximately 40% of rated turbine load.

It IS NOT recommended to operate a GE-design DLN-I combustion system in any mode other than Premix Steady State for long periods of time. What is a "long period of time?" Essentially, more than two- to four hours or so. GE has set up guidelines for how to account for extended periods of operation of DLN-I combustion systems in modes other than Premix Steady State. For example, one (1) hour of operation in Lean-Lean or Extended Lean-Lean combustion mode is the equivalent of operating ten (10) hours in Premix Steady State. That means that the next maintenance outage will have to occur 10 hours earlier for every hour of operation in Lean-Lean or Extended Lean-Lean combustion mode. It should be clear: Extended operation in Lean-Lean (or Extended Lean-Lean) is hard on the unit.

DLN-I combustion systems WERE NOT designed to be operated in Primary or Lean-Lean (or Extended Lean-Lean) combustion modes for long periods of time. Primary and Lean-Lean combustion modes are transitory mode--they are necessary combustion modes which must be passed through on the way to Premix Steady State.

Now, for Extended Lean-Lean combustion mode. Extended Lean-Lean combustion mode is a temporary mode--it only exists as a means of keeping the unit running while the operator takes appropriate action to get the unit back into Premix Steady State combustion mode. In the development days of DLN-I when a primary zone re-ignition occurred or if the unit failed to transition back to Lean-Lean from Premix Steady State during unloading the unit would be tripped--which is not really good for the hot gas path parts (combustion liners; fuel nozzles; transition pieces; turbine nozzles and buckets; etc.). So, Extended Lean-Lean was developed in order to keep the unit running so that the unit wouldn't be tripped and the operator--and their supervisors--could decide what to do. ("What to do" means re-trying to get back into Premix Steady State, or unloading the unit and shutting it down to investigate the cause for failure to remain in Premix Steady State combustion mode.)

AGAIN--GE-DLN-I combustion systems WERE NOT designed to be operated for extended periods of time in any combustion mode other than Premix Steady State. Yes; the Mark* will permit operation in Lean-Lean or Extended Lean-Lean or even Primary combustion modes and will not automatically shut down the unit or trip it (unless there are other serious problems). IT'S UP TO THE OPERATORS AND THEIR SUPERVISORS to decide what to do when the unit can't be operated in Premix Steady State combustion mode. Now, sometimes--in emergency situations--it's critical to keep the unit running in Lean-Lean or Extended Lean-Lean or Primary combustion mode for extended periods of time. That's understandable. BUT, that time must be taken into account when planning for maintenance outages, AND when determining how long to remain in some combustion mode other then Premix Steady State. As has been written, operation for extended periods in combustion modes OTHER THAN Premix Steady State is hard on the hot gas path parts. Very hard.

If the Mark* automatically tripped the unit every time it experienced a primary zone re-ignition or couldn't remain in Premix Steady State people who complain very, Very, VERY LOUDLY about how unreliable the Mark* turbine control system was (they already complain enough about the Mark*!!!) and GE turbines--which are usually very reliable machines compared to their competition--would get a bad reputation. That's why GE didn't decide to automatically trip or shutdown the unit if it couldn't operate continuously in Premix Steady State; they left it up to thinking operators and their supervisors to make logical, rational decisions about what to do if there are problems getting into or remaining in Premix Steady State.

It's all related. IBH allows a wider load range (sometimes called "turn down") of operation in the lowest NOx emissions mode: Premix Steady State. The unit can transition in Premix Steady State earlier with IBH and can remain in Premix Steady State longer (down to a lower load) with IBH. IBH is there to protect the compressor, and that all happens in the background. The benefit of IBH (besides protecting the axial compressor!) is that it allows a wider load range in Premix Steady State (the lowest NOx emissions mode). But, there are no additional or lesser combustion modes possible with or without IBH--it's all the same combustion modes.
 
Hi,
Our engine timers shows the operation time of IBH, total fire time and all modes except premix mode. Is it right to get the value of pemix time from(total fire time minus IBH time)

Your answer is very very appreciated.
Regards,
hider7777,

On a GE-design heavy duty gas turbine with DLN-I, IBH operates in Primary- and Lean-Lean combustion modes and for only part of the time the unit is running in Pre-mix Steady State combustion state. (I don't recall precisely but I think might also only at low loads in Extended Lean-Lean combustion mode.)

If your engine timers do not record Pre-mix fired time that would be HIGHLY unusual. It may be that the display doesn't show the value of Pre-mix fired time, but it would be extremely unusual if the Mark wasn't actually recording the time.

Anyway, stranger things have happened and this might just have to be added to that list.

Look, if you know total fired time and Primary- and Lean-Lean (and I'm presuming Extended Lean-Lean) fired times you can add all the individual combustion mode fired times together and subtract that sum from the Total Fired Time to arrive at the Pre-mix Steady State fired time.

Hope this helps! Again, IBH serves to protect the axial compressor when the IGVs are closed below approximately 57 DGA (DeGrees Angle). (Actually, IBH usually operates at minimum air flow up to (during loading) or beginning at (during unloading) approximately 62 DGA.) So, it's not supposed to be active during higher loads when operating in Pre-mix Steady State combustion mode.
 
Dear hider7777,

You discussed this with a DCS engineer. I'm going to guess that you are looking at a non-GE DCS display (NOT an GE Mark* HMI display) which is supposed to be displaying information retrieved from the Mark* (via the HMI, probably). Please confirm where you are viewing the fired timer values--a DCS (non-GE DCS) or a GE Mark* HMI 'Timers and Counters' display.

Only YOU can answer your question by adding up the fired times you have available on your screen. For example, if the Total Fired Time was 17,890 hours, and the Primary Fired Time was 3,120 hours, the Lean-Lean Fired Time was 2,467 hours and the Extended Lean-Lean Fired Time was 233 hours, the difference between the Total Fired Time and the other three Fired Times would be (17,890-(3,210+2467+233))=17,890-5,820=12,070 Hours--which would be a reasonable estimate of Premix Fired Time for a unit with 17,890 hours Total Fired Time. How hard is this mathematics?!?!!!??! (Not very.) If you can't do the maths yourself, at least post the values you have instead of making us guess at what they are!!! Total Fired Time should be equal to the total amount of time that flame was detected in the unit, which includes ALL DLN-I combustion modes (Primary, Lean-Lean, Premix Steady-State, and Extended Lean-Lean). If you can only see three values on a display (Primary, Lean-Lean, and Extended Lean), then the Premix Steady State value should be equal to the Total Fired Time minus the total of the other three Fired Times. Give us the data you are seeing--and tell us where exactly you are getting the data--and we can help with the problem.

It's NOT likely that GE isn't showing unreal values of combustion mode times; it's MORE LIKELY that someone who has developed and programmed an engine timer display on a non-GE DCS is not converting the information being received properly so the display values look incorrect. If you would refer to a GE Mark* HMI 'Timers and Counters' display you would probably see more realistic, and even complete, values. Again, it would be extremely unusual if the value of Premix Steady State fired time did not appear on a GE Mark* HMI 'Timers and Counters' display--EXTREMELY UNUSUAL. Because, it's VERY LIKELY that the value IS BEING CALCULATED (accumulated) in the application code (the software running in the Mark*), and the standard GE Mark* HMI displays are usually configured to show all the relevant, accumulated values--and Premix Steady State is relevant. Very relevant.

Because there are some transition times (such as from Lean-Lean to Premix Steady State) sometimes there is a very small difference between the total of all the fired times and the Total Fired Time. Again, I think Total Fired Time is the total time that flame was detected in the unit, which may not include some short transit periods. So, the sum of all the individual fired times may not exactly equal the Total Fired Time. But, it shouldn't differ by very much. The transit time from Lean-Lean to Premix Steady State isn't more than a couple of minutes, if that, so we're not talking about very much time that might not be accumulating between combustion modes. And, I think it's ONLY the Lean-Lean to Premix Steady State time that isn't being accumulated, no other transit times. (But it would be necessary to see the application code running in your unit to know that for sure.)

Give us some good data--you can even add a clear photo of the display you are getting your information from to this post!!! (Notice I said "clear photo.")
 
hider7777,

I'm beginning to believe this turbine doesn't have either a GE Mark* turbine control system or a GE Mark* HMI.... Neither of which really matters--except if the unit doesn't have a GE-provided DLN-I combustion system, and then all bets are really off.

Based on the information provided, this is seemingly straightforward mathematics:

Fired Time in Extended Lean-Lean Mode:4.4 hours
Fired Time in Lean-Lean Mode:1199.9 hours
Primary Mode Fired Time:2850.4 hours
Fired Time in Secondary Mode:1.7 hours
Total Fired Time:13992.4 hours
Premix Fired Time:13992.4-(4.4+1199.9+2850.4+1.7)=9936 Hours
I am presuming that "Fired Time in Secondary Mode" means some large portion of the time when switching between Lean-Lean and Premix Steady State combustion modes when there is only diffusion flame in the Secondary combustion zone (which is a very small period of time, less than two minutes or so per combustion mode transition).

As for calculating fired time at Base Load, and at Peak Load--that would only be possible if another portion of the mysterious display you send a partial copy of also had accumulators for Base Load fired hours and Peak Load fired hours (again, something usually calculated by the Mark* and shown on a GE Mark* HMI 'Timers and Counters' display). Again, it's looking more and more like a non-GE turbine control system and/or non-GE HMI.
 
My point PRECISELY!!!

The data from the GE Mark* has to be converted from its format to display on the DCS. Can't happen any other way. And, often those DCS engineers don't know all the tricks of the trade when making the conversions, particularly on large numerical values. AND, they don't always get all the pertinent and relevant information on the displays--because they don't always know what's pertinent and relevant.

Go find the GE HMI ('cause I'm pretty damn sure you ain't doin' LVDT calibrations with the DCS!) and have a look at the 'Timers and Counters' display. You'll probably be surprised at what you'll find. (Or maybe not.) But, if you're questioning the data you're looking at--you gotta go to the source!
 
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