Hello,I am trying to learn about DLN tuning,what DLN is and etc,especially about GE,ex GE machines?Do you have any book that you use?or articles where these problematics are described?
Learning DLN tuning without complete knowledge of what DLN is.Hello,I am trying to learn about DLN tuning,what DLN is and etc,especially about GE,ex GE machines?Do you have any book that you use?or articles where these problematics are described?
thanks,I am trying to learn about the control part of a gas turbine,usually frame 5 turbines.I am new to the job so a lot of my questions might seem a little bit strangeLearning DLN tuning without complete knowledge of what DLN is.
Well, That is a big task. I do have respect for those that are trying to learn.
However, I looked at some of your previous posts. Your interest was the speed sensors. I wired up the six speed sensors on a Frame 7EA today. Tomorrow I will send a picture.
Hello CSA,I am trying to become a control engineer about frame 6 gas turbines.and I trying to learn about them.I am being trained about DLN,but it is an intensive course at my company and honestly I am not learning much.But as tyou said it would be very helpful to learn first what DLN isnikidi.control,
This topic has been covered before on Control.com. Previous threads can be found and reviewed using the 'Search' feature at the top of every Control.com webpage.
There are multiple types of DLN, and while the process of tuning is basically the same, the actual procedures for the various types can differ greatly, as can the types of instrumentation required and the time for testing.
If you can be more specific about what you are trying to understand, we can probably provide more information.
BUT, to my knowledge--there aren't any books about DLN tuning (well, there are, but they are all about combustion and combustion dynamics and have a lot of chemistry and maths--nothing that is really going to help someone unfamiliar with tuning to limit emissions (NOx and/or CO). There has been a lot written about various aspects of DLN operation and tuning to eliminate specific issues (such as blowout), but this is basically an on-the-job learning experience. Some companies/OEMs (Original Equipment Manufacturers) have developed spreadsheets for use in tuning and analysis--but most are considered proprietary. DLN tuning is a very big business--meaning companies make a LOT of money performing it--in many parts of the world. BUT., in some parts of the world DLN is just a nuisance, and tuning is almost never performed (until some damage is found or occurs because there were long-running issues which were ignored). In some parts of the world violating emissions limits comes with civil AND criminal penalties. BIG money--and prison time (seriously!!!). In other parts of the world, emissions limits are not enforced, and in fact, emissions monitors (which can fail often) aren't kept calibrated or running. So, many plants don't even know what their emissions are (which is BAD because when emissions are out of limits, BAD things can happen to hot gas path parts--REALLY BAD things!).
Again, tell us what you're after, and we can try to help you understand it a little better. But, as Curious_One says--trying to understand DLN tuning without first understanding DLN (at least the type of DLN in use on the machine(s) at the site where you work) is going to be pretty difficult. DLN tuning really requires a very good understanding of the equipment and principles involved.
Hope this helps!!!
Also visible in the photo are the seismic vibration sensors for #1 bearing. The bently nevada keyphasor box and one the the bently nevada vibration prox probesLearning DLN tuning without complete knowledge of what DLN is.
Well, That is a big task. I do have respect for those that are trying to learn.
However, I looked at some of your previous posts. Your interest was the speed sensors. I wired up the six speed sensors on a Frame 7EA today. Tomorrow I will send a picture.
Hello CSA,my company (SHELL OIL Company) wanted me to learn something about DLN because it might useful for me in the future.Your response is great as always!I thank you for the clarity and also taking the time of giving a lengthy response!I just took an introductory course,if I have any other question I will ask them,Thank you for your availability!nikidi.control,
So, we don't know how important emissions are at the Company/plant where you work. We don't know if the emissions monitoring equipment is maintained properly and calibrated regularly. We don't know why you are being trained in DLN tuning. It would help to know.
The main causes of problems with DLN-I combustion systems which were running well and producing emissions within specification but suddenly go out of compliance (emissions limits; guarantees) are:
1) Unstable grid frequency. This results in unstable turbine-generator speed, which results in fluctuating air flow through the axial compressor, which results in the unit being unable to remain in Premix Steady State combustion mode.
2) Unstable gas fuel supply pressure--either from the gas fuel supplier or on-site compressor or pressure regulating station/valve, or because the SRV (Stop-Ratio Valve) is unstable for some reason.
3) Ignition source(s) in the primary combustion zone causing the low-emissions premix combustion fuel mixture to ignite into a high-temperature diffusion flame. This usually results from liquids entrained in the gas fuel flow that collect and carbonize into a blackish substance that can get so hot it ignites the premix combustion gases into a diffusion flame. This can be liquid fuels (diesel; gasoline) entrained in the gas fuel supply; or lubricating oil (from the compressors in the gas fuel supply system); and contaminants in the gas fuel supply that get past filters and separators and "plate" on fuel nozzle tips and get hot.
4) Large variances in fuel flow-rates to individual combustors. Gas fuel delivery systems rely on manifolds and pressure and fuel nozzle orifice sizes that are nearly identical to result in equal flows to all the multiple combustors. If rocks or other contaminants (metal scarf; metal shavings; rags; cigarette butts; gasket material; etc.) block fuel nozzle orifices in one or more combustors this can reduce the fuel flowing into the combustor and cause emissions problems as well as exhaust temperature spreads.
5) IBH control valve mis-operation and/or instability. Pretty self-explanatory
6) Large ambient temperature changes, such as from one season to another. Particularly when starting machines from a cool or cold condition and the ambient temperatures are much lower than normal, problems getting into and remaining in Premix Steady State can occur. Sometimes, just waiting 15-30 minutes (if possible) for the turbine and IBH manifold and inlet ductwork and bellmouth to warm up, as well as turbine internals, can easily result in a successful transition to Premix Steady State on a subsequent attempt. (Some machines in some locations have to be re-tuned every fall or every spring.... That's why "auto-tune" systems are very popular--even if few of them work reliably or are even used for very long and are abandoned after a couple of years. Mostly because of lack of understanding, poor maintenance and too much faith in automation and controls.)
Those are the most common problems. There are others, much less common. Cracks in combustion liners and transition pieces; failed or failing nozzle side seals; high exhaust duct back pressures--these are some or the other less common problems.
DLN-I combustion systems like stable operating conditions. Stable frequency (speed). Stable gas fuel supply pressure. Stable gas control operation. Clean gas fuel supply conditions. A clean axial compressor, along with clean inlet air filters, and low or normal exhaust duct back pressure.
And, there is only so much DLN tuning can accomplish. If the fuel nozzle flows are well out of tolerance (usually, more than 10% difference in flow-rate between the highest and lowest fuel nozzles) this can cause problems. If combustion liners with incorrect dilution hole sizes are installed in the machine (usually from questionable vendors/suppliers) this can cause problems. If turbine nozzles are in poor condition, and/or shrouds are in poor shape, or fuel nozzle restrictions occur because of fuel cleanliness issues, or the fuel constituents/components change suddenly and by significant amount--these can all cause problems which DLN tuning will probably NOT be able to resolve. If the IGV LVDTs are not properly calibrated, or are improperly calibrated, or the IGV actuator is excessively worn (a real problem particularly on older, poorly maintained GE-design Frame 5- and Frame 6 heavy duty gas turbines), this can cause emissions problems which might be solved with DLN tuning.
Again--DLN tuning can only do so much. And ,in reality--it's really very little. Most DLN emissions problems are either the result of improperly maintained or calibrated emissions monitoring systems, or technician-induced problems (poor LVDT calibrations of gas control valve(s) and/or the IGVs), or dirty fuel, or dirty oil (causing problems with the electro-hydraulic servo-valves used for hydraulic actuators), or dirty machines or incorrect clearances on worm machines well past a maintenance outage date, or on incorrect combustion liners and/or fuel nozzles. The Mark* is quite surprisingly the cause of VERY FEW emissions problems--though it gets the majority of blame and suspicion for most of emissions problems.
This is only a brief introduction to DLN-I systems and tuning. It is a very complex subject, and has lots of subltle nuances and differences. If you have specific questions, you can try asking them here. It is critical to understand how DLN-I combustors operate and what their limitations are and what can—and can’t—be done to affect NOx emissions levels. It’s also important to know that there are MANY parameters that can affect NOx emissions levels that are not monitored or controlled by the Mark* but which get blamed on the Mark* OR which many people believe the Mark* can be used to “compensate” or overcome in order to continue to run the turbine.
DLN combustion is not well-suited to some applications—particularly plants synchronized to grids that experience frequent frequency disturbances. DLN-I likes stable operating conditions (stable frequency; stable gas fuel supply (pressure and dew point and flow and cleanliness, including the removal of entrained liquids)). If the plant has to occasionally supply a nearby facility with electricity when separated from the grid and the load(s) are subject to large variations the DLN-I combustion system is probably not going to be able to remain in low emissions mode at all times—and the Mark* will be blamed, falsely.
There are MANY more aspects of DLN-I combustion systems and operation (dynamics; IBH; igniters; fuel characteristics; flame detection; flame detector cooling). It’s a very complicated and touchy system—but when it is well understood and operated properly it reduces NOx emissions. But—it’s NOT “set-it-and-forget-it.” Operating a DLN-I combustor-equipped turbine IS NOT like operating any conventional combustor-equipped GE-design heavy duty gas turbine. Trying to use a DLN-I combustor-equipped turbine in a plant that has to control MW across a utility tie-line is frustrating and the Mark* (incorrectly) gets the blame. While the Mark* will permit continued operation in Extended Lean-Lean combustion mode, that’s VERY HARD on hot gas parts. The OEM equates one hour of Extended Lean-Lean operation to TEN hours of Premix Steady State operation.
It’s a good low NOx emissions system, but robust is not a word that is associated with DLN-I combustion systems.
Lately, the gas control valves supplied by the OEM are decreasing in quality—but a lot of the valve problems are related to poor quality fuel. And, electro-hydraulic servo valve issues are almost ALWAYS the result of poor oil maintenance (contrary to false public opinion).
Hope this helps. I have probably exceeded 10,000 characters….