Best book or articles to learn about DLN tuning especially GE machines?

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?
 
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.

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.
 
nikidi.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!!!
 
Learning 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.
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 strange
 
nikidi.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!!!
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 is
 
Learning 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.
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 probes
 

Attachments

nikidi.control,

Is your company primarily training you to tune DLN-I combustor-equipped gas turbines? And, if so, are they explaining why and how DLN-I combustion systems work—or are they just giving you a procedure for tuning they want you to use (to avoid using a company or contractor to perform the tuning)?

GE-design Frame 5 and Frame 6 heavy duty gas turbines use GE’s DLN-I (that’s a Roman numeral one) combustion system. This combustion system uses combustion liners that have two combustion zones—called primary and secondary. By controlling the fuel flow-rates into the two combustion zones the temperature of the combustion gases in the combustion can be controlled.

Nitrogen oxide formation, NOx, which is the “N” in DLN, is a function of the temperature of the combustion of hydrocarbon fuels such as natural gas and liquid fuels like diesel fuel and gasoline. NOx is a primary component of a type of air pollution called smog that results in a haze in the atmosphere that is unhealthy and unsightly.

The UV (Ultraviolet) radiation emitted by the normal process of combustion (which results in high NOx formation) results in a flame that is visible to humans as a blue-orange flame and can be detected using sensors which are common in most combustion processes (boilers and gas turbines). In a DLN combustor operating in low NOx emissions mode (called Premix Steady State combustion mode) the UV radiation produced by the combustion reaction is undetectable using the same sensors—even though combustion is still occurring.

During the starting and initial loading of a gas turbine with DLN-I combustors it is important to note that combustion occurs at high temperatures and NOx formation is high. However, by varying the fuel flow-rates to the two combustion zones it is possible to reduce the temperature of the combustion reaction and thereby reduce the formation of NOx emissions.

It is important also to know that the low-temperature combustion reaction that results in low NOx emissions is a rather unstable combustion mode and is subject to returning to a high-temperature combustion reaction producing high NOx emissions and a visible flame. And, if the fuel flow-rates to the two combustion zones in a DLN-I combustion system are not very quickly adjusted when this occurs the combustors can be severely damaged.

The turbine control system and the typical devices used to monitor combustion cannot actually measure the temperature of the combustion reaction as it’s occurring in the DLN-I combustion system. And, because the combustion in GE-design heavy duty gas turbines occur in multiple, separate and individual combustors it would require multiple, separate devices in each combustor to accurately monitor combustion reaction temperatures—and that would be very expensive. (In fact, GE-design heavy gas turbine control systems do not monitor air-fuel (or fuel-air) ratios—or even use exhaust gas oxygen content for controlling the fuel flow or emissions. In this regard, they are less sophisticated than the lowest-cost automobiles with variable fuel injection and O2 sensors in the exhaust system.)

I’m about to hit the friggin’ 10,000 character limit of Control.com posts—which is absurd and frustrating and makes ZERO sense in light of the fact that replies automatically quote the previous post adding to the characters appearing in a reply AND to the storage space required for archiving the threads….). So, time permitting I will pick this up again later.

Hope this helps!
 
Really?

Seriously?

Does this information (about speed pick-ups and vibration sensors) belong in a thread about DLN books/articles?

If anything, shouldn’t it be in the other thread by the original poster?
 
nikidi.control,

So, the other main concept behind DLN-I low NOx emissions combustion systems is that the majority of the air entering the combustion liner does so through the primary combustion zone. The reason for that is that when the unit is operating in Premix Steady State the majority of the fuel is directed to the primary combustion zone, and that requires a lot of air for combustion. Also, the air entering the primary combustion zone mixes ("premixes") with the fuel where it combusts (burns) in a low-temperature flame without generating UV radiation which can be detected by flame sensors. Those low-temperature combustion gases pass through a venturi (a "nozzle" of sorts) into the secondary combustion zone where a small amount of fuel is flowing and a high-temperature diffusion flame is burning (one that generates UV radiation which is detected by flame sensors).

In it's simplest form, it is this "split" of fuels between the primary- and secondary combustion zones that results in low NOx emissions, and relatively low CO (Carbon Monoxide) emissions as well. Under near ideal conditions with combustion liners and fuel nozzles made with OEM (Original Equipment Manufacturer) orifices and dilution holes and with fuel which matches that used to design the combustion system and components and with properly maintained and calibrated gas fuel control valves approximately 80% of the total fuel flow to the turbine combustors is directed into the primary combustion zone and approximately 20% of the fuel is directed to the secondary combustion zone. By changing this split of fuel flows to the two combustion zones it is possible to have an effect on NOx (and CO) emissions. THIS is called tuning--the process of changing the fuel splits slowly whilst monitoring emissions levels in order to find the optimal NOx (and often CO) emissions levels.

Tuning, therefore, requires a working and calibrated emissions monitoring system, often called a CEMS (Continuous Emissions Monitoring System). In some parts of the world in preparation for testing and tuning and certification of an emissions source (such as a gas turbine) it is necessary for a company to come to site with a mobile emissions monitor to find the optimal location of emissions sensors and to also verify (certify) the accuracy of the in-situ (site) CEMS equipment. Maintaining CEMS equipment is a costly and expensive endeavour--and it requires knowledgeable people and calibration gases. Usually, CEMS calibrations are performed (often automatically) once per day. And if the calibration is found to be inaccurate, it usually gets performed two or three times more (per day). This consumes a lot of calibration gas, and a lot of time. And, in some parts of the world if the CEMS equipment can't be brought back into specification/calibration in a few hours, then the emissions source must be shut down (the gas turbine stopped) until such time as the CEMS equipment is back within specification/calibration. There are companies and CEMS equipment manufacturers that provide remote monitoring and support of CEMS equipment (at a pretty high cost)--but if the laws of the region or country prevent operation without working CEMS equipment then it's money well-spent sometimes.

But, I digress. The idea is that tuning requires a working emissions monitoring system. And tuning with a marginally working CEMS is a waste of time.

DLN-I combustion systems get to Premix Steady State combustion mode by actually shutting off the flow of fuel to the primary combustion zone and directly all fuel flow to the turbine to the secondary combustion zone for a short period of time. Why? To extinguish the diffusion (high temperature) flame in the primary combustion zone. Once the flame detectors in the primary combustion zone sense the absence of high temperature diffusion flame, most of the fuel flowing to the secondary combustion zone is then redirected back to the primary combustion zone. If everything is working correctly the fuel flowing into the primary combustion zone WILL NOT ignite into a diffusion flame, but rather will combust (burn) in a low temperature "premix" flame.

The thing about Premix Steady State combustion mode is that is usually can only exist in a small range of the turbine's load range. For a machine NOT equipped with and using IBH (Inlet Bleed Heat--a VERY poor name for the function it serves) that load range is only about 80-100% of rated load on an ISO day (an ISO day refers to ambient conditions being as per the turbine nameplate) on a machine in new and clean condition (meaning relatively clean inlet air filters; relatively clean IGVs (Inlet Guide Vanes); a relatively clean axial compressor with in-spec (in specification) ; a turbine section (nozzles, buckets and shrouds) in good condition with in-spec clearances; and an exhaust duct back pressure in specification.

Using IBH can almost double the load range the unit can operate in low-emissions Premix Steady State combustion mode, from about 40-100% load. This also means that the unit can get into Premix Steady State combustion mode sooner than would otherwise be possible.

IBH is NOT included on all machines, and on many of the machines it is included on it cannot be disabled (in other words, it can't be turned off). On some machines it is installed on, it can be turned on and off. And it makes sense--on occasion--to do so, but generally most sites want to get into Premix Steady State as soon as possible, and remain in Premix Steady State as long as possible. Particularly in locations where the unit can't be operated for very long periods of time out of Premix Steady State. These places usually have a maximum amount of time they can be in "start-up" mode and operate in the "lower" combustion modes (Primary and Lean-Lean), and they have a maximum amount of time they can remain in operation when NOT in low emissions mode whilst trying to return to Premix Steady State.

DLN-I has very few adjustments which can be made to get a unit operating reliably in low emissions Premix Steady State and within limits of operation (sometimes called the "emissions guarantee"). Really, about the ONLY adjustment field personnel can make without disassembling the machine is to change the fuel splits (the amount of total fuel flow-rate going to the primary- and secondary combustion zones). DLN-I requires a pretty narrow range of air-fuel (or fuel-air) mixture--but remember: The Mark* DOES NOT know what the actual air-fuel (or fuel-air) mixture is for the turbine. AND, in reality there are actually multiple air-fuel (or fuel-air) mixtures--one for EACH combustor (which can have small differences in fuel and/or air flow into and through the combustor and still be within specification). AND, there is NO adjustment for the amount of air flow entering the combustors--no combustion air valves. There's only the IGVs--and that ONLY affect the total air flow into the turbine's combustors, but can't be used to change the air flows into individual combustors.

The other adjustments which can affect or be used to affect NOx (and to an extent, CO) emissions are the dilution hole sizes in the secondary combustion zone of the combustion liner. BUT, to change the dilution hole size the liners have to be removed from the turbine and sent to a shop that is capable of making the changes and adding or re-applying any coatings lost or required during the process of changing the dilution hole sizes.

Another possible affect that can be made is the fuel nozzle orifice sizes. Fuels often do change over the life of a gas turbine-based power plant. And this can affect many different aspects of turbine operation--notably, the emissions levels.

So, as you can see, DLN-I is kind of "touchy" (meaning it is sensitive to several different parameters)--and only one of the parameters is easily changed.

Another thing which can adversely affect emissions after tuning is gas fuel control valve LVDT calibration. Because, it's the LVDT calibration that determines what valve positions correspond to the fuel flow-rate through the valve(s). If an LVDT calibration is performed and it noticeably changes the scaling of the LVDT feedback that can change the fuel flow-rate through the valve and into one or both of the combustion zones--which can affect the emissions being produced by the unit. That's ANOTHER reason why simply "calibrating" a gas valve (or all of the gas valves) IS NOT a good idea--especially on a DLN combustor-equipped machine. Done improperly, or cavalierly (without proper review and analysis) the emissions levels can suddenly change--and for "no apparent" reason. Well, except, that that damned Mark* is causing emissions to be out of compliance (out of guarantee). When the Mark* didn't change anything--it was the technician to instructed the Mark* to make changes, and didn't review/analyze the resulting changes. And the Mark* gets the blame when it was the technician's fault.

I'm probably nearing that blasted 10,000 character limit again....

To be continued.
 
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….
 
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….
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!
 
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