In my plant we are having total 8 GTS of 34.5MW of GE Frame 6B . I have question that how DLN works in 6B. It having only primary, secondray and transfer manifold.

 

DLN 1.5, eh? I haven't personally worked on one of these versions of DLN combustion systems but since you posted that the combustion system has primary, secondary and transfer manifolds (and nozzles) I presume it is very similar to DLN-I and that it may have some kind of emissions monitoring and feedback which might also make some kind of fuel flow adjustments when in one of the combustion modes that uses both primary and secondary fuel manifolds/nozzles (as in changing the fuel split between primary and secondary manifolds/nozzles to control emissions levels). Many DLN-I combustor-equipped GE-design heavy duty gas turbines did not have any kind of continuous emissions monitors or use any external continuous emissions monitors to adjust fuel splits. There is some kind of version which uses a CLEC (which I don't know exactly what that stands for--but I think the C and EC stand for Continuous and Emissions Control, respectively).

DLN-I is referred to as "staged combustion"--meaning that fuel flows and combusts in one or both of the two combustion zones and the fuel flow rates to the combustion zones is controlled and varied by dividing the fuel as necessary (I'm not referring to the start-up Primary combustion mode--only Lean-Lean, Premix and possible Extended Lean-Lean (which was only intended to be a temporary mode--never a continuous mode of operation).

During starting and initial loading all of the fuel flows through the primary gas manifold and nozzles into the primary combustion zone; this is known as Primary combustion mode. As the machine is load at a point the fuel flow is divided between Primary and Secondary fuel manifolds and nozzles and fuel flows into both the primary and secondary combustion zones; this is known as Lean-Lean. As the machine is loaded further all of the fuel is directed to the secondary combustion zone through the secondary manifold and nozzles AND the transfer manifold and nozzles. It is necessary to use the transfer manifold and nozzles because some versions of the DLN-I system can't flow enough fuel through the secondary manifold and nozzles during the transfer from Lean-Lean to Premix combustion modes. But the transfer manifold and nozzles are used only during the brief period when the machine is transferring from Lean-Lean to Premix combustion modes. During this Lean-Lean to Premix transfer period the flame in the primary combustion zone is extinguished because the fuel flow to the primary combustion zone is completely shut off. Once diffusion flame is extinguished in the primary combustion zone for a short period (a few seconds) fuel is then readmitted into the primary combustion zone through the primary manifold and nozzles and the fuel combusts in a very lean manner which greatly reduces the formation of NOx and also reduces the amount of CO2 to a certain extent. The fuel flow-rate between the two combustion zones is determined by tuning--and possibly by the feedback of some kind of continuous emissions monitor on a very few machines (maybe ones with DLN-1.5?). It's usually about 80% of total fuel flow-rate to the primary combustion zone and about 10% of the total fuel flow-rate to the secondary combustion zone. The fuel being burnt in the secondary combustion zone burns in a diffusion flame (at least most of it does) which can be detected using typical flame sensors. The fuel that is burning in the primary combustion zone during Premix combustion IS NOT burning in a diffusion flame--it IS burning, but the flame cannot be detected with typical flame sensors.

In a nutshell, that's DLN-I, and possibly DLN-1.5. Tuning DLN-I involves measuring emissions levels at the gas turbine exhaust (before any HRSG with auxiliary duct burners) and then making adjustments to the fuel flow-rates to the primary and secondary combustion zones which in Premix combustion mode to bring the emissions levels into compliance and guarantee (if possible... sometimes it's necessary to change fuel nozzles and/or combustion liners to bring emissions into full compliance and meet guarantee levels).

There should be some training manuals around from the time of commissioning which you should be able to get some visual aids and descriptions of DLN-1.5 from. Or, look in the Operations & Maintenance Manuals provided with the GE turbines and auxiliaries for information.

There should also be a document called the Control Specification which may have some information on the DLN-1.5 system and operation and parameters in one of the sections (probably the Gas Fuel section, usually Sect. 05.nn.nn).

 

Thanks for the reply sir..can please share the document for referance.

 

@paras0701,

I don't have any documents for reference. Look in the training manuals from commissioning and the Operations & Maintenance Manuals provided with the turbines and auxiliaries. The best place choice would be the training manuals used during commissioning (or just prior to commissioning).

I just want to try to explain the term "staged." One of the many meanings of staged is things occur in an orderly, planned, logical manner. In the case of DLN-I combustion staging refers to the burning of fuel in one or both of two combustion zones--the primary combustion zone and the secondary combustion zone. So, for example, during starting and initial loaded operation of the machine with DLN-I (and most likely DLN-1.5) fuel is burned only in the primary combustion zone of the axial combustors in a diffusion flame (a yellow-orange flame). This is known as Primary combustion mode.

As the machine load is increased (and that occurs when the fuel flow-rate is increased) the fuel flow-rate is then divided between the primary- and the secondary combustion zones and is still burned in a diffusion flame in both zones. This is know as Lean-Lean combustion mode. The two combustion zones are located in different parts of the combustor with a venturi between them. Hot gases from the primary combustion zone flow through the venturi and into the secondary combustion zone. The typical division of fuel flow-rate between the two combustion zones (primary and secondary) is about 50-50--meaning about 50% of the total fuel flow-rate is sent to the primary combustion zone and about 50% of the total fuel flow-rate is sent to the secondary combustion zone.

As load is increased still further (meaning the fuel flow-rate is increased) the fuel from the primary combustion zone is reduced and flows into the secondary combustion zone. Some of that total fuel flow-rate is temporarily sent to the transfer manifold and nozzles because, usually, the amount of fuel flowing is very near the limit of the secondary fuel nozzles so by sending some of the fuel flow-rate to the transfer nozzles (which mixes with the fuel already flowing into and burning in the the secondary combustion zone) a smoother combustion mode transfer occurs--and a smooth stable flow is important to flame stability as well as load stability.

All of this is occurring because it is necessary to extinguish the diffusion flame in the primary combustion zone--and that occurs when the fuel flowing into the primary combustion mode is reduced to, basically, zero. Once the flame sensors in the primary combustion zone indicate the loss of diffusion flame for a very few seconds the process of re-introducing fuel into the primary combustion zone begins. The fuel flowing through the transfer manifold and nozzles and secondary manifold and nozzles is reduced as the fuel flow-rate to the primary manifold and nozzles is increased.

At some point the fuel flowing through the transfer manifold and nozzles is reduced to zero. MOST of the fuel flowing through the secondary manifold and nozzles is burning in a diffusion flame that can be and is detected with the secondary flame sensors. However, the fuel flowing through the primary manifold and nozzles into the primary combustion zone is burning in a very air-rich and fuel-lean mixture--which greatly reduces the formation of NOx emissions. This "DLN flame" can't be detected by the primary zone flame sensors but nonetheless the fuel is burning; the temperature of the gases in the primary combustion zone is much higher than the temperature of the axial compressor discharge air flowing into the primary combustion zone which means combustion is occurring--it's just not in a yellow-orange diffusion flame which is VERY hot and it's the high temperature of the diffusion flame that creates NOx emissions which are undesirable.

So, the "movement" of the diffusion flame from the primary combustion zone to include the secondary combustion zone, then the extinguishment of the diffusion flame in the primary combustion zone and the establishment of the "DLN flame" in the primary combustion zone is the act of "staging" that leads to the description of the DLN-I system as being "staged"--the diffusion flame is "moved" from primary to secondary combustion zones, and then the diffusion flame is extinguished in the primary combustion zone and finally the "DLN flame" is established in the primary combustion zone.

All of this is done because prior to DLN (Dry Low NOX) combustion systems the only way to decrease the formation of NOX emissions was to use water or steam to cool the diffusion flame temperature. The water used in that process is non-recuperable--meaning that once it's injected into the combustors to quench (cool) the diffusion flame temperature is flows through the turbine section of the machine and into the exhaust and eventually out of the exhaust stack and into the atmosphere and can't be recovered and reused--not any part of the water injected into the combustors to reduce the NOx emissions. And, in today's world (even with sea-level rise!) water is very expensive. Not only is the water expensive but it has to be treated to be boiler-quality water--which requires expensive treatment systems and chemicals, both of which cost even more money. So, by developing the Dry Low NOx combustion system(s) it is no longer necessary to use water (or steam) to reduce the formation of NOx emissions in the gas turbine. (The physical components of the DLN combustion system(s) are expensive, but probably not as expensive as continuously using and treating water which is lost and gone forever once it leaves the turbine so it has to be continually replenished.) It should also be noted that using water or steam to reduce NOx emissions cannot achieve the low levels of NOx emissions that DLN systems can, so that's another reason DLN is a good choice for heavy duty gas turbine combustion systems.

Again, if you're working at the site hopefully somewhere on such a large facility there will be some kind of "library" where manuals and drawings (electrical drawings; construction drawings; etc.) are kept and made available to the personnel working at the site. I am PAINFULLY aware that many people are hired into power plants with very little, sometimes no, experience and are given minimal training. The thought process of manager is two-fold: First, training is expensive and they believe that everyone who is presently working at the power plant knows everything and can train the newly hired people. Also, in many parts of the world if someone completes a training course and receives some kind of certificate--at company expense--those employees will almost immediately begin looking for a new, higher-paying job because they have a certificate of training which makes them a more valuable employee to hire (because they don't have to be trained...). It's insanity and it's very short-sighted--meaning that the logic is only meant to save money now and increase profits now. Those same managers will also hire someone who has a training certificate because they won't have to pay to train them--so companies are really "poaching" from other companies (paying more money to hire experienced people trained by other companies). So, most companies just won't spend money on training (after initial commissioning). Hell, some companies won't even spend money on training during commissioning (YES--it's true! Sad, but true!). And we're talking about electric power generation--sometimes for a very large profitable factory or plant nearby that is highly reliant on the stable supply of electricity. It is something of a testament to automation (control systems) that they can keep a plant running with minimal operator and technician training. But, when something unusual happens--and it does more often than people think it would or should--untrained operators just don't know what to do, what should be happening when it's not happening, and what shouldn't be happening when it is happening. This is how equipment gets damaged, sometimes catastrophically, sometimes with human injury or worse.

Okay, we now return to our regularly scheduled programming.

Again, what I know is what I gained from 40+ years of experience in the power generation industry. The company I worked for DID believe in training when I was hired, but with changes in management training became less and less frequent. So, people working in the field had to have contacts in the factory as well as access to other colleagues to learn and grow--if they didn't tire of working in the field before their desire to learn and grow in their profession decreased. When I retired, I got rid of almost everything work-related that I had--some of it I was forced to surrender or destroy as it was considered company proprietary and secret; the rest of it I had no further use for and didn't want to store it or move it when I changed homes.

Ask around about the training manuals used before and/or during commissioning.

 

Ok sir..thanks for the reply..

 

@paras0701,

This topic of DLN-I has been covered MANY times on Control.com. There have even been some hand-sketches submitted in responses to threads which can be very helpful. ALL of that information is available by using the Search feature of Control.com. You may not find exactly what you're looking for the first couple of searches that you make--but I guarantee you that will learn something from just about every thread you read. There are more than 20+ years of GE Speedtronic and Mark* turbine control posts and responses, and many, Many, MANY questions have been asked and answered multiple times.

I want to tell you that DLN-I has been used on GE-design Frame 5, Frame 6B and Frame 7E/EA machines--and for all intents and purposes the systems are very much alike. Over the two-plus decades that DLN-I has been used it has gone through a few changes. The design of the gas transfer valve has changed, some machines do not have a gas transfer valve, manifold and nozzles (these are called 'transfer-less' systems), and some other auxiliaries have also changed (such as IBH (Inlet Bleed Heating--which is a really poor name for the function that it provides). But, still--DLN-I is DLN-I in function if not exact details. The fuel is "staged" into the different combustion zones of the axial combustors to achieve Premix operation (sometimes called Premix Steady State operation)--and while it seems complicated at first in reality it is simple (it's just all of the hardware and control devices and schemes that are required to make the staging happen that is complicated--in the beginning).

Now, if you have other more specific questions we can try to answer them. But, if you really want to learn and understand the GE-design Frame 6B machines at your site the VERY BEST thing you can do is to get yourself copies of the P&IDs for the various systems of the machine. Get them in A3 size if you can. And then start studying them. One line (pipe) at a time on one drawing at a time. Yes--in the beginning it seems SOOO confusing, but in actuality GE P&IDs are really among the simplest of any machine or manufacturer anywhere in the world. Usually on the first page of every P&ID there is a NOTES section--and they usually have some very important information (though sometimes it seems like it is written in a secret code). But by reading the NOTES section as you study the P&IDs they will begin to make more and more sense and even help you to understand what is being shown on the diagrams.

We don't know what your function is or will be at the installation where you are working, but, no matter--studying and learning the P&IDs will help you understand a LOT more about the machine and its systems. Save the ToolboxST stuff for later--learn the P&IDs. Make notes on the P&IDs (in pencil); use highlighters on the P&IDs. They are YOUR copies and you should be making notes as you learn. If you have questions we can usually provide some help. JUST DON'T BE INTIMIDATED BY THE P&IDs. I guarantee they will help you to understand the systems and the machines quicker than just about anything--but you have to make an effort and if you have specific questions we can help (especially if you can take photos of what it is on the diagrams you are having trouble understanding and post them to Control.com).

If you have specific questions about operating sequences, we can try to answer them. We can even try to answer questions about Process- and Diagnostic Alarm messages that come up from time to time during starting, operation, shutdown and cooldown operation.

Lastly, in the Operations & Maintenance Manuals there should be individual sections for each of the systems of the P&IDs. They are brief but sometimes they can be very helpful in understanding the equipment and some of the philosophies about the design and devices of the systems. BE AWARE, though, that those system descriptions in the Manuals are usually pretty generic and may not be exactly as depicted on the P&IDs. What's on the P&IDs is CORRECT; what's written in the manuals is usually some expression of the intent of the systems and devices--not always the exact, correct descriptions of the devices and systems, but because that's about all there is you still need to consult them if only in the beginning as you try to learn each system one at a time.

It's NOT impossible--but it's not easy. It's not too difficult if you use the resources you have--including asking your colleagues, though you will quickly learn that some colleagues aren't all the good at explaining things to people so they can understand it, and that's one of the BIG drawbacks of trying to use site personnel, some of whom may have been working there for several years, to train newly hired personnel. But, that's all part of working at a large installation, and we all have to learn that.

 

Thanks sir for guidance.you have provided great explanation.

 

@paras0701,

It's entirely possible that the gas fuel control valves are some of the later modules/skids which have multiple independent valves for controlling gas pressure before the valves acting as primary-, secondary- and transfer gas control valves. Some older systems had a primary gas control valve, a gas splitter valve, and a transfer valve as well as a SRV (Stop-Ratio Valve). The Gas Fuel P&ID will tell you what kind of system you have (but you did mention the system has a primary, secondary and transfer valve--so that indicates, more or less, that the machines have the IGCV (Independent Gas Control Valve assembly/module/skid) for controlling gas fuel flow to the manifolds and fuel nozzles.

No matter what the gas fuel control valve specific arrangement is, they all operate as described previously--controlling the fuel flow and fuel flow rates to the various combustion zones and nozzles in the axial combustors.