Questions About Combustion Nozzle Design

J

Thread Starter

jameelrahman

hi folks

myself rahman working as a graduate trainee engineer in gas based power plant with frame 6fa.

Can you people please explain about combustion nozzles. today i saw the nozzle, since i had a question. there are many annulus in the nozzles with two swirler. why swirler is designed there? and tell me the various gas path in a single nozzle? i saw one hole in the middle and some 10 to 12 holes (don't know exactly) around the middle hole. whats that for?

pls reply...forget to say that, we used dln 2 combustion system.
 
Hi,

The BEST place for anyone new to GE-design heavy duty gas turbines to start is by obtaining their own copies of the unit P&IDs (GE used to call them 'Schematic Piping Diagrams' or "Piping Schematics." They are about the simplest drawings to understand--and absolutely critical to becoming familiar with equipment and devices and operation. (There is also a document called the 'Piping Symbols Drawing' which is helpful in understanding the various symbols--though most should be fairly intuitive.)

The reason I say you need to obtain your own, personal copies of these drawings is because you should make notes on them as you study and refer to them. I always try to get the largest size copies the local photocopier on site will make, to have as much room as possible to make notes.

Next, one needs to consult the 'System Description' tabs of the Operation and Service Manual provided with the unit to be able to get a very basic understanding of some of the systems and components and intended operation. These are supposed to be unit-specific--but quite often they are very generic. So, read them for "intent"--not for literal content. There should be one System Description for each of the various systems of the P&IDs. They are brief, but do have some very important and useful information--just be careful NOT to trust everything you read. Compare what you read to the P&IDs, and if you have questions, we're here to help.

DLN-2 combustion systems use multiple nozzles to reduce the NOx (and to some extent the CO) emissions by "injecting" the fuel into different areas inside the combustor. Some of the fuel is burned in diffusion flame--usually from the openings at the very tip of the nozzles. The other orifices along and around the body of the nozzles are used to inject the fuel where it can be "premixed" with very large quantities of air--which causes the fuel to be combusted (create a temperature rise) but NOT with a diffusion flame. And, without a diffusion flame, the NOx formation is much lower.

Also, the diffusion flame at the tips of the nozzles helps to reduce the CO output (the CO is actually burned by the high-temperature diffusion flame).

The premixed fuel and air results in a very, very lean air/fuel (fuel/air) mixture that, when exposed to a high-temperature (created by the small diffusion flames) can combust--again at a lower temperature than diffusion flame occurs, and with a much lower NOx output.

The swirlers help with the mixing of the air and fuel--both the premixed fuel and the diffusion flame fuel.

You really need to also look at the combustion liners to really understand how the fuel is admitted into different areas of the liners through the various orifices and openings along and at the tip of the nozzles.

Again, "all" knowledge comes from reviewing and understanding the P&IDs--and that's true of any process plant. And ESPECIALLY true of GE-design heavy duty gas turbines (which is a "process"). If you want to understand GE-design heavy duty gas turbines, the absolute best place to start is by getting your own copies of the P&IDs, reviewing them in conjunction with reading the various System Descriptions in the Manuals provided with the unit (the turbine, auxiliaries and generator), and making notes as you learn and become familiar with the equipment.

Then, you need to take your newfound knowledge out to the turbine, when it's shut down and being taken apart to find the devices so you know where they are located and start to examine them--as you are doing now.

Again, you've stumbled across a very good site which has more than 10 years of GE-design heavy duty gas turbine-related posts, along with a very good 'Search' feature cleverly hidden at the far right of the Menu bar at the top of every control.com webpage. (Use the Search 'Help' the first couple of times--the context is not intuitive.) You will find a LOT of very helpful and useful information here--mostly controls related, but then a lot of field devices and instruments are part of the control system (like fuel nozzles!) and we can help with a lot of the questions you might have--if they haven't already been answered!

Welcome to the site! And good luck with your learning!
 
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