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-   -   LNCFS - pulverized burner (http://www.cfd-online.com/Forums/fluent/65619-lncfs-pulverized-burner.html)

Geisel June 21, 2009 10:00

LNCFS - pulverized burner
 
Hello everyone,

This is my first post here, until now I was only passive reader of forum.
For my studies project, I am trying to manage a combustion in LNCFS (Low-NOx Concentric Firing System), but there are a couple of things that are not proper understandable itself for me.
I would be glad, if someone help me by answering a few of questions.

What is the LNCFS ?

It is used mostly in lignite fired boilers. Due to a lot of moisture content in fuel, it must be dryied by hot flue gases (or air, it depends on percent of moisture) taken from upper part of combustion chamber.
The whole process of combustion in burner is provided by small amount of oxide, so it prevents from creating NOx... In upper parts of CC a rest of air is blowed by SOFA points into inside.

Where is my problem ?

I tried to cope with this problem using tutorial 13 "Using the Non-Premixed Combustion Model".


The questions are:
1. Preparing a PDF table:

The fuel blend containts pulverized coal flux, some air and some recirculated flue gas. Everything has a one temperature (160 C in my issue).

I put additional species (e.g. CO2) into SPECIES MODEL in PDF in Oxid collumn. Is that correct? What with the temperatures (Fuel and Oxid)? In tutorial there are a different values for each.
Or maybe I must consider the two streams separately, Fuel = only coal
Oxid = Air + Flue Gas.

2. Preparing the injections.
My burner is composed of 3 coal nozzles.
Each has a couple of core air points, and additional air nozzles.
There is a sketch of it:

Code:

1st nozzle                      2nd and 3rd               
@@    @@                    @@  @@

###O###                    ###O###                Between 1st and 2nd is a
###O###                    ###O###                ~1500 mm distance
###O###                    ###O###
OOOOOOO                    OOOOOOO                LEGEND:
###O###                    ###O###                @@ - additional air nozzle
###O###                    ###O###                O - core air
###O###                    ###O###                # - pulverized coal
                                                                % - additional air nozzle
@@  @@                      %  %  %

                                  ###O###
    ||                          ###O###
    ||                          ###O###
    ||                          OOOOOOO
    ||                          ###O###
    \  /                          ###O###
    \/                          ###O###
                                  @@  @@

The question is, have I to make new injection for each pulverized coal point (represented by 9x#, so it would be 6 injections (I put symmetry line))
What is about the INJECTION TYPE, can I choose surface not group like in tutorial ?

3. In my project, there are no walls, the combustion process is executed into the abyss (I choose pressure outlet BC).
Is there a requirement to have a hot walls in this type of model?
How can I force the flow in this abyss (in combustion chamber there is a negative pressure made by ID fan).

4. How can I change axis values from 2.23e03 into 2230 ?

5. I would be glad if someone share with me with some advice in this matter.



I am sorry for any occured language mistakes, English is not my mother language.


Thanks a lot :)

Best regards.


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