CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Coal combustion - volatile species

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   October 20, 2008, 22:06
Default Coal combustion - volatile species
  #1
Venky
Guest
 
Posts: n/a
Hi,

I got question for combustion CFD Engineers,

How to determine the appropriate stoichiometric ratios of species? (Vol. Species -> xH2O + yCH4 + zCO + gaseous species)

How to set the reaction to go instantaneously or with some delay?

How to avoid to avoid low temperature (below 273 K) in the PC Boiler?

Is PDF a good approch for Coal combustion?

Thanks in advance Venky
  Reply With Quote

Old   October 21, 2008, 22:03
Default Re: Coal combustion - volatile species
  #2
Allan Walsh
Guest
 
Posts: n/a
I would have to believe that there is some experimental data for the fractions of the gas species evolved during devolatilization. This would be a good starting point. You will probably find there are appreciable amounts of CO2 and H2. Use whatever data you have to determine a mass fraction breakdown that at least satisfies the fuel elemental analysis and fraction of volatiles. Then, calculate the heat of reaction of volatiles and the amount of oxygen needed for combustion. Are these close to measured values? Then you probably aren't far off.

How to set the reaction? Kinetics and turbulence mixing rate.

You can set the minimum temperature. If lots of cells are dropping below 273K, something is likely wrong. The heat capacity of particle or gas? Heats of formation?

No personal experience with PDF.
  Reply With Quote

Old   October 22, 2008, 07:14
Default Re: Coal combustion - volatile species
  #3
Venky
Guest
 
Posts: n/a
Hi Allan, Thanks for your answers.

1. I dont have the experimental data for the fractions of the gas species of coal. I have proximate and ultimate analysis from i determine the molecular wt and heat of formation of volatile CxHyOz. From Measurment i have air excess =1.27 And i have no problems with stoichiometry calculation. And they are close to experimental values.

2. For Coal should I change the speed of reaction. Does it depends on the coal?

3. I have 20 cells below 273K out of 8 Million cells. So i think it should be a problem. LCV of coal 23200 KJ/Kg and heat of formation of volatiles = -417MJ/Kmol

4. I am not planing for PDF model but i will give a try while finish my thesis.

Thanks once again. Venky
  Reply With Quote

Old   October 22, 2008, 13:39
Default Re: Coal combustion - volatile species
  #4
Allan Walsh
Guest
 
Posts: n/a
Sounds reasonable.

20 cells less than 273K shouldn't be too much of an issue if it doesn't change with iteration.

I assume that you are doing pulverized coal burners? Are the low temperatures around the burners? Could you have large sensible energy sink terms due to particle heating and large particle concentrations due to discrete nature of particle tracking?
  Reply With Quote

Old   October 22, 2008, 19:28
Default Re: Coal combustion - volatile species
  #5
venky
Guest
 
Posts: n/a
yes, its a 535MWe tangentially fired pulverized coal boiler. They are near the burner zone, but my results are not yet converged. High temp (>5000 K) decreased when I change from first order scheme to second order but not low temperature cells, i have to wait and see.

1,Could you have large sensible energy sink terms due to particle heating and large particle concentrations due to discrete nature of particle tracking? *** this might increase the temperature isn't it!!!

2,What are the best coal sub models? for volatiles and char.

thanks again Allan. venky

  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Please Help- Coal Combustion!!! Michael FLUENT 2 November 14, 2009 08:52
combustion coal please help me!!!!!!!!!!!!!!! Andres FLUENT 1 October 21, 2008 23:49
coal combustion jarek CFX 4 November 28, 2007 00:23
Coal Combustion AYYAPILLAI MURALI Main CFD Forum 0 May 18, 2000 02:31
coal combustion Ben Williams Main CFD Forum 4 April 26, 2000 00:11


All times are GMT -4. The time now is 21:34.