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Problem on EDC model for coal combustion

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Old   March 9, 2010, 19:25
Smile Problem on EDC model for coal combustion
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lei
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Lei Chen
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Dear friends,
I am having a difficult time working on EDC model with coal combustion. My case is a 2d and 3d coal-fired combustor, and the model configurations are as follows:
*Pressure based solver
*k-epsilon turbulence model
*CPD for coal devolatilization
*volatiles decompose into CO, H2, Hydrocarbons (a global reaction)
*surface reactions for char oxidation
*JL 4-step mechanism for hydrocarbon combustion (I double checked the reaction rates units and constants, they should be right)
*defult settings for EDC model
*operating condition 4 bar
Before trying to use EDC, I used Finite Rate/Eddy Dissipation model for the turbulent-chemistry interaction in both 2d and 3d case, and it seems reasonable. I would try to use EDC because it allows reversible reaction, and seems more advanced by considering kinetics rates in fine scale.
But when I swich to the EDC model, the combustion temperature drops gradually from 1900 K to the inlet temperature, which indicates no reaction at all. The CO concentration is as high as 10%, which meas devolatilization, char oxidation take place, however CO oxidation doesn't take place.
Even when I added a CO reaction CO+0.5O2->CO2, and remain the wall temperature as 1900 K, the outlet temperature is high (~1820 K), but CO is still there.
Could you kindly help on this if you have experience with EDC model, especially when use it with coal combustion?
My questions:
1) Is EDC compatible with DPM, or coal combustion? (it should be, as said in the user guide, and some people used it in some publications)
2) What may be the problems caused this high CO concentration?
Thank you so much!
-Lei

Last edited by lei; March 9, 2010 at 19:37. Reason: give more information
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Old   March 17, 2011, 12:29
Default Smile Problem on EDC model for coal combustion
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wwa
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hello,
it is possible that high temperature is the reason of your problem. 1800 K at the outlet seems to be quite high. If your reactions are reverse as you said, CO2 dissociates to make CO more dominant. You can try to modify your boundary conditions to reduce temperature for example.

and DPM with EDC is compatible. i didn't have any troubles using it.

Peter
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Old   March 18, 2011, 02:06
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Byron Smith R J
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hai
check the air fuel ratio too
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