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Old   October 15, 2008, 11:07
Default Coal Volatilization
  #1
michele
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Dear all,

I want to model coal combustion using advanced kinetic scheme, like Eddy Dissipation Concept.

Is it possible with species transport model (like EDM, EDC, etc.) to define several gaseous species from volatilization of discrete phase combusting particles, or only one species can be defined?
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Old   October 15, 2008, 13:02
Default Re: Coal Volatilization
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Allan Walsh
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What we have done is to use an intermediate volatile "species". The composition of the species can be determined from the fuel elemental composition, and the fractions of volatiles and char carbon.

Thus, the volatile species will have some composition (CxHyOz and could include S and N and others). The volatile species is set in the Fluent material panel as a gas with the appropriate molecular weight and heat of formation. (The heat of formation is the difference in the heating value of the products versus the measured heating value of the fuel).

Then we set up the appropriate reaction of Vol. Species -> xH2O + yCH4 + zCO .... including whatever gaseous species you are interested in - in the appropriate stoichiometric ratios. The reaction can be set to go instantaneously or with some delay if desired.

This approach has been satisfactory for our combustion modeling reeds.
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Old   October 15, 2008, 13:48
Default Re: Coal Volatilization
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Michele Vascellari
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Thank you Allan for your answer,

Your approach is very interesting for my calculations, but I need another clarification.

How can I define the istantaneous reaction? Considering very high pre-exponential factor and low activation energy in arrhenius equation, with respect to the other reactions?

Thank you again for your help!

Michele
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Old   October 16, 2008, 13:03
Default Re: Coal Volatilization
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Allan Walsh
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Setting the Arrhenius parameters will remove any kinetic limitations but sometimes the turbulent reaction rate will be limiting. If desired, the parameters in the turbulent reaction rate can be artificially increased to remove this limitation since for the psuedo volatile species, they don't have any physical meaning.

Since the fraction of fuel volatilized, and the volatiles composition, should be indexed to other factors such as the heat flux to the fuel particle, my approach has its limitations. But, I haven't had the time or initiative to try and implement a more complicated scheme.
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Old   October 17, 2008, 04:19
Default Re: Coal Volatilization
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Michele Vascellari
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Thank you again for the answer,

I have another question, how do you consider the heavy hydrocarbons, like TAR, etc.?

Michele

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