Hello Muhammad,

You can use/copy any material from the database for the biomass. For the E-E granular model, you have to define only the material density inside the material properties window to match your biomass density and you can use submodels for the other required material properties, such as granular viscosity, frictional viscosity etc., in the phase settings window, depending on your case, after you checked the "granular" option below the phase material drop-down menu.

Hope this helps.

Regards,

Stephan

Hi Stephan,

Thank you for your kind reply.

this far i know, but i don't know how to define biomass composition (using granular aproach) which is given by elemental and proximate analysis. i don't know even if it is the right approach

my problem is biomass gasification. biomass in the form of granular phase is fed into the reactor.

the process is subdivided into devolitilization and homogeneous and heterogeneous reactions.

Regards

Ok, then I have to ask what you want to model in Fluent in detail? Is it the entire gasification process (i.e. flow and chemical reaction(s))? This sounds pretty complicated for biomass gasification, because it should involve not only chemical reactions but also mass transfer from the solid phase (i.e. biomass) to the gas/vapor phase.

However, generally speaking, you could combine the granular phase Euler-Euler model with a material mixture approach from the species transport model (models -> Species -> Species transport enabled) to account for the chemical reactions. The species transport model generates a mixture material template in the materials windows (by default it contains N2, O2 and H2O vapor). Even though I don't know any details of biomass gasification processes, it seems to make sense to define the granular phase as a generic biomass material (as a substrate of the chemical reaction) and use the mixture for the gas phase formed during the reaction steps (i.e. CO, CO2, H2 etc.). Obviously you have to know the stochiometry of the biomass conversion (i.e. how much mol CO2 is formed per mol biomass for instance), but if this is known from the elemental analysis you can define source terms for the individual compounds depending on the reaction kinetics.

Hope this helps.

Best,

Stephan

yes, it is the entire gasification process that I want to model in fluent.

I am employing the chemical reactions through species transport model which as you said generates a mixture material template.

as far as your suggestion regarding definition of granular phase as generic biomass material is concerned. i have some confusion here.

If i define generic biomass material having granular properties, the granular material on entering the system is devolatilized according to reaction given below

biomass (granular)==> char + volatiles (co+co2+h2...)+steam+ash (A)

if i am not wrong to understand, you were talking about stoichiometry of volatiles which i can compute through an empirical model.

the issue at hand is modeling this reaction A in the fluent, since there is no option for reaction of generic granular particle, unless chemical composition is specified.

what i just did is that I got empirical formula (which is not an appropriate alternative of molecular formula, and i don't know the molecular mass) of biomass from elemental analysis and inserted the chemical formula in create/edit materials. in this way i can model the reaction A (fig attached). please shed light on this if it is the right approach

Sorry for inconvenience

thanks alot

Hello Muhammed,

I start to get the complete picture of your problem, and I have to admit that I never tried to model anything like this. As far as I know, there is no option to define two different mixtures for the granular and gaseous phase in Fluent, and you are correct that you cannot define chemical reactions for the granular phase, unless it is a species mixture. Plus in your case both subtrates and products could be granular in nature (biomass, ash, and char).

One possibilty could be user-defined mass sources for the biomass (more specifically a mass sink in your case) and for the products using UDF's. Given that the reaction is 1st order and the reaction rate is known, the code for the species mass fraction of a specific compound (e.g. CO2) could look something like this:

#include "udf.h"

#define Rmax 0.01 /*maximum reaction rate (1/s)*/

/*c = cell index, t = thread pointer, dS = derivative of source (not needed in this case), eqn = equation number*/

DEFINE_SOURCE(VGCsource,c,t,dS,eqn)

{

real VG;

VGC = C_YI(c,t,0) * C_R(c,t); /*Conc. of volatile species in mixture*/

return = -Rmax*VGC; /*Source term*/

}

Then you would need the DEFINE_MASS_TRANSFER macro to account for the "mass loss" of the solid/granular substrate phase. This is explained on pages 169ff in the UDF manual (v17.0).

I don't know if you have to consider the subthreats here because you work with two Euler phases. Again, these are just some "half-baked" thoughts - I don't have any experiences with this, but it might help you to further develop your model. Since this is a very specific problem, you might get help also in a pure CFD forum, like www.CFD-online.com.

Good luck.

Best,

Stephan

Thanks a lot Stephan, your analysis was very insightful and really helped me. I have got some rough idea on implementing the model, thanks to your guidance.

I will look into UDF manual and literature to implement it.

Best Regards

Thanks, Uzair and Stephan, this discussion is currently helping in understanding computational biomass pyrolysis.