I am facing a difficulty in selecting which model TO should for this KIND OF PROBLEM etc.......................

[U]Model description[/U]

The mixture of iron ore and coal particle make up a composite pellet which is considered as a porous medium. Both solid and gas phases are assumed to be continuum. The pellet shape is assumed to be spherical. these are the reactions which are happening inside the pellet.

3Fe2O3 + CO = 2Fe3O4 + CO2

Fe3O4 + CO = 3FeO + CO2

FeO + CO = Fe + CO2

CO2 + C = 2CO

eq solved include - continuity, mass balance , momentum eq that's all

rate of the first 3 reactions are given by

Ri= Si*ni*(4phi*(r^2))*kio*exp(-Ei/RT)*(Cco-(Cco2/keq))

Ri = Reaction rate Equation (mol/m3.s)

S = Shape factor of particles

r = Average particle radius (m)

ko = pre-exponential constant (m/s)

Ea = Activation Energy (J/mol)

R = Universal Gas constant. (J/ mol.K)

Cco , Cco2 = concentration of Cco , Cco2 (mol/ m3)

n = number of particles of solid reactants for reaction i in the mixture (m^-3) etc

In reality there are 2 different type of solid particle of different sizes are there which interact with gas as surface reactions,

which model should i start with................KINDLY HELP ME OUT GUYS. THANKS A LOT IN ADVANCE