THERMOCHEMICAL CONVERSION: AN INTRODUCTION TO FAST PYROLYSIS - Biomass as a Sustainable Energy Source for the Future - page 381

The physical processes described by the model include:

￿ Convective and radiative heat transfer from the surrounding fluid/environment to

the surface of the biomass particle

￿ Radiative, convective, and conductive heat transfer inside the biomass particle

￿ Momentum transfer to account for nonzero pressure gradients and nonuniform

velocity

￿ Variable properties (thermal conductivity, porosity, and permeability)

￿ Accumulation of volatile enthalpy and mass in the biomass pores

￿ Volatile convection and diffusion in the pores of both the virgin biomass and the

charred region

The model assumes:

￿ No secondary vapor decomposition and gasification of char

￿ No particle shrinkage/swelling ) constant volume

￿ Symmetry

These assumptions result in the following equations:

∂ ρ b
∂

= − r 1 ð Eq : 11 : 5 Þ

t

∂ ρ ab
∂

= r 1 − r 2 − r 3 ð Eq : 11 : 6 Þ

t

∂ ρ c
∂

= ν c r 2 ð Eq : 11 : 7 Þ

t

∂ ε ρ g
∂

+ ∂ ρ g u
∂

+ ∂ ρ g v
∂

= ν g r 2 + r 3 ð Eq : 11 : 8 Þ

t x y

∂

T
∂

ρ g c p , g u ∂

T
∂

ρ g c p , g v ∂

T
∂

ρ c c p , c + ρ b c p , b + ρ ab c p , ab + ε ρ g c p , g

t + x + y

0
@

1
A + ∂
∂

0
@

1
A + Q r

ð Eq : 11 : 9 Þ

= ∂
∂

λ x ∂

T
∂

λ y ∂

T
∂

x x y y

B x
η

∂ p
∂

u = − ð Eq : 11 : 10 Þ

x

B y
η

∂ p

v= −

y +

ρ g g ð Eq : 11 : 11 Þ

∂

p = ρ g R u T
MW g

The ideal gas law ð Eq : 11 : 12 Þ

: