MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...

Table 7.7. Rate Data and Experimental Conditions
Condition #2 Condition #4
Description of condition Methane fuel-lean, 8% CO fuel-lean, 9.6% post-
FFB reactivity between 4”
post-flame oxygen flame oxygen
and 6” 1.10 × 10 -3 gC/cm 2 /sec 1.18 × 10 -3 gC/cm 2 Average gas temperature
/sec
between 4” and 6” 1743 K 1743 K
Average TGA reactivity of
the chars collected at 4”
above the flame
1.14 × 10 -3 gC/gC remaining/sec
(3.39 × 10 -7 gC/cm 2 /sec)*
0.27 × 10 -3 gC/gC remaining/sec
(7.21 × 10 -8 gC/cm 2 /sec)*
823 K, 10% oxygen, 823 K, 10% oxygen,
TGA conditions
0.85 atm
0.85 atm
Char particle diameters 62 μm 60 μm
Char density 0.377 g/cm 3
0.367 g/cm 3
N2 BET surface area 71.6 m 2 /g 49.2 m 2 /g
* Reaction rates based on the external surface area were calculated from the TGA rates
based on the mass of carbon remaining.
In modeling the data by Monson (1992) and Mathias (1996) it was found that the
micro-pores made insignificant contributions to the effective diffusivity. Therefore, two
parameters related to pore structures are required: the macro-porosity ( M) and average
radius of macro-pores (r p1). The macro-porosity was estimated as 0.3. The N 2 BET
surface areas were assumed to represent the surface area contributed by macro-pores (in
this study, pores are classified into only two categories: macro-pores and micro-pores;
pores with a diameter greater than 20 Å are considered here to be macro-pores) and were
used to estimate the average pore radius:
r p 1 = 2 M
p S m
112
(7.15)