MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...

The HP-CBK was used to predict the burnouts for all the experiments conducted at 1, 5,
10 and 15 atm, using the above-mentioned gas temperature and wall temperature profiles.
The experiments conducted at 15 atm had extremely low wall temperatures (e.g., 631 K)
and low gas temperatures (e.g., 987 K), and hence were not considered due to ignition
problems. Ignition problems were also observed by other researchers. For example, Field
(1969) observed that a 38-μm char sample was not ignited at low gas temperature and
wall temperature (< 1230 K).
Results
In minimizing the standard deviation of model predictions, two observations were
made: 1) The Langmuir rate equation reduced to the zero-th order equation, implying an
apparent reaction order of 0.5 in Zone II; and 2) The diffusivity contributed from
micropores can be neglected compared to that from the macropores.
The kinetic and pore structure parameters used in this study are listed in Table
7.6. The best-fit calculations of burnouts from the HP-CBK are compared with the
experimental measurements in Figures 7.6 and 7.7. The HP-CBK model was able to
predict particle burnouts with a standard deviation of 14% and a maximum error of 36%.
Table 7.6. Parameters Used in Modeling the Data by Monson (1992).
A 0 = 2.42 × 10 3 mol/cm 3 /sec E 0 = 21.7 kcal/mol
Total Porosity = 0.5 (Pre-set) Macro-porosity M = 0.25
Macro-pore radius r p1 = 2000 Å (Pre-set)
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