MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
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Langmuir rate equation, the reaction order should increase with temperature. However,<br />
some experiments showed that the reaction order of the char-oxygen reaction decreased<br />
with increased particle temperature at constant oxygen concentration (Ranish and Walker,<br />
1993; Banin et al., 1997a). These observations indicated that either the adsorption-<br />
desorption interpretation of the Langmuir rate equation or the belief that E a is less than E d<br />
is not true.<br />
The understanding from this project is: 1) the mechanism of the Langmuir rate<br />
equation is not well understood, and the adsorption-desorption interpretation may not be<br />
true; 2) impurities can affect the activation energies of different processes to different<br />
extents. Keeping these two points in mind, it is no surprise that E 1 (E a is not used since<br />
the mechanism is not known) can be less than, equal to, or greater than E 0.<br />
Observed Activation Energy in Zone I<br />
An expression (Eq. 7.22) was developed to relate the observed activation energy<br />
to the activation energies of k 1p and K p under Zone I conditions, provided that the oxygen<br />
partial pressure at the external surface of the particle (P os) is constant.<br />
HP-CBK Model<br />
The High Pressure Carbon Burnout Kinetics model (HP-CBK) was developed in<br />
this project. This new model was based on the CBK model developed by Hurt et al.<br />
(1998b). The HP-CBK was shown to be satisfactory in modeling char oxidation at both<br />
atmospheric and elevated pressures. The HP-CBK model used: 1) intrinsic Langmuir<br />
kinetics rather than global n-th order kinetics; 2) the analytical solution of the<br />
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