MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...

too complicated for practical use and therefore are seldom used. Several continuum,
microscopic models were reviewed by Smith et al. (1994).
Stoichiometry of the Carbon-Oxygen Reaction
CO and CO 2 are two possible products of char oxidation. The overall reactions
leading to these two products are, respectively,
C + O 2 → CO 2 + ΔH 1
C + 1
2 O 2 → CO + ΔH 2
9
(2.1)
(2.2)
where H 1 and H 2 are the heats of reaction for Reactions 2.1 and 2.2. If the fraction of
carbon converted to CO 2 is denoted as , the overall carbon-oxygen reaction can be
expressed as
1 +
C +
2 O2 → CO2 + (1 − )CO + ΔH1 + (1 − )ΔH 2 (2.3)
The stoichiometric coefficient of oxygen in the above equation is denoted as o . That is,
o
= 1+
2
(2.4)
The fraction of carbon converted to CO 2 ( ) is often calculated from the CO/CO 2 product
ratio, which is often empirically correlated with an Arrhenius equation (Arthur, 1951;
Tognotti et al., 1990; Mitchell et al., 1992):
CO
CO 2
= 1 −
= Ac exp(− Ec ) (2.5)
RTP The stoichiometric coefficient of oxygen represents a major uncertainty in modeling char
oxidation.