Abstract
We examine the extent of conversion of CO to CO 2 in the boundary layers of char particles burning in gaseous environments containing 6% and 12% oxygen, 16% H 2 O, and the balance N 2 . Our computational model considers elementary finite-rate homogeneous and heterogeneous chemical reactions. The gas-phase CO/O 2 /H 2 O reaction mechanism has been well-established in numerous previous flame models. We have taken an accepted adsorption/de-sorption surface mechanism and made it quantitative by assigning rate parameters that lead to char-particle temperatures in agreement with measurements. For several ambient gaseous environments, we have applied the model over a range of particle diameters. The results show that relatively little CO 2 is formed in the boundary layers of small particles (less than 100 microns). Correspondingly, little thermal energy is transferred to the particle surface as a result of CO conversion in the boundary layer. Thus for small particles, any CO 2 formation must occur on the particle surface, not in the surrounding gas. Therefore, the results support the applicability of the one-film model for particles in the pulverized-coal size range.
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