Complete Burning and Extinction of a Carbon Particle in an Pxidizing Atmosphere

Abstract

The departure from an equilibrium gas phase behavior is described in order to obtain the rate of mass loss M of a pure carbon particle immersed in an oxidizing atmosphere over a wide range of the Damköhler number D_g (representing either the particle size or the ambient pressure). For equilibrium flow (D_g →∞) complete burning of CO occurs at a flame sheet standing either adjacent to or at a certain distance of the particle. In the former case oxygen is not totally consumed and the burning rate M depends on both, the direct oxidation C + O₂ and the indirect oxidation C + CO₂. In the latter case oxygen does not reach the particle and M depends solely on the indirect oxidation. By lowering D_g and treating the flame as a thin but finite zone we establish the dependence of M on both heterogeneous reactions as well as on the homogeneous reaction CO + O₂. The burning rate is reduced when D_g decreased and the flame moves towards the particle. This behavior persists until the critical Damkohler number D_g° is reached marking the extinction of the CO + O₂ flame.