COMBUSTION OF CARBON PARTICLES OF A FLUIDISED BED.

Measurements of carbon combustion rate in a fluidised bed, the carbon being in dilute mixture with sand at 1103 to 1173 K, show the relative importance of diffusion and of chemical kinetics in determining the rate of combustion. It appears that for each carbon particle, oxygen diffuses to the carbon surface where it reacts to form CO which then burns around the carbon. This picture is consistent with recent measurements of carbon temperatures of up to 150 K above bed temperature. Such temperatures are not high enough to give significantt reduction of CO//2 to CO at the carbon surface. For carbon particles larger than about 1 mm in diameter, the CO burns near the surface and hence the overall surface reaction is effectively C plus O//2 yields CO//2. For smaller particles, the CO diffuses away and burns in the interstices between the surrounding sand particles.