Effects of catalytic mineral matter on CO/CO{sub 2} ratio, temperature and burning time for char combustion. Quarterly progress report No. 2, January--March 1990

Abstract

The importance of the CO{sub 2}/CO ratio of carbon oxidation products is illustrated by examination of the heats of reaction for formation of these two products. The heat released by formation of CO{sub 2} is a factor of 3.5 higher than for CO so the temperature of a particle will depend strongly on the CO{sub 2}/CO ratio produced. If gas diffusion through the boundary layer is fast, increased direct production Of CO{sub 2} produces a higher temperature and a higher burning rate. If the supply of oxygen to the surface is limited by diffusion through the boundary layer, production of CO{sub 2} consumes half as much carbon as production of CO so carbon consumption rate is reduced even though temperature may be somewhat higher. Models of these complex interactions have been developed; however the CO{sub 2}/CO ratio produced by the carbon-oxygen reaction must, at present be assumed or inferred from measurement of particle temperature. CO{sub 2}/CO ratios can be strongly influenced by catalytic material in the carbon and by the char temperature. In this program we are measuring the CO{sub 2}/CO ratio for both catalyzed and uncatalyzed chars over a wide range of temperature. These results will then be used to develop predictive models for char temperature and burning rates. Measurements of CO{sub 2}/CO ratio for an uncatalyzed char (spherocarb) were reported in the Oct-Dec 1989 progress report. This ratio varied from a maximum of 1.5 at 700 K and 100% oxygen to 0.06 at 1430 K and 5% oxygen.