LAUSR

Coal O 2 /CO 2 combustion is a promising carbon capture and storage technology for coal-fired power plant. Char consumption rate prediction is essential for the boiler design, but challenging for O 2 /CO 2 combustion since char reaction behavior within dual reactive gas media is complex. There is also a doubt of whether or not the O 2 reaction and CO 2 reaction occur independently, whereby the overall rate would be simply additive, or the two reactions compete for the same char actives, in which case the rate prediction could be more complicated. Here, the competitive behavior for O 2 and CO 2 reactions of char active sites was investigated via thermogravimetric approach, with a focus on the effect of temperature and inherent mineral composition. For char combustion within O 2 /CO 2 environment with molar fractions of 30/70, the contribution of O 2 to char consumption is the same as the O 2 reaction alone. However, as being out-competed by O 2 , only 37% CO 2 could occupy char active sites and react. Consequently, the overall char reaction rate within O 2 /CO 2 is only 83% of the sum of that for individual gases at 900 °C. With increasing temperature, this ratio becomes even smaller, as the contribution of CO 2 that being out-competed (to the sum of individual gases) is larger. With increasing O 2 fraction, it occupied more active sites, thus further inhibiting CO 2 reaction. The inherent alkali and alkaline earth metal provides the char with more active sites, thus muting the competition and inhibition for CO 2 gasification.