Separate physicochemical effects of CO 2 on the coal char combustion: An experimental and kinetic study

The overall impact of CO 2 on the coal char combustion is complicated due to the interplay between the CO 2 thermal effect and chemical effect (including the gasification endothermicity, and its direct additional carbon consumption). To assess the impact of these factors on the carbon consumption process, we conduct a quantitative study on the separate physicochemical effects of CO 2 through experimental and kinetic research. Two oxygen concentrations (15% and 21% O 2 ), representing industrial boiler and air combustion environments, were selected. The experiment research on its thermal effect (evaluated by carbon conversion ratios) is performed at 1773 K in a high-temperature drop tube furnace. The chemical effect of CO 2 is predicted for a 100 mu m coal char particle using a self-developed char burning kinetics model. Results indicate that the carbon conversion ratios show a V-type distribution with higher CO 2 concentrations, as a result of its complex physicochemical effects, with minimal carbon conversion points around the CO 2 concentrations of 5-10 vol.%. The thermal effect initially increases with higher CO 2 concentrations from 0 to 10 vol.%, but it declines with a further increase in CO 2 concentrations, while the endothermicity effect of the gasification reaction increases with higher CO 2 concentrations. The relative contribution of the endothermicity effect on the char consumption is 20.4% in the 21%O 2 /10CO 2 /N 2 environment, lower than the thermal effect (29.9%), but it continuously increases and becomes the most influential inhibitory factor at higher CO 2 concentrations. The strongest suppression effect of CO 2 corresponds to the CO 2 concentrations of 10 vol.%. (c) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The impact of CO2 on coal char combustion is complex due to its thermal and chemical effects. Experimental results show that carbon conversion ratios exhibit a V-type distribution with increasing CO2 concentrations, with minimum conversion points at 5-10%. The endothermicity effect of gasification reaction becomes more influential at higher CO2 concentrations.