Experimental and kinetics studies on separate physicochemical effects of steam on coal char combustion

• Published in: Combustion and flame 2020-10, Vol.220, p.168-177
• Main Authors: Niu, Yanqing, Liu, Siqi, Yan, Bokang, Lv, Yuan, Lei, Yu, Wang, Denghui, Hui, Shi'en
• Format: Article
• Language: English
• Subjects: Burnout; Carbon; Carbon conversion; Char combustion; Chemical effects; Coal; Combustion; Consumption; Conversion ratio; Dilution; Gasification; Gasification endothermicity; Gasification reaction; High temperature; Kinetics; Oxidation; Specific heat; Temperature effects; Tube furnaces
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/j.combustflame.2020.06.035

The synthetic effect of H2O on the combustion characteristics of coal char is complicated due to its thermal (high volumetric heat capacity), chemical, and dilution (thereby low oxygen concentration) effects. To assess the impact of these factors on the carbon consumption process, we conduct a quantitative study on the net effect of H2O gasification through experimental and kinetic research. The experiment research is performed at 1773 K in a high-temperature drop tube furnace. The thermal effects of H2O are stripped off the net effect by introducing Ar into the bulk gas to neutralize its high heat capacity. We assess the chemical effects of gasification (gasification endothermicity, and its additional carbon consumption) for a 100 µm coal char particle reacting in environments of varying O2, H2O, and Ar using a self-developed char burning kinetics model. The relative contributions of H2O gasification and oxidation to carbon consumption are also discussed. Results indicate that the reduced carbon consumption through the negative effect of gasification (e.g., thermal effects and the gasification endothermicity) exceeds the additional carbon consumption from gasification reaction in the early combustion stages (