Boudouard reaction accompanied by graphitization of wrinkled carbon layers in coke gasification: A theoretical insight into the classical understanding

• Published in: Fuel (Guildford) 2021-08, Vol.297, p.120747, Article 120747
• Main Authors: Zi-Zhao, Ding, Zhang, Sun, Qiang, Lu, Ming-Hui, Dou, Rui, Guo, Jie-Ping, Wang, Guang-Yue, Li, Ying-Hua, Liang
• Format: Article
• Language: English
• Subjects: Blast furnaces; Boudouard reaction; Carbon dioxide; Carbon layer; Carbon monoxide; Coke; Coke fired furnaces; Density functional theory; Gasification; Gasification mechanism; Graphitization; Intermediates; Molecular dynamics; Oxidation; Photoelectron spectroscopy; Photoelectrons; Potential barriers; Reconstruction; X-ray diffraction
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2021.120747

[Display omitted] •Microscopic mechanism of coke gasification is obtained theoretically and experimentally.•Formation path of CO is clarified, which is accompanied by graphitization of coke residue.•Defects act as key intermediates in reconstruction and flattening of carbon layers.•Variable activation energies of coke gasification are explained by DFT.•The essential relationship between coke strength and gasification is established. The carbon dioxide gasification mechanism of coke was investigated by combining a particulate coke reaction experiment and theoretical calculations. Characterization results obtained via X-ray diffraction and X-ray photoelectron spectroscopy showed that the increase of graphitic carbon proportion, that is, a graphitization process, led to a decrease in the strength of the coke residue. Molecular dynamics simulations based on a reactive force field corresponded closely to the experimental characterization results. From this, the main formation path of carbon monoxide was identified to be accompanied by the reconstruction of carbon matrix. It is confirmed that defects on the carbon layer acted as key intermediates in the layer reconstruction and flattening. The energy and potential barrier of the obtained elementary reactions were determined by means of density functional theory. The highest potential barrier of the carbon layer oxidation by carbon dioxide molecules indicated that it was the rate-controlling step of the coke gasification process. Moreover, compared with the other carbon atoms, those with large wrinkle degree were likely to react with carbon dioxide to form a flat carbon layer. This work explains why different coke samples have significantly different activation energies for the carbon dioxide gasification reaction. Furthermore, the essential relationship between the coke strength and the gasification reaction is established, thereby providing theoretical support for improved utilization of coke in a blast furnace.