Using molecular dynamics simulations to study the non-thermal effects of microwave radiation on the mechanism of char gasification

• Published in: Renewable energy 2023-01, Vol.202, p.784-796
• Main Authors: Su, Jian, Zhao, Deng, Feng, Haoyuan, Wu, Tianyu, Liu, Hua, Wang, Huashan, Guo, Shuai, Liu, Hui
• Format: Article
• Language: English
• Subjects: Char; Density functional theory; Microwave gasification; Non-thermal effect; ReaxFF
• ISSN: 0960-1481; 1879-0682
• DOI: 10.1016/j.renene.2022.11.125

Studying the chemical effects of alternating electric fields on char gasification is key to exploring the non-thermal effects of microwaves on the reaction mechanism. The gasification mechanism of char in the presence of an electric field was explored through molecular dynamics (MD) simulations and quantum chemical calculations. The results show that the promotion effect of 0.02 V/Å alternating electric field on the gasification reaction rate of char is about 8 times that of non-electric field, and the square wave electric field and static electric field are 6.79 times and 5.39 times respectively, this effect increases exponentially as the field intensity increases. Interestingly, the use of alternating electric fields showed, for the first time, that the changes in the electric field intensity and direction also have a significant effect. In terms of the adsorption process during gasification, the electric field promotes the formation of O and OH free radicals (about 5 times of no electric field) and increases the polarity of the char edge, both of which are conducive to adsorption. The electric field can weaken the curling of char macromolecules and expose more active carbon sites, thus increasing the overall reaction rate. For the desorption process during gasification, the presence of the electric field promotes the deformation and tear of char, which destroys its aromaticity, loosening the carbon-oxygen compounds at the carbon edge, which facilitates the desorption of CO, the desorption rate is about 10 times that of non-electric field system. Further, the change in direction of the electric field also promotes the desorption process. The results from this study suggest that the remarkable effects of alternating electric fields on char molecules can have an impact on the field of solid fuel gasification. [Display omitted]