Reactive force field molecular dynamics (ReaxFF-MD) simulation of lignite combustion under an external electric field

Abstract

To qualitatively and quantitatively evaluate the impact of an external electric field (EEF) on lignite combustion, the microreaction behaviors of lignite combustion under different EEF intensities and various coal-oxygen equivalent ratios (ER) were simulated using the ReaxFF-MD approach. The results show that when the ER increased from 0.5 to 2, the number of effective collisions of molecules in the system increased, which promoted the combustion behavior of lignite, and the total proportion of gas molecules and low-C content products increased by 17 %. However, the changes in EEF intensity had different effects on lignite combustion. The EEF increased the intermolecular diffusion rate and the number of effective collisions, but a high-intensity EEF curbed the formation of hydrocarbons. Overall, the EEF inhibited the combustion process of lignite. When the equivalence ratio was 1, the EEF intensity increased from 0 to 1 V/Å, the amount of C-containing products reduced by 41 %, while the proportion of semi-coke increased by three times. Additionally, the EEF inhibited the reaction of functional groups. Under the EEF of 0.5 V/Å, the time for –OH to generate H2O was extended by 34.8 ps while the time for –COOH to generate CO2 was delayed by 42 ps. This inhibitory effect increased prominently with increasing intensity of the EEF. Finally, the EEF had a significant influence on the breaking of chemical bonds, thereby inhibiting the progress of chemical reactions involved in the combustion process.