Based on the general coal model, the processes of pyrolysis of coals of different rank were studied by molecular dynamics simulations with the ReaxFF reactive force field. Simulations were performed over wide temperature ranges both for heating from 300 K to 3000 K and a constant temperature range from 2000 K to 3500 K. The pyrolysis of coals of different coal rank under different heating conditions was analyzed. The temperature at which the structure units began to be consumed heavily and the temperature at which the consumption was complete were elevated. In terms of the time scale, the rise of the heating rate caused the reactions to occur earlier. It was found that the pathway of coal pyrolysis at different heating rates was not affected, and the initial reaction pathways of five kinds of coal pyrolysis were obtained. Under the pyrolysis conditions of 2000 K to 3500 K, we observed the change in the total molecular number of different coal rank coal systems with temperature, reflecting the degree of cracking. At the same time, carbon monoxide and hydrogen were chosen as the typical products. The change rules of the temperature were obtained, and the formation mechanisms of different stages were discussed. The comparison of coals of different coal rank showed that the temperature had more influence on the lower rank coal. The results observed in this work are broadly in agreement with the literature. This work demonstrates a new methodology for investigating the overall behaviors and the underlying complex mechanisms of the pyrolysis of coals of different rank.
Keywords: Coal pyrolysis; Coals of different rank; Heating rates; ReaxFF reactive force field; Temperatures.