Molecular dynamics simulations study of brown coal pyrolysis using ReaxFF method

Abstract

Two brown coal models were built to investigate the pyrolysis of coal using the ReaxFF molecular dynamics simulations. The Hatcher model and Morwell model were selected as representations of brown coal. For the purpose of studying the effect of heating rate on coal pyrolysis, ReaxFF-MD simulations were performed at temperatures from 300 to 2000 K with heating rate of 10, 100, and 1000 K/ps, respectively. Results showed that the pyrolysis reaction was enhanced under higher heating rate condition, and hydrogen, methyl, ethylene, acetylene, formaldehyde, and heavy compounds C14+ were the main products of coal pyrolysis. Plenty of radical fragments were also found in the pyrolysis process, and the pyrolysis reaction was promoted at high temperatures, which is consistent with the experimental results. The distributions of final products were greatly influenced by the initial structure of brown coal. The mass of aromatic nucleus mainly transformed into heavy char and tar (the C40+ compounds).