Pyrolysis is a potential way to realize clean and efficient utilization of tar-rich coal. Pyrolytic efficiency is controlled by both the intrinsic properties of coal and the external pyrolysis conditions. The intrinsic properties of coal are primarily determined by its formation environment. This study revealed the pyrolysis mechanism under varied coal-forming environments (intrinsic factor) and pyrolysis conditions (external factor). The BS coal formed in a deep-water reducing environment has excellent tar yield potential due to its high vitrinite content. The ST coal from a shallow-water reducing environment is more inclined to generate gas and semicoke. The study further reveals that the pressure mainly promoted the secondary reaction by prolonging the retention time of volatiles, thereby inhibiting the tar yield. This mechanism is resulted in decreased tar yields from 9.53% to 8.81% and from 4.91% to 1.91% for the two coal groups. Combining the characteristic of low viscosity at 300 °C for tar with the patterns of porosity and permeability changes in pyrolyzed coal samples under varying temperatures. Basing on these findings, this paper proposes a collaborative optimization strategy: optimizing vitrinite-rich coal sources and utilizing medium-temperature (300–400 °C) process conditions.
Zhang et al. (Sun,) studied this question.