Mechanism of coal-pyrolysis under elevated pressure and rapid heating conditions

Abstract

The coal-pyrolysis experiment under elevated pressure conditions using a pressurized thermobalance has been carried out to clarify the mechanisms and the processes at conditions changing from normal pressure to higher pressure (10.6 ata) and from slow (0.1 K/s) to rapid heating rate (20 K/s). Simultaneously, a new pyrolysis model which can describe a pressure effect on the evolution behavior has been developed based on the FLASHCHAIN® model including a quantitative estimation of the volatilized gases and released tar vapor. From the experiment, the tar vapor formation is suppressed and the yields of CH 4 gas shows increasing behavior at higher pressure conditions. Because the mole fraction of tar vapor decreased with the increase of the pressure by Raoult's law, and the recombination reactions of remaining metaplast (precursor of tar) within the coal are activated, resulting in more chars and more gas yields (CH4, CO2). At rapid heating rate conditions, the conversion from the metaplast to the volatile matter would be more active, because the reaction temperature range for thermal pyrolysis shifts to higher range with increase of heating rate. It was found that the rapid heating rate affects the molecular structure of the coal substantially.