In
this paper, typical Chinese bituminous coal was pyrolyzed rapidly
and repeatedly in a high-frequency furnace at 1000 °C to investigate
the changes of coal physicochemical structures, reactivities, and
their relationship. The physicochemical structure was mainly characterized
by Fourier transform infrared spectroscopy, Raman spectroscopy, pore
analysis, and so forth. The results showed that after the rapid pyrolysis,
the specific surface area reduced significantly, the average particle
size and the content of amorphous carbon structure increased first
and then decreased, the content of the oxygen-containing group exposed
to the surface decreased, and the aromaticity increased gradually.
The reactivities were analyzed by thermogravimetric analysis, including
slow pyrolysis (from 105 to 1000 °C) and in situ gasification
(at 850, 900, 950, and 1000 °C). For slow pyrolysis, the primary
decomposition peak of pretreated samples was inhibited, whereas the
secondary peak was enhanced. For in situ gasification, the reactivity
was promoted after rapid pyrolysis according to the reactivity index.
The Coats–Redfern method and model-free method were adopted
for kinetic analysis. These reactivity changes were discussed with
the evolution of the physicochemical structure in detail. For example,
the variation of the decomposition peak in slow pyrolysis was implied
by the content of the aliphatic and aromatic in the samples. Besides,
the first rapid pyrolysis was found to be more crucial than the second
rapid pyrolysis for the changes of the coal structure and reactivity.