Effects of Fe2O3 addition on the thermoplasticity and structure of coking coal matrix during thermoplastic stage of pyrolysis

Abstract

Effects of Fe2O3 addition on the thermoplasticity and structure of coking coal matrix were performed by blending Fe2O3 with coking coal matrix during thermoplastic stage of pyrolysis. Thermoplasticity and thermal behavior of coal matrix were characterized by Gieseler plastometer and Thermogravimetry analyzer. Structure of coal matrix at different pyrolysis temperatures during thermoplastic stage was investigated by using X-ray diffraction and Fourier transform infrared spectroscopy. Fluid phase collected from the coal matrix by two-stage extraction was identified by Gas chromatography-mass spectrometer analysis. The results show that the added Fe2O3 decreased the plastic range, maximum Gieseler fluidity and weight loss rate of coal matrix, and inhibited the cleavage of Cal-Cal, Cal-Car, Cal-O, Cal-S and Cal-N bonds during thermoplastic stage. Further, the inhibiting effect resulted from the added Fe2O3 made the decrease of aromaticity and average stacking height, increase of interlayer spacing of the crystallite, and ascending of aliphatic chain length and hydrocarbon-generating potential of coal matrix. Consequently, the formed fluid phase would be reduced, reflected in the disappearance of ethylbenzene, o-xylene and unbranched alkanes with carbon atoms in 24–26, resulting in coal thermoplasticity declining. This contributes to a better understanding of coke strength decrease in producing highly reactive iron coke.