Abstract
ABSTRACT To research the effect of freeze-thaw cycles of liquid nitrogen (LN2) on gas emission characteristics of different coal types, using low-field nuclear magnetic resonance device (NMR) and the emission of gas (Eg) experimental platform built independently, the pore structure characterization and dispersion characteristics of saturated anthracite and coking coal samples after 3, 6, and 9 exposures were studied. The experimental results show that the LN2 freeze-thaw cycles can significantly increase the Eg of coal under experimental conditions and have different effects on the gas emission characteristics of anthracite and coking coal. After exposure, the T2 spectra area (AT2) of anthracite and coking coal increases by 51.58% and 67.06%, the Eg max increases by 37.26% and 41.44%, and the initial gas emission velocity (Vg0) increases by 91.18% and 80.77%. In the freeze-thaw cycles, the changes of Eg and Vg0 are correlated with the changes of AT2 to a certain extent. The freeze-thaw cycles of LN2 can effectively transform the pore structure of coal, improve the permeability of coal seam, and promote the migration of coal gas. The research results of this paper provide theoretical support for the cryogenic cracking of coal seam by LN2, anti-permeability, and suction promotion in coal mine site.
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