Research on the influence of liquid nitrogen freeze-thaw cycles on gas emission characteristics of coal

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 (E_g) 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 E_g 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 (A_T2) of anthracite and coking coal increases by 51.58% and 67.06%, the E_{g max} increases by 37.26% and 41.44%, and the initial gas emission velocity (V_g0) increases by 91.18% and 80.77%. In the freeze-thaw cycles, the changes of E_g and V_g0 are correlated with the changes of A_T2 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.

Graphical Abstract

KEYWORDS:

• freeze-thaw cycle
• gas emission characteristics
• pore structure
• NMR
• anthracite coal
• coking coal

Acknowledgments

This work was supported by the Key R&D and Promotion Projects in Henan Province (No. 202102310222).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1. The in-text callouts for Figure 3 and table 1.

Additional information

Funding

This work was supported by the the Key R&D and Promotion Projects in Henan Province [202102310222].