Nano-scale pore distribution characterisation of coal using small angle X-ray scattering--颗粒学报PARTICUOLOGY

Jia, P., Jia, J., & Nadimi, S. (2023). Nano-scale pore distribution characterisation of coal using small angle X-ray scattering. Particuology, 81, 73-85. https://doi.org/10.1016/j.partic.2022.12.014

Nano-scale pore distribution characterisation of coal using small angle X-ray scattering

Peng Jia ^{a b}, Jinzhang Jia ^a *, Sadegh Nadimi ^b *

a College of Safety Science and Engineering, Liaoning Technical University, Fuxin, Liaoning, 123000, China
b School of Engineering, Newcastle University, NE1 7RU, UK

doi.org/10.1016/j.partic.2022.12.014

Volume 81, October 2023, Pages 73-85

Received 2 October 2022, Revised 28 November 2022, Accepted 18 December 2022, Available online 11 January 2023, Version of Record 19 January 2023.

E-mail: jiajinzhang@lntu.edu.cn, sadegh.nadimi-shahraki@ncl.ac.uk

Highlights

• SAXS is used to characterise nano-scale pore distribution and changes of coal after freezing.

• Change of pore size distribution is mainly concentrated in the radius of 0–7 nm.

• Both pore fractal dimension and radius of gyration of coal increase after freezing.

Abstract

In the process of coal seam fracturing with liquid nitrogen (LN2), the change of coal pore structure has an important influence on the efficiency of coalbed methane (CBM) extraction. The nano-scale pore size distribution (PSD) in coal particles before and after freezing with LN₂ are experimentally studied in this work. Coal samples are collected from four coal mines, where coal and gas outburst accidents have occurred. Small angle X-ray scattering technology (SAXS) and scanning electron microscopy (SEM) are used to study the pore structure changes of coal samples quantitatively and qualitatively. It is found that the scattering intensity of coal samples increases after freezing. The PSD of all samples significantly changes in the range of 0.8–7 nm, showing new pore spaces in 0.8–4 nm and fewer pores in the 4–7 nm range. Both the pore fractal dimension and the radius of gyration of coal samples increase after freezing and are mainly affected by the changes in pores and the anisotropy of the coal matrix. Crack expansion and pore connections are observed in the surface structure of the coal sample using SEM. This study provides a better understanding of the nano-scale mechanism of coal seam fracturing with LN₂ for the prevention of coal and gas outbursts.

Graphical abstract

Keywords

Coalbed methane; Small angle X-ray scattering; LN2 freezing; Pore size distribution (PSD); Particle characterisation; Fractal dimension

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