Enhancement effects of NaCl solution on pore structure of coal with high-voltage electric pulse treatments

Significance 

Increasing stringent measures on carbon emissions have favored the development of alternative clean energy technologies. In particular, gas energy has recently attracted the attention of researchers due to its numerous areas of applications. However, the increasing mining depths have posed a great threat to gas extraction. This can be attributed to the induced high ground stress, low permeability, and high adsorption rates. To this end, to ensure safety during mining processes, several conventional methods including hydraulic measures have been put in place. Unfortunately, most of these techniques have numerous limitations thus preventing their efficiency especially in enhancing the permeability.

Scientists have identified high voltage electrical pulses technology as a promising method for improving permeability during oil extraction. Developed in the mid-twentieth century, its applications have been extended in solving numerous challenges experienced in oil and gas mining. In coal bed methane extraction, the high-voltage electrical pulse can be applied as either electrical fragmentation of electrohydraulic fragmentation. The former enhances permeability by discharging the liquid surrounded electrode while the latter relies on the tensile failure induced during the interaction between the coal seam and the discharge electrode. However, this will be realized through a fundamental understanding of the breakage of coal samples saturated by sodium chloride solution.

To this note, researchers at China University of Mining and Technology: Xiangliang Zhang (PhD candidate), Professor Baiquan Lin, Dr. Yanjun Li, Dr. Chuanjie Zhu, Jia Kong and Dr. Yong Li from the Key Laboratory of Coal Methane and Fire Control accessed the feasibility of improving the gas-extraction rate of coal seams. Specifically, by using high-voltage electrical pulses effects, they investigated the pore structure characteristics of coal saturated by sodium chloride solution. Additionally, they examined the electrical breakdowns of coal. Their work is currently published in the research journal, Fuel.

In brief, the research team prepared a 1mol/L solution of sodium chloride to investigate the electrical breakdown in air. To enhance the viability of the experiment, a self-designed experimental system was designed to improve the permeability of coal. Furthermore, the breakdown effects on coal as well as the relationship between the breakdown voltage and peak current were determined through various analysis such as EDS and SEM analysis.

The authors observed two types of electrical breakdown of coal in the environment i.e. internal and surface breakdowns which were accompanied by various forms of breakages including surface cracks, breakage from one side and complete comminution. This was attributed to the internal tension effects induced by the high-voltage electrical pulses. Furthermore, the occurrence of cracks and improved internal pore structure exhibited significant potential for enhancing the coal bed methane extraction.

In summary, the research team successfully developed and demonstrated the feasibility of a novel fracturing and permeability improving method based on the combined effects of the high-voltage electric pulses and hydraulic fracturing. In general, they noted the difference in the breakdown voltages and the peak currents. Altogether, the study will significantly advance the extraction of gas thus promoting sustainability.

About the author

Xiangliang Zhang– A PhD Candidate student in the Graduate School of Safety Engineering at China University of Mining and Technology. He graduated with a bachelor degree of School of Safety Engineering from China University of Mining. And he get the chance to pursue a doctorate degree directly. His research interests mainly focus on High voltage electrical pulses (including high voltage crushing solid, Plasma technology), and Coalbed methane recovery (including CH4 adsorption, seepage, Gas transport in coal seam).

About the author

Baiquan Lin – Professor, doctoral supervisor; National Excellent Scientist; State Work Safety experts; Jiangsu Ten Outstanding Patent inventor; Editorial Advisory Board member of 《Journal of Mining & Safety Engineering》, 《Mining Safety & Environmental Protection》, 《Journal of Mining Science & Technology》.

He headed over 60 research projects, including the National Natural Science Foundation, National 973 Project, State Technology Supporting Project, the enterprise authorized project and was awarded the second prize of National Scientific and Technological Progress 1, provincial awards on technology advancement over 20. He published over 300 academic essays, authored over 10 books.

Reference

Zhang, X., Lin, B., Li, Y., Zhu, C., Kong, J., & Li, Y. (2019). Enhancement effect of NaCl solution on pore structure of coal with high-voltage electrical pulse treatment. Fuel, 235, 744-752.

Go To Fuel

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