Experimental research on the effect of plasma on the pore-fracture structures and adsorption-desorption of coal body

This paper is aimed at investigating the influence of plasma technology on desorption and adsorption features of coal in the fracture scale and proving that plasma technology boasts a wide prospect in the field of coalbed methane extraction. In this paper, CT was combined with low-temperature liquid nitrogen adsorption to analyze the pore and fracture variations of coal before and after plasma breakdown. More importantly, a self-designed desorption experimental system was used to explore variations of gas desorption with time in the fracture scale. According to the research results, the fragmentation effect of plasma is reflected by the generation of cracks in the macro-scale and the improvement of pores in the micro-scale; the fracture is generated from the section near the electrode, and the fracture growth rate after breakdown can reach 18–41 times; the action of plasma can crush coal into little pieces and promote the porosity by over hundreds of times. The appearance of semi-open pores in the liquid nitrogen adsorption test shows that part of closed pores in the coal body are opened by plasma. Moreover, the plasma channel can weaken the adsorption capacity of coal to gas, which is similar to the temperature effect. Meanwhile, the plasma channel increases the desorption amount of coal by 50%–70% and greatly improves the desorption rate of coal due to the influence of interconnected cracks.