Study on the Response Law of Coal Pore Structure and Permeability Affected by Acidification Time

In order to study the pore alteration and permeability of coal affected by acid liquor, samples were collected from the Yuwu coal mine in the Qinshui basin, Shanxi Province, and taken as the study object. Hydrochloric acid (HCl) with a 10% volume concentration was used to treat these coal samples. The pore structure characteristics and gas permeability of this coal with different treatment times were measured by laboratory experiments. The fractal theory was introduced to analyze the complexity of the sample pore and the changing rules of coal permeability. The research results show that acid liquor has a significant influence on the pore structure of YW coal. Under the effect of acid treatment, the micropore volume of the coal sample is reduced, but both the mesopore and macropore volume are increased. The fractal dimension of acidulated coal samples changes in the range of 2.57-2.81, and it is exponentially decreased with the increase of the treatment time. This indicates that the acid treatment can make the YW coal surface become smooth, and the pore structure tends to be smooth. The acidification method is able to effectively enhance the coal permeability with a maximum increment of about 9.43 times. After 30 h of acid treatment, the total pore volume, fractal dimension, and gas permeability of this coal tend to be stable. The acid treatment time should be controlled at around 30 h.