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

In order to study the pore change and permeability of coal affected by acid liquor, samples were collected from Huoerxinhe Coalmine in Qinshui Coal Field, Shanxi Province and taken as the study object. The hydrochloric acid(HCl) with the 10% of volume concentration was used to treat these coal samples. The pore structure characteristics and gas permeability of coal with different treatment time were measured by laboratory experiments. The fractal theory was introduced to analyze the complexity of coal pore and the changing rules of coal permeability. The research results show that acid liquor has significant influence on coal pore. Under the effect of acid treatment, the micropore volume of coal reduces, but the macropore volume increases. The mesopore in coal is less affected by acid treatment. The fractal dimension of acidulated coal samples changes in the range of 2.59 to 2.81, and it decreases with the increase of treatment time. This indicates that the acid treatment can make the coal surface become smooth and the pore structure tends to be simple. Acidification method enables to effectively increase the coal permeability with the maximum growth of about 10.04 times. After 20 h of acid treatment, the total pore volume, fractal dimension and permeability of coal samples tend to be stable. The acid treatment time should be controlled at around 20 h.