An Experimental Study on CO2 Displacing CH4 Effects of Different Rank Coals

Abstract

In order to study the effect of different rank coals on the displacement of CH4 by CO2 and prevent the gas-related disasters, a series of experiments were carried out. For this purpose, we selected low-rank lignite raw from Datong coalfield of Shanxi Province, medium-rank bituminous coal raw from Xutuan coalfield of Anhui Province, and high-rank anthracite raw coal from Yangquan coalfield of Shanxi Province. The results showed that (1) the shape of the displacement adsorption curve of the mixed gas and the shape of the single-dimensional adsorption curve of the pure gas are both steep at the beginning, with the increase of the pressure, the curve becomes more and more gentle. The difference is that it is lower than the single-dimensional gas adsorption curve. (2) The separation factor in the coal samples used in the experiment shows a trend of first decreasing and then increasing with the decrease of coal rank. The displacement factor has the same trend as the separation factor of each coal rank, which is $Z_{ij}\left(\text{anthracite}\right)>Z_{ij}\left(\text{lignite}\right)>Z_{ij}\left(\text{bituminous}\text{coal}\right)$ . (3) The amount of displaced CH4 in the displacement/adsorption process has enhanced with the increase in pressure, and the trend for different coals is $Q_Z\left(\text{bituminous}\text{coal}\right)>Q_Z\left(\text{anthracite}\right)>Q_Z\left(\text{lignite}\right)$ . In addition, displacement showed the order $ƞ\left(\text{lignite}\right)>ƞ\left(\text{anthracite}\right)>ƞ\left(\text{bituminous}\text{coal}\right)$ . The injection ratio of bituminous coal and anthracite decrease with the increase in pressure, while that of lignite increase first and later decreased. (4) In gas injection displacement, on the long time, the displacement effect of high coal rank is better than that of low coal rank.