Impact research of CH₄ replacement with CO₂ in hydrous coal under high pressure injection

Liwei Chen¹, Mingzhen Zhao¹, Xiaohua Li¹, Yuan Liu¹

¹School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, China

Min. miner. depos. 2022, 16(1):121-126

https://doi.org/10.33271/mining16.01.121

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      ABSTRACT

      Purpose. Based on high-pressure gas injection technology that enhances coal seam gas drainage, the effect of CH₄ replacement with CO₂ in aquiferous coal has been studied.

      Methods. Using the laboratory experimental method and the self-built high-pressure gas injection experimental device, high-pressure CO₂ is injected into coal with different moisture contents to replace CH₄ under different adsorption equilibrium pressures.

      Findings. With an increase in coal moisture content, the adsorption capacity of coal for CH4 and CO₂ gradually weakens, the adsorption capacity for CO₂ is always greater than that of CH4, and the CH₄ replacement rate and the CO₂ injection ratio gradually decrease. It is concluded that the CH₄ replacement rate and the CO₂ injection ratio are negatively correlated with the water content of coal. With an increase of the pre-adsorption equilibrium CH4 pressure (0.5, 0.75, 1.0, 1.3 and 2.0 MPa), the CH4 replacement rate and the CO₂ injection ratio first sharply and then slowly increase. The transition point is 1.3 MPa (pre-adsorption equilibrium pressure of CH₄).

      Originality. Based on the adsorption characteristics of coal seam gas injection, the influence of coal water content and gas injection pressure on CH₄ replacement rate and CO₂ injection ratio is analyzed, and the mechanism is studied.

      Practical implications. The experimental results have important guiding significance for selecting reasonable gas injection pressure and the source of gas to drive its injection into underground coal seam.

      Keywords: moisture, coal, equilibrium pressure, methane, carbon dioxide, replacement ratio, injection ratio

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