Study on diffusion characteristics of CO2 in low permeability coal under sub-critical conditions

Abstract

In order to study the diffusion characteristics of CO2 in low-permeability raw coal under subcritical conditions (gas pressure lower than 6 MPa and temperature lower than 39 ℃), the CO2 adsorption/desorption experiments and diffusion experiments were carried out by the volumetric method to study adsorption/desorption and diffusion characteristics of CO2 in raw coal. The results show that the increase of pressure will promote the adsorption of CO2 by coal, and the increase of temperature will inhibit the adsorption of CO2 by coal, and there is a desorption hysteresis phenomenon in the adsorption/desorption process of CO2 in raw coal. When the equilibrium pressure is constant, the diffusion amount of CO2 in the raw coal at different temperatures is positively related to the diffusion time, the CO2 diffusion rate is inversely proportional to the diffusion time, and the CO2 diffusion coefficient D increases with the increase of temperature. Under the medium and low pressure environment, the temperature change within a certain range (15-35 ℃) has little effect on the diffusion rate of CO2 in the raw coal. When the equilibrium temperature is constant, the amount of CO2 diffusion in the raw coal under different pressures is proportional to the diffusion time, the CO2 diffusion rate is inversely proportional to the diffusion time, and the CO2 diffusion coefficient D increases with the increase of pressure; when the temperature is 15 ℃, within a certain range, the pressure change (0.5-3.5 MPa) has very little effect on the diffusion rate of CO2 in the raw coal.

Keywords

• sub-critical condition
• desorption lag
• diffusion amount
• diffusion velocity
• diffusion coefficient