Study on the factors affecting the adsorption of CO₂ from power plant flus gas in coal left in goaf area

Utilizing the adsorption characteristics of coal rock in the goaf to storage CO₂ not only reduces the cost of carbon capture and separation, but also prevents spontaneous combustion of coal left in goaf area. The effects of pore structure, mineral content and moisture content on the CO₂ adsorption characteristics of coal were investigated using adsorption experiments at ambient temperature and pressure, ASAP specific surface area and pore size analysis experiments. Then the quantitative relationship equations of factors affecting CO₂ adsorption in coal were fitted, and the importance weights of each influence was calculated by Random Forest algorithm. The results shown that, the pore size distribution of three coals from the mining area of Dananhu (DNH), Hegang (HG) and Tongxin (TX) were basically the same. The number of pores in the range of 0.5-0.7 nm and 0.8-0.9 nm was more, and that in the range of 0.7-0.8 nm was less. The number of micropores was the fundamental reason for the difference in CO₂ adsorption capacity of three coals. At ambient temperature and pressure, the saturated adsorption amount of CO₂ in coal increased with the increasing specific surface area, and decreased with the increasing mineral content and moisture content. The more the number of micropores of coal, the more significant the influence of mineral content and moisture content on the adsorption amount. After the coal reached the critical moisture content, the saturated CO₂ adsorption amount gradually tended to be stable because the water molecules hindered the flow channels of CO₂ molecules, resulting in the CO₂ molecules not being able to enter into the pores inside the coal. The specific surface area had the greatest influence on the adsorption amount, followed by the moisture content and pore volume, and the mineral content was the weakest. Specific surface area and moisture content had a combined importance weight of 75.1%, which was much higher than the other two factors. According to the fitting equation, the saturated adsorption amount of CO₂ in coal can be inferred by determining the specific surface area, mineral content and moisture content of coal, which provide a theoretical basis for CO₂ adsorption and storage by coal left in goaf area.