Studies on the influence of moisture on the sorption and structural properties of hard coals

Abstract

In the conducted research, the effect of moisture on CO2 sorption and transport processes and changes occurring in the coal pore structure were investigated in detail. The measurements were carried out under isothermal (313 K) and isobaric conditions (0.1−0.8 MPa) on the original device - a manometric sorptomat. Coal sorption capacities, Langmuir sorption isotherms, effective diffusion coefficients and structural parameters were analysed. The obtained sorption capacities of the tested samples relative to CO2 for pressures 0.1, 0.3 and 0.8 MPa confirmed that moisture significantly (even up to 6 times) reduces the sorption capacity of coal relative to CO2, and the largest reduction in sorption capacities was noted on coal with the lowest vitrinite reflectance. It was observed that the increase of the sorption equilibrium pressure decreases the effect of the reduction of the sorption capacity of coal under the influence of moisture, and above 1.0 MPa this effect disappears completely. The critical moisture content was estimated, above which there is no further reduction of the coal sorption capacity due to the increase in moisture content. It was observed that the influence of moisture on CO2 diffusion in its pore space is not clear. Structural analysis were carried out by low-pressure CO2 adsorption at 273 K and 0−0.1 MPa. After increasing the coal moisture content, the surface area decreased by 50 % and a decrease in the volume of available pores with diameters in the range of 0.5−0.6 nm was noted.