Gas transport through porous strata from underground reaction source; the influence of the gas kind, temperature and transport-pore size

The mean transport-pore model was applied for description of the gas transport through the porous stratum above the gas source in the underground coal gasification (UCG). For modeling of gas diffusion and permeation textural parameters of the porous stratum samples determined by nitrogen physical adsorption, high pressure mercury porozimetry, isobaric binary diffusion and single gas permeation were used. Relevance of both transport mechanisms was judged and it was determined that the prevailing transport mechanism is gas permeation. The effect of process parameters of UCG was investigated for this gas transport mechanism. Followed were the (mean) temperature, pressure, kind of transported gas and stratum pore size. It was found that the pressure increase influences the speed of the gas front movement more significantly than the temperature increase. Similarly, the effect of pore sizes was lower than the effect of the pressure increase. The front of individual gases will move in the order hydrogen > ammonia > methane > hydrogen sulfide > carbon dioxide > carbon monoxide and the rate of the hydrogen front movement will be approximately twice higher than the movement of CO2 front.