Study On Behavior Of Nitrogen-Oxygen Mixture For Coalbed Methane Adsorption-Desorption

From the viewpoint of coal mine safety and the effect of injecting gas into coalseam to displace CH₄,a series of experiments that gas adsorption-desorption andinjecting gas into coal seam to displace coal methane have been conducted on the basisof the measurement method of methane adsorption capacity. And both the laws of thecoal adsorption-desorption ability to N₂-O₂mixtures and single component gasincluding CH₄, N₂, O₂, and the law of injecting gas into coal seam to displace CH₄havebeen studied in this paper.In the adsorption-desorption experiment of coal samples from the No.15coal seamof Shigang coal mine of Yangquan area, the results have showed that the coal adsorptionability to CH₄is stronger than N₂, and N₂is stronger than O₂. By means of changing theconcentration ratio of N₂-O₂mixtures, it has showed that the coal adsorption ability toN₂-O₂mixtures has been enhanced along with the increasing concentration of N₂, butthe coal adsorption capacity to O₂has increased a little along with the increasingconcentration of O₂. Within the range of mixed gas adsorption equilibrium pressuretested and during the experiments that by injecting different concentrations ratio ofN₂-O₂mixtures to displace CH₄, the result has showed that the maximum capacity aboutthe coal adsorption ability to O₂is0.36ml/g. In the experiment of injecting differentconcentration ratio of N₂-O₂mixtures into coal seam to displace CH₄, when the CH₄adsorption equilibrium pressures are the same, the result has indicated that there is a fewdifferences in those effects of displacement. And because of the small proportion of O₂in mixtures, the coal adsorption capacity to O₂is weaker than other gases, so theconcentration of residual O₂is very low. Besides, the higher the CH₄adsorptionequilibrium pressure is,the harder the displacement ability of CH₄by injecting themixtures and the fewer the displacement capacity will be. In the experiment ofinjection-displacement-desorption, with the increase of injected gas, both the pressureand the coal adsorption capacity to the N₂-O₂mixtures has enhanced a lot. But when thepressure of mixtures reaches a certain extent, the coal adsorption ability to CH₄enhances and the displacement desorption capacity of CH₄decreases.On the basis of analyzing the effect of injecting gas to displace CH₄and the adsorption capacity of O₂in the process of injection, and in order to ensure thesufficient air source when injecting gas into the coal, the conclusion can be obtained asfollows: during the experiment in number15coal seam of ShiGang coal mine, wheninjecting N₂-O₂mixtures to displace CH₄, choosing the air （containing about80%N₂） ismore reasonable.