Study On The Influence Of Exposed Area On Coal Adsorption And Desorption

In the process of coal mining,the sectional area of roadway,the working face length and mining height are broken,and traces of goaf,gas extraction from borehole aperture size distribution of coal and coal wall area are involved in the exposed area of the coal,coal exposure area will influence the gas emission in the process of excavation and stoping,the gas extraction efficiency and the efficiency of nitrogen injection co2 fire extinguishing.Therefore,it is of great significance to study the influence of exposed area on adsorption and desorption for gas prevention and mine fire prevention.In the past,the influence of exposed area on gas adsorption and desorption characteristics was often ignored in coal adsorption and desorption studies.This paper takes huayang No.2 coal mine as the research object.Firstly,industrial analysis is carried out to test the basic composition of coal samples.Scanning electron microscopy,cryogenic nitrogen adsorption and cryogenic carbon dioxide adsorption were used to characterize the pore structure of coal samples.The isothermal adsorption desorption tests of methane,carbon dioxide and nitrogen on coal samples under different exposure area and adsorption time were carried out by isothermal adsorption desorption test instrument.Comsol numerical simulation software was used to simulate the desorption capacity of methane,carbon dioxide and nitrogen in different exposed areas.The main conclusions are as follows:(1)The micropores in the coal samples of Huayang No.2 Mine provide most of the pore volume and specific surface area in the coal body,of which the micropore volume accounts for more than 99%of the total pore volume and the specific surface area of micropore accounts for more than 99.5%of the total specific surface area.The pores in the coal are mainly ink-bottle shaped pores.The specific surface area and pore volume provided by micropores are much larger than those provided by mesopores.(2)With the increase of exposed area,the adsorption capacity per unit pressure increases.The larger the exposed area,the greater the adsorption capacity.The adsorption capacity per unit pressure under low pressure is greater than that under high pressure.In the process of gas desorption,the desorption amount per unit pressure increases with the increase of exposed area,and the larger the exposed area,the greater the desorption amount.When the exposed area is 100%,48.23%and9.66%,the nitrogen desorption capacity per unit pressure is 3.4077cm~3/g/MPa,2.9843cm~3/g/MPa and 2.8909cm~3/g/MPa,respectively.The desorption capacity of methane per unit pressure were 3.5247cm~3/g/MPa,3.4355cm~3/g/MPa and3.2182cm~3/g/MPa,respectively.The desorption capacity of carbon dioxide per unit pressure is 12.3324cm~3/g/MPa,11.9629cm~3/g/MPa and 11.9102cm~3/g/MPa.(3)Under the conditions of different exposure area of coal to gas adsorption and desorption process is not entirely reversible,gas adsorption in the exposed parts,first part exposed after reaching adsorption equilibrium,produce obvious absorption area and the interface of the adsorption area,gas to close some diffusion,finally the entire coal sample to reach adsorption equilibrium;Gas desorption is also carried out in the exposed part first,and the desorption speed of the exposed part is greater than that of the closed part,resulting in the interface between the exposed part with low adsorption capacity and the closed part with high adsorption capacity.Finally,the whole coal sample is completely desorption.Under different gas pressures,the larger the coal exposed area is,the shorter the adsorption equilibrium time is;The adsorption equilibrium time of gas decreases with the increase of gas pressure.