Effect Of Pore Structure Of Anthracite On Adsorption And Desorption Characteristics Of Methane

In the safe production of coal mine,in order to reduce the risk of coal and gas outburst and maximize the use of clean energy in production,it is very important to study the adsorption/desorption characteristics and diffusion performance of coal seam.Coal contains a large number of pores,by studying the structural characteristics of these pores can be to a large extent to understand the microscopic characteristics of coal samples,and then compare and analyze the physical chemistry properties of coal samples,therefore,it is necessary to combine the adsorption/desorption law of coal to gas with the pore characteristics.In this paper,the coal samples from 1901 working face and 1901 working face of 9 coal seam in Xintian coal mine and 159#and 207#coal samples from 12000 return air bottom pumping roadway in Nuodong coal mine are selected as experimental research objects,the pore structure characteristics of each experimental coal sample and its relationship with gas adsorption/desorption performance and diffusion performance were analyzed.The main conclusions reached are as follows:(1)The water content of 4 coal samples in No.9 coal seam in Xintian Coal Mine and No.20 coal seam in Nuodong coal mine is 1.875%?2.515%,ash is 10.54%?23.38%,volatile is 10.05%?11.09%,all of them belong to anthracite.Firmness factor of two coal samples of No.9 coal seam in Xintian coal mine is 1.67?1.87,the firmness coefficient of two coal samples of No.9 coal seam in Nuodong Coal Mine is0.4?0.45,and the initial velocity of gas emission of four coal samples is 17.7?35.35mm Hg,according to the detailed rules for prevention and control of coal and gas outburst,both coal seams have outburst risk.(2)Based on the BJH-N₂model,the pore volume distribution of four experimental coal samples presented a multi-peak situation,which contained discontinuous pore structure.Combined with the analysis of N₂adsorption method and CO₂adsorption method,the pore volume of four experimental coal samples was mainly micropore,the specific surface area of each coal sample is mainly micropore,which provides a place for gas storage and migration in coal.The maximum of fractal dimension D₁and D₂is coal sample of No.9 coal seam in Xintian Coal Mine,which shows that the surface is roughest and the pore structure is most complex,while the pore structure of coal sample NO.20 in Nuodong Coal Mine is more simple.(3)Through quantitative characterization,it is proved that pores below 1.5nm are adsorption pores:combined with the analysis of micropore filling theory and surface covering theory,the proportion of methane volume adsorbed by four coal samples in micropore filling form and total methane volume is between 91%?98%,and the proportion of methane volume covered by single layer adsorption form is between 2%?9%.From the proportion,it can be concluded that the occurrence of gas in coal is mainly micropore filling and single layer adsorption Most of methane exists in the pores with 0.38?1.5nm pore size in the form of micropore filling.(4)The influence of pore of coal sample on gas diffusion ability:combining with the free path of methane molecule and the pore volume distribution of BJH-N₂,the diffusion process of each coal sample can be divided into three diffusion regions:2?64nm is Knudsen diffusion region,64?72nm is transition diffusion region,72?100nm is the Fike diffusion region.Through the correlation study of each diffusion zone and diffusion parameters,we can know that Northen diffusion plays a dominant role in the diffusion performance of coal.(5)The influence of pore structure on diffusion of four experimental coal samples in Northen diffusion zone:the BJH specific surface area of No.9 coal seam in Xintian coal mine is 2.553?3.320m²/g,and that of No.20 coal seam in Nuodong coal mine is 2.586?5.203m²/g.The BJH pore volume of NO.9 coal seam of Xintian Coal Mine is 0.003?0.005m L/g,and that of NO.20 coal seam of Nuodong coal mine is0.007?0.011m L/g.According to BJH analysis method,the most probable pore size of NO.9 coal seam in Xintian coal mine is 2.823?2.915nm,and that of NO.20 coal seam in Nuodong coal mine is 2.954?3.412nm.In addition,based on the analysis of desorption rate of each coal sample,it can be concluded that the diffusion ability of coal sample of No.9 coal seam in Xintian coal mine is weaker than that of No.20 coal seam in Nuodong coal mine.This paper has a total of 35 pictures,24 tables and 106 references.