Influence Of Metamorphic Grade On Gas Adsorption/desorption Characteristics Of Outburst Coal

Coal metamorphism and pore structure are the main factors affecting gas adsorption and desorption characteristics.Taking the metamorphosed metamorphic coals as the research object,the laboratory tests and analysis were used.This study selected five kinds of metamorphic coal samples,which are Liaoning Daxing Mine?DX?,Shanxi Shuangliu Mine?SL?,Anhui Yangliu Mine?YL?,Shanxi Sijiazhuang Mine?SJZ?and Anhui Wolonghu Mine?WLH?.In this paper,the qualitative and quantitative analysis of the pore structure and micro-level analysis of the gas desorption kinetic characteristics of coal samples was carried out,which explores the effect of metamorphic degree on the gas desorption kinetic characteristics of coal and gas outburst coal.The main results are as follows:?1?This paper uses infrared spectroscopy to obtain five kinds of metamorphic coal samples oxygen functional groups mainly including hydroxyl,carboxyl,carbonyl and ether bonds,carbon-containing functional groups mainly including methyl,methylene,methine,benzene ring and other functional groups including mercapto group and disulfide bonds.The degree of order in the coal is reflected by the half-width ratio of the peak spectra in Raman spectra first order of G and D1.The internal order of the coal samples is SJZ>WLH>SL>YL>DX.?2?The pore characteristics and key parameters of coal samples are obtained by scanning electron microscopy,mercury injection,liquid nitrogen,and CO2 adsorption experiments.The pore structure of the DX and WLH are mainly micropores,followed by minipores and mesopores,and macropores lacking development.The pore structure of the SL are mainly minipores and macropores,followed by micropores and mesopores.The pore structure of the YL are mainly minipores and mesopores,followed by micropores and macropores.The pore structure of the SJZ are mainly micropores and minipores,followed by mesopores,and macropores lacking development.DX,SL,YL,SJZ,and WLH coal samples pore volumes are 0.00497,0.00129,0.000234,0.00140,and 0.0353 m L/g,respectively.Coal samples pore under2 nm volumes are 0.0639,0.0300,0.0420,0.0857,0.0971 m L/g.?3?The limiting adsorbed amount a value of DX,SL,YL,SJZ and WLH coal samples are 25.13,21.03,17.24,50.00 and 47.65 m³/t,which b value are 0.42,0.54,1.37,1.03,0.75 MPa^-1,respectively.The value of?a?is used to characterize coal gas adsorption capacity.The coal gas adsorption capacity firstly decreases and then increases with increasing metamorphic degree.The coal gas adsorption capacity increases as the pore under 2 nm volume and specific surface area of coal increases.?4?The coal gas desorption capacity is studied using cumulative desorption quantity in 1 and 120 minutes.The coal gas desorption capacity firstly decreases slowly and then increases with the increase of coal metamorphism.The coal gas desorption capacity increases as the pore under 2 nm volume and specific surface area of coal increases.?5?Based on the experimental results of desorption diffusion,the diffusion coefficients of coal samples are calculated by fitting the classical diffusion model.The coal gas diffusion capacity firstly decreases and then increases with the increase of coal metamorphism.The coal gas diffusion capacity increases as the pore between10 and 100 nm volume and specific surface area of coal increases.The research results above provide the basis for the prevention and treatment of coal and gas outbursts.