| During the tectonic evolution of coal seam,the coal particle size gradually decreases due to geological action.This evolution process changes the particle size distribution of coal,the pore structure characteristics and the coal gas ad-desorption performance.Therefore,it is of great significance to study the tectonic evolution process of coal seam for the pore structure characteristics and the differences in ad-desorption and diffusion properties.In this paper,the coal samples?SJZY?and coal samples?SJZR?with less tectonic action are selected from the 15106 roadway of15#coal seam in Sijiazhuang coal mine.During the tectonic evolution of coal seam,a series of physical and chemical changes will take place,accompanied by the continuous crushing and pulverization of coal.However,due to the complexity and unsimulability of the process,this paper breaks the coal sample into different particle sizes in the laboratory to simulate its physical changes,so as to study the influence of tectonism on coal.Through the analysis of coal seam tectonic structure and laboratory experiments,the influence of coal seam tectonic evolution on coal pore structure and gas ad-desorption and diffusion performance is analyzed.Based on the appearance of the pulverized coal particle size on gas ad-desorption ability strong,the paper calculated the SJZY and SJZR coal sample under the different size of gas expansion energy,combining previous research results,determine the pulverized coal is one of necessary conditions of the process of coal and gas outburst,and based on the analysis of the coal pulverization and fast desorption of prominent effects.1)The content of moisture,volatiles and fixed carbon in SJZY coal sample is higher than that in SJZR coal sample in tectonic evolution.The firmness cofficient f of SJZY coal sample and SJZR coal sample was measured as 1.14 and 0.15respectively.The maximum adsorption volume of N2 in SJZY coal sample increased from 1.41ml/g to 15.19ml/g,and that in SJZR coal sample increased from 5.53ml/g to 19.86ml/g.The span of CO2 adsorption volume of SJZY coal sample is 5.96ml/g,and that of SJZR coal sample is 1.96ml/g,indicating that the adsorption volume of SJZY coal sample fluctuates widely with particle size.The N2 desorption isotherm of two kinds of coal samples shows that the pore shapes of the two kinds of coal samples are mostly columnar.2)BJH-N2 model shows that the pore volume distribution of two kinds of coal samples is a multi-peak state,and there are discontinuous pore structures in the coal samples.The DFT-CO2 model shows that the four fluctuating peaks of the two coal samples with the peak quantity between 1-3mm and 0.5-1mm in large particle size eventually become a peak,indicating that the continuity of the coal samples with the pore diameter between 0.4-0.7nm becomes better.The maximum pore diameters of the two coal samples are both 0.35nm at the peak of coal sample no.1,and the maximum pore diameters of the pore volume distribution with the pore diameter<0.4nm have not been changed by tectonic action.The DFT-N2 model shows that the peak quantity of the two coal samples does not change significantly.3)The micropore volume of SJZY coal sample is between 0.218×10-3ml/g and2.13×10-3ml/g,and the maximum value is 9.771 times of the minimum value.The pore volume of SJZR coal sample is between 1.16×10-3ml/g and 2.58×10-3ml/g,and the maximum value is 2.224 times of the minimum value.The BET specific surface area of SJZY coal sample is between 0.719m2/g and 3.117m2/g,and the minimum and maximum values are obtained at 0.5-1mm and<0.074mm respectively,with a difference of 4.335 times.The BET specific surface area of SJZR coal sample is between 2.386m2/g4.022m2/g,and the minimum and maximum values are obtained at 0.5-1mm and<0.074mm respectively,with a difference of 1.686 times.It indicates that the micropore volume and specific surface area will gradually increase and the gas adsorption capacity will be enhanced during the structural evolution of coal seam.The fractal dimension D1 of pore structure of SJZY coal sample is between2.4692.683,and that of SJZR coal sample is between 2.4382.598.The minimum and maximum values of both coal samples were obtained at<0.074mm and 1-3mm,in which the maximum value of SJZY coal sample was 1.087 times of the minimum value,and the maximum value of SJZR coal sample was 1.066 times of the minimum value.The fractal dimension of SJZY coal sample with different particle sizes is higher than that of SJZR coal sample,which indicates that the pore structure of SJZR coal sample is simpler than that of SJZY coal sample,which is closely related to the large tectonic action of SJZR coal sample.4)The a value of SJZY coal sample is between 27.6988 and 42.8633ml/g,with a span of 15.1645ml/g.SJZR coal sample is between 37.624943.0575ml/g,with a span of 5.4326ml/g.For desorption Q300 of two kinds of coal samples:SJZR coal sample increased by 5.15m3/t,SJZY coal sample increased by 2.25m3/t;For Q60,SJZR coal sample increases by 5.69m3/t,and SJZY coal sample increases by3.04m3/t.In addition to 1-3mm particle size,desorption rate of SJZR coal sample at the 10min was lower than that of SJZY coal sample,and the difference between them increased to-0.1?g·min?when the particle size was 0.074mm.The effective diffusion coefficient of SJZY coal sample is between 1.94×10-57.14×10-5,and that of SJZR coal sample is between 5.90×10-51.65×10-4.By comparing the two coal samples,it can be found that for the same particle size,the effective diffusion coefficient of SJZR coal sample is 1.953.63 times that of SJZY coal sample.5)With the gradual decrease of coal particle size in the tectonic evolution process,the average gas desorption velocity of SJZY coal sample increased from0.03033ml/g·s to 0.10467ml/g·s in the first 30 seconds,and that of SJZR coal sample increased from 0.09567ml/g·s to 0.26733ml/g·s.When the particle size of SJZY coal sample is less than 0.23mm,it exceeds the critical gas desorption velocity of 0.05646ml/g·s,while the SJZR coal sample exceeds this critical value under six particle sizes.The gas expansion energy of each particle size section of SJZY coal sample is between 177.8kJ/t and 613.6kJ/t,in which the maximum value is 3.5 times of the minimum value.The gas expansion energy of each particle size section of SJZR coal sample is between 560.9kJ/t and 1567.3kJ/t,in which the maximum value is 2.8times of the minimum value.By analyzing the role of pulverization and fast desorption of gas in promoting outburst development process,it is concluded that small particle size"pulverized coal"and fast desorption of gas adsorbed in coal play a decisive role in promoting outburst process. |
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