| Guizhou province has rich coal resources,poor permeability of coal seams,and most of them have the coal and gas outburst risk.In recent years,although the frequency of occurrence of gas disasters has been decreasing,it still poses a great threat to the safety of coal mine production and the life safety of workers.Therefore,it is of great research value and practical significance to study the law of gas desorption and release initial velocity for low permeability and difficult-extracting outburst coal seams in Guizhou mining area.In this paper,4 low permeability and difficult to extract outburst coal seams(including the 9~#coal seam in Qianbei,8~#coal seam in Zhina,17~#coal seam in Liupanshui and 17~#coal seam in Xingyi)which are in rich coal area are selected as research objects.With the help of the Autopore IV9510 fully-automatic mercury porosimeter and the 3H-2000PS1/2 automatic surface area and pore size analyzer,the pore characteristics of the test coal samples were analyzed.Based on the HCA gas adsorption device and the improved WT-1 gas diffusion velocity tester,the gas desorption and initial speed test of release under different water content,particle size and temperature were carried out.The relationship between the pore characteristics of coal and the above experiments is discussed.The influence of temperature,particle size and water content on the test results were analyzed theoretically.By used the numerical analysis method to derive the temperature and moisture content,particle size and the coupling effect between the solution of quantitative laws on coal seam gas desorption.Through this study,the main progress has been made in the following aspects:1)Four classifications of coal seam gas desorption and three stages of gas desorption and coal extraction are expounded.The relevant research results of gas desorption theory are introduced,and the empirical formula and application scope of coal seam gas desorption are summarized.2)The qualitative analysis of 4 coal seam coal samples was carried out with the results of industrial analysis,sturdy coefficient and true density test.3)The pore volume and specific surface area of coal samples with different particle sizes in9~#coal seam in the Qianbei are analyzed by using the mercury pressure test.By compared the adsorption capacity of 3 different particle size coal samples,it was found that the particle size is0.3~0.45mm,the coal sample is the most powerful,the particle size is 0.2~0.3mm,the coal sample ability is weak,and the particle size is 0.3~0.45mm,the coal sample has the strongest restraint ability to the gas.The specific surface area,pore size distribution,and pore volume distribution of coal samples with different particle sizes in the four test coal seams were analyzed with cryogenic liquid nitrogen tests.It was found that the pore volume of Qianbei,Liupanshui and Xingyi coalfield are mainly composed of micropores and small holes,and their pore area is mainly contributed by micropores.The pore volume and pore area of the Zhina coalfield are mainly consist of micropores.In the four coal seams,the contribution of micropores to the pore area of coal samples with different particle sizes almost increases with decreasing particle size.4)The results of gas desorption tests at different temperatures,different particle sizes and different moisture contents indicate that the increase of temperature can promote coal seam gas desorption,and he increase of particle size and increase of water content all inhibit it.It can be seen from all the test results that the most severe time period of gas desorption is 0~30min,and the gas desorption rate in this period is larger than that in the same time period.Under different temperature and particle size,the desorption rate of coal samples in 0~30min is between59.42~80.99%,and the corresponding value of coal samples is between 55.8~66.67%under different moisture content.5)The temperature control system of the existing WT-1 gas diffuser speed measuring instrument has been reconstructed,and the initial speed test of gas diffusion under different temperature,different particle size and different moisture content has been carried out.The experimental results show that the initial velocity of gas emission is negatively correlated with temperature,particle size and moisture content.When the adjacent temperature,particle size and moisture content change,the stable interval of initial velocity of release is different.6)Analyzing the influence of pore characteristics on coal seam gas desorption and initial velocity of exhalation,it was found that the micropore area in coal is the primary reason for the inverse correlation between initial velocity and particle size of coal seam gas desorption and diffusion.The influence mechanism of temperature,particle size and water content on the law of gas desorption and initial velocity change of coal seam gas is analyzed theoretically.On the other hand,the gas desorption velocity of each gas desorption test is analyzed from the dynamic point of view.It is found that the initial desorption rate increases with the increase of temperature and particle size,and decreases with the increase of water content.Under the action of concentration difference,the coal seam gas evolves slowly from desorption to slow desorption.The regression analysis shows that the initial velocity of gas dispersion in the test coal seam has exponential function relation with temperature,particle size and water content.7)According to the test results,the calculation formulas of temperature and moisture content,temperature and particle size and the coupling effect of coal seam gas desorption.Based on the experimental results,the quantitative relation of coupling of temperature-moisture content and temperature-particle size was deduced.It is found that coal seam gas desorption can be divided into four areas when temperature and moisture content are coupled.The coupling action of the second region is to promote the desorption of coal seam gas,and the other three regions all restrain it.When the temperature and particle diameter are coupled,the coupling effects can be divided into 3 cases.They all play an inhibitory role on coal seam gas desorption,and the effect will decreases with the increase of particle size and temperature. |
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