| Coal seam gas content is the most basic and important parameter for the exploration and evaluation of coalbed gas resources,the prediction of coal seam gas outburst risk,the design of mine ventilation,and the prevention and control of mine gas.Accurate measurement of coal seam gas content is of great significance.For the widely used direct method to measure the gas content in coal seams,the calculation of gas loss is based on the adsorption and desorption laws of gas,which is greatly influenced by the environmental conditions and the nature of the coal,making it difficult to determine the gas content accurately.The freezing sampling technology of coal creates the low temperature and high pressure environmental conditions for coal samples.Low temperatures can be used to suppress the gas desorption of coal samples during the sampling process,and the amount of gas loss is greatly reduced,resulting in a more accurate gas content.The article relies on the research of coal freezing sampling technology and compares the adsorption and desorption law of gas under multi-factors by orthogonal experiments,and conducts sensitivity analysis and regression analysis on the five factors of coal particle size,temperature,pressure,moisture of coal,and forming pressure.It shows that the use of coal freezing sampling technology can achieve suppression of coal gas desorption and verify the feasibility of coal freezing sampling technology.At the same time,based on the structure and working principle of the typical coal and rock frozen sampler,COMSOL Multiphysics was used to simulate the coal core temperature field variation and freezing rate under the electronic refrigeration condition and the phase changes of cold source liquid nitrogen.The feasibility and rational of the structure of the typical coal and rock frozen sampler.According to numerical simulation results,the structure and boundary conditions of the frozen sampler were improved to meet the practical engineering applications,which lays a solid foundation for the design and improvement of the coal and rock frozen sampler,and promotes the development of the frozen sampling technology.The main results obtained in this paper are as follows:1.The sensitivity of coal particle size,temperature,pressure,moisture,and forming pressure to the gas desorption capacity of coal is: "C"(pressure)> "B"(temperature)> "A"(particle size)> "D"(Moisture)> "E"(Forming Pressure);2.The multivariate quadratic regression equation for five factors can show the trend of gas desorption capacity of coal with various factors,except the effect of limiting particle size and limit moisture.And the impact of coal forming pressure needs a followup experimental study to verify;3.Coal frozen sampling technology is reasonable and feasible.4.The temperature of the coal core gradually decreases with the increase of the freezing time.The temperature at each point in the coal core increases with decreasing radial coordinate r,and the lower the electronic cooling temperature,the faster the freezing speed.5.The phase change cold source has a better cooling effect on the coal core than the electronic refrigeration.6.When the freezing width at the bottom of the coal core increases within a certain range,the blocking effect of nitrogen on the frozen area is smaller,and the freezing efficiency of liquid nitrogen is higher.When the freezing width exceeds a certain range,the blocking effect of nitrogen on the frozen area Instead,it will increase;7.The typical structural coal and rock frozen sampler is less feasible when the refrigerant is liquid nitrogen;8.The improved coal ice sampler can improve the freezing efficiency of liquid nitrogen,reduce the consumption rate of liquid nitrogen,and have a better coal core freezing effect than the typical structure. |
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