Study On Gas Desorption Law Of Granular Coal Under Negative Pressure Environment

Coal seam gas content is the basic parameter for evaluating and predicting gas reserves and gas emission.It is used as the main regional prediction index when preventing coal and gas outburst disasters.Therefore,accurate determination of coal seam gas content is the key to effective prevention and control of coal mine gas disasters.Negative pressure slag discharge fixed-point sampling to determine coal seam gas content is a new type of fixed-point sampling technology.During the entire negative pressure sampling process,the coal sample is transported and collected under the action of negative pressure suction.The gas in the coal sample first experiences negative pressure.The gas emission under pressure environment then enters the emission process under normal pressure environment.This sampling technology realizes fast fixed-point sampling very well.The amount of gas loss in the sampling process is the main source of error in the measurement of gas content,and the calculation of the amount of gas loss directly affects whether the measurement of coal seam gas is accurate.Therefore,the study of the gas desorption law of granular coal and the estimation model of gas loss in the sampling process urgently needs to be further in-depth.In order to obtain the law of desorption of gas in coal during negative pressure sampling,a model for calculating gas loss during negative pressure sampling was established,and a granular coal gas desorption that simulated the desorption of granular coal gas during the whole process of negative pressure sampling was built.experiment system.The coal samples were collected from the long flame coal of Xinyi Coal Mine,and the adsorption equilibrium pressures were 0.5MPa,0.74 MPa,1.0MPa,1.5MPa,2.0MPa,and the desorption negative pressures were-10 k Pa,-20 k Pa,-30 k Pa,-40 k Pa.And the desorption experiments of granular coal gas under the conditions of1 min,2min,and 3min under the conditions of negative pressure-negative pressure to atmospheric pressure.The research results show that:(1)Under the same negative pressure condition of the coal sample,the total amount of gas desorption in the same desorption time increases monotonously with the adsorption equilibrium pressure.The higher the adsorption equilibrium pressure,the greater the initial gas desorption speed and the faster the attenuation speed;under the same adsorption equilibrium pressure condition,The greater the negative pressure value of the desorption environment,the greater the cumulative desorption volume,the greater the initial gas desorption speed and the faster the decay speed.The longer the sampling time,the greater the loss during the negative pressure phase.(2)Using COMSOL numerical simulation software,the law of diffusion coefficient change in the process of gas migration is obtained by numerical solution method,and the dynamic diffusion coefficient conforms to the form of power function;under the same adsorption equilibrium pressure,the initial diffusion coefficient increases as the negative pressure value increases.Monotonously increasing,negative pressure environment promotes gas desorption and diffusion(3)Through comparative analysis of gas loss estimation methods commonly used at home and abroad,the logarithmic method and the t method were used to calculate the gas loss during negative pressure sampling for downhole gas desorption data.The results show that the accuracy of the logarithmic method is higher than that of the (?) method.The relative error of the estimated gas loss is between-56.25% and16.45%.The relative error is small in a high negative pressure environment,and as the sampling time increases,the relative error decreases.According to the linear relationship formula between the environmental negative pressure value and the estimation error,the gas loss calculation formula after error analysis and correction is obtained.The paper has 52 pictures,13 tables,and 90 references.