Study Of Desorption And Emission Of Coal Gas Under Sonic Waves

Greenhouse effect results in abnormal global climate changes, frequently occurred environmental geological disasters, and influences human living environment seriously. Coal bed methane is a kind of greenhouse gas affecting atmospheric environment. Its effect is 21 times of that of CO2, and 7 times of that of NO2. According to statistics, Chinese coal mine discharge approximately 70-90 million m3 of gas every year, accounted for about 30% of the total emitted volume of methane of the world. Because of low permeability of most coal body in China, the efficiency of coal gas extraction is still a bottleneck of atmospheric pollution control. In order to improve the external condition of coal gas desorption and emission, coal-gas coupling dynamic mechanics and sonic waves'effect on gas desorption and emission are studied.A set of large-scale simulation system is developed to study the characteristics of stress field, seepage velocity and coal gas desorption and emission under non-acoustic field and the acoustic field. Experimental results show that:①Assumpting there is no deformation in surrounding rock, the total stress declines slightly with time, gas pressure decreases with time in accordance with the law of logarithm, effective stress increases with time in accordance with the law of logarithm during the process of free gas being transmitted to absorpted gas.②Assumpting there is no deformation in surrounding rock, total stress and gas pressure decrease with time in accordance with the law of exponent, gas emission speed declines with time according to the logarithmic law during the process of gas emission.③In the process of coal gas emission, the unloading effect or stress releasing effect in high stress area are stronger than that in low stress area.④Under the effect of acoustic waves propagation, coal cementing strength is destroyed, internal coal fractures is prolonged and widened, and the permeability of coal is improved. The waves have no more obvious effect on coal permeability when fractures are fully opened.⑤Under the action of stable acoustic waves, effective stress of coal body decrease with time according to logarithmic law.⑥Sonic waves produce dynamic effect and promote gas desorption and migration;⑦In the process of sound propagation, part of the energy is converted into heat. On one hand, free gas volume swelled and coal gas pressure increase, on the other hand, gas desorption and migration is promoted.This study aimed at how to promote coal gas desorption and emission, and proposed some new views on the basis of experiments. It has certain theoretical significance for improving the efficiency of coal gas extraction and for the control of air pollution caused by Mine gas emission.