Study On Desorption Characteristics Of Methane In Coal Under Controlled Microwave Irradiation

Pre-drainage of coal seam gas is one of the most effective methods to prevent the mine gas disaster and reduce greenhouse gas emissions in mining area.However,70% of the high gas seam in China is low permeability coal seam and the gas in the coal seam is difficult to desorption during mining,To solve this problem,in this thesis,according to the new idea of "controlled microwave irradiation(CMI)method to promote coal gas desorption and diffusion",using the self-developed experimental device of coal-rock gas desorption under CMI and the scanning electron microscopy(SEM),the effect of CMI to methane desorption and diffusion characteristic,temperature and surface structure morphology of coal were investigated,the warming effect and damage effect of CMI on the coal were analyzed,the mechanism of the controlled microwave irradiation on the desorption characteristics of methane in coal was discussed.The theoretical foundation of CMI method to enhance coal seam gas extraction was established.The following conclusions were obtained:(1)The action of CMI can greatly promote the desorption of methane in coal,so that the desorption of methane in coal rises abruptly after the action of CMI while in the desorption equilibrium and the decay rate of methane desorption slows down,enhances the desorption and diffusion capacity of methane in coal.(2)Compared with the classical diffusion model,the dynamic diffusion coefficient model can better describe the desorption kinetics of methane in the coal under the action of the CMI.Under the same desorption time,the methane diffusion coefficient of the coal under the CMI is larger than that without CMI,which indicates that the CMI can improve the methane diffusion capacity of the coal sample.(3)Coal can absorb microwave and will have the electromagnetic radiation thermal effect under the action of the CMI,which makes the coal temperature rise rapidly and the initial heating rate is large,then the heating rate decreases slightly and remains basically stable.(4)The penetration and selective absorption characteristics of the microwave irradiation on the coal can cause a significant damage effect,so that coal body will loss water,mineral interface will crack and appear the formation of holes and other forms of damage,which leads to the expansion of pores and the formation of new fissures in the coal body.(5)The mechanism of the CMI on the desorption characteristics of methane in coal is mainly due to the warming effect and damage effect induced by the CMI,which improves the temperature of the coal body and changes the surface structure of the coal body.This can enhance the activity of methane molecules,improve the methane diffusion coefficient of coal,change the diffusion resistance of coal in the desorption process of methane,increase the desorption and diffusion rate of methane in coal and reduce the diffusion resistance,so as to improve the coal desorption and diffusion capacity of methane in coal.