Double Excitation And Mechanism Of Microwave On Methane Desorption And Carbon Dioxide Adsorption In Coal

The main factor that restricts the gas extraction of China is that the permeability and the desorption speed is slow.In view of the present situation of gas extraction in China,many experts and scholars have successively proposed a series of methods to strengthen the gas extraction of coal seam,such as hydraulic fracturing,deep hole blasting,high pressure pulse water jet and gas injection displacement.In recent years,the field of electric field,sound field,electromagnetic field,etc.,which can cause the change of the adsorption and desorption characteristics of gas,are also introduced into the experimental research of coal seam gas extraction,and it is eager to find a new method for prediction and control of gas disaster in the course of the study.Recently,CO₂-ECBM,the double benefit technology of coalbed methane mining and greenhouse gas storage,has been paid more and more attention all over the world,and CO₂ adsorption-ECBM desorption is the key part of this technology.The microwave is used as a high-frequency electromagnetic wave to act on the coal body to produce thermal effect and electromagnetic field effect.As a new applied field,it is possible to promote the gas desorption,increase the permeability of the coal body,and change the gas desorption and carbon dioxide adsorption characteristics of the coal body.It can be speculated that microwave radiation will produce double excitation effect on CH₄ desorption-CO₂ adsorption in coal.In order to explore this effect,we can also find a new method to excite CO₂-ECBM by physical field,the theoretical analysis and the laboratory inquiry methods are combined to study the influence of the desorption characteristics of the coal body under the microwave real-time loading and the influence of the microwave on the carbon dioxide adsorption,and the mechanism of its action.It mainly includes:?1?Self-designed experimental device for methane desorption in the coal under the action of real-time loading microwave and the coal body to adsorb the carbon dioxide device immediately after the gas desorption experiment is finished by the microwave acting coal body.By means of the device,the microwave can be continuously loaded and loaded in real time during the desorption process of the coal.According to the different microwave power,the experimental scheme adopts discontinuous microwave loading and continuous microwave loading.The high power microwave?2450 MHz,900W?is adopted the discontinuous loading mode,and the low-power microwave?2450 MHz,less than 500W?can be adopted the continuous loading mode.?2?The coal-like methane desorption experiment under the action of intermittent microwave loading and the coal-like carbon dioxide adsorption test after the end of the intermittent loading are carried out.The experimental scheme is the same as the microwave power setting of the coal sample,and the experimental results are as follows:the cumulative desorption amount and the desorption rate of the methane at different loading times and the change of the adsorption capacity of the coal sample to the carbon dioxide after the completion of the microwave loading.The experimental results show that microwave intermittent loading has a significant effect on the desorption of methane in the coal,and the longer the microwave action time,the higher the methane desorption amount of the coal in the same desorption time,and the adsorption capacity of the carbon dioxide after the intermittent loading is enhanced.Compared with the microwave-free working condition,the cumulative desorption amount of the coal-like methane under the microwave intermittent loading is increased by 1.51-2.36 times,and the carbon dioxide adsorption capacity is increased by 1.47-2.29 times.Meanwhile,the microwave intermittent loading can promote the desorption rate of methane and the adsorption rate of carbon dioxide in the experimental coal body.?3?The methane desorption experiment of the coal under different power microwave continuous loading and the carbon dioxide adsorption experiment of the coal sample after the continuous loading were carried out,it was found that the microwave continuous loading could continuously promote the desorption of methane in the coal and the carbon dioxide adsorption capacity could be increased after the microwave action.And the experimental coal body is continuously loaded with three groups of different microwave power for 180 minutes.The total desorption amount of methane was 2.64 times,2.94times,2.98 times,and the adsorption of carbon dioxide increased by 1.20,2.12 and 3.56times,respectively.At the same time,it was found that the higher the desorption rate of methane in the higher coal of microwave power,The more the amount of methane accumulated in the same time,the greater the amount of adsorbed carbon dioxide.?4?The desorption kinetics of methane in coal under the microwave loading are analyzed by the classical diffusion model.The results show that the microwave real-time loading can significantly improve the diffusion coefficient of the coal body.The diffusion coefficient increases by 2.48-26.04 times under the microwave real-time loading compared with the microwave-free working condition,and the stronger the microwave action energy,the stronger the diffusion capacity.The comparative analysis shows that the high-power microwave continuous loading is more favorable for improving the diffusion coefficient of the coal body,promoting the desorption of the methane in the coal,and increasing the absorption energy consumption of the carbon dioxide after the microwave action.?5?The mechanism of the effect of microwave loading on the desorption characteristics of methane and the adsorption of carbon dioxide in coal shows that the integrated function of the microwave includes the thermal effect and the effect of microwave on the damage of the coal body.The results show that the microwave loading experiment can change the pore structure of the coal body,increase the specific surface area of the experimental coal sample,enhance the adsorption property of the coal body,increase the average pore diameter,And the longer the microwave action time,the more obvious the effect of the methane desorption effect and the carbon dioxide adsorption effect.