Study on desorption and diffusion characteristics of coalbed methane under ultrasonic excitation

In order to reveal mechanism of high-efficiency extraction of coalbed methane by ultrasonic，a new experimental equipment was invented for absorption/desorption research of methane on coal.The methane desorption rules of coal under different ultrasonic excitations were experimentally studied.The results show that there is no difference in dynamic behaviors of methane desorption on coal with or without acoustic wave influence，which are all in accordance with diffusion model.During the entire process of methane desorption in coal，the initial desorption rateis relatively large.With the increase of time，the desorption rate gradually decreases and eventually approaches 0，and the desorption law can well follow the diffusion model； the desorption amount of methane in coal increases under the action of ultrasound，and the larger the ultrasonic power，the increase in desorption amount increases，and the desorption amount increases by 26.1% to 65.6%.Based on the theory of heat and mass transfer，Biot's criterion of mass transmission decreases and diffusion coefficient increases under acoustic wave stimulation，indicating that ultrasonic can promote the desorption and diffusion of methane.