Characteristics Of Methane Adsorption And Desorption On Coal Under Acoustic Wave Effect

China has a large reserve of coal bed methane which, as a governable andrelatively cleaning energy, is the harmful source of the coalmine major dynamicdisasters, therefore, coal seam gas exploiting is imperative, no matter from theperspectives of utilization of resource, safety in production or the environmentalprotection. The technology of acoustic wave increasing methane drainage rate was putforward in the paper. And the adsorption, desorption and diffusion tests of methane oncoal under different acoustic intensities and different acoustic frequencies were carriedout by using the self-made coal bed gas adsorption-desorption system. And the effect ofacoustic wave on the parameters of adsorption and desorption models was studied. Thepaper discussed the mechanisms of acoustic wave promoting desorption and diffusionof methane, the main achievements of the study are as follows:The tendency of isothermal adsorption curve for coal adsorbing methane under theeffect of acoustic wave is in accord with the tendency of the curve without acousticeffect. With the influence of acoustic wave, amount of coal adsorbing methane falls asacoustic intensity increases the ability for coal to adsorb methane declines. Theadsorption characteristics can be described by the four models, and the Langmuir andD-R models can be more precisely. and the parameters of a、K’、Qm、Qndecreaselinearly with the increase of acoustic intensity. So that new models for coal adsorbingmethane are established by introducing the parameters of acoustic intensity J into theexisting models.The characteristics of coal’s desorption remain relatively unchanged with andwithout influence of acoustic wave. The desorption quantity rises linearly with acousticintensity. The initial desorption rate is great, and the desorption rate decreases to0finally as the time goes on. And the desorption amount under acoustic wave greater thanno acoustic wave, and decreased with increasing of acoustic intensity. The desorptioncharacteristics can be described by the four models, and the diffusion models can bemore precisely. And the parameters of α1，Qd∞，Qd∞1increase linearly with the increaseof acoustic intensity. New model for coal desorbing methane is established byintroducing J into the existing model.According to the experiment of desorption of methane on coal under the effect ofacoustic wave and no acoustic wave, the effect of acoustic wave on Fick diffusion model parameters was analyzed. The diffusion coefficient DFincreased with theincreasing of acoustic intensity, and the parameter of Bi’ reduced. The internal diffusionresistance reduced while the diffusion ability enhanced under the effect of acousticwave.The mechanism of acoustic wave promoting the desorption and diffusion ofmethane on coal mainly due to mechanical vibration and heat effect.And the heat effectexperiment indicated that temperature increased because of coal absorbing sound power,which is conducive to the desorption and diffusion of methane.