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目前,对于超声波作用下的煤层气吸附—解吸规律及超声波促进煤层气解吸机理的研究还有待于进一步深入。为此,利用自行设计的实验平台,开展了超声波作用下的煤样等温吸附—解吸实验(实验煤样采自山西晋城成庄煤矿和高平建业煤矿的下二叠统山西组15号煤层)。实验结果显示,未加载超声波时,伴随着压力的逐渐增大,煤样对CH_4的吸附量逐渐增加;但在加载超声波后,随着超声波功率的增大,煤样的吸附能力逐渐减弱,且随着系统压力的释放,煤样的解吸速率逐步增大。超声波使得煤样吸附能力降低的原因主要在于:①超声波的热效应使得煤样内部温度升高,降低了煤样的吸附能力:②煤岩表面势能的提高以及超声波作用下色散力的产生,使得CH_4气体分子被吸附的概率降低。而煤样解吸速率增大的原因可解释为:在施加超声波的情况下,煤体内部质点发生微位移并产生新的裂隙、微裂隙和孔隙,从而促进了煤层气的解吸和扩散。结论认为:超声波功率与煤样Langmuir常数呈负相关关系,利用所得到的实验数据可以拟合Langmuir常数与超声波功率之间的函数关系,据此可建立超声波与煤岩吸附特性之间的数值关系。
At present, the research on the law of adsorption and desorption of coalbed methane under ultrasonic wave and the mechanism of ultrasonic desorption of coalbed methane needs to be further studied. Therefore, the isothermal adsorption-desorption experiment of coal sample under ultrasonic wave was carried out by using self-designed experimental platform (experimental coal samples were collected from No.15 coal seam of Lower Permian Shanxi Formation of Chengzhuang Coal Mine in Jincheng, Shanxi Province and Gaoping Jianye Coal Mine in Shanxi Province) . The experimental results show that when the ultrasonic wave is not loaded, the adsorption amount of CH4 gradually increases along with the increase of pressure. However, after the ultrasonic wave is loaded, the adsorption capacity of the coal sample gradually decreases with the increase of the ultrasonic power With the release of system pressure, the desorption rate of coal gradually increased. Ultrasound makes coal sample adsorption capacity reduction mainly due to: ① ultrasonic thermal effect makes the coal sample internal temperature increases, reducing the adsorption capacity of coal samples: ② coal surface potential energy and the dispersion of ultrasonic force generated, making CH_4 The probability of gas molecules being adsorbed decreases. The reason for the increase of desorption rate of coal sample can be explained as follows: Under the condition of applying ultrasonic wave, the micropores inside the coal body are slightly displaced and new fissures, micro-fissures and pores are generated, which promotes the desorption and diffusion of CBM. It is concluded that there is a negative correlation between the ultrasonic power and the Langmuir constant of the coal sample, and the experimental data obtained can be used to fit the Langmuir constant as a function of the ultrasonic power. Based on this, the numerical relationship between the ultrasonic and coal adsorption characteristics can be established .