低频振动对煤样解吸特性的影响

 为研究低频振动对煤样解吸瓦斯性能的影响，研制瓦斯吸附解吸激振与测试系统。试验结果表明，在低频振动作用下，随着频率降低，解吸量和解吸速度增大，衰减速度越快；煤样瓦斯的解吸强度、衰减系数随时间变化逐渐减小。采用瓦斯解吸速度和振动理论的相关知识分析试验结果，认为低频扰动会导致煤的孔隙性减弱、渗透率降低、扩散速率减慢，不利于瓦斯分子的解吸。扰动作用下，吸附伴生分子虽然获得脱附能，但由于扩散速率的减慢，解吸速度很慢，解吸量小；无扰动作用时，煤样原有的孔隙性没有改变，虽然吸附伴生分子没有获得脱附能，然而由于渗透率较大，扩散速率相对较大，解吸速度相对有振动作用时反而较快，解吸量大。因此，低频振动使煤样的孔隙性减弱，增大分子的平均自由程，导致分子在煤样中扩散变慢，同时在运动层面上由于形成数层细小的孔隙层，增加煤样内部的吸附位，从而减缓瓦斯在煤样中的解吸。

INFLUENCE OF LOW-FREQUENCY VIBRATION ON DESORPTION CHARACTERISTICS OF COAL SAMPLES

The excited and testing system of gas adsorption and desorption is developed to study the influence of low-frequency vibration on gas desorption characteristics of coal sample. The test results show that the amount and velocity of gas desorption increase，and the velocity of attenuation becomes fast with the decrease in vibration frequency；the attenuation coefficient and desorption intensity of coal sample gradually decrease with time. Using related knowledge about the theory of gas desorption velocity and vibration to analyze the test results. It is shown that low-frequency vibration can lead the porosity of coal to weakening，permeability to decrease and diffusion rate to slow down，all of which are no advantage for the coal gas desorption. With the effects of disturbances，adsorpted accompanying molecules can obtain desorption energy，but the gas desorption capacity is small because of the decrease in diffusion rate and desorption velocity；without the effects of disturbances，the porosity of coal sample doesn¢t change. Although the adsorpted accompanying molecules cannot obtain desorption energy，the desorption velocity and gas desorption capacity are larger than those in the effect of vibration because of the larger diffusion rate and permeability. Therefore，the weakening of the porosity of coal samples and increased molecular mean free path under low-frequency vibration can lead to slow diffusion of molecules. Meanwhile，lots of tiny porosity layers are formed at the vibration face，which increase the adsorption sites inside the coal samples；and then slow down the coal gas desorption.