中文摘要：

为了分析煤阶对液氮冷冻致裂效果的影响,对高阶无烟煤和中阶焦煤开展了液氮冷冻试验,利用超声波测试仪测试液氮冷冻致裂前后的波速变化,分析了煤阶、饱水对液氮冷冻效果的影响。结果表明：无烟煤饱水后波速下降,焦煤饱水后波速增长;对于干燥煤样,液氮作用后无烟煤的损伤程度要比焦煤的损伤程度严重;饱水煤样液氮冷冻致裂效果更好;饱水无烟煤液氮作用后,波速平均下降19.8%;饱水焦煤液氮冷冻致裂作用后,波速平均下降27.6%;在饱和状态下,液氮作用后焦煤的损伤程度比无烟煤更显著。

英文摘要：

In order to investigate the effects of the coal ranks on fracturing low-permeability coal bed through liquid nitrogen cooling,the meta anthracite and the medium coking coal were obtained and immersed in liquid nitrogen.The wave velocities before and after liquid nitrogen cooling were measured by ultrasonic tester.The effects of coal ranks and saturation on liquid nitrogen fracturing coal samples are investigated.The results show that： after the saturation,the wave velocity of the anthracite decreases,and the wave velocity of the coking coal increases.For dried coal samples,after liquid nitrogen cooling the damage of the anthracite is more serious than that of the coking coal.Saturated coal samples after liquid nitrogen cooling are much effectively damaged and fractured.The average wave velocity of the saturated anthracite samples and coking coal samples after liquid nitrogen cooling decreased by about 19.8% and 27.6%,respectively.The damages of the later are much more significant.