松散煤体中声波传播特性及主要路径实验研究

Experimental study on acoustic wave propagation characteristics andmain paths in loose coal

松散煤体高温点精准探测一直是煤堆和煤仓煤自燃火灾防控领域的主要难题,研究声波测温法探测松散煤体温度异常具有重要的实际意义。声波在松散煤体中传播路径的确定是声学测温技术在松散煤体中应用的前提与基础,为了探究声波在松散煤体中的传播特性和主要路径,以长焰煤、瘦煤、无烟煤为研究对象,考虑松散煤体的级配特性,采用声波飞渡时间测试系统,分别测试了声波在纯气体环境以及松散煤体饱和气体环境中的声波飞渡时间,计算了声波在3种气氛环境下不同煤样中飞渡时间的变化率。结果表明:伪随机信号的互相关结果较好,其互相关结果的伪峰与主峰之间相差较大,对主峰判定的干扰较小;声波的传播速度与气体摩尔质量呈反比,声波在氮气、空气及二氧化碳3种气体介质中传播时,在二氧化碳中传播速度最慢,在氮气与空气中的速度相近;相较于气体环境中的传播,声波在同一种气氛条件下松散煤体中的飞渡时间变长,但飞渡时间变化规律与纯气体环境中相同(飞渡时间由长到短依次为二氧化碳、空气、氮气),表明声波飞渡时间与煤的变质程度关系较小;对无烟煤煤样进行重新装样后测试发现,声波飞渡时间变短,但是在松散煤体饱和二氧化碳与饱和空气中的飞渡时间依旧相差较小;在3种气氛环境的不同煤样中,声波在氮气-空气气氛中飞渡时间变化率最小;在氮气-二氧化碳气氛中的变化率最大;不同环境中声波飞渡时间变化率的变化趋势相同,表明声波在松散煤体中传播时主要沿着松散煤体空隙进行传播。研究结果可为声波测温在松散煤体中应用提供一定的理论依据。

Accurate detection of high temperature points in loose coals has always been a major problem in the field of coal spontaneous combustion fire prevention and control in coal piles and coal bunkers.It is of practical significance to study the detection of temperature anomalies in loose coal bodies by acoustic thermometry.The determination of the propagation path of sound waves in loose coals is the premise and basis for the application of acoustic temperature measurement technology in loose coals.In order to explore the propagation characteristics and main paths of sound waves in loose coals,this paper takes long-flame coal,lean coal,and anthracite as the research objects,considering the gradation characteristics of loose coals,the tests were conducted using the sound wave flying time test system,respectively.The flying time of sound waves in a pure gas environment and in the saturated gas environment of loose coals were calculated.The results show that the cross-correlation results of pseudo-random acoustic signals are better,and the difference between the pseudo-peaks and the main peaks of the cross-correlation results is large,and the interference to the determination of the main peaks is small.The propagation speed of the sound wave is inversely proportional to the molar mass of the gas.When the sound waves propagate in nitrogen,air and carbon dioxide,the propagation speed is the slowest in carbon dioxide,and the speed in nitrogen and air is similar.Compared to the propagation in a gas environment and the sound waves under different atmosphere conditions,the flying time in loose coals is longer,and the change law is the same as in the gas environment(the flying time in descending order is carbon dioxide,air,nitrogen),indicating that the acoustic wave flying time has a small relationship with the degree of coal metamorphism.After reloading the anthracite coal sample,the acoustic wave flying time is shortened,but the acoustic wave flying time with saturated carbon dioxide and saturated air in loose coals is still small.With different coal samples in three atmospheres,the change rate of acoustic wave flying time in nitrogen-air atmosphere is the smallest.The rate of change is the largest in a nitrogen-carbon dioxide atmosphere.The change trend of the change rate of the acoustic wave flying time in different environments is the same,indicating that the acoustic wave propagates mainly along the gaps of the loose coals when it propagates in the loose coals.The research results can provide a certain theoretical basis for the application of acoustic temperature measurement in loose coals.