煤自然发火过程颗粒堆积体结构形态演化实验研究

Structure variation of coal particle packing during the spontaneous combustion

在煤炭开采、储存及运输过程中,煤炭常以颗粒堆积体的形式暴露于氧化环境之中,煤颗粒堆积结构直接影响了堆积体内高温火源的形成与蔓延规律,是形成非控制灾害的关键影响因素之一。煤自然发火过程中堆积结构形态演化规律研究对煤堆内高温火源预测及煤矿火灾防控具有重要意义。以马道头矿8404工作面的煤样为研究对象,制备了5组不同氧化温度下的堆积试样,利用微焦显微Computed Tomography(CT)实验平台对试样进行显微断层扫描。获得显微断层CT图像序列后,采用几何均值滤波算法与大津算法(Otsu Method)对显微断层序列进行图像处理,降低原始图像中的噪声并将其转化为二值图像序列。基于处理后的二值图像序列,应用三维重构算法重构了各组试样堆积结构。定量分析了煤颗粒堆积体孔隙率、颗粒体积、颗粒表面积等结构参数的演化规律。研究结果表明:随着氧化温度升高,煤颗粒堆积体孔隙率、颗粒数量与平均颗粒比表面积增大,平均颗粒体积与表面积减少,其中300~400℃温度段的变化最明显,300℃与400℃时堆积结构内平均颗粒体积分别为14.95与2.50 mm^3;平均颗粒表面积为36.17与9.13 mm^2;煤颗粒堆积体孔隙率变化与煤颗粒形态变化有关,实验煤样两者变化阈值均在300℃附近,当氧化温度高于此阈值时,煤颗粒堆积体内颗粒裂解加剧,孔隙结构连通性提高,氧化过程更加剧烈。

During the process of coal mining,storage and transportation,the coal is exposed to the oxidation environment as packing structure,which is a critical factor for the formation and spreading of the high-temperature region and uncontrolled disasters.Hence,the variation law of packing structure during the period of spontaneous combustion stresses the importance of high-temperature region predicting and disaster prevention.5 kinds of oxidized coal samples,with different oxidation temperatures,are made of the coal from 8404 working face of Madaotou Mine.Geometric mean filtering algorithm and Otsu algorithm are applied to the raw section series,obtained by the Micro-CT,to reduce the noise level and image binarization,respectively.Based on the series of binary image,3D reconstruction algorithm was employed to build the packing structures of samples.The variation laws of structure parameters,such as porosity,mean particle volume,mean particle surface,which were quantitatively studied.The results showed that as the oxidation temperature increases,the porosity,the particle amount of the packing and the averaged particle specific surface area increase and the mean particle volume and mean particle surface area decrease.When the oxidation temperature is in the range of 300-400℃,the variation of the packing structure is the most obvious.The averaged particle volumes of packing structures,with the oxidation temperature of 300℃and 400℃,are 14.95 and 2.50 mm^3 respectively.The averaged particle surface area of packing structures,with the oxidation temperature of 300℃and 400℃,are 36.17 and 9.13 mm^2 respectively.Moreover,the variation of the porosity is closely related with the variation of the change of particle morphology and they both have a threshold value approximates to 300℃for the tested coal samples.When the oxidation temperature is higher than the threshold,the enhanced particles cracking and the improved pore connectivity result in a more intense oxidation process.