Structure variation of coal particle packing during the spontaneous combustion

During the process of coal mining,storage and transportation,the coal is exposed to the oxidation environ- ment 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 stres- ses 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 filte- ring 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 tem- perature increases,the porosity,the particle amount of the packing and the averaged particle specific surface area in- crease 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 pack- ing structures,with the oxidation temperature of 300 ℃ and 400 ℃ ,are 14. 95 and 2. 50 mm3 respectively. The aver- aged parti2cle surface area of packing structures,with the oxidation temperature of 300 ℃ and 400 ℃ ,are 36. 17 and 9. 13 mm respectively. Moreover,the variation of the porosity is closely related with the variation of the change of par- ticle 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.