煤的热解破裂过程——孔裂隙演化的显微CT细观特征

Pyrolytic cracking in coal: Meso-characteristics of pore and fissure evolution observed by micro-CT

利用μCT225FCB型高精度工业CT试验机进行了不同温度下褐煤、气煤细观结构演化的显微CT试验,发现煤在低温阶段(<300℃),由于煤中水分和自由气体的散失而产生大量裂纹;在高温阶段(>300℃),有机质的热解导致煤中大量孔隙裂隙的形成,煤的这种产生孔隙裂隙的方式与无机岩石(如花岗岩、砂岩等)明显不同,称这种因热解作用导致煤等一类富含有机质的岩石发生破坏的现象为热解破裂。与无机岩石的热破裂过程相比,煤的热解破裂在破裂机理、裂纹起始位置、裂纹形态方面具有显著的独特性。煤热解破裂过程中,当温度低于300℃时因煤中自由水和自由气体的散失而形成以细长裂纹为主的孔隙裂隙系统;当温度高于300℃时因煤中热解产物的逸出而形成以圆形或椭圆形孔洞为主的孔隙裂隙系统。300℃前新生裂隙不仅起始于煤中的硬质颗粒之间,更普遍的起始于有机质中;300℃后孔隙裂隙的形成主要起始于有机质内。

Mesostructure evolution of various grade coals including lignite and gas coal at elevated temperature was observed by high-resolution computerized tomography technology. At low temperature phase( <300 ℃),quantity of cracks were induced by the release of water component and free gas in coal matrix,and a great number of pores and fissures were induced by the pyrolysis of coal emerge at high temperature phase( >300 ℃). The authors name this phenomenon,the organic-matter-rich rock like coal generates damage due to its pyrolysis effect,as pyrolytic cracking which is definitely different from thermal cracking in inorganic rock such as granite,sandstone,etc. Compared with thermal cracking,it is unique for pyrolytic cracking that involving damage mechanism,initial damage location and crack morphology. The morphology of newly formed cracks induced by the release of water component and free gas less than 300 ℃ is gracile crack which is formed not only at the boundary of two hard minerals but also widely in organic matter. Also the morphology of newly formed cracks induced by pyrolysis at greater than 300 ℃ is circularand elliptical pore which is formed only in organic matter.