液态CO_2溶浸作用下煤体孔隙结构损伤特性研究

Characteristics of coal porous structure damage subjected to liquid carbon dioxide cooling

为分析液态CO_2作用后煤体的孔隙结构变化,开展了3种不同变质程度煤样的液态CO_2溶浸实验,采用压汞法测试了煤样溶浸前后的孔容分布,分析了低温液态CO_2溶浸作用下煤体的损伤特性。结果表明:液态CO_2溶浸煤体后大孔孔容增加,中、小、微孔孔容减小,溶浸过程中存在微孔→小孔→中孔→大孔的转化;液态CO_2溶浸过程主要为温度应力对煤体的损伤作用,损伤后总孔容降低,这是由于煤体孔隙破坏后形成宏观裂隙网络,损伤效应包括原生孔隙转化及新孔隙生成;低温作用下形成煤体基质收缩应力及水结冰膨胀挤压应力,形成拉伸、剪切、挤压等综合破坏及孔隙扩容作用,进一步增加了煤体的渗透性。

In order to analyze the variation of coal pore structure under the treatment of liquid CO2,leaching experiments of three coal samples with different metamorphic degree were carried out. Pore volume distribution of raw coal and treated coal with the leaching experiment was tested by the mercury intrusion method. Based on the variation of pore volume,damage property of coal under the effect of low temperature liquid CO2 was analyzed. The results indicated that macro-pore volume increases contrary to the decrease of volume of mesopore,small pore and micro-pore. Pore volume goes through the basic process of micro-pore→small pore→mesopore→macropore. In the leaching process,the temperature stress caused the damage of coal and the decrease of whole pore volume which are results from the formation of the macro fracture network caused by coal pore breakage. The damage effect contains the transformation of original pores and generation of new pores. The comprehensive tensile-shear-compression failure and the effect of enlarging volume,which are caused by the shrinkage induced stresses of coal matrix and compressive stresses of frozen water finally increase coal permeability.