应用CT技术研究瘦煤在不同温度下孔隙变化特征

Study on pore characteristics of lean coal at different temperature by CT technology

应用μCT225kvFCB型高精度(μm级)CT试验分析系统,对直径1mm的瘦煤从18℃到600℃高温下的热破裂过程进行了显微CT观测和分析.发现了瘦煤的热破裂规律:300℃煤样中大量小的孔隙贯通成大的孔隙团,因此瘦煤的热破裂阈值在300℃附近,从常温到300℃煤样的孔隙率增加了0.5倍左右.研究了煤样在100～600℃范围内热破裂孔隙分布的分形规律,研究发现:从100℃到600℃,煤样的分形维数D随温度升高呈现先减小、后增加的趋势.孔隙的演化规律:由初始较规则的小孔隙变形,过渡到大量较规则、小孔隙贯通成不规则的大的孔隙团,之后孔隙团缩合减小趋于规则.分布初值的对数随温度升高呈现先降低后增加的趋势;从18℃到600℃孔隙数量的演化规律为先减小后增加.

To investigate the micro-pores development of coal under high temperature, experimental studies were performed with fine specimen of lean coal as small as 1 mm in diameter through a micro-CT system μCT225kVFCB. Through statistic analysis, some fundamental characteristics of pores development are discovered with temperature rising from 18 °C to 600 °C. It was demonstrated that the thermal cracking temperature threshold is 300 °C for lean coal. From room temperature to 300 °C the porosity of coal increased by 0. 5 times. Fractal analysis demonstrates that, most of the original regular small pores become connected and gradually grow to irregular and larger pores as the effect of thermal expansion and cracking with temperature rising. Above 400 °C, the size of the pores becomes smaller again while the pore number increases with the complicated effect of pyrolysis of the coal. The study is significant for insight into the micro-structure development of coal under high temperature.