Study of micro-pores development in lean coal with temperature

To investigate micro-pores development of coal under high temperature, experimental studies were performed with fine specimens of lean coal as small as 1 mm in diameter through a new micro-CT system. Through statistical analysis, some fundamental characteristics of pore development are discovered as the temperature increases from 18 to 600 degrees C. From 18 to 200 degrees C, the porosity of lean coal slightly decreases as a result of dehydration, degassing and thermal expansion of the solid framework. From 200 to 400 degrees C, the porosity increases greatly due to a coupling effect of the physical reactivity and pyrolysis. Above 400 degrees C, the porosity gradually decreases as a complicated chemical effect of the pyrolysis. Analytic results demonstrate that 70-80% of pores radii of the coal are in the range 0.4-2 mu m. Less than 1% of pores are 20-30 mu m in radius when temperature is lower than 200 degrees C. About 0.1% of pores are 30-100 mu m in radius as temperature rising from 300 to 600 degrees C. As the temperature rises and approaches a critical temperature of 400 degrees C, most of the original regular small pores become connected and gradually grow to irregular and larger pores. Above the critical temperature, the pores become more irregular again while the density of pores increases with the complicated effect of pyrolysis of the coal. (C) 2012 Elsevier Ltd. All rights reserved.