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 °C. From 18 to 200 °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 °C, the porosity increases greatly due to a coupling effect of the physical reactivity and pyrolysis. Above 400 °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 μm. Less than 1% of pores are 20–30 μm in radius when temperature is lower than 200 °C. About 0.1% of pores are 30–100 μm in radius as temperature rising from 300 to 600 °C. As the temperature rises and approaches a critical temperature of 400 °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.

► Micro-pores and fissures of lean coal under high temperature is examined.
► Porosity develops due to the effect of thermal cracking and pyrolysis.
► Geometry and distribution of micro-pores and fissures are counted and analyzed.
► 400 °C is found as a critical value for pyrolysis of the tested lean coal.
► 80% of pores radius is in the range 0.4–2 μm under the tested temperature range.