Preliminary Surface Structure Transition of Coal Particles during Prepyrolysis with CO_2 Laser

摘要

A new method was developed to study the preliminary surface textural change of a single coal particle heated rapidly to 500℃ with well-characterized CO_2 laser under nitrogen at atmospheric pressure. The SEM observable changes of surface texture were not observed up to 485℃ with heating rates above 6300℃ s~(-1), even with coking coal. However, the changes were observed at about 440℃ at heating rates of ≤1800℃ s~(-1) even with weak-coking coal. These results suggest that the effect of heating rate on softening and melting (plasticity) of the coal particles shows that there are limited and optimum ranges of heating rate for the increase of plasticity. In addition, at heating rates of 50-240℃ s~(-1) for two kinds of coal, the change of surface texture (initial structural relaxation) begins around 240-260℃, the initial softening (first melting phase) begins around 290-310℃, the second melting phase appears around 400-410℃, and the uniformly melting temperature is around 420-440℃. The heating rate (< 240℃ s~(-1)) seems to have little effect on the temperature range at which the initial structural relaxation and initial softening occur for two kinds of coal.