Preliminary surface structure transition of coal particles during prepyrolysis with CO2 laser

A new method was developed to study the preliminary surface textural change of a single coal particle heated rapidly to 500 degrees C with well-characterized CO2 laser under nitrogen at atmospheric pressure. The SEM observable changes of surface texture were not observed up to 485 degrees C with heating rates above 6300 degrees C s(-1), even with coking coal. However, the changes were observed at about 440 degrees C at heating rates of less than or equal to 1800 degrees C 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 degrees C s(-1) for two kinds of coal, the change of surface texture (initial structural relaxation) begins around 240-260 degrees C, the initial softening (first melting phase) begins around 290-310 degrees C, the second melting phase appears around 400-410 degrees C, and the uniformly melting temperature is around 420-440 degrees C. The heating rate (<240 degrees C 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.