Changes for optical properties of vitrinite in coking coals during carbonization

The changes for optical properties of vitrinite in coking coals during carbonization is of great significance to reveal the structural change and reactivity in carbonization reaction. The softening and melting characteristics of vitrinite during carbonization, which were from 3 coking coals with different rank, were studied by heating stage microscope. The changes for optical properties of vitrinite and its influence on the optical structure of coke were studied by petrological analysis. The results show that the optical properties of carbonized vitrinite in coking coals increase in stages. The optical properties of carbonized vitrinite have little change when the carbonization temperature is lower than 300 ℃. The temperature at which the reflectance begin to rise rapidly is closely related to the rank, as low rank coking coal A is 375 ℃, medium rank coking coal B is 400 ℃, and high rank coking coal C is 475 ℃. The bireflectance of carbonized vitrinite in low rank coking coal A and medium rank coking coal B decrease significantly at about 425 ℃, while that of high rank coking coal C decreases slightly at the temperature range of 475-500 ℃. When the carbonization temperature is higher than 600 ℃, the optical properties of the carbonized vitrinite in three coking coals increase rapidly at a linear rate approximately.