Effect of microstructure of rapid pyrolysis char on its gasification reactivity

To investigate the relationship between microstructure of rapid pyrolysis chars under different temperatures and their gasification reactivities, three Chinese typical coals with different ranks were pyrolyzed in a drop-tube furnace at 800~1 400 ℃. The structure of chars obtained was characterized by using XRD (X-ray diffraction) and N₂ gas adsorption method, and the CO₂ gasification reactivity of chars was examined using TGA (thermogravimetric analyzer). The results show that the specific surface area increases with the increasing of pyrolysis temperature and reaches maximum value at 1 200 ℃, while the gasification reactivity of NM lignite and SF bitumite chars lowers relatively. The gasification reactivity of ZY anthracite char increases gradually at 800~1 200 ℃, while the maximum value of specific surface area appears at 900 ℃. It is proved that there is not a good correlation between the specific surface area and the gasification reactivity of chars. However, the change of gasification reactivity of three chars with increasing pyrolysis temperature is in accordance with the development of carbon crystallite structure of chars which reflects the graphitization progress of chars. It is concluded that the change of carbon crystallite structure of chars has a greater influence on the gasification reactivity of chars made by rapid pyrolysis.