Correlation between Char Gasification Characteristics at Different Stages and Microstructure of Char by Combining X-ray Diffraction and Raman Spectroscopy

A comprehensive and reliable correlation between the gasification characteristics and char structure will be helpful to propose a tentative reaction pathway. The rapid-pyrolysis char samples were prepared with a novel high-temperature vertical quenching furnace at high temperatures from 900 to 1500 degrees C with different residence times. The physicochemical structure and gasification reactivity of chars were systematically analyzed. Results demonstrated that the chemical structures were slightly influenced by the residence time at lower pyrolysis temperatures (900 and 1000 degrees C), while the graphitization degree was increased by the prolongation of the residence time at 1100 degrees C. With the increase of the pyrolysis temperature, L-c,L-a/d(002), a and I-G/I-all monotonously increased, while I-D1/I-G and I-D3/I-G monotonously decreased. Additionally, the specific surface area was not considered in the correlations because it was not the main factor affecting the reactivity. The isothermal and non-isothermal gasification reactivities of coal char gradually decreased with the increase of the pyrolysis temperature to some extent. However, I-D1/I-G could act as a rough indicator for evaluating the characteristic temperatures of chars. It was also revealed that the reaction rate was controlled by various chemical structural factors at different stages. Hence, the correlations based on the chemical structure parameters by combining X-ray diffraction and Raman spectroscopy showed credibility on the prediction of char characteristic temperatures as the critical factor varied with the gasification stage.