A study of the relationships between coal heterogeneous chemical structure and pyrolysis behaviours: Mechanism and predicting model

Coal is naturally heterogeneous on chemical structure, which significantly affects its pyrolysis behaviours. However, due to the limit of characterization tools, quantification of the chemical structural heterogeneity and its effects on pyrolysis are still challenging. In this study, a quantification method for chemical structural heterogeneity by Raman mapping technique was firstly proposed, and the heterogeneous chemical structure of coal was investigated. The results show that the distributions of the chemical structure are highly uneven, even though the average structural characteristics are highly similar. Besides, the effects of chemical structural heterogeneity on pyrolysis behaviours were studied. It is found that except for the average structural properties, the chemical structural heterogeneity affects the pyrolysis behaviours significantly. It is attributed to the different pyrolysis mechanisms and uneven distribution of these chemical structures with different reactivity. The effects of the average chemical structures and the chemical structural heterogeneity on the pyrolysis behaviours are independent. Furthermore, new predicting models for pyrolysis behaviours by considering both the average structure and the chemical structural heterogeneity were established and validated. The final models were proved to be adequate to effectively predict the pyrolysis behaviours of raw and blended coals.