Effect of Kaolin on the Thermal Conversion Performance of Zhundong Sub-bituminous Coal

In order to investigate how kaolin affects the structure and thermal conversion performance of Zhundong sub-bituminous coal (ZSBC), this study focused on analyzing the pyrolysis, combustion, and gasification of both ZSBC and a mixture of kaolin and Zhundong sub-bituminous coal (ZSBC-K) using the TG-DTG technique. The findings demonstrated that the addition of kaolin enhanced the pyrolysis and combustion performance of ZSBC-K. To explain the above phenomena, the composition and structure of char from ZSBC and ZSBC-K were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the addition of kaolin decreased the degree of graphitization of char and increased the relative content of oxygen on the surface of the char. Moreover, the addition of kaolin increased the degree of disorder of the char and formed more char pores. The rich pores were conducive to the entry of the gasification agent into the coal char particles, which enhanced the gasification activity. Additionally, the coal char mixed with kaolin contains several oxygen-containing functional groups and defect sites that facilitate the cracking and gasification performance of the macromolecular network’s aromatic ring structure.