Studying effects of solid structure evolution on gasification reactivity of coal chars by in-situ Raman spectroscopy

This study focuses on characteristics of structure evolution during pyrolysis and subsequent char gasification of lignite and bituminous coal. Coal pyrolysis was conducted on induction-heating reactor. As pyrolysis temperature increased, the graphitization degree of char increased, and the amount of C-O and -CH in char decreased, resulting in poorer gasification reactivity of char. Char gasification was conducted by thermogravimetric analyzer (TGA), high-temperature stage microscope (HTSM) and in-situ Raman system to investigate gasification reactivity, in-situ evolution of morphology structure and in-situ evolution of carbon structure, respectively. As gasification proceeded, the projected area of char particle decreased rapidly first and then kept consistent, and degree of graphitization of char gradually increased. In-situ Raman parameters indicated difference in increasing rate of graphitization between lignite char and bituminous char decreased with increasing temperature. Higher temperature deactivated the alkali metals, leading to attenuation of their inhibitory effect on graphitization. Gasification reactivity index R-0.9 was in positively correlated with in-situ ID1/IG value, and corresponding correlation coefficient (R-2) for TGA and HTSM were 0.8108 and 0.9829, respectively. The higher R-2 for HTSM was due to the weaker diffusion effect. In-situ Raman parameter was more suitable for predicting gasification reactivity of single particle char.