Mechanism and interaction of alkaline-earth metal migration induced ash transformation and carbon structure evolution for single coal particle high-temperature gasification

The current study focused on alkaline-earth metal migration induced ash transformation and carbon structure evolution for single coal particle high-temperature gasification, with visualization experiments and surface analysis techniques. The alkaline earth metals were found to aggregate to the peripheral reaction surface, while the rest remained in the initial scattered distribution. A migration index was defined and reached an extreme value in the middle reaction stage and increased with temperature, especially for the Ca element and followed by Mg. Raman spectra show the aggregation of Ca on the particle surface disrupted the carbon structure, leading to an increase in the disordered carbon content and improving the char reactivity. The aggregation behavior led to mineral transformation and melting to a liquid slag layer on the particle surface as a eutectic. Finally, a mechanism of the aggregation behavior of ionic Ca on a single particle scale was proposed in this study.