Yallourn (YL), Taiheiyo-Kushiro (TK), Grose Valley (GV), and Tatung Yunkang (TY) coal chars loaded with various alkaline earth carbonates were gasified with carbon dioxide by a thermobalance. The measured catalytic activity of additions was mainly discussed in terms of the reaction with mineral matters in the coal char checked by X-ray diffraction (XRD).
All the carbonates except for magnesium raised the gasification reactivity of coal chars, but the catalytic effect was not so large as that on phenol-formaldehyde resin char (PFC) free from ash. The catalytic activity was particulary small with GV-and TK chars of higher ash content and their gasification residues at 900°C produced XRD peaks assingned to aluminosilicates (Ca₂Al₂SiO₇, CaAl₂Si₂O₈, SrAl₂Si₂O₈, and BaAl₂Si₂O₈) and silicates (Ca₃Si₂O₇, SrSiO₃, BaSi₂O₅, and Ba₂SiO₄) which could not be observed with the PFC residue. Deminerallization of the two chars by acid treatment enhanced the catalytic effect and the XRD peaks disappeared. According to temperature-programmed XRD, the above alkaline earth aluminosilicates and silicates were formed at about 700-750°C. Above this temperature, the pronounced catalytic activity loss was found to occur. These results indicate that, during the gasification, alkaline earth carbonates react with alumina and silica components of coal ash to lose their catalytic activities.

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