Exploring Influence of MgO/Na ₂ O on Melting Characteristics and Viscosity–Temperature Characteristics of Coal Slags Under Entrained Flow Gasification Condition

ABSTRACT Characteristics of high alkali in Zhundong coal ash may cause ash‐related slag discharge problems at entrained‐flow‐bed (EFB) gasifier. In this study, through exploring melting characteristics and viscosity–temperature characteristics, it is found that MN05, MN14, and MN23 show low FTs (< 1160°C). Subsequently, with MgO/Na 2 O ratio increasing, the crystals transformed into Mg‐rich crystals melted at higher temperature, and some SiO 2 require higher temperatures to participate in new crystals formation, which causes FT increasing. MN23 shows the best viscosity–temperature characteristics due to synergism of MgO and Na 2 O. For slag discharge from EFB gasifiers, MN05, MN14, and MN23 are suitable due to low T cv and wide Δ T . With MgO/Na 2 O ratio increasing, the initial crystallization temperature increases because of stronger polarization ability of Mg 2+ than Na + , and crystal size shows an increasing trend. The viscosity of molten liquid slag decreases due to decrease in polymerization degree with MgO/Na 2 O ratio increasing, and molar ionic potential ( α ) is linearly positively correlated with η 1530°C . For MN05 and MN14, T cv appears before the initial crystallization temperature, suggesting that the viscosity increase may be related to liquid‐network evolution and the increase in bulk melt viscosity before crystallization becomes evident. MN32, MN41, and MN50 show high T cv due to crystallization. The obvious viscosity increase of MN23 may be influenced by crystallization and polymerization degree changes.