Influence of ash composition on slag properties and network structure in coal gasification fine slag: A high-temperature melting perspective

Entrained-flow gasification technology is central to large-scale coal utilisation, but generates significant amounts of coal gasification fine slag (CGFS), leading to environmental problems. This study investigates a novel high-temperature melting system for CGFS treatment, identifying key operational parameters through experiments and thermodynamic simulations. Three distinct CGFS types—high calcia (HC), high iron oxide (HI), and high silica-alumina (HSA)—were investigated, with a systematic evaluation of the impact of varying SiO2/Al2O3 (S/A) ratios (1.8, 2.3, 2.8, and 3.3) on inorganic transformations and slag viscosity-temperature behavior during melting. Results show that HC slag forming a glassy slag with excellent fluidity, ideal for continuous discharge. Reducing S/A ratio lowers the temperature for liquid phase formation, increases liquid phase quantity at higher temperatures, and enhances fluidity. In HC slag, Si predominantly exists in Q2 and Q3 structures, exhibiting strong alkali excitation activity that diminishes with increasing S/A ratios. HC slag exhibited the highest NBO/TO value, which decreased with increasing S/A ratios.S/A Additionally, the mean reactivity index of Al reached 100 % in both HC and HI slags, compared to 63.43 % in HSA slag, indicating more complex formations and an increased presence of Q4 structures. These findings establish crucial technical guidance for enhancing resource utilisation of the CGFS.