Understanding Ash Fusion and Viscosity Variation from Coal Blending Based on Mineral Interaction

The ash-fusion and viscosity temperature characteristics (AFV) of three typical coals [high-silica alumina Changzi coal (CZ), high-calcium Hebi coal (HB), and high-iron Zhaolou coal (ZL)] and their mixtures were analyzed, and the AFV variation mechanism by blending was investigated. Each of the three coals is unsuitable for entrained-flow gasification. With an increasing HB mass ratio, the CZ mixture ash-fusion temperature (AFT) decreased (0-30%) and then increased slowly (>30%) and the critical-viscosity temperature (T-cv) decreased (0-40%) and then increased (>40%). With an increase in the ZL mass ratio, the AFT and T-cv, decreased gradually. For the CZ mixture entrained-flow gasification, the appropriate blending ratios of HE and ZL were 20-60 and 60-100%, respectively. The AFV characteristics were determined from the mineral and amorphous matter contents through the interaction and evolution of different minerals. The formation of low-melting-point minerals (e.g., anorthite, gehlenite, and hercynite) and their eutectics resulted in decreases in AFT and T-cv. Crystal precipitation {gehlenite (Ca2Al2SiO7) and spinel [(Fe,Mg)Al2O4]} from molten ashes at a certain temperature increased the ash/slag viscosity. The FactSage calculation can simulate the AFV variation and provide a promising tool to predict the AFV of mixed ashes.