The effects of Na2O/K2O flux on ash fusion characteristics for high silicon-aluminum coal in entrained-flow bed gasification

Composite additives are widely used to regulate coal ash fusion characteristics to meet the requirement of entrained-flow bed gasification. In this paper, the effects and corresponding mechanisms of the Na2O/K2O ratio on ash fusion behavior of high silicon-aluminum coal (Jincheng coal, JC) were investigated. The results showed that at the same total mass fractions of Na2O and K2O (15%), the JC ash fusion temperatures (AFTs) decreased quickly and then increased slowly with increasing Na2O/K2O ratio, the lowest AFT reached when Na2O/K2O ratio was at 9/6. The variations in volume and morphology of mixed JC ashes during heating indicated the AFT variation. The mineral change from KAlSi2O6 (MP: 1686 degrees C) to NaAlSiO4 (MP: 1100 degrees C) with increasing Na2O/ K2O mass ratio mainly resulted in a decrease in the AFT. This indicated that the Na2O/K2O synergy flux effect was related to the formation of a NaAlSiO4-KAlSiO4 eutectic structure. The AFT variation with increasing Na2O/ K2O ratio was also explained by the fact that a quick increase and then a slow decrease in the temperature at which all solid phase changes into liquid-phase was calculated by FactSage.