Experimental study on ash melting behavior of Xinjiang high-alkali coal blended with low-alkali coal during coal combustion

In this study, one typical Xinjiang high-alkali coal (HA coal) and another low-alkali coal (LA coal) have been mixed to study the ash melting behavior as a function of coal blending ratio, through the use of AFTs, XRF tests of samples. Moreover, the thermodynamic equilibrium calculation and ternary phase diagram CaO–SiO₂–Al₂O₃ analysis were also used to clarify the mechanism of blended coal ash melting behavior and to optimize the coal blending ratio. The results indicate that the trend of AFTs is not linearly related to the blending ratio of coal mixtures. Instead, it is highly linked with the changes on the liquidus temperature from the ternary phase diagram systems. The initial melting temperature of HA coal ash is approximately 275 °C lower than that of LA coal ash due to the existence of alkali and alkaline metals, although it has relative higher ash fusion temperature. The mixing of LA coal is not only beneficial to reduce the amount of vaporized sodium, but also increases the initial melting temperature of blended ash due to the physical and chemical reactions between alkali and silica particles.