Effect of Na2O on mineral transformation of coal ash under high temperature gasification condition

In order to reveal the mechanism of Na2O influence on ash fusion temperatures (AFTs), effect of Na2O on mineral transformation of two coal ashes with different SiO2+Al2O3 levels were investigated by XRD and FT-IR under reducing atmosphere at high temperature. Thermodynamic software package FactSage was used to calculate the ΔG of reactions between minerals to reveal the mechanism of Na2O influence on mineral transformation. It is found that the effect of Na2O on mineral compositions depends on SiO2+Al2O3 levels of coal ash. For ash with 82.89% SiO2+Al2O3 while Na2O content is 5%–20%, albite and nepheline are formed, leading to a decrease of AFTs. However, only nepheline is formed when Na2O content is higher than 20%. For ash with 47.85% SiO2+Al2O3, when Na2O content is less than 10%, no Na-containing mineral is observed. When Na2O content is higher than 10%, Na-containing minerals such as combeite, lazurite and sodium aluminium oxide are formed, resulting in a decrease of AFTs. Furthermore, FactSage results reveal that Na-containing mineral is easily formed at high temperature due to low ΔG of the reactions.