Effects of sodium and potassium on fusion characteristics of petroleum coke ash with high vanadium and nickel

Abstract Ash fusion temperatures (AFTs) are widely employed to evaluate petroleum coke ash fusibility, which has significant effects on its high-value and clean utilization. Sodium (Na) and potassium (K) both are considered to be the effective components to improve the ash fusion characteristics for slag tapping of entrained flow gasifiers. Herein, the effects of (Na2O + K2O) and Na2O/K2O mass ratio on the fusion behaviors of petroleum coke ash with high vanadium (V) and nickel (Ni) were investigated by AFTs tests in conjunction with X-ray diffraction and thermodynamic equilibrium calculations. The results demonstrated that AFTs followed a significant decline with the increase in (Na2O + K2O) content. Vanadium trioxide (V2O3), coulsonite (FeV2O4), nickel (Ni) and nepheline ((Na,K)AlSiO4) were the dominant crystalline minerals formed in high-temperature ash. The formation of low-melting (Na,K)AlSiO4 was responsible for the variation in AFTs because of the low ionic potential of Na+ and K+. AFTs dropped slightly as the Na2O/K2O mass ratio decreased from 10/0 to 4/6, and then exhibited a sharp rise. The mixed alkaline effect between Na and K effectively influenced the AFTs variations. When the Na2O/K2O mass ratio was higher than 8/2, Na existed in eutectics or amorphous matters rather than Na-bearing crystalline species at high temperatures. As the Na2O/K2O mass ratio further decreased, the crystalline phase (Na,K)AlSiO4 was converted into high-melting leucite (KAlSi2O6), which resulted in the sharp increase in AFTs.