Interactions of vanadium-rich slags with crucible materials during viscosity measurements

Slag chemistry is important for the assessment of flow behaviour of slags produced during gasification of coal and coal–petroleum coke blends. Slags containing vanadium species react readily with the crucible and spindle materials used for viscosity measurements. Interaction of vanadium-rich slags with various materials has been investigated in order to obtain a better understanding of the impact of containment materials on the resulting slag chemistry and viscosity. The bulk and phase compositions of two petroleum coke slags in Al₂O₃, Mo, Pt and Ni crucibles produced under different laboratory conditions were analysed, and kinetics of slag composition changes at 1400 °C were determined. Mechanisms of the slag interactions with crucibles are described. They involve exchanging of crucible and slag constituents, formation of interfaces with distinct compositions, and continuously changing phase equilibria in the system. For slag processed in Ni and Pt crucibles, reduction of Fe and Ni from oxide to metallic form occurs and is followed by dissolution into the crucible materials. Viscosity of slags with Mo, Ni and Al₂O₃ crucibles are determined in the temperature range 1200–1500 °C. Resulting changes in the bulk composition of the processed slag has an impact on the slag viscosity. At given temperatures, viscosities of the slags produced in different crucibles are different. The impact of crucible materials and their applicability in viscosity measurements of high vanadium-containing slags are also discussed in order to define the optimal conditions.