Application of Liquidus Projections in SiO₂-Al₂O₃-CaO Systems with Fe₂O₃ and V₂O₅ to Study the Dissolution of Alumina Crucibles in Gasification Slags Containing Vanadium

Entrained flow gasification occurring above 1400 °C is a technique to convert petroleum coke, a byproduct of petroleum refining, into synthesis gas. The molten ash/slag formed in the process has a high amount of V and Ni compounds, which are corrosive to the reactor walls. Slag viscosity is an important parameter that must be controlled to tap the slag from the gasifier. The viscosity of the slags is measured in high-temperature viscometers. Alumina crucibles, used in viscosity measurements, were severely corroded by high V/Ni slags in several in-house experiments. To study the chemistry of these dissolutions, saturation solubilities of alumina crucibles in the slags (at 1500 °C) and precipitated primary phases were determined from liquidus projections prepared in Factsage. The 10 slags considered in this study were composed of SiO₂ (<50.2 wt %), Al₂O₃ (<29.2 wt %), Fe₂O₃ (<41.4 wt %), CaO (<16.6 wt %), NiO (<20.4 wt %), and V₂O₅ (<20.5 wt %). The precipitated primary phases were corundum (solid solution), spinel (solid solution), V_spinel (solid solution), mullite (solid solution), and anorthite. Experiments were performed with ash placed on alumina discs in a reducing atmosphere. The ash compositions were based on previous in-house viscosity and ash melting experiments. Saturation solubilities were above 30 wt % in multiple tests with perforated and intact crucibles. In two such cases, hercynite, which can inhibit slag penetration into a crucible, was predicted as a primary phase. In another test with an intact crucible, anorthite, which leads to indirect dissolution, was predicted as a primary phase and was also identified in the X-ray diffraction (XRD) results of the slag-crucible interface. Here, saturation solubility was 8.9 wt %. It was concluded that determination of saturation solubilities and primary phases would lead to successfully measuring the viscosity of slags containing V and Ni in alumina crucibles.