The viscosity of slag from an operating integrated gasification combined cycle (IGCC) plant utilising petroleum coke and a synthetic petcoke slag with the same composition made from chemical grade oxides in a reducing environment for gasification application were investigated in this study. A high temperature rotating bob-type viscometer was used to measure viscosity between temperatures of 1250–1375 °C. Natural and synthetic ash had similar viscosities above 1300 °C in this study. The viscosity was predicted by using FactSage, a thermodynamic modelling software, in conjunction with different viscosity models, available in the open literature. Percentage deviations of predicted viscosities from different models with experimentally measured values ranged from about 41 to 151%. Crystallisation of the slag was noted in SEM-EDS (scanning electron microscopy– energy dispersive spectroscopy) and FactSage results. Solid phases from FactSage predictions were used to modify the Kalmanovitch–Frank model with the Roscoe method. It predicted the viscosity of the slag accurately between 1250 and 1375 °C. Average percentage deviation from measured natural ash viscosity was about 11%.

Entrained flow gasification occurring above 1400 degrees 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 degrees 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.

In entrained flow gasifiers, inorganic species in solid fuels are converted to slag, which flows continuously along the gasifier’s refractory lining. Slag viscosity is critical for its continuous flow and, consequently, reliable operation of the gasifier. Viscosity of synthetic petcoke ash was measured in a high temperature viscometer (up to 1500 °C) using high alumina crucibles. Crucible material was found to dissolve in slag, causing thinning and leading to formation of holes on the walls. To explain this dissolution, thermodynamic equilibrium calculations were performed in FactSage™ (Thermfact/CRCT, Montreal, QC, Canada and GTT-Technologies, Aachen, Germany) using different synthetic petcoke ash compositions in 100% H₂, 5% H₂/ 95% N₂, 69.5% CO/30.5% CO₂, and 100% O₂ atmospheres. An inverse correlation was found between crucible dissolution and alumina content in the slag. Rates of dissolution of alumina from crucible into slag varied significantly in the different atmospheres. The correlation was validated experimentally by heating six synthetic slags with varying compositions to 1500 °C in 5% H₂/N₂ (to simulate viscometer’s atmosphere) gas. SEM-EDS analysis of the samples confirmed that the sample with lower initial content of alumina in the slag showed higher amounts of aluminum at the slag–crucible interface. Additions of alumina in the synthetic petcoke ash (containing up to 49.74% V₂O₅) mitigated crucible dissolution.

Gasifying petroleum coke (petcoke) offers a promising route to low-carbon energy, hydrogen, and chemical intermediates. However, vanadium- and iron-rich slags aggressively corrode high-chromia refractories in entrained-flow gasifiers, shortening service life and increasing maintenance costs. To address this, we developed an in situ high-temperature X-ray diffraction (HT-XRD) protocol, which involved failure analysis of previous experiments, to attempt the measurement of dissolution kinetics at the liquid petcoke slag/solid high chromia refractory interface under gasifier-relevant conditions (1500 °C, 70% CO–30% CO₂). Thermodynamic modeling (FactSage 8.3, 1100–1500 °C) predicted Pt stability under the defined conditions, and testing in a furnace on unstrained Pt under similar conditions confirmed these predictions; however, experiments performed on the Pt heating strip on an Anton Paar HTK2000 nonambient chamber contradicted these predictions with premature failure of the Pt heating strip. We believe this is related to interfacial reactions with slag/refractory species occurring under tensile stress. SEM-EDS confirmed Pt interdiffusion with Cr, Al, and Si. The addition of a MgO (110) single crystal between the Pt strip and the refractory eliminated this issue and provided a simple, low-cost solution that enabled stable isothermal runs up to just under 2 h. In theory, XRD peak-area decay of Cr₂O₃ should yield time-resolved consumption rates and enable accelerated screening of refractory and slag chemistries. In reality, we were unable to see a significant Cr₂O₃ XRD peak decay under the conditions achievable with the available instrumentation. Improvements in nonambient stage designsuch as enhanced thermal stability and longer high-temperature operation available on newer versions of this nonambient chamber from Anton Paar and lessons learned from this research could further expand the technique’s utility across industrial corrosion studies.