A FactsSage Simulation Study on the Interaction of Synthetic Petcoke Slags with Alumina Crucibles

Abstract

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.

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

“…V was absent in tests 1c* and 1d*, and the crucibles were intact . Karri et al explained the dissolution of alumina crucibles by NiO . Solubilities in tests 1c and 1d were found to be less than those of tests 1a and 1b.…”

“…The 5%H 2 –95% N 2 gas mixture does not show p O2 in equilibrium calculations due to the lack of O 2 in the initial mixture. Based on the phase changes observed in equilibrium calculations of several crucible-slag combinations in Factsage, Karri et al 8 concluded that a 5% H 2 –95% N 2 gas mixture has a very similar effect on oxide mixtures as 70% CO–30% CO 2 . Thus, for tests 1 and 2, p O2 was the same as that obtained in 30% CO 2 .…”

“…Crucibles after completion of tests 1a* and 1b* were found to be perforated. In our previous studies, tests 2a, 8 2b* (ash composition same as 2b), 8 2c* (ash composition same as 2c), 8 3, 43 4, 44 and 5 45 were performed to measure slag viscosities in alumina crucibles in an in-house high-temperature viscometer. The atmospheres used and the maximum temperatures attained during the experiments are listed in Table 1 .…”

“…However, Al 2 O 3 and Mo crucibles cannot be completely reliable for measuring the viscosity of the petcoke ash slag. In a study by Karri et al, 8 synthetic petcoke ash samples were prepared with about 20 and 60 wt % V 2 O 5 along with about 3 wt % NiO and viscosity measurements attempted in alumina crucibles. The slags in both experiments caused crucible material dissolution, forming perforations at the bottom.…”

“…The predicted values of the slag penetration depth in other cases were much higher than the experimental results. To study dissolution in a petcoke ash and Al 2 O 3 crucible system, Karri et al 8 performed thermodynamic equilibrium calculations in the software Factsage. 12 Stable phases were predicted between solid alumina (representing a crucible) and the mixture of oxides (representing ash/slag) at temperatures above 1000 °C.…”