Thermodynamic effects of calcium and iron oxides on crystal phase formation in synthetic gasifier slags containing from 0 to 27 wt.% V2O3

• Phase equilibria of the coal–petcoke gasifier slags were experimentally studied.
• CaO and FeO increased the liquid slag phase field in compositions studied.
• The mullite crystal formation was suppressed in slags with >9 wt.% FeO.
• Karelianite precipitates were present if slag contained >2 wt.% V2O3.
• Isothermal phase diagrams at 1500 °C in 10−8 atm Po2 were constructed.

Thermodynamic phase equilibria in synthetic slags (Al2O3–CaO–FeO–SiO2–V2O3) were investigated with 0–27 wt.% vanadium oxide corresponding to industrial coal–petroleum coke (petcoke) feedstock blends in a simulated gasifier environment. Samples encompassing coal–petcoke mixed slag compositions were equilibrated at 1500 °C in a 64 vol.% CO/36 vol.% CO2 atmosphere (Po2 ≈ 10−8 atm at 1500 °C) for 72 h, followed by rapid water quench, then analyzed by inductively coupled plasma optical emission spectrometry, X-ray diffractometry, and scanning electron microscopy with wavelength dispersive spectroscopy. With increasing CaO content, FeO content, or both; the slag homogeneity region expanded and a composition range exhibiting crystals was reduced. The mullite (Al6Si2O13) crystalline phase was not present in the slags above 9 wt.% FeO while the karelianite (V2O3) crystalline phase was always present in compositions studied if a sufficient amount of vanadium existed in the slag. Based on the present experimental equilibrium evaluation, a set of isothermal phase diagrams showing effects of CaO and FeO on thermodynamic phase stabilities in the vanadium-bearing slags is proposed. Some uses of the diagrams for potential industrial practice are discussed.

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