Interaction of Iron with Alumina Refractory Under Flash Ironmaking Conditions
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A novel flash ironmaking technology (FIT) has been developed at the University of Utah to overcome the shortcomings of the existing ironmaking processes. This technology is based on the direct reduction of iron ore concentrate with a reductant gas such as hydrogen, natural gas, or coal gas in a flash furnace, thus bypassing the problematic pelletization/sintering and cokemaking steps required in blast furnace ironmaking.[1–5] In the development of the new process and its scale-up, the choice and design of refractories is expected to play a pivotal role for several reasons. Since the refractories must withstand high temperature, they are quite expensive and failure in the refractories results in the loss of production time and often the end product itself. These issues are greatly affected by economic
RAHUL SARKAR and H.Y. SOHN are with the Department of Metallurgical Engineering, University of Utah, Salt Lake City, Utah 84112. Contact e-mail: [email protected] Manuscript submitted December 17, 2018. Article published online May 31, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS B
factors, and the refractory most suitable for this process might not necessarily be the one that lasts the longest, but rather the one that gives the best balance between the cost of installation and its performance.[6] Thus, investigating the interactions of candidate refractories with iron and iron oxide powders under flash ironmaking conditions is of great significance. This paper summarizes the interactions of pure alumina (Al2O3) refractory with iron (Fe) powder under conditions relevant to the novel flash ironmaking technology (FIT).
II.
THEORETICAL CONSIDERATIONS
A. Thermodynamics 1. The Fe-O-Al system The flash ironmaking system consists of a number of different components. The gas phase is made up of H2, CO, H2O, and CO2 in various concentrations. The condensed phases that interact with the gas as well as the refractory are iron and iron oxides plus some oxide gangues. Thermodynamic analysis of this system is complicated and hence requires some simplification. The gas phase consisting of H2, CO, H2O, and CO2 can be VOLUME 50B, AUGUST 2019—2063
represented, as far as its interaction with the refractory is concerned, by a single parameter, viz., the partial pressure of oxygen (pO2 ) since there is little incorporation of hydrogen or carbon into the refractory. [In some experiments, however, a thin layer of AlH3 phase was observed on the surface.] The examinations of refractory cross sections revealed that the phases formed in the main affected zone consisted entirely of Fe, Al, and O. Hence, it is argued that for interactions of iron (Fe) with pure alumina (Al2O3) refractory, the affected region can be represented as a Fe-O-Al system for the development of a thermodynamic basis for this study. In the presence of oxygen, the only component that can be oxidized in this system is Fe because Al2O3 is already fully oxidized. Thus, the possible phases that can be formed in this system can be determined from the FeO-Fe2O3-Al2O3 phase
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