Analysis of the Hydrogen Reduction Rate of Magnetite Concentrate Particles in a Drop Tube Reactor Through CFD Modeling
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TRODUCTION
THE blast furnace process currently produces more than 90 pct of primary iron, with the balance by alternate processes such as direct-reduced iron (DRI) and smelting reduction. Although the blast furnace has a high production rate and other advantages, it suffers from high energy consumption and CO2 emissions. A novel ironmaking technology is under development at the University of Utah.[1–9] In this process, iron is produced from fine iron oxide concentrate particle in a flash process, utilizing hydrogen, natural gas, or coal gas as the reducing agent as well as a fuel. These reducing gases offer high reactivity and eliminate or decrease carbon dioxide emissions during ironmaking. Flash ironmaking also allows the direct use of concentrate to bypass the problematic pelletization/sintering and cokemaking steps in the blast furnace process. Traditional thermogravimetric analysis (TGA) system and drop tube reactor (DTR) are two experimental apparatuses used in the study of kinetics of gas–solid reaction. TGA is typically used when the gas–solid reaction time is in the order of minutes or longer.[10–12] The DTR system is useful for fast reactions that take only several seconds, like flash process and fast pyrolysis of biomass, coal and other fuels. Sohn et al.[6,8,9] have investigated the gaseous reduction of iron oxide
DEQIU FAN and MOHAMED ELZOHIERY, Ph.D. Students, YOUSEF MOHASSAB, Research Associate, and HONG YONG SOHN, Professor, are with the Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112. Contact e-mail: [email protected] Manuscript submitted on October 29, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
concentrate particles under various experimental conditions using a DTR aimed at generating a database to be used for the design of a flash ironmaking reactor. The residence time in their work was calculated by considering the length of the reaction zone, the linear velocity of the gas, and the terminal falling velocity of particles under the assumption of constant particle velocity and temperature. Qu[13] has conducted a series of experiments on the reduction kinetics of fine hematite ore particle at different temperature ranging from 1550 K to 1750 K (1277 C to 1477 C) with different reaction time (210 to 2020 ms) in a high temperature DTR. Particle residence time was calculated by iteratively solving the particle motion equation under constant particle temperature assumption in their work. In situ particle temperature measurement and realtime tracking of particle inside the DTR would require sophisticated and intrusive experimental techniques, e.g., particle image velocimetry (PIV) and optical access to the DTR interior.[14–17] Moreover the use of H2 atmosphere at high temperature adds an extra layer of complexity to use these techniques. Furthermore, temperature measurements in the reactor during the experiments in this work as well as CFD simulations found that there was a narrow, low temperature region near the tip of the water-cooled tube through which the carrie
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