Hydrogen Reduction Kinetics of Hematite Concentrate Particles Relevant to a Novel Flash Ironmaking Process
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RODUCTION
MORE than 90 pct of primary iron is currently produced by the blast furnace process, with the balance by alternate processes such as direct-reduced iron (DRI) and smelting reduction. Although the blast furnace has high production rates and other advantages, it suffers from the problems of its high energy consumption and CO2 emission. A novel flash ironmaking process is under development at the University of Utah,[1–7] in which iron ore concentrate is flash-reduced by gaseous reductants at temperatures above 1423 K (1150 C). This flash ironmaking process is expected to significantly reduce energy consumption and carbon dioxide emissions and eliminate the problematic steps of sintering, pelletization, and cokemaking. Previous research on gas–solid reduction of iron oxide has typically involved samples larger than concentrate particles, such as ore fines and pellets as well as temperature ranges substantially lower than in the new flash ironmaking process. Ray and Kundu[8] pointed out that hematite was reduced with iron diffusing inward FENG CHEN, formerly Visiting Ph.D. Student with the Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112, is now Ph.D. Student with the School of Minerals Processing and Bioengineering, Central South University, Changsha, 410083 Hunan, P.R. China. YOUSEF MOHASSAB, Research Associate, and HONG YONG SOHN, Professor, are with the Department of Metallurgical Engineering, University of Utah. Contact e-mail: [email protected] TAO JIANG, Professor, is with the School of Minerals Processing and Bioengineering, Central South University. Manuscript submitted January 6, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
and had an activation energy of 90 kJ/mol in the temperature range from 1073 K to 1273 K (800 C to 1000 C) in CO–N2 system. Edstrom[9] studied the reduction of natural hematite crystals by hydrogen below 1273 K (1000 C) and found that the hematite crystal swelled at first, but shrunk during the later stages when reduced by hydrogen. Hematite particles of 105 to 140 lm size were reduced by hydrogen in a silica tubefluidized bed reactor by Srinivasan and Sheasby[10] in the temperature range from 923 K to 1173 K (650 C to 900 C). They found that a pore-free magnetite layer was formed adjacent to the hematite phase, but the magnetite layer developed porosity with further reduction. Piotrowski et al.[11] reduced hematite particles of 91 lm average size to wustite by carbon monoxide at 973 K to 1173 K (700 C to 900 C). The nucleation and growth kinetic model was applied to the initial stages of the reduction process, which gradually shifted to diffusion control as reduction proceeded. They determined activation energy to be 58 kJ/mol. Moreover, Sturn et al.[12] found that the phase boundary reaction was the most likely rate-controlling step for the reduction of hematite particle of diameter 177 lm by hydrogen in a temperature range from 673 K to 803 K (400 C to 530 C). Fruehan et al.[13] investigated the reduction of hematite particles of 180 to 2
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