Transient Interaction Between Reduction and Slagging Reactions of Wustite in Simulated Cohesive Zone of Blast Furnace
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RODUCTION
THE blast furnace cohesive zone serves as a transition region between the upper lump zone and lower dripping zone. This zone directly determines the secondary distribution of the gas flow and the heat transfer inside a high-temperature region.[1] Thus, understanding the structure and the formation mechanism of the cohesive zone is highly important for the smooth operation and low carbon emission of a blast furnace. The position and thickness of the cohesive zone is principally dependent on the softening and melting properties of its iron-bearing burden.[2,3] Sinter, pellet, lump ore, and other raw materials have been employed to investigate the softening and melting behavior,[4–8]
KAIHUI MA, JUNYI DENG, DONGDONG WANG, YANG XU, ZHEHAN LIAO, and CHENGFENG SUN are with the College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China. JIAN XU, SHENGFU ZHANG, and LIANGYING WEN are with the College of Materials Science and Engineering, Chongqing University and also with the Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and Advanced Materials, Chongqing University, Chongqing 400044, China. Contact e-mail: [email protected] Manuscript submitted October 17, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
and various indices have been proposed to evaluate the effects of the added compounds on the formation of the cohesive zone.[9–12] For example, Al2O3 was found to have priority over MgO to enter into a slag, and the latter mainly existed in the FeO-MgO solid solution.[13] Thus, the softening temperature decreased, and the bed permeability deteriorated.[4] By contrast, further increase in MgO concentration increased the softening temperature and the liquidus temperature of the slag.[5] The general increase in the softening and melting interval not only increased the thickness of the cohesive zone but also moved its position downward. However, several works did not show that MgO greatly affected the softening properties of an iron-bearing burden.[6,7] The softening, melting, and permeability of CaO-FeOSiO2 ternary mixture were also investigated.[8] The gaseous reduction of iron oxides has been studied based on thermodynamic and kinetics.[9–14] However, most experiments have been performed below 1400 K.[15–17] Wang et al. found that the replacement of N2 by CO significantly increased the reduction rate at 1673 K.[18] Thus, the gaseous reduction of iron oxide by CO in the blast furnace cohesive zone could not be neglected. Moreover, Inoue et al. found that the wustite (FeO) reduction rate constant increased when 0.5 pct of CaO in mass fraction was added.[19] FeO doped with SiO2 was also found to promote the reduction rate at
high temperature. This phenomenon was due to the larger pores and the less-dense metal, but the reduction process was retarded when the temperature was below 1000 K.[20,21] Hayashi et al. found that FeO reduction was extremely suppressed by Al2O3 or SiO2 because of the formation of dense iron, while the simultaneous dissolution of Al2O3 and SiO2 accelerated
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