Effect of Chlorine on the Viscosities and Structures of CaO-SiO 2 -CaCl 2 Slags
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INTRODUCTION
IN recent years, the hazards from chlorine in blast furnace (BF) to gas pipelines, BF top gas recovery turbine unit, and so on have appeared more clearly; one reason for that is HCl and other acid gases are brought into the BF dry-dedusting system which should have been absorbed by gas washing water in BF wet-dedusting system,[1–4] and another reason is that the chlorine brought into BF increases from the injection of low-quality coals and waste plastics,[5,6] the employment of imported ores after seawater beneficiation, sinter sprayed with CaCl2,[7] and coke coked by coals and waste plastics. Meanwhile, the increase of chlorine affects the BF smelting process, metallurgical properties of raw materials and fuels and characteristics of molten slag simultaneously,[8–10] and the certain extent of circulation and accumulation of chlorine in BF makes these effects more obvious.[11,12] It is normally known that the chlorine can be absorbed by the BF slag, hence will have an effect on the slag performance. However, only few works on the effect of chlorine on molten slag were carried out, CUI WANG, Ph.D. Candidate, JIANLIANG ZHANG, Professor, ZHENGJIAN LIU, Associate Professor, KEXIN JIAO and GUANGWEI WANG, Lecturers, and JUNQIANG YANG, Master Candidate, are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, No. 30 Xueyuan Rd, Hadian District, Beijing 100083, P.R. China. Contact e-mail: [email protected] KUOCHIH CHOU, Professor, is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing. Manuscript submitted January 10, 2016. Article published online October 28, 2016. 328—VOLUME 48B, FEBRUARY 2017
Myoung et al.[6] investigated the viscosity of CaOSiO2-12 mass pct Al2O3-10 mass pct MgO BF slag by adding CaCl2 powder and discovered that the viscosity at temperatures high than 1700 K (1427 C) was less than that of slags without chlorine by about 2.5 dPaÆs as the chlorine content increased up to 3.2 mass pct, while the influence mechanism was not further analyzed. The influence of CaF2 on the structure of silicate glasses had been studied in great detail, and the conclusions could be classified into four conflicting views: (a) CaF2 completely performs as the role of modification in basic silicate glasses,[13,14] (b) CaF2 is present as F coordinated with Ca2+ and has no impact on the depolymerization of silicate network,[15–18] (c) the CaF2 additive contributes to the breakage of Si-O bonds only in acidic silicate glasses,[19–21] (d) CaF2 performs as the role of modification with its concentration less than 10 mass pct, and has no impact for higher CaF2 concentration.[21,22] In order to clarify the effect of chlorine on the slags, the viscosities of the fundamental CaO-SiO2-CaCl2 slags were investigated in the present study, and the critical temperature (TCR), activation energy, and Raman spectra of the slags were analyzed for the mechanism research.
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EXPERIMENTAL
A. Slag Preparation for Viscosity Measurement Slag sa
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