Effect of Firing Temperature and Reducing Gas Composition during Low-Temperature Reduction of Nanocrystalline Fe 2 O 3
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ENTLY, self-fluxing sinter serves as the principal charging material for blast furnaces, and its use has contributed greatly toward improved blast furnace operation, with decreased fuel consumption and increased productivity. However, compared with other charging materials, self-fluxing sinter has a relatively higher rate of size degradability. Excess degradation during reduction generates fines, which, in addition to lowering the permeability of the bed, cause hangings and slips to occur, and thus detrimentally affects the furnace operation.[1–6] Stable furnace operation is therefore partly dependent on control and improvement of the size degradability of the sinter during reduction. There are many recent publications in the field of characterization of iron ore sinter,[7–10] but little work dealing with low-temperature degradation aspects of sinter is reported in the literature. Various sinter microstructures were produced in the laboratory using the same iron ore blend, varying only sinter basicity and carbon content of the blend via limestone and coke additions, respectively. The sinter cakes were subjected to low-temperature, size-degradation tests, and their structural composition was determined by Pimenta.[11] A relationship has been established between sinter structural composition and its size degradation under low-temperature reducing conditions. Also, varying the gas composition led to development M. BAHGAT, Researcher, and M.I. NASR, CMRDI President, are with the Central Metallurgical Research and Development Institute (CMRDI), Cairo 11421, Egypt. Contact e-mail: m_bahgat70@ yahoo.com M.H. KHEDR, Associate Professor, Faculty of Science and E.K. SEDEEK, Postdoctoral Student, Faculty of Industrial Teaching, are with the Benisuef University, Benisuef, Cairo, Egypt. Manuscript submitted 28 May 2006. METALLURGICAL AND MATERIALS TRANSACTIONS B
of a new reduction test procedure, which is more sensitive to microstructural variations than the conventional standard test (reduction degradation index). Zhang et al.[12] recognized that preoxidation and sintering of ilmenites affect their reducibility, but literature data on this matter are inconsistent. Nakajima et al.[13] showed that sinter suffered degradation particularly in the temperature range of 600 °C to 800 °C in the shaft. Furthermore, Takada et al.[14] showed that degradation of sinter was influenced by the reduction conditions as well as by the sinter quality itself. Degradation increased with the residence time at 500 °C to 700 °C in the shaft, even though the same quality of sinter was used. Two main factors affect the reduction behavior of iron-bearing materials in terms of reduction rate and size degradation, namely, the nature of the materials and the reduction conditions. The microstructure of the agglomerates is influenced by the starting materials, shaping methods, and sintering conditions, especially at high temperature. Even in the case of synthesized hematite compacts, the starting materials and sample preparation methods were different from one investiga
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