Interfaces Between Coke, Slag, and Metal in the Tuyere Level of a Blast Furnace
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st furnace (BF) ironmaking continues to evolve under the double pressure of high cost and emission reduction.[1–3] As a counter-current reduction furnace, the bed permeability at lower section, between the cohesive zone and hearth, is critical for its influence on the characteristics of reactions in this area, which in turn affect the product quality, production rate, and fuel consumption as well as campaign life of the blast furnace, as discussed in recent publications.[4,5]
KEJIANG LI and KEXIN JIAO, Ph.D. Candidates, JIANLIANG ZHANG and TIANJUN YANG, Professors, ZHENGJIAN LIU and GUANGWEI WANG, Lecturers, JIANBO ZHONG, Master Candidate, and MENGFANG WEI, Engineer, are with the School of Metallurgical and Ecological Engineering and State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, No. 30 Xueyuan Rd, Haidian District, Beijing 100083, P.R. China. Contact e-mail: [email protected] MANSOOR BARATI, Professor, is with the Department of Materials Science and Engineering, University of Toronto, Toronto, ON M5S 3E4, Canada. Manuscript submitted January 17, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
Due to the complexity and severity of environment (high temperature, high pressure, and multiphase coexistence) of the BF lower zone, it is impossible to observe phenomena that occur inside directly. Thus, very little is known as yet about the interactions of various materials (coke-to-slag, coke-to-metal, slag-to-metal) in this area, and no report has been published about the interfaces between coke, metal, and slag in this area. However, a tuyere drilling technique, which allows to obtain samples from an operating blast furnace, provides a source of potentially useful information about various important inner phenomena in the tuyere level.[6,7] As the primary solid material in the BF lower zone, coke is the main sample obtained using the tuyere drilling technique. Thus, previous studies about tuyere drilling samples focused mainly on the changes in coke characteristics in this zone,[8] i.e., carbon structural order,[9–12] mineral transformation,[10,13–16] and reactivity and strength.[17] However, besides solid coke, slag and metal also exist in liquid state in the tuyere level, and they can be extracted with coke samples simultaneously during the tuyere drilling process. As shown in Figure 1, below the cohesive zone, the preheated blast blown into the furnace through the tuyeres reacts with all the phases in this zone; primary slag is formed from the unreduced ore, limestone, and ash of coke and coal as well as impurities of the ore; liquid iron is formed by the reduction of iron oxides from the primary slag; the metal and slag descend through the coke bed together; and then, the metal descends through the slag zone and joints to the metal pool. Thus, coke–slag reaction, coke– metal reaction, and metal–slag reaction all may occur in the tuyere level due to their coexistence in this zone.[18] The samples in which coke, slag, and metal coexist could provide meaningful informa
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