Modeling of Thermochemical Behavior in an Industrial-Scale Rotary Hearth Furnace for Metallurgical Dust Recycling
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INTRODUCTION
THE steel industry generates a significant amount of dust waste (usually termed ‘‘metallurgical dusts’’), approximately 8 to 12 pct of steel output, from sintering YU-LIANG WU is with the Department of Energy Conservation and Environmental Protection, Materials Energy Conservation Center, Beijing 100834, People’s Republic of China. ZE-YI JIANG is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. XIN-XIN ZHANG is with the Beijing Engineering Research Center for Energy Saving and Environmental Protection, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. QING-GUO XUE is with the Beijing Key Laboratory for Energy Saving and Emission Reduction of Metallurgical Industry, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. AI-BING YU is with the Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia. YANSONG SHEN is with the School of Chemical Engineering, University of New South Wales, Sydney, NSW 2052, Australia. Contact e-mail: [email protected] Manuscript submitted November 2, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
processes, pelletizing processes, blast furnaces, oxygen converters, and rolling processes.[1] For example, China’s crude steel output was about 0.8 billion tons in 2014; that is, nearly 100 million tonnes of dusts were generated.[2] Typically, metallurgical dusts contain 30 to 70 pct iron, as well as other elements, such as C, Zn, Pb, K, or Na. In the past, these dusts were mainly recycled by sintering for recovering Fe and C, which leads to a damage in sinter quality and also has a negative effect on blast furnace operation due to the accumulation of heavy and alkali metal elements in iron circle.[3,4] A rotary hearth furnace (RHF) was originally used for heating steel rolls and has recently been proposed for recycling the metallurgical dusts due to its efficient performance in reducing iron oxides to metal Fe and removing Zn, Pb, K, and Na from dusts.[5] In this process, various metallurgical dusts, added with adhesive bond and carbon-containing powder (if necessary) for an appropriate C/O ratio, are well mixed and then compressed into cold composite pellets using a briquetting machine. After drying, the raw pellets are fed into the RHF for direct reduction. During the direct
reduction process, metal Fe is reduced from iron oxides; zinc vapor reduced from ZnO diffuses out of the pellets and then is reoxidized into solid particles of oxides; PbO is removed by volatilization of both PbO itself and its reduced product Pb; and removal of K and Na, existing as chlorides, is attributed to volatilization of KCl and NaCl. Then the metallized pellets are charged into the blast furnace after cooling as a burden material; Zn, Pb, K, and Na products are collected in secondary dusts by a flue gas treating system for further use.[6] Besides, an RHF can be used also for direct reduction of or
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