CFD Modeling of Flow, Temperature, and Concentration Fields in a Pilot-Scale Rotary Hearth Furnace
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DUST and sludge are generated at every stage of steel production process, such as sintering, coke making, blast furnace process, converter furnace process. These materials usually contain iron, carbon, and a small amount of zinc, thus recycling dust and sludge has both environmental and economic benefits. From several de-zinc processes now available, rotary hearth furnace (RHF)[1–3] process is considered as one of the most effective technologies for treating metallurgical wastes based on the overall evaluation of treatment capacity, profitability, and operational flexibility. Dust and sludge are mixed in a given ratio, and then pelletized into green pellets. After being dried, the pellets are charged into RHF, where they are heated to about 1573 K (1300 C) for 10 to 20 minutes. During the heating process, the iron oxides are reduced to iron and discharged outside the furnace for further processing. Meanwhile, the zinc oxide is reduced to metal zinc and gasified into the off gas. Vapor of zinc is oxidized in the off gas and collected as secondary dust shipped to a zinc refining plant to extract metal zinc. There are several commercial-scale RHFs in the world such as Japan and USA. In China, research work on RHF began in 1990s, but no industrial plant has been developed at that time, however, with the increasing pressure of environmental protection, many YING LIU, Doctoral Candidate, FU-YONG SU, Lecturer, and ZHI WEN, Professor, are with the School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] ZHI LI, General Manager, HAI-QUAN YONG, Senior Engineer, and XIAO-HONG FENG, Manager, are with the CISDI Industrial Furnace Co. Ltd., Chongqing 400013, P.R. China. Manuscript submitted July 17, 2013. Article published online January 11, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
steel mills begin to introduce RHF to process the dust and sludge in recent years. The direct reduction of composite pellets has been extensively investigated in recent years.[4–9] It is generally agreed that iron oxides or zinc oxide reduced by carbon occurs mainly through the gaseous intermediates CO and CO2. Figure 1 illustrates the main characteristics of RHF. A shallow layer of composite pellets in the hearth is depicted under a stream of off gas moving in the opposite direction. Temperature difference between the surface and the core of the pellet was found during the reduction process,[10] and, therefore, heat transfer from the outside to the surface and through the inside of pellet may limit the total reduction rate. Since the furnace temperature is relatively high, above 1273 K (1000 C), energy consumed by chemical reactions in the pellets mainly comes from radiation heat transfer from the fuel gas and furnace refractory walls to the surface of the pellets.[11] Radiation heat transfer is largely affected by flame temperature and the composition of combustion gas. However, post-combustion of CO generated by the layer of composite pellets during reduction proce
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