Computational Fluid Dynamics (CFD) Investigation of Submerged Combustion Behavior in a Tuyere Blown Slag-fuming Furnace
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SMELTING industries often produce slag that contains a significant amount of metal oxides, which are often discarded as waste. Significant metal values can be recovered from the slag by proper treatment. Zinc slag fuming is such a process, in which a reductant source (usually coal) is injected in the molten slag bath to reduce dissolved ZnO from the bath into metallic zinc vapor. The process can be carried out in either a conventional tuyere blown furnace or top-submerged lance (TSL) smelting furnace. Commercial development of the process using tuyeres was made by the Anaconda Copper Mining Co. and Consolidated Mining and NAZMUL HUDA, Postdoctoral Research Fellow, JAMAL NASER, Associate Professor, and G.A. BROOKS, Professor, are with the Faculty of Engineering and Industrial Science, Swinburne University of Technology, Hawthorn, Melbourne, VIC 3122, Australia. Contact e-mail: [email protected] M.A. REUTER, Director, is with Outec Oyj, FI-02200 Espoo, Finland. R.W. MATUSEWICZ, Manager, is with Outotec Pty. Limited, Wheelers Hill, VIC 3150, Australia. Manuscript submitted October 7, 2011. Article published online June 13, 2012. 1054—VOLUME 43B, OCTOBER 2012
Smelting Co. in the 1920s.[1] Zinc slag fuming by TSL technology started with pilot plant studies in the 1980s and has progressed to the treatment of close to 800 9 106 Kg/year of zinc-bearing feeds in the form of residues and slags.[2] Conventional slag fuming is carried out on a batch basis in a rectangular-tuyere blown furnace as shown on the schematic cross-sectional view in Figure 1. Approximately 50 9 103 Kg of charge (either molten slag or solid slag) is fed to the furnace at the beginning of each fuming cycle. Two opposing sets of submerged tuyeres are employed to inject air and pulverized coal into the molten slag bath to carry out combustion and reducing reactions. The system usually operates within a temperature range of 1423 K to 1573 K (1150 C to 1300 C). The overall reactions occurring in the bath, as given in Eqs. [1] through [3], are governed by the supply of carbon at the gas–liquid interface.[1,3,4] Each fuming cycle, also termed as ‘‘fuming period,’’ usually operates for 150 minutes, with an additional 30 minutes for charging and tapping. Quarm[5] described the basic operating principle of the commercial slag-fuming furnace. Inside the fuming furnace, the following reactions take place: METALLURGICAL AND MATERIALS TRANSACTIONS B
Fig. 1—Schematic illustration of fuming furnace cross section (image taken from Richards et al.[13]).
ZnOðslagÞ þ C ! ZnðgÞ þ COðgÞ
½1
CðcoalÞ þ CO2 ! 2CO
½2
ZnOðslagÞ þ COðgÞ ! ZnðgÞ þ CO2ðgÞ
½3
II.
LITERATURE SURVEY
Although conventional slag fuming has been commercially operative since the 1920s, only a few studies related to slag-fuming kinetics and details of fluid dynamic behavior inside the slag-fuming furnace have been found in the open literature. The earliest studies were performed in the 1950s by Bell et al.[6] and by Kellogg[7,8] and in 1960s by Quarm[5,9,10] to investigate the details of sla
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