Entrainment of a two-layer liquid through a taphole
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10/31/03
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Entrainment of a Two-Layer Liquid through a Taphole ˇ JONG-LENG LIOW, MIKKO JUUSELA, N.B. GRAY, and I.D. SUTALO Entrainment through a taphole of a two-layer system has been investigated. The results showed that for liquids with low viscosities, the minimum dimensionless clearance from the taphole before entrainment occurs can be predicted theoretically and was related to the Froude number as Fr0.4. At low Froude numbers less than 1, fluids with low viscosities resulted in the entrainment showing a positive deviation from the critical Froude number. This allowed tapping to be carried out without entrainment occurring, even when the liquid-liquid interface was within the region of the taphole diameter. For liquids with appreciable viscosities, the entrainment showed a negative deviation from the critical Froude number. This occurs for the tapping of slag and results in entrainment at a higher liquid-liquid interface height than is predicted theoretically. Entrainment was more likely to happen for slag tapping than for matte tapping. A ledge below the taphole was found to reduce entrainment, enabling the liquid-liquid interface to be closer to the taphole during tapping. This resulted in improved slag removal efficiencies and reduced matte or metal entrainment, coupled with less slag left in the furnace after tapping. The length of the ledge from the taphole into the slag was found to be the controlling parameter for entrainment, while the ledge thickness had no effect on entrainment.
I. INTRODUCTION AND PREVIOUS WORK
TAPPING is a common process in the metallurgical industry for the removal of metal, matte, or slags from a furnace. The matte or metal is the valuable component. During the tapping of slag in a copper smelter, the goal is to ensure that the valuable matte or copper entrained in the slag is low enough for the slag to be disposed directly after tapping. During the tapping of slag or metal, the goal is to ensure that so little slag is entrained that no further slag cleaning steps are required. There are two major mechanisms for matte losses[1] in slags: chemical and mechanical. The chemical losses are dictated by the thermodynamic equilibrium of the system, where a higher oxygen potential results in a higher copper concentration in the matte and an increased amount of oxidized copper reporting into the ferrous silicate slag. The dissolution of sulfides in slag is greatly affected by the silica content of the slag; sulfidic and entrained copper are higher when smelting proceeds with a low-silica slag. At high matte grades, the sulfidic copper dissolution is small and the chemically dissolved copper is dominated by oxidic copper dissolution. Equilibrium tests provide the maximum solubility values of copper, but, in operating plants, the smelter slags have copper concentrations higher than the equilibrium values. This is often attributed to mechanical mechanisms. Two important mechanical mechanisms for entrainment have been identified: the physical dispersion of matte in slag by
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