The ignition and combustion of chalcopyrite concentrate particles under suspension-smelting conditions
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INTRODUCTION
S I N C E its development by International Nickel Company and Outukumpu Oy in the late 1940s and early 1950s, 1~-3] the flash-smelting process has found wide application in the production of copper and nickel mattes, where it has replaced the conventional reverberatory furnace. The attractiveness of the flash-smelting process has increased greatly with the availability of inexpensive tonnage oxygen. [4-6] Flash smelting has proved to be superior to other processes because of its lower fuel requirements, reduced fugitive-emission problem, easier control, and higher production rate.[7] In the flash-smelting process, fine particles of dry sulfide concentrate and flux are injected into the furnace along with oxygen-enriched air, tonnage oxygen, or preheated air mixed with fuel in the form of a turbulent divergent jet. The dry charge is dispersed in the furnace flame zone, and the concentrate particles in the jet ignite at some distance from the burner. The temperature at which ignition occurs under heat- and mass-transfer effects in the furnace determines the reactor length necessary to achieve ignition. Since virtually no reaction occurs before the particle ignites, it is very important that this length be reduced to optimize shaft length. The use of preheated air is one way to achieve this. Sohn and co-workers tS-~~ developed a comprehensive mathematical model of the flash-smelting process that incorporates the turbulent fluid dynamics of the particleladen gas jet, heat and mass transfer (including the radiation between the wall and the particles), and chemical reactions. The ignition phenomenon in the process can be described as part of the overall model, but the computation using this model is extremely complex, involving extensive computer time and much fine-tuning of the numerical procedure. A simplified treatment of the ignition process, even one requiring approximation, would H.Y. SOHN, Professor, is with the Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112-1183. P.C. CHAUBAL, formerly Assistant Professor, Department of Metallurgical Engineering, University of Utah, is Staff Engineer, Research Laboratories, In/and Steel Company, East Chicago, IN 46312. Manuscript submitted November 2, 1992. METALLURGICAL TRANSACTIONS B
be helpful to obtain not only quick results but also greater insight into the problem. Recognizing the importance of the ignition problem in the flash-smelting process, Jorgensen and coworkers H~-~7I and Otsuka and Soma cl8~ have performed extensive studies of the ignition of sulfide minerals under simulated suspension-smelting conditions. The experiments were conducted in a laminar-flow furnace wherein the gas and particles are made to flow downward in laminar flow. Although the conditions inside a laminar-flow furnace do not resemble the turbulent nature of the flow fields inside a flash-smelting furnace, studies in a similar system, i.e., pulverized-coal combustors, have shown that the minimum scale of a turbulent eddy is 10 to 100 times
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