Continuous oxygen steelmaking with copper-, tin-, and zinc-contaminated scrap
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1/1/04
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Continuous Oxygen Steelmaking with Copper-, Tin-, and Zinc-Contaminated Scrap N.A. WARNER In the context of a new zero-gas-emission process for continuous oxygen steelmaking, desorption of copper, tin, and zinc from liquid scrap are modeled. Additive diffusional-resistance concepts show that zinc elimination at atmospheric pressure is entirely straightforward. For copper and tin, a reduced pressure (2.5 mbar) and a relatively high temperature (1780 °C) are preferred. Sulfur must be added above the stoichiometric requirements to volatilize tin sulfide. Copper elimination by physical desorption is completely predictable, but with tin, interfacial chemical kinetics may possibly exert an influence. Based on exclusive transport control and the currently available pumping capacity for vacuum degassing steel, the engineering feasibility of refining continuously melted steel scrap is established. Dimensions are estimated for producing 2 Mtpa of steel with a scrap-to-virgin iron ratio of 3 to 1. Electrical conductive heating is required to raise the liquid-scrap temperature toward the limits imposed by current refractories. With the proposed new technology, copper, tin, and zinc are all recovered as by-product metals. Pretreatment of steel scrap is not advocated, other than simple physical segregation at the source.
I. INTRODUCTION
CURRENT best steelmaking practice is not zero gas emission. Therefore, CO2 sequestration, oxygen production, and power generation, all integrated with the proposed continuous steelmaking route, as introduced recently by the author,[1,2,3] would probably be omitted from a firstgeneration plant, with the option that they could be readily retrofitted when the financial case becomes overwhelmingly supportive. Under these conditions for 2 Mtpa liquid steel, the estimated total cost is believed to be in the region of $170 per ton of liquid steel, assuming conventional refractory-lined furnace construction and other costs loosely scaled mostly from a British Steel Technical Note and updated to 1997 costs using the CAPRI Index, so that a comparison can be made with steel-industry data presented by Wagner.[4] The $170 per ton liquid-steel figure is based on the iron mix as one unit virgin iron to three units scrap and assumes that oxygen is supplied at $40 per metric ton, as used by Fruehan and Nassaralla[5] in their review of alternative steelmaking processes (scrap at $126 per ton and received coal at $55 per ton). Iron-ore fines are assumed to be available (c.i.f.) at $37 per ton Fe, as given by Wagner. Accordingly, it may be compared directly with the $232 figure given by Wagner[4] for an electric arc furnace with scrap. However, this is not the whole story. There are important beneficial attributes of the proposed continuous steelmaking route, which a simple comparison does not take into account. 1. The combination of abolition of expensive refractory hearths and substitution by permanent linings of residual solid-melt materials, as well as widespread use of lightN.A. WA
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