EAF furnace

The furnace is tapped by tilting it, forcing the metal to flow out through the spout. Opposite the spout, an operable door allows deslagging and sampling operations to be carried out prior to tapping. 

After slag removal the metal composition is controlled and adjusted if necessary. Finally the metal is deoxidised by adding aluminium or other agents into the melt stream during tapping, to prevent the formation of CO bubbles during solidification. Additional desulphurisation and or dephosphorisation refining can be executed in an AOD or VODC converter (see Section 2.4.9 and 2.4.10). 

The alkaline MgO based lining of this EAF makes it possible to refine the metal in the furnace itself Therefore it is possible to charge the fixmace with virtually any combination of scrap and foundry returns. The basic lining practice is used when the purchased scrap contains higher phosphoras and/or sulphur levels than desirable. 

Dephosphorisation of ihe melt is performed by periodic additions of lime during meltdown. Upon the injection of oxygen in the bath, phosphorous oxide is formed and trapped in the slag, together with other metallic oxides and impurities. The lime keeps the slag very basic, which stabilises the phosphorous oxide. At the same time carbon is burnt out. After sufficient reaction time, the oxygen injection is stopped and the slag is fully removed. 

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Table 3.10 Typical emission values for EAF furnaces [29, Batz, 1986]...

Dust emissions are comparable to EAF furnaces dusts, both in quantity and quality. AOD dust emissions have lower levels of residuals (organic) from the scrap charge, but on the other hand have a higher level of metal oxide (Cr, Ni), as it is mainly stainless steel which is processed in... 

Table 4.12 Energy and temperature data for EAF furnace melting with normal slag and foamy slag...

The above-mentioned techniques are applicable to all new and existing EAF furnaces, with the following limitations ... 

Direct Reduction. Direct reduction processes are distinguished from other ironmaking processes in that iron oxide is converted to metallic iron without melting. Because this product, called direct reduced iron (DRI), is soHd, it is most suitable for melting in an electric arc furnace (EAF) as a substitute for scrap (see Furnaces, electric). The briquetted form of DRI, hot briquetted iron (HBI) is used when the product is to be transported. Briquetting increases density and chemical stabiUty. The predominant direct reduction processes (MIDREX and HyL III) are based on natural gas as a fuel and reductant source. They are economically attractive in regions where natural gas is cheap and abundant, especially if iron ore is available nearby (see Iron BY DIRECT reduction). ... 

Ferrous foundries consist of two types steel foundries in which electric furnaces (EAF and induction) are used, and iron foundries in which hot-blast cupolas and/or electric furnaces are used. Electric furnaces use virtually 100% scrap charges. Cupolas are shaft furnaces which use preheated air, coke, fluxes, and metallic charges. Scrap is over 90% of the metallic charge. Cupolas accounted for about 64% of total iron foundry scrap consumption in 1994 and electric furnaces accounted for about 34%. The balance was consumed by other furnaces, such as air furnaces. Iron foundry products have a high carbon content and the scrap charge usually contains a high percentage of cast iron or is used in combination with pig iron. 

The electric arc furnace (EAF) (together with the basic oxygen vessel) is one of... 

The composition of EAF dust can vary greatly, depending on scrap composition and furnace additives. EAF dust usually has a zinc content of more than 15%, with a range of 5 to 35%. Other metals present in EAF dust include lead (2-7%), cadmium (generally 0.1-0.2% but can be up to 2.5% where stainless steel cases of nickel-cadmium batteries are melted), chromium (up to 15%), and nickel (up to 4%). 

In this process EAF dust, other zinc-bearing wastes, recycled materials, coke or coal, lime, and silica are mixed and fed to a rotary furnace. The zinc and other volatile nonferrous metals in the feed are entrained in the furnace off-gas and are carried from the furnace to an external dust collection system. The resulting oxide (zinc calcine) is a crude zinc-bearing product that is further refined at zinc smelters. A byproduct of the process is a nonhazardous, iron-rich slag that can be used in road construction. Solidification technologies change the physical form of the waste to produce a solid structure in which the contaminant is mechanically trapped. 

Ladle metallurgical furnace (LMF) processes are used to refine molten steel from the BOF or EAF prior to ingot or continuous casting. These processes include the following steps ... 

For the most part, the zinc materials recovered from secondary materials such as slab zinc, alloys, dusts, and compounds are comparable in quality to primary products. Zinc in brass is the principal form of secondary recovery, although secondary slab zinc has risen substantially over the last few years because it has been the principal zinc product of electric arc furnace (EAF) dust recycling. Impure zinc oxide products and zinc-bearing slags are sometimes used as trace element additives in fertilizers and animal feeds. About 10% of the domestic requirement for zinc is satisfied by old scrap. 

Electric furnaces, 12 286-318 76 144, 145. See also Electric arc furnace (EAF) Fuel-fired furnaces applications for, 12 315-316 arc furnaces, 12 297-306 classification of, 12 286 economic aspects of, 12 313-314 health and safety factors related to, 12 314 induction furnaces, 12 307-313 in phosphorus manufacture, 19 8-11 resistance furnaces, 12 287-297 for secondary slags, 14 759-760 Electric furnace steelmaking processes,... 

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