The Electric Arc Furnace

The electric arc furnace has been applied as a replacement for the blast furnace by RSR Corporation for the purpose of treatment of reverberatory furnace slags (Eby, 1990). 

Slag temperature is relatively high and high iron levels are not required to maintain a fluid slag as is the case in the blast furnace. Hence FeO Si02 ratios can be in the range 0.15 to 0.4, with CaO Si02 ratios around 1.0. This will avoid the formation of a speiss phase. 

Sulfur in the charge will form a matte phase usually composed of CaS and FeS. 

The lead content of slag is between 0.5 and two per cent and the total of lead, antimony, arsenic and tin is generally less than 4.5 per cent, compared with six to 12 per cent for the blast furnace. The slag is disposed of in landfill. 

The RSR furnace is 4.8 m internal diameter by 4 m high and is fitted with three 355 mm diameter graphite electrodes, rated at 4.0 MVA. Electrode consumption is around 7 kg/t of slag smelted. Constmction is a water-cooled steel shell lined with chrome magnesite brick, with a suspended domed roof Electrodes are sealed into the roof 

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Reduction to Liquid Metal. Reduction to Hquid metal is the most common metal reduction process. It is preferred for metals of moderate melting point and low vapor pressure. Because most metallic compounds are fairly insoluble in molten metals, the separation of the Hquified metal from a sohd residue or from another Hquid phase of different density is usually complete and relatively simple. Because the product is in condensed form, the throughput per unit volume of reactor is high, and the number and si2e of the units is rninimi2ed. The common furnaces for production of Hquid metals are the blast furnace, the reverberatory furnace, the converter, the flash smelting furnace, and the electric-arc furnace (see Furnaces, electric). 

Electric-Arc Furnace. The electric-arc furnace is by far the most popular electric steelmaking furnace. The carbon arc was discovered by Sir Humphry Davy in 1800, but it had no practical appHcation in steelmaking until Sir William Siemens of open-hearth fame constmcted, operated, and patented furnaces operating on both direct- and indirect-arc principles in 1878. At that early date, the avadabiHty of electric power was limited and very expensive. Furthermore, carbon electrodes of the quaHty to carry sufficient current for steel melting had not been developed (see Furnaces, electric). 

The electric arc furnace process accounted for about 25% of the 1982 U.S. steelmaking capacity (14). Most of the raw material used for the process is steel scrap. Pollutants generated by the electric furnace process are primarily particulate matter and CO. The furnaces are hooded, and the gas stream containing the particulate matter is collected, cooled, and passed to a bag-house for cleaning. Venturi scrubbers and ESPs are used as control devices at some mills. Charging and tapping emissions are also collected by hoods and ducted to the particulate matter control device. 

There are two process routes for making steel in the UK today the electric arc furnace and the basic oxygen converter. The latter requires a charge of molten iron, which is produced in blast furnaces. The raw materials for producing molten iron are iron ore, coking coal, and fluxes (materials that help the chemical process) - mainly limestone. 

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

Increasingly today, steels after they have been tapped (poured) from the furnace undergo a further stage of processing called secondary steelmaking before the steel is cast. This applies to both the basic oxygen process route and to the electric arc furnace route. 

The impure iron is made into steel by burning out most of the carbon, sulfur, and phosphorus. Today there are three common furnace types for making steel—the open-hearth furnace (85% of U.S. production), the electric arc furnace (10%), and the Bessemer converter (5%). These furnaces differ in construction but the chemistry is basically similar. 

The electric arc furnace is used for special purpose steels. Because the environment can be... 

Bohm (Ref 4) claimed that he invented a similar process earlier than Willson and applied for patent in 189L hut the patent was not issued until 1895- The electric arc furnace method invented in 1892 is essentially the same as the current method of manuf of CaCj. Detailed description of the method is given in Refs 5,6,7 8. The coml prod contains CaO,graphite and some other impurities... 

In 1903 the electric-arc furnace superseded this primitive original technique. In the arc process, nitric acid was produced directly from nitrogen and oxygen by passing air through an electric-arc furnace. 

Given the assumption that an acceptable stochastic risk from disposal in a hazardous waste facility is about 10 3 (see Table 7.1), the stochastic risk index due to the presence of radionuclides in the electric arc furnace waste is (2.5 X 10 5)/10 3 = 0.025. Since this result is much less than unity, the waste clearly would be classified as low-hazard due only to the presence of 137Cs, and there is no need to perform a less conservative analysis. 

This result is much less than unity. Therefore, based on the assumptions used in this analysis, the electric arc furnace waste would be classified as low-hazard. 

The example analyses for electric arc furnace dust in Section 7.1.7 and a hazardous chemical waste in Section 7.1.8 lead to an important conclusion about these particular wastes. The concentrations of heavy metals, especially lead, in the electric arc furnace waste clearly are sufficiently high that long-term exposure to the waste by an inadvertent intruder may need to be precluded in order to ensure that deterministic effects would not occur. In addition, for either waste, the stochastic risk that could result from unrestricted release of a disposal site might exceed acceptable levels, due to the concentrations of heavy metals that induce stochastic effects. Both of these factors indicate that these wastes may be classifiable as low-hazard only if perpetual control would be maintained over near-surface disposal sites to prevent long-term exposures of inadvertent intruders. Such a conclusion also was obtained in the example of uranium mill tailings discussed in Section 7.1.5. 

Alkaline Earth Phosphides.—An impure calcium phosphide, made by exposing lime at a red heat to the vapour of phosphorus, was used in the preparation of phosphine.2 Calcium phosphide probably is also formed during the manufacture of phosphorus by the electric furnace method g.v.). It has been prepared by heating calcium phosphate and lamp black in the electric arc furnace, and appeared as a crystalline reddish-black substance.3 Calcium phosphide prepared in this manner is only acted upon slowly by water at the ordinary temperature, but readily by aqueous solutions of strong acids. Concentrated nitric and sulphuric acids, and oxygen and chlorine, do not attack it at ordinary temperatures, but on heating it is oxidised, e.g. by chlorine above 100° C. and by oxygen above 300° C. 

After graphitization, the electrodes are machined to a desired, final configuration. In the electric arc furnace, elecrodes are joined by threaded graphite connecting pins, called nipples, screwed into threaded sockets that have been machined in the electrode end faces. Such a configuration forms a continuous column in the electric arc furnace. 

The first patent for the use of chromium in steel was granted in 1865 - but the large-scale use of chromium had to wait until chromium metal could be produced by the alumino-thermic route, developed in the early 1900s and when the electric arc furnace could smelt chromite into the master alloy, ferrochromium. 

Two more stable phosphorus allotropes are red and black phosphorus. Small amounts of these are are also produced for special purposes from the white phosphorus product of the electric arc furnace. Red phosphorus is obtained by heating white phosphorus at 400°C for several hours, which yields a complex polymeric material, more dense (2.20 g/cm ) and considerably more stable than the white variety. Red phosphorus is not only stable in air, but far less toxic than white phosphorus. Black phosphorus is more dense again (2.25-2.69g/cm ), and has a different more complex structure. It is obtained by heating the white variety at 220 to 370°C for 8 days plus requires either a pressure exceeding 10 kg/cm or a seed crystal of black phosphorus. This product has a structure resembling graphite, is a good electrical conductor, and can be lit with a match only with difficulty [10] (Table 10.3). 

The ionic liquid ChCl with urea was applied to the processing of electric arc furnace (EAF) dust by Abbott and coworkers [18]. It was found that the solubility of ZnO, Cu O, and PbO was good, zinc and lead can be selectively removed and subsequently electrowon from the liquid, whereas the insoluble iron and aluminosilicates can be recycled through the electric arc furnace. The process developed for treating EAF dust involves extraction of lead and zinc from matrix, isolation of lead, and recovery of zinc. The pilot plant built for 5-kg dust extraction batches is given in Fig. 5.1 [19]. 

The steel components of the batteries melt down and report to the steel product. For every 1% addition of batteries by weight, the steel increases by approximately 0.2%. However the batteries also contain small amounts of residual metals such as nickel, tin and copper. For a 1% addition of batteries, the total of these residual elements increases by approximately 0.01%. This can be problematical to certain grades of steel, but for reinforcement and structural steels, this is insignificant. However it is the presence of the residual copper which ultimately restricts the addition of batteries to the electric arc furnace. A 3% addition, resulting in a copper increase of approximately 0.015%, is generally considered to be the limit for battery additions without adversely affecting the product. 

The addition of batteries to the electric arc furnace steelmaking process is very simple. No modifications or additions are necessary for the installation. The batteries are... 

In addition to the cost balance shown in Table 4, the electric arc furnace operators benefit from an additional recycling fee of between 50 and 100 per tonne of batteries recycled, dependant upon quantity and other commercial factors. At an addition of 1% of scrap weight this is equivalent to a cost reduction of 6 1 per tonne of scrap and, hence, typically equal to 1.1 per tonne of product. This is a very significant additional economic benefit for the operator. In some cases, a proportion of this profit is allocated by agreement with local environment agencies, to additional environmental improvements within the facility. 

For the Provineial Executive of Zuid-Holland, the dioxin level was not therefore considered significant. The other determining factors for the acceptance of batteries into the electric arc furnaces of Nedstaal B.V. were the mercury and cadmium contents. In both eases, the levels measured were well below the aceeptance level of the stringent standards set within the Waste Incineration Air Emissions Decree. 

Batteries are continually fed into a 3.5 MVA electric arc furnace via an automatic feeding system during the melting process. Unlike the electric arc furnace steelmaking route, which can only facilitate batteries up to approximately 3% of the feed, the Valdi process loads batteries into a furnace which is void of steel except for a small heel. 

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