The document files on electric-arc steelmaking furnaces provide information on the following topics: history of process development, process descriptions and analyses, process efficiency and costs, process assessment through 2000 and future prospects, steel production data and forecasts, operating data for U.S. furnaces, electric furnaces vs. open-hearths, smelting iron in electric furnaces, product distribution of electric-furnace steel, ultra-high-power (UHP) furnaces, their operation and outlook, water cooling, DC furnaces, CONSTEEL process, Stelco/Lake Erie electric furnace, environmental standards, oxy-fuel burners and lances, retractable vs. fixed burners, North American furnace lists, furnace operations in Asia and Europe, arc-furnace electrodes, their manufacture and consumption, carbon and graphite used for electrodes, profile of the U.S. graphite industry, Union Carbide Corporation electrode business, role of Union Oil in the electrode and needle coke markets, Soderberg electrodes, and the Association of European Electrode Producers.
The files also contain biographical data and other information on electric-furnace innovators Vincent J. Nolan and William E. Schwabe. The book and reference collection contains Acheson Electrodes by Acheson Electrode Company, The Carbon Electrode and Electric Furnace Electrodes by National Carbon Company, Steel Melting Furnaces by Carnegie-Illinois Steel Corporation, and EAF Technology, State of the Art and its Future Evolution by the IISI Committee on Technology.
Analysis: The electric furnace is a tilting, refractory-lined shell, often with water-cooled sidewalls, a curved bottom, and a removable roof, which also may be water cooled and through which graphite electrodes are inserted, three electrodes in AC furnaces and one in DC furnaces. Once the electrodes are lifted and the roof pivoted aside, the furnace is top charged, in most cases with 100% recycled scrap, but at times with mostly scrap, supplemented by DRI or pig iron to serve as diluents. The charge also may be comprised mainly of DRI or even hot metal.
Once the roof is closed and the electrodes are reinserted, the melting process begins. Electric power, usually purchased from a utility company and turned into usable melting energy by a transformer (80MVA avg.), is conducted by the electrodes and discharged as a high-temperature arc (3500 deg. C max.) into the metallic charge, with oxy-fuel burners often used to speed the melting process. On average, the process consumes some 390kWh/ton of electricity and has a tap-to-tap time of about one hour. Upon completion of the melt, the furnace is tilted to transfer its molten steel (above 1600 deg. C) into a ladle.
In the period immediately after World War II, fundamental changes in technology significantly broadened the scope of electric-furnace steelmaking. Long used to produce small quantities of specialty-alloy and stainless steels, the electric furnace underwent a number of improvements that transformed it into a scrap-based, higher-volume producer of carbon steel. Furnace size was increased, ultra-high power was applied, and advances were made in furnace electrodes, electrode holders, furnace refractories, and top-charging techniques.
These changes made it possible for integrated steel plants to augment their steel capacities without having to provide additional hot-metal support, and they also lowered the investment threshold for entering the carbon-steel business on a smaller, non-integrated basis. This led to the founding of many electric-furnace-based steel companies, particularly in the 1960s, when new minimills started to link their electric furnaces to continuous casting.
By 1970, the minimill concept had been implemented in North America , Europe , and the Far East , and in the United States alone, the 25 post-war years had seen the installation of more than 150 electric furnaces, many capable of melting between 135 and 180 tons per heat. In 1970, Northwestern Steel and Wire Company, a leader in implementing electric-furnace technology, built the world’s largest furnace at Sterling , Illinois . Having a shell diameter of 9.75m, the furnace was capable of melting more than 360 tons per heat.
Between 1950 and 1970, world electric-furnace steel production increased more than fourfold, from 20 million to 88 million tons, increasing the electric-furnace share of the world’s total crude steel output from some 10-15%. Since 1970, despite periodic problems surrounding the availability and cost of purchased electricity and ferrous scrap, electric-furnace steel output has remained on a path of long-term growth, and the world’s electric furnaces now melt more than 300 million annual tons of steel, about one-third of all the steel produced.
Helping to drive this long-term growth have been continual improvements in process technology, such as off-gas utilization for scrap preheating, oxygen and fuel injection, water cooling, and direct-current melting to name a few. Among the results have been enhanced process efficiency, faster production, energy conservation, and lower electrode and refractory consumption.
Just in the 1990’s, according to IISI, worldwide furnace production rose from 61 to 94 tons/hour, average tap weights climbed from 86 to 110 tons, and oxygen usage rose from 809 to 1101scf/ton. At the same time, average tap-to-tap times declined from 105 to 70 minutes, and electricity requirements fell from 405 to 392kWh/ton. Underscoring the significance of this progress, 3-hour-plus tap-to-tap times were common as recently as 1970, and now some furnace operators are looking forward to producing 30-minute heats.