The Archive’s document files on direct reduction contain one of the most comprehensive collections of information ever assembled on this solid-state method of making iron. Regarding direct reduction, itself, the contents encompass the following topics: physical chemistry, process alternatives, history and status, potential growth and outlook, economics, use of coal vs. gas, use of coal gasification, iron-ore pellets and other raw-material needs, use of ores from Latin America, recycling waste oxides, environmental aspects and guidelines, location at iron-ore mines, use in Minnesota, use in developing nations and Latin America, potential and limitations in the United States, comparison to the blast furnace, potential for floating plants, rotary-kiln processes, plasma technology, an interview with Dr. Willy Korf on direct reduction, and world plant lists for 1952-82, 1973-74, and 1991.
Information is provided on the following direct-reduction processes: ACCAR, ARMCO, BULLS, CAP/Powder Metallurgy, DRC/Hockin, FASTMET, FIOR and FINMET, FLUFER, HYL and HYL III, INMETCO, Iron Carbide, Kinglor Metor, Krupp/Codir, LS-Rior, MIDREX, Midrex EDR, MTU Cold-Bond Pellets, Nippon Steel DR, PelleTech, PUROFER, R-N Direct Iron, Salem DR, SL/RN, Strategic-Udy, and THAGARD HTFW.
The files describe direct-reduction operations at the following companies, plants, and locations: Acos Finos Piratini S.A.; Armco/Houston; British Steel/Hunterston; Dalmine Siderca; Dampier, Australia; Dunswart Iron and Steel Works, Ltd.; Falconbridge/Ontario; FIOR/Venezuela; Gilmore Steel; Hamburger Stahlwerke GmbH; HYL/Puebla; INMETCO/Elwood City; Iron Carbide/Trinidad and Tobago; Krupp/Codir in South Africa; Korf/Georgetown Ferreduction; MIDREX at ACINDAR, QUASCO, and in Latin America; Mukand Iron & Steel Works Ltd.; Norddeutsche Ferrowerke GmbH; SCAW Metals Ltd.; and SL/RN at ISCOR, Falconbridge, and New Zealand Steel Ltd.
Regarding the output from direct reduction, namely direct-reduced iron or DRI, the following subjects are covered: projected demand, supply and demand outlook in 1980, world DRI statistics for 1970-2000, output by plant and process, its importation, impact of its use on scrap and iron-ore demand, role in reducing coke consumption, substitution for scrap, storage and handling of DRI, its transportation, stockpiling to store energy, and its various end uses (in blast furnaces, BOF/LD converters, electric furnaces, UHP electrics, those used in flat-rolled steel production, open-hearths, large-scale integrated plants, and in steelmaking generally).
Of particular note, the direct-reduction files contain New Technologies in Iron Ore Processing by Battelle-Institute E.V.; Environmental Aspects of and Guidelines for DR Route to Steelmaking by the U.N. Environment Programme (Hogan, W.T. and Koelble, F.T., Fordham University, participants); 1974-2001 collection of Direct from Midrex, the Midrex newsletter; and also from Midrex, World Direct Reduction Statistics, from 1970-2000. In the book and reference collection are Direct Reduced Iron: Technology and Economics of Production and Use, edited by Robert L. Stephenson and Ralph M. Smailer; and Direct Reduction as an Ironmaking Alternative in the United States, a study for the U.S. Department of Commerce and Lehigh University by Father Hogan and Frank T. Koelble.
Analysis: Direct reduction refers to any process for removing the oxygen in iron ore (about 30% of its content by weight) by reducing the ore below its melting point to obtain a porous, metallic iron called DRI. Compared to blast-furnace iron, most DRI is significantly lower in carbon (2% C max.) and generally contains 6% or more of unreduced or partially reduced iron oxides and non-ironbearing substances or gangue. Originally called sponge iron, the name change to DRI was appropriate, for although sponge iron is also produced by solid-state reduction, it is a coherent, porous mass of substantially pure iron (more than 98.5% Fe), used principally as a source of metallics for powder metallurgy. The DRI used for steelmaking is a notably different metallic product.
The difference between DRI and ferrous scrap must also be emphasized, since DRI is sometimes referred to inaccurately as synthetic or manufactured scrap. Because scrap has passed through a molten state, it does not have the unreduced iron oxides and gangue that DRI has. However, DRI is more uniform in composition, of known analysis, and virtually free of scrap’s residual alloys or tramp elements, some of which are not removed in the steelmaking process and thereby limit scrap’s application in refining a variety of steel grades.
In DRI production, the reducing agents or sources of reducing gas that drive off the iron ore’s oxygen content in the form of water vapor and carbon dioxide include synthesis-gas mixtures in gas-based direct-reduction processes and heated coal in coal-based processes. In the former, the reducing gas is most often obtained by the steam reforming or partial oxidation of natural gas and is then passed through an ore-filled vessel. In the latter, single or multiple process units are used to achieve coal gasification, gas desulfurization, and iron-ore reduction. In both cases, medium-BTU gas containing carbon monoxide and hydrogen reacts with the iron oxide and converts it to DRI.
Although direct reduction is widely regarded as a newer technology, it actually predates the blast furnace, with simple hearth or shaft arrangements having been used in primitive times to interact iron ore, carbon from charcoal, and oxygen from a natural draft to obtain a pasty raw iron for hammering into various shapes. In the 1800’s, hundreds of process designs and techniques were devised and promoted without notable acceptance, and not until the 1950s were the first commercial plants constructed. Since then, only 25 or so processes have developed beyond the pilot-plant stage, and today, only a handful account for nearly all of the DRI produced.
World DRI output, which was less than one million annual tons in 1970, has now reached the 50-million-ton level. Gas-based processes account for some 90% of the total and coal-based processes for the remaining 10%. Among the former, the MIDREX process produces some 65% of the total, HYL and HYLIII about 20%, and FIOR/Finmet just over 5%. By contrast, SL/RN, the leading coal-based process, accounts for just 3% of the total. In 2003, India led all other countries with a DRI output of 7.7 million tons, followed by Venezuela at 6.9 million, with Mexico and Iran tied for third, both producing 5.6 million tons.
One process approach with promise for increasing coal-based direct reduction, particularly where the availability and cost of natural gas have been inhibiting DRI output, involves the reduction in a rotary-hearth furnace of cold-bonded pellets containing a mixture of ore and coal fines to establish many reduction sites within each pellet. The rotary hearth permits these pellets to be processed without breaking apart, as they would from the tumbling action within a rotary kiln, and because the carbon and oxide elements are intimately contained within the pellets, oxide reduction occurs within minutes, compared to hours in other coal-based approaches for reducing conventional oxide pellets from the outside in by means of gas-to-solid diffusion.
The reduction of cold-bonded pellets in a rotary-hearth furnace has been performed commercially since 1978 by INMETCO at Ellwood City , Pennsylvania to process steel-plant wastes, and other versions of the technology have undergone testing by Midrex, Kobe Steel, and Steel Dynamics as the FASTMET, Iron Dynamics, and the ITmk3 processes. An ITmk3 demonstration plant was started up in northeastern Minnesota in May 2003 to test the reduction of taconite concentrates, and the plants iron output has been used successfully by Steel Dynamics at its Butler, Indiana electric-furnace shop.