Direct reduction furnace

Iron oxide also can be reduced in a direct reduction furnace, which operates at much lower temperatures (1300-2000°F) than a blast furnace and produces a solid "sponge iron" rather than molten Iron. Because of the milder reaction conditions, the direct reduction furnace requires a higher grade of iron ore (with fewer impurities) than that used in a blast furnace. The iron from the direct reduction furnace is called DRI (directly reduced iron) and contains —95% iron, with the balance mainly silica and alumina. 

Direct reduction furnace a furnace In which Iron oxide Is reduced to Iron metal using milder reaction conditions than In a blast furnace. (21.8)... 

Ironmaking refers to those processes which reduce iron oxides to iron. By the nature of the processes, the iron produced usually contains carbon and/or other impurities which are removed in downstream processing. There are three principal categories of ironmaking processes, in order of commercial importance blast furnace, direct reduction, and direct smelting. 

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). ... 

The most common method of converting iron ore to metallic iron utilizes a blast furnace wherein the material is melted to form hot metal (pig iron). Approximately 96% of the world s iron is produced this way (see Iron). However, in the blast furnace process energy costs are relatively high, pollution problems of associated equipment are quite severe, and capital investment requirements are often prohibitively expensive. In comparison to the blast furnace method, direct reduction permits a wider choice of fuels, is environmentally clean, and requires a much lower capital investment. 

The high lead slag from the smelting furnace is tapped continuously and transferred down a heated launder directly into the reduction furnace through a port in the side of the vessel. Lump coal for reduction is fed continuously to the furnace by conveyor and dropped direcdy into the bath. Heating for the endothermic reduction reactions is provided by oil injected down the lance. The combustion air stoichiometry is set at 95% of that required for complete oil combustion. Air is injected into the top of the furnace to afterbum the volatile materials from the coal and provide additional heat to the top of the furnace. Reduction temperatures range from 1170 to 1200°C to maintain slag duidity. 

Methods exist to make impure iron direcdy from ore, ie, to make DRI without first reducing the ore in the blast furnace to make pig iron which has to be purified in a second step. These processes, generally referred to as direct-reduction processes, are employed where natural gas is readily available for the reduction (see also Ironbydirectreduction). Carbonization of iron ore to make iron carbide as an alternative source of iron units is in its infancy as of the mid-1990s but may grow. 

An alternative commercial form of a metallic mixed lanthanide-containing material is rare-earth siUcide [68476-89-1/, produced in a submerged electric-arc furnace by the direct reduction of ore concentrate, bastnasite, iron ore, and quart2. The resulting alloy is approximately 1/3 mischmetal, 1/3 sihcon, and 1/3 iron. In addition there are some ferro-alloys, such as magnesium—ferrosilicons, derived from cerium concentrate, that contain a few percent of cerium. The consumption of metallic cerium is overwhelmingly in the mixed lanthanide form in ferrous metallurgy. 

The technology for the production of titania slag by direct reduction smelting in electric arc furnaces (particularly for smelting of iron titanates and ilmenites having lower amounts of titania) is very old and the process has been in vogue in Canada, Norway, South Africa,... 

The Alcan (Aluminum Company of Canada) process is based on the direct reduction of the ore to form an aluminum alloy (by carbothermic reduction carried out in an electric arc furnace at about 2000 °C). The alloy is then reacted with aluminum trichloride at 1300 °C to form aluminum monochloride. The monochloride is next contacted with molten droplets of aluminum to form aluminum metal the trichloride is regenerated for further reaction ... 

HyL [Hojalata y Lamina] A direct reduction ironmaking process in which pellets or lumps of ore are reduced in a batch reactor using a mixture of hydrogen and carbon monoxide. Used in countries which have natural gas and cannot afford to invest in blast furnaces. Developed in the 1950s in Mexico by the Hojalata y Lamina Steel Company (now Hylsa) and the MW Kellogg Company, and now operated in nine other countries too. See DR. 

ITmk3 [mark 3 indicates that this is a third generation ironmaking process, marks one and two being the blast furnace and direct reduction] A modification of the Fastmet process, for making molten iron. Pelleted iron ore fines are reduced with a solid reductant. The iron in the reduced pellets separates as molten metal, uncontaminated by gangue. Developed in 1996 by Midrex Corporation and Kobe Steel. Commercialization is expected in 2003. 

Other markets for char include iron, steel, and sili-con/ferro-silicon industries. Char can be used as a reducing agent in direct reduction of iron. Ferro-silicon and metallurgical-grade silicon metal are produced carbothermally in electric furnaces. Silica is mixed with coke, either iron ore or scrap steel (in the case of ferro-silicon), and sawdust or charcoal in order to form a charge. The charge is then processed by the furnace to create the desired product. Char can be substituted for the coke as a source of reducing carbon for this process. Some plants in Norway are known to have used coal-char in the production of silicon-based metal products as late as mid-1990.5 The use of char in this industry is not practiced due to lack of char supply. 

Ironmaking processes, 14 498-521 blast furnace, 14 498-509 direct reduction, 14 509-520 direct smelting, 14 520-521 Iron-manganese-silicon steels, 22 712 Iron melting channel melting furnaces, 12 316... 

Since hydrogen burns cleanly and reacts completely with oxygen to produce water vapor, this makes it more desirable than fossil fuels for essentially all industrial processes. For example, the direct reduction of iron or copper ores could be done with hydrogen rather than smelting by coal or oil in a blast furnace. Hydrogen can be used with conventional vented burners as well as unvented burners. This would allow utilization of almost all of the 30 to 40% of the combustion energy of conventional burners that is lost as vented heat and combustion by-products. 

One of the more important alternatives to the blast furnace for the production of iron is direct reduction of pelletised ore in a shaft reactor. The reducing gas mixture is usually obtained by steam reforming of natural gas and flows upward,countercurrent to the downward flow of solids. Sponge iron obtained by direct reduction may be used directly in arc furnaces for steel production. 

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