The direct reduction of iron is the reduction of iron from iron ore or pellets using gases (CO, H 2 , NH 3 ), solid carbon , gases, and solid carbon together. The process is carried out at a temperature of about 1000 ° C, at which the waste rock is not brought to slagging , impurities ( Si , Mn , P , S ) are not restored, and the metal is clean [1] . The following terms are also found in the literature: metallization (partial metallization) of ores, direct iron production, homeless (off-mine) iron metallurgy, and coke-free iron metallurgy [2] . The product of the process is called Direct Reduced Iron (DRI).
Content
History
Attempts to obtain steel bypassing the blast furnace process were undertaken in the USSR as early as the 1950s [3] . Industrial production of iron directly from ore, bypassing the blast-furnace (using coke) process, appeared in the 1970s . The first plants of direct reduction of iron were inefficient, and the final product had relatively many impurities. The wide distribution of this process began in the 1980s , when the mining and metallurgical complex began to make extensive use of natural gas , which was ideally suited for the direct reduction of iron ore. In addition, in addition to natural gas, in the process of direct reduction of iron, it was possible to use the products of gasification of coal (in particular, brown ), associated gas of oil production and other reducing fuel.
Technological changes that occurred in the 1990s have significantly reduced the capital and energy intensity of various processes of direct reduction of iron, resulting in a new leap in the production of DRI products (from the English Direct Reduction of Iron ) [4] .
Process classification
The most preferred, according to most experts, is the classification by type of product obtained:
- the production of partially metallized (metallization degree 30-50%) materials for blast furnaces;
- production of highly metallized product (degree of metallization 85–95%) in solid form (sponge iron) for remelting in steelmaking units to produce steel ;
- obtaining a metallized product in a plastic state ( crusty iron) for various purposes, including as a variant of pyrometallurgical enrichment of difficultly-rich, poor and complex ores;
- production of liquid metal (iron or intermediate) for remelting in steelmaking furnaces [5] .
Comparison with the domain process
Processing capabilities of poor iron ores
The blast furnace process produces standard iron from iron ores with any iron content, and the iron content only affects the technical and economic indicators of the process. Metallization of poor ores can be effective only for the production of blister iron and liquid metal. Partially metallized materials and sponge iron obtained from poor ores is inefficient. When producing partially metallized materials from poor ores, it is necessary to expend more heat to heat the waste rock and increase the consumption of reducing agent. The production of sponge iron from ores containing more than 2.5–3.0% of waste rock leads to a sharp increase in energy consumption in the smelting process of metallized pellets due to a sharp increase in the amount of slag [5] .
Presence of impurity elements
The blast furnace is able to fully ensure the production of iron-equivalent sulfur. Removal of copper, phosphorus, arsenic from a blast furnace in a blast furnace is impossible. Low-temperature processes for obtaining sponge iron do not ensure the removal of associated elements, that is, all associated elements present in the original ore remain in the spongy iron and enter the steel-smelting unit. The same applies to the production of fritted metal (some degree of sulfur removal is possible here). Obtaining a liquid metal allows you to remove volatile elements (zinc, alkali metals) from the process, and the degree of removal of sulfur, arsenic and phosphorus depends on the mode of the process [6] .
Physical properties of ore
In a blast furnace, only lump iron ore material is processed, and the size of the pieces should not be less than 3-5 mm. Hence the need for the process of sintering ores. This requirement remains mandatory for the production of spongy and frittered iron in shaft and rotary kilns. Low-temperature metallization of crushed ores is possible in special units (for example, fluidized bed apparatus). For most methods of non-domain production of liquid metal, the size of the ore pieces does not matter, therefore, it is possible to exclude from the metallurgical redistribution of expensive sintering processes of small ores [7] .
Use of non-deficient fuels
Modern blast furnaces use only metallurgical coke as fuel. First of all, this is due to the high strength properties of coke, which remain at high temperatures. None of the currently known (2007) types of solid fuels can compete with coke in this regard. Most of the known methods and technologies of iron metallurgy do not require the use of coke as a component of the charge. Reducing gases obtained by various methods (mainly in the production of sponge iron), non-deficient types of coal, brown coal and their products, petroleum products, etc. can be used. [7]
Using new types of energy
Despite the fact that the use of plasma energy, atomic energy and other new energy sources for blast furnace production is not excluded, the greatest effect from their use is observed in the case of the receiving metal. This increases the chances of new technologies in competition with the domain process in the future [8] .
Technology
Sponge iron processes are carried out at moderate temperatures using a gaseous or solid reducing agent in various aggregates: shaft, tubular, tunnel, muffle , reflective , electric heating furnaces, periodic retorts, conveyor machines, fluidized bed reactors , etc. Sometimes these units are connected in complexes in which are most often combined with an electric furnace (electrodomain or arc ) to produce liquid metal (iron and steel ). Most often, sponge iron is used as a high-purity additive to steel scrap . The most stable demand for sponge iron is observed in countries with insufficient blast-furnace production capacity and supply of steel scrap.
The main processes used in working, construction and design facilities for the production of sponge iron are processes using shaft furnaces and batch-retorting. Processes using rotary kilns and solid reducing agents find industrial applications mainly in the processing of metallurgical wastes - dusts and sludges that contain impurities of zinc, lead, etc., as well as complex iron ores (rich in titanium, chromium, nickel, manganese, etc. .) not suitable for use in blast furnaces. The processes in the fluidized bed are less common due to a number of specific features (strict requirements for particle size distribution , gas-dynamic limitations of the existence of the fluidized bed, temperature conditions, etc.).
The processes of metallization in shaft furnaces are in many ways similar to the processes occurring in the blast furnace mine at moderate temperatures. However, there are significant differences: there is no coke in the shaft furnace; hydrogen plays an important role in the reduction of iron oxides; The reducing gas is the only source of heat that provides all the thermal needs of the process.
In the recovery process, the pellets are burned and treated in a shaft furnace with hot gas (solid fuel) conversion products that contain hydrogen . Hydrogen easily restores iron :
- ,
it does not contaminate iron with impurities such as sulfur and phosphorus , which are common impurities in coal . Iron is obtained in solid form and subsequently melted in electric furnaces. To produce a ton of iron by direct reduction from ore, it is necessary to expend about 1000 m 3 of hydrogen.
At its core, the process of direct reduction of iron is the reduction of iron from ores , bypassing the blast furnace process , that is, coke is not involved in the process.
The most mature and widely used process is the Midrex process. Since 1983, four modules of the Midrex metallization process with a total capacity of 1,700 thousand tons of metallized pellets per year have been operating at the Oskolsky Electrometallurgical Combine . The structure of each module includes: shaft furnace metallization, reformer (natural gas conversion reactor); inert gas production system; aspiration system. The water management system, the candle, the control room and the power supply are common to each module pair.
The shaft furnace for metallization consists of a loading (intermediate) bunker; upper dynamic valve with loading distributor and loading pipes; recovery zones; intermediate zone; cooling zones; refractory lining; constantly operating feeders; lower dynamic shutter and pendulum feeder (for unloading the finished product) [9] .
Direct Recovery Products
Sponge Iron
Sponge iron is a product that is obtained as a result of the reduction of iron ore material without melting it at a temperature of less than 1000–1200 ° C. Depending on the type of raw material, sponge iron is a porous piece of reduced ore (rarely sinter ) or pellets, and in some cases metal powder. Since the volume changes of the material are relatively small during restoration, the density of sponge iron is less than the density of the raw materials, and the porosity is high. Usually, the apparent density of lumpy spongy iron is 2–4 g / cm 3 , and the porosity is 50–80%.
In some processes of the reduction of fine ore, scale or concentrate in a fixed bed (for example, in the Hoganes process), simultaneous sintering of the starting powder material occurs. The density of the resulting briquette depends to some extent on the reduction temperature. Due to the low density of the sponge iron, its bulk density is less than scrap, which sometimes leads to the necessity of briquetting (pressing) before melting. Briquetting is carried out on presses of various types at specific pressures of 1–3 tf / cm 2 ; you get the density of the briquettes to 5 g / cm 3 .
The highly developed surface and the high interconnected porosity of sponge iron cause its increased oxidizability during storage and transportation in adverse atmospheric conditions, although the data available on this issue are contradictory. Briquetting reduces oxidability.
The chemical composition of sponge iron is determined mainly by the composition of the raw material. Compared to scrap, it is significantly cleaner in terms of the content of non-ferrous metal impurities. The content of waste rock in it is higher than in the original ore, in proportion to the degree of recovery. Usually raw materials are rich ores or concentrates, therefore, sponge iron is not subjected to additional purification and it contains all the impurities of waste rock raw materials. Upon receipt of sponge iron from poor raw materials, it is subjected to enrichment by magnetic separation .
Sponge iron is used to melt steel (mainly in electric furnaces), cementation of copper (its deposition from sulfuric acid solutions) and the production of iron powder.
Metallized Batch
Metallized charge is called partially reduced iron ore raw material used in a blast furnace and in oxygen converters for cooling smelting (instead of ore and scrap). The degree of reduction of the metallized charge usually does not exceed 80%, while for sponge iron it most often does not fall below 90%.
Bic iron
Critical iron, produced now, differs from that of the crits , which several centuries ago were obtained in crumbled furnaces in the form of large pieces and forged directly into products. Critical iron is currently produced in tubular rotary kilns from poor iron and nickel-iron ores by reducing them at 1100–1200 ° C. It is a fairly small (particle size 1-15 mm) metal particles with mechanical impurities and inclusions of slag . The amount of slag impurities, depending on the grinding scheme and the magnetic separation of the intermediate product, is 10–25%. When processing chrome-nickel ores, the resulting clay contains nickel. Usually, kritsa is also high in phosphorus and sulfur. As a rule, critsu is used in blast furnaces, and in some countries in electric furnaces for steel or ferronickel smelting.
Cast iron or carbon intermediate
Cast iron or carbon semi-finished product is produced in rotary kilns or in electric furnaces directly connected to the reduction furnace, where the reducing agent is solid fuel. Cast iron, obtained by non-domain methods, does not differ from the usual blast furnace ; in some cases, receive a semi-product with a lower content of some impurities than in iron. The redistribution of pig iron and semi-finished products to steel is carried out in known steel-smelting units without difficulty, and in the case of intermediate products - with somewhat lower costs than the redistribution of blast furnace iron [10] .
Practical processes and their aggregates
- Hard Recovery [11]
Gas reduction
- Raw materials (Oxidized pellets and lump ore) → Shaft furnaces (Purofer, Midrex, Arex, Hyl III, Hyl ZR)
- Raw Materials (Oxidized Pellets and Lump Ore) → Retorts (Hyl I)
- Raw materials (ore fines, waste) → Fluidized bed reactors (Fior, Finmet, Cincored, Spirex, Iron Carbide)
Coal Recovery
- Tube furnaces (OSI, TDR, DRC, Ghaem, SL / RN, Jindal, Siil, Codir)
- Rotary Hearth Furnaces (Comet, Fastmet, Inmetco, Dry Iron, Iron Dinamics)
- Fluidized bed reactor (Circofer)
- Multiple rotary kiln (Primus)
- Liquid Phase Recovery [11]
- Processes with melting generator ( , Finex)
- Liquid bath processes (DIOS, Romelt (also known as PZHV), Hismelt, AusIron, Tecnored, AISI Direct, Ironmaking, CCF)
- Jet-emission processes (IRSID, BISRA, SIR)
- Other processes
- Dored, Krupp-Renn, Eketorp-Wallach, Bush method, process in a boiling Kawasaki slag layer, COIN [12]
See also
- Hot briquetted iron
- Oskol Electrometallurgical Plant
Links
Notes
- ↑ Yusfin, 1994 , p. 178.
- ↑ Yusfin, Pashkov, 2007 , p. 5-6.
- ↑ Pegushin. On the threshold of the future
- ↑ Yusfin, 1994 , p. 4-5.
- ↑ 1 2 Yusfin, Pashkov, 2007 , p. 7
- ↑ Yusfin, Pashkov, 2007 , p. 7-8.
- ↑ 1 2 Yusfin, Pashkov, 2007 , p. eight.
- ↑ Yusfin, Pashkov, 2007 , p. 8-9.
- ↑ Yusfin, 1994 , p. 180-181.
- ↑ Knyazev, 1972 , p. 12-13.
- ↑ 1 2 Rybenko, 2018 , p. 18.
- ↑ Hodosov, 2016 , p. 24
Literature
- Yusfin Yu. S. , Gimmelfarb A. A., Pashkov N. F. New metal production processes. - Moscow: Metallurgy, 1994. - 320 p. - ISBN 5-229-02229-X .
- Khodosov I.Ye. Development and research of the processes of obtaining metallized materials using the raw material base of Kuzbass. Abstract of dissertation for the degree of candidate of technical sciences . - Novokuzets: as a manuscript, 2016. - 164 p.
- Knyazev V.F., Gimmelfarb A.I., Nemenov A.M. Beskox Copper Iron Metallurgy. - Moscow: Metallurgy, 1972. - 272 p.
- Yusfin Yu.S. , Pashkov N.F. Iron Metallurgy: a textbook for universities. - Moscow: Academic Book ICC, 2007. - 464 p. - ISBN 978-5-94628-246-8 .
- Rybenko I.A. Development of theoretical foundations and development of resource-saving technologies for direct reduction of metals using the method and tool system for modeling and optimization. Abstract of dissertation for the degree of Doctor of Technical Sciences . - Novokuzets: as a manuscript, 2018. - 308 p.