Direct reduced iron

Last updated
Hot-briquetted iron Hot-briquetted iron.JPG
Hot-briquetted iron

Direct reduced iron (DRI), also called sponge iron, [1] is produced from the direct reduction of iron ore (in the form of lumps, pellets, or fines) into iron by a reducing gas which either contains elemental carbon (produced from natural gas or coal) or hydrogen. When hydrogen is used as the reducing gas there are no greenhouse gases produced. Many ores are suitable for direct reduction.

Contents

Direct reduction refers to solid-state processes which reduce iron oxides to metallic iron at temperatures below the melting point of iron. Reduced iron derives its name from these processes, one example being heating iron ore in a furnace at a high temperature of 800 to 1,200 °C (1,470 to 2,190 °F) in the presence of the reducing gas syngas, a mixture of hydrogen and carbon monoxide, or pure hydrogen. [2]

Production of direct-reduced iron and breakdown by process DRI evolution.svg
Production of direct-reduced iron and breakdown by process

Process

Direct reduction processes can be divided roughly into two categories: gas-based and coal-based. In both cases, the objective of the process is to remove the oxygen contained in various forms of iron ore (sized ore, concentrates, pellets, mill scale, furnace dust, etc.) in order to convert the ore to metallic iron, without melting it (below 1,200 °C (2,190 °F)).

The direct reduction process is comparatively energy efficient. Steel made using DRI requires significantly less fuel, in that a traditional blast furnace is not needed. DRI is most commonly made into steel using electric arc furnaces to take advantage of the heat produced by the DRI product. [3]

Benefits

Direct reduction processes were developed to overcome the difficulties of conventional blast furnaces. DRI plants need not be part of an integrated steel plant, as is characteristic of blast furnaces. The initial capital investment and operating costs of direct reduction plants are lower than integrated steel plants and are more suitable for developing countries where supplies of high grade coking coal are limited, but where steel scrap is generally available for recycling.[ citation needed ] Many other countries use variants of the process.

Factors that help make DRI economical:

Problems

Direct reduced iron is highly susceptible to oxidation and rusting if left unprotected, and is normally quickly processed further to steel. [5] The bulk iron[ page needed ] can also catch fire since it is pyrophoric. [6] Unlike blast furnace pig iron, which is almost pure metal, DRI contains some siliceous gangue (if made from scrap, not from new iron from direct reduced iron with natural gas), which needs to be removed in the steel-making process.

History

Producing sponge iron and then working it was the earliest method used to obtain iron in the Middle East, Egypt, and Europe, where it remained in use until at least the 16th century.

The advantage of the bloomery technique is that iron can be obtained at a lower furnace temperature, only about 1,100 °C or so. The disadvantage, relative to a blast furnace, is that only small quantities can be made at a time.

Chemistry

The following reactions successively convert hematite (from iron ore) into magnetite, magnetite into ferrous oxide, and ferrous oxide into iron by reduction with carbon monoxide or hydrogen. [7]

Carburizing produces cementite (Fe3C):

Economy

India is the world’s largest producer of direct-reduced iron. [8]

Uses

Sponge iron is not useful by itself, but can be processed to create wrought iron or steel. The sponge is removed from the furnace, called a bloomery, and repeatedly beaten with heavy hammers and folded over to remove the slag, oxidize any carbon or carbide, and weld the iron together. This treatment usually creates wrought iron with about three percent slag and a fraction of a percent of other impurities. Further treatment may add controlled amounts of carbon, allowing various kinds of heat treatment (e.g. "steeling").

Today, sponge iron is created by reducing iron ore without melting it. This makes for an energy-efficient feedstock for specialty steel manufacturers which used to rely upon scrap metal.

Food

Hydrogen-reduced iron is used as a source of food-grade iron powder, for food fortification and for oxygen scavenging. This elemental form is not absorbed as well as ferrous forms, [9] but the oxygen-scavenging function keeps it attractive. Purity standards for this use are established in 1977. [10]

See also

Related Research Articles

<span class="mw-page-title-main">Haber process</span> Main process of ammonia production

The Haber process, also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia. The German chemists Fritz Haber and Carl Bosch developed it in the first decade of the 20th century. The process converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using an iron metal catalyst under high temperatures and pressures. This reaction is slightly exothermic (i.e. it releases energy), meaning that the reaction is favoured at lower temperatures and higher pressures. It decreases entropy, complicating the process. Hydrogen is produced via steam reforming, followed by an iterative closed cycle to react hydrogen with nitrogen to produce ammonia.

<span class="mw-page-title-main">Iron</span> Chemical element, symbol Fe and atomic number 26

Iron is a chemical element; it has symbol Fe and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, just ahead of oxygen, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust, being mainly deposited by meteorites in its metallic state, with its ores also being found there.

<span class="mw-page-title-main">Electrolysis</span> Technique in chemistry and manufacturing

In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential. The word "lysis" means to separate or break, so in terms, electrolysis would mean "breakdown via electricity".

<span class="mw-page-title-main">Coke (fuel)</span> Hard fuel containing mostly carbon

Coke is a grey, hard, and porous coal-based fuel with a high carbon content and few impurities, made by heating coal or oil in the absence of air—a destructive distillation process. It is an important industrial product, used mainly in iron ore smelting, but also as a fuel in stoves and forges when air pollution is a concern.

<span class="mw-page-title-main">Steelmaking</span> Process for producing steel from iron ore and scrap

Steelmaking is the process of producing steel from iron ore and/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon are removed from the sourced iron, and alloying elements such as manganese, nickel, chromium, carbon and vanadium are added to produce different grades of steel.

Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.

<span class="mw-page-title-main">Blast furnace</span> Type of furnace used for smelting to produce industrial metals

A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. Blast refers to the combustion air being supplied above atmospheric pressure.

<span class="mw-page-title-main">Industrial processes</span> Process of producing goods

Industrial processes are procedures involving chemical, physical, electrical, or mechanical steps to aid in the manufacturing of an item or items, usually carried out on a very large scale. Industrial processes are the key components of heavy industry.

<span class="mw-page-title-main">Iron(II,III) oxide</span> Chemical compound

Iron(II,III) oxide, or black iron oxide, is the chemical compound with formula Fe3O4. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe2O3) which also occurs naturally as the mineral hematite. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙ Fe2O3. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is ferrimagnetic, but is sometimes incorrectly described as ferromagnetic. Its most extensive use is as a black pigment (see: Mars Black). For this purpose, it is synthesized rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.

Decarburization is the process of decreasing carbon content, which is the opposite of carburization.

An Ellingham diagram is a graph showing the temperature dependence of the stability of compounds. This analysis is usually used to evaluate the ease of reduction of metal oxides and sulfides. These diagrams were first constructed by Harold Ellingham in 1944. In metallurgy, the Ellingham diagram is used to predict the equilibrium temperature between a metal, its oxide, and oxygen — and by extension, reactions of a metal with sulfur, nitrogen, and other non-metals. The diagrams are useful in predicting the conditions under which an ore will be reduced to its metal. The analysis is thermodynamic in nature and ignores reaction kinetics. Thus, processes that are predicted to be favourable by the Ellingham diagram can still be slow.

<span class="mw-page-title-main">Electrometallurgy</span>

Electrometallurgy is a method in metallurgy that uses electrical energy to produce metals by electrolysis. It is usually the last stage in metal production and is therefore preceded by pyrometallurgical or hydrometallurgical operations. The electrolysis can be done on a molten metal oxide which is used for example to produce aluminium from aluminium oxide via the Hall-Hérault process. Electrolysis can be used as a final refining stage in pyrometallurgical metal production (electrorefining) and it is also used for reduction of a metal from an aqueous metal salt solution produced by hydrometallurgy (electrowinning).

<span class="mw-page-title-main">Iron oxide cycle</span>

For chemical reactions, the iron oxide cycle (Fe3O4/FeO) is the original two-step thermochemical cycle proposed for use for hydrogen production. It is based on the reduction and subsequent oxidation of iron ions, particularly the reduction and oxidation between Fe3+ and Fe2+. The ferrites, or iron oxide, begins in the form of a spinel and depending on the reaction conditions, dopant metals and support material forms either Wüstites or different spinels.

<span class="mw-page-title-main">Schikorr reaction</span> Transformation of Fe(OH)2 into Fe3O4 with hydrogen release

The Schikorr reaction formally describes the conversion of the iron(II) hydroxide (Fe(OH)2) into iron(II,III) oxide (Fe3O4). This transformation reaction was first studied by Gerhard Schikorr. The global reaction follows:

The Corex Process is a smelting reduction process created by Primetals as a more environmentally friendly alternative to the blast furnace. Presently, the majority of steel production is through the blast furnace which has to rely on coking coal. That is coal which has been cooked in order to remove impurities so that it is superior to coal. The blast furnace requires a sinter plant in order to prepare the iron ore for reduction. Unlike the blast furnace, smelting reduction processes are typical smaller and use coal and oxygen directly to reduce iron ore into a usable product. Smelting reduction processes come in two basic varieties, two-stage or single-stage. In a single-stage system the iron ore is both reduced and melted in the same container. In a two-stage process, like Corex, the ore is reduced in one shaft and melted and purified in another. Plants using the Corex process have been put use in areas such as South Africa, India, and China. First COREX process was installed in 1988 at South Africa.

Chemical looping reforming (CLR) and gasification (CLG) are the operations that involve the use of gaseous carbonaceous feedstock and solid carbonaceous feedstock, respectively, in their conversion to syngas in the chemical looping scheme. The typical gaseous carbonaceous feedstocks used are natural gas and reducing tail gas, while the typical solid carbonaceous feedstocks used are coal and biomass. The feedstocks are partially oxidized to generate syngas using metal oxide oxygen carriers as the oxidant. The reduced metal oxide is then oxidized in the regeneration step using air. The syngas is an important intermediate for generation of such diverse products as electricity, chemicals, hydrogen, and liquid fuels.

Adrien C. B. Chenot was a French engineer best known for his inventions in metallurgy as well as his research on manufactured gases. He is notably the inventor of one of the first modern methods of direct reduction of iron ore, based on the use of coal reacting with the ore in retorts. He exhibited the first samples of pre-reduced iron ore at the Lisbon Universal Exhibition of 1849, and was awarded the "Grandes Medailles d'Or" at the Paris Universal Exposition of 1855.

<span class="mw-page-title-main">Direct reduction</span> A set of processes for obtaining iron from iron ore

In the iron and steel industry, direct reduction is a set of processes for obtaining iron from iron ore, by reducing iron oxides without melting the metal. The resulting product is pre-reduced iron ore.

Direct reduction is the fraction of iron oxide reduction that occurs in a blast furnace due to the presence of coke carbon, while the remainder - indirect reduction - consists mainly of carbon monoxide from coke combustion.

<span class="mw-page-title-main">Krupp–Renn Process</span> A direct reduction steelmaking process used from the 1930s to the 1970s.

The Krupp–Renn process was a direct reduction steelmaking process used from the 1930s to the 1970s. It used a rotary furnace and was one of the few technically and commercially successful direct reduction processes in the world, acting as an alternative to blast furnaces due to their coke consumption. The Krupp-Renn process consumed mainly hard coal and had the unique characteristic of partially melting the charge. This method is beneficial for processing low-quality or non-melting ores, as their waste material forms a protective layer that can be easily separated from the iron. It generates Luppen, nodules of pre-reduced iron ore, which can be easily melted down.

References

Notes
  1. "What is direct reduced iron (DRI)? definition and meaning". Businessdictionary.com. Retrieved 2011-07-11.
  2. "Direct reduced iron (DRI)". International Iron Metallics Association. 14 November 2019.
  3. R. J. Fruehan, et al. (2000). Theoretical Minimum Energies to Produce Steel (for Selected Conditions)
  4. "Steel making today and tomorrow". Archived from the original on 20 December 2020.
  5. "Direct Reduced Iron (DRI) - Cargo Handbook - the world's largest cargo transport guidelines website". www.cargohandbook.com. Retrieved 2022-06-18.
  6. Hattwig, Martin; Steen, Henrikus (2004), Handbook of explosion prevention and protection, Wiley-VCH, pp. 269–270, ISBN   978-3-527-30718-0. (dead link 24 October 2019)
  7. "MIDREX" (PDF).
  8. "2022 World Direct Reduction Statistics" (PDF). Midrex Technologies. 2021. Retrieved 25 January 2021.
  9. Zimmermann, Michael B.; Winichagoon, Pattanee; Gowachirapant, Sueppong; Hess, Sonja Y.; Harrington, Mary; Chavasit, Visith; Lynch, Sean R.; Hurrell, Richard F. (2005). "Comparison of the efficacy of wheat-based snacks fortified with ferrous sulfate, electrolytic iron, or hydrogen-reduced elemental iron: Randomized, double-blind, controlled trial in Thai women". The American Journal of Clinical Nutrition. 82 (6): 1276–1282. doi: 10.1093/ajcn/82.6.1276 . PMID   16332661.
  10. Shah, Bhagwan G.; Giroux, Alexandre; Belonje, Bartholomeus (1977). "Specifications for reduced iron as a food additive". Journal of Agricultural and Food Chemistry. 25 (3): 592–594. doi:10.1021/jf60211a044. PMID   858856.
Bibliography