Steelmaking
Basic oxygen steelmaking uses liquid pig-iron from a blast furnace and scrap steel as the main feed materials.
Electric arc furnace (EAF) steelmaking uses scrap steel or direct reduced iron (DRI).
Cast iron is a hard, brittle material that is difficult to work, whereas steel is malleable, relatively easily formed and versatile.
Early modern methods of producing steel were often labor-intensive and highly skilled arts.
The Bessemer process and subsequent developments allowed steel to become integral to the global economy.
[5][6] Hartwell wrote that the Song dynasty (960–1279 CE) innovated a "partial decarbonization" method of repeated forging of cast iron under a cold blast.
[7] Hartwell stated that the earliest center where this was practiced was perhaps the great iron-production district along the Henan–Hebei border during the 11th century.
High-quality steel was also made by the reverse process of adding carbon to carbon-free wrought iron, usually imported from Sweden.
The most difficult and laborious part of the process was the production of wrought iron in finery forges in Sweden.
In 1740, Benjamin Huntsman developed the crucible technique for steel manufacture at his workshop in Handsworth, England.
[10] Adventurer Johan Albrecht de Mandelslo described the process in a book published in English in 1669.
He wrote, "They have, among others, particular invention for the melting of iron, without the using of fire, casting it into a tun done about on the inside without about half a foot of earth, where they keep it with continual blowing, take it out by ladles full, to give it what form they please."
The Bessemer process allowed steel to be produced without fuel, using the iron's impurities to create the necessary heat.
Secondary steelmaking involves adding or removing other elements such as alloying agents and dissolved gases.
[13] Basic oxygen steelmaking (BOS)involves melting carbon-rich pig iron and converting it into steel.
Refractories (materials resistant to decomposition under high temperatures)—calcium oxide and magnesium oxide—line the smelting vessel to withstand the heat, corrosive molten metal, and slag.
[15] Electric arc furnaces make steel from scrap or direct reduced iron.
Skipping this preparatory step makes the HIsarna process more energy-efficient and lowers the carbon footprint.
Tight control of ladle metallurgy produces high grades of steel with narrow tolerances.
[22] The bulk of these emissions are from the industrial process in which coal provides the carbon that binds with the oxygen from the iron ore in a blast furnace in:[23] Additional CO2 emissions result from mining, refining and shipping ore, basic oxygen steelmaking, calcination, and the hot blast.
[24] Coal and iron ore mining are energy intensive, and damage their surroundings, leaving pollution, biodiversity loss, deforestation, and greenhouse gas emissions behind.
In this step, the oxygen binds with the undesired carbon, carrying it away in the form of CO2 gas, an additional emission source.
After this step, the carbon content in the pig iron is lowered sufficiently to obtain steel.
[26] It acts as a chemical flux, removing impurities (such as sulfur or phosphorus (e.g. apatite or fluorapatite)[27]) in the form of slag and lowers CO2 emissions according to reactions such as: SiO2 + CaO → CaSiO3 This use of limestone to provide a flux occurs both in the blast furnace (to obtain pig iron) and in the basic oxygen steel making (to obtain steel).
Hot blast air is typically heated by burning fossil fuels, an additional emission source.
[33] European projects from HYBRIT, LKAB, Voestalpine, and ThyssenKrupp are pursuing strategies to reduce emissions.
As of 2022[update], separating the CO2 from other gases and components in the system, and the high cost of the equipment and infrastructure changes needed, have prevented adoption, but the emission reduction potential has been estimated to be up to 65% to 80%.
[40] For the European Union, it is estimated that the hydrogen demand for HDR would require 180 GW of renewable capacity.
[citation needed] The HIsarna ironmaking process is a way of producing iron in a cyclone converter furnace without the pre-processing steps of choking/agglomeration, which reduces the CO2 emissions by around 20%.
