{{Short description|Type of furnace used for smelting to produce industrial metals}}
{{Use dmy dates|date=December 2024}}
[[File:Alto Horno, Puerto de Sagunto, España, 2015-01-04, DD 91.JPG|thumb|upright=1.1|Former [[Altos Hornos del Mediterráneo|AHM]] blast furnace in Port of Sagunt, [[Valencia]], Spain]]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]].<ref>{{Cite web |date=11 October 2024 |title=Blast furnace {{!}} Definition, Temperature, Diagrams, & Facts {{!}} Britannica |url=https://www.britannica.com/technology/blast-furnace |access-date=8 November 2024 |website=www.britannica.com |language=en}}</ref>

In a blast furnace, fuel ([[coke (fuel)|coke]]), [[ores]], and [[Flux (metallurgy)|flux]] ([[limestone]]) are continuously supplied through the top of the furnace, while a hot blast of (sometimes [[oxygen]]-enriched) [[air]] is blown into the lower section of the furnace through a series of pipes called [[tuyeres]], so that the [[#Process engineering and chemistry|chemical reactions]] take place throughout the furnace as the material falls downward. The end products are usually molten metal and [[slag]] phases tapped from the bottom, and [[flue gas]]es exiting from the top.<ref>{{cite journal |last1=Schmult |first1=Brian |title=Evolution of the Hopewell Furnace Blast Machinery |journal=IA. The Journal of the Society for Industrial Archeology |date=2016 |volume=42 |issue=2 |pages=5–22}}</ref> The downward flow of the ore along with the flux in contact with an upflow of hot, [[carbon monoxide]]-rich combustion gases is a [[countercurrent exchange]] and chemical reaction process.<ref>{{cite journal |last1=Spirin |first1=N A |last2=Yaroshenko |first2=Yu G |last3=Lavrov |first3=V V |title=Development of heat-transfer circuits in the blast furnace |journal=IOP Conference Series: Materials Science and Engineering |date=September 2016 |volume=150 |issue=1 |article-number=012022 |doi=10.1088/1757-899X/150/1/012022 |bibcode=2016MS&E..150a2022S |doi-access=free }}</ref>

In contrast, air furnaces (such as [[reverberatory furnace]]s) are naturally aspirated, usually by the [[convection]] of hot gases in a [[Chimney-flue|chimney flue]]. According to this broad definition, [[bloomery|bloomeries]] for iron, [[blowing house]]s for [[tin]], and [[smelt mill]]s for [[lead]] would be classified as blast furnaces. However, the term has usually been limited to those used for smelting [[iron ore]] to produce [[pig iron]], an intermediate material used in the production of commercial iron and [[steel]], and the shaft furnaces used in combination with [[sinter plant]]s in [[base metals]] smelting.<ref>P J Wand, "Copper smelting at Electrolytic Refining and Smelting Company of Australia Ltd., Port Kembla, N.S.W.", in: '' Mining and Metallurgical Practices in Australasia: The Sir Maurice Mawby Memorial Volume'', Ed J T Woodcock (The Australasian Institute of Mining and Metallurgy: Melbourne, 1980) 335–340.</ref><ref>R J Sinclair, ''The Extractive Metallurgy of Lead'' (The Australasian Institute of Mining and Metallurgy: Melbourne, 2009), 9–12.</ref>

Blast furnaces are estimated to have been responsible for over 4% of global [[greenhouse gas emissions]] between 1900 and 2015, and are difficult to decarbonize.<ref name=":0">{{Cite news |last1=Pooler |first1=Michael |date=January 2019 |title=Cleaning up steel is key to tackling climate change |url=https://www.ft.com/content/3bcbcb60-037f-11e9-99df-6183d3002ee1 |url-access=subscription |url-status=live |archive-url=https://ghostarchive.org/archive/20221210/https://www.ft.com/content/3bcbcb60-037f-11e9-99df-6183d3002ee1 |archive-date=10 December 2022 |access-date=7 July 2021 |website=[[Financial Times]]}}</ref>

==Process engineering and chemistry==
[[File:VysokePece1.jpg|thumb|upright=1.1|Blast furnaces of [[Třinec Iron and Steel Works]] in [[Czech Republic]]]]
[[File:Geography of Ohio - DPLA - aaba7b3295ff6973b6fd1e23e33cde14 (page 111) (cropped2).jpg|thumb|upright=1.1|Charcoal burning iron blast furnace in [[Jackson County, Ohio]], 1923]]
[[File:Blast Furnace Reactions.jpg|thumb|upright=1.1|Rising [[carbon monoxide]] reduces [[iron oxide]]s to pure [[iron]] through a series of reactions that occur at different areas within a blast furnace.]]
Blast furnaces operate on the principle of [[redox|chemical reduction]] whereby carbon monoxide converts iron oxides to elemental iron.

Blast furnaces differ from [[bloomery|bloomeries]] and [[reverberatory furnace]]s in that in a blast furnace, flue gas is in direct contact with the ore and iron, allowing carbon monoxide to diffuse into the ore and reduce the iron oxide. The blast furnace operates as a [[countercurrent exchange]] process whereas a bloomery does not. Another difference is that bloomeries operate as a batch process whereas blast furnaces [[Continuous production|operate continuously]] for long periods. Continuous operation is also preferred because blast furnaces are difficult to start and stop. Also, the carbon in pig iron lowers the melting point below that of steel or pure iron; in contrast, iron does not melt in a bloomery.

[[Silica]] has to be removed from the pig iron. It reacts with [[calcium oxide]] (burned limestone) and forms silicates, which float to the surface of the molten pig iron as slag. Historically, iron was produced with charcoal to prevent sulfur contamination.<ref name=QS>{{cite book |last1=Skrabec |first1=Quentin R. |title=The Metallurgic Age: The Victorian Flowering of Invention and Industrial Science |date=24 January 2015 |publisher=McFarland & Company |location=Jefferson, NC |isbn=978-1-4766-1113-6 |page=53 |url=https://books.google.com/books?id=CAwyBgAAQBAJ&dq=iron+smelting+charcoal&pg=PA53 |language=en}}</ref>

In a blast furnace, a downward-moving column of ore, flux, [[coke (fuel)|coke]] (or charcoal<ref name=QS/>) and their reaction products must be sufficiently porous for the flue gas to pass through, upwards. To ensure this permeability the particle size of the coke or charcoal is of great relevance. Therefore, the coke must be strong enough so it will not be crushed by the weight of the material above it. Besides the physical strength of its particles, the coke must also be low in sulfur, [[phosphorus]], and ash.<ref>{{Ullmann |doi=10.1002/14356007.a14_461.pub2|title=Iron|year=2006|last1=Oeters|first1=Franz|last2=Ottow|first2=Manfred|last3=Meiler|first3=Heinrich|last4=Lüngen|first4=Hans Bodo|last5=Koltermann|first5=Manfred|last6=Buhr|first6=Andreas|last7=Yagi|first7=Jun-Ichiro|last8=Formanek|first8=Lothar|last9=Rose|first9=Fritz|last10=Flickenschild|first10=Jürgen|last11=Hauk|first11=Rolf|last12=Steffen|first12=Rolf|last13=Skroch|first13=Reiner|last14=Mayer-Schwinning|first14=Gernot|last15=Bünnagel|first15=Heinz-Lothar|last16=Hoff|first16=Hans-Georg}}</ref>

The main chemical reaction producing the molten iron is:
:Fe<sub>2</sub>O<sub>3</sub> + 3CO → 2Fe + 3CO<sub>2</sub><ref name="Formulae">{{cite web | title = Blast Furnace | publisher = Science Aid | access-date = 30 December 2007 | url = http://www.scienceaid.co.uk/chemistry/industrial/blastfurnace.html | archive-url = https://web.archive.org/web/20071217143213/http://www.scienceaid.co.uk/chemistry/industrial/blastfurnace.html | archive-date = 17 December 2007}}</ref>

This reaction might be divided into multiple steps, with the first being that preheated air blown into the furnace reacts with the carbon in the form of coke to produce [[carbon monoxide]] and heat:

:2 C<sub>(s)</sub> + O<sub>2(g)</sub> → 2 CO<sub>(g)</sub><ref name="InorganicChemistry">{{Citation | last = Rayner-Canham & Overton | title = Descriptive Inorganic Chemistry, Fourth Edition | place = New York | publisher = W. H. Freeman and Company | pages = 534–535 | year = 2006 | isbn = 978-0-7167-7695-6 }}</ref>

Hot carbon monoxide is the [[reducing agent]] for the iron ore and reacts with the [[iron oxide]] to produce molten iron and [[carbon dioxide]]. Depending on the temperature in the different parts of the furnace (warmest at the bottom) the iron is reduced in several steps. At the top, where the temperature usually is in the range between {{convert|200|and|700|C}}, the iron oxide is partially reduced to iron(II,III) oxide, Fe<sub>3</sub>O<sub>4</sub>.

:3 Fe<sub>2</sub>O<sub>3(s)</sub> + CO<sub>(g)</sub> → 2 Fe<sub>3</sub>O<sub>4(s)</sub> + CO<sub>2(g)</sub><ref name="InorganicChemistry"/>

The temperatures {{Convert|850|C}}, further down in the furnace, the iron(II,III) is reduced further to iron(II) oxide:

:Fe<sub>3</sub>O<sub>4(s)</sub> + CO<sub>(g)</sub> → 3 FeO<sub>(s)</sub> + CO<sub>2(g)</sub><ref name="InorganicChemistry"/>

Hot carbon dioxide, unreacted carbon monoxide, and [[nitrogen]] from the air pass up through the furnace as fresh feed material travels down into the reaction zone. As the material travels downward, the counter-current gases both preheat the feed charge and decompose the limestone to [[calcium oxide]] and carbon dioxide:

:CaCO<sub>3(s)</sub> → CaO<sub>(s)</sub> + CO<sub>2(g)</sub><ref name="InorganicChemistry"/>

The calcium oxide formed by decomposition reacts with various acidic impurities in the iron (notably [[silica]]), to form a [[fayalite|fayalitic]] slag which is essentially [[calcium silicate]], {{chem|[[Calcium|Ca]]|[[Silicon|Si]]|[[Oxygen|O]]|3}}:<ref name="Formulae"/>
:SiO<sub>2</sub> + CaO → CaSiO<sub>3</sub>{{sfn|Ganguly|2011}}<ref name="openstax">{{Cite book|last1=Flowers|first1=Paul|url=https://openstax.org/books/chemistry/pages/1-introduction|title=Chemistry|last2=Robinson|first2=William R.|last3=Langley|first3=Richard|last4=Theopold|first4=Klaus|publisher=[[OpenStax]]|year=2015|isbn=978-1-938168-39-0|language=en|section=Occurrence, Preparation, and Properties of Transition Metals and Their Compounds|section-url=https://openstax.org/books/chemistry/pages/19-1-occurrence-preparation-and-properties-of-transition-metals-and-their-compounds}}</ref>

As the iron(II) oxide moves down to the area with higher temperatures, ranging up to {{convert|1200|C}} degrees, it is reduced further to iron metal:

:FeO<sub>(s)</sub> + CO<sub>(g)</sub> → Fe<sub>(s)</sub> + CO<sub>2(g)</sub><ref name="InorganicChemistry"/>

The carbon dioxide formed in this process is re-reduced to carbon monoxide by the [[coke (fuel)|coke]]:

:C<sub>(s)</sub> + CO<sub>2(g)</sub> → 2 CO<sub>(g)</sub><ref name="InorganicChemistry"/>

The temperature-dependent equilibrium controlling the gas atmosphere in the furnace is called the [[Boudouard reaction]]:

::2CO {{eqm}} CO<sub>2</sub> + C

The [[pig iron]] produced by the blast furnace has a relatively high carbon content of around 4–5% and usually contains too much sulphur, making it very brittle, and of limited immediate commercial use. Some pig iron is used to make [[cast iron]]. The majority of pig iron produced by blast furnaces undergoes further processing to reduce the carbon and sulphur content and produce various grades of steel used for construction materials, automobiles, ships and machinery. Desulphurisation usually takes place during the transport of the liquid steel to the steelworks. This is done by adding ''calcium oxide'', which reacts with the [[iron sulfide]] contained in the pig iron to form [[calcium sulfide]] (called ''lime desulfurization'').<ref>{{Cite web|url=https://www.tec-science.com/material-science/steel-making/from-pig-iron-to-crude-steel/|title=From pig iron to crude steel|last=tec-science|date=21 June 2018|website=tec-science|language=en-US|access-date=2 November 2019}}</ref> In a further process step, the so-called [[Basic oxygen furnace|basic oxygen steelmaking]], the carbon is oxidized by blowing oxygen onto the liquid pig iron to form ''crude steel''.

==History==
{{See also|History of ferrous metallurgy}}
[[File:Yuan Dynasty - waterwheels and smelting.png|thumb|upright=1.1|An illustration of furnace bellows operated by [[waterwheel]]s from the ''Nong Shu'', by [[Wang Zhen (inventor)|Wang Zhen]] in 1313 during China's [[Yuan dynasty]]]]
[[File:Chinese Fining and Blast Furnace.jpg|thumb|upright=1.1|A Chinese fining and blast furnace in ''[[Tiangong Kaiwu]]'', 1637]]
Cast iron has been found in [[China]] dating to the 5th century BC, but the earliest extant blast furnaces in China date to the 1st century AD and in the West from the [[High Middle Ages]].<ref name="Golas1999">{{cite book|author=Peter J. Golas|title=Science and Civilisation in China: Volume 5, Chemistry and Chemical Technology, Part 13, Mining|url=https://books.google.com/books?id=TSiII7s2wLkC&pg=PA152|year=1999|publisher=Cambridge University Press|isbn=978-0-521-58000-7|page=152|quote=...earliest blast furnace discovered in China from about the first century AD}}</ref> They spread from the region around [[Namur (province)|Namur]] in [[Wallonia]] (Belgium) in the late 15th century, being introduced to England in 1491. The fuel used in these was invariably charcoal. The successful substitution of coke for charcoal is widely attributed to British inventor [[Abraham Darby I|Abraham Darby]] in 1709. The efficiency of the process was further enhanced by the practice of preheating the combustion air ([[hot blast]]), patented by British inventor [[James Beaumont Neilson]] in 1828.<ref>Simcoe, Charles R. "The Age of Steel: Part II." Advanced Materials & Processes 172.4 (2014): 32–33. Academic Search Premier.</ref>

=== China ===
{{See also|History of metallurgy in China}}
Archaeological demonstrates that iron-smelting techniques and bloomeries were brought to China by nomadic peoples around 800 BC. [[Wrought iron]] artifacts were originally only found in the northwest, but by the 6th century BC, luxury items such as swords and knives were widespread.<ref>"The Earliest Use of Iron in China" by Donald B. Wagner in ''Metals in Antiquity'', by Suzanne M. M. Young, A. Mark Pollard, Paul Budd and Robert A. Ixer (BAR International Series, 792), Oxford: [[Archaeopress]], 1999, pp. 1–9.</ref> [[Bloomery]] iron originally co-existed with blast furnaces and c[[Cast iron|ast iron]], which were invented shortly after wrought iron technology entered China. Cast iron pieces have been found alongside wrought iron in [[Shanxi Province]] dating to the 9th-8th centuries BC, however it is uncertain if these cast iron pieces were accidental byproducts of a smelting process. By the early [[Han dynasty|Han period]], bloomery production appears to have largely disappeared in China. Wagner argues that its disappearance is more likely to have resulted from Han state control than from competition with blast furnace technology.<ref>{{Cite book |last=Wagner |first=Donald B. |title=Science and Civilisation in China: Vol. 5, Part 11: Ferrous Metallurgy |date=2008 |publisher=Cambridge University Press |isbn=978-0-521-87566-0 |pages=105-114, 246-247}}</ref>

Compared to [[bloomery]] iron, China's development of the blast furnace significantly increased iron production capacity. While [[cast iron]] is more brittle this enabled for mass production of implements such as agricultural tools, while [[decarburization]] processes such as [[Finery forge|fining]] were used to convert cast iron into [[wrought iron]] which was were preferred for weapons. Nearly all Han period weapons are made of wrought iron or steel, with the exception of axe-heads, of which many are made of cast iron.<ref>{{Cite book |last=Wagner |first=Donald B. |title=Science and Civilisation in China: Volume 5, Chemistry and Chemical Technology, Part 11, Ferrous Metallurgy |date=2008 |publisher=Cambridge University Press |isbn=978-0-521-87566-0 |pages=1-2, 159-169}}</ref>

Although [[cast iron]] farm tools and weapons were widespread in China by the [[5th century BC]],<ref name="casting">{{cite web |last1=Rubin |first1=Han |last2=Jianli |first2=Chen |title=Casting iron in ancient China |url=https://archaeology.pku.edu.cn/2013Casting-iron-in-ancient-China.pdf |publisher=[[University of Peking]] |access-date=22 May 2025}}</ref> the earliest excavated Chinese blast furnaces are Han-period examples dating from at least the [[1st century BC]].<ref>{{Cite book |last=Science and Civilisation in China, Vol. 5, Part 11: Ferrous Metallurgy (Cambridge University Press, 2008). Best pages p. 113 |first=Donald B |title=Science and Civilisation in China, Vol. 5, Part 11: Ferrous Metallurgy |date=2008 |publisher=Cambridge University Press |page=113}}</ref> Later traditional Chinese blast furnaces varied greatly in size, from small “dwarf” furnaces to large furnaces approaching 10 m in height.{{sfn|Wagner|2008|p=6}}

The efficiency of the blast furnace was enhanced by the engineer [[Du Shi]] in the 1st cenruy AD, who applied the power of [[waterwheel]]s to [[piston]]-[[bellows]].<ref>{{Citation | last = Needham | first = Joseph | title = Science and Civilisation in China, Volume 4: Physics and Physical Technology, Part 2, Mechanical Engineering | place = Taipei | publisher = Cambridge University Press | page = 370 | year = 1986 | isbn = 0-521-05803-1 }}</ref> Early water-driven reciprocators for operating blast furnaces were built according to the structure of horse powered reciprocators that already existed. That is, the circular motion of the wheel, be it horse driven or water driven, was transferred by the combination of a [[belt drive]], a crank-and-connecting-rod, other [[connecting rods]], and various shafts, into the reciprocal motion necessary to operate push bellows.<ref>{{cite book |author=Hong-Sen Yan, Marco Ceccarelli |title=International Symposium on History of Machines and Mechanisms |url=https://books.google.com/books?id=Dkq6_mdW43IC&q=han+dynasty+crank+and+connecting+rod&pg=PA249 |publisher=Springer Science and Business Media|isbn=978-1-4020-9484-2|pages=235–249|year=2009 }}</ref><ref name="needham volume 4 part 2 118">{{harvnb|Needham|1986|pp=118&ndash;119}}.</ref> Donald Wagner suggests that early blast furnace and cast iron production evolved from furnaces used to melt [[bronze]]. Usage of the blast and [[cupola furnace]] remained widespread during the [[Song dynasty|Song]] and [[Tang dynasty|Tang dynasties]].<ref name="The Coming of the Ages of Steel">{{cite book|title=The Coming of the Ages of Steel|url=https://books.google.com/books?id=uMwUAAAAIAAJ&pg=PA54|publisher=Brill Archive|page=54|id=GGKEY:DN6SZTCNQ3G|year = 1961}}</ref> By the 11th century, the [[Song dynasty]] Chinese iron industry made a switch of resources from [[charcoal]] to [[Coke (fuel)|coke]] in casting iron and steel, sparing thousands of acres of woodland from felling. This may have happened as early as the 4th century AD.<ref>Donald B. Wagner, 'Chinese blast furnaces from the 10th to the 14th century' ''Historical Metallurgy'' 37(1) (2003), 25–37; originally published in ''West Asian Science, Technology, and Medicine'' 18 (2001), 41–74.</ref>{{sfn|Ebrey|Walthall|Palais|2005|page=148}}

Blast furnaces were also later used to produce [[gunpowder]] weapons such as cast iron [[Shell (projectile)|bomb shells]] and cast iron [[cannon]]s during the [[Song dynasty]].{{sfn|Liang|2006}}
=== Kingdom of Kush ===
{{See also|Meroe}}
Metalworking is thought to have taken place in Meroë, probably through [[bloomery|bloomeries]] and [[blast furnace]]s the earliest use of which in Africa, Meroe, the ancient capital of the Kingdom of Kush in modern-day Sudan, was one of the largest and most influential iron-producing centers in sub-Saharan Africa..<ref>{{Cite journal|last1=Humphris|first1=Jane|last2=Charlton|first2=Michael F. |last3=Keen |first3=Jake |last4=Sauder |first4=Lee |last5=Alshishani |first5=Fareed |year=2018 |title=Iron Smelting in Sudan: Experimental Archaeology at The Royal City of Meroe |journal=Journal of Field Archaeology |volume=43 |issue=5 |pages=399 |doi=10.1080/00934690.2018.1479085 |issn=0093-4690|doi-access=free }}</ref> [[Archibald Sayce]] reportedly referred to it as "the [[Birmingham, England|Birmingham]] of Africa",<ref name=HakemUNESCO>{{cite book | last1= Hakem |first1=A.A.|last2= Hrbek|first2=I. |last3= Vercoutter|first3= J. | year = 1981 | chapter = The Civilization of Napata and Meroe | editor-last= Mokhtar|editor-first= G. | title = Ancient Civilizations of Africa | series= General History of Africa|via={{abbr|UNESCO|United Nations Educational, Scientific and Cultural Organisation}} | volume= II | location = Paris/London/Berkeley, CA | publisher = UNESCO/Heinemann/University of California Press | pages = 298–325, esp. 312f | isbn= 0435948059 | chapter-url = https://books.google.com/books?id=gB6DcMU94GUC&pg=PA312 }}</ref>

=== Medieval Europe ===
Examples of improved bloomeries are the Stuckofen,<ref>{{cite book |last1=Strassburger |first1=Julius H. |title=Blast Furnace-theory and Practice |date=1969 |publisher=Gordon and Breach Science Publishers |isbn=978-0-677-10420-1 |page=4 }}</ref> sometimes called wolf-furnaces,<ref>Douglas Alan Fisher, [http://www.davistownmuseum.org/toolPreBlastFurnace.html Excerpt from The Epic of Steel] {{webarchive|url=https://web.archive.org/web/20070225050049/http://www.davistownmuseum.org/toolPreBlastFurnace.html |date=25 February 2007 }}, Davis Town Museum & Harper & Row, NY 1963.</ref> which remained until the beginning of the 19th century. Instead of using natural draught, air was pumped in by a ''[[trompe]]'', resulting in better quality iron and an increased capacity. This pumping of air in with bellows is known as ''cold blast'', and it increases the [[fuel efficiency]] of the bloomery and improves yield. They can also be built bigger than natural draught bloomeries.

====Oldest European blast furnaces====
The oldest known blast furnaces in the Europe were built at [[Durstel]] in [[Switzerland]], the Märkische [[Sauerland]] in [[Germany]], and at [[Lapphyttan]] in [[Sweden]] in the [[12th century|12th]] and [[13th century|13th]] centuries.<ref>{{Cite journal |last1=Gassmann |first1=Guntram |last2=Schwab |first2=Roland |date=2025-08-02 |title=New evidence for early pig iron production and refining technology on the foothills of the Swabian Mountains, Germany |url=https://doi.org/10.1007/s12520-025-02288-2 |journal=Archaeological and Anthropological Sciences |volume=17 |issue=8 |pages=1, 176 |article-number=176 |doi=10.1007/s12520-025-02288-2 |bibcode=2025ArAnS..17..176G |issn=1866-9565}}</ref><ref>Jockenhövel, Albrecht ''et al.'' (1997) [https://www.uni-muenster.de/UrFruehGeschichte/forschen/maerkischessauerland_engl.html "Archaeological Investigations on the Beginning of Blast Furnace-Technology in Central Europe"] {{webarchive|url=https://web.archive.org/web/20130224111115/http://www.uni-muenster.de/UrFruehGeschichte/forschen/maerkischessauerland_engl.html|date=24 February 2013}} Abteilung für Ur- und Frühgeschichtliche Archäologie, Westfälische Wilhelms-Universität Münster; abstract published as: Jockenhövel, A. (1997) "Archaeological Investigations on the Beginning of Blast Furnace-Technology in Central Europe" pp.&nbsp;56–58 ''In'' Crew, Peter and Crew, Susan (editors) (1997) ''Early Ironworking in Europe: Archaeology and Experiment: Abstracts of the International Conference at Plas Tan y Bwlch 19–25 September 1997'' (Plas Tan y Bwlch Occasional Papers No 3) Snowdonia National Park Study Centre, Gwynedd, Wales, {{OCLC|470699473}}; archived here [https://web.archive.org/web/20130224111115/http://www.uni-muenster.de/UrFruehGeschichte/forschen/maerkischessauerland_engl.html] by [[WebCite]] on 11 March 2012</ref> At Noraskog, in the Swedish parish of Järnboås, traces of even earlier blast furnaces have been found possibly from around 1100.<ref>A. Wetterholm, 'Blast furnace studies in Nora bergslag' (Örebro universitet 1999, Järn och Samhälle) {{ISBN|91-7668-204-8}}</ref> These early blast furnaces, like the [[Chinese history|Chinese]] examples, were very inefficient compared to those used today. The iron from the Lapphyttan complex was used to produce balls of [[wrought iron]] known as [[Osmond iron|osmond]]s which were traded internationally; a possible reference of such occurs in a treaty with [[Novgorod]] from 1203 and confirmed references of such trade exist in English customs accounts from the 1250s and 1320s.<ref>N. Bjökenstam, 'The Blast Furnace in Europe during the Middle Ages: part of a new system for producing wrought iron' in G. Magnusson, ''The Importance of Ironmaking: Technological Innovation and Social Change'' I (Jernkontoret, Stockholm 1995), 143–153 and other papers in the same volume.</ref>

Whether the European blast furnaces  developed independently or ultimately derived from earlier Chinese technology remains uncertain. Both possibilities have been proposed, but direct evidence demonstrating transmission across Eurasia is lacking.<ref>{{Cite book |last=Wagner |first=Donald B. |title=Science and Civilisation in China: Volume 5, Chemistry and Chemical Technology, Part 11, Ferrous Metallurgy |date=2008 |publisher=Cambridge University Press |isbn=978-0-521-87566-0 |page=349, 356}}</ref><ref>{{Cite book |last=Craddock |first=Paul T. |title=Early Metal Mining and Production |date=1995 |publisher=Edinburgh University Press |isbn=978-0-7486-0498-2 |pages=251–252}}</ref>

====Cistercian contributions====
The General Chapter of the [[Cistercians|Cistercian]] monks spread some technological advances across Europe. This may have included the blast furnace, as the Cistercians are known to have been skilled [[Metallurgy|metallurgists]].{{sfn|Woods|2005|page=34}} According to Jean Gimpel, their high level of industrial technology facilitated the diffusion of new techniques: "Every monastery had a model factory, often as large as the church and only several feet away, and waterpower drove the machinery of the various industries located on its floor." Iron ore deposits were often donated to the monks along with forges to extract the iron, and after a time surpluses were offered for sale. The Cistercians became the leading iron producers in [[Champagne (province)|Champagne]], France, from the mid-13th century to the 17th century,{{sfn|Gimpel|1976|page=67}} also using the [[phosphate]]-rich slag from their furnaces as an agricultural [[fertilizer]].{{sfn|Woods|2005|page=35}}

Archaeologists are still discovering the extent of Cistercian technology.{{sfn|Woods|2005|page=36}} At [[Laskill]], an outstation of [[Rievaulx Abbey]] and the only medieval blast furnace so far identified in [[Great Britain|Britain]], the slag produced was low in iron content.{{sfn|Woods|2005|page=37}} Slag from other furnaces of the time contained a substantial concentration of iron, whereas Laskill is believed to have produced cast iron quite efficiently.{{sfn|Woods|2005|page=37}}<ref>{{cite journal|author=R. W. Vernon, G. McDonnell and A. Schmidt|title=An integrated geophysical and analytical appraisal of early iron-working: three case studies|journal=Historical Metallurgy|volume=32|issue=2|year=1998|pages=72–75,&nbsp;79}}</ref><ref name="Woods">David Derbyshire, [https://www.telegraph.co.uk/news/uknews/1397905/Henry-stamped-out-Industrial-Revolution.html 'Henry "Stamped Out Industrial Revolution"'] {{webarchive|url=https://web.archive.org/web/20140613091020/http://www.telegraph.co.uk/news/uknews/1397905/Henry-stamped-out-Industrial-Revolution.html |date=13 June 2014 }}, ''[[The Daily Telegraph]]'' (21 June 2002); cited by Woods.</ref> Its date is not yet clear, but it probably did not survive until [[Henry VIII of England|Henry VIII]]'s [[Dissolution of the Monasteries]] in the late 1530s, as an agreement (immediately after that) concerning the "smythes" with the [[Thomas Manners, 1st Earl of Rutland|Earl of Rutland]] in 1541 refers to blooms.<ref>{{Citation | last = Schubert | first = H. R. | title = History of the British iron and steel industry from c. 450 BC to AD 1775 | publisher = Routledge & Kegan Paul | pages = 395–397 | year = 1957}}</ref> Nevertheless, the means by which the blast furnace spread in medieval Europe has not finally been determined.

=== Origin and spread of early modern blast furnaces ===
[[File:HautfourneauXVIII 1nb.jpg|thumb|upright=1.1|Drawing of an 18th-century blast furnace]]
[[File:Lohtaja.vaakuna.svg|thumb|upright=1.1|Early modern blast furnace pictured in the former coat of arms of [[Lohtaja]]]]
Due to the increased demand for iron for casting cannons, the blast furnace came into widespread use in France in the mid 15th century.<ref name="Tylecote_1992"/><ref>{{cite book|title= The Genius That Was China: East and West in the Making of the Modern World|last1= Merson|first1= John|year= 1990|publisher= The Overlook Press|location= Woodstock, New York|isbn= 0-87951-397-7|page= [https://archive.org/details/geniusthatwaschi0000mers/page/69 69]|postscript= A companion to the PBS Series "The Genius That Was China"|url= https://archive.org/details/geniusthatwaschi0000mers/page/69}}</ref>

The direct ancestor of those used in France and England was in the [[Namur]] region, in what is now [[Wallonia]] (Belgium). From there, they spread first to the [[Pays de Bray]] on the eastern boundary of [[Normandy]] and from there to the [[Weald]] of [[Sussex]], where the first furnace (called Queenstock) in [[Buxted]] was built in about 1491, followed by one at [[Newbridge, East Sussex|Newbridge]] in [[Ashdown Forest]] in 1496. They remained few in number until about 1530 but many were built in the following decades in the Weald, where the iron industry perhaps reached its peak about 1590. Most of the pig iron from these furnaces was taken to [[finery forge]]s for the production of [[bar iron]].<ref name="Queenstock">{{cite journal |first1=Brian |last1=Awty |first2=Christopher |last2=Whittick |title=The Lordship of Canterbury, iron-founding at Buxted, and the continental antecedents of cannon-founding in the Weald |journal=Sussex Archaeological Collections |volume=140 |year=2002 |pages=71–81 |doi=10.5284/1085896 |doi-access=free}}</ref>

The first British furnaces outside the Weald appeared during the 1550s, and many were built in the remainder of that century and the following ones. The output of the industry probably peaked about 1620, and was followed by a slow decline until the early 18th century. This was apparently because it was more economic to import iron from [[Sweden]] and elsewhere than to make it in some more remote British locations. Charcoal that was economically available to the industry was probably being consumed as fast as the wood to make it grew.<ref>P. W. King, 'The production and consumption of iron in early modern England and Wales' ''Economic History Review'' LVIII(1), 1–33; G. Hammersley, 'The charcoal iron industry and its fuel 1540–1750' ''Economic History Review'' Ser. II, XXVI (1973), pp.&nbsp;593–613.</ref>

The first blast furnace in [[Russia]] opened in 1637 near [[Tula, Russia|Tula]] and was called the Gorodishche Works. The blast furnace spread from there to central Russia and then finally to the [[Urals]].<ref name="dwip">{{Citation | last = Yakovlev | first = V. B. | title = Development of Wrought Iron Production | journal = Metallurgist | volume = 1 | issue = 8 | page = 545 | publisher = Springer | location = New York| year = 1957 | doi = 10.1007/BF00732452| s2cid = 137551466 }}</ref>

==== Coke blast furnaces ====
[[Image:Blast Furnaces at Blists Hill.jpg|thumb|upright=1.1|The original blast furnaces at [[Blists Hill Victorian Town|Blists Hill]] in [[Madeley, Shropshire|Madeley, England]]]]
[[File:THC 2003.902.116 Charging the Experimental Blast Furnace.tif|thumb|upright=1.1|Charging the experimental blast furnace, a photo from the Fixed Nitrogen Research Laboratory in [[Washington D.C.]], 1930]]
[[File:Доменная печь, Истье.JPG|thumb|upright=1.1|Remnants of a blast furnace in [[Russia]] first commissioned in 1715 by order of [[Peter the Great]] with the help of Holland masters.{{citation needed|date=January 2023}}]]
In 1709, at [[Coalbrookdale]] in Shropshire, England, [[Abraham Darby I|Abraham Darby]] began to fuel a blast furnace with [[coke (fuel)|coke]] instead of [[charcoal]]. Coke's initial advantage was its lower cost, mainly because making coke required much less labor than cutting trees and making charcoal, but using coke also overcame localized shortages of wood, especially in Britain and elsewhere in Europe. Metallurgical grade coke will bear heavier weight than charcoal, allowing larger furnaces.<ref name="Landes_1969">
{{cite book
|title=The Unbound Prometheus: Technological Change and Industrial Development in Western Europe from 1750 to the Present
 |last=Landes	
 |first= David. S.
|author-link= David Landes
|year= 1969|publisher =Press Syndicate of the University of Cambridge
|location= Cambridge; New York
|isbn=  0-521-09418-6|pages=90–93
}}
</ref><ref>
{{cite book
|title=The Most Powerful Idea in the World: A Story of Steam, Industry and Invention
 |last1= Rosen
 |first1= William
|year= 2012 
|publisher = University of Chicago Press
|isbn= 978-0-226-72634-2 |page=149
}}
</ref> A disadvantage is that coke contains more impurities than charcoal, with sulfur being especially detrimental to the iron's quality. Coke's impurities were more of a problem before hot blast reduced the amount of coke required and before furnace temperatures were hot enough to make slag from limestone free flowing.  (Limestone ties up{{explain|date=November 2024}} sulphur. Manganese may also be added to tie up{{clarify|date=November 2024}} sulphur.)<ref>{{cite book|title=A History of Metallurgy, Second Edition |last=Tylecote |first=R. F. |year= 1992|publisher =Maney Publishing, for the Institute of Materials |location= London|isbn=978-0-901462-88-6}}</ref>{{rp|123–125}}<ref name ="McNeil1990">{{cite book |title=An Encyclopedia of the History of Technology |last=McNeil |first=Ian |year=1990 |publisher=Routledge |location=London |isbn=0-415-14792-1 |url=https://archive.org/details/isbn_9780415147927 }}</ref><ref>{{cite web|url=http://www.steel.org/making-steel/how-its-made/processes/processes-info/coke-production-for-blast-furnace-ironmaking.aspx|title=Coke for Blast Furnace Ironmaking|website=steel.org|archive-url=https://web.archive.org/web/20170208204105/https://www.steel.org/making-steel/how-its-made/processes/processes-info/coke-production-for-blast-furnace-ironmaking.aspx|archive-date=8 February 2017}}</ref><ref name="Tylecote_1992">{{cite book|title=A History of Metallurgy, Second Edition |last=Tylecote |first=R. F.|year= 1992|publisher =Maney Publishing, for the Institute of Materials |location= London|isbn=978-0-901462-88-6}}</ref>{{rp|122–123}}

Coke iron was initially only used for [[foundry]] work, making pots and other cast iron goods. Foundry work was a minor branch of the industry, but Darby's son built a new furnace at nearby Horsehay, and began to supply the owners of [[finery forge]]s with coke pig iron for the production of bar iron. Coke pig iron was by this time cheaper to produce than charcoal pig iron. The use of a coal-derived fuel in the iron industry was a key factor in the British [[Industrial Revolution]].<ref>{{Citation | last = Raistrick | first = Arthur | title = Dynasty of Iron Founders: The Darbys and Coalbrookedale | place = York | publisher = Longmans, Green | year = 1953}}</ref>{{sfn|Hyde|1977|page=159}}<ref>{{Citation | last1 = Trinder | first1 = Barrie Stuart | last2 = Trinder | first2 = Barrie | title = The Industrial Revolution in Shropshire | place = Chichester | publisher = Phillimore | year = 2000 | isbn = 1-86077-133-5}}</ref> However, in many areas of the world charcoal was cheaper while coke was more expensive even after the Industrial Revolution: e. g., in the US charcoal-fueled iron production fell in share to about a half {{circa|1850}} but still continued to increase in absolute terms until {{circa|1890}},<ref>{{cite conference |last=Baker |first= A. J. |title= Charcoal Industry in the U.S.A.|url= https://www.fpl.fs.fed.us/documnts/pdf1985/baker85a.pdf|archive-url=https://web.archive.org/web/20150522202649/https://www.fpl.fs.fed.us/documnts/pdf1985/baker85a.pdf|archive-date=22 May 2015|conference= Symposium on Forest Products Research International--Achievements and the Future|location=Pretoria |publisher=Forest Service, U.S. Department of Agriculture, Madison, WI|access-date=22 May 2025}}</ref><ref>{{Cite journal |last=Schallenberg |first=Richard H. |date=July 1975 |title=Evolution, adaptation and survival: the very slow death of the American charcoal iron industry |url=https://www.tandfonline.com/doi/full/10.1080/00033797500200331 |journal=Annals of Science |language=en |volume=32 |issue=4 |pages=341–358 |doi=10.1080/00033797500200331 |issn=0003-3790}}</ref> while in [[João Monlevade]] in the [[Brazilian Highlands]] charcoal-fired blast furnaces were built as late as the 1930s and only phased out in 2000.<ref>{{cite web |title=ArcelorMittal Monlevade |url=https://thebeautyofsteel.com/steel-plants-archive/arcelormittal-monlevade/ |website=thebeautyofsteel.com |publisher=The Beauty of Steel |access-date=23 May 2025 |location=Prague|last=Macha|first=Victor}}</ref>

Darby's original blast furnace has been archaeologically excavated and can be seen in situ at Coalbrookdale, part of the [[Ironbridge Gorge]] Museums. Cast iron from the furnace was used to make [[girder]]s for the world's first cast iron bridge in 1779. [[The Iron Bridge]] crosses the [[River Severn]] at Coalbrookdale and remains in use for pedestrians.

[[File:Germany First Coke Blast Furnace Miniature DM.jpg|thumb|upright=1.1|The first coke blast furnace in [[Germany]] (1794-), depicted in a miniature in the [[Deutsches Museum]]]]

====Steam-powered blast====
The steam engine was applied to power blast air, overcoming a shortage of water power in areas where coal and iron ore were located. This was first done at Coalbrookdale where a [[Newcomen engine|steam engine]] replaced a horse-powered pump in 1742.<ref>A. Raistrick, ''Dynasty of ironmasters'' (Sessions, York, 1989), 138–139.</ref>  Such engines were used to pump water to a reservoir above the furnace. The first engines used to blow cylinders directly was supplied by [[Boulton and Watt]] to [[John Wilkinson (industrialist)|John Wilkinson]]'s [[Willey, Shropshire|New Willey]] Furnace.<ref>H.W. Dickinson and Rhys Jenkins, ''James Watt and the steam engine'' (Moorland, Ashbourne 1981 edn), 111–112.</ref> This powered a [[blowing engine|cast iron blowing cylinder]], which had been invented by his father [[Isaac Wilkinson]]. He patented such cylinders in 1736,<ref>English patent, no.553.</ref> to replace the leather bellows, which wore out quickly. Isaac was granted a second patent, also for blowing cylinders, in 1757.<ref>English patent, no.713.</ref> The steam engine and cast iron blowing cylinder led to a large increase in British iron production in the late 18th century.<ref name="Tylecote_1992"/>

====Hot blast====
[[Hot blast]] was the single most important advance in fuel efficiency of the blast furnace and was one of the most important technologies developed during the [[Industrial Revolution]].<ref>
{{cite book
|title=The Unbound Prometheus: Technological Change and Industrial Development in Western Europe from 1750 to the Present
 |last=Landes	
 |first= David. S.
|author-link=David Landes
|year= 1969|publisher =Press Syndicate of the University of Cambridge
|location= Cambridge; New York
|isbn=  0-521-09418-6|page=92
}}
</ref><ref>{{Cite web
 |last1        = Ayres
 |first1       = Robert
 |author1-link = Robert Ayres (scientist)
 |title        = Technological Transformations and Long Waves
 |year         = 1989
 |page         = 21
 |url          = http://www.iiasa.ac.at/Admin/PUB/Documents/RR-89-001.pdf
 |archive-url   = https://web.archive.org/web/20120301220936/http://www.iiasa.ac.at/Admin/PUB/Documents/RR-89-001.pdf
 |archive-date  = 1 March 2012
|access-date  = 17 October 2013
}} Fig. 7 shows C/Fe ratio time series.</ref> Hot blast was patented by [[James Beaumont Neilson]] at [[Wilsontown Ironworks]] in Britain in 1828. Within a few years of the introduction, hot blast was developed to the point where fuel consumption was cut by one-third using coke or two-thirds using coal, while furnace capacity was also significantly increased. Within a few decades, the practice was to have a "stove" as large as the furnace next to it into which the waste gas (containing CO) from the furnace was directed and burnt. The resultant heat was used to preheat the air blown into the furnace.{{sfn|Birch2005|pages=181-189}} Hot blast enabled the use of raw [[anthracite]] coal, which was difficult to light, in the blast furnace. Anthracite was first tried successfully by George Crane at [[Ynyscedwyn Ironworks]] in south Wales in 1837.{{sfn|Hyde|1977|page=159}} It was taken up in America by the [[Lehigh Crane Iron Company]] at [[Catasauqua, Pennsylvania]], in 1839. Anthracite use declined when very high capacity blast furnaces requiring coke were built in the 1870s.

==Modern applications of the blast furnace==
[[File:Hochofenprozess1.svg|thumb|right|1 - In/outlet; 2 - Drying and preheating; 3 - Reduction; 4 - Carbon dissolution; 5 - Fusion; 6 - Tapping / A - Feedstock; B - Hot blast; C - Slag; D - Pig iron; E - Gas outlet]]

=== Iron blast furnaces ===
The blast furnace remains an important part of modern iron production. Modern furnaces are highly efficient, including [[Cowper stove]]s to [[hot blast|pre-heat]] the blast air and employ recovery systems to extract the heat from the hot gases exiting the furnace. Competition in industry drives higher production rates. The largest blast furnace in the world is in South Korea, with a volume around {{convert|6000|m3 |cuft|abbr=on}}. It can produce around {{convert|5650000|t|lt|abbr=}} of iron per year.<ref>{{Citation|title=POSCO Gwangyang blast furnace emerges as world largest| url=http://english.donga.com/List/3/all/26/406398/1 |website = The Dong-a Ilbo|date = 10 June 2013}}</ref>

This is a great increase from the typical 18th-century furnaces, which averaged about {{convert|360|t}} per year. Variations of the blast furnace, such as the Swedish electric blast furnace, have been developed in countries which have no native coal resources.

According to ''[[Global Energy Monitor]]'', the blast furnace is likely to become obsolete to meet [[climate change]] objectives of reducing carbon dioxide emission,<ref>{{Cite web|date=29 June 2021|title=Steel sector may be saddled with up to $70 bln stranded assets -report|url=https://www.reuters.com/business/energy/steel-sector-may-be-saddled-with-up-70-bln-stranded-assets-report-2021-06-29/|access-date=10 July 2021|website=Reuters}}</ref> but [[BHP]] disagrees.<ref name=":1" />  An alternative process involving [[direct reduced iron]] (DRI) is likely to succeed it,<ref>{{cite journal |last1=Kiessling |first1=Sandra |last2=Darabkhani |first2=Hamidreza Gohari |last3=Soliman |first3=Abdel-Hamid |title=The Bio Steel Cycle: 7 Steps to Net-Zero CO<sub>2</sub> Emissions Steel Production |journal=[[Energies (journal)|Energies]] |date=24 November 2022 |volume=15 |issue=23 |page=8880 |doi=10.3390/en15238880|doi-access=free }}</ref> but this also needs to use a blast furnace to melt the iron and remove the [[gangue]] (impurities) unless the ore is very high quality.<ref name=":1">{{Cite web|title=Pathways to decarbonisation episode two: steelmaking technology|url=https://www.bhp.com/media-and-insights/prospects/2020/11/pathways-to-decarbonisation-episode-two-steelmaking-technology/|url-status=live|archive-url=https://web.archive.org/web/20201105063202/https://www.bhp.com/media-and-insights/prospects/2020/11/pathways-to-decarbonisation-episode-two-steelmaking-technology/ |archive-date=5 November 2020 }}</ref>

==== Oxygen blast furnace ====
The oxygen blast furnace (OBF) process, developed from the 1970s to the 1990s, has been extensively studied theoretically because of the potentials of promising energy conservation and {{CO2}} emission reduction.<ref>{{cite journal |last1=Zhang |first1=Wei |last2=Dai |first2=Jing |last3=Li |first3=Chengzhi |last4=Yu |first4=Xiaobing |last5=Xue |first5=Zhengliang |last6=Saxén |first6=Henrik |title=A Review on Explorations of the Oxygen Blast Furnace Process |journal=Steel Research International |date=January 2021 |volume=92 |issue=1 |article-number=2000326 |doi=10.1002/srin.202000326 |s2cid=224952826 |url=https://urn.fi/URN:NBN:fi-fe2022012811123 }}</ref> This type may be the most suitable for use with CCS.<ref name=":1" /> The main blast furnace has of three levels; the reduction zone ({{convert|523–973|K|C F|abbr=on}}), slag formation zone ({{convert|1073–1273|K|C F|abbr=on}}), and the combustion zone ({{convert|1773–1873|K|C F|abbr=on}}).

OBFs are usually combined with top gas recycling. The problem with this, besides significant oxygen expenditures, is the uneven distribution of gas recycled from the top of the furnace to the middle, which collides with the hot gas from below. As of 2023, the technology is only practiced on the experimental level in Sweden, Japan and China.<ref>{{Cite journal |last1=Yu |first1=Jiyong |last2=Xu |first2=Runsheng |last3=Zhang |first3=Jianliang |last4=Zheng |first4=Anyang |date=2023-08-15 |title=A review on reduction technology of air pollutant in current China's iron and steel industry |url=https://www.sciencedirect.com/science/article/abs/pii/S0959652623018176 |journal=Journal of Cleaner Production |volume=414 |article-number=137659 |doi=10.1016/j.jclepro.2023.137659 |bibcode=2023JCPro.41437659Y |issn=0959-6526}}</ref>

=== Blast furnaces in copper and lead smelting ===
{{further|Water jacket furnace (metallurgy)}}
Blast furnaces are currently rarely used in copper smelting, but modern lead smelting blast furnaces are much shorter than iron blast furnaces and are rectangular in shape.<ref name = "Sinclair77">R J Sinclair, ''The Extractive Metallurgy of Lead'' (The Australasian Institute of Mining and Metallurgy: Melbourne, 2009), 77.</ref> Modern lead blast furnaces are constructed using water-cooled steel or copper jackets for the walls, and have no refractory linings in the side walls.<ref name = "Sinclair75">R J Sinclair, ''The Extractive Metallurgy of Lead'' (The Australasian Institute of Mining and Metallurgy: Melbourne, 2009), 75.</ref> The base of the furnace is a hearth of [[Fire brick|refractory material]] (bricks or castable refractory).<ref name = "Sinclair75"/> Lead blast furnaces are often open-topped rather than having the charging bell used in iron blast furnaces.<ref>R J Sinclair, ''The Extractive Metallurgy of Lead'' (The Australasian Institute of Mining and Metallurgy: Melbourne, 2009), 76.</ref>

The blast furnace used at the [[Nyrstar]] [[Port Pirie]] lead smelter differs from most other lead blast furnaces in that it has a double row of tuyeres rather than the single row normally used.<ref name = "Sinclair77"/> The lower shaft of the furnace has a chair shape with the lower part of the shaft being narrower than the upper.<ref name = "Sinclair77"/> The lower row of tuyeres being located in the narrow part of the shaft.<ref name = "Sinclair77"/> This allows the upper part of the shaft to be wider than the standard.<ref name = "Sinclair77"/>

===Zinc blast furnaces===
The blast furnaces used in the [[Zinc smelting#Blast furnace process (Imperial Smelting Process)|Imperial Smelting Process]] ("ISP") were developed from the standard lead blast furnace, but are fully sealed.<ref name = "Sinclair89">R J Sinclair, ''The Extractive Metallurgy of Lead'' (The Australasian Institute of Mining and Metallurgy: Melbourne, 2009), 89.</ref> This is because the zinc produced by these furnaces is recovered as metal from the vapor phase, and the presence of oxygen in the off-gas would result in the formation of zinc oxide.<ref name = "Sinclair89"/>

Blast furnaces used in the ISP have a more intense operation than standard lead blast furnaces, with higher air blast rates per m<sup>2</sup> of hearth area and a higher coke consumption.<ref name = "Sinclair89"/>

Zinc production with the ISP is more expensive than with [[Zinc smelting#Electrolysis process|electrolytic zinc]] plants, so several smelters operating this technology have closed in recent years.<ref>R J Sinclair, ''The Extractive Metallurgy of Lead'' (The Australasian Institute of Mining and Metallurgy: Melbourne, 2009), 90.</ref> However, ISP furnaces have the advantage of being able to treat zinc concentrates containing higher levels of lead than can electrolytic zinc plants.<ref name = "Sinclair89"/>

===Manufacture of stone wool===
[[File:Blast furnace tuyeres.jpg|thumb|upright=1.1|Tuyeres of a blast furnace in [[Gerdau]], Brazil]]
Stone wool or [[Mineral wool|rock wool]] is a spun mineral [[fibre]] used as an [[Thermal insulation|insulation]] product and in [[hydroponic]]s. It is manufactured in a blast furnace fed with [[diabase]] rock which contains very low levels of metal oxides. The resultant slag is drawn off and spun to form the rock wool product.<ref>{{cite web|archive-url = https://web.archive.org/web/20100210081645/http://www.rockwool.co.uk/about%2Brockwool/what%2Bis%2Bstone%2Bwool-c7- |archive-date = 10 February 2010|title = What is stone wool?|website =  rockwool.co.uk |url = http://www.rockwool.co.uk/about+rockwool/what+is+stone+wool-c7-}}</ref> Very small amounts of metals are also produced which are an unwanted [[by-product]].

==Modern iron process==
[[File:Blast furnace NT.PNG|thumb|right|350px|'''Blast furnace placed in an installation''' {{ordered list
    |Iron ore + limestone sinter
    |Coke
    |Elevator
    |Feedstock inlet
    |Layer of coke
    |Layer of sinter pellets of ore and limestone
    |Hot blast (around 1200&nbsp;°C)
    |Removal of slag
    |Tapping of molten pig iron
    |Slag pot
    |Torpedo car for pig iron
    |Dust cyclone for separation of solid particles
    |Cowper stoves for hot blast
    |Smoke stack
    |Feed air for Cowper stoves (air pre-heaters)
    |Powdered coal
    |Coke oven
    |Coke
    |Blast furnace gas downcomer
}}]]

[[File:VysokaPec.jpg|thumb|right|350px|'''Blast furnace diagram''' {{ordered list
    |[[Hot blast]] from [[Cowper stove]]s
    |Melting zone (''bosh'')
    |Reduction zone of [[ferrous oxide]] (''barrel'')
    |Reduction zone of [[ferric oxide]] (''stack'')
    |Pre-heating zone (''throat'')
    |Feed of ore, limestone, and coke
    |Exhaust gases
    |Column of ore, coke and limestone
    |Removal of [[slag]]
    |Tapping of molten [[pig iron]]
    |Collection of waste gases
}}]]{{Update section|reason=hydrogen and ccs are mentioned in another section but info is out of date – I guess the process should be described in this section|date=July 2021}}
Modern furnaces are equipped with an array of supporting facilities to increase efficiency, such as ore storage yards where barges are unloaded. The raw materials are transferred to the stockhouse complex by ore bridges, or [[Hopper car|rail hopper]]s and [[Railcar|ore transfer cars]]. Rail-mounted scale cars or computer controlled weight hoppers weigh out the various raw materials to yield the desired hot metal and slag chemistry. The raw materials are brought to the top of the blast furnace via a [[skip (container)|skip]] car powered by winches or conveyor belts.<ref name="AISI">American Iron and Steel Institute (2005). [https://web.archive.org/web/20070510164459/http://www.steel.org/AM/Template.cfm?Section=Home&template=%2FCM%2FHTMLDisplay.cfm&ContentID=5433 How a Blast Furnace Works]. steel.org.</ref>

There are different ways in which the raw materials are charged into the blast furnace. Some blast furnaces use a "double bell" system where two "bells" are used to control the entry of raw material into the blast furnace. The purpose of the two bells is to minimize the loss of hot gases in the blast furnace. First, the raw materials are emptied into the upper or small bell which then opens to empty the charge into the large bell. The small bell then closes, to seal the blast furnace, while the large bell rotates to provide specific distribution of materials before dispensing the charge into the blast furnace.<ref name=et>{{cite book |last1=McNeil |first1=Ian |title=An Encyclopedia of the History of Technology |date=2002 |publisher=Taylor & Francis |isbn=978-0-203-19211-5 |page=163 }}</ref><ref>{{cite book |last1=Strassburger |first1=Julius H. |title=Blast Furnace-theory and Practice |date=1969 |publisher=Gordon and Breach Science Publishers |isbn=978-0-677-10420-1 |page=564 }}</ref> A more recent design is to use a "bell-less" system. These systems use multiple hoppers to contain each raw material, which is then discharged into the blast furnace through valves.<ref name=et/> These valves are more accurate at controlling how much of each constituent is added, as compared to the skip or conveyor system, thereby increasing the efficiency of the furnace. Some of these bell-less systems also implement a discharge chute in the throat of the furnace (as with the Paul Wurth top) in order to precisely control where the charge is placed.<ref>{{Citation|last=Whitfield |first=Peter |title=Design and Operation of a Gimbal Top Charging System |url=http://www2.sea.siemens.com/NR/rdonlyres/FFA8AF1C-1791-46E8-AA09-917BB28D8701/0/038.pdf |access-date=22 June 2008 |archive-url=https://web.archive.org/web/20090305185028/http://www2.sea.siemens.com/NR/rdonlyres/FFA8AF1C-1791-46E8-AA09-917BB28D8701/0/038.pdf |archive-date=5 March 2009 }}</ref>

The iron making blast furnace itself is built in the form of a tall structure, lined with [[refractory]] brick, and profiled to allow for expansion of the charged materials as they heat during their descent, and subsequent reduction in size as melting starts to occur. Coke, [[limestone]] flux, and iron ore (iron oxide) are charged into the top of the furnace in a precise filling order which helps control gas flow and the chemical reactions inside the furnace. Four "uptakes" allow the hot, dirty gas high in carbon monoxide content to exit the furnace throat, while "bleeder valves" protect the top of the furnace from sudden gas pressure surges. The coarse particles in the exhaust gas settle in the "dust catcher" and are dumped into a railroad car or truck for disposal, while the gas itself flows through a [[venturi scrubber]] and/or electrostatic precipitators and a gas cooler to reduce the temperature of the cleaned gas.<ref name="AISI"/>

The "casthouse" at the bottom half of the furnace begins with the "bosh": that portion of the blast furnace above the [[tuyere]]s and below the stack.<ref>{{cite book|last=Thrush|first=Paul W.|title=A Dictionary of Mining, Mineral, and Related Terms|location=Washington, D.C.|publisher=Bureau of Mines, U.S. Department of the Interior|date=1968|oclc=3629|url=https://books.google.com/books?id=b4IAavjDLjEC|page=127}}</ref> Shaped like an inverted, truncated cone,{{sfn|Reese|1923|page=29}} it is the part of the blast furnace where ore turns molten.{{sfn|Reese|1923|page=30}} Next is the bustle pipe (a large-diameter annular pipe to deliver heated air under pressure to the tuyeres{{sfn|Cavaliere|2016|p=157}}) and the equipment for casting the liquid iron and slag. Once a "taphole" is drilled through the refractory clay plug, liquid iron and slag flow down a trough through a "skimmer" opening, separating the iron and slag. Modern, larger blast furnaces may have as many as four tapholes and two casthouses.<ref name="AISI"/> Once the pig iron and slag has been tapped, the taphole is again plugged with refractory clay.

The tuyeres are used to implement a [[hot blast]], which is used to increase the efficiency of the blast furnace. The hot blast is directed into the furnace through water-cooled copper nozzles called tuyeres near the base. The hot blast temperature can be from {{convert|900|to|1300|C|F}} depending on the stove design and condition. The temperatures they deal with may be {{convert|2000|to|2300|C|F}}. [[Oil]], [[tar]], [[natural gas]], powdered [[coal]] and [[oxygen]] can also be injected into the furnace at tuyere level to combine with the coke to release additional energy and increase the percentage of [[Reducing agent#Examples of redox reaction|reducing gases]] present which is necessary to increase productivity.<ref name="AISI"/>

The exhaust gasses of a blast furnace are generally cleaned in the [[dust collector]] –  such as an [[inertia]]l separator, a [[baghouse]], or an [[electrostatic precipitator]]. Each type of dust collector has strengths and weaknesses – some collect fine particles, some coarse particles, some collect electrically charged particles. Effective exhaust clearing relies on multiple stages of treatment.<ref>{{cite web|url=https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/488404/Reg_60_response_dated_02-09-13.pdf|title=Comparison of techniques employed at Scunthorpe Integrated Steelworks with those in the BAT Conclusions for Iron and Steel Production published in the Official Journal of the European Union|date=8 March 2012|access-date=19 January 2021|publisher= HM Government UK}}</ref>  Waste heat is usually collected from the exhaust gases, for example by the use of a [[Cowper stove]], a variety of [[heat exchanger]].

==Environmental impact==
[[File:Proceso de fundicion en la Fabrica de Artillería de La Cavada.svg|thumb|right|Side view of schematic]]
[[Fossil fuel]] (coke, natural gas) use in blast furnaces is a source of [[greenhouse gas emissions]] and the blast furnace is the most emission intensive stage of the steel making process.<ref>{{cite journal |last1=Liang |first1=Wang |last2=Wang |first2=Guangwei |last3=Xu |first3=Runsheng |last4=Ning |first4=Xiaojun |last5=Zhang |first5=Jianliang |last6=Guo |first6=Xingmin |last7=Jiang |first7=Chunhe |last8=Wang |first8=Chuan |date=August 2023 |title=Life cycle assessment of blast furnace ironmaking processes: A comparison of fossil fuels and biomass hydrochar applications |journal=Fuel |volume=345 |article-number=128138 |bibcode=2023Fuel..34528138L |doi=10.1016/j.fuel.2023.128138}}</ref><ref name=":2">IEA-GHG, 2000. Greenhouse Gas Emissions from Major Industrial Sources – Iron and Steel Production. Report no. PH3/30. Cheltenham, UK, IEA Greenhouse Gas R&D Programme. https://ieaghg.org/docs/General_Docs/Reports/PH3-30%20iron-steel.pdf Accessed 30 July 2021.</ref> For every tonne of steel produced in an integrated steel mill, 1.6-2.2 tonnes of CO<sub>2</sub> emissions are produced, 70% of which are attributed to the operation of the blast furnace.<ref name=":2" /> Fuels and reductants such as [[plastic waste]],<ref>{{Cite journal |last1=Knepper |first1=M. |last2=Babich |first2=A. |last3=Senk |first3=D. |last4=Bürgler |first4=Thomas |last5=Feilmayr |first5=Christoph |last6=Kieberger |first6=N. |date=22 October 2012 |title=Waste Plastics Injection: Reaktion Kinetics and Effect on the Blast Furnace Process |url=https://www.researchgate.net/publication/347574211 |access-date=31 July 2024 |website=ResearchGate}}</ref> biomass<ref>{{cite journal |last1=Wang |first1=Chuan |last2=Mellin |first2=Pelle |last3=Lövgren |first3=Jonas |last4=Nilsson |first4=Leif |last5=Yang |first5=Weihong |last6=Salman |first6=Hassan |last7=Hultgren |first7=Anders |last8=Larsson |first8=Mikael |date=September 2015 |title=Biomass as blast furnace injectant – Considering availability, pretreatment and deployment in the Swedish steel industry |url=http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-165060 |journal=Energy Conversion and Management |volume=102 |pages=217–226 |bibcode=2015ECM...102..217W |doi=10.1016/j.enconman.2015.04.013}}</ref> and hydrogen<ref name=":3">{{cite journal |last1=Pei |first1=Martin |last2=Petäjäniemi |first2=Markus |last3=Regnell |first3=Andreas |last4=Wijk |first4=Olle |date=18 July 2020 |title=Toward a Fossil Free Future with HYBRIT: Development of Iron and Steelmaking Technology in Sweden and Finland |journal=Metals |volume=10 |issue=7 |page=972 |doi=10.3390/met10070972 |doi-access=free}}</ref> are being used by steelmakers<ref>{{cite journal |last1=De Ras |first1=Kevin |last2=Van de Vijver |first2=Ruben |last3=Galvita |first3=Vladimir V |last4=Marin |first4=Guy B |last5=Van Geem |first5=Kevin M |date=December 2019 |title=Carbon capture and utilization in the steel industry: challenges and opportunities for chemical engineering |journal=Current Opinion in Chemical Engineering |volume=26 |pages=81–87 |bibcode=2019COCE...26...81D |doi=10.1016/j.coche.2019.09.001 |hdl=1854/LU-8635595|hdl-access=free }}</ref> as possible alternatives to fossil fuels, although cost and availability remain a challenge{{Citation needed|date=August 2024}} and deployment is limited.

[[Electric arc furnace|Electric arc furnaces (EAF)]] are cited as an alternative steel production path which avoids the use of blast furnaces, however, depending on the characteristics of the steel product required the two furnace types are not always interchangeable. Furthermore, EAFs utilize steel scrap as a feedstock but estimates suggest that there will not be enough scrap available to meet future steel demand.<ref>{{Cite web |last=IEA |date=2020 |title=Iron and Steel Technology Roadmap |url=https://www.iea.org/reports/iron-and-steel-technology-roadmap |access-date=6 August 2024 |website=[[International Energy Agency]]}}</ref> Using hydrogen gas as a reductant to produce DRI (so called H2-DRI) from iron ore, which is then used as a feedstock for an EAF provides a technologically feasible, low emission alternative to blast furnaces.<ref name=":3" /> The H2-DRI EAF production route is in a fledgling state, with just one plant in operation.<ref>{{Cite web |title=Hybrit |url=https://www.hybritdevelopment.se/en/ |access-date=7 August 2024 |website=Hybrit |language=en-US}}</ref>

ULCOS (Ultra Low [[Carbon Dioxide|CO<sub>2</sub>]] [[Steelmaking]])<ref>http://www.ulcos.org {{webarchive|url=https://web.archive.org/web/20081121182534/http://www.ulcos.org/|date=21 November 2008}}</ref> was a European programme exploring processes to reduce blast furnace emissions by at least 50%. Technologies identified include carbon capture and storage (CCS) and alternative energy sources and reductants such as hydrogen, electricity and biomass.<ref>ICIT-Revue de Métallurgie, September and October issues, 2009</ref>[[File:Dust catcher drawing.png|thumb|upright=1.1|A drawing of a blast furnace dust catcher]]

=== Carbon capture, utilisation, and storage (CCUS) ===
For existing blast furnaces, [[carbon capture and storage|carbon capture, utilisation, and storage]] (CCUS) is a potential solution to abate emissions. This involves capturing CO<sub>2</sub> from the furnace's waste gases before they are released, and then either transporting it for permanent underground storage (CCS) or using it to create other products (CCU).<ref>{{Cite journal|title=Retrofitting Blast Furnaces for Producing Green Steel and Green Urea|url=https://www.ijee.latticescipub.com/wp-content/uploads/papers/v5i2/B187105021125.pdf
|journal=Indian Journal of Environment Engineering|language=en|volume=5|pages=19–25|doi=10.54105/ijee.B1871.05021125|issn= 2582-9289|last1=Nallapaneni|first1=Sasidhar|date=2025
|issue=2
|access-date=21 November 2025}}</ref> As of early 2025, no commercial-scale CCUS facility is in full operation on a primary steelmaking plant. However, several large-scale pilot and demonstration projects are underway.<ref>{{cite web |title=Global Status of CCS 2024 |url=https://www.globalccsinstitute.com/resources/global-status-report/|website= Executive Report Global CCS Institute |access-date=15 July 2025}}</ref> The high costs, estimated at $50 to $100 per tonne of CO<sub>2</sub> for industrial sources, and the lack of transport and storage infrastructure remain significant barriers to widespread deployment.<ref>{{Cite web |title=Direct Air Capture - Energy System |url=https://www.iea.org/energy-system/carbon-capture-utilisation-and-storage/direct-air-capture |access-date=2025-07-15 |website=IEA |language=en-GB}}</ref>

==Preserved historic blast furnaces==
{{Main|List of preserved historic blast furnaces}}
Historically it was normal procedure for a decommissioned blast furnace to be demolished and either replaced with a newer, improved one, or to have the entire site demolished and treated for follow-up use of the area. In recent decades, several countries have realized the historic value of blast furnaces and have transformed them into museums. Examples can be found in the [[Czech Republic]], France, Germany, Japan, [[Luxembourg]], [[Poland]], [[Romania]], [[Mexico]], [[Russia]], Spain, [[United Kingdom]], and [[United States]].

==Gallery==
<gallery>
File:Alto horno antiguo Sestao.jpg|Abandoned blast furnace in [[Sestao]], Spain. The furnace itself is inside the central girderwork.
File:Old blast furnace gas cleaning plant 2012-05-02.jpg|Part of the gas cleaning system of a blast furnace in [[Monclova]], Mexico. This one is about to be de-commissioned and replaced.
</gallery>

==See also==
*[[Basic oxygen furnace]]
*[[Zinc smelting#Blast furnace process (Imperial Smelting Process)|Blast furnace zinc smelting process]]
*[[Crucible steel]]
*[[Extraction of iron]]
*[[Water gas]], produced by a "steam blast"
*[[FINEX (steelmaking process)|FINEX]]
*[[Krupp-Renn Process]]
*[[Flodin process]]
*[[Steelmaking]]
*[[:Category:Ironworks and steelworks in England|Ironworks and steelworks in England]], which covers ironworks of all kinds.
<!--please do not list individual ironworks here: the article is quite long enough. -->
*[[Shaft furnace breather]]
*[[Direct reduction]]
*[[Direct reduction (blast furnace)]]
*[[Coking factory]]
*[[Water jacket furnace (metallurgy)|Water jacket furnace]]

==References==
{{Reflist|35em}}

===Bibliography===
{{Refbegin}}
*{{Cite book |last=Birch |first=Alan | title= The Economic History of the British Iron and Steel Industry, 1784–1879 |year= 2005 |publisher= Routledge |isbn=0-415-38248-3}}
*{{cite book |last1=Cavaliere |first1=Pasquale |title=Ironmaking and steelmaking processes: greenhouse emissions, control, and reduction |date=2016 |publisher=Springer International |location=Cham |isbn=978-3-319-39529-6 }}
*{{Cite book| last1 = Ebrey | first1 = Patricia Buckley | last2 = Walthall | first2 = Anne | last3 = Palais | first3 = James B. | title = East Asia: A Cultural, Social, and Political History | place = Boston | publisher = Houghton Mifflin | year = 2005 | isbn = 0-618-13384-4 | url = https://archive.org/details/eastasiacultural00ebre_0 }}
* {{cite book |last1=Ganguly |first1=Ananya |title=Fundamentals of Inorganic Chemistry |date=2011 |publisher=[[Pearson Education]] |location=Delhi |isbn=978-81-317-6649-1 |pages=13–6}}
*{{Cite book | last = Gimpel | first = Jean | title = The Medieval Machine: The Industrial Revolution of the Middle Ages | place = New York | publisher = Holt, Rinehart and Winston | year = 1976 | isbn = 0-03-014636-4}}
*{{Cite book |last=Hyde |first=Charles K. |title=Technological Change and the British iron industry, 1700–1870 |year=1977 |publisher=Princeton University Press |location=Princeton |isbn=0-691-05246-8 |url-access=registration |url=https://archive.org/details/technologicalcha0000hyde }}
* {{Cite book |last=Liang |first=Jieming |year=2006 |title=Chinese Siege Warfare: Mechanical Artillery & Siege Weapons of Antiquity |publisher=Leong Kit Meng |isbn=981-05-5380-3 |location=Singapore, Republic of Singapore}}
*{{cite news|last=Reese|first=A.K.|title=Modern Blast-Furnace Practice|work=Engineering Production|date=January 11, 1923|accessdate=April 7, 2025|url=https://books.google.com/books?id=8vAXX0XVIVUC}}
*{{cite book|last=Wagner|first=Donald B.|year=2008|title=Science and Civilization in China Volume 5–11: Ferrous Metallurgy|publisher=Cambridge University Press}}{{ISBN?}}
*{{Cite book |last=Woods |first=Thomas |title=How the Catholic Church Built Western Civilization |year=2005 |isbn=0-89526-038-7 |publisher=Regnery Publ. |location=Washington, D.C. |url-access=registration |url=https://archive.org/details/howcatholicchurc0000wood }}
{{Refend}}

==External links==
{{Commons}}
*[https://web.archive.org/web/20141223190954/http://www.steel.org/Making%20Steel/How%20Its%20Made/Processes/How%20a%20Blast%20Furnace%20Works.aspx American Iron and Steel Institute]
*[https://www.bbc.co.uk/history/british/victorians/launch_ani_blast_furnace.shtml Blast Furnace animation ]
*[https://web.archive.org/web/20150106211900/http://www.stahlseite.de/ Extensive picture gallery about all methods of making and shaping of iron and steel in North America and Europe. In German and English.]
*{{HAER |survey=PA-651 |id=pa4149 |title=Blast Furnace Study |data=342}}
*[https://www.britannica.com/eb/art-1535 Schematic diagram of blast furnace and Cowper stove]

{{Iron and steel production}}
{{Authority control}}

{{DEFAULTSORT:Blast Furnace}}
[[Category:Blast furnaces| ]]
[[Category:Chinese inventions]]
[[Category:Firing techniques]]
[[Category:Industrial buildings and structures]]
[[Category:Industrial furnaces]]
[[Category:Industrial Revolution]]
[[Category:Metallurgy]]
[[Category:Smelting]]
[[Category:Steelmaking]]