View source for Engineering:Blast furnace

{{Short description|Type of furnace used for smelting to produce industrial metals}}
[[File:Alto Horno, Puerto de Sagunto, España, 2015-01-04, DD 91.JPG|thumb|upright=1.1|Former AHM blast furnace in Port of Sagunt, Valencia, Spain]]
A '''blast furnace''' is a type of metallurgical furnace used for [[Engineering:Smelting|smelting]] to produce industrial metals, generally [[Chemistry:Pig iron|pig iron]], but also others such as [[Chemistry:Lead|lead]] or [[Chemistry:Copper|copper]].  ''Blast'' refers to the combustion air being supplied above [[Physics:Atmospheric pressure|atmospheric pressure]].<ref>See: [[Physics:Draft (boiler)|Draft (boiler)]]</ref>

In a blast furnace, fuel ([[Chemistry:Coke (fuel)|coke]]), ores, and [[Engineering:Flux (metallurgy)|flux]] ([[Earth:Limestone|limestone]]) are continuously supplied through the top of the furnace, while a hot blast of air (sometimes with [[Chemistry:Oxygen|oxygen]] enrichment) is blown into the lower section of the furnace through a series of pipes called tuyeres, so that the chemical reactions take place throughout the furnace as the material falls downward. The end products are usually molten metal and [[Chemistry:Slag|slag]] phases tapped from the bottom, and waste gases ([[Physics:Flue gas|flue gas]]) exiting from the top of the furnace.<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, [[Chemistry:Carbon monoxide|carbon monoxide]]-rich combustion gases is a [[Physics:Countercurrent exchange|countercurrent exchange]] and chemical reaction process.<ref>[http://iopscience.iop.org/article/10.1088/1757-899X/150/1/012022/pdf ''Development of heat transfer circuits in the blast furnace, IOP Conference Series: Materials Science and Engineering'']</ref>

In contrast, air furnaces (such as reverberatory furnaces) are naturally aspirated, usually by the [[Astronomy:Convection|convection]] of hot gases in a chimney flue. According to this broad definition, [[Chemistry:Bloomery|bloomeries]] for iron, blowing houses for [[Chemistry:Tin|tin]], and smelt mills for [[Chemistry:Lead|lead]] would be classified as blast furnaces. However, the term has usually been limited to those used for smelting [[Earth:Iron ore|iron ore]] to produce [[Chemistry:Pig iron|pig iron]], an intermediate material used in the production of commercial iron and steel, and the shaft furnaces used in combination with [[Engineering:Sinter plant|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 [[Earth:Greenhouse gas emissions|greenhouse gas emissions]] between 1900 and 2015, but are difficult to decarbonize.<ref name=":0" />

==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 oxides to pure iron through a series of reactions that occur at different areas within a blast furnace.]]
Blast furnaces operate on the principle of [[Chemistry:Redox|chemical reduction]] whereby carbon monoxide converts iron oxides to elemental iron.  Blast furnaces differ from [[Chemistry:Bloomery|bloomeries]] and reverberatory furnaces 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 [[Physics:Countercurrent exchange|countercurrent exchange]] process whereas a bloomery does not. Another difference is that bloomeries operate as a batch process whereas blast furnaces 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.

[[Chemistry:Silica|Silica]] has to be removed from the pig iron. It reacts with [[Chemistry:Calcium oxide|calcium oxide]] (burned limestone) and forms silicates, which float to the surface of the molten pig iron as slag.  Historically, to prevent contamination from sulfur, the best quality iron was produced with charcoal.

The downward moving column of ore, flux, [[Chemistry:Coke (fuel)|coke]] or charcoal and reaction products must be sufficiently porous for the flue gas to pass through.  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, [[Chemistry:Phosphorus|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 = 2007-12-30 | url = http://www.scienceaid.co.uk/chemistry/industrial/blastfurnace.html | url-status = dead | 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 [[Chemistry:Carbon monoxide|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>

The hot carbon monoxide is the reducing agent for the iron ore and reacts with the [[Chemistry:Iron oxide|iron oxide]] to produce molten iron and [[Chemistry:Carbon dioxide|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 200&nbsp;°C and 700&nbsp;°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 850&nbsp;°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 [[Chemistry:Nitrogen|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 [[Chemistry:Calcium oxide|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 [[Chemistry:Silica|silica]]), to form a [[Chemistry:Fayalite|fayalitic]] slag which is essentially [[Chemistry:Calcium silicate|calcium silicate]], {{chem|[[Chemistry:Calcium|Ca]]|[[Chemistry:Silicon|Si]]|[[Chemistry:Oxygen|O]]|3}}:<ref name="Formulae"/>
:SiO<sub>2</sub> + CaO → CaSiO<sub>3</sub><ref name="form2sci">Dr. K. E. Lee, Form Two Science (Biology Chemistry Physics)</ref><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=978-1938168390|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 1200&nbsp;°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 [[Chemistry: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 [[Physics:Boudouard reaction|Boudouard reaction]]:

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

The [[Chemistry:Pig iron|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 [[Chemistry:Cast iron|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 [[Chemistry:Iron sulfide|iron sulfide]] contained in the pig iron to form [[Chemistry:Calcium sulfide|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=2018-06-21|website=tec-science|language=en-US|access-date=2019-11-02}}</ref> In a further process step, the so-called basic oxygen steelmaking, the carbon is oxidized by blowing oxygen onto the liquid pig iron to form ''crude steel''.

Although the efficiency of blast furnaces is constantly evolving, the chemical process inside the blast furnace remains the same. One of the biggest drawbacks of the blast furnaces is the inevitable carbon dioxide production as iron is reduced from iron oxides by carbon and as of 2016, there is no economical substitute – steelmaking is one of the largest industrial contributors of the CO<sub>2</sub> emissions in the world (see greenhouse gases).<ref>{{Cite journal|last1=Wang|first1=Peng|last2=Ryberg|first2=Morten|last3=Yang|first3=Yi|last4=Feng|first4=Kuishuang|last5=Kara|first5=Sami|last6=Hauschild|first6=Michael|last7=Chen|first7=Wei-Qiang|date=2021-04-06|title=Efficiency stagnation in global steel production urges joint supply- and demand-side mitigation efforts|journal=Nature Communications|language=en|volume=12|issue=1|pages=2066|doi=10.1038/s41467-021-22245-6|pmid=33824307|issn=2041-1723|pmc=8024266|bibcode=2021NatCo..12.2066W}}</ref> Several alternatives are being investigated such as plastic waste, biomass or hydrogen as reducing agent, which can substantially reduce the carbon emissions.<ref>{{Cite journal|date=2019-12-01|title=Carbon capture and utilization in the steel industry: challenges and opportunities for chemical engineering|url=https://www.sciencedirect.com/science/article/abs/pii/S221133981930036X|journal=Current Opinion in Chemical Engineering|language=en|volume=26|pages=81–87|doi=10.1016/j.coche.2019.09.001|issn=2211-3398|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.|s2cid=210619173}}</ref> The injection of, for example, hydrogen into blast furnaces can reduce carbon emissions by 20 percent.<ref>{{Cite web |last=Hoffmann |first=Christian |last2=Van Hoey |first2=Michel |last3=Zeumer |first3=Benedikt |date=April 2020 |title=Decarbonization challenge for steel: Hydrogen as a solution in Europe |url=https://www.mckinsey.com/~/media/McKinsey/Industries/Metals%20and%20Mining/Our%20Insights/Decarbonization%20challenge%20for%20steel/Decarbonization-challenge-for-steel.pdf |publisher=McKinsey & Company |page=6}}</ref>

The challenge set by the greenhouse gas emissions of the blast furnace is being addressed in an ongoing{{When|date=July 2021}} European Program called ULCOS (Ultra Low CO<sub>2</sub> [[Engineering:Steelmaking|Steelmaking]]).<ref>http://www.ulcos.org {{webarchive|url=https://web.archive.org/web/20081121182534/http://www.ulcos.org/ |date=21 November 2008 }}</ref> Several new process routes have been proposed and investigated in depth to cut specific emissions ({{CO2}} per ton of steel) by at least 50%. Some rely on the capture and further storage (CCS) of {{CO2}}, while others choose decarbonizing iron and steel production, by turning to hydrogen, electricity and biomass.<ref>ICIT-Revue de Métallurgie, September and October issues, 2009</ref> In the nearer term, a technology that incorporates CCS into the blast furnace process itself and is called the Top-Gas Recycling Blast Furnace is under development, with a scale-up to a commercial size blast furnace under way.{{Update inline|date=July 2021}}

==History==
[[File:Yuan Dynasty - waterwheels and smelting.png|thumb|upright=1.1|An illustration of furnace bellows operated by waterwheels from the ''Nong Shu'', by 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 {{wipe|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 [[History:High Middle Ages|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 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 English inventor Abraham Darby in 1709. The efficiency of the process was further enhanced by the practice of preheating the combustion air ([[Engineering:Hot blast|hot blast]]), patented by Scottish 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 ===
Archaeological evidence shows that bloomeries appeared in China around 800 BC. Originally it was thought that the Chinese started casting iron right from the beginning, but this theory has since been debunked{{Clarify|reason=how does the discovery debunk the hypothesis?|date=July 2021}} by the discovery of 'more than ten' iron digging implements found in the tomb of Duke Jing of Qin (d. 537 BC), whose tomb is located in Fengxiang County, Shaanxi (a museum exists on the site today).<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> There is however no evidence of the bloomery in China after the appearance of the blast furnace and cast iron. In China, blast furnaces produced cast iron, which was then either converted into finished implements in a cupola furnace, or turned into wrought iron in a fining hearth.{{sfn|Wagner|2008|p=230}}

Although [[Chemistry:Cast iron|cast iron]] farm tools and weapons were widespread in China by the 5th century BC, employing workforces of over 200 men in iron smelters from the 3rd century onward, the earliest blast furnaces constructed were attributed to the Han dynasty in the 1st century AD.<ref name="ebrey 30">Ebrey, p.&nbsp;30.</ref> These early furnaces had clay walls and used [[Chemistry:Phosphorus|phosphorus]]-containing minerals as a [[Engineering:Flux (metallurgy)|flux]].<ref>[http://www.staff.hum.ku.dk/dbwagner/KoreanFe/KoreanFe.html Early iron in China, Korea, and Japan] {{webarchive|url=https://web.archive.org/web/20070205063947/http://www.staff.hum.ku.dk/dbwagner/KoreanFe/KoreanFe.html |date=5 February 2007 }}, Donald B. Wagner, March 1993</ref> Chinese blast furnaces ranged from around two to ten meters in height, depending on the region. The largest ones were found in modern Sichuan and Guangdong, while the 'dwarf" blast furnaces were found in Dabieshan. In construction, they are both around the same level of technological sophistication.{{sfn|Wagner|2008|p=6}}

The effectiveness of the Chinese human and horse powered blast furnaces was enhanced during this period by the engineer Du Shi (c.&nbsp;AD&nbsp;31), who applied the power of waterwheels to [[Engineering:Piston|piston]]-[[Engineering:Bellows|bellows]] in forging cast iron.<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 a push bellow.<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 [[Chemistry:Bronze|bronze]]. Certainly, though, iron was essential to military success by the time the State of Qin had unified China (221&nbsp;BC). Usage of the blast and cupola furnace remained widespread during the Song and 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 [[Chemistry:Charcoal|charcoal]] to [[Chemistry: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><ref>Ebrey, p.&nbsp;158.</ref>

The primary advantage of the early blast furnace was in large scale production and making iron implements more readily available to peasants.{{sfn|Wagner|2008|p=169}} Cast iron is more brittle than wrought iron or steel, which required additional fining and then cementation or co-fusion to produce, but for menial activities such as farming it sufficed. By using the blast furnace, it was possible to produce larger quantities of tools such as ploughshares more efficiently than the bloomery. In areas where quality was important, such as warfare, wrought iron and steel were preferred. 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.{{sfn|Wagner|2008|p=1}}

Blast furnaces were also later used to produce [[Chemistry:Gunpowder|gunpowder]] weapons such as cast iron [[Engineering:Shell (projectile)|bomb shells]] and cast iron [[Engineering:Cannon|cannon]]s during the Song dynasty.{{sfn|Liang|2006}}

=== Medieval Europe ===
The simplest [[Engineering:Forge|forge]], known as the Corsican, was used prior to the advent of [[Religion:Christianity|Christianity]]. Examples of improved bloomeries are the Stuckofen,<ref>{{cite book|author=Julius H. Strassburger |title=Blast Furnace-theory and Practice |url=https://books.google.com/books?id=n7oOAAAAQAAJ |access-date=12 July 2012 |year=1969 |publisher=Gordon and Breach Science Publishers |isbn=978-0-677-10420-1 |page=4}}</ref> sometimes called wolf-furnace,<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 ''[[Physics:Trompe|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 [[Physics:Fuel efficiency|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 West were built in Durstel in {{wipe|Switzerland}}, the Märkische Sauerland in {{wipe|Germany}}, and at [[Place:Lapphyttan|Lapphyttan]] in Sweden, where the complex was active between 1205 and 1300.<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 examples, were very inefficient compared to those used today. The iron from the Lapphyttan complex was used to produce balls of [[Chemistry:Wrought iron|wrought iron]] known as osmonds, and these were traded internationally – a possible reference occurs in a treaty with Novgorod from 1203 and several certain references in accounts of English customs from the 1250s and 1320s. Other furnaces of the 13th to 15th centuries have been identified in Westphalia.<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>

The technology required for blast furnaces may have either been transferred from China, or may have been an indigenous innovation. Al-Qazvini in the 13th century and other travellers subsequently noted an iron industry in the Alburz Mountains to the south of the Caspian Sea. This is close to the silk route, so that the use of technology derived from China is conceivable. Much later descriptions record blast furnaces about three metres high.<ref>Wagner 2008, 349–351.</ref> As the Varangian Rus' people from [[Place:Scandinavia|Scandinavia]] traded with the Caspian (using their Volga trade route), it is possible that the technology reached Sweden by this means.<ref>Wagner 2008, 354.</ref> The Vikings are known to have used double bellows, which greatly increases the volumetric flow of the blast.<ref>{{cite web|url=http://www.warehamforge.ca/ROMiron/index.html|title=Adventures in Early Iron Production – An overview of experimental iron smelts, 2001–2005|first= Darrell|last = Markewitz |website=www.warehamforge.ca |url-status=live|date = 25 March 2006|archive-url=https://web.archive.org/web/20150922082031/http://www.warehamforge.ca/ROMiron/index.html |archive-date=22 September 2015}}</ref>

The Caspian region may also have been the source for the design of the furnace at Ferriere, described by Filarete,<ref>Wagner 2008, 355.</ref> involving a water-powered bellows at Semogo in Valdidentro in northern Italy in 1226. In a two-stage process the molten iron was tapped twice a day into water, thereby granulating it.<ref>{{cite journal |last1=Awty |first1=B. G. |title=The Blast Furnace in the Renaissance Period: ''Haut Fourneau'' or ''Fonderie''? |journal=Transactions of the Newcomen Society |date=January 1989 |volume=61 |issue=1 |pages=65–78 |doi=10.1179/tns.1989.005}}</ref>

====Cistercian contributions====
The General Chapter of the Cistercian monks spread some technological advances across Europe. This may have included the blast furnace, as the Cistercians are known to have been skilled [[Chemistry:Metallurgy|metallurgists]].<ref name="Woods 34">Woods, p.&nbsp;34.</ref> 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 [[Earth:Champagne (province)|Champagne]], France, from the mid-13th century to the 17th century,<ref name="Gimpel">Gimpel, p.&nbsp;67.</ref> also using the [[Chemistry:Phosphate|phosphate]]-rich slag from their furnaces as an agricultural [[Chemistry:Fertilizer|fertilizer]].<ref>Woods, p.&nbsp;35.</ref>

Archaeologists are still discovering the extent of Cistercian technology.<ref name="Woods36">Woods, p.&nbsp;36.</ref> At Laskill, an outstation of Rievaulx Abbey and the only medieval blast furnace so far identified in Britain, the slag produced was low in iron content.<ref name="Woods37">Woods, p.&nbsp;37.</ref> Slag from other furnaces of the time contained a substantial concentration of iron, whereas Laskill is believed to have produced cast iron quite efficiently.<ref name="Woods37"/><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 [[Biography: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 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 [[Place:Normandy|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 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 [[Chemistry:Finery forge|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 {{wipe|Russia}} opened in 1637 near 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 in 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 {{wipe|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 [[History:Coalbrookdale|Coalbrookdale]] in Shropshire, England, Abraham Darby began to fuel a blast furnace with [[Chemistry:Coke (fuel)|coke]] instead of [[Chemistry:Charcoal|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 on the Continent.  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.
|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= 978-0226726342 |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 sulfur.  Manganese may also be added to tie up sulfur.)<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=978-0901462886}}</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=0415147921 |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|url-status=dead|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=978-0901462886}}</ref>{{rp|122–123}}

Coke iron was initially only used for [[Engineering:Foundry|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 [[Chemistry:Finery forge|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 [[History:Industrial Revolution|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><ref>Hyde</ref><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> 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 [[Engineering:Girder|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 {{wipe|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 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 [[Company:Boulton and Watt|Boulton and Watt]] to John Wilkinson's 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 [[Physics: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====
[[Engineering: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 [[History:Industrial Revolution|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.
|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
 |title        = Technological Transformations and Long Waves
 |year         = 1989
 |page         = 21
 |url          = http://www.iiasa.ac.at/Admin/PUB/Documents/RR-89-001.pdf
 |url-status      = dead
 |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 Scotland 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.<ref name="Neilson">Birch, pp.&nbsp;181–189.</ref>

Hot blast enabled the use of raw [[Chemistry:Anthracite|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.<ref>Hyde, p.&nbsp;159.</ref> 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==
=== Iron blast furnaces ===
The blast furnace remains an important part of modern iron production. Modern furnaces are highly efficient, including Cowper stoves to [[Engineering: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 ''[[Organization:Global Energy Monitor|Global Energy Monitor]]'', the blast furnace is likely to become obsolete to meet [[Earth:Climate change|climate change]] objectives of reducing carbon dioxide emission,<ref>{{Cite web|date=2021-06-29|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=2021-07-10|website=Reuters}}</ref> but [[Company:BHP|BHP]] disagrees.<ref name=":1" />  An alternative process involving [[Physics:Direct reduced iron|direct reduced iron]] is likely to succeed it,{{Citation needed|date=July 2021}} 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 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 |date=January 2021 |title=A Review on Explorations of the Oxygen Blast Furnace Process |url=https://onlinelibrary.wiley.com/doi/10.1002/srin.202000326 |journal=Steel Research International |language=en |volume=92 |issue=1 |pages=2000326 |doi=10.1002/srin.202000326 |s2cid=224952826 |issn=1611-3683}}</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}}).

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 [[Chemistry: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 [[Chemistry: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 [[Chemistry: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 [[Company:Gerdau|Gerdau]], Brazil]]
Stone wool or [[Chemistry:Mineral wool|rock wool]] is a spun mineral fibre used as an [[Physics:Thermal insulation|insulation]] product and in hydroponics. 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
    |[[Engineering:Hot blast|Hot blast]] from Cowper stoves
    |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 [[Chemistry:Slag|slag]]
    |Tapping of molten [[Chemistry:Pig iron|pig iron]]
    |Collection of waste gases
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 [[Engineering:Hopper car|rail hopper]]s and 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 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>{{Citation | last = McNeil | first = Ian | title = An encyclopaedia of the history of technology | publisher = Taylor & Francis | page = 163 | year = 1990 | url = https://books.google.com/books?id=WW4Q-vMA6IMC | isbn = 0-415-01306-2}}</ref><ref>{{Citation | last = Strassburger | first = Julius H. | title = Blast furnace: Theory and Practice | publisher = Taylor & Francis | page = 564 | year = 1969 | url = https://books.google.com/books?id=xLsOAAAAQAAJ | isbn = 0-677-10420-0}}</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=2008-06-22 |url-status=dead |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 [[Chemistry:Refractory|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, [[Earth:Limestone|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 [[Engineering:Venturi scrubber|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 contains the bustle{{Clarify|date=July 2021}} pipe, water cooled copper tuyeres 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 [[Engineering:Tuyere|tuyere]]s are used to implement a [[Engineering:Hot blast|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 900&nbsp;°C to 1300&nbsp;°C (1600&nbsp;°F to 2300&nbsp;°F) depending on the stove design and condition. The temperatures they deal with may be 2000&nbsp;°C to 2300&nbsp;°C (3600&nbsp;°F to 4200&nbsp;°F). [[Chemistry:Oil|Oil]], [[Chemistry:Tar|tar]], [[Chemistry:Natural gas|natural gas]], powdered [[Earth:Coal|coal]] and [[Chemistry:Oxygen|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 gases present which is necessary to increase productivity.<ref name="AISI"/>

The exhaust gasses of a blast furnace are generally cleaned in the [[Chemistry:Dust collector|dust collector]] –  such as an [[Physics:Inertia|inertia]]l separator, a [[Engineering:Baghouse|baghouse]], or an [[Physics:Electrostatic precipitator|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 [[Physics:Heat exchanger|heat exchanger]].

The IEA Green House Gas R&D Programme (IEAGHG) has shown that in an integrated steel plant, 70% of the {{CO2}} is directly from the blast furnace gas (BFG). It is possible to use carbon capture technology on the BFG before the BFG goes on to be used for heat exchange processes within the plant. In 2000, the IEAGHG estimated using that chemical absorption to capture BFG would cost $35/t of {{CO2}} (an additional $8–20/t of {{CO2}} would be required for {{CO2}} transportation and storage). This would make the entire steel production process in a plant 15–20% more expensive.<ref>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 July 30, 2021.</ref>

==Environmental impact==
[[File:Dust catcher drawing.png|thumb|upright=1.1|A drawing of a blast furnace dust catcher]]
The results showed that [[Earth:Climate change|global warming]] potential and [[Biology:Ocean acidification|acidification]] potential were the most significant environmental impacts. On average producing a tonne of steel emits 1.8 tonnes of {{CO2}}.<ref name=":0">{{Cite news|title=Cleaning up steel is key to tackling climate change|url=https://www.ft.com/content/3bcbcb60-037f-11e9-99df-6183d3002ee1 |archive-url=https://ghostarchive.org/archive/20221210/https://www.ft.com/content/3bcbcb60-037f-11e9-99df-6183d3002ee1 |archive-date=10 December 2022 |url-access=subscription|url-status=live|access-date=2021-07-07|website=[[Social:Financial Times|Financial Times]]|date=January 2019|last1=Pooler|first1=Michael}}</ref><ref>{{Cite web|url=https://www.iea.org/data-and-statistics/charts/direct-co2-intensity-of-the-iron-and-steel-sector-in-the-net-zero-scenario-2010-2030|title=Direct CO2 intensity of the iron and steel sector in the Net Zero Scenario, 2010-2030 – Charts – Data & Statistics|website=IEA}}</ref> However, a steel mill using a top gas recycling blast furnace (TGRBF) producing a tonne of steel will emit 0.8 to 1.3 tonnes of {{CO2}} depending upon the recycle rate of the TGRBF.<ref>{{Cite journal|last1=Ho|first1=Minh T.|last2=Bustamante|first2=Andrea|last3=Wiley|first3=Dianne E.|date=November 2013|title=Comparison of {{CO2}} capture economics for iron and steel mills|url=https://linkinghub.elsevier.com/retrieve/pii/S1750583613003010|journal=International Journal of Greenhouse Gas Control|language=en|volume=19|pages=145–159|doi=10.1016/j.ijggc.2013.08.003|bibcode=2013IJGGC..19..145H }}</ref>

==Decommissioned blast furnaces as museum sites==
{{Main|Engineering:List of preserved historic blast furnaces}}
For a long time, it was normal procedure for a decommissioned blast furnace to be demolished and either be replaced with a newer, improved one, or to have the entire site demolished to make room for follow-up use of the area. In recent decades, several countries have realized the value of blast furnaces as a part of their industrial history. Rather than being demolished, abandoned steel mills were turned into museums or integrated into multi-purpose parks. The largest number of preserved historic blast furnaces exists in Germany; other such sites exist in Spain, France, the [[Place:Czech Republic|Czech Republic]], Great Britain. Japan, Luxembourg, {{wipe|Poland}}, Romania, Mexico, {{wipe|Russia}} and the [[Engineering:List of preserved historic blast furnaces#United States|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
*[[Chemistry:Zinc smelting#Blast furnace process (Imperial Smelting Process)|Blast furnace zinc smelting process]]
*[[Engineering:Crucible steel|Crucible steel]]
*Extraction of iron
*[[Chemistry:Water gas|Water gas]], produced by a "steam blast"
*[[Engineering:FINEX (steelmaking process)|FINEX]]
*Krupp-Renn Process
*[[Engineering:Flodin process|Flodin process]]
*[[Engineering:Steelmaking|Steelmaking]]
<!--please do not list individual ironworks here: the article is quite long enough. -->
*Shaft furnace breather
*[[Chemistry:Direct reduction|Direct reduction]]
*[[Chemistry:Direct reduction (blast furnace)|Direct reduction (blast furnace)]]

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

===Bibliography===
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*{{Citation |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 }}
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*{{Citation |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.]
*[https://www.britannica.com/eb/art-1535 Schematic diagram of blast furnace and Cowper stove]

{{Iron and steel production}}

{{DEFAULTSORT:Blast Furnace}}
[[Category:Industrial Revolution]]
[[Category:Metallurgy]]
[[Category:Steelmaking]]

{{Sourceattribution|Blast furnace}}