- Blast furnace
A blast furnace is a type of metallurgical
furnaceused for smeltingto produce metals, generally iron.
In a blast furnace, fuel and
oreare continuously supplied through the top of the furnace, while air (sometimes with oxygen enrichment) is blown into the bottom of the chamber, so that the chemical reactions take place throughout the furnace as the material moves downward. The end products are usually molten metal and slagphases tapped from the bottom, and flue gases exiting from the top of the furnace.
Blast furnaces are to be contrasted with air furnaces (such as
reverberatory furnaces), which were naturally aspirated, usually by the convection of hot gases in a chimney flue. According to this broad definition, bloomeries for iron, blowing houses for tin, and smelt mills for lead, would be classified as blast furnaces. However, the term has usually been limited to those used for smelting iron oreto produce pig iron, an intermediate material used in the production of commercial iron and steel.
Blast furnaces existed in China from about the 5th century BC, and in the West from the
High Middle Ages. They spread from the region around Namur in Belgiumin the late 15th century, being introduced to England in 1491. The fuel used in these was invariably charcoal. The successful substitution of coke for charcoalis widely attributed to Abraham Darby in 1709. The efficiency of the process was further enhanced by the practice of preheating the blast, patented by James Beaumont Neilsonin 1828.
The blast furnace is distinguished from the bloomery in that the object of the blast furnace is to produce molten metal that can be tapped from the furnace, whereas the intention in the bloomery is to avoid it melting so that carbon does not become dissolved in the iron. Bloomeries were also artificially blown using bellows, but the term "blast furnace" is normally reserved for furnaces where iron (or other metals) are refined from ore.
The Ancient World
The oldest extant blast furnaces were built during the
Han Dynastyof China in the 1st century BC. However, cast ironfarm tools and weapons were widespread in China by the 5th century BC, while 3rd century BC iron smelters employed an average workforce of over two hundred men.Ebrey, p. 30.] These early furnaces had clay walls and used phosphorus-containing minerals as a flux. [ [http://www.staff.hum.ku.dk/dbwagner/KoreanFe/KoreanFe.html Early iron in China, Korea, and Japan] , Donald B. Wagner, March 1993] The effectiveness of the Chinese blast furnace was enhanced during this period by the engineer Du Shi(c. 31 AD), who applied the power of waterwheels to piston- bellowsin forging cast iron. [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 = 0521058031.]
While it was long thought that the Chinese had developed the blast furnace and cast iron as their first method of iron production, Donald Wagner (the author of the above referenced study) has published a more recent paper [ [http://staff.hum.ku.dk/dbwagner/EARFE/EARFE.html The earliest use of iron in China] , Donald B. Wagner, 1999] that supersedes some of the statements in the earlier work; the newer paper still places the date of the first cast iron artifacts at the 4th and 5th century BC, but also provides evidence of earlier bloomery furnace use, which migrated in from the west during the beginning of the Chinese
Bronze Ageof the late Longshan culture(2000 BC). He suggests that early blast furnace and cast iron production evolved from furnaces used to melt bronze. Certainly, though, iron was essential to military success by the time the State of Qinhad unified China (221 BC). By the 11th century, the Song DynastyChinese iron industry made a remarkable switch of resources from charcoalto bituminous coalin casting iron and steel, sparing thousands of acres of prime timberland from felling. [Ebrey, p. 158.]
In Europe, iron was made in bloomeries by the
Greeks, Celts, Romans, and Carthaginians during the ancient period. Several examples have been found in France, and materials found in Tunisia suggest they were used there as well as in Antioch during the Hellenistic Period. Though little is known of it during the Dark Ages, the process probably continued in use. An improved bloomery, named the Catalan forge, was invented in Catalonia, Spain during the 8th century. Instead of using natural draught air was pumped in by bellows, resulting in better quality iron and an increased capacity.
The oldest known blast furnaces in the West were built in
Dürstelin Switzerland, the Märkische Sauerlandin Germany, and at Lapphyttanin Swedenwhere the complex was active between 1150 and 1350. [ [http://www.uni-muenster.de/UrFruehGeschichte/kier1.htm Archaeological Investigations on the Beginning of Blast Furnace-Technology in Central Europe] ] At Noraskog in the Swedish county of Järnboås there have also been found traces of blast furnaces dated even earlier, possibly to around 1100. [A. Wetterholm, 'Blast furnace studies in Nora bergslag' (Örebro universitet 1999, Järn och Samhälle) ISBN 91-7668-204-8 ] 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 wrought ironknown as osmonds, and these were traded internationally – a possible reference occurs in a treaty with Novgorodfrom 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. [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), 143–53 and other papers in the same volume.]
Knowledge of certain technological advances was transmitted as a result of the General Chapter of the Cistercian monks. This may have included the blast furnace, as the Cistercians are known to have been skilled metallurgists.Woods, p. 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 within time surpluses were being offered for sale. The Cistercians became the leading iron producers in Champagne, France, from the mid-13th century to the 17th century,Gimpel, p. 67.] also using the
phosphate-rich slag from their furnaces as an agricultural fertilizer. [Woods, p. 35.]
Archaeologists are still discovering the extent of Cistercian technology.Woods, p. 36.] At
Laskill, an outstation of Rievaulx Abbeyand the only medieval blast furnace so far identified in Britain, the slag produced was low in iron content.Woods, p. 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. [R. W. Vernon, G. McDonnell and A. Schmidt, 'An integrated geophysical and analytical appraisal of early iron-working: three case studies' "Historical Metallurgy" 31(2) (1998), pp. 72–5, 79] David Derbyshire, 'Henry "Stamped Out Industrial Revolution"', " The Daily Telegraph" (21 June 2002); cited by Woods.] Its date is not yet clear, but it probably did not survive until Henry VIII's Dissolution of the Monasteriesin the late 1530s, as an agreement (immediately after that) concerning the "smythes" with the Earl of Rutland in 1541 refers to blooms. [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.] Nevertheless, the means by which the blast furnace spread in medieval Europe has not finally been determined.
Early modern blast furnaces: origin and spread
The direct ancestor of those used in France and England was in the Namur region in what is now
Belgium. From there, they spread first to the Pays de Brayon the eastern boundary of Normandyand from there to the Wealdof Sussex, where the first furnace (called Queenstock) in Buxtedwas built in about 1491, followed by one at Newbridgein Ashdown Forestin 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 forges for the production of bar iron. B. Awty & C. Whittick (with P. Combes), 'The Lordship of Canterbury, iron-founding at Buxted, and the continental antecedents of cannon-founding in the Weald' "Sussex Archaeological Collections" 140 (2004 for 2002), pp. 71–81.]
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
Swedenand 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. [ 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. 593–613.]
The first blast furnace in Russia opened in 1637 near Tula and was called the Gorodishche Works. The blast furnace spread from here to the center of Russia and then finally to the
Urals.cite journal | last = Yakovlev | first = V. B. | title = Development of Wrought Iron Production | journal = Metallurgist | volume = Volume 1 | issue = Number 8 | pages = 545 | publisher = Springer | location = New York | date = August 1957 | url = http://www.springerlink.com/content/hx515m2689563420/ | doi = 10.1007/BF00732452 | id = 0026-0894 | accessdate = 2008-01-13]
Coke blast furnaces
In 1709, at
Coalbrookdalein Shropshire, England, Abraham Darby began to fuel a blast furnace with coke instead of charcoal. Coke iron was initially only used for foundrywork, 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 forges 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. [Citation | last = Raistrick | first = Arthur | title = Dynasty of Iron Founders: The Darbys and Coalbrookedale | place = York | publisher = Longmans, Green | year = 1953.] [Hyde] [Citation | last = Trinder | first = Barrie Stuart | last2 = Trinder | first2 = Barrie | title = The Industrial Revolution in Shropshire | place = Chichester | publisher = Phillimore | year = 2000 | isbn = 1860771335.] Darby's old blast furnace has been archaeologically excavated and can be seen in situ at Coalbrookdale, part of the Ironbridge GorgeMuseums.
A further important development was the change to
hot blast, patented by James Beaumont Neilsonat Wilsontown Ironworksin Scotland in 1828. This further reduced production costs. 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.Birch, pp. 181–9.]
A further significant development was the application of raw
anthracitecoal to the blast furnace, first tried successfully by George Crane at Yniscedwynironworks in south Wales in 1837. [Hyde, p. 159.] It was taken up in America by the Lehigh Crane Iron Companyat Catasauqua, Pennsylvaniain 1839.
The blast furnace remains an important part of modern iron production. Modern furnaces are highly efficient, including Cowper stoves to 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 furnaces have a volume around 5580 m3 (190,000 cu ft) [Citation | title = Made in Ukraine | url = http://www.madeinua.info/view.aspx?type=ja&lang=2&jaid=261 | accessdate = 2008-05-20.] and can produce around 80,000 tonnes (88,000 short tons) of iron per week.
This is a great increase from the typical 18th-century furnaces, which averaged about 360 tonnes (400 short tons) 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.
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 rail hoppers 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. [http://www.steel.org/AM/Template.cfm?Section=Home&template=/CM/HTMLDisplay.cfm&ContentID=5433 AISI] ]
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 the 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. The bell is then rotated a predetermined amount in order to distribute the charge more accurately. The small bell then opens to empty the charge into the large bell. The small bell then closes, to seal the blast furnace, while the large bell dispenses the charge into the blast furnace.Citation | last = McNeil | first = Ian | title = An encyclopaedia of the history of technology | publisher = Taylor & Francis | page = 163 | year = 1990 | url = http://books.google.com/books?id=WW4Q-vMA6IMC | isbn = 0415013062.] [Citation | last = Strassburger | first = Julius H. | title = Blast furnace: Theory and Practice | publisher = Taylor & Francis | page = 564 | year = 1969 | url = http://books.google.com/books?id=xLsOAAAAQAAJ | isbn = 0677104200.] 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. 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 chute in order to precisely control where the charge is placed. [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 | accessdate = 2008-06-22.]
The iron making blast furnace itself is built in the form of a tall
chimney-like structure lined with refractorybrick. Coke, limestoneflux, 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 to exit the furnace dome, while "bleeder valves" protect the top of the furnace from sudden gas pressure surges. The coarse particles in the 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 scrubberand a gas cooler to reduce the temperature of the cleaned gas.
The "casthouse" at the bottom half of the furnace contains the bustle pipe, 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.
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 900 °C to 1300 °C (1600 °F to 2300 °F) depending on the stove design and condition. The temperatures they deal with may be 2000 °C to 2300 °C (3600 °F to 4200 °F). Oil, tar, natural gas, powdered coaland oxygencan also be injected into the furnace at tuyere level to combine with the coke to release additional energy which is necessary to increase productivity.
The main chemical reaction producing the molten iron is:
:Fe2O3 + 3CO → 2Fe + 3CO2cite web | title = Blast Furnace | publisher = Science Aid | accessdate = 2007-12-30 | url = http://www.scienceaid.co.uk/chemistry/industrial/blastfurnace.html]
Preheated blast air blown into the furnace reacts with the carbon in the form of coke to produce
carbon monoxideand heat. The carbon monoxide then reacts with the iron oxideto produce molten iron and carbon dioxide. 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, decompose the limestone to calcium oxideand carbon dioxide, and begin to reduce the iron oxides in the solid state. The main reaction controlling the gas atmosphere in the furnace is called the Boudouard reaction:
The decomposition of limestone in the middle zones of the furnace proceeds according to the following reaction:
:CaCO3 → CaO + CO2
The "pig" iron produced by the blast furnace has a relatively high carbon content of around 4–5%, making it very brittle, and of little 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 content and produce various grades of steel used for tools and construction materials.
Although the efficiency of blast furnaces is constantly evolving, the chemical process inside the blast furnace remains the same. According to the
American Iron and Steel Institute: "Blast furnaces will survive into the next millennium because the larger, efficient furnaces can produce hot metal at costs competitive with other iron making technologies." 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 there is no economical substitute – steelmaking is one of the unavoidable industrial contributors of the CO2 emissions in the world (see greenhouse gases).
Basic oxygen furnace
*Blast furnace zinc smelting process
Extraction of iron
*, which covers ironworks of all kinds.
*cite book |last=Birch |first=Alan |last2 = Birch |first2 = Alan |title= The Economic History of the British Iron and Steel Industry, 1784-1879 |year= 2005 |publisher= Routledge |isbn=0415382483
*Citation | last = Ebrey | first = 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 = 0618133844.
*Citation | 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 = 0030146364.
*cite book |last=Hyde |first=Charles K. |title=Technological Change and the British iron industry, 1700-1870 |date=1977 |publisher= Princeton University Press |location=Princeton |isbn= 0691052468
*cite book |last=Woods |first=Thomas |title=How the Catholic Church Built Western Civilization |date=2005 |isbn=0-89526-038-7
* [http://www.scienceaid.co.uk/chemistry/industrial/blastfurnace.html Science Aid: Blast Furnace] How iron is extracted, for high school level
* [http://www.bbc.co.uk/history/british/victorians/launch_ani_blast_furnace.shtml Blast Furnace animation ]
* [http://www.steel.org/AM/Template.cfm?Section=Home&template=/CM/HTMLDisplay.cfm&ContentID=5433 How a Blast Furnace works] Illustrated.
* [http://www.davistownmuseum.org/toolPreBlastFurnace.html Precursors of the Blast Furnace]
* [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.]
* [http://www.radwerk-vordernberg.at Blast Furnace Museum Radwerk IV]
* [http://www.britannica.com/eb/art-1535 Schematic diagram of blast furnace and Cowper stove]
* [http://www.ironfurnaces.com ironfurnaces.com - a free wiki dedicated to preserving the history and location of historic blast iron furnaces]
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