Open hearth furnaces are one of a number of kinds of
furnaceA furnace is a device used for heating. The name derives from Latin fornax, oven. The earliest furnace was excavated at Balakot, a site of the Indus Valley Civilization, dating back to its mature phase...
where excess carbon and other impurities are burnt out of the
pig ironPig iron is the intermediate product of smelting iron ore with coke, usually with limestone as a flux. Pig iron has a very high carbon content, typically 3.5–4.5%, which makes it very brittle and not useful directly as a material except for limited applications.The traditional shape of the molds...
to
produce steelSteelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.-Modern...
. Since
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
is difficult to manufacture due to its high
melting pointThe melting point of a solid is the temperature range at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point...
, normal fuels and furnaces were insufficient and the open hearth furnace was developed to overcome this difficulty. Most open hearth furnaces were closed by the early 1990s, not least because of their fuel inefficiency, being replaced by the basic oxygen furnace or
electric arc furnaceAn is a furnace that heats charged material by means of an electric arc.Arc furnaces range in size from small units of approximately one ton capacity up to about 400 ton units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a...
.
Technically perhaps, the first primitive open hearth furnace was the Catalan forge, invented in Spain in the 8th century, but it is usual to confine the term to certain 19th century and later steelmaking processes, thus excluding
bloomeriesA bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...
(including the Catalan forge),
finery forgeIron tapped from the blast furnace is pig iron, and contains significant amounts of carbon and silicon. To produce malleable wrought iron, it needs to undergo a further process. In the early modern period, this was carried out in a finery forge....
s, and puddling furnaces from its application.
Sir
Carl Wilhelm SiemensCarl Wilhelm Siemens was a German born engineer who for most of his life worked in Britain and later became a British subject.-Biography:...
developed the
Siemens regenerative furnace in the 1850s, and claimed in 1857 to be recovering enough heat to save 70-80% of the fuel.
Open hearth furnaces are one of a number of kinds of
furnaceA furnace is a device used for heating. The name derives from Latin fornax, oven. The earliest furnace was excavated at Balakot, a site of the Indus Valley Civilization, dating back to its mature phase...
where excess carbon and other impurities are burnt out of the
pig ironPig iron is the intermediate product of smelting iron ore with coke, usually with limestone as a flux. Pig iron has a very high carbon content, typically 3.5–4.5%, which makes it very brittle and not useful directly as a material except for limited applications.The traditional shape of the molds...
to
produce steelSteelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.-Modern...
. Since
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
is difficult to manufacture due to its high
melting pointThe melting point of a solid is the temperature range at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point...
, normal fuels and furnaces were insufficient and the open hearth furnace was developed to overcome this difficulty. Most open hearth furnaces were closed by the early 1990s, not least because of their fuel inefficiency, being replaced by the basic oxygen furnace or
electric arc furnaceAn is a furnace that heats charged material by means of an electric arc.Arc furnaces range in size from small units of approximately one ton capacity up to about 400 ton units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a...
.
Technically perhaps, the first primitive open hearth furnace was the Catalan forge, invented in Spain in the 8th century, but it is usual to confine the term to certain 19th century and later steelmaking processes, thus excluding
bloomeriesA bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...
(including the Catalan forge),
finery forgeIron tapped from the blast furnace is pig iron, and contains significant amounts of carbon and silicon. To produce malleable wrought iron, it needs to undergo a further process. In the early modern period, this was carried out in a finery forge....
s, and puddling furnaces from its application.
The Siemens regenerative furnace
Sir
Carl Wilhelm SiemensCarl Wilhelm Siemens was a German born engineer who for most of his life worked in Britain and later became a British subject.-Biography:...
developed the
Siemens regenerative furnace in the 1850s, and claimed in 1857 to be recovering enough heat to save 70-80% of the fuel. This furnace operates at a high temperature by using
regenerative preheatingAn air preheater is a general term to describe any device designed to heat air before another process with the primary objective of increasing the thermal efficiency of the process...
of fuel and air for
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
. In regenerative preheating, the exhaust gases from the furnace are pumped into a chamber containing bricks, where heat is transferred from the gases to the bricks. The flow of the furnace is then reversed so that fuel and air pass through the chamber and are heated by the bricks. Through this method, an open-hearth furnace can reach temperatures high enough to melt steel, but Siemens did not initially use it for that.
The regenerators are the distinctive feature of the furnace and consist of fire-brick flues filled with bricks set on edge and arranged in such a way as to have a great number of small passages between them. The bricks absorb most of the heat from the outgoing waste gases and return it later to the incoming cold gases for combustion.
Open hearth steelmaking
In 1865, the french engineer Pierre-Emile Martin took out a license from Siemens and first applied his furnace for making
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
. Their process was known as the
Siemens-Martin process, and the furnace as an "open-hearth" furnace. The most appealing characteristic of the Siemens regenerative furnace is the rapid production of large quantities of basic steel, used for example to construct high-rise buildings. The usual size of furnaces is 50 to 100 tons, but for some special processes they may have a capacity of 250 or even 500 tons. The Siemens-Martin process complemented rather than replaced the
Bessemer processThe Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. The process was independently discovered in 1851 by William Kelly...
. It is slower and thus easier to control.
The
basic oxygen steelmaking is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. The LD-converter is named after the Austrian placenames Linz and Donawitz . The vast majority of steel manufactured in the world is produced using the basic oxygen furnace...
replaced the open hearth furnace. In the US, steel production using the inefficient open hearth furnaces had stopped by 1992. The nation with the highest share of steel produced with open hearth furnaces (almost 50%) remains Ukraine.
http://www.energystar.gov/ia/business/industry/41724.pdf
Further reading
- K. Barraclough, Steelmaking 1850-1900 (Institute of Metals, London 1990), 137-203.
- W. K. V. Gale, Iron and Steel (Longmans, London 1969), 74-77.
External links
- Precursors to the Blast Furnace
- Administering Doses of Liquid Iron to Steel Furnaces, Popular Science
Popular Science is an American monthly magazine founded in 1872 carrying articles for the general reader on science and technology subjects. Popular Science has won over 58 awards, including the ASME awards for its journalistic excellence in both 2003 and 2004...
monthly, February 1919, page 64, Scanned by Google Books: http://books.google.com/books?id=7igDAAAAMBAJ&pg=PA64