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Reverberatory furnace

Reverberatory furnace

Overview
A reverberatory furnace is a metallurgical
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

 or process furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...

 that isolates the material being processed from contact with the fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

, but not from contact with combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 gases. The term reverberation is used here in a generic sense of rebounding or reflecting
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...

, not in the acoustic
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...

 sense of echoing.


Process chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 determines the optimum relationship between the fuel and the material, among other variables.
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Encyclopedia
A reverberatory furnace is a metallurgical
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

 or process furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...

 that isolates the material being processed from contact with the fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

, but not from contact with combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 gases. The term reverberation is used here in a generic sense of rebounding or reflecting
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...

, not in the acoustic
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...

 sense of echoing.

Operation



Process chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 determines the optimum relationship between the fuel and the material, among other variables. The reverberatory furnace can be contrasted on the one hand with the blast furnace
Blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore and flux are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions...

, in which fuel and material are mixed in a single chamber, and, on the other hand, with crucible, muffling, or retort furnaces, in which the subject material is isolated from the fuel and all of the products of combustion including gases and flying ash. It has been stated in some contexts that the reverberatory furnace also typically separates the material from the hot gases, but this does not seem to be the case in general. Indeed, some applications require contact between the material and the hot gas. There are, however, a great many furnace designs, and the terminology of metallurgy has not been very consistently defined, so it is difficult to categorically contradict the other view.

Applications and comparison with blast furnace


The applications of these devices fall into two general categories, metallurgical melting furnaces, and lower temperature processing furnaces typically used for metallic ores and other minerals.

A reverberatory furnace is at a disadvantage from the standpoint of efficiency compared to a blast furnace due to the spatial separation of the burning fuel and the subject material, and it is necessary to effectively utilize both reflected radiant heat and direct contact with the exhaust gases (convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

) to maximize heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

. Historically these furnaces have used solid fuel, and bituminous coal
Bituminous coal
Bituminous coal or black coal is a relatively soft coal containing a tarlike substance called bitumen. It is of higher quality than lignite coal but of poorer quality than Anthracite...

 has proven to be the best choice. The brightly visible flames (due to the substantial volatile component) give more radiant heat transfer than anthracite coal
Anthracite coal
Anthracite is a hard, compact variety of mineral coal that has a high luster...

 or charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...

.

Contact with the products of combustion, which may add undesirable elements to the subject material, is used to advantage in some processes. Control of the fuel/air balance can alter the exhaust gas chemistry toward either an oxidizing or a reducing mixture, and thus alter the chemistry of the material being processed. For example cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

 can be puddled in an oxidizing atmosphere to convert it to the lower-carbon mild steel or bar iron.

Reverberatory furnaces (in this context, usually called air furnaces) were formerly also used for melting brass, bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

, and pig iron
Pig iron
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...

 for foundry
Foundry
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...

 work.

History



The first reverberatory furnaces were perhaps in the medieval period, and were used for melting bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

 for casting bells. They were first applied to smelting metals in the late 17th century. Sir Clement Clerke
Clement Clerke
Sir Clement Clerke, 1st Baronet was an important English entrepreneur, whose greatest achievement was the application of the reverberatory furnace to smelting lead and copper, and to remelting pig iron for foundry purposes.-Background:Clement Clerke was the third son of George Clerke of...

 and his son Talbot built cupolas or reverberatory furnaces in the Avon
River Avon, Bristol
The River Avon is an English river in the south west of the country. To distinguish it from a number of other River Avons in Britain, this river is often also known as the Lower Avon or Bristol Avon...

 Gorge below Bristol
Bristol
Bristol is a city, unitary authority area and ceremonial county in South West England, with an estimated population of 433,100 for the unitary authority in 2009, and a surrounding Larger Urban Zone with an estimated 1,070,000 residents in 2007...

 in about 1678. In 1687, while obstructed from smelting lead (by litigation), they moved on to copper. In the following decades, reverberatory furnaces were widely adopted for smelting these metals and also tin. They had the advantage over older methods that the fuel was mineral coal, not charcoal or 'white coal' (chopped dried wood).

In the 1690s, they (or associates) applied the reverberatory furnace (in this case known as an air furnace) to melting pig iron for foundry
Foundry
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...

 purposes. This was used at Coalbrookdale
Coalbrookdale
Coalbrookdale is a village in the Ironbridge Gorge in Shropshire, England, containing a settlement of great significance in the history of iron ore smelting. This is where iron ore was first smelted by Abraham Darby using easily mined "coking coal". The coal was drawn from drift mines in the sides...

 and various other places, but became obsolete at the end of the 18th century with the introduction of the foundry
Foundry
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...

 cupola, which was a kind of small blast furnace, and a quite different species from the reverberatory furnace.

The puddling furnace, introduced by Henry Cort
Henry Cort
Henry Cort was an English ironmaster. During the Industrial Revolution in England, Cort began refining iron from pig iron to wrought iron using innovative production systems. In 1783 he patented the puddling process for refining iron ore...

 in the 1780s to replace the older finery process
Finery forge
Iron 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....

, was also a variety of reverberatory furnace.

Aluminium smelting


Today, reverberatory furnaces are widely used to smelt secondary aluminium scrap for eventual use by die-casting industries.

The simplest reverberatory is nothing more than a steel box lined with alumina refractory brick with a flue at one end and a vertically lifting door at the other. Conventional oil or gas burners are placed usually either side of the furnace to heat the brick and the eventual bath of molten metal is then poured into a casting machine to produce ingots.