Reverberatory furnace
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A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term reverberation is used here in a generic sense of rebounding or reflecting, without the more common acoustic denotation.
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[edit] Operation
Process chemistry 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, 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.
[edit] 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) to maximize heat transfer. Historically these furnaces have utilized solid fuel, and bituminous coal 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 or charcoal.
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 can be puddled in an oxidizing atmosphere to convert it to the lower-carbon mild steel or bar iron.
Reverberatory furnaces (here usually called air furnaces) were formerly also used for melting brass (i.e. bronze) and pig iron for foundry work.
[edit] History
The first reverberatory furnaces were perhaps in the medieval period, and were used for melting bronze for casting bells. They were first applied to smelting metals in the late 17th century. Sir Clement Clerke and his son Talbot built cupolas or reverberatory furnaces in the Avon Gorge below Bristol 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 purposes. This was used at Coalbrookdale and various other places, but became obsolete at the end of the 18th century with the introduction of the foundry 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 in the 1780s to replace the older finery process, was also a variety of reverberatory furnace.
[edit] References
- Encyclopædia Britannica, 14th ed.
- J. Day & R. F. Tylecote (eds.), The Industrial Revolution in Metals (1991)
- P. W. King, 'Sir Clement Clerke and the Adoption of coal in metallurgy' Transactions of the Newcomen Society 73(1) (2001-2), 33-53.
