Jump to content

Water jacket furnace (metallurgy)

Add links
From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by TrimmerinWiki (talk | contribs) at 09:47, 28 December 2024. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

A water jacket furnace is a type of blast furnace used to smelt non-ferrous metallic ores, most typically ores of copper or silver-lead. It takes its name from the water jacket arrangement used to cool the lower furnace casing and prolong the life of the furnace hearth. Nearly entirely replaced, by flash smelting of ore concentrates, the water jacket furnace is now virtually an obsolete technology.

The terminology is also used for an indirect heating device used in the petroleum oil and gas industry, generally known as a water jacket heater[1] or water bath heater, which should not be confused with the metallurgical water jacket furnace.

History

Water jacket furnaces under construction

In the mid 19th Century, most non-ferrous smelting was done using reverberatory furnaces. Blast furnaces were used to smelt sulphide copper ore in the Harz Mountains of Germany. The mines at Burra in South Australia tried to adopt the technology, in 1847, but without success because the German furnace design, using horse-powered bellows to provide the air blast, was not well suited to their carbonate copper ore.[2]

The 'water jacket' blast furnace design for non-ferrous smelting arose in North America, during the 1870s,[3] and an alternative name for it, in Australia, was 'American water jacket furnace'.[4] The design evolved from earlier German cupola furnace designs, with the distinguishing innovation being a well-controlled cooling of the furnace shell.[3]

Water jacket furnaces began to be common in the later part of the century, from the 1880s, particularly for smelting sulphide ores. Unlike reverberatory furnaces, water jacket furnaces could be made in a factory and then assembled at site.[3]

Not all situations and ores were well-suited to water jacket furnace operation. Some attempts to apply them were costly failures, such as at the North Lyell mine, at Crotty, Tasmania,[5] and Lloyd's Mine at Burraga[6] and the Overflow Mine at Bobadah, both in New South Wales.[7] However, the furnaces were hugely successful, when well applied, such as at the vast Anaconda Copper Mine, in Butte, Montana, the Mt Lyell Mine in Tasmania,[5] and at many other mines.

Water jacket furnaces only ever partially displaced reverberatory furnaces in the copper industry, until both furnace types were displaced, almost entirely, by flash smelting, between around 1949 and 1980.[8]

Technology and application

Smelting

Small round water jacket furnace for silver-lead ore

A water jacket furnace could be used to reduce non-ferrous oxide ores mixed with coke, to produce metal, but its main use was smelting the more common sulphide ores. The feedstock was the ore, coke and fluxes. When smelting lead sulphide ores, a water jacket furnace produces molten lead and slag. Lead and silver often occur in the same ore body. Separating silver metal from the crude lead produced by a furnace needed a second process of refining, such as the Parkes process.

The pyrometallurgical process of a water jacket furnace, when smelting copper sulphide ores, is fundamentally different to a conventional blast furnace used to make iron, or a water jacket furnace used to make lead. The conventional blast furnace process produces molten metal by reducing the ore, and separating out the silica as slag. Water jacket furnaces, when smelting sulphide copper ores, used an oxidation reaction that produces molten copper matte, which must be further treated in a convertor (similar in concept to a Bessemer convertor) or reverberatory furnace to produce copper metal. The product of that conversion process is known as blister copper.[3] If the smelter did not have a convertor, the matte was poured into moulds and allowed to solidify.

The smelting of sulphide ores in a water jacket furnace can be viewed as concentrating the non-ferrous metallic portion of the ore, as matte, and separating out some impurities, such as silica and iron, in the mainly iron silicate slag, and much of the sulphur, as sulphur dioxide in the off-gas. The molten slag and matte separate, with the denser molten matte accumulating at the bottom of the furnace, with a layer of molten slag immediately above it.[3]

Depending upon the composition of the ore being smelted, the choice of a suitable flux was particularly important.[9] Fluxes used could be limestone, iron oxide, or silica (quartz), depending upon what was needed to create slag and to minimise the loss of copper with that slag. When both 'basic' (oxide or carbonate) ores and 'siliceous' sulphide ores were available, feeding the furnaces with a mixture of the two copper ore types reduced the amount of other fluxes needing to be added.[10][11]

Advantages and disadvantages

Rectangular cross-section water jacket furnace. The charging doors are at the top on the side that is not visible.

Water jacket furnaces had some advantages over reverberatory furnaces. Fuel consumption was lower. Sulphide ores could be smelted without first roasting the ore. Production per furnace was generally higher. Low grade ore could be smelted, because the water jacket furnace could more readily discharge large amounts of molten slag. Because solidified slag is unsuitable to backfill the voids (stopes) created by underground mining, disposal of large volumes of slag, from smelting of low grade ores, was a significant problem. Some mines treated molten slag with water to create granulated slag, which could be used to backfill stopes.[12] Otherwise, the molten slag was dumped and large slag dumps accumulated near the smelter, becoming a lasting legacy of smelting operations.[13]

Smelting of low grade ores became less prevalent, once the froth flotation process was used to produce ore concentrates.

Another advantage of the water jacket furnace was that, while out of service, the bottom of the furnace, if so designed, could be 'dropped' for cleaning it up or for repair. Over time, a significant amount of copper material would accumulate in the bottom of a reverberatory furnace which could not be accessed without effectively demolishing the furnace.[14]

A disadvantage of the water jacket furnace was that it could not handle fine ore well and was so was better suited to lump ore. Fines tended to either choke the furnace or were blown into the flue by the air blast. Eventually, the second problem, only, would be solved by capturing the flue dust and recycling it.[3]

An initial disadvantage of the water jacket furnace was its use of coke as fuel. It could not use the cheaper fuels such as firewood or fine raw coal that could be used to fire a reverberatory furnace. That disadvantage was offset by lower overall fuel consumption. In the first years of the 20th Century, the perfection of a technique known as pyritic smelting greatly reduced coke consumption, when smelting suitable ores such as chalcopyrite, by optimizing the use of the sulphur and iron in the ore itself, as a fuel generating heat.[15][16] The iron oxide so produced combined with molten silica to form an iron silicate slag.[16]

Water jacket furnaces needed blowers and a cooling water supply, and were more complex to build and operate than the reverberatory furnaces. Water jacket furnaces, like other blast furnaces, are best operated continuously, and smelters that used them had to work continuously too.

Differences from conventional blast furnace design

The design of water jacket furnaces differ from the conventional blast furnaces used for smelting iron ore, which use a hot blast. Water jacket furnaces typically used a cold air blast, typically provided by a positive-displacement blower, such as a Roots blower. Preheating of the air blast was used on some water jacket furnaces, but preheating of the blast had no advantage when the furnace was being used for pyritic smelting of copper ore.[17][18]

The horizontal cross-section of water jacket furnaces was usually rectangular—although circular and oval cross-section ones did exist[4]—whereas conventional blast furnaces always have a circular horizontal cross-section. In some larger furnace designs, molten metal / matte and molten slag were tapped at the opposite narrow ends of the rectangular base. Water jacket furnaces typically had a higher number of smaller tuyeres than a conventional blast furnace.

Typically, the feedstock was fed into a water jacket furnace through a sliding door arrangement in the side of the upper furnace structure,[17][4] but not via the top itself as in a blast furnace for iron. At the top of a water jacket furnace there was a fixed flue. The off-gas was not suitable to be recycled as a fuel, as is done in a blast furnace making iron (blast furnace gas). However, the sulphur dioxide in the flue gases, from those furnaces using the pyritic smelting process, could be used to make sulphuric acid, which reduced the level of air pollution created by the smelter.[19] If the flue gas needed to be dispersed to the atmosphere, a tall chimney was necessary.[20] to ensure that the noxious gases from smelting, largely sulphur dioxide, were carried far from the smelter and any nearby settlement. Dust carried in the flue gas was often collected, as it had a significant metallic content.[21]

In contrast to a conventional blast furnace, at least in the ultimate form of the water jacket furnace used for copper smelting, both matte and slag were run off more or less continuously. There was a separate slag spout to run off slag. However, the molten matte run from the furnace, under this arrangement, still contained a proportion of slag. The matte was run first into a vessel known as a 'settler' to allow any slag to accumulate on the surface, from where it could overflow from the settler. From tap holes at the bottom of the settler, the molten matte was run into ladles, which were used to transport the matte to a convertor, where it was processed to make blister copper.[21] The 'settler' presented a hazard to furnace operators.[22]

Other applications

A variant of the water jacket furnace was used to smelt lead-zinc ores using the Imperial Smelting Process. In that case, the furnace was completely sealed, to allow the zinc to be recovered, from flue gases, in its vapour phase.[23]

Water jacket furnaces were used to reprocess copper smelter slag that still contained a significant amount of copper, especially slag from smelting high-grade copper ore in reverberatory furnaces.

Although rarely done, small water jacket furnaces have been used to recover gold from quartz rock—particularly if the ore was very rich in gold or sulphide ores of other metals were also present—as an alternative to crushing the rock and extracting the gold using other methods.[24][25] However, it was a very inefficient method of extracting gold.[26]

Where gold and silver were present in copper ores, the precious metals were present in the copper matte produced by a water jacket furnace. The precious metals could later be separated from blister copper, using electrolytic copper refining, and delivered in the form of dore bullion.

Demise

As the typical average ore grades of copper mines declined, ore smelting became uneconomic and was largely superseded by a process consisting of ore concentration, especially using froth flotation, and smelting of ore concentrates. The water jacket furnace was less well suited to that new regime—especially large ones that had been used to smelt low grade ores—and, after the introduction of flash smelting, from around 1949, had fallen out of favour by 1980.[8] It is now a largely forgotten technology.

  • Water jacket furnaces
  • Section through a water jacket furnace, most likely one at Mount Lyell in Tasmania. At bottom left is the 'settler'.
    Section through a water jacket furnace, most likely one at Mount Lyell in Tasmania. At bottom left is the 'settler'.
  • Lower part of a water jacket furnace used to smelt copper ore.
    Lower part of a water jacket furnace used to smelt copper ore.
  • Great Cobar mine - Water jacket furnaces, from outside the smelter building, showing furnace flues to main flue, and slag wagons (1912)
    Great Cobar mine - Water jacket furnaces, from outside the smelter building, showing furnace flues to main flue, and slag wagons (1912)
  • Great Cobar mine - Pouring molten copper matte from a water jacket furnace, viewed from inside the smelter building (June 1912)
    Great Cobar mine - Pouring molten copper matte from a water jacket furnace, viewed from inside the smelter building (June 1912)
  • Great Cobar mine, feeding floor of furnaces (1912)
    Great Cobar mine, feeding floor of furnaces (1912)
  • Great Cobar mine, slag runoff into ladle wagons (1912). The flue dust collection hoppers are visible below the brickwork.
    Great Cobar mine, slag runoff into ladle wagons (1912). The flue dust collection hoppers are visible below the brickwork.
  • Anaconda Copper, Montana, charging equipment at the upper level of furnaces (c.1912)
    Anaconda Copper, Montana, charging equipment at the upper level of furnaces (c.1912)
  • Anaconda Copper, water jacket furnaces showing settlers (c.1912)
    Anaconda Copper, water jacket furnaces showing settlers (c.1912)
  • Anaconda Copper - Flue dust hoppers and tracks underneath (c.1912)
    Anaconda Copper - Flue dust hoppers and tracks underneath (c.1912)
  • Smelter and sulphuric acid plant, Copperhill, Tenessee, 1939.
    Smelter and sulphuric acid plant, Copperhill, Tenessee, 1939.
  • Small water jacket furnace for copper smelting, Hancock, Michigan, c.1906.
    Small water jacket furnace for copper smelting, Hancock, Michigan, c.1906.
  • Surviving lower portion of a water jacket furnace, Zeehan, Tasmania
    Surviving lower portion of a water jacket furnace, Zeehan, Tasmania

See also

References

  1. ^ "Water Jacket Heater/INDIRECT HEATER_Luoyang Runcheng Petrochemical Equipment Co.,LTD.---Focus on ASME Test Separator since 2004". www.lrcoilequipment.com. Retrieved 22 December 2024.
  2. ^ "Ore Smelting at the Burra Mine". www.burrasa.info. Retrieved 3 December 2024.
  3. ^ a b c d e f Bell, Peter; McCarthy, Justin (September 2010). "The Evolution of Early Copper Smelting Technology in Australia (Part I)" (PDF). Journal of Australasian Mining History. 8: 6–10.
  4. ^ a b c "MODERN COPPER SMELTING". Adelaide Observer. 28 March 1903. p. 31. Retrieved 22 December 2024.
  5. ^ a b Bell, Peter; McCarthy, Justin (September 2011). "The Evolution of Early Copper Smelting Technology in Australia (Part II)" (PDF). Australasian Journal of Mining History. 9: 20–23.
  6. ^ "Lloyd's Copper Mine". The Sydney Morning Herald. 15 December 1906. p. 6. Retrieved 13 September 2020.
  7. ^ "BOBADAH". Lachlander and Condobolin and Western Districts Recorder. 27 October 1899. p. 11. Retrieved 27 December 2024.
  8. ^ a b Graphic from Constraints and Ingenuity: The Case of Outokumpu and the Development of Flash Smelting in the Copper Industry, 22 June 2015, retrieved 4 December 2024
  9. ^ "Sectional Water Jacket Furnace". Australian Town and Country Journal. 15 July 1893. p. 24. Retrieved 5 December 2024.
  10. ^ "DOES THE C.S.A. MINE JUSTIFY THE LINE?". Cobar Herald. 5 June 1914. p. 4. Retrieved 5 December 2024.
  11. ^ "Cobar's Prospects". Western Age. 13 September 1918. p. 3. Retrieved 5 December 2024.
  12. ^ Bell, Peter; McCarthy, Justin (September 2010). "The Evolution of Early Copper Smelting Technology in Australia" (PDF). Journal of Australasian Mining History. 8: 11–12, 18–19.
  13. ^ "OLD COBAR". Dubbo Dispatch and Wellington Independent. 2 March 1928. p. 2. Retrieved 25 September 2024.
  14. ^ "The Queen Bee Mine". Western Age. 2 December 1914. p. 2. Retrieved 10 January 2023.
  15. ^ Bell, Peter; McCarthy, Justin (September 2010). "The Evolution of Early Copper Smelting Technology in Australia" (PDF). Journal of Australasian Mining History. 8.
  16. ^ a b Levy, Donald M. (1912). "Modern Copper Smelting". Gutenberg. pp. 169–188.
  17. ^ a b Levy, Donald M. (1912). "Modern Copper Smelting". gutenberg. pp. 141–144.
  18. ^ "BLAYNEY COPPER MINE. THE PYRITIC SMELTING AND THE HOT-AIR BLAST". Lithgow Mercury. 16 March 1900.
  19. ^ Levy, Donald M. (1912). "Modern Copper Smelting". Gutenberg. pp. 188–191.
  20. ^ "GREAT COBAR PASSES". Daily Telegraph (Sydney). 13 October 1921. p. 6. Retrieved 14 August 2024.
  21. ^ a b Levy, Donald M. (1912). "Modern Copper Smelting". Gutenberg. pp. 159–170.
  22. ^ "Copper Mine Fatality Enquiry". Cobar Herald. 5 November 1909. p. 4. Retrieved 27 December 2024.
  23. ^ Sinclair, Roderick J (2005). The Extractive Metallurgy of Zinc (PDF). Australasian Institute of Mining and Metallurgy. pp. 201–210. ISBN 978-1-920806-34-7.
  24. ^ "THE CUNNINGAR SMELTING PLANT". The Ballarat Star. 10 December 1885. p. 4.
  25. ^ "OPENING OF THE CUNINGAR GOLD REEFING WORKS". Goulburn Herald. 10 December 1885. p. 2.
  26. ^ "John Dye La Monte - The Wrong Man in the Right Place at the Right Time". www.thetreasury.org.nz. Retrieved 5 December 2024.
Wikimedia Commons has media related to Water jacket furnaces.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Water_jacket_furnace_(metallurgy)&oldid=1265724937"