A water jacket furnace is a type of blast furnace used to smelt non-ferrous metallic ores, most typically ores of copper, lead, or silver-lead. In a modified form it could also recover zinc. It takes its name from the water jacket arrangement used to cool the lower furnace casing and prolong the life of the furnace hearth. It is sometimes referred to as a water-jacketed blast furnace, copper blast furnace, or lead blast furnace. The water jacket furnace is now virtually an obsolete technology for copper smelting, being nearly entirely replaced, by flash smelting of copper ore concentrates. It remains in use, in a modified form, for lead smelting. 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 or water bath heater, which should not be confused with the metallurgical water jacket furnace.
History 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. There were two other attempts at reducing (roasted or 'calcinated') copper ore to metallic copper, in blast furnaces, in Australia; the Rosemorrin smelter (c. 1847 — c.1849) at Woolwich, now a suburb of Sydney, and the Carangara Mine smelter (1850 — 1851), at Cornish Settlement, now Byng, New South Wales.The 'water jacket' blast furnace design for non-ferrous smelting arose in North America, during the 1870s, and an alternative name for it, in Australia, was 'American water jacket furnace'. The design evolved from earlier German cupola furnace designs, with the distinguishing innovation being a well-controlled cooling of the furnace shell. 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. 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, and Lloyd's Mine at Burraga and the Overflow Mine at Bobadah, both in New South Wales. 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, 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.
Technology and application
Smelting
Lead and silver-lead ore smelting
A water jacket furnace can be used to reduce non-ferrous oxide ores mixed with coke, to produce metal and slag. When smelting lead, the feedstock is lead oxide, coke and fluxes. When smelting lead sulphide ores, the ore is first sintered to form a lead oxide sinter. Lead and silver ores often occur in the same ore body. Separating silver metal from the crude lead produced by a furnace requires a second process of refining, such as the Parkes process. When smelting lead, there was the added complication that measures were necessary to protect workers from harmful lead vapours.
Copper ore smelting The pyrometallurgical process of a water jacket furnace, when smelting copper sulphide ores, was 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. If a smelter did not have a convertor, the matte was poured into moulds and allowed to solidify. The smelting of sulphide copper 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. Depending upon the composition of the ore being smelted, the choice of a suitable flux was particularly important. 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.
Advantages and disadvantages
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