The Imperial Smelting Furnace ISF

The Imperial Smelting Furnace (ISF) was primarily developed as a blast furnace for the production of zinc. It relies on the concept of reducing zinc oxide in a shaft furnace to produce zinc vapour in the furnace gases. By maintaining high temperatures at the top of the shaft reversion to zinc oxide can be prevented. The hot furnace gases are ducted from the furnace to a condenser where they are chilled using a spray of molten lead at around 500°C, which condenses and absorbs the zinc from the gas stream. This concept requires close control of furnace gas composition and a sealed top furnace. 

The ISF was developed from the standard lead blast furnace, but with evolutionary change to a more intensive operation, more akin to the iron blast furnace conditions at the tuyere level. The standard ISF design had an upper shaft cross-section of 17.2 m and a cross-section at tuyere level or hearth area of 13.2 m. Data for the standard ISF is compared with the lead blast furnace in Table 6.1 and demonstrates the higher intensity operation. 

Comparison of the Imperial Smelting Furnace and lead blast furnace. 

Furnace type Lead blast furnace Imperial Smelting Furnace 

ISF plants operating in 2000 are hsted in Table 6.2. A number of these plants have subsequently 

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In 1960 the first standard commercial scale Imperial Smelting Furnace (ISF) was constructed at Swansea in the UK, as an adaptation of the lead blast furnace, to simultaneously produce zinc and lead. The furnace operated with a hot top to retain zinc in the vapour phase. The top was sealed and gases passed through a lead splash condenser to strip zinc from the gas phase into a lead-zinc bullion which could be cooled for separation of crude zinc and lead metals. The ratio of zinc to lead production from these units is generally more than 2 1, and lead production from the standard unit is close to 40 000 t/a. Thirteen plants were constructed around the world but due to unfavourable economics a number of these have now closed. Details are given in Chapter 6. 

Bulk concentrates contain both zinc and lead, typically in a ratio of about 2 1. Total metal content is usually 45-60 per cent (zinc plus lead), with at least 10 per cent of each, as well as copper, and other impurities. This material is generally treated at Imperial Smelting Furnace (ISF) plants, where both zinc and lead are directly recovered. Major sources of bulk concentrates include the Mount Isa mine in Australia, the Brunswick mine in Canada, and the Red Dog mine in the USA. These mines produce bulk material in addition to larger quantities of lead and zinc concentrates. However, some smaller mines (El Brocal in Peru, for instance) have bulk concentrates as their sole product, although this is unusual. 

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