KIVCET furnace

These operations are all conducted in the single unit of the Kivcet furnace, which consists of a smelting shaft, gas removal shaft, and electrothermic part. A schematic of the Kivcet process is shown in Figure 5 (13). The electrothermal part is separated from the smelt shaft in the gas space by a partition... 

Smelting Kaldo Flash Smelter I Updraught Sinter Machine / Updraught Sinter Machine/ Kivcet Furnace ... 

Source of Gas Kaldo Cu-Smelter Raw Gas from Sinter Machine i Sinter Machine Kivcet Furnace... 

The smelter treats all of the zinc plant residues, which constitute approximately 45-50% of the charge. The percentage of zinc plant residues is a function of the smelter elemental limits and maintains a specific heat balance in the KIVCET furnace. Residues fiom the oxide leach plant and sulphide leach plant are blended and pumped to the feed plant at a specific gravity of 1.75. The residues are filtered through two Ingersoll-Rand Lasta plate filter presses. The total residue filtering capacity is 825 dry t/d, with the filter cake containing 20-22% moisture. 

The sidewalls of the KIVCET furnace are constructed with water-cooled copper jackets. A total of two hundred and seven independent cooling elements are supplied through a eentral distribution system. The cooling water is maintained at 40°C and the outlet temperature is measured frequently to monitor jacket integrity. Typieal outlet temperatures are 43-50°C depending on jacket location. Tap-hole insert temperatures are monitored during tapping. Typically each tap-hole insert will have a service life of two himdred taps. 

The first feed went into the KIVCET furnace on March 31, 1997. The start-up of the new slag-fuming furnace was three months later in June 1997. The initial period of operation was hampered by mechanical problems that prevented sustained periods of operation imtil a major shutdown in November 1997 when several mechanical deficiencies were corrected. This... 

Oxygen supply interruptions to the KIVCET furnace have caused a number of extended furnace outages. The supplier of the oxygen has made major efforts to reduce the interruptions with further improvements planned in 2000. Cominco brought a 1,500-t oxygen storage tank into service in January 2000 to provide a backup supply. 

When the KIVCET furnace bath is accreted, it is very difficult for heat to be transferred under the water-cooled partition wall from the electric fiimace to the coke checker. Thus, lead in slag is difficult to control. The reaction shaft can be operated in a more reducing environment by raising the coal in the feed and increasing the feed-to-oxygen ratio. In this manner, it is possible to operate with lead in slag at 2-5%. This practice has many detrimental side effects. Accretion growths block the bullnose and limit the draft on the reaction shaft. 

Throughput in the KIVCET furnace since start-up is shown in Figure 4. The furnace is now operating at sustained rates above the design cq>acity of 56 t/h. The main bottlenecks facing the plant in 2000 are elevated radiant boiler outlet temperatures and accretions in the boiler/precipitator areas. 

Figure 4 - KIVCET Furnace Throughput as a Percentage of Design (1208 t/d)...

Three roasters operate in parallel to produce calcine. There are two 84-m fluidized bed roasters and a suspension roaster. Off-gas from the roasters is mixed with off-gas from the KIVCET furnace and is then processed in the sulphur gas handling area. By-products include calomel, sulphuric acid, liquid sulphur dioxide, and ammonium sulphate fertilizers. 

The complex system of recycle streams betwe i and within each of ftie operating units ensures a higih overall recovery of the major products. For example, lead, bismuth and precious metals are recovered firom both the lead concentrates and the zinc concentrates treated. Recovery of lead is also significantly enhanced by operation of ftie slag fuming and oxide leaching circuits. Lead not recovered directly to bullion in the KIVCET furnace is recycled... 

With increased focus on the recovery of metal values in stockpiled slags and residues, impurity control becomes an even more important consideration. Operation of the KIVCET furnace at design capacity and the restart of one of the older slag fuming furnaces have enabled treatment of these stockpiles. As the stockpiles were being accumulated they formed natural bleeds for undesirable impurities such as the halides, and now the challenge will be to control... 

The production of indium and germanium products is important, and as was expected with the start-up of the KIVCET furnace and a new slag fuming furnace, the production has been expanded. The associated indium-germanium plant has now the capacity to produce 60-70 totmes of refined indium and 30-35 tonnes of contained germanium in germanium dioxide. Further expansion of germanium production is planned and will be implemented as necessary to match demand increases. 

Through changing proportions of the fluxes, a charge was made up whose calorific value corresponded closely to that of the lead-zinc feed that provided the best smelting results achieved in the Kivcet furnace. The feed turned out to be the one whose composition can be varied over a rather wide range lead 22-42%, zinc 5.0-7.6%, copper 8-10% and calcimn oxide 0.3-0.8%. The calorific value of the feed ranges from 600-660 kcal/kg, which is similar to the case of a lead-zinc sulphide mixture. 

Feed smelting in the Kivcet furnace and smelting products hoping... 

A key feature of the Kivcet furnace is the layer of incandescent coke floating on the slag bath at the base of the smelting shaft. The molten phases from the flash burner impinge on the coke layer and trickle through into the slag bath beneath. Reduction occurs within this layer and the main reactions involved are shown in Equations 7.15 to 7.18. Also shown below is the heat of reaction at 1200°C. 

Table 7.4 provides details of a number of Kivcet furnaces and operating conditions. 

Perillo, A, Carminati, A, Schueimann, P and Berger, N, 1990. The Kivcet furnace construction at Porto Vesme in Proceedings Lead-Zinc 90, The Minerals, Metals and Materials Society (TMS) Symposium, Anaheim, pp 903-917. 

Maintenance materials are simply estimated as 2.5 per cent of the direct construction capital cost for each Section. This cost will be lower for a new plant but should rise to the 2.5 per cent level for a well established plant. Coal is used in the Kivcet furnace at a cost of US 80/t in place of coke used for the blast furnace at US 160/t. 

Power is estimated from typical consumption figures for each area and a power cost of six cents per kilowatt hour in this example. Similarly coal and other fuels are estimated on the basis of typical energy consumption data provided in Chapter 16. Gas fuels are higher in this case due to its use for Kivcet furnace feed drying. In this case waste heat steam can be used to generate power and give a credit of 337 kWh per tonne of lead. 

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