An overview of PGM Smelting in Zimbabwe Ã¢Â€Â“ Zimplats ... - saimm

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The original granulated matte pumping and dewatering system was removedin 2002, and replaced with shaft-less screw conveyors from the bottom of thegranulation tank. The system dewaters matte to moisture levels averaging 4%.The matte is then dried and exported to Impala Refining Services (IRS).The operating parameters for the converters are listed in Table II.Table II: Converter operating parametersParameter Units ConverterDiameter x Length ft 10 x 15Operating Total Charge / (ladles) 5Product Output / (White matte) t 16-18Number of tuyeres 18Tuyere length mm 1200Tuyere diameter mm 50Blowing temperatures °C 1220-1250Air Flowrate Nm³h -1 8 500Air Pressure kPa 128Blowing Cycle Time minutes 600-720Granulation Time minutes 50-60Silica used per blow t 18-22Matte treated per blow t 5672ELECTROSTATIC PRECIPITATORThe two major sources of off-gas are the 13.5 MVA furnace and the two 10’ x 15’Peirce-Smith Converters. Off-gas from these two main sources is combined andsent through the Electrostatic Precipitator before eventually being vented to theatmosphere.The furnace operation is such that sealing of the furnace creates and maintains anegative pressure, at a gas temperature of approximately 425ºC and amaximum draft of 4 Nm 3 /s measured over 24 hours. Instantaneous peak flowsare such that dust loading is approximately 3 468 kg/h at a dust concentrationof 241 g/Nm 3 . An emergency stack is installed which can be used to isolate theducting system downstream. A pneumatically actuated damper is installed forthis. At the front end of the furnace, two matte tapping hoods above each of thetapholes are provided to minimize sulphur dioxide emissions whilst tappingmatte. The two ducts are routed to join up with the main furnace off-gas duct.Converter off-gases are collected in air-cooled hoods that cover the convertermouth when the converter is in the blowing position. Dilution air drawn inthrough the gap between the hood and the converter reduces the off-gastemperature to less than 500ºC (representing a dilution in excess of 200% of
process blowing gas). The gas handling system is based on an instantaneouspeak flow, with a maximum temperature of 450ºC, gas flow of 9.8 Nm 3 /s, dustloading of 240 kg/h, and a dust concentration of 6.8 g/Nm 3 . At the apex of theconverter hood is a gas distribution box where gas flow is either to theconverter off-gas duct or to the emergency stack.The furnace and converter off-gas are routed to enter a mixing chamber justahead of a three-field electrostatic precipitator. The mixing chamber effectivelymixes converter and furnace off-gases before they enter the ESP. A mixingchamber dilution damper modulates the flow to bleed in cold air to control theprecipitator inlet temperature to 350ºC. In the precipitator, there are 15collector plates per electrode field; each collector plate is 11 m high and 3.5 mlong, providing a total collection surface area of 1 155 m 2 per electrostatic field.The precipitator is designed for the following operating conditions - gas volumeof 13.78 Nm 3 /s, operating temperature of 350ºC, inlet dust of 64.3 g/Nm 3 , and aprecipitator inlet pressure of 1.2 kPa. The precipitator has an outlet dustloading of 50 mg/Nm 3 and a collection efficiency 99.9%. In 2003, a CO monitorwas installed following an explosion in the precipitator. The explosion wassuspected to have been caused by coal, which was being used in the converters.CONCLUSIONThe Zimplats Smelter has undergone some design changes since it wascommissioned in 1997: these being the Hatch modifications in 1998, and theZimplats modifications from 2001 to 2005.The design between 1997 and 1998 has resulted in the furnace being called an‘Elkem/Hatch’ furnace. The period from January 2002 to the current time hasseen the furnace being run at full power (12.5 MW) for sustained periods oftime.A major run-out occurred in July 2003, which saw 25% of the furnace sidewalland part of the hearth being repaired locally by Zimplats. Furtherimprovements have been implemented, with the main intention of reducingrisk on the furnace and increasing the efficient utilisation of smelter unitprocesses.It is the belief of Zimplats management that the smelter can treat concentrateequivalent to 3.5 Mt/a of ore if the furnace undergoes a full reline.REFERENCES1. J. Sarvinis, S. de Vries, K. Joiner, G. van Mierlo, N. Voermann, F. Stober, C. Rule, P. Majoko,Improvements to BHP Hartley Platinum Smelting Furnace, Hatch Associates Ltd,Mississauga, Ontario, Canada.2. H. Wepener, B. Kruger, and W. Beylevled, Audit of the Zimplats Smelter, October 2001.3. Overview of SMC operations, Zimplats internal document.73
Page 2 and 3: Construction of the Smelter commenc
Page 4 and 5: • Storage silos (150 t and 350 t)
Page 6 and 7: 68• Electrode seals• New feed-p
Page 8 and 9: 9(NiO) + 7FeS = 3Ni3S2 + 7FeO + SO2
Page 12: 4. Review of SMC, Concentrator and

An overview of PGM Smelting in Zimbabwe Ã¢Â€Â“ Zimplats ... - saimm

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