Unique smelting in South Africa
15 Jan 2000
As part of the project to exploit the mineral deposits at Namakwa Sands in South Africa, a mineral company is employing a unique smelting operation to extract valuable substances from the iron/titanium ore ilmenite with the help of technology from BOCto keep the system safe.
The result of joint research between the Anglo American Corporation and Mintek, the project is based around dc plasma arc smelting, which Namakwa Sands says is more stable than the ac alternative, and is believed to be the first application of the technology to ilmenite smelting.
The Namakwa deposits a valuable source of rutile (TiO2), zircon (ZrSiO4) and ilmenite are some 300km north of Cape Town. The ilmenite is smelted to produce titania slag, a form of TiO2, and pig iron. Carbon monoxide is a by-product of the process, so to keep concentrations to a safe level nitrogen is used to dilute it. Some of the CO gas is used to heat the ilmenite pre-heater plant, and nitrogen is used here to blanket the ilmenite to prevent it from oxidising in the pre-heating phase.
This nitrogen requirement means there are two BOC pressure swing adsorption plants on site, one capable of producing 500 normal m3/h of 99 per cent pure nitrogen for use in purging the smelter, and the second producing 300 normal m3/h for the pre-heater. A 32000 litre liquid nitrogen storage tank provides back-up.
When the 25MW smelter first came on-line, solidification of molten metal inside the ladle proved a problem. To overcome this, the ladle's refractory lining is kept at a temperature of 1300 C. BOC devised the technical solution, providing a specially adapted horizontally mounted 750kW oxy-paraffin burner to heat the ladle while it is held on its side in a special cradle. Ignition and heating are controlled using feedback from a thermocouple installed in the ladle hood, while the temperature is controlled by switching between two burners of different power settings.
A second, 35MW ilmenite smelter has been commissioned to the same general design.
