Published: 1987
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Although South Africa is blessed with considerable reserves of chromite ore, as much as 70 per cent of the ore as mined occurs in the form of fines. The conventional submerged-arc furnace operation for the production of ferro-chromium requires the agglomeration of fines for stable and efficient furnace performance. Good-quality coke and coal are not readily available, and there is likely to be a scarcity of these carbonaceous products in the future. The submerged-arc furnace has in all probability reached a plateau as far as developments to improve its efficiency are concerned. This factor, together with the knowledge that the future of the ferrochromium industry depended on the utilization of the vast reserves of fine ore mined in the Transvaal, prompted Middelburg Steel & Alloys (MS&A), with Mintek's assistance, to embark on a programme to build an ASEA 16 MVA furnace at its Krugersdorp works. The design of the furnace is based on the transferred-arc concept using hollow graphite electrodes, which was developed by ASEA for the d.c.-arc Elred process. The furnace has been used successfully for the melting of ferrochromium fines and the smelting of chromite (including the co-melting of alloy fines), and has the advantage of producing ferrochromium with very low residual elements, which is much sought after by speciality steelmakers. The encouraging results obtained since the commissioning of the facility in 1983, particularly in the recoveries of chromium, have confirmed MS&A's faith in the process, and future developments will be aimed at reducing the energy requirements through the preheating or prereduction of fines by, for example, fluidized-bed technology.