Role of technical innovation on production delivery at the Polokwane Smelter

摘要

The single six-in-line furnace of the Polokwane Smelter is the largest installed high-intensity furnace for platinum group metals (PGM) base metals sulphide smelting in the world. The furnace employs state-of-the art technology to deliver a planned throughput of 650 000 t/a dry concentrate at a design 68 MW power input. This furnace, at double the capacity of previously existing PGM furnaces, offers low unit operating and capital cost through the resulting economies of scale. Key features of the design include:rnuse of water-cooled copper HATCH matte tapblocks, Waffle, plate and flanker coolersrn1. patent-pending air-cooled copper fin radiator sidewall cooling of matte zonern2. patent-pending wall hold-down spring systemrn3. effective 3-dimensional furnace binding systemrn4. patent-pending HATCH electrodesrn5. operation aided by HATCH Integrated Furnace Controller (IFC).rnParamount to the design of the furnace was consideration of the process requirement to achieve high-intensity smelting of a high proportion of UG2 feed containing up to 4% Cr_2O_3 content. Operation at higher slag Cr_2O_3 levels leads directly to higher bath temperatures. It also increases the potential for undesirable precipitation of solid spinel phases at the matte-slag interface, or as build-up on the hearth.rnFundamental to addressing the chrome issue was selection of adequate transformer capacity to permit operation at deep electrode immersion (immersed up to 75% of the slag layer thickness) and ability to operate at high hearth power density (up to 250 kW/m~2) to substantially prevent build-up of spinel on the hearth. Such build-up, if not otherwise controlled, rapidly reduces the effective bath volume for smelting, and can lead to premature furnace stoppage.rnAdoption of the water-cooled copper HATCH Waffle coolers in the slag zone is key to permitting sustainable operation at the high resulting sidewall heat fluxes (design of 110 kW/m~2 average, 220 kW/m~2 furnace global peak (cooling water design), and over 440 kW/m~2 cooler design peak). It also permits operation with reduced lime addition as a basic slag conditioner, so lowering the specific energy requirement for smelting.rnA further, but little appreciated metallurgical benefit of highly stirred high-intensity smelting, is the exceptionally low slag PGM losses that result. These and other pertinent operational features facilitated by the up-front selection of an appropriate high-intensity furnace design will be presented.