A kinetic model of the Peirce-Smith converter

• Main Author: Kyllo, Andrew Kevin
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/8802

The Peirce-Smith converter, as used for copper and nickel converting, has changed little in the eighty years since its introduction. Over this time other metal production techniques have been developed, including considerable improvements to non-ferrous smelting. These improvements have had only a small effect on non-ferrous converting. The tenacity of the Peirce-Smith converter can be attributed to its simplicity of operation, however, it is not an efficient process. While the converter itself is limited primarily by its overall heat balance, process improvement has been limited by the belief that it operated at thermodynamic equilibrium. A kinetic model has been developed to gain a better knowledge of the operation of the Peirce-Smith converter. The model consists of two parts; a model of the gas flow in the bath, and an overall model considering both the heat and mass flows around the converter. The gas flow model calculates the bubble growth on the tuyere to detachment, and its subsequent rise through the bath. A combination of Kelvin-Helmolz and Rayleigh-Taylor instability theories is used to determine the stability of the bubble, both during growth and while rising through the bath. This allows the calculation of bubble breakup, which can be used to determine the total gas/liquid interfacial area. The gas flow model calculates the amount of oxygen reacting within each phase, as well as the heat lost to the gas and the total interfacial area. These values are applied to the overall model which then calculates the heat and mass balances within the converter. Material flows are based on mass-transfer considerations, with each phase being considered separately. Both mass and heat-transfer occur between all phases present, and each phase is assumed to be in internal equilibrium. As well as calculating the behaviour of the more abundant elements within the converter, the behaviour of the more important minor elements is considered. The model is validated using published physical modelling results, as well as measurements made on operating converters. The model results indicate that the efficiency of the Peirce-Smith converter may be improved by a number of methods, provided that some means of controlling the bath temperature is available. Increasing the tuyere submergence and decreasing the tuyere size are predicted to provide a substantial improvement in operation efficiency, without adversely affecting the minor element removal. The use of low levels of oxygen enrichment also improves efficiency, but tends to reduce the extent of minor element removal. Higher levels of oxygen enrichment are predicted to alter the overall process chemistry, with the amount of iron reacting being controlled by liquid-phase mass-transfer. This improves both the overall process efficiency and the extent of minor element removal.