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Analysis of transport phenomena in a combusting sulfide particle cloud : with implications to the flash smelting of high-grade copper concentrates Caffery, Grant A.


High-grade copper concentrates are becoming increasingly important as feed materials for flash smelting furnaces. Escondida concentrate from Chile is one of the most important of these high-grade concentrates. When smelting concentrate blends with Escondida loadings in excess of approximately 20 wt-%, BHP's San Manuel furnace observed unreacted concentrate accumulating at the bottom of the reaction shaft. This limited the quantity of Escondida concentrate that could be smelted by the furnace and therefore increased its treatment costs. The objective of this project was to suggest operational improvements to optimise furnace performance at high Escondida loadings by gaining an understanding of the influence of high-grade concentrate on the flash smelting behaviour of concentrate blends. This objective was achieved by conducting experimental and Computational Fluid Dynamics (CFD) studies on the flash smelting process. Results from the experimental study show that sulfide flash smelting can be described using group combustion theory. Furthermore results suggest addition of highgrade concentrate to the blend reduces the oxygen-to-concentrate ratio and increases the oxygen enrichment. This lowers the heat transfer effectiveness factor of the particles within the'cloud and the burner exit velocity, in turn reducing the cloud heat transfer coefficient. The lower rate of heat transfer to the particles increases the distance required for them to reach their ignition temperature. At some Escondida loading, the heat-up time of the particles becomes so large that there is insufficient residence time for particles to react with the available oxygen, leading to the observed operational problems. To overcome these problems requires that the heat transfer characteristics of the concentrate burner be improved. Therefore experimental and CFD studies were conducted to compare the performance of a swirl burner to a bluff-body burner. The bluff-body burner was used to approximate the concentrate burner used in industry. Some differences between the bluff-body burner investigated in this study and the industrial concentrate burner may cause the observed results for the bluff-body burner to differ from those of the industrial concentrate burners. It was found that the swirl burner gives superior performance to the bluff body burner due to two effects: 1) formation of an internal re-circulation zone which transfers heat from the combustion zone to the fresh mixture, increasing the heat transfer rate to the concentrate particles; and 2) reduction of the volume of the stagnant zone within the shaft, increasing the average particle residence time.

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