TRANSACTION PAPER

Computational fluid dynamic modelling of a waste-heat boiler associated with flash smelting of base metal sulphides

J.J. Bezuidenhout^I; Y. Yang^II; J.J. Eksteen^I

^IDepartment of Process Engineering, University of Stellenbosch, South Africa
^IIDepartment of Materials Science and Engineering, Delft University of Technology, The Netherlands

SYNOPSIS

The waste-heat boiler is used within the Sulphide flash smelting process as the main dust and energy recovery unit. The large volume of off-gas discharged from the flash smelter is at a very high temperature (1350°C) and contains a significant dust load that subjects the downstream waste-heat boiler to tough and demanding conditions. The boiler cavity is especially prone to dust accretions, fouling, and corrosion caused by accumulation of molten particles and precipitation of sulphuric acid.
Computational fluid dynamics (CFD) is applied within a qualitative study to model the flow and heat transfer distribution throughout the waste-heat boiler. The commercial CFD package, Fluent 6.2.16, was applied to a modified waste-heat boiler (23 m × 11 m × 5.4 m) within the Outokumpu flash smelting process.
This investigation focuses on the geometric modifications to the typical boiler design, which includes elevation of the ceiling, placement of flow-obstructing baffles and radiation plates parallel within the flow path. Also investigated were various boiler operating conditions such as the circulation of process off-gas, air leakage from the dust discharging hoppers and variation in inlet gas composition.
The geometric modifications had the desired effect of increasing the volumetric utilization and therefore enhancing heat transfer between the boiler surface and the gas stream and dust segregation. Introducing circulated off-gas at a rate of 20 m/s and at a 45° angle to the front of the waste boiler further enhanced cooling while reducing the high impact of the furnace-uptake gas-stream on the boiler ceiling. The placement of radiation plates was found to be very effective in enhancing the heat transfer surface and distributing gas flow within the boiler. These results present recommendations towards an improved waste-heat boiler design.

Keywords: flash smelting, waste-heat boiler, CFD simulation, off-gas cooling

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References

1. YANG, Y., JOKILAAKSO, A., AHOKAINEN, T., and TEPPO, O. Numerical simulation of fluid flow and heat transfer in a waste-heat boiler of the Outokumpu flash smelting process, EPD Congress 1995: Proceedings of a symposium sponsored by the Extraction and Processing Division, held at the TMS Annual Meeting in Las Vegas, Nevada, Feb. 12-16, 1995, pp. 417-431.         [ Links ]

2. DAVENPORT, W.G., JONES, D.M., KING, M.J., and PARTELPOEG, E.H., Flash smelting: analysis, control and optimization, TMS, USA, 2001.         [ Links ]

3. WESTERLUND, A.M., PIEHL, O., and ABECK, W., Tons and profit from understanding gas cooling and heat recovery, Proceedings of the Copper 99 International Symposium, vol. V. George, D.B., Chen, W.J., Mackey, P.J. and Weddick, A.J. (eds.), Phoenix, Arizona, USA, Oct. 10-13, 1999, pp. 83-94.         [ Links ]

4. PEIPPO, R., HOLOPAINEN, H., and NOKELAINEN, J., Copper smelter waste heat boiler technology for the next millennium, Proceedings of the Copper 99 International Symposium, vol. V. George, D.B., Chen, W.J., Mackey, P.J. and Weddick, A.J. (eds.), Phoenix, Arizona, USA, Oct. 10-13, 1999, pp. 71-82.         [ Links ]

5. GONZALES, T.W. and JONES, D.M. Flash smelting at Magma Copper Company San Manuel Smelter A subsidiary of Magma Copper Company, Extractive Metallurgy of Copper, Nickel and Cobalt, vol. II, Proceedings of the Paul E. Queneau International Symposium, Landolt, C.A. (ed.), Feb. 21-25, 1993, pp. 1395-1407.         [ Links ]

6. YANG, Y. Computer simulation of gas flow and heat transfer in waste-heat boilers of the Outokumpu copper flash smelting process, Acta Polytechnica Scandinavica, Chemical Technology Series, no. 242, Helsinki, Finland. Finnish Academy of Technology, 1996.         [ Links ]

7. YANG, Y., JOKILAAKSO, A., TASKINEN, P., and KYTÖ, M. Using computational fluid dynamics to modify a waste-heat boiler design. JOM (Journal of Minerals, Metals and Materials), vol. 51, no. 5, 1999, pp. 36-39, 47.         [ Links ]

8. PATANKAR, V.S. Numerical Heat Transfer and Fluid Flow, Hemisphere Publishing Corporation, 1980.         [ Links ]

9. FLUENT and GAMBIT User's guide, 2001.         [ Links ]

10. HAHN, Y.B. and SOHN, H.Y. Mathematical modeling of sulfide flash smelting process: Part II, Quantitative analysis of radiative heat transfer, Metallurgical Transactions B, (21B), 1990, pp.959-966.         [ Links ]

11. HOTTEL, H.C. and SAROFIM, A.F. Radiative Transfer, McGraw-Hill Inc, USA, 1967.         [ Links ]

12. DRUMMOND, W. The cooling of hot, dirty, corrosive, non-ferrous smelter gases with particular reference to waste heat boilers, Smelter Process Gas Handling and Treatment. Smith T.J.A. and Newman C.J. (eds.), TMS, San Diego, California, 1992, pp. 73-94.         [ Links ]

Paper received Aug. 2007
Revised paper received Mar. 2008