TRANSACTION PAPERS

 

CFD simulation and experimental measurement of nickel solids concentration distribution in a stirred tank

 

 

A. Ochieng^I; M.S. Onyango^II; K.H. Kiriamiti^III

^IDepartment of Chemical Engeering, Vaal University of Technology, Vanderbijlpark, South Africa
^IIDepartment of Chemical and Metallurgical Engineering, Tshwane University of Technology, Pretoria, South Africa
^IIIDepartment of Chemical and Process Engineering, Moi University, Kenya

 

 

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SYNOPSIS

Solids suspension influences the quality of mixing and energy requirement in a solid-liquid system, both of which determine the efficiency of industrial processes such as nickel precipitation. Nickel solids concentration distribution in a stirred tank was investigated using computational fluid dynamics (CFD) and experimental methods. The concentration distribution of the nickel solids was compared with that of sand and glass. The laser Doppler velocimetry (LDV) method was used to measure the velocity field for the liquid-only system and an optical technique was employed to determine the axial solids concentration distribution. Regions of inhomogeneity in the tank were identified. It was found that, for a given solids loading, the solids concentration distribution depended on both particle size and particle size distribution. High solids loadings were investigated and a difference in the concentration distribution pattern was obtained with nickel, flint glass and sand particles. The CFD simulation results highlighted problems that could be associated with some conventional experimental methods of determining solids concentration distribution in a stirred tank.

Keywords: nickel; CFD; simulation; mixing; solids suspension

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References

1. WILLIS, B. and ESSEN, J.V. Precipitation of nickel metal by hydrogen reduction: A new perspective, Nickel, Cobalt Conference Proceedings, Atlanta 2000 Nickel/Cobalt Conference, Perth, 15-17 May 2000.         [ Links ]

2. ARMENATE, P.M. and NAGAMINE, E.U. Effect of low off-bottom impeller clearance on the minimum agitation speed for complete suspension of solids in stirred tanks, Chemical Engineering Science, vol. 53, no. 9, 1998. pp. 1757-1775.         [ Links ]

3. KUZMANIC, B. and LJUBICIC, N. Suspension of floating solids with uppumping pitched blade impellers; mixing time, power characteristics, Chemical Engineering Journal, vol. 84, no. 3, 2001. pp. 325-333.         [ Links ]

4. ZWIETERING, T.N.H. Suspending of solids particle in liquid by agitators, Chemical Engineering Science, vol. 8, 1958. pp. 244-253.         [ Links ]

5. BARRESI, A. and BALDI, G. Solids suspension in an agitated vessel, Chemical Engineering Science, vol. 42, no. 12, 1987. pp. 2949-2956.         [ Links ]

6. MONTANTE, G., PINELLI, D., and MAGELLI, F. Scale up criteria for the solids distribution in a slurry reactor stirred with multiple impellers, Chemical Engineering Science, vol. 58, 2003. pp. 5363-5372.         [ Links ]

7. MERSMANN, A., WERNER, F., MAURER, S., and BARTOSCH, K. Theoretical prediction of the minimum stirrer speed in mechanically agitated suspensions, Chemical Engineering and Processing, vol. 37, no. 6, 1998. pp. 503-510.         [ Links ]

8. KEE, C.S. and TAN, B.H.R. CFD simulation of solids suspension in mixing vessels, The Canadian Journal of Chemical Engineering, vol. 80, 2002. pp. 1-6.         [ Links ]

9. BARRUÉ, H., KAROUI, A. N. LE SAUZE, J. and COSTES, F. Illy, Comparison of aerodynamics and mixing mechanisms of three mixers: Oxynator™ gas-gas mixer, KMA and SMI static mixers, Chemical Engineering Journal, vol. 84, no. 3, 2001. pp. 343-354.         [ Links ]

10. BRUCATO, A. CIOFALO, M., GRISAFI, F., and MICALE, G. Numerical prediction of flow fields in baffled stirred vessels: A comparison of alternative modelling approaches, Chemical Engineering Science, 1998b, vol. 53, no. 21. pp. 3653-368.         [ Links ]

11. OCHIENG, A. and ONYANGO, M.S. Drag models and solids concentration distribution in a stirred tank, Powder Technology, vol. 181, 2008. pp. 1-8.         [ Links ]

12. GIDASPOW, D. Multiphase flow, fluidization: Continuum, kinematic theory description, Academic Press, New York. 1994.         [ Links ]

13. FAJNER, D., MAGELLI, F., NOCENTINI, M., and PASQUALI, G. Solids concentration profiles in a mechanically stirred, staged column slurry reactor, Chemical Engineering Research and Design, vol. 63, 1985. p. 235.         [ Links ]

14. AEA TECHNOLOGY. CFX5 Flow solver user guide, Computational Fluid Dynamics Services, Harwell, Oxfordshire UK: AEA Industrial Technology. 2003.         [ Links ]

15. OCHIENG, A., ONYANGO, M.S., KUMAR, A., KIRIAMITI, H.K., and MUSONGE, P. Mixing and power draw in a tank stirred by a Rushton turbine at a low clearance, Chemical Engineering and Processing Journal, vol. 47, no. 5, 2008. pp. 842-851.         [ Links ]

16. BRUCATO, A., GRISAFI, F., and MONTANTE, G. Particle drag coefficients in turbulent fluids. Chemical Engineering Science, vol. 53, no. 18, 1998a. pp. 3295-3314.         [ Links ]

17. BHATTACHARYA, S. and KRESTA, S.M. CFD simulations of three-dimensional wall jets in a stirred tank, Canadian Journal of Chemical Engineering, vol. 80, no. 4, 2002. pp. 695-709.         [ Links ]

18. OCHIENG, A., ALISON, E. LEWIS. CFD simulation of nickel solids concentration distribution in a stirred tank. Minerals Engineering Journal, vol. 19, 2006. pp. 180-189.         [ Links ]

 

 

Paper received Feb. 2009
Revised paper received Nov. 2009