“Controlling pH in a Precipitation Plant”

Authors: Kjell Støle-Hansen and Bjarne A. Foss,
Affiliation: NTNU, Department of Engineering Cybernetics
Reference: 1997, Vol 18, No 4, pp. 261-272.

Keywords: pH control, metals, chemical industry, dynamic models

Abstract: This paper deals with pH control in a precipitation and dissolution process. The process is a part of the electrolyte purification plant at Falconbridge Nikkelverk in Kristiansand, Norway. The process including the present strategy for pH control are presented, and experienced weaknesses with this strategy are described. A rigorous dynamic model of the process is briefly summarized. This model was developed in earlier work with the purpose of being a tool for control design. Because of the precipitation in form of hydroxides and the limited dissolution rate of nickel carbonate, the process is approximately linear in pH. Therefore, an alternative strategy for pH control based on adding derivative and feed forward action is suggested. The alternative control strategy is by simulations shown to give severe improvements in performance. The robustness of the proposed controller is briefly analysed.

PDF PDF (1928 Kb)        DOI: 10.4173/mic.1997.4.2

DOI forward links to this article:
[1] Juri M. Seletzky, Ute Noak, Jens Fricke, Eike Welk, Werner Eberhard, Christof Knocke and Jochen Büchs (2007), doi:10.1002/bit.21359
[1] Asbjørnsen, O. A. (1972). Reaction invariants in the control of continuous chemical reactions, Chem. Eng. Sci., 27, pp.709-717 doi:10.1016/0009-2509(72)85007-3
[2] FNA, (1994). Private communication with personnel at Falconbridge Nikkelverk A/S during the period 1994 - 1997, .
[3] Gustafsson, T. K., Skifvars, B. O., Sandström, K. V. Waller, K. V. (1995). Modelling of pH for Control, Ind. Eng. Chem. Res., 34, 820-827 doi:10.1021/ie00042a014
[4] Gustafsson, T. K. Waller, K. V. (1992). Nonlinear and Adaptive Control of pH, Ind. Eng. Chem. Res., 31, 2681-2693 doi:10.1021/ie00012a009
[5] Herskovitch, H. Z., McAvoy, T.J. Athansios, I.L. (1978). Canadian Journal of Chemical Engineering, 56, .
[6] Holcroft, G., Rosato, L., Perrier, M. Berk, D. (1995). Dynamics of the Jarosite Conversion Process, Preprints from DYCORD+'95, Helsingør, Denmark.
[7] McAvoy, T. J., Hsu, E. Lowenthal, S. (1972). Dynamics of pH in a Controlled Stirred Tank Reactor, Ind. Eng. Chem. Proc. Dev., 11, 68-70 doi:10.1021/i260041a013
[8] Newell, R. B. Lee, P. L. (1988). Applied process control - a case study, Prentice Hall.
[9] Rosseland, E. W. (1993). Operational manual for the electrolyte purification section, Falconbridge Nikkelverk, Kristiansand.in Norwegian.
[10] Sandström, K. V. Gustafsson, T. K. (1994). A study of the dynamics of calcium-phosphate precipitation in pH-control systems, Report 94-5, Åbo Akademi, Process Control Laboratory.
[11] Slotine, J.-J. E. Li, W. (1991). Applied Nonlinear Control, Prentice-Hall International, Inc.
[12] Støle-Hansen, K. Dotterud, O.M. (1996). Dynamic Modelling of a Precipitation Process in an Aqueous Solution, Computers chem. Engng., 20, Suppl., ppS629-634.
[13] Traa, S. (1994). Precipitation of Lead from Nickel Chloride Solutions, M.Sc. thesis.in Norwegian. Dep. of Chemical Engineering, the Norwegian Institute of Technology.
[14] Waller, K. V. Gustafsson, T. K. (1986). Fundamental Properties of Continous pH Control, ISA Trans. 22, No. 1. 12-34.
[15] Waller, K. V. Mäkilä, P. M. (1981). Chemical Reaction Invariants and Variants and Their Use in Reactor Modelling, Simulation and Control, Ind. Eng. Chem. Proc. Dev., 20, 1-11 doi:10.1021/i200012a001
[16] Wright, R. A. Kravaris, C. (1995). pH Control in the Presence of Precipitation Equilibria, Preprints from DYCORD+'95, Helsingør, Denmark.

  title={{Controlling pH in a Precipitation Plant}},
  author={Støle-Hansen, Kjell and Foss, Bjarne A.},
  journal={Modeling, Identification and Control},
  publisher={Norwegian Society of Automatic Control}