Controlling pH in a Precipitation Plant

• Main Authors: Kjell Støle-Hansen, Bjarne A. Foss
• Format: Article
• Language: English
• Published: Norwegian Society of Automatic Control 1997-10-01
• Series: Modeling, Identification and Control
• Subjects: pH control; metals; chemical industry
• Online Access: http://www.mic-journal.no/PDF/1997/MIC-1997-4-2.pdf
• ISSN: 0332-7353; 1890-1328

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.