| Continuous monitoring and control of the AlF3 content of the cryolitic melt in aluminium electrolysis Vicky Vassiliadou1; Antonis Peppas2; Maria Taxiarchou3; Ioannis Paspaliaris3; 1MYTILINEOS HOLDINGS S.A, Agios Nikolaos, Greece; 2NATIONAL TECHNICAL UNIVERSITY OF ATHENS, Zografos Campus, Greece; 3NATIONAL TECHNICAL UNIVERSITY OF ATHENS, Athens, Greece; PAPER: 378/Molten/Regular (Oral) SCHEDULED: 14:00/Wed. 30 Nov. 2022/Game ABSTRACT: The aim of this paper is to summarize the mathematical equations applied to the modelling of the physicochemical properties of the aluminium electrolysis cryolite melts and the study of the effect on the properties of its aluminium fluoride content and the development of a methodology for the direct determination of its concentration in the electrolysis bath that can be applied in industrial scale electrolysis cells.<br />The AlF<sub>3</sub> content of the electrolyte melt is one of the most important parameters affecting the physicochemical properties of the electrolysis bath. In the current industrial practice, the determination of AlF<sub>3</sub> concentration in the bath is performed through periodic sampling, chemical analysis of the selected samples and, based on the chemical analysis results, the appropriate quantity of AlF<sub>3</sub> addition is determined. This procedure is time consuming, and its major disadvantage is that between the time of sampling and analysis until the addition of the corrective AlF<sub>3</sub> quantity, the AlF<sub>3</sub> content of the bath has changed. This creates a serious problem in the proper control of the AlF<sub>3</sub> concentration in the electrolysis bath and the stable operation of the electrolysis cell.<br />A methodology for the real time determination of the AlF<sub>3</sub> content of the electrolysis bath has been developed based on the measurement of the bath resistance. According to the proposed methodology, a given change in the anode cathode distance is applied and the corresponding change in the bath resistance is measured and, from its value, the bath electrical resistivity is determined. The value of the electrical resistivity is correlated to the value of the theoretical electrical resistivity of the bath and through an appropriate algorithm the AlF3 content of the bath is determined in real time with sufficient accuracy. References: Haupin W., Kvande H. (2016). “Thermodynamics of Electrochemical Reduction of Alumina”, Essential Readings in Light Metals, Bearne G., Dupuis M., Tarcy G. (eds). <br />Haupin W., Kvande H. (2002). "Mathematical Model of Fluoride Evolution from Hall-Héroult Cells", Proceedings from the International Jomar Thonstad Symposium, (ed.) A. Solheim and G.M. Haarberg, Trondheim, Norway, October 16 - 18, pp. 53-65.<br />Gusberti V. (2014). “Modelling the mass and energy balance of aluminium reduction cells”. Ph.D. thesis, University of New South Wales.<br />Antille J., von Kaenel R., Bugnion L. (2016). “Hall-Héroult Cell Simulator: A Tool for the Operation and Process Control”, Light Metals, Williams E. (ed). <br />Kolås S. (2007). "Defining and Verifying the 'Correlation Line' in Aluminum Electrolysis", JOM, Vol. 59, No. 5, pp. 55-60.<br />Jessen S. W. (2008). “Mathematical Modeling of a Hall Héroult Aluminium Reduction Cell”. Master Thesis, Technical University of Denmark |
