Siberian Federal University, Krasnoyarsk, Russia:

P. V. Polyakov, Professor-Consultant of a Chair of Metallurgy of Non-Ferrous Metals, e-mail: p.v.polyakov@mail.ru
N. A. Sharypov, Senior Lecturer of a Chair of Automation of production processes in metallurgy, e-mail: Nikita.Sharypov@gmx.com
V. A. Osipova, Assistant Professor of a Chair of Automation of production processes in metallurgy
A. A. Pianykh, Associate Professor of a Chair of Thermal Engineering and Fluid Dynamics

Anode current distribution is one of the important performance parameters of an aluminium reduction cell strongly influencing the key performance indicators (KPI). In modern industrial practice, current distributions for cells with prebaked anodes are estimated using the сoefficient of unequal current distribution. The uneven distribution of current is typical not only of the cell, but also of the individual anode. The influence of parameters on current distribution is analyzed. One of the reasons of unequal current distribution, both in the cell and in an individual anode, is the presence of irregularities at the anode bottom. To study the influence of irregularities, which in technological practice are usually called spikes, bellies, and mushrooms, the physical picture and the mathematical model of anode performance are considered. Components of the voltage drop in the anode with and without a spike are determined. One of the possible causes of the appearance of irregularities is the formation of a passivating layer of perfluorocarbons (PFC) on the anode bottom. On the basis of literature review possible reactions based on perfluorocarbons formation are analyzed. The described model consists of two anodes, for one of which a abnormality (spike) cylindrical shape is given. The mathematical model includes the equation of thermal conductivity. The model takes into account anode and bubble overvoltages. The Peltier heat in the model in the form of a boundary condition on the anode bottom is given. As a result of solving the system of equations (model) in the ANSYS, the fields of temperature distribution and current density are obtained. The distribution of the electric potential and current in the spike was presented. The current density in the spike reaches 3.5 A/cm², with a current density at the anode bottom without a spike of 1.2 A/cm²; the temperature of the electrolyte in the region of the spike is, on average, 4 ^oC higher than in the absence of a abnormality on the anode bottom; the electric potential in the spike with respect to the cathode aluminum is approximately 3.54 V, which confirms the possibility of the reactions of formation of perfluorocarbons and the creation of a passivation layer on the part of the anode bottom.
The paper was written using the results, taken during the project 02.G25.31.0181 “Development of high performance energy saving aluminium reduction technology RA-550” implementation as a part of complex projects realization program of high efficiency production development, approved by Russian Federation government regulation No. 218 from April the 9^th, 2010.

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