The influence of the initial shape and position of an anode and the curvature of the aluminum on the current distributio
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I. INTRODUCTION
THE current distribution in aluminum electrolysis cells has been investigated and modeled by several authors,[1,2,3] as reviewed previously.[4–8] As a part of an ongoing study, the current distribution in a Søderberg cell was calculated[4] to supplement measured data,[5] and the current distribution on prebaked anodes was studied.[6] The length of time that it takes to establish a constant shape of the anode side was calculated, and that shape was compared to measurements. The fraction of the current which passes through the sides of the anodes was determined, depending on the width of the gap between two adjacent anodes and between the anode and the sidewall.[7] The following questions were also addressed in Reference 7. (1) What are the differences in calculated current densities along the electrodes for two approximations of current distribution (the primary current distribution and secondary current distribution)? (2) What is the influence of the sideledge on the current densities, especially, (a) the effect of the anode-sideledge distance and (b) the effect of the shape of the sideledge? The present work analyzes some assumptions/simplifications used in the previous calculations[6,7,8] in order to see their influence on the accuracy of the calculations. We examine the influence of (1) a modified initial anode shape, (2) the curvature of the surface of the liquid aluminum, and (3) an anode being set too high or too low. The two-dimensional (2-D) cross sections considered are shown in Figures 1 and 2. The model cell is a 150 kA prebaked cell with 20 anodes (145 3 67 cm), with an initial height of 60 cm. The sketch of the typical anode with studs, yoke, and hanger can be seen in Figure 3. J. ZORIC, Research Scientist, formerly with SINTEF Materials Technology Group for Flow Technology, is with Telenor AS, Research and Development, N-7005 Trondheim, Norway. J. THONSTAD, Professor, is with the Department of Electrochemistry, Norwegian University of Science and Technology, N-7034 Trondheim, Norway. T. HAARBERG, Senior Scientist, is with the SINTEF Materials Technology Group for Flow Technology, N7034 Trondheim, Norway. Manuscript submitted April 21, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
Previously, the secondary current distribution for a 150 kA prebaked cell was studied.[6,7,8] Anodic and cathodic current densities were calculated for different gaps between two adjacent anodes or the anode/sidewall (sideledge). The current density at the working face of the anode (underside) was assumed to be 0.75 A cm22. The steady-state shapes were calculated (a moving-boundary problem) for anodes with an initial rectangular shape. It took 6 to 8 days until a steady state was obtained, depending on the width of the gap between the two anodes or between the anode and the sidewall/sideledge. This time can be shortened if the initial shape is made closer to the final, rounded-off steady-state shape. Some producers make anodes where the corners are cut off in order to reduce the risk of thermal cracking.
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