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Cell performance and anodic processes in aluminium smelting studied by product gas analysis

by Dorreen, Mark Murray

Abstract (Summary)
Aluminium smelting is an energy intensive process, and as a result there has been considerable and ongoing research over a number of decades on the energy efficiency of various aspects of the process. One of the most important measures is current efficiency, which has been shown to have direct relationships with current density, cell temperature, electrolyte chemistry, and anode-cathode distance. The effects of these variables on current efficiency are generally accepted, however there remains debate over the influence of the alumina concentration in the electrolyte on current efficiency. This research relied upon the development of a laboratory scale aluminium smelting cell where the current efficiency was measured via sampling of the product gases. A modified oxygen balance was used, with gas analysis performed using online mass spectrometry. The findings of this research agreed with the accepted current efficiency trends, showing a current density influence of 17.25 %CE per A/cm2, over the range 0.3 and 1.1 A/cm2. The influence of electrolyte chemistry was -7.8 %CE per unit cryolite molar ratio, between cryolite ratios 1.99 and 3. The anode-cathode distance was shown to have no influence on current efficiency in this cell, contradicting the established findings, however this was expected because of the design of the cell with no metal pad at the cathode and therefore constant mass transfer conditions at all the anode-cathode distances used. The most significant finding concerning current efficiency is that the variation with alumina concentration is so small, -0.0376 %CE/wt% Al2O3, that there is effectively no influence. While in many other studies an influence was found, the values and direction of the relationship varied. This suggests that in many cases the observed variation in current efficiency was actually caused by a change in the level of stability in the cell, by processes such as dissolution of sludge from the cathode or the thermal disturbance of alumina feeding, whereas in this research the cell was stable under all operating conditions.
Bibliographical Information:

Advisor:Dr Margaret Hyland; Professor Barry Welch

School:The University of Auckland / Te Whare Wananga o Tamaki Makaurau

School Location:New Zealand

Source Type:Master's Thesis

Keywords:fields of research 290000 engineering and technology

ISBN:

Date of Publication:01/01/2000

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