Abstract
Carbon anodes are consumed in electrolysis cells during aluminum production. Carbon consumption in pre-bake anode cells is 400–450 kg C/t Al, considerably higher than the theoretical consumption of 334 kg C/t Al. This excess carbon consumption is partly due to the anode manufacturing processes. Net carbon consumption over the last three years at Emirates Aluminium (EMAL, also known as Emirates Global Aluminium (EGA) Al Taweelah) was analyzed with respect to anode manufacturing processes/parameters. The analysis indicates a relationship between net carbon consumption and many manufacturing processes, including anode desulfurization during anode baking. Anode desulfurization appears to increase the reaction surface area, thereby helping the Boudouard reaction between carbon and carbon dioxide in the electrolysis zone, as well as reducing the presence of sulfur which could inhibit this reaction. This paper presents correlations noted between anode manufacturing parameters and baked anode properties, and their impact on the net carbon consumption in electrolytic pots. Anode reactivities affect the carbon consumption in the pots during the electrolysis of alumina. Pitch content in anodes, impurities in anodes, and anode desulfurization during baking were studied to find their influence on anode reactivities. The understanding gained through this analysis helped reduce net carbon consumption by adjusting manufacturing processes. For an aluminum smelter producing one million tonnes of aluminum per year, the annual savings could be as much as US $0.45 million for every kg reduction in net carbon consumption.
Highlights
Carbon anodes are consumed in Hall–Héroult electrolysis cells during aluminum production.The carbon anode consumption rate is expressed as “net carbon consumption” (NCC) and is a frequently used parameter for evaluating anode performance in reduction cells
The analysis shows how anode properties are influenced by anode manufacturing processes—and the ultimate impact on Netcarbon carbonconsumption consumption (NCC)
Theoretical carbon consumption is a result of the electrolytic reduction of alumina to aluminum according to Equation (1), which is for 100% current efficiency
Summary
Carbon anodes are consumed in Hall–Héroult electrolysis cells during aluminum production. The carbon anode consumption rate is expressed as “net carbon consumption” (NCC) and is a frequently used parameter for evaluating anode performance in reduction cells. In every smelter carbon plant, efforts are made to adjust anode manufacturing processes to sustain anode quality despite changing the raw material quality. Pot operational parameters and practices are optimized to minimize excess carbon consumption so as to reduce any negative impact on metal production cost. Use of different quality cokes impacts anode quality, which in turn affects anode performance and consumption in reduction cells. Several papers have been published on the influence of anode properties and pot operation parameters on NCC [1,2,3].
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