Anode paste consumption for aluminum production

Abstract

 In Russia, most aluminum smelters are equipped with cells with self-baking anodes featuring an urgent problem of lowering the anode paste consumption, since the share of anode materials in the cost of aluminum varies from 8 to 20 %. To solve this problem, it is necessary to determine the anode paste demand. The method for calculating the specific anode paste consumption used at aluminum smelters has a poor accuracy. The paper discusses the main errors of this method, shows the stages of anode paste consumption calculation, assesses the adequacy of calculations and gives recommendations for method improvement. It is shown that in general the considered method adequately reflects carbon consumption processes, but the final result of calculations may differ significantly from the actual one. The values taken constant to simplify the calculation, in fact, may vary during the electrolysis, which leads to a significant change in the final result of calculations. For example, an increase in the CO2 fraction from 0.45 to 0.5 leads to a decrease in the anode paste consumption by 15.3 kg/tonAl. At the same time, it is known that the composition of anode gases changes sharply as the anode effect occurs: the CO2 fraction decreases, and the CO fraction increases. In summer, at high ambient temperatures, the proportion of both vaporized pitch and anodes with an increased surface temperature rise. As the latter changes to 0.25, the consumption increases by 6.6 kg/tonAl. The same applies to air oxidation. The number of depressurized cells may increase with the subsequent increase in the carbon consumption. It is necessary to pay attention to factors affecting the anode quality. Incorrectly selected particle size distribution or worn equipment may significantly degrade the anode quality and lead to an increase in carbon consumption. It is necessary to make adjustments to the calculation in order to consider the peculiarities of carbon monoxide formation properly.