Consumption of carbon anodes in aluminium electrolysis

摘要

This thesis on the carbon cosumption of the anodes in aluminium electrolysis focuses on the mechanisms of the excess consumption, especially on the dusting problem of Soederberg anodes. Laboratory investigations were made of the effects of baking temperature, current density, anode impurities, anode consumption and anode types. The current distribution was studied in industrial Soederberg cells. The formation of carbon dust from the sides of the industrial anodes were estimated by combining results from laboratory and industry. The air-burning of industrial Soederberg anodes was estimated by direct measurement of the wear in the side parts of the anodes. The current distribution in the measured industrial cell was simulated by a mathematical model. Some general theory behind the anode consumption is provided. Some of the conclusions are as follows. It is found that the carbon consumption decreases by 9% per 100(sup o)C increase in baking temperature in the range of 925(sup o)C - 1250(sup o)C. At low current densities the carbon consumption of prebaked anodes is more affected by current density than is that of Soederberg anodes. Consumption decreases for both as the anode current increases. Several impurity compounds catalyse the consumption, while sulphur is an inhibitor. The carbon consumption of Soederberg anodes made of green coke is 30% below that of normal Soederberg anodes. The green coke anode has the lowest dust formation of any carbon anode. 125 refs., 60 figs., 11 tabs.