Quality of anode. Overview of Problems and Some Methods of their Solution Part 1. Coal Foam in an aluminum electrolyzer

Abstract

The goal of any aluminum plant is to increase electrolyzer productivity and current efficiency, reduce electricity and carbon consumption. These indicators depend significantly on the quality of the anode blocks [1; 2; 3]. In turn, the quality of the anodes is also, to a certain extent, determined by the properties of the anode cinders involved in the recycling of the anodes. One of the indicators of the anode blocks quality is the amount of carbon foam that is removed during the operation of the anode. Over the past decades, the world's aluminum industry has been paying considerable attention to the study of its negative impact on electrolysis performance. A large amount of carbon foam in the electrolyte leads to operational problems and various technological disturbances that include [4]:  a slower heating of the new anode, so that more time is needed to equalize the current on the anodes;  the need to reduce the distance between the anode and the cathode VGH at a given voltage setting due to an uncontrolled increase in the electrical resistance of the electrolyte;  the increase in the coefficient of dynamic viscosity of the electrolyte;  the decrease in the rate of dissolution and distribution of alumina, since carbon foam prevents its free distribution in the electrolyte;  -a slower heat removal from melt, which leads to an imbalance in current distribution in the bath;  the increase of electrical resistance of electrolyte, since carbon foam acts as an insulator;  the cyclic increase in the temperature of melt, accompanied by an increased consumption of fluoride salts. The negative effect of the foam is also manifested in the increased consumption of anode carbon, in the increase in the resistance and temperature of the electrolyte, and in a significant decrease in the current yield. Foam can cause the formation of irregularities on the base of the anode, which in foreign literature are called "mushrooms", "thorns", in the Russian - "cones". The presence of the cone carries the risk of short-circuiting the anode with the cathode directly, or through a layer of liquid aluminum, which leads to temperature fluctuations and a decrease in current efficiency by an average of 1.5%. The amount of foam formed depends on the electrolyzer design, the conditions of the technology, the quality of the anodes used, the time of problem detection, and many other reasons. The article provides a brief overview of Russian and foreign studies devoted to the study of the causes of the coal foam appearance in electrolytes of aluminum electrolyzes, as well as proposals aimed at improving the quality of the anode and reducing the yield of coal foam.