Study On Oxidizing Characteristics Of The Electrode In Thermal Bake-out For Aluminum Reduction Cells

Aluminum reduction cell is the major equipment in aluminum reduction production. The life of cells is an all-round technical and economic target in aluminum industry. It not only reflects high or low level of manufacturing technique for aluminum reduction, but also affects the stability of aluminum reduction and the cost of products as well. For new reduction cells or cells after being heavily repaired, bake-out and start-up must be made before putting into production. But the method of bake-out for reduction cells plays a decisive role for the life of cells.In 1999, the thermal bake-out for the reduction cell was first put on trial and obtained success in Chongqing University, which fills in a gap for this technology in China. Compared with electric resistance bake-out, thermal bake-out provides better preheating control, so thermal bake-out is a kind of very good method for preheating aluminum reduction cells. But by reason that the electrode of cells is exposed in the high temperature mixed fume all the time during the thermal bake-out, oxidation may occur in the surface of the cathode and anode and also the ramming paste and ramming paste of the edge. If this problem cannot be handled very well, it will greatly restrict the application and popularization of this kind of good bake-out method for cells.In this article, the electric resistance furnace is used to heat the carbon cathode , anode and ramming paste samples of aluminum reduction cell, the temperature regulator used to regulate heating-up of the electric resistance furnace and high temperature mixed fume is inlet into melting chamber as oxidizing atmosphere. According to the conditions mentioned above, it simulates the bake-out process of high temperature fume for aluminum reduction cell and determines the situation of weight loss by electronic balance on the condition of different temperature and atmosphere.Experiment shows that the oxidation rate of cathode, anode and the ramming paste of the aluminum reduction cell in high temperature fume rises very fast when the temperature is below 700 C, but the absolute value is still in lower level; and when the temperature rises to 700 C, the oxidation rate is tending towards stability. During the whole experimental process, the maximum oxidation rate of the electrode sample is approximately 9% of that in air. After the air excess coefficient is greater than 1.1, the oxidation rate of the electrode is increased more quickly; when the coefficient is less than 1.1, the oxidation rate is increased slowly.After calculation and analysis, the interface chemical reaction plays a leading role when the temperature is below 850 C during the process of high temperature fume bake-out for aluminum reduction cells. The aluminum reduction cell begins to start up when the temperature is about 850 C, so the interface chemical reaction is a restrictive link of electrode oxidation in the whole bake-out process.In the real bake-out process, it suggests that the air excess coefficient of burning should be controlled within 1 in order to avoid electrode being oxidized by high temperature fume; when the temperature is below 700 C, it rises slowly in temperature to bake out thoroughly and uniformly; when above 700 C, it speeds up in heating-up to reduce the electrode oxidation.The study result of this article provides very good reference basis for the application and popularization of the technology of high temperature fume bake-out for aluminum reduction cells.