Theory And Realization Of High Temperature Fume Bake-out Technology For Aluminum Reduction Cells

Though the reduction aluminum industry of China is in an unprecedented booming age, the life of aluminum reduction cells is totally shorter than that abroad. The baking-out of aluminum reduction cell highly affects the life of reduction cells, therefore, the research and development of bake-out technology is of great importance for the production of aluminum.Aiming at the deficiency of direct flame heating bake-out technology used internationally, this paper innovatively put forward a kind of novel fuel bake-outtechnique-high temperature fume bake-out for aluminum reduction cells. In thistechnique, the high temperature fume created from fuel burning is used to heat the aluminum cell. Also in the paper research work, the high temperature fume bake-out device has been developed according with the requirements of high temperature fume baking parameters. Furthermore, some of the theoretical problems relating to this technique were studied profoundly and systematically in this paper.Against the heavily oxidizing problem on surface of the carbon electrode and ramming paste in the fume, the oxidizing properties were firstly experimented. The results showed that when temperature is below 700, the oxidation rate of carbon in the fume is below 0.5 mg/min.cm2, which is only 3-5% of that in air. When temperature is above 700, the oxidation rate is increased very fast, but it is still 9% of that in air. In addition, the oxidation mechanism of carbon is also studied by thermodynamic and kinetic theory. From that, the oxidation rate of carbon depends on the interface chemical reaction. Within the temperature range of bake-out, the oxidation reaction of carbon in the fume belongs to the first-order reaction. The relationship between the reaction rate constant and temperature differs greatly in various temperature zones: Ink=-13617/T +7.1823 (below 700 ), Ink= -4452.5/T- 2.5997 (above 700).The theoretical calculation of heat transfer and the experimenting, on the simulating cell baked in high temperature fume, revealed that the high temperature fume bake-out technique possesses a wide range of heating speed adjusting. So that, this technique can perfectly meet the preheating requirements for the start-up of aluminum reduction cells. Owing to its flexible adjustment and convenient control on heating-up speed and temperature distribution, this technique can overcome the shortcomings ofthe bake-out by liquid aluminum and coke granule. Comparing with other bake-out methods such as coke granule bake-out, liquid aluminum bake-out and graphite bake-out, this technique makes the cell heating-up and bake-out become uniformly, and also makes temperature of the surface of cathode heat-up automatically according to a given optimized heating-up curve. As a result, the cathode crack caused by thermal stress can be avoided and the joint and ramming paste of the edge can be baked thoroughly, which can not be realized by other bake-out methods.Against the characteristics of high temperature fume bake-out, a study was also given in the coefficient of heat conductivity of cathode block effecting on the cathode temperature distribution. When the coefficient of heat conductivity of cathode block is 6~10w/m.K, temperature of the cathode lower surface is 753-817, the temperature difference of the upper and lower surface is 103-163. When using the cathode block whose coefficient of heat conductivity below 6w/m.K, more temperature differences appear so that it could not satisfy the needs of the cell bake-out. Accordingly, when the coefficient of heat conductivity is below 6w/m.K, it does not recommend to use high temperature fume bake-out to heat the cell.The key equipments in high temperature fume bake-out are the burner and dispensing house. According to the special requirements for it, the burner was mathematically modeled. The results showed that the existence of prechamber in the burner is beneficial to improve the combustion efficiency. The maximum combustion efficiency is 60% without perchamber, which is very low. When a prechamber added, the combust...