Study Of Simulation And Optimization On The Electro-Thermo-Stress Field And Sodium Expansion Stress Field In 300kA Aluminum Reduction Cells

Funded by the National Natural Science Foundation of China (No.50374081), with the help of Finite Element (FE) software, the electrical and thermal field during the heating-up and the thermo-stress field as well as the sodium expansion stress field after start-up in aluminum reduction cell were simulated and optimized. The main research contents and achievements are as follows:(1) The thermal stress has been optimized by using increasing resistivity coke bed from the side to the center of the cell to preheat the cell has been carried out. Results of good temperature distribution were obtained, the average temperature in the cathode increased a little and the value was 931℃, the difference in temperature decreases by more than 8% in the end cathode carbon block No.1 to No.3 and more than 30% in the center cathode carbon block No.4 to No.13, the average heating-up rate decreased by 12% in cathodes, the average temperature gradient decreased by 22%.(2)The sodium penetration and sodium expansion in the cathode carbon blocks have been simulated by computer. The results indicate that the sodium concentrations after 30 days start-up in anthracitic carbon, semigraphitic carbon, semigraphitized carbon and graphitized carbon are 1.98%, 1.67%, 1.53% and 0.52% respectively, but after one year start-up, the values are 3.65%, 3.47%, 3.37% and 2.01% respectively. The thermal stresses in anthracitic carbon, semigraphitic carbon, semigraphitized carbon and graphitized carbon after heating-up are 13.0 MPa, 17.5 MPa, 13.4 MPa and 9.29 MPa respectively, the stresses are intensified around the steel bar slots, while after 30 days start-up, because of the sodium expansion, the stresses are 71.0 MPa, 47.3 MPa, 30.8 MPa and 11.3 MPa respectively, which are intensified around the steel bar slots and the surface of the carbon.(3)The electrical field and the thermal field were optimized in aluminum reduction cell. The results show that the thermal gradients in anthracitic carbon, semigraphitic carbon, semigraphitized carbon and graphitized carbon after heating-up are 1023℃/m, 851℃/m, 809℃/m and 795℃/m respectively, during the production process, the voltage drop are 272.2mV, 240.2 mV, 229.6 mV and 195.4 mV respectively.(4)The FE models of the cathode carbon blocks with diverse shapes of collector bar slots (partial cylinder at the top, rectangle at the top, the collector bar slots are drilled through the carbon or separated) and different numbers of collector bar slots (1 or 2) were built to optimize the construction formation of the cathode. The results show that the stress in the cathode using the collector bar slots that were drilled through the carbon is the lowest. The largest equivalent stress in the cathode with two partial cylinder collector bar slots is 10.9MPa, which is decreased by 14% compares to the carbon that used rectangler collector bar slots.