Research On The Numerical Simulation And Optimization Of Magnetohydrodynamic Stability And Busbar Configuration In Aluminum Electrolysis Cell

With the rapid development of the metallurgy industry especially in the electrolysis of aluminum, electrolysis cell with higher current and efficiency, larger capacity, environmental protection oriented is the trends and the principal target that the researchers of aluminum industry are trying to tackle with. The research and development of 500kA and higher capacity cell has been the key to improve and retrofit the technical level. The busbar configuration and MHD stability of fluid in the cell have already become one of the most important factors in the design and development of new cell. With the help of analysis of MHD instability in the electrolysis cell, it can greatly improve the performance and current efficiency and increase the life duration of aluminum electrolysis cell.In this study, the busbar configuration and optimization of 500kA cell based on the MHD stability evaluation and computation was conducted. Firstly, the brief introduction was given about the contemporary situation of the basic principle of the electrolysis cell as well as its strength and weakness, the main approaches and methods adopted in the numerical simulation of processes in the electrolysis cell were also summarized and argued.Secondly, the coupled numerical simulation of the multi-physical fields in a 300kA cell under running in a plant in Henan province was conducted while the computation results has been compared with the measurements, the electromagnetical fields and fluid flow with moving interface were calculated with the finite element method and finite volume method separately together with General Scalar Potential approach (GSP) andκ-εturbulence model. The unusual situation of anode changing in the corner was also simulated with the custom code based on the commercial software ANSYS, it enabled us taking a deep insight of the physical fields under AC processes.Thirdly, based on the shallow water approach of the two layered fluid flow in the electrolysis cell, the source and mechanism of the magnetohydrodynamic instability in the electrolysis cell were analyzed and discussed with the help of linear stability analysis method. Three mechanisms of MHD instability such as K-H instability, traveling wave instability and gravity wave instability under the influence of magnetic fields have been discussed mathematically, factors mostly influencing the stability were shown clearly with the derivation. A new and simple evaluation method of the MHD instability was proposed and calculated with statistical analysis of the lorentz force fields and the interface vibrations, which was applied to the choice of 5 point entry riser ratio in the design of a new 500kA cell and it was found that the riser ratio of 10:9:10:9:10 can reach more stable cell among those busbar configurations under different riser ratio.Fourthly, the numerical model of 500kA cell was built with ANSYS and the custom code was employed to calculate the electromagnetic fields under combinations of variant busbar configuration parameters, such as entry riser ratio, vertical location of the cathode bus and the bus around the ends, bus passing under cell, number of neighboring cells, distance between the rows of cells, etc. All configurations under different parameters were evaluated with the custom stability function.Finally, the problem of busbar configuration in 500kA cell was simplified and reduced to the combination of a group of parameters of different types. The genetic algorithm was employed for the numerical optimization of the busbar configuration based on the custom object function, that is, MHD stability indicator. The computation results of the optimum busbar configuration were analyzed and discussed, it was found that the cell with optimized busbar can reach a low value of vertical B_zor average B_z as well as horizontal gradient of B_z and lower velocity in the melt, and the interface vibration can be lowered than expected. It is shown that the numerical optimization of busbar configuration with genetic method can greatly improve the efficiency and decrease the cost for the design and development of a new cell.