| Aluminum electrolysis cells are gradually developing towards large-scale capacity,and the potential safety hazards of cells in industrial production have been exposed because of the interfacial wave instability.The establishment of interfacial stability models and the quantitative analysis of index in aluminum electrolysis cells are important basis of realizing stability,saving energy,and promoting efficiency.In the view of the limitations in interfacial stability models such as incomplete calculation parameters and disregard of quantitative measurement indexes,a completely interfacial stability analysis method,which comprehensively investigates several factors affecting the interfacial fluctuations,has been developed and applied to analyze of the interfacial stability in a 500 k A cell,supported by the fundamental research funds for the Central South University.The main contents and conclusions are as follows:(1)Taking account of the factors affecting the interfacial wave instability in whole cells,the controlling equation of interfacial stability with interaction of Kelvin-Helmholtz(K-H)and magnetohydrodynamic(MHD)instability has been built up according to the shallow water future of fluid system.The coupling mechanism of the two instabilities was investigated and the threshold values M_c and N_c,which describe the two instabilities were obtained.The results show that the mechanism of two instabilities is independent from each other,where M_c depends on the density and thickness of bath and metal layers,and N_c depends on the aspect ratio of the cell as well as the oscillation frequency.(2)Based on the theory of bubble dynamics and magneto-hydrodynamics,the influence of bubbles at the bottom(zoneⅠ)and side channel of the anode(zoneⅡ)on the interfacial wave stability was investigated,and the force on the bubbles at the bottom of the anode in the horizontal direction and the bubble thickness were analyzed.The variation curve of the pressure coefficient of interfacial wave at the zoneⅡwas calculated.The calculation results show that the bubble thickness at the bottom of the anode in a 500 k A cell is about 3.8 mm.There is a minimum value of the pressure at the center of zoneⅡ,and the pressure coefficient decreases as one moves from the side channel,which proves that the force of the bubble at the zoneⅡhas a greater influence on the interfacial stability,while the bubble at the zoneⅠhas little influence.(3)According to the results of the mode coupling interfacial stability equations and combined with the theory of the Fourier series method and the finite element method(FEM),the quantitative analysis method was proposed to describe the interfacial stability,and the discrete data of the vertical magnetic field were fitted into the continuous function by using the least residual square method.Based on this,the frequency spectrum and mainly contributing modulus were analyzed by using MATLAB custom code,focusing on how the anode-cathode distance(ACD)and the aspect ratio affected the interfacial wave stability.The parameters of the cells were optimized,and the interfacial stability calculation software was established by App Designer.The modal analysis method was applied to the stability analysis of a 500 k A cell,the results show that there are four unstable frequencies,mainly in the range of 0.05-0.30 Hz.The critical ACD is0.041 m,when maintain this ACD,the energy consumption will be reduced by 120 k W·h per ton of aluminum. |
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