Effect of Local Cathode Current Increasing on Bath-Metal Two-Phase Flow Field in Aluminum Reduction Cells
WANG Fuqiang1,2, LIU Wei2, WANG Zhaowen1()
1. School of Metallurgy, Northeastern University, Shenyang 110819, China 2. Shenyang Aluminum and Magnesium Engineering and Research Institute Co. , Ltd. , Shenyang 110001, China
Cite this article:
WANG Fuqiang, LIU Wei, WANG Zhaowen. Effect of Local Cathode Current Increasing on Bath-Metal Two-Phase Flow Field in Aluminum Reduction Cells. Acta Metall Sin, 2020, 56(7): 1047-1056.
The stability of the magnetohydrodynamics (MHD) of aluminum reduction cell is determined by the bath-metal two-phase flow field. So, konwing how to optimize the metal flow field and restrain the bath/metal interface deformation is the key to maintain the stable and efficient operation of cell. Many previous works on the bath-metal flow field are based on the static electromagnetic force stirring the melt, however, it should be have some deviation from the actual cell state. A three dimensional bath-metal two-phase quasi-steady flow model (based on transient electromagnetic force) for full 500 kA aluminum reduction cell was built by means of numerical simulation in this work, and validated by metal velocity and bath/metal interface deformation measurement in industrial cells. The effects of 60% increase of local cathode current on melt flow distribution and interface deformation were simulated and evaluated according to abnormal 6 cases in realistic electrolytic process. It was found that the increase of local cathode current has little effects on the general pattern of flow field and interface deformation in cell, but the amplitude of local metal velocity and interface deformation would be changed in certain extent. The increase of local cathode current in A2~A3 could decrease the interface height in middle cell of downstream side (side B), with anode cathode distance (ACD) increasing by 3.0%. But the other 5 cases could deteriorate the low ACD zone further in side B, especially the increase of local cathode current in A10A11, with average ACD decreasing by 4.6% in B12~B20. The solution is to cut cathode flexes partially in abnormal position to decrease the effect on the bath-metal two-phase flow. According to the evaluation results, it is found that the uneven distribution of cathode current may be helpful to decrease the interface deformation and improve the MHD stability of cell. Based on this finding, the bath-metal two-phase flow field was changed by increasing the proportion of cathode current at the two ends of cell, the middle part of cell and side A and side B respectively, and then was analyzed in this work. The simulation results show that it is beneficial to restrain the interface deformation by increasing the cathode current at both ends of cell properly, and it is also helpful to solve the cooling problem at cell ends. In particular, when the cathode currents at A1~A4 and A21~A24 increase by 28%, the distribution trend of melt flow field remains unchanged basically, and the maximum of metal velocity under A19~A20 increases by 10%, and the maximum of interface height decreases by 2.4 mm, and the average of ACD under B7~B18 increases by 9.5%. It provides a valuable reference for optimizing the busbar design and improving the cell MHD stability.
Fig.1 Bath-metal two-phase flow physical model (TE—tapping end, DE—duct end)
Fig.2 Simulated metal velocity distribution of normal state
Range / m
Ratio / %
-0.05~-0.04
0.3
-0.04~-0.03
2.0
-0.03~-0.02
7.0
-0.02~-0.01
21.8
-0.01~0
8.4
0~0.01
23.9
0.01~0.02
23.8
0.02~0.03
12.8
0.03~0.04
0.1
Table 2 Interface deformation range distribution of normal state
Fig.3 Simulated bath/metal interface deformation of normal state
Fig.4 Positions of metal velocity measure points and flow direction
Fig.5 Comparisons between simulation and measurement metal velocity
Fig.6 Comparisons between simulation and measurement interface deformation
Case
Location
Metal velocity / (m·s-1)
Interface deformation / m
Max.
Aver.
Min.
Max.
1
A2A3
0.215
0.064
-0.046
0.031
2
A6A7
0.184
0.068
-0.045
0.032
3
A10A11
0.184
0.072
-0.053
0.032
4
A14A15
0.179
0.071
-0.054
0.031
5
A18A19
0.199
0.067
-0.044
0.031
6
A22A23
0.206
0.067
-0.047
0.031
Table 3 Comparisons of two-phase flow field simulations for 6 cases after increasing the local cathode current by 60%
Fig.7 Simulated two-phase flow fields after increasing the local cathode current for case 1 (a1, b1), case 2 (a2, b2), case 3 (a3, b3), case 4 (a4, b4), case 5 (a5, b5), case 6 (a6, b6) (The current increase locations are shown in square frames) (a1~a6) metal velocity (b1~b6) interface deformation
Fig.8 Anode cathode distance (ACD) changement ratios at side A (a) and side B (b)
Case
Location
Current increase
Metal velocity / (m·s-1)
Interface deformation / m
%
Max.
Aver.
Min.
Max.
11
AB: 1~4, 21~24①
10
0.201
0.065
-0.045
0.030
12
AB: 1~4, 21~24
20
0.209
0.064
-0.053
0.029
13
AB: 5~20②
5
0.177
0.067
-0.044
0.032
14
B: 1~4, 21~24③
14
0.191
0.067
-0.049
0.031
15
B: 1~4, 21~24
28
0.196
0.067
-0.056
0.030
16
B: 1~4, 21~24
42
0.197
0.067
-0.061
0.030
17
A: 1~4, 21~24④
14
0.197
0.065
-0.044
0.029
18
A: 1~4, 21~24
28
0.207
0.063
-0.041
0.029
19
A: 1~4, 21~24
42
0.215
0.061
-0.041
0.030
Table 4 Summary of two-phase flow field simulation results for 9 cases used to compare
Fig.9 ACD changement ratios at side B for case 13~case 16 (a) and case 11, case 12, case 17~case 19 (b)
Fig.10 Simulated two-phase flow fields for case 11 (a1, b1), case 12 (a2, b2), case 17 (a3, b3), case 18 (a4, b4), case 19 (a5, b5) (The current increase locations are shown in square frames) (a1~a5) metal velocity (b1~b5) interface deformation
[1]
Liu Y X, Li J, et al. Modern Aluminum Electrolysis [M]. Beijing: Metallurgical Industry Press, 2008: 338
(刘业翔, 李 劼等. 现代铝电解 [M]. 北京: 冶金工业出版社, 2008: 338)
[2]
Urata N, Arita Y, Ikeuchi H. Magnetic field and flow pattern of liquid aluminum in the reduction cells [A]. Light Metals [C]. Warrendale: Metallurgical Society of AIME, 1975: 233
[3]
Mori K, Shiota K, Urata N, et al. Surface oscillation of liquid metal in aluminum reduction cells [A]. Light Metals [C]. Warrendale: Metallurgical Society of AIME, 1976: 77
[4]
Arita Y, Ikeuchi H. Numerical calculation of bath and metal convection patterns and their interface profile in Al reduction cells [A]. Light Metals [C]. Warrendale: Metallurgical Society of AIME, 1981: 357
[5]
Tarapore E D. Magnetic fields in aluminum reduction cells and their influence on metal pad circulation [A]. Light Metals [C]. Warrendale: Metallurgical Society of AIME, 1979: 541
[6]
Ai D K. The hydrodynamics of the hall-héroult cell an overview [A]. Light Metals [C]. Warrendale: Metallurgical Society of AIME, 1985: 593
[7]
Moreau R, Evans J W. An analysis of the hydrodynamics of aluminum reduction cells [J]. J. Electrochem. Soc., 1984, 131: 2251
[8]
Moreau R J, Ziegler D. The moreau-evans hydrodynamic model applied to actual hall-héroult cells [J]. Metall. Trans., 1988, 19B: 737
[9]
Zikanov O, Thess A, Davidson P A, et al. A new approach to numerical simulation of melt flows and interface instability in hall-héroult cells [J]. Metall. Mater. Trans., 2000, 31B: 1541
[10]
Potočnik V, Laroche F. Comparison of measured and calculated metal pad velocities for different prebake cell designs [A]. Light Metals [C]. Warrendale: TMS, 2001: 419
[11]
Severo D S, Gusberti V, Schneider A F, et al. Comparison of various methods for modeling the metal-bath interface [A]. Light Metals [C]. Warrendale: TMS, 2008: 413
[12]
Bojarevics V, Sira S. MHD stability for irregular and disturbed aluminium reduction cells [A]. Light Metals [C]. Warrendale: TMS, 2014: 685
[13]
Dupuis M, Bojarevics V. Influence of the cathode surface geometry on the metal pad current density [A]. Light Metals [C]. Warrendale: TMS, 2014: 479
[14]
Severo D S, Schneider A F, Pinto E C V, et al. Modeling magneto-hydrodynamics of aluminum electrolysis cells with ANSYS and CFX [A]. Light Metals [C]. Warrendale: TMS, 2005: 475
[15]
Zhou P, Zhou N J, Mei C, et al. Numerical calculation and industrial measurements of metal pad velocities in hall-héroult cells [J]. Trans. Nonferrous Met. Soc. China, 2003, 13: 208
[16]
Li M, Zhou J M, Wang C H. Coupled simulation of multiple physical fields in a 300 kA aluminum electrolysis cell [J]. Chin. J. Process Eng., 2007, 7: 354
Zhou J M, Li M, Jiang S J. Two-phase simulation and its interface tracking of fluid flow in aluminum electrolysis cell [J]. J. Cent. South Univ. (Sci. Technol.), 2007, 38: 267
Liu W, Li J, Lai Y Q, et al. Development and application of electro-magneto-flow mathematic model of aluminum reduction cells [J]. Chin. J. Nonferrous Met., 2008, 18: 909
Xu Y J. A study of multi-physical fields coupled modeling and structure optimization of large-scale energy-saving aluminum reduction cells [D]. Changsha: Central South University, 2010
(徐宇杰. 铝电解槽内熔体运动数学建模及应用研究 [D]. 长沙: 中南大学, 2010)
[20]
He Z, Li B K, Wang F, et al. Impact of the novel cathode convex on the electrolyte/aluminum interface wave in a reduction cell [J]. J. Northeastern Univ. (Nat. Sci.), 2011, 32: 704
He Z, Xia T, Xiong W, et al. Mathematical models for the novel cathode convexes in a reduction cell [J]. J. Metall., 2013, 2013: 196891
[22]
Hua J S, Droste C, Einarsrud K E, et al. Revised benchmark problem for modeling of metal flow and metal heaving in reduction cells [A]. Light Metals [C]. Warrendale: TMS, 2014: 691
[23]
Wang Q, Li B K, He Z, et al. Simulation of magnetohydrodynamic multiphase flow phenomena and interface fluctuation in aluminum electrolytic cell with innovative cathode [J]. Metall. Mater. Trans., 2014, 45B: 272
[24]
Zhan S Q. Numerical simulation and application of multiphase flow dynamics behavior in melts of aluminum reduction cells [D]. Changsha: Central South University, 2015
Hua J S, Rudshaug M, Droste C, et al. Modelling of metal flow and metal pad heaving in a realistic reference aluminum reduction cell [A]. Light Metals [C]. Warrendale: TMS, 2016: 339
[26]
Hua J S, Rudshaug M, Droste C, et al. Numerical simulation of multiphase magnetohydrodynamic flow and deformation of electrolyte-metal interface in aluminum electrolysis cells [J]. Metall. Mater. Trans., 2018, 49B: 1246
[27]
Liu W, Zhou D F, Liu Y F, et al. Simulation and measurements on the flow field of 600 kA aluminum reduction pot [A]. Light Metals [C]. Warrendale: TMS, 2015: 479
[28]
Dupuis M, Pagé M. Modeling gravity wave in 3D with openfoam in an aluminum reduction cell with regular and irregular cathode surfaces [A]. Light Metals [C]. Warrendale: TMS, 2016: 909
[29]
Feng Y Q, Schwarz M P, Yang W, et al. Two-phase CFD model of the bubble-driven flow in the molten electrolyte layer of a hall-héroult aluminum cell [J]. Metall. Mater. Trans., 2015, 46B: 1959
[30]
Mei C. Simulation and Optimization of Nonferrous Metallurgy Furnace [M]. Beijing: Metallurgical Industry Press, 2001: 74
(梅 炽. 有色冶金炉窑仿真与优化 [M]. 北京: 冶金工业出版社, 2001: 74)
[31]
Bradley B F, Dewing E W, Rogers J N. Metal pad velocity measurements by the iron rod method [A]. Light Metals [C]. Warrendale: Metallurgical Society of AIME, 1984: 541
