Effect of Local Cathode Current Increasing on Bath-Metal Two-Phase Flow Field in Aluminum Reduction Cells

WANG Fuqiang^{1}^{,}^{2}, LIU Wei^{2}, WANG Zhaowen^{1}()

1. School of Metallurgy, Northeastern University, Shenyang 110819, China 2. Shenyang Aluminum and Magnesium Engineering and Research Institute Co. , Ltd. , Shenyang 110001, China

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.

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.

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, 21~24^{①}

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: 5~20^{②}

5

0.177

0.067

-0.044

0.032

14

B: 1~4, 21~24^{③}

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, 21~24^{④}

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

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