Reducing Amperage in Pot Operation: Alumina Shortage Concern

The group discussion focuses on pot operation at reduced amperage due to a shortage of alumina. Details include normal operation specifications, calculations for operating voltage at 300 kA, breakdown of new pot voltages, adjustments in ACD and bath height at 300 kA, and the amount of bath needed to restore the original bath height. The discussion provides insights into managing operational challenges in the aluminum production process.

• Pot operation
• Amperage reduction
• Alumina shortage
• Aluminum production
• Voltage optimization

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1. Group Discussion 3 POT OPERATION AT REDUCED AMPERAGE

2. Part A: DUE TO A SHORTAGE OF ALUMINA

3. Normal Operation 360 pots at 350 kA 4 Rectifiers operating, 1 spare ACD = 3.4 cm Bath height = 18 cm Piston effect = 4.6 change of immersion/change in ACD Amount of bath in channels = 166 kg/cm Piston factor = 4.6 VPot VAnode VCathode VExt VBubbles VBath VBEMF VAl = 4.20 V = 0.36 V = 0.25 V = 0.26 V = 0.20 V = 1.31 V = 1.82 V = 2.05 V

4. Current Situation 14.6 cm 18 cm 3.4 cm

5. 1) Operating voltage at 300 kA at the same internal heat 1) Operating voltage at 300 kA at the same internal heat Internal heat Q = I x (VPot VExt VAl) Q = 350 kA x (4.20 0.26 2.05) = 661.5 kW VPot at 300 kA: 661.5 = 300 x ( VPot(300) 0.26 x 300/350 2.05) VPot(300) = 661.5 / 300 + 0.22 + 2.05 = 4.48 V Note: Assumed is that VExt is proportional with the amperage.

6. 2) New pot voltage breakdown at 300 kA 2) New pot voltage breakdown at 300 kA 350 kA: VAnode VCathode VExt VBubbles VBath VBEMF VPot 300 kA: VAnode VCathode VExt VBubbles VBath VBEMF VPot = 0.36 V = 0.25 V = 0.26 V = 0.20 V = 1.31 V = 1.82 V + 4.20 V = 0.36 x 300/350 = 0.25 x 300/350 = 0.26 x 300/350 = Unchanged = Unchanged = 0.31 V = 0.21 V = 0.22 V = 0.20 V = 1.72 V = 1.82 V 4.48 V VBath = 4.48 0.31 0.21 0.22 0.20 1.82

7. 3) ACD at 300 kA? 3) ACD at 300 kA? ACD (300 kA) = ACD350 x VBath300/VBatch350 ACD (300 kA) = 3.4 x 1.72 / 1.31 = 4.46 cm

8. 4) New bath height and anode immersion at 300 kA? 4) New bath height and anode immersion at 300 kA? At 350 kA the bath height is 18 cm 1) Change in ACD = 4.46 3.40 = 1.06 cm 2) Change in bath height = 1.06 x 4.6 = 4.9 cm 3) New bath height = 18 4.9 = 13.1 cm 4) New immersion = 13.1 4.46 = 8.64 cm 8.64 cm 13.1 cm 4.46 cm

9. 5) How much bath is needed to restore the original bath height? 5) How much bath is needed to restore the original bath height? Height difference inside the channels is 4.9 cm (see diagram) Mass of bath = 166 kg/cm x 4.9 x 360 pots /1000 kg/tonne = 293 tonne 18 13.1 = 4.9 cm 13.1 cm 4.46 cm

10. Part B: DUE TO ONE RECTIFIER OUT OF SERVICE

11. New situation Line amperage goes down from 350 kA to 270 kA At 350 kA: 14.6 cm 18 cm 3.4 cm

12. 6) New pot voltage at 270 kA with 100 kW less internal heat? 6) New pot voltage at 270 kA with 100 kW less internal heat? Internal heat (270 kA) = 661.5 100 = 561.5 kW 561.5 kW = 270 kA x (VPot 0.26 x 270/350 2.05) VPot = 561.5/270 + 0.20 + 2.05 = 4.33 V

13. 7) New ACD at 270 kA? 7) New ACD at 270 kA? 270 kA: VAnode VCathode VExt VBubbles VBath VBEMF VPot 350 kA: VAnode VCathode VExt VBubbles VBath VBEMF VPot = 0.36 x 270/350 = 0.25 x 270/350 = 0.26 x 270/350 = Unchanged = Unchanged = 0.28 V = 0.19 V = 0.20 V = 0.20 V = 1.64 V = 1.82 V 4.33 V = 0.36 V = 0.25 V = 0.26 V = 0.20 V = 1.31 V = 1.82 V + 4.20 V VBath = 4.33 0.28 0.19 0.20 0.20 1.82 ACD (270 kA) = 3.4 x 1.64 / 1.31 = 4.26 cm

14. 8) New bath height and anode immersion at 270 kA? 8) New bath height and anode immersion at 270 kA? At 350 kA the bath height is 18 cm 1) Change in ACD = 4.26 3.40 = 0.86 cm 2) Change in bath height = ACD x Piston Effect = 0.86 x 4.6 = 4.0 cm 3) New bath height = 18 4 = 14 cm 4) New immersion = 14 4.26 = 9.74 cm 9.74 cm 14.0 cm 4.26 cm

15. 9) Additional measures to keep the heat in the pot? 9) Additional measures to keep the heat in the pot? Increased thickness of anode cover Increased content of alumina in cover material (30% 40%) Stop the heat exchanger Reduce the pot exhaust flow Ensure all holes are closed within pot crusts Reduce the height of the metal pad Reduce excess AlF3 to allow the temperature to stay up

16. 10) Minimum amperage at which pot is thermally stable? 10) Minimum amperage at which pot is thermally stable? Thermally stable 661.5 kW of heat Max. voltage is 1600 V for 360 pots or 4.44 V per pot. By iteration: 661.7 = INew x (4.44 0.26 x INew/350 2.05): INew = 306 kA

17. 11) Is this increase in amperage sustainable 11) Is this increase in amperage sustainable wrt the rectifiers? If Yes for how long? What are the the rectifiers? If Yes for how long? What are the consequences of overloading the RT? consequences of overloading the RT? wrt the load on the load on Normal: 350 kA from 4 rectifiers = 87.5 kA per rectifier New conditions: 270 kA from 3 rectifiers: 90 kA per rectifier 306 kA from 3 rectifiers: 102 kA per rectifier Rectifiers are overloaded for N-2 operation. Not recommended. Can loose one other one.