A CASE STUDY ON POT CELL DESIGN TO SAVE DC ENERGY

1 A CASE STUDY ON POT CELL DESIGN TO SAVE DC ENERGY PRESENTATION AT : KNOWLEDGE EXCHANGE PLATFORM,NEW DELHI By PRATAP SINGH HARISH GANGISETTI Team Members : KUWAR ANANTH VIKRAM SINGH SWAPNIL HIRAVE RAVI SHANKAR SMARAN SUGURU

2 Vision We aspire to become leading Aluminium Producer, integrating sustainable development, global standards of excellence in our business practices and will achieve lowest cost productions by leveraging the mining potential of India with optimization of assets, thereby generating superior returns to all stakeholders Mission Zero harm and material risk reduction Build value for stakeholder Produce Value Added Products Contribute to exchequer/ Indian Govt. Grow through innovation Lead in good governance practices Operational excellence Efficient supply chain & Logistics management Unleash employee potential Build and Strengthen brand equity Mr.Anil Agarwal, Group Chairman Values Entrepreneurship Excellence Growth Trust Sustainability Innovation

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4 2400 MW IPP Aluminium smelter 1 (0.5 million T/Annum) 1215 MW CPP Aluminium Smelter-2 (1.25 million T/Annum)

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6 Electrical Energy is vital to the aluminum industry's survival COP of aluminum represents 34% of Electrical energy Adoption of new technology is highly capital intensive Reduction of specific energy consumption from base line as per PAT norms 14.5 14 13.5 13 14.3 13.7 DC Energy kwh/mt 13.5 13.2 16% 34% COP of aluminium 1% 1% 2% 2% 1% 43% Alumina Power Carbon Manufacturing Cell relining & start up Manpower Admin Others(RM) 12.5 2011-12 2012-13 2013-14 Target

7 36% 2% Electricity Fuel 64% 98% Power Other Cost DC SEC= 2.98*Volts/pot Current Efficiency Focus is on DC energy reduction 5% 95%

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10 Cell Cleaning Buffing Grinding Bottom Insulation Lining Calcium Silicate Blocks High Strength Insulation Bricks Silicon Carbide Block Installation DIM Compaction Layer 1 Compaction Layer 2 Compaction DIM Leveling & Height measurement Cathode Installation Cathode Placement Cathode Block Alignment Window holes Sealing Slot Ramming Light Pouring Refractory Casting Light Pouring Refractory Castable High Strength Insulation Casting Low Strength Insulation Bricks Kraft paper High Strength Insulation Castables Refractory Lining Refractory Brick Lining SiC side wall lining Monolithic cathode Ramming Pot Preheating Slot Ramming Fillet Ramming

11 List of 8 problems which have major impact on power Prob. No Problem 1 Cathode Voltage Drop 2 High Energy consumption during cell start up 3 Abnormal cell operation 4 Anode Voltage Drop 5 Abnormal Bath Chemistry 6 High voltage drop at Bus bar joints 7 High A.E frequency 8 Long Duration Preheating of cathode surface

12 Cathode voltage Drop: Cathode Voltage Drop (CVD) is about 6 9 % of the overall cell voltage CVD includes the drop on Collector Bar, Carbon block, Liquid metal & carbon block interface, Ramming paste & collector bar& sealing paste interface

13 GOAL STATEMENT Reduction of DC power consumption 14000KWH/MT to <13000 KWH/MT of Al through modification in cathode Lining

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15 High Voltage drop due to structure Dimensions of block High Voltage Drop in cathode (CVD) Porosity Cathode Flex Drop Bolt Drop Preheating Duration Joint Drop Pot Preparation Surface Finish Coke Laying Riser Drop External Bus Bar Drop Online power on Bubble induced voltage Bath composition Resistance of cathode Graphite % in block Resistance of collector bar Chemical Dimensions of Bar Composition of bar Electrolyte Voltage drop Resistance of Anode block Cathode forming Compaction of paste Resistance of paste Graphite % in Paste Stub Drop Clamp Drop High DC power Consumption Anode Bus bar Drop High Power for Start Up of cell High Voltage Drop due to Electrolyte High Voltage Drop due to Anodic Part

16 Problem Description: Voltage Drop in cathode (CVD) Voltage drop due to structure Cell Start up Voltage Drop due to electrolyte Voltage drop due to Anodic part Root Causes Potential Root Cause Probable Corrective Action Responsibility Resistance of collector bar Resistance of Cathode Feasibility of height or width Cross section of the bar increase Pot lining Team Higher % of impurities Lower % of impurities Pot lining Team Cross section of the cathode block No Feasibility ---- Resistance can be decrease by Resistance of the cathode block increasing graphite % Pot lining Team Porosity in the cathode block Low porosity,lower resistanc Pot lining Team Resistance can be decrease by Resistance of paste Resistance of the ramming paste increasing graphite % Pot lining Team Under Compaction of ramming Pefect compaction reflects paste uniform current flow Pot lining Team Resistance due to metal Constant ---- ---- Riser Drop Constant ---- ---- Cathode Flex drop Bolt Drop Good Surface finishing of contact area Pot lining Team Joint Drop Constant ---- ---- External Bus bar Drop Constant ---- ---- Pot preperation ---- ---- online power on Online power on Fuse implementation Pot start up team Preheating duration Coke laying Trial on different patterns of coke laying Pot start up team Bath Composition Constant ---- ---- Electrolyte voltage drop Constant ---- ---- Bubble induced voltage drop Constant ---- ---- Resistance of Anode block ---- ---- Carbon Team Stub drop ---- ---- Carbon Team Anode Bus bar Drop Clamp Drop Tightness of clamp Pot Operation team

17 Voltage Drop in Cathode 1 Dimension of Collector Bar 2 Composition of Collector Bar 3 Graphite % in Cathode Block 4 Graphite % in Ramming Paste 5 Compaction of Ramming Paste

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19 Ohms law : V=I*R Where V-voltage, I-Current, R-Resistance Plot between voltage and resistance at constant current Varying Resistance: R=ρl/A Where ρ-specific resistivity (Constant) l- Length of the current carrying bar(constant) A- Surface area of bar Fig. Collector Bar

20 Cathode Block with collector bar Increase in cross section of collector bar can decrease the resistance of the bar

21 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 360 Tested Cells 2628,1528,1438,1531,2134,2118,1416,2629,1207,25151431 Reference cells 1126,2133,1733,1602,1510,1411,2238,1219,2101,2828,2119 CV D (mv) 440 420 400 380 360 340 320 300 65 mm Width 70 mm Width Cell Age (in days) BENEFITS: Gain of 9 mv on CVD (29 KWH/MT)

22 Control of Chemical impurities decreases the resistivity of metallic conductors Chemical Properties Existing Collector Bar Changed Composition Collector Bar Electrical Resistivity (ER) 130-140 µ Ω mm 110-120 µ Ω mm % of Iron < 99.3 % <99.3% % of Carbon (C) < 0.12% <0.06% % of Manganese (Mn) 0.25% - 0.50% <0.45% % of sulphur 0.05% max 0.05% max % of phosporus 0.05% Max 0.05% Max

23 Tested Cells 1132,2306,2219,2801,1305 Reference cells 2809,2235,2816,1603,1127,1524 CV D (mv) 390.0 370.0 350.0 330.0 310.0 Changed Che. Com. vs Normal = 9 mv 290.0 270.0 250.0 Avg CVD (After) Avg CVD(before) 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 Cell Age (in days) BENEFITS: Gain of 9 mv on CVD (29 KWH/MT)

24 Resistivity Increase in graphite content reduces the resistivity of carbon cathode 3 2 1 Cathode Blocks Grades of cathode Block

25 Property Units Earlier Block Existing Block Apparent Density g/cm 3 1.62 1.67 Open Porosity % 12 15 Compressive Strength MPa 32 36 Flexural Strength MPa 9 9 Graphite % 30 50 Specific Electrical Resistivity µω.m 37 24 Thermal conductivity(at 30 o C) W/K.m 10 20 Ash Content % 4 2 CTE(20-200 o C) µm/k-m 3.1 -

26 15 45 75 105 135 165 195 225 255 285 315 345 375 405 435 465 495 525 555 585 615 645 675 705 735 765 795 Test Cells 1617,2110,1403,2213,1823,1634,1505,2424,2130,1228,2226 Reference cells 1323,2115,1517,2726,2305,1334,1113,1409,2805,1508,2810 CV D (mv) 430.0 410.0 390.0 370.0 350.0 330.0 310.0 290.0 270.0 250.0 = 29 mv 30% graphitic 50 % graphitic Cell Age (in days) BENEFITS: Gain of 29 mv on CVD (93 KWH/MT)

27 Ramming Paste Increase in graphite % in ramming paste decreases the resistance of the paste Property Unit Previous Paste Current Paste Bulk Density g/cm 3 1.56 1.7 Mass loss on baking % 7.4 9 Bulk density g/cm 3 1.47 1.54 Open porosity % 20 18 Specific Electrical Resistivity µω.m 57 44 Thermal Conductivity W/K.m 5 7 Compressive strength MPa 20 16 Ash Content % 4.3 2.5

28 Test Cells 1307,2615,1826,2335,2606,1434 Reference cells 2819,1709,1132,1302,1613,2809 340 330 CV D (mv) 320 310 300 290 280 270 260 = 5 mv Before increase in % graphite After increase in % graphite 15 30 45 60 75 90 105 120 135 150 165 180 Cell Age (in days) BENEFITS: Gain of 5 mv on CVD (16 KWH/MT)

29 Right Compaction of ramming paste gives minimum drop along the paste Poor Compaction Good Compaction Earlier Ramming Paste Present Ramming Paste

30 Ramming of paste in gaps After ramming surface seems monolithic cathode BENEFITS: Lower cathode voltage drop

31 Initiatives Gain Gain in Specific Power Change in Dimension of collector 9 mv 29 KWH/MT bar Change in Collector Bar composition 9 mv 29 KWH/MT Change in % of graphite in cathode block Change in % of graphite in Ramming paste 29 mv 93 KWH/MT 5 mv 16 KWH/MT

32 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 360 375 390 405 420 435 450 465 480 495 510 525 540 555 570 585 600 615 630 645 660 675 690 705 720 735 750 765 780 795 810 825 840 855 Learnings: Analytical Ability Team Work Self Confidence 400 CV D (mv) 350 300 = 47 mv 250 Cell Age (in days) Tangible Benefits : Total gain in specific power consumption : 167 KWH/MT which is equivalent to 15 Lacs/Cell/Year

33 Improvement on Pot Heat Balance Advance Cathode (100% Graphitized) Trial with Copper cored collector bar. Improvement in Line Amperage

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36 Prob. No. PROBLEM Pratap Harish Ananth Swapnil Ravi Smaran RATING RANKING 1 Cathode Voltage Drop 10 8 10 9 8 9 54 1 2 High Energy consumption during cell start up 8 10 9 6 6 9 48 2 3 Abnormal cell operation 4 5 4 6 5 6 30 5 HIGH POWER CONSUMPTION DUE TO CATHODE VOLTAGE DROP 4 Anode Voltage Drop 8 7 7 5 4 6 37 4 5 Abnormal Bath Chemistry 4 6 5 3 1 9 28 6 6 High voltage drop at Bus bar joints 2 1 3 2 1 1 10 8 7 High A.E frequency 4 3 2 4 2 8 23 7 8 Long Duration Preheating of cathode surface 6 5 8 8 7 6 40 3

37 SL. NO 1 PROBLEM/ CAUSE STANDARD OBSERVATION JUDGEMENT Resistance of the collector bar As per design provided by the GAMI width should be 65 and tolerance ± 5mm Width can be increased by 5mm 2 Change in chemical composition of collector bar Carbon percentage should be < 0.06% and resistivity < 130-140 µ Ω mm By decreasing the carbon percentage to <0.04 % resistivity is <110-120 µ Ω mm 3 Graphite % in cathode block As per the design provided by the GAMI 30% graphitic blocks Energy consumption can be decreased by increasing Graphite % in cathode blocks 4 Graphite % in cold ramming paste Electrical Resistivity should be less than < 57 µ Ω mm Electrical resistivity can further decrease by increasing graphite content in the paste 5 Ramming Compaction Even compaction through out the periphery of the cathode block SOP modified to ensure ramming pressure in between 6.5 to 7 bar