Dr LJ Erasmus June 2013

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Phillip Whitehead
6 years ago
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1 Dr LJ Erasmus June 2013

2 Self baking Electrode Mr Söderberg, Sem& Westley Det norske Aktieselskabfor Electrokemisk Industri, Oslo /14/2013 2

3 SöderbergElectrodes A Triumph of Materials Engineering Anthracite Pitch Requirements Mechanical integrity Ability to sustain enormous temperatures Oxidation resistance

4 SöderbergPaste Unbaked paste Anthracite 78% Tar 22% Bulk density 1.63 kg/m 3 Plastisity 39% (20 50%) Baked paste Bulk density 1.45 kg/m 3 Compressive strength 14.6 N/mm 2 Bending strength 3.34 N/mm 2 Modulus of elasticity 2.81 kn/mm 2 Electrical resistivity 76.7 µωm (room temp) Volatiles 12.6% 6/14/2013 4

$Prod. -4 mm fraction Medium size Coarse size SCALE BINDER 120 C 180 C PREHEATER PREHEATER 180 C Sold MIXER CASTING WATER COOLIN G PACKAGING / STACKING$

5 Söderberg Electrode Paste Production Process Anthracite CRUSHER + 16 mm mm SCREEN +2 mm SCREEN mm CALCINING FURNACE BALL MILL -63 µm Ball Mill Prod. -4 mm fraction Medium size Coarse size SCALE BINDER 120 C 180 C PREHEATER PREHEATER 180 C Sold MIXER CASTING WATER COOLIN G PACKAGING / STACKING 6/14/2013 5

6 Types of electrode pastes

7 Electrode Column designs

8 Electrode slipping Electrode slip mechanism Maintenance ring Casing Upper ring Pneumatic cylinder Pneumatic slip cylinders Lower ring Pneumatic cylinder Slip ring

9 Electrode Management Casing Design Solid and liquid paste levels Electrode baking 450 C Isotherm Electrode slipping Furnace operation Shut down practice

10 Casing design Steel Current capacity Sufficient steel to provide sufficient strength to carry the electrode Tensile strength Sufficient windows in fins for baked paste bridge formation Shearing strength

11 Casing

12 SöderbergElectrode Column WINDOWS CASING FINS PASTE CYLINDERS ELECTRODE CASING CONTACT CLAMPS LIQUI D PASTE BAKED ELECTRODE 6/14/

13 Solid and Liquid Paste Levels SOLID PASTE LEVEL LIQUID PASTE LEVEL LIQUID PASTE BAKED ELECTRODE 6/14/

14 Solid level control Segregation as the solid pushes into the liquid Electrode break Liquid level = 2.2 x Electrode diameter Maximum liquid paste temperature = 80 C Prevent boiling and fuming, with subsequent segregation

15 Liquid level control High liquid level Segregation Course anthracite particles settles to the bottom Electrode break Low liquid level Not sufficient hydrostatic head to force gases down Not sufficient depth to carry un-molten paste cylinders Electrode Break

16 Baking Mechanism Baking when the paste devolatilise Between 450 C 500 C The carbon residue then binds the anthracite Volatiles forced down electrode Due to higher temperatures volatiles are cracked to carbon and hydrogen This carbon strengthens the bond between anthracite particles

17 Baking Mechanism The baking region is critical and must be managed A constant baking rate must be maintained to prevent shifts of baking zones Stoppages can cause paste shrinkage Weak points in the electrode

18 Temperature Zones 25 C -Solid paste 70 C Completely softened 300 C Solidification sets in 700 C Solidified

19 The 450 C Isotherm PLC SCADA THERMOCOUPLE LIQUID PASTE ±450 C h h BAKED ELECTRODE 6/14/

20 Electrode Baking W = I 2 R (Maximum Current) Baking Temperature Temperature from Fins Temperature from Contact Clamps = + + Temperature from Environment 6/14/

21 Electrode Baking Zones CASING PASTE CHARGE FINS 80 ºC SOFT PASTE POWER SUPPLY 200 ºC CONTACT SHOE HIGH ELECTRODE CURRENT NOLMAL CONDITIONS HIGH SLIPPING RATE 500 ºC 1200 ºC BAKING ZONE BAKED ELECTRODE 2000 ºC 2500 ºC FURNACE CHARGE

22 Temperature profile 6/14/

23 Baking zones under different operating conditions

24 Soft Break Casing failure Too high current in casing

25 Common Reasons for Electrode Breakages

26 Baked Electrode Properties High thermal and electrical conductivity Compressive and tensile strength Low Coefficient of Thermal Expansion Thermal Shock resistance Uniform anthracite distribution Low consumption 6/14/

27 In Action 6/14/

28 In Action 6/14/

29 Production of extruded graphite electrodes Process uses calcined petroleum coke as filler and coal tar pitch as binder May involve multiple re-impregnation and re-baking steps. 6/14/

30 Petroleum coke quality Sulphur Cause puffing during baking Ni & V Oxidation catalysts Accelerate pin-holing 6/14/

31 Graphite electrodes 6/14/

32 6/14/

33 Energy efficiency The greatest source of energy in the future will be using it more efficiently, Bill Colton, Exxon s vice-president 6/14/

Our Test Equipment for Carbon Materials in the Electrode Industry

Our Test Equipment for Carbon Materials in the Electrode Industry EQUIPMENT LIST AND LABORATORY ANALYSIS CARBON TEST EQUIPMENT COKE AND GRANULAR CARBON 01-141 C02 REACTIVITY COKE 5-142 AIR REACTIVITY COKE