Steel Recycling with Graphite Electrodes - An Industrial Success Story - 2 nd German Polish Symposium October 16 th 2013 TU Bergakademie Freiberg 1
Steel Making Processes Blast Furnace & Electric Arc Furnace Blast Furnace (BOF) Iron Oxide Electric Arc Furnace (EAF) Steel Scrap docstock.com steeluniversity.com Steel Steel
2014e 2015e 2013e 2012 2011 2010 Steel Making Processes World Steel Market 10 6 t 2000 1800 1600 1400 1200 1000 800 600 400 200 0 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 EAF steel output BOF steel output 27% - 31% of the total steel between 2008 & 2012
Steel Making Processes Use of Graphite Electrodes Graphite electrodes are used in so called mini mills. These are steel plants, where steel scrap is melted in a recycling process. The electrode enables an energy transfer to melt steel scrap via an electric arc. DC furnace at Peiner Traeger
5 Improvements in Electrode Production - Some Examples -
Steel Recycling with Graphite Electrodes Graphite Electrode Production Process raw material storage coke, graphite Pitch weighing mixing crushing / milling screening, sieving extrusion / vibromolding baking, impregnation, re-baking storages for classified fractions + - graphitization
Graphite Electrodes Major Developments Raw Material Improvement: Needle Coke https://www.osha.gov/dts/shib/shib082903c.html Needle coke for GE: Elongated shape orientation in green processing Low in ash content Low CTE along needle High thermal conductivity Low electrical resistivity along needle High graphitizability
Graphite Electrodes Major Developments Raw Material Improvement: Needle Coke needle coke + extrusion = axial grain orientation Full employment of graphite s anisotropic properties: Low resistivity & low CTE in strand direction High tensile strength in strand direction High bending strength in perpendicular direction
Graphite Electrodes Major Developments Graphitization Acheson graphitization indirect heating Increased productivity Decreased specific energy consumption Castner or length-wise graphitization (LWG) direct heating
Graphite Electrodes Major Developments Diameter Increase - Break-through for a new generation of high-power EAFs Productivity increase at constant tip loss rate 700 mm / 28'' 750 mm / 30'' 800 mm / 32'' Tip loss rate 100% 110% 120% productivity 120 130 140 150 160 170 180 Max. current in ka SGL Group 1 st to present 800 mm GE in 2000
11 Improvements in Furnace Technology - Some Examples -
Improvements in Furnace Technology Major Developments Slag foaming ~ 1920 2010 UHP (U > 1000 V, i >~ 25 A/cm²) Water spraying Oxygen lances Electrode diameter Taping weight
Improvements in Furnace Technology Ultimate Furnace (300 mt) AC-Furnace at Çolakoğlu/TR
Technology Improvements in Furnace Technology Electrode Consumption Mechanisms Continuous Discontinuous ka On C C C 30 A /cm² C C Off CO CO C O 2 O 2 CO CO O 2 O 2 O 2 O 2 approx. 10.000 C Tip sublimation Surface oxidation Stub end losses Breaks
15 Summary
Steel Recycling with Graphite Electrodes An Industrial Success Story 1810 Electric arc, Davy EAF steel production, mio t 400 Technology Innovations: 1866 Dynamo concept, Siemens 1891 Electric arc furnace, Moissan 1896 Acheson / Castner graphitization 392 10 1906 EAF steel, Remscheid O 2 lances Foamed slag 283 8 300 Electric arc furnace technology: Water spraying 6,5 DC- technology Lance manipulation 6 200 From carbon to graphite electrodes High volage > 1000V Graphite electrode production: GE 350 GE 500 GE 600 GE 700 GE 800 118 Chamber coking / pitch coke Acheson graphitization Delayed coking/petrol coke 11 Needle coke Super needle coke Castner graphitization 1,1 X needle coke 4 2 100 Graphite consumption*, kg /t 1850 1900 year 1950 2000 * w/o ladle furnaces
Steel Recycling with Graphite Electrodes An Industrial Success Story Thank you for your attention!
18 Backup
Steel Recycling with Graphite Electrodes Global Steel Use
Steel Recycling with Graphite Electrodes Crude Steel Production 1995 to 2025 EAF Steel CAGR = 2,0% 2019 [Mt] BOF Steel 1146 1656 478 CAGR = 3,8% 695 760 350 CAGR = 1,2% 236 1178 1324 524 796 1995 2005 2015 YEAR Steel Production will further demonstrate a sound Growth. EAF Steel will grow stronger than BOF. Areas of EAF Growth will be Asia, Near & Middle East, and Africa. 2025
Steel Recycling with Graphite Electrodes Effects of Graphitization Graphitization = crystal development (from amorphous to polycrystalline material) change of physical material properties: Property Increase Decrease Impact on Application in EAF Electrical Conductivity X very good Thermal Conductivity X very good Flexural Strength X worse, but... CTE X good Young s Modulus X good - indifferent Volume X no direct impact Weight X no direct impact Porosity X no direct impact Apparent Density X no direct impact additionally material gets softer and easier to machine
Steel Recycling with Graphite Electrodes AC vs. DC Furnace Technology AC - Furnace Some Pros DC - Furnace Lower capital cost Lower maintenance cost Higher operation reliability Less impact on the electrical grid Less oxidation
Steel Recycling with Graphite Electrodes Typical Figures for an AC Furnace with 600 mm Electrodes Shell diameter 6-8 m Secondary current 50-70 ka Secondary voltage 600-1500 V Column length 6-8 m (3 electrodes) Tapping weight 80-130 t Tapping temperature 1620-1680 C Tap to tap time 50-80 min Power on time 42-75 min Electric energy consumption 350-550 kwh/t Total energy consumption 600 700 kwh/t Oxygen consumption 15-45 Nm 3 /t Electrode consumption 1.2-2.8 kg/t