plasma project fourth draft - mike script
TRANSCRIPT
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Electric Arc Furnaces in Steelmaking
Michael GaribaldiRose-Lyne McCall
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Many applications of steel
Piping
Construction
Automobiles
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Steelmaking Processes
Steel
Siemens
Process
Bessemer
Process
Basic Oxygen Furnace
Electric Arc
Furnace
Crucible
Process
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Main ways to produce steel
Basic Oxygen Furnace Electric Arc Furnace
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Electric Arc Furnace Products
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Key parameters for steelmaking
Composition
TemperatureTime
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EAF Mechanical Systems
• An EAF has three primary functions:1. Containment of steel scrap2. Heating and melting of steel scrap3. Transfer of molten steel to the next
processing stage
• Achieved through 3 different systems
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Mechanical systems of an EAF
Hydraulic System Cooling water system• Provides
power for EAF movements: electrode movement
• Ensures good movements of EAF components
Lubrication system
• Provides cooling of various EAF elements: shell cooling
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Off-Gas Direct Evacuation System
• Proper ventilation in the furnace is important for:
- Pollution control- Limitations of excessive emissions- Limitations of dust build-up
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Electrical Systems of an EAF
• Large amount of current supplied to sustain an electrical arc
• EAF is typically composed of two electrical systems:1. Primary system: supplies power from
electrical utility2. Secondary system: steps down voltage from
primary and supplies power to EAF
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Electrical Systems of an EAF
Primary System Secondary System• Vacuum switch• Motorized Disconnect
Switch• EAF Transformer• Tap Changer
• Delta Closure• Furnace Power Cables• Bus Bar / Current
Conducting Arm• Electrode Heads /
Contact Pads• Electrode Regulation
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Focus on Electrode Components
• Electrode heads / Contact Pads:o Copper plates usuallyo Final connection between power supply and
graphite electrodeo Must withstand extreme mechanical and
thermal conditions
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Major Components of an EAF
Arc
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The Furnace ShellHearth Roof
• Contains metal and slag
• Back lining – magnesite bricks
• Working lining – dolomite or magnesite mass
• Exposed to the most radiant heat
• Roof lining: alumina, magnesite bricks
• Water cooled
Sidewalls• Withstand
thermal shock and corrosive nature of slag
• Hot spots on walls due to arc radiation
• Same lining as roof
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The Carbon Electrodes• Deliver power to furnace
and form electrical arc• Graphite electrodes used
in modern steelmakingo High thermal capacity
• Position: at apexes of equilateral triangle
• Electrode spacing is crucial
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The Arc• Arc discharge between electrodes and
furnace charge• Arc is plasma of hot ionized gases (thermal
plasma)• Temperature about 6000°F• AC current (converted from DC)
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EAF: Process Overview
• Furnace Charging
• Melting• Refining• De-
slagging• Tapping• Furnace
turn-around
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Furnace Charging1. Selection of steel grade2. Preparation of the charge bucket to ensure good
melting conditions3. Scrap must be layered according to size and
density to facilitate melting and to protect roof and sidewalls from electrical discharge
4. Preventative measures to prevent caving-in of material – this could break electrodes
5. Addition of lime and carbon
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Melting• Both electrical and chemical energy
supplied to EAF• Charge begins at intermediate voltage• Electrodes bore into the scrap• High voltage, long arc formed
o Long arc unstable initially: current swings, rapid vibration of electrodes
o As more steel melts, arc stabilizes and power input is increased further
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Refining• Removal of impurities and undesired
components that effect quality, i.e. P, S, Al, Si...
• Oxygen blown into bath simultaneously with melting, allowing for refining and melting to be performed in a side-by-side operation
• All undesired products leave in slag
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De-slagging
• Furnace is tilted and slag door is opened• Slag is poured off top of bath• Slag door is located higher than bath level
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Tapping• Once desired steel temperature and composition
are achieved, tap-hole is opened and furnace is tilted
• Steel pours into ladle for transfer
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Furnace Heat Balance• 300 kWh/ton minimum required for
melting of steel scrap• Melting point at 2768°F• Total theoretical energy requirement: 350
– 370 kWh/ton• Energy distribution depends mostly on
material being melted
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Electric Arc Furnaces• High electricity
demand• Uses only recycled
metal
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Basic Oxygen Furnaces
• Uses recycled steel as well as new molten iron
• Depends on the blast furnace operation step before it
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Electrolysis for steelmaking
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Pros & ConsMethod Advantages Disadvantages
Electric Arc Furnace
Uses 100% recycled metal Large capital cost
Flexibility of the process Large amounts of sludge produced
Can use various raw materials Dust and GHG emissionsLocation near steel product markets Requires lots of electricity
Basic Oxygen Furnace
Self-sufficient Dependence on blast furnace material
High production rates Emission of contaminants and GHG
Electrolysis
No GHG emissions Still at the testing phase
Purer steel producedWould not be able to produce large quantities of steel
Requires less energy
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Environmental Concerns
• High sound levels• Dust collection• Slag production• Cooling water demand• Heavy truck traffic for scrap and materials• Effects of electricity generation
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Future of EAF• Sustainability • Possible replacement by newer
technologies• Future of steel, stainless steel and alloys
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Future of EAF• Not a “green” technology – carbon footprint is
very large due to off-gas
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Future of EAF• Stainless steel allows for stronger construction
than almost any other material available• Alternative materials such as carbon nanotubes in
development
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References• Jones, Jeremy, A.T.. "Electric Arc Furnace
Steelmaking." Mannesmann Demag Corp. Web. 22 Nov. 2013.
• "Parts of the Electric Arc Furnace." Electric Arc Furnace. N.p., n.d. Web. 23 Nov. 2013. http://www.postech.ac.kr/mse/cml/Eng/eaf.htm.