EAF Slag
19 July 2012Prepared by: YD TRIPATHI
Slag – What is it?
Metallurgy relies on “slag” to:
• remove unwanted elements from the metal
• purify the metal by forming oxides and floating them off the molten metal
„
Slag usually consists of metal oxides and acts as
• a destination for impurities
• a thermal blanket (stopping excessive heat loss)
• an erosion reducer for the refractory lining of the furnace
• an erosion reducer for electrodes
„
19 July 2012Prepared by: YD TRIPATHI
Effective steel production goes hand-in-
hand with effective slag control
• Production capacity (number of heats)
• Refractory wear
• Energy consumption
• Additive consumption
• Quality of metal (grade)
• electrode consumption
19 July 2012Prepared by: YD TRIPATHI
The EAF furnace
19 July 2012Prepared by: YD TRIPATHI
High-tech refractory
19 July 2012Prepared by: YD TRIPATHI
EAF Slag
19 July 2012Prepared by: YD TRIPATHI
EAF Slag – Main Requirements
Compatibility with the refractories
MgO saturated since most slag lines consist of magnesia-carbon refractories
� Good “foaming” properties and correct viscosity
Foam at the right time and long enough to enable to achieve
optimal refining capabilities
„ Lower energy consumption
„ Lower metal loss
„ Metal cleaning/refining
19 July 2012Prepared by: YD TRIPATHI
Additives for Slag making
High Calcium Lime (Ca source)
„ Dolomitic Lime (Ca, Mg source)
„ Pre-blended Lime Mixes (Met Grade) Ca Mg mix
„ MgO – Carbon Briquettes, Balls (Mg and C source)
„Spent magnesia bricks
19 July 2012Prepared by: YD TRIPATHI
General EAF slag composition
% MgO 8
% CaO 43
% FeO 26
% MnO 6
% Al2O3 4
% SiO2 13
19 July 2012Prepared by: YD TRIPATHI
Some examples of Slag analysis
19 July 2012Prepared by: YD TRIPATHI
Slag formation in the EAF – meltdown
Slag formers are either charged with the scrap or blown
into the furnace.
„ The Si and Al in the scrap are oxidized first to form SiO2
and Al2O3 (fluxing oxides).
„ As oxygen is blown into the furnace, the principal flux
(FeO) is generated.
„ The "slag balance" now starts to shift and the slag
becomes more liquid.
19 July 2012Prepared by: YD TRIPATHI
Slag formation in the EAF – foaming
„ Carbon (in the form of coke or coal) is lanced into the slag
layer, partially combusting to form carbon monoxide gas
„ This causes the slag to foamachieving greater thermal efficiency
better arc stability
better electrical efficiency
„ The slag blanket also covers the arcs, preventing damage to
the furnace roof and sidewalls from radiant heat.
19 July 2012Prepared by: YD TRIPATHI
Slag formation in the EAF
19 July 2012Prepared by: YD TRIPATHI
The dynamics of the FeO balanceFeO is generated by oxygen injection:
Fe + ½ O2 (g) = FeO
FeO is reduced by carbon injection:
FeO + C = Fe + CO (g)
The rate of FeO generation must be
balanced by carbon injection
„ To achieve a stable foam, the reaction of C with FeO is more effective than the reaction of C with O
„ A good foamy slag reduces radiant heat loss from the bath and improves the efficiency of electrical power input to the bath
„ Slag foaming also allows for higher rates of electrical energy input to the bath without risking damage to the furnace roof, shell and side walls
19 July 2012Prepared by: YD TRIPATHI
Slag Forming reactionsLiquid Phase Chemical reactions Enthalpy Energy
Si + O2 SiO2 - 8.94 kWh/kgSi -11.20 kWh/m3 O2
Mn + 0.5 O2 MnO - 1.93 kWh/kgMn - 9.48 kWh/m3 O2
2Cr + 1.5 O2 Cr2O3 - 3.05 kWh/kgCr -9.42 kWh/m3 O2
2Fe + 1.5 O2 Fe2O3 -2.05 kWh/kgFe -6.80 kWh/m3 O2
Fe + 0.5 O2 FeO - 1.32 kWh/kgFe - 6.58 kWh/m3 O2
C + 0.5 O2 CO -2.55 kWh/kgC - 2.73 kWh/m3 O2
2Al +1.5 O2 Al2O3 - 5.29 kWh/kgAl -13.84 kWh/m3 O2
Mo + O2 MoO - 1.70 kWh/kgMo - 7.25 kWh/m3 O2
S + O2 SO2 - 2.75 kWh/kgS - 3.94 kWh/m3 O2
2P + 2.5 O2 P2O5 - 5.54 kWh/kgP - 5.54 kWh/m3 O2
Gaseous Phase Chemical reactions Enthalpy Energy
C + O2 CO2 - 9.10 kWh/kgC - 4.88 kWh/m3 O2
CO + 0.5 O2 CO2 - 7.01 kWh/m3 O2
H2 + 0.5 O2 H2O -5.99 kWh/m3 O2
19 July 2012Prepared by: YD TRIPATHI
Slag variables and impact on viscosity
FeO content (fluxing component)
• Increasing the FeO decreases slag viscosity
„ MgO content (refractory component)
• Increasing the MgO increases slag viscosity
„ Temperature
• Increasing temperature decreases viscosity
„ Slag basicity
• Slag basicity controls the timing and the extent of foaming
19 July 2012Prepared by: YD TRIPATHI
The “right” slagOptimum slag viscosity
• The most important factor affecting slag viscosity is the presence of suspended second phase particles (MW & C2S) in the slag
„ FeO content of the slag
• Sufficient FeO in the slag is required to react with carbon and
generate CO gas bubbles
• Too much FeO is equated with iron loss
„ MgO content of the slag
• Sufficient MgO “in solution” is required to minimize refractory wear
and prolong foaming
Modeling by means of thermodynamic data based on the major oxides
enables fast tuning of the slag and optimizing the slag just in time.
19 July 2012Prepared by: YD TRIPATHI
% MgO vs basicity for dual saturation
19 July 2012Prepared by: YD TRIPATHI
Slag Formation in the EAF
19 July 2012Prepared by: YD TRIPATHI
Modeling of the slagFour variables:
• MgO content
• FeO content
• Temperature
• Basicity
By fixing basicity and temperature, the phase relations as a function of
MgO and FeO content can be determined and modeled.
The MgO content can be optimized for a particular basicity to sustain
foaming and minimizing refractory wear…
…to hit the so-called "sweet spot"
19 July 2012Prepared by: YD TRIPATHI
Analytical requirements to
hit the sweet spot…
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Flux calculation- Example
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Why to optimize slag former usage?
19 July 2012Prepared by: YD TRIPATHI
Thanks
19 July 2012Prepared by: YD TRIPATHI
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