Carbon Injection into Electric Arc Furnace
Slags
McMaster University
Materials Science and Engineering
Graduate Seminar 701
Supervisor: Prof. Ken. Coley
Tai Xi Zhu
April 1, 2011
Agenda
 Introduction
 Literature reviews
 Experimental method and results
 Discussion of model and results
 Future works
2
Introduction- Electric Arc Furnace
(EAF)
 EAF produces engineered steel from recycled
scrap metal
 Primary processes include:
 Scrap charging
 Pre-heating with burner and melting with electrical
arc
 Second charge
 Carbon and oxygen injection
 Tapping
3
Introduction-Electric Arc Furnace (EAF)
4
Introduction-Electric Arc Furnace (EAF)
5
Introduction-Electric Arc Furnace (EAF)
6
Introduction- Slag Foaming
Carbon is injected to react with molten slags, it
decreases iron oxides and optimize slag
foaming
Protect electrode
Reduce noise
Increase furnace lining service life
Improve energy and thermal efficiency
 Focused research in carbon/coal injected into
EAF slags
7
Literature Reviews
 Reaction of injected carbon with oxides in slags
C(injected, s) + O (slag) = CO (g).
8
Schematic representation of carbon-gas and slag-gas reaction (M. King Thesis 2009)
Literature Reviews

M. King (2009) developed model for the reaction of carbon particles
injected into slag and it predicts total amount of carbon in the slag and
rate of gas(CO) generation during carbon injection into EAF slags
nCtot  Rp nc o (
tot
gas
n

1co ( pco2  pco2 c ) 
) 1  exp(
t) 


 pco2 ) 
1  co  pco2

1  co  pco2
1co ( pco2 c
 M co  (M co  M co ) pco 2 3
 Rp (
) ka (ao  pco (1  ao ))3 t 4
3 co  ( co  co ) pco
2
2
2
9
2
2
pCO2 is the equilibrium pressure of CO2 in bubble surrounding [atm] the carbon
pcCO2 is the pressure of CO2 at the carbon-gas interface[atm].
𝑛°C is initial number of moles
Mi and ρi are molar mass and density of CO and CO2 respectively
aO is equilibrium CO/CO2 partial pressure in slag
𝑅𝑝 is carbon particle injection rate [particles s-1]
𝑘𝑎 is rate constant for reaction at slag-gas interface [mol m-2 atm-1 s-1]
t is carbon residence time in slag[s]
Literature Reviews
10
Literature Reviews
 Foam index Σ – “how long can bubble survive”
It is intermediate parameter that helps us to understand foaming processing
in EAF furnace, it was firstly defined by Ito and Fruehan(1989), in the unit of
time(sec), and represented ideal average foam/bubble traveling time through
foam layers.
h
h


Qg / A Vgs
Δh - change of foam height
Qg -gas flow rate
Vgs- superficial gas velocity [m/s]
11
Literature Reviews
 Development of foam index Σ

  115

Jiang and Fruehan (1991)
 1.2
  115 0.2 0.9
  d avg
Zhang and Fruehan (1995)
 Eeff
  5 10
(  gd avg ) 2
5
12
Ghag et al. (1998)
Literature Reviews
 Development of foam index Σ
  150

Lahiri-Seethanraman (2002)
 d avg
  3.391104 ( wt %CaO) 3.66  4.835 1014 ( wt %SiO2 ) 8.26
2.603 103 ( wt % FeO) 1.318
Morales et al. (2002) – Dynamic foam index
13
Literature Reviews
 Critical bubble wall thickness proposed by J. van
der Schaaf and Beerkens’ (J. Colloid Interface Sci.,
2006)
tcri  0.11(
AH (
davg
2

)2
)0.25
AH – Hamaker Constant (J)
davg – average buble diameter
σ - surface tension (N/m)
14
Experimental Method
15
Carbon injection into EAF slags experimental setup (Thesis, M. King, 2009)
Experimental Method
16
Experimental Results
Exp.
16
Exp. 24
Exp. 32
Exp. 33
Exp. 34
Exp. 35
Exp. 36
Exp.37
Exp. 38
Carbon
injection
rate
[mol s-1]
0.033
8
0.0338
0.0391
0.0566
0.0749
0.0352
0.0484
0.0576
0.0561
Maximum
carbon
gasification
rate
[mol s-1]
0.027
0
0.0360
0.0325
0.0646
0.1127
0.0398
0.0357
0.0635
0.0701
Slag foam 0.050
height [m]
8
0.0767
0.134
0.177
0.190
0.158
0.171
0.165
0.191
0.379
0.762
0.504
0.309
0.729
0.889
0.476
0.329
Foam index
[s]
17
0.329
Experimental Results
0.25
y = 0.0653x + 0.1524
Slag Foam Height [m]
0.2
0.15
y = 1.2377x - 0.115
0.1
0.05
0
0
0.1
0.2
0.3
0.4
0.5
Superficial Gas Velocity [m/s]
18
Slag foam height vs. superficial gas velocity
0.6
0.7
Discussions
 Experimental results demonstrate that after a critical
point, foam height continued to increase as a function
of superficial gas velocity but at a much reduced rate.
.
This critical point is strongly dependent upon slags
volume
19
Discussions
 Assumption:
each gas bubble is spherical
Critical point happens when all molten slag is consumed
Particulate carbon is injected into slag at constant rate
Critical bubble wall thickness is average bubble wall
thickness at steady state
20
Discussions
2.50E-03
Bubble diameter(m)
2.00E-03
1.50E-03
1.00E-03
Lahiri Model
Zhang-Fruehan Model
5.00E-04
0.00E+00
0
21
0.05
0.1
Foam Height (m)
0.15
Slag foam height vs. Bubble diameter
0.2
0.25
Discussions
7.00E-04
Lahiri Model
Zhang-Fruehan's model
Bubble thickness [m]
6.00E-04
5.00E-04
4.00E-04
3.00E-04
2.00E-04
1.00E-04
0.00E+00
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Foam height [m]
22
Slag foam height vs. bubble wall thickness
0.16
0.18
0.2
23
Conclusion
 Increase in slag foaming with carbon injection
rate is limited by slag volume
 This phenomenon is likely caused by either an
increase in the energy required to grow
bubbles beyond a certain size or by the
increased tendency to rupture of bigger
bubble.
24
Improvement of M. King’s works
t < ∑ (foam index)
nCtot  Rp nc o (

1co ( pco2  pco2 c ) 
) 1  exp(
t) 


 pco2 ) 
1  co  pco2

1  co  pco2
1co ( pco2 c
t > ∑ (foam index) but < t_inj
(
25
dnc tot
)C  g  Rp nc o [exp(
dt
1co ( pco2 c  pco2 )
1  co  pco2
t )  exp(
1co ( pco2 c  pco2 )
1  co  pco2
(t  )]
Improvement of M. King’s works
26
Improvement of M. King’s works
27
Future Works
 Improve previous work done by
M. King
 Extend theory of critical carbon
injection point to other slag
volumes
28
Acknowledge
 Dr. K. S. Coley and Dr. G. A. Irons
 Dr. S. Ray
 Owen Kelly and Dr.Kumar Krishnaposharody –
experiments
 Dr. F.Z. Ji (ArcelorMittal) and M. Kingexperimental and theoretical advice
 Natural Sciences and Engineering Research
Council of Canada (NSERC)
Thank You
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Tai Xi Zhu
Carbon Injection into Electric Arc Furnace Slags
McMaster University