carbon injection into electric arc furnace slags carbon injection into electric arc furnace slags...
TRANSCRIPT
Carbon Injection into Electric Arc Furnace Slags
McMaster University Materials Science and Engineering
Graduate Seminar 701Supervisor: Prof. Ken. Coley
Tai Xi Zhu
April 1, 2011
2
Agenda
Introduction
Literature reviews
Experimental method and results
Discussion of model and results
Future works
3
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
4
Introduction-Electric Arc Furnace (EAF)Introduction-Electric Arc Furnace (EAF)
5
Introduction-Electric Arc Furnace (EAF)Introduction-Electric Arc Furnace (EAF)
6
Introduction-Electric Arc Furnace (EAF)Introduction-Electric Arc Furnace (EAF)
7
Introduction- Slag Foaming
Carbon is injected to react with molten slags, it decreases iron oxides and optimize slag foamingProtect electrodeReduce noiseIncrease furnace lining service lifeImprove energy and thermal efficiency
Focused research in carbon/coal injected into EAF slags
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Literature Reviews Reaction of injected carbon with oxides in slags
C(injected, s) + O (slag) = CO (g).
Schematic representation of carbon-gas and slag-gas reaction (M. King Thesis 2009)
9
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
2 2 2
2 2 2
1
1
1 ( )( ) 1 exp( )
( ) 1
cco co co co cotot o
C p c cco co co co co
p p pn R n t
p p p
2 2
2
2 2
2 3 3 4( )
( ) ( (1 ))3 ( )
co co co cototgas p a o co o
co co co co
M M M pn R k a p a t
p
pCO2 is the equilibrium pressure of CO2 in bubble surrounding [atm] the carbonpc
CO2 is the pressure of CO2 at the carbon-gas interface[atm]. 𝑛°C is initial number of molesMi and ρi are molar mass and density of CO and CO2 respectivelyaO 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]
10
Literature Reviews
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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.
/ sg g
h h
Q A V
Δh - change of foam height Qg -gas flow rate - superficial gas velocity [m/s]s
gV
12
Literature Reviews
Development of foam index Σ
115
Jiang and Fruehan (1991)
Zhang and Fruehan (1995)
1.2
0.2 0.9115
avgd
52
5 10( )
eff
avg
E
gd
Ghag et al. (1998)
13
Literature Reviews
Development of foam index Σ
Lahiri-Seethanraman (2002)
Morales et al. (2002) – Dynamic foam index
150avgd
4 3.66 14 8.262
3 1.318
3.391 10 ( % ) 4.835 10 ( % )
2.603 10 ( % )
wt CaO wt SiO
wt FeO
14
Literature Reviews
Critical bubble wall thickness proposed by J. van der Schaaf and Beerkens’ (J. Colloid Interface Sci., 2006)
2
0.25( )20.11( )
avgH
cri
dA
t
AH – Hamaker Constant (J)
davg – average buble diameter
σ - surface tension (N/m)
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Experimental Method
Carbon injection into EAF slags experimental setup (Thesis, M. King, 2009)
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Experimental Method
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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]
0.0338
0.0338 0.0391 0.0566 0.0749 0.0352 0.0484 0.0576 0.0561
Maximum carbon gasification rate[mol s-1]
0.0270
0.0360 0.0325 0.0646 0.1127 0.0398 0.0357 0.0635 0.0701
Slag foam height [m]
0.0508
0.0767 0.134 0.177 0.190 0.158 0.171 0.165 0.191
Foam index [s]
0.329 0.379 0.762 0.504 0.309 0.729 0.889 0.476 0.329
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Experimental Results
Slag foam height vs. superficial gas velocity
0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.650
0.05
0.1
0.15
0.2
0.25
f(x) = 0.0653035790762368 x + 0.152370715336983
f(x) = NaN x + NaN
Superficial Gas Velocity [m/s]
Sla
g F
oam
Heig
ht
[m]
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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
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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
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Discussions
Slag foam height vs. Bubble diameter
0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20.00E+00
5.00E-04
1.00E-03
1.50E-03
2.00E-03
2.50E-03
Lahiri Model
Polynomial (Lahiri Model)
Zhang-Fruehan Model
Polynomial (Zhang-Fruehan Model)
Foam Height (m)
Bub
ble
diam
eter
(m)
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Discussions
Slag foam height vs. bubble wall thickness
0 0.05 0.1 0.15 0.2 0.250.00E+00
5.00E-05
1.00E-04
1.50E-04
2.00E-04
2.50E-04
3.00E-04
3.50E-04
Lahiri Model
Polynomial (Lahiri Model)
Foam height [m]
Bub
ble
thic
knes
s [m
]
23
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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.
25
Improvement of M. King’s works
t < ∑ (foam index)
2 2 2
2 2 2
1
1
1 ( )( ) 1 exp( )
( ) 1
cco co co co cotot o
C p c cco co co co co
p p pn R n t
p p p
t > ∑ (foam index) but < t_inj
2 2 2 2
2 2
1 1( ) ( )[exp( ) exp( ( )]
1 1( )
c cco co co co co co
co co co co
tot ocp cC g
p p p pt t
p p
dnR n
dt
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Improvement of M. King’s works
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Improvement of M. King’s works
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Future Works
Improve previous work done by M. King
Extend theory of critical carbon injection point to other slag volumes
AcknowledgeDr. K. S. Coley and Dr. G. A. IronsDr. S. RayOwen Kelly and Dr.Kumar
Krishnaposharody –experimentsDr. F.Z. Ji (ArcelorMittal) and M.
King- experimental and theoretical advice
Natural Sciences and Engineering Research Council of Canada (NSERC)
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Tai Xi ZhuCarbon Injection into Electric Arc Furnace Slags
McMaster University
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