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

8

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

11

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)

15

Experimental Method

Carbon injection into EAF slags experimental setup (Thesis, M. King, 2009)

16

Experimental Method

17

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]

19

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

20

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

21

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)

22

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

26

Improvement of M. King’s works

27

Improvement of M. King’s works

28

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

Thank You