Improving of Refining Efficiency Using Electromagnetic Force Driven Swirling Flow in Metallurgical Reactor

Baokuan Li (Speaker)Fengsheng QiNortheastern University, China

Fumitaka TsukihashiThe University of Tokyo, Japan

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Inclusions are mainly removed by attachment of argon gas bubbles in molten steel.

Removal rate of inclusions depend on the number, size, shape, self- motion and distribution of gas bubbles in melt.

A optimum behavior of argon gas bubbles for refining efficiency is very important.

life of RH equipment is also affected by attachment and action of gas bubbles near wall.

Vacuum

Molten steel +inclusions

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Research background

Argon gas bubbles

Argon gas bubbles

• Swirling flow is produced by the application of rotating magnetic field, and effect of swirling flow included:

• Efficient mixing and

• Efficient separation of inclusions by improving probability of attachment, collisions and coalescence with dispersed gas bubbles in Refining processes.

Vacuum

Molten steel + inclusions

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Air

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Innovative Steelmaking -Application of Swirling Flow

Gas distributor

Nozzle distribution

Rotameter

Manometer

Ultrasonic flowmeterRH degassing vessel

Impeller

Water model experiments examine the research ideas

Effect of impeller input power on gas bubbles distribution, shutter speed is 1/125 second. Q=0.25 m3/h. (a) 0, (b) 20 W, (c) 25 W and (d) 35 W

(a) (c) (d)(b)

67

89

10

0 5 10

15

20

25

30

35

40

6.944×10-5m3/s

11.111×10-5m3/s

16.667×10-5m3/s

Cir

cula

tion

flo

w r

ate,

10-5

m3 /

s

Input power, W

Effect of plane blade impeller on circulation flow rate of RH vessel

3u

2w number Swirl

upleg

downleg

A

Qu

(Yokoya et al )

nDW

Nozzle diameter is 2 mm, gas flow rate is 0.25 m3/h, strobe light speed is 1/2000s. swirl number is 0, 0.23, 0.53, 0.68, respectively.

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Nozzle diameter is 2 mmGas flow rate 0.25 l/h

Swirl number

Ave

rage

d ga

s bu

bble

dia

met

er a

t out

let o

f no

zzle

, mm

Effect of swirl number on the gas bubble diameter at outlet of nozzle

Argon gas bubbles

Mathematical model

• A homogeneous model for the two-phase turbulent flow in the RH vessel with the rotating magnetic field in the up-leg.

• The momentum equation for gas phase is ignored.

• The previous model is only valid for bottom blown reactors.

Vacuum

Molten steel + inclusions

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( )

( )

V

V V V p F g

02

e

FormulationSpitzer et al. [1]

k turbulence model

= g ( )1 Liq

rr

vBF

rr

vBF mr

)(2

1

)(8

1

20

32220

cossin

sincos

FFF

FFF

ry

rx

)()()()()()(zzyyxxz

wwy

vvvx

uuu eeeslipslipinslipin

)(2gLr rF

Centripetal force and horizontal slip velocity caused by rotating magnetic field

Up-leg

Nozzle

zy

x

Gas jet zone1 2

9

)(222 rR

V gLr

sin,cos rsliprslip Vv Vu

Penetrating velocity and slip velocity

])(lnexp[)lnexp()exp( 2210 ggslip dadaaw

Vertical slip velocity

Horizontal penetrating velocity:

Qg : total argon gas flow rate, n :nozzle number A : cross nozzle inlet area

α : gas volume fraction (at inlet α0)

nA

Qvu g

inin

Boundary conditions and solution method

Flow field

Gas volume fraction

Blackage technique

Volume factor ffor fluid

for solidArea factor f

for fluid

for solid

Free surface and symmetrical sections:Vn

Near wall The wall law function is used to calculate k and

V A

in

e

1

0

1

0

0 0

,

,,

,

,

,

: , ,

Inlet is calculated by Thermodynamic equation of gas

Other sections

:

:

n

in

0

Self-developed computer code in Fortran language

Vacuum

water

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B0 = 0.1 mTFrequency = 50 Hz

Calculated flow velocities at horizontal sections of RH degassing vessels, (a) up-leg, (b) bottom of vacuum chamber, (c) middle of vacuum chamber, and (d) surface of vacuum chamber.

(a)

(d)(c)

(b)

(a)

(b)(c)(d)

B0 = 0.1 mTFrequency = 50 Hz

0

0.1

0.2

0.3

0.4

0.5

0.6

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.1 0.2 0.3 0.4 0.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

00.1 0.2 0.3 0.4 0.5

Computed gas volume fraction at main sections of RH degassing vessels, (a) no swirling flow (b) with swirling flow.

(a) (b)

B0 = 0.1 mTFrequency = 50 Hz

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

-0.04 0 0.04

Ver

tica

l vel

ocit

y, m

/s

Diameter of up-leg, m

No swirling flowWith swirling flow0.1

0.2

0.3

0.4

0.5

-0.04 0 0.04

Gas

vol

ume

frac

tion

Diameter of up-leg, m

No swirling flowWith swirling flow

Gas volume distribution of RH degassing vessel

Velocity distribution of RH degassing vessel

CONCLUSIONS

Water model experiments showed that the gas bubbles maybe moved toward the central zone in up-leg in RH vessel under the swirling flow. the size of gas bubbles produced from nozzle become small and number of gas bubbles increases. the gas bubbles are dispersed in the whole up-leg. Residence time and journey of gas bubbles in up-leg is prolonged. The numerical results showed that a swirling flow may be produced and extended into the vacuum chamber in case that rotating magnetic field is applied in up-leg. The maximum of gas volume fraction moves toward the center zone of the up-leg. The upward velocity distribution in up-leg changes from M type to parabolic type.

Control of size, shape and distribution of argon gas bubbles

Change of collisions, coalescence and attachment of the inclusions

Argon gas bubbles

Vacuum

Molten steel + inclusions

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Air

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The future works --- application of swirling flow