Improving of Refining Efficiency Using Electromagnetic
Force Driven Swirling Flow in Metallurgical Reactor
Baokuan Li (Speaker)
Fengsheng Qi
Northeastern University, China
z
Fumitaka Tsukihashi
y
x
o
The University of Tokyo, Japan
Research background
Vacuum
Pump
Inclusions are mainly removed by
attachment of argon gas bubbles in
molten steel.
Argon gas bubbles
Removal rate of inclusions depend
on the number, size, shape, selfmotion and distribution of gas
bubbles in melt.
θ
r
Air
A optimum behavior of argon gas
bubbles for refining efficiency is
very important.
z
Molten steel +inclusions
y
o
x
life of RH equipment is also affected
by attachment and action of gas
bubbles near wall.
Innovative Steelmaking Application of Swirling Flow
•
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
Pump
Argon gas bubbles
θ
r
Air
z
Molten steel + inclusions
y
o
x
Water model experiments examine the research ideas
Manometer
Impeller
Gas distributor
Rotameter
Nozzle distribution
RH degassing vessel
Ultrasonic flowmeter
(a)
(b)
(c)
(d)
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
9
8
7
6
Circulation flow rate, 10-5 m3/s
10
6.944×10-5m3/s
11.111×10-5m3/s
16.667×10-5m3/s
40
35
30
25
20
15
10
5
0
Input power, W
Effect of plane blade impeller on circulation flow rate of RH vessel
2w
Swirl number 
3u
u
Q downleg
A upleg
W  nD
(Yokoya et al )
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.
Averaged gas bubble diameter at outlet of nozzle, mm
Effect of swirl number on the gas bubble
diameter at outlet of nozzle
6
5
4
3
2
Nozzle diameter is 2 mm
Gas flow rate 0.25 l/h
1
0
0
0.1
0.2
0.3
0.4
Swirl number
0.5
0.6
0.7
Mathematical model
Vacuum
Pump
Argon gas bubbles
• A homogeneous model for the twophase turbulent flow in the RH
vessel with the rotating magnetic
field in the up-leg.
θ
r
• The momentum equation for gas
phase is ignored.
Air
• The previous model is only valid
for bottom blown reactors.
z
Molten steel + inclusions
y
o
x
Formulation

  ( V )  0





2
V ( V )  e  V  p  F  g
Spitzer et al. [1]
v
1
Fr   B02 (   ) 2  2 m r 3
8
r
v
1
F  B02 (   )r
2
r
Fx  Fr cos   F sin 
F y  Fr sin   F cos 
k   turbulence model
 = g  (1   ) Liq
(u  u in  u slip )


 





 (v  v in  v slip )
 ( w  wslip )

( e
)  ( e
)  ( e
)
x
y
z x
x
y
y
z
z
Penetrating velocity and slip velocity
Horizontal penetrating velocity:
uin  v in 
Up-leg
1 2
y
nA
Qg : total argon gas flow rate,
n :nozzle number
A : cross nozzle inlet area
Nozzle
z
Qg
Gas jet zone
α : gas volume fraction (at inlet α0)
x

Centripetal force and horizontal slip velocity
caused by rotating magnetic field
Fr  r ( L   g )
2
R 2 2 r
Vr  2( L   g )
9
u slip  Vr cos , v slip  Vr sin 
Vertical slip velocity
wslip  exp( a0 ) exp( a1 ln d g ) exp[ a2 (ln d g )2 ]
Boundary conditions and solution method
Blackage technique
Flow field
 1, for fluid
 1, for fluid
Volume factor f V  
, Area factor f A  
0, for solid
0, for solid

0
n
Near wall: The wall law function is used to calculate e , k , and 
Free surface and symmetrical sections:Vin  0,
Gas volume fraction
Inlet:  in is calculated by Thermodynamic equation of gas
Other sections:

0
n
Self-developed computer code in Fortran language
Vacuum
Pump
θ
r
Air
z
water
y
o
x
B0 = 0.1 mT
Frequency = 50 Hz
B0 = 0.1 mT
Frequency = 50 Hz
(d)
(c)
(b)
(a)
(a)
(b)
(c)
(d)
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.
B0 = 0.1 mT
Frequency = 50 Hz
0.7
0.7
0.6
0.6
0.6
0.5
0.5
0.5
0.4
0.4
0.4
0.3
0.3
0.3
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
0.1
0.2
0.3
(a)
0.4
0.5
0
0
0.1
0.2
0.3
0.4
0.5
(b)
Computed gas volume fraction at main sections of RH
degassing vessels, (a) no swirling flow (b) with swirling flow.
0.8
0.5
Vertical velocity, m/s
Gas volume fraction
0.7
0.4
0.3
0.2
0.1
No swirling flow
With swirling flow
-0.04
0
0.6
0.5
0.4
0.3
No swirling flow
With swirling flow
0.2
0.1
0.04
-0.04
Diameter of up-leg, m
Gas volume distribution
of RH degassing vessel
0
0.04
Diameter of up-leg, m
Velocity distribution of
RH degassing vessel
CONCLUSIONS
Water model experiments showed that the gas bubbles may
be 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 upleg. The upward velocity distribution in up-leg changes from
M type to parabolic type.
The future works
--- application of swirling flow
Vacuum
Pump
Argon gas bubbles
θ
Control of size, shape and
distribution of argon gas
bubbles
r
Change of collisions,
coalescence and attachment
of the inclusions
Air
z
Molten steel + inclusions
y
o
x