Plunging Jets in Steel Tapping

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2012 ISIJ 814

ISIJ International, Vol. 52 (2012), No. 5, pp. 814822

Numerical Study of Multiphase Flow Dynamics of Plunging Jets of

Liquid Steel and Trajectories of Ferroalloys Additions in a Ladle

during Tapping Operations

Jafeth RODRGUEZ-AVILA,1)Rodolfo D. MORALES2)and Alfonso NJERA-BASTIDA3)

1) Graduate Student, Instituto Politcnico Nacional-ESIQIE, Department of Metallurgy and Materials Engineering, Ed. 7,

UPALM, Col. Lindavista, D.F. CP 07738 Mexico. E-mail: [email protected]

2) Instituto Politcnico Nacional-ESIQIE, Department of Metallurgy and Materials Engineering, Ed. 7, UPALM, Col. Lindavista,

D.F. CP 07738 and K&E Technologies President, Manizales 88, Col. Residencial Zacatenco, D.F. CP 07369 Mexico. E-mail:

[email protected], [email protected]

3) Formerly Graduate Student. Now at Instituto Politcnico Nacional-ESIQIE, Department of Metallurgy and Materials

Engineering, Ed. 7, UPALM, Col. Lindavista, D.F. CP 07738 Mexico.

(Received on September 27, 2011; accepted on November 24, 2011)

A multiphase numerical analysis focused on flow dynamics and particle trajectories during steel tapping

operations was developed. The numerical results indicate that lighter additions than steel (ferrosilicon and

aluminum) are independent from bath level, fall height and flow dynamics of the melt. Neutral buoyant

additions (FeMn) are strongly dependent on fluid dynamics of the melt and bath height. Denser additions

(like FeNb) yields long residence time inside the melt before first emerging to the bath surface. However,

when this ferroalloy is added at high bath levels, close to the end of tapping, the particles remain in the

corner formed by the bottom and the wall of the ladle during long times prolonging their melting rates.

KEY WORDS: tapping steel; air bubbles; additions; ferroalloys.

1. Introduction

Tapping is probably the most important operation leading

to clean steel production since it is during this time that

deoxidizers and alloying elements, in form of ferroalloys or

metallic, are added and slag carryover must be avoided to

simplify later ladle furnace operations. Naturally, initial

oxygen content in steel governs the efficiency of those addi-

tions but certainly air entrainment by the plunging jet and

the bath surface turbulence contribute to form a multiphase

flow made of liquid steel, air and solid particles of deoxi-

dizer. Under these circumstances excessive air entrainmentworks as a cushion dampening the steel motion and hinder-

ing the mixing and the melting-dissolution processes of fer-

roalloys. Ferroalloy additions to molten steel initially freeze

a shell of steel around the particles and this shell melts back

after the ferroalloy or metal13)(like Al and Ni) addition has

melted within this shell. Hereof, the residence time of fer-

roalloys particles inside the melt during steel tapping is

important to have high alloying and deoxidizing efficien-

cies. Assuming thermodynamic equilibrium, complete mix-

ing conditions and efficient ferroalloys dissolution, the

group of the authors demonstrated that the amounts and

types of inclusion chemistries depend on the additionsequence during steel tapping, steel level in the ladle and

oxygen concentration in the melt.4,5)Therefore, those find-

ings underline the importance of an efficient mixing process

assisted by the momentum transfer effects of the jet plung-

ing into the melt. Final oxygen levels, assuming thermody-

namic equilibrium during steel tapping, depend then on

efficient mixing and melting-dissolution processes of fer-

roalloys and aluminum. Due to these reasons it is important

to know the trajectories and residence times of particles of

ferroalloys in molten steel. The problem this paper is deal-

ing with had been already analyzed by Guthrie et al.6)who

employed a balance of forces on a particle and evaluated the

importance of drag, buoyancy, added mass and history forces

acting on a particle submerged into a liquid. Their physical

and mathematical models included experiments of wooden

particles with different densities into a tank of still water.After the mathematical analysis of their experiments these

authors concluded that the history term in the balance of

forces has negligible influence on the particle dynamics

emphasizing the importance of drag, buoyancy and mass

added forces. Maximum depth penetration of particles, for

a given initial entry velocity, depend on the density ratio

between the particle of ferroalloy and steel, higher ratios

mean deeper penetrations. Tanaka et al.7) performed also

physical and mathematical modeling for ferroalloys addi-

tions in a 250 ton steel ladle. They established, through

dimensional analysis, modeling criteria for addition sizes

and entry velocities between a model and the actual ladlelinked by the square root of the scale factor of the model.

These authors simulated the effects of steel motion on

spherical particle trajectories assuming a one-way coupling

mechanism between liquid and particles (liquid steel flow


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influences particle dynamics). According with these authors

buoyant additions, such as aluminum and FeSi, are hardly

affected by the flow pattern of steel since buoyancy force is

so large that the dynamic behavior of these particles does

not change even when compared with conditions of particles

in a stagnant liquid. The reverse is true for denser particles

whose trajectories are strongly influenced by fluid flow

dynamics. The penetration of either, dense or light additionsis improved when they are injected close or in the plunging

steel jet. Maximum penetration depths and total immersion

times were substantially smaller when particles with differ-

ent geometries like cubes and cylinders are added to the

bath. However, as Guthrie et al.1,2) have shown, and cited

above, when a ferroalloy enters a bath of liquid steel, a solid

steel shell very rapidly forms around it. This shell formation

would tend to mask sharp irregularities in particles shape

maintaining valid the approximation of a spherical shape. In

another work, Mazumdar and Guthrie8)applied their model

to the CAS (Composition Adjustment by sealed Argon

Bubbling Systems) process and found that the shape andsize of particles have negligible effect on the overall nature

of particle trajectories except for those with densities close

to that of liquid steel. Efforts in the direction to model phys-

ically plunging water jets dragging air have been reported

by Hammad9)using PIV measurements and Iguchi et al.10)

who employed LDV measurements. The first authors found

two-phase flow dynamics very sensitive to ambient pertur-

bations, such as free surface instability and external vibra-

tions. On the other hand, LDV measurements were not pos-

sible in the developing region of the two-phase flow.

Therefore, water models to explain plunging steel jets are

limited and can be used only for qualitative estimations of

these complex flows. In the present work mathematical

modeling approach is adopted since, possibly, it can provide

closer results to those observed in the steelmaking practice.

Hereby, in order to complement the knowledge so far

developed in this field and to apply it to the actual steelmak-

ing conditions various aspects, not considered in precedent

works, must be addressed. These aspects are the air dynam-

ics during steel tapping, air entrainment by the plunging jet,

air bubbles dynamics generated and associated with the

entry jet and effects of steel level in the ladle at different

stages of the steel tapping operation. The final aim of the

present work is then to build a frame where the factors influ-

encing ferroalloys efficiency may be identified consideringconditions closer to those found in current steelmaking pro-

cesses.

2. Mathematical Model

2.1. Multiphase Model

The computational approach of this model involves the

solution of Navier-Stokes Equations for a multiphase flow

through an explicit method using the Volume of Fluid

(VOF) model11,12)in order to define sharp interfaces, among

air and liquid steel. As the problem is of a multiphase nature

some important simplifications, as a first attempt to dealwith these complex flows, are made. These assumptions are

as follows:

There are not heat losses, therefore, buoyant-thermal

forces are neglected and gravity-inertial forces are the

main mechanisms for steel mixing during tapping.

Plunging steel jet forms a perfect cylinder from the

Eccentric Bottom Tapping (EBT) nozzle of the furnace

to the bath surface or plunging point.

The plunging jet is centered in the ladle geometric cen-

tre.

The multiphase flow is one-way coupled, meaning that

steel flow influences particle dynamics, but particlesmotions do not affect liquid steel flow.

There is not slag phase in the system, which implicitly

means that slag carryover does not exist attaining then

an ideal perfect tapping operation.

Steel throughput at tapping is constant.

The three-dimensional (3-D), multiphase and unsteady

turbulent fluid flow model of steel tapping operations was

simulated through the solution of a set of continuity equa-

tions, one for each phase, and a set of momentum transfer

equations for all phases and the standard k- two-equationturbulence model as is explained below.

2.1.1. Continuity Equation

The tracking of the interface(s) between each pair of

phases is accomplished by the solution of the continuity

equation for the volume fraction of one (or more) of the

phases. For the qth phase, this equation has the following

form:

(1)

where is the mass transfer rate from phase q to phase

p and is the mass transfer from phase p to phase q.

Since there is not a source term on the right-hand side of Eq.

(1), , is zero. Moreover assuming that air is essentially

insoluble in liquid steel there is not mass transfer between

both phases and . Therefore, the full right

hand side of Eq. (1) is zero. Assuming that pis the primary

phase (liquid steel) and qis the secondary phase (air) Eq. (1)

is solved for air and the volume fraction of liquid steel will

be computed from the following constraint:

................................ (2)

Density and viscosity of the mixture are calculated

through the weighted volume fraction of each phase accord-

ing to the following Equations:

............................. (3)

............................. (4)

2.1.2. Momentum Equation

A single momentum equation is solved throughout the

domain, and the resulting velocity field is shared among the

phases. The momentum equation expressed through time

averaged flow variables, shown below, is dependent on the

volume fractions of all phases through the averaged proper-

ties of density and viscosity.

... (5)

where p is pressure (Pa), eff is the turbulence-adjusted

11

q

q q q q q pq qpp

n

tv S m m

q

( )+

= + ( )=( )

mpqm

qp

Sq

m mpq qp= =0

qqn

==

11

==

q qqn

1

==

qqn

q1

+

=

+

+

( ) ( )

u

t

u u

x

p

x x

u

xgi

i j

j i j

effi

j


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2.3. Computing Approach

A finite volume computational technique embedded in

the FLUENTpackage was employed to solve all equations

of the multiphase model based on a turbulence model of

two-Equations known as k-model. The computational cellinvolves the full volume of the ladle plus the 3D space locat-

ed between the ladle top and the tip of the EBT nozzle. The

computational grid is structured in the lower and upper partof the ladle; where the EBT nozzle delivers liquid steel a

hybrid cell was constructed. Figure 2shows the computa-

tional grid with a total of 657 986 cells for the complete

computational domain. The discretization scheme of this

grid is the so called PRESTO for the pressure equation, First

Upwind for equations of momentum, turbulent kinetic ener-

gy and dissipation rate of turbulent kinetic energy and Geo-

reconstruct for the Volume Fraction equation in the VOF

model. For the Pressure-Velocity coupling the PISO algo-

rithm was employed together with skewness-neighbor cou-

pling and skewness correction of 1. Relaxation factors for

pressure, density, body forces, momentum, turbulent kineticenergy, dissipation rate of kinetic energy and turbulent vis-

cosity were 0.3, 1.0, 1.0 0.5, 0.8, 0.8 and 1.0, respectively.

The time step was constant an equal to 0.001 seconds using

sub-time steps governed by a constant Courant number of

0.25. The calculation method is explicit solving the pressure

and momentum equations, after the beginning of a new time

step, and later the continuity is solved. The explicit method

is preferable over implicit methods when density variations

among the involved phases are very large and Geo-recon-

struct discretization is suitable for small numerical diffusion

effects and when definition of sharp interfaces are required

which is just the case of the present problem. Besides, this

formulation does not require iterative solution of the trans-

port equation during each time step, as is needed for the

implicit scheme. When the Euler explicit scheme is used, a

time-dependent solution must be computed, which is just the

case of the present work.

2.3.1. Boundary Conditions

Boundary conditions applied in this work are; velocity in

the nozzle tip, no-slip conditions in ladle wall and ladle bot-

tom, atmospheric pressure on the bath surface and wall

functions to link melt velocities in the boundary layers with

bulk melt velocities outside. Convergence criterion was

established as that when the sum of residual for all flowequations was smaller than 105. Initial speed of ferroalloys

and metallic additions is that calculated by the free fall

velocity given by .

3. Results

3.1. Velocity Fields by Plunging Jet

Figures 3(a), 3(b), 3(c) and 3(d) show the velocity fields

during steel tapping for steel filling levels of 10, 30, 50 and

75 tons, respectively. The first figure shows essentially the

effects of the plunging steel jet on the surrounding air which

receives momentum to form long recirculating flows at eachside of the jet. Steel, in the ladle bottom, Fig. 3(a), observes

a horizontal flow without well defined recirculations. At 30

tons, Fig. 3(b), air forms four recirculating flows, two small-

er ones in contact with the melt and other two, long ones,

in the upper side of the ladle. Steel forms recirculating flows

at both sides of the jet. Besides, along the jet there is the for-

mation of a boundary layer of air with larger velocities at

the metal-gas interface. At 50 tons, Fig. 3(c), the flow pat-

tern described by the precedent figure remains, however, the

two recirculating air flows in contact with the melt are now

smaller. The steel flow forms two longer vertical recirculat-

ing flows just as it does when the steel level is 30 tons. At75 tons, Fig. 3(d), the flow patterns suffer radical changes;

the two recirculating flows of air remain. However, flow

pattern of steel now indicates vertical-downwards displace-

ments toward the ladle bottom without forming recirculating

flows; rather three smaller recirculation flows are formed

along the jet length and one in the ladle corners as is indi-

a) b)

Fig. 2. Computational grid a) External isometric view b) Internal

isometric view.

v gh= 2

a) b)

c) d)

Fig. 3. Velocity fields during steel tapping for steel levels a) 10

ton, b) 30 ton, c) 50 ton, and d) 75 ton.


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cated by numbers 14. These changes of flow patterns in the

two-phase system must have considerable influence on the

mixing of ferroalloys and metallic additions as will be seen

later.

3.2. Dynamics of Air Bubbles in Molten Steel

Air bubbles play an important role on nitrogen and hydro-

gen pickup even if steel is tapped with high ppm of oxygenfrom the furnace. Figure 4(a) shows the distribution of bub-

bles as seen from the ladle bottom where it is clear that the

air entrained by the plunging jet forms bubbles in the melt

following a radial pattern due to the momentum transfer

imparted by the melt. Owing to the same reasons, air bub-

bles emerge to the atmosphere in regions close to the ladle

wall and in middle positions between the plunging jet and

the ladle wall as is seen in Fig. 4(a). Figure 4(b) shows the

distribution of air bubbles in molten steel at 30 tons level,

various features are visible in this figure as follows:

Firstly, the distribution of bubbles is homogeneous in the

melt volume, secondly, the plunging jet entrains an appre-ciable amount of air into the molten steel, and thirdly, some

of the bubbles shapes acquire the typical spherical cap shape

of moderate Reynolds numbers. Figure 5(a) shows the air

bubbles distribution at a melt level of 50 tons. Again it is

evident that air distribution is homogeneous in the melt vol-

ume and that the plunging jet drags considerable amounts of

air into the melt. The plunging jet entrains large volumes of

air by dragging mechanisms in the boundary layer between

the jets surface and the surrounding air. The two-phase

plunging jet inside the melt is disintegrated by its impact

with the ladle bottom leading to mechanisms of bubbling

breakouts. Some bubbles shapes keep the typical spherical-

cap geometry and the bath surface yields a complex topog-

raphy due to the distortion effects of air bubbles emerging

from the bath. Indeed, the emerging air bubbles from thebulk molten steel have an even distribution in the melt vol-

ume which is slightly different to that observed at lower

melt levels. Figure 5(b) shows air bubbles distributions in

the melt volume at a level of 70 tons. Different to the any

of the precedent cases now the gas phase is concentrated

around the plunging jet. Large bubbles are developed due to

the entrainment of air by the plunging jet, but few bubbles

are developed close to the ladle walls. Besides, again some

shapes of air bubbles keep the spherical-cap geometric typ-

ical of moderate Reynolds numbers. Since there are not

sources of direct measurements of steel velocities during

actual tapping operations it was decided to build a 1/3 scalemodel of the industrial ladle following Froude scale criteri-

on with purposes to perform qualitative comparisons with

results of mathematical simulations. Figures 6(a) and 6(b)

show the air bubbles distributions at water levels equiva-

lents to 10 and 75 tons of steel in the ladle. Both figures

should be compared with Figs. 4(a) and 5(b), respectively.

As is seen, distribution pattern of air bubbles in water and

steel are, qualitatively speaking, very similar. Thereby, these

experimental visualizations provide the ground to assume

here that the mathematical model has the capability to pre-

dict reasonable reliable results of steel-air complex flows.

However, it is recognized that future water velocity mea-

surements must be performed to come out with more certain

knowledge.

a) b)

Fig. 4. Distribution of bubbles in the melt to different levels a) 10

ton (seen from the ladle bottom), b) 30 ton.

a) b)

Fig. 5. Distribution of bubbles in the melt to different levels a) 50

ton, b) 70 ton.

a)

b)

Fig. 6. Dispersion of air bubbles in the ladle model. a) Air bubbles

distributed along the radial direction at 10 tons. b) Air bub-

bles distributed along the plume at 75 tons.


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3.3. Dynamics of Ferroalloys

3.3.1. Effects of Particle Size

Residence time of a ferroalloy particle inside the melt is

critical in order to be efficiently melted and dissolved in the

bath. In principle denser and larger particles have more

chance to be available for alloying and deoxidation purposes

than light and small ones. Here therefore, the time which a

particle remains inside the melt since its introduction untilits first emergence in the bath surface, before it may be

introduced again in the bath by melt currents, is defined as

the minimum residence time (MRT). Figures 7(a) and 7(b)

show the effects of two particle sizes (1 and 5 cm) of a dense

ferroalloy such as ferromanganese when both are falling in

the midpoint between the entry jet and the ladle wall at a

bath level of 50 tons. It is clearly seen that independently

from the particle size generally this ferroalloy has long paths

(with large particles, 5 cm, having longer MRT than small

ones, (1 cm). On the other side, buoyant ferroalloys such as

ferrosilicon yield completely opposite behaviors with regard

to dense ferromanganese as can be seen in Figs. 7(c) and 7(d)for the same sizes of 1 and 5 cm falling in the bath under the

same conditions described above. As is seen in those figures

paths and residence times of both particles are very short and

emerge soon from the bath. These particles, especially those

of sizes like 1 cm will remain on the bath surface during the

complete tapping time with significant losses of efficiency.

3.3.2. Effects of Particle Density

Among all tapping variables particle density has the most

profound effects on ferroalloy availability in the melt bulk.

Figures 8(a)8(d) show the trajectories and residence times

of particles with a size of 5 cm falling in the midpoint

between the entry jet and the ladle wall at a bath level of

50 tons for ferromanganese, ferrosilicon, aluminum and fer-

roniobium, respectively. Ferromanganese yields long trajec-

tories having longer times for the melting process while the

buoyant additions of aluminum and ferrosilicon float outfrom the bath having less availability inside the melt. Spe-

cial mention deserves the behavior of ferroniobium which is

heavier than liquid steel. As is seen in Fig. 8(d) this ferroalloy

yields long MRT and at this bath level can be predicted that

the particle has the chance to be efficiently melted. At this

steel tonnage availability of ferroniobium to interact with the

melt is practically independent from the falling position of

these particles (diameter of 5 cm) as can be seen in Figs. 9(a)

a) b)

c) d)

Fig. 7. Addition of ferroalloys with different size a) FeMn diame-

ter of 1 cm MRT 5.6 s. b) FeMn diameter of 5 cm MRT

22.2 s. c) FeSi diameter of 1 cm MRT 0.5 s. d) FeSi

diameter of 5 cm MRT 0.8 s.

a) b)

c) d)

Fig. 8. Different types of ferroalloy with diameter of 5 cm andsteel level at 50 ton. a) FeMn MRT 22.2 s, b) FeSi MRT

0.8 s, c) Al MRT 1 s, d) FeNb MRT 15.4 s.

a) b) c)

Fig. 9. Falling position of ferroniobium particles with diameter of

5 cm at 50 ton, a) Close to the jet, MRT 14.1 s; b) At mid

point, MRT 18.2 s; c) Close to ladle wall, MRT 20.5 s.


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9(c) for locations close to the jet, in the midpoint between

the jet and the ladle wall and close to the ladle wall, respec-

tively. It is clear that in any of three cases ferroniobium

yields long trajectories having more chance for efficient

melting processes with falling positions close to the ladle

wall favoring longer MRT. However, at higher bath levels

such as, for instance, 70 tons a complete different result

emerges as can be seen in Fig. 10for a ferroniobium particleof 5 cm diameter falling close to the entry jet, in the mid-

point between the jet and the ladle wall and close to the wall,

respectively. Indeed, in the three cases the particles sunk to

the ladle bottom where steel motion is very weak and

remain there during long times. These particles subjected to

very weak convection currents, either natural or forced,

have to spend very long times to be completely melted giv-

ing place to inaccurate reports of niobium chemistry before

sending the ladle to the caster, or even at the caster turret,

which is a fact commonly lived in the steelmaking shop.

3.3.3. Effects of Falling PositionFerromanganese with a neutral density is a good example

to analyze the effects of the falling position. Figures 11(a)

11(c) show the trajectories for particles with a diameter of

5 cm at a bath level of 50 tons and falling positions includ-

ing close to the entry jet, the midpoint between the jet and

the ladle wall and close to the ladle wall, respectively. Free

fall close to the jet represents the best conditions to attain

high ferromanganese availability followed by the midpoint

position. Nevertheless, the position closest to the ladle wall

yields irregular trajectories mainly promoted by the ascend-

ing steel stream along the ladle wall as a result of the

momentum transfer imparted by the plunging jet. For buoy-

ant alloys is clear that the best falling position must be as

close as possible to the jet or in the jet itself where the driv-ing forces provided by the plunging jet will push them well

inside the melt.

3.3.4. Minimum Residence Times

As was previously defined the minimum residence times

(MRT) refers to those minimum times that a particle

remains in the metal bulk before it emerges to the bath sur-

face. It does not mean that a particle that emerges fast from

the bath will not render a complete melting process as it will

have the chance to reentry into the bath, but certainly the

MRT provides a qualitative measure of the ferroalloy avail-

ability. Figure 12 shows a bar plot for MRT statistics forthose particles with diameters of 5 cm corresponding to fer-

rosilicon, ferromanganese, aluminum and ferroniobium for

a ladle level of 30 tons at different falling positions. Each

bar represents the mean value of the MRT for 100 simula-

tions and the numbers in each bar correspond to the standard

deviations for each case. Buoyant additions, ferrosilicon and

aluminum, have longer times when the falling position is

close to the jet and very short times at any other position.

Standard deviations of these times for buoyant additions are

small which means that the falling events and their conse-

quences on the dynamic behavior of particles in the melt

have high repeatability (meaning independence from the

flow pattern). Ferromanganese has longer residence times

when the falling position is close to the jet but it is in this

location where the standard deviation is relatively large.

Such a behavior is in agreement with the changing flow pat-

terns of the turbulent regime near the jet which induces also

unsteady changes in local flow turbulence. That condition is

not certainly observed in locations apart from the neighbor-

hoods of the plunging jet where the standard deviations of

the MRT are smaller. Regarding ferroniobium it is important

to observe that the falling location close to the ladle wall

yields the largest MRT but the standard deviation is also theFig. 10. Ferroniobium particle of 5 cm diameter falling close to theentry jet, in the midpoint between the jet and the ladle

wall and close to the wall.

a) b) c)

Fig. 11. Trajectories for FeMn particles with a diameter of 5 cm

at a bath level of 50 tons and falling positions a) Close to

the jet MRT 9.4 s, b) At mid point MRT 14.5 s, c) Close to

ladle wall MRT 1.6 s.

Fig. 12. Bar plot for statistics of MRT for particles of 5 cm for a

ladle level of 30 ton. Numbers in each bar indicate the

standard deviation of MRT for one hundred simulations.


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largest. Figure 13shows the MRT corresponding to a bath

level of 50 tons where is seen that buoyant additions yield

longer time magnitudes when the falling position is close to

the jet. In the case of ferromanganese this tonnage allows

long MRT when the falling position is the midpoint between

the jet and the ladle wall. Comparing these results with those

in Fig. 10 and the next Fig. 14for a steel level of 70 tons it

is evident that a level of 50 tons allows longer MRT for fer-romanganese especially when the falling position is the mid-

point, although, the standard deviation is large. Ferroniobi-

um additions observe ideal conditions for their addition

during tapping at this level of 50 tons since the MRT are

large and the standard deviations are small meaning high

repeatability of events. Dynamic behavior of ferroniobium

particles at a steel level of 70 tons, see Fig. 14, yields also

large MRT however, as was pointed above, these are not

necessarily good conditions because particles remain in the

ladle bottom where convection currents are very small

which may lead to long melting times. In the case of ferro-

manganese, at this tonnage, the largest MRT is observedwhen the falling position is close to the jet and repeatability

of additions events is high since the standard deviations are

small. For buoyant additions, Al and ferrosilicon, the most

recommendable falling location remains that close to the

plunging jet, yet, the high turbulence of that location induc-

es relatively large standard deviations. Therefore, availabil-

ity of buoyant or light additions can sometimes be optimum,

i.e., large MRT and some other times are not optimum, i.e.

short MRT.

3.4. Discussion

Addition of buoyant additions whenever possible shouldbe carried out close or just in the plunging jet to induce long

MRTs and large particle trajectories and this effect will be

favored with high steel levels in the ladle. Other falling loca-

tions will lead, generally, to very short MRTs and fast

emerging particles with minor effects of particle sizes and

resulting in low alloying efficiencies. Therefore, particle

dynamics of ferrosilicon and aluminum are very similar.

From a practical standpoint it can be said that MRTs of

buoyant additions to steel baths are independent from fluid

flow patterns in the ladle with the exception of the plunging

jet neighborhood. Even, if the melt in the ladle would be

stagnant buoyant additions will show the similar behaviorsto those described here whenever the addition are made out-

side the influence of the plunging jet. Naturally, with denser

additions fluid flow plays more important roles on alloys

availability as is discussed below.

For neutral floating particles such as ferromanganese the

best falling position is the mid point between the jet and the

ladle wall at a tonnage of 50 tons and this is due to the drag-

ging effects on these particles exerted by the recirculating

flow of the melt. When the falling position is located close

to the ladle wall the MRT decreases considerable and the

standard deviation grows meaning that sometimes these par-

ticles will go deep into the melt and at some other times they

will emerge relatively fast all depending on the instanta-

neous fluid flow structure. Addition of ferromanganese

reaches the highest MRT at steel levels of 50 tons with a

falling position in the middle of the plunging jet and the

ladle wall. At a steel level of 30 tons the MRT of ferroman-

ganese is longer in a falling position close to the jet and

improves when the steel level is 70 tons. The same trend is

observed when the falling position is close to the ladle wall.

MRTs of neutral particles are then dependent on the instan-

taneous fluid flow pattern and the best steel level for effi-

cient alloying is at level of approximately 70% of the total

steel tonnage in the ladle.

Heavier additions than steel like FeNb, have the largestMRTs and alloying efficiency is independent from steel

tonnage in the ladle. However, close to a level of complete

ladle filling heavy additions sink to stagnant melt regions

being subjected to low melting rates. The most recommend-

able steel level for these additions would be about 60% of

the total steel tonnage when the melt has been deoxidized

and melt streams do not carry them to stagnant regions.

Bringing on now the metallurgical aspects it can be said

that a recommendable and ideal tapping procedure for low

carbon aluminum killed steels, even for ultra low carbon

steels, would be the following:

Compact plunging jets by ensuring good surface con-ditions of the EBT nozzle and avoid slag carry-over.

Start the tapping with and addition of coke for pre-

deoxidation purposes forming a steel cushion. Add,

simultaneously any synthetic slag if that is indicated by








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Plunging Jets in Steel Tapping

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