Optimization of Liquid Steel Flow in an Industrial Tundish

Tong Qiufang1,a, Wu Zhonghua1,b and Arun S. Mujumdar2,c 1College of Mechanical Engineering, Tianjin University of Science and Technology, Tianjin, China

2Minerals, Metals and Materials Technology Centre (M3TC), National University of Singapore,

Singapore, 117576

atongqiufang@163.com

,

bwddhua@gmail.com

,

cmpeasm@nus.edu.sg

Keywords: Computational fluid dynamics, Steel making, Tundish.

Abstract. A computational fluid dynamic (CFD) model was developed to study the fluid flow

phenomena taking place in an industrial tundish. Numerical results showed spatial distributions of the

velocity vectors, the residence time and fields of turbulence kinetic energy. Selected computer

simulation results were validated with experimental data. The effect of the impact pad and interior

dams on the hydrodynamics of liquid steel flow were studied numerically and optimized to reduce the

fraction of dead volume zones and augment nonmetallic inclusions to float into the slag. A novel

design of a turbo-stopper was proposed and its function to decelerate the ladle shroud jet and direct

the flow back to reduce slag entrapment was discussed. Such numerical results improved our

understanding of the hydrodynamics of liquid steel flow in the tundish and contribute to an optimized

operation.

Introduction

The tundish in the steelmaking process provides a reserve of liquid steel of a specified temperature,

thus enabling the exchange of main ladles and carrying out of sequential casting. The nature of liquid

steel flow in the tundish plays a significant role in inclusion floatation, molten steel temperature and

component homogenization. It is generally need to optimize the character of the steel flow in the

tundish. With the given outer shape of tundish, it is possible to optimize by adjustments of the inner

arrangement, e.g. by installation of different elements (dams, weirs, baffles) [1]. Efforts are being

made worldwide to obtain the most favorable shape of tundish interior by using dams, overfills and

partitions, which is in favor of nonmetallic inclusions floating into the slag, and also reduce the share

of dead zones, short-circuit flow.

Some researchers in the past used the water model to evaluate the existing or new tundish design

configurations. For example, Dainton, A.E. used water model to develop a novel tundish flow system

incorporating a new turbulence suppresser design [2]. However, water model operations are

expensive and time-consuming. More researchers use numerous model to simulate the liquid

behaviors in the tundish to explain the effect of tundish’s working space shape and steel flow

conditions on the inclusion floating processes, or to evaluate the new designs of tundish geometries.

Merder, et al developed a mathematical model to study the fluid flow phenomena taking place in

continuous casting tundish-A six-strand tundish [3]. Numerical results include spatial distribution of

the velocity vectors, temperature of steel flowing in the tundish, etc.

The primary purpose of the investigation carried out was to develop a computational fluid

dynamics (CFD) model to simulate the flow behaviors in the tundish. Numerical results improved our

understanding of the flow dynamics in the tundish. Different geometry designs will be proposed

evaluated and then optimized using the numerical model. After an optimized geometry design was

achieved, a water-model facility will be constructed and the experiments will be carried out to

evaluate its performance. Such process contribute to reduce the time and cost of novel tundish

geometry.

Advanced Materials Research Vols. 634-638 (2013) pp 1752-1755Online available since 2013/Jan/11 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.634-638.1752

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Mathematical Modeling

Figure.1 shows the physical model of an industrial-scale tundish. This tundish has a length of 1520

mm, width of 320 mm and height of 600 mm. The ladle shroud nozzle has a diameter of 52mm and

the casting strand nozzle is 36 mm in diameter. At the bottom wall, there are two blocks: One is the

impact pad of 300×300×90mm and put under the ladle shroud nozzle. The function is to reduce the

turbulence energy caused by the falling liquid steel jet from the ladle. Another is the dam of

300×62×62mm and put at a location x=1088 mm. Since the geometry is symmetry on the x-z plane,

half of the geometry is computed. In this study, we use water to replace the liquid steel. The reason is

that their surface tension coefficients are almost the same, which allows us to capture the main flow

characteristics in the tundish. The thermo physical properties of water and air are given in Table 1.

Figure.1. Physical model of the tundish

Table 1. Properties of water and air

Properties Water Air

Density (kg/m3) 1000 1.225

Viscosity (kg/m⋅s) 0.07 1.7894e-05

Surface tension (N/m) 0.072

The water flow behaviors in the tundish above were simulated by the developed computational

fluid dynamics (CFD) model, which was described in detail in reference [4]. The CFD model

included the Navies-Stocks continuity, and momentum governing equations. The flow turbulence was

simulated using the low-Reynolds number k-epsilon turbulence model. Also, the Volume of Fluid

(VOF) multiphase model was applied here. All the equations were solved using a commercial CFD

software-Fluent 6.3.

Results and Discussion

Figure.2 shows the flow pathlines in the tundish with and without impact pad and dam. From

Figure.2a, it is found that the flow of water from the ladle shroud nozzle divided itself into two

separate flows after it fall on the bottom wall and heads in the horizontal direction. One flow heads to

the left side wall of the tundish, rises up along the wall and then rains down. This causes a big

circulation zone observed on the left side of the shroud nozzle. The other flow headed in the

horizontal direction on the right side of the shroud nozzle. However, the flow also divides itself into

three separate flows at a distance of 100mm close to the nozzle. One flow flows back and forms a big

circulation zone on the right side of the shroud nozzle. The second flow deviates from the horizontal

direction and forms the third circulation zone at the upstream of the casting nozzle. The third flow

heads to the casting nozzle along the bottom wall. The residence time of this flow should be less than

the average one and it can be called “short-circuit” flow. When the coming liquid steel practically

immediately gets into the outlet of the tundish, it is undesirable with regard to steel purity and thermal

homogeneity of cast steel in individual strands. In Figure.2a, three big circulation zones are observed

inside which the residence time of flow is longer than the average one and can be called “dead

volumes”. Dead volume is defined as the area where the liquid steel stays in tundish longer than the

Advanced Materials Research Vols. 634-638 1753

double of the average residence time [5]. Existence of dead volume can substantially decrease the

active volume of tundish. It can also lead to the unsteady temperatures of steel cast in individual

casting strands and so lead to the increase of the breakout danger.

(a)

(b)

Figure.2. Flow pathlines in the tundish with (a) /without (b) impact pad and dam

Figure.2b shows the flow pathlines in the tundish with dam when the equilibrium state is reached.

Compared with Figure.2a, it is found that the flows in the tundish are redirected by the impact pad

under the shroud nozzle and the dam located in front of the casting nozzle and a relative homogenous

residence time of flows is achieved. The used impact pad fully inhibits the direct flow to the casting

nozzle along the bottom wall-the “short-circuit” flow and increases its residence time. Also, the

impact pad reduces the sizes of the two circulation zones near to the shroud nozzle. The third

circulation zone observed in Figure.2a diminishes due to the stepping dam located in the front of the

casting nozzle. The present results show that the introduction of impact pad, and dams, etc can

redirect the flow movement and reduce “short-circuit” flow and dead volumes in the tundish. The

optimization of impact pad and dams will be carried out in sequential research work.

In Fig.2, we can see that the ladle shroud jet caused two big recirculation regions in the tundish.

Since the flow turbulence in the recirculation zone is also relative high and bigger inclusions may

generate in the high turbulent zone due to collisions of smaller inclusion, which reduce the steel

quality. Hence, the turbulence-stoppers or suppresser were proposed in the tundish. Turbo-stoppers

can decelerate the ladle shroud jet and direct the flow back to reduce slag entrapment. Figure.3a

shows a proposed circular turbo-stopper in the tundish and Figure.3b shows the flow vector near the

turbo-stopper. In Figure.3b, we can see that the incoming ladle shroud jet first reached to the

turbo-stopper bottom wall and then the jet is re-directed back due to the circular side wall shape of the

turbo-stopper. The flows re-directed is counter-currently with the incoming shroud jet and hence,

reduce the jet entrainment of surrounding liquid and slag. Only a very small recirculation zone is

observed near the turbo-stopper in Figure.3b.

.

(a) Turbo-stopper (TS) (b) Flow vectors near TS

Figure.3. The proposed turbulence stopper and flow field caused in the tundish

1754 Advances in Chemical, Material and Metallurgical Engineering

Figure.4 shows the velocity magnitude distribution in the tundish with/without turbo-stopper. In

Figure.4a, the shroud jet first reaches the tundish bottom wall and then it spread along the bottom

wall, caused two big circulation regions. While in Figure.4b, due to the limitation of turbo-stopper,

the shroud jet can’t spread along the bottom wall. The high velocity magnitude region size reduces

largely in Figure.4b. Thus, the turbo-stopper can efficiently decelerate the ladle shroud jet and

suppress the flow turbulence caused.

(a)

(b)

Figure.4. The velocity magnitude distribution in the tundish without (a) and with (b) the circular

turbo-stopper

Conclusions

Three-dimensional computational fluid dynamics simulations had been carried out to study the flow

behaviors in an industrial-scale tundish. Tundish designs with/without impact pad and dam were

compared. It is found that the undesirable short-circuit flow, dead volumes exist in the proposed

tundish. The introduction of the impact pad and stepping dam will regulate the flow behaviors in the

tundish and inhibit the short-circuit flow and dead volumes, which improve the tundish performance

and steel quality.

A circular turbulence stopper was introduced in the tundish. It is found that the turbo-stopper can

redirected the flow and reduce largely the ladle shroud jet entrainment of surrounding liquid and slag.

References

[1] Ghosh, A. Secondary steelmaking: principles and applications. New York: CRC Press, 2000,

285-295.

[2] Dainton, A.E. Development of a novel tundish flow system-the application and results in North

American steelplants: 28th Seminar on Melting, Refining and Solidification of the ABM, Brazil:

May 12-14, 1997.

[3] Merder, T., Boguslawski, A. and Warzecha, M. Modelling of flow behaviour in a six-strand

continuous casting tundish. Metallurgical, 2007, 46(4): 245-249.

[4] Wu, Z.H. and Mujumdar, A.S. CFD modeling of liquid steel flow behaviors in industrial tundish:

Third baosteel biennial academic conference, Shanghai, China: Sep 26-28, 2008.

[5] Levenspiel, O. Chemical Reaction Engineering, 2 Ed. New York: Wiley, 1972.

Advanced Materials Research Vols. 634-638 1755

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