Jiang_et_al_2010
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Jiang_et_al_2010

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International Journal of Minerals, Metallurgy and Materials
Volume 17, Number 2, April 2010, Page 143
DOI: 10.1007/s12613-010-0204-0

Corresponding author: Jing-she Li E-mail: lijingshe@ustb.edu.cn
© University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg 2010

Water modeling of molten steel flow in a multi-strand
tundish with gas blowing

Jing Jiang1), Jing-she Li1), Hua-jie Wu2), Shu-feng Yang1), Tao Li1), and Hai-yan Tang1)
1) School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China
2) Engineering Research Institute, University of Science and Technology Beijing, Beijing 100083, China
(Received: 2 April 2009; revised: 20 May 2009; accepted: 2 June 2009)

Abstract: Fluid flow characteristics in a four-strand tundish with gas blowing were studied by water modeling experiments. It is found that
gas blowing can greatly improve the flow characteristics in the tundish with a turbulence inhibitor. It dramatically increases the peak concen-
tration time, and greatly decreases the dead volume, and reduces the minimum residence time. The gas blowing location, gas flow rate, and
porous plug area greatly influence the flow characteristics in the tundish; the gas blowing location near the baffle, smaller gas flow rate, and
smaller porous plug area are better for improving the fluid flow characteristics. Using gas blowing can reduce the difference of flows at the
middle outlets and side outlets for the multi-strand tundish. Bubbles produced by gas blowing can absorb small inclusions and provide the
condition for inclusion collision and aggregation. Therefore, introducing gas blowing into a tundish and combining the turbulence inhibitor
can improve inclusion floating and removal, and the cleanness of molten steel can be advanced.

Keywords: continuous casting; tundish; water modeling; gas blowing; porous plug

1. Introduction

Besides using weirs, dams, baffles with holes, and turbu-
lence inhibitors, gas blowing is another important way to
improve the fluid flow and inclusion removal in the tundish.
The principle of this method is that the generated small bub-
bles from the tundish bottom can form a bubbling curtain
that works as a dam and as an efficient transporting mecha-
nism of inclusions toward the bath surface to be captured by
a suitable slag [1].

A few studies have been carried out for investigating the
flow and inclusion behaviors in a tundish with gas blowing.
Zhong [2] investigated the effects of the argon bubbling
curtain on the flow characteristics in a 1:3 reduced scale
two-strand tundish water model. It was found that gas
blowing hardly influenced the minimum residence time but
significantly increased the peak concentration time and
shortened the tail of resident time distribution (RTD) curves.
Zhang [3-5] studied the fluid flow and inclusion motion in
an argon bottom blown tundish by water modeling and

mathematical modeling, which found that the position of gas
blowing and gas flow rate had remarkable effects on the
steel fluid flow and the RTD curve. In the same way,
Ramos-Banderas et al. [6] found that higher flow rates of
gas lead to the decrease in the plug flow fraction of the fluid
in the tundish. Yamanaka et al. [7] investigated the tundish
using argon bubbling through porous plugs, and they
claimed a 50% improvement in the removal of inclusions in
the 50 to 100 mm range. Tao [8] reported that the inclusion
index of the slab cast with argon bubbling was decreased
from 0.733-0.898 mg/kg to 0.421-0.433 mg/kg. Investiga-
tions of gas bubbling in continuous casting tundishes were
carried out by Marique and a 25%-50% improvement in the
removal of inclusions was reported [9].

In previous literatures, all the studies focused on the one-
or two-strand tundish, and the reports on gas blowing in a
multi-strand tundish are few. In the present article, the ef-
fects of gas blowing on the flow characteristics in a
four-strand tundish with 25 t capacities were investigated in
a reduced scale water model. The optimum porous plug area,

144 Int. J. Miner. Metall. Mater., Vol.17, No.2, Apr 2010

the optimum location of the porous brick, and the optimum
gas flow rate were determined by measuring the RTD
curves in water modeling experiments. The prototype tun-
dish configuration studied is shown in Fig. 1. A turbulence
inhibitor and a baffle with 3 holes were used in the tundish.

Fig. 1. Original tundish configurations (unit: mm).

2. Experimental procedure

In the water modeling experiments, to insure the similar-
ity of fluid flowing between the model tundish and the pro-
totype tundish in isothermal and non-reactive systems, geo-
metrical and dynamic similarities must be satisfied between
the two vessels. In the present work, the ratio of the geomet-
rical similarity of the model tundish to the prototype is cho-
sen to be 1: 2.5. Dynamic similarity requires respecting si-
multaneous equality of both turbulent Reynolds and Froude
numbers, but it is impossible to keep the condition satisfied
in reduced scale modeling studies. The computational and
experimental studies of Singh and Koria [10] showed that
the magnitude of turbulent Reynolds number under the tur-
bulent flow range in different tundishes is very similar.
Therefore, Froude numbers of the model and prototype tun-
dishes are maintained to be equivalent in this work. Ac-
cording to the Froude similarity criterion (Frm=Frp, where,
m—model, p—prototype),
the characteristic length: Lm=λLp=0.4Lp (1)
the characteristic velocity: Um=λ0.5Up=0.63Up (2)
the volumetric flow rate: Qm=λ2.5Qp=0.10Qp (3)

The casting speed is 0.5 m/min, and the diameter of the
round billet is 280 mm×325 mm. The parameters of the pro-
totype tundish and model tundish are shown Table 1.

A sketch map of the experimental apparatus is shown in
Fig. 2. The RTD curve of the fluid flowing in the tundish
can be obtained by the stimulus-response technique to in-
vestigate the effect of different tundish configurations on the

fluid flow characteristics in the tundish. Before measuring,
the liquid levels of the ladle and the tundish were raised to
the predetermined height. Then, the tundish nozzles were
opened. After attaining the steady-state flow condition, 200
mL KCl saturated solution was used as a tracer and was in-
jected into the water stream flowing through the ladle nozzle.
One conductivity probe connected to a conductivity meter
was installed below one of the outlets of the tundish to
measure the instantaneous concentration of the tracer as a
function of time. The measurement data were plotted with a
recorder and input into a computer to construct RTD curves.
From the RTD curves, the minimum residence time (tmin),
peak concentration time (tmax), and mean residence time (tav),
could be obtained for every experiment. Considering there
was fluid exchange between the fluids in the dead zone and
in the active zone, the flow model proposed by Sahai and
Emi [11] was employed in this work to calculate the dead
volume fraction (Vdv), but the fractions of plug flow and
well mixed volumes were still calculated with the modified
mixed model from Ahuja and Sahai [12].

Table 1. Parameters of the prototype tundish and model tun-
dish

Parameter Prototype Model
Flow volume per nozzle / (L·h−1) 2730 276

Diameter of the nozzle / mm 80 32
Depth of liquid / mm 900 360

Distance between two nozzles / mm 621 248
Depth of nozzle penetration / mm 150 60

Fig. 2. Sketch map of water modeling experiments.

In this study, 11 cases (case 1 is the prototype tundish)
were investigated, in which 4 different locations of gas
blowing, 4 different gas blowing rates, and 3 sizes of porous
plugs were studied. Fig. 3 shows the details of the experi-
mental cases. The porosity of porous plugs used in the ex-
periment is 15%, and the average diameter of