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Physical Modeling and Optimization of Bottom Tuyere Configuration and Blowing Parameters in a Top and Bottom Combined Blowing Converter.

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Dev. Chem. Eng. Mineral Process. I4(3/4), pp. 343-352, 2006.
Physical Modeling and Optimization of
Bottom Tuyere Configuration and Blowing
Parameters in a Top and Bottom Combined
Blowing Converter
Liang-Cai Zhong*, Jun-Ying Chen', Zhe-Long Lei,
Chen-Xi Ji, Ying-Xiong Zhu and Mao-Fa Jiang
Department of Ferrous Metallurgy, Northeastern University,
PO Box 312, Shenyang, Liaoning, P. R. China
#
Shaoguan Iron & Steel Co., Shaoguan 512123, P. R. China
Optimizing experimentsfor the bottom tuyere configuration and blowing parameters
of the 120 tonne top and bottom combined blowing converter at Shaoguan Iron &
Steel Co. were carried out in a reduced-scale water model. Results showed that the
former configuration with 6 bottom tuyeres in the converter was not suitable with
bath stirring because of the two tuyeres arranged in 0.330 pitch circle which caused
the cavity deformation and stirring energy loss. Ideal bath stirring in the converter
was obtained by using a new arrangement with 4 bottom tuyeres, two being in 0.57D
pitch circle and the other two in 0.420 pitch circle. The optimal blowing parameters
of the converter with the new bottom tuyere configuration were 1.26 Nm3/h of bottom
gasflow rate, 160 mm of top lance height, and 30.52 Nm3/hof top gas flow rate.
Introduction
The technology of top and bottom combined blowing is very important in
oxygen-based steelmaking. In comparison with the process of top blowing converters,
it has the benefits of smoother blowing procedure, lower iron oxides in end-point slag,
higher iron yield, less alloy consumption, and easier production of low and ultra-low
carbon steel [ 13. In top and bottom combined blowing converters, the bottom tuyere
configuration has an significant influence on bath mixing, kinetics of slag-metal
reactions, decarbonization rate, and splashing and spitting [2-4]. Roth et al. [ 5 ]
studied the effects of bottom blowing in metallurgical reactors and found the best
mixing results were obtained when eccentric tuyere configurations were applied. Paul
and Ghosh [6] investigated mixing and mass transfer rates of slag-metal in top and
* Authorfor correspondence (zhongIc@l26.com).
343
L . 4 . Zhong, J,-Y. Chen, Z.-L.
Lei, C.-X.Ji, E-X.Zhu and M.-E Jiang
bottom blown converters with water model experiments. Their results showed that
bath mixing time decreases as the gas flow rate per tuyere is increased. Roth et al. [7]
researched the fluid flow and mixing performance under different top lance tip, lance
height, bottom nozzle arrangement and blowing rate in combined blowing
experiments. They concluded that small amounts of bottom stirring gas have a great
effect on bath mixing, and the mixing time decreases slightly with increasing bottom
blowing rate.
In the present work, the 120 tonne combined blowing converter of the Shaoguan
Iron and Steel Co. was used as a prototype and its bottom tuyere configuration was
optimized by physical modeling experiments. Based on the optimized bottom tuyere
configuration, optimal parameters for the combined blowing process, such as top
oxygen lance height, flow rate of top gas blowing and bottom gas injection, were
determined.
Experimental Details
Figure 1 is a schematic of the experimental apparatus used for the physical modeling.
A 1/10 reduced-scale model of the converter was made of 10 mm thick plexiglass.
The dimensions of the prototype and the model are given in Figure 2. The diameters
of the model converter mouth and body and the radius of the model bottom were
determined by taking 200 mm lining corrosion in the prototype into account. Water
and air were used to simulate molten steel, oxygen and bottom injection gas. The air
was supplied by a compressor which pumped the air into a gas container. The air flow
rate was controlled by rotameters. The top lance was fabricated from 22 mm diameter
copper tube with a four-laval-hole nozzle, made of plexiglass, at one end. The
included angle between each hole center line and the nozzle center line was 13".
Bottom tuyeres were also made of 10 mm diameter, 20 mm long, plexiglass rod with
one hollow end. Three holes (diameter 1 mm) were drilled at the other end of the rod.
50 mi of 4N NaCl solution was employed as a tracer for bath mixing time
measurements. The tracer was added into the bath with a glass tube whose end was
fixed, and immersed into a position 5 mm from the bath surface; a conductivity probe
was placed at 180" From the tracer addition position at the bath bottom as shown in
Figure 1. The probe was connected to a conductivity meter and the signals were
recorded. The time when the bath conductivity reached 95% of the value
corresponding to steady-state conditions was considered to be the bath mixing time.
The dynamic similarity bemeen the model converter and the prototype was
considered by using the modified Froude number. By letting the modified Froude
number in the model be equal to that in the prototype, then:
...(1)
where u is velocity of gas injected into the bath; p is density; L is characteristic
length; g is gravity acceleration; and subscripts m for the model, p for prototype, I for
liquid phase, and g for gas phase. Experimental conditions in this work are given in
Table 1.
344
Physical Modeling and Optimization in a Blowing Converter
U
Figure 1. Schematic of the experimental apparatus
1. converter; 2. oxygen lance; 3. glass tube; 4. bottom tuyeres; 5. water; 6. conductwiry probe; ?.flow
meter; 8. surge tank; 9. air compressor; 10. gas container; 11. conductiviry meter; 12. recorde,:
t
t
(a)
(b)
Figure 2. Dimensions of the prototype (a) and the model (b).
345
L.-C. Zhong, J.-!I Chen, Z.-L. Lei, C.-X Ji, Y-X.Zhu and M.-E Jiang
Parameter
Top gas ow rate
Qr(Nm /h)
P
Bottom gas rate
QB (Nm3/W
Top lance height
hL (mm)
Bath depth (mm)
Prototype
Model
22000,24000,26000,28000 27.98,30.52,33.07,35.61
360,504,720,1080,1440
0.42,0.59,0.84,
1.26,1.68
1400,1600,1800,2000
140,160,180,200
1300
130
The gas flow rates in the model were calculated from those in the prototype by:
.*.(2)
Q, = A2’QP
where 1 is the geometrical similarity ratio. The pressure of gas was taken into
consideration in the modeling experiments.
The bottom tuyere configurations investigated in the experiments are shown in
Figure 3. The mode M is the former bottom tuyere configuration. Three or four
experiments for a group of particular operating conditions were carried out, and the
mean value of the measured data was assumed to be the bath mixing time.
Type
A
B
C
D
E
F
G
H
I
J
K
L
M
Bottom tuyere
configuration
1346
3467
3567
2346
2356
3678
13458
34561
13451
13467
23456
123456
1346910
Vormer Wpe)
Figure 3. Bottom tuyere configurations in the experiments.
346
Physical Modeling and Optimization in a Blowing Converter
Results and Discussion
Figure 4 shows the relationship between the bath mixing time and the different
bottom tuyere configurations for top gas flow rates of 27.98 Nm3/h and 33.07 Nm3/h,
top lance height of 180 mm, and bottom gas flow rate of 0.84 Nm3/h. The two
horizontal lines in Figure 4 indicate the mixing time under the same conditions
without bottom gas injection. It can be seen that the bath mixing time in the top and
bottom combined blown converter is obviously lower than that in the top blown
converter. The bottom tuyere configurations have a significant influence on the bath
mixing time.
From Figure 4 it is known that the bath mixing time of configuration F is the
lowest obtained from all the configurations. Therefore, it can be concluded that the
bottom tuyere configuration F is the best one in all the configurations investigated in
the present work. Figure 4 also shows that the former bottom tuyere configuration
(configuration M) has higher mixing time than most other configurations. The bath
mixing time for the optimal bottom tuyere configuration can be reduced by about 36%
when compared with that for the former configuration in the experimental conditions.
The reason why the former bottom tuyere configuration has a higher mixing time is
that there are two bottom tuyeres located in the 0.33D pitch circle, as seen in Figure 3
(configuration M).
The location of the two bottom tuyeres is close to the central area of the vessel
bottom so that the plumes from the two tuyeres deform the cavity formed by the top
gas jet into an ‘00’shape. However, the cavity shape from configuration F is almost a
regular circle as shown in Figure 5 . The two plumes from the two bottom tuyeres in
the 0.33D pitch circle meet with the top gas jets in the bath, and such phenomenon
decreases the stirring energy of bottom and top gases. As a result, the bath mixing
time is longer for the former bottom tuyere configuration. This result agrees well with
the conclusion obtained by Oymo and Guthrie [S] who suggested that the region
between 0.2 and 0.35Din a circular arrangement of tuyeres for combined blowing
should be avoided. It can be observed from the experiments that the bottom tuyere
configuration F can causes re-circulating flows in the bath, not only in the vertical
direction but also the horizontal direction. Such re-circulating flows are favorable to
the bath stirring. In the other configurations, such re-circulating flows are not so
strong.
In most of the bottom tuyere configurations, differences in the bath mixing time
between the two top gas flow rates is not evident in the same configuration, which
indicates that bath stirring in combined blowing converters is mainly dependent upon
bottom gas injection, not on the top gas jets. It can be seen in Figure 4 that the mixing
time at the high top gas flow rate in the bottom tuyere configuration L is obviously
longer than that at the low top gas flow rate. It is known from Figure 3 that
configuration L is a symmetrical bottom tuyere arrangement. The re-circulating flows
in the horizontal direction for this configuration are weakened by the higher top gas
flow rate, which results in a longer mixing time.
The influence of bottom gas flow rate and top lance height on bath mixing time, at
different top gas flow rates, is presented in Figures 6 to 9 for configurations F and M.
From these figures it can be seen that bath mixing time for configuration F is lower
than that for configuration M under the blowing conditions investigated, especially at
347
L.-C. Zhong, J.-E Chen, Z.-L. Lei, (2.-X Ji, E-XZhuandM-F: Jiang
h,=180 mm
27.98 Nm3/h
To blown converter
70
Q,
.-E
50
.-X
40
c
5
30
20
10
0
A
B
C
D
E
F
G
H
I
J
K
L
M
Bottom tuyere configuration
Figure 4. Bath mixing time in different bottom tuyere configurations.
Figure 5. Cavity shape formedfrom confi urations Mand F at Qr=27.98 Nm3’h,
hL=180 mm and Q8=0.84 Nm h.
5
348
Physical Modeling and Optimization in a Blowing Converter
higher bottom gas flow rates. For the case of configuration M, usually the bath mixing
time first increases at lower bottom gas flow rates. Then, it deceases at higher bottom
gas flow rates. Such phenomena are associated with the bottom tuyere arrangement.
In the range of lower bottom gas flow rate, the percentage of bottom gas momentum
for bath stirring decreases when the bottom gas flow rate increase due to the
momentum counteraction between top gas and bottom gas, as described above. Only
when the bottom gas flow rate is larger than some critical value, does the bottom gas
has enough momentum to stir the bath. Therefore it is concluded that the bottom
tuyere configuration in top and bottom combined blowing converters is extremely
important. If an unsuitable bottom tuyere configuration is employed, then bath stirring
becomes aggravated.
For configuration F, bath mixing time decreases at bottom gas flow rate from 0.4
Nm3/h to 1.26 Nm3/h and then does not change much at higher bottom gas flow rate.
It is indicated that the bath stirring can be improved by increasing bottom gas flow
rate for the bottom tuyere configuration F at low bottom blowing rate. However, when
the bottom gas flow rate is larger than 1.26 Nm3/h, the effect of bottom gas flow rate
on the bath mixing time is not remarkable. Among all the experimental conditions, the
lowest bath mixing time is obtained at bottom gas flow rate of 1.26 Nm3/h, top lance
height of 160 mm and top gas flow rate of 30.52 Nm3/h for configuration F.
80
Q,=27.98 Nm3/h
70
Q
-0- 160
-v-
200
Configuration M
60
W
;.
.-CX
50
2
40
30
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Bottom gas flow rate(Nm3k)
Figure 6, Effect of bottom gas rate and top lance height on bath mixing time at
Qr=27.98 Nm3/h.
349
L.-C. Zhong, J.-E Chen, Z,-L. Lei, C.-X.Ji, E X Zhu and M.-EJiang
I
"
80
Q,=30.52 Nm3/h
-0- 140 -A- 180
-0- 160 -v- 200
70
Configuration M
2 60
hi
.-E
C
:z
-
50 lA3; ; -A.
\ -
W::.
-5.
2 40 -
b-L;-%.., T -2:-
.
Configuration F
:*--- - z x z z = = s - - - = +
----
b----..:.
30
- * -. - n - = - = - - - - -
1
I
1
I
I
I
I
0.8
0.6
0.4
Ihr
I
1.0
1.2
I
-0
1-0,
I
1.4
c
1.6
Bottom gas flow rate(Nm3/h)
Figure 7. Effect of bottom gas rate and top lance height on bath mixing time at
Q ~ = 3 0 . 5 Nm3/h.
2
80
. Q,=33.07 Nm3/h
-0- 140
70
-A- 180
9 60
hi
.i
.G
50
Configuration F
--
40
\
'0
30
l
0.4
.
1
0.6
.
1
0.8
*
-V
- -- -- :.= -- -- - -0
- -A
-0:--------
1
1.0
,
1
1.2
.
1
1.4
,
1
,
1.6
Bottom gas flow rate(Nm3/h)
Figure 8. Effect of bottom gas rate and top lance height on bath mixing time at
Q ~ = 3 3 . 0 Nm3/h.
7
350
Physical Modeling and Optimization in a Blowing Converter
.*
- --
0-r2 40 - 0- -,-U'00.--=-<.-- --0zB - =- - - =- --- --- --- --- -0-0
- -- = z - - -v - - - - - - -- =
- - - ------A
.A- - - - - - n - - - - - - - - - - A -
0.
L
~
- ;g
~
30
I
1
.
1
.
Configuration F
I
I
,
Figure 9. Efect of bottom gas rate and top lance height on bath mixing time at
Qr=35. 61 Nm3/h.
Conclusions
Bottom tuyere configurations and blowing process parameters were optimized for the
120 tonne top and bottom combined blowing converter in a 1/10 reduced-scale water
model. It was found that the former bottom tuyere configuration (configuration M) of
the converter detracted from bath stirring, due to the two tuyeres located in the 0.33D
pitch circle which caused the counteraction between the momentum of bottom gas
and top gas jets. Among the bottom tuyere configurations investigated in the present
work, configuration F had the lowest bath mixing time and was determined to be the
ideal arrangement of bottom tuyeres. Bath mixing time decreased with an increase in
bottom gas flow rate from 0.42 Nm3/h to 1.26 Nm3/h, and did not change significantly
when the bottom gas flow rate is greater than 1.26 Nm3/h for configuration F. Strong
bath stirring was achieved at a bottom gas flow rate of 1.26 Nm3/h, top lance height of
160 mm, and top gas flow rate of 30.52 Nm3/h, for a bottom tuyeres arrangement
given by configuration F.
References
1. Ishihara, S. 1982. Iron & Steelmaker, 9(3), 43-48.
2. Fiege, L., Schiel, V., Schroer, H., et al. 1983. Siahl u. Eisen, 103(4), 159-162.
3. Ajmani, S.K., and Chatterjee, A. 1996. Ironmaking Steelmaking, 23(4), 335-345.
4. Fabritius, T.M.,
Luomala, M., Virtanen, E., et al. 2002. ISlJInt., 42(8), 861-567.
35I
L.-C. Zhong, J.-Y Chen, Z.-L. Lei, C.-X. Ji, Y-X Zhu andM.-F: Jiang
5
6
7
8
352
Roth, C , Peter, M , Schindler, M , et al 1995 Sfeel Res ,66(8), 325-330
Paul, S , and Ghosh, D 1986 Merall Trans, 17B,461-469
Roth. C , Peter, M , Schindler, M , et a1 1999 Sfeel Res ,70( 12), 502-507
Oymo, D and Guthrie, R I L 1984 Proc Mixed Gas Blowing 41h Process Technology Conference
ISS/UME, Warrendale, Pennsylvania, USA, p 45
.
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