Materials Transactions, Vol. 51, No. 9 (2010) pp. 1602 to 1608 #2010 The Japan Institute of Metals
Effect of Gas Bottom Blowing Conditions on Fluid Flow Phenomena and Mixing Time of Molten Iron inside an Ironmaking Smelter Chau-Jeng Su1; *1 , Jaw-Min Chou1; *2 and Shih-Hsien Liu2 1
Department of Materials Science and Engineering, I-SHOU University, No. 1, Sec. 1, Syuecheng Rd., Dashu Township, Kaohsiung 84001, Taiwan, R. O. China 2 Iron Making Process Development Section, Steel & Aluminum Research & Development Dept., China Steel Corporation, No. 1, Chung-Kang Rd., Siaogang District, Kaohsiung 81233, Taiwan, R. O. China This study uses a water model experiment to investigate the effects of gas bottom blowing conditions on fluid flow phenomena and the mixing time of molten iron within an ironmaking smelter. Our experimental setup adopted four tuyeres in a square-corner placement. The parameters for trials include bottom-blowing tuyere size (7:515:0 mm) and the bottom blowing gas flow rate (320480 NL/min). Experimental results show that the bubble size decreased and the invading depth became deeper as the tuyere size decreased and the total gas flow rate increased. Consequently, the spout height of the liquid surface became higher. The results of the mixing experiment indicate that under any bottom blowing gas flow rates, the 10.0 mm tuyere has the shortest mixing time. Except for the 7.5 mm tuyere, the 10.0 mm, 12.5 mm, and 15.0 mm tuyeres had shorter mixing times and better mixing effects as the gas flow rate increased. Therefore, the best combination for mixing iron phase in a smelter is to use a 10.0 mm tuyere and a gas flow rate of 480 NL/min, which has the appropriate intensity of the total blown energy and the degree of stirred liquid bath. [doi:10.2320/matertrans.M2010104] (Received March 23, 2010; Accepted June 17, 2010; Published July 28, 2010) Keywords: gas bottom blowing, fluid flow, ironmaking smelter, mixing time, water model
1.
Introduction
The direct smelting reduction method of iron ore is one of innovative iron-making processes. Entering the ironmaking smelter, iron ore is heated firstly, then melted into the molten slag phase, and finally reduced to molten iron. Basically, the major reduction of liquid iron oxides occurs at the interface between molten slag and liquid iron. Its reaction mechanism is that liquid iron oxides are reduced by the dissolved carbon of liquid iron. From the viewpoint of reaction kinetics, enlargement of the interface area between molten slag and liquid iron can increase the smelting reduction rate, then enhance the productivity of the iron-making process. In fact, the mixing efficiency of molten iron with slag significantly affects the reaction efficiency inside the ironmaking smelter. Therefore, the purpose of this study was to investigate the effect of gas bottom blowing condition on mixing molten iron and slag inside ironmaking smelter using the simulation technique of water model experiments, then provides process design and operation useful information to enhance the productivity1,2) of the process. Basically, the function of the gas bottom blowing in the ladle is different from that in the ironmaking smelter. In steel refining, the main function of the gas bottom blowing is to make the distribution of temperature and chemical composition more uniform inside the vessel. In order to suppress the inclusion formation inside the steel slab, the stirring intensity should be controlled under a certain level to prevent slag entrapment in the liquid steel. Hence, phenomena observed and data collected about the gas bottom blowing in the case of the refining ladle can not be applied correctly to the case of the ironmaking smelter. *1Graduate
Student, I-SHOU University author, E-mail:
[email protected]
*2Corresponding
In fact, it is extremely difficult to visually observe phenomena and directly measure properties of the fluid flow field inside pyrometallurgical vessels due to extremely high temperature (Temperature > 1400 C) of fluids. Therefore, water model technique has been adopted to simulate the flow behavior of molten iron and slag inside the vessel in some related research works.1–10) The bottom blowing and stirring process inside an ironmaking smelter forms a system in which gas and liquid coexist. Under different bottom blowing conditions, the system in a smelting reduction furnace exhibits different behaviors, including bubbling, jetting, and various turbulence phenomena. These behaviors affect fluid flow pattern and mixing efficiency of molten iron with slag significantly, which in turn affect refractory material erosion around the tuyere tip and the stirring effect of iron slag.11) Previous studies4,12) show that blowing gas forms bubbles in the liquid phase under a low bottom blowing gas flow rate. Due to the buoyant, bubbles rise to the liquid surface, then to cause circulating fluid flow. Changing some operating conditions, such as the gas flow rate and the size and number of tuyeres, changes the volume, the shape, and the number of bubbles as well as the amount of the total blown energy with bottom blown gas transferred to the liquid. The bubble volume and the amount of the total blown energy transferred to the liquid also increase as the gas flow rate increases. When the gas flow rate increases to a certain level, the bubbles combine with the corresponding liquid to form a gas/liquid mixture that rises from the tuyere tip to the liquid surface. This rising phenomenon in the gas/liquid mixture is called ‘‘plume’’. This plume causes the liquid to flow downward along the smelter wall, producing the so-called circulation flow. Under a high flow and high blowing gas flow rate, no bubbles form around the tuyere tip. Instead, the liquid exhibits a continuous gas phase called ‘‘jetting’’. However, the turbulence makes
Effect of Gas Bottom Blowing Conditions on Fluid Flow Phenomena and Mixing Time of Molten Iron inside an Ironmaking Smelter
Experimental Method
2.1 Experimental apparatus A transparent acrylic water model, shown in Fig. 1,16) is geometrically 60% scale-down from the pilot ironmaking smelter designed by China Steel Corporation. Also the water model was filled with the water of 480 mm height (the 146L weight of water in the vessel). All experiments used four tuyeres (type of tuyere is copper pipe; all outer diameter were 20 mm, inner diameter were 7.5, 10.0, 12.5, and 15.0 mm) in the square-corner placement, as Fig. 2 shows. The parameters for injection trials included the bottomblowing tuyere size (7.5 mm, 10.0 mm, 12.5 mm, and 15.0 mm) and total gas flow rate (320 NL/min, 400 NL/min, and 480 NL/min).
0
2.
Fig. 1 Photograph of the water model.
16
jetting separate into some larger bubbles and lots of small bubbles at a particular distance above the tuyere tip. Under these gas blowing conditions, the fluid flow type does not exhibit plume or jetting. If the gas flow rate is as high as or greater than the speed of sound, jetting will extend far from the tuyere tip, and the phenomenon of jetting separating bubbles will no longer occur. In this bottom blowing condition, gas momentum instead of bubble transmission, produces liquid movement. Joo et al.,13) Chung et al.,14) Zhu et al.9) and Turkoglu et al.15) adopted the water model technique to measure the mixing time in the simulated experiments to investigate mixing efficiency inside the refining ladle of steelmaking. In their studies, common conclusions are summarized as follows: As a tuyere was located on the symmetrical center of the bottom of a water model, the flow field was symmetrical and the mixing efficiency was low. Comparatively, in the case of offcentered placement of the tuyere on the bottom, the more turbulent flow and the higher mixing efficiency was obtained under the same gas blowing condition. Matway et al.,3) and Mazumdar et al.4) applied the water model technique to investigate the fluid flow inside the converter and the ladle, respectively. Chen et al.11) used a computer to simulate stirring and mixing states in a smelting reduction furnace. They divided the effect of gas flow rates on the mixing of molten iron and slag phases into three parts for discussion. A high gas flow rate (400 NM3 /h) causes high-speed blowing gas to leave the liquid surface, worsening mixing in the furnace. An intermediate gas flow rate (200 NM3 /h and 300 NM3 /h) also stirs the liquid surface and subsequently damages the firebricks on the furnace wall. A low gas flow rate (100 NM3 /h) has an appropriate stirring effect on the liquid surface. In sum, the stirring intensity of bottom blown gas of a smelting reduction furnace is much stronger than that of a ladle or converter. As fewer studies have examined the smelting reduction furnace, relevant issues could not have further investigation. Therefore, in this study, the simulated experiments of the ironmaking smelter using the water model were conducted to investigate the fluid flow and mixing degree of molten iron under different gas bottom blowing conditions. The target of the research is to find the optimum gas bottom blowing condition of bath mixing in a pilot ironmaking smelter.
1603
230
150
20
(unit : mm)
Fig. 2 The position of four tuyeres with square-corner placement on the bottom of the water model.
2.2
Similarity conversion of bottom blowing conditions between the water model and the ironmaking vessel In order to simulate the gas stirring condition inside the ironmaking vessel, the equivalence of modified Froude number (NFr 0 ). Also, According to previous research,16,17) the bottom-blowing nitrogen flow range on an actual ironmaking vessel system can be converted into the air flow range of a water model system using eq. (1): Qiv ¼ 1:295 5=2 Qwm
ð1Þ
Qwm : gas flow rate for the water model Qiv : gas flow rate for the ironmaking vessel : geometrical scale factor 2.3 Bubble type and observation Three analysis results were used to investigate the relationship between gas bottom blowing conditions and bubble flow types: (1) bubble size, (2) bubble invading depth, and (3) spout height of the liquid surface. 2.3.1 Bubble size and invading depth During stirring process, the large plume bubble that bottom gas injection fragment into small dispersed bubbles, then disintegration of small bubbles are invaded into liquid bath with circulating flow. The difference between the deepest point of the bubble invading zone and the static water surface height is defined as the bubble invading depth. The method of
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C.-J. Su, J.-M. Chou and S.-H. Liu
Total gas flow rate:480NL/min
Total gas flow rate:480NL/min
10.0mm
Table 1 The calculated total energy (J/s) of the bottom blown gas in the experiments. (Condition: 480 mm liquid height and four tuyeres). 320 NL/min
400 NL/min
480 NL/min
7.5 mm
72.27
122.9
194.5
10.0 mm
41.00
61.58
88.74
12.5 mm
32.46
44.84
59.85
15.0 mm
29.39
38.82
49.47
bubble invading depth
Fig. 3
Measured the region of the bubble invading.
the bubble invading depth is used a photograph to analyze and measure the bubble invading depth. We plotted a horizontal line on the liquid surface, and then moved toward the bottom blowing tuyere tip to calculate the number of bubbles the line penetrated. When the number was 15, we defined the length between the liquid surface and this position as the bubble invading depth (as Fig. 3 shows). Also, to measure the size of bubbles, then to established fluid flow phenomena for the liquid bath in water modeling system. The method of bubble size is used on a photograph of the gasliquid fluid flow, we plotted vertical lines 0.5, 1.5, and 2.5 cm from the two sides of the center of the water model. We then used a vernier scale to measure the size of bubbles which the vertical lines passed through. We determined the actual size of each bubble using a scale map of the photograph, where the scale was 100 mm:14.88 mm. Finally, we averaged all of the bubble sizes (there were about 200 bubbles measured on each photo). 2.3.2 Definition of spout height In this experiment, the water model is filled with the water of about 480 mm height. The water surface height without gas bottom blowing is measured after 30 minutes settling down. This height is defined as the static water surface height. When gas stirring starts, the water bath surface exhibits a taller and dynamic profile of a spout zone due to the existence of a group of ascending gas bubbles inside the water bath. The difference between the highest point of the spout zone and the static water surface height is defined as the spout height. 2.4 Measurement of mixing time A potassium chloride solution is used for the conductive liquid in the mixing experiment. (The potassium chloride concentration is 30 mass%, and 50 ml is poured into the water model.) The mixing time is defined as the interval between when the conductive liquid is poured and when the conductivity values detected by different conductivity meters are balanced and the variation in these values is less than 0.1% balanced conductivity. The placement of conductivity meters also affects the mixing time. Thus, in this study, one conductivity meter is located in the position of the bottom center of 5 cm and is 2 cm above the bottom. Another is located at the center of the liquid’s surface and 5 cm deep. 2.5 Calculation for total energy of blown gas In the research of Kishimoto et al.7) and Krishnakumar et al.,8) it was indicated that the total energy ("total ) of the blown gas consists of two parts: buoyancy energy and kinetic energy. The gas bubble transfers its buoyancy energy and
kinetic energy to the stirred liquid during ascending. The energy transfer makes liquid circulate inside the vessel. The transfer efficiency of the total energy depends on the gas blowing condition. The main purpose of this research was to search the gas blowing condition that could creates high mixing efficiency of molten slag/iron with the low total energy of the blown gas flow. Kinetic energy and buoyancy energy can be calculated using eq. (6) and eq. (3), respectively. "k ¼
1 2 m_ u 2 g
"b ¼ n_RTL ln Where
ð2Þ P1 P2
8 dm dV > > < m_ ¼ ¼ g ¼ g Q dt dt Q 4Q > > : ug ¼ ¼ A d2
ð3Þ
(4) (5)
And, substituting eq. (4) and eq. (5) into eq. (2) can derive 1 1 4Q 2 8g Q3 "k ¼ m_ ug2 ¼ g Q ¼ ð6Þ 2 2 d2 2 d4 Where "b : buoyancy energy (J/s) "k : kinetic energy of the injected gas (J/s) n_: molar gas flow rate (mol/s) R: gas constant (8.314 J/mol.K) TL : temperature of liquid (K) P1 : pressure at the liquid bottom (Pa) P2 : pressure at the liquid surface (Pa) g : density of gas (kg/m3 ) m_ : mass flow rate (kg/s) ug : velocity of bottom blown gas (m/s) Q: gas flow rate (m3 /s) d: internal diameter of tuyere (m) Theoretically, the total energy of bottom blown gas can be calculated using the following equation. "total ¼ "b þ "k ¼ n_RTL ln
P1 8g Q3 þ 2 4 P2 d
ð7Þ
The calculated total energy values with the bottom blown gas under different gas bottom blowing conditions in the experiments are listed in Table 1. 3.
Results and Discussion
3.1 Macro fluid flow observation after gas blowing Figure 4 shows a macro fluid flow photo under total gas
Effect of Gas Bottom Blowing Conditions on Fluid Flow Phenomena and Mixing Time of Molten Iron inside an Ironmaking Smelter
Total gas flow rate:480NL/min
7.5mm
10.0mm
10
Ave. Size of Decomposed Bubbles/mm
Total gas flow rate:320NL/min
1605
9
8
Tuyere Size 7.5mm 10.0mm 12.5mm 15.0mm
7
6
5
4
300
400
500
Total Gas Flow Rate, Q/NL·min-1 Fig. 6 Relationship between total gas flow rate and average size of decomposed bubbles.
15.0mm
Ave. Size of Decomposed Bubbles/mm
10 Total Gas Flow Rate 320 NL/min 400 NL/min 480 NL/min
9
8
7
6
Total Gas Flow Rate 320 NL/min 400 NL/min 480 NL/min
35
30
25
20
15
10
0
4
8
12
16
20
Tuyere Size, D/mm
5
4
Ave. Bubble Invading Depth/mm
40
Fig. 4 Marco Fluid flow photo under total gas flow rates of 320 NL/min and 480 NL/min using different tuyere sizes.
0
4
8
12
16
20
Fig. 7 Relationship between tuyere size and average bubble invading depth.
Tuyere Size, D/mm Fig. 5 Relationship between tuyere size and average size of decomposed bubbles.
flow rates of 320 NL/min and 480 NL/min using different tuyere sizes. Under a total gas flow rate of 320 NL/min, the degrees of the liquid disturbance and spurts on the liquid surface increased significantly as the tuyere size decreased. These relationships also apply to a total gas flow rate of 480 NL/min. Figure 4 also shows that the degrees of bubble distribution and liquid surface disturbance under a high gas flow rate were higher than those under a low gas flow rate. 3.1.1 Bubble size Figure 5 shows the relationship between tuyere size and average bubble size under different total gas flow rates. These results indicate that when the tuyere size increased from 7.5 to 15.0 mm under a total gas flow rate of 320 NL/min, the bubble size increased from 6.84 to 7.41 mm. This means that the bubble size decreased as the tuyere size decreased. These relationships also apply to total gas flow rates of 400 NL/min and 480 NL/min. Figure 6 shows the relationship between
the total gas flow rate and average bubble size under different tuyere sizes. These results indicate that when the total gas flow rate increased from 320 to 480 NL/min under a tuyere size of 7.5 mm, the bubble size decreased from 6.84 to 4.96 mm. This means that the average bubble size decreased as the total gas flow rate increased and the tuyere size decreased. Therefore, under the same total gas flow rate, the more the blowing kinetic energy via the smaller the tuyere size, that improves much stirring intensities of liquid bath. This made the severe degree of collision between the cavities formed by gas injected via every bottom blown tuyere would be become more significant, which resulted in much disintegration of small bubbles. Moreover, the collision degree increased as the total gas flow rate increased. 3.1.2 Bubble invading depth Figure 7 shows the relationship between tuyere size and bubble invading depth under different total gas flow rates. The results in this figure indicate that when the tuyere size increased under a total gas flow rate of 320 NL/min, the bubble invading depth decreased from 18.5 to 15.2 cm. These relationships also apply to total gas flow rates of 400 NL/min
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C.-J. Su, J.-M. Chou and S.-H. Liu 20 Tuyere Size 7.5mm 10.0mm 12.5mm 15.0mm
35
30
Ave. Spout Height/mm
Ave. Bubble Invading Depth/mm
40
25
20
300
400
5
0
500
Total Gas Flow Rate, Q/NL·min
-1
300
400
500
Total Gas Flow Rate, Q/NL·min-1
Relationship between total gas flow rate and bubble invading depth.
Fig. 10 Relationship between total gas flow and spout height.
60
20 Total Gas Flow Rate 320 NL/min 400 NL/min 480 NL/min
15
Total Gas Flow Rate 320 NL/min 400 NL/min 480 NL/min
50
Mixing Time/s
Ave. Spraying Height/mm
10
15
10
Fig. 8
15
Tuyere Size 7.5mm 10.0mm 12.5mm 15.0mm
10
40
30
20
5
10
0
0 0
4
8
12
16
20
Tuyere Size, D/mm Fig. 9
Relationship between tuyere size and spout height.
and 480 NL/min, i.e., the larger the tuyere size, the shallower the relative invading depth. Figure 8 shows the relationship between the total gas flow rate and invading depth under different tuyere sizes. The results in this figure indicate that regardless of tuyere size, the invading depth increased as the total gas flow rate increased from 320 to 480 NL/min. The results above (3.1.1) can describe this phenomenon in terms of bubble size, i.e., the smaller the tuyere size and the higher the gas flow rate, the smaller the bubble size. This reduces bubble buoyancy and provides bubbles with a higher intensity of the bottom blown gas. Consequently, the invading depth increased as the size of bubbles decreased. 3.1.3 Spout height of the liquid surface Figure 9 shows the relationship between tuyere size and spout height under different total gas flow rates. The results in this figure indicate that when the tuyere size increased from 7.5 to 15.0 mm under a total gas flow rate of 320 NL/min, the spout height decreased from 8.3 to 6.9 cm. This means that the spout height decreased as the tuyere size increased. These relationships also apply to total gas flow rates of 400 NL/min and 480 NL/min. Figure 10 shows the relationship between the total gas flow rate and spout height under different tuyere
0
4
8
12
16
20
Tuyere Size, D/mm Fig. 11 Relationship between tuyere size and mixing time.
sizes. The results in this figure indicate that when the total gas flow rate increased from 320 to 480 NL/min under the tuyere size of 7.5 mm, the spout height increased from 8.3 to 12.4 cm. This means that the spout height increased as the total gas flow rate increased. These relationships also apply to the tuyere sizes of 10.0 mm, 12.5 mm, and 15.0 mm. During gas stirring process, the water bath surface exhibits a taller and dynamic profile of a spout zone due to the existence of a group of ascending gas bubbles inside the water bath. Additionally, the blowing speed and the kinetic energy increased as the tuyere size decreased and the gas flow rate increased, then to increase the spout height of liquid. 3.2 Evaluation of mixing effects Figure 11 shows the relationship between tuyere size and mixing time under different total gas flow rates. Under a total gas flow rate of 480 NL/min, the mixing time was minimal when the tuyere size was 10.0 mm. This means that the best mixing effect was achieved under this operating condition. In contrast, under the same condition, the mixing time was the longest when the tuyere size was 7.5 mm, representing the worst mixing effect. When the tuyere size exceeded 10.0 mm,
Effect of Gas Bottom Blowing Conditions on Fluid Flow Phenomena and Mixing Time of Molten Iron inside an Ironmaking Smelter 60
Mixing Time/s
50
40
Tuyere Size 7.5mm 10.0mm 12.5mm 15.0mm
30
20
10
0 200
300
400
500
Total Gas Flow Rate, Q/NL·min-1 Fig. 12 Relationship between gas flow rate and mixing time.
the mixing time decreased as the tuyere size decreased. These mixing time relationships also apply to total gas flow rates of 320 NL/min and 400 NL/min. Figure 11 also shows that in the case of the 10.0 mm, 12.5 mm, or 15.0 mm tuyere, the mixing time was shorter and the mixing effect was better when the gas flow rate increased. Figure 12 shows the relationship between total gas flow rate and mixing time. The result indicates that except for the 7.5 mm tuyeres, the mixing time decreases as the total gas flow rate increases. This is because when the total gas flow rate increases, the total energy of the gas flow applied to the liquid also increases, as described above. However, in the case of the 7.5 mm tuyeres, the mixing time increases as the total gas flow rate increases. The reason is that under the same total gas flow rate, the speed of the total gas flow increases as the inner diameter of the tuyere decreases. From section 3.1, when the flow velocity increases, the spout height also increases, and most of kinetic energy of the bottom-blowing gas may dissipate in the air. Therefore, the energy of gas available to stir the liquid decreases, the mixing of the liquid phase worsens, and consequently the mixing time also increases. But, the 7.5 mm tuyere yielded worse mixing effects as the gas flow rate increased. Therefore, the best choice for mixing is to use a 10.0 mm tuyere and a gas flow rate of 480 NL/min.
maximal, as Table 1 indicates. The experimental results in Section 3.1 also indicate that although there were lots of small bubbles and deeper invading depths, the spout heights exceeded the liquid surface so that total energy of the bottomblowing gas could dissipate. Consequently, some kinetic energy from the bottom-blowing gas might dissipate into the air, reducing the stirring energy applied to the liquid and degrading the liquid mixing and stirring effects. We also found that under the same blowing condition of the 7.5 mm tuyere, the gas blowing dissipation became severe and the mixing effect degraded as the total gas flow rate increased. In the simulation of the CFD model done by Chen et al.11) for a smelting reduction vessel with gas bottom blowing, the same conclusion as the above phenomenon was drawn. The reason for this phenomenon is that the more energy dissipates for ejecting liquid up to the freeboard of the vessel in the case of too high intensity of the total blown energy. Additionally, the research of Su et al.17) also indicated that an increase of the total energy of the blown gas via reducing the tuyere size could not enhance the mixing efficiency of molten iron and slag inside the ironmaking smelter. As the tuyere size increased to 10.0 mm, the mixing time was the shortest. It means that there was no gas channeling happened in the stirred liquid bath and more total blown energy could be transferred to the liquid. Also, tuyeres measuring 12.5 mm and 15.0 mm had less gas blowing energy, hindering the bubble groups from touching the liquid and limiting the stirring ability. Thus, when the tuyere sizes ranged from 10.0 mm to 15.0 mm, the mixing effect became worse as the tuyere size increased. Moreover, under tuyere sizes of 10.0 mm, 12.5 mm, and 15.0 mm, the mixing effect increased as the gas flow rate increased. As described above, when the tuyere size was smaller than 10.0 mm, the excessive spout height dissipated the gas blowing energy. Also, when the tuyere size exceeded 10.0 mm, the shallower invading depths of the bubble groups and the less severe disturbance caused insufficient liquid stirring energy. Therefore, during the gas-liquid phase stirring process, the appropriate intensity of the total blown energy and the degree of stirred liquid bath could improve the mixing effect. This study shows that the best blowing combination for mixing is to use a 10.0 mm tuyere and a gas flow rate of 480 NL/min. 4.
Relationship between bubble fluid flow observation and mixing effects Due to high flow rates of the bottom blown gas in experiments of this study, the mixing of the liquid bath is mainly contributed from the turbulence of liquid flow inside the vessel. Actually, the intensity of the turbulence can not be measured easily. Therefore, the mixing time was defined and measured in this study to investigate the effect of the gas bottom blowing conditions on the mixing efficiency of the liquid bath. Therefore, the results above indicate that when the tuyere size became smaller and the gas flow rate increased, the bubble size decreased, the invading depth increased, and the spout height increased. However, the best choice for mixing was to use a 10.0 mm tuyere. This is because under the same gas flow rate, theoretical total blowing energy calculated by the 7.5 mm tuyere was
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Conclusions
3.3
(1) The bubble size decreased and the invading depth became deeper as the tuyere size decreased and the total gas flow rate increased. Consequently, the degree of stirred liquid bath became higher. (2) The experimental results of the mixing effects show that under any bottom blowing gas flow rates, the 10.0 mm tuyere had the shortest mixing time. Except for the 7.5 mm tuyere, the 10.0 mm, 12.5 mm, and 12.5 mm tuyeres had shorter mixing times and better mixing effects when the gas flow rate increased. (3) This study adopts four tuyeres in the square-corner placement, showing that the best combination for mixing iron phase in a smelter is to use a 10.0 mm tuyere and a gas flow rate of 480 NL/min, which has the appropriate intensity of the total blown energy and the degree of stirred liquid bath.
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