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Design and application of five-hole oxygen lance nozzle for 100 t converter

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Design and application of five-hole oxygen lance nozzle for 100 t converter

Abstract: In view of the problems of poor slag removal effect and serious slag sticking to steel in the oxygen lance in the smelting of low silicon molten iron, a five-hole oxygen lance nozzle was designed and developed based on the theory of compressible fluid and the principle of interaction between jet and molten pool. The main process parameters are: The angle between the nozzle holes is 13°, Ma 2.0, the throat diameter is 36.8 mm, the outlet diameter is 47.8 mm, the design oxygen pressure is 0.80 MPa, and the design oxygen supply intensity is 3.8 m³/(min·t). The oxygen lance position is controlled at 1.3~1.9m, and the molten pool impact depth, impact area and mixing time are all within a reasonable range. Production practice shows that using a five-hole nozzle shortens the oxygen blowing time by 0.5 min, reduces oxygen consumption by 1.1 m³/t, increases the dephosphorization rate by 4.1 percentage points, reduces the FeO content in the final slag by 1.2 percentage points, and increases the steel tapping rate by 1.7 percentage points in one carbon drawing. , basically solved the problems existing in converter low-silicon molten iron smelting, and the converter technical indicators have been significantly improved.

Keywords: converter; oxygen lance; five-hole nozzle; design; application

In the converter steelmaking process, the oxygen lance is a key equipment that provides high-speed oxygen jet to the converter. The structural parameters and operating parameters of the oxygen lance nozzle directly affect technical and economic indicators such as steelmaking output, quality, consumption and cost. Chenggang 100t converter increases the oxygen jet impact area by increasing the number of nozzle holes and improves the slag-removing capacity. Panzhihua Iron and Steel Co., Ltd.’s 200t converter and Tangshan Iron and Steel Co., Ltd.’s 65t converter both improve the slagging effect by expanding the angle between the oxygen lance nozzles. In order to solve the problems of poor slagging effect of the four-hole oxygen lance nozzle in smelting, the oxygen lance sticking to slag and steel, and affecting the production rhythm. The Long Products Division designed and developed a five-hole oxygen lance nozzle based on the compressible fluid theory and on-site production conditions, and optimized key parameters such as the nozzle Mach number, operating pressure, nozzle hole angle and nozzle hole size. Production practice shows that the five-hole nozzle basically solves the above problems and has better blowing effect.

1 Basic conditions for converter steelmaking

The steelmaking production line includes: hot metal stirring and desulfurization equipment, 3 double-blown converters, 2 LF refining furnaces, and 4 square (rectangular) billet continuous casting machines. It mainly produces steel for construction, angle steel, mining steel and metal products. The top blowing oxygen supply of the converter adopts 273 oxygen lance equipped with four-hole oxygen lance nozzle, the automatic steelmaking adopts the sub-lance + secondary model technology, and the bottom blowing of the converter is equipped with 6 double-ring seam bottom blowing guns arranged symmetrically. The basic process parameters of the converter and the conditions of molten iron entering the furnace are shown in Table 1 and Table 2 respectively. The composition and temperature of molten iron fluctuate widely. The average silicon content of molten iron is 0.39%, and the proportion of low-silicon molten iron reaches more than 70%. Converter smelting using four-hole nozzles has problems such as poor slag removal and oxygen lance sticking to slag and steel, indicating that the four-hole oxygen lance nozzles are not suitable for low-silicon hot metal smelting, and it is necessary to optimize and improve the oxygen lance nozzles.

Table 1 Basic process parameters of converter

Project Parameters
average steel tapping 120t
Furnace volume ratio 0.92  m³/t
Furnace height 9.000 mm
Furnace shell outer diameter 6.450 mm
Furnace mouth diameter 2.800 mm
molten pool diameter 4.660 mm
molten pool depth 1.450 mm
Bottom blow flow 200~600  m³/h
Oxygen flow 18000~27000m³/h
working oxygen pressure 0.8~1.0 MPa
oxygen main pressure 1.8~1.9 MPa
Oxygen blowing time 12~14 min

Table 2 Main components and temperature of molten iron

project Mass percentage/% Molten iron temperature/℃
C Si S Mn P
minimum value 3.50 0.07 0.090 0.03 0.070 1253
maximum value 5.30 1.12 0.120 0.35 0.115 1457
average value 4.70 0.39 0.036 0.08 0.096 1360

2 Five-hole nozzle design

2.1 Nozzle Mach number design

According to the compressible fluid theory, the size of the Mach number Ma determines the speed of the airflow at the nozzle outlet. The relationship between the oxygen jet velocity and oxygen pressure and Ma is shown in Figure 1.

Design and application of five-hole oxygen lance nozzle for 100 t converter

Figure 1 Relationship between compressible fluid velocity, pressure and Mach number

As Ma increases, both the jet velocity and oxygen pressure increase significantly. When Ma increases to about 2.0, the increase in jet velocity decreases significantly, while the increase in oxygen pressure increases significantly. Based on the experience of similar converters at home and abroad, Ma is generally selected from 1.98 to 2.2. Based on the long product converter furnace type and early production practice, the Ma of the five-hole nozzle was selected as 2.0.

2.2 Design of other parameters of nozzle

Based on the compressible fluid theory and nozzle design principles, combined with the actual converter production of the long product department, the main process parameters of the five-hole nozzle are shown in Table 3.

Compared with the four-hole nozzle, the nozzle angle of the five-hole nozzle becomes larger, the Ma decreases, the design oxygen pressure decreases, and the oxygen supply intensity remains basically the same. The design purpose of the five-hole nozzle is to reduce the impact depth of the nozzle on the molten pool by reducing the oxygen pressure and nozzle outlet speed while maintaining the oxygen supply intensity, and appropriately increase the impact area of the molten pool. To improve the slagging effect during the smelting process of low silicon molten iron.

Table 3 Main process parameters of nozzle

Item Angle/(°)  Ma Throat diameter/mm Outlet diameter/mm Design oxygen pressure/MPa Oxygen supply intensity/(m³·min-1·t-l)
Five-hole nozzle 13 2.0 36.8 47.8 0.80 3.8
Four hole nozzle 12.5 2.05 41 54.4 0.88 3.9

2.3 Oxygen gun position control

The literature provides the basic oxygen lance gun position calculation formula:

Design and application of five-hole oxygen lance nozzle for 100 t converter

In the formula: Hj is the basic oxygen lance position, mm; dy is the diameter when the air flow meets the molten steel, mm, dy=dr/9; dr is the diameter of the molten pool, mm; de is the diameter of the nozzle outlet, mm. αe is the nozzle expansion angle, (°).

Substituting the nozzle parameters into equation (1), the basic gun position of the five-hole nozzle is 1787mm, which can be controlled according to 1800 mm in actual production.

For the oxygen lance position control of the multi-hole nozzle, combined with theoretical calculations and jet test measured data, the oxygen lance position control range for the best smelting effect is (25~40) de, 1195~1912 mm, and the actual production is 1200~1900 mm . The oxygen lance position of the five-hole nozzle is controlled from 1300 to 1900 mm, and the minimum is not less than 1200 mm. The principles are that the slag does not dry back, does not splash, quickly decarburizes, dephosphorizes, and desulfurizes, and the molten pool heats up quickly and evenly.

2.4 Effect of oxygen jet on molten pool

The impact depth and impact area of the molten pool are important indicators for evaluating the effect of oxygen jet on the molten pool. If the impact depth is insufficient, the oxygen absorption degree of the molten pool will be reduced, and the oxygen utilization rate and decarburization speed will be reduced. If the impact depth is too large, the furnace bottom will be easily damaged and slag formation will be affected. Therefore, the appropriate impact depth must be controlled to meet the requirements of the smelting process.

The impact depth of the oxygen jet on the molten pool is:

Design and application of five-hole oxygen lance nozzle for 100 t converter

In the formula: h is the impact depth, mm; H is the oxygen lance position, cm; p₀ is the stagnation pressure, MPa; d is the diameter of the throat, mm; θ is the angle between the nozzles, (°).

When the oxygen jet impacts the surface of the molten pool, a pit is formed on the surface of the molten pool. The shape of the pit mainly depends on the blowing pressure and gun position. The calculation formula for the impact area of the jet impacting the molten pool is:

Design and application of five-hole oxygen lance nozzle for 100 t converter

In the formula: S is the impact area, m²; d is the impact diameter, m; H₁ is the height of the gun position, m.

The stirring energy of the oxygen jet to the molten pool is

Design and application of five-hole oxygen lance nozzle for 100 t converter

In the formula: s is the impact energy of the jet on the molten slag, W/m³; V is the volume of the slag, m³; Q is the gas flow rate, m³/min; M is the gas molecular weight; n is the number of nozzle holes. de is the nozzle outlet diameter, m.

The calculation formula for the mixing time of the molten pool is:

Design and application of five-hole oxygen lance nozzle for 100 t converter

In the formula: r is the mixing time, s; L₀ is the molten pool depth, m.

According to equations (2) to (4), the impact depth and impact area of the oxygen jet on the molten pool under different gun positions are shown in Figure 2. The stirring kinetic energy and mixing time of the molten pool under different gun positions obtained according to equations (5)~(6) are shown in Figure 3.

When the oxygen gun position is 1200 and 1900 mm, the impact depth of the oxygen jet on the molten pool is 920 and 732 mm respectively, and the impact area is 0.80 and 1.78 m² respectively. Therefore, when the oxygen lance position is controlled between 1300 and 1900 mm, the impact depth and impact area of the oxygen jet remain within a reasonable range. The molten pool has good mixing and stirring effects, and the molten pool reacts quickly and smoothly, which is beneficial to improving oxygen utilization. Figure 3 shows that the reasonable control range of the oxygen lance gun position is 1300 to 1900 mm from the perspective of the stirring kinetic energy and mixing time of the molten pool under different gun positions.

Design and application of five-hole oxygen lance nozzle for 100 t converter

Figure 2 Impact depth and impact area of different oxygen lance gun positions

Design and application of five-hole oxygen lance nozzle for 100 t converter

Figure 3 Stirring kinetic energy and mixing time at different oxygen gun positions

3 Production and application effects

A five-hole nozzle test was carried out in a 100 t converter, and the test results were compared with the four-hole nozzle. The comparison of the main process indicators under the same molten iron conditions and molten iron consumption is shown in Table 4. When the silicon content of the molten iron is low, compared with the four-hole nozzle, the five-hole nozzle shortens the oxygen blowing time by 0.5 min, reduces backdrying during the blowing process, increases the thermal efficiency in the furnace, improves oxygen utilization, and reduces oxygen consumption by 1.1 m³/t. The impact area of the five-hole nozzle on the molten pool is increased, the reaction effect of the molten pool is significantly improved, the dephosphorization rate of the converter is increased from 81.5% to 85.6%, and the FeO content of the final slag is reduced from 18.56% to 17.36%. The tapping rate of one-time carbon drawing increased from 86.8% to about 88.5%, and the technical and economic indicators of the converter improved significantly.

Table 4 Comparison of main technical indicators of different nozzles

index Four-hole nozzle Five-hole nozzle comparison
Silicon content of molten iron/% 0.39 0.35 -0.04
Oxygen blowing time/min 13.9 13.4 -0.5
Oxygen consumption/(m³·t-l) 44.86 43.76 -1.1
Molten iron consumption/(kg·t-1) 935 930 -5
End temperature/℃ 1666 1662 -4
Dephosphorization rate/% 81.5 85.6 4.1
Nozzle survival/furnace 500 512 12
Final slag FeO content/% 18.56 17.36 1.2
One-time carbon tapping rate/% 86.8 88.5 1.7

4 Conclusion

(1) Based on the current hot metal conditions and the actual converter production, in order to improve the slag removal effect in the smelting process, a five-hole oxygen lance nozzle was designed and developed. The nozzle hole angle of the nozzle is 13°, Ma2.0, and the design oxygen pressure is 0.8 MPa.

(2) Analysis and calculation of the molten pool impact depth, impact area, stirring kinetic energy and mixing time show that the reasonable gun position range of the five-hole nozzle is 1300 ~ 1900 mm.

(3) Production practice shows that under the same production conditions, five-hole nozzles are compared with four-hole nozzles. The oxygen blowing time is shortened by 0.5 min, the oxygen consumption is reduced by 1.1 m³/t, the dephosphorization rate is increased by 4.1 percentage points, the FeO content of the final slag is reduced by 1.2 percentage points, and the one-time carbon drawing tapping rate is increased by 1.7 percentage points. The problems existing in converter low-silicon molten iron smelting have been basically solved, and the technical indicators of the converter have been significantly improved.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

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