KR20080077359A - An improved lance for ld steelmaking - Google Patents

Abstract

An improved lance for LD steelmaking comprises a plurality of peripheral supersonic nozzles provided with a single inlet high pressure gas supply line and a central nozzle. The central nozzle is a subsonic nozzle provided with a separate low pressure gas supply line (1) independent of the high pressure gas supply line (2) for the peripheral nozzles. The flow rate through the central subsonic nozzle is controllable for varying generation of liquid metal droplets during the blow, according to the process requirement.

Description

Improved Lance for Eld Steelmaking {AN IMPROVED LANCE FOR LD STEELMAKING}

The present invention relates generally to an improved lance for LD steelmaking. In particular, the present invention provides a multi-hole lance design with a central separately-controllable subsonic nozzle for varying the production of liquid metal droplets according to process requirements. ).

Steel is produced through many processes, such as the basic oxygen furnace, electric arc furnace and Kaldo process. Among them, the basic oxygen furnace or LD steelmaking method is widely used all over the world due to the efficiency of the process and the quality of the steel produced. The LD steelmaking method is a refining process of liquid pig iron containing carbon, phosphorus, magnesium, manganese, aluminum and the like as a major impurity with a very high ratio of iron. The impurities are removed by an oxidation reaction using gaseous oxygen as the oxidant. The oxygen gas is injected into the LD vessel through a water-cooled lance with a copper head by multiple supersonic jets. Argon gas is also injected through pipes to carry air (tuyres) at the bottom of the vessel to stir the liquid metal completely. The process of injecting oxygen gas from the upper portion of the vessel through the lance and injecting argon gas through the bottom of the vessel is called a combined blowing process. The refining process in the LD vessel can be summarized in the following way. Liquid pig iron is injected into the container along with metal scraps. Most of the reactions occurring in the LD vessel are exothermic and the metal scraps can be easily dissolved because the overall LD steelmaking process is an auto-generation process (ie no heat supply from outside). Also as flux flux calcium monoxide (CaO) is added according to the required base ratio defined as the weight ratio of calcium monoxide to silicon dioxide (SiO ₂ ) and the blowing of oxygen gas over the liquid metal begins. The impurities are oxidized and oxides other than carbon oxides form a liquid slag that floats on the liquid metal. Carbon is oxidized to carbon monoxide (CO) through the liquid slag. This causes the slag layer to increase in volume and form what is commonly referred to as "slag foam." The slag foam includes liquid slag and liquid metal droplets ejected into the vessel by impinging an oxygen jet on the liquid metal surface and gases released from the liquid metal. The foam thus formed completely covers the lance head and partially covers the lance itself, taking up a large volume of the container. The foam creates a large interfacial region between the liquid metal and the slag thereby promoting interfacial reactions such as dephosphorization.

The control of the oxygen lance is essential because the LD steelmaking method is very dynamic and the conditions in the vessel are constantly changing during the oxygen injection period. Therefore, the oxygen lance is operated with different heights of the lance to control the impact strength of the supersonic jet. The height of the lance is defined as the distance of the lance tip to the flat liquid metal surface before the start of spraying. At the start of the injection, the steelmaker's main concern is to quickly form liquid slag and completely dissolve the charged calcium monoxide (CaO) in the vessel. It can be seen that strong injection or low lance height would be disadvantageous at this stage since the oxidation of carbon is undesirable. Thus, the lance is operated at a higher height, for example an initial lance height of 2.2 m.

During the initial period, the slag begins to form with the necessary chemical and physical features. Currently, only foamed slag promotes significant dephosphorization reactions by increasing the interface area between the slag and the metal, thus oxidizing carbon to produce more carbon monoxide (CO) gas, making the foamed slag. It is necessary. Thus, the lance height is reduced to provide a strong injection. The reduced height is about 1.5 m. As long as the dephosphorization reaction is involved at this stage, the generation of metal droplets is also very important. Primarily, the lance is operated at this short height so that most injections can promote the oxidation of carbon.

During the final injection stage, the carbon content in the steel is very low and the generation of carbon monoxide (CO) gas is greatly reduced. Since the slag does not generate carbon monoxide gas, it is no longer in the form of a bubble, and it can be understood that a thick liquid slag layer is formed on the metal surface. Strong spraying and the generation of liquid metal droplets at this stage are undesirable for the same reasons mentioned in the pre-spraying step. Thus, the height of the lance is increased back to the height of the initial lance to provide a weaker injection.

Through the above description, it is clear that the physical requirements of the lance change completely during the injection into the LD vessel. In some stages of spraying, the generation of droplets is very important, but in some other stages the generation of liquid metal droplets can adversely or detrimentally operate the LD vessel. It is clear that the lance plays a much greater role than simply providing oxygen gas into the vessel. Proper design of the lance and control during injection can greatly improve the efficiency of the steelmaking process and thereby enhance the quality of the steel produced.

The lance has a detachable head made of copper and with fixed nozzles. Through nozzles oxygen is injected into the vessel at supersonic speeds in the range of Mach 2.0-2.4. The number of supersonic nozzles in the lance is determined based on the size of the container, the dosage, and other operating conditions. A typical lance can have six supersonic nozzles inclined 17.5 ^o from the longitudinal axis to minimize jet agglomeration. The nozzles are designed to produce a supersonic jet with a release rate of Mach 2.2. All nozzles have one oxygen supply with a pressure of 13.5 bar. The lance used is water cooled to prevent damage from high temperatures in the LD vessel.

There is a need to improve the dephosphorization reaction in the LD vessel. As already mentioned, the lance structure and control during blow will have a significant impact on the quality of the steelmaking process and the steel produced.

One object of the present invention is to improve the formation of liquid metal droplets so as to increase the slag-metal interface region for improving the dephosphorization reaction in the LD vessel. Since dephosphorization is essentially an interfacial reaction between the slag and the metal, increasing the metal droplets enhances the efficiency of dephosphorization. Therefore, in the present invention, efforts have been made to improve the droplet generation in the LD vessel. The metal droplet formation is essentially a function of the lance. As such, the function of the oxygen jet must be considered very carefully under steelmaking conditions or very similar conditions in order to improve the production of the metal droplets. The provision of a central hole in the oxygen lance is known to produce many metal droplets and cause spitting. Spitting is disadvantageous because it may cause blockage of the container inlet and further shorten the life of the lance and the container lining. Thus, although the center hole can produce many droplets, it also has disadvantages.

Apart from improving the droplet generation, the central hole further has further advantages which are not known so far in the steel industry. The influence of high density slag foam on the supersonic jet characteristics in the LD vessel was considered. It is known that the slag foam absorbs all the momemtum provided by the oxygen jet and the jet loses its momentum completely to the slag. As such, existing knowledge of supersonic oxygen jet characteristics in the LD vessel may be considered to be misleading. Although the droplet generation studies conducted using Hydrodynamic Models of LD vessels do not reveal the true droplet production mechanism within the LD vessel, they provide a basis for improving understanding of droplet formation. . Because peripheral jets are exposed to the slag foam, the peripheral jets are expected to lose all momentum to the slag layer through the jet-slag foam interface. The gas jet does not have enough momentum to reach the molten metal surface and thus cannot produce as much metal droplets as needed.

However, as the present theory suggests, the central jet will be less or less wrapped by slag foam as compared to the surrounding jet. The reason is that the peripheral jet will protect the central jet and serve as a protective cover for the central jet from high density slag foam. Moreover, there is positive pressure due to the presence of the central jet and this positive pressure will also push some droplet entrainment of the slag foam into the space between the surrounding jets. This means that the central jet will not lose its own momentum to the slag layer and will reach the metal surface with concentrated momentum. That is, concentrated momentum with very high velocity will destroy the metal surface in order to produce many metal droplets needed to enhance the dephosphorization.

Therefore, it is clear that having a central jet would be beneficial to increase the production of metal droplets that could improve the rate of dephosphorization.

As mentioned above, if the foamed slag is not present during the initial and final stages of spraying, the central jet will cause massive spitting, ie the release of liquid metal through the vessel inlet. Therefore, it is not desirable to have a very strong injection through the center hole during the whole process of the LD steelmaking method. Since there is no protection from the slag foam, spitting or the generation of strong metal droplets during the initial and final stages of spraying will damage the lance. The presence of the slag foam slows down the formation of the metal droplets and protects the lance and the container refractory from collision of the metal droplets. It is evident from the discussion that having a strong jet through the central hole acts disadvantageously during the two stages of jetting.

If the supersonic nozzle is operated at a pressure ratio lower than the designed pressure ratio, in other words, if the nozzle is sprayed less so that the flow rate is reduced to avoid spitting during the initial stage, the pressure, velocity, Impacts or strong discontinuities in temperature and density of the gas can occur within the diverging portion of the nozzle itself. Such impacts formed at the diverging portion will severely affect the performance of the supersonic nozzle and will significantly reduce the life of the nozzle. Moreover, such impacts formed within the branching of the nozzle under steelmaking conditions can absorb hot slag foam and metal droplets into the nozzle and cause severe corrosion and failure of the lance. It is evident that the supersonic nozzle does not allow for the considerable amount of flow control required at the different stages of the LD steelmaking process.

Due to the problems to be considered above, in the present invention it can be derived to have a subsonic nozzle, ie a nozzle with a converging part, which makes it easier to control the flow rate and by varying the supply pressure The flow rate of can also be obtained. Moreover, the problem of shock formation does not exist in the nozzle providing subsonic speed. The description also makes it clear that it is not possible to control the flow rate through the center hole only if all the nozzles have the same gas supply line. As mentioned above, the generation of droplets only needs to be increased during the intermediate duration of the injection, and the production of many droplets during the initial and final stages of injection is undesirable. For the operation of such lances, flow rate control through the center hole is required and as mentioned above, control of the flow rate through the center hole is not possible with the same oxygen gas supply for all nozzles. Thus, in the present invention, an independent and controllable gas supply is provided for the central hole. All six other peripheral supersonic nozzles can share a high pressure gas supply.

As such, the present invention includes a plurality of peripheral supersonic nozzles having a high pressure gas supply line of a single inlet and one central nozzle, wherein the central nozzle is a subsonic nozzle having a separate low pressure gas supply line. The flow rate passing through provides an improved lance for LD steelmaking, characterized in that it is controllable to change metal droplet generation in accordance with process requirements during injection.

1 schematically shows an arrangement of a six-hole lance design,

2 shows a typical geometrical arrangement of a supersonic nozzle,

3 shows a schematic view of an LD container,

4 schematically shows a seven-hole lance with a separate air supply line used in hydrodynamic model experiments, FIG.

Figure 5 (a) is a view showing the degree of droplet generation in the case of a conventional 6-nozzle lance,

Figure 5 (b) is a view showing the degree of generation of droplets in the case of the inventors 7-hole lance,

6 shows a schematic representation of a droplet generation mechanism;

7 is a graph showing droplet generation rates of 7-hole lances having different flow rates,

8 is a diagram illustrating a calculation model and a mesh used in a mathematical simulation;

9 shows a near appearance for nozzles;

FIG. 10 shows velocity contours for a 7-hole lance with a 17.5 ^o tilt angle when vessel walls and metal surface are present, FIG.

11 shows a temperature profile due to a collision in nozzles with an angle of 17.5 ^o ,

12 is a velocity contour showing a collision location on a metal surface;

13 shows the velocity profile at different axial positions (a) X = 0.5m, (b) X = 1.0m, (c) X = -1.5m, (d) X = 2.0m,

14 shows a schematic diagram of a domain with boundary conditions used for high density environmental simulation;

15 is a plot of the mixing density contour near the nozzle outlet at any time;

16 shows momentum flow contours at different axial positions (a) nozzle outlet, (b) X = 0.5m, (c) X = 1.5m, and (d) X = 2.5m,

17 shows a schematic representation of a seven-hole lance structure.

Since it can be seen that the central hole will increase the generation of droplets, the droplet generation mechanism is a hydrodynamic model for the 1: 6 scale scale model with the central hole as shown in the schematic diagram of FIG. 3. ) Through experiments. A 1: 6 scaled down container model of plexiglass was used. Existing scale models and proposed lance structures are designed to study the advantages of the central hole in increasing droplet generation.

The top of the container is made of stainless steel, and the cylinder and bottom of the container are made of plexiglass to visualize the experiments. The lance is made of copper with the flexibility to design the lance tip differently for research.

The reduced lance as shown in FIG. 4 is designed to have six peripheral nozzles and one central nozzle. There are two separate air lines, where line 1 is connected to all six outer peripheral nozzles, while line 2 is connected to the central nozzle. The flow through the central nozzle is individually controlled by a series of pressure regulators and a set of air flow rotameters connected in series. On the other hand, the flow through the six peripheral nozzles is controlled through another pressure regulator and an air flow rotameter. By using two different lance tips 3, the inclination of the peripheral nozzles with respect to the central axis was investigated at 17.5 ° (as is actually present) and also 22 °.

The droplet generation mechanisms were investigated when all seven holes were in operation and compared with the case with only six peripheral nozzles. 5 (a) and 5 (b), the intensity of droplet generation is shown for each of spraying through only the peripheral nozzles and spraying through all seven holes. It can be seen visually that operating the central hole with peripheral nozzles increases the droplet generation even more than operating with only the peripheral nozzles.

It was observed during the experiment that there was a critical flow rate after the onset of droplet generation began. The mechanism for the accelerated droplet generation rate due to the presence of the central jet is illustrated schematically in FIG. 6. The central jet impinges the liquid metal vertically and creates a strong depression in the center of the liquid surface. The depression thus created is substantially wavy and provides " lips out of the central water paddle " as shown schematically in FIG. Such water lips formed around the paddle are cleaved by the side jets and result in improved droplet production. The side jets also prevent the slag foam from entering the intermediate space between the surrounding jets in a real vessel, so that a central jet with high momentum reaches the metal bath surface and is schematically illustrated in FIG. 6. Enable droplet generation similar to that of

Quantification of droplet generation was studied to understand the optimum flow rates provided through the central nozzle to maximize the droplet generation rate. The droplet generation rate can be measured by placing a collecting pan having a volume of 400 * 100 * 50mm ³ and the measurements are performed on a new seven-hole lance with six existing nozzle lances and one central nozzle. It became. The pan dimensions are defined to allow for efficient droplet generation surrounding one nozzle with six peripheral nozzles. The droplet generation rate is expressed as the mass ratio (g / sec) of the droplets collected in the pan.

The droplet generation rate was studied for various flow rates through the central nozzle to select the optimum flow rate through the central nozzle to maximize the droplet generation. The flow rate ratio, X, is defined as the ratio of the flow rate through the central hole to the flow rate of one of the peripheral nozzles.

Referring to FIG. 7, the droplet generation ratio with respect to the flow rate ratio is shown. The flow rate through the central nozzle varies from a low rate of 25% to a high rate of 125%. An optimum flow rate through the central nozzle can be obtained by balancing the control of splashing and spitting due to bath spilling outside the vessel inlet and improved droplet generation. . It is very clear that the droplet generation rate is increased by gradually increasing the flow rate through the central hole. It is shown in FIG. 7 that when the flow rate ratio X given through the central nozzle is 100, the droplet generation nearly doubles and reaches its maximum. If this flow rate is exceeded, there is intense splashing and spitting outside the inlet of the LD water model, which is detrimental to the operation of the LD vessel. As such, the optimal flow rate ratio (X through the center hole) from the hydrodynamic model experiments is determined to maximize the droplet generation rate without splashing and spitting outside the vessel.

Numerical simulations were performed using the commercial fluid dynamics calculation software "FLUENT" to study the properties of the jet coming from the seven-hole lance having six peripheral holes and one center hole described above. The inclination angle of the surrounding jet is initially selected to be 17.5 °, which is the same as that of the conventional six-hole lance structure. For the above reasons, a central subsonic nozzle was added for the jet flow prediction.

  Only half of the total flow domain was simulated by separating the entire domain using the vertical intermediate plane of the vessel to reduce the computational time of the numerical analysis for the new lance structure. Thus, two complete supersonic jets and two semisonic jets were numerically simulated. The central subsonic jet was also simulated as half the jet. The dimensions of the supersonic nozzles of FIG. 2 are maintained at the previous dimensions (ie inlet diameter 32.7 mm, passage diameter 25.7 mm and outlet diameter 37.3 mm).

Since the optimum flow rate obtained from the hydrodynamic model experiment is 1 (unity), the subsonic nozzle is designed to have an outlet diameter (54 mm) larger than the outlet diameter (37.3 mm) of the surrounding supersonic nozzle. This is required to push the same mass flow rate through one of the supersonic nozzles and the central subsonic nozzle.

In order to accommodate a larger central nozzle, the lance pipe diameter must be increased to 100 mm compared to conventional lance dimensions. The volume flow rate through the central subsonic nozzle is maintained about the same as the volume flow rate of one of the surrounding supersonic jets. This means that the mass flow rate through one of the surrounding supersonic nozzles is different compared to the central subsonic nozzle. This is due to the fact that the nozzle outlet temperature drops to 150K due to the supersonic flow at the outer nozzles. This results in a much higher gas density at the outlet of the supersonic nozzle if the pressures are nearly the same everywhere in the vessel. Subsonic central jets do not reach such low temperatures at the nozzle outlet.

The ratio between the flow rate through one supersonic nozzle and the flow rate through the subsonic nozzle is maintained as a variable because one wants to change the flow through the central subsonic nozzle during injection. In order to keep the numerical results small, it was decided to study the flow caused by the jet for only two volume flow rate ratios. The two volume flow rate ratios were chosen to be 1.0 and 0.5. The simulation result for the volume flow rate ratio 1.0 is as follows.

8 and 9 illustrate a calculation model and a mesh used for numerical simulation of the seven-hole lance structure proposed above. More than 1.3 million grid nodes were used in the simulation of jet flow. The simulation was run with a k-ε standard model. Twelve processors with one teraflop Linux cluster were used for the simulation and it took about 72-80 times to complete one flow simulation. It is well known that the k-ε turbulence model predicts the flow characteristics of multiple jets with a slight deviation from the actual flow, but the deviations are not large. However, it is easy to get a reasonable solution quickly with a k-ε model with short computation time. The k-ε model is used for the same reason as above.

Referring to FIG. 10, for a seven-hole lance, the velocity contour curve in the plane of symmetry is shown in the presence of the vessel wall and the metal surface with respect to the tilt angle of 17.5 ° of the peripheral nozzles. In numerical simulations, the metal surface is assumed to be a horizontal layer without pressure. It can be seen from FIG. 10 that the jets faithfully follow their geometric path and the interaction between them is small. It can be seen from FIG. 10 that the jets only interact at medium altitudes. There is little interaction of the jets near the metal surface. This is due to the central stagnation zone of the metal surface. Higher stagnation pressure in this region pushes the jets away and reduces cohesion.

Referring to Figure 11, the impacts formed at the nozzle end of the seven-hole lance structure are shown by a temperature contour curve. It can also be seen that there are smaller impacts at the exit of the subsonic nozzle. This is due to the temperature difference and slight pressure difference between the ambient atmosphere and the nozzle outlet. This can be reduced by increasing the angle of the converging portion of the nozzle. In this simulation, the angle is kept at 10 degrees.

With reference to FIG. 12, the velocity contour curve is shown in a plane of symmetry to indicate the location of impact of the jets on a metal surface. The geometric radiation of the jets is also shown on the liquid metal surface by dark circles. It can be seen that the jets follow an almost geometric path and the agglomeration is minimal due to the presence of the center jet and the stagnation area at the bottom. In Fig. 12 the velocity contour curve is only shown for speeds less than 150 m / s. It can be observed that the supersonic jets and the central subsonic jet arrive at the liquid metal bath at about the same speed, although the outlet speeds of the respective nozzles are different. The speeds near the metal bath are comparable since the subsonic nozzle outlet diameter (54 mm) is larger than the supersonic nozzle outlet diameter (37.3 mm).

Referring to Figure 13, the velocity contour curves at different axial distances from the nozzle tip for a 7-hole lance are shown. It can be seen from FIG. 13 that there are very few interactions between the jets up to an axial distance of 1 m. At a distance of 1.5 m there is considerable interaction between the jets. However, the bottom stagnation area pushes the jets away and the cohesion is reduced at 2m. The streaks shown in FIG. 13 (d) are due to the presence of the central jet.

The gas in the central jet cannot pass through the metal surface and must pass through the surrounding supersonic jets (in the simulation). This kind of flow characteristics may not occur in a real vessel because the metal surface in the simulation assumes a flat wall without pressure. The impact of the central jet in the LD vessel will create a depression, which will completely change the flow characteristics.

One jet results are discussed here to explain the effect of slag foam on the jet properties. A suitable range of possible ambient density values (foam / emulsion) in the LD vessel can be calculated by assuming a uniform decarburization ratio during the injection. The average slag volume fraction present in the foam in the container will range from 12-15%. This results in an average density around 360-450 Kg / m ³ .

The numerical domain and boundary conditions used are shown in FIG. 14. The diameter of the vessel required for a single presymmetric nozzle is calculated by using 1/6 of the original vessel cross section (since only one of the six nozzles is simulated). Moreover, the liquid metal surface is assumed to be a flat wall without shear stress. The height of the lance (the distance between the liquid metal surface and the nozzle tip) is chosen to be 3.5 m to investigate the action of the jet on the long axial distance. The actual lance height in the vessel varies from 1.5 to 2.2 m.

The simulation is performed using two-dimensional line-symmetric variable RANS with a volume of fluid polyphase model to track the boundaries between each phases. There is no difference between oxygen and carbon monoxide. Thus only one gas phase is considered. The actual k-ε turbulence model is used to terminate the equation system. The PISO algorithm is used for pressure-velocity coupling. The second order upwind discretization scheme is used for all other flow variables except for the temperature at which the power law scheme is used. The average slag volume fraction (15%) calculated from the stable decarburization rate is patched to the vessel domain as an initial guess. During the calculation, the slag moves freely throughout the domain according to local flow conditions, unlike the previous simulation. In addition, when the gas jet enters a stationary atmosphere, surface tension is not included in the simulation, and a high velocity gas jet causes flow to the atmosphere.

Due to the momentum delivered to the atmosphere, the surrounding fluid adjacent to the jet boundary begins to move in the main flow direction of the jet fluid. Thus, the surrounding fluid at adjacent locations moves towards the jet due to the flow caused by the jet. Atmospheric slag rushes towards the jet boundary due to the flow caused by the jet. Here, slag accumulates and the volume fraction / local density increases. Momentum delivered from the jet moves the slag slowly, and the slag covers the high speed jet core. A slag foam density contour curve near the nozzle tip is shown in FIG. 15 to show the slag accumulation at the nozzle tip and the movement of the slag along the jet.

Synthetic momentum flow rate (ρV) at different axial positions at any particular time is shown in FIG. 16. It is worth noting that the maximum momentum flow rate, as shown in FIG. 16, does not occur in the jet axis but occurs in a radial direction away from it.

 The high velocity core of the jet continuously pushes momentum momentarily forward and diffusely into the front layer of the jet. The speed at that axis is still maximum at any axis position.

Thus, the diffuse transfer of axial momentum in the radial direction will be towards the shear layer in the jet axis. Since the jet is diverging, the spin velocity v will be towards the shear layer in the jet, so that the net transfer of momentum in the radial direction (ρuv) will also be towards the shear layer.

Because the density of the shear layer fluid (slag + gas) is much higher than that of the jet gas, the shear layer is enormously speeded up, such as the storage of thermal energy in a reservoir with higher and special heat / temperature capacitance without significant temperature differences. Higher momentum fluxes can be stored without increasing. Moreover, gravity is helping the slag layer to gain momentum. That is, the slag layer moves in the direction of gravity acceleration.

The momentum transferred from the high velocity jet core to the high density shear layer will add to the momentum imparted by the gravitational acceleration. From the plot of the momentum flux rates shown in FIG. 16, it can be seen that the momentum flux ratio in the high density shear layer is at least a second order size higher than the high speed jet core. The discussion above shows that the high density slag-gas foam present in the LD vessel confers some interesting flow characteristics of supersonic gas jets. The understanding of the depressions created during the injection can be completely changed.

It is important to note that multiple supersonic jets in LD steel vessels will also be constrained to those properties mentioned above due to the presence of high density slag foam. It is clear from the above discussion that the surrounding supersonic jets will lose all of their momentum to the adjacent slag layer. The slag layers will move into the liquid metal pool with very high momentum and create complex depression contours. However, in the new seven-hole structure, the pressure in space between the supersonic jets will prevent entrainment into this region due to the presence of a central jet.

Thus, the central jet will not or minimally recognize the slag foam and, unlike the supersonic jets, will not completely lose its momentum to the slag foam. Thus, the central jet is expected to reach the liquid metal surface at a very high speed compared to the supersonic jets and generate more droplets. The production of this kind of droplets is not possible with a six-hole structure because all six supersonic jets will completely lose their momentum in the relatively slow moving slag layer. It is clear from the above discussion that the seven-hole structure is more efficient than the conventional six-hole structure.

One embodiment of the present invention having a seven-hole structure is shown schematically in FIG. 17 shows one central jet and six peripheral supersonic jets. The central jet is controlled separately by one separate gas supply line, while the peripheral nozzles have one injection gas supply line. The gas supply line for the six peripheral supersonic jets and the gas supply line for the central subsonic jet are equipped with two separate control valves with actuators. Since the central jet has a subsonic nozzle, the central jet can be operated during different stages of injection, and the flow rate can also be changed depending on the process conditions.

The flow rate through the central subsonic nozzle is maintained as a variable. In numerical and experimental simulations, the volume flow rate ratio of one of the center subsonic nozzle and the supersonic nozzles is maintained as a variable. The maximum value of the ratio remains as 1 in numerical simulations. Based on this, the dimensions of the central nozzle are calculated. The outlet diameter of the subsonic nozzle is 54 mm and the outlet diameter of the supersonic nozzle is 37.3 mm (old value).

The angle of inclination of the surrounding jets is maintained at 17.5 °. In order to confirm the performance of a seven-hole lance with a modified angle with respect to the surrounding jets, a study was performed on the jet layout with the slope of the side jets 22 °. Moreover, the inclination angles of the surrounding supersonic nozzles can be equal or alternating. Alternately changing tilt angles can have distinct advantages. As mentioned earlier, wrapping the slag foam over the jet surface slows down the gas jet and the slag layer surrounding the jet reaches the liquid metal surface with high momentum. The impact of the slag layer on the liquid metal will produce many slag droplets in the liquid metal and create an interface region for the slag-metal reaction. By maintaining alternating angles of inclination, the surface area of the jet covered by the slag layer can be increased and more slag can reach the liquid metal with high momentum. This is expected to improve interfacial reactions such as dephosphorization.

Through numerical and experimental simulations, it was also concluded that the following seven-hole lance structure is the preferred embodiment by considering the different dynamics in the LD steelmaking vessel. The structure is much better than the existing structure and can perform better in steelmaking conditions.

Six peripheral supersonic nozzles with one gas supply line.

Larger central subsonic nozzle with a separate gas supply line.

The central nozzle can be operated during different stages of injection if necessary, and the flow rate can also be easily changed without adversely affecting the nozzle life. The inclination angle of the surrounding jets is maintained at 17.5 °. This angle can be increased by additional modifications.

Advantageous features of the present invention are to provide better on / off control of the central nozzle during injection due to the separate gas supply line. This will strongly control the spitting of the metal droplets away from the vessel.

Larger subsonic nozzles in the center of the lance head are useful for controlling the flow of oxygen through the center nozzle. This means more flexibility and control over the process.

The scheme provides for increased metal droplet generation. Since the central jet is protected from slag foam by surrounding jets, the central jet reaches a metal bath at high speed and promotes increased droplet generation.

This approach improves the efficiency in dephosphorization. Improved metal droplet generation will particularly promote interfacial reactions such as dephosphorization.

Although the present invention has been described with reference to specific embodiments which are helpful for understanding, the present invention is not limited to these embodiments. It is possible to change the detailed configuration and form by those skilled in the art without departing from the object and scope of the present invention. It is shown that the purpose for improving dephosphorization in LD steelmaking can be achieved by increasing metal droplet generation. In other process industries where there may be other objects achievable by increasing liquid droplet generation, the manner of the present invention can be used.

Claims (7)

A plurality of peripheral supersonic nozzles having a high pressure gas supply line of a single inlet; And one central nozzle; The central nozzle is a subsonic nozzle with a separate low pressure gas supply line; The flow rate through the central nozzle is controllable to vary the generation of liquid metal droplets in accordance with process requirements during injection. 10. The improved lance of claim 1 wherein said lance comprises six peripheral supersonic nozzles and a central subsonic nozzle. 3. The improved lance according to claim 1 or 2, wherein the central subsonic nozzle has only a converging portion to easily control the flow rate through the converging portion. 4. The improved lance of claim 1 wherein the central subsonic nozzle has an outlet diameter that is greater than the outlet diameter of the peripheral supersonic nozzle. 5. 2. The gas supply line for the plurality of peripheral supersonic nozzles and the gas supply line for the central subsonic nozzle are provided with two separate control valves with actuators to control the flow therethrough. Improved lance made. 6. The control valve according to claim 5, wherein the control valve provided for the central subsonic nozzle changes the flow through it to prevent spitting during the initial stage of injection, and changes the intensity of the metal droplet generation rate during the injection. An improved lance characterized by controlling the dynamics of reactions. 7. The improved lance of claim 1 wherein the peripheral supersonic nozzles can have an angle of inclination that varies equally or alternately from the longitudinal axis of the lance.

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