JP2009516070A - 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

  In a broad sense, the present invention relates to an improved lance for LD steelmaking. In particular, the present invention relates to a multi-hole lance design with a central separately controllable subsonic nozzle to vary the formation of liquid metal droplets according to process requirements.

  Steel is produced by a number of processes such as a basic oxygen furnace (BOF) process, an electric arc furnace (EAF) process, and a cardo process. Of these, basic oxygen furnace (BOF) or LD steelmaking processes are now widely used around the world because of the effectiveness of the process and the quality of the steel produced. The LD steelmaking process is a refining process for liquid pig iron containing carbon, phosphorus, magnesium, manganese, aluminum and the like as main impurities together with a very high proportion of iron. These impurities are removed by an oxidation reaction using oxygen gas as an oxidizing agent. Oxygen gas is introduced into the LD vessel by a plurality of supersonic jets through a water cooling lance using a copper head. Furthermore, argon gas is introduced from the tuyere at the bottom of the container in order to completely stir the liquid metal. This process of blowing oxygen gas from the top through the lance and injecting argon from the bottom is called an upper bottom blowing process.

The refining process in the LD container can be summarized as follows. Liquid pig iron is put into a container together with metal scrap. Most of the reactions that occur in LD containers are exothermic reactions, and the entire LD steelmaking process is an automatic generation process, ie no external heat supply is required, so these metal scraps can be easily melted. According to the required value of basicity, defined as the weight ratio of lime to silicic acid (CaO / SiO ₂ ), lime as a flux (CaO) is also added and oxygen gas starts to be blown into the liquid metal. The Impurities are oxidized and oxides other than carbon oxides form a molten slag that floats on top of the liquid metal. The carbon is oxidized as carbon monoxide (CO) gas that passes through the molten slag. This increases the volume of the slag layer, forming what is commonly referred to as a “slag foam” (slag foam). The slag foam includes molten slag, gas generated from the liquid metal, and liquid metal droplets that are introduced into the container as the oxygen jet impinges on the liquid metal surface. A slag foam is thus formed, completely covering the lance head and partly the lance itself, occupying a large volume of the container. Slag foam forms a large interfacial region between the liquid metal and slag, which promotes interfacial reactions such as dephosphorization.

  Since the LD steelmaking process is extremely dynamic and the state in the container continuously changes during the oxygen blowing period, it is essential to control the oxygen lance. Thus, the oxygen lance is operated at different lance heights to control the intensity of the supersonic jet impact. The lance height is defined as the distance of the lance tip at any time relative to the flat liquid metal surface before the start of blowing. At the start of blowing, the steelmaker's main interest is to immediately form molten slag and completely dissolve the lime charged. It can be seen that lowering the hard blow or lance height is disadvantageous because carbon oxidation is not preferred at this stage. Thus, the lance is operated higher, for example the initial lance height is 2.2 m.

  During the initial period, the slag begins to form with the necessary chemical and physical properties. Next, it is necessary to produce foamy slag by producing more CO gas by oxidizing the carbon. This is because only foamy slag can increase the interfacial area between the slag and the metal, thereby promoting an important reaction of dephosphorization. Thus, the height of the lance is lowered to provide a hard blow. The lowered height can be approximately 1.5 m. At this stage, the formation of metal droplets is also very important as far as the dephosphorization reaction is concerned. In most cases, the lance is operated at this lower height for most blows to promote carbon oxidation.

  In the final stage of blowing, the carbon content of the steel is very low and the generation of CO gas is greatly reduced. It should be understood that because no CO gas is produced, the slag is no longer foamy and a thick liquid slag layer is formed on top of the metal surface. Hard blow and liquid metal droplet formation at this stage are undesirable for the same reasons as shown earlier in the blow. Thus, the lance height is increased again to the initial lance height to provide a softer blow.

  From the above discussion it is clear that the physical demands on the lance change completely during the blowing into the LD container. At some stage of blowing, the formation of droplets is of primary importance, and at some other stage, the formation of liquid metal droplets is disadvantageous and can be detrimental to the operation of the LD container. It is clear that the lance plays a much more important role as a device for supplying simple oxygen gas to the container. By appropriately performing the design of the lance and the control during blowing, the effect of the steelmaking process can be greatly improved, thereby improving the quality of the steel produced.

The lance is made of copper and has a detachable head to which the nozzle is fixed. Oxygen is blown into the container through the nozzle at supersonic speed in the range of Mach number 2.0 to 2.4. The number of lance supersonic nozzles is determined based on the dimensions of the container, the input mass, and other operating conditions. A typical lance can have six supersonic nozzles with an inclination angle of 17.5 ° from the vertical axis to minimize jet coalescence. The nozzle is designed to produce a supersonic jet with an exit Mach number of 2.2. All nozzles are independently supplied with oxygen at a pressure of 13.77 kgf / cm ² (13.5 bar). The lance used is water-cooled to protect it from the high temperature of the LD container.

  There is a need to improve dephosphorization in LD containers. As already mentioned, lance design and control during blowing have a great influence on the steelmaking process and the quality of the steel produced.

  One object of the present invention is to improve the formation of liquid metal droplets in order to increase the slag-metal interface area that promotes dephosphorization within the LD container. Since dephosphorization is essentially an interfacial reaction between slag and metal, increasing the number of metal droplets improves dephosphorization efficiency. Therefore, in the present invention, an effort is made to promote the generation of droplets in the LD container. The formation of metal droplets is essentially a function of the lance. Therefore, in order to promote the formation of metal droplets, the function of the oxygen jet needs to be carefully considered under steelmaking conditions or conditions very close thereto.

  It has been found that providing a central hole in the oxygen lance results in the formation of many metal droplets and spitting. Spitting is disadvantageous because it can result in blockage of the mouth of the container and further reduce the useful life of the lance and container lining. Thus, the central hole can produce many droplets, but also has drawbacks.

  In addition to facilitating droplet formation, the central hole has other advantages not previously known in the steel industry. The effect of high density slag foam based on the characteristics of supersonic jet in LD vessel was studied. The slag foam absorbs all the momentum supplied by the oxygen jet and the jet has been found to completely lose momentum relative to the slag. Therefore, current knowledge regarding the characteristics of supersonic oxygen jets in LD vessels is considered wrong. Although droplet generation studies conducted using a hydrodynamic model of the LD vessel do not reveal the true mechanism of droplet generation in the LD vessel, they are intended to facilitate understanding of droplet formation Provides the basis for As the surrounding jet is exposed to the slag foam, it is expected that all of the momentum will be lost to the slag layer via the jet-slag foam interface. Since the gas jet does not have sufficient momentum to reach the molten metal surface, it cannot produce metal droplets as needed.

  However, as this discussion suggests, the central jet is covered only slightly or not at all by the slag foam compared to the peripheral jet. The reason is that the peripheral jet covers the central jet and creates a protective covering from the dense slag foam to the central jet. In addition, there is a positive pressure due to the presence of the central jet, which also forces small entrainment of slag foam into the space between the peripheral jets. This is because the central jet does not lose momentum with respect to the slag layer, but it reaches the metal surface with a concentrated momentum, i.e. a high speed to tear the metal surface, and produces a metal drop that promotes dephosphorization, which is often required. To do.

  Thus, it is clear that having a central jet is advantageous in increasing the production of metal droplets that can improve the dephosphorization rate.

  As explained above, if there is no foamy slag during the first and last stages of blowing, the central jet creates a large amount of spitting, i.e. the liquid metal is ejected through the mouth of the container. It is therefore not advisable to have a very strong blow through the central hole during all stages of the LD steelmaking process. Large spitting or metal droplet formation during the first and last stages of blowing damages the lance as there is no protection from slag foam. The presence of slag foam is expected to reduce the velocity of the metal droplets and protect the lance and container refractories from metal droplet impact. It is clear from the above discussion that there is a strong blow through the central hole, which is disadvantageous during these two stages of blow.

  If the supersonic nozzle is operated at a pressure ratio lower than the design pressure ratio in order to reduce the flow rate to avoid spitting in the first stage, in other words, if nozzle blowing is reduced, the nozzle Gas pressure, velocity, temperature, and concentration shocks or strong disruptions can occur in their divergent areas. Such an impact in the divergent region can greatly affect the performance of the supersonic nozzle, greatly reducing the useful life of the nozzle. In addition, under steelmaking conditions, such impacts formed inside the diverging area of the nozzle can cause hot slag foam and metal droplets to be drawn into the nozzle, resulting in considerable corrosion and lance failure. There is. It is clear that it is impossible to significantly control the flow rate as needed at different stages of the LD steelmaking process via a supersonic nozzle.

  From the considerations given above, it has been found that the present invention comprises a subsonic nozzle, i.e. a nozzle with only a converging region. Using it, it is easy to control the flow rate, and a wide range of flow rates can be achieved by changing the supply pressure. In addition, there is no impact formation problem with nozzles that provide subsonic speeds. From this description it is also clear that if all nozzles have the same gas supply line, only the flow rate through the central hole cannot be controlled. As explained earlier, the formation of droplets only needs to be increased during the middle period of blowing, and it is not desirable that many droplets be produced at the beginning and end of the blowing. With respect to such a lance operation, it is necessary to control the flow rate through the central hole, which is impossible when the same oxygen gas is supplied to all the nozzles as described above. Thus, in the present invention, a separate controllable gas supply is provided for the central hole. All other six peripheral supersonic nozzles can have a shared high pressure gas supply.

  The present invention thus provides an improved lance for LD steelmaking comprising a plurality of peripheral supersonic nozzles with a single suction high pressure gas supply line and a central nozzle, the central nozzle being a separate low pressure gas supply. A subsonic nozzle having a line, the flow rate through the central subsonic nozzle can be controlled to produce a variety of liquid metal droplets being blown according to process requirements.

  Next, the present invention will be described with reference to the drawings.

  Since the central hole has been found to increase droplet generation, the mechanism of droplet generation is a hydrodynamic model experiment based on a 1: 6 reduced model with a central hole as shown in the schematic diagram of FIG. Researched through. A 1: 6 scale model of an LD container made with Plexiglas was used. Scale models of existing and proposed lance designs have been created to study the advantage of the central hole that increases droplet generation.

  The top of the container is made of stainless steel, and the cylinder and the bottom of the container are made of plexiglas because they need to be transparent to visualize the experiment. The lance is made of copper with the provision of lance ends of different designs for investigation.

  The reduced lance was designed with six peripheral nozzles with the central nozzle shown in FIG. There are two separate air lines, line 1 connected to all six outer peripheral nozzles, while line 2 is connected to the central nozzle. The flow through the central hole is individually controlled by a set of pressure regulators and air flow rotameters connected in series, whereas the flow through the six surrounding nozzles is another set of pressure regulators and air. Controlled by a flow rotameter. The inclination of the surrounding nozzle relative to the central axis was investigated at 17.5 ° and 22 ° (as it actually exists) by using two different lance tips 3.

  The mechanism of droplet generation was investigated when all seven holes were actually operating and compared with the case where only six peripheral nozzles were actually operating. In FIGS. 5 (a) and 5 (b), the strength of droplet generation is shown for each case blowing through only the peripheral nozzle, and for all seven holes. It can be visually understood that the range of droplet generation is much greater when the central hole with the peripheral nozzle is operating than the range of droplet generation with only the peripheral nozzle.

  During the experiment, it was observed that there was a critical flow rate at which droplet formation began. The mechanism by which the droplet generation rate is accelerated due to the presence of the central jet is schematically illustrated in FIG. The central jet impacts the liquid metal vertically and forms a large dent in the center of the liquid surface. The so-formed dent has a wave-like nature and forms a “wave tip outside the central puddle” as schematically shown in FIG. The tip of the water wave thus formed around the puddle is then torn by the side jet and promotes droplet formation. These side jets are also thought to prevent the slag foam from entering the central space between the peripheral jets in the actual vessel, thus preventing the central jet with its high momentum from reaching the metal bath surface. Ensuring that droplet production similar to that schematically shown in FIG. 6 is possible.

In order to understand the optimum value of the central nozzle flow rate for maximizing drop generation rate, quantification of drop generation was studied. The drop generation rate is measured by placing a collection pan with dimensions of 400 x 100 x 50 mm ³ and the measurement is carried out on a new 7-hole lance with the current 6-nozzle lance and the central nozzle. It was. The size of the collection pan was determined to surround one of the six peripheral nozzles and measure the effect of droplet formation. The droplet generation rate is expressed by the mass velocity (g / sec) of the droplet collected in the collecting dish.

  In order to select the optimal flow rate through the central nozzle that maximizes droplet generation, the rate of droplet generation was studied by varying the flow rate through the central nozzle. The flow ratio X is defined as the ratio of the flow rate through the center hole to the ratio of the flow rate of one of the peripheral nozzles.

  The drop production rate plotted against the flow rate ratio is shown in FIG. The flow rate through the central nozzle was varied from a low flow rate of 25% to a high flow rate of 125%.

  The optimum flow rate through the central nozzle is obtained by maintaining a balance between improved drop production and control of splashing and spitting by the bath flowing out of the vessel mouth. It was very clear that as the flow rate through the central hole increased, the drop generation rate improved. FIG. 7 shows that when the flow ratio X given through the central nozzle is 1 (100%), droplet generation is almost doubled and reaches a maximum value. If this flow rate is exceeded, there will be vigorous splashing and popping from the mouth of the water model of the LD container, which is harmful to the operation of the LD container. Thus, from an experiment with a hydrodynamic model, the optimal flow ratio X through the central hole was determined. The optimum flow rate ratio X maximizes the droplet generation rate without jumping out or splashing from the container.

  In order to study the characteristics of the jet exiting the 7-hole lance described above with 6 surrounding holes and 1 central hole, the numerical value is calculated using the commercially available fluid dynamics calculation software FLUENT. Simulation was performed. The tilt angle of the peripheral jet was selected to be 17.5 ° as an initial value. This is the same as the current 6-hole lance design. A central subsonic nozzle was added to perform jet flow prediction for the reasons previously discussed.

  In order to reduce the computation time of the numerical simulation for the new lance design, only half of the total flow area was simulated by dividing the entire area using a vertical midplane. Therefore, two full supersonic jets and two half supersonic jets were numerically simulated. The central subsonic jet was also simulated as a half jet. The dimensions of the supersonic nozzle of FIG. (2) were kept at the conventional dimensions, namely the inlet diameter 32.7 mm, the throat diameter 25.7 mm, and the outlet diameter 37.3 mm.

  Since the optimal flow ratio obtained from the hydrodynamic model experiment was 1, the subsonic nozzle was designed with a larger outlet diameter (54 mm) compared to the peripheral supersonic nozzle (37.3 mm diameter). This is necessary to push the same mass flow through one of the central subsonic nozzle and the supersonic nozzle.

  In order to accommodate the larger central nozzle, the lance pipe diameter had to be increased by 100 mm compared to existing lance dimensions. The volume flow through the central subsonic nozzle was kept approximately the same as one of the peripheral supersonic jets. This means that the mass flow rate through one of the peripheral supersonic nozzles is different compared to the central subsonic nozzle. This is due to the nozzle outlet temperature being reduced to 150K due to supersonic flow at the outer nozzle. This results in a much higher gas density at the outlet of the supersonic nozzle, assuming that the pressure is almost uniform everywhere in the container. For subsonic central jets, such low temperatures are not reached at the nozzle exit.

  Since it is intended to change the flow through the central subsonic nozzle during blowing, the ratio of the flow through the subsonic nozzle to the flow through one supersonic nozzle is kept variable. In order to keep the computational effort small, it was decided to study the flow induced by the jet only with respect to the two volume flow ratios. These were selected to be 1.0 and 0.5. The results of the simulation are shown below for a volumetric flow ratio of 1.0.

  FIGS. 8 and 9 show the calculation model and mesh used in the numerical simulation of the 7-hole lance design suggested above. More than 1.3 million grid nodes were used for jet flow simulation. The simulation was performed using a standard k-ε model. The simulation used 12 processors with 1 teraflop Linux clusters, and approximately 72-80 were used to complete one flow simulation. The k-ε turbulence model is known to predict the flow characteristics of a plurality of jets having a certain amount of deviation from the actual flow, but the deviation is not large. However, it is easy to get a reasonable solution immediately using the k-ε model with a short computation time. For this reason, this model was used.

  In FIG. 10, the velocity profile in the symmetry plane of the seven-hole lance in the presence of the vessel wall and metal surface is shown for a 17.5 ° tilt angle of the peripheral nozzle. In numerical simulations, the metal surface was assumed to be a stress free horizontal layer. It can be seen from FIG. 10 that the jet follows its geometric path and the interference between them is small. It can be seen from FIG. 10 that the jets interfere only at intermediate heights. Jet interference closer to the metal surface is negligible. This is due to the central stagnation region on the metal surface. The higher stagnation point pressure in this region pushes the jet away and reduces coalescence.

  In FIG. 11, the impact formed at the tip of a nozzle with a seven-hole lance design is indicated by temperature contours. It can be seen that there is a smaller impact at the outlet of the subsonic nozzle. This is because there is a temperature difference between the surroundings and the nozzle outlet, and the pressure difference is smaller. This can be reduced by increasing the angle of the converging part of the nozzle. For this simulation, the angle is kept at 10 °.

  In FIG. 12, the velocity contours are plotted on a symmetrical plane to show the impinging position of the jet on the metal surface. The geometric protrusion of the jet was also indicated on the liquid metal surface by a black circle. It can be seen that the jet almost follows the geometric path and coalescence is minimal due to the presence of the central jet and the bottom stagnation region. In FIG. 12, the velocity shape is shown only for velocity magnitudes of 150 m / s or less. It can be observed that the supersonic jet and the central subsonic jet reach the liquid metal bath at approximately the same speed, but the exit velocity at each nozzle is different.

  The subsonic nozzle outlet diameter (54 mm) is wider than the supersonic nozzle outlet diameter (37.3 mm), so the speeds near the metal bath match.

  In FIG. 13, for a seven hole lance, the velocity contours are plotted at different axial distances from the nozzle tip. From FIG. 13, it can be seen that the interaction between the jets is minimal up to an axial distance of 1 m. At a distance of 1.5 m there is a large interaction between the jets. However, the stagnation area at the bottom separates the jet and coalescence is lowered by 2 m. The stripes shown in FIG. 13 (d) are due to the presence of the central jet.

  Since the gas in the central jet cannot pass through the metal surface (in the simulation), it must pass through the surrounding supersonic jet. Since the simulation assumes that the metal surface is an unstressed flat wall, this type of flow feature may not occur in a real vessel. In an LD vessel, the impact of the central jet creates a dent, which completely changes the nature of the flow.

To explain the effect of slag foam on jet properties, the results of a single jet are discussed here. The expected range of possible values of ambient density (foam / emulsion) in the LD vessel was calculated by assuming a uniform decarburization rate throughout the blow. The average slag volume fraction of the foam inside the container is in the range of 12-15%. This is in the range of an average ambient density of 360-450 Kg / m ³ .

  The numerical regions and boundary conditions used are shown in FIG. The vessel diameter required for a single axisymmetric nozzle was calculated using 1/6 of the original vessel cross-sectional area (since only one of the six nozzles was simulated). Furthermore, the liquid metal surface was assumed to be a flat wall without shear. In order to study jet behavior over long axial distances, the lance height (distance between the nozzle tip and the surface of the liquid metal) was taken to be 3.5 m. The actual lance height in the container varies from 1.5 to 2.2 m.

  The simulation was performed using a 2D axisymmetric unsteady RANS with a multistage model of fluid volume (VOF) to track the interface of the stage. No distinction was made between oxygen and carbon monoxide gas. Therefore, only one gas phase was considered. A feasible k-ε turbulence model was used to approximate the mathematical system. The PISO algorithm was used to combine pressure and speed. A second-order upwind discretization scheme was used for all flow variables except the temperature at which the power scheme was used. The average slag volume fraction (15%) calculated from the steady decarburization rate was applied to the vessel area as an initial guess. During the calculation, the slag can move freely throughout the region depending on local flow conditions, unlike previous simulations. When entering a static environment, the surface tension is not included in this simulation, and a high-speed gas jet causes a flow around it.

  Due to the momentum transmitted to the surroundings, the surrounding fluid adjacent to the jet boundary begins to move in the overwhelming direction of the jet fluid. Therefore, due to this flow induced by the jet, the fluid around the adjacent location moves towards the jet. The slag flows vigorously towards the jet boundary with the flow induced by the jet with the surrounding gas. Here, slag accumulates and the volume fraction / local density increases. The slag is moved by the momentum transmitted from the jet, and the slag gently covers the core of the high-speed jet. To show the accumulation of slag at the nozzle tip and its movement along the jet, the density profile of the slag foam near the nozzle tip was plotted in FIG.

  The resulting momentum flux rate (pV) at different axial positions is shown in FIG. 16 for a particular time. It does not make sense that the maximum momentum flow rate ratio does not occur in the jet axis, but occurs radially away from it as shown in FIG. The high velocity core of the jet causes the momentum to be continuously moved to the jet shear layer, both convectively and diffusively. The speed at the axis is still maximum at any axis position.

  Therefore, the diffusive transmission of the axial momentum in the radial direction is from the jet axis toward the shear layer. Since the jet is diffusing, the radial velocity v is directed to the shear layer in the jet, so the total convection transfer (ρuv) in the radial direction is also directed to the shear layer.

  Since the density of the fluid (slag + gas) in the shear layer is very high compared to the jet gas, the shear layer accumulates thermal energy in a reservoir with a higher specific heat / temperature capacity without a significant temperature difference Just as you do, you can accumulate higher momentum flux without significantly increasing speed. Furthermore, gravity helps the slag layer gain momentum. That is, the slag layer moves in the direction of gravitational acceleration.

  The momentum transmitted from the high-speed jet core to the high-density shear layer is in addition to the momentum given by the gravitational acceleration. From the momentum flux rate plot shown in FIG. 16, the momentum flux rate in the dense shear layer is at least two orders of magnitude higher than the core of the high speed jet. From the above discussion, it is clear that the dense slag-gas bubbles in the LD vessel give rise to some interesting flow characteristics of the supersonic gas jet. The understanding of dents formed during blowing can be completely changed.

  It is important to note that the multiple supersonic jets inside the LD steel vessel are also affected by the properties as indicated above due to the presence of dense slag foam. From the above discussion, it is clear that peripheral supersonic jets lose all their momentum in the slag layer adjacent to them. The slag layer moves toward the liquid metal pool with very high momentum and forms a complex dent shape. Due to the presence of the central jet in the new seven-hole design, the pressure in the space between the supersonic jets prevents this region from being entrained.

  Thus, the central jet does not hit or minimally hit the slag foam and, unlike a supersonic jet, does not lose its momentum completely to the slag foam. Therefore, it is expected that the central jet reaches the surface of the liquid metal at a very high speed as compared with the supersonic jet and generates more droplets. This type of droplet generation is not possible with a six-hole design, since all six supersonic jets lose their momentum completely in a relatively slowly moving slag layer. From the above discussion, it is clear that the 7-hole design is more effective than the 6-hole conventional design.

  One embodiment of the present invention having a seven hole design is shown schematically in FIG. It shows six peripheral supersonic jets with a central jet. The central jet is controlled separately by a separate gas supply line, whereas the surrounding supersonic jet has a single inlet gas supply line. The gas supply lines for the six supersonic jets and the gas supply line for the central subsonic jet comprise two separate control valves with actuators. The central jet is operated during different stages of blowing, and since it is a subsonic nozzle, the flow rate can be changed according to process requirements.

  The flow rate through the central subsonic nozzle is kept variable. In numerical and experimental simulations, the ratio of the volume flow through the central subsonic nozzle to the volume flow through one of the supersonic nozzles remains variable. The maximum value of this ratio is kept at 1 in the numerical simulation. The size of the central nozzle can be calculated by recognizing this. The outlet diameter of the subsonic nozzle is 54 mm, and the outlet diameter of the supersonic nozzle is 37.3 mm (existing value).

  The inclination angle of the peripheral jet is kept at 17.5% (existing value). In order to understand the performance of a seven-hole lance with a modified angle with respect to the peripheral jet, a study was carried out on a jet array having an angle of 22 ° with respect to the inclination of the side jet. Furthermore, the tilt angles of the peripheral supersonic nozzles can be equal or can alternate. Alternating tilt angles can have distinct advantages. As previously indicated, covering the slag foam on the jet surface causes the gas jet to have a lower velocity, and the slag layer covering the jet reaches the surface of the liquid metal with high momentum. This impact of the slag layer on the liquid metal causes many slag droplets to form in the liquid metal, creating an interfacial region for the slag-metal reaction. By maintaining alternating tilt angles, 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 promote interfacial reactions such as dephosphorization.

  The following seven-hole lance design achieved the preferred embodiment by numerical and experimental simulations and simultaneously considering the different dynamics inside the LD steel vessel. This design is much better than current designs and can function in better steelmaking conditions.

  The six surrounding supersonic nozzles have a single gas supply line. The central larger subsonic nozzle has a separate gas supply. The central nozzle can be operated during various stages of blowing as needed, and the flow rate can also be easily changed without compromising the useful life of the nozzle. The tilt angle of the peripheral jet is kept at 17.5 °. This angle can be increased with further changes.

  An advantageous feature of the present invention provides better on / off control of the central nozzle being blown by a separate gas supply line. This gives strong control of spitting metal droplets from the container.

  A larger subsonic nozzle in the center of the lance head is useful for controlling the flow of oxygen through the central nozzle. This means more flexible control throughout the process.

  This system results in improved metal droplet generation. Since the central jet is protected from the slag foam by the peripheral jet, it reaches the metal bath at a high rate and promotes improved droplet formation.

  This system provides improved efficiency in dephosphorization. Improved metal droplet formation facilitates interfacial reactions, particularly dephosphorization.

  The present invention has been described with reference to several embodiments that are merely exemplary and not intended to be limiting. Changes in detail and form may be made by those skilled in the art without departing from the scope and spirit of the invention. It has been shown that the objective of improving dephosphorization in LD steelmaking processes is achieved by increasing the formation of liquid metal droplets. The system of the present invention can also be used in other processing industries where there may be other objectives that can also be achieved by increasing the production of liquid droplets.

Schematic of lance design with 6 holes. A diagram of the general geometric arrangement of supersonic nozzles. Schematic of LD container. FIG. 2 is a schematic diagram of a seven-hole lance with a separate air supply line used in a hydrodynamic model experiment. (A) is a figure which shows the range of the production | generation of the droplet in the case of the present 6 nozzle lance. (B) is a figure which shows the production | generation range of the droplet in the case of the 7 hole lance of this invention. Schematic of the mechanism of droplet generation. FIG. 6 is a diagram of droplet generation rates using a seven-hole lance with different flow ratios. Diagram of computational model and mesh used for numerical simulation. A close-up view of the nozzle. FIG. 5 is a velocity profile for a 7-hole lance with a tilt angle of 17.5 ° with the presence of a container wall and a metal surface. FIG. 3 is a temperature contour diagram with impact at a nozzle having an angle of 17.5 °. FIG. 4 is a velocity contour diagram showing a collision position with a metal surface. FIG. 6 is a velocity contour diagram at different axial positions (a) X = 0.5 m, (b) X = 1.0 m, (c) X = 1.5 m, and (d) X = 2.0 m. FIG. 4 is a schematic diagram of a region having boundary conditions used for high density ambient simulation. The density contour map of mixing near the nozzle outlet at a certain moment. Diagram of momentum flux rate at different axial positions (a) nozzle outlet, (b) 0.5 m, (c) 1.5 m, and (d) 2.5 m. Schematic of lance design with 7 holes.

Claims (7)

In the improved lance for LD steelmaking,
A plurality of peripheral supersonic nozzles with a single inlet high pressure gas supply line;
With a central nozzle,
The central nozzle is a subsonic nozzle with a separate low pressure gas supply line;
An improved lance wherein the flow rate through the central subsonic nozzle is controllable to vary the production of liquid metal droplets during blowing as required by the process.   The improved lance of claim 1, comprising six peripheral supersonic nozzles and one central subsonic nozzle.   The improved lance according to claim 1 or claim 2, wherein the central subsonic nozzle comprises only a converging region in order to easily control the flow rate through the subsonic nozzle.   The improved lance according to any one of claims 1 to 3, wherein the central subsonic nozzle has a larger outlet diameter than the peripheral supersonic nozzle.   The gas supply line for the plurality of peripheral supersonic nozzles and the gas supply line for the central subsonic nozzle comprise two separate control valves with actuators to control the flow rate. Improved lance as described in.   The control valve provided in the central subsonic nozzle is for changing the flow through the subsonic nozzle in order to avoid spitting during the first stage of blowing; 6. An improved lance according to claim 5, for controlling the dynamics of the reaction during blowing by varying the magnitude of the velocity.   7. An improved lance according to any one of the preceding claims, wherein the peripheral supersonic nozzle can have an angle of inclination from the vertical axis of the lance that is equal or alternating.

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