JP6036096B2 - Converter blowing method - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a converter blowing method for decarburizing and refining molten iron by blowing oxygen gas from an upper blowing lance to a hot metal bath surface, and more specifically, a converter blowing method capable of reducing the amount of dust generated during blowing. About.

  In a converter in which hot metal is decarburized and refined to produce molten steel from hot metal, high-speed jet oxygen gas (industrial pure oxygen) is blown onto the hot metal surface from an upper blowing lance and decarburized and refined. On the hot metal bath surface to which oxygen gas is sprayed, a recess (referred to as “fire point” or “cavity”) is formed by the pressure of the impinging oxygen gas. At this hot point, oxygen gas in the high-speed jet collides, so that a phenomenon occurs in which molten iron and molten slag droplets scatter from the hot metal surface. It adheres to the inner wall as a bare metal. The phenomenon in which droplets of hot metal and molten slag scatter from the hot metal surface is called “spitting”. Part of the hot metal and molten slag scattered by spitting out of the furnace together with the exhaust gas is recovered as dust.

  When spitting becomes violent, the amount of dust generated increases and iron yield deteriorates, or the amount of deposit metal at the converter furnace entrance increases, impeding the introduction of hot metal and cold iron sources into the furnace. Many methods have been proposed to suppress spitting because it adversely affects operations.

  For example, a method for reducing the overlapping of fire spots formed by a plurality of nozzles arranged at the tip of the upper blowing lance has been proposed (see Patent Document 1). Further, in order to more effectively reduce the overlapping of the hot spots, a method of using an upper blowing lance in which two types of nozzles having different inclination angles (an angle formed by the longitudinal direction of the lance and the nozzle injection direction) are alternately arranged is used. Has also been proposed (see Patent Document 2).

  In addition, a method has been proposed in which the energy of the oxygen gas jet is reduced by making the nozzle porous so as to control the occurrence of splash on the hot metal bath surface (Patent Documents 3 and 4). Furthermore, during the decarburization reaction peak period from the beginning to the middle of decarburization refining, the energy of the oxygen gas jet is reduced by overexpanding or underexpanding the oxygen gas jet injected from the laval nozzle of the top blowing lance. Proposing a method to suppress spitting and reduce the oxygen gas supply amount and optimize the expansion of this oxygen gas jet to accelerate the decarburization reaction when the decarburization reaction from the middle to the end of the blowing is reduced. (See Patent Documents 5 to 8).

JP-A-60-165313 JP 2009-52090 A JP-A-10-102122 Japanese Patent Laid-Open No. 9-256022 Japanese Patent Laid-Open No. 9-209021 JP 2002-212623 A JP 2002-212624 A JP 2003-105425 A

  However, the above prior art has the following problems.

  That is, in the method of reducing the overlapping of the hot spots proposed in Patent Document 1, since the inclination angle needs to be widened, the hot spot area becomes large, and CO gas accumulates in the slag, so that the slag is ejected from the converter. Phenomenon (called “sloping”) occurs, or the bare surface of the iron bath widens and fume dust increases.

  Further, in the method proposed in Patent Document 2, since the nozzle tilt angle is different, a difference occurs in the linear velocity of each oxygen gas jet, and the granular iron scattered by the splash enters the nozzle hole having a low linear velocity, There are problems such as nozzle clogging and lance burning.

  In addition, the methods proposed in Patent Documents 3 and 4 have a problem that the hot spot area increases due to the formation of a porous material, thereby increasing fume dust.

  Moreover, since the technique which makes the expansion state of the jet flow proposed by patent documents 5-8 improper is especially out of the range of an appropriate expansion at the time of many oxygen gas supply amounts in a high carbon region, it is optimal. There is a problem that it is impossible to determine a simple acid delivery pattern.

  The present invention has been made in view of the above circumstances, and its purpose is to perform spitting and slopping in decarburizing and refining the hot metal by blowing oxygen gas from the top blowing lance onto the hot metal bath surface in the converter. It is an object of the present invention to provide a converter blowing method that can suppress the generation of ash and, as a result, greatly reduce the amount of dust generated.

The gist of the present invention for solving the above problems is as follows.
[1] Using an upper blowing lance in which a plurality of Laval nozzles are arranged at equal intervals on a concentric circle with an inclination angle θ at the tip of the upper blowing lance, oxygen gas is blown from the upper blowing lance to the hot metal bath surface in the converter. When the volume of the hot spot dent formed on the hot metal bath surface by the oxygen gas jet jetted obliquely downward from the top blowing lance is defined by the following equation (1) , Using a top blowing lance designed on the basis of the blowing conditions that are planned so that the volume of the hot spot dent defined by the formula (1) is 1.0 to 2.0 m ³ , and (1 The oxygen gas supply amount and the lance height are adjusted so that the volume of the hot spot dent defined by the formula is 1.0 to 2.0 m ³ , and oxygen gas is blown from the upper blowing lance. The converter blowing method.

In equation (1), V is the volume of the hot spot recess (m ³ ), n is the number of holes in the Laval nozzle (−), L is the hot spot depth (m) per Laval nozzle, and A is the Laval nozzle 1 The hot spot area per hole (m ² ), the hot spot depth L per Laval nozzle is defined by the following equation (2), and the hot spot area A per Laval nozzle is (3 ) To (6).

However, in the formulas (2) to (6), F _O2 is the oxygen gas supply amount (Nm ³ / hr) from the top blowing lance, n is the number of holes in the Laval nozzle (−), dt is the throat diameter (mm in the Laval nozzle) ), H is the lance height (m) of the top blowing lance, π is the circularity ratio, D is the diameter of the fire point (m), γ is the fire point interference rate (−), and φ is the free spread of the oxygen gas jet Angles (deg) and de are outlet diameters (m) of Laval nozzles, P is a distance (m) between centers of adjacent fire points, and θ is an inclination angle (deg) of Laval nozzles.
[2] The converter blowing method according to [1], wherein five or more Laval nozzles are arranged and the inclination angle θ is 14 ° or less.
[3] The converter blowing method according to [1] or [2] above, wherein the throat diameter dt of the Laval nozzle is 50 mm or more.

According to the present invention, the volume of the hot spot dent formed on the hot metal bath surface by the oxygen gas jet from the top blowing lance is controlled within the range of 1.0 to 2.0 m ³ . Even when the amount of oxygen gas supply is increased, it is possible to reduce the amount of fume dust generated due to splashing caused by spitting and the increase in the hot spot area, even if the amount of oxygen gas supply is increased. Therefore, the productivity of the converter can be significantly improved as compared with the prior art by improving the iron yield and reducing the work of removing the adhering metal from the converter furnace port.

It is the schematic which shows the state which injects oxygen gas toward the hot metal bath surface in a converter from an upper blowing lance, and has performed decarburization refining to hot metal. It is a figure which shows the investigation result of the relationship between the volume of the dent of a hot spot, and dust generation speed.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view showing a state where the lance height is H and oxygen gas is injected from the top blowing lance 1 toward the hot metal bath surface in the converter, and the hot metal 11 is decarburized and refined. Here, the lance height H is a distance from the lower end of the top blowing lance 1 to the average bath surface position of the hot metal 11 in the converter.

  As shown in FIG. 1, the upper blowing lance 1 is composed of a cylindrical lance body 2 and a lance tip 3 connected to the lower end of the lance body 2 by welding. 4, which is composed of three types of concentric steel pipes consisting of an intermediate pipe 5 and an inner pipe 6, that is, a triple pipe. A plurality of Laval nozzles 7 are installed on the copper lance tip 3 so as to face in a vertically oblique downward direction. Yes. The Laval nozzle 7 has an angle formed by the longitudinal direction (axial direction) of the upper blowing lance 1 and the injection direction of the Laval nozzle 7 as θ (the angle θ is referred to as “inclination angle”), and is concentric with the center position of the bottom surface of the lance tip 3 as the center. A plurality are arranged on the top at equal intervals.

  The gap between the outer pipe 4 and the middle pipe 5 and the gap between the middle pipe 5 and the inner pipe 6 serve as a cooling water flow path for cooling the upper blowing lance 1. The cooling water supplied from a water supply joint (not shown) provided in the pipe passes through the gap between the inner pipe 5 and the inner pipe 6 to reach the lance tip 3 and is reversed at the lance tip 3 to be externally piped. The water is discharged from a drainage joint (not shown) provided at the upper portion of the upper blowing lance 1 through a gap between the intermediate pipe 4 and the middle pipe 5. The water supply / drainage route may be reversed. Further, the inside of the inner pipe 6 serves as a supply flow path for oxygen gas to the Laval nozzle 7, and the oxygen gas supplied from the upper part of the upper blow lance 1 to the inside of the inner pipe 6 passes through the inner pipe 6 and becomes a Laval nozzle. 7 is ejected into a converter (not shown).

  The Laval nozzle 7 is composed of two cones whose cross section is reduced and enlarged. The reduced portion is the throttle portion 8, the enlarged portion is the skirt portion 10, and the transition portion from the throttle portion 8 to the skirt portion 10. The narrowest part is called a throat 9, and oxygen gas that has passed through the inner tube 6 passes through the throttle portion 8, the throat 9, and the skirt portion 10 in this order, and is a supersonic or subsonic jet. Is fed into the converter. The inner diameter of the throat 9 is called a throat diameter dt, and the inner diameter of the tip outlet of the skirt portion 10 is called an outlet diameter de. The spread angle of the skirt part 10 is usually 10 ° or less. In the Laval nozzle 7 shown in FIG. 1, the constricted portion 8 and the skirt portion 10 are conical, but for the Laval nozzle 7, the constricted portion 8 and the skirt portion 10 do not need to be conical, and the inner diameter changes in a curve. The throttling portion 8 may be a straight cylindrical shape having the same inner diameter as the throat 9.

  Oxygen gas jets (also referred to as “oxygen jets”) jetted obliquely downward from the respective Laval nozzles 7 spread at an angle having a free spread angle φ, and enter the hot metal 11 accommodated in a converter (not shown). The hot spot 12 is formed on the hot metal bath surface by collision. The hot spot 12 has a shape recessed from the bath surface of the surrounding molten metal 11 due to the collision energy of the oxygen gas jet. The free spread angle φ is equal to the spread angle of the skirt portion 10.

  Note that the fire point 12 is not overlapped until the oxygen gas jet from the adjacent Laval nozzle 7 reaches the hot metal bath surface by increasing the inclination angle θ or limiting the number of installed Laval nozzles 7. Although it has a substantially circular shape, if the oxygen gas jets overlap before reaching the hot metal bath surface, the adjacent circles will become overlapping fire points. In the present invention, the degree of overlap of the hot spots 12 is defined as the interference rate. The interference rate is in the range of 0 to 1.0, the interference rate = 0 when the oxygen gas jets do not overlap, and the interference rate = 1.0 when all interfere to form one circular fire point. . This interference rate is obtained by geometrically calculating the locus of the oxygen gas jet based on the lance height H, the tilt angle θ, the free spread angle φ, the outlet diameter de, and the number of installed Laval nozzles 7, and It can be obtained from the overlap of the trajectories.

At the fire point 12, a reaction (C + O → CO) between carbon in the molten iron and oxygen gas occurs, and the decarburization reaction proceeds. Phosphorus present in the hot metal is also oxidized, and a dephosphorization reaction (5P + 2O → P ₂ O ₅ ) also proceeds. These are exothermic reactions, and therefore the temperature of the hot spot 12 is a high temperature of 1800 ° C. or higher.

  The present inventors examined reducing the amount of dust generated in the decarburization refining of hot metal performed in this way. In this examination, spitting, which is the main cause of dust generation, is caused by the kinetic energy of the oxygen gas jet on the hot metal bath surface. Similarly, the fire point 12 generated by the kinetic energy of the oxygen gas jet on the hot metal bath surface. It came to the thought that the volume of the dent had some influence on the dust generation amount.

Therefore, various types of top blowing lances were prototyped, the operation conditions were changed, and a test was conducted to investigate the relationship between the volume of the recess at the hot spot 12 and the dust generation rate. The survey results are shown in FIG. As shown in FIG. 2, it was found that the dust generation is reduced as the volume of the recess of the hot spot 12 is smaller. It was also found that when the volume of the recess at the hot spot 12 exceeded 2.0 m ³ , the generation of dust increased and was not much different from the conventional one. In addition, when the volume of the dent of the hot spot 12 is less than 1.0 m ³ , the flow velocity of the oxygen gas jet becomes too small, and the granular iron scattered by the splash enters the inside of the Laval nozzle 7, and the Laval nozzle 7 is clogged. It has also been found that the top blowing lance 1 may be burned out. From these results, in order to reduce the amount of dust generation, it was confirmed that it was necessary to limit the volume of the recess of the fire point 12 within a range of 1.0 to 2.0 m ³ .

  Note that the dust generation speed in FIG. 2 is obtained by obtaining the dust recovered by the dust collector of the exhaust gas recovery facility for recovering the exhaust gas generated in the converter per ton of molten steel and per unit blowing time. The dust includes dust generated by splashing due to spitting and fume dust generated by expanding the area of the fire point 12. The fact that the fume dust is reduced means that the area of the fire point 12 does not become large. Therefore, it is understood that both the suppression of spitting and the suppression of slipping can be suppressed by applying the present invention. It was.

  Conventionally, when the inclination angle θ of the Laval nozzle 7 is small, it is considered that the oxygen gas jet strongly collides with the hot metal bath surface, that is, a so-called hard blow state, so that dust is generated a lot. However, according to the present invention, it has been clarified that even if the inclination angle θ is reduced, dust generation can be suppressed by appropriately managing the volume of the recess of the hot spot 12. .

  In applying the present invention, the volume of the depression 12 at the hot spot 12 is obtained by calculation based on a geometric technique as described below.

  The volume of the hot spot 12 depression formed by each Laval nozzle 7 is determined by the product of the area of the hot spot 12 per hole in each Laval nozzle and the depth L of the hot spot 12 per hole in each Laval nozzle. As shown in the following equation (1), the volume of the recesses of all the fire points 12 is obtained by the product of the number of holes (= the number of installations) of the Laval nozzle 7 and the volume of the recesses for each Laval nozzle. .

However, in the formula (1), V is the volume (m ³ ) of all the hot spot dents, n is the number of holes in the Laval nozzle (−), L is the hot spot depth (m) per Laval nozzle, and A is It is the fire spot area (m ² ) per Laval nozzle.

  Here, as shown in the following equation (2), the hot spot depth L per hole of the Laval nozzle depends on the oxygen gas supply amount, the number of holes of the Laval nozzle 7, the throat diameter dt of the Laval nozzle 7, and the lance height H. It is determined.

In Equation (2), F _O2 is the oxygen gas supply amount (Nm ³ / hr) from the top blowing lance, n is the number of holes in the Laval nozzle (−), dt is the throat diameter (mm) of the Laval nozzle, and H is the upper It is the lance height (m) of the blowing lance.

  Further, the hot spot area A per Laval nozzle is obtained by the product of the diameter of the hot spot 12 and the interference rate of the hot spot 12 as shown in the following equation (3). The diameter of the fire point 12 is defined by the following formula (4), and the interference rate is defined by the following formula (5). In addition, P (distance between the centers of the adjacent fire points 12) in the equation (5) is defined by the following equation (6).

  However, in the formulas (3) to (6), π is the circular rate, D is the diameter of the fire point (m), γ is the fire point interference rate (−), and H is the lance height of the top blowing lance ( m), θ is the inclination angle (deg) of the Laval nozzle, φ is the free spreading angle (deg) of the oxygen gas jet, de is the outlet diameter of the Laval nozzle (m), P is the distance between the centers of adjacent fire points (m), n Is the number of holes (−) in the Laval nozzle.

The present invention has been made on the basis of the above examination results, and the converter blowing method according to the present invention uses an upper blowing lance 1 in which a plurality of Laval nozzles 7 are arranged at equal intervals on a concentric circle. In the converter blowing method of decarburizing and refining the hot metal 11 by blowing oxygen gas from 1 to the hot metal bath surface in the converter, the volume of the recess of the hot spot 12 defined by the above formula (1) is 1.0. Based on the blowing conditions (oxygen gas supply amount F _O2 , lance height H) scheduled to be ˜2.0 m ³ , the number n of holes of the Laval nozzle 7 installed in the upper blowing lance 1, the throat diameter dt, The outlet diameter de, the inclination angle θ, and the free spread angle φ are determined, and the upper blowing lance 1 having the Laval nozzle 7 designed in this way is used, and the volume of the recess of the hot spot 12 defined by the equation (1) is oxygen gas supply amount so as to 1.0～2.0M ³ Fine lance Adjust the height H, blown from the lance 1 blown above the oxygen gas.

  In this case, from the above test, as the shape of the Laval nozzle 7 under typical operation conditions, the number n of holes of the Laval nozzle 7 is preferably 5 or more, the inclination angle θ is 14 ° or less, and the throat diameter dt is preferably 50 mm or more. I found out. This is because when the number of holes n is 4 or less, there is a tendency for hard blow and dust generation to increase. As the tilt angle θ increases, the hot spot area increases and slopping easily occurs, and the throat diameter dt increases. This is because the bath surface dynamic pressure becomes smaller, and soft blows tend to reduce dust generation.

As described above, according to the present invention, the volume V of the recesses of all the hot spots 12 formed on the hot metal bath surface by the oxygen gas jet from the top blowing lance 1 is controlled to 1.0 to 2.0 m ³ . Therefore, it is possible to simultaneously suppress the occurrence of spitting and the occurrence of slopping, and it is possible to reduce the amount of dust generated during blowing even when the oxygen gas supply amount is increased. .

  When a furnace capacity of 240 tons is used, an oxygen gas is supplied from the top blowing lance, Ar gas or nitrogen gas is blown from the bottom blowing tuyere as a stirring gas, and the hot metal is decarburized and refined. A test using two types of top blowing lances, lances A and B shown in Table 1, was conducted to compare the amount of dust generated.

A typical operating conditions, depressions volume fire point when the oxygen gas supply amount 650 nm ³ / min, the lance height 2.1m is Lance A in 1.77 m ^3, the lance B in 2.53M ³ Met.

  Table 2 shows the amount of dust generated when these two types of top blowing lances are used. In Table 2, a test using the lance A is indicated as an example of the present invention, and a test using the lance B is indicated as a comparative example.

  As shown in Table 2, in the example of the present invention using the lance A, the depth of the hot spot formed by the oxygen gas jet and the area of the hot spot are reduced, so that the volume of the hot spot is reduced and the dust is reduced. It has been confirmed that the amount of generated is reduced by about 1.0 kg / t.

Also, the top blow lance with the same number of holes and throat diameter as the lance A and an inclination angle θ of 18 ° (lance C, fire when the oxygen gas supply amount is 650 Nm ³ / min and the lance height is 2.1 m) A test using a point indentation volume of 2.26 m ³ was also attempted. However, since dust generation was large and slopping occurred, the result was not favorable.

DESCRIPTION OF SYMBOLS 1 Top blowing lance 2 Lance body 3 Lance tip 4 Outer pipe 5 Middle pipe 6 Inner pipe 7 Laval nozzle 8 Constriction part 9 Throat part 10 Skirt part 11 Hot metal 12 Fire point H Lance height θ Inclination angle φ Oxygen gas jet free spread angle

Claims (3)

Using upper blowing lance Laval nozzle of multiple identical shape top lance tip are arranged at equal intervals on a concentric circle at all the same inclination angle theta, blowing oxygen gas to the molten iron bath surface in the converter in the upper lance in converter blowing process for decarburization refining molten iron, the volume of the recess of the fire spot formed on the molten iron bath surface by the oxygen gas jets injected from the top lance obliquely downward below the (1) equation using Te And using a top blowing lance designed based on the blowing conditions planned so that the volume of the hot spot dent determined by the equation (1) is 1.0 to 2.0 m ³ , and ( 1) The upper lance is blown with oxygen gas at the oxygen gas supply amount and the lance height of the blasting conditions scheduled so that the volume of the hot spot dent determined by the equation is 1.0 to 2.0 m ^3. A method of blowing a converter.

In equation (1), V is the volume of the hot spot recess (m ³ ), n is the number of holes in the Laval nozzle (−), L is the hot spot depth (m) per Laval nozzle, and A is the Laval nozzle 1 The hot spot area per hole (m ² ), the hot spot depth L per Laval nozzle is defined by the following equation (2), and the hot spot area A per Laval nozzle is (3 ) To (6).

However, in the formulas (2) to (6), F _O2 is the oxygen gas supply amount (Nm ³ / hr) from the top blowing lance, n is the number of holes in the Laval nozzle (−), dt is the throat diameter (mm in the Laval nozzle) ), H is the lance height (m) of the top blowing lance, π is the circularity ratio, D is the diameter of the fire point (m), γ is the fire point interference rate (−), and φ is the free spread of the oxygen gas jet Angles (deg) and de are outlet diameters (m) of Laval nozzles, P is a distance (m) between centers of adjacent fire points, and θ is an inclination angle (deg) of Laval nozzles.   5. The converter blowing method according to claim 1, wherein five or more Laval nozzles are arranged and the inclination angle θ is 14 ° or less.   The converter blowing method according to claim 1 or 2, wherein a throat diameter dt of the Laval nozzle is 50 mm or more.

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