JP7406096B2 - Blowing method in converter - Google Patents

Description

The present invention relates to a blowing method in a converter.

In a converter, when decarburizing hot metal, oxygen gas is blown onto the hot metal from a nozzle hole in a nozzle portion formed in a top blowing lance (see Patent Document 1).

Patent Document 1 discloses a technology that extends the life of the lance by dispersing the wear parts of the lance by changing the height of the lance when charging auxiliary materials into the converter according to the number of times the top blow lance is used. There is.

JP2002-88411A

By the way, during the decarburization treatment of hot metal, a water-cooled triple structure lance is often used because a large heat load is applied to the top blowing lance. However, even if a water-cooled triple structure lance is used, the nozzle portion will wear out as the number of times it is used increases, and as a result, it is thought that the nozzle hole will become larger than when it was new. When the nozzle hole becomes larger, the jet of oxygen gas from the nozzle hole becomes weaker and the oxygen decarburization efficiency decreases, so the nozzle part needs to be replaced regularly.

The present invention has been made in view of the above circumstances, and an object of the present invention is to extend the life of the nozzle part by suppressing wear and tear of the nozzle part due to increased use in a blowing method using a top blowing lance. .

The blowing method in a converter according to the first aspect of the present invention includes: a cylindrical main body in which a refrigerant flow path and a gas supply path are formed; A blowing method for blowing oxygen gas onto a hot metal bath surface in a converter from the nozzle hole of the top blowing lance using a top blowing lance equipped with a nozzle portion having a plurality of nozzle holes, the method comprising:
The above-mentioned top-blowing lance is designed to satisfy the equation (1), and the amount of radiant heat E received by the outlet of the nozzle hole from the hot spot formed on the surface of the hot metal bath satisfies the equation (2). The lance height is set and the oxygen gas is blown from the nozzle hole onto the hot metal bath surface.
100×S _N /S _L <20%...(1)
However, in equation (1), _SN is the total cross-sectional area (m ² ) of the exit of the nozzle hole, and S _L is the area (m ² ) of the lower surface of the nozzle.
E=Q _HOT ×N×S _N <12kW...(2)
However, in equation (2), Q _HOT is the thermal radiation intensity of the hot spots (kW/m ² ), N is the number of hot spots, and S _N is the total cross-sectional area of the exit of the nozzle hole (m ² ).

In the blowing method in the converter of the first aspect, a top blowing lance designed to satisfy equation (1) is used, and the amount of radiant heat E received by the outlet of the nozzle hole from the fire point satisfies equation (2). Decarburization is performed by setting the lance height as follows and blowing oxygen gas from the nozzle hole onto the surface of the hot metal bath. In this way, the above-mentioned blowing method uses a top-blowing lance that does not satisfy equation (1), and has a higher flame resistance compared to a blowing method that performs decarburization treatment at a lance height that does not satisfy equation (2). As the distance from the point to the nozzle hole increases, the total cross-sectional area of the nozzle hole exit becomes smaller relative to the area of the lower surface of the nozzle, so it is possible to suppress wear and tear on the nozzle part due to radiant heat from the fire point. can.

A blowing method in a converter according to a second aspect of the present invention is a blowing method in a converter according to the first aspect, wherein the main body portion includes an outer tube, a middle tube, and an inner tube arranged on the same axis. The refrigerant flow path is formed by a gap between the outer tube and the middle tube and a gap between the middle tube and the inner tube, and the gas supply path is formed inside the inner tube. Ori,
The above-mentioned refrigerant flow is obtained by using the above-mentioned top blowing lance designed such that the difference between the outer diameter D ₁ of the above-mentioned outer pipe and the inner diameter d ₁ of the above-mentioned outer pipe is 0.025 m or less, and using equation (3). The flow rate W is set so that the flow velocity V of the refrigerant flowing through the refrigerant flow path is 2.0 m/sec or more, and the temperature of the refrigerant supplied to the refrigerant flow path is set to 60° C. or lower, and the hot metal is removed from the nozzle hole. The oxygen gas is blown onto the bath surface.
V=W/((d ₁ ² - D ₂ ² )×π×900)...(3)
However, in equation (3), W is the flow rate of the refrigerant (m ³ /hr), d ₁ is the inner diameter (m) of the outer tube, and D ₂ is the outer diameter (m) of the middle tube.

In the second aspect of the blowing method in a converter, a top blowing lance designed so that the difference between the outer diameter D ₁ of the outer tube and the inner diameter d ₁ of the outer tube is 0.025 m or less, and ( 3) Set the flow rate W so that the flow velocity V of the refrigerant determined by the formula is 2.0 m/sec or more, and set the temperature of the refrigerant supplied to the refrigerant flow path to 60°C or less to pour the hot metal bath from the nozzle hole. Decarburization treatment is performed by spraying oxygen gas onto the surface. In the above blowing method, for example, the difference between the outer diameter D ₁ of the outer tube and the inner diameter d ₁ of the outer tube is 0.025 m or less, but the flow velocity V of the refrigerant determined by equation (3) is 2.0 m/ Compared to the blowing method in which the refrigerant supply temperature exceeds 60°C, the top blowing lance can be appropriately cooled (appropriate temperature state can be maintained), so Shortening of the life of the top blowing lance can be suppressed.

According to one aspect of the present invention, in a blowing method using a top-blowing lance, it is possible to suppress wear and tear of the nozzle portion due to an increase in the number of times of use, thereby extending the life of the nozzle portion.

FIG. 2 is a schematic diagram for explaining a blowing method in a converter according to an embodiment of the present invention, showing a state in which oxygen gas is being blown from the nozzle hole of the top blowing lance toward the hot metal bath surface in the converter. ing.

An embodiment of the present invention will be described below.

FIG. 1 shows a lower section of the top blowing lance 20 used in the blowing method in the converter of this embodiment. The top blowing lance 20 has a cylindrical shape and is movable vertically upward and downward by a lifting device (not shown). By moving the top blowing lance 20 up and down, the lower part of the top blowing lance 20 can be inserted into or removed from the converter (not shown). Further, the top blowing lance 20 can be stopped at an arbitrary height position by a lifting device. Note that the arrow UP in FIG. 1 indicates upward in the vertical direction.

Further, the top blow lance 20 can be tilted in its axial direction with respect to the vertical direction by an angle adjusting device (not shown). By tilting the axial direction of the top blowing lance 20 with respect to the vertical direction, the position of the fire point and the range of the fire point, which will be described later, can be changed. In addition, in FIG. 1, the central axis of the top blow lance 20 is indicated by the symbol AXL.

The top blow lance 20 includes a main body 22 formed in a cylindrical shape and a nozzle part 24 joined to one end (in this embodiment, the lower end) of the main body 22 in the axial direction.

The main body portion 22 is a cylindrical member made of steel, and has a refrigerant flow path 26 through which the refrigerant C flows and a gas supply path 28 through which oxygen gas (gas containing oxygen) G is supplied. The main body portion 22 is composed of an outer tube 30, a middle tube 32 disposed inside the outer tube 30, and an inner tube 34 disposed inside the middle tube 32. The tube 32 and the inner tube 34 are each arranged on the same axis. Further, the refrigerant flow path 26 is formed by a gap S1 between the outer tube 30 and the middle tube 32 and a gap S2 between the middle tube 32 and the inner tube 34. On the other hand, the gas supply path 28 is formed inside the inner tube 34. In other words, the gas supply path 28 is formed by the internal space of the inner tube 34.

The nozzle section 24 is a lid member made of copper, and is joined to the lower end of the main body section 22 by welding. Specifically, annular ribs 22A, 22B, and 22C each having a shape corresponding to the outer tube 30, the middle tube 32, and the inner tube 34 are formed on the upper surface of the nozzle portion 24 (the surface on the joint side with the main body portion 22). The tops of these annular ribs 22A, 22B, and 22C are welded to the lower ends of the outer tube 30, the middle tube 32, and the inner tube 34. Furthermore, a communication passage 22D is formed between the annular rib 22A and the annular rib 22B of the nozzle portion 24, which communicates the gap S1 between the outer tube 30 and the middle tube 32 and the gap S2 between the middle tube 32 and the inner tube 34. has been done. This communication path 22D constitutes a part of the refrigerant flow path 26. For example, as shown in FIG. 1, when the refrigerant C is supplied to the gap S1, the refrigerant C flows from the gap S1 through the communication path 22D into the gap S2, and from the gap S2 (refrigerant flow path 26). be discharged. Note that when the refrigerant C is supplied to the gap S2, the refrigerant C flows from the gap S2 through the communication path 22D into the gap S1 in the opposite direction to the arrow shown in FIG. 26).

Further, a plurality of nozzle holes 36 communicating with the gas supply path 28 are formed in the nozzle portion 24 . These nozzle holes 36 face diagonally downward in the vertical direction with the vertical direction aligned with the central axis AXL, and the gas injection direction is with respect to the axial direction of the top blow lance 20 (the same direction as the central axis AXL). It is tilted at an angle θ. Further, a plurality of nozzle holes 36 are arranged concentrically around the central axis AXL of the top blowing lance 20 at regular intervals.

The nozzle hole 36 is a through hole with a constricted middle portion, that is, a De Laval nozzle hole. Specifically, in the nozzle hole 36 of this embodiment, the hole diameter decreases from the inlet toward the middle portion, and increases from the middle portion toward the outlet. That is, the nozzle hole 36 of this embodiment has a portion where the diameter of the hole decreases (hereinafter, appropriately referred to as the "throttled portion 36A") and a portion where the diameter increases (hereinafter, appropriately referred to as the "skirt portion 36B"). ), and an intermediate portion with the smallest hole diameter (hereinafter appropriately referred to as "throat 36C"). Note that the diameter of the throat 36C, which has the smallest diameter among the nozzle holes 36, is referred to as the throat diameter _dT . Further, the outlet of the skirt portion 36B has the largest hole diameter among the nozzle holes 36, and the outlet diameter of the skirt portion 36B is appropriately referred to as the outlet diameter _dE of the nozzle hole 36. Here, the oxygen gas G supplied to the gas supply path 28 is accelerated through the constricted part 36A, throat 36C, and skirt part 36B of the nozzle hole 36, and is supplied into the converter as a supersonic jet, for example. .
Note that the present invention is not limited to the above configuration. For example, the nozzle hole 36 may have the same hole diameter from the inlet to the middle portion.

The jet of oxygen gas G injected diagonally downward in the vertical direction from each nozzle hole 36 spreads at an angle with a free spread angle of φ, collides with the hot metal 50 accommodated in the converter, and causes a ignition point on the hot metal bath surface. 52 is formed. Due to the collision energy of the oxygen gas jet, the hot spot 52 has a shape that is recessed relative to the bath surface of the surrounding hot metal 50. Here, the free expansion angle φ is equivalent to the expansion angle of the skirt portion 36B.

By the way, in a converter, when hot metal is decarburized, oxygen gas is injected from a nozzle hole of a top blowing lance onto the hot metal. In a 300-ton converter, the rate of oxygen delivery to the top blowing lance reaches 40,000 to 60,000 Nm ³ /h. The reason why the oxygen gas G is sprayed is to react with carbon in the molten iron to produce molten steel. Therefore, it is important to increase the decarburization oxygen efficiency because the higher the reaction efficiency between oxygen and carbon contained in the oxygen gas that top-blown the hot metal, the more quickly the decarburization process will be completed. During decarburization, a large heat load is placed on the top blowing lance, so a water-cooled triple structure is often used. The nozzle part forming the tip of the top blowing lance is often made of copper, and the cylindrical main body of the top blowing lance is often made of steel. The heat load on the top blowing lance includes heat from the molten iron and the furnace wall, as well as radiant heat from the reaction area (flame point) between oxygen and molten iron. In particular, since oxidation reactions of various hot metal components occur at the hot point, the temperature is said to be much higher than the average temperature of molten iron (2000 to 3000°C in actual measurements). Even if the top-blown lance has a water-cooled triple structure, if it is operated with a water volume and material within an economically reasonable range, the nozzle part (nozzle hole) will wear out after several hundred uses, and the nozzle hole will become worse than when it was new. It is estimated that it will become larger. When the nozzle hole becomes large, the jet of oxygen gas G becomes weaker and the decarburization oxygen efficiency decreases, so it is necessary to periodically replace the nozzle part. Copper nozzle parts are expensive and require a certain number of man-hours to replace. For this reason, the present inventors believed that extending the replacement cycle of the nozzle part would be effective in greatly reducing costs and improving productivity.

Therefore, the present inventors investigated ways to suppress wear and tear on the nozzle portion of the top blowing lance due to increased use. As a result, it was found that wear and tear on the nozzle part was caused by thermal fatigue caused by repeated temperature rises and falls, wear caused by the falling off of adhered base metal, slag, etc., and deformation due to heat. Therefore, the present inventors considered suppressing the amount of radiant heat that the outlet of the nozzle hole receives from the fire point to be lower than a threshold value. As a result, the heat load on the nozzle is reduced by moving the nozzle part that receives heat from the radiant heat from the fire point further away, and by reducing the ratio of the exit diameter of the nozzle hole to the bottom surface of the nozzle part that receives heat. I found out what to do. The conditions for reducing the heat load on the nozzle section, which were discovered by the present inventors, will be explained.

Condition [1]
Using the top-blowing lance 20 designed to satisfy the following formula (1), the amount of radiant heat E that the outlet of the nozzle hole 36 receives from the hot spot 52 formed on the bath surface of the hot metal 50 is as follows (2 ) The lance height H is set to satisfy the equation, and oxygen gas G is blown from the nozzle hole 36 onto the bath surface of the hot metal 50.

Expression (1) will be explained.
100×S _N /S _L <20%...(1)
However, in equation (1), S _N is the total cross-sectional area (m ² ) of the exit of the nozzle hole 36, and S _L is the area (m ² ) of the lower surface of the nozzle portion 24. Note that the area of the lower surface of the nozzle portion 24 is a projected area.

Note that S _N in equation (1) is determined by equation (1-1) below.
S _N =N×πd _E ² /4...(1-1)
However, in equation (1-1), _dE is the exit diameter (m) of the nozzle hole 36.

Furthermore, S _L in equation (1) is determined by equation (1-2) below.
S _L = πD ₁ ² /4...(1-2)
However, in equation (1-2), D ₁ is the outer diameter of the lance, that is, the outer diameter (m) of the outer tube 30.

Expression (2) will be explained.
E=Q _HOT ×N×S _N <12kW...(2)
However, in equation (2), Q _HOT is the thermal radiation intensity of the hot spot (kW/m ² ), and N is the number of hot spots (in this embodiment, since adjacent hot spots do not overlap, the number of nozzle holes 36 ), S _N is the total cross-sectional area of the exit of the nozzle hole 36 (m ² ).

Note that Q _HOT in equation (2) is determined by equation (2-1) below.
Q _HOT = ε×T ⁴ ×σ×A/3600/π/R ² ...(2-1)
However, in equation (2-1), ε is the emissivity (1.0 in this embodiment), T is the temperature at the fire point (°C), and σ is the Stefan Boltzmann coefficient = 20.4 × 10 ^-8 (KJ ×m ⁻² ×K ⁻⁴ ×h ⁻¹ ), A is the fire spot area (m ² ), and R is the distance (m) from the fire spot 52 to the tip of the nozzle portion 24 . Note that the distance R is determined by R=H/cosθ. Further, the flash point temperature T was kept constant at 2000°C.

Further, the fire spot area A is the surface area of a cone with a fire spot radius of D and a fire spot depth of L. Specifically, it is determined by the spark spot area A(m ² )=πD{D+(L ² +D ² ) ^0.5 }. Further, the fire spot radius D is determined by D=R×tanθ, and the fire spot depth L (m) is determined by l/1000. Furthermore, the above l for determining the spark spot depth L is determined by d _T v ₀ cos θ=0.731 ^0.5 (l+H). d _T is the throat diameter (mm) of the nozzle hole 36, _v0 is the linear gas flow velocity (m/s), θ is the inclination angle (deg) of the nozzle hole 36, and d is the throat diameter (mm) of the nozzle hole 36. The height H is the distance (mm) from the tip of the nozzle section 24 to the stationary bath surface. Note that the linear gas flow velocity v ₀ is determined by v ₀ =4Q ₀₂ /(Nπd ² ). Q ₀₂ is the oxygen delivery rate (Nm ³ /s) from the top blowing lance 20.

By satisfying condition [1], the ratio of the exit diameter of the nozzle hole 36 to the lower surface 24A that receives heat of the nozzle portion 24 becomes smaller, and the distance R from the fire point 52 to the tip of the nozzle portion 24 becomes longer, that is. , the nozzle portion 24 becomes farther from the fire point 52. This reduces the thermal load on the nozzle section 24.

Condition [2]
Using the top blow lance 20 designed so that the difference between the outer diameter D ₁ of the outer tube 30 and the inner diameter d ₁ of the outer tube 30 is 0.025 m or less, and the refrigerant flow path determined by equation (3) The flow rate W is set so that the flow velocity V of the refrigerant C flowing through the refrigerant flow path 26 is 2.0 m/sec or more, and the temperature of the refrigerant C supplied to the refrigerant flow path 26 is set to 60° C. or lower, and the hot metal is discharged from the nozzle hole 36. Oxygen gas G is sprayed onto the bath surface of 50.

Equation (3) will be explained.
V=W/((d ₁ ² - D ₂ ² )×π×900)...(3)
However, in equation (3), W is the flow rate (m ³ /hr) of the refrigerant C, d ₁ is the inner diameter (m) of the outer tube 30, and D ₂ is the outer diameter (m) of the inner tube 32.

By satisfying condition [2], the top blowing lance 20 can be appropriately cooled (an appropriate temperature state can be maintained), thereby suppressing shortening of the life of the top blowing lance 20 due to heat load. I can do it.

Next, the functions and effects of one embodiment of the present invention will be explained.

Since the blowing method in the converter of this embodiment satisfies condition [1], compared to the blowing method that does not satisfy condition [1], the blowing method for the nozzle part 24 with respect to the radiant heat from the fire point 52 is Since the heat load is reduced, wear and tear on the nozzle portion 24 can be suppressed. This suppresses wear and tear on the nozzle section 24 due to increased use, and extends the life of the nozzle section 24. As a result, the replacement cycle of the nozzle part 24 is extended, reducing the cost associated with replacing the nozzle part 24 and improving productivity in refining.

In addition, since the above blowing method satisfies condition [2], the top blow lance 20 can be appropriately cooled compared to the blowing method that does not satisfy condition [2], and the top blow lance 20 can be cooled properly due to the heat load. Shortening of the life of the lance 20 can be suppressed. As a result, the replacement cycle of the nozzle part 24 is further extended, so that the cost associated with the replacement of the nozzle part 24 is reduced and the decline in productivity in refining is further improved.

Next, the following tests were conducted to verify the effects of the present invention. In the test, Example 1-11 to which the present invention was applied and Comparative Example 1-4 which did not meet the conditions of the present invention were used. Note that various parameters of Examples and Comparative Examples are as shown in Table 1.

The test conditions will be explained below.
The test was evaluated based on the number of times the top blowing lance was used when the decarburization oxygen efficiency η _C decreased by 10% from immediately after the start of use of the top blowing lance. As for the evaluation criteria, if the number of times of use at the time of 10% decrease was 300 times or more, it was evaluated as "○", and if it was less than 300 times, it was evaluated as "x". Regarding the number of times the lance is used, the process of decarburizing molten iron with a carbon concentration of 3.0% by mass or more to 0.3% by mass or less is counted as one time. In other words, blowing exclusively for dephosphorization is not counted as one time. The evaluation results are shown in Table 1.

The oxygen delivery rate during the test was set at 50,000 Nm ³ /hr. Further, the refrigerant flow rate V and the refrigerant flow rate W were set as shown in Table 1, and the refrigerant temperature was set at 20-25°C.
Since the lance height H may change during blowing, the average lance height during blowing is used as the lance height. Further, as a test top-blowing lance, a lance in which the difference between the outer diameter D ₁ and the inner diameter d ₁ of the outer tube was 0.01 mm was used.

As shown in Table 1, in Examples 1 to 11, a top-blown lance satisfying S _N /S _L <20% was used, and the lance height H was set so that the amount of radiant heat E was 12 kW or less. Therefore, even if the top blowing lance was used over 300 times, the decarburization oxygen efficiency η _C decreased by 10% or less. That is, it is estimated that in Examples 1 to 11 to which the present invention is applied, wear and tear on the nozzle portion due to an increase in the number of times the top blow lance is used is suppressed.

On the other hand, in Comparative Examples 1 and 2, the radiant heat amount E exceeded 12 kW, so the decarburization oxygen efficiency η _C decreased by more than 10% when the top blowing lance was used 300 times or more. In addition, in Comparative Examples 3 and 4, although the radiant heat amount E is 12 kW or less, S _N /S _L exceeds 20%, so similarly to Comparative Examples 1 and 2, when the top-blown lance is used more than 300 times. The decarburization oxygen efficiency η _C decreased by more than 10%.
That is, in Comparative Examples 1 to 4, the lance height H was not set so that S _N /S _L <20% and the amount of radiant heat E was 12 kW or less, so compared to Examples 1 to 11, It is presumed that the effect of suppressing wear and tear on the nozzle part due to an increase in the number of times the top blow lance is used is low.

Further, as shown in Table 1, the parameters of Example 1 are the same as those of Examples 10 and 11 except for the parameters related to the flow rate V of the refrigerant. In this Example 1, since the refrigerant flow velocity V is set to 2.0 m/sec or more, the top blowing lance It is possible to maintain the temperature at an appropriate temperature. As a result, it is estimated that in Example 1, shortening of the life of the top blowing lance due to thermal load is suppressed compared to Example 10 and Example 11. The same applies to Example 2-9 in which the flow velocity V of the refrigerant is set to 2.0 m/sec or more.

From the above test results, it was possible to confirm the usefulness of one embodiment of the present invention.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above, and it is of course possible to implement various modifications other than the above without departing from the spirit thereof. It is.

20 Top blowing lance 22 Body part 24 Nozzle part 24A Lower surface 26 Refrigerant flow path 28 Gas supply path 30 Outer tube 32 Middle tube 34 Inner tube 36 Nozzle hole 50 Hot metal 52 Spark point C Refrigerant G Oxygen gas R Distance S1 Gap S2 Gap d _E Outlet diameter

Claims (2)

A top comprising: a cylindrical main body portion in which a refrigerant flow path and a gas supply path are formed; and a nozzle portion joined to a lower end of the main body portion and in which a plurality of nozzle holes communicating with the gas supply path are formed. A blowing method in which a blowing lance is used to blow oxygen gas from the nozzle hole of the top blowing lance onto the hot metal bath surface in a converter,
The above-mentioned top-blowing lance is designed to satisfy the equation (1), and the amount of radiant heat E received by the outlet of the nozzle hole from the hot spot formed on the surface of the hot metal bath satisfies the equation (2). A blowing method in a converter, in which the oxygen gas is sprayed from the nozzle hole onto the hot metal bath surface by setting a lance height.
100×S _N /S _L <20%...(1)
However, in equation (1), S _N is the total cross-sectional area (m ² ) of the exit of the nozzle hole, and S _L is the projected area (m ² ) of the nozzle portion.
E=Q _HOT ×N×S _N <12kW...(2)
However, in equation (2), Q _HOT is the thermal radiation intensity of the hot spots (kW/m ² ), N is the number of hot spots, and S _N is the total cross-sectional area of the exit of the nozzle hole (m ² ). The main body portion has an outer tube, a middle tube, and an inner tube arranged on the same axis,
The refrigerant flow path is formed by a gap between the outer tube and the middle tube and a gap between the middle tube and the inner tube,
The gas supply path is formed inside the inner tube,
The above-mentioned refrigerant flow is obtained by using the above-mentioned top blowing lance designed such that the difference between the outer diameter D ₁ of the above-mentioned outer pipe and the inner diameter d ₁ of the above-mentioned outer pipe is 0.025 m or less, and using equation (3). The flow rate W is set so that the flow velocity V of the refrigerant flowing through the refrigerant flow path is 2.0 m/sec or more, and the temperature of the refrigerant supplied to the refrigerant flow path is set to 60° C. or lower, and the hot metal is removed from the nozzle hole. The blowing method in a converter according to claim 1, wherein the oxygen gas is sprayed onto a bath surface.
V=W/((d ₁ ² - D ₂ ² )×π×900)...(3)
However, in equation (3), W is the flow rate of the refrigerant (m ³ /hr), d ₁ is the inner diameter (m) of the outer tube, and D ₂ is the outer diameter (m) of the middle tube.