Method for discharging slag

Abstract

To provide a slag discharging method capable of efficiently discharging slag by blowing gas from a lance in a state where the risk of erosion of the lance is small.SOLUTION: Disclosed is a method for discharging slag where a ladle having molten iron and slag is tilted, a lance is lowered from the upper side of the ladle, the horizontal position of the tip of the lance is included in a semicircular region centered on an arc at a point on the circumference of the ladle on the side opposite to a slag discharge port when the ladle is viewed from the upper side, the height of the tip of the lance is within a range of 100 mm above the surface of the stationary slag and 100 mm below the surface of the stationary slag, and the angle formed by the advancing direction of gas exiting the outlet of the lance and the surface of the stationary slag is 45 degrees or larger, the gas is blown onto the molten iron at a flow rate at which the tip of the lance is exposed, and the slag is raked out using a slag raking device to discharge the slag from the slag discharge port.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for discharging slag using a rake. [Background technology]

[0002] Conventionally, in KR desulfurization, molten pig iron is charged into a ladle, and flux is added while stirring the molten pig iron with a stirring blade, and desulfurization is performed. The slag generated in the desulfurization process has a lower density than the molten pig iron, so it floats on the surface of the molten pig iron. When discharging the slag, the stirring blade is lifted from the molten pig iron, and the ladle is tilted while a rake is used to scrape the slag out from the top of the ladle.

[0003] On the other hand, methods have also been proposed for discharging slag by blowing gas above or into the molten iron. Patent Document 1 discloses a technique in which a gas outlet is provided at the top of the inner wall of the slag discharge port of an electric furnace, and gas is blown from the outlet to guide the slag to the port. Patent Document 2 discloses a technique in which a lance is immersed in the molten iron and gas is blown from within the molten iron to generate bubbles, and the slag is quickly discharged by the rise of the bath caused by the gas bubbles and the wave motion phenomenon of the slag layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-139662 A [Patent Document 2] Japanese Patent Application Publication No. 6-194066 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method described in Patent Document 1, even if gas is blown, a hole about the diameter of the lance outlet is formed in the slag, and it is difficult to fluidize the high-density molten iron and slag with the kinetic energy of the gas, so the slag removal effect is small. Also, in the method described in Patent Document 2, since it is assumed that the lance is immersed in the molten iron, the lance tip is subject to severe corrosion, which causes problems in terms of maintenance and cost.

[0006] In consideration of the above-mentioned problems, the present invention aims to provide a slag discharge method that can efficiently discharge slag by spraying gas from a lance with a low risk of lance melting. [Means for solving the problem]

[0007] When discharging slag from a ladle, the conventional method involves using a rake to scrape out the slag while tilting the ladle, but the rake interferes with the ladle, making it difficult to scrape out the slag that has accumulated at the back or edge of the ladle, resulting in problems with slag removal efficiency. On the other hand, in a method of discharging slag by blowing gas from a lance, there is a high risk of the lance tip melting if the lance tip is immersed in the molten iron. Therefore, the inventors of the present invention have conducted extensive research into a method in which the rake is used to scrape out the slag while the ladle is tilted, while also blowing gas so that the slag that has accumulated at the back or edge of the ladle can be scraped out. As a result, they have found gas blowing conditions that allow gas to be blown onto the surface of the molten iron with the tip of the lance exposed, and the rocking of the molten iron to scrape out the slag that has accumulated at the back or edge of the ladle.

[0008] The present invention is as follows. [1] A method for discharging slag, comprising tilting a ladle containing molten iron and slag, and using a slag scraping device to scrape out the slag and discharge it from a slag discharge port, A lance is lowered from above the ladle, The horizontal position of the tip of the lance is included in a semicircular area having a center on a circumference of the ladle opposite to the slag discharge port when viewed from above the ladle, The height of the tip of the lance is set within a range of 100 mm above the stationary slag surface to 100 mm below the stationary molten iron surface, And the angle between the direction of travel of the gas coming out of the outlet of the lance and the stationary slag surface is 45 degrees or more; A method for discharging slag, comprising spraying the gas onto the molten iron at a flow rate such that the tip of the lance is exposed. [2] The method for discharging slag described in [1] above, characterized in that the angle between the direction of travel of the gas leaving the outlet of the lance and the stationary slag surface is 60 degrees or more. [3] The method for discharging slag according to the above [1] or [2], characterized in that the thickness of the slag is adjusted to 100 mm or less before spraying the gas. Effect of the Invention

[0009] According to the present invention, gas can be sprayed from the lance in a state where the risk of melting the lance is small, and slag can be efficiently discharged. [Brief description of the drawings]

[0010] [Figure 1] FIG. 13 is a diagram for explaining the process of discharging slag while the ladle is tilted. [Diagram 2] FIG. 4 is a diagram for explaining a lance height condition in an embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram for explaining a mechanism for improving the scraping efficiency by a rake in an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining the position of a lance tip in an embodiment of the present invention. [Diagram 5] FIG. 4 is a diagram for explaining a lance height in an embodiment of the present invention. [Figure 6] FIG. 2 is a diagram for explaining a method for scraping out slag in an embodiment of the present invention. [Figure 7] FIG. 13 is a diagram showing the results of the surface coverage rate of slag in an embodiment of the present invention. [Figure 8] FIG. 13 is a diagram showing the results of the slag removal efficiency index in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an example in which slag is discharged after KR desulfurization will be described.

[0012] FIG. 1 is a diagram for explaining the manner in which slag is discharged while the ladle is tilted. When discharging the slag, the ladle 1 containing the molten pig iron 2 and the slag 3 is tilted by a tilting device (not shown), and the slag is scraped out by using a rake 4 while gas is blown from a lance 5. The gas blown from the lance 5 toward the molten pig iron 2 penetrates the slag 3, causing the molten pig iron near the lance outlet to flow up and down locally. As shown in FIG. 3, the flow of the molten pig iron causes the slag 3 to flow in a direction away from the gas blowing area, and as a result, the slag at the back or edge of the ladle gathers toward the slag discharge port 6, and the slag can be easily scraped out by moving the rake 4 by a slag scraping control device (not shown). The type of gas blown at this time may be N2 gas or an inert gas such as Ar, but N2 gas is preferable from the viewpoint of cost.

[0013] Next, the conditions of the height, angle and position of the lance will be described. FIG. 2 is a diagram for explaining the conditions of the lance height in this embodiment. After tilting the ladle 1, the lance 5 provided on the upper part of the ladle 1 is lowered, and as shown in FIG. 2, the lance outlet position (lance tip) is within a range of 100 mm above the stationary slag surface to 100 mm below the stationary molten pig iron surface so that gas is sprayed. If the lance tip is located above the stationary slag surface by more than 100 mm, the collision range of the gas on the slag surface increases due to the gas spread angle, while the penetration of the slag becomes insufficient to sufficiently expose the molten pig iron surface, and the molten pig iron flow effect is not obtained sufficiently. On the other hand, if the lance tip is located below the stationary molten pig iron surface by more than 100 mm, the lance tip cannot be sufficiently exposed even if a depression is formed on the molten pig iron surface by gas spraying, and the lance tip is easily melted and damaged.

[0014] The gas flow rate when discharging the slag is not limited to a specific range, but should be such that the molten pig iron fluidization effect is obtained and the gas blowing at least penetrates the slag so that the lance tip does not come into contact with the molten pig iron surface. For example, when the lance tip position is adjusted to a position 100 mm below the stationary molten pig iron surface, the gas flow rate should be such that the gas blowing at least forms a depression in the molten pig iron surface so that the lance tip does not come into direct contact with the molten pig iron and slag. When the lance tip position is adjusted to a position 100 mm above the stationary slag surface, the gas flow rate should be such that the gas blowing at least penetrates the slag so that the molten pig iron fluidization effect is obtained.

[0015] In addition, when adjusting the lance height to the above-mentioned range, gas may be blown after adjusting the lance height, but it is preferable to lower the lance to the above-mentioned range while blowing gas. For example, when adjusting the position of the lance tip to a position 100 mm below the surface of the stationary molten pig iron, if the lance is lowered while blowing gas, the molten pig iron and slag are removed from the vicinity of the lance tip before the lance tip reaches that position, and the lance tip can be prevented from coming into direct contact with the molten pig iron. This can reduce the risk of lance melting compared to the case where gas is blown after adjusting the lance height, although there is a possibility that the lance tip may come into contact with the molten pig iron or slag that has splashed on it.

[0016] Next, the angle and position of the lance will be described. When adjusting the position of the lance tip within the above range, the angle of the lance is set so that the angle between the direction of travel of the gas coming out of the lance outlet and the stationary slag surface is 45 degrees or more, as shown in FIG. 1. If this angle is less than 45 degrees, it becomes difficult for the gas to penetrate the slag by blowing, and it becomes difficult to obtain the fluidization effect of the molten iron. Preferably, the angle between the direction of travel of the gas coming out of the lance outlet and the stationary slag surface is 60 degrees or more. For example, in the case of equipment in which the lance is oriented perpendicular to the horizontal plane, when the lance is lowered with the ladle tilted, the angle between the direction of travel of the gas coming out of the lance outlet and the stationary slag surface is 90 degrees, but this angle may be 90 degrees.

[0017] The horizontal position of the lance tip is within a semicircular region whose center is a point 7 on the circumference of the ladle 1 opposite the slag discharge port 6 when viewed from above, as shown within the dashed line in Figure 3. If the position of the lance tip is outside this range, even if the molten iron is made to flow up and down by blowing gas, the slag that has accumulated at the back of the ladle will not move toward the slag discharge port 6, and the slag cannot be sufficiently scraped out using the rake 4, resulting in a decrease in slag discharge efficiency.

[0018] The direction of the lance is not particularly limited as long as the lance angle is within the above-mentioned range. In the example shown in FIG. 1, the lance is oriented so that the gas comes out toward the opposite side of the slag discharge port, but the lance may be oriented so that the gas comes out toward the slag discharge port, for example. However, as described above, the horizontal position of the lance tip is within a semicircular region with the point 7 on the circumference of the ladle 1 opposite the slag discharge port 6 as viewed from above, so there are operational restrictions, such as when the tilt angle of the ladle is small when discharging the slag. Therefore, as shown in FIG. 1, it is preferable to lower the lance from an oblique direction and direct the lance so that the gas comes out toward the opposite side of the slag discharge port, since this has fewer operational restrictions.

[0019] Furthermore, the smaller the slag thickness, the less energy is required to move the slag by blowing gas, and the more susceptible it is to the effects of the wave motion of the molten iron flowing up and down. Therefore, when the slag thickness is large, it is acceptable to tilt the ladle and only scrape off the slag with a rake without blowing gas until the slag reaches a certain thickness. For example, the thickness of the slag generated by KR desulfurization is considered to be about 200 mm as a guideline, although it varies depending on the conditions. Therefore, it is preferable to only tilt the ladle and scrape off the slag with a rake until the slag thickness reaches 100 mm, and then lower the lance and blow gas when the slag thickness reaches 100 mm or less.

[0020] The method of scraping out the slag with a rake is not particularly limited, but since the slag is gathered from the vicinity of the area where the gas is blown toward the slag discharge port side, for example, the rake is used to scrape out an area on the side including the slag discharge port and a little away from the edge of the ladle, as shown by the dotted line in Figure 6. The slag in this area may be scraped out randomly, or the slag may be scraped out while shifting in the width direction by the width of the rake.

[0021] In addition, in this embodiment, the discharge of slag after KR desulfurization has been described as an example, but as long as it is possible to tilt the vessel containing the molten iron and scrape it out using a rake, and it is possible to blow gas from a lance, the present invention is not limited to the discharge of slag after KR desulfurization. For example, the present invention can also be applied to discharge from a ladle in secondary refining and discharge from an electric furnace. EXAMPLES

[0022] Next, an embodiment of the present invention will be described, but the conditions are merely examples of conditions for confirming the feasibility and effects of the present invention, and the present invention is not limited to the description of the embodiment. The present invention can be implemented in various ways to achieve the object of the present invention without departing from the gist of the present invention.

[0023] In this example, a general thermal fluid simulation was performed to evaluate the slag removal efficiency after KR desulfurization under various conditions. First, the condition was set to 310 tons of molten iron in the ladle, and the slag thickness was set to the conditions shown in Table 1. Then, the lance was lowered while blowing N2 gas from the tip of the lance, and the horizontal position of the lance tip was adjusted to position A shown in FIG. 4(a) or position B shown in FIG. 4(b). Specifically, position A was set to a position d / 4 (d: diameter of ladle 1 at the height of the stationary slag surface) away from point 7 on the circumference opposite to the slag removal opening 6 when viewed from above the ladle 1. Position B was set to a position d / 4 away from the center of the slag removal opening 6 toward the center of the ladle.

[0024] The lance angle during spraying was as shown in Table 1, the outlet hole diameter at the tip of the lance was 12 mm, and the flow rate of N2 gas was 200 Nm 3 / h. The lance height was adjusted in five stages as shown in Figure 5. The lance heights were as follows, and the conditions shown in Table 1 were used for each sample. Height 1: The tip of the lance is 200 mm above the stationary slag surface. Height 2: The tip of the lance is 90 mm above the stationary slag surface. Height 3: The tip of the lance is 10 mm above the surface of the stationary molten iron. Height 4: The tip of the lance is 90 mm below the surface of the stationary molten iron. Height 5: The tip of the lance is 200 mm below the surface of the stationary molten iron.

[0025] The method of scraping out the slag using the rake was the same for all samples. Specifically, as shown in Fig. 6, the slag in the area on one side including the slag discharge port and located d / 8 inward from the edge of the ladle 1 (the area indicated by the dotted line in Fig. 6, hereafter sometimes referred to as the slag scraping area) was scraped out with the rake 4. At this time, the slag was scraped out from the back of the ladle toward the slag discharge port 6 while shifting in the width direction by the width of the rake 4.

[0026] In addition, the surface coverage of the slag and the slag removal efficiency index were calculated based on the amount of slag collected in the slag scraping area by gas blowing. Here, the surface coverage represents the surface coverage immediately before the ladle is tilted to remove the slag while gas is being blown, and is defined as follows:

[0027] When the area of ​​the region inside the ladle viewed from above, behind the horizontal dashed line representing the diameter in Figure 6, at a position halfway through the slag thickness immediately before discharge while the ladle is tilted, is A0, and when the area of ​​the region covered by slag while gas is being sprayed within the same region is A2, the surface coverage rate of the slag was calculated as (A0 + A2) / (2 × A0) × 100. The area of ​​the region covered by slag was calculated using a thermal fluid simulation.

[0028] In addition, assuming that the slag removal efficiency index in Comparative Example 1, where gas blowing was not performed, was 1, the total amount of slag in the ladle was B0, and the amount of slag that had gathered in the slag scraping area due to gas blowing was B1, the slag removal efficiency index in the cases other than Comparative Example 1 was calculated as 1+B1 / B0. The amount of slag that had gathered in the slag scraping area was calculated by thermal fluid simulation. The surface coverage of the slag in each sample is shown in Figure 7, and the slag removal efficiency index in each sample is shown in Figure 8. Specific values ​​for these are shown in Table 1.

[0029] [Table 1]

[0030] As shown in Table 1, in all of Examples 1 to 8, the slag removal efficiency index was 1.02 or more, which improved the slag removal efficiency index compared to the case where gas spraying was not performed. In addition, when gas spraying was performed, the smaller the slag thickness, the more the slag removal efficiency index improved.

[0031] On the other hand, in Comparative Example 2, the position of the lance tip was too high, so the gas could not penetrate the slag, and the vertical flow of the molten pig iron was too small, so the slag that had accumulated near the gas collision area and on the edge of the ladle could not be collected in the slag scraping area. In Comparative Example 3, the angle at which the gas was blown was too small, so the gas could not penetrate the slag, and the vertical flow of the molten pig iron was too small, so the slag that had accumulated near the gas collision area and on the edge of the ladle could not be collected in the slag scraping area.

[0032] In Comparative Examples 4 and 5, gas was blown in the slag scraping area, so the slag that had accumulated near the area where the gas collided and at the back of the ladle could not be gathered in the slag scraping area. In Comparative Example 6, gas was blown directly into the molten iron to make it flow in the vertical direction, so the slag removal efficiency index was equivalent to that of the Examples, but the lance tip was positioned too deep, so the lance tip was always immersed in the molten iron when the slag was being discharged, resulting in significant corrosion damage to the lance tip.

[0033] Although this embodiment is a result of a thermal fluid simulation, the above-mentioned slag surface coverage rate and slag removal efficiency index can be obtained by actual measurement. That is, the area covered by slag required to obtain the slag surface coverage rate can be confirmed from a camera image taken by a camera, and the area of ​​the area can be calculated. Furthermore, the amount of slag that has gathered in the slag removal area required to obtain the slag removal efficiency index can be determined by obtaining the amount of slag removed by gas blowing from a camera image taken of the vicinity of the exposed molten iron, and the amount of slag that has been removed can be regarded as the amount of slag that has gathered in the slag removal area. [Explanation of symbols]

[0034] 1 ladle 2. Molten iron 3. Slug 4. Rake 5. Lance 6. Slag outlet

Claims

1. A method for discharging slag, comprising tilting a ladle containing molten iron and slag, and using a slag scraping device to scrape out the slag and discharge it from a slag discharge port, A lance is lowered from above the ladle, The horizontal position of the tip of the lance is included in a semicircular area having a center on a circumference of the ladle opposite to the slag discharge port when viewed from above the ladle, The height of the tip of the lance is within a range of 100 mm above the stationary slag surface to 100 mm below the stationary molten iron surface, The angle between the direction of travel of the gas coming out of the outlet of the lance and the stationary slag surface is set to 45 degrees or more. A method for discharging slag, comprising spraying the gas onto the molten iron at a flow rate such that the tip of the lance is exposed.

2. 2. The method for discharging slag according to claim 1, characterized in that the angle between the direction of travel of the gas emerging from the outlet of the lance and the surface of the stationary slag is set to be 60 degrees or more.

3. 3. The method for discharging slag according to claim 1, wherein the thickness of the slag is adjusted to 100 mm or less before the gas is sprayed onto the slag.

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