METHOD FOR REMOVING METAL FROM THE FURNACE MOUTH AND METHOD FOR OPERATING A FURNACE

Abstract

To provide a method for removing metal from a converter mouth and a method for operating the converter, capable of removing metal adhering to the converter mouth while suppressing reduction in productivity of the converter.SOLUTION: In a method for removing the metal from a converter mouth, the metal 28 adhering to the mouth 20 of the converter 12 is melted and removed by blowing oxygen gas. Oxygen gas is sprayed on the metal in the state that molten metal 26 exists in the converter 12.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for removing metal from the throat of a converter, in which oxygen gas is blown onto the metal adhering to the throat of the converter to dissolve and remove the metal, while molten iron is present in the converter, and a method for operating a converter. [Background technology]

[0002] In the refining of molten iron using a converter, a top-blowing lance is inserted into the furnace through the throat, and high-purity oxygen gas is blown from the top-blowing lance toward the molten iron in the converter to remove impurities and carbon from the molten iron through an oxidation reaction. During molten iron refining, the high-velocity oxygen gas blows some of the molten iron upward, causing it to adhere to the throat and solidify and deposit near the throat. Furthermore, after refining is completed, some of the molten iron solidifies and deposits near the throat when the furnace is tilted for tapping or slag removal. If the amount of metal adhering near the throat increases, the diameter of the throat is narrowed by the metal, making it difficult to charge scrap iron, molten pig iron, and auxiliary materials through the throat. Furthermore, if metal adheres near the throat, the molten steel cannot be obtained, resulting in a decrease in the converter's tapping yield.

[0003] As described above, when metals adhere to the throat of a converter, various problems arise, and therefore a technique for removing the metals adhered to the throat is desired. As a technique for removing metals, Patent Document 1 discloses a method for removing metals at the throat of a converter-type refining furnace when the furnace is not being refining, in which oxygen gas is blown onto the metals adhering to the throat using a metal-melting lance having an oxygen supply passage therein, thereby removing the metals. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-251735 Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology disclosed in Patent Document 1, oxygen gas is sprayed onto the metal adhering to the throat during non-refining periods to dissolve and remove the metal. This means that the converter cannot be used while the metal is being dissolved and removed, resulting in a problem of reduced productivity of the converter. The present invention has been made in consideration of the problems of the prior art, and its object is to provide a method for removing metal adhering to the throat of a converter and a method for operating a converter, which can remove metal adhering to the throat of a converter while suppressing a decrease in productivity of the converter. [Means for solving the problem]

[0006] The means for solving the above problems are as follows. [1] A method for removing metal from the throat of a converter, in which oxygen gas is blown onto the metal adhering to the throat of a converter to dissolve and remove the metal, in which oxygen gas is blown onto the metal while molten metal is present in the converter. [2] A method for removing metal at the throat of a converter according to [1], in which the oxygen gas is sprayed onto the metal using a top-blowing lance used in refining molten iron, the top-blowing lance having an attachment attached to its tip for spraying the oxygen gas in a radial direction. [3] The method for removing metal at the throat of a converter according to [1] or [2], wherein the oxygen gas is blown onto the metal during decarburization refining. [4] The method for removing metal at the furnace throat of a converter according to [3], wherein the oxygen gas is blown onto the metal after a predetermined time has elapsed since the start of decarburization refining. [5] The method for removing metal at the converter furnace throat according to [4], wherein the time is the time from when the decarburization refining starts until the carbon concentration of the molten iron reaches a predetermined carbon concentration or less through the decarburization refining. [6] A method for operating a converter, comprising the steps of removing metal from the converter furnace throat by the method for removing metal from the furnace throat according to any one of [1] to [5], while introducing oxygen gas from the bottom tuyeres to continue decarburization refining. [Effects of the Invention]

[0007] According to the present invention, when molten metal is present in a converter, oxygen gas is blown onto the metal adhering to the vicinity of the throat to dissolve and remove the metal, thereby making it possible to remove the metal adhering to the vicinity of the throat of the converter while suppressing a decrease in productivity of the converter. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a state in which decarburization refining of molten iron is carried out using converter equipment in which the converter throat metal removal method according to this embodiment can be carried out. [Figure 2] FIG. 2 is a cross-sectional schematic diagram showing the state in which oxygen gas is blown onto metal using converter equipment. [Figure 3] FIG. 3 is an enlarged schematic view of part A in FIG. [Figure 4] FIG. 4 is a graph showing the tapping yields of the invention examples and the comparative examples. [Figure 5] FIG. 5 is a graph showing the scrap consumption rate for the invention example and the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described below with reference to an embodiment. Fig. 1 is a cross-sectional schematic diagram showing a state in which decarburization refining of molten iron 22 is carried out using a converter furnace 10 in which a converter furnace throat ingot removal method according to this embodiment can be carried out. The converter furnace 10 has a converter 12, a top-blowing lance 14, and an ingot melting lance (described later). The converter 12 has a bottom-blowing tuyeres 16 and a gas introduction pipe 18 for introducing a stirring gas 27 into the bottom-blowing tuyeres 16.

[0010] In the converter furnace 10 shown in FIG. 1 , oxygen gas (mainly industrially pure oxygen gas) is blown from a top-blowing lance 14 toward molten iron 22 charged into the furnace through a furnace throat 20, thereby performing decarburization refining of the molten iron 22. In the decarburization refining, the carbon contained in the molten iron 22 undergoes a decarburization reaction with oxygen in the oxygen gas blown from the top-blowing lance 14, thereby reducing the carbon concentration of the molten iron 22 and adjusting the carbon concentration of the molten iron 22 to within a target carbon concentration range. In the decarburization refining, a CaO-based flux such as quicklime is added to the converter 12 as a dephosphorization agent and a slag basicity adjuster. The CaO-based flux turns to slag and forms molten slag 24 in the furnace. In this embodiment, the molten iron 22 and the molten slag 24 are collectively referred to as molten metal 26. The molten iron 22 may be either molten pig iron or molten steel, and may also contain a molten cold iron source. The oxygen gas blown from the top blowing lance 14 has an oxygen concentration of, for example, 99.5% by volume or more.

[0011] Flying particles of molten iron 22 adhere to and accumulate near the throat 20 of the converter 12, forming ingots 28. The ingots 28 adhering to the throat 20 grow larger as the converter 12 continues to operate. As the ingots 28 grow larger, they impede the charging of molten iron 22 and scrap iron into the converter 12. To prevent this, it is necessary to dissolve and remove the ingots 28 adhering to the throat 20 before they grow larger.

[0012] In the converter throat metal removal method according to this embodiment, oxygen gas (mainly industrially pure oxygen gas) is blown onto the metals 28 adhering to the vicinity of the throat 20 while molten metal 26 is present in the converter 12, thereby dissolving and removing the metals 28. As shown in FIG. 1 , when decarburization refining of molten iron 22 is performed using a converter furnace facility 10, a top-blown lance 14 and a metal-melting lance for refining are prepared in advance, and during decarburization refining, the top-blown lance 14 is replaced with the metal-melting lance, and oxygen gas is blown onto the metals 28 from the metal-melting lance to dissolve and remove the metals 28. Here, replacing the top-blown lance 14 with the metal-melting lance means that a metal-melting lance is prepared in advance above the converter 12 in a usable state, the positions of the metal-melting lance and the top-blown lance 14 are changed, and the metal-melting lance is inserted into the converter 12 in place of the top-blown lance 14.

[0013] FIG. 2 is a cross-sectional schematic diagram showing the blowing of oxygen gas onto ingots 28 using converter equipment 10. As shown in FIG. 2, the top-blown lance 14 is replaced with a metal-melting lance 30, and oxygen gas is blown from the metal-melting lance 30 onto ingots 28 adhering to the vicinity of the throat 20. This allows secondary combustion of the converter gas generated by decarburization refining and the ingots 28 to oxidize and generate heat, thereby dissolving and removing the ingots 28 adhering to the vicinity of the throat 20, and allowing the ingots 28 to be recovered. The flow rate of the oxygen gas blown onto the ingots 28 from the metal-melting lance 30 is preferably set to a flow rate that allows the ingots 28 to be dissolved and removed in a short time, so as to prevent a temperature drop in the molten metal 26 from making it difficult to discharge the molten iron 22 from the converter 12 and to prevent re-adhesion of the ingots to the throat 20 when the molten iron 22 is discharged. The oxygen gas blown onto the ingots 28 also has an oxygen concentration of, for example, 99.5% by volume or more.

[0014] The height of the metal-melting lance 30 is preferably adjusted according to the state of the metal 28 attached so that the maximum heat-generating part of the flame formed by the oxygen gas blowing is located at the position where the metal 28 is attached. On the other hand, if the height of the metal-melting lance 30 is made too high and oxygen gas is blown onto the furnace throat 20 where no metal 28 is attached, the oxygen may be blown directly onto the converter auxiliary equipment (skirt) having an internal water-cooling structure, or the molten metal may splash (splash), causing localized melting of the skirt steel shell and water leakage, which is undesirable. Also, if the height of the metal-melting lance 30 is made too low and oxygen gas is blown onto refractory material where no metal 28 is attached, the refractory may be melted and damaged, which is undesirable.

[0015] Even during the melting and removal of the ingots 28, oxygen gas is introduced as the stirring gas 27 into the molten iron 22 from the bottom-blown tuyeres 16 to continue the decarburization refining. When the carbon concentration of the molten iron 22 falls within the target carbon concentration range, the decarburization refining of the molten iron 22 is terminated. After the melting and removal of the ingots 28, the ingot melting lance 30 may be replaced with the top-blown lance 14, or the ingot melting lance does not have to be replaced with the top-blown lance 14. When the ingot melting lance 30 is replaced with the top-blown lance 14 after the melting and removal of the ingots 28, oxygen gas may be blown onto the molten iron 22 from the top-blown lance 14 again to continue the decarburization refining of the molten iron 22. On the other hand, when the ingot melting lance 30 is not replaced with the top-blown lance 14 after the melting and removal of the ingots 28, the decarburization refining is continued by introducing oxygen gas into the molten iron 22 from the bottom-blown tuyeres 16, as described above.

[0016] As described above, in the converter furnace throat ingot removal method according to this embodiment, oxygen gas is blown onto the ingot 28 while the molten metal 26 is present in the converter 12, thereby melting and removing the ingot 28. This allows the ingot 28 to be removed while the converter 12 is in use, thereby suppressing a decrease in productivity of the converter facility 10. Furthermore, by melting and removing the ingot 28 while the molten metal 26 is present in the converter 12, the ingot 28 can be recovered in the molten iron 22, thereby suppressing a decrease in the tapping yield during converter operation.

[0017] In the above embodiment, an example in which oxygen gas is introduced from the bottom-blowing tuyeres 16 during the melting and removal of the ingots 28 has been described. However, this is not limiting, and oxygen gas does not necessarily have to be introduced from the bottom-blowing tuyeres 16 during the melting and removal. Even without introducing oxygen gas from the bottom-blowing tuyeres 16, decarburization and refining of the molten iron 22 proceeds due to oxygen derived from iron oxide recovered by the melting and removal of the ingots 28. Furthermore, in the later stage of decarburization and refining, carbon diffusion in the molten iron 22 becomes the rate-limiting factor for the decarburization reaction. Therefore, decarburization and refining of the molten iron 22 proceeds even after the lance is replaced with the ingot melting lance 30. Since decarburization and refining proceeds without introducing oxygen gas from the bottom-blowing tuyeres 16, it can be seen that a decrease in productivity of the converter furnace facility 10 can be suppressed by blowing oxygen gas onto the ingots 28 while the molten metal 26 is present in the converter 12 to melt and remove the ingots 28. However, it is preferable to introduce oxygen gas as stirring gas 27 from the bottom-blowing tuyeres 16 into the molten iron 22 even during the dissolution and removal of the metal 28, which further suppresses a decrease in productivity of the converter facility 10.

[0018] Furthermore, after a predetermined time has elapsed since the start of decarburization refining of the molten iron 22, it is preferable to replace the top-blowing lance 14 with a metal melting lance 30 and blow oxygen gas onto the metal 28 adhering to the vicinity of the furnace throat 20 to dissolve and remove the metal 28. The metal 28 dissolved and removed by blowing oxygen gas contains a large amount of oxygen. When such metal 28 containing a large amount of oxygen is mixed with molten iron with a high carbon concentration, the decarburization reaction progresses rapidly, causing bumping, and spitting (also known as slopping) in which a mixture of the molten iron 22 and molten slag 24 in the furnace is ejected from the furnace throat 20. In contrast, after a predetermined time has elapsed since the start of decarburization refining, the carbon concentration of the molten iron 22 has decreased due to the decarburization refining. Therefore, even if metal 28 containing a large amount of oxygen is mixed with the molten iron 22, the decarburization reaction does not progress rapidly, thereby suppressing spitting. In this way, by dissolving and removing the ingot 28 after a predetermined time has elapsed since the start of decarburization refining, spitting that occurs when the ingot 28 is dissolved and removed can be suppressed.

[0019] As described above, the occurrence of spitting depends on the carbon concentration of the molten iron 22. Therefore, the time from the start of decarburization refining to the start of dissolution and removal of the ingots 28 can be predetermined based on the carbon concentration of the molten iron 22, which decreases as a result of decarburization refining. That is, this time is predetermined as the time until the carbon concentration of the molten iron 22 reaches a predetermined carbon concentration or less through decarburization refining. The predetermined carbon concentration of the molten iron 22 is, for example, 1.0 mass% or less. It has been confirmed that by starting dissolution and removal of the ingots 28 after waiting for a certain time from the start of decarburization refining until the carbon concentration of the molten iron 22 reaches 1.0 mass% or less, spitting does not occur even if the dissolved and removed ingots 28 are mixed with the molten iron 22. This result shows that by starting dissolution and removal of the ingots 28 after waiting for a certain time until the carbon concentration of the molten iron 22 reaches 1.0 mass% or less, the ingots 28 adhering to the furnace throat 20 can be dissolved and removed while preventing spitting. It is more preferable that the carbon concentration of the molten iron 22 at which the dissolution and removal of the base metal 28 is started is 0.4 mass % or less.

[0020] Furthermore, immediately after the start of decarburization refining, the temperature of the molten iron 22 is low, and therefore the temperature of the converter gas near the throat 20 is also low. This low temperature of the converter gas near the throat 20 makes it difficult for the oxygen in the oxygen gas blown onto the ingots 28 to ignite. Therefore, even if oxygen gas is blown onto the ingots 28 from the ingot melting lance 30, secondary combustion of the converter gas cannot be immediately initiated, and it may take a long time to dissolve and remove the ingots 28 adhering to the throat 20. In contrast, as decarburization refining progresses, the temperature of the molten iron 22 rises because the decarburization reaction is an exothermic reaction. This increase in the temperature of the molten iron 22 also increases the temperature of the converter gas near the throat 20, making it easier for the oxygen in the oxygen gas blown onto the ingots 28 to ignite. As a result, blowing oxygen gas onto the ingots 28 from the ingot melting lance 30 makes it easier for secondary combustion of the converter gas to occur, and the ingots 28 adhering to the throat 20 can be dissolved and removed in a short time.

[0021] Next, the metal melting lance 30 will be described. Figure 3 is an enlarged schematic view of part A in Figure 2. Figure 3(a) is an enlarged schematic view of part A, and Figure 3(b) is a cross-sectional view taken along line B-B of Figure 3(a). The arrow in Figure 3(b) indicates the direction of oxygen gas ejection. As shown in Figures 3(a) and (b), the metal melting lance 30 is a lance having the same structure as the top-blowing lance 14 used in refining molten iron 22, with an attachment 32 attached to the tip of the lance for ejecting oxygen gas radially in the radial direction of the lance. The attachment 32 may be attached by fastening it with a bolt to the center hole of the lance tip at the tip of the top-blowing lance 14.

[0022] By using the metal melting lance 30 configured as described above, oxygen gas can be sprayed onto the metal 28 adhering to the furnace throat 20, thereby dissolving and removing the metal 28. Furthermore, if the attachment 32 is removed from the metal melting lance 30, it can be used as a top-blowing lance 14 for refining, so that even if a problem such as a water leak occurs in the top-blowing lance 14, oxidation refining can be continued.

[0023] Although the present embodiment has been described using an example of decarburization refining, the method is not limited to decarburization refining, and may be a preliminary treatment for desiliconization or dephosphorization of the molten iron 22, as long as the ingots 28 adhering to the furnace throat 20 are dissolved and removed in the presence of the molten metal 26. This allows the oxidation refining of the molten iron 22 to proceed even during the dissolution and removal of the ingots 28, thereby suppressing a decrease in productivity of the converter 12. [Example]

[0024] An example will be described in which oxygen gas is sprayed onto the ingots 28 adhering to the throat 20 of the converter 12 using the converter equipment 10 shown in Figures 1 and 2 to dissolve and remove the ingots 28. In this example, the height from the molten metal surface to the ingot melting lance 30 is set to 4.4 to 4.6 m, and a 300 Nm blast is directed from this position toward the ingots adhering to the throat 20 during decarburization refining. 3 / min of industrial pure oxygen was blown, and the bottom blowing tuyeres were 16 to 40 Nm 3 / min of industrially pure oxygen was introduced to continue decarburization refining. After decarburization refining, the state of adhesion of ingots 28 at the throat 20 was checked, and the amount of ingots 28 adhering to the throat 20 was found to have decreased. This operation was performed for 12 charges, and the number of operations for removing ingots at the throat was reduced by 30% compared to the conventional method. As a result, the operating rate of the converter equipment 10 improved by 0.5%. This confirmed that a decrease in productivity of the converter equipment 10 could be suppressed. On the other hand, in the comparative example, decarburization refining was performed without dissolving and removing ingots. This operation was performed for 20 charges, and the tapping yield and scrap consumption rate of the invention example and the comparative example were confirmed. The tapping yield was calculated using the following formula (1). Tap yield (%) = (tapped steel amount (t) / weight of metal raw materials charged to the converter (t, excluding the amount of raw materials removed from the steel by oxidative combustion, such as C and Si)) × 100 (1)

[0025] Fig. 4 is a graph showing the tapping yield (%) of an example and a comparative example. As shown in Fig. 4, the comparative example, in which the ingot 28 was not dissolved and removed during decarburization refining, had a tapping yield of 97.2%. This result is thought to be due to the fact that part of the molten iron 22 adhered to the throat 20 and turned into ingot during decarburization refining, resulting in a lower tapping yield. On the other hand, the example of the invention, in which the ingot 28 was dissolved and removed during decarburization refining, had a tapping yield of 99.9%. In the example of the invention, too, part of the molten iron 22 adhered to the throat 20 during decarburization refining and turned into ingot, but the ingot was recovered by blowing oxygen gas to dissolve and remove it, which is thought to be why a high tapping yield was achieved.

[0026] FIG. 5 is a graph showing the scrap consumption rate (kg / t) for the example and the comparative example. The scrap consumption rate is the amount of scrap (kg) used to produce 1 ton of molten steel. As shown in FIG. 5, the scrap consumption rate for the comparative example, in which the ingots 28 were not melted and removed during decarburization refining, was 23.4 kg / t. This result was due to the scrap being charged through a small charging chute because the ingots 28 adhered to the throat 20, reducing the throat diameter. On the other hand, in the example in which the ingots 28 were melted and removed during decarburization refining, scrap could be charged through a normal charging chute, resulting in a higher scrap consumption rate than the comparative example. These results confirm that by implementing the converter throat ingot removal method according to this embodiment and the converter operation method using this converter throat ingot removal method, it is possible to suppress a decrease in productivity of the converter facility 10, increase the steel tapping yield, and increase the scrap consumption rate. [Explanation of symbols]

[0027] 10 Converter equipment 12 Converter 14 Top blowing lance 16 Bottom-blown tuyere 18 Gas inlet pipe 20 Hearth 22 Molten Iron 24 Molten slag 26 Molten Metal 27 Stirring gas 28 Bullion 30 Metal melting lance 32 Attachment 34 volts

Claims

1. A method for removing metal from the throat of a converter, comprising blowing oxygen gas onto the metal adhering to the throat of a converter to dissolve and remove the metal, a converter furnace throat ingot removal method, comprising: spraying the oxygen gas onto the ingot after a predetermined time has elapsed since the start of decarburization refining of the molten iron while the molten metal is present in the converter.

2. 2. The method for removing metal at the throat of a converter according to claim 1, wherein the oxygen gas is sprayed onto the metal using a top-blowing lance used in refining molten iron, the top-blowing lance having an attachment attached to its tip for spraying the oxygen gas in a radial direction.

3. 2. The converter furnace throat ingot removal method according to claim 1, wherein the time is a time from when the decarburization refining starts until the carbon concentration of the molten iron reaches a predetermined carbon concentration or less as a result of the decarburization refining.

4. 3. The converter furnace throat ingot removal method according to claim 2, wherein the time is a time from when the decarburization refining starts until the carbon concentration of the molten iron reaches a predetermined carbon concentration or less as a result of the decarburization refining.

5. A method for operating a converter, comprising: introducing oxygen gas from a bottom tuyeres to continue decarburization refining while removing the metal by the method for removing metal at the converter furnace throat according to any one of claims 1 to 4.

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