Molten oxide foaming control method and molten iron refining method

Abstract

To provide a novel method enabling foaming control of molten oxide.SOLUTION: A method for controlling the foaming of molten oxide includes blowing gas into the molten oxide through a blowing hole of gas blowing means. The gas blowing means has a conductive part. The conductive part has the blowing hole. When the gas is blown into the molten oxide from the blowing hole, the molten oxide and the conductive part come into contact with each other, and a potential difference between the molten oxide and the conductive part is controlled.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present application discloses a method for controlling foaming of molten oxides and a method for refining molten iron. [Background technology]

[0002] Methods of refining molten iron by the blast furnace-converter process and the electric furnace process are known. In both refining processes, impurities such as silicon, phosphorus, and carbon in the metal are reduced and removed. Carbon in the metal is oxidized and removed as CO gas by blowing high-pressure oxygen gas onto the molten iron or by reacting with FeO in the molten oxide generated by adding quicklime, etc. At this time, the CO gas generated remains in the molten oxide, causing the molten oxide to foam and expand, a phenomenon called foaming. Foaming has the effect of promoting the refining reaction by providing stirring and increasing the reaction interface area, but it also causes problems such as slopping, in which the molten oxide overflows from the furnace throat due to excessive foaming, and a decrease in the slag discharge rate due to insufficient foaming when the molten oxide is discharged. Therefore, in the refining process, it is important to control the foaming of the molten oxide from the viewpoint of improving productivity. Patent Documents 1 to 3 are known as methods for controlling foaming in the refining process. Patent Document 1 discloses a method of changing the gas pressure in the furnace depending on the degree of foaming measured. Patent Document 2 discloses a method of adding coke powder together with a desiliconizing material while molten iron is being received in a molten iron ladle. Patent Document 3 discloses a method of adding a substance that has a foaming calming effect. Meanwhile, Patent Documents 4 and 5 disclose methods of injecting gas into molten metal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 62-224613 [Patent Document 2] Japanese Patent Application Publication No. 8-209215 [Patent Document 3] Patent Publication No. 2021-147670 [Patent Document 4] JP 2016-107312 A [Patent Document 5] JP 2017-024069 A Summary of the Invention [Problem to be solved by the invention]

[0004] The method disclosed in Patent Document 1 is a method of controlling foaming by the gas pressure in the furnace, but the range of gas pressure in the furnace that can be controlled within the range of operating conditions is narrow, so the control of foaming is limited. In addition, the method disclosed in Patent Document 2 is a method of suppressing foaming by injecting coke powder together with a desiliconizing material while the molten iron is being received in a molten iron ladle, and has no effect of promoting foaming. Furthermore, due to the recent increase in interest in zero carbon worldwide, the method of injecting coke powder to generate CO gas goes against the trend of technological development. The method disclosed in Patent Document 3 is a method of calming slag foaming by injecting a substance that has a calming effect on slag foaming, and has no effect of promoting foaming. In addition, unnecessary components are mixed in as a calming agent, which may make the subsequent refining process complicated. On the other hand, the methods disclosed in Patent Documents 4 and 5 are directed to molten metal as the target of gas injection, and have a different mechanism from foaming.

[0005] As described above, a new method capable of controlling foaming, such as maintaining, easing, and promoting foaming, is needed. [Means for solving the problem]

[0006] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> 1. A method for controlling foaming of a molten oxide, comprising: blowing gas into the molten oxide through a blowing hole of a gas blowing means; The gas blowing means has a conductive portion, the conductive portion has the blowing hole, When the gas is blown into the molten oxide from the blowing hole, the molten oxide comes into contact with the conductive part, and a potential difference between the molten oxide and the conductive part is controlled. A method for controlling forming of molten oxide. <Aspect 2> A method for controlling foaming of a molten oxide according to embodiment 1, comprising the steps of: The potential difference is controlled to be less than 1 V. A method for controlling forming of molten oxide. <Aspect 3> A method for controlling foaming of a molten oxide according to embodiment 1, comprising the steps of: The potential difference is controlled to be 1 V or more. A method for controlling forming of molten oxide. <Aspect 4> A method for controlling foaming of a molten oxide according to any one of aspects 1 to 3, comprising: the gas comprises a gas inert to the molten oxide; A method for controlling forming of molten oxide. <Aspect 5> A method for controlling foaming of a molten oxide according to embodiment 4, comprising the steps of: The gas contains at least one selected from Ar, He, and N2; A method for controlling forming of molten oxide. <Aspect 6> A method for controlling foaming of a molten oxide according to any one of aspects 1 to 3, comprising: the gas comprises a gas active with respect to the molten oxide; A method for controlling forming of molten oxide. <Aspect 7> A method for controlling foaming of a molten oxide according to embodiment 6, comprising the steps of: The gas contains at least one selected from O2, CO, CO2, H2, and H2O; A method for controlling forming of molten oxide. <Aspect 8> A method for controlling foaming of a molten oxide according to any one of aspects 1 to 7, comprising: The potential difference is controlled so that the potential of the conductive portion is higher than the potential of the molten oxide. A method for controlling forming of molten oxide. <Aspect 9> A method for refining molten iron, comprising the steps of: The forming control method according to any one of aspects 1 to 8 includes blowing gas into a molten oxide present on the surface of the molten iron to generate bubbles in the molten oxide. A method of refining molten iron. Effect of the Invention

[0007] The method of the present disclosure allows for control of foaming, including maintaining, quenching and promoting foaming of the molten oxide. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic diagram for explaining a forming control method according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram for explaining a forming control method according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 1. Method for controlling forming of molten oxide The forming control method of the present disclosure will be described with reference to the drawings. However, the forming control method of the present disclosure is not limited to the illustrated form. As shown in Figs. 1 and 2, the forming control method of the molten oxide 10 according to one embodiment includes blowing a gas 30 into the molten oxide 10 from a blowing hole 22 of a gas blowing means 20. Here, the gas blowing means 20 has a conductive part 21. The conductive part 21 has the blowing hole 22. In this embodiment, when the gas 30 is blown into the molten oxide 10 from the blowing hole 22, the molten oxide 10 and the conductive part 21 come into contact with each other, and the potential difference between the molten oxide 10 and the conductive part 21 is controlled.

[0010] 1.1 Molten oxide The type of the molten oxide 10 is not limited. The molten oxide 10 may be, for example, molten slag. The molten oxide 10 may contain, for example, at least Ca, Si, and Fe as constituent elements. In this case, the basicity (CaO / SiO2) of the molten oxide 10 is not particularly limited. For example, a higher effect is likely to be obtained when the basicity is 0.5 or more and 6.0 or less. A higher effect is likely to be obtained when the molten oxide 10 contains, for example, 20 mass% or more and 70 mass% or less of CaO, or 5 mass% or more and 50 mass% or less of SiO2. Also, a higher effect is likely to be obtained when the molten oxide 10 contains, for example, 5 mass% or more and 60 mass% or less of FeO. The viscosity of the molten oxide 10 may be, for example, 0.01 Pa·s or more and 10 Pa·s or less at 1600°C. The molten oxide 10 may be present on the surface of another liquid. For example, the molten oxide 10 may be present on the surface of molten iron. The molten oxide 10 may have a certain thickness or more in a state where no bubbles are present. For example, the molten oxide 10 may have a thickness of 5 mm or more in a state where no bubbles are present. The upper limit of the thickness is not particularly limited. The molten oxide 10 may also contain a solid phase. The solid phase is the remaining CaO added to form the molten oxide, crystals formed by cooling the molten oxide, etc. A higher effect is likely to be obtained when the solid phase rate is 50% or less.

[0011] 1.2 Gas injection means The gas blowing means 20 may be any one capable of blowing gas into the molten oxide 10 while applying a potential difference described below. The gas blowing means 20 has a conductive part 21, and the conductive part 21 has a blowing hole 22. As shown in FIG. 1, the gas blowing means 20 may be a nozzle or lance having at least a conductive part 21 at a tip portion and at least one blowing hole 22 at the tip portion. Alternatively, as shown in FIG. 2, the gas blowing means 20 may have a furnace wall (conductive part 21) made of a conductive material and a hole (blow hole 22) provided in the furnace wall. The gas blowing means 20 may be connected to a gas supply source. The configuration of the gas blowing means 20 from the gas supply source to the blowing hole 22 is not particularly limited. The configuration of the gas blowing means 20 other than the conductive part 21 and the blowing hole 22 is not particularly limited as long as it is capable of applying a potential difference described below.

[0012] The conductive part 21 refers to a part having conductivity to such an extent that a potential difference can be applied, as described below. As described below, the conductive part 21 comes into contact with the molten oxide 10 during gas injection. Therefore, the conductive part 21 is preferably made of a conductive material that has low reactivity with the molten oxide 10 and is not easily dissolved. In one embodiment, the conductive part 21 may be made of a metal or an ion-conductive refractory material. For example, the material of the conductive part 21 may be at least one selected from an iron-based alloy including stainless steel, copper, tungsten, and zirconium oxide. The shape of the conductive part 21 depends on the shape of the gas injection means 20. The conductive part 21 may also have a water-cooling mechanism.

[0013] The conductive part 21 has a blowing hole 22. When the gas 30 is blown into the molten oxide 10, the blowing hole 22 is disposed in the molten oxide 10. By blowing the gas into the molten oxide 10 from the blowing hole 22, bubbles can be generated in the molten oxide 10. In this embodiment, the diameter of the bubbles blown from the blowing hole 22 can be controlled by controlling the potential difference described later, regardless of the shape of the blowing hole 22. In particular, when the opening diameter (circle equivalent diameter) of the blowing hole 22 is 0.1 mm or more and 50 mm or less, and particularly 0.3 mm or more and 25 mm or less, the control range of the bubble diameter becomes wider. The number of the blowing hole 22 provided in the conductive part 21 is at least one, and may be two or more. In addition, the conductive part 21 may be porous. That is, a plurality of fine holes may be formed in the conductive part 21, and the gas 30 may be blown into the molten oxide 10 from the holes.

[0014] 1.3 Gas The type of gas 30 to be blown into the molten oxide 10 is not particularly limited. In one embodiment, the gas 30 may contain a gas inert to the molten oxide 10. Specifically, the gas 30 may contain at least one selected from Ar, He, and N2. In this case, the gas 30 may contain 90% by volume to 100% by volume, or 95% by volume to 100% by volume, of a gas inert to the molten oxide 10. When the gas 30 inert to the molten oxide 10 is blown, the gas 30 does not substantially react with the molten oxide 10, and the gas 30 is likely to maintain a constant bubble diameter. For example, when the gas 30 is blown into the molten oxide 10 to generate large bubbles in the molten oxide 10, the gas 30 being an inert gas maintains the large bubbles in the molten oxide 10, and the effect of maintaining or calming the foaming as described below can be expected. That is, in the method for controlling foaming according to one embodiment, a gas inert to the molten oxide 10 is blown into the molten oxide 10, and the potential difference described below is controlled (e.g., the potential difference is controlled to less than 1 V), thereby maintaining or calming the foaming of the molten oxide 10. By using the gas 30 inert to the molten oxide 10, for example, it becomes possible to control the foaming of the molten oxide 10 without substantially affecting the refining process.

[0015] In one embodiment, the gas 30 may contain a gas active against the molten oxide 10. Specifically, the gas 30 may contain at least one selected from O2, CO, CO2, H2, and H2O. In this case, the gas 30 may contain more than 50 vol% and 100 vol% or less of the gas active against the molten oxide 10, 70 vol% or more and 100 vol% or less, 90 vol% or more and 100 vol% or less, or 95 vol% or more and 100 vol% or less. When the gas 30 active against the molten oxide 10 is blown, the gas 30 reacts with the molten oxide 10. The reaction reduces the interfacial tension between the molten oxide 10 and the gas 30 (the surface tension of the molten oxide 10), the diameter of bubbles that can stably exist in the molten oxide 10 becomes smaller, and the gas 30 splits and becomes smaller. By generating small bubbles in the molten oxide 10, it is expected to promote forming, as described later. This effect occurs even after applying a potential difference to generate small bubbles, and therefore, by combining it with the application of a potential difference to be described later, a further foaming promotion effect can be obtained. For example, when small bubbles are generated in the molten oxide 10 by blowing the gas 30 into the molten oxide 10, the small bubbles become even smaller in the molten oxide 10 because the gas 30 is an active gas, and thus foaming is further promoted. That is, in a foaming control method according to an embodiment, foaming of the molten oxide 10 may be promoted by blowing an active gas into the molten oxide 10 and controlling the potential difference to be described later (for example, by controlling the potential difference to be 1 V or more).

[0016] There is no particular limit to the flow rate or volume of the gas 30 injected into the molten oxide 10. In this embodiment, the diameter of the bubbles generated in the molten oxide 10 can be controlled by controlling the potential difference, which will be described later, regardless of the flow rate or volume of the gas 30. In particular, when the flow rate of the gas 30 is 100 cm 3 / sec or more 8500cm 3 / sec or less, especially 100cm 3 / sec or more 5000cm 3When the flow rate is equal to or less than 1 / sec, the range of control of the bubble diameter becomes wider. The flow velocity and flow rate of the gas 30 can be easily controlled by the front pressure of the gas 30 supplied to the gas blowing means 20, etc.

[0017] 1.4 Control of potential difference In this embodiment, when the gas 30 is blown into the molten oxide 10 from the blowing hole 22 as described above, it is important that the molten oxide 10 and the conductive part 21 come into contact with each other and that the potential difference between the molten oxide 10 and the conductive part 21 is controlled. By controlling the potential difference between the molten oxide 10 and the conductive part 21, the wettability of the molten oxide 10 to the conductive part 21 is controlled, and the diameter of the bubbles generated in the molten oxide 10 is controlled. For example, when it is desired to maintain or calm the foaming of the molten oxide 10, it is preferable to generate large bubbles in the molten oxide 10. By generating large bubbles in the molten oxide 10, the large bubbles rise while merging with small bubbles, become even larger bubbles, and quickly leave the surface of the molten oxide 10 to the outside of the molten oxide 10. That is, the bubbles in the molten oxide 10 are removed, and the foaming is maintained or calmed. For example, when foaming of the molten oxide 10 actively occurs and grows, the growth of the foaming can be suppressed and the foaming can be maintained by generating large bubbles in the molten oxide 10. Also, when the foaming is relatively gentle, it is possible to calm the foaming by generating large bubbles in the molten oxide 10. On the other hand, when it is desired to promote the foaming of the molten oxide 10, it is effective to generate small bubbles in the molten oxide 10. By generating small bubbles in the molten oxide 10, the small bubbles are more likely to remain in the molten oxide 10, and the foaming is promoted.

[0018] According to the findings of the present inventors, when the potential difference is controlled to 1 V or more, the wettability of the molten oxide 10 with respect to the conductive part 21 is improved, the contact angle of the molten oxide 10 with respect to the conductive part 21 becomes less than 90°, and the bubble diameter of the gas 30 blown through the blowing hole 22 of the conductive part 21 tends to become relatively small. Although the potential difference varies somewhat depending on the composition of the molten oxide 10 and the material of the conductive part 21, it is preferable to control it to 1 V or more and 100 V or less, and more preferably to 1 V or more and 50 V or less. In this case, the potential difference can be determined according to the material of the conductive part 21, etc. When the potential difference exceeds 100 V, the electrode reaction occurs actively, and the progress of the erosion of the conductive part 21 and the counter electrode becomes rapid, which may shorten their service life.

[0019] When the bubble diameter of the gas 30 injected into the molten oxide 10 is made relatively small, the bubble diameter may be, for example, 0.1 mm or more and 8 mm or less. In addition, the ratio of the bubble diameter to the thickness of the molten oxide 10 in the absence of bubbles (bubble diameter / thickness) may be 1 or less.

[0020] According to the findings of the present inventors, when the potential difference is controlled to less than 1 V, the wettability of the molten oxide 10 with respect to the conductive part 21 deteriorates, the contact angle of the molten oxide 10 with respect to the conductive part 21 becomes 90° or more, and the bubble diameter of the gas 30 blown through the blowing hole 22 of the conductive part 21 tends to become relatively large. Although the potential difference varies somewhat depending on the composition of the molten oxide 10 and the material of the conductive part 21, it is preferably controlled to 0.01 V or more and less than 1 V, and more preferably 0.1 V or more and less than 1 V.

[0021] When the bubble diameter of the gas 30 injected into the molten oxide 10 is made relatively large, the bubble diameter may be, for example, 8 mm or more and 50 mm or less. In addition, the ratio of the bubble diameter to the thickness of the molten oxide 10 in the absence of bubbles (bubble diameter / thickness) may be 1 or more or 1 or less.

[0022] In the present embodiment, there is no particular limitation as to which of the potential of the molten oxide 10 and the potential of the conductive portion 21 is higher. According to the knowledge of the present inventor, for example, by controlling the potential difference so that the potential of the conductive portion 21 is higher than the potential of the molten oxide 10 (so that the conductive portion 21 is the anode (+) and the molten oxide 10 is the cathode (-)), the bubble diameter of the gas 30 blown into the molten oxide 10 can be made smaller. In other words, when it is desired to promote the forming of the molten oxide 10, it is preferable to control the potential difference so that the potential of the conductive portion 21 is higher than the potential of the molten oxide 10.

[0023] The means for applying a potential difference between the molten oxide 10 and the conductive part 21 is not particularly limited. For example, as shown in Figs. 1 and 2, a conductive electrode 40 and the conductive part 21 are each connected to a power supply unit 50 or the like, and the electrode 40 is immersed in the molten oxide 10, thereby applying a potential difference between the molten oxide 10 and the conductive part 21. The electrode 40 may be made of the same material as the conductive part 21, or may be made of a different material. In this case, the potential difference between the molten oxide 10 and the conductive part 21 can be controlled by controlling the power supply unit 50 or the like.

[0024] 2. Specific applications The forming control method according to the present embodiment can be applied to a refining process in an electric furnace or a converter. By applying the forming control method according to the present embodiment to the refining process, many advantages can be expected.

[0025] For example, in electric furnace refining, the amount of molten oxide discharged by slag (unintentional overflow from the discharge door due to an increase in the amount of molten oxide or foaming by the operator) or tilting slag discharge (tilting the electric furnace to discharge the molten oxide in the furnace) generated during refining of iron source such as scrap charged in the furnace changes depending on the state of foaming of the molten oxide. For example, controlling foaming makes it easy to control the amount of molten oxide discharged outside the furnace. In addition, in electric furnace refining, it is important to operate in a submerged arc state in which the arc generated from the electrode is covered with molten oxide from the viewpoints of increasing the heat transfer efficiency by the arc, preventing damage to the refractory material in the furnace, and reducing nitrogen pickup in the metal. By using the foaming control method according to this embodiment, it becomes possible to operate in a submerged arc state by locally foaming the molten oxide around the electrode.

[0026] In converter refining, the foaming of the molten oxide intensifies during blowing, and the productivity is reduced by a phenomenon called slopping, in which the molten oxide overflows from the furnace throat. In addition, the iron yield is also reduced due to the loss of iron contained in the molten oxide. In response to this, by using the foaming control method according to the present embodiment, it is possible to maintain appropriate foaming or calm excessive foaming by injecting gas with a sublance or the like during blowing so that the bubble diameter becomes large. On the other hand, when the molten oxide is discharged from the furnace throat, it is required to promote foaming and increase the efficiency of discharge. In this case, it is possible to promote foaming by injecting gas under conditions that result in a small bubble diameter and lengthening the residence time of the bubbles in the molten oxide.

[0027] Furthermore, by using a gas that is active against molten oxides (such as CO or O2) as the gas injected into various refining processes, the gas bubbles can be further refined by the reaction between the molten oxide and the gas after the gas is injected into the molten oxide, which is expected to further promote foaming.

[0028] As described above, the forming control method according to the present embodiment also brings about a great advantage in the operation of various refining processes. The forming control method according to the present embodiment can be preferably applied to, for example, a refining process of molten iron. That is, the refining method of molten iron according to one embodiment includes injecting gas into molten oxide present on the surface of the molten iron by the forming control method according to the present embodiment, thereby generating bubbles in the molten oxide. The molten iron in this case is obtained by melting various iron sources. The iron source may include at least one selected from solid iron sources such as scrap, reduced iron, pig iron, and granulated pig iron. Alternatively, the iron source may include blast furnace pig iron. The molten iron may include various elements other than iron. The composition of the elements other than iron depends on the type of iron source. As described above, the refining method of molten iron according to the present embodiment may be refining in a converter or may be refining in an electric furnace. The refining conditions may be the same as those of the conventional method, except that forming control is performed by the method according to the present embodiment.

[0029] 3. Supplementary Information As described above, according to the method of the present embodiment, it is possible to control foaming, such as easing, maintaining, and promoting foaming of the molten oxide. Note that even if the method does not intend to control foaming, the method is within the technical scope of the present invention as long as the following (1) to (3) are satisfied and the foaming is ultimately controlled. (1) The method includes blowing a gas 30 from the blowing holes 22 of the gas blowing means 20 into the molten oxide 10 . (2) In this method, the gas blowing means 20 has a conductive part 21 , and the conductive part 21 has the blowing hole 22 . (3) In this method, when the gas 30 is blown into the molten oxide 10 from the blowing hole 22, the molten oxide 10 comes into contact with the conductive portion 21, and the potential difference between the molten oxide 10 and the conductive portion 21 is controlled. EXAMPLES

[0030] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention can adopt various conditions as long as it does not deviate from the gist of the invention and achieves its object.

[0031] 1. Relationship between potential difference and contact angle In an electric resistance furnace with an Ar atmosphere, 8 g of molten slag (30 mass% CaO-30 mass% SiO2-40 mass% FeO) was dropped onto a Pt substrate. In this state, the droplet shape of the dropped slag was photographed from the side of the electric resistance furnace with a CCD camera. From the photographed image, the contact angle between the substrate metal and the molten slag was measured. The experimental temperature at this time was 1300°C. As a result of the measurement, the contact angle between the molten slag and the Pt substrate was 83°.

[0032] Next, a potential difference was applied between the molten slag and the Pt substrate by connecting one end of the power supply to the molten slag side and the other end to the Pt substrate side. Table 1 below shows the contact angle value for each potential difference. As shown in Table 1 below, by applying a potential difference of less than 1V between the molten slag and the Pt substrate, the contact angle became larger than when no potential difference was applied. In other words, the wettability of the molten slag to the substrate deteriorated. When the applied potential difference was further increased, the contact angle decreased, and the wettability of the molten slag to the substrate improved. From the above, it was found that the wettability of the molten slag to the substrate can be controlled by applying a potential difference between the molten slag and the substrate. From this result, it is considered that when gas is blown from a conductive gas blowing means to the molten slag, the contact angle of the molten slag to the gas blowing means can be controlled by applying a potential difference between the molten slag and the gas blowing means, and thereby the bubble diameter of the blown gas can be controlled.

[0033] [Table 1]

[0034] 2. Relationship between potential difference and bubble diameter An experiment was carried out in which gas was blown into molten slag using a conductive nozzle and the bubble diameter was measured. A nozzle made of heat-resistant stainless steel SUS310S with a diameter of 20 mm and a gas blowing hole with an inner diameter of 0.3 mm was installed at the center of the bottom of an alumina crucible (outer diameter 85 mm × inner diameter 75 mm × height 180 mm) so that gas could be blown into the crucible. 400 g of slag (30 mass% CaO-30 mass% SiO2-40 mass% FeO) was placed in the crucible and melted and held at 1300 °C in an Ar atmosphere using an electric resistance furnace. After the slag was melted, one end of a power supply was connected to the nozzle and the other end was connected to a tungsten rod immersed in the slag in order to apply a potential difference between the slag and the nozzle. The potential difference between the slag and the nozzle was changed in various ways, and a 0.83 cm nozzle was installed at the bottom of the crucible. 3 Ar gas was blown into the slag at 1 / sec (standard flow rate). The slag surface was observed from the top of the furnace, and the bubbles that rose to the surface were photographed. The photographed images were analyzed to calculate the bubble diameter as a circle equivalent diameter. Table 2 below shows the bubble diameter values ​​for each potential difference. As shown in Table 2 below, when a potential difference of less than 1 V was applied, the bubble diameter became larger than when no potential difference was applied. Furthermore, by applying a potential difference of 1 V or more, the bubble diameter became smaller as the potential difference increased. This result shows that the behavior of the results of the contact angle measurement experiment above corresponds to the behavior of the bubble diameter in this experiment.

[0035] [Table 2]

[0036] 3. Considerations when changing gas types Next, in the same apparatus configuration as above, the type of gas injected into the slag was changed from Ar to CO, and the bubble diameter was calculated for each of the cases where the potential difference between the molten slag and the nozzle was 0 V, 0.5 V, and 10 V. Table 3 below shows the bubble diameter value for each potential difference for the cases where Ar was used as the injected gas and CO was used as the injected gas. As shown in Table 3 below, in all cases where the potential difference between the molten slag and the nozzle was 0 V, 0.5 V, and 10 V, the bubble diameter when CO gas was injected was smaller than the bubble diameter when Ar gas was injected. This is thought to be because the CO gas reacted with the molten slag, which reduced the interfacial tension between the molten slag and the gas (the surface tension of the slag), thereby reducing the diameter of the bubbles stably present in the slag, and the injected gas was split and reduced in size.

[0037] [Table 3]

[0038] 4. Study of forming control by voltage application The effect of voltage application on the foaming control of molten slag was evaluated. In the same device configuration as above, the potential difference between the molten slag and the nozzle was changed from 0 to 100 V, and the 3Ar gas was injected into the slag at a flow rate of 1000 / sec (standard flow rate). At this time, the foaming height was continuously measured using a laser distance meter, and the height at which foaming stabilized at each potential difference was taken as the foaming height for that potential difference. The "foaming height" is the height of the molten slag when gas was injected minus the height of the molten slag when gas was not injected. Table 4 below shows the foaming height measured at each potential difference as a ratio based on the potential difference of 0V. As shown in Table 4 below, when the potential difference was less than 1V, the foaming height was smaller than when no potential difference was applied. This is because the bubble diameter of the injected gas was large, so the bubble floating speed in the molten slag was high, and the time that the bubbles remained in the molten slag was shortened. On the other hand, by increasing the potential difference to 1V or more, the foaming height was larger than when no potential difference was applied. This is because the bubble diameter of the blown gas becomes smaller, so the bubble rise speed in the molten slag is slower and the bubble residence time in the molten slag becomes longer.

[0039] [Table 4]

[0040] 5. When applying to actual equipment In the case of a molten iron refining process, the CO bubbles generated by the reaction of C in the molten iron with FeO in the molten slag (hereinafter referred to as "reaction bubbles") have a bubble diameter of about several mm, and these small bubbles contribute to foaming.

[0041] On the other hand, from the results of the above examples, when the potential difference between the molten slag and the nozzle is less than 1 V, the diameter of the gas bubbles injected is more than 10 mm, which is much larger than the diameter of the bubbles generated by the above reaction. Therefore, the large bubbles generated by the gas injected into the molten slag merge with the bubbles generated by the reaction to become larger bubbles, which rise quickly in the molten slag and maintain or decrease the foaming height. In other words, it is possible to maintain or calm the foaming.

[0042] In addition, from the results of the above examples, when the potential difference between the molten slag and the nozzle is 1V or more, the diameter of the bubbles of the injected gas is about a few mm, which is about the same as the diameter of the bubbles caused by the above reaction. Therefore, the foaming height increases as the number of small bubbles that contribute to foaming increases in the slag. In other words, foaming can be promoted.

[0043] 6. Supplementary Experimental Results When applying a potential difference between the molten slag and the nozzle, by passing a current through the molten slag as the cathode (-) and the nozzle as the anode (+), the bubble diameter decreased by about 12% on average and the foaming height increased by about 16% on average at each potential difference compared to when the polarity was reversed, that is, when the molten slag was the anode (+) and the nozzle was the cathode (-). Therefore, it was found that, in order to reduce the bubble diameter and increase the foaming height, that is, to promote foaming, it is particularly effective to pass a current through the molten slag as the cathode (-) and the nozzle as the anode (+).

[0044] Since the effect of polarity was hardly observed on the contact angle, it is believed that the effect of polarity on the surface tension of the molten slag is small. The bubble diameter of the dynamically injected gas is affected by the viscosity as well as the surface tension of the molten slag, and the smaller the viscosity, the smaller the bubble diameter. Therefore, it is believed that the polarity when applying a potential difference affects the viscosity of the molten slag. In the results of this study, the bubble diameter became smaller when electricity was applied to the molten slag as the cathode (-) and the nozzle as the anode (+), so it is believed that the viscosity of the molten slag decreased when electricity was applied to the molten slag as the cathode (-) and the nozzle as the anode (+).

[0045] The results shown in Tables 1 to 4 above are for when a current is passed through the molten slag as the cathode (-) and the nozzle as the anode (+). However, it was confirmed that the bubble diameter becomes smaller by applying a potential difference even when a current is passed through the molten slag as the anode (+) and the nozzle as the cathode (-).

[0046] In the above embodiment, the molten oxide is a molten slag having a predetermined chemical composition, and the gas injection means is a conductive nozzle. However, the technology of the present disclosure is not limited to this. By controlling the potential difference, it is possible to control the bubble diameter of the gas injected into the molten oxide regardless of the type of molten oxide or the type of gas injection means, and it is considered that the foaming control of the molten oxide is possible.

[0047] 7. Summary From the above results, it can be said that the foaming of molten oxide can be controlled by a method that satisfies the following (1) to (3). (1) The method includes blowing a gas into the molten oxide through a blowing hole of a gas blowing means. (2) In the method, the gas blowing means has a conductive part, and the conductive part has the blowing hole. (3) In this method, when the gas is blown into the molten oxide from the blowing hole, the molten oxide comes into contact with the conductive part, and the potential difference between the molten oxide and the conductive part is controlled. [Explanation of symbols]

[0048] 10 Molten oxide 20 Gas injection means 21 Conductive part 22 Blow Hole 30 Gas 40 electrodes 50 Power supply

Claims

1. 1. A method for controlling foaming of a molten oxide, comprising: blowing gas into the molten oxide through a blowing hole of a gas blowing means; The gas blowing means has a conductive portion, the conductive portion has the blowing hole, When the gas is blown into the molten oxide from the blowing hole, the molten oxide comes into contact with the conductive part, and a potential difference between the molten oxide and the conductive part is controlled. A method for controlling forming of molten oxide.

2. 2. The method for controlling foaming of a molten oxide according to claim 1, The potential difference is controlled to be less than 1 V. A method for controlling forming of molten oxide.

3. 2. The method for controlling foaming of a molten oxide according to claim 1, The potential difference is controlled to be 1 V or more. A method for controlling forming of molten oxide.

4. 2. The method for controlling foaming of a molten oxide according to claim 1, the gas comprises a gas inert to the molten oxide; A method for controlling forming of molten oxide.

5. 5. The method for controlling foaming of a molten oxide according to claim 4, The gas is Ar, He and N ２ At least one selected from A method for controlling forming of molten oxide.

6. 2. The method for controlling foaming of a molten oxide according to claim 1, the gas comprises a gas active with respect to the molten oxide; A method for controlling forming of molten oxide.

7. 7. A method for controlling foaming of a molten oxide according to claim 6, comprising the steps of: The gas is O ２ , CO, CO ２ , H ２ and H ２ At least one selected from O A method for controlling forming of molten oxide.

8. 2. The method for controlling foaming of a molten oxide according to claim 1, The potential difference is controlled so that the potential of the conductive portion is higher than the potential of the molten oxide. A method for controlling forming of molten oxide.

9. A method for refining molten iron, comprising the steps of: The forming control method according to any one of claims 1 to 8 includes blowing gas into a molten oxide present on the surface of the molten iron to generate bubbles in the molten oxide. A method of refining molten iron.

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