Method for refining molten iron

Abstract

The present invention provides a method for refining molten iron that can be performed without loss of opportunity and stably in a safe state without water vapor explosion when using the heat possessed by high-temperature slag remaining in a reaction vessel for preheating of a cold iron source. It is a method for refining molten iron that uses the heat possessed by slag generated after refining of molten iron of a previous heat for preheating of a cold iron source, the method comprising: a first step of tapping the molten iron after refining from the reaction vessel in a state where the slag remains as residual slag in the reaction vessel; a second step of setting a cooling material for forming solidified slag by cooling the residual slag as the cold iron source charged from a waste notch; and a third step of charging molten iron of a next heat into the reaction vessel for refining, and in the second step, a K value calculated by a given relational expression using a mass Wsl of the residual slag, a mass Wsc of the cold iron source charged from the waste notch, and a temperature Tf of a high-temperature object remaining in the furnace of the first step is less than 0, and a waiting time T after charging of the cold iron source is not set.

Description

Technical Field

[0001] This invention relates to a method for refining molten iron. More specifically, this invention relates to a method for refining molten iron by introducing a cold iron source into the slag remaining in a reaction vessel such as a converter, and by fully utilizing the heat of the slag to preheat the cold iron source.

[0002] In this specification, expressions like "x~y" indicate "above x and below y," including boundary values. Additionally, chemical formulas such as "SiO2" indicate compounds of that composition, and expressions like "iron" and "phosphorus" indicate the presence of that element, regardless of its form. T.Fe refers to total iron, regardless of its form, representing the total amount of iron. M.Fe refers to metallic iron. Expressions like [M] indicate that element M is contained in molten iron. (R) indicates that compounds with the chemical formula R are contained in the slag.

[0003] "Molten iron" refers to a molten metal containing iron as its main component, including "molten pig iron" containing about 3-4 mass% carbon and "molten steel" containing less than 2 mass% carbon. The unit of mass, "t," represents 1000 kg. Background Technology

[0004] In recent years, with the increasing demand for reducing CO2 emissions, there has been a requirement to increase the amount of chilled iron used in the steelmaking process. By loading molten pig iron and chilled iron from the blast furnace into the reaction vessel, the proportion of molten pig iron relative to the molten iron filled into the reaction vessel and refined can be reduced (hereinafter also referred to as the molten pig iron blending ratio). Moreover, this ultimately reduces the amount of molten pig iron used per unit of crude steel production.

[0005] There are various types of chills. For example, scrap iron is placed in a stockpile, while reduced iron fed from the furnace top is stored in underground silos and is generally managed at room temperature. These chills are loaded into the reaction vessel from scrap chutes or furnace top hoppers. To ensure that the loaded chills are completely melted in the molten iron, additional heat is required to heat the chills until they melt.

[0006] Therefore, if more cold iron sources are to be utilized, the portion of heat that cannot be compensated for by the inherent heat of the molten pig iron itself or the combustion heat of impurities needs to be supplemented by heating materials or by external forced heat application methods. Examples of heating materials include earthy graphite, ferrosilicon, and silicon carbide. Examples of heat application methods include burners and electric arc discharge.

[0007] However, within the reaction vessel, impurities are removed by adding slag, which is formed on top of the molten iron. This slag reaches high temperatures of 1300–1400°C during dephosphorization and 1600–1700°C during decarburization, containing a high amount of heat. Typically, this treated slag is solidified by adding cooling materials such as dolomite and remains inside the reaction vessel; any slag that does not completely solidify is discharged. This is because if the slag is not solidified, the iron oxide in it will react violently with the carbon in the molten pig iron, causing slag boiling.

[0008] However, if the heat of the slag itself, which is usually not effectively utilized due to being discharged from the reaction vessel, can be used to preheat the scrap, the heat required for heating and melting the chilled iron source can be reduced. Furthermore, compared to when the chilled iron source is at room temperature, the molten pig iron blending rate can be further reduced.

[0009] Therefore, several methods have been disclosed that can preheat a cold iron source using residual slag remaining in the reaction vessel while preventing slag boiling. For example, Patent Document 1 discloses a technique for tapping steel while leaving decarburized slag generated by decarburization treatment remaining in the reaction vessel, and for charging a solid iron source into the residual slag. It shows that when charging molten pig iron after charging the solid iron source, the following conditions must be met: Wsl / Wsc·(2-N) -2 The method of charging molten pig iron under the condition that Wsc < 1. In the formula, Wsc is the amount of solid iron source charged (t / ch), Wsl is the amount of decarburized slag residue (t / ch), and N is the number of reciprocating tilts of the refining vessel.

[0010] In addition, Patent Document 2 discloses a method for adding a solid iron source to the furnace residue (slag, molten iron) after steel tapping from a converter and solidifying the residual molten iron.

[0011] The technology disclosed in Patent Document 1 aims to reuse decarburized slag, while the technology disclosed in Patent Document 2 aims to prevent the outflow of residual molten iron in the converter during slag discharge. Although their purposes are different, they can both be applied to preheating the cold iron source using slag in the reaction vessel.

[0012] Existing technical documents

[0013] Patent documents

[0014] Patent Document 1: Japanese Patent Application Publication No. 2004-256839

[0015] Patent Document 2: Japanese Patent Application Publication No. 2009-228102 Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] However, the aforementioned prior art has the following problems that must be solved. Specifically, the technology described in Patent Documents 1 and 2 is completely incapable of handling the potential steam explosion that may occur when a chill containing moisture enters the high-temperature slag inside the reaction vessel due to a difference in specific gravity. Examples of chills containing moisture include, for instance, water that inevitably enters the depressions of plate-shaped waste during rainy days, and damp, powdery waste.

[0018] For handling reasons, chills are usually stored in roofed but not enclosed factory buildings. In such storage locations, the chills cannot be prevented from getting wet from wind and rain. To remove moisture, the chills need to be preheated at their storage location. This not only requires the introduction of equipment for preheating but also contradicts the purpose of utilizing idle heat.

[0019] Furthermore, the existing technology described above also presents problems as a countermeasure to suppress the reaction with molten pig iron. Regarding the solid iron source charge Wsc in the formula shown in Patent Document 1, it is a value determined based on the production plan, and is not a controllable parameter, assuming the premise of ensuring production volume. Therefore, the only options are to reduce the amount of decarburized slag residue Wsl, or to increase the number of reciprocating tilts N. The former results in a decrease in the total heat of the slag, thus failing to meet the purpose of preheating the cold iron source, while the latter leads to a decrease in the productivity of molten iron due to the increase in non-steelmaking time.

[0020] In Patent Document 2, the solid iron source is added to solidify the residual molten iron in the reaction vessel, and the slag is discharged from the furnace in a molten state. Therefore, the method described in Patent Document 2 cannot achieve the purpose of preheating the cold iron source using the residual slag. Furthermore, Patent Document 2 describes keeping the solid iron source in the molten slag by setting its size to less than 1 mm, but it is difficult to ensure a sufficient amount of such solid iron source.

[0021] In light of these problems, the inventors conducted repeated and in-depth research, and discovered that since the steam explosion is caused by the rapid volume expansion of water when the moisture contained in the chilled iron source comes into contact with the slag and other residual high-temperature materials in the furnace, the focus was on conditions to avoid such rapid volume expansion of moisture. Here, when the moisture contained in the chilled iron source evaporates upon contact with the residual high-temperature materials in the furnace, the amount of water evaporated per unit volume of moisture mainly depends on the temperature of the residual high-temperature materials in the furnace.

[0022] When the surface temperature of the residual high-temperature material inside the furnace is around 90°C to 140°C, the higher the surface temperature, the faster the moisture evaporates. Furthermore, when the surface temperature of the residual high-temperature material inside the furnace is around 140°C to 300°C, the higher the surface temperature, the longer it takes for the moisture to evaporate.

[0023] Furthermore, it is known that the surface temperature of the residual high-temperature material in the furnace reaches its peak at around 300°C, and then the higher the surface temperature of the residual high-temperature material in the furnace, the faster the water evaporates again (Leidenfrost effect).

[0024] Therefore, this invention focuses on the Leidenfrost effect that occurs when moisture contained in the chilled iron source comes into contact with high-temperature residual materials in the furnace, such as slag. It explores a method to prevent moisture contained in the chilled iron source from being introduced into the reaction vessel when the surface temperature of the high-temperature residual materials in the furnace is about 140°C to about 300°C, and the evaporation time of moisture is shortened at the temperature of high-temperature slag.

[0025] Specifically, when a chill is introduced into a reaction vessel containing residual slag that is considered as high-temperature slag, the chill comes into contact with the high-temperature slag, causing the temperature of the slag to decrease. Since the amount of temperature decrease in the high-temperature slag depends on the ratio of the amount of chill introduced to the amount of residual slag, it can be assumed that by setting the time for moisture evaporation accordingly based on the ratio Wsc / Wsl(-) of the amount of chill introduced into the reaction vessel for preheating to the amount of residual slag in the reaction vessel, and the temperature Tf of the residual high-temperature material in the furnace after the slag is left to remain, it is possible to limit the conditions under which a steam explosion caused by the reaction between the residual slag and the moisture in the chill can occur, and this condition has been identified.

[0026] Furthermore, it was discovered that, based on a given formula relating the amount of residual slag Wsl in the reaction vessel, the amount of chilled iron source Wsc loaded into the reaction vessel using a scrap chute, and the temperature of the residual high-temperature material in the furnace, namely the temperature Tf of the residual high-temperature material in the furnace, which includes the treatment that leaves the slag residue, a condition was set for adding the remaining chilled iron source after a waiting time following loading a given amount of chilled iron source into the reaction vessel using a scrap chute.

[0027] This invention was made to solve the above-mentioned problems. Its purpose is to propose a condition in which the heat of the high-temperature slag remaining in the reaction vessel is used to preheat the cold iron source, so as to achieve a safe and stable operation without any chance of loss when the water vapor explosion caused by the reaction between the residual slag and the moisture in the cold iron source occurs.

[0028] Methods for solving problems

[0029] In view of these issues, the inventors conducted in-depth research and found that by using the ratio of the amount of residual slag in the reaction vessel to the amount of cold iron source put into the reaction vessel, and the temperature of the residual high-temperature material in the furnace after the slag is left to remain, the conditions under which a steam explosion cannot occur can be defined.

[0030] The present invention, which advantageously solves the above-mentioned problems, is a method for refining molten iron by using the heat of the slag generated after the refining of the previous heat of molten iron to preheat a cold iron source. The method includes: a first step, in which molten iron after refining is tapped from the reaction vessel while a portion or all of the slag remains as residual slag in the reaction vessel; a second step, in which a cold iron source is loaded from a scrap chute and used as a cooling material for forming solidified slag by cooling the residual slag; and a third step, in which molten iron from the next heat is loaded into the reaction vessel for refining. In the second step, the K value calculated by the following formula (1) based on the mass of the residual slag Wsl, the mass of the cold iron source loaded from the scrap chute Wsc, and the temperature Tf of the residual high-temperature material in the furnace in the first step is less than 0, and no waiting time T is set after the loading of the cold iron source.

[0031] K = Wsc - 8.64 × 10 -7 ×Tf 1.947 ×Wsl···(1)

[0032] In equation (1), Wsc (kg) represents the mass of the cold iron source loaded from the scrap chute, Wsl (kg) represents the mass of the residual slag, and Tf (°C) represents the temperature of the residual high-temperature material in the furnace during the first process.

[0033] Furthermore, the present invention, which advantageously solves the above-mentioned problems, is a method for refining molten iron by using the heat of the slag generated after the refining of the previous batch of molten iron to preheat a chill source. This method includes: a first step, in which, with part or all of the slag remaining as residual slag in the reaction vessel, the refined molten iron is tapped from the reaction vessel; and a second step, in which a chill, loaded from a scrap chute, is used as the cooling material for forming solidified slag by cooling the residual slag. The source or the chill source fed from the top of the furnace; and the third step, the molten iron of the next batch is loaded into the above-mentioned reaction vessel for refining. In the second step, the K value calculated by the following relationship (1) using the mass of the residual slag Wsl, the mass of the chill source fed from the scrap chute Wsc, and the temperature of the residual high-temperature material in the furnace in the first step is less than 0. After loading the chill source, the waiting time T is set to more than 60 seconds. After the waiting time T, the remaining chill source is fed from the scrap chute or the top of the furnace.

[0034] K = Wsc - 8.64 × 10 -7 ×Tf 1.947 ×Wsl···(1)

[0035] In equation (1), Wsc (kg) represents the mass of the cold iron source loaded from the scrap chute, Wsl (kg) represents the mass of the residual slag, and Tf (°C) represents the temperature of the residual high-temperature material in the furnace during the first process.

[0036] It should be noted that, for the refining method of molten iron of the present invention, a more preferred solution is: (a) in the third step described above, a waiting time T1 is set before the next batch of molten iron is loaded into the reaction vessel; etc.

[0037] The effects of the invention

[0038] According to the present invention, the heat of the high-temperature slag remaining in the reaction vessel can be fully used for the preheating of the cold iron source, and the refining of molten iron with full utilization of the preheating of the cold iron source can be carried out stably and without loss in a safe state without water vapor explosion. Attached Figure Description

[0039] Figure 1 This is a schematic conceptual diagram illustrating a preferred equipment configuration for a refining method for molten iron suitable for the present invention.

[0040] Figure 2 This is a graph showing the results of a confirmation test of slag steam explosion by introducing a water-soaked cold iron source into the slag.

[0041] Figure 3 It is a graph showing the results of a confirmation test of steam explosion in molten iron by immersing a water-wetted cold iron source into molten iron.

[0042] Symbol Explanation

[0043] 1. Reaction vessel

[0044] 2 Refractory materials

[0045] 3. Steel tapping hole

[0046] 4. Slag

[0047] 5. Cold iron source

[0048] 6 Waste chute

[0049] 7. Cranes

[0050] 8. Residual molten iron

[0051] 9. Molten pig iron ladle

[0052] 10 Molten Iron

[0053] 11 Oxygen supply spray gun

[0054] 12 Oxygen

[0055] 13 Bottom-blown gas system

[0056] 14. Furnace top hopper

[0057] 15. Material fed into the furnace top

[0058] 15A Solid Reduced Iron Detailed Implementation

[0059] The embodiments of the present invention will now be described in detail. It should be noted that the accompanying drawings are illustrative and may sometimes differ from reality. Furthermore, the following embodiments are examples of apparatuses and methods used to embody the technical concept of the present invention, and are not intended to limit the scope of the invention to the following. That is, the technical concept of the present invention can be modified in various ways within the scope of the claims. Preferred embodiments of the present invention will now be described in detail with reference to the relevant background.

[0060] [First Implementation]

[0061] The iron refining method of this embodiment is a method for preheating molten iron by using the heat of the slag generated after the refining of the previous heat of molten iron. The method includes: a first step, in which molten iron after refining is tapped from the reaction vessel while a portion or all of the slag remains as residual slag in the reaction vessel; a second step, in which a cooling material for forming solidified slag by cooling the residual slag is provided as a cold iron source loaded from a scrap chute; and a third step, in which molten iron of the next heat is loaded into the reaction vessel for refining.

[0062] The following describes each step of the refining method for molten iron according to this embodiment.

[0063] The iron refining method of this embodiment is carried out in a reaction vessel such as a converter refining furnace or an induction melting furnace. Therefore, the iron refining method of this embodiment can be applied to the Multi-Refining Converter method (hereinafter referred to as the "MURC method"), which continuously performs desiliconization, dephosphorization, slag removal, and decarburization in the same converter. In addition, the iron refining method of this embodiment can also be applied to the Double-slag Refining Process method (hereinafter referred to as the "DRP method"), which maximizes the utilization of silicon in molten pig iron as a heat source and increases the amount of scrap input in the converter.

[0064] (Step 1: The process of tapping refined molten iron from the reaction vessel while leaving residual slag in the vessel)

[0065] The iron refining method of this embodiment is a method of refining molten iron by using the heat of the slag generated after the refining of the previous batch of molten iron to preheat the molten iron from a cold iron source.

[0066] The first step of the iron refining method of this embodiment is to tap the refined molten iron from the reaction vessel while some or all of the slag produced from the refining of the previous heat of molten iron remains as residual slag in the reaction vessel. The residual slag is molten slag in a molten state. It should be noted that the temperature of the slag remaining in the reaction vessel is 1700~1300°C.

[0067] The amount of slag remaining in reaction vessels such as converter refining furnaces can be a portion or all of the slag produced from the refining of molten pig iron in the previous heat. The amount of slag remaining in the reaction vessel can be determined in relation to the amount of cooling material charged into the reaction vessel in the second step described later to solidify the remaining slag.

[0068] It should be noted that in the first step, the residual slag remaining in the reaction vessel is solidified by being cooled by the cooling material in the second step described later, becoming solidified slag.

[0069] Figure 1 (a) to (c) show suitable apparatus configurations for implementing the iron refining method of this embodiment. The molten iron from the previous heat is refined using a reaction vessel 1. Through refining the molten iron from the previous heat, the molten iron becomes refined molten iron 10. The reaction vessel 1 is a container such as a converter-type refining furnace lined with refractory material 2. Furthermore, the reaction vessel 1, such as the converter-type refining furnace lined with refractory material 2, is tilted, and the refined molten iron is tapped to the outside of the reaction vessel 1 through the tapping hole 3.

[0070] It should be noted that there is sometimes about 1 ton of so-called residual molten iron 8 in the reaction vessel 1. This residual molten iron 8 is the refined molten iron 10 generated after the refining of the previous batch of molten iron in the pretreatment process, and it remains in the reaction vessel 1.

[0071] The refractory 2 lining the reaction vessel 1 can be made of a material with sufficient corrosion resistance to the slag 4 produced from the refining of the previous heat of molten iron. MgO-C bricks are generally used. Furthermore, to prevent the refractory 2 from dissolving into the slag 4, the processing temperature may sometimes be adjusted, or, depending on the composition of the slag 4, a lightly calcined dolomite or other MgO source may be added from the top hopper 14 as the top feed material 15.

[0072] Through the refining of the molten iron from the previous heat, slag 4 is generated in reaction vessel 1. The composition of slag 4 is not particularly limited, but it is a steelmaking slag with CaO, SiO2, and FeO as the main components, and also contains Al2O3, MgO, P2O5, MnO, S, M.Fe (metallic iron), etc.

[0073] Here, FeO represents iron oxides, such as FeO and Fe2O3. The basicity C / S, expressed as the mass ratio of CaO to SiO2 in the slag, is mostly 0.5 to 4.5, and the concentration of FeO in the slag is mostly 3 to 40 mass%. For this slag 4, slag-promoting materials such as TiO2, which are used to lower the melting point of slag 4, can also be added as top feed material 15.

[0074] (Step 2: The process of loading the chill source from the scrap chute into the reaction vessel)

[0075] The second step in the iron refining method of this embodiment involves loading a chill source from a scrap chute while some or all of the slag generated from the refining of the previous heat of molten iron remains in the reaction vessel. In this second step, the chill source 5 can be loaded into the reaction vessel 1 from either the scrap chute 6 or the furnace top. Loading the chill source 5 from the furnace top can, for example, be done using the furnace top hopper 14.

[0076] Specifically, such as Figure 1 As shown in (a), with some or all of the slag 4 remaining as residual slag in the reaction vessel 1, the reaction vessel 1 is tilted toward the waste chute 6 containing the chill source 5. The front end of the waste chute 6 is inserted into the reaction vessel 1. Then, the crane 7 is used to tilt the waste chute 6 and load the chill source 5 into the reaction vessel 1.

[0077] Besides carbon steel scrap and pig iron scrap, the chill source 5 can also load solid reduced iron 15A, such as granular pig iron and reduced iron, that can be rolled up to the furnace top hopper 14 and placed in the scrap chute 6 as reduced iron. Examples of carbon steel scrap include heavy scrap steel, briquetted scrap steel, steel shavings, freshly cut scrap steel, and steel cutting powder. Examples of pig iron scrap include old pig iron and pig iron cutting powder. Here, the chill source 5 is a chill source that easily contains moisture, often containing some moisture. For example, the chill source 5 may contain powdery scrap such as steel cutting powder, steel pipes, motors, and briquetted scrap steel, or porous scrap that easily contains moisture.

[0078] In the second step, after the chill source 5 is loaded into the reaction vessel 1, the operation of mixing the chill source 5 with the slag 4 is sometimes carried out by reciprocating tilting of the reaction vessel 1. Reciprocating tilting of the reaction vessel 1 is not necessary, but from the viewpoint of promoting the dispersion of the chill source 5 and the solidification of the slag 4, reciprocating tilting of the reaction vessel 1 is more preferable.

[0079] As mentioned earlier, there is sometimes about 1 ton of residual molten iron 8 in the reaction vessel 1. This residual molten iron 8 is the refined molten iron generated after the refining of the previous heat of molten iron as a pretreatment. Therefore, the reaction vessel 1 contains residual high-temperature material formed by the mixture of slag 4, cold iron source 5 and residual molten iron 8.

[0080] In the second process, the residual slag present in the reaction vessel 1 is generated after the refining of the previous batch of molten iron. Even if it coexists with the residual molten iron 8 which is the refined molten iron, it will be cooled and solidified by the cold iron source 5 loaded from the scrap chute 6 or the cold iron source 5 fed from the top of the furnace, thus becoming solidified slag.

[0081] Here, in the second step of the iron refining method of this embodiment, the chill source 5 loaded into the reaction vessel 1 can be a chill source that easily contains moisture, including powdered chill sources and chill sources with voids. The chill source that easily contains moisture is preferably loaded from the scrap chute 6. It should be noted that in the iron refining method of this embodiment, when solid reduced iron 15A or similar reduced iron is used as the chill source 5, from the viewpoint of easily adjusting the amount of this reduced iron added into the reaction vessel 1, it is desirable to use the furnace top hopper 14 or similar device to feed solid reduced iron 15A into the reaction vessel 1 from the furnace top.

[0082] Furthermore, the chill source 5 may contain reduced iron, and the length of the reduced iron in the longitudinal direction is 300 mm or less. That is, in the iron refining method of this embodiment, when the chill source 5 is loaded into the reaction vessel 1 such as a converter-type refining furnace, a solid reduced iron 15A with a large specific surface area can be used. In other words, by using solid reduced iron as the chill source 5, the iron refining method of this embodiment makes it easy for residual slag to adhere to the surface of the solid reduced iron 15A, and can also quickly promote the solidification of residual slag as molten slag.

[0083] Furthermore, as a cold iron source 5 used to cool residual slag to form solidified slag, by setting the length of the solid reduced iron 15A in the longitudinal direction to 300 mm or less, the solidification of residual slag can be carried out rapidly.

[0084] Thus, in the iron refining method of this embodiment, by introducing a cold iron source 5 into the reaction vessel 1 to solidify the residual slag, even when the next batch of molten pig iron is introduced, the violent reaction between the oxygen in the slag 4 and the carbon in the molten pig iron, which would otherwise cause the molten pig iron to boil violently, can be avoided.

[0085] In the second process, the residual slag and a small amount of residual molten iron 8 present in reaction vessel 1 constitute the residual high-temperature material in the furnace. The temperature of the residual high-temperature material in the furnace is set as the temperature of the residual high-temperature material in the furnace, Tf (°C).

[0086] Here, in the general refining of molten iron, the solidification temperature of the slag 4 in the reaction vessel 1 using a heating furnace was measured, and the following results were obtained: if the slag temperature of the slag 4 is below 1100℃, the residual slag will solidify under any conditions and become solidified slag.

[0087] Furthermore, in general iron refining, within the temperature range that can be considered during iron decarburization refining, even slag 4 with various modifications to its composition such as basicity and iron oxide concentration, can be solidified by setting the temperature of slag 4 to below 1100°C. On the other hand, in general decarburization refining to which the iron refining method of this embodiment is applicable, the highest temperature at the end of iron refining is 1750°C.

[0088] From this perspective, it is clear that in the iron refining method of this embodiment, in order to completely solidify part or all of the residual slag 4 produced by refining the molten iron in the previous heat, it is sufficient to load a cold iron source 4 into the reaction vessel 1 with an amount of heat required to reduce the temperature of the residual high-temperature material in the furnace containing the residual slag and residual molten iron 8, i.e., the temperature Tf (°C) of the residual high-temperature material in the furnace, from 1750°C to 1100°C.

[0089] Therefore, in the second step, considering the relationship between the mass of the residual slag Wsl, the mass of the chill source 5 loaded from the waste chute 6 Wsc, and the temperature of the residual high-temperature material in the furnace Tf, the waiting time can be determined by subtracting the product of the mass of the residual slag Wsl (kg) and the temperature of the residual high-temperature material in the furnace Tf (°C) of the reaction vessel 1 from the mass of the chill source 5 Wsc (kg). Specifically, considering the relationship between the mass of the residual slag Wsl, the mass of the chill source 5 loaded from the waste chute Wsc, and the temperature of the residual high-temperature material in the furnace Tf, the K value calculated by the following formula (1) is obtained.

[0090] K = Wsc - 8.64 × 10 -7 ×Tf 1.947 ×Wsl···(1)

[0091] In equation (1), Wsc represents the mass of the chilled iron source 5 loaded from the scrap chute 6, Wsl represents the mass of the residual slag, and Tf (°C) represents the temperature of the residual high-temperature material in the furnace of the reaction vessel 1 used to treat the slag 4. It should be noted that the introduction of equation (1) will be explained later.

[0092] In the iron refining method of this embodiment, the mass Wsc of the cold iron source 5 loaded into the reaction vessel 1 from the scrap chute 6, the mass Wsl of the residual slag, and the temperature Tf (°C) of the residual high-temperature material in the furnace of the reaction vessel 1 are selected as parameters for determining the waiting time T, and the relationship between them is considered to calculate the K value calculated by the relationship (1).

[0093] Here, the K value calculated using formula (1) is used to determine whether a waiting time T is needed to allow the moisture contained in the chill source 5 to evaporate. That is, in the second step, it is possible to determine whether to set a waiting time T after loading the chill source 5 based on the K value calculated using formula (1).

[0094] In other words, in the iron refining method of this embodiment, the waiting time T for evaporating the moisture contained in the aforementioned cold iron source 5 can be determined based on the K value calculated by using the relationship between the amount of cold iron source 5 loaded from the scrap chute 6 Wsc, the amount of residual slag Wsl, and the temperature Tf (°C) of the residual high-temperature material in the reaction vessel 1 after the first process of the blown slag 4. Alternatively, the waiting time T can be set to not be set.

[0095] That is, in the iron refining method of this embodiment, as long as the K value calculated by formula (1) is less than 0, the waiting time T after the cold iron source 5 is loaded into the reaction vessel 1 is not set.

[0096] Figure 2 This is a graph showing the results of a slag steam explosion confirmation test where a chill is added to the slag. The slag steam explosion confirmation test uses slag and a water-soaked chill to confirm whether a steam explosion occurs when the chill is added to the slag. It should be noted that the details of the slag steam explosion confirmation test are explained later.

[0097] like Figure 2 As shown, it can be clearly understood that there is region A (hereinafter referred to as "slag boiling region A") where slag boiling occurs, region C (hereinafter referred to as "steam explosion region C") where steam explosion occurs, and regions B1 and B2 where neither slag boiling nor steam explosion occurs.

[0098] here, Figure 2 The symbol "●" in the diagram represents the conditions under which slag boiling and steam explosion do not occur, while the symbol "×" represents the conditions under which steam explosion occurs. That is, as shown... Figure 2As shown, the slag boiling zone A, the steam explosion zone C, and the zones B1 and B2 where slag boiling and steam explosion do not occur can be sorted out by the temperature Tf (°C) of the residual high-temperature material in the furnace and the ratio W' (kg) of the amount of cold iron source charged to the amount of residual slag Wsl' (kg) W' / Wsl' (-).

[0099] based on Figure 2 The results of the slag steam explosion confirmation test, which showed that the cold iron source was put into the slag, were given. The conditions used in the iron refining method of this embodiment were limited: the mass Wsc of the cold iron source 5 loaded from the scrap chute 6 satisfied that the K value calculated by the relation (1) was less than 0.

[0100] That is, the conditions used in the iron refining method of this embodiment limit the K value calculated by relation (1) to be less than 0. Moreover, the K value calculated by relation (1) to be less than 0 limits the condition that the cold iron source 5 is temporarily stopped from being loaded from the scrap chute 6 and the area B1 in which the steam explosion does not occur is temporarily stopped, and then the steam explosion area C is avoided.

[0101] According to the conditions used in the iron refining method of this embodiment, namely, the condition that the K value calculated by formula (1) is less than 0, the mass Wsc of the cold iron source 5 loaded from the scrap chute 6 into the reaction vessel 1 is loaded relative to the mass Wsl of the residual slag present in the reaction vessel 1, within the range where the K value calculated by formula (1) is less than 0, so that the moisture contained in the cold iron source 5 can avoid the steam explosion zone C.

[0102] Here, the steam explosion zone C is the area where a steam explosion occurs when the water contained in the cold iron source 5 comes into contact with the slag 4 immediately after the cold iron source 5 is put into the reaction vessel 1 from the waste chute 6 or shortly thereafter.

[0103] Thus, the condition for the second step in the iron refining method of this embodiment is to set the K value calculated by formula (1) to be less than 0, which is used to prevent the water vapor contained in the cold iron source 5 from exploding after the cold iron source 5 is loaded into the reaction vessel 1.

[0104] The refining method for molten iron in this embodiment focuses on the following: the mass Wsl of the residual slag 4 generated after the refining of the previous batch of molten iron, which remains in the reaction vessel 1 as residual slag, the amount Wsc of the cold iron source 5 charged into the reaction vessel 1, and the temperature Tf (°C) of the residual high-temperature material containing the residual molten iron 8 in the furnace after the treatment to leave the slag 4. It was found that setting the K value calculated by using these values ​​through the relation (1) to be less than 0 prevents the water vapor of the water contained in the cold iron source 5 from exploding.

[0105] The condition for preventing the explosion of water vapor contained in the cold iron source 5, which is defined in the conditions of the second process, namely, the condition that the K value calculated by relation (1) is less than 0, is based on the results of the slag water vapor explosion confirmation test and the results of the molten iron water vapor explosion confirmation test of the cold iron source 5 that has been wetted by water being put into the molten iron 10.

[0106] That is, the conditions of the second step in the iron refining method of this embodiment are based on the Leidenfrost effect that occurs when the moisture contained in the cold iron source 5 comes into contact with the furnace slag 4 and other residual high-temperature materials in the furnace. Based on rigorous experiments described later, the conditions are set such that the surface temperature of the residual high-temperature materials in the furnace is around 140~300°C, which shortens the evaporation time of moisture at the temperature of the high-temperature slag, so that the moisture from the cold iron source 5 is not brought into the reaction vessel 1.

[0107] Thus, by taking advantage of the selectable conditions in the second step of the iron refining method according to this embodiment, steam explosions caused by moisture contained in the cold iron source 5 can be avoided in advance.

[0108] In other words, the refining method of molten iron in this embodiment can prevent the slag 4 from boiling violently due to the violent reaction between the oxygen in the residual slag and the carbon in the molten iron 10 when the next batch of molten iron 10 is charged, as well as the steam explosion caused by the moisture contained in the cold iron source 5.

[0109] It should be noted that in the iron refining method of this embodiment, the residual slag mass Wsl of the slag 4 produced by refining the molten iron in the previous heat can be calculated based on the amount of slag-forming agent added in that heat, the gangue components contained in other added by-products, and the estimated values ​​of the weight of iron oxide and manganese oxide produced by the oxidation of molten iron.

[0110] Thus, in the iron refining method of this embodiment, by setting the K value calculated by formula (1) to be less than 0, the moisture contained in the cold iron source 5 loaded from the scrap chute 6 into the reaction vessel 1 can be evaporated without setting a waiting time, thereby avoiding a steam explosion. That is, the iron refining method of this embodiment uses formula (1) to calculate the K value as an indicator for determining whether to set a waiting time T, and can avoid the steam explosion zone C based on the calculated K value.

[0111] Furthermore, the refining method for molten iron in this embodiment sets the K value calculated by formula (1) to be less than 0, so there is no need to set a waiting time T for the moisture contained in the cold iron source 5 to evaporate. Therefore, the refining of molten iron that fully utilizes the preheating of the cold iron source 5 can be carried out stably and without any chance of loss under safe conditions.

[0112] (Step 3: The process of refining the next batch of molten iron by loading it into the reaction vessel)

[0113] The iron refining method of this embodiment includes a third step: refining by charging the next batch of molten iron into the aforementioned reaction vessel. That is, as... Figure 1 As shown in (b), the third step is to tilt the reaction vessel 1 toward the crane 7 again, tilt the molten pig iron ladle 9 to load the next batch of molten iron 10 into the reaction vessel 1, and then refine the next batch of molten iron.

[0114] The third step in the iron refining method of this embodiment includes desiliconization, dephosphorization, and decarburization treatments for the next heat of iron 10. The third step in the iron refining method of this embodiment includes pretreatment for desiliconization and dephosphorization, intermediate slag removal, decarburization, and final dephosphorization. That is, refining processes such as desiliconization, dephosphorization, and decarburization can be continuously performed within the reaction vessel 1.

[0115] It should be noted that when molten iron 10 is loaded into the reaction vessel 1, if the moisture brought into the furnace (which serves as the reaction vessel 1) by the cold iron source 5 (such as scrap) has not evaporated and remains, there is a risk of steam explosion due to the reaction between the molten iron 10 and the moisture. Therefore, when loading scrap containing moisture into the reaction vessel 1, it is preferable to set a waiting time T1 separately from the end of the scrap loading to the start of the loading of molten iron 10. The waiting time T1 can be set uniformly or determined according to Wsc / Wsl. In addition, to shorten the waiting time T1 required for evaporation in order to disperse the moisture, it is preferable to shake the furnace after the scrap loading into the reaction vessel 1 is completed. Furthermore, the waiting time T1 separately set in the second process from the end of the loading of the cold iron source 5 from the scrap chute 6 into the reaction vessel 1 to the loading of the next batch of molten iron 10 will be explained later.

[0116] Specifically, after the molten iron 10 is loaded into the reaction vessel 1, as follows: Figure 1 (c) shows the reaction vessel 1 being erected. Then, oxygen 12 is blown from the oxygen lance 11 into the molten iron 10 or slag 4, and the molten iron 10 is stirred using stirring gas blown in from the bottom-blown gas system 13. Next, it is transferred to the refining process where impurities are oxidized and removed. Before or during the refining process of the molten iron 10, a top feed material 15 is sometimes added from the top hopper 14. The top feed material 15 can be slag-forming materials such as lime, or cooling materials such as ore. In addition to slag-forming materials such as lime and cooling materials such as ore, the top feed material 15 can also be solid reduced iron 15A that can be hoisted to the top hopper 14.

[0117] In this way, in the iron refining method of this embodiment, the amount of cold iron source 5 allowed to be charged into the reaction vessel 1 is limited to avoid steam explosion caused by moisture contained in the cold iron source 5 charged from the scrap chute 6 into the reaction vessel 1. Therefore, the amount of cold iron source 5 charged from the scrap chute 6 is sometimes less than the required total amount of cold iron source Wt.

[0118] In this case, after the remaining chill source 5, which is insufficient relative to the total chill source input Wt, is loaded into the chill source 5 from the scrap chute 6, solid reduced iron 15A can be fed into the reaction vessel 1 from the furnace top. That is, the reaction vessel 1 is upright, and solid reduced iron 15A is fed into the furnace top hopper 14. Solid reduced iron 15A refers to chill source 5 of the size that can be rolled up to the furnace top hopper 14, such as granular pig iron or reduced iron.

[0119] In the iron refining method of this embodiment, solid reduced iron 15A can be added after the cold iron source 5 is loaded into the reaction vessel 1 from the scrap chute 6, whether before or after the refining process of the next batch of iron 10.

[0120] However, if the molten iron temperature is as low as it is before the refining process of the next batch of molten iron 10 begins, the temperature drop of the molten iron in the initial stage of the refining process will be greater due to the heat absorption accompanying the melting of the cold iron source 5.

[0121] Therefore, when the temperature of the molten iron drops to the temperature obtained by adding approximately 60°C to the solidification temperature of the molten iron calculated according to the C-Fe binary system state diagram, the gas outlet of the bottom-blown gas system 13 will be blocked due to the solidification of the molten iron 10 or the growth of the solidified phase of the cold iron source 5.

[0122] In this situation, the inability to effectively stir the molten iron 10 has adverse effects, such as slag over-oxidation 4, reduced iron yield, and decreased refining properties of the molten iron 10. Furthermore, gas ejecting from the gaps in the furnace wall along the seams of the refractory 2 can cause equipment malfunctions such as refractory 2 falling off. Therefore, it is preferable to feed solid reduced iron 15A from the furnace top hopper 14 after the start of the refining process of the molten iron 10, which utilizes the heat of combustion of impurities generated by oxygen to raise the iron temperature.

[0123] When supplying stirring gas from the bottom-blown gas system 13, a certain flow rate of gas is continuously circulated as a standby gas flow, even before the refining process of the next heat of molten iron 10, to prevent blockage of the gas nozzle. The flow rate of the standby gas flow is based on the amount of residual molten iron 8, slag 4, and the diameter of the gas nozzle of the bottom-blown gas system 13, ensuring that the gas ejection pressure is not lower than the static pressure. The type of gas blown into the bottom-blown gas system 13 is typically an inert gas, such as N2 or Ar.

[0124] Next, the preferred embodiment of the iron refining method of the present invention will be described in detail with reference to the relevant background. That is, the slag steam explosion confirmation test and the molten iron steam explosion confirmation test will be described in detail, which are prerequisites for explaining the technical matters included in the second step of the iron refining method of this embodiment.

[0125] <Confirmation Test for Slag Steam Explosion>

[0126] Figure 2 This is a graph showing the results of a confirmatory test for steam explosion in slag when a water-soaked cold iron source is introduced into the slag furnace. That is, Figure 2 The slag steam explosion confirmation test shown was conducted based on the following conditions: even when the test was carried out within the scope of the suitable examples described in Patent Document 1, it was not possible to stably suppress the steam explosion; and it was necessary to clearly and quantitatively show the conditions under which the steam explosion phenomenon occurred.

[0127] The slag steam explosion confirmation test is conducted according to the following steps. First, after meeting the requirements... Figure 1 In a small high-frequency melting furnace containing the necessary components, a ternary system slag of CaO-SiO2-FetO was melted, and the slag temperature was adjusted. Then, while the power supply to the melting furnace was cut off, a water-soaked chill was added to the molten slag to check for the presence or absence of steam explosion. Then, using a ladle made from a graphite crucible, carbon-saturated molten iron smelted at 1200-1300°C in another furnace was scooped and loaded into the melting furnace from above the slag.

[0128] Here, the slag composition includes CaO concentration of 20-50 mass%, SiO2 concentration of 10-40 mass%, and FeO concentration of 10-40 mass%. Additionally, the slag temperature Tf' is 1200-1700℃, and the ratio of the amount of chilled iron input Wsc' (kg) to the amount of molten slag Wsl' (kg), Wsc' / Wsl'(-), is in the range of 0.1-50.

[0129] It should be noted that the chill source used iron sheets with a length and width ranging from 3 to 15 mm, a thickness ranging from 3 to 7 mm, a carbon concentration of less than 30 massppm, and an oxygen concentration of less than 150 massppm. The iron sheets used as the chill source were immersed in room temperature water for approximately 1 minute. Then, the chill source, which had been slightly drained before being placed into the aforementioned melting furnace, was used for a slag steam explosion confirmation test.

[0130] The results of the confirmatory test for slag steam explosion using slag and a water-soaked chill are presented in... Figure 2 .here, Figure 2 The symbol "●" in the diagram represents the conditions under which slag boiling and steam explosion do not occur, while the symbol "×" represents the conditions under which steam explosion occurs. For example... Figure 2 As shown, the inventors discovered that the slag boiling zone A, the steam explosion zone C, and the zones B1 and B2 where slag boiling and steam explosion do not occur can be sorted out by the ratio of slag temperature Tf' and the amount of cold iron source Wsc' (kg) to the amount of residual slag Wsl' (kg) Wsc' / Wsl' (-).

[0131] In the slag boiling zone A where the mass of the amount of chilled iron source Wsc' (kg) relative to the mass of the residual slag Wsl' (kg) is lower than Wsc' / Wsl', the slag will not boil even immediately after the chilled iron source is introduced or shortly thereafter.

[0132] Subsequently, due to the gas generated when carbon-saturated molten iron is charged, the slag will undergo violent boiling, which is a characteristic of the violent boiling zone A of the slag.

[0133] From this technical point of view, in the iron refining method of this embodiment, in order to avoid slag boiling caused by the gas generated when carbon-saturated molten iron is charged into the reaction vessel, Figure 2 The slag boiling zone A shown requires the amount of chill source needed to solidify all the residual slag remaining in the reaction vessel after blowing.

[0134] Furthermore, if the mass ratio of the amount of chilled iron source Wsc' (kg) to the amount of residual slag Wsl' (kg) Wsc' / Wsl' continues to increase, the slag boiling zone will be moved from the slag boiling zone A to the zone B1 where slag boiling and steam explosion do not occur (hereinafter referred to as the "slag boiling and steam explosion avoidance zone B1"). Moreover, based on... Figure 2 The diagram shown illustrates that, as an example, the boundary between the slag boiling zone A and the slag boiling and steam explosion avoidance zone B1 can be approximated by the following relationship (1A).

[0135] It should be noted that in the iron refining method of this embodiment, the relation (1A) may vary slightly depending on the iron refining conditions, and is not limited to the range that can represent the boundary line between the slag boiling zone A and the slag boiling and steam explosion avoidance zone B1.

[0136] Wsc' / Wsl'=5.224×10 -7 ×Tf 2 -1.779×10 -4 ×Tf-0.4321···(1A)

[0137] Furthermore, if the mass ratio Wsc'(kg) of the added chill source to the residual slag Wsl'(kg) of the residual slag is further increased, making it greater than the value that can be calculated using equation (1), then the steam explosion zone C, where steam explosions occur immediately after the chill source is added or shortly thereafter, will be reached. Moreover, based on... Figure 2 The diagram shown illustrates that, as an example, the boundary between the slag boiling and steam explosion avoidance zone B1 and the steam explosion zone C can be approximated by the following relationship (1B).

[0138] It should be noted that in the iron refining method of this embodiment, the relation (1B) may vary slightly depending on the iron refining conditions, and is not limited to the range that can represent the boundary between the slag boiling and steam explosion avoidance zone B1 and the steam explosion zone C.

[0139] Wsc' / Wsl'=8.64×10 -7 ×Tf 1.947 ···(1B)

[0140] Furthermore, if the mass ratio of the amount of chilled iron source Wsc' (kg) to the amount of residual slag Wsl' (kg) continues to increase, Wsc' / Wsl', then a region B2 where steam explosions no longer occur (hereinafter referred to as "slag boiling and steam explosion avoidance region B2") will be reached. Moreover, based on... Figure 2 The diagram shown illustrates that, as an example, the boundary between the steam explosion zone C and the slag boiling and steam explosion avoidance zone B2 can be approximated by the following relationship (2).

[0141] It should be noted that in the iron refining method of this embodiment, the relation (2) may vary slightly depending on the iron refining conditions and is not limited to the range that can represent the boundary line between the steam explosion zone C and the slag boiling and steam explosion avoidance zone B2.

[0142] Wsc' / Wsl'≥6.591×10-6 ×Tf 1.695 ···(2)

[0143] It should be noted that, at least within the scope of this experiment, the distinction between slag boiling zone A, steam explosion zone C, and slag boiling and steam explosion avoidance zones B1 and B2 has not been determined based on slag composition. Furthermore, the theoretical basis for determining the threshold values ​​of slag boiling zone A, steam explosion zone C, and slag boiling and steam explosion avoidance zones B1 and B2 remains unclear.

[0144] The inventors believe that the slag boiling zone A on the lower side of Wsc' / Wsl' is formed because the amount of cold iron source input is less than the amount of residual slag, resulting in the dissolved slag not being fully solidified, and the reaction between C in the molten iron and FeO in the slag proceeding violently.

[0145] In other words, it can be inferred that the reaction between the C in the molten iron and the FeO in the slag [C] + (FeO) = CO↑ + Fe is a liquid-liquid reaction.

[0146] Furthermore, in the steam explosion zone C on the side where the mass of the cold iron source Wsc' (kg) relative to the mass of the residual slag Wsl' (kg) is higher than the ratio Wsc' / Wsl', slag violently splashes upwards. This suggests that the steam explosion is caused by the rapid vaporization of moisture in the waste by the high-temperature slag.

[0147] <Confirmation Test for Molten Iron Steam Explosion>

[0148] Figure 3 This is a graph showing the results of a confirmatory test of steam explosion in molten iron, in which a water-wetted cold iron source is immersed in molten iron. That is, Figure 3 The molten iron steam explosion confirmation test shown is conducted to confirm whether a molten iron steam explosion occurs when a water-soaked cold iron source is added to the molten iron remaining in the reaction vessel. Here, the reaction vessel contains not only residual slag, but sometimes also residual molten iron from the pretreatment process.

[0149] Therefore, the confirmatory test for molten iron steam explosion confirmed whether a molten iron steam explosion occurred when a water-soaked cold iron source was added to the residual molten iron in the reaction vessel. The results of the molten iron steam explosion confirmatory test are shown below. Figure 3 .

[0150] Figure 3 The symbol "●" represents the conditions for a steam explosion without molten iron, and the symbol "×" represents the conditions for a steam explosion with molten iron.

[0151] The confirmation test for molten iron steam explosion is conducted through the following steps. First, under the condition that... Figure 1 Molten iron was melted in a small high-frequency melting furnace, and the temperature of the molten iron was adjusted. Then, while the power supply to the melting furnace was cut off, a water-soaked chill was added to the molten iron. At this time, a test was conducted to confirm whether there was a steam explosion in the molten iron. Here, the molten iron temperature Tf'' was 1200℃~1700℃, and the ratio of the amount of chill added Wsc'' (kg) to the amount of dissolved molten iron Wrm'' (kg), Wsc'' / Wrm''(-), was in the range of 0.1~3.0. The chill was the same as that used in the above slag steam explosion confirmation test, and was supplied to the molten iron steam explosion confirmation test in the same way.

[0152] like Figure 3 As shown, the inventors discovered that, similar to slag, the region D where steam explosion occurs in molten iron and the region E where steam explosion does not occur in molten iron can be determined by the ratio of molten iron temperature Tf'' and the amount of cold iron source Wsc'' (kg) to the amount of molten iron Wrm'' (kg) Wsc'' / Wrm'' (-).

[0153] In region D (hereinafter referred to as "molten iron steam explosion region D"), it was confirmed that steam explosions such as upward spraying of molten iron occurred immediately after the addition of the cold iron source or shortly thereafter. According to Figure 3 It can also be clearly seen that the range of the ratio Wsc'' / Wrm'' of the amount of cold iron source Wsc'' (kg) to the amount of molten iron remaining Wrm'' (kg) is significantly narrower than the slag boiling zone A and the steam explosion zone C clearly defined in the slag steam explosion confirmation test.

[0154] Furthermore, in actual converter operation, while the amount of residual molten iron in the reaction vessel is approximately 1 ton, the amount of residual slag exceeds 10-20 tons. Therefore, as long as the requirements are met... Figure 2 The amount of chilled iron source above the lower limit of the relation (1A) automatically becomes the amount that can avoid Figure 3 The mass ratio of the amount of cold iron source Wsc'' to the amount of residual molten iron Wrm'' in the molten iron steam explosion zone D is Wsc'' / Wrm''.

[0155] Therefore, even if there are residual slag and residual molten iron in the reaction vessel, there is no problem as long as the following relationship (1)' or relationship (2)' of the boundary lines of the slag boiling and steam explosion avoidance zones B1 and B2 can be satisfied.

[0156] Relation (1)'

[0157] 5.224×10 -7 ×Tf' 2-1.779×10 -4 ×Tf'-0.4321 <Wsc’ / Wsl’≤8.64×10 -7 ×Tf' 1.947 ···(1)'

[0158] Relation (2)'

[0159] Wsc' / Wsl'≥6.591×10 -6 ×Tf' 1.695 ···(2)'

[0160] That is, in the second step of the iron refining method of this embodiment, the relationship (1) used to calculate the index K value for determining whether to set the waiting time T is based on the relationship between the mass of the residual slag Wsl and the mass of the cold iron source Wsc loaded from the scrap chute. This relationship is based on the slag steam explosion confirmation test and the iron steam explosion confirmation test.

[0161] Furthermore, the relation (1) used to calculate the K value of the index used to determine whether to set the waiting time T defines the boundary line between the slag boiling and steam explosion avoidance zone B1 and the steam explosion zone C as defined by the slag steam explosion confirmation test and the molten iron steam explosion confirmation test.

[0162] From this technical point of view, in the iron refining method of this embodiment, when the cold iron source is loaded into the reaction vessel in order to use the heat of the residual slag generated after the refining of the previous batch of iron for the preheating of the cold iron source, the K value of the index used to determine whether to set the waiting time T is calculated using the relation (1). Based on the calculated K value, the slag boiling zone A and the steam explosion zone C can be avoided.

[0163] As a result, the iron refining method of this embodiment can avoid slag boiling caused by gas generated when molten iron is loaded into the reaction vessel, and can avoid steam explosion when cold iron source is loaded into the reaction vessel.

[0164] In this way, the iron refining method of this embodiment can optimize the weight of cooling material used to solidify the slag remaining in the reaction vessel from the refining of the previous batch of iron.

[0165] Furthermore, the refining method for molten iron in this embodiment solidifies the slag residue generated from the blowing of the previous heat of molten iron to form solidified slag. Therefore, even when the next heat of molten iron is charged, the oxygen in the decarburized slag will not react violently with the carbon in the molten pig iron to cause the molten iron to boil violently.

[0166] Therefore, the refining method of molten iron in this embodiment is based on the K value calculated by relation (1) and the K value is less than 0. Therefore, no given waiting time T is set for evaporating the moisture contained in the cold iron source, and no water vapor explosion occurs caused by the reaction of the moisture contained in the cold iron source with the slag and the evaporation of the moisture.

[0167] It should be noted that, for the iron refining method of this embodiment, when the mass Wsc (kg) of the cold iron source fed into the scrap chute is part of the total cold iron source fed into the chute Wt (kg), the remaining cold iron source can be fed into the furnace top hopper or the like as a surplus cold iron source after the cold iron source from the scrap chute is loaded into the reaction vessel.

[0168] As described above, according to the iron refining method of the first embodiment, even if a cold iron source is charged while slag from the refining of the previous batch of iron remains in the reaction vessel, a steam explosion will not occur. Furthermore, the iron refining method of the first embodiment uses formula (1) to calculate the K value, which serves as an indicator for determining whether to set a waiting time T. Based on the calculated K value, the steam explosion zone C can be avoided without setting a waiting time.

[0169] Furthermore, since the iron refining method of the first embodiment does not require setting a waiting time for the moisture contained in the cold iron source to evaporate, it can safely and stably carry out iron refining with full utilization of the preheating of the cold iron source without any chance of loss.

[0170] Furthermore, the iron refining method of this embodiment solidifies the slag generated from the refining of the previous heat and remaining in the reaction vessel. Therefore, even if the moisture in the chilled iron reacts with the slag when the next heat of iron is added, a water vapor explosion will not occur. In other words, the iron refining method of this embodiment allows for a significant increase in the amount of chilled iron used, making a substantial contribution to reducing CO2 emissions.

[0171] [Second Implementation]

[0172] The iron refining method of the second embodiment is characterized in that, in the above embodiment, when the K value is less than 0, the waiting time is set to 60 seconds or more, and after the waiting time has elapsed, the remaining cold iron source is fed from the scrap chute or the top of the furnace.

[0173] That is, the refining method for molten iron in this embodiment has the following technical features: based on the K value calculated by the above-mentioned formula (1), in the case that the moisture contained in the cold iron source reacts with the residual slag and the moisture evaporates, resulting in a steam explosion, the feeding of the cold iron source from the scrap chute to the reaction vessel is temporarily stopped, and a given waiting time T is set for the moisture contained in the cold iron source to evaporate.

[0174] In other words, the iron refining method of this embodiment is based on the premise that a cold iron source is loaded into the reaction vessel to solidify the entire amount of residual slag. After the cold iron source is loaded in such a way that the K value calculated by the above formula (1) is less than 0, a given waiting time T is set.

[0175] Furthermore, in the refining method of molten iron in this embodiment, after a given waiting time T, the moisture contained in the cold iron source evaporates.

[0176] Then, in the iron refining method of this embodiment, when the mass Wsc of the cold iron source loaded into the scrap chute is part of the total cold iron source input Wt, the amount of cold iron source that is insufficient in the total cold iron source input Wt can be fed from the scrap chute or the top of the furnace as the remaining cold iron source.

[0177] Here, in the iron refining method of this embodiment, the required total chill input Wt is the sum of the mass of chill input Wsc fed through the scrap chute and the mass of the remaining chill input charged from the scrap chute or furnace top hopper after a given waiting time T. The remaining chill input is the mass obtained by subtracting the mass of chill input Wsc charged from the scrap chute from the total amount Wt fed into the reaction vessel in the next heat of iron refining.

[0178] Thus, the iron refining method of this embodiment can avoid the reaction between the moisture contained in the cold iron source and the residual slag, and the evaporation of the moisture leading to a steam explosion. By loading the mass of the remaining cold iron source from the scrap chute or the top of the furnace into the reaction vessel after a given waiting time T, it is possible to ensure that the total amount of cold iron source required for the next heat of iron refining, Wt, is loaded into the reaction vessel.

[0179] It should be noted that after a given waiting time T, the remaining chill source that can be fed from the scrap chute or the furnace top hopper can be a chill source containing moisture or a chill source that does not contain moisture, such as solid reduced iron.

[0180] Here, in the second step of the iron refining method of this embodiment, the given waiting time T for evaporating the moisture contained in the chill needs to be sufficient to prevent the moisture contained in the chill from reacting with the slag and causing a steam explosion due to the evaporation of the moisture. The waiting time T is 60 seconds or more.

[0181] By setting the waiting time T to 60 seconds or more, steam explosions can be prevented even if the moisture in the chilled iron source evaporates. While a waiting time of 60 seconds or more is sufficient, from the viewpoint of refining molten iron with no chance of loss and by making full use of the preheated chilled iron source, a waiting time of 120 seconds or less is preferred.

[0182] It should be noted that in the iron refining method of this embodiment, the waiting time T depends on the moisture content of the water contained in the cold iron source, so that the temperature of the residual high-temperature material in the furnace after the slag remains, and does not depend on the composition of the slag.

[0183] As described above, in the iron refining method according to the second embodiment, since a waiting time T is set to prevent the water in the cold iron source from reacting with the slag and causing a steam explosion due to the evaporation of the water, a steam explosion will not occur even when a cold iron source is loaded.

[0184] Furthermore, the iron refining method of the second embodiment, by setting an appropriate waiting time, can refining molten iron that has been preheated by fully utilizing the cold iron source in a safe and stable manner without any chance of loss.

[0185] Furthermore, according to the iron refining method of the second embodiment, if the mass Wsc of the cold iron source fed into the scrap chute after a given waiting time T is part of the total cold iron source Wt, the amount of cold iron source that is insufficient in the total cold iron source Wt can be charged or fed into the scrap chute or the furnace top as the remaining cold iron source.

[0186] [Third Implementation]

[0187] The iron refining method of the third embodiment is characterized in that, in the iron refining methods of the first or second embodiment, when performing the third step described above, a waiting time T1 is further set before the next heat of molten iron is loaded into the reaction vessel. That is, in the iron refining method of this embodiment, even if moisture brought into the reaction vessel by the cold iron source such as scrap from the scrap chute has not evaporated and remains, a steam explosion caused by the residual moisture can be avoided when loading the next heat of molten iron in the third step.

[0188] In the iron refining method described above, even if the chill is charged in a manner that prevents steam explosion caused by moisture contained in the chill through the second step, sometimes the evaporation of moisture contained in the chill is insufficient. If, in the second step, the moisture contained in the chill charged from the scrap chute has not evaporated sufficiently, a steam explosion caused by residual moisture may occur when the next batch of molten iron is charged into the reaction vessel in the third step.

[0189] From this technical point of view, the iron refining method of this embodiment further sets a waiting time T1, which is different from the aforementioned waiting time T, before the next batch of molten iron is charged into the reaction vessel. The waiting time T1 depends on the type of chill source charged from the scrap chute and is preferably 30 to 150 seconds. When the waiting time T1 is set to 30 seconds or more, the evaporation of moisture contained in the chill source charged from the scrap chute becomes sufficient, which is therefore preferable. When the waiting time T1 is set to 150 seconds or less, iron refining can be carried out stably and without loss under safe conditions, which is also preferable. Furthermore, the waiting time T1 can be uniformly set according to the converter's operating mode, or it can be determined based on Wsc / Wsl. Furthermore, in order to shorten the waiting time T1 required for moisture dispersion and evaporation, it is preferable to perform furnace shaking after the chill source charging in the second step is completed.

[0190] [Other Implementation Methods]

[0191] The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. The structure and details of the present invention can be modified in various ways that can be understood by those skilled in the art within the technical scope of the present invention.

[0192] Example

[0193] <Example 1 of the Invention>

[0194] Part or all of the slag after blowing is taken as residual slag, and the amount is adjusted to 10 kg of slag remaining in the induction melting furnace. The composition of the residual slag in the induction melting furnace is adjusted to CaO concentration of 50 mass%, SiO2 concentration of 22 mass%, and FeO concentration of 28 mass%. The temperature of the residual high-temperature material in the furnace, Tf (°C), is set as the temperature of the slag remaining in the induction melting furnace. Considering the temperature of the residual molten iron remaining in the induction melting furnace after the previous heat of molten iron blowing, the slag temperature is set to 1400°C.

[0195] Next, 10 kg of cold iron source was prepared to be loaded into the induction melting furnace. The cold iron source to be loaded into the induction melting furnace was made of iron sheet with a length and width of 3~15 mm, a thickness of 3~7 mm, a C concentration of less than 30 massppm, and an O concentration of less than 150ppm.

[0196] The K value was calculated using the following formula (1): the amount of cold iron source Wsc (kg) after the iron sheet was lightly drained, the amount of residual slag Wsl (kg), the temperature of the residual high-temperature material in the furnace Tf (°C).

[0197] As a result, the value of K calculated by relation (1) is -1.5. Thus, in Invention Example 1, since the calculated value of K is less than 0 (K<0), no waiting time T is specifically set. Moreover, in Invention Example 1, it was confirmed that even when the drained iron sheet is loaded into the residual slag in the induction melting furnace, no steam explosion occurs.

[0198] Furthermore, in Example 1 of the invention, dry iron sheets that have not been soaked in water are fed into the converter from the top hopper of the furnace, which is used as a cold iron source to be loaded into the induction melting furnace.

[0199] That is, it was found that in Invention Example 1, the heat of the residual slag in the induction melting furnace can be fully used for preheating of the cold iron source, and the refining of molten iron can be carried out under safe conditions without steam explosion. The refining results of molten iron in Invention Example 1 are shown in Table 1.

[0200] <Examples 2-8 of the Invention>

[0201] The composition of the slag remaining in the induction melting furnace, the temperature of the residual high-temperature material in the furnace, the slag temperature of the slag remaining in the induction melting furnace, and the amount of cold iron source for the iron sheet were changed. Apart from these changes, the refining of molten iron was carried out in the same manner as in Invention Example 1.

[0202] Here, in Invention Examples 2-8, since the K value calculated by relation (1) is set to be less than 0 (K<0), no waiting time T is specifically set. It was confirmed that even when the drained iron sheet, i.e., the cold iron source, is loaded into the residual slag in the induction melting furnace in Invention Examples 2-8, no steam explosion occurs. The refining results of the molten iron in Invention Examples 2-8 are shown in Table 1.

[0203] <Comparative Examples 1-4>

[0204] The composition of the slag remaining in the induction melting furnace, the temperature of the residual high-temperature material in the furnace, the slag temperature of the slag remaining in the induction melting furnace, and the amount of cold iron source for the iron sheet immersed in water were changed. Apart from these changes, the refining of molten iron was carried out in the same manner as in Invention Example 1. Here, in Comparative Examples 1 to 4, the K value calculated by relation (1) was set to be 0 or higher (K≥0).

[0205] Furthermore, it was confirmed that steam explosions occurred when residual slag, which was used as a drained iron sheet (i.e., a chill source), was introduced into the induction melting furnace in Comparative Examples 1-4. The refining results of the molten iron in Comparative Examples 1-4 are shown in Table 1.

[0206]

[0207] According to Table 1, it can be clearly seen that even if the residual slag in the induction melting furnace is loaded into the drained iron sheet, the amount of cold iron source Wsc (kg), the amount of residual slag Wsl (kg) and the temperature Tf (°C) of the residual high-temperature material in the furnace are adjusted by using the relationship (1) so that the K value is less than 0 (K<0), the steam explosion can be avoided.

[0208] On the other hand, it can be clearly stated that when the drained iron sheet is loaded into the induction melting furnace with residual slag, if the amount of cold iron source Wsc (kg), the amount of residual slag Wsl (kg), and the temperature Tf (°C) of the residual high-temperature material in the furnace are adjusted by using the relationship (1) so that the K value is above 0 (K≥0), a steam explosion will occur.

[0209] <Examples 9-14 of Inventions>

[0210] The composition of the slag remaining in the induction melting furnace, the temperature of the residual high-temperature material in the furnace Tf (°C), the slag temperature of the slag remaining in the induction melting furnace, and the amount of cold iron source Wsc (kg) of the iron sheet immersed in water were changed. The K value calculated by formula (1) was set to 0 or more (K≥0). Except for this, the refining of molten iron was carried out in the same way as in Invention Example 1. That is, in Invention Examples 9 to 14, the K value calculated by formula (1) was set to 0 or more (K≥0).

[0211] Here, based on the refining results of molten iron in Invention Examples 1-8 and Comparative Examples 1-4, it is clear that a steam explosion will occur in Invention Examples 9-14. Therefore, in Invention Examples 9-14, the water-soaked iron sheets are divided into two groups, designated as chilled iron source I and chilled iron source II, respectively. Then, chilled iron sources I and II are respectively added to the slag. A waiting time T is set for the evaporation of moisture contained in the first added iron sheet, i.e., chilled iron source I. Then, after the set waiting time T has elapsed, the second added iron sheet, i.e., chilled iron source II, is added.

[0212] It should be noted that in Invention Examples 9-14, from the viewpoint of fully evaporating the moisture contained in the iron sheet and completely preventing the occurrence of steam explosion, the waiting time T was set to 60 seconds or more. The refining results of the molten iron in Invention Examples 9-14 are shown in Table 2.

[0213] <Comparative Examples 5-7>

[0214] The waiting time T for evaporating the moisture contained in the first iron sheet, i.e., the cold iron source I, was set to less than 60 seconds. Otherwise, the refining of the molten iron was performed in the same manner as in Invention Examples 9 to 14. The refining results of the molten iron in Comparative Examples 5 to 7 are shown in Table 2.

[0215]

[0216] According to Table 2, it can be clearly seen that even if the residual slag in the induction melting furnace is loaded into the drained iron sheet, and the amount of cold iron source Wsc (kg), the amount of residual slag Wsl (kg), and the temperature Tf (°C) of the residual high-temperature material in the furnace are adjusted by means of K value above 0 (K≥0) through the relation (2), a steam explosion can be avoided by setting the waiting time T to more than 60 seconds.

[0217] On the other hand, it is clear that if the waiting time T is set to less than 60 seconds, the moisture contained in the water-soaked iron sheet cannot be completely evaporated, and thus a steam explosion cannot be avoided.

[0218] Furthermore, based on the refining results of the molten iron in Examples 9 to 14 of the Invention, it was also determined that the waiting time T, which is independent of the amount of residual slag in the slag and the amount of cold iron source in the water-soaked iron sheet, is 60 seconds or more.

[0219] <Examples of Inventions 15-20>

[0220] Next, the steam explosion caused by the contact between the moisture contained in the iron sheet (scrap) used as a chill source and the molten iron was investigated. In Invention Examples 15-20, the composition of the slag remaining in the induction melting furnace, the temperature of the residual high-temperature material in the furnace Tf (°C), i.e., the slag temperature of the residual slag in the induction melting furnace, and the amount of chill source Wsc (kg) of the iron sheet soaked in water were changed, and the K value calculated by relation (1) was set to 0 or more (K≥0), and the refining of molten iron was carried out in the same manner as in Invention Example 1. That is, in Invention Examples 15-20, the refining of molten iron was carried out in the same manner as in Invention Examples 9-14, with the K value calculated by relation (1) set to 0 or more (K≥0).

[0221] In Invention Example 15, to prevent a steam explosion between the slag and the chill, 13.0 kg of chill I was added to the 10.0 kg of residual slag in the induction melting furnace until the range of relation (2) was satisfied. The chill I was an iron sheet without moisture. After 60 seconds of adding chill I, the drained iron sheet, i.e., chill II 2.0 kg, was added to the induction melting furnace. After adding chill II to the induction melting furnace, 10 seconds, which was set as a waiting time T1, were added to the induction melting furnace, and it was confirmed whether there was a steam explosion.

[0222] Furthermore, in Invention Example 15, using the aforementioned refining conditions for molten iron, 10 refining tests were conducted on each molten iron to confirm whether steam explosions occurred in each test. Moreover, after the 10 refining tests were completed, the probability of steam explosions was calculated based on the number of times steam explosions occurred.

[0223] It should be noted that, for steam explosions, the occurrence of steam explosions between slag and chilled iron sources and between molten pig iron and chilled iron sources were confirmed, and the respective steam explosion probabilities were calculated.

[0224] In addition, Examples 16-20 changed the temperature Tf (°C) of the residual high-temperature material in the furnace, that is, the slag temperature of the residual slag in the induction melting furnace, the amount of water-free iron sheet as chill source I and the amount of drained iron sheet as chill source II loaded into the induction melting furnace, and the waiting time T1 set after the chill source II is loaded into the induction melting furnace. Apart from these changes, the refining of molten iron was carried out in the same way as in Example 15.

[0225] Then, the steam explosion probabilities of steam explosions occurring between slag and chilled iron sources and between molten pig iron and chilled iron sources were calculated. The refining results of the molten iron in Examples 15-20 are shown in Table 3.

[0226] <Examples 21-26 of the Invention>

[0227] The waiting time T1 for evaporating the moisture contained in the second iron sheet (i.e., chilled iron source II) was set to 30 seconds or more. Otherwise, the refining of the molten iron was performed in the same manner as in Examples 15-20. Furthermore, in Examples 21-26, the probabilities of steam explosions occurring between the slag and chilled iron source, and between the molten pig iron and chilled iron source, were calculated. The refining results of the molten iron in Examples 21-26 are shown in Table 3.

[0228]

[0229] According to Invention Examples 15-20 in Table 3, since the waiting time T1 before the next batch of molten iron is loaded into the induction melting furnace is shortened to 10-20 seconds, the probability of steam explosion between slag and cold iron source is 0%, but the probability of steam explosion between molten pig iron and cold iron source does not reach 0%.

[0230] Furthermore, it can be clearly seen from Invention Examples 21 to 26 in Table 3 that when the waiting time T1 is set to 30 to 40 seconds, both the probability of a steam explosion occurring between the slag and the chill source and the probability of a steam explosion occurring between the molten pig iron and the chill source are 0%.

[0231] Based on the above results, it is confirmed that by setting the waiting time T1 to 30 seconds or more, not only can a steam explosion caused by contact between the slag and the moisture contained in the scrap iron be avoided, but also a steam explosion caused by contact between the molten iron in the next heat and the moisture contained in the scrap iron be avoided. That is, it can be clearly understood that, according to the present invention, by setting the waiting time T1 to 30 seconds or more, a stable method for refining molten iron that completely prevents steam explosions can be provided.

[0232] As described above, according to Invention Examples 1-26 and Comparative Examples 1-7, the heat of the high-temperature slag remaining in the induction melting furnace can be fully utilized for preheating of the cold iron source, and the refining of molten iron that fully utilizes the preheating of the cold iron source can be achieved in a safe state without the risk of steam explosion.

[0233] Industrial applicability

[0234] The iron refining method of the present invention is applicable to the blast furnace-converter process, can reduce the molten pig iron blending rate, and helps to reduce CO2 emissions, thus being useful in industry.

Claims

1. A method for refining molten iron, wherein the heat of the slag generated after the refining of the previous batch of molten iron is used to preheat the molten iron from a cold iron source, the method comprising: In the first step, while leaving part or all of the slag as residual slag in the reaction vessel, the refined molten iron is tapped from the reaction vessel. In the second step, the cooling material used to form solidified slag by cooling the residual slag is set as a cold iron source loaded from the scrap chute; and The third step involves loading the next batch of molten iron into the reaction vessel for refining. In the second step, the K value calculated using the following relationship (1) between the mass of the residual slag Wsl, the mass of the chill source Wsc charged from the scrap chute, and the temperature Tf of the residual high-temperature material in the furnace in the first step is less than 0. The waiting time T after the cold iron source is loaded is not set. K = Wsc-8.64×10 -7 ×Tf 1.947 ×Wsl···(1) In equation (1), Wsc (kg) represents the mass of the cold iron source loaded from the scrap chute, Wsl (kg) represents the mass of the residual slag, and Tf (°C) represents the temperature of the residual high-temperature material in the furnace during the first process.

2. A method for refining molten iron, wherein the heat of the slag generated after the refining of the previous batch of molten iron is used to preheat the molten iron from a cold iron source, the method comprising: In the first step, while leaving part or all of the slag as residual slag in the reaction vessel, the refined molten iron is tapped from the reaction vessel. In the second step, the cooling material used to form solidified slag by cooling the residual slag is set as a chill source loaded from the scrap chute or a chill source fed from the top of the furnace; and The third step involves loading the next batch of molten iron into the reaction vessel for refining. In the second step, the K value calculated using the following relationship (1) between the mass of the residual slag Wsl, the mass of the chill source Wsc charged from the scrap chute, and the temperature Tf of the residual high-temperature material in the furnace in the first step is less than 0. After the chill source is installed, the waiting time T is set to more than 60 seconds. After this waiting time T has elapsed... The remaining chilled iron source is fed from the scrap chute or the top of the furnace. K = Wsc-8.64×10 -7 ×Tf 1.947 ×Wsl···(1) In equation (1), Wsc (kg) represents the mass of the cold iron source loaded from the scrap chute, Wsl (kg) represents the mass of the residual slag, and Tf (°C) represents the temperature of the residual high-temperature material in the furnace during the first process.

3. The method for refining molten iron according to claim 1 or 2, wherein, In the third step, a waiting time T1 is set before the next batch of molten iron is loaded into the reaction vessel.

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