Methods for refining molten iron

Abstract

This invention provides a method for refining molten iron by using the heat of the high-temperature slag remaining in the reaction vessel for preheating a chilled iron source, and by refining molten iron stably and without the risk of loss in a safe state without slag boiling. This method for refining molten iron utilizes the heat of the slag generated after refining to preheat the chilled iron source. The method includes: a first step, tapping refined molten iron from the reaction vessel while leaving residual slag in the reaction vessel; a second step, using chilled iron sources loaded from a scrap chute and fed from the furnace top as cooling materials for forming solidified slag by cooling the residual slag; and a third step, loading the next batch of molten iron into the reaction vessel for refining. In the second step, the mass of the residual slag Wsl, the mass of the chilled iron source Wsc loaded from the scrap chute, and the mass of the chilled iron source Wh is fed from the furnace top hopper satisfy given conditions.

Description

Technical Field

[0001] This invention relates to a method for refining molten iron. More specifically, it relates to a method for refining molten iron that can prevent the violent boiling of molten pig iron even when the amount of chill material containing chill source is greatly increased and slag remains in the converter before the next heat of molten pig iron is charged.

[0002] That is, the present invention relates to a method for refining molten iron by increasing the amount of cold iron source in the converter to reduce greenhouse gas emissions, and by effectively utilizing the slag generated after refining as slag-forming material during the refining of molten pig iron.

[0003] 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.

[0004] "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

[0005] 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 from the blast furnace and chilled iron 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.

[0006] In recent years, from the perspective of preventing global warming, there has been a demand for the development of technologies to reduce CO2 emissions. The so-called United Steelworks extract iron from iron ore and use the extracted iron as raw material to manufacture final products such as steel plates, steel pipes, structural steel, bars, and galvanized iron plates. In the past, United Steelworks used carbon sources to reduce iron ore and produce molten pig iron. In the production of this molten pig iron, 500 kg of carbon source was required for every ton of molten pig iron to facilitate the reduction of iron ore.

[0007] On the other hand, when steel is manufactured using chilled iron sources such as scrap iron or solid reduced iron as raw materials, the carbon source required for the reduction of iron ore is not needed. Therefore, when steel is manufactured using chilled iron sources as raw materials, only the energy sufficient to melt the chilled iron sources is required. From this technical point of view, manufacturing steel using chilled iron sources as raw materials can significantly reduce CO2 emissions.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] In other words, if the next heat of molten pig iron is charged while molten decarburized slag remains in the reaction vessel such as a converter, there is a problem of violent reaction between the iron oxide in the decarburized slag and the carbon in the molten pig iron, resulting in slag boiling. To solve this problem, methods such as waiting for the decarburized slag to solidify before charging the next heat of molten pig iron have been adopted, as well as methods that force the decarburized slag to solidify by adding cooling materials such as raw dolomite, CaCO3, iron ore, and iron oxide scale to the decarburized slag.

[0012] However, if excessive amounts of slag-forming materials are added to the converter, the amount of slag produced in the converter will increase. On the other hand, when the amount of cooling materials required for the refining of the next batch of molten pig iron is added to the converter, the amount of decarburized slag that can be solidified is limited, and the unsolidified decarburized slag needs to be discharged outside the converter.

[0013] 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.

[0014] The sensible heat of the slag produced during the refining of molten pig iron in a converter has not been effectively utilized previously. Therefore, by fully utilizing the sensible heat of the slag from the refining of molten pig iron for the preheating of the cold iron source, the amount of cold iron source used in the converter can be increased without the need for a new heat source. Generally, molten pig iron produced in a blast furnace is decarburized and refined in a converter to become steel. The decarburized slag produced during the refining of molten pig iron in this converter is not discharged from the converter when the molten steel is tapped, but is reused in the next heat of molten pig iron refining, partially or entirely remaining in the converter.

[0015] Theoretically, compared to the phosphorus concentration in the slag from pretreatment blowing at a lower refining temperature of molten pig iron in the converter, the phosphorus concentration in the decarburized slag from decarburization blowing at a higher refining temperature of molten pig iron is lower. Therefore, by using the decarburized slag from decarburization blowing for dephosphorization blowing of molten pig iron, the dephosphorization reaction of the slag from decarburization blowing can be facilitated, thereby reducing the amount of slag-forming material that needs to be added to the converter.

[0016] That is, by pre-treating the molten pig iron used in the next heat by leaving the decarburized slag generated after decarburization blowing of the molten pig iron used in the previous heat in the converter at a high temperature, it is expected that the amount of slag-forming materials to be added will be greatly reduced and the amount of cold iron source will be greatly increased.

[0017] From this technical perspective, when charging the next heat of molten pig iron while the slag and molten steel from the previous heat remain, a method to avoid CO boiling in converter operation is proposed: adding a certain amount of deoxidizer (C, Si, Al) to the decarburized slag (e.g., Patent Document 1). Specifically, Patent Document 1 discloses a converter operation method in which, in converter operation involving two or more consecutive heats of pre-treated blown molten pig iron without slag discharge, after tapping the previous heat, a predetermined amount or more of deoxidizer is added to the slag in the converter and mixed, followed by the addition of the main raw material and slag-forming agent for the next heat.

[0018] Furthermore, 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 2 discloses a technique for tapping steel while decarburized slag generated through decarburization treatment remains 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.

[0019] In addition, Patent Document 3 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.

[0020] The technology disclosed in Patent Document 2 aims to reuse decarburized slag, while the technology disclosed in Patent Document 3 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.

[0021] Existing technical documents

[0022] Patent documents

[0023] Patent Document 1: Japanese Patent Application Publication No. 4-52207

[0024] Patent Document 2: Japanese Patent Application Publication No. 2004-256839

[0025] Patent Document 3: Japanese Patent Application Publication No. 2009-228102 Summary of the Invention

[0026] The problem that the invention aims to solve

[0027] However, the aforementioned existing technologies have the following problems that must be addressed.

[0028] In the converter operation method described in Patent Document 1, the cost of deoxidizers is a major issue, and they are currently almost never used in practice. In the refining method for molten pig iron described in Patent Document 2, arbitrarily tilting the refining vessel accelerates the aging of its tilting mechanism, leading to increased equipment maintenance costs. Furthermore, even if the decarburized slag produced in the refining method of molten pig iron is reused in the decarburization blowing process of molten pig iron, it cannot be expected to contribute to the dephosphorization reaction, nor can it be expected to reduce the reduction effect of new slagging agents.

[0029] Furthermore, in the refining method for molten pig iron described in Patent Document 2, when using waste containing moisture as a chill source, there is a risk of steam explosion when the high-temperature molten slag comes into contact with the waste. Therefore, countermeasures such as preheating the waste containing moisture with a burner to remove the moisture are adopted.

[0030] However, the following problem exists: in order to preheat the waste containing moisture with a burner to remove moisture, the required investment in heating equipment and fuel costs will increase.

[0031] That is, the problem with the technology described in Patent Documents 2 and 3 is that it is completely unable to cope with the potential for slag boiling when a chilled iron source containing moisture enters the high-temperature slag in the reaction vessel due to the difference in specific gravity. Examples of chilled iron sources containing moisture include, for example, water that inevitably enters the depressions of plate-shaped waste during rainy days, and damp powdery waste.

[0032] 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.

[0033] 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 2, it is a value determined based on the steel production plan, assuming the need to ensure steel production volume, and is technically a non-controllable parameter. Therefore, the only options are to reduce the amount of decarburized slag residue Wsl or 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.

[0034] In Patent Document 3, 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 3 cannot achieve the purpose of preheating the cold iron source using the residual slag.

[0035] Furthermore, Patent Document 3 describes a method of keeping the solid iron source in the molten slag by setting the size of the solid iron source to less than 1 mm, but it is difficult to ensure a sufficient amount of such solid iron source.

[0036] In view of these problems, the inventors have repeatedly conducted in-depth research and found that the steam explosion, which is the cause of slag boiling, is caused by the rapid volume expansion of water when the water contained in the cold iron source comes into contact with the slag and other residual high-temperature materials in the furnace. Therefore, they focused on conditions to avoid such rapid volume expansion of water.

[0037] Here, when the moisture contained in the cold iron source comes into contact with the residual high-temperature material in the furnace and evaporates, the amount of moisture evaporated per unit of moisture mainly depends on the temperature of the residual high-temperature material in the furnace.

[0038] 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.

[0039] 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).

[0040] Therefore, this invention focuses on the Leidenfrost effect that occurs when moisture contained in the cold iron source comes into contact with high-temperature residual materials in the furnace, such as slag. It explores a method to prevent moisture caused by the cold 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 moisture evaporation time is shortened at the temperature of the high-temperature slag.

[0041] Specifically, when a chill is introduced into a reaction vessel containing high-temperature slag, the chill comes into contact with the high-temperature slag, causing the slag temperature 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, the conditions for preventing slag bumping caused by the reaction between the residual slag and the moisture in the chill can be defined and identified 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, Wsc(kg) to Wsl(kg), and the final temperature Tf(°C) of the treated molten iron with residual slag.

[0042] Furthermore, it was discovered that, based on a given formula relating the amount of residual slag Wsl (kg) in the reaction vessel, the amount of chilled iron Wsc (kg) fed into the reaction vessel via a scrap chute, and the final temperature Tf (°C) of the molten iron after the slag residue treatment, a condition is met by feeding a given amount of chilled iron into the reaction vessel via a scrap chute and then feeding a top chilled iron that does not contain moisture.

[0043] The present invention was made to solve the above-mentioned problems, and its purpose is to propose a condition in which the heat of the high-temperature slag remaining in the reaction vessel is used for the preheating of the cold iron source, and can be carried out stably and without loss in a safe state without slag boiling.

[0044] Furthermore, the objective of this invention is to provide a refining method for molten iron that can prevent violent boiling of the molten pig iron due to the violent reaction between oxygen in the slag and carbon in the molten pig iron, even when the next batch of molten pig iron is charged with slag remaining in a reaction vessel such as a converter.

[0045] Furthermore, the objective of this invention is to provide a refining method for molten iron that significantly reduces the amount of heating materials and slag-forming materials and significantly increases the amount of chilled iron material containing chilled iron sources by fully utilizing the sensible heat of the slag generated in the refining process of molten pig iron for preheating chilled iron materials.

[0046] Furthermore, the objective of this invention is to provide a method for refining molten iron that can prevent steam explosions even when the amount of chill material containing chill sources is greatly increased and the next batch of molten pig iron is charged with slag remaining in the converter.

[0047] Methods for solving problems

[0048] In light of these issues, the inventors conducted in-depth research and discovered that by setting the ratio of the mass of residual slag in the reaction vessel to the total amount of cold iron source charged into the reaction vessel, the temperature of the residual high-temperature material in the furnace after slag treatment, the mass of cold iron source charged from the scrap chute, and the mass of cold iron source fed from the top of the furnace, slag boiling will not occur during the refining of molten iron.

[0049] 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 loaded from a scrap chute and a cold iron source fed from the top of the furnace are used as cooling materials to form 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 mass of the residual slag Wsl, the mass of the cold iron source Wsc loaded from the scrap chute, and the mass of the cold iron source Wh from the top of the furnace satisfy any one of the following conditions (A) to (C).

[0050] Condition (A): The total amount W of the cold iron source is loaded within the range of the following relations (1) and relations (2), wherein the total amount W of the cold iron source is the sum of the mass Wsc of the cold iron source loaded from the scrap chute and the mass Who of the cold iron source fed from the top of the furnace.

[0051] Condition (B): The mass Wsc of the cold iron source loaded from the scrap chute is set within the range of the following relationship (2), and the remaining part required as cooling material is set as the cold iron source fed from the top of the furnace later or simultaneously. The total amount W of the cold iron source satisfies the following relationship (1), wherein the total amount W of the cold iron source is the sum of the mass Wsc of the cold iron source loaded from the scrap chute and the mass Who of the cold iron source fed from the top of the furnace.

[0052] Condition (C): The mass Who of the cold iron source fed from the top of the furnace is set to the range of the following relationship (3), and the remaining part required as cooling material after the cold iron source is fed from the top of the furnace is set as the cold iron source loaded from the scrap chute.

[0053] Relation (1):

[0054] W / Wsl>5.224×10 -7 ×Tf 2 -1.779×10 -4 ×Tf-0.4321

[0055] Relation (2):

[0056] W / Wsl≤8.64×10 -7 ×Tf 1.947

[0057] Relation (3):

[0058] W / Wsl≥6.591×10 -6 ×Tf 1.695

[0059] In the above relations (1) to (3),

[0060] Wsl represents the mass (t) of residual slag.

[0061] W represents the mass (t) of the chilled iron source that is loaded before the molten pig iron is loaded.

[0062] Tf represents the temperature (°C) of the residual high-temperature material in the furnace during the first process.

[0063] It should be noted that the refining method for molten iron of the present invention includes the following more preferred solutions to the problem:

[0064] (a) A chill source that is prone to containing moisture is loaded from a waste chute, the chill source comprising a powdered chill source and a chill source with voids.

[0065] (b) The chill source loaded in step 2 above contains reduced iron;

[0066] (c) When the temperature Tf of the residual high-temperature material in the furnace is higher than the melting point of the reduced iron, the reduced iron is fed into the reaction vessel from the top of the furnace in multiple batches, and the amount of reduced iron fed into the reaction vessel from the top of the furnace for the first time, Who1(t), is less than 6.6% by mass relative to the mass Wsl(t) of the residual slag in the reaction vessel.

[0067] (d) The refining of the molten iron includes: a pretreatment blowing process for desiliconizing and dephosphorizing the molten iron in the next heat; an intermediate slag removal process for removing the slag remaining in the reaction vessel by tilting the reaction vessel; and a decarburization process for decarburizing and final dephosphorizing by adding by-products to the reaction vessel.

[0068] (e) The refining of the molten iron includes: a desiliconization blowing process, in which the molten iron of the next heat is desiliconized; an intermediate slag removal process, in which the slag remaining in the reaction vessel is removed by tilting the reaction vessel; and a dephosphorization blowing process, in which dephosphorization is carried out by adding by-products to the reaction vessel; etc.

[0069] The effects of the invention

[0070] According to the present invention, the heat of the high-temperature slag remaining in the reaction vessel can be fully utilized for preheating the cold iron source, and the refining of molten iron with full utilization of the preheated cold iron source can be carried out stably and safely without slag boiling, without any chance of loss. According to the present invention, even when the next heat of molten pig iron is charged with decarburized slag remaining in the converter, the violent reaction between the iron oxide in the decarburized slag and the carbon in the molten pig iron, which would otherwise cause the molten pig iron to boil violently, can be avoided.

[0071] Furthermore, the present invention can eliminate the problems and disadvantages of the prior art. When the decarburized slag generated in the previous heat before the end of refining is reused as the slagging agent for the next heat, the decarburized slag can be efficiently cooled and solidified without increasing the burden on operation and equipment, thereby increasing the amount of recycling in the next heat. It can also increase the amount of cold iron source and reduce the amount of new slagging agent. Attached Figure Description

[0072] 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.

[0073] Figure 2This is a graph showing the results of a slag boiling confirmation test in which a water-soaked cold iron source is added to the slag.

[0074] Figure 3 This is a graph showing the results of a confirmation test of boiling out molten iron by immersing a water-wetted cold iron source into molten iron.

[0075] Symbol Explanation

[0076] 1. Reaction vessel

[0077] 2 Refractory materials

[0078] 3. Steel tapping hole

[0079] 4. Slag

[0080] 5. Cold iron source

[0081] 6 Waste chute

[0082] 7. Cranes

[0083] 8. Residual molten iron

[0084] 9. Molten pig iron ladle

[0085] 10 Molten Iron

[0086] 11 Oxygen supply spray gun

[0087] 12 Oxygen

[0088] 13 Bottom-blown gas system

[0089] 14. Furnace top hopper

[0090] 15. Material fed into the furnace top

[0091] 15A Solid Reduced Iron Detailed Implementation

[0092] 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 actual embodiments. 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.

[0093] Next, the preferred embodiments of the present invention will be described in detail with reference to the relevant background.

[0094] [First Implementation]

[0095] The refining method for molten iron in this embodiment 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 loaded from a scrap chute and a cold iron source fed from the top of the furnace are used as cooling materials 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 mass of the residual slag Wsl, the mass of the cold iron source Wsc loaded from the scrap chute, and the mass of the cold iron source Wh is fed from the top of the furnace satisfy any one of the following conditions (A) to (C).

[0096] The following describes each step of the refining method for molten iron according to this embodiment.

[0097] Here, in the second step of the iron refining method of this embodiment, conditions (A) to (C) are:

[0098] "Condition (A): The total amount W of the cold iron source is loaded within the range of the following relations (1) and relations (2), wherein the total amount W of the cold iron source is the sum of the mass Wsc of the cold iron source loaded from the scrap chute and the mass Who of the cold iron source fed from the top of the furnace."

[0099] Condition (B): The mass Wsc of the chill source loaded from the scrap chute is set within the range of the following relationship (2), and the remaining portion required as cooling material is set as the chill source fed from the top of the furnace after or at the same time as the chill source loaded from the scrap chute. The total amount W of the chill source satisfies the following relationship (1), where the total amount W of the chill source is the sum of the mass Wsc of the chill source loaded from the scrap chute and the mass Who of the chill source fed from the top of the furnace.

[0100] Condition (C): The mass Who of the cold iron source fed from the top of the furnace is set to the range of the following relationship (3). After the cold iron source is loaded from the scrap chute, the remaining portion of the cold iron source required as cooling material is set as the cold iron source loaded from the scrap chute.

[0101] Furthermore, the relations (1) to (3) used in the conditions (A) to (C) of the iron refining method in this embodiment are as follows:

[0102] "Relationship (1): W / Wsl>5.224×10" -7 ×Tf 2 -1.779×10 -4 ×Tf-0.4321

[0103] Relationship (2): W / Wsl≤8.64×10 -7 ×Tf 1.947

[0104] Relationship (3): W / Wsl≥6.591×10 -6 ×Tf 1.695

[0105] In the above relationships (1), (2) and (3), Wsl represents the mass (t) of the residual slag, W represents the mass (t) of the chilled iron source charged before the molten pig iron is charged, and Tf represents the temperature (°C) of the residual high-temperature material in the furnace in the first process.

[0106] The iron refining method of this embodiment is carried out in a reaction vessel such as a converter-type refining 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.

[0107] (Step 1: The process of tapping refined molten iron from the reaction vessel while leaving residual slag in the vessel)

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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. 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.

[0113] 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 generated after the refining of the previous batch of molten iron in the pretreatment process, and it remains in the reaction vessel 1.

[0114] 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.

[0115] 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.

[0116] 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 FeO concentration 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.

[0117] (Step 2: The process of feeding the chilled iron source into the reaction vessel from the scrap chute and the top of the furnace)

[0118] The second step in the iron refining method of this embodiment involves charging a chill source from the scrap chute or the top of the furnace while some or all of the slag generated from the refining of the previous heat of iron remains in the reaction vessel. In this second step, the chill source 5 can be charged into the reaction vessel 1 from either the scrap chute 6 or the top of the furnace. Charging the chill source 5 from the top of the furnace can be done, for example, using the top hopper 14.

[0119] 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.

[0120] In addition to carbon steel scrap and pig iron scrap, the cold iron 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, newly cut scrap steel, and steel cutting powder. Examples of pig iron scrap include old pig iron and pig iron cutting powder.

[0121] Here, cold iron source 5 is a cold iron source that easily contains moisture, and often contains some moisture. For example, cold iron source 5 is powdery waste such as steel cutting shavings, steel pipes, motors, and compressed scrap steel, or waste with voids. These cold iron sources 5 are prone to containing moisture.

[0122] 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.

[0123] 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, chilled iron source 5 and residual molten iron 8.

[0124] 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 loaded from the scrap chute 6 or the cold iron source fed from the top of the furnace, thus becoming solidified slag.

[0125] 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 or other reduced iron is used as the chill source 5, from the viewpoint of easily adjusting the amount of reduced iron added to the reaction vessel 1, it is desirable to use the furnace top hopper 14 or the like to feed solid reduced iron into the reaction vessel 1 from the furnace top.

[0126] 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 converter, solid reduced iron 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, and can also quickly promote the solidification of residual slag as molten slag.

[0127] 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 in the longitudinal direction to 300 mm or less, the solidification of the residual slag can be carried out rapidly.

[0128] 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 iron oxide in the slag 4 and the carbon in the molten pig iron can be avoided, thus preventing the molten pig iron from boiling violently.

[0129] 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).

[0130] Here, in the general refining of molten iron, the solidification temperature of the slag in the reaction vessel 1, such as a heating furnace, was measured, and the following results were obtained: if the slag temperature is below 1100℃, the residual slag will solidify under any conditions and become solidified slag.

[0131] Furthermore, in general iron refining, within the temperature range that can be considered during iron decarburization refining, even slags with various alterations to their composition, such as basicity and iron oxide concentration, can be solidified by setting the temperature of the slag 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.

[0132] 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 input a cold iron source 5 that can ensure the amount of heat required to reduce the temperature of the residual high-temperature material in the furnace, which includes 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.

[0133] Therefore, in the second step, the cold iron source 5 is loaded or fed into the residual slag in such a way that the mass of the residual slag Wsl, the mass of the cold iron source Wsc(t) loaded from the scrap chute, the mass of the cold iron source Who(t) fed from the top of the furnace, and the temperature of the residual high-temperature material Tf(°C) in the furnace satisfy any one of the following conditions (A) to (C).

[0134] That is, in the iron refining method of this embodiment, the mass of residual slag Wsl(t), the mass of cold iron source Wsc(t) charged from the scrap chute, and the mass of cold iron source Who(t) fed from the top of the furnace are used as cold iron source 5 to be charged or fed into the residual slag present in the reaction vessel 1 in such a way that any one of the following conditions (A) to (C) is met.

[0135] Here, in the second step, the total mass of the chill source Wsc, which is loaded into the residual slag in the reaction vessel 1 from the waste chute 6, and the mass of the chill source Who, which is fed from the top of the furnace, is the total mass of the chill source loaded before the molten pig iron is loaded, which is the mass of the chill source W(t).

[0136] The following explains the conditions (A) to (C) that must be met when the chill source 5 is loaded into or added to the reaction vessel 1.

[0137] <Cold Iron Source Loading Conditions (A)>

[0138] Figure 2 This is a graph showing the results of a slag boiling confirmation test where a chill is added to the slag. The slag boiling confirmation test uses slag and a water-soaked chill to confirm whether slag boiling occurs when the chill is added to the slag. It should be noted that the details of the slag boiling confirmation test are explained later.

[0139] like Figure 2 As shown, it is clear that regions A and C where slag bumping occurs and regions B1 and B2 where slag bumping does not occur exist. Here, Figure 2 The symbol "●" in the diagram represents the condition under which slag boiling does not occur, and the symbol "×" represents the condition under which slag boiling occurs. That is, as shown... Figure 2As shown, the regions A and C where slag boiling occurs and the regions B1 and B2 where slag boiling does not occur can be organized 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 added to the amount of residual slag Wsl' (kg) W' / Wsl' (-).

[0140] based on Figure 2 The conditions (A) limiting the results of the slag boiling confirmation test shown define the amount of chill source W charged within the range of the following equations (1) and (2) relative to the mass Wsl of the residual slag. This amount of chill source W is the sum of the mass Wsc of the chill source charged from the scrap chute and the mass Who of the chill source charged from the top of the furnace. Here, equations (1) and (2) are described below. It should be noted that the introduction of equations (1) and (2) is as described later.

[0141] Relationship (1): W / Wsl>5.224×10 -7 ×Tf 2 -1.779×10 -4 ×Tf-0.4321

[0142] Relationship (2): W / Wsl≤8.64×10 -7 ×Tf 1.947

[0143] That is, condition (A) is a condition that limits the introduction of the cold iron source 5 into the residual slag present in the reaction vessel 1 within the region B1 where slag boiling does not occur.

[0144] According to condition (A), relative to the mass Wsl of the residual slag present in the reaction vessel 1, the mass W of the chill source 5 is charged within the range of the following relationships (1) and (2), where the mass W of the chill source 5 is the sum of the mass Wsc of the chill source 5 charged from the scrap chute 6 and the mass Who of the chill source 5 fed from the top of the furnace, thereby passing through the region A where slag boiling occurs and avoiding entering the region C where slag boiling occurs.

[0145] Here, area A, where slag boiling occurs, is the region where slag boiling occurs due to the reaction of iron oxide in the unsolidified slag with carbon in the molten pig iron when the next batch of molten iron 10 is charged. Area C, where slag boiling occurs, is the region where slag boiling occurs due to the explosion of steam from moisture contained in the chill sluice 5 immediately after it is added from the scrap chute 6 or shortly thereafter.

[0146] Thus, according to the selectable condition (A) in the second step of the iron refining method of this embodiment, it is possible to avoid in advance: slag boiling caused by the gas generated by the violent reaction between iron oxide in the residual slag and carbon in the molten pig iron when the next batch of molten iron 10 is charged, and slag boiling caused by the steam explosion caused by the moisture contained in the cold iron source 5.

[0147] In the iron refining method of this embodiment, the residual slag mass Wsl(t) of part or all 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.

[0148] Thus, in the iron refining method of this embodiment, by selecting condition (A) in the second step and setting the weight of the cooling materials such as the cold iron source 5 and solid reduced iron used to completely solidify the slag 4 remaining in the reaction vessel 1 such as the converter refining furnace, the remaining slag can be completely solidified into solid slag.

[0149] As a result, the iron oxide contained in the residual slag, which is the molten slag, solidifies into solidified slag due to the decarburization of the slag, and thus does not react with the carbon contained in the next batch of molten pig iron charged into the converter refining furnace.

[0150] That is, in the iron refining method of this embodiment, by selecting condition (A) in the second step, the sensible heat energy of the residual slag remaining in the reaction vessel 1 can be absorbed by the cooling materials such as waste material and cold iron source 5 instead of being discharged, thus avoiding waste and achieving its effective utilization.

[0151] In other words, by selecting condition (A) in the second process, the iron refining method of this embodiment can eliminate the problems and disadvantages of the prior art. When the decarburized slag generated in the previous heat before the end of refining is reused as a slagging agent for the next heat, the decarburized slag can be efficiently cooled and solidified without increasing the burden on operation and equipment, thereby increasing the amount of recycling in the next heat. It can also increase the amount of cold iron source 5 and reduce the amount of new slagging agent.

[0152] It should be noted that, under condition (A), the chill source 5 can be loaded into the reaction vessel 1 from the scrap chute 6 or from the furnace top hopper 14. From the viewpoint of ensuring the total amount of chill source required to refine the next heat of molten iron 10 into the reaction vessel 1, the chill source 5 is preferably loaded into the reaction vessel 1 from the scrap chute 6.

[0153] <Cold Iron Source Loading Conditions (B)>

[0154] based on Figure 2 The conditions (B) for confirming the slag boiling test results of adding chills to the slag, as shown, limit the mass Wsc of the chill 5 charged from the scrap chute 6 to the range of the following relationship (2). The remaining portion of the required chill 5 is defined as the chills added from the top of the furnace after or simultaneously with the chills added from the scrap chute 6, and the total amount W of the chills satisfies the above relationship (1). This total amount W of the chills is the sum of the mass Wsc of the chills charged from the scrap chute and the mass Who of the chills added from the top of the furnace. Here, relationship (2) is as follows. It should be noted that the introduction of relationship (2) will be explained later.

[0155] Relationship (2): W / Wsl≤8.64×10 -7 ×Tf 1.947

[0156] That is, condition (B) defines the condition that the cold iron source 5 is temporarily stopped in the area of ​​the range that avoids the slag boiling zone C by stopping the feeding of the cold iron source 5 from the scrap chute 6, and then the cold iron source 5 is fed from the furnace top hopper 14 in order to avoid the slag boiling zone A.

[0157] According to condition (B), relative to the mass Wsl of the residual slag present in the reaction vessel 1, the mass W of the chill source 5 is charged within the range of the above relationship (2). The mass W of the chill source 5 is the sum of the mass Wsc of the chill source 5 charged from the scrap chute 6 and the mass Who of the chill source 5 fed from the top of the furnace. This can avoid the area C where the slag boiling occurs due to the steam explosion caused by the moisture contained in the chill source 5.

[0158] Here, the area C where slag boiling occurs is the range where slag boiling occurs due to the explosion of water vapor in the cold iron source 5 immediately after it is fed from the waste chute 6 into the cold iron source 5 or shortly thereafter.

[0159] Thus, the condition (B) of the second step in the iron refining method of this embodiment is to prevent the water vapor of the water contained in the chill source 5 from exploding after the chill source 5 is loaded into the reaction vessel 1, and ultimately avoid the area of ​​boiling over due to the slag not solidifying. The iron refining method of this embodiment focuses on the weight Wsl of the residual slag 4 remaining in the reaction vessel 1 as residual slag, which is part or all of the slag 4 generated after the refining of the previous heat of iron, the amount W of the chill source 5 loaded into the reaction vessel 1, and the temperature Tf (°C) of the high-temperature residue in the furnace containing the residual iron 8 after the treatment to leave the slag residue. Based on the values ​​calculated by using these values ​​through a given formula, the condition for preventing the water vapor of the water contained in the chill source 5 from exploding was discovered.

[0160] The conditions for preventing the explosion of water vapor from the moisture contained in the chill source 5, as specified in condition (B) of the second step, are based on the results of the slag boiling confirmation test described later, and the results of the molten iron boiling confirmation test in which the water-soaked chill source 5 is added to the molten iron 10. That is, condition (B) of the second step included in the molten iron refining method of this embodiment focuses on the Leidenfrost effect that occurs when the moisture contained in the chill source 5 comes into contact with the slag or other residual high-temperature materials in the furnace. Based on rigorous experiments described later, the condition is set such that the surface temperature of the residual high-temperature materials in the furnace, where the evaporation time of moisture is shortened at the temperature of the high-temperature slag, is around 140~300°C, so that the moisture caused by the chill source 5 is not introduced into the reaction vessel 1.

[0161] Thus, according to the selectable condition (B) in the second step of the iron refining method of this embodiment, the cold iron source 5 that is insufficient relative to the total amount of cold iron source required before charging the next batch of molten pig iron can be supplemented by the cold iron source 5 fed from the top of the furnace, i.e., the mass W(t) of the cold iron source 5, thereby preventing the slag from boiling over due to the steam explosion caused by the moisture contained in the cold iron source 5.

[0162] <Cold iron source loading conditions (C)>

[0163] based on Figure 2 The conditions (C) limiting the results of the slag boiling confirmation test in which the chill source is fed into the slag are defined as follows: the mass Who of the chill source fed from the top of the furnace is defined as the range of the following formula (3). After the chill source is loaded into the scrap chute, the remaining portion required as cooling material is defined as the chill source loaded into the scrap chute. Here, formula (3) is as follows. It should be noted that the introduction of formula (3) will be explained later.

[0164] Relationship (3): W / Wsl≥6.591×10 -6 ×Tf 1.695

[0165] That is, condition (C) is a condition that, when the chill source 5 is charged into the reaction vessel 1, the area C where slag boiling occurs is first avoided by charging the chill source 5 from the top of the furnace, and then the remaining portion required as cooling material is charged as the chill source 5 from the scrap chute 6.

[0166] According to condition (C), relative to the mass Wsl of the residual slag present in the reaction vessel 1, the mass Who of the cold iron source 5 fed from the top of the furnace is fed within the range of the above relationship (3), thereby passing through the region C where slag boiling occurs and reaching the region B2 where slag boiling does not occur.

[0167] It should be noted that in the second step, the chill source 5 loaded into the reaction vessel 1 may contain reduced iron, and the chill source 5 fed from the top of the furnace preferably contains reduced iron. The reduced iron may contain solid reduced iron or powdered reduced iron.

[0168] Here, the area B2 where slag boiling does not occur is the area beyond the area C where slag boiling occurs, which is crossed by loading sufficient cold iron source 5 into the reaction vessel 1. It is the area where slag boiling does not occur immediately after the cold iron source 5 is loaded from the scrap chute 6 or shortly thereafter, due to the steam explosion caused by the moisture contained in the cold iron source 5.

[0169] Thus, according to the selectable condition (C) in the second step of the iron refining method of this embodiment, after the chill source 5 is fed from the furnace top hopper 14, the chill source 5 that is insufficient relative to the total amount of chill source 5 required before the next batch of molten pig iron is fed can be supplemented by the chill source 5 loaded from the scrap chute 6, which is the mass W of the chill source 5, and the slag boiling caused by the water vapor explosion of the moisture contained in the chill source 5 is avoided in advance.

[0170] In the iron refining method of this embodiment, the selection of conditions (A) to (C) regarding the relationship between the mass of residual slag Wsl, the mass of the cold iron source 5 charged from the scrap chute 6 Wsc, and the mass of the cold iron source 5 fed from the top of the furnace can be appropriately set according to the converter operation of refining the next batch of iron 10.

[0171] In the second step, to solidify the slag 4 remaining in the reaction vessel 1, such as the converter-type refining furnace, it is preferable to use the chill source 5, considering the viewpoint of significantly increasing the amount of chill source 5 used. Furthermore, in the second step, other cooling materials besides the chill source 5 used to solidify the slag 4 remaining in the reaction vessel 1 can also be used.

[0172] As a cooling material, any material capable of solidifying the molten slag is acceptable, with no particular limitations. Examples of suitable cooling materials include dolomite, calcium carbonate, natural stone, and iron oxide scale. As waste material, it can be scrap iron, etc. Dolomite can be raw dolomite, calcined dolomite, or any mineral or rock. Natural stone can be iron ore, chromium ore, manganese ore, etc. As for iron oxide scale, any oxide formed on the surface of steel when exposed to air at high temperatures is acceptable, with no particular limitations on its composition.

[0173] It should be noted that, in the second step of the iron refining method of this embodiment, from the viewpoint of reducing CO2 gas emissions, it is preferable to use a large amount of chill 5 to solidify the slag 4 remaining in the reaction vessel 1. The amount of chill 5 used to solidify the slag 4, which is the residual slag charged into the reaction vessel 1, can be set considering its relationship with the mass of the residual slag 4 remaining in the reaction vessel 1 in the first step described above. The temperature of the chill 5 used to solidify the slag 4 remaining in the converter-type refining furnace can be room temperature, typically 15~25°C.

[0174] (Step 3: The process of refining the next batch of molten iron by loading it into the reaction vessel)

[0175] 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 10.

[0176] The third step in the refining method of molten iron 10 in this embodiment includes desiliconization, dephosphorization and decarburization of the molten iron in the next heat.

[0177] Specifically, after molten iron 10 is poured in, as follows Figure 1 As shown in (c), the reaction vessel 1 is made upright. 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. Sometimes, before or during the refining process of the molten iron 10, a top feed material 15 is 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.

[0178] Thus, the iron refining method of this embodiment takes into account the relationship between the amount of cold iron source 5 Wsc that is loaded into the reaction vessel 1 from the scrap chute 6, the amount of residual slag Wsl (kg) that is residual slag 4 inside the reaction vessel 1, and the temperature Tf (°C) of the residual high-temperature material in the furnace that is treated to leave slag 4 in the first step. Based on the values ​​calculated from these data, it is possible to avoid boiling over caused by steam explosion of the water contained in the cold iron source 5.

[0179] In this way, in the iron refining method of this embodiment, the amount of cold iron source 5 allowed to be loaded into the reaction vessel 1 is limited to avoid steam explosion caused by the moisture contained in the cold iron source 5 loaded from the scrap chute 6 into the reaction vessel 1.

[0180] Therefore, the amount of chilled iron source 5 fed from the scrap chute 6 is sometimes less than the total amount of chilled iron source required for refining the molten iron 10 in the next heat, i.e., the amount of chilled iron source W.

[0181] In this case, after the amount of chill source 5 that is insufficient relative to the total amount of chill source W as chill source is fed into the chill source 5 from the scrap chute 6, solid reduced iron 15A is fed into the reaction vessel 1 from the furnace top hopper 14. That is, the reaction vessel 1 is upright, and solid reduced iron 15A is fed into the furnace top hopper 14 as the remaining portion of the chill source 5. It should be noted that solid reduced iron 15A refers to chill sources of granular pig iron, reduced iron, etc., that can be rolled up to the furnace top hopper 14.

[0182] 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.

[0183] 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.

[0184] 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 boiling confirmation test and the iron boiling confirmation test will be described in detail. These tests are prerequisites for explaining the technical matters used in the second step of the iron refining method of this embodiment to limit the relationship between the mass of residual slag Wsl, the mass of chilled iron source Wsc charged from the scrap chute, and the mass of chilled iron source Who fed from the furnace top hopper.

[0185] <Slag Boiling Confirmation Test>

[0186] Figure 2 This is a graph showing the results of a slag boiling confirmation test in which a water-soaked cold iron source is added to the slag. That is, Figure 2The slag boiling confirmation test shown was conducted based on the following conditions: even when the test was conducted within the scope of the suitable examples described in Patent Document 2, it was not possible to stably suppress slag boiling; and it was necessary to clearly and quantitatively show the conditions under which the slag boiling phenomenon occurred.

[0187] The slag boiling 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 any slag boiling. Then, using a ladle made from a graphite crucible, molten C-saturated iron at 1200-1300°C, smelted in another furnace, was scooped and loaded into the melting furnace from above the slag.

[0188] Here, the slag composition includes CaO concentrations of 20-50 mass%, SiO2 concentrations of 10-40 mass%, and FeO concentrations of 10-40 mass%. Additionally, the slag temperature Tf' is 1200-1700℃, and the ratio W' (kg) of the added chill to the amount of melted slag Wsl' (kg) is in the range of 0.1-50. It should be noted that the chill used is an 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 150 massppm. This chill was immersed in room temperature water for approximately 1 minute. Then, the chill, slightly drained before being added to the aforementioned melting furnace, was used for a slag boiling confirmation test.

[0189] The results of the slag boiling confirmation test using slag and a water-soaked chill are shown in... Figure 2 .here, Figure 2 The symbol "●" in the diagram represents the condition under which slag boiling does not occur, and the symbol "×" represents the condition under which slag boiling occurs. For example... Figure 2 As shown, the inventors discovered that regions A and C where slag boiling occurs and regions B1 and B2 where slag boiling does not occur can be sorted out by the ratio W' / Wsl'(-) of slag temperature Tf' and the amount of cold iron source W' (kg) to the amount of residual slag Wsl' (kg).

[0190] In the slag boiling region A (hereinafter referred to as "slag boiling region A"), where the mass of the amount of cold iron source W' (kg) relative to the amount of residual slag Wsl' (kg) is lower than W' / Wsl', the slag will not boil even immediately after the cold iron source is introduced or shortly thereafter.

[0191] Subsequently, due to the gas generated when saturated iron C is added, the slag will undergo violent boiling, which is a characteristic of the violent boiling zone A of the slag.

[0192] Furthermore, if the mass ratio W'(kg) of the added chill source to the residual slag amount Wsl'(kg) of the residual slag is further increased, the slag boiling will be moved from the slag boiling zone A to the zone B1 where slag boiling does not occur (hereinafter referred to as the "slag boiling avoidance zone B1"). Moreover, based on... Figure 2 The diagram shown illustrates that, as an example, the boundary between the slag boiling region A and the slag boiling avoidance region B1 can be approximated by the following relationship (1).

[0193] It should be noted that in the iron refining method of this embodiment, the relation (1) 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 region A and the slag boiling avoidance region B1.

[0194] W' / Wsl'=5.224×10 -7 ×Tf 2 -1.779×10 -4 ×Tf-0.4321···(1)

[0195] Furthermore, if the mass ratio W' (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 slag boiling region C (hereinafter referred to as "slag boiling region C") will be reached, where slag is sprayed onto the top of the melting furnace immediately after the chill source is added or shortly thereafter. Moreover, based on Figure 2 The chart shown illustrates that, as an example, the boundary between the slag boiling avoidance zone B1 and the slag boiling zone C can be approximated by the following relationship (2).

[0196] 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 slag boiling avoidance zone B1 and the slag boiling zone C.

[0197] W' / Wsl'=8.64×10 -7 ×Tf 1.947 ···(2)

[0198] Furthermore, if the mass ratio Wsc' / Wsl' of the amount of chilled iron source W' (kg) relative to the amount of residual slag Wsl' (kg) continues to increase, then a region B2 where slag boiling no longer occurs (hereinafter referred to as "slag boiling avoidance region B2") will be reached. Moreover, based on... Figure 2 The chart shown illustrates that, as an example, the boundary between the slag boiling region C and the slag boiling avoidance region B2 can be approximated by the following relationship (3).

[0199] It should be noted that in the iron refining method of this embodiment, the relation (3) 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 region C and the slag boiling avoidance region B2.

[0200] Wsc' / Wsl'≥6.591×10 -6 ×Tf 1.695 ···(3)

[0201] It should be noted that, at least within the scope of this experiment, the distinction between slag boiling zones A and C and slag boiling avoidance zones B1 and B2 has not been determined to be dependent on slag composition. Furthermore, the theoretical basis for determining the threshold values ​​of slag boiling zones A and C and slag boiling avoidance zones B1 and B2 remains unclear.

[0202] The inventors believe that the slag boiling zone A on the side with lower W' / 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 proceeds violently.

[0203] 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.

[0204] Furthermore, in the slag boiling zone C where the mass ratio of the input chill source Wsc' (kg) to the residual slag Wsl' (kg) is higher than that of the residual slag, slag violently splashes upwards. This suggests that the slag is exploding due to the rapid vaporization of moisture in the waste by the high-temperature slag.

[0205] <Confirmation Test for Rapid Boiling of Molten Iron>

[0206] Figure 3 This is a graph showing the results of a confirmation test of boiling out molten iron by immersing a water-wetted cold iron source into molten iron. That is, Figure 3 The hot iron boiling confirmation test shown is conducted to confirm whether hot iron boiling occurs when a water-soaked cold iron source is added to the residual hot iron in the reaction vessel.

[0207] That is, the reaction vessel contains not only residual slag, but sometimes also residual steel from the pretreatment process, i.e., residual molten iron. Therefore, the hot iron boiling confirmation test was conducted to determine whether hot iron boiling occurred when a water-soaked chilled iron source was added to the residual molten iron in the reaction vessel. The results of the hot iron boiling confirmation test are shown below. Figure 3 . Figure 3 The symbol "●" in the diagram represents the condition for violent boiling without iron, and the symbol "×" represents the condition for violent boiling of molten iron.

[0208] The confirmation test for molten iron boiling is conducted through the following steps. First, in 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 to the melting furnace was cut off, a chilled iron source that had been soaked in water was added to the molten iron. At this time, a test was conducted to confirm whether the molten iron was boiling over. Here, the molten iron temperature Tf'' was 1200℃~1700℃, and the ratio of the amount of chilled iron source added W'' (kg) to the amount of molten iron dissolved Wrm'' (kg), W'' / Wrm''(-), was in the range of 0.1~3.0. The chilled iron source was supplied in the same way as in the above slag boiling over confirmation test.

[0209] like Figure 3 As shown, the inventors discovered that, similar to slag, the region D where molten iron boils violently and the region E where molten iron does not boil violently can be determined by the ratio W'' / Wrm''(-) of the molten iron temperature Tf'' and the amount of cold iron source W''(kg) to the amount of molten iron Wrm''(kg).

[0210] In region D where molten iron boils violently (hereinafter referred to as "molten iron boiling region D"), it was confirmed that molten iron would boil upwards immediately after the addition of a cold iron source or shortly thereafter. According to Figure 3 It can also be clearly seen that the range of the ratio W'' / Wrm'' of the amount of cold iron source W'' (kg) to the amount of molten iron remaining Wrm'' (kg) is significantly narrower than the slag boiling regions A and C that were clearly identified in the slag boiling confirmation test.

[0211] 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 (1) in the equation automatically becomes the amount that can avoid... Figure 3 The mass ratio of the amount of cold iron source to the amount of residual molten iron in the boiling zone D of molten iron is W'' / Wrm''.

[0212] 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)' that defines the boundary lines of the slag boiling avoidance zones B1 and B2 can be satisfied.

[0213] Relation (1)':

[0214] 5.224×10 -7 ×Tf' 2 -1.779×10 -4× Tf'-0.4321 <Wsc’ / Wsl’≤8.64×10 -7 ×Tf' 1.947

[0215] Relation (2)':

[0216] Wsc' / Wsl'≥6.591×10 -6 ×Tf' 1.695

[0217] That is, in the second step of the iron refining method of this embodiment, the relations (1) to (3) used to limit conditions (A) to (C) are based on the slag boiling confirmation test and the iron boiling confirmation test. These conditions (A) to (C) limit the relationship between the mass of residual slag Wsl and the total amount of chilled iron source W, which is the sum of the mass of chilled iron source Wsc charged from the scrap chute and the mass of chilled iron source Who fed from the top hopper of the furnace. Moreover, the relations (1) to (3) used to limit conditions (A) to (C) limit the boundary lines of the slag boiling region A and the slag boiling avoidance region B1, the boundary lines of the slag boiling avoidance region B1 and the slag boiling region C, and the boundary lines of the slag boiling region C and the slag boiling avoidance region B2, as determined by the slag boiling confirmation test and the iron boiling confirmation test.

[0218] 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 slag boiling region A and the slag boiling region C are avoided based on the relationship (1)~(3).

[0219] 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.

[0220] In this way, the iron refining method of this embodiment can optimize the weight of the cold iron source used to solidify the slag remaining in the reaction vessel from the refining of the previous batch of molten pig iron.

[0221] Furthermore, the iron refining method of this embodiment solidifies the slag residue generated from the blowing of the previous heat of molten pig iron to form solidified slag. Therefore, even when the next heat of molten pig 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 pig iron to boil violently.

[0222] Furthermore, the iron refining method of this embodiment allows for the introduction of a chilled iron source into the residual slag in the reaction vessel produced from the refining of the previous heat of molten iron. Even if the moisture contained in the chilled iron source reacts with the residual slag, there will be no slag boiling due to the explosion of water vapor from the moisture. In other words, the iron refining method of this embodiment allows for a significant increase in the amount of chilled iron source used, making a substantial contribution to reducing CO2 emissions.

[0223] As described above, according to the iron refining method of the first embodiment, even when a cold iron source is charged into a reaction vessel such as a converter refining furnace while the slag generated from the blowing of the previous batch of molten pig iron remains as residual slag, the slag will not boil over due to the gas generated when the molten iron is charged, and the slag boiling over caused by steam explosion can be avoided.

[0224] [Second Implementation]

[0225] The iron refining method of the second embodiment is characterized in that, in the above embodiment, when the temperature Tf (°C) of the residual high-temperature material in the furnace is higher than the melting point of the reduced iron added in the second step, the reduced iron is added to the reaction vessel from the top of the furnace in multiple batches, and the amount of reduced iron added to the reaction vessel from the top of the furnace for the first time, Who1 (t), is 6.6% by mass or less relative to the amount of residual slag Wsl (t) remaining in the reaction vessel.

[0226] That is, in the iron refining method of this embodiment, when using a cold iron source containing reduced iron as the cold iron source for input into the reaction vessel, from the viewpoint of easily adjusting the amount of reduced iron input into the reaction vessel, the reduced iron is input from the top of the furnace. Furthermore, in the iron refining method of this embodiment, the reduced iron is input into the reaction vessel from the top of the furnace in multiple stages, and the amount of reduced iron initially input from the top of the furnace is limited.

[0227] Here, in the iron refining method of this embodiment, the condition is that the temperature Tf (°C) of the residual high-temperature material in the furnace is higher than the melting point of the reduced iron added in the second step described above. That is, the premise of the iron refining method of this embodiment is that in the first step of tapping the refined molten iron from the reaction vessel while leaving residual slag in the reaction vessel, the temperature Tf (°C) of the residual high-temperature material in the furnace containing residual slag and residual molten iron in the reaction vessel is higher than the melting point of the reduced iron added from the top hopper of the furnace, and the added reduced iron will melt.

[0228] It should be noted that the temperature Tf (°C) of the residual high-temperature material in the furnace is in the range of 1300~1700°C, and the melting point of reduced iron is 1450°C.

[0229] That is, in the iron refining method of this embodiment, after the refined iron is tapped from the reaction vessel while some or all of the slag produced by refining the previous heat of iron remains in the reaction vessel as residual slag, and a large amount of solid reduced iron is added from the top of the furnace, sometimes the molten reduced iron adheres to the bottom blow plug of the converter, which serves as the reaction vessel, because a portion of the solid reduced iron melts.

[0230] When molten reduced iron adheres to the bottom blow plug of the converter, a major operational malfunction can occur, such as blockage of the bottom blow plug.

[0231] Therefore, the inventors discovered that in the iron refining method of this embodiment, when solidifying the residual slag to form solidified slag, firstly, large-sized scrap, i.e., cold iron source, is loaded from the scrap chute, and then reduced iron is added from the top of the furnace in multiple batches.

[0232] In other words, in the iron refining method of this embodiment, solid reduced iron is added to the reaction vessel from the top of the furnace in multiple batches, so that the solid reduced iron dissolved in the initial stage of converter operation does not adhere to the bottom blow plug of the converter, and the amount of the first (initial) addition of solid reduced iron is limited to a given amount.

[0233] In the iron refining method of this embodiment, the amount of reduced iron that is first fed into the reaction vessel from the top of the furnace, Who1(t), is 6.6% by mass or less relative to the amount of residual slag Wsl(t) remaining in the reaction vessel.

[0234] When the amount of reduced iron initially added to the reaction vessel Who1(t) is 0.5% by mass or more and 6.6% by mass or less relative to the amount of residual slag Wsl(t) remaining in the reaction vessel, the situation will not occur where the molten solid reduced iron adheres to the bottom blow plug of the converter, which is the reaction vessel, due to partial melting of the solid reduced iron itself. Therefore, it is preferred.

[0235] Thus, in the iron refining method of this embodiment, by setting solid reduced iron to be fed from the top of the furnace and limiting the amount of reduced iron who1(t) fed in the first (first) feeding of solid reduced iron to be fed to a given amount, it is possible to prevent the molten solid reduced iron from adhering to the bottom blow plug of the converter and clogging the bottom blow plug.

[0236] As described above, the iron refining method according to the second embodiment can achieve the following: the slag generated from the refining of the previous batch of iron and remaining in the reaction vessel is solidified, and the preheating of the cold iron source can be fully utilized stably and without loss in a safe state without slag boiling and without preventing the molten solid reduced iron from adhering to the bottom blow plug of the converter.

[0237] [Third Implementation]

[0238] The refining method for molten iron according to the third embodiment is characterized in that, in the above embodiment, the refining of molten iron includes: a pretreatment blowing process for desiliconizing and dephosphorizing the molten iron in the next heat; an intermediate slag removal process for removing the slag remaining in the reaction vessel by tilting the reaction vessel; and a decarburization process for decarburizing and final dephosphorizing by adding by-products to the reaction vessel.

[0239] That is, the iron refining method of this embodiment applies the iron refining method of the above embodiment to the "MURC method," which allows for continuous desiliconization, dephosphorization, slag removal, and decarburization in the same converter. The iron refining method of this embodiment, which allows for continuous desiliconization, dephosphorization, slag removal, and decarburization in the same converter, can also be applied to situations where the temperature Tf (°C) of residual high-temperature materials in reaction vessels such as converter-type refining furnaces is raised to around 1700°C.

[0240] Specifically, in this embodiment, the iron refining method involves intermediate slag discharge after dephosphorization of the molten iron in the converter, leaving only the desiliconized and dephosphorized molten iron. The remaining phosphorus and decarburization are then achieved using slag with only a small amount of newly added lime. The refined molten iron from the previous heat is then tapped from the converter, allowing the remaining low-phosphorus slag to be reused for dephosphorization of the next heat of molten pig iron.

[0241] In other words, the iron refining method of this embodiment is a converter operation method that can produce the iron required to improve the purity of steel while suppressing the discharge of slag and realizing the effective utilization of resources such as slag and cold iron source.

[0242] Furthermore, the iron refining method of this embodiment is a process in a reaction vessel such as a converter. By recycling the slag at a high temperature, heat recovery can also be achieved. Therefore, the amount of cold iron source that can be used can be increased to the same level as that of conventional converter-based iron refining without pretreatment, thereby improving its productivity.

[0243] Thus, the iron refining method of this embodiment is implemented by the following steps: a pretreatment blowing process for desiliconization and dephosphorization; an intermediate slag discharge process for discharging slag from the converter-type refining furnace by tilting the furnace; and a decarburization process for adding CaO-type by-products to the converter-type refining furnace and blowing them to achieve decarburization and final dephosphorization. Therefore, by leaving the slag at the end of decarburization refining to the pretreatment blowing process, the dephosphorization reaction is facilitated, and the amount of new slag-forming agent added can be reduced.

[0244] Thus, the iron refining method of this embodiment can meet the manufacturing requirements of high-grade steel and the stable manufacturing requirements of low-phosphorus and low-sulfur steel. Moreover, the iron refining method of this embodiment can prevent the temperature of the molten iron charged into the converter from dropping and is not limited by the amount of cold iron source used.

[0245] As described above, the iron refining method according to the third embodiment can solidify the slag generated from the refining of the previous heat and remaining in the reaction vessel, and perform a series of converter operations, including loading the cold iron source from the scrap chute into the reaction vessel, without slag boiling. The iron refining method of the third embodiment can meet the manufacturing requirements of high-grade steel and the stable manufacturing requirements of low-phosphorus and low-sulfur steel, and can refining iron by preheating the cold iron source with no chance of loss and with stable utilization.

[0246] [Fourth Implementation]

[0247] The refining method for molten iron according to the fourth embodiment is characterized in that, in the above embodiment, the refining of molten iron includes: a desiliconization blowing process, in which the molten iron of the next heat is desiliconized; an intermediate slag removal process, in which the slag remaining in the reaction vessel is removed by tilting the reaction vessel; and a dephosphorization blowing process, in which dephosphorization is performed by adding by-products to the reaction vessel.

[0248] That is, the iron refining method of this embodiment is to apply the iron refining method of the above embodiment to the "DRP method" which can maximize the use of silicon contained in the iron as a heat source and increase the amount of cold iron source input in the converter.

[0249] Specifically, the iron refining method of this embodiment includes: without pre-treating the iron by desiliconization, loading the molten iron into a reaction vessel such as a converter, interrupting the desiliconization blowing process after the molten iron has been desiliconized, intermediately discharging the high-SiO2 content slag present in the furnace to the outside of the furnace, and then starting the dephosphorization blowing process again. This iron refining method of this embodiment can be applied when the temperature Tf (°C) of the residual high-temperature material in the reaction vessel such as a converter refining furnace is set to around 1400°C.

[0250] In other words, the iron refining method of this embodiment, by intermediately discharging the high-SiO2 content slag out of the furnace during the blowing process of high-SiO2 content molten iron, can reduce the SiO2 content in the subsequent dephosphorization blowing. Therefore, the iron refining method of this embodiment can maximize the utilization of the heat of silicon oxidation in the molten iron while suppressing the amount of lime required for dephosphorization.

[0251] As described above, the iron refining method according to the fourth embodiment can achieve the following: the slag generated from the refining of the previous batch of iron and remaining in the reaction vessel is solidified without slag boiling; the amount of lime required for dephosphorization is suppressed while maximizing the utilization of the heat of silicon oxidation in the iron; and the preheating of the cold iron source is utilized stably and without any chance of loss.

[0252] [Other Implementation Methods]

[0253] 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.

[0254] Example

[0255] <Example 1 of the Invention (Example No. 6)>

[0256] In a converter, molten pig iron undergoes pretreatment blowing, intermediate slag removal, and decarburization blowing, resulting in molten steel that is tapped from the converter. In the refining of the previous heat of molten pig iron, the composition (wt%) of the molten pig iron used is set as follows: C: 3.9~4.2, Si: 0.2~0.5, Mn: 0.20~0.30, P: 0.080~0.120, S: 0.001~0.003. After decarburization blowing of this molten pig iron, the temperature of the molten steel before tapping is set to 1650°C. Then, the weight of the decarburized slag remaining in the converter is adjusted to 10~20 t. In Example 1, the weight of the decarburized slag remaining in the converter is set to 15 (t).

[0257] Then, the waste material, used as a cooling material, is loaded into the converter using a waste chute. In Invention Example 1, 8 tons of waste material are loaded into the converter using a waste chute. Furthermore, solid reduced iron is fed into the converter from the top hopper while the converter body is kept upright. At this time, the amount of solid reduced iron fed into the top hopper is varied. In Invention Example 1, 3 tons of solid reduced iron are fed into the top hopper.

[0258] As the next heat of molten pig iron, the same molten pig iron as the previous heat is charged into the converter for pretreatment blowing. Furthermore, the molten pig iron proportion is set within a given range. In Invention Example 1, 289 tons of molten iron is charged into the converter, and the molten pig iron proportion is set to 96.3%. In the implementation of pretreatment blowing, consideration is taken into account silicon oxides produced by the oxidation of silicon in the molten pig iron, calcium oxide contained in the by-products added during the pretreatment, and silicon oxide and calcium oxide produced by the refining of the previous heat of molten pig iron and remaining in the slag of the next heat.

[0259] Next, new lime was added from the top hopper of the furnace, so that the basicity (CaO / SiO2) in the pretreated blown slag reached 1.2~2.0.

[0260] The temperature of the molten pig iron at the end of the pretreatment blowing process was adjusted to 1300℃~1400℃. In addition, the oxygen supply and iron ore input were adjusted so that the carbon concentration in the molten pig iron at the end of the pretreatment blowing process reached 2.5wt%~3.5wt%.

[0261] Here, given the potential risk of not being able to guarantee the temperature of the molten pig iron at the end of the pretreatment blowing process is 1300℃~1400℃, carbon materials, intended as heating agents, are introduced into the converter. Thus, after the pretreatment blowing process is completed, with molten pig iron remaining in the converter, the converter body is tilted to discharge the slag produced during the pretreatment blowing process. The weight of the discharged slag is measured using a weighing gauge installed in the slag pot.

[0262] In addition, a portion of the molten pig iron obtained after pretreatment blowing was collected as a metal sample, and the metal sample was analyzed using an analyzer located on the equipment side. Then, after intermediate slag removal, the furnace was uprighted, and decarburization blowing of the molten pig iron obtained after pretreatment blowing was carried out. Considering the phosphorus content in the slag remaining in the converter after intermediate slag removal and the phosphorus concentration in the molten pig iron remaining in the converter after pretreatment blowing, the newly added lime and other slagging agents were adjusted so that the phosphorus concentration in the molten steel at the end of decarburization blowing reached the set target value. After decarburization blowing, the molten steel in the converter was tapped into the ladle.

[0263] Furthermore, a visual observation-based assessment was conducted to determine whether there was any boiling over or boiling over caused by steam explosion at the time point when the next batch of molten pig iron was charged into the converter. The results of Invention Example 1 are shown in Tables 1-2.

[0264]

[0265]

[0266] <Examples 2-8 of the Invention (Examples No. 7-13)>

[0267] The weights of the decarburized slag remaining in the converter, the weight of the scrap charged from the scrap chute, the weight of the solid reduced iron fed from the top hopper, the weight of the molten iron charged into the converter, and the molten pig iron ratio were changed. Except for these changes, the refining of the molten pig iron in the next heat was performed in the same manner as in Invention Example 1. The results of Invention Examples 2-8 are shown in Tables 1-2.

[0268] Comparative Examples 1-8 (Examples No. 1-5, No. 14-16)

[0269] As Comparative Example 1 (Example No. 1), chilled iron and molten pig iron were charged without any residual slag from the previous heat, and pretreatment blowing, intermediate slag removal, and decarburization blowing were performed before tapping. Naturally, no boiling occurred when the molten pig iron was charged. To set the furnace temperature of the molten pig iron after pretreatment blowing to the target value, carbon materials for heating were added during the pretreatment blowing process. Additionally, to adjust to the target basicity, calcined lime was added from the top hopper of the furnace.

[0270] In Comparative Examples 2-3 (Examples No. 2-3), with slag remaining in the furnace from the previous heat, a cold iron source was fed from the waste chute, and then molten pig iron was charged into the converter, and pretreatment blowing, intermediate slag removal, and decarburization blowing were carried out.

[0271] In addition, in Comparative Examples 4 to 8 (Examples No. 4 to 5, Examples No. 14 to 16), with the slag from the previous heat still remaining in the furnace, cold iron sources were fed into the converter from the waste chute, solid reduced iron was fed into the top hopper, and then molten pig iron was charged into the converter, and pretreatment blowing, intermediate slag removal, and decarburization blowing were carried out.

[0272] As a result, as the amount of residual slag from the previous heat increased, the amount of new lime added in the pretreatment blowing was lower than that in Comparative Example 1 (Example No. 1), and the same phosphorus concentration was obtained after pretreatment blowing (Examples No. 2-16).

[0273] In Comparative Examples 2-5, when the molten pig iron proportion was increased to approximately 97%, i.e., the amount of chilled iron added was low relative to the slag residue of the previous furnace, a boiling phenomenon was observed when charging the molten pig iron, causing safety issues. This can be attributed to the fact that the slag remaining in the furnace did not completely solidify and reacted with the carbon in the molten pig iron, violently producing CO gas (Examples No. 2-5).

[0274] When a sufficient amount of chilled iron source is charged relative to the slag residue of the previous furnace, i.e., when the relationship (1) is satisfied, no boiling phenomenon is observed when molten pig iron is charged. This can be attributed to the fact that by charging a sufficient amount of chilled iron source, the slag remaining in the furnace is completely solidified (Examples No. 6 to 13 corresponding to Invention Examples 1 to 8).

[0275] As the molten pig iron ratio decreases, it is necessary to compensate for the molten heat of the chilled iron source. Therefore, carbon materials for heating are required during the pretreatment blowing process. However, compared to Comparative Example 1 (Example No. 1), the amount of carbon materials required for heating is low for the level of residual slag from the previous furnace. This can be attributed to the fact that the chilled iron source is heated by the residual slag in the furnace (Examples No. 7-13 corresponding to Invention Examples 2-8).

[0276] On the other hand, in Comparative Examples 6-8, when the molten pig iron ratio was reduced to approximately 82%, i.e., when the amount of chilled iron added was at a high level relative to the slag residue of the previous furnace, a steam explosion phenomenon was observed in the water contained in the chilled iron when it was charged into the furnace, causing a safety problem. This can be attributed to the fact that a large amount of chilled iron was charged into the furnace from the scrap chute, reaching the area where a steam explosion occurred, thus causing a steam explosion (Examples No. 14-16).

[0277] <Example 9 of the Invention (Example No. 20)>

[0278] In a converter, molten pig iron undergoes desiliconization blowing, intermediate slag removal, and dephosphorization blowing, with the resulting molten steel tapped from the converter. In the refining of the previous heat of molten pig iron, the composition (wt%) of the molten pig iron used is set as follows: C: 3.9~4.2, Si: 0.2~0.5, Mn: 0.20~0.30, P: 0.080~0.120, S: 0.001~0.003. After dephosphorization blowing of this molten pig iron, the temperature of the molten steel before tapping is set to 1380℃. Then, the weight of the dephosphorization slag remaining in the converter is adjusted to 20t.

[0279] Then, the waste is loaded into the converter as a cooling material using a waste chute. In Invention Example 9, 4 tons of waste are loaded into the converter using a waste chute. Furthermore, solid reduced iron is fed into the converter from the top hopper while the converter body is kept upright. At this time, the amount of solid reduced iron fed into the top hopper is varied. In Invention Example 9, 4 tons of solid reduced iron are fed into the top hopper.

[0280] As the next heat of molten pig iron, the same molten pig iron as the previous heat is charged into the converter, and desiliconization blowing is performed. Furthermore, the molten pig iron proportion is set within a given range. In Invention Example 9, 292 tons of molten iron is charged into the converter, and the molten pig iron proportion is set to 97.3%. In the implementation of desiliconization blowing, the silicon oxides produced by the oxidation of silicon in the molten pig iron, the calcium oxide contained in the by-products added during the desiliconization blowing, and the silicon oxide and calcium oxide contained in the slag produced by the refining of the previous heat of molten pig iron and remaining in the next heat are considered.

[0281] Next, new lime was added from the top hopper of the furnace, so that the basicity (CaO / SiO2) in the slag after desiliconization blowing reached 1.2~2.0.

[0282] The temperature of the molten pig iron at the end of the desiliconization blowing process was adjusted to 1300℃~1400℃. Here, given the potential risk of not being able to guarantee the temperature of the molten pig iron at the end of the desiliconization blowing process to be 1300℃~1400℃, carbon materials, used as heating materials, were added to the converter. Thus, after the desiliconization blowing process was completed, with molten pig iron remaining in the converter, the converter body was tilted to discharge the slag produced during the desiliconization blowing process. The weight of the discharged slag was measured using a weighing gauge installed in the slag hopper.

[0283] Then, after the intermediate slag removal, the furnace was upright, and dephosphorization blowing of the molten pig iron obtained after desiliconization blowing was carried out. Considering the phosphorus content in the slag remaining in the converter after intermediate slag removal and the phosphorus concentration in the molten pig iron remaining in the converter after desiliconization blowing, the newly added lime and other slagging agents were adjusted to ensure that the phosphorus concentration in the molten steel at the end of dephosphorization blowing reached the set target value. After dephosphorization blowing, the molten steel in the converter was tapped into the ladle.

[0284] Furthermore, a visual observation-based assessment was conducted to determine whether there was any boiling over or boiling over caused by steam explosion at the time point when the next batch of molten pig iron was charged into the converter. The results of Invention Example 9 are shown in Tables 3-4.

[0285] It should be noted that in Table 3, Solid Reduced Iron I (Furnace Top) represents the weight of solid reduced iron initially fed from the furnace top hopper before being fed into the cold iron source from the scrap chute, and Solid Reduced Iron II (Furnace Top) represents the weight of solid reduced iron fed from the furnace top hopper after the scrap is loaded from the scrap chute.

[0286]

[0287]

[0288] <Examples 10-14 of the Invention (Examples No. 21-22, Examples No. 25-27)>

[0289] The weight of the dephosphorized slag remaining in the converter, the weight of the scrap charged from the scrap chute, the weight of the solid reduced iron fed from the top hopper, the weight of the molten iron charged into the converter, and the molten pig iron ratio were changed. Otherwise, the refining of the molten pig iron in the next heat was carried out in the same manner as in Invention Example 9.

[0290] It should be noted that in Invention Examples 12-14 (Examples No. 25-27), after a large amount of solid reduced iron was first fed into the furnace top hopper, molten iron was refined by loading scrap into the scrap chute. The results of Invention Examples 10-14 are shown in Tables 3-4.

[0291] Comparative Examples 9-13 (Examples No. 17-19, Examples No. 23-24)

[0292] As Comparative Example 9 (Example No. 17), chilled iron and molten pig iron were charged without any residual slag from the previous heat, and desiliconization blowing, intermediate slag removal, and dephosphorization blowing were performed before tapping. Naturally, no boiling occurred when the molten pig iron was charged. To set the furnace temperature of the molten pig iron after desiliconization blowing to the target value, carbon materials for heating were added during the desiliconization blowing process. Additionally, to adjust to the target basicity, calcined lime was added from the top hopper.

[0293] In Comparative Example 10 (Example No. 18), with the slag 20(t) from the previous heat still remaining in the furnace, a cold iron source was fed from the waste chute, and then the molten pig iron was transferred into the converter to carry out desiliconization blowing, intermediate slag discharge, and dephosphorization blowing.

[0294] In addition, in Comparative Examples 11-13 (Examples No. 19, 23-24), with the slag from the previous heat still remaining in the furnace, cold iron sources were fed into the converter from the waste chute, solid reduced iron was fed into the top hopper, and then molten pig iron was charged into the converter, and desiliconization blowing, intermediate slag discharge, and dephosphorization blowing were carried out.

[0295] As a result, as the amount of residual slag from the previous heat increased, the amount of new lime added during desiliconization blowing was lower than that in Comparative Example 9 (Example No. 17), and the phosphorus concentration after dephosphorization blowing was the same (Examples No. 18-27).

[0296] In Comparative Examples 10 and 11, when the molten pig iron proportion was increased to approximately 99%, i.e., the amount of chilled iron added was low relative to the slag residue of the previous furnace, a boiling phenomenon was observed when charging the molten pig iron, causing safety issues. This can be attributed to the fact that the slag remaining in the furnace did not completely solidify and reacted with the carbon in the molten pig iron, violently producing CO gas (Examples No. 18-19).

[0297] The situation where a sufficient amount of chilled iron source was charged relative to the slag residue of the previous furnace satisfies the relationship (1), and therefore no boiling phenomenon was observed when molten pig iron was charged. This can be attributed to the fact that by charging a sufficient amount of chilled iron source, the slag residue in the furnace was completely solidified (Examples No. 20-22, 25-27 corresponding to Invention Examples 9-14).

[0298] As the molten pig iron ratio decreases, it is necessary to compensate for the molten heat of the chilled iron source. Therefore, carbon materials for heating are required during desiliconization blowing. However, compared to Comparative Example 9 (Example No. 17), the amount of carbon materials required for heating is low for the level of residual slag from the previous furnace. This can be attributed to the fact that the chilled iron source is heated through the residual slag in the furnace (Examples No. 20-22, 25-27 corresponding to Invention Examples 9-14).

[0299] On the other hand, in Comparative Examples 12-13 (Examples No. 23-24), when the molten pig iron ratio was reduced to approximately 87%, i.e., when the amount of chilled iron added was at a high level relative to the slag residue of the previous furnace, a steam explosion phenomenon was observed in the water contained in the chilled iron when it was charged into the furnace, causing a safety problem. This can be attributed to a large amount of chilled iron being charged into the furnace from the scrap chute, reaching the area where a steam explosion occurred, thus causing a steam explosion (Examples No. 23-24).

[0300] As described above, according to Invention Examples 1-14 and Comparative Examples 1-13, the heat contained in the high-temperature slag remaining in the converter can be fully utilized for preheating of the cold iron source, and the refining of molten iron can be achieved by fully utilizing the preheating of the cold iron source under a safe state without slag boiling or steam explosion.

[0301] Industrial applicability

[0302] 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 materials used to form solidified slag by cooling the residual slag are provided as a chill source fed from the scrap chute and 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 mass of the residual slag Wsl, the mass of the chill source Wsc charged from the scrap chute, and the mass of the chill source Who fed from the top of the furnace must satisfy any one of the following conditions (A) to (C). Condition (A): The total amount W of the cold iron source is loaded within the range of the following relations (1) and relations (2), wherein the total amount W of the cold iron source is the sum of the mass Wsc of the cold iron source loaded from the scrap chute and the mass Who of the cold iron source fed from the top of the furnace. Condition (B): The mass Wsc of the cold iron source loaded from the scrap chute is set within the range of the following relationship (2), and the remaining part required as cooling material is set as the cold iron source fed from the top of the furnace later or simultaneously. The total amount W of the cold iron source satisfies the following relationship (1), wherein the total amount W of the cold iron source is the sum of the mass Wsc of the cold iron source loaded from the scrap chute and the mass Who of the cold iron source fed from the top of the furnace. Condition (C): The mass Who of the chill source fed from the top of the furnace is set within the range of the following relationship (3), and after the chill source is fed from the top of the furnace, the remaining portion required as cooling material is set as the chill source loaded from the scrap chute. Relation (1): W / Wsl>5.224×10 -7 ×Tf 2 -1.779×10 -4 ×Tf-0.4321 Relation (2): W / Wsl≤8.64×10 -7 ×Tf 1.947 Relation (3): W / Wsl≥6.591×10 -6 ×Tf 1.695 In the above relations (1) to (3), Wsl represents the mass (t) of residual slag. W represents the mass (t) of the chilled iron source that is loaded before the molten pig iron is loaded. Tf represents the temperature (°C) of the residual high-temperature material in the furnace during the first process.

2. The method for refining molten iron according to claim 1, wherein, A chill source that is prone to containing moisture is loaded from a waste chute. The chill source includes powdered chill source and chill source with voids.

3. The method for refining molten iron according to claim 1, wherein, The chill source loaded in the second step contains reduced iron.

4. The method for refining molten iron according to claim 3, wherein, When the temperature Tf of the residual high-temperature material in the furnace is higher than the melting point of the reduced iron, the reduced iron is added to the reaction vessel from the top of the furnace in multiple batches. The amount of reduced iron added to the reaction vessel from the top of the furnace for the first time, Who1(t), is less than 6.6% by mass relative to the mass Wsl(t) of the residual slag in the reaction vessel.

5. The method for refining molten iron according to any one of claims 1 to 4, wherein, The refining of the molten iron includes: The pretreatment blowing process is used to desiliconize and dephosphorize the molten iron in the next heat. The intermediate slag removal process involves tilting the reaction vessel to remove the slag remaining in the vessel; and The decarbonization process involves adding by-products to the reaction vessel to perform decarbonization and final dephosphorization.

6. The method for refining molten iron according to any one of claims 1 to 4, wherein, The refining of the molten iron includes: The desiliconization blowing process is used to desiliconize the molten iron in the next heat. The intermediate slag removal process involves tilting the reaction vessel to remove the slag remaining in the vessel; and The dephosphorization blowing process involves adding by-products to the reaction vessel to carry out dephosphorization.

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