Method for preheating a cold iron source

Abstract

The present invention provides a technique for using the heat possessed by high-temperature slag for preheating of a cold iron source. In a preheating method of a cold iron source, a part or all of the total amount Wt (kg) of the cold iron source is put into a part or all of the residual slag in a reaction vessel, and the ratio Wsc / Wsl (-) of the amount Wsc (kg) of the part of the cold iron source put into the reaction vessel using a waste chute to the amount Wsl (kg) of the residual slag in the reaction vessel is controlled within a range satisfying the following (1) or (2) formula for the temperature Tf (°C) of the high-temperature substance remaining in the furnace using the treatment of the residual slag, 5.224 x 10 －7 ×Tf 2 - 1.779 x 10 －4 ×Tf - 0.4321 < Wsc / Wsl ≤ 8.64 x 10 －7 ×Tf 1.947 … (1) formula, Wsc / Wsl ≥ 6.591 x 10 －6 ×Tf 1.695 … (2) formula.

Description

Technical Field

[0001] This invention relates to a method for preheating the cold iron source by introducing a cold iron source into slag remaining in a reaction vessel such as a converter, and by utilizing the heat of the slag.

[0002] In this specification, "x~y" indicates "above x and below y", including critical values. Additionally, chemical formulas such as "SiO2" indicate compounds containing this composition, and expressions such as "iron" and "phosphorus" indicate the inclusion of the element regardless of its form. T.Fe refers to total iron, representing the total amount of iron regardless of its form. M.Fe refers to metallic iron. [M] indicates the presence of element M in molten iron. (R) indicates the presence of compounds with the chemical formula R in slag. "Molten iron" refers to a molten metal containing iron as its main component, including "molten pig iron" containing approximately 3-5% C by mass and "molten steel" containing approximately 2% or less C by mass. The unit of mass, "t", represents 1000 kg. Background Technology

[0003] The recent decrease in CO2 emissions and increased demand have led to a need to increase the use of chilled iron in steelmaking processes. By adding chilled iron to the reaction vessel along with the molten iron from the blast furnace, the proportion of molten iron to refined iron can be reduced (hereinafter referred to as the molten iron blending ratio). Furthermore, this results in a reduction in the amount of molten iron used per unit of crude steel production.

[0004] There are various sources of chilled iron. For example, scrap iron is stored in the yard, while reduced iron added to the furnace is stored in underground silos and is usually managed at room temperature. These chilled iron sources are loaded into the reaction vessel from scrap chutes or furnace-tophoppers. In order for the loaded chilled iron sources to completely dissolve in the molten iron, the chilled iron sources need to be heated to the point of melting from other supplies.

[0005] Therefore, if more cold iron source is needed, the portion that cannot be fully compensated by the heat inherent in the molten iron itself or the combustion heat of impurities must be supplemented by heating materials or by using an externally forced heat-conducting unit. Examples of heating materials include soil graphite, ferrosilicon, and silicon carbide. Examples of heat-conducting mechanisms include burners and electric arc discharge.

[0006] However, within the reaction vessel, slag is added to the molten iron and used to remove impurities. This slag reaches a high temperature of 1300-1400°C during dephosphorization and 1600-1700°C during decarburization, containing high calorific value. Typically, the treated slag is solidified by adding cooling materials such as dolomite and remains within the reaction vessel; the incompletely solidified portion is discharged outside. This is because if the slag is not solidified, the iron oxide in the slag reacts rapidly with the carbon in the molten iron, causing a sudden boiling of the slag.

[0007] However, if the heat of the slag itself, which cannot be effectively utilized due to discharge into the container, can be used to preheat the scrap, the heat required for heating and melting the cold iron source can be reduced. Consequently, the pig iron mixing ratio can be reduced compared to when the cold iron source is at room temperature.

[0008] Therefore, several methods have been disclosed that can prevent these sudden boilings and preheat the cold iron source using the residual slag remaining in the reaction vessel. For example, Patent Document 1 discloses a technique of tapping steel with decarburized slag generated through decarburization treatment remaining in the reaction vessel, and then charging a solid iron source into the residual slag. It also indicates that when charging 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.

[0009] In addition, Patent Document 2 discloses a method for solidifying the residual molten iron, such as slag or molten iron, in the furnace after steel tapping from the converter by adding a solid iron source.

[0010] The technology disclosed in Patent Document 1 can be applied to the recycling of decarburized slag, and the technology disclosed in Patent Document 2 can be applied to prevent the outflow of residual molten iron in the converter during slag discharge. Although the purposes of the two are slightly different, they can both be applied to the preheating of the cold iron source using slag in the reaction vessel.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 2004-256839

[0014] Patent Document 2: Japanese Patent Application Publication No. 2009-228102 Summary of the Invention

[0015] The technical problem that the invention aims to solve

[0016] However, there are issues that must be addressed in the aforementioned existing technologies.

[0017] That is, the problem with the technology described in Patent Document 1 or 2 is that it is impossible to deal with the sudden boiling of slag that may occur 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 wetted powdery waste.

[0018] For ease of transport, chilled iron sources are mostly stored in buildings with roofs but not airtight enclosures. In such storage areas, it's impossible to prevent the chilled iron sources from getting wet from wind and rain. After removing the moisture, preheating is necessary at the storage location. This not only requires the introduction of equipment for this preheating but also defeats the purpose of utilizing heat.

[0019] Furthermore, the existing technology described above also presents problems as a countermeasure to suppress the reaction with molten iron. If ensuring production volume is the primary concern, the amount of solid iron source Wsc in the formula shown in Patent Document 1 is a value determined based on the production plan and is not a control parameter. Therefore, reducing the amount of residual slag Wsl or increasing the number of reciprocating tilts N is problematic. The former fails to achieve the purpose of preheating the cold iron source because the total heat capacity of the slag is reduced, while the latter reduces productivity due to the increased non-steelmaking time.

[0020] In Patent Document 2, the solid iron source is added to solidify the residual molten iron in the reaction vessel, and the slag is discharged directly from the furnace in a molten state. Therefore, the method described in Patent Document 2 cannot achieve the purpose of preheating the cold iron source using the residual slag. It describes a method where the solid iron source is made smaller than 1 mm, allowing it to remain in the molten slag, but it is difficult to ensure a sufficient quantity of such a solid iron source.

[0021] The present invention was made to solve the above-mentioned problems, and its purpose is to provide the following conditions: when the heat of the high-temperature slag remaining in the reaction vessel is used for the preheating of the cold iron source, it can be carried out stably without the occurrence of sudden boiling of the slag and without causing opportunity loss in a safe state.

[0022] Methods for solving problems

[0023] The inventors conducted in-depth research on these issues and found that by using the ratio of the amount of residual slag in the reaction vessel to the amount of cold iron source fed into the reaction vessel, and the temperature of the residual high-temperature material in the furnace after the treatment of residual slag, the conditions under which slag boil-off can be specified.

[0024] The preheating method for the chill source of the present invention, which advantageously solves the above-mentioned problems, is characterized in that, after the molten iron refined by slag added to the molten iron filled in the reaction vessel is discharged from the reaction vessel, a portion or all of the total amount of chill source Wt (kg) is added to a portion or all of the residual slag in the reaction vessel, wherein the ratio Wsc / Wsl (kg) of the residual slag in the reaction vessel to the amount of chill source Wsc (kg) added to the reaction vessel using a scrap chute is controlled within the range of the following formula (1) or (2) to satisfy the temperature Tf (°C) of the residual high-temperature material in the furnace after the treatment with the residual slag. 5.224×10 －7 ×Tf 2 -1.779×10 －4 ×Tf-0.4321 <Wsc / Wsl≤8.64×10 －7 ×Tf 1.947 …(1) formula, Wsc / Wsl ≥ 6.591 × 10 －6 ×Tf 1.695 …(2) formula.

[0025] Furthermore, a more preferred solution to the problem of the preheating method for the chill source of the present invention is as follows: (a) a chill source that easily contains moisture, including a powdered chill source and a chill source with voids, is arranged in the length direction of the scrap chute at a position X within a range that satisfies the following formulas (3) and (4) respectively, relative to the ranges of formulas (1) and (2); (b) when the amount of chill source Wsc fed into the scrap chute is a part of the total amount of chill source Wt, after feeding the chill source into the scrap chute, the remaining chill source, etc., is fed into the furnace hopper. X≥(1.226×10 －5 ×Tf 2 -2.589×10 －2 ×Tf+17.75)×(Wsl / Wsc) …(3) formula, X≥8.618×10 －5 ×Tf 1.947 ×(Wsl / Wsc) …(4) formula.

[0026] Here, X (%) represents the loading position of waste in the length direction of the waste chute as a percentage, with 0% at the front end of the waste chute on the side opposite to the reaction vessel and 100% at the end of the waste chute opposite to the reaction vessel.

[0027] Invention Effects

[0028] According to the present invention, the heat of the high-temperature slag remaining in the reaction vessel can be effectively utilized for the preheating of the cold iron source, and the slag will not boil over suddenly. The preheating of the cold iron source can be carried out stably and without loss under safe conditions. Attached Figure Description

[0029] Figure 1 This is a schematic conceptual diagram illustrating a preferred device structure applicable to the preheating method of the cold iron source involved in this invention.

[0030] Figure 2 This is a graph showing the results of a slag boilover confirmation test in which a water-wetted cold iron source is added to the slag.

[0031] Figure 3 It is a graph showing the results of a confirmation test of the sudden boiling of molten iron by immersing a water-wetted cold iron source into molten iron.

[0032] Figure 4 This is a schematic side cross-sectional view showing the loading of a chill source into a scrap chute.

[0033] Figure 5 This indicates that the total amount of cold iron source meets the requirements. Figure 2 The graph shows the effect of position X on the scrap chute of the cold iron source containing moisture on the slag boil-off under the condition of region B2.

[0034] Figure 6 This is a graph showing the relationship between the loading position X of the chill containing moisture in the scrap chute and the mass ratio of the chill to the residual slag, indicating the influence of the initial temperature of the residual high-temperature material in the furnace on the threshold of whether slag boils suddenly.

[0035] Figure 7 This is a graph showing the effect of the relationship between the minimum temperature of molten iron and the C concentration in pig iron on the blockage of the bottom blower outlet. Detailed Implementation

[0036] The embodiments of the present invention will now be described in detail. Furthermore, the accompanying drawings are illustrative and may sometimes differ from actual drawings. Additionally, the following embodiments illustrate apparatus and methods for embodying the technical concept of the present invention, and do not specify the structure as described below. That is, the technical concept of the present invention can be modified in various ways within the scope of the claims.

[0037] Figure 1 This describes a preferred apparatus structure for implementing the preheating method for the cold iron source according to the present invention. The reaction vessel 1, such as a converter lined with refractory material 2, is tilted, and molten iron is discharged outside the reaction vessel 1 through the tapping hole 3. Then, as... Figure 1As shown in (a), with some or all of the slag 4 remaining in the reaction vessel 1, the reaction vessel 1 is tilted toward the scrap chute 6 into which the chill source 5 is loaded. The front end of the scrap chute 6 is inserted into the reaction vessel 1. Then, using a crane 7, the scrap chute 6 is tilted to load the chill source 5 into the reaction vessel 1. Sometimes, about 1 ton of pre-treated molten iron, the so-called residual molten iron 8, is present in the vessel.

[0038] After the cold iron source 5 is put in, as Figure 1 As shown in (b), the reaction vessel 1 is tilted again toward the crane 7. Simultaneously, the molten iron ladle 9 is tilted to load molten iron 10 into the reaction vessel 1. After loading the molten iron 10, as... Figure 1 As shown in (c), the reaction vessel 1 is made upright. Then, while blowing oxygen 12 from the acid lance 11 into the molten iron 10 or slag 4, the molten iron 10 is stirred using gas blown in from the bottom-blown gas system 13. Then, it is transferred to the refining process for the oxidation and removal of impurities. Before or during the above refining process, the furnace feed material 15 is sometimes also introduced into the furnace from the furnace hopper 14.

[0039] In addition to slag-forming materials such as lime and cooling materials such as ore, the furnace-charged material 15 can also be a furnace-cooled iron source of a size that can be lifted on the furnace hopper.

[0040] The composition of slag 4 is not specifically defined, but it is generally a steelmaking slag mainly composed of CaO, SiO2, and FeO, and also contains Al2O3, MgO, P2O5, MnO, S, and M.Fe (metallic iron). Here, FeO represents iron oxides, such as FeO and Fe2O3. The basicity C / S ratio, indicated by 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% by mass. For this slag 4, as a substance to lower the melting point of the slag, slag-promoting materials such as TiO2 can also be added as furnace input material 15.

[0041] The refractory 2 lining the reaction vessel is made of a refractory material that is sufficiently resistant to corrosion of the slag 4. MgO-C type bricks are usually used. Furthermore, the processing temperature is adjusted to prevent the refractory from dissolving into the slag, or a MgO source such as lightly calcined dolomite is added as an on-furnace feedstock 15 depending on the composition of the slag 4.

[0042] In addition to carbon steel scrap and pig iron scrap, the chilled iron source 5 can also be loaded into the scrap chute 6, where it can be rolled up by the furnace hopper 14 for iron granules, reduced iron, etc. Examples of carbon steel scrap include heavy scrap, briquetted scrap, crushed scrap, fresh shavings, and steel grinding shavings. Examples of pig iron scrap include scrap pig iron and pig iron grinding shavings. Here, powdery scrap such as grinding shavings, pipes, motors, and briquetted scrap, and scrap with pores, are prone to containing moisture.

[0043] After the chill source 5 is loaded, the mixture of chill source 5 and slag 4 is sometimes achieved 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 is preferred.

[0044] In this embodiment, the amount of chilled iron source 5 fed from the scrap chute is determined by the temperature of the residual high-temperature material in the furnace after the treatment of residual slag, such as the final temperature of the residual molten iron 8, and the amount of residual slag. Thus, there may be a situation where the amount of chilled iron source fed from the scrap chute 6 is less than the required total amount. In this case, after the chilled iron source 5 is fed from the scrap chute 6, the reaction vessel 1 is uprighted, and the furnace feed material 15 is fed from the furnace hopper 14 as the furnace feed material. The furnace feed material refers to a chilled iron source, such as granular iron or reduced iron, that can be rolled up into the furnace hopper 14.

[0045] Whether before or after the refining process begins, the cold iron source 5 can be added to the furnace after being fed into the scrap chute. However, when the molten iron temperature is low, as before refining begins, the temperature drop in the initial stage of refining is greater due to the heat absorption accompanying the melting of the cold iron source. Therefore, when the molten iron temperature drops to the temperature obtained by adding approximately 60°C to the molten iron solidification temperature calculated according to the C-Fe binary system phase diagram, the gas outlet of the bottom-blown gas system 13 becomes blocked due to the solidification of the molten iron or the growth of the solidified phase of the cold iron source. In such cases, this causes adverse effects such as ineffective agitation of the bath, for example, slag over-acidification, reduced iron yield, and decreased refining characteristics. In addition, gas ejects from the gaps in the furnace wall along the joints of the refractory, leading to equipment failures such as refractory detachment. Therefore, it is preferable to add the cold iron source to the furnace after the refining process, in which the temperature of the molten iron can be increased by utilizing the heat of combustion of impurities generated by oxygen, has begun.

[0046] In the agitation gas supply from the bottom-blown gas system 13, from the viewpoint of preventing nozzle clogging, a certain flow rate of gas is continuously flowing as a standby flow rate before the refining process. The standby flow rate is based on the amount of residual molten iron 8, slag 4, and the gas nozzle diameter of the bottom-blown gas system 13, with the gas ejection pressure not lower than the static pressure as a benchmark. The type of gas blown into the bottom-blown gas system 13 is generally an inert gas, such as N2 or Ar.

[0047] Next, the preferred embodiments of the present invention will be described in detail with reference to the prior art.

[0048] (First Implementation)

[0049] <Slag Boiling Confirmation Test>

[0050] Even when experiments were conducted within the suitable examples of Patent Document 1, the first embodiment failed to stably suppress slag boil-off, necessitating a clear and quantitative description of the conditions causing slag boil-off. Figure 1 In a small high-frequency melting furnace, a CaO-SiO2-FetO ternary slag is melted, and the slag temperature is adjusted. Then, while the power supply to the melting furnace is cut off, a chilled iron source immersed in water is added to the molten slag to check for any sudden boiling. Then, using a ladle made by machining a graphite crucible, molten C saturated iron smelted in another furnace at 1200~1300℃ is taken out and loaded into the furnace from the slag.

[0051] Here, the slag composition includes a CaO concentration of 20–50 wt%, a SiO2 concentration of 10–40 wt%, and a FeO concentration of 10–40 wt%. Additionally, the slag temperature Tf' is 1200–1700°C, and the ratio of the amount of chill input Wsc' (kg) to the amount of molten slag Wsl' (kg), Wsc' / Wsl' (-), is in the range of 0.1–50. Furthermore, 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 ppm by mass, and an O concentration of less than 150 ppm by mass. This chill is immersed in water at room temperature for approximately 1 minute. Then, the chill, after being gently drained of water before being placed into the melting furnace, is used for testing.

[0052] The results of the slag boil-out confirmation test using slag and a water-wetted chill are shown in... Figure 2 . Figure 2 The symbol "●" indicates the condition without slag boil-off, and the symbol "×" indicates the condition where slag boil-off occurs. According to... Figure 2 The inventors discovered that regions A and C where slag boil-off occurs and regions B1 and B2 where slag boil-off does not occur can be organized using the ratio of the amount of cold iron source input Wsc' (kg) to the amount of molten slag Wsl' (kg) Wsc' / Wsl' (-) and the slag temperature Tf'.

[0053] The slag boiling zone A on the side where the mass of the cold iron source relative to the residual slag is lower than Wsc' / Wsl' will not cause the slag to boil even immediately after or shortly after the cold iron source is added. This boiling is characterized by the slag boiling caused by gases generated during the subsequent addition of saturated iron (C). The zone B1 that does not cause such boiling can be approximated by the following equation (1A).

[0054] (1A)

[0055] Wsc' / Wsl'>5.224×10 －7 ×Tf 2 -1.779×10－4 ×Tf-0.4321

[0056] However, if the mass ratio of the chill source to the residual slag, Wsc' / Wsl', is higher than the value that can be calculated on the right side of equation (1A), a sudden boiling will occur, such as when the chill source is first added or when the slag is blown onto the melting furnace. The region C in which such a sudden boiling begins can be approximated by the following equation (1B).

[0057] (1B)

[0058] Wsc' / Wsl'>8.64×10 －7 ×Tf 1.947

[0059] If the mass ratio of the cold iron source to the residual slag, Wsc' / Wsl', is further increased, slag boilover will no longer occur. It was determined that such a region B2 can be approximated by the following equation (2).

[0060] (2)

[0061] Wsc' / Wsl'≥6.591×10 －6 ×Tf 1.695

[0062] Regarding the distinction between the aforementioned slag boilover zones A and C and the slag boilover-free zones B1 and B2, at least within the scope of this experiment, it was determined that there was no slag composition dependence. The theoretical basis for determining the threshold values ​​of the slag boilover zones A and C and the non-boiling zones B1 and B2 is unclear. The inventors believe that in boilover zone A, where Wsc' / Wsl' is lower, the slag is not fully solidified due to the smaller amount of chilled iron input relative to the amount of slag, and the reaction between the C in the molten iron and the FeO in the slag proceeds rapidly. That is, this reaction [C] + (FeO) = CO↑ + Fe is presumed to be a liquid-liquid reaction. Furthermore, in boilover zone C, where the mass of the chilled iron relative to the residual slag is higher than Wsc' / Wsl', the slag exhibits a violent upward ejection of slag. Therefore, it is presumed that the moisture in the waste rapidly vaporizes due to the high-temperature slag, causing a steam explosion.

[0063] <Confirmation Test for Sudden Boiling of Molten Iron>

[0064] The reaction vessel contains not only slag but sometimes also residual steel from the pretreatment process. Therefore, tests were conducted to confirm whether sudden boiling of the molten iron occurred when a water-wetted chilled iron source was introduced into the vessel to confirm the presence of molten iron. The results of the molten iron sudden boiling confirmation test are shown below. Figure 3 . Figure 3The symbol “●” indicates the condition where there is no sudden boiling of molten iron, and the symbol “×” indicates the condition where sudden boiling of molten iron occurs. Molten iron is melted in a small high-frequency melting furnace, and the temperature of the molten iron is adjusted. Then, while the power to the melting furnace is cut off, a chilled iron source immersed in water is added to the molten iron. At this time, a test is conducted to confirm whether there is sudden boiling of molten iron. Here, the molten iron temperature Tf'' is 1200℃~1700℃, and the ratio of the amount of chilled iron source added Wsc'' (kg) to the amount of molten iron melted Wrm'' (kg), Wsc'' / Wrm'' (-), is in the range of 0.1~3.0. The chilled iron source is the same material used in the above-mentioned test to confirm whether there is sudden boiling of slag, and is provided for the test in the same way.

[0065] like Figure 3 As shown, the inventors discovered that, similar to slag, the boiling region D and the non-boiling region E of molten iron can be sorted out using the ratio Wsc'' / Wrm'' (-) of molten iron temperature Tf'' and the amount of cold iron source Wsc'' (kg) to the amount of molten iron Wrm'' (kg).

[0066] In region D, where molten iron spontaneously boils, a sudden boiling event was confirmed where molten iron sprayed upwards immediately after the addition of a chiller. The range of the mass ratio of this chiller to the residual molten iron was significantly narrower compared to regions A and C in the slag spontaneous boiling confirmation test. Furthermore, in actual operation, the amount of residual molten iron in the reaction vessel is approximately 1 t, while the amount of slag exceeds 10 t to 20 t. Therefore, if the requirements are met... Figure 2 The amount of chilled iron source above the lower limit of formula (1A) becomes capable of automatically avoiding Figure 3 The mass ratio of the amount of cold iron source to the amount of residual molten iron in the molten iron boiling zone D is Wsc'' / Wrm''. Therefore, even if there are actually both slag and residual molten iron in the reaction vessel, there is no problem as long as the following equation (1)' or (2)' representing the slag boiling avoidance zones B1 and B2 can be satisfied.

[0067] (1)' formula

[0068] 5.224×10 －7 ×Tf' 2 -1.779×10 －4 ×Tf'-0.4321 <Wsc' / Wsl'≤8.64×10 －7 ×Tf' 1.947

[0069] (2)'

[0070] Wsc' / Wsl'≥6.591×10 －6 ×Tf' 1.695

[0071] (Second Implementation)

[0072] The second embodiment is based on the necessity of avoiding slag boil-off even when a portion of the chill source used has a powdery or porous structure that is particularly prone to moisture absorption. While satisfying... Figure 1 In a small high-frequency melting furnace, a small amount of molten iron and CaO-SiO2-FetO ternary slag are melted, and the temperatures of the molten iron and slag are adjusted. Then, while the power supply to the melting furnace is cut off, a cold iron source immersed in water is added to the molten slag to check for any sudden boiling of the slag. Then, saturated iron at 1200~1300℃, which has been smelted in another furnace, is loaded into the furnace from above the previous slag using a ladle made from a graphite crucible.

[0073] Here, the slag composition includes a CaO concentration of 20–50% by mass, a SiO2 concentration of 10–40% by mass, a FeO concentration of 10–40% by mass, a slag and metal temperature Tf''' of 1200–1700°C, and a ratio of the amount of chilled iron input Wsc''' (kg) to the amount of molten slag Wsl''' (kg) Wsc''' / Wsl''' (-) of 0.1–50. Furthermore, the ratio of the amount of chilled iron input Wsc''' (kg) to the amount of molten iron Wrm''' (kg) Wsc''' / Wrm''' (-) of 0.1–3. In addition to using iron sheets 5A with a length and width of 3-15 mm, a thickness of 3-7 mm, a C concentration of less than 30 ppm by mass, and an O concentration of less than 150 ppm by mass as the cold iron source, an iron source with multiple recesses of about 2 mm depth on each side of a pure iron sheet 5B with each side cut to 1 cm was also used. After immersing in room temperature water for about 1 minute, the water was gently drained before being put into the melting furnace, and the resulting iron source was used for testing.

[0074] In the aforementioned slag boilover confirmation test, when using a chill source that is prone to containing moisture, even if the total amount of chill source is... Figure 2 Even in region B2, where there is no slag boil-off, slag ejection, which is believed to be caused by steam explosion, can still occur. The inventors conducted a detailed analysis of the cause and determined that by using a chilled iron source that readily contains moisture, the slag boil-off region C does not change. That is, when the chilled iron source is continuously added without being added all at once, the mass ratio of the added scrap to the residual slag, Wsc''' / Wsl''', increases from... Figure 2 The slag enters the region C that causes sudden boiling of slag midway through the expansion of the slag-free zone B1. At this time, the introduction of a chill source that easily contains moisture revealed that slag was ejected before the mass ratio Wsc''' / Wsl''' reached the slag-free zone B1 after the chill source was added.

[0075] For this verification, such as Figure 4 As shown, relative to the length of the waste chute 6, the chute front position 6A is 0% and the chute end position 6B is 100%. Within this range, various changes are made to the position X (%) of the cold iron source (pure iron 5B) that is particularly prone to containing moisture. Then, verification is performed in the same order as the above-mentioned slag boilover confirmation test.

[0076] exist Figure 5 In this context, as an example, the ratio of the mass of input waste to residual slag when all iron sources are input, Wsc''' / Wsl''', becomes... Figure 2 The experiment was conducted in area B2, where slag boiling did not occur. At this time, the slag and molten iron temperatures Tf''' were set to 1600℃. Figure 5 The summary chart shows whether or not there is slag boiling. Figure 5 The symbol “●” indicates the condition where there is no slag boil-off, and the symbol “×” indicates the condition where slag boil-off occurs. In particular, when using a chill source 5 that easily contains moisture, even if the mass ratio of the input scrap to the residual slag when all the chill sources are input is Wsc''' / Wsl''', which is the slag boil-off non-boiling area B2, there are cases where slag boil-off occurs and cases where it does not occur. It is determined that this area can be defined by the location X of the input chill source that easily contains moisture and the mass ratio of the input scrap to the residual slag Wsc''' / Wsl'''.

[0077] exist Figure 6 In this paper, the threshold of slag boil-off is represented by a curve, showing the relationship between position X at various temperatures and the mass ratio of input scrap to residual slag (Wsc''' / Wsl''') when all iron sources are input. Here, the slag and molten iron temperatures (Tf''') are in the range of 1200~1700℃. Furthermore, the mass ratio of input scrap to residual slag (Wsc''' / Wsl''') when all iron sources are input is... Figure 2 The conditions of regions B1 and B2, where slag boil-off did not occur on the upper and lower sides. Based on... Figure 6 The results show that these thresholds can be approximated by the following formula.

[0078] (one) Figure 2 When the upper slag boil-off zone B2 did not occur

[0079] (2) '' formula

[0080] Wsc''' / Wsl'''≥6.591×10 －6 ×Tf''' 1.695

[0081] (4)'

[0082] X≥8.618×10 －5 ×Tf''' 1.947 ×(Wsl''' / Wsc''')

[0083] (two) Figure 2 When the slag boil-off did not occur in area B1 on the lower side

[0084] (1) '' style

[0085] 5.224×10 －7 ×Tf''' 2 -1.779×10 －4 ×Tf'''-0.4321 <Wsc''' / Wsl'''≤8.64×10 －7 ×Tf''' 1.947

[0086] (3)'

[0087] X≥(1.226×10 －5 ×Tf 2 -2.589×10 －2 ×Tf+17.75)×(Wsl''' / Wsc''')

[0088] The slag temperature Tf', molten iron temperature Tf'', and slag and molten iron temperature Tf''' are synonymous in that they refer to the temperature of the high-temperature material in contact with water, and therefore can be uniformly considered as the temperature of the high-temperature material Tf (°C). In practical applications, it is difficult to measure the temperature of the residual slag in the furnace each time. Since the slag temperature is approximately the same as the molten iron temperature, and the time between the end of one treatment and the start of the next is long, the slag temperature drops excessively, which is unacceptable for the purpose of this invention. Therefore, the temperature of the high-temperature material Tf (°C) can be used as the final molten iron temperature for treatments involving residual slag. However, when cooling material is added before the cold iron source is fed from the scrap chute to the residual slag, it is preferable to determine Tf by considering the cooling capacity of the cooling material and the expected temperature drop based on its amount added, or to measure the slag temperature.

[0089] Wsc', Wsc'', Wsc''', Wsl', Wsl'', Wsl''', and Wrm'' are separated only to distinguish different test conditions. Therefore, they refer to the amount of cold iron source fed from the scrap chute (suffix sc), the amount of residual slag in the furnace (suffix sl), and the amount of residual molten iron in the furnace (suffix rm), and are therefore all synonymous and can be set as Wsc, Wsl, and Wrm respectively.

[0090] (Third implementation method)

[0091] The third embodiment addresses a situation where the amount of chills fed from the scrap chute is less than the total amount of chills that should be fed into the process. This is because, in this invention, the amount of chills fed from the scrap chute is determined by the final temperature of the molten iron remaining in the slag and the amount of residual slag. This satisfies... Figure 1 The converter, which consists of the components required by the first and second embodiments, receives chills from the scrap chute and undergoes a refining process to remove impurities with oxygen. Afterward, molten iron is discharged from the converter taphole into a ladle, and the slag is carried to the next processing stage. In this next processing stage, a test is conducted where the same processing sequence is followed. However, if the amount of chills (Wsc) received from the scrap chute as specified in the first embodiment is insufficient relative to the total amount of chills (Wt) to be processed, an insufficient amount of on-furnace chills is received from the on-furnace hopper before the chills are received from the scrap chute.

[0092] In the aforementioned experiments, it was confirmed that the splashing rate increased with the number of consecutive trials. The inventors investigated the cause and found that the cold iron source fed into the furnace, before being introduced from the scrap chute into the residual molten iron and slag, caused the slag solidified phase of mixed iron directly above the bottom-blown gas nozzle to solidify, clogging the nozzle. The resulting slag over-oxidation was identified as the cause of the splashing. Figure 7 As shown, such blockage of the bottom-blowing nozzle occurs when the lowest bath temperature Tmin (°C) reached by the molten iron during processing is the liquidus temperature Tliq (°C) obtained from the C-Fe binary system state diagram at the C concentration Cc (mass%) in the molten iron, plus a temperature below 60°C. Figure 7 The symbol “○” indicates the condition where there is no nozzle blockage, and the symbol “×” indicates the condition where nozzle blockage occurs.

[0093] Therefore, the inventors set the timing of adding the furnace chill, which is placed before being added from the scrap chute, to be done after the chill is added from the scrap chute. Specifically, the minimum bath temperature Tmin is calculated using the temperature Tin (°C) of the molten iron being charged and the temperature change ΔT (°C).

[0094] Tmin = Tin + ΔT

[0095] In addition, the temperature change ΔT (°C) is calculated using the following formula based on the Si concentration Csi (mass%), the pig iron mixing ratio Y (%), and the temperature Tin of the charged molten iron. Regarding the calculation of the Si concentration Csi, considering the actual Si combustion efficiency of the furnace, the Si concentration Csi in the pig iron is set to less than 0.4 mass% if it accounts for the increase in Si source such as FeSi, and set to 0.4 mass% if it is greater than 0.4 mass%.

[0096] ΔT={76930×Csi-(100-Y)×2000}÷215

[0097] Next, the nozzle clogging limit temperature Tn (°C) is obtained by adding 60°C to the liquidus temperature Tliq (°C) at the C concentration Cc (mass%) of the molten iron. Taking into account cooling capacity (kcal / kg), the maximum amount of furnace chill to be supplied, Wschn (kg), that is not lower than this nozzle clogging limit temperature Tn is calculated. Furthermore, when the furnace chill is supplied from the scrap chute until the refining process begins, it is limited to Wschn (kg). Then, the amount of chill supplied that is insufficient relative to the total amount Wt required after the refining process begins is supplied as the furnace chill.

[0098] Based on the change in the timing of the cold iron source input to the furnace as described above, and while meeting the requirements of implementation methods 1 and 2, continuous operation tests are conducted, and nozzle blockage does not occur, allowing slag to remain stably in the furnace.

[0099] Industrial availability

[0100] The preheating method for cold iron sources involved in this invention is applicable to blast furnace-converter processes, thereby reducing the pig iron mixing ratio and helping to reduce CO2 emissions, and is therefore useful in industry.

[0101] Explanation of reference numerals in the attached figures

[0102] 1: Reaction vessel; 2: Refractory; 3: Tape hole; 4: Slag; 5: Cold iron source; 5A: Iron sheet; 5B: Pure iron sheet; 6: Scrap chute; 6A: (Scrap chute) front end position; 6B: (Scrap chute) end position; 7: Crane; 8: Residual molten iron; 9: Pig iron ladle; 10: Molten iron; 11: Acid lance; 12: Oxygen; 13: Bottom blowing gas system; 14: Furnace hopper; 15: Furnace feed material; X: (Loading position of cold iron source that easily contains moisture).

Claims

1. A method for preheating a chilled iron source, comprising, after the molten iron refined from slag added to molten iron filling a reaction vessel is discharged from the reaction vessel, adding a portion or all of the total amount of chilled iron source Wt (kg) to a portion or all of the remaining slag in the reaction vessel, The ratio Wsc / Wsl (-) of the amount of residual slag in the reaction vessel to the amount of cold iron source Wsc (kg) fed into the reaction vessel using the waste chute is controlled within the range of satisfying the following formula (1) or (2), wherein formula (1) or (2) uses the temperature Tf (°C) of the residual high-temperature material in the furnace after the treatment of the residual slag. 5.224×10 －7 ×Tf 2 -1.779×10 －4 ×Tf-0.4321 <Wsc / Wsl≤8.64×10 －7 ×Tf 1.947 …(1) formula, Wsc / Wsl ≥ 6.591 × 10 －6 ×Tf 1.695 …(2) formula.

2. The preheating method for the cold iron source according to claim 1, wherein, The chills, which are prone to containing moisture and include both powdered chills and chills with voids, are positioned at position X along the length of the scrap chute within the ranges of equations (1) and (2), respectively satisfying equations (3) and (4) below. X≥(1.226×10 －5 ×Tf 2 -2.589×10 －2 ×Tf+17.75)×(Wsl / Wsc)…(3)equation、 X≥8.618×10 －5 ×Tf 1.947 ×(Wsl / Wsc)…(4)Formula, Here, X (%) represents the loading position of waste in the length direction of the waste chute as a percentage, with 0% at the front end of the waste chute on the side opposite to the reaction vessel and 100% at the end of the waste chute opposite to the reaction vessel.

3. The preheating method for the cold iron source according to claim 1 or 2, wherein, When the amount of chilled iron source Wsc fed into the scrap chute is a part of the total amount of chilled iron source Wt, the remaining chilled iron source is fed into the furnace hopper after the chilled iron source is fed into the scrap chute.

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