JP7464843B2 - Method for foaming and settling slag and method for refining with converter - Google Patents

Description

The present invention relates to a method for foaming and settling slag and a converter refining method.

The molten iron produced in blast furnaces and other facilities during the steel manufacturing process has a high C concentration of 4-5% by mass and a high P concentration of around 0.1% by mass. If this molten iron is cast and rolled as is without adjusting the carbon and phosphorus contents, it is difficult to use it as a steel product due to its low workability and toughness. Therefore, in the refining process, dephosphorization and decarburization are carried out and various components are adjusted to produce steel that meets the required quality.

Currently, the pre-treatment of refining is mainly performed using a converter furnace, which has good productivity and reaction efficiency. For example, Non-Patent Document 1 discloses a method in which blast furnace molten iron is charged into a converter and desiliconization and dephosphorization blowing is performed, the blowing is temporarily stopped, the converter is tilted, a part of the desiliconization and dephosphorization slag is discharged from the throat, the converter is returned to the vertical position, and then decarburization blowing is performed (hereinafter, referred to as a continuous treatment method).
Furthermore, Patent Document 1 discloses another method in which blast furnace molten pig iron is charged into a converter for desiliconization blowing, the blowing is temporarily stopped and the converter is tilted to discharge part of the desiliconization slag from the throat, the converter is returned to a vertical position, and then the dephosphorization blowing is continued, and further, after the dephosphorization blowing, the molten pig iron is temporarily discharged from the converter and separated from the dephosphorization slag, and only the molten pig iron is recharged into another converter for decarburization blowing (hereinafter referred to as a separation treatment method).

The former (continuous processing method) is an operating form using one converter, in which slag is discharged from the throat between the desiliconization/dephosphorization blowing and the decarburization blowing. The latter (separate processing method) is an operating method using two converters, in which at least one converter is used for desiliconization/dephosphorization blowing, and slag is discharged from the throat of the converter between the desiliconization blowing and the dephosphorization blowing. Hereinafter, the operation of discharging slag from the converter between two blows will also be referred to as intermediate slag discharge. Both methods have in common the fact that the volume of slag is increased by utilizing the foaming phenomenon of slag that occurs during blowing in order to efficiently discharge slag from the throat.

The foaming of converter slag occurs when a large number of CO bubbles are generated during blowing due to the reaction of C in the molten iron with oxygen gas or FeO in the slag, and the generated CO bubbles remain in the slag. In both the continuous processing method and the separate processing method, the foamed slag in the converter is discharged from the throat and stored in a slag ladle installed below the converter. The more the amount of slag discharged to the slag ladle increases, the less SiO ₂ and P ₂ O ₅ remain in the converter, and the amount of refining materials such as quicklime used in refining after intermediate slag discharge can be reduced. Here, the foaming height of the slag generated during blowing (the amount of foamed slag) tends to decrease after the end of blowing. Therefore, in order to increase the amount of slag discharged from the converter to the slag ladle (the amount of slag discharged), it is necessary to discharge a large amount of foamed slag in a short time.

Here, slag foaming continues to occur even after it has been discharged into the slag discharge pan. When attempting to discharge a large amount of slag in a short period of time, the strong stirring caused by the kinetic energy of the falling slag in the slag discharge pan causes the slag to foam violently, causing it to overflow from the pan. As a countermeasure to this problem, a substance that calms the foaming (hereafter referred to as foaming calming material, or simply calming material) is introduced into the slag discharge pan in an attempt to solve the problem.

Many of the foaming suppression methods that have been tried so far aim at the destruction (breaking of bubbles) of bubbles that remain in the slag. For example, Patent Document 2 discloses a foaming suppression material formed with pulp waste as the main component. This foaming suppression material rapidly generates gas in the slag by a reaction of combustion or pyrolysis, and the foam is broken by the volume expansion energy, causing the slag to shrink. Patent Document 3 discloses a foaming suppression material in which organic matter such as pulp waste is mixed and molded with iron ore or the like to increase the specific gravity, and the foam is allowed to penetrate into the slag, thereby enhancing the foaming effect of gas generation. Patent Document 4 discloses a suppression material (foaming inhibitor) containing raw dolomite, and discloses a suppression method that utilizes the slag viscosity reducing effect of CaO and MgO, which are thermal decomposition products of this raw dolomite. Patent Document 5 discloses a foaming inhibitor containing a synthetic resin containing at least aluminum hydroxide and calcium carbonate as its components. Patent Document 6 discloses a slag foaming quenching material that contains 50% by mass or more of hydroxide and has a heat absorption capacity of 1800 J/g or more, and exemplified the hydroxide by Al(OH) ₃ and Ca(OH) ₂ .

In addition to being highly effective, it is preferable that the calming material be economical, so efforts have been made to utilize waste materials. For example, Patent Document 7 discloses a calming material that uses waste rubber, and Patent Document 8 discloses a solid material molded from combustible garbage.

JP 2013-167015 A Japanese Patent Application Laid-Open No. 54-32116 Japanese Patent Application Laid-Open No. 63-250412 JP 2003-213314 A Japanese Patent No. 6005310 International Publication No. 2018/150862 Japanese Patent Application Laid-Open No. 59-133309 JP 2005-213606 A

Iron and Steel, No. 1, 2001, pp. 21-28

As mentioned above, in the converter-type pretreatment process, a sedative is used to suppress foaming of the slag in the slag ladle. Details will be given later, but there are five requirements for a sedative: instantaneous effect (immediate action), sustained effect, cost-effectiveness, safety during use, and possibility of effective use (reuse) of the slag.

In order to suppress the sudden foaming that occurs in the slag pan when slag is discharged from the converter, the effect of the calming agent must be high (immediately effective), that is, the effect must be seen immediately after the calming agent is added. In addition, the slag pan containing the slag is transported by cart or rail, and CO bubbles continue to be generated during this time. Therefore, there is a risk that the slag in the slag pan will overflow during transportation due to the so-called "post-expansion" that causes the slag to gradually expand. Therefore, it is preferable that the calming agent not only has a high immediate effect, but also has a long-lasting calming effect. In addition, it is preferable that the calming agent is inexpensive and economical, and that it does not generate substances that deteriorate the working environment (e.g., black smoke and dust) when added to the slag. Furthermore, since the slag recovered by the slag pan may be reused as a raw material for roadbed materials and cement, it is also preferable that the calming agent does not remain in the slag as an impurity.

However, the calming agents in Patent Documents 2 and 3 break down bubbles only by generating gas, so their effect does not last and it is difficult to suppress post-bubbling. In addition, they require mixing of raw materials, adjustment of moisture content, compression molding, etc., so their production is time-consuming and costly. Furthermore, the ash contained in pulp waste slag may generate dust, and organic matter such as cellulose may generate black smoke or remain in the slag as slag.

The calming agent of Patent Document 4, which is produced by the thermal decomposition of carbonates, promotes the solidification (skinning) of the slag surface, and CO2 bubbles tend to remain, which leads to swelling. Furthermore, oxides (e.g., CaO, MgO) generated by the thermal decomposition of _CO2 gas tend to remain undissolved in the slag, which may cause volume expansion when the slag is used as a roadbed material. The calming agents of Patent Documents 7 to 8 may generate black smoke due to rubber or combustible waste, or may leave slag (impurities) in the slag.

The sedative material of Patent Document 5 has the risk that the synthetic resin will generate black smoke or become cinders and remain in the slag.
The calming agent in Patent Document 6 describes that adding hydroxides Al(OH) ₃ or Ca(OH) ₂ to the slag can improve the calming rate by cooling the slag. However, _Al2O3 produced by the thermal decomposition of Al(OH) ₃ increases the slag viscosity, and _CaO produced by the thermal decomposition of Ca(OH) ₂ increases the slag melting point, so that CO bubbles tend to remain and there is a risk of swelling.

The present invention has been made in consideration of the above-mentioned problems, and proposes a foaming calming method and converter refining method that use a superior calming material. The object of the present invention is to provide a foaming calming method and converter refining method for slag that are efficient and economical, and do not deteriorate the working environment or leave impurities behind. The foaming calming method of the present invention can be used, for example, in a converter refining method (continuous processing method) in which desiliconization and dephosphorization blowing, slag removal, and decarburization blowing are performed continuously in one converter, or in a converter refining method (separate processing method) in which desiliconization blowing, slag removal, and dephosphorization blowing are performed in one of two converters.

The slag foaming and settling method according to the present invention, which is in line with the above objectives, is as follows:

〔３〕 前記鎮静材のＦｅＯＯＨ及びＦｅ(ＯＨ)_３の含有比率が３５質量％以上であることを特徴とする〔１〕又は〔２〕に記載のスラグのフォーミング鎮静方法。
〔４〕 前記鎮静材のＦｅＯＯＨ及びＦｅ(ＯＨ)_３の含有比率が５０質量％以上であることを特徴とする〔１〕又は〔２〕に記載のスラグのフォーミング鎮静方法。
〔５〕 前記鎮静材の粒度は、粒径２０ｍｍ未満が７０質量％以上であることを特徴とする〔１〕乃至〔４〕のいずれか１つに記載のスラグのフォーミング鎮静方法。
〔６〕 １基の転炉に溶銑を装入して脱珪・脱燐吹錬を行った後、炉内に溶銑を残したまま転炉を傾動させてスラグを炉口から排出し、
転炉を垂直に戻した後に引き続いて脱炭吹錬を行い、
脱燐吹錬後のスラグ排出時に〔１〕乃至〔５〕のいずれか１つに記載のフォーミング鎮静方法を用いることを特徴とする転炉精錬方法。
〔７〕 ２基の転炉の片方に溶銑を挿入して脱珪吹錬を行った後、炉内に溶銑を残したまま転炉を傾動させてスラグを炉口から排出し、
転炉を垂直に戻した後に引き続いて脱燐吹錬を行い、
脱珪吹錬後のスラグ排出時に〔１〕乃至〔５〕のいずれか１つに記載のフォーミング鎮静方法を用いることを特徴とする転炉精錬方法。 [1] A method for foaming and settling slag, comprising the steps of:
A process of calming the foaming by adding a calming agent containing iron ore containing at least one of iron hydroxides FeOOH and Fe(OH) ₃ to the slag discharged into a slag pan,
A method for settling slag by foaming, characterized in that the total mass of iron hydroxides (FeOOH and Fe(OH) ₃ ) contained in the settling material is 1.0% or more in terms of mass ratio with respect to the amount of slag discharged.
[2] The sedative material is made of iron ore,
The method for foaming and settling slag according to [1], characterized in that the input rate X _ore defined by the formula (1) is 1.0 or more.

[3] The method for foaming and settling slag according to [1] or [2], characterized in that the content ratio of FeOOH and Fe(OH) ₃ in the settling material is 35 mass% or more.
[4] The method for foaming and settling slag according to [1] or [2], characterized in that the content ratio of FeOOH and Fe(OH) ₃ in the settling material is 50 mass% or more.
[5] A method for foaming and settling slag according to any one of [1] to [4], characterized in that the particle size of the settling material is such that 70 mass% or more of the material has a particle size of less than 20 mm.
[6] After charging molten iron into one converter and blowing it for desiliconization and dephosphorization, the converter is tilted while leaving the molten iron in the furnace, and the slag is discharged from the throat;
After the converter is returned to the vertical position, decarburization blowing is carried out.
A converter refining method, comprising the steps of: discharging slag after dephosphorization blowing; and using a foaming settling method according to any one of [1] to [5].
[7] After pouring molten iron into one of the two converters and blowing it into a desiliconized slag furnace, the converter is tilted while leaving the molten iron in the furnace, and the slag is discharged from the throat.
After the converter is returned to the vertical position, dephosphorization is carried out.
A converter refining method, comprising the steps of: discharging slag after desiliconization blowing; and using the foaming settling method according to any one of claims 1 to 5.

According to the present invention, by using iron ore containing FeOOH or Fe(OH) ₃ as part or all of the calming material, foaming can be calmed efficiently and economically, and the deterioration of the working environment and the remaining impurities in the slag can be reduced.

FIG. 13 is a graph showing the change in slag height over time in a small furnace experiment.

The following is a detailed explanation of an embodiment of the present invention. In the following explanation, "~" may be used to indicate a range, which means "greater than or equal to that value, inclusive" to "less than or equal to that value, inclusive."

In the dephosphorization blowing process in a converter, a high-velocity oxygen jet is blown onto the surface of the molten iron to oxidize the P in the molten iron and remove _it as _P2O5 into the slag. In parallel with this, the Si in the molten iron is also oxidized and transferred to the slag as _SiO2 . The C in the molten iron reacts with oxygen gas or FeO in the slag to generate CO bubbles, some of which remain in the slag, causing foaming.

After the slag has foamed to a suitable degree, it is discharged from the throat of the converter into a slag ladle installed below the converter, but foaming also occurs in the slag ladle. This is because part of the molten iron is torn off by the oxygen jet during blowing and suspended in the slag as iron granules, and the carbon (C) contained in these iron granules generates CO bubbles in the slag ladle by the reaction of formula (A).
C + FeO = CO (g) + Fe (A)

In addition, the kinetic energy of the falling slag causes strong stirring in the slag disposal ladle, generating a large amount of CO bubbles and causing the slag to foam violently. For this reason, it is necessary to add a substance that has a foaming calming effect to prevent the slag from overflowing.

To achieve a high sedation effect, it is important to promote bubble breaking. The inventors considered it necessary to have multiple bubble breaking mechanisms work simultaneously, and focused on hydroxides. Like carbonates, hydroxides generate gas through a thermal decomposition reaction at high temperatures, promoting bubble breaking. However, because their thermal decomposition temperature is lower than that of carbonates, gas generation is faster and a high immediate effect can be expected. Furthermore, if the reaction products contribute to reducing the viscosity of the slag, this effect can be expected to continue promoting bubble breaking. In other words, efficient foaming sedation can be expected due to the effects of both rapid bubble breaking due to gas generation (instantaneous) and bubble breaking due to viscosity reduction (sustainable).

Since hydroxides of the components contained in the slag do not cause the problems of black smoke or dust generation or residual impurities, Ca(OH) ₂ , Al(OH) ₃ , Mg(OH) ₂ , FeOOH, and Fe(OH) ₃ were selected as such substances, and the foaming calming effect was verified in a small furnace experiment under the composition and temperature conditions assumed for the slag discharged from the furnace port of the above-mentioned continuous processing method and separate processing method. In the following explanation, FeOOH and Fe(OH) ₃ are collectively referred to as "iron hydroxide". Fe(OH) ₂ is not included in iron hydroxide because Fe(OH) ₂ is oxidized to Fe(OH) ₃ in an environment where oxygen is present, and is almost nonexistent.

The small reactor experiment was carried out as follows.
In an iron crucible, 100 g of slag with a basicity (CaO/ _SiO2 ) of 1.0 and an iron oxide concentration of 30 mass% was melted and held at 1350°C, and pig iron was added to the slag from above to cause foaming. After adding the pig iron, an iron rod was immersed in the slag at 30 second intervals to adhere to it, and the slag height was measured. Two minutes after adding the pig iron, 1 g of hydroxide reagent was immersed in the slag to evaluate the slag's calming effect.

The change in slag height over time is shown in Figure 1. In the small furnace experiment, the slag height was measured every 30 seconds, and the height immediately before immersion in the calming agent was not measured, so the points in Figure 1 are connected by dashed lines.
As shown in Figure 1, FeOOH and Fe(OH) ₃ caused a large reduction in slag height, and the subsequent reforming (post-expansion) was also small. In contrast, Ca(OH) ₂ , Mg(OH) ₂ , and Al(OH) ₃ did not cause the slag height to decrease as much as iron hydroxide (FeOOH, Fe(OH) ₃ ), and post-expansion occurred. Thus, the small-scale furnace experiment demonstrated that iron hydroxide is excellent in both instantaneous and sustained effects, and that FeOOH and Fe(OH) ₃ have almost the same effects.

The thermal decomposition reaction of FeOOH is represented by formula (B), and the thermal decomposition reaction of Fe(OH) ₃ is represented by formula (C). In both cases _{, Fe2O3} and _H2O are produced.
2FeOOH = _{Fe2O3 + H2O} (B)
2Fe(OH) ₃ = _{Fe2O3 + 3H2O} (C)
Therefore, the calming effect of iron hydroxide is due to both the generation of _H2O gas due to the thermal decomposition reaction and the reduction in slag viscosity due to _the reaction product _Fe2O3 .

Furthermore, iron hydroxide has a specific gravity of 3 to 4, which is equal to or slightly greater than that of slag, so it disperses efficiently within the slag, whereas other substances all have a specific gravity of 2.5 or less, so they tend to float to the surface due in part to the gas generated by the substances themselves. For this reason, it is presumed that they are inferior to iron hydroxide in both instantaneous release and durability.

The inventors came up with the idea of using a substance containing iron hydroxide as a slag foaming stabilization material based on the results of the small furnace experiments described above. The slag foaming stabilization method and converter refining method of the present invention are described below.

In the present invention, a substance containing iron hydroxide is used as the sedative. As described above, iron hydroxide is superior among hydroxides in both instantaneous and sustained effects. For example, iron ore is used as the sedative. Specifically, iron ore containing iron hydroxide (FeOOH and/or Fe(OH) ₃ ) is used as part or all of the sedative. The components other than Fe contained in iron ore are _SiO2 , _{Al2O3 ,} MgO, and other components of slag, so that adding iron ore to the slag does not cause concerns about deterioration of the working environment or residual impurities, and it is a relatively inexpensive substance containing iron hydroxide.

Next, the suitable amount of sedative to be added to the slag pan will be explained.
In the present invention, a settling material containing iron hydroxide is added in a mass corresponding to the mass of slag discharged into the slag disposal ladle (the amount of slag discharged (W _slag )). In the present invention, as shown in formula (2), it is specified that the settling material is added so that the total mass of iron hydroxide (FeOOH and Fe(OH) ₃ ) contained in the settling material is 1.0% or more by mass relative to the amount of slag discharged ( _W slag ). The value of 1.0% or more by mass ratio is based on the examples described below.

In the present invention, iron ore containing at least one of FeOOH and Fe(OH) ₃ , which are iron hydroxides, is used as a part or all of the sedative. If the total mass of iron hydroxide contained in the sedative satisfies formula (2), a substance other than iron ore containing at least one of FeOOH and Fe(OH) ₃ , such as iron hydroxide powder, may be used as a part of the sedative. In addition, the present invention does not exclude the use of a substance that does not contain FeOOH and Fe(OH) ₃ as a part of the sedative, but as long as the total mass of iron hydroxide contained in the sedative satisfies formula (2), the effect can be fully enjoyed. Note that if only iron ore containing at least one of FeOOH and Fe(OH) ₃ , which are iron hydroxides, is used as the sedative, the sedative is inexpensive and each process for sedating the foaming can be simplified, so that productivity can be improved and costs can be reduced.

When only iron ore is used as the sedative, the total mass (W _ore(FeOOH+ Fe(OH)3)) of iron hydroxides (FeOOH and Fe(OH) ₃ ) contained in the sedative (hereinafter referred to as sedative ore) can be calculated based on the total mass (W _ore ) of the iron ore (sedative ore) using formula (3).

The iron ore used in the sedative ore may be one or more brands, so long as it contains at least one of FeOOH and Fe(OH) ₃ . It may also contain iron oxide brands that do not contain iron hydroxide. When using multiple brands of iron ore, it is preferable to use a mixture that is previously mixed in a predetermined ratio. In addition, in formula (3), when one brand of iron ore is used, the total mass of the iron ore (sedative ore) (W _ore ) indicates the mass of the one brand of iron ore used, and the total mass of the iron hydroxide (W _{ore(FeOOH+Fe(OH)3)} ) indicates the total mass of the iron hydroxide (FeOOH and Fe(OH) ₃ ) contained in the one brand of iron ore. In addition, when multiple brands of iron ore are used, the total mass of iron ore (sedative ore) (W _ore ) indicates the total mass of the multiple brands of iron ore used, and the total mass of iron hydroxide (W _{ore(FeOOH+Fe(OH)3)} ) indicates the total mass of iron hydroxide (FeOOH and Fe(OH) ₃ ) contained in the multiple brands of iron ore used. In other words, when multiple brands of iron ore are used, the FeOOH ratio (X _ore(FeOOH) ) and Fe(OH) ₃ ratio (X _ore(Fe(OH)3) ) of the iron ore indicate the FeOOH ratio and Fe(OH) ₃ ratio of the mixture of multiple brands of iron ore based on their blending ratio.

Here, when only iron ore is used as the settling agent, W _{ore(FeOOH + Fe(OH)3)} in formula (3) is equal to the total mass of iron hydroxide contained in the settling agent W _{ore(FeOOH + Fe(OH)3)} in formula (2). Therefore, from the above formulas (2) and (3), formula (4) can be obtained, which shows the relationship between the mass of the settling agent ore added (iron ore input amount W _ore ) and the amount of slag discharged (W _slag ).

Here, in the case where only iron ore is used as the settling material, the "feed rate X ore " defined by formula (5) is used as an index for determining whether the slag foaming settling method and converter refining method implemented, including the examples described below, _are within the scope of the present invention.

In addition, in the same manner as the charge rate X _ore when the settling agent is limited to only iron ore, when a slag foaming settling method and a converter refining method are carried out, which include a step of settling foaming by charging a settling agent containing iron ore containing at least one iron hydroxide of FeOOH and Fe(OH) ₃ , the "charge rate X" defined by formula (6) can be used as an index for determining whether the method is within the scope of the present invention. Here, when a plurality of substances (iron ore containing at least one iron hydroxide of FeOOH and Fe(OH) ₃ , and other substances) are used as the settling agent, the total mass (W) of the settling agent indicates the total mass of the plurality of substances used, and the FeOOH ratio (X _(FeOOH) ) of the settling agent and the Fe(OH) ₃ ratio (X _(Fe(OH)3) ) of the settling agent indicate the FeOOH ratio and the Fe(OH) ₃ ratio of a mixture of the plurality of substances based on their blending ratios.

Here, if the amount of calming agent (W) or the amount of iron ore (W _ore ) is small and the value of "amount of charge X" or "amount of charge X _ore " is less than 1.0, the gas generation and viscosity reduction effects are insufficient, making it difficult to obtain the calming effect. In addition, the more the amount of calming agent (W) or the amount of iron ore (W _ore ) is, the more likely it is to have a reliable effect, but if it is charged in excess, the temperature of the slag will drop, the surface will become skinned, and after-swelling will easily occur. Therefore, it is preferable that the amount of calming agent (W) or the amount of iron ore (W _ore ) is such that the mass of iron hydroxide relative to the mass of slag in the slag discharge pan is 5.0% or less in mass ratio, i.e., the value of "amount of charge X" or "amount of charge X _ore " is 5.0 or less.

The content of iron hydroxide (FeOOH and Fe(OH) ₃ ) in the sedative (including sedative ore) is preferably 35% by mass or more, more preferably 50% by mass. If the content of iron hydroxide in the sedative is too low, the amount of components other than iron hydroxide added will be excessive when the value of the input rate X or the input rate _Xore is set to 1.0 or more.

In addition, when iron ore is used as a part or all of the sedative, it is preferable to use iron ore with a content ratio of iron hydroxide (FeOOH and Fe(OH) ₃ ) of 50 mass% or more. This is because iron ore with a high ratio of Fe ₂ O ₃ generates less H ₂ O gas by thermal decomposition and is less likely to exhibit a sedative effect. In addition, since SiO ₂ and Al ₂ O ₃ , which are gangue components, have the effect of increasing the viscosity of slag, and MgO has the effect of increasing the melting point of slag, there is a risk that they may inhibit the dissipation of gas from the foamed slag surface. Therefore, the total ratio of these components (SiO ₂ , Al ₂ O ₃ , and MgO) contained in the iron ore is preferably less than 50 mass%, more preferably less than 20 mass%. In addition, the content ratio of FeOOH and Fe(OH) ₃ can be measured by X-ray diffraction method, infrared absorption spectroscopy, etc.

The mineral phase of iron ore varies greatly depending on the place of origin, but it is preferable that the iron ore used as the sedative is of a so-called inferior quality. Inferior quality iron ore has a high content of FeOOH and Fe(OH) ₃ (for example, the content ratio of FeOOH and Fe(OH) ₃ ) is 50 mass% or more, and also has a high ratio of fine ore. In other words, since the surface area is large, the thermal decomposition reaction is fast and it exhibits excellent instantaneous properties. In addition, since it is considered to be of inferior quality as a blast furnace raw material, it is inexpensive, and since it is abundant, there is little concern about depletion.

The particle size of the calming agent added in the present invention is preferably such that particles with a particle size of less than 20 mm make up 70% by mass or more, and more preferably 80% by mass or more. This is because if the particle size of the calming agent is 20 mm or more, it is difficult for it to dissolve quickly in the slag, and the calming effect of foaming tends to be reduced.

The calming material does not necessarily need to be continuously added to the slag discharge pan, and there are no limitations on the method of adding the calming material as long as it can calm the foaming of the slag. However, from the viewpoint of making the calming material act effectively on the CO bubbles on the surface of the discharged slag, it is preferable to discharge the slag into the slag discharge pan and add the calming material to the slag discharge pan at approximately the same time, and it is more preferable to add the calming material from above the slag discharge pan so that it is mixed under the layer of CO bubbles that has formed on the surface of the slag. Note that addition may be stopped if it is predicted that the slag will not overflow based on the foaming state of the slag in the slag discharge pan.

According to the slag foaming calming method using the calming material described above, when discharging (discharging) slag from the throat of the converter, the calming material is introduced into the slag ladle to calm the foaming of the slag in the slag ladle, and a large amount of slag can be discharged from the converter without causing slag overflow. The slag foaming calming method described above can also be used when molten pig iron is charged into the converter for blowing, the blowing is temporarily stopped, the converter is tilted, and the slag is discharged into the slag ladle installed below the converter while leaving the molten pig iron in the converter. Specifically, for example, it can be used in the converter blowing method described below.

The molten pig iron charged in one converter is subjected to desiliconization and dephosphorization blowing, and the converter is tilted. When the slag in the converter is discharged from the throat while the molten pig iron remains in the converter, the above-mentioned slag foaming and settling method is applied (i.e., the above-mentioned settling material is charged into the slag discharge ladle), and after the slag is discharged, the molten pig iron in the converter is subjected to decarburization blowing (converter refining method using one converter: see Non-Patent Document 1).
In addition, desiliconization blowing is performed on molten pig iron charged in at least one of two or more converters and the converter is tilted. When the slag in the converter is discharged from the throat while the molten pig iron remains in the converter, the above-mentioned slag foaming and settling method is applied (i.e., the above-mentioned settling material is charged into the slag pan), and after the slag is removed, dephosphorization blowing is performed on the molten pig iron in the converter (converter refining method using two or more converters: see Patent Document 1).

The above-mentioned converter slag refining methods are similar in that they use the foaming phenomenon to discharge slag from the furnace throat, so the effects can be enjoyed by using the slag foaming settling method of the present invention. Also, even in methods other than the converter slag refining methods described above, if foaming settling is required at the stage of discharging slag from one refining vessel to another, the above-mentioned slag foaming settling method can be used to prevent slag overflow.

The following describes specific examples of the present invention based on Tables 1 to 3.

The effect of the silencing agent in the above-mentioned slag foaming silencing method was confirmed in a converter blowing method (continuous processing method) using one converter, and in a converter blowing method (separate processing method) using two or more converters. 400 t of molten pig iron was charged into a converter (internal volume: 300 ^m3 ) and slag was blown. The blowing was temporarily stopped, the converter was tilted, and the slag in the converter was discharged for 4 minutes into a slag ladle (height from the bottom to the ladle rim: 4.5 m, internal volume: ⁷⁰ m3) installed below the furnace body. Immediately after slag discharge started, the silencing agent was continuously charged into the slag ladle using the charging chute. Note that when no silencing agent was used, only slag was discharged into the slag ladle.

The state inside the slag draining pan was observed during slag draining, and slag draining was stopped when the slag reached the height of the rim of the pan. If the slag surface did not reach the height of the rim of the pan, slag draining was stopped four minutes after the start of slag draining.

After the slag was discharged, the slag discharge pan was left to stand for 5 minutes, and the presence or absence of slag overflow due to post-swelling was visually determined. After the slag was discharged, the mass of the slag and settling material charged into the slag discharge pan was measured using a weighing machine attached to the mobile cart on which the slag discharge pan was placed, and the mass of the settling material charged into the slag discharge pan was subtracted to evaluate the amount of slag discharged (W _slag ). The more excellent the foaming and settling effect of the settling material, the greater the amount of slag discharged (W _slag ). This is because the settling material prevents the slag surface from reaching the height of the rim of the slag discharge pan.

The composition of the sedative used in this example is shown in Table 1.
Sedative A is iron ore mainly composed of _FeOOH , sedative B is iron ore containing both FeOOH and Fe(OH) ₃ , sedative C is iron ore mainly composed of _Fe2O3 , and sedative D is hydrated lime.

Table 2 shows examples of slag disposal after desiliconization and dephosphorization blowing using the continuous treatment method. The underlines in the table indicate areas outside the scope of the present invention. In the continuous treatment method, a slag disposal amount of 12 tons or more was considered to be good. The slag composition had a basicity (CaO/ _SiO2 : mass ratio) of 1.0 to 1.2, an iron oxide concentration of 20 to 30 mass%, and a temperature of 1330 to 1350°C.

Examples 1 to 6 in Table 2 are examples of the invention, and Examples 1 to 4 are examples of the invention in which iron ore A or iron ore B was used alone as a settling agent. Examples 5 and 6 are examples of the invention in which a settling agent in which iron ore A and iron ore C were mixed in a ratio of 2:1 (FeOOH and Fe(OH) ₃ : 56% by mass) and a settling agent in which iron ore B and iron ore C were mixed in a ratio of 2:1 (FeOOH and Fe(OH) ₃ : 37% by mass) were used. In all cases, the charge rate X _ore was 1.0 or more, which was within the range of the present invention, and therefore slag could be discharged for 4 minutes without the slag reaching the height of the pot rim, and the amount of discharged slag was 12 tons or more. In addition, no swelling occurred after the slag was discharged. In Example 4 of the present invention, the mass ratio of 20 mm or more was higher than in Example 1, so that the dissolution into slag was slower and the amount of discharged slag was less than in Example 1.

Examples 7 to 10 are comparative examples. In Examples 7 to 10, the input rate X _ore was less than 1.0, which was outside the range of the present invention, and the amount of slag discharged was 10 tons or less. In addition, in Examples 8 to 10, post-swelling also occurred.

Table 3 shows examples of slag discharged after desiliconization blowing in the separation treatment method. The underlines in the table indicate the parts outside the scope of the present invention. In the separation treatment method, a discharge amount of 8 tons or more was considered to be good. The slag composition had a basicity (CaO/ _SiO2 ) of 0.6 to 0.8, an iron oxide concentration of 20 to 30 mass%, and a temperature of 1300 to 1330°C.

Examples 11 to 16 in Table 3 are examples of the invention, with Examples 11 to 14 being examples of the invention where iron ore A or iron ore B was used alone as the settling agent, and Examples 15 and 16 being examples of the invention where a settling agent consisting of a mixture of iron ore A and iron ore C in a ratio of 2:1 (FeOOH and Fe(OH) ₃ : 56% by mass) and a settling agent consisting of a mixture of iron ore B and iron ore C in a ratio of 2:1 (FeOOH and Fe(OH) ₃ : 37% by mass) were used. In all cases, the charge rate Xore was 1.0 or more, which was within the range of the present invention, and therefore slag could be discharged for 4 minutes without the slag reaching the height of the pot rim, and the amount of discharged slag was 8 tons or more. In Example 12, the mass ratio of 20 mm or more was higher than in Example 9, so that dissolution into the slag was slower and the amount of discharged slag was less than in Example 9.

Examples 17 to 20 are comparative examples. In Examples 17 to 20, the input rate X _ore was less than 1.0, which was outside the range of the present invention, and the amount of slag discharged was 7 tons or less. In addition, in Examples 18 to 20, post-swelling also occurred.

Claims (7)

A method for settling foaming of slag, comprising the steps of:
A process of calming the foaming by adding a calming agent containing iron ore containing at least one of iron hydroxides FeOOH and Fe(OH) ₃ to the slag discharged into a slag pan,
A method for settling slag by foaming, characterized in that the total mass of iron hydroxides (FeOOH and Fe(OH) ₃ ) contained in the settling material is 1.0% or more in terms of mass ratio with respect to the amount of slag discharged. The calming material is made of iron ore,
2. The method for settling slag foaming according to claim 1, wherein the input rate X _ore defined by the formula (1) is 1.0 or more.

3. The method for foaming and settling slag according to claim 1, wherein the content ratio of FeOOH and Fe(OH) ₃ in the settling material is 35 mass% or more. 3. The method for foaming and settling slag according to claim 1, wherein the content ratio of FeOOH and Fe(OH) ₃ in the settling material is 50 mass% or more. The slag foaming and settling method according to any one of claims 1 to 4, characterized in that the particle size of the settling material is such that 70% or more by mass are less than 20 mm in particle size. Molten iron is charged into one converter and desiliconized and dephosphorized. After that, the converter is tilted while the molten iron remains in the furnace, and the slag is discharged from the throat.
After the converter is returned to the vertical position, decarburization blowing is carried out.
A converter refining method, comprising using the foaming settling method according to any one of claims 1 to 5 when discharging slag after dephosphorization blowing. After pouring molten iron into one of the two converters and blowing it into a desiliconized slag furnace, the converter is tilted while leaving the molten iron in the furnace, and the slag is discharged from the throat.
After the converter is returned to the vertical position, dephosphorization is carried out.
A converter refining method, comprising using the foaming settling method according to any one of claims 1 to 5 when discharging slag after desiliconization blowing.

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