JP2022021235A - Production method of modified converter slag and production method of granular material for road bed material - Google Patents

Abstract

To modify a converter slag having high basicity generated in a converter refining process, that is, a converter slag having high refining capacity into a converter slag applicable to a road bed material without burden of a steelmaking process by a simple device configuration.SOLUTION: In a production method of a modified converter slag, a reformer mixed slag is obtained by spraying a powdery granulated slag reformer to a molten converter slag during flowing-down or to a position where the molten converter slag flows down into a slag-retaining vessel while flowing down the molten converter slag from the converter into the slag-retaining vessel, and mixing the slag reformer with the molten converter slag. Next, the reformer mixed slag is held in the slag-retaining vessel to form a reformer reaction slag. Next, the reformer reaction slag is discharged from the slag-retaining vessel, cooled and solidified to form a solidified slag. The solidified slag is pulverized and subjected to steam aging to obtain the modified converter slag.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing modified converter slag, and more particularly to a method for producing modified converter slag for using converter slag generated in a converter refining step as a roadbed material.

The converter slag generated in the converter refining process is a kind of steelmaking slag, and is currently mainly used for so-called low-grade applications such as temporary materials for civil engineering work and ground improvement materials for roads. This is because when a part of the lime source added as a refining agent in the converter refining step remains as free CaO in the converter slag, the free CaO reacts with water (hydration reaction). When the converter slag is buried in the ground and such a hydration reaction occurs, the volume of the buried converter slag may expand more than twice, and there is a risk of destroying the surrounding structures. ..

In order to use steelmaking slag containing converter slag for higher-grade roadbed materials, concrete aggregates, stone raw materials, etc., the free CaO is reduced or the expansion due to the hydration reaction of the free CaO is calmed down. There is a need. Hereinafter, reducing the amount of free CaO in the steelmaking slag or preventing expansion due to the hydration reaction of the free CaO is also referred to as modification of the steelmaking slag. JIS A 5015: 2018 (Road Steel Slag) stipulates that the water immersion expansion ratio should be 1.0% or less when steelmaking slag is used as a roadbed material.

As a method of suppressing the expansion of steelmaking slag, an aging method in which the hydration reaction of free CaO is promoted in advance is adopted. Prior to the 1990s, slag was piled up outdoors and subjected to atmospheric aging treatment that caused a hydration reaction with air and rainwater. However, the atmospheric aging treatment required a period of 3 to 6 months or more. Therefore, the accelerated aging treatment was developed and put into practical use in the 1990s (Non-Patent Document 1). The accelerated aging treatment includes a steam aging method in which steelmaking slag is put into the cooling yard, covered with a heat-resistant sheet, and steam is blown into the steelmaking slag from the bottom of the cooling yard, and a forced hydration reaction is performed by high-pressure steam in a closed container. A pressurized steam aging method or the like that promotes slag can be mentioned. Of these, the steam aging method, which has a simple equipment configuration, is currently used more often (Non-Patent Document 2).

Further, in Patent Document 1, the steelmaking slag is heat-treated at a temperature equal to or higher than the melting temperature, preferably 10 ° C. or higher higher than the melting temperature to reduce free CaO in the steelmaking slag and to reduce the water absorption rate of the steelmaking slag. A method for modifying steelmaking slag to reduce the amount of slag is described. Patent Document 2 discloses a method for melt-modifying steelmaking slag having a high basicity. In this method, the steel-making slag is melt-reformed by spraying the reformer onto the steel-making slag in the melt-reforming treatment apparatus using a SiO ₂ -containing substance as the reforming material. In the method, when the steelmaking slag having a solid phase ratio of 0.5 or more before the start of the melt reforming treatment is used, the temperature TM of the steelmaking slag before the start of the melt reforming treatment and the steelmaking slag. This is a method of starting the melt reforming treatment under the condition that the relationship with the liquidus temperature T _LL of is satisfied with _TM + 150 ° C. ≧ T _LL .

Japanese Unexamined Patent Publication No. 2005-306654 Japanese Unexamined Patent Publication No. 2010-285634

Takeshi Sasaki et al. "Development of Steam Aging Treatment for Steelmaking Slag" Nippon Steel & Sumitomo Metal Technical Report No. 399 (2014) p21-25 Kazuhiro Horii et al. "Overview of Current Status of Steel Slag Utilization and Development Status of New Effective Utilization Technology" Nippon Steel & Sumitomo Metal Technical Report No. 399 (2014) p3-9

However, when the converter is operated with the basicity of the slag increased for the purpose of ensuring the dephosphorization ability during converter refining, the steam aging method is applied to the obtained converter slag. However, the free CaO cannot be reduced and the stabilization of the converter slag becomes insufficient. Here, the basicity is a ratio of the mass concentration of CaO to the mass concentration of SiO ₂ in the converter slag, that is, a value represented by (mass% CaO) / (mass% SiO ₂ ). Further, even if the free CaO can be reduced, there is a problem that aging requires at least several days and the productivity is low.

Further, when the basicity of the converter slag is high, the method described in Patent Document 1, that is, heat treatment at a temperature higher than the melting temperature by 10 ° C. or higher, and then slow cooling may not be sufficient for reforming.

The method described in Patent Document 2 is as follows: 1) After refining, after steelmaking, the converter slag remains in the converter, and the metal remaining in the converter is burned while sending acid to melt and reform. It is charged into the quality treatment equipment to preheat the converter slag. Preheat the converter slag 3) Set the _blowoff temperature of the converter to (TLL-150) ° C or higher, charge it into the melt reforming treatment equipment, and start the melting reforming treatment. It has not been widely adopted because it requires the addition of a processing process that imposes a burden on the steelmaking process, such as keeping the temperature above (T _LL -150) ° C, and the introduction of additional equipment, which complicates the equipment configuration. rice field.

Therefore, according to the present invention, even if the converter slag has a high basicity generated in the converter refining process, that is, the converter slag having a high refining ability, the simple device configuration allows the roadbed to be used without the burden of the steelmaking process. The purpose is to reform the converter slag that can be applied to materials.

By spraying powdery granular slag modifier onto the molten converter slag being discharged, the present inventors have a simple equipment configuration, and can also be used for roadbed materials without burdening the steelmaking process. It was found that the converter slag can be modified to satisfy the applicable water immersion expansion ratio of 1.0% or less.

The present invention has been made based on the above findings. That is, the gist structure of the present invention is as follows.

[1] While flowing the molten converter slag generated in the hot metal refining step in the converter from the converter into the slag holding container, the molten converter slag flowing down or the molten converter slag. Is sprayed with a powdery granular slag modifier to the position where the slag flows down into the slag holding container, and the slag modifier is mixed with the melt converter slag to form a modifier mixed slag.
Next, the modified material mixed slag is held in the slag holding container to obtain a modified material reaction slag.
Next, the modified material reaction slag is discharged from the slag holding container, cooled and solidified to obtain solidified slag.
Next, the solidified slag was crushed to obtain crushed slag.
Next, a method for manufacturing a reforming converter slag, wherein the crushed slag is steam-aged to obtain a reforming converter slag.

[2] The method for producing a modified converter slag according to the above [1], wherein the slag modifier contains powders and granules having a particle size of 4.5 mm or less.

[3] The modified converter slag according to the above [1] or [2], wherein the basicity of the molten converter slag before mixing the slag modifier is 3.6 or more and 4.2 or less. Production method.

[4] The method for producing a modified converter slag according to any one of [1] to [3] above, wherein the calculated value of the basicity of the modified material mixed slag is 3.3 or less.

[5] The modification according to any one of [1] to [4] above, wherein the melt converter slag flows down into the slag holding container from a height of 4 m or more with respect to the bottom surface of the slag holding container. How to make converter slag.

[6] Any of the above [1] to [5], wherein the discharge time required for the melting converter slag in the converter to flow down from the converter to the slag holding container is 30 seconds or more and 90 seconds or less. The method for manufacturing a modified converter slag according to item 1.

[7] The method for producing a modified converter slag according to any one of [1] to [6] above, wherein the slag modifying material contains 90% by mass or more of SiO ₂ .

[8] The reforming converter according to any one of [1] to [7], wherein the reforming material mixed slag is held in the slag holding container for 10 minutes or more to obtain the reforming material reaction slag. How to make slag.

[9] A method for producing a granular material for roadbed material using the modified converter slag according to any one of the above [1] to [8].

According to the present invention, even a converter slag having a high basicity generated in a converter refining process, that is, a converter slag having a high refining ability can be used as a road without burdening the steelmaking process by a simple device configuration. It can be reformed into a converter slag satisfying a water immersion expansion ratio of 1.0% or less, which is also applicable to roadbed materials.

It is a figure for demonstrating the structure of the apparatus which sprays a slag modifier to a molten converter slag flowing down from a converter. It is a scatter diagram which shows the relationship between the basicity of a converter slag and the concentration (mass%) of free CaO. It is a scatter diagram which shows the relationship between the basicity of a converter slag and a water immersion expansion ratio.

Hereinafter, an embodiment of the present invention will be described. In the present specification, the “reformed converter slag” refers to a converter slag that satisfies a water immersion expansion ratio of 1.0% or less. The water immersion expansion ratio is measured in accordance with JIS A 5015: 2018.

The method for manufacturing the reforming converter slag according to the present embodiment is as follows.
While flowing the molten converter slag generated in the hot metal refining process in the converter from the converter into the slag holding container, the molten converter slag flowing down or the molten converter slag is the slag. A powdery granular slag modifier is sprayed onto the position where the slag is poured into the holding container, and the slag modifier is mixed with the melt converter slag to obtain a modifier mixed slag.
Next, the modified material mixed slag is held in the slag holding container to obtain a modified material reaction slag.
Next, the modified material reaction slag is discharged from the slag holding container, cooled and solidified to obtain solidified slag.
Next, the solidified slag was crushed to obtain crushed slag.
Next, it is a method of manufacturing a reforming converter slag in which the crushed slag is steam-aged to obtain a reforming converter slag.

[Modifying material mixing process]
First, a hot metal refining step (hereinafter, also referred to as a converter refining step) is performed in the converter to generate molten converter slag (hereinafter, also referred to as molten converter slag). Next, after the completion of the converter refining step, the molten converter slag flows down into the slag holding container, and at a position where the molten converter slag flowing down or the molten converter slag flows down into the slag holding container. On the other hand, the slag modifier is sprayed and the slag modifier is mixed with the melt converter slag to obtain the modifier mixed slag. According to the configuration, the melt converter slag and the slag modifier are mixed by utilizing the kinetic energy flowing down into the slag holding container, and therefore, it is described in Patent Document 2. As such, no additional equipment such as a burner for spraying the slag reformer onto the melt converter slag and a stirrer for stirring the slag reformer and the melt converter slag is required. The cost can be reduced. In addition, compared to the case where the melt converter slag and the slag modifier are mixed in various containers, it is possible to suppress the aggregation and solidification of the slag modifier on the bath surface or inside of the melt converter slag. , The melt converter slag and the slag modifier can be uniformly mixed, and the composition of the modifier mixed slag can be made more uniform. If the melt converter slag and the slag modifier are not sufficiently mixed, the melt converter slag in the portion where the slag modifier is not sufficiently mixed may remain with high basicity. On the other hand, according to the present embodiment, since the melt converter slag and the slag reformer can be uniformly mixed, it is possible to provide a higher quality reformer slag. Furthermore, since it is not necessary to raise the blow-off temperature to reform the slag or to occupy the converter before and after steelmaking, the cost of the steelmaking process does not increase and the productivity does not decrease. The load in the process is small.

As a simple method of reforming converter slag with a reforming material, the reforming material is put into the converter before steelmaking after the completion of the converter refining process, and the melt converter slag is used in the converter. A method of mixing with the modifier is conceivable. However, depending on the method, if the basicity is lowered to a level where the molten converter slag in the converter is sufficiently modified by adding the reforming material, the dephosphorization ability of the molten converter slag is lowered. For this reason, the phosphorus transferred from the molten steel to the molten converter slag during smelting may be transferred (restored phosphorus) to the molten steel again after the modifier is added, and as a result, the phosphorus in the molten steel may not be sufficiently reduced. There is. Therefore, when the reforming material is put into the converter after the completion of the converter refining process and before the steel is discharged, the amount of slag is increased by putting more lime into the converter at the start of refining. Even if the basicity of the melt converter slag decreases after the modifier is added, it is necessary to prevent the restoration of phosphorus from occurring due to the effect of increasing the amount of slag. On the other hand, in the present embodiment, since the reforming material is mixed with the molten converter slag outside the converter, there is no risk of condensate in the molten steel in the converter, and lime during converter refining. There is no need to increase the input amount of.

Particle size of the slag modifier: 4.5 mm or less The particle size of the slag modifier is preferably 4.5 mm or less. By setting the particle size of the slag modifier to 4.5 mm or less, when the slag is dispersed and mixed in the melt converter slag to form a modifier-mixed slag, the slag modifier is buoyant in the modifier-mixed slag. It is possible to more preferably prevent ascending. Further, if the particle size of the slag reforming material is 4.5 mm or less, the time required for the reaction with the melt converter slag to proceed to the center of the slag reforming material can be shortened, so that the reaction can be completed before the reaction is completed. It is possible to more preferably prevent the solidification of the melt converter slag from progressing. Although the lower limit of the particle size of the slag modifier is not particularly limited, it is more suitable to prevent the sprayed slag modifier from being rolled up by the flow of the surrounding gas, and the slag modifier is more preferably to be used as a melt converter slag. For mixing, the particle size of the slag modifier is preferably 0.5 mm or more. The particle size of the slag modifier is more preferably 0.7 mm or more, still more preferably 1.4 mm or more. The particle size of the slag modifier is more preferably 4.0 mm or less, still more preferably 2.4 mm or less.

The components of the slag modifier are not particularly limited and may be conventionally known components. The slag modifier preferably contains 90% by mass or more of SiO ₂ . SiO ₂ reacts with free CaO to reduce the basicity of converter slag. In order to efficiently reform the converter slag, the higher the content of SiO ₂ in the slag reformer, the more preferable. More preferably, the slag modifier contains SiO ₂ in an amount of 95% by mass or more.

The slag modifier may be sprayed on the molten converter slag that is flowing down, or may be sprayed on the position where the molten converter slag is poured into the slag holding container. Further, the spraying speed of the slag reforming material when the slag reforming material is sprayed onto the melt converter slag is not particularly limited, but can be 200 kg / min or more and 350 kg / min or less. The slag modifier is preferably sprayed onto the position where the melt converter slag flows down into the slag holding vessel. By spraying the slag reformer to the position where the melt converter slag flows down into the slag holding container, the melt converter slag is prevented from solidifying, and the slag reformer is more preferably melted converter slag. Can be mixed with.

Molten converter before mixing slag modifier Slag basicity: 3.6 or more and 4.2 or less The basicity of melt converter slag before mixing slag modifier should be 3.6 or more. Is preferable, and 4.2 or less is preferable. The basicity of the melt converter slag before mixing the slag modifier can be directly analyzed or obtained as a so-called calculated basicity. Here, the calculated basicity is the ratio of the CaO pure content (CaO /) to the SiO ₂ pure content in the auxiliary raw material (including the slag remaining from the precharge) added in the furnace by the start of steel ejection in the smelting. Obtained by SiO ₂ ). Of course, the slag may be collected and analyzed before the slag modifier is mixed, and the basicity of the melt converter slag before the slag modifier may be mixed may be directly measured. In one example, melt converter slag is collected, analyzed, and measured during steel ejection immediately after the completion of the refining process. By setting the basicity of the melting converter slag to 3.6 or more, recovery of phosphorus can be suppressed. Further, by setting the basicity of the melt converter slag to 4.2 or less, the basicity of the modified material mixed slag can be reduced to a required level without using a large amount of slag modifier. That is, even if the slag modifier is sprayed during a limited period in which the melt converter slag is allowed to flow from the converter into the slag holding container, the basicity of the modified material mixed slag is reduced to a required level. Can be made to. The basicity of the melt converter slag before mixing the slag modifier is more preferably 3.8 or more. Further, the basicity of the melt converter slag before mixing the slag modifier is more preferably 4.0 or less. The basicity of the melt converter slag before mixing the slag modifier was determined by the auxiliary materials (burnt lime, limestone, dolomite, silica stone, recycled) to be put into the converter at the start of the refining process and during the treatment. It can be adjusted by the amount of steelmaking slag).

In the molten converter slag, the converter is usually tilted to the discharge side after the steel is discharged and flows down from the furnace mouth of the converter into the slag holding container. At this time, it is preferable to flow down into the slag holding container from a height of 4 m or more with respect to the bottom surface of the slag holding container. By flowing the melt converter slag from a height of 4 m or more with respect to the bottom surface of the slag holding container, the slag modifier is further mixed in the melt converter slag by the flow generated by the flow of the melt converter slag. It will be easier. The higher the height at which the melt converter slag flows down, the more vigorous the flow when it flows down into the slag holding container, and the easier it is for the slag modifier to be mixed into the melt converter slag. The melt converter slag flows down into the slag holding container from a height of 5 m or more, more preferably 6 m or more with respect to the bottom surface of the slag holding container.

The discharge time required for the molten converter slag in the converter to flow down from the converter to the slag holding container is preferably 30 seconds or more and 90 seconds or less. By setting the discharge time to 30 seconds or more, a sufficient amount of slag modifier can be mixed during the discharge of the melt converter slag. On the other hand, in general, the discharge of molten converter slag from a converter tilts the converter and causes the molten converter slag to flow down from the furnace mouth of the converter, so that the molten converter slag is discharged at a constant small flow rate. It's difficult to do. Therefore, by setting the discharge time to 90 seconds or less, the flow rate of the melt converter slag does not decrease too much, and it can be suitably mixed with the slag modifier. The discharge time is more preferably 50 seconds or more. The discharge time is more preferably 80 seconds or less. The discharge time required for the molten converter slag in the converter to flow down from the converter to the slag holding container starts from the timing when the converter is tilted toward the drain side and the slag begins to flow out from the furnace mouth. , Measure the timing when the slag does not flow out from the furnace mouth as the end point. Regardless of the amount of molten converter slag discharged from the converter, the discharge time required for the molten converter slag in the converter to flow down from the converter to the slag holding container can be measured. That is, even when the total amount of the molten converter slag is discharged from the converter, or even when the entire amount of the molten converter slag is not discharged, the converter is tilted to the discharge side and the converter is tilted from the furnace mouth. To measure the discharge time required for the melt converter slag in the converter to flow down from the converter to the slag holding container based on the timing when the slag begins to flow out and the timing when the slag stops flowing out from the furnace mouth. Can be done.

Calculated basicity of modified material mixed slag: 3.3 or less The calculated basicity of modified material mixed slag obtained by mixing melt converter slag and slag modifier is 3.3 or less. Is preferable. Here, the calculated value of the basicity of the modified material mixed slag is an estimated value of the amount and component composition of the molten converter slag remaining in the converter immediately after the molten steel is ejected. It is a ratio of the mass concentration of CaO to the mass concentration of SiO ₂ in the modified material mixed slag obtained in consideration of the amount of the slag modifier to be added and the component composition. For example, when the amount of molten converter slag discharged is 9000 kg and the composition of the components is CaO: 45% and SiO ₂ : 11%, when 360 kg of a slag modifier having 100% SiO ₂ is added, The calculated value of the basicity of the modified material mixed slag is 3.0. When the calculated value of the basicity of the modified material mixed slag is 3.3 or less, the amount of SiO ₂ supplied by the slag modifier is more suitable for the amount of CaO contained in the melt converter slag. Therefore, the amount of free CaO in the melt converter slag can be more preferably reduced.

In the present embodiment, the converter slag can be modified by a simple device configuration without adopting a complicated device configuration. The converter and the slag holding container may have conventionally known configurations. As the converter, any of a top-blown converter, an top-bottom blown converter, and a bottom-blown converter can be suitably applied. As the slag holding container, a so-called slag holding / transport container, which is a so-called slag pot, can be applied. Normally, converter slag is discharged to a slag pan, transported to a slag processing plant by being towed by a diesel vehicle or the like, and discharged by tilting the slag pan around a tilting axis at the slag processing plant. This slag pan is usually made of cast iron and has a shape of an upper end opening such as an elliptical shape, a perfect circular shape, and a rectangular shape. In addition, no refractory material is laid on the inner surface of the container. The slag holding container is not limited to the above-mentioned slag pan as long as it can hold the molten slag discharged from the converter and the slag modifier for a certain period of time. Further, the configuration of the device for spraying the slag modifier is not particularly limited, but as shown in FIG. 1, for example, (i) the slag modifier is stored and a container that can be internally pressurized with a gas is provided. Dispenser 3 configured to be able to cut out the slag reformer from the valve provided at the bottom, (ii) Feed pipe 4 connected to the downstream side of the dispenser 3 and carrying the cut out slag reformer in an air flow. , (Iii) Pressurize the nozzle 5 (Lance nozzle in one example), (iv) and the dispenser 3 which are connected to the end of the feed pipe 4 and spray the slag reformer onto the melt converter slag, and also slag reformer. A configuration including a gas supply control device 6 for supplying the gas required for transporting the material to the dispenser 3 can be adopted. The gas used for transporting the slag modifier can be, for example, nitrogen gas.

[Holding process]
The modified material mixed slag obtained as described above is in a state in which the slag modifier is suspended in the melt converter slag. Next, the modified material mixed slag is held in a slag holding container to obtain a modified material reaction slag. In the holding step, the melt converter slag in the modifier mixed slag and the slag modifier react sufficiently to reduce the amount of free CaO in the melt converter slag, and the modifier reaction with low basicity. It can be a slag.

The holding time in the holding step is not particularly limited. Here, since the slag modifier is a solid powder or granular material, the reaction form in which the element or molecule in the melt converter slag diffuses and reacts in the powder or granular material from the surface to the center of the slag modifier. Take. Therefore, in order to completely react the slag reformer with the melt converter slag, the holding time in the holding step is such that the elements or molecules in the melt converter slag diffuse into the powder particles of the slag reformer and react. It is preferable that the time is longer than that. That is, it is preferable to hold the modified material mixed slag in a slag holding container for 10 minutes or more. For holding the modified material mixed slag in the slag holding container, the slag holding container containing the modified material mixed slag may be allowed to stand in the same place, or the slag holding container containing the modified material mixed slag may be transported. Even so, it is sufficient that the state of holding the modified material mixed slag is maintained for a certain period of time. From the viewpoint of sufficiently advancing the reaction, the molten phase is present in the modified material mixed slag, and the slag holding capacity (the amount of the modified material mixed slag that can be held in the slag holding container and the amount of the modified material mixed slag that can be held in the slag holding container and the amount discharged in the steelmaking process). The longer the holding time is, the more preferable it is, as long as the balance with the amount of converter slag allows. The modified material mixed slag is more preferably held in a slag holding container for 20 minutes or longer, more preferably 30 minutes or longer.

Further, the holding temperature in the holding step is not particularly limited. According to this embodiment, since the melt converter slag immediately after steelmaking is mixed with the slag reformer, a sufficient amount of heat required to melt the slag reformer and react with the melt converter slag is secured. Has been done. Therefore, it is not necessary to heat the modified material mixed slag in the slag holding container. The holding temperature of the modified material mixed slag in the slag holding container in the holding step is preferably 950 ° C. or higher, and preferably 1250 ° C. or lower.

[Cooling / solidification process]
Next, the modified material reaction slag is discharged from the slag holding container, cooled and solidified to obtain solidified slag. The modified material reaction slag is discharged from the slag holding container to a slag discharge yard or the like, cooled and solidified. The flow at the time of discharge causes the modifier reaction slag to be agitated again. Therefore, even if the molten phase and the solid phase are mixed in the reforming material reaction slag at the timing of discharge, the molten phase and the solid phase are mixed again and the solid phase is suspended in the molten phase. (Macro uniform mixing state). The modified material reaction slag after discharge is cooled and solidified in the slag discharge yard or the like. The method for cooling the modifier reaction slag after discharge is not particularly limited. In order to improve the uniformity of the solidified slag produced by cooling and solidifying the reforming material reaction slag, it is preferable to adopt cooling with a slow cooling rate, but if it is necessary to shorten the cooling time, sprinkle water. Cooling may be performed.

[Crushing process]
Next, the solidified slag is crushed into crushed slag. For crushing, a known crusher such as a rod mill, a cone crusher, an impact crusher, or a jaw crusher can be used. The particle size of the crushed slag can be determined according to the purpose. In the present invention, the crushed slag preferably has a particle size of 40 mm or less. By setting the particle size of the crushed slag to 40 mm or less, the modified converter slag obtained after steam aging can be particularly preferably applied to the roadbed material. For example, when the solidified slag is crushed to obtain crushed slag of 40 mm or less, the procedure described below can be used. The solidified slag is roughly crushed by a heavy machine such as a shovel car and put into a vibrating sieve (primary sieve), and the solidified slag having a particle size exceeding 40 mm is collected on the sieve. The solidified slag on the sieve is put into a crusher, crushed (primary crushing), and placed on a vibrating sieve (secondary sieve) installed on the downstream side of the crusher. The surface of the secondary sieve (solidified slag having a particle size of more than 40 mm) is put into the crusher again and crushed (secondary crushing) until the size becomes 40 mm or less. Here, the bare metal and grain iron contained in the solidified slag may be removed by performing magnetic force sorting as necessary before and after the primary crushing of the solidified slag.

The particle size distribution may be adjusted by removing fine particles of crushed slag by sieving or the like, and then subjected to steam aging. For example, when the crushed slag contains 80% by volume or more of particles having a particle size of 10 mm or more and 40 mm or less, the particles of the crushed slag are treated with an appropriate filling density during steam aging, so that the water immersion expansion ratio is 1.0%. A modified converter slag that satisfies the following can be produced with a higher yield.

[Steam aging process]
The crushed slag is then steam aged to obtain modified converter slag. Steam aging can be performed according to a conventionally known method.

In addition, the manufacturing conditions other than the above-mentioned conditions can be applied by a conventional method.

The modified converter slag produced by the method for producing modified converter slag according to the present embodiment can be suitably applied to high-grade applications such as roadbed materials, aggregates for concrete, and stone raw materials. The modified converter slag according to the present embodiment can be particularly suitably applied to the production of granular materials for roadbed materials. In the present specification, the granular material for roadbed material refers to granular converter slag that has undergone at least a solidification step and a crushing step and can be applied as a raw material for roadbed material.

(Invention Example)
An experiment was conducted using the apparatus having the schematic configuration shown in FIG. First, hot metal was put into the upper bottom blowing type converter, and refining was performed while blowing oxygen from above. The blowing in the converter was completed at the blowing stop temperature of 1654 ° C. The basicity of the melt converter slag at the end of blowing was 3.61. After the blowing was completed, the furnace body was tilted to the steel ejection side and molten steel was ejected from the steel ejection holes. The phosphorus concentration in the molten steel after the steel was discharged from the converter was 0.011% by mass. Immediately after steel removal, the furnace body is tilted to the discharge side (reverse steel side), and the melt converter slag flows down from the converter into the slag holding container from a height of 5.5 m with respect to the bottom surface of the slag holding container. At the same time, a slag modifier having a composition of ingredients accepted into the dispenser of SiO ₂ : 96% (Al ₂ O ₃ : 3%, Fe ₂ O ₃ : 1%) and a particle size of 1.4 mm to 2.4 mm is added to nitrogen. It was conveyed by gas and sprayed from a lance nozzle onto the molten converter slag flowing down to obtain a reforming material mixed slag. About half of the molten converter slag in the converter was flowed down in 84 seconds, and 534 kg of the slag modifier was sprayed onto the molten converter slag in the flow. Immediately after the completion of the flow into the slag holding container, the basicity of the modified material mixed slag was 2.82. Next, the modified material mixed slag was held in the slag holding container for 15 minutes to obtain a modified material reaction slag. Next, the modified material reaction slag was discharged from the slag holding container into the slag discharge yard in a hot state, and sprinkled cooling was carried out to obtain solidified slag. The basicity of the solidified slag was 2.68, and the content of free CaO was 2.73% by mass. Table 1 shows the basicity of the solidified slag and the results of free CaO in each example of the invention. Further, FIG. 2 shows a graph in which the basicity of solidified slag is on the horizontal axis and the mass% of free CaO is on the vertical axis.
The solidified slag obtained above was roughly crushed with a shovel car, then subjected to a primary sieve to collect solidified slag having a particle size of more than 40 mm, and the top of the sieve was crushed with a tire type roll mill (primary crusher). The solidified slag crushed by the tire type roll mill was sieved by a secondary sieve, and the solidified slag still having a particle size of more than 40 mm was crushed by a gear type rod mill until the particle size became 40 mm or less. All of the slag under the sieve thus obtained was mixed to obtain crushed slag having a particle size of 40 mm or less. The obtained crushed slag was steam-aged to finally obtain a modified converter slag. Steam aging was carried out by stacking crushed slag, covering the outer surface with a sheet, and blowing steam into the piled slag. The layer thickness of the piled slag was about 3 m. After the start of steam blowing, the indicated value of the thermometer installed in the slag layer reached the vicinity of 100 ° C., and then the steam blowing was continued for 48 hours. After the steam blowing was stopped, it was air-cooled for about 48 hours.

(Comparative Example 1)
Refining was carried out in the same manner as in the invention example, and the blowing in the converter was completed at the blowing stop temperature of 1655 ° C. The basicity of the melt converter slag at the end of blowing was 5.00. A slag reforming material 3t having the same composition as that of Invention Example 1 was put into the converter from a hopper provided on the furnace immediately after the completion of the converter blowing, and the steelmaking was started. The slag reforming material is held in the converter slag on the molten steel for 6 minutes during steel ejection to form a modified material mixed slag, and after steelmaking, the converter is tilted to the slag side and discharged. It was slagged. The basicity of the modified material mixed slag was 2.61. The phosphorus concentration in the molten steel after the steel was discharged from the converter was 0.014% by mass, which was higher than that of the invention example. Although the basicity of the molten converter slag at the end of smelting was 5.00, which was higher than that of the invention example 3.61, the phosphorus concentration in the molten steel after the converter was ejected was higher than that of the invention example. It is probable that due to the introduction of the slag modifier into the converter, the basicity of the melt converter slag was lower than that at the end of smelting, and thus rephosphorus was generated during steelmaking. Subsequently, as in the example of the invention, the reformed material mixed slag was flowed down to the slag discharge yard in a hot state, and sprinkled cooling was carried out to obtain solidified slag. The slag basicity of the solidified slag after cooling was 2.76, and the content of free CaO was 2.77% by mass. The basicity of the solidified slag after cooling and the results of free CaO including other examples of Comparative Example 1 are shown in Table 1 and FIG.
The obtained solidified slag was pulverized and steam-aged under the same conditions as in the invention.

(Comparative Example 2)
Refining was carried out in the same manner as in the invention, and the blowing in the converter was completed at the blowing stop temperature of 1666 ° C. The basicity of the melt converter slag at the end of blowing was 3.32. Next, with the slag reforming material 1t having the same composition as that of Invention Example 1 placed in front of the slag holding container, the molten converter slag in the converter is poured down into the slag holding container to form the modified material mixed slag. did. The basicity of the modified material mixed slag was 3.28, which did not decrease much from the basicity of the melt converter slag. Next, the modified material mixed slag was held in the slag holding container for 15 minutes to obtain a modified material reaction slag. Subsequently, as in the example of the invention, the reforming material reaction slag was flowed down to the slag discharge yard in a hot state, and sprinkled cooling was carried out to obtain solidified slag. In addition, sintered unmelted slag modifier was observed at the bottom of the slag holding container after the modified material reaction slag was discharged. The basicity of the solidified slag after cooling was 3.8, and the content of free CaO was 8.10% by mass. The basicity of solidified slag and the results of free CaO including other examples of Comparative Example 2 are shown in Table 1 and FIG. The obtained solidified slag was subjected to the same pulverization and steam aging treatment as in the invention.

As shown in FIG. 2, in the example of the present invention, the converter slag having a high basicity is modified into a solidified slag having a basicity of 3.3 or less by a simple apparatus configuration without burdening the steelmaking process. We were able to.

An experiment in which refining was performed in the same manner as in the invention example, and the calculated basicity of the modified material mixed slag was changed by changing the basicity of the melt converter slag at the end of blowing and the amount of the modified material added. The water immersion expansion ratio of the obtained reforming converter slag was measured. The results are shown in FIG. The vertical axis of FIG. 3 shows the measured value of the water immersion expansion ratio of the reforming converter slag, and the horizontal axis shows the calculated basicity of the reforming material mixed slag when the reforming converter slag is reformed on the vertical axis. .. From FIG. 3, if the slag reforming material is sprayed on the melt converter slag so that the calculated value of the basicity of the modified material mixed slag is 3.3 or less, the water immersion expansion ratio can be increased by steam aging for 48 hours. It can be seen that it can be 0% or less.

1 converter 2 slag holding container 3 dispenser 4 feed piping 5 nozzle 6 gas supply control device

Claims (9)

While flowing the molten converter slag generated in the hot metal refining process in the converter from the converter into the slag holding container, the molten converter slag flowing down or the molten converter slag is the slag. A powdery granular slag modifier is sprayed onto the position where the slag is poured into the holding container, and the slag modifier is mixed with the melt converter slag to obtain a modifier mixed slag.
Next, the modified material mixed slag is held in the slag holding container to obtain a modified material reaction slag.
Next, the modified material reaction slag is discharged from the slag holding container, cooled and solidified to obtain solidified slag.
Next, the solidified slag was crushed to obtain crushed slag.
Next, a method for manufacturing a reforming converter slag, wherein the crushed slag is steam-aged to obtain a reforming converter slag. The method for producing modified converter slag according to claim 1, wherein the slag modifier contains powders and granules having a particle size of 4.5 mm or less. The method for producing modified converter slag according to claim 1 or 2, wherein the basicity of the molten converter slag before mixing the slag modifier is 3.6 or more and 4.2 or less. The method for producing a modified converter slag according to any one of claims 1 to 3, wherein the calculated value of the basicity of the modified material mixed slag is 3.3 or less. The method for manufacturing a modified converter slag according to any one of claims 1 to 4, wherein the melt converter slag flows down into the slag holding container from a height of 4 m or more with respect to the bottom surface of the slag holding container. .. The one according to any one of claims 1 to 5, wherein the discharge time required for the melting converter slag in the converter to flow down from the converter to the slag holding container is 30 seconds or more and 90 seconds or less. Method for manufacturing modified converter slag. The method for producing a modified converter slag according to any one of claims 1 to 6, wherein the slag modifying material contains 90% by mass or more of SiO ₂ . The method for producing a modified converter slag according to any one of claims 1 to 7, wherein the modified material mixed slag is held in the slag holding container for 10 minutes or more to obtain the modified material reaction slag. A method for producing a granular material for roadbed material using the reforming converter slag according to any one of claims 1 to 8.

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