JP2005220382A - Method for recycling steelmaking slag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently recycling slag generated when a pretreatment of molten iron is applied. <P>SOLUTION: In the method for recycling steelmaking slag, at least a part of the slag having ≥2 mass% phosphorus concentration generated when the pretreatment of the molten iron is applied, is supplied into a sintering machine as sintering raw material, or mixed with molten iron tapped from a blast furnace or supplied into dephosphorizing process in the molten iron. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to effective use of slag generated in a steel making process. More particularly, the present invention relates to the efficient recycling of slag with a high phosphorus concentration.

  In recent years, there has been an increasing need for high-purity steels with a very low content of impurities and non-metallic inclusions. In general, the hot metal produced in the blast furnace is refined in the converter, but it is difficult to achieve a sufficiently high purity and the efficiency is poor only by the converter refining. Therefore, the purity of the hot metal produced in the blast furnace is enhanced by refining treatment called hot metal pretreatment and secondary refining in addition to refining treatment in the converter. At present, the process of blast furnace → hot metal pretreatment → converter → secondary refining is widely adopted as a manufacturing process of high purity steel. In addition to the converter, secondary refining is adopted after refining treatment in an electric furnace.

As the hot metal preliminary treatment, various treatments such as dephosphorization, desiliconization, and desulfurization are performed. For example, dephosphorization is achieved by adding CaO, Na ₂ CO ₃ , CaF ₂ or the like as a desulfurizing agent. In the hot metal pretreatment such as dephosphorization and desiliconization, slag such as dephosphorization slag and desiliconization slag is generated. The cost required for slag treatment also affects the price competitiveness of the steel produced. For this reason, various techniques have been proposed so far for efficient hot metal pretreatment, reduction of slag generation amount, and the like.

For example, a method for recycling converter slag has been proposed. Specifically, a method using converter slag as a dephosphorization flux (see Patent Document 1), a method using converter slag as a blast furnace raw material or a sintered raw material (see Patent Document 2), and the like have been proposed. In Patent Document 1, bauxite, iron ore, manganese ore and the like are added, and the basicity, Al ₂ O ₃ concentration, T.I. By using the converter slag in which the Fe concentration and the MnO ₂ concentration are controlled as a dephosphorization flux, the cost of the dephosphorization process is reduced. In Patent Document 2, after the converter slag is mixed for 40 to 60 charges and then recycled as a sintering raw material or a blast furnace raw material, variations in the components of the recycled converter slag are suppressed.

In addition, regarding recycling of dephosphorization slag, a method has been proposed in which part of the slag used last time remains in the container and is used again for dephosphorization treatment to reduce the amount of slag produced (Patent Document). 3).
Japanese Patent No. 3321536 JP-A-6-240316 JP 2002-256325 A

  As described above, various techniques have been proposed for slag generated during hot metal pretreatment in a steelmaking process. However, the demand for the development of an excellent hot metal pretreatment method is still strong.

  Accordingly, an object of the present invention is to provide a method for effectively recycling slag generated during hot metal pretreatment.

The present invention
(1) At least a part of the slag having a phosphorus concentration of 2% by mass or more generated during hot metal pretreatment is supplied as a sintering raw material to a sintering machine, mixed with hot metal discharged from a blast furnace, or hot metal dephosphorization A method for recycling steelmaking slag, characterized by being supplied to a process,
(2) The method for recycling steelmaking slag, wherein the slag having a phosphorus concentration of 2% by mass or more is dephosphorization slag generated during dephosphorization treatment,
It is.

  By using the method of the present invention, the amount of slag discharged out of the system is reduced. In addition, the usefulness of slag discharged outside the system as a resource increases.

  The present inventor paid attention to the concentration of phosphorus contained in slag as a means for reducing the amount of slag and enhancing the usefulness of slag discharged outside the system as a resource.

The phosphoric acid concentration (P ₂ O ₅ ) in the slag can be used as an index for measuring the effectiveness of the flux input for dephosphorization. In general, the higher the phosphoric acid concentration (P ₂ O ₅ ) in the slag, the more effectively the slag was effectively utilized for dephosphorization. FIG. 1 is a graph showing the relationship between the phosphorus concentration (P ₂ O ₅ ) in the slag and the phosphorus concentration [P] in the hot metal when the hot metal is dephosphorized. In the figure, “SV” indicates a slag volume charged per ton of hot metal. The basicity ([CaO] / [SiO ₂ ]) is constant.

In the present application, the “phosphorus concentration in the slag” means the concentration of phosphorus when the contained phosphorus is converted to P ₂ O ₅ with respect to the total mass of the slag, and the “phosphorus concentration in the molten iron” It means phosphorus concentration with respect to the total mass of hot metal. In the present application, “(P ₂ O ₅ )” means the former unless otherwise specified, and “[P]” means the latter unless otherwise specified. In the present application, “%” indicates “% by mass” unless otherwise specified.

The phosphorus concentration (P ₂ O ₅ ) in the slag is theoretically the mass balance given the total phosphorus mass contained in the system, the phosphorus concentration [P] remaining in the hot metal and the dephosphorization slag amount. Automatically calculated from For example, if the phosphorus concentration [P] remaining in the hot metal decreases, the phosphorus concentration (P ₂ O ₅ ) contained in the dephosphorization slag increases. Moreover, if the amount of dephosphorization slag used is small, the phosphorus concentration (P ₂ O ₅ ) contained in the dephosphorization slag increases. Therefore, when the phosphorus concentration (P ₂ O ₅ ) is increased, the phosphorus concentration [P] remaining in the hot metal may be decreased or the amount of slag used may be decreased.

  However, there is a limit in reducing the phosphorus concentration [P] remaining in the hot metal. Moreover, when the amount of lime is reduced in order to reduce the amount of slag, the basicity of the slag is lowered and the dephosphorization ability of the slag is lowered. Moreover, when dephosphorizing in a converter, the contact between oxygen and hot metal increases due to a decrease in the amount of slag, preferentially decarburization reaction occurs, and dephosphorization efficiency is reduced.

  Another index for dephosphorizing slag is phosphorus distribution ratio “(P) / [P]”. The phosphorus distribution ratio “(P) / [P]” is the phosphorus concentration (P) in the slag with respect to the phosphorus concentration [P] remaining in the hot metal. A higher phosphorus distribution ratio indicates higher slag dephosphorization ability. Essentially, the phosphorus distribution ratio is independent of the effect of the phosphorus concentration [P] remaining in the hot metal. However, in reality, the phosphorus distribution ratio varies depending on the phosphorus concentration [P] remaining in the hot metal.

  FIG. 2 is a graph showing the relationship between the phosphorus concentration [P] remaining in the hot metal and the phosphorus distribution ratio “(P) / [P]”. In FIG. 2, as the phosphorus concentration [P] increases, the phosphorus distribution ratio “(P) / [P]” decreases accordingly. That is, when the total phosphorus mass contained in the system is constant, the phosphorus distribution ratio is greatly influenced by the phosphorus concentration [P] remaining in the hot metal. This fact indicates that in the high [P] region, the dephosphorization ability of the slag is not sufficiently extracted.

  One of the reasons why slag dephosphorization is not fully utilized is thought to depend on phosphorus mass balance constraints. The present invention relaxes the mass balance restriction to draw out the dephosphorization ability of slag, thereby reducing the dephosphorization flux amount and reducing the slag amount discharged out of the system.

  The present invention is characterized in that, by recycling slag having a high phosphorus concentration prior to the dephosphorization step, the phosphorus concentration in the hot metal is increased, and the dephosphorization ability of the slag is sufficiently extracted. Improvement of the phosphorus concentration in the dephosphorized slag is easier as the phosphorus concentration contained in the hot metal before dephosphorization is higher.

This will be described with reference to FIG. The four lines labeled “SV = 30 kg / t” and “SV = 40 kg / t” indicate the phosphorus concentration [P] in the hot metal and the phosphorus concentration in the slag (P ₂ ) when the SV is constant. O ₅₎ is a graph showing the relationship between. Of the four lines, the solid line indicates the case where the phosphorus concentration contained in the hot metal to be dephosphorized is 0.10%, and the broken line is the case where the phosphorus concentration contained in the hot metal to be dephosphorized is 0. It shows the case of 14%. When the phosphorus concentration [P] in the hot metal is reduced to 0.02% by dephosphorization of the hot metal having a phosphorus concentration of 0.10%, the phosphorus concentration (P ₂ O ₅ ) in the slag is 4.5%. (Point A). In this case, the change in the phosphorus concentration in the hot metal is 0.08%. On the other hand, in order to make the phosphorus concentration (P ₂ O ₅ ) in the slag 4.5% using the same slag for the hot metal having a phosphorus concentration of 0.14%, the phosphorus concentration [P] in the hot metal is What is necessary is just to reduce to about 0.06% (point B). In this case, the change in the phosphorus concentration in the hot metal is also 0.08%.

  In these dephosphorization reactions, the change value of the phosphorus concentration in the molten iron is the same, and the change value of the phosphorus concentration in the slag is also the same. However, the apparent dephosphorization capacity required for slag is different. That is, when reducing 0.10% to 0.02%, higher dephosphorization ability is required than when reducing 0.14% to 0.06%. Considering the case of further reducing the phosphorus concentration in the hot metal, this difference is more obvious. Further dephosphorization of the hot metal having a phosphorus concentration of 0.02% in the hot metal results in a significant reduction in dephosphorization efficiency due to the influence of the rate of movement of phosphorus in the hot metal. On the other hand, it is relatively easy to dephosphorize hot metal having a phosphorus concentration of 0.06% in the hot metal. That is, when the initial phosphorus concentration in the hot metal is high, the dephosphorization ability of the slag can be effectively utilized.

In the present invention, from such a viewpoint, slag having a high phosphorus concentration, such as dephosphorization slag, is supplied to the dephosphorization step or a step before the dephosphorization step, and then rephosphorized in the hot metal. As a result, the phosphorus concentration in the hot metal during the dephosphorization process is increased, the dephosphorization slag's original dephosphorization ability is fully exhibited, and a slag having a high phosphorus concentration (P ₂ O ₅ ) is obtained. That is, the present invention supplies at least a part of the slag having a phosphorus concentration of 2% by mass or more generated during the hot metal pretreatment to be mixed with the hot metal discharged from a blast furnace, as a raw material for sintering, or This is a steelmaking slag recycling method that is supplied to the hot metal dephosphorization process.

  The phosphorus concentration of the slag reused as a sintering raw material or hot metal pretreatment slag is not particularly limited, but in order to effectively increase the phosphorus concentration in the hot metal by recovery, And 2% by mass or more, preferably 3% by mass or more. The origin of the slag is not particularly limited as long as the above-described phosphorus concentration is satisfied. Preferably, dephosphorized slag generated during the dephosphorization treatment of hot metal is used. Dephosphorization slag is advantageous in increasing the phosphorus concentration of molten iron because of its high phosphorus concentration. The “dephosphorization process” means a process performed mainly for removing phosphorus from pig iron.

  The slag having a phosphorus concentration of 2% by mass or more may be supplied to the sintering machine as a sintering raw material, may be mixed with the hot metal discharged from the blast furnace, or the hot metal supplied to the dephosphorization process. It may be mixed. Here, “mixing” means that hot metal and slag are present in the same container and are mixed. If necessary, it may be forcibly stirred.

  The method and conditions for supplying the slag to the sintering raw material and the sintering machine may be appropriately determined according to a conventionally known method and the apparatus actually used. For example, Japanese Patent Application Laid-Open No. 59-123706 discloses a method of using recovered slag after drying, sieving, magnetic separation, and crushing, and then using it in a sintering machine or a blast furnace. Although the method disclosed in Japanese Patent Application Laid-Open No. 59-123706 is described with respect to recycling of desulfurized slag, recycling of dephosphorized slag can be achieved by a similar method. Japanese Patent Application Laid-Open No. 2003-138305 discloses a method of recycling to either a sintering machine or a blast furnace based on components and / or particle sizes. It goes without saying that known techniques other than these can be referred to.

  As described above, the supply point of slag having a phosphorus concentration of 2 mass% or more may be a sintering machine, hot metal discharged from a blast furnace, or hot metal supplied to the dephosphorization step. It may be. Which process the slag is supplied to may be determined according to the steel type to be manufactured. For example, when extremely low phosphorous steel is included in the steel grade to be produced, slag is not supplied to the sintering machine, but is mixed with hot metal discharged from the blast furnace or supplied to the hot metal dephosphorization process. It is advisable to adopt a form of mixing with hot metal to be dephosphorized. If slag with a high phosphorus concentration is supplied to the sintering machine, it affects all the hot metal produced. For this reason, in order to manufacture an ultra-low phosphorus steel, the phosphorus concentration of the hot metal having a high phosphorus concentration must be made very low, which increases the effort in the refining process. If the slag is supplied to the hot metal discharged from the blast furnace, or if the slag is supplied to the hot metal dephosphorization process, the addition of slag can be controlled for each heat. If not necessary, it is possible to select not to add slag. That is, by adopting a form in which the hot metal discharged from the blast furnace and the slag are mixed, the degree of freedom in manufacturing is improved and process optimization is facilitated.

  Hereinafter, the present invention will be described using preferred embodiments. However, the technical scope of the present invention is not limited to the following embodiments. For example, improvements such as no desulfurization treatment of hot metal and no desiliconization treatment may be added. Further, when supplying the dephosphorized slag to the sintering machine, the same effect can be obtained by increasing the phosphorus concentration [P] in the hot metal.

  FIG. 4 is a block diagram for explaining the hot metal treatment process. In the figure, the solid line indicates the flow of pig iron, and the broken line indicates the flow of slag.

  Blast furnace raw materials such as iron ore, sintered ore, limestone, and coke are supplied to the blast furnace, and a smelting process is performed (S101). The hot metal discharged from the blast furnace is supplied to the torpedo car. The torpedo car is charged with dephosphorization slag as will be described later. The hot metal supplied to the torpedo car is desiliconized by injection desiliconization (S102). The desiliconized hot metal is further desulfurized by KR desulfurization treatment (S103). Thereafter, the hot metal is charged into the converter, and dephosphorized by dephosphorization blowing in the converter (S104). The dephosphorized hot metal is discharged from the converter and then charged into the converter again, and decarburized and blown in the converter (S105).

  A part of the dephosphorization slag generated by the dephosphorization blowing is charged into an empty torpedo car and moved to the blast furnace outlet (S106). The hot metal discharged from the blast furnace is supplied to the torpedo car in which the dephosphorization slag is charged. When a slag is conveyed using a torpedo car, the slag can be efficiently conveyed by effectively using existing facilities. The slag that is not charged into the torpedo car is discharged and used as a roadbed material (S107). A part of the dephosphorization slag generated by the dephosphorization blowing may be supplied to the hot metal dephosphorization process to increase the phosphorus concentration of the hot metal to be dephosphorized (S108).

  An embodiment in the case where the phosphorus concentration of hot metal is reduced from 0.100% to 0.035% by using a process of mixing a part of dephosphorization slag with hot metal discharged from a blast furnace will be described. However, numerical values such as phosphorus concentration and slag generation amount used in the following description are merely numerical values that can be used in one embodiment.

  The amount of phosphorus contained in the hot metal discharged from the blast furnace is 1.0 kg per ton of hot metal. The amount of phosphorus contained in the hot metal after the dephosphorization treatment is 0.35 kg per ton of hot metal. Therefore, the amount of phosphorus preferably discharged out of the system is approximately 0.65 kg / t. Here, it is assumed that the amount of slag produced in converter dephosphorization blowing is 40 kg for 1 ton of hot metal.

  FIG. 5 is a phosphorus balance diagram in one embodiment of the present invention.

From the blast furnace, pig iron with a phosphorus concentration of 0.10% is extracted and supplied to the torpedo car. The torpedo car is preliminarily charged with dephosphorization slag having a phosphorus concentration (P ₂ O ₅ ) of 6.0%, and pig iron is supplied thereto. Pig iron is desiliconized and desulfurized in a torpedo car. The phosphorus concentration [P] in the hot metal after the desiliconization treatment is increased to 0.14% by recovery from slag having a high phosphorus concentration. The phosphorus content per ton of hot metal is 1.40 kg.

Hot metal having a phosphorus concentration [P] of 0.14% is charged into the converter, and the hot metal is dephosphorized using a dephosphorizing agent until the phosphorus concentration [P] in the hot metal reaches 0.035%. In this case, the hot metal after the dephosphorization treatment contains 0.35 kg of phosphorus per ton of hot metal. If it does so, it will be the calculation in which 1.05 kg of phosphorus is contained in slag per ton of hot metal. As described above, the amount of slag produced per ton of hot metal is 40 kg. Then, the phosphorus concentration (P ₂ O ₅ ) in the dephosphorized slag is calculated from the following formula.

  That is, the phosphorus concentration in the dephosphorized slag is 6.0% by mass.

  Of this dephosphorization slag 40 kg / t, 15.3 kg / t is charged into an empty torpedo car and conveyed to a blast furnace. The remaining 24.7 kg / t of dephosphorized slag is discharged out of the system. The torpedo car charged with dephosphorization slag is charged with hot metal discharged from the blast furnace. The hot metal in which the phosphorus concentration is reduced to 0.035% is conveyed to the decarburization process. At this time, the mass of phosphorus atoms discharged out of the system per ton of hot metal can be obtained from the following formula.

  That is, the mass of phosphorus atoms discharged out of the system per ton of hot metal is 0.65 kg.

  The amount of phosphorus atoms contained in the dephosphorized slag to be recycled is 0.40 kg per ton of hot metal from the following formula, assuming that the phosphorus in all the dephosphorized slag is reduced to hot metal.

  That is, 0.04% of phosphorus is recovered from the hot metal, which corresponds to the above-described rate of increase in phosphorus concentration (0.10% → 0.14%) in the hot metal in the hot metal pretreatment. With such a steady flow, dephosphorization slag can be recycled.

  Here, in order to show the effect of this invention, it illustrates about embodiment which performs hot metal preliminary | backup process on the same conditions except not recycling slag.

  FIG. 6 is a balance diagram of phosphorus in an embodiment in which slag is not recycled. Like the embodiment shown in FIG. 5, pig iron with a phosphorus concentration of 0.10% is extracted from the blast furnace and supplied to the torpedo car. Pig iron is desiliconized and desulfurized in a torpedo car. The phosphorus concentration [P] in the hot metal after the silicon removal treatment is 0.10%, which is the same as that in the blast furnace. The phosphorus content per ton of hot metal is 1.00 kg.

Similar to the embodiment of FIG. 5, when the phosphorus concentration [P] of hot metal is reduced to 0.035%, the discharge slag has an amount of phosphorus equivalent to 0.065%, that is, 0.000 per ton of hot metal. It needs to contain 65 kg of phosphorus atoms. If the amount of dephosphorized slag produced is also 40 kg / t, the phosphorus concentration (P ₂ O ₅ ) in the dephosphorized slag is 3.7% from the following formula.

  The hot metal in which the phosphorus concentration is reduced to 0.035% is conveyed to the decarburization process. At this time, the mass of phosphorus atoms discharged out of the system per ton of hot metal can be obtained from the following formula.

  That is, the mass of phosphorus atoms discharged out of the system per ton of hot metal is 0.65 kg as in the embodiment of FIG.

  From the comparison between FIG. 5 and FIG. 6, it can be seen that a reduction in the amount of dephosphorization slag discharged out of the system is achieved by applying the method of the present invention. Specifically, in the embodiment of FIG. 6, the amount of dephosphorization slag discharged outside the system is 40.0 kg / t, whereas in the embodiment of FIG. The amount of phosphorus slag has decreased to 24.7 kg / t.

By applying the method of the present invention, the phosphorus concentration (P ₂ O ₅ ) in the slag discharged out of the system is improved. Specifically, in the embodiment of FIG. 6, the phosphorus concentration (P ₂ O ₅ ) in the slag discharged out of the system is 3.7%, whereas in the embodiment of FIG. The phosphorus concentration (P ₂ O ₅ ) in the slag discharged to the outside has increased to 6.0%.

In addition, the utility of the discharged slag as a resource can be increased by applying the method of the present invention. Specifically, the dephosphorized slag recycled by applying the present invention is discharged out of the system as desiliconized slag. The basicity of the slag can be controlled in a range suitable for slag resource recycling, for example, (CaO) / (SiO ₂ ) = 1.0 to 1.8. Thereby, the value as a resource of discharged slag increases. The usage of the discharged slag is not particularly limited. For example, it can be reused as a roadbed material. Furthermore, when the dephosphorization slag is sufficiently mixed with the molten iron again, the reduction of FeO and the transition to the molten iron of the granular iron proceed, and it is possible to contribute to the improvement of the yield.

In addition, (P) / [P] which shows the dephosphorization ability of slag changes as follows between the embodiment of FIG. 5 and the embodiment of FIG.
-Without slag recycling: 3.7% x (62/142) /0.035=46
-With slag recycling: 6.0% x (62/142) /0.035=75
Thus, by recycling slag having a high phosphorus concentration, the dephosphorization ability inherent to the dephosphorization slag can be utilized more effectively.

  Conditions such as the sintering process, blast furnace, desiliconization process, desulfurization process, dephosphorization process, decarburization process, and transportation by a torpedo car are not particularly described, but the knowledge already obtained may be referred to as appropriate. For example, desiliconization is performed by introducing iron oxide such as mill scale or sintered ore into the hot metal in a blast furnace casting bed or transfer container. The dephosphorization is performed by blowing a dephosphorizing agent mixed with lime, iron oxide, meteorite, etc. into the molten iron together with gas, transferring the phosphorus in the molten iron to the slag phase, and then discharging the slag. By selecting the dephosphorizing agent and the processing conditions, it is possible to perform the desulfurization treatment together with the dephosphorization.

The molten iron during dephosphorization process, a phosphorus concentration in the slag (P 2 _{O 5),} is a graph showing the relationship between phosphorus concentration in the molten iron [P]. It is a graph which shows the relationship between phosphorus concentration [P] which remains in hot metal, and phosphorus distribution ratio "(P) / [P]". Is a graph showing the relationship between the phosphorus concentration in the molten iron [P] and the phosphorus concentration in the slag (P 2 _{O 5).} It is a block diagram for demonstrating the hot metal processing process. It is a balance diagram of phosphorus in one embodiment of the present invention. It is a balance diagram of phosphorus in embodiment which does not recycle slag.

Claims (2)

  At least a part of the slag with a phosphorus concentration of 2% by mass or more generated during hot metal pretreatment is supplied to the sintering machine as a sintering raw material, mixed with hot metal discharged from a blast furnace, or supplied to the hot metal dephosphorization process A method for recycling steelmaking slag, characterized by:   The method for recycling steelmaking slag, wherein the slag having a phosphorus concentration of 2% by mass or more is dephosphorization slag generated during dephosphorization treatment.

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