JP7364899B2 - Melting method of cold iron source with slag reduction - Google Patents

Description

The present invention relates to a method for melting cold iron sources with slag reduction.

Regarding the amount of steelmaking slag discharged, improvements in hot metal pretreatment are beginning to reduce the amount of discharged slag. On the other hand, regarding the use of the discharged steelmaking slag, since steelmaking slag has a high basicity, there are problems with its utilization such as expansion due to water immersion and elution with high pH water. Measures such as steam aging are being taken to counter this.

On the other hand, technology has been developed to reduce and reform discharged slag to convert it into slag equivalent to blast furnace slag, to expand its uses, and at the same time to recover valuable Fe and P contained in the slag. At this time, in order to minimize the required energy, it is effective to directly reduce the high-temperature steelmaking slag without cooling and solidifying it, and various methods have been devised for this purpose.

Patent Document 1 discloses that hot steelmaking slag is flowed from a slag supply container (slag holding furnace) onto molten iron housed in an electric furnace, a reducing agent is supplied to the molten slag layer, and the molten iron and the molten slag layer are A steelmaking slag reduction treatment method is disclosed, which continues the reduction treatment of hot steelmaking slag in a non-oxidizing atmosphere while heating the hot steelmaking slag by applying electricity and intermittently discharging the molten slag in the molten slag layer or the molten iron. There is. Reduction treatment of steelmaking slag is carried out to reform the steelmaking slag into materials that can be used for various purposes such as cement raw materials, earthwork materials, ceramic products, etc., and also to remove valuable elements such as Mn and P from the steelmaking slag into molten iron. After that, Fe and Mn are recycled to the steel manufacturing process, and P is recovered as an oxide by subjecting the molten iron to oxidation treatment, and the purpose is to use it as a phosphate fertilizer or a phosphate raw material. In the structure of Patent Document 1, molten slag is not directly charged into an electric furnace, but is temporarily held in a slag holding furnace placed adjacent to the electric furnace, and a molten slag layer is placed on the molten iron layer in the electric furnace as a buffer zone. After the molten slag is formed, molten slag is gradually injected while adjusting the injection amount, which poses a problem in that the scale of the equipment increases.

The invention described in Patent Document 2 is an electric furnace for forming a molten iron layer and a molten slag layer, which has a shallow bottom section at the bottom of the furnace, and the molten slag is introduced from a conveying container toward the shallow bottom section. do. By continuously reducing and melting and reforming the molten slag in an electric furnace, valuable substances (valuable elements such as Fe and P) in the molten slag are recovered to the molten iron layer that is the lower layer of the molten slag layer. The recovered high-phosphorus molten iron is subjected to dephosphorization treatment to oxidize P in the molten iron and transfer it to the slag, thereby separating the high-phosphorus molten iron into high-phosphate slag and molten iron. High phosphate slag can be recycled as phosphate fertilizer, phosphate raw material, etc. Additionally, molten iron is recycled into the steelmaking process and fed into a converter or the like. Since the molten slag is injected into the shallow bottom part, it is possible to prevent the molten slag immediately after being injected from being violently mixed with the molten iron layer in the electric furnace, and to prevent the formation of forming. On the other hand, as a result of providing the shallow bottom portion, there is a problem that the internal volume of the furnace is reduced.

In an electric furnace, a source of cold iron, such as scrap, is melted to form molten steel. When attempting to perform secondary refining and continuous casting of molten steel melted in an electric furnace together with the molten steel melted in a converter at a converter factory, the heat size of an electric furnace is usually smaller than that of a converter. However, since the ladle capacity does not match the existing secondary refining and continuous casting machines, and the timing cannot be matched well, it is difficult to install it alongside a converter. In addition, electric furnace steel has high [N] and tramp elements, and there are steel types that can only be produced using converter steel.

Patent Document 3 discloses an arc system that includes a melting chamber and a shaft-shaped preheating chamber directly connected to the upper part of the melting chamber, and introduces exhaust gas generated in the melting chamber into the preheating chamber to preheat a cold iron source in the preheating chamber. A method of operating an arc furnace using a furnace is disclosed. The arc furnace is operated with the carbon concentration of the molten metal discharged from the arc furnace being 1 mass% or more. By setting the carbon concentration of the molten metal to 1 mass% or more, hot metal (molten metal) produced using an arc furnace can be mixed with blast furnace hot metal and incorporated into a part of the process flow by the blast furnace-converter method.

International publication WO2014/003123 International publication WO2018/110171 Japanese Patent Application Publication No. 2010-265485

The present invention reduces steelmaking slag in an electric furnace containing molten iron, reforming the steelmaking slag into a material that can be used for various purposes such as cement raw materials, earthwork materials, and ceramic products. When reducing and recovering valuable elements such as Mn and P in molten iron, and then recycling the molten iron from which Fe and Mn have been recovered to the steel manufacturing process, without using large-scale equipment as described in Patent Document 1, A method for melting a cold iron source accompanied by slag reduction, which does not require the provision of a shallow bottom part as described in Patent Document 2 in the shape of the bottom of an electric furnace, and which can produce molten iron that can be easily recycled into the converter process. The purpose is to provide. Furthermore, the P produced by reducing steelmaking slag is also intended to be recovered as an oxide by oxidizing molten iron and used as a phosphate fertilizer or a phosphoric acid raw material.

That is, the gist of the present invention is as follows.
[1] A cold iron source is charged into an electric furnace containing seed hot water, molten steelmaking slag is charged from above the pile of cold iron source, and cold iron is heated by direct current or alternating current arc heating. After partially melting the slag, a carbonaceous material is introduced into the molten pool as a reducing agent, and a slag modifier containing at least one of SiO ₂ and Al ₂ O ₃ is introduced to reduce and dissolve the slag. A method for melting a cold iron source accompanied by slag reduction, characterized in that the molten iron is carburized, the molten iron is discharged from a tap hole leaving a seed metal, and the reduced slag is discharged from a slag discharge port.
[2] The steelmaking slag is charged through an opening formed by moving the furnace lid of the electric furnace or opening the slag inlet of the furnace lid, and the steelmaking slag is charged into a slag pot containing the steelmaking slag. In this case, the steelmaking slag to be charged is the solidified steelmaking slag that has been further deposited on the pile of the cold iron source or on the pile of the cold iron source. The method for melting a cold iron source accompanied by slag reduction according to [1], characterized in that the melting method is performed by charging the source above the slag.
[3] The cooling with slag reduction described in [1] or [2], characterized in that the reducing agent and the slag modifier are supplied through a raw material input pipe provided on the furnace lid while being arc heated. How to dissolve iron sources.
[4] During slag reduction, a lance is inserted into the slag layer, and stirring gas is blown through the lance to stir the slag. After energization, the molten iron layer is blown from the bottom or gas is stirred from the lance. The method for melting a cold iron source accompanied by slag reduction according to any one of [1] to [3].
[5] Any one of [1] to [4], characterized in that, together with the reducing agent and the slag modifier, one or both of waste containing phosphoric acid and high-phosphate iron ore is input through a raw material input pipe. A method for melting a cold iron source accompanied by slag reduction according to item 1.

The present invention reduces steelmaking slag in an electric furnace containing molten iron, reforming the steelmaking slag into a material that can be used for various purposes such as cement raw materials, earthwork materials, and ceramic products. Valuable elements such as Fe and P are reduced and recovered in molten iron, and then when the molten iron with recovered Fe content is recycled to the steelmaking process, a cold iron source is charged into an electric furnace containing a seed bath, By charging molten steelmaking slag or high-temperature solidified steelmaking slag from above the pile of cold iron sources, processing can be carried out without increasing the scale of the equipment or reducing the internal volume of the furnace. becomes.

FIG. 3 is a diagram showing a situation in which steelmaking slag is charged from above the deposited portion of the cold iron source in the cold iron source melting method of the present invention. It is a figure which shows the addition situation of a carbonaceous material and a slag modifier in the melting|melting method of the cold iron source of this invention. FIG. 3 is a diagram showing the state of stirring of a molten iron layer in the cold iron source melting method of the present invention. FIG. 3 is a diagram showing a situation in which steelmaking slag is charged from above the deposited portion of the cold iron source in the cold iron source melting method of the present invention. FIG. 3 is a diagram showing the addition status of carbonaceous material and slag modifier and the stirring status of the slag layer in the method for melting a cold iron source of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
First, an outline of a method for melting a cold iron source accompanied by slag reduction using the electric furnace of the present invention will be explained.

In the pig iron making process, hot metal is produced using a blast furnace, and in the steel making process, pig iron is refined into steel using a converter or the like. This steelmaking process consists of two steps: desulfurization, dephosphorization, and decarburization, which remove sulfur, phosphorus, carbon, etc. from the molten metal, and composition adjustment by removing gases such as hydrogen and sulfur remaining in the molten steel. It includes a subsequent refining process and a casting process in which molten steel is cast using a continuous casting machine.

In the steelmaking process, dephosphorization and decarburization are mainly performed in converters. Inside the converter, hot metal is refined using a flux whose main component is calcium oxide. At this time, C, Si, P, Mn, etc. in the hot metal are oxidized by the oxygen blown into the converter, and the oxides combine with calcium oxide to become slag. Furthermore, in each of the desulfurization, dephosphorization, and decarburization steps, slags having different components (desulfurization slag, dephosphorization slag, and decarburization slag) are generated. The slag remaining in the ladle after continuous casting is called ladle slag.

In the present invention, steelmaking slag is a general term for slag generated in a steelmaking process, and the steelmaking slag is a concept that includes desulfurization slag, dephosphorization slag, decarburization slag, and ladle slag. Further, steelmaking slag in a high temperature molten state is referred to as molten slag, and similarly, desulfurization slag, decarburization slag, and dephosphorization slag in molten state are respectively referred to as molten desulfurization slag, molten dephosphorization slag, and molten decarburization slag.

In the slag treatment process, the steelmaking slag produced in the above steelmaking process is transported in its molten state from the converter to the electric furnace, and the steelmaking slag charged into the electric furnace is continuously reduced, melted, and reformed. , Valuables (valuable elements such as Fe and P) in the molten slag are recovered to the molten iron layer which is the lower layer of the molten slag layer.

Conventionally, a molten iron bath is formed in advance in an electric furnace, molten steelmaking slag is added to the molten iron bath, and carbonaceous material is introduced into the molten pool as a reducing agent to perform slag reduction melting and reforming treatment. was. At this time, it is important to suppress slag forming when slag is introduced. For this reason, as mentioned above, in Patent Document 1, a reduced molten slag layer is formed as a buffer zone on a molten iron layer in an electric furnace, and then molten slag is gradually injected while adjusting the injection amount. means are adopted. Furthermore, Patent Document 2 is characterized in that the electric furnace has a shallow bottom section, and molten slag is introduced from a conveying container toward the shallow bottom section.

By the way, in an electric furnace, a cold iron source such as iron scrap, pig iron, reduced iron, etc. is charged into the electric furnace and melted by arc heating to form molten iron. In order to promote dissolution of the cold iron source, a seed bath is formed in the electric furnace, and by increasing the carbon concentration in the seed bath and the melted molten iron, the melting of the cold iron source is promoted. In the early stage of melting after the cold iron source is charged into the electric furnace, seed hot water is stored at the bottom of the electric furnace, and the cold iron source is piled up to form a deposited area.

In the present invention, when a cold iron source is charged into an electric furnace and a cold iron source pile is formed, molten steelmaking slag is poured over the cold iron source pile. The idea was to suppress the stirring of slag and molten iron, and as a result, suppress the forming of slag.
As shown in FIGS. 1 and 4, the cold iron source 23 is charged into the electric furnace 1 containing the seed water 28, and the steelmaking slag, which is in a molten state or solidified at high temperature, is poured from above the deposited part of the cold iron source 23. After partially melting the cold iron source 23 by direct current or alternating current arc heating, slag forming is performed by introducing carbon material 26 as a reducing agent into the molten pool, as shown in FIGS. 2 and 5. It was found that the reductive melting modification of the slag proceeded satisfactorily. At this time, in the electric furnace, a slag modifier 27 is added to adjust the basicity of the slag, reduce oxides such as Fe and P in the molten slag, and convert granulated iron (iron content) from the slag. separation progresses. If the deposited thickness of the cold iron source 23 formed immediately below the slag is not sufficient, solidified slag 25 is introduced, and the solidified slag 25 is deposited on the cold iron source 23 deposited portion to form steelmaking slag. It may be charged onto the solidified slag 25 and the unmelted cold iron source 23 that are piled up (see FIG. 4).

As the cold iron source charged into the electric furnace, iron scrap, shaped pig iron, reduced iron, etc. can be used. It is preferable that the electric furnace is provided with a preheating furnace for preheating the cold iron source, and the cold iron source preheated in the preheating furnace is charged into the electric furnace. As shown in FIG. 4, the preheating furnace is equipped with a shaft-type preheating furnace 7 directly connected to the upper part of the electric furnace, and exhaust gas generated in the electric furnace is introduced into the preheating furnace to cool the cold iron in the preheating furnace 7 The source can be preheated.

As the steelmaking slag charged into the electric furnace, steelmaking slag in a molten state or steelmaking slag solidified at a high temperature can be used.

Coke, coal, etc. can be used as the carbon material used as the reducing agent and carburizer. By adding the carbonaceous material, the reduction reaction of oxides such as Fe and P in the slag layer proceeds, and the molten iron layer is carburized to increase the carbon concentration of the molten iron. When the carbon concentration of the molten iron is 1% by mass or more, the molten iron can be used as it is, or after dephosphorizing the molten iron, it can be mixed with blast furnace hot metal and used as the main raw material charged in the converter.

The steelmaking slag charged into the electric furnace is a high basicity slag with high basicity (CaO/SiO ₂ mass ratio), and is difficult to melt as it is because of its high melting point. Furthermore, in order to reduce the P component in the slag and transfer it into the molten iron layer, it is preferable that the basicity of the slag is low. Therefore, in the present invention, a slag modifier containing at least one of SiO ₂ and Al ₂ O ₃ is further introduced into the electric furnace. By mixing the steelmaking slag and the slag modifier, the basicity of the slag decreases, the Al ₂ O ₃ concentration increases, and as a result, the melting point of the slag after mixing can be lowered, which improves the dissolution of the steelmaking slag. It becomes possible to proceed with slag reduction quickly. It is preferable that the slag component after addition of the slag modifier has a basicity of 0.8 to 1.3 and an Al ₂ O ₃ content of 8 to 13% by mass.

The preferred ranges of the SiO ₂ concentration, Al ₂ O ₃ concentration in the slag modifier, and the amount of the slag modifier added (ratio to the steelmaking slag to be charged) vary depending on the components of the steelmaking slag to be charged. After the steelmaking slag and the slag modifier are mixed, it is sufficient that the basicity of the slag is 1.3 or less and the Al ₂ O ₃ concentration is 8% by mass or more. For example, by appropriately blending silica sand with a _SiO2 concentration of 99% by mass, brick waste with an _Al2O3 concentration of 83% by mass, and fly ash with a _SiO2 concentration of 59% by mass and _{an Al2O3} concentration of 23% by _mass , By adjusting the slag composition to an optimum range, slag dissolution can be suitably promoted. As the slag modifier, in addition to fly ash, silica sand, and brick waste, sewage sludge ash, aluminum dross, and the like can be used.

As a result, high-phosphorus molten iron containing phosphorus separated from molten slag is recovered, and the molten slag, which is steelmaking slag, is reduced and reformed to recover high-quality reduced slag equivalent to blast furnace slag. . This reduced slag has a lower content of FeO, P ₂ O ₅ , etc. than before reduction, so it can be recycled into cement raw materials, ceramic products, etc. Furthermore, if the components of the molten slag are adjusted so that its basicity is low, it will have low expansion properties, so it can be used as a roadbed material, aggregate, or stone.

Furthermore, by dephosphorizing the recovered high-phosphorus molten iron and oxidizing the P in the molten iron and transferring it to the slag, the high-phosphorus molten iron becomes high-phosphate slag and molten iron (low-phosphorus hot metal). It is separated into High phosphate slag can be commercialized as phosphate fertilizer, phosphate raw material, etc. Furthermore, molten iron (low-phosphorus hot metal) is recycled into the steelmaking process, mixed with blast furnace hot metal, and then fed into a converter or the like.

The outline of the slag treatment process according to this embodiment has been described above. This process preferably targets molten dephosphorization slag among the various steelmaking slags produced in the steelmaking process. Molten dephosphorization slag has a lower temperature than molten decarburization slag, but contains more granulated iron and phosphoric acid, and generally has a lower basicity. Therefore, by melting and reforming the molten dephosphorization slag through reduction treatment rather than oxidation treatment, the recovery efficiency of valuable elements (Fe, P, etc.) in this process can be increased, and the modification to lower basicity can be achieved. It also reduces the amount of energy required because it reduces the amount of material used. Therefore, in the following description, an example in which molten dephosphorization slag is mainly used as the molten slag to be treated will be described. However, the molten steelmaking slag of the present invention is not limited to molten dephosphorization slag, and any steelmaking slag generated in the steelmaking process, such as molten desulfurization slag and molten decarburization slag, can be used.

By reducing in an electric furnace, the upper heat of the slag works advantageously, and by suspending the reducing agent in the slag, it is possible to suppress the CO reaction between the slag metals and suppress slag foaming.

As the electric furnace used in the present invention, any of a stationary DC current furnace, a tilting DC current furnace, and an AC current furnace may be used. As shown in FIGS. 2 and 4, an electrode 3 is provided through the furnace lid 2 of the electric furnace 1, and the cold iron source and steelmaking slag are heated by the heating by the electrode 3, and a molten iron layer 21, A molten slag layer 22 is formed.

In the electric furnaces shown in FIGS. 1 to 3, the furnace lid is not provided with a slag inlet, and when charging slag into the electric furnace 1, the furnace lid 2 is moved laterally, thereby forming a slag inlet. Steelmaking slag 24 is charged into electric furnace 1 from slag ladle 4 via the opening (see FIG. 1).

In the electric furnace shown in FIGS. 4 and 5, a slag inlet 6 is installed in the furnace lid 2. Steelmaking slag is charged into the electric furnace via an opening formed by opening the slag inlet 6 of the furnace lid 2. In the example shown in FIG. 4, a gutter 5 is provided, the slag pot 4 is tilted, the steelmaking slag 24 flows down into the gutter 5, and the steelmaking slag 24 is fed into the electric furnace 1 from the slag input port 6 via the gutter 5. is charged. Further, in the electric furnace shown in FIGS. 4 and 5, a preheating furnace 7 is arranged on the furnace lid 2. A cold iron source is supplied from the cold iron source hopper 8 into the preheating furnace 7, and the temperature of the cold iron source is raised in the preheating furnace 7 using sensible heat of the electric furnace exhaust gas. Regarding the arrangement positions of the slag inlet 6 and the preheating furnace 7 in the electric furnace 1, in the example shown in FIG. The diagram is drawn as shown. Preferably, the slag inlet 6 and the preheating furnace 7 are arranged at 90 to 120 degrees with respect to the central axis of the electric furnace 1.

As shown in FIGS. 2 and 5, a raw material input pipe 9 is disposed on the furnace lid 2. As shown in FIGS. The carbon material 26 and the slag modifier 27 can be introduced into the electric furnace via the raw material input pipe 9 . It is preferable that the carbonaceous material 26 and the slag modifier 27 are made into granules and supplied from the raw material input pipe 9 while being arc heated. In order to prevent decarburization loss due to air intrusion into the electric furnace, it is preferable to maintain the electric furnace in a sealed state as much as possible and perform the reduction treatment and carburization in a non-oxidizing atmosphere. Regarding the addition of carbonaceous material, powdered carbonaceous material may be added by being blown into the slag layer.

Preferably in the present invention, the slag layer 22 or the molten iron layer 21 can be stirred by inserting the lance 13 into the slag layer 22 or the molten iron layer 21 in the electric furnace 1 and blowing stirring gas from the tip of the lance 13. . The lance 13 can be inserted into the furnace through the opening of the slag door 12 of the electric furnace 1 (see FIGS. 3 and 5).

During reduction of the slag, in order to preferentially heat the slag by arc heating and promote stirring within the slag, a gas blowing lance may be inserted into the slag layer to stir the gas. In the example shown in FIG. 5, the tip of the lance 13 inserted through the slag door 12 is immersed in the slag layer 22, and the slag layer 22 is stirred by blowing inert gas from the tip of the lance 13.

When the cold iron source is completely melted, the carbon concentration in the molten iron layer increases, and the temperature rises, the energization is stopped, and after the energization is finished, the tip of the lance 13 is immersed in the molten iron layer 21 to stir the gas. By doing so, the slag metal temperature can be made uniform. In the example shown in FIG. 3, the tip of the lance 13 inserted through the slag door 12 is immersed in the molten iron layer 21, and the molten iron layer 21 and the slag layer 22 are stirred by blowing inert gas from the tip of the lance 13. Is going. The gas may be blown into the molten iron layer 21 by bottom blowing instead of the lance dipping described above.

Along with the reducing agent and slag modifier, one or both of waste containing phosphoric acid and high-phosphate iron ore can be input through the raw material input pipe. As waste containing phosphoric acid, phosphoric acid sources generated in sewage treatment etc. can also be recovered, and the silica source contained therein can be used as a slag modifier. In particular, sludge incineration ash can be preferably used. This increases the P concentration in the molten iron, dephosphorsizes the molten iron in the next process, increases the P ₂ O ₅ concentration in the dephosphorization slag, and increases its value as a raw material for phosphate fertilizers or other phosphorus products. can be increased. Harmful elements with low boiling points such as Cd, As, and Pb contained in sewage sludge are vaporized and removed by the high-temperature arc flame and do not remain in the hot metal or high-phosphate slag, so they can be safely recycled.
By increasing the amount of steelmaking slag charged, the P concentration in the molten iron can also be increased.

By applying the present invention to a method for melting cold iron sources using an electric furnace, there is no need to introduce new flux when melting cold iron sources, and steelmaking slag with a high concentration of P ₂ O ₅ can be used instead. can.

Iron sources produced using the blast furnace method are produced by reducing iron ore with coke, and therefore generate a large amount of _CO2 . Therefore, as part of global warming countermeasures, there is a need to reduce the ratio of blast furnace steelmaking and increase the ratio of electric furnace steelmaking, which melts iron scrap using electrical energy. On the other hand, as mentioned above, when attempting to perform secondary refining and continuous casting of molten steel melted in an electric furnace together with the molten steel melted in a converter at a converter factory, the electric furnace heats up more than the normal converter. Due to its small size, the ladle capacity does not match the existing secondary refining and continuous casting machines at converter plants, and the timing cannot be matched well, so it is difficult to install it alongside a converter. In addition, electric furnace steel has high [N] and tramp elements, and there are steel types that can only be produced using converter steel.

In contrast, in the present invention, hot metal having a carbon concentration of 1% by mass or more is melted in an electric furnace. Even if the heat size of the electric furnace is smaller than the heat size of the converter, it can be made to match the heat size of the converter by mixing hot metal produced in the electric furnace and blast furnace hot metal. As a result, it becomes possible to produce hot metal in an electric furnace in a steelmaking factory that has a converter. Further, even if the cold iron source is melted in an electric furnace, the tramp element concentration and molten steel nitrogen concentration can be reduced by diluting it with blast furnace hot metal and blowing it in a converter.

[Example 1]
As shown in FIGS. 1 and 2, the present invention was carried out using an electric furnace in which the furnace cover 2 of the electric furnace 1 was removed and an iron source was charged therein.

Slide open the furnace lid 2 of the electric furnace 1 (DC or AC electric furnace) containing about 40 tons of hot metal as the seed bath 28, and pour in 60 tons of cold iron source preheated to 800°C in a charging bucket (not shown). It was charged into an electric furnace. Iron scrap and molded pig iron were used as cold iron sources. As shown in FIG. 1, in the electric furnace 1, a layer of seed hot water 28 is formed at the bottom, and a cold iron source 23 forms a deposited portion.

Molten decarburization slag or molten dephosphorization slag produced in a converter is used as the steelmaking slag 24, and is transported in a slag ladle 4, and is piled up in the electric furnace 1 by tilting the slag ladle 4, as shown in FIG. 50 tons of steelmaking slag 24 was charged from above the cold iron source 23 in a molten state. The charged steelmaking slag had a temperature of 1350°C, a composition of CaO: 37.1%, SiO ₂ : 15.3%, T. Fe: 21% _{, P2O5} : 3.2%.

After the steelmaking slag charging was completed, the furnace lid 2 was closed, the electrode 3 was lowered, and arc heating treatment was started at an output of 50 MW (see FIG. 2).
When the molten pool was formed, as shown in FIG. 2, a total of 7.5 tons of coke powder was intermittently introduced from above as carbonaceous material 26 via the raw material input pipe 9 provided on the furnace lid 2. The sealed state was maintained as much as possible to prevent decarburization loss due to air intrusion.
On the way, the furnace lid was opened and an additional 60 tons of cold iron source was charged.
In addition to the addition of the carbonaceous material 26, 7.0 tons of silica sand and 4.0 tons of brick scraps mainly consisting of alumina were added as the slag modifier 27. The overall average composition of the slag modifier 27 was 63% by mass of SiO ₂ and 30% by mass of Al ₂ O ₃ . In order to promote the reduction reaction in the slag and the carburization of the metal layer, the lance 13 was inserted into the furnace through the slag door 12, the lance was immersed in the slag layer, and nitrogen gas was stirred at 60 Nm ³ /h (lance (See Figure 5 for the arrangement of 13).

When the cold iron source is completely melted, the hot metal [C] is 2%, and the temperature exceeds 1500°C, the electricity supply is stopped, and the tip of the lance 13 is immersed in the molten iron layer 21 as shown in FIG ^. Nitrogen gas stirring was performed for 1 hour to make the slag metal temperature uniform.

After the electric furnace refining was completed, the electric furnace was tilted to discharge the hot metal constituting the molten iron layer 21 from the tapping hole 11 into a ladle (not shown), leaving about 40 tons of seed metal in the furnace. The electric furnace was tilted to the opposite side, the slag door 12 was opened to serve as a slag discharge port, and the reduced slag was discharged from the slag port. The amount of hot metal discharged was 133 tons, and the amount of reduced slag was 46 tons. The metal components were C: 2.1%, P: 0.41%, and Si: 0.12%. The slag component is T. Fe: 1.0%, _P2O5 : 0.31%, CaO: 39.6%, _SiO2 : 31.6 _% .

The hot metal contained in the ladle was subjected to dephosphorization treatment with a dephosphorization agent containing oxygen, an oxidizing agent of iron oxide, and quicklime, so that P in the hot metal was 0.11%. After the dephosphorization treatment, 137 tons of blast furnace hot metal was added to the hot metal to make 270 tons, and the mixture was charged into a converter. The amount of slag obtained from the dephosphorization treatment was 6.1 tons, and the slag components were T. Fe: 12.5%, P ₂ O ₅ : 15.1%, and after cooling, it was pulverized to obtain a fertilizer raw material.

[Example 2]
As shown in FIGS. 4 and 5, the present invention was carried out using an electric furnace 1 equipped with a preheating furnace 7 and into which a cold iron source is charged. Iron scrap was used as the cold iron source. A slag inlet 6 is arranged in the furnace cover 2 at a position 120° from the preheating furnace 7 with respect to the central axis of the electric furnace 1 . Further, a gutter 5 is provided for guiding the molten slag flowing out from the slag ladle 4 to the slag inlet 6.

The cold iron source 23 was put into the preheating furnace 7 from the cold iron source hopper 8, and after the temperature of the cold iron source 23 was raised to about 800°C in the preheating furnace 7, the cold iron source 23 was intermittently discharged into the electric furnace 1. . Next, the lid of the slag inlet 6 was opened. Since the deposited thickness of the cold iron source 23 formed directly under the slag input port 6 was slightly thin, 20 tons of solidified steelmaking slag (solidified slag 25) was input from the slag input port 6, and the cold iron source 23 was deposited at Solidified slag 25 was deposited on top. Next, 30 tons of molten steelmaking slag 24 is injected into the furnace from the slag inlet 6 from the slag pot 4 via the gutter 5, and onto the solidified slag 25 and unmelted cold iron source 23 piled up directly below. Fully charged. At that time, electricity supply was stopped in order to suppress the reduction reaction of the slag. The charged steelmaking slag had a temperature of 1350°C, a composition of CaO: 37.1%, SiO ₂ : 15.3%, T. Fe: 21% _{, P2O5} : 3.2%.

After the slag charging was completed, the slag input port 6 was closed, the electrode 3 was lowered, and arc heating treatment was started with an output of 50 MW.
When the molten pool was formed, as shown in FIG. 5, a total of 7.5 tons of coke powder was intermittently introduced from above as carbonaceous material 26 via the raw material input pipe 9 provided on the furnace lid 2. In order to prevent decarburization loss due to air intrusion, the sealed state was maintained as much as possible.
In addition to the addition of the carbonaceous material 26, 7.0 tons of silica sand and 4.0 tons of brick scraps mainly consisting of alumina were added as the slag modifier 27. The overall average composition of the slag modifier 27 was 63% by mass of SiO ₂ and 30% by mass of Al ₂ O ₃ . In order to promote the reduction reaction in the slag layer and the carburization of the molten iron layer, the lance 13 is inserted into the furnace through the slag door 12, and as shown in ^FIG . Nitrogen gas was blown in and stirring was performed.

When the charged cold iron source of 120 t was completely melted and the C content of the molten iron layer 21 exceeded 2% and the temperature exceeded 1500°C, the electricity supply was stopped. The lance 13 was lowered to a position where the tip of the lance 13 was immersed in the molten iron layer 21 (see FIG. 3), and stirring was performed by blowing nitrogen gas at 60 Nm ³ /h to equalize the slag metal temperature.

After the electric furnace refining was completed, the electric furnace was tilted to discharge the hot metal constituting the molten iron layer 21 from the tapping hole 11 into a ladle (not shown), leaving about 40 tons of seed metal in the furnace. The electric furnace was tilted to the opposite side, the slag door 12 was opened, and the reduced slag was discharged from the slag port. The amount of hot metal discharged was 133 tons, and the amount of reduced slag was 52 tons. The metal components were C: 2.1%, P: 0.41%, and Si: 0.12%. The slag component is T. Fe: 1.0%, _P2O5 : 0.31%, CaO: 39.6%, _SiO2 : 31.6 _% .

The hot metal contained in the ladle was subjected to dephosphorization treatment with a dephosphorization agent containing oxygen, an oxidizing agent of iron oxide, and quicklime, so that P in the hot metal was 0.11%. After the dephosphorization treatment, 137 tons of blast furnace hot metal was added to the hot metal to make 270 tons, and the mixture was charged into a converter. The slag obtained by dephosphorization weighed 6.1 tons, and the slag components were T. Fe: 12.5%, P ₂ O ₅ : 15.1%, and after cooling, it was pulverized to obtain a fertilizer raw material.

1 Electric furnace 2 Furnace lid 3 Electrode 4 Slag pot 5 Gutter 6 Slag input port 7 Preheating furnace 8 Cold iron source hopper 9 Raw material input pipe 11 Tap hole 12 Slag door 13 Lance 21 Molten iron layer 22 Slag layer 23 Cold iron source 24 Steelmaking slag 25 Solidified slag 26 Carbon material 27 Slag modifier 28 Seed water

Claims (5)

A cold iron source is charged into an electric furnace containing seed hot water, molten steelmaking slag is charged from above the pile of cold iron source, and the cold iron source is partially heated by direct current or alternating current arc heating. After melting, a carbonaceous material is put into the molten pool as a reducing agent, and a slag modifier containing at least one of SiO ₂ and Al ₂ O ₃ is added to reduce the slag and the melted molten iron. A method for melting a cold iron source accompanied by slag reduction, characterized in that after carburizing and discharging hot metal from a tap hole leaving a seed hot metal behind, the reduced slag is discharged from a slag discharge port. The steelmaking slag is charged through an opening formed by moving the furnace lid of the electric furnace or opening the slag inlet of the furnace lid, and is charged directly from the slag pot containing the steelmaking slag. The steelmaking slag to be charged shall be charged through a gutter, and at that time, the steelmaking slag to be charged may be placed on top of the pile of the cold iron source or on top of the solidified steelmaking slag further deposited on the pile of the cold iron source. The method for melting a cold iron source accompanied by slag reduction according to claim 1, characterized in that the method comprises charging the cold iron source with slag reduction. The cold iron source with slag reduction according to claim 1 or 2, characterized in that the reducing agent and the slag modifier are supplied through a raw material input pipe provided on the furnace lid while being arc heated. Dissolution method. During slag reduction, a lance is inserted into the slag layer, and stirring gas is blown through the lance to stir the slag. After energization, the molten iron layer is blown from the bottom or gas is stirred from the lance. A method for melting a cold iron source accompanied by slag reduction according to any one of claims 1 to 3. Any one of claims 1 to 4, characterized in that, together with the reducing agent and the slag modifier, one or both of waste containing phosphoric acid and high-phosphate iron ore are input through a raw material input pipe. A method for melting a cold iron source with slag reduction as described in .

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