TWI664294B - Dephosphorization method of molten iron - Google Patents

Abstract

The invention provides a method for dephosphorization of molten iron which can improve the dephosphorization efficiency of molten iron. A method for dephosphorizing molten iron, which is performed by adding a dephosphorizing refining agent to the molten iron, wherein the dephosphorizing refining agent includes a total pore volume in a range of 0.1 μm or more and 2.0 μm or less in a sum of 0.1 mL / g or more and a lime-based dephosphorizing agent in a range where R-CO ₂ is 1% by mass or more.

Description

Dephosphorization method of molten iron

The invention relates to a method for dephosphorization of molten iron which can improve dephosphorization efficiency.

In recent years, the quality required for steel materials has become increasingly strict, and it is sought to reduce impurity elements represented by phosphorus or sulfur. In order to meet such requirements, dephosphorization treatment is usually performed in the molten iron stage in the steel making step. This dephosphorization treatment is performed by adding an oxygen source such as gaseous oxygen or solid iron oxide to the molten iron as a dephosphorizing agent, and oxidizing phosphorus in the molten iron with the oxygen in the dephosphorizing agent to form an oxide ( P ₂ O ₅ ), and slag (slag for dephosphorization refining) is allowed to absorb the generated phosphoric acid.

As a dephosphorization refining agent for forming a slag for dephosphorization refining, a lime-based dephosphorization refining agent is generally used. From the viewpoint of environmental protection measures in recent years, reduction of slag generated in a steel-making step has been sought. The dephosphorization treatment of the molten iron is a low-temperature treatment favorable to the dephosphorization reaction, so it can be treated with a smaller amount of slag. The dephosphorization treatment of the molten iron in the above-mentioned manner is performed by adding a dephosphorizing refining agent to the molten iron in the converter and blowing gaseous oxygen upward, or blowing in molten iron in a mixing car or a molten iron pot. Dephosphorizing agents or methods of blowing dephosphorizing agents and dephosphorizing refining agents, etc., and the dephosphorizing treatment is performed according to the equipment or environment of each iron plant.

Patent Document 1 discloses a method for dephosphorization of molten iron, which improves the melting of slag for dephosphorization refining by using a CaF ₂ based solvent such as fluorite as a desulfurization refining agent. Physical properties, and improve dephosphorization efficiency. However, in recent years, from the viewpoint of environmental protection, there has been a situation in which a limit standard for the amount of fluorine deposited from the slag has been strengthened. For the slag for dephosphorization refining, it is also necessary to reduce the fluorine concentration to the limit. Therefore, it is strongly desired to develop a method for efficiently dephosphorizing the molten iron without using a CaF ₂ based solvent such as fluorite.

As a dephosphorization method that does not use a CaF ₂ based solvent such as fluorite, for example, Patent Document 2 discloses a method in which a converter-type furnace is used, and a dephosphorization solvent that does not substantially contain fluorine is used. The slag after the dephosphorization treatment is formed to reduce the melting point of the slag and improve the slag discharge performance of the slag after the dephosphorization treatment. 1. When dephosphorizing the molten iron, the slag basicity defined by the mass concentration ratio of CaO and SiO ₂ in the slag after the dephosphorization treatment is set to 2.5 or more and 3.5 or less. 2. The temperature of the molten iron after the dephosphorization treatment is set to 1,320 ° C or more and 1,380 ° C or less. 3. Before 60% of the total blowing time has elapsed until the end of the blowing, the flow rate of the bottom blowing gas is kept to be 0.18 Nm ³ / min or less per ton of molten iron, thereby removing the slag after the dephosphorization treatment. The T. Fe concentration is set to 5 mass% or more.

Patent Document 3 discloses a dephosphorization method for performing dephosphorization treatment on molten iron by adding a dephosphorization vehicle solvent and oxygen blowing up and bottom blowing to dephosphorize the molten iron in the following manner. 1. Set the bottom-blown stirring power to 1.0 kW / t or more. 2. The alkalinity ((mass% CaO) / (mass% SiO ₂ )) of the slag after the treatment is set to 0.6 or more and 2.5 or less. 3. Adjust the amount of the solvent for dephosphorization and / or the amount of the bottom-blown gas to be blown so that the end-point temperature of the treatment becomes 1250 ° C or higher and 1400 ° C or lower.

Patent Document 4 discloses a dephosphorization treatment method for adding molten CaO source-based dephosphorizing solvent to the molten iron in the converter, and applying oxygen to the molten iron bath surface from an upper blowing nozzle (lance). In the method, a dephosphorization treatment is performed as follows. 1. Set the supply rate of oxygen from the top blowing nozzle to 1.5 Nm ³ / (minute · hot metal-ton) to 5.0 Nm ³ / (minute · hot metal-ton). 2. The powdered granular dephosphorizing solvent is blown from an upper blowing nozzle so that at least a part of the dephosphorizing solvent is blown to the fire point generated on the surface of the molten iron by the blowing of oxygen. Attach to hot metal bath surface. 3. slag basicity ((mass% CaO) / (mass% SiO ₂₎₎ after the treatment becomes 1.0 or more and less than 2.5 manner be adjusted.

Patent Document 5 discloses a method for performing a dephosphorization treatment as follows. 1. For the molten iron held in the molten iron holding container, iron oxide is added from above the bath surface, and a dephosphorizing refining agent is blown under the bath surface to dephosphorize the molten iron. 2. The iron oxide is added in such a manner that the input area of the bath surface of the iron oxide is in an area ratio of 40% or more of the blowout area of the bath surface of the dephosphorizing refining agent. [Prior Art Literature] [Patent Literature]

Patent Literature 1: Japanese Patent Laid-Open No. 8-3611 Patent Literature 2: Japanese Patent Laid-Open No. 2008-106296 Patent Literature 3: Japanese Patent Laid-Open No. 7-70626 Patent Literature 4: Japanese Patent Laid-Open No. 2008-266666 Patent Document 5: Japanese Patent Laid-Open No. 2001-288507

[Problems to be Solved by the Invention] As described above, the methods disclosed in Patent Documents 2 to 5 can significantly reduce the amount of CaF ₂ based solvent used, but the dephosphorization rate and use of CaF ₂ based solvent Compared to the situation. That is, the methods disclosed in Patent Documents 2 to 5 have aspects that should be improved in terms of efficiently performing dephosphorization of molten iron. The present invention has been made in view of such a situation, and an object of the present invention is to provide a method for dephosphorization of molten iron which can improve the dephosphorization efficiency of molten iron. [Means for solving problems]

The features of the present invention that solve such problems are as follows. (1) A method for dephosphorization of molten iron, which is performed by adding a dephosphorization refining agent to the molten iron, wherein the dephosphorization refining agent includes a total pore volume in a range of pore diameters from 0.1 μm to 2.0 μm Lime-based dephosphorizing agent whose sum is 0.1 mL / g or more and R-CO ₂ is 1 mass% or more. (2) The method for dephosphorizing molten iron according to (1), wherein the dephosphorizing refining agent contains the lime-based dephosphorizing agent in an amount of 50% by mass or more. (3) The method for dephosphorizing molten iron according to (1), wherein the dephosphorizing refining agent is all the lime-based dephosphorizing agent. [Effect of the invention]

In the method for dephosphorizing molten iron of the present invention, a lime-based dephosphorizing agent is used in which the sum of the total pore volume within a predetermined range and the content of R-CO ₂ are within a specific range. By using such a lime-based dephosphorizing agent, a fire point cooling effect and a slagging promoting effect of CaO slag turning into slag can be obtained, thereby improving the dephosphorizing efficiency of molten iron.

The inventors have found that by using a lime in which the sum of the total pore volume in the range of pore diameters of 0.1 μm to 2.0 μm is set to 0.1 mL / g or more, and R-CO _{2 is} set to 1% by mass or more. The dephosphorizing agent can improve the dephosphorization efficiency of the molten iron, thereby completing the present invention. Hereinafter, an embodiment of a method for dephosphorizing molten iron according to the present invention using a converter-type reaction vessel having a bottom blowing port will be described. However, the method for dephosphorizing molten iron of the present invention is not limited to a reaction vessel such as a converter, and a molten iron transfer vessel such as a torpedo car or a molten iron pot may also be used.

FIG. 1 is a schematic cross-sectional view showing a state in which molten iron is dephosphorized using a converter. The reaction container 10 is a converter-type reaction container. The reaction container 10 includes a container body 12 that contains molten iron 20, and an up-blowing nozzle 14 that adds a gaseous oxygen source 24 such as oxygen, a solid oxygen source 26 such as iron oxide, and a dephosphorizing refining agent 28 to the molten iron 20. The side of the container body 12 is provided with a tap hole 16 for tapping the molten iron 20 after dephosphorization. The bottom of the container body 12 is provided with a plurality of bottom blowing holes 18 for blowing an inert gas 30 into the molten iron 20. The molten iron 20 contained in the container body 12 may be molten iron tapped from the blast furnace, or it may be desilicate by blowing oxygen in a blast furnace casting bed, a molten iron transfer container, or a converter after tapping from the blast furnace. Processed molten iron.

In the molten iron 20 tapped from the blast furnace and contained in the reaction vessel 10, a gaseous oxygen source 24 such as oxygen and a solid oxygen source 26 such as iron oxide are added from the upper blowing nozzle 14 (hereinafter, the gaseous oxygen source 24 and solid The oxygen source 26 is also referred to as an "oxygen source") and a dephosphorizing refining agent 28. An oxygen source is added to the molten iron 20 from the upper blowing nozzle 14, and the phosphorus in the molten iron 20 is oxidized to generate a phosphorus oxide.

The phosphorus oxide is captured by the dephosphorization refining slag 22 (the slag 22 for dephosphorization refining is sometimes referred to as "slag 22") containing the dephosphorization refining agent 28 and the like added from the upper blowing nozzle 14. Thus, the dephosphorization treatment of the molten iron 20 is performed. In addition, the measured value of the phosphorus concentration of the molten iron 20 tapped from the blast furnace, the dephosphorization oxygen efficiency of the oxygen source empirically obtained, and the phosphorus of the molten iron 20 after the target dephosphorization treatment are added to the top blowing nozzle 14. After adding the calculated amount of oxygen source to the concentration, and dephosphorizing the molten iron 20 to within the target phosphorus concentration range, the addition of the oxygen source from the upper blowing nozzle 14 is stopped to complete the dephosphorization process.

In the method for dephosphorizing molten iron of the present embodiment, a dephosphorizing refining agent 28 is used, which includes a total pore volume in a pore having a diameter of 0.1 μm or more and 2.0 μm or less in a pore having a lime-based dephosphorizing agent. Lime-based dephosphorizing agent whose sum is 0.1 mL / g or more and R-CO ₂ is 1 mass% or more. In the dephosphorization refining agent 28, the sum of the total pore volume in the pores with a diameter of 0.1 μm or more and 2.0 μm or less is 0.1 mL / g or more and R-CO ₂ is 1% by mass or more. The dephosphorizing refining agent of the dephosphorizing agent is, for example, calcium ferrite or calcium aluminate.

The pore diameter is that the lime within the range physically improves the wettability of the molten iron and the refining agent, and promotes the penetration of the molten iron into the pores on the surface of the refining agent. Thereby, the surface area of the refining agent in contact with the molten iron is increased, and the disintegration of CaO described later is further promoted, so that the dephosphorization efficiency is improved. In addition, the greater the amount of lime in the range of 0.1 μm to 2.0 μm, the more the slag is promoted to slag. The larger the sum of the total pore volume, the more the slag will be promoted and the dephosphorization efficiency will be improved. Therefore, the upper limit of the sum of the total pore volume may not be specified. When such a dephosphorizing refining agent 28 is added to the molten iron 20, among the lime-based dephosphorizing agent contained in the dephosphorizing refining agent 28, CaO is generated by the generation of CO ₂ gas represented by the following formula (1). The disintegration promotes the slag formation of CaO to the slag 22.

CaCO ₃ ®CaO + CO ₂ … (1) The pore size distribution of the lime-based dephosphorizing agent was measured by the following method. The lime was subjected to constant temperature drying at 120 ° C for 4 hours as a pretreatment, and the pore diameter of about 0.0036 μm was determined by mercury intrusion method using AutoPore IV9520 manufactured by Micromerities. The pore distribution of ~ 200 μm was used to calculate the cumulative pore volume curve. A total pore volume of pores having a diameter in a range of 0.1 μm to 2.0 μm is calculated from the cumulative pore volume curve. The pore diameter was calculated using the Washburn equation, that is, the following equation (2).

P × D = -4 × σ × cosθ… (2) In the formula (2), P is pressure (Pa), D is pore diameter (μm), and σ is mercury surface tension (= 480 dynes / cm (Dyne / cm)), θ is the contact angle of mercury with the sample (= 140 °).

R-CO ₂ is a value indicating the content ratio (mass%) of CO ₂ caused by CaCO ₃ remaining in quicklime. When the degree of calcination is high, CaCO ₃ decreases and the ratio of R-CO ₂ decreases. By using a solid carbon-sulfur analyzer (CS analyzer) to determine the concentration of C in the lime, and in terms of the amount of CO ₂ is calculated R-CO _2. When the dephosphorizing refining agent 28 is added to the molten iron 20, the dephosphorizing refining agent 28 is preferably added to the molten iron bath surface at the same position as that of the gaseous oxygen source 24. That is, the formula (1) is an endothermic reaction and therefore has a fire point cooling effect. The dephosphorization reaction becomes more thermodynamically at a lower temperature, and the reaction is promoted. Therefore, the dephosphorization reaction is promoted by the fire-point cooling effect of the lime-based dephosphorizing agent and the slagging promotion effect of CaO slagging into the slag 22. For the purpose of expanding the surface area of the lime-based dephosphorizing agent and improving the reactivity of the lime-based dephosphorizing agent, when the top blowing nozzle 14 and the carrier gas are added to the molten iron bath surface together, it is preferable to use an average particle size of 1 Lime-based dephosphorizing agent below mm. The measurement method of the average particle diameter is as follows. Take 1 kg of lime-based dephosphorizing agent, 0.100 mm or less, 0.100 mm to 0.150 mm or less, 0.150 mm to 0.212 mm or less, 0.212 mm to 0.250 mm or less, 0.250 mm to 0.300 mm or less, 0.300 mm or more ～ 0.355 mm or less, 0.355 mm to 0.425 mm or less, 0.425 mm to 0.500 mm or less, 0.500 mm to 0.600 mm or less, 0.600 mm to 0.710 mm or less, 0.710 mm to 0.850 mm or less, 0.850 mm to 1.000 mm The sieve was sieved in 13 steps of less than mm and exceeding 1.000 mm, and the average particle diameter was calculated by the mass ratio using the following formula (3).

[Equation 1]

In the formula (3), Wi is a mass ratio of the particle diameter di, and the particle diameter di is a median diameter of the mesh size of each sieve.

In the case of adding on a furnace such as a rotary furnace, if the average particle diameter is small, the addition yield is significantly deteriorated. Therefore, when adding on a furnace, it is preferable to use a lime-based dephosphorization having an average particle diameter of about 5 μm to 30 μm. Agent.

A lime-based dephosphorizing agent having a total pore volume of 0.1 μm or more and 2.0 μm or less in a range of 0.1 mL / g or more and R-CO ₂ of 1% by mass or more can be appropriately used. CO ₂ is a dephosphorization refining agent 28 for quicklime having a content of 2% by mass or less. Among them, for the purpose of improving the fire-point cooling effect of the lime-based dephosphorizing agent and the slagging promotion effect of CaO slagging into the slag 22, the content ratio of the lime-based dephosphorizing agent to the dephosphorizing refining agent 28 is preferable. It is preferably 50% by mass or more, and more preferably the content ratio of the lime-based dephosphorizing agent to the dephosphorizing refining agent 28 is 100% by mass.

Previously, when the Si concentration of the molten iron 20 was 0.4% by mass or more, there was a possibility that the slag 22 was ejected from the furnace mouth portion by slag forming. Therefore, the addition of an oxygen source to the molten iron 20 was required The oxygen supply rate becomes a factor that reduces productivity. However, in the method for dephosphorizing molten iron in the present embodiment, slagging can be suppressed by the exhaust effect of CO ₂ generated in the reaction of the above formula (1), so there is no need to reduce the oxygen supply rate. Therefore, in the method for dephosphorizing molten iron according to this embodiment, when dephosphorizing molten iron having a Si concentration of 0.4% by mass or more, dephosphorizing treatment can be performed without reducing productivity.

The alkalinity ((mass% CaO) / (mass% SiO ₂ )) of the slag 22 after the dephosphorization treatment is preferably about 1.8 to 3.5. If the alkalinity of the slag 22 after the dephosphorization treatment is less than 1.8, it is difficult to perform the dephosphorization reaction of the molten iron, which is not preferable. Even if the alkalinity of the slag 22 after the dephosphorization treatment is higher than 3.5, the dephosphorization speed does not increase, and the cost of lime is increased, so it is not good.

An inert gas 30 is blown into the molten iron 20 from the bottom blowing port 18, and the molten iron 20 is stirred. Thereby, the dephosphorization efficiency of the molten iron 20 can be further improved. In order to obtain the stirring effect of the molten iron 20, the blowing amount of the inert gas 30 is preferably set to 0.02 Nm ³ / (minute · molten iron-ton) or more. On the other hand, if the stirring of the molten iron 20 is performed too strongly, C in the molten iron accelerates the reduction rate of FeO in the slag 22, and the concentration of FeO contributing to the dephosphorization reaction decreases, which is not preferable. Therefore, the blowing amount of the inert gas 30 is preferably set to 0.5 Nm ³ / (minute · molten iron-ton) or less. In the method for dephosphorizing molten iron of the present embodiment, an example is shown in which the inert gas 30 is blown from the bottom blowing port 18, but it is not limited to this, and oxygen gas may be blown in place of or together with the inert gas 30. . In the unit of the blowing amount of the inert gas 30, "the molten iron-ton" means the blowing amount of the inert gas 30 per ton of the molten iron contained in the reaction container 10.

As the gas oxygen source 24 added from the upper blowing nozzle 14, oxygen (including industrial pure oxygen), air, oxygen-enriched air, and a mixed gas of oxygen and an inert gas can be used. When dephosphorizing the molten iron 20, it is preferable to use oxygen. By using oxygen, the dephosphorization reaction speed can be accelerated compared with the case of using other gases. In the case of using a mixed gas, in order to accelerate the dephosphorization reaction rate, it is preferable to increase the oxygen concentration compared to air.

As the solid oxygen source 26 added from the upper blowing nozzle 14, iron ore, mill scale, sand iron, dust collecting dust (blast furnace, converter, sintering step, etc.) containing iron components recovered from the exhaust gas can be used Dust) and other sources of iron oxide. In the method for dephosphorizing molten iron in this embodiment, these solid oxygen sources 26 are blown and added to the bath surface of the molten iron 20 from the upper blowing nozzle 14. Thereby, the oxygen potential of the slag 22 can be increased, and a dephosphorization promoting effect by the fire-point cooling can be obtained.

When the solid oxygen source 26 is added from the upper blowing nozzle 14, the solid oxygen source 26 is preferably a supply system different from the supply system of the gas oxygen source 24, and is added to the bath of the molten iron 20 to which the gas oxygen source 24 is blown Near the surface.

Regarding the bath surface position of the molten iron 20 to which the gaseous oxygen source 24 is added, the ignition point is advantageous in that the decarburization reaction caused by the gaseous oxygen source 24 becomes a high temperature exceeding 2000 ° C. due to the heat generated by the decarburization reaction and the like. On the other hand, the lower the temperature of the dephosphorization reaction, the more the reaction is promoted. Therefore, the dephosphorization reaction substantially occurs at a fire point peripheral portion that is slightly away from the fire point at approximately 1800 ° C or lower.

Therefore, when the solid oxygen source 26 is added from the upper blowing nozzle 14, it is preferable to add the solid oxygen source 26 to the supply system different from the supply system of the gaseous oxygen source 24 by using a carrier gas having a low oxygen concentration. A peripheral portion of the fire point of the gaseous oxygen source 24 is blown. By using a carrier gas having a low oxygen concentration, the solid oxygen source 26 is added to the peripheral portion of the fire point below 1800 ° C, so that the temperature of the portion is not increased excessively, and the good dephosphorization reactivity of the solid oxygen source 26 is further increased. Promote dephosphorization of molten iron. The phosphorus distribution ratio (the ratio of the phosphorus concentration in the slag to the phosphorus concentration in the molten steel), which is an indicator of the dephosphorization ability at 1550 ° C, will also be approximately twice the phosphorus distribution ratio at 1600 ° C in terms of thermodynamic estimation. .

The configuration of the upper blowing nozzle 14 having a supply system different from the supply system of the gas oxygen source 24 is only required to have at least a double pipe structure, and only one of the double pipe structures is required as the flow path of the gas oxygen source 24 It is sufficient to use the other of the double tube structure as the flow path of the solid oxygen source 26. Further, a plurality of nozzle holes along an imaginary circle with the central axis of the upper blow nozzle 14 as a center, and nozzle holes arranged on the central axis of the upper blow nozzle 14 may be provided. A plurality of nozzle holes are provided to add a gas oxygen source 24, and a solid oxygen source 26 is added to the nozzle holes provided on the central axis. By adding the solid oxygen source 26 and the gas oxygen source 24 in the manner described above, the solid oxygen source 26 can be added to the position of the bath surface surrounded by a plurality of fire points formed by the addition of the gas oxygen source 24, and the solid The temperature at which the oxygen source 26 is added is maintained at a high temperature state lower than the fire point, so it is more preferable. A plurality of nozzle holes may be provided along an imaginary circle having the central axis of the upper blowing nozzle 14 as a center, and the gas oxygen source 24 and the solid oxygen source 26 may be alternately added from the plurality of nozzle holes by changing the time.

The solid oxygen source 26 added to the molten iron 20 may not be added to the vicinity of the bath surface of the molten iron to which the gaseous oxygen source 24 is added. However, when there are few solid oxygen sources 26 added to the vicinity of the molten iron bath surface to which the gaseous oxygen source 24 is added, the FeO concentration in the slag 22 becomes low. FeO in the slag 22 contributes to the dephosphorization reaction. Therefore, if the FeO concentration in the slag 22 becomes low, the dephosphorization efficiency decreases. In order to prevent the FeO concentration in the slag 22 from being lowered, it is preferable to add a solid oxygen source 26 capable of securing a predetermined FeO concentration in the slag 22 to the vicinity of the molten iron bath surface to which the oxygen source 24 is added.

On the other hand, regarding the solid oxygen source 26 added to the vicinity of the molten iron bath surface to which the gaseous oxygen source 24 is added, the upper limit of the amount of addition is set as long as the amount of heat discharged from the molten iron 20 is not excessively increased according to the equipment specifications. Just fine. For example, in the case of performing a dephosphorization treatment using a converter-type reaction vessel of 100 to 350 tons, it is preferable to 1 Nm ^{3 of} a gaseous oxygen source 24 (oxygen purity in a standard state) added to a molten iron bath surface. The solid oxygen source 26 in the range of 0.1 kg to 2.0 kg is added near the surface of the molten iron bath to which the gaseous oxygen source 24 is added, and the range of 0.3 kg to 2.0 kg is more preferable. The solid oxygen source 26 is added to the vicinity of the molten iron bath surface to which the gaseous oxygen source 24 is added.

FeO concentration of slag 22 when the amount of solid oxygen source 26 added to the vicinity of the molten iron bath surface to which gaseous oxygen source 24 is added is less than 0.1 kg with respect to 1 Nm ³ of gaseous oxygen source 24 Decline, so it is not good. If the added amount of the solid oxygen source 26 is more than 2.0 kg with respect to the gaseous oxygen source 24 of 1 Nm ³ , the amount of heat discharged in the molten iron bath surface where the solid oxygen source 26 is added becomes large, and the slag 22 is not sufficiently slagged. , The dephosphorization efficiency decreases, so it is not good. The solid oxygen source added to a position other than the vicinity of the bath surface of the molten iron bath surface to which the gaseous oxygen source 24 is added can be added to the molten iron 20 by methods such as top-up addition and injection addition.

In the case of using the gaseous oxygen source 24, the temperature of the molten iron is increased by the heat of oxidation reaction. In the case of using the solid oxygen source 26, the sensible heat, latent heat, and decomposition heat of the solid oxygen source 26 are greater than the heat of oxidation reaction. The temperature of the molten iron has dropped. Therefore, regarding the usage ratio of the gaseous oxygen source 24 and the solid oxygen source 26, as long as the amount of the gaseous oxygen source 24 added and the amount of the solid oxygen source 26 added to the vicinity of the molten iron bath surface to which the gaseous oxygen source 24 is added are maintained, The range may be set in accordance with the target temperature after the dephosphorization treatment of the molten iron 20.

It is preferable to adjust the addition of the solid oxygen source 26 added to the vicinity of the molten iron bath surface to which the gaseous oxygen source 24 is added so that the FeO concentration in the slag 22 is within a range of 10% by mass to 50% by mass. the amount. Thereby, the dephosphorization efficiency of the molten iron 20 can be improved. By setting the FeO concentration in the slag 22 to a range of 10% by mass or more and 30% by mass or less, the dephosphorization efficiency of the molten iron 20 can be further improved, so it is more preferable.

In the method for dephosphorizing molten iron in this embodiment, an example is shown in which an inert gas 30 is blown in from the bottom blowing port 18 and the molten iron 20 is stirred, but it is not limited to this. For example, when the molten iron is dephosphorized by using a molten iron transfer container such as a torpedo car or a molten iron pot, the molten iron 20 may be blown with an inert gas 30 from an injection nozzle immersed in the molten iron 20 Stir. [Example]

After desilication of the molten iron tapped from the blast furnace using a blast furnace caster, the molten iron was transported in a 250-ton hot-water pot. After desulfurization was performed by a mechanical stirring method, desulfurization was carried out by using a blowing nozzle in a converter. Phosphorus treatment.

Add 10 kg / (hot metal-ton) of sand iron with an average particle size of 500 μm as a solid oxygen source. Regarding the addition of the sand iron, the addition from the upper blowing nozzle with the gas for transportation and the addition from the upper hopper of the furnace were used. At a rate of 25,000 Nm ³ / h, oxygen was added from the upper blowing nozzle as a gaseous oxygen source. As a dephosphorizing refining agent, a dephosphorizing refining agent having an average particle diameter of 2 kg or less of 10 kg / (hot metal-ton) was added from a supply system of a gaseous oxygen source.

The measuring method of the average particle diameter of a dephosphorization refining agent is as follows. Take 1 kg of dephosphorizing refining agent, 0.100 mm or less, 0.100 mm to 0.150 mm or less, 0.150 mm to 0.212 mm or less, 0.212 mm to 0.250 mm or less, 0.250 mm to 0.300 mm or less, 0.300 mm to 0.355 mm or less, 0.355 mm to 0.425 mm or less, 0.425 mm to 0.500 mm or less, 0.500 mm to 0.600 mm or less, 0.600 mm to 0.710 mm or less, 0.710 mm to 0.850 mm or less, 0.850 mm to 1.000 mm or more In the following, sieving was performed in 13 steps exceeding 1.000 mm, and the average particle diameter was calculated at a mass ratio using the above formula (3). Before the start of dephosphorization, the concentration of Si in the molten iron was 0.15% by mass, the concentration of C was 4.5% by mass, the basicity of the slag was 2.0, and the ratio of CaO to oxygen was CaO / O = 1.5 (kg / Nm ³ ) Adjustment.

Table 1 shows the content ratio (% by mass) of the lime-based dephosphorizing agent contained in the dephosphorizing refining agents used in Comparative Examples 1 to 6 and Examples 1 to 28, and the fineness of the lime-based dephosphorizing agent. Sum of total pore volume (mL / g) with a pore diameter of 0.1 μm or more and 2.0 μm or less, R-CO ₂ content ratio (% by mass), phosphorus concentration of molten iron before dephosphorization (% by mass) ), Phosphorus concentration (mass%), dephosphorization rate (%), and end temperature (° C) of the molten iron after dephosphorization treatment. Calcium ferrite is used as a dephosphorizing refining agent other than the lime-based dephosphorizing agent. The dephosphorization rate is a value calculated using the phosphorus concentration of the molten iron before the dephosphorization treatment, the phosphorus concentration of the molten iron after the dephosphorization treatment, and the following formula (4).

[Equation 2]

[Table 1]

In Comparative Examples 1 to 6, the sum of the total pore volume in the range of 0.1 μm or more and 2.0 μm or less containing a lime-based dephosphorizing agent was less than 0.1 mL / g, or the value of R-CO ₂ was not A comparative example in which a dephosphorizing refining agent of a lime-based dephosphorizing agent of 1% by mass or more is subjected to dephosphorization treatment. Examples 1 to 28 use a total pore volume in a range of 0.1 μm or more and 2.0 μm or less containing a lime-based dephosphorizing agent to add a total of 0.1 mL / g or more and R-CO ₂ to 1 mass Examples in which the dephosphorizing refining agent of the lime-based dephosphorizing agent is dephosphorized by more than%. The dephosphorization rates of Comparative Examples 1 to 6 were lower than those of Examples 1 to 28. Based on this, it was confirmed that by using a total pore volume in a range including 50% by mass or more of a pore diameter of 0.1 μm or more and 2.0 μm or less is 0.1 mL / g or more and R-CO ₂ is 1% by mass The dephosphorization refining agent of the above lime-based dephosphorizing agent can improve the dephosphorization efficiency of the molten iron.

Examples 17 to 28 use lime-based desulfurization using a total pore volume in a range of pore diameters of 0.1 μm or more and 2.0 μm or less in a range of 0.1 mL / g or more and R-CO ₂ of 1% by mass or more. An example of a dephosphorizing refining agent composed of a phosphorous agent. The dephosphorization rates of Examples 17 to 28 were higher than those of Comparative Examples 1 to 6 and Examples 1 to 16. From this, it was confirmed that the sum of the total pore volume in the range of all the dephosphorizing refining agents having a pore diameter of 0.1 μm or more and 2.0 μm or less was 0.1 mL / g or more and R-CO ₂ was 1 mass% or more. In the case of a lime-based dephosphorizing agent, the dephosphorization efficiency of molten iron can be further improved.

Lime-based dephosphorizing agent A lime-based dephosphorizing agent having a total pore volume in a range of 0.1 μm or more and 2.0 μm or less in a sum of 0.1 mL / g or more and R-CO ₂ of 1% by mass or more The above-mentioned fire point cooling effect and CaO slag conversion into slag slag promotion effect can improve the dephosphorization efficiency of molten iron. Therefore, the dephosphorization of molten iron is performed by using a dephosphorizing refining agent containing a lime-based dephosphorizing agent capable of improving the dephosphorizing efficiency of molten iron, and the dephosphorizing refining agent is used without the lime-based dephosphorizing agent. Compared with the dephosphorization of molten iron, the dephosphorization efficiency can be improved.

10‧‧‧Reaction container

12‧‧‧ container body

14‧‧‧up blowing nozzle

16‧‧‧outlet

18‧‧‧ bottom hair dryer

20‧‧‧ hot metal

22‧‧‧ Slag

24‧‧‧Gas oxygen source

26‧‧‧Solid oxygen source

28‧‧‧ dephosphorizing refining agent

30‧‧‧ inert gas

FIG. 1 is a schematic cross-sectional view showing a state in which molten iron is dephosphorized using a converter.

Claims (2)

A method for dephosphorizing molten iron, which is performed by adding a dephosphorizing refining agent to the molten iron, wherein the dephosphorizing refining agent includes a total pore volume in a range of pore diameters of 0.1 μm to 2.0 μm. A lime-based dephosphorizing agent having an amount of 0.1 mL / g or more and an R-CO ₂ of 1% by mass or more, wherein the dephosphorizing refining agent includes the lime-based dephosphorizing agent in an amount of 50% by mass or more. The method for dephosphorizing molten iron according to item 1 of the scope of the patent application, wherein all the dephosphorizing refining agents are the lime-based dephosphorizing agents.