JP2013209678A - Method of manufacturing molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing molten steel, excellent in flame catching efficiency and productivity, and capable of increasing a compounding ratio of a cold iron source such as an iron scrap when manufacturing molten steel from hot metal.SOLUTION: A first top-blowing lance 3 has an oxidizing gas-supplying path for supplying oxygen gas for refining and supplying a flux using the oxygen gas as gas for conveyance, and a fuel-supplying path. Fuel is supplied from the fuel-supplying path by using the first top-blowing lance, and simultaneously, the oxygen gas is supplied toward hot metal 14 in a converter from the oxidizing gas-supplying path. While forming flame below the top-blowing lance by combusting the fuel with a part of the oxygen gas, lime-based flux 13 is supplied to the hot metal from the oxidizing gas-supplying path to perform dephosphorizing treatment. The acquired hot metal is then charged into the other converter, and while forming flame below the leading end of a second top-blowing lance using the second top-blowing lance with the same configuration as that of the first top-blowing lance, flux is supplied from the oxidizing gas-supplying path together with the oxygen gas so that the hot metal is subjected to decarburization refining, thereby manufacturing molten steel from the hot metal.

Description

  In the present invention, the hot metal discharged from the blast furnace is charged into the converter, the hot metal is subjected to dephosphorization treatment as a preliminary treatment, and then the hot metal is discharged from the converter and then charged into another converter. In addition, the present invention relates to a method for producing molten steel from hot metal by decarburizing and refining hot metal in this converter. Specifically, when producing molten steel from molten iron using a converter, respectively, dephosphorization treatment and decarburized refining are performed respectively. It is related with the manufacturing method of the molten steel which can raise the compounding ratio of cold iron sources, such as iron scrap, by adding in a furnace in the state which heated or fuse | melted the solvent used as a refining agent.

  When producing molten steel from hot metal, pretreatment (dephosphorization treatment, desulfurization treatment) that removes impurities (phosphorus and sulfur) in the hot metal before hot metal decarburization and refining in the converter is performed. Developed hot metal pretreatment technology to reduce slag generation in decarburization and refining in converters, manufacture high quality steel products with few impurities, or use manganese ore as an inexpensive source of manganese for steel product components, etc. Has been realized.

On the other hand, in recent years, reduction of CO ₂ emissions has become an important issue in the steelmaking process from the viewpoint of environmental protection. In the steelmaking process, the ratio of cold iron sources such as iron scrap is increased as the iron source used. Attempts have been made to reduce the mixing ratio of hot metal. This is because in the manufacture of hot metal in a blast furnace, a large amount of energy is required to reduce and melt the iron ore, while the cold iron source only requires heat of melting. This is because when the cold iron source is used, the amount of energy used for reducing heat of the iron ore can be reduced, and the amount of CO ₂ generated can be greatly reduced.

  However, in the molten steel production process using a combination of a blast furnace and a converter, the melting heat source of the cold iron source is the sensible heat of the molten iron and the combustion heat due to the oxidation of carbon and silicon in the molten iron. The amount is naturally limited. In addition, the dephosphorization treatment performed as a pretreatment reduces the silicon concentration and carbon concentration in the hot metal, and further, the number of treatment steps increases, resulting in a decrease in the hot metal temperature. This is a major obstacle to improving the mixing ratio of the cold iron source.

  For this reason, in order to increase the blending ratio of the cold iron source, the dephosphorization treatment as a preliminary treatment is abandoned and the dephosphorization refining and decarburization refining are performed at the same time in the converter. In the case of decarburizing and refining hot metal that has undergone dephosphorization treatment in a converter, a method of supplementing heat energy by adding a heating material such as a carburizing material or ferrosilicon into the converter has been performed. . However, by performing the dephosphorization process, not only can cost reduction and quality improvement of the steel material be achieved, but also the amount of slag generated can be reduced. It is desirable to perform a dephosphorization process, and then to perform only decarburization refining in the converter, and at the same time increase the blending ratio of cold iron sources such as iron scrap. The use of the carburized material has a problem that the sulfur concentration of the molten steel increases due to the sulfur contained in the carburized material, and the heat generating material such as ferrosilicon is expensive, and the use of the heat generating material causes an increase in manufacturing cost. .

Furthermore, the CO gas generated in the converter in by secondary combustion in a converter furnace _{(2CO + O 2 → 2CO 2} ) and CO ₂ gas by decarburization reaction during decarburization refining, wearing heat generated by the secondary combustion to the molten steel A method for heat-compensating the hot metal by heating is also well known. However, an excessive increase in the secondary combustion rate causes an increase in the exhaust gas temperature, resulting in a problem that the life of the converter refractory is reduced.

  Thus, in hot metal dephosphorization and decarburization refining, many means have been proposed to increase the thermal margin of the hot metal and expand the blending ratio of the cold iron source. For example, in Patent Document 1, in performing dephosphorization as a hot metal pretreatment, a carbon source is added to the generated slag during the dephosphorization process, and an oxygen source is blown into the slag to burn the carbon source. A method has been proposed in which the heat of combustion is applied to the hot metal.

  In Patent Document 2, a heat transfer medium such as iron scrap powder, alloy iron powder, and quick lime powder is supplied to the hot metal in the smelting vessel together with oxygen gas from the top blowing lance to decarburize and refine the hot metal and melt iron or chromium. When carrying out reduction or the like, the secondary combustion rate in the smelting vessel is controlled within the range of 10 to 55%, the secondary combustion heat is made to reach the heat transfer medium, and the heat transferred to the secondary combustion heat is made. A method of heating the hot metal with a heat medium has been proposed.

  Patent Document 3 discloses that when hot metal is oxidized and refined in a converter, it is independent of an oxygen gas ejection main hole and a supply flow path for oxygen gas ejected from the main hole, and includes fuel gas, oxygen gas, and Using an upper blowing lance having a five-pipe structure having a flux supply sub-hole capable of simultaneously ejecting a refining flux, the oxygen gas jets ejected from the main hole are kept separated from each other, and the oxygen gas jet A converter refining method has been proposed in which a flame is formed at the tip of a sub-hole independently, and a refining flux is allowed to pass through the flame to promote hatching of the refining flux.

JP-A-9-20913 JP 2001-323312 A Japanese Patent Laid-Open No. 11-80825

  However, the above prior art has the following problems.

That is, in Patent Document 1, the hot metal temperature is increased by adding a carbon source to the generated slag, but the sulfur contained in the carbon source is mixed into the hot metal, and the sulfur concentration in the hot metal is increased. . Moreover, since it is necessary to ensure the combustion time of a carbon source, there exists a problem that refining time becomes long, productivity falls, and manufacturing cost rises. Furthermore, since the carbon source is burned, there is also a problem that the amount of CO ₂ generated naturally increases.

  In Patent Document 2, it is necessary to control the secondary combustion rate in accordance with the supply speed of the heat transfer medium. As a means for realizing this, the upper blow lance is obtained while obtaining the secondary combustion rate based on the analysis result of the exhaust gas composition. It shows how to adjust the lance height. In general, when the lance height is increased, the amount of atmospheric gas (mainly CO gas) accompanying the oxygen gas jet from the top blowing lance increases, the secondary combustion rate increases, and conversely, the lance height increases. When the height is reduced, the secondary combustion rate is lowered. That is, when the secondary combustion rate is increased as in Patent Document 2, the oxygen gas jet from the top blowing lance is attenuated, the decarburization speed is reduced, the decarburization refining time is lengthened, and the productivity is reduced to produce. There is a problem that costs increase. The lance height is the distance between the tip of the top blowing lance and the hot metal bath surface in the stationary state.

  In Patent Document 3, a five-way pipe composed of a sub-hole oxygen gas and refining agent flow path, a fuel gas flow path, a main-hole oxygen gas flow path, a cooling water supply flow path, and a cooling water drain flow path. The top blow lance of the structure is used, and the flow path of the sub-hole oxygen gas and the refining agent and the flow path of the fuel gas are merged at the tip of the lance to form a combustion flame. Further, the sub-hole oxygen gas and the refining agent are merged at the upper portion of the lance, but an inert gas such as Ar gas is used as a refining agent transport gas until the refining agent is merged.

  That is, in Patent Document 3, substances that pass through the supply passages for the sub-hole oxygen gas and the refining agent are oxygen gas, inert gas, and refining agent. The problem here is that a refining agent (such as iron oxide, iron ore, and ironworks generated dust) containing a metal or carbon and oxygen gas simultaneously pass through one channel. That is, Patent Document 3 is an effective technique for raising the hot metal temperature, but when passing through the supply flow path in the lance, a spark is caused by friction between the refining agent and the flow path wall (usually made of steel). Oxygen gas and a part of the refining agent may react to generate heat and burn in the flow path, which poses a problem in facility safety management.

  Further, Patent Document 3 merely describes hot metal decarburization refining in a converter, and does not describe how to perform hot metal dephosphorization as a preliminary treatment. In other words, if the heat capacity of hot metal is increased by decarburization refining, the mixing ratio of the cold iron source will increase accordingly, but the operation of increasing the heat capacity of hot metal also in the dephosphorization process will further increase the mixing ratio of the cold iron source. Get higher. Reference 3 does not describe this point.

  The present invention has been made in view of the above circumstances. The object of the present invention is to charge the molten iron discharged from the blast furnace into the converter and subject the molten iron to dephosphorization as a preliminary treatment. After hot metal is discharged from the converter, it is charged into another converter, and decarburization and refining of the hot metal is performed in this converter, thereby producing heat and heat in the flow channel of the top blowing lance. By adding a powdered medium solvent used as a refining agent in dephosphorization and decarburization refining to the furnace in a heated or molten state without fear of combustion, it is excellent in heat receiving efficiency and productivity, and iron scrap It is providing the manufacturing method of the molten steel which can raise the compounding ratio of cold iron sources, such as.

The gist of the present invention for solving the above problems is as follows.
[1] A refining oxidizing gas supply flow path for supplying an oxidizing gas for dephosphorization refining and supplying a powdered lime-based solvent using the oxidizing gas as a carrier gas, and a fuel supply for supplying fuel And a first hot-blow lance having separate flow paths, supplying fuel from the fuel supply flow path, and simultaneously sending oxidizing gas from the refining oxidizing gas supply flow path in the converter The refining oxidation is performed using the oxidizing gas as a carrier gas while supplying the gas toward the surface and burning the fuel with a part of the oxidizing gas to form a flame below the front end of the first upper blowing lance. The powdered lime-based solvent is supplied from the reactive gas supply channel to the hot metal bath surface in the converter, the hot metal in the converter is dephosphorized, and the obtained hot metal after the dephosphorization treatment is Hot water is discharged from the converter to the hot metal holding container, and this hot metal is charged into another converter for oxidation for decarburization and refining. A refining oxidizing gas supply flow path for supplying gas and supplying a powdered medium solvent using the oxidizing gas as a carrier gas and a fuel supply flow path for supplying fuel; Using an upper blowing lance, fuel is supplied from the fuel supply passage, and at the same time, an oxidizing gas is supplied from the refining oxidizing gas supply passage toward the hot metal bath surface in the converter, and the oxidizing gas is supplied. While partly combusting the fuel to form a flame below the tip of the second top blowing lance, the powdered solvent is removed from the refining oxidizing gas supply channel using the oxidizing gas as a carrier gas. A method for producing molten steel, comprising supplying to a hot metal bath surface in a converter, decarburizing and refining the molten iron in the converter, and thus producing molten steel from the molten iron.
[2] The first upper blowing lance and the second upper blowing lance are formed from the center side in the cross-sectional structure from the refining oxidizing gas supply flow path, the cooling water drain flow path, the fuel supply flow path, and the cooling water. The method for producing molten steel according to the above [1], which has a quadruple pipe structure having a water supply channel.

According to the present invention, in the dephosphorization treatment in the converter performed as a pretreatment for the hot metal, and in the decarburization refining in the converter of the hot metal subjected to the dephosphorization treatment, a powdered medium used as a refining agent The solvent is heated by the flame formed below the tip of the top blowing lance, and the heat of the flame is applied to the hot metal via the powder medium solvent, so the temperature of the hot metal rises and the hot metal dephosphorization and decarburization An increase in the blending ratio of cold iron sources such as iron scrap in refining can be realized, thereby making it possible to significantly reduce CO ₂ emissions compared to the prior art.

  In the supply from the top blowing lance of the powdered medium solvent, an oxidizing gas for dephosphorizing or decarburizing and refining is used as a carrier gas. It is mainly composed of hydroxide, fluoride, etc., does not contain any combustible substance such as metal or carbon, and can prevent heat generation and combustion in the flow path of the top blowing lance.

  Further, in the present invention, as the carrier gas for the powder medium solvent, an oxidizing gas for dephosphorizing and refining that is indispensable for dephosphorization and decarburizing or refining is used. The use of an inert gas such as nitrogen gas or Ar gas, which has been used as a carrier gas, is unnecessary, which is economically advantageous.

It is a schematic sectional drawing which shows an example of the converter equipment provided with the top blow lance of the quadruple pipe structure used when implementing the dephosphorization process and decarburization refining of hot metal which concern on this invention. It is a general | schematic expanded longitudinal cross-sectional view of the upper blowing lance shown in FIG. It is a general | schematic expanded longitudinal cross-sectional view of the top blowing lance used by the comparative example.

  Hereinafter, the present invention will be specifically described.

The present invention is intended to reduce CO ₂ emissions when a hot metal produced in a blast furnace is subjected to dephosphorization treatment as a preliminary treatment, and the dephosphorized hot metal is decarburized and refined in a converter to produce molten steel. The purpose is to increase the blending ratio of cold iron sources such as iron scrap. The converter has a large free board, and it is possible to vigorously stir the hot metal, which not only has a high melting capacity of the cold iron source, but also quickly removes phosphorous with a small amount of lime-based solvent. Therefore, in the present invention, the dephosphorization treatment performed as a preliminary treatment is also performed using a converter similarly to the decarburization refining.

  The hot metal used in the present invention is a hot metal produced in a blast furnace, and this hot metal is received in a hot metal transfer container such as a hot metal ladle or a topped car and transferred to a converter for performing dephosphorization treatment and decarburization refining. To do. When dephosphorization is performed, in order to efficiently perform dephosphorization with a small amount of lime-based solvent, silicon in the hot metal is removed in advance before the dephosphorization (referred to as “hot metal desiliconization”). It is preferable to reduce the silicon content of the hot metal to 0.20 mass% or less, desirably 0.10 mass% or less. When the desiliconization process is performed, the slag generated during the desiliconization process is discharged before the dephosphorization process.

  Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of a converter facility equipped with an upper blowing lance having a quadruple pipe structure used when carrying out hot metal dephosphorization treatment and decarburization refining according to the present invention, and FIG. FIG. 2 is a schematic enlarged longitudinal sectional view of the upper blowing lance 3 shown in FIG. 1. In the present invention, the decarburization and refining of the hot metal that has been subjected to the dephosphorization treatment is also performed using the same converter equipment (but not the same converter equipment) as shown in FIG. Therefore, here, the converter equipment that performs the dephosphorization process is indicated as the converter equipment 1, and the converter equipment that performs the decarburization refining of the hot metal that has been subjected to the dephosphorization process is indicated as the converter equipment 1A. In the present invention, the dephosphorization treatment and the decarburization refining are performed using the upper blow lance 3 having the same structure of the quadruple pipe. The upper blow lance 3 used in the dephosphorization treatment is used as the first upper blow lance 3. On the other hand, the upper blow lance 3 used in the decarburization process is called a second upper blow lance.

  In the present invention, the converter equipment 1A used for hot metal dephosphorization and the converter equipment 1A used for decarburization refining are composed of an iron shell 4 and a refractory 5 is enforced inside the iron shell 4. A furnace body 2 and an upper blowing lance 3 (first upper blowing lance) which is inserted into the furnace body 2 and is movable in the vertical direction are provided. An upper portion of the furnace body 2 is provided with a hot water outlet 14 for pouring hot metal 14 after dephosphorization treatment or molten steel (not shown) after decarburization refining, and at the bottom of the furnace body 2. Are provided with a plurality of bottom blowing tuyere 7 for blowing the gas 16 for stirring. The bottom blowing tuyere 7 is connected to a gas introduction pipe 8.

  The top blowing lance 3 includes a refining oxidizing gas supply pipe 9 for supplying a dephosphorizing refining oxidizing gas or a decarburizing refining oxidizing gas, propane gas, liquefied natural gas, coke oven gas, A fuel supply pipe 11 for supplying fuel such as oil and heavy oil, and a cooling water supply pipe and a drain pipe (not shown) for supplying and discharging cooling water for cooling the top blowing lance 3 ,It is connected. As the oxidizing gas for dephosphorization, oxygen gas, air, oxygen-enriched air, mixed gas of oxygen gas and rare gas (Ar gas or the like) is used, and oxygen gas is generally used. As the oxidizing gas for decarburization refining, oxygen gas, a mixed gas of oxygen gas and rare gas is used, and oxygen gas is generally used. The oxygen gas is industrial pure oxygen gas. FIG. 1 shows an example of oxygen gas that is generally used as an oxidizing gas for dephosphorization and decarburization.

  The refining oxidizing gas supply pipe 9 is branched into a powder medium solvent supply pipe 10 in the middle, and the branched powder medium solvent supply pipe 10 is a dispenser provided in the middle of the powder medium solvent supply pipe 10. The refining oxidizing gas supply pipe 9 is joined again via the refining oxidizing gas supply pipe 9, and the refining oxidizing gas supply pipe 9 is connected to the upper blowing lance 3 on the downstream side after the joining. The dispenser 12 contains a powdered medium solvent 13 used as a refining agent, and the dephosphorizing refining oxidizing gas or decarburizing refining oxidizing gas introduced into the powdered medium solvent supply pipe 10 is It functions as a conveying gas for the medium solvent 13 accommodated in the dispenser 12, and the powdered medium solvent 13 accommodated in the dispenser 12 passes through the powder medium solvent supply pipe 10 and the refining oxidizing gas supply pipe 9 in order. Is supplied to the upper blowing lance 3 and is blown toward the hot metal 14 from the tip of the upper blowing lance 3. As the solvent 13, a lime-based solvent is used in the case of dephosphorization, and a lime-based solvent, manganese ore, or a mixture thereof is used in the case of decarburization refining.

  The refining oxidizing gas supply pipe 9 is provided with a flow rate adjusting valve 25, and the powder medium solvent supplying pipe 10 is provided with a flow rate adjusting valve 26, and the refining oxidizing gas supply pipe 9 and the powdery state are provided. The flow rate of the dephosphorizing refining oxidizing gas or the decarburizing refining oxidizing gas passing through the solvent supply pipe 10 can be arbitrarily adjusted by the flow rate adjusting valve 25 and the flow rate adjusting valve 26. That is, after a predetermined amount of the medium solvent 13 is added to the hot metal 14, only the refining oxidizing gas can be supplied toward the hot metal 14.

  As shown in FIG. 2, the upper blow lance 3 is composed of a cylindrical lance body 17 and a copper cast lance tip 18 connected to the lower end of the lance body 17 by welding or the like. 17 is composed of four concentric steel pipes, that is, a quadruple pipe, that is, an innermost pipe 21, an inner pipe 22, an intermediate pipe 23, and an outer pipe 24. The refining oxidizing gas supply pipe 9 communicates with the innermost pipe 21, the cooling water drain pipe communicates with the inner pipe 22, the fuel supply pipe 11 communicates with the middle pipe 23, and the cooling water supply pipe serves as the outer pipe. 24. That is, the oxidizing gas for dephosphorization refining, the oxidizing gas for decarburizing refining, or the medium solvent 13 using these oxidizing gases as the carrier gas passes through the innermost pipe 21, and fuel such as propane gas is supplied. The gap between the inner pipe 22 and the inner pipe 23 passes through, the gap between the innermost pipe 21 and the inner pipe 22 is a cooling water drainage channel, and the gap between the inner pipe 23 and the outer pipe 24 is a cooling water supply flow. It is a road. The cooling water is configured to reverse at the position of the lance tip 18.

  The inside of the innermost tube 21 communicates with the main hole nozzle 19 disposed at the tip of the lance tip 18, and the gap between the inner tube 22 and the middle tube 23 communicates with the fuel injection hole 20. The fuel injection hole 20 is open to the main hole nozzle 19. The main hole nozzle 19 is a nozzle for spraying an oxidizing gas for dephosphorization refining, an oxidizing gas for decarburizing refining, or a solvent 13 using these oxidizing gases as a carrier gas, and the fuel injection hole 20 is It is a nozzle for injecting fuel. That is, the inside of the innermost pipe 21 serves as a refining oxidizing gas supply flow path for supplying a dephosphorizing refining oxidizing gas or a decarburizing refining oxidizing gas, and a gap between the inner pipe 22 and the middle pipe 23. Is a fuel supply flow path. The gap between the innermost tube 21 and the inner tube 22 is a cooling water drainage channel, and the gap between the middle tube 23 and the outer tube 24 is a cooling water supply channel. A plurality of main hole nozzles 19 are arranged at substantially equal intervals on the same circumferential line centering on the axis of the upper blowing lance 3. In FIG. 2, the cooling water drainage channel is installed inside the fuel supply channel, but the cooling water drainage channel may be arranged outside the fuel supply channel, The drainage channel and the cooling water supply channel may be interchanged.

  As shown in FIG. 2, the main hole nozzle 19 has the shape of a Laval nozzle composed of two cones, a portion whose cross section is reduced (referred to as a “throttle portion”) and a portion where the cross section is enlarged (referred to as a “skirt portion”). The refining oxidizing gas is injected from the main hole nozzle 19 at supersonic speed or subsonic speed. The fuel injection hole 20 is disposed so as to open in the skirt portion of the main hole nozzle 19. In FIG. 2, only one fuel injection hole 20 is opened for one main hole nozzle 19, but a plurality of fuel injection holes 20 may be opened for one main hole nozzle 19. In the Laval nozzle, the portion having the smallest cross-sectional area that is the boundary between the two cones of the throttle portion and the skirt portion is called a throat.

  In the upper blow lance 3, fuel is injected from the fuel injection hole 20, and an oxidizing gas for dephosphorization refining or an oxidizing gas for decarburization refining is injected from the main hole nozzle 19, or oxidation of these By injecting the medium solvent 13 together with the property gas, a flame can be formed below the tip of the upper blowing lance 3.

  In order to increase the mixing ratio of the cold iron source using the converter equipment 1 and the converter equipment 1A having this structure, first, the hot metal 14 is dephosphorized in the converter equipment 1 and then the dephosphorization process is performed. The molten iron 14 is subjected to decarburization refining in the converter facility 1 </ b> A to produce molten steel from the molten iron 14. Hereinafter, the dephosphorization process will be described in order.

  In performing dephosphorization treatment on the hot metal 14 using the converter equipment 1, first, a cold iron source is charged into the furnace body 2. The cold iron source used is iron scrap such as slabs and steel plate crops and city scraps generated at steelworks, bullion recovered from slag by magnetic sorting, and cold iron, reduced iron, etc. can do. Before and after the completion of the charging of the cold iron source, the stirring gas 16 starts to be blown from the bottom blowing tuyere 7.

The blending ratio of the cold iron source is preferably a total value of the blending ratio in the dephosphorization treatment and the blending ratio in the decarburization refining, and is preferably 5% by mass or more. The blending ratio of the cold iron source is defined by the following formula (1).
Mixing ratio of cold iron source (% by mass) = Cold iron source blending amount × 100 / (molten iron blending amount + cold iron source blending amount) (1)
This is because if the total blending ratio of the cold iron source from the dephosphorization process to the decarburization refining is less than 5% by mass, not only the effect of improving the productivity but also the effect of reducing the CO ₂ generation amount is small. The upper limit of the blending ratio of the cold iron source does not need to be particularly determined, and the hot metal temperature after the dephosphorization treatment can be added up to an upper limit that can maintain the target range.

  After charging the cold iron source into the furnace body 2, the hot metal 14 is charged into the furnace body 2. The hot metal 14 used can be processed with any composition, and may be subjected to desulfurization or desiliconization before the dephosphorization. Incidentally, the main chemical components of the hot metal 14 before the dephosphorization treatment are: carbon: 3.8 to 5.0 mass%, silicon: 0.3 mass% or less, phosphorus: 0.08 to 0.2 mass%, sulfur : About 0.05% by mass or less. However, if the amount of slag 15 generated in the furnace body during the dephosphorization process increases, the dephosphorization efficiency decreases. As described above, the amount of slag generated in the furnace body is reduced to increase the dephosphorization efficiency. Therefore, it is preferable to previously reduce the silicon concentration in the hot metal to 0.20 mass% or less, desirably 0.10 mass% or less by desiliconization treatment. Moreover, if the hot metal temperature is in the range of 1200 to 1450 ° C., dephosphorization can be performed without any problem.

  Next, an oxidizing gas for dephosphorization refining is supplied to the dispenser 12, and the powdered lime-based medium solvent as the medium solvent 13 is molten together with the oxidizing gas for dephosphorizing refining from the main hole nozzle 19 of the top blowing lance 3. Spray toward the bath surface. The fuel is injected from the fuel injection hole 20 of the top blowing lance 3 before and after the spraying of the medium solvent 13 (hereinafter referred to as “lime-based medium solvent 13” in the case of dephosphorization treatment). The fuel supplied from the fuel injection hole 20 and the oxidizing gas which is injected from the main hole nozzle 19 and which is a conveying gas for the lime-based solvent 13 and is also an oxidizing gas for dephosphorization refining are the main hole nozzle. After the 19 skirts are mixed, the atmospheric temperature may be high, and the oxidizability injected from the main hole nozzle 19 when the fuel concentration reaches the combustion limit range without an ignition device. Combustion is caused by part of the gas, and a flame is formed below the upper blowing lance 3. The lime medium solvent 13 passes through the formed flame, receives the heat of the flame, is heated or heated / melted, and is sprayed onto the bath surface of the hot metal 14 in the heated or molten state. As a result, the heat of the flame reaches the hot metal 14 via the lime-based medium solvent 13, the temperature of the hot metal 14 rises, and the dissolution of the added cold iron source is promoted.

  At the same time, an oxidizing gas for dephosphorization and refining that partially functions as a transfer gas is sprayed from the main hole nozzle 19 toward the bath surface of the hot metal 14.

In the dephosphorization reaction of the hot metal 14, phosphorus in the hot metal reacts with oxygen in the oxidizing gas or iron oxide generated by oxygen to form a phosphor oxide (P ₂ O ₅ ), and this phosphor oxide becomes a lime-based medium. It progresses by being absorbed by the slag 15 formed by the hatching of the solvent 13. Moreover, the dephosphorization rate increases as the hatching of the lime-based medium 13 is promoted.

  That is, in the present invention, in the heated or molten state, the lime-based solvent 13 sprayed on the hot metal bath surface immediately hatches to form slag 15, and the supplied dephosphorizing oxidizing gas and Phosphorus oxide is formed by reaction with phosphorus in the hot metal. Combined with the strong stirring of the hot metal 14 and the slag 15 by the stirring gas 16, the formed phosphorous oxide is quickly absorbed into the hatched slag 15, and the dephosphorization reaction of the hot metal 14 proceeds promptly.

As the lime-based medium solvent 13, a lime-based medium solvent such as quick lime (CaO), limestone (CaCO ₃ ), slaked lime (Ca (OH) ₂ ), dolomite (CaO—MgO) is used. A mixture of quicklime with fluorite (CaF ₂ ) or alumina (Al ₂ O ₃ ) as a hatching accelerator can also be used as the lime-based solvent 13. Further, converter slag (CaO—SiO ₂ -based slag) generated in the decarburizing and refining process of the hot metal 14 can be used as all or part of the lime-based solvent 13. Note that it is not necessary to supply the entire amount of the lime-based solvent 13 to be added from the top blowing lance 3, and supply the oxidizing gas from the top blowing lance 3 after charging the cold iron source or hot metal 14 into the furnace body 2. Before performing, a part of the lime-based medium solvent 13 may be put in advance separately from the furnace hopper to the furnace body 2.

  Not only the heat of flame is transmitted to the hot metal 14 by the lime-based solvent 13, but also the combustion heat of the flame existing above the hot metal 14 is transmitted to the hot metal 14, so that the hot metal 14 is vigorously stirred. The dissolution of the cold iron source inside is promoted. That is, the melting of the charged cold iron source is completed during the dephosphorization process.

  Thereafter, when the phosphorus concentration in the hot metal 14 becomes the target value or less, all the supply from the top blowing lance 3 to the hot metal 14 is stopped and the dephosphorization process is completed. In this case, it is not necessary to continue supplying the lime-based medium solvent 13 from the top blowing lance 3 until the dephosphorization process is completed. Only the oxidizing gas for refining may be supplied. Further, during this dephosphorization treatment, iron oxide such as iron ore may be placed on the furnace body 2 from the furnace hopper as a solid oxygen source. After the dephosphorization process, the furnace body 2 is tilted, and the hot metal 14 subjected to the dephosphorization process is discharged into a hot metal holding container such as a ladle or a converter charging pot through the hot water outlet 6. After the hot metal 14 is discharged, the furnace body 2 is tilted to discharge the slag 15 in the furnace body to the slag container.

  Thereafter, the hot metal 14 discharged from the hot metal holding container is charged into the furnace body 2 of another converter 1A equipped with the upper blow lance 3 (second upper blow lance) having a quadruple pipe structure shown in FIG. Then, decarburization refining is performed on the hot metal 14. Also in the case of decarburization refining, a flame is formed at the tip of the top blowing lance 3, the medium solvent 13 used as a refining agent is heated and melted in this flame, and the heat of the flame is passed through the medium solvent 13 in the furnace body. The hot metal 14 is heated. As described above, in the case of decarburization refining, one or more of lime-based medium solvent and manganese ore are used as the medium solvent 13.

  Also in the case of decarburization refining, a cold iron source similar to the cold iron source used in the above dephosphorization treatment is charged in the furnace body 2 in advance before the molten iron 14 is charged. The heat source for melting the cold iron source in this decarburization refining process depends on the sensible heat of the hot metal 14, the carbon concentration in the hot metal and the amount of heat received from the flame. If the source blending ratio is set high, the cold iron source blending ratio must be set low in the decarburization refining process using the hot metal 14. Accordingly, the mixing ratio of the cold iron source in the decarburizing and refining process is such that the total value of the mixing ratio in the dephosphorizing process and the mixing ratio in the decarburizing and refining process is 5% by mass or more. It is preferable to set according to the blending ratio.

  When the hot metal 14 is charged into the furnace body 2, the top blowing lance 3 is inserted into the furnace body 2, and Ar gas or the like is blown into the hot metal 14 as the stirring gas 16 from the bottom blowing tuyere 7. From the main hole nozzle 19, an oxidizing gas for decarburizing and refining is sprayed onto the hot metal bath surface, and at the same time, a powdered medium solvent 13 is injected using the oxidizing gas for decarburizing and refining as a carrier gas, and a fuel injection hole 20. Then, gas fuel such as propane gas, natural gas and coke oven gas, or hydrocarbon liquid fuel such as heavy oil and kerosene is supplied.

A flame is formed at the tip of the upper blowing lance 3, and the solvent 13 is heated or heated / melted by receiving the heat of the flame through the formed flame, and the bath of the molten iron 14 is heated or melted. Sprayed on the surface. Thereby, the heat of the flame reaches the hot metal 14 via the medium solvent 13, the temperature of the hot metal 14 rises, and the dissolution of the added cold iron source is promoted. Further, the decarburization reaction (2C + O ₂ → 2CO) proceeds by the oxidizing gas for decarburization refining supplied from the main hole nozzle 19.

  As the solvent 13 supplied from the main hole nozzle 19 of the top blowing lance 3, a lime-based solvent (such as quick lime or dolomite) or manganese ore is used as described above. Moreover, it is not necessary to supply all of these auxiliary materials from the top blowing lance 3, and some of these may be added from the furnace hopper. Furthermore, the supply from the top blowing lance 3 and the addition of the upper part may be used in combination.

  When a lime-based solvent is used as the solvent 13, the slag that not only heats the flame to the molten iron 14 but also the lime-based solvent sprayed on the molten metal bath immediately hatches to cover the bath surface. 15 is formed to prevent spitting (scattering of metal) or to promote dephosphorization reaction. When manganese ore is used as the solvent 13, not only does the heat of the flame reach the molten iron 14, but the manganese ore is reduced by the carbon in the molten iron and functions as a manganese source for adjusting the molten steel components.

  The oxidizing gas supplied from the main hole nozzle 19 of the top blowing lance 3 reacts with the carbon in the hot metal, the decarburization reaction proceeds, and the carbon concentration of the hot metal 14 decreases. When the carbon concentration has decreased to the target value, all the supply from the top blowing lance 3 to the iron bath is stopped and the decarburization refining is finished. In this case, it is not necessary to continue supplying the solvent 13 from the top blowing lance 3 until the decarburization refining is completed. Only gas may be supplied. The added cold iron source dissolves during the decarburization process.

  In this way, the molten iron 14 discharged from the blast furnace is subjected to dephosphorization and decarburization and molten steel is produced from the molten iron 14. The produced molten steel is poured out into a ladle and, if necessary, subjected to secondary refining with an RH vacuum degasser or the like, and then cast into a slab with a continuous casting machine.

As described above, according to the present invention, the dephosphorization treatment in the converter equipment 1 performed as a preliminary treatment for the hot metal 14 and the decarburization refining of the hot metal subjected to the dephosphorization treatment in the converter equipment 1A. , The powdered medium solvent 13 used as a refining agent is heated by a flame formed below the tip of the upper lance 3, and the heat of the flame is made to reach the molten iron 14 via the medium solvent 13. As a result, it is possible to increase the blending ratio of cold iron sources such as iron scrap in dephosphorization and decarburization refining, thereby significantly reducing CO ₂ emissions compared to the past. It becomes possible.

  When supplying from the top blowing lance 3 of the medium solvent 13, an oxidizing gas for dephosphorization refining or an oxidizing gas for decarburizing refining is used as a carrier gas. In addition, the main component is hydroxide, fluoride, etc., and it does not contain a combustible substance such as metal or carbon, so that heat generation and combustion in the flow path of the top lance 3 can be prevented. Further, as the transporting gas for the solvent 13, the oxidizing gas for dephosphorizing or indispensable for the dephosphorizing process and decarburizing refining is used. The use of an inert gas such as nitrogen gas or Ar gas which has been used is unnecessary, which is economically advantageous.

  Hot metal and iron scrap are charged into the furnace body of a small converter facility having the same structure as the converter facility shown in FIG. 1 and having a furnace capacity of 2.5 tons, and the hot metal dephosphorization is performed using this small converter device. Processed. After the dephosphorization process, the hot metal is poured into a hot metal holding container, and the hot metal and iron scrap after the dephosphorization process have the same structure as the converter equipment shown in FIG. The decarburization refining was performed by charging the furnace body of the converter facility (example of the present invention).

  The top blow lance used in this dephosphorization treatment and decarburization refining is of a quadruple pipe structure, similar to the top blow lance shown in FIG. 2, and is used for dephosphorization refining or decarburization from the center side in the cross section. A refining oxidizing gas supply channel, a refining oxidizing gas supply flow channel, a cooling water drainage flow channel, a fuel supply flow channel, and a cooling water supply water flow channel are provided.

  The main hole nozzle is a three-hole Laval nozzle with a throat diameter of 7 mm, and has an angle of 15 ° with respect to the lance center axis. The fuel injection hole opens at a position 20 mm from the outlet of the main hole nozzle, and the nozzle diameter is 2 mm. Oxygen gas was used as an oxidizing gas for dephosphorization and oxidizing gas for decarburizing and refining.

In the dephosphorization process, after iron scrap is charged into the furnace body, hot metal having a temperature of 1350 ° C. is charged, and then the top blow is performed while Ar gas is blown into the hot metal as a stirring gas from the bottom blowing tuyere. From the main hole nozzle of the lance, oxygen gas for dephosphorization refining is sprayed on the hot metal bath surface, and at the same time, quick lime (= lime-based medium solvent) is sprayed on the hot metal bath surface using this oxygen gas as a carrier gas, and Propane gas was ejected from the fuel injection hole of the top blowing lance to perform dephosphorization treatment. In this dephosphorization treatment, iron ore was added on top from a hopper on the furnace. The amount of iron scrap charged is adjusted so that the hot metal temperature at the end of the dephosphorization process is 1400 ° C., and quick lime is the basicity of slag in the furnace at the end of the dephosphorization process (mass% CaO / mass%). The amount of addition was adjusted so that (SiO ₂ ) was 2.5.

  In the decarburization refining process, iron scrap was charged into the furnace body, dephosphorization treatment was performed, and hot metal with a temperature of 1350 ° C. was charged, and then molten iron with Ar gas as a stirring gas from the bottom blowing tuyere While blowing in, oxygen gas for decarburization and refining is blown onto the hot metal bath surface from the main hole nozzle of the top blowing lance, and at the same time, quick lime (= solvent) is directed to the hot metal bath surface using this oxygen gas as a carrier gas. Then, propane gas was ejected from the fuel injection hole of the top lance and decarburization refining was performed. In this case, the amount of iron scrap charged was adjusted so that the molten steel temperature at the end of decarburization refining was 1680 ° C. and the carbon concentration in the molten steel was 0.05 mass%. The amount of quicklime was adjusted so that the basicity of the slag in the furnace at the end of decarburization refining was 3.5.

  As a comparative example, in a small converter having a furnace capacity of 2.5 tons, an upper blowing lance similar to the upper blowing lance disclosed in Patent Document 3 is used. Dephosphorization treatment and decarburization refining were performed according to the above-described example of the present invention using the refining method disclosed in No. 3. FIG. 3 shows a schematic enlarged vertical sectional view of the top blowing lance used in the comparative example. In FIG. 3, reference numeral 3A is an upper blow lance, 17A is a lance body, 18A is a lance tip, 27 is a fuel combustion oxidizing gas and refining powder injection nozzle, 28 is a fuel injection hole, and 29 is a main hole nozzle. , 30 is the innermost tube, 31 is the inner tube, 32 is the inner tube, 33 is the outer tube, and 34 is the outermost tube, and the upper blow lance 3A is oxidizable for fuel combustion from the center side in the cross section. Gas and refining powder supply flow path (inside the innermost pipe 30), fuel supply flow path (gap between the innermost pipe 30 and the inner pipe 31), refining oxidizing gas supply flow path (with the inner pipe 31) A gap between the middle pipe 32), a cooling water drainage channel (gap between the middle pipe 32 and the outer pipe 33), and a cooling water supply channel (gap between the outer pipe 33 and the outermost pipe 34).

  In other words, in the upper blow lance 3A, the refining powder is supplied into the innermost pipe 30 using an inert gas such as Ar gas as a carrier gas, but the innermost pipe 30 is oxidized for fuel combustion. A gas for refining, an inert gas such as Ar gas (carrier gas), and an oxidizing gas for fuel combustion are injected from the injection nozzle 27 through which the innermost tube 30 communicates. It is configured to be. The injection nozzle 27 is a straight type nozzle having an inner diameter of 11.5 mm, the fuel injection hole 28 is a slit-like nozzle that opens in an annular shape with a gap of 1.0 mm, and the main hole nozzle 29 that injects refining oxygen gas is The throat diameter is a three-hole Laval nozzle having a diameter of 7 mm, and has an angle of 15 ° with respect to the lance center axis.

  From this top blowing lance 3A, powdery quick lime and powdered iron ore are supplied as refining powder, Ar gas is used as a conveying gas for these refining powders, an oxidizing gas for fuel combustion, and Oxygen gas was used as the oxidizing gas for refining. That is, the difference between the present invention example and the comparative example is that the comparative example uses Ar gas as the carrier gas for the refining powder, and the iron ore added in the dephosphorization treatment of the present invention example. In the comparative example, the stone is supplied from the top blowing lance 3A.

  Table 1 shows the temperature and composition of the hot metal used in the dephosphorization treatment and decarburization refining in the inventive examples and the comparative examples.

  In addition, the blowing speed of powder such as a powder medium solvent in the dephosphorization treatment and decarburization refining in the present invention example and the comparative example, the propane gas blowing flow rate, the oxygen gas blowing flow rate for refining, the Ar gas flow rate for powder transfer, Table 2 shows the operating conditions such as the bottom blowing stirring gas blowing flow rate and the lance height.

  Table 3 shows the operation results (the refining time, the amount of iron scrap, the inert gas basic unit, the CO gas concentration in the exhaust gas) in the inventive examples and the comparative examples. The inert gas basic unit is the total value of the stirring Ar gas blown from the bottom blowing tuyere and the Ar gas used as the carrier gas for the refining powder.

  As is apparent from Table 3, when the inert gas intensity is compared between the present invention example and the comparative example, the present invention example that does not use an inert gas as the carrier gas is lower and more expensive Ar gas. As a result, it was confirmed that a significant reduction in refining costs can be realized by applying the present invention.

  In addition, since an inert gas is not used as the carrier gas, in the present invention, the CO gas concentration of the exhaust gas can be increased compared to the comparative example, that is, the calorific value of the exhaust gas can be increased, It was found that it can be used more effectively as fuel gas.

DESCRIPTION OF SYMBOLS 1 Converter equipment 2 Furnace main body 3 Top blowing lance 4 Iron skin 5 Refractory 6 Outlet 7 Bottom blowing tuyere 8 Gas introduction pipe 9 Refining oxidizing gas supply pipe 10 Powdered medium solvent supply pipe 11 Fuel supply pipe 12 Dispenser 13 Medium Solvent 14 Hot Metal 15 Slag 16 Gas for Stirring 17 Lance Body 18 Lance Tip 19 Main Hole Nozzle 20 Fuel Injection Hole 21 Innermost Pipe 22 Inner Pipe 23 Middle Pipe 24 Outer Pipe 25 Flow Control Valve 26 Flow Control Valve

Claims (2)

A refining oxidizing gas supply flow path for supplying a oxidizing gas for dephosphorization refining and supplying a powdery lime-based solvent using the oxidizing gas as a carrier gas; and a fuel supply flow path for supplying fuel Using a first top blowing lance, each having
At the same time as supplying the fuel from the fuel supply channel, the oxidizing gas is supplied from the refining oxidizing gas supply channel toward the hot metal bath surface in the converter, and the fuel is supplied by a part of the oxidizing gas. While combusting to form a flame below the tip of the first top blowing lance, the powdery lime-based medium solvent is transferred from the refining oxidizing gas supply flow path into the converter using the oxidizing gas as a carrier gas. Supply to the hot metal bath surface, dephosphorizing the hot metal in the converter,
Next, the molten iron obtained after the dephosphorization treatment is discharged from the converter into a hot metal holding container, and this hot metal is charged into another converter,
A refining oxidizing gas supply flow path for supplying a oxidizing medium gas for decarburization refining and supplying a powdered medium solvent using the oxidizing gas as a carrier gas; and a fuel supply flow path for supplying fuel. Use a second top blowing lance that each has separately,
At the same time as supplying the fuel from the fuel supply channel, the oxidizing gas is supplied from the refining oxidizing gas supply channel toward the hot metal bath surface in the converter, and the fuel is supplied by a part of the oxidizing gas. While burning and forming a flame below the tip of the second upper blowing lance, the powdery solvent is fed from the refining oxidizing gas supply flow path into the hot metal bath in the converter using the oxidizing gas as a carrier gas. To the surface, decarburizing and refining the hot metal in the converter,
Thus, a method for producing molten steel, comprising producing molten steel from molten iron.   The first upper blow lance and the second upper blow lance are formed from the center side in the cross-sectional structure from the refining oxidizing gas supply passage, the cooling water drain passage, the fuel supply passage, and the cooling water supply passage. The method for producing molten steel according to claim 1, wherein the steel has a quadruple tube structure.

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