JP5928094B2 - Method for refining molten iron - Google Patents

Description

  The present invention uses an upper blowing lance having a burner function to form a flame below the tip of the upper blowing lance, and heats the powdered refining agent while heating the powdery refining agent with the formed flame. The present invention relates to a method for refining molten iron which is sprayed on molten iron in a furnace and subjected to oxidative refining treatment on molten iron.

From the viewpoint of environmental protection, suppression of CO ₂ emissions in the steel manufacturing process has become an urgent task. In order to reduce CO ₂ emissions, in the steelmaking process, measures such as increasing the amount of cold iron source such as iron scrap as the iron source and reducing the mixing ratio of hot metal in the molten iron have been studied and It has been implemented. The reason for increasing the amount of cold iron used is that, in the production of steel products, the production of hot metal (molten iron) in a blast furnace requires a large amount of energy to reduce and melt iron ore and a large amount In contrast to exhausting CO ₂ , the cold iron source only requires heat of dissolution, and the more this cold iron source is used in the steelmaking process, the more energy consumption and CO ₂ generation will be reduced. There is a point that can be. Molten iron means a molten iron source, for example, molten iron produced in a blast furnace, molten steel obtained by melting iron scrap in an electric furnace, and molten steel that has been decarburized and refined from molten iron.

  In the steel manufacturing process consisting of a combination of a blast furnace and a converter, the heat source for melting the cold iron source is mainly sensible heat of the hot metal and the combustion heat of carbon and silicon in the hot metal. For this reason, in this steel manufacturing process, a large amount of cold iron sources cannot be dissolved originally. In addition, the preliminary dephosphorization treatment is performed on the hot metal, and the temperature of the hot metal decreases with the addition of this treatment step. Furthermore, the carbon and silicon in the hot metal are oxidized by the preliminary dephosphorization treatment and their concentration is reduced, which is a disadvantageous factor for dissolving the cold iron source. Note that the hot metal preliminary dephosphorization treatment is a step of removing phosphorus in the hot metal to some extent by performing dephosphorization treatment in advance in the hot metal stage before decarburization and refining treatment in the converter.

  In view of this, many methods have been proposed for increasing the thermal margin of hot metal and molten steel in preliminary dephosphorization and decarburization refining in a converter. For example, in Patent Document 1, a carbon source is added to generated slag during preliminary dephosphorization treatment, an oxygen source is blown into the slag, the carbon source is combusted, and the combustion heat from the combustion is attached to the hot metal. A method of heating has been proposed.

  Patent Document 2 discloses a method for increasing the hatchability of flux in order to improve metallurgical reaction characteristics such as dephosphorization. In this method, in addition to oxygen gas, a fuel gas such as natural gas and a flux such as quicklime are supplied from the top blowing lance, and the flux is supplied to the molten iron in a molten state by passing through the combustion flame of the fuel gas. Is possible.

JP-A-9-020913 JP-A-11-080825

However, the above prior art has the following problems. In patent document 1, although a hot metal temperature rises by adding a carbon source in production | generation slag, mixing of the sulfur contained in a carbon source is caused, and the sulfur concentration in steel becomes high. In addition, there is a problem that the refining time becomes long to ensure the combustion time of the carbon source, and the manufacturing cost increases. Furthermore, since the carbon source is burned, there is a problem that the amount of CO ₂ generated naturally increases.

  In Patent Document 2, when performing an oxidation refining process in a converter using an upper blowing lance, the upper blowing lance height may vary during the blowing. When the top blowing lance height fluctuates, the flame length and the lance height are greatly different. As a result, it is considered that the powdery refining agent does not effectively heat.

  The present invention has been made in view of the above circumstances, and its object is to use an upper blowing lance having a burner function, and to form a burner flame at the lower end of the upper blowing lance, through the upper blowing lance. The powdered smelting agent is applied to the hot metal by oxidative smelting treatment such as preliminary dephosphorization and decarburization smelting by spraying the powdered smelting agent on the molten iron to which the cold iron source is added in the converter while heating with this flame. It is to provide a method for refining molten iron that can efficiently heat the agent and stably increase the blending ratio of the cold iron source in the hot metal.

The gist of the present invention for solving the above problems is as follows.
(1) Using an upper blow lance having separately a powdery refining agent supply channel, a fuel gas supply channel, an oxidizing gas supply channel for combustion of fuel gas, and an oxidizing gas supply channel for refining The fuel gas is supplied from the fuel gas supply channel and the combustion oxidizing gas is supplied from the combustion oxidizing gas supply channel toward the bath surface of the molten iron accommodated in the converter. To form a flame in front of the nozzle of the upper blowing lance,
Supplying the powdery refining agent from the powdery refining agent supply flow path, supplying the refining oxidizing gas while spraying the powdery refining agent toward the molten iron bath surface while heating with the flame. A method for refining molten iron that supplies oxidizing gas for refining toward a bath surface of molten iron from a flow path,
A method for refining molten iron, characterized in that the flame is formed while satisfying the following equation (1) for a flow rate ratio between a fuel gas and an oxidizing gas for combustion.
0.4 ≦ (G / F) / (G / F) _st ≦ 1.0 (1)
However, in the formula (1), G: combustion oxidizing gas supply rate (Nm ³ / min), F: fuel gas supply rate (Nm ³ / min), (G / F) _st : fuel gas and the fuel This is the ratio of the stoichiometric coefficient to the oxidizing gas required for complete combustion of the gas.
(2) The combustion oxidizing gas supply rate G is adjusted so that the discharge flow velocity V _G of the combustion oxidizing gas satisfies the following equation (2): A method for refining molten iron.
0.2 ≦ V _G /C≦1.0 (2)
However, in the formula (2), V _G : discharge flow rate of combustion oxidizing gas (Nm / sec),
C: Sound velocity (Nm / sec).
(3) The powdery refining agent includes at least one of iron oxide, a lime-based solvent, and a combustible substance, and the powdery refining agent is directed to a molten iron bath surface together with an inert gas. The method for refining molten iron according to (1) or (2) above, wherein the molten iron to which the cold iron source is added is subjected to oxidative refining treatment.
(4) The method for refining molten iron according to (3), wherein the molten iron is hot metal, and the oxidative refining treatment is a preliminary dephosphorization treatment of hot metal.

According to the present invention, the fuel gas supplied from the fuel gas supply flow path of the upper blowing lance for forming the burner flame below the tip thereof, and the combustion oxidizing property supplied from the combustion oxidizing gas supply flow path Since the flow rate ratio to the gas is controlled to be within a predetermined range with respect to the ratio of the stoichiometric coefficient between the fuel gas and the oxidizing gas for combustion required for complete combustion of the fuel gas. The ratio (l / d) between the top blowing lance height d (m) and the flame length l (m) can be set to 0.8 or more and 1.2 or less. As a result, the heat of the flame can be effectively transferred to the powdery smelting agent supplied from the top blowing lance, so that the heated powdery smelting agent improves the thermal margin of the molten iron, and In the oxidative refining treatment of molten iron in a furnace, it becomes possible to greatly increase the blending ratio of cold iron sources such as iron scrap. Moreover, it is possible to reduce the amount of carbonized material for carburizing in order to keep the heat receiving efficiency to the molten iron stable and high, and there is an effect of reducing CO ₂ emission.

It is a schematic sectional drawing which shows the converter equipment used when implementing this invention. It is a general | schematic expanded longitudinal cross-sectional view of the top blowing lance used when implementing this invention. It is a graph which shows the relationship between the flow rate ratio of propane gas and combustion oxygen gas, and a flame length index. The values (l / d) of the flame length l with respect to the lance height d and the values (l / d) with respect to the amount of heat applied on the basis of the case where the flame length l and the lance height d are equal (l / d = 1) It is a graph which shows the relationship with the value (heat index) of the heat gain in / d.

  The present invention is directed to an oxidation refining process performed by supplying a refining oxidizing gas from a top blowing lance to hot metal contained in a converter. As this oxidative refining treatment, hot metal preliminary dephosphorization treatment and hot metal decarburization refining treatment are currently carried out, and the present invention can be applied to both oxidative refining treatments. When the present invention is applied to hot metal decarburization and refining, even if the present invention is applied to hot metal that has been subjected to preliminary dephosphorization, the present invention is applied to hot metal that has not been subjected to preliminary dephosphorization. It doesn't matter which way you do it. The present invention can also be applied to the case where the present invention is applied to a preliminary dephosphorization treatment and the hot metal refined by the preliminary dephosphorization treatment is decarburized and refined in a converter.

  The hot metal (molten iron) used in the present invention is a hot metal (molten iron) manufactured in a blast furnace. Transfer to a converter where phosphorus treatment and decarburization are performed. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, taking hot metal preliminary dephosphorization treatment in a converter as an example.

  FIG. 1 is a schematic cross-sectional view showing a converter facility used in carrying out the present invention. As shown in FIG. 1, a converter facility 1 includes a furnace body 2 and an upper blowing lance 3 that is inserted into the furnace body 2 and is movable in the vertical direction. The furnace body 2 has an outer shell made of an iron skin 4. A refractory 5 is provided inside the iron skin 4. A top 6 of the furnace body 2 is provided with a hot water outlet 6 for pouring hot metal 26 after the dephosphorization process, and a plurality of bottoms for injecting a stirring gas 28 into the furnace bottom of the furnace body 2. A blowing tuyere 7 is provided. The bottom blowing tuyere 7 is connected to a gas introduction pipe 8. The converter has a larger freeboard than the hot metal transfer container such as hot metal ladle or topped car, and it is possible to vigorously stir the hot metal, which not only increases the melting capacity of the cold iron source but also reduces the amount of lime. The dephosphorization process can be performed quickly with the amount of the system solvent used.

  The upper blowing lance 3 cools the powdery refining agent supply pipe 9, the fuel gas supply pipe 10, the combustion oxidizing gas supply pipe 11, the refining oxidizing gas supply pipe 12, and the upper blowing lance 3. A cooling water supply pipe and a drain pipe (not shown) for supplying and discharging cooling water are connected. The powdery refining agent supply pipe 9 is supplied with a powdery refining agent 29 containing at least one of iron oxide, lime-based solvent, and combustible substance together with inert gas such as nitrogen gas and Ar gas. . Gas fuel such as propane gas, liquefied natural gas, and coke oven gas is supplied to the fuel gas supply pipe 10. The combustion oxidizing gas supply pipe 11 is supplied with a combustion oxidizing gas such as oxygen gas or air for burning the supplied fuel gas. As the oxidizing gas for combustion, oxygen gas is generally used. The refining oxidizing gas supply pipe 12 is supplied with a refining oxidizing gas such as oxygen gas. As the oxidizing gas for refining, oxygen gas (industrial pure oxygen), oxygen-enriched air, or a mixed gas of oxygen gas and rare gas is used, but oxygen gas is generally used. In FIG. 1, oxygen gas is supplied as the oxidizing gas for combustion and the oxidizing gas for refining.

  It is possible to use hydrocarbon-based liquid fuels such as heavy oil and kerosene instead of fuel gas, but this may occur due to the possibility of clogging at the nozzle at the outlet of the flow path of the top blowing lance 3. In the form, it is preferable to use fuel gas (gaseous fuel). If gaseous fuel is used, there are advantages such that not only clogging of nozzles and the like can be prevented, but also the supply speed can be easily adjusted, and misfire can be prevented because ignition is easy.

  The other end of the powdery refining agent supply pipe 9 on the side not connected to the upper blowing lance 3 is connected to a dispenser 13 containing the powdery refining agent 29. Further, the dispenser 13 is connected to the powdery refining agent transport gas supply pipe 9A. The inert gas supplied to the dispenser 13 through the powdery refining agent transfer gas supply pipe 9A functions as a transfer gas for the powdery refining agent 29 stored in the dispenser 13, and the powder stored in the dispenser 13 The fine smelting agent 29 is supplied to the upper blowing lance 3 through the powdery smelting agent supply pipe 9 and can be sprayed from the tip of the upper blowing lance 3 toward the hot metal 26. In FIG. 1, nitrogen gas is supplied to the upper blowing lance 3 as a conveying gas for the powdery refining agent 29.

  FIG. 2 is a schematic cross-sectional view of an upper blowing lance according to the present invention. As shown in FIG. 2, the upper blow lance 3 has a cylindrical lance body 14 and a lance tip 15 made of a copper casting connected to the lower end of the lance body 14 by welding or the like. The lance body 14 is composed of six types of concentric steel pipes, that is, six-fold pipes, that is, an innermost pipe 20, a partition pipe 21, an inner pipe 22, an intermediate pipe 23, an outer pipe 24, and an outermost pipe 25.

  The powdery refining agent supply pipe 9 communicates with the innermost pipe 20, and the powdery refining agent 29 passes through the innermost pipe 20 together with the carrier gas. The fuel gas supply pipe 10 communicates with the partition pipe 21, and fuel gas such as propane gas passes through the gap between the innermost pipe 20 and the partition pipe 21. The combustion oxidizing gas supply pipe 11 communicates with the inner pipe 22, and the fuel combustion oxidizing gas passes through the gap between the partition pipe 21 and the inner pipe 22. The refining oxidizing gas supply pipe 12 communicates with the middle pipe 23, and the refining oxidizing gas passes through the gap between the inner pipe 22 and the middle pipe 23. Each of the cooling water supply pipe and the drain pipe communicates with either the outer pipe 24 or the outermost pipe 25, and the cooling water has a gap between the middle pipe 23 and the outer pipe 24 and the outer pipe 24 and the outermost pipe 25. Pass through the gap. Although the cooling water passes through the gap between the middle pipe 23 and the outer pipe 24 and the gap between the outer pipe 24 and the outermost pipe 25, either one may be used as the water supply flow path. The cooling water is configured to reverse at the position of the lance tip 15.

  The inside of the innermost tube 20 communicates with the center hole 16 disposed substantially at the axial center position of the lance tip 15, and the gap between the innermost tube 20 and the partition tube 21 is an annular nozzle around the center hole 16. Alternatively, the gap between the partition pipe 21 and the inner pipe 22 communicates with the fuel gas injection holes 17 that are opened as a plurality of concentric nozzle holes, and an annular nozzle or a plurality of concentric circles are formed around the fuel gas injection holes 17. The combustion oxidizing gas injection holes 18 opened as individual nozzle holes communicate with each other, and a plurality of gaps between the inner tube 22 and the intermediate tube 23 are provided around the combustion oxidizing gas injection holes 18. It communicates with the hole 19. The center hole 16 is a nozzle for spraying the powdery refining agent 29 together with the carrier gas, the fuel gas injection hole 17 is a nozzle for injecting the fuel gas, and the combustion oxidizing gas injection hole 18 is for burning the fuel gas. The nozzle for injecting the oxidizing gas and the peripheral hole 19 are nozzles for spraying the oxidizing gas for refining. That is, the inside of the innermost pipe 20 is a powdery refining agent supply flow path 31, the gap between the innermost pipe 20 and the partition pipe 21 is a fuel gas supply flow path 32, and the gap between the partition pipe 21 and the inner pipe 22 is A combustion oxidizing gas supply flow path 33 is formed, and a gap between the inner pipe 22 and the intermediate pipe 23 is a refining oxidizing gas supply flow path 34. The gap between the middle pipe 23 and the outer pipe 24 and the gap between the outer pipe 24 and the outermost pipe 25 serve as a cooling water supply channel or a drain channel. In other words, the top blow lance 3 has a powdery refining agent supply flow path 31, a fuel gas supply flow path 32, a combustion oxidizing gas supply flow path 33, and a refining oxidizing gas supply flow path 34 separately. And a cooling water supply channel and a drain channel.

  The center hole 16 is a straight nozzle, and the peripheral hole 19 is in the shape of a Laval nozzle composed of two cones, a portion whose cross section is reduced and a portion where the cross section is enlarged, but the center hole 16 is also a Laval nozzle shape. It does not matter. The fuel gas injection holes 17 and the combustion oxidizing gas injection holes 18 are straight nozzles that open in the shape of an annular slit, or straight nozzles that have a circular cross section. In the Laval nozzle, the position where the cross section is the narrowest, which is the boundary between the two cones of the reduced portion and the enlarged portion, is called a throat.

  In order to increase the blending ratio of the cold iron source using the converter equipment 1 having this configuration, the dephosphorization treatment according to the present invention is performed on the hot metal 26 as follows.

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. The blending ratio of the cold iron source is preferably 5% by mass or more based on the total iron source to be charged (mixing ratio of the cold iron source (mass%) = cold iron source blending amount × 100 / (molten iron blending amount). + Cold iron source blending amount)). This is because when the blending ratio of the cold iron source is less than 5% by mass, not only the effect of improving the productivity is small but also the effect of reducing the amount of CO ₂ generation 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 preliminary dephosphorization treatment can be added up to an upper limit capable of maintaining the target range. Before and after the cold iron source is charged, the stirring gas 28 starts to be blown from the bottom blowing tuyere 7.

  After the cold iron source is charged into the furnace body 2, the hot metal 26 is charged into the furnace body 2. The hot metal 26 used can be processed with any composition, and may be subjected to desulfurization or desiliconization before the preliminary dephosphorization. Incidentally, the main chemical components of the hot metal 26 before the preliminary 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 27 produced in the furnace body during the preliminary dephosphorization process increases, the dephosphorization efficiency decreases. Therefore, in order to increase the dephosphorization efficiency by reducing the amount of slag generated in the furnace, Before removing phosphorus, the silicon in the hot metal is removed in advance (referred to as “desiliconization of hot metal”), and the silicon concentration in the hot metal is reduced to 0.20 mass% or less, preferably 0.10 mass% or less in advance. It is preferable to keep it. Moreover, if the hot metal temperature is in the range of 1200 to 1400 ° C., dephosphorization can be performed without any problem. When the desiliconization process is performed, the slag generated during the desiliconization process is discharged before the dephosphorization process.

  Next, an inert gas is supplied to the dispenser 13, and the powdery refining agent 29 is sprayed from the center hole 16 of the upper blowing lance 3 toward the bath surface of the hot metal 26 together with the inert gas. Before and after the spraying of the powdery refining agent 29, fuel gas is injected from the fuel gas injection hole 17 of the upper blowing lance 3, and oxidizing gas such as oxygen gas is injected from the combustion oxidizing gas injection hole 18, A flame is formed below the nozzle front surface of the upper blowing lance 3 toward the bath surface of the hot metal 26.

  In generating a flame at the tip of the upper blowing lance 3, the following (1) is set so that the ratio (l / d) of the upper blowing lance height d to the flame length l is 0.8 or more and 1.2 or less. ) Adjusting the fuel gas supply amount and the combustion oxidizing gas supply amount supplied to the top blowing lance 3 within the range satisfying the formula, that is, adjusting the flow rate ratio between the fuel gas and the combustion oxidizing gas. A flame is generated to completely burn the fuel gas in the freeboard of the converter.

0.4 ≦ (G / F) / (G / F) _st ≦ 1.0 (1)
G: Supply rate of oxidizing gas for combustion of top blowing lance (Nm ³ / min)
F: Fuel gas supply speed of top blowing lance (Nm ³ / min)
(G / F) _st : Ratio of the stoichiometric coefficient between the fuel gas and the oxidizing gas for combustion required for complete combustion of the fuel gas.

  Here, the top blowing lance height d is the distance from the bath surface of the hot metal 26 at rest to the tip of the nozzle front surface of the top blowing lance along the vertical direction. The assumed value of the top blowing lance height d in the present invention is in the range of 2.0 to 5.0 m. This is because the value of the free board in the converter into which the hot metal 26 is charged is generally in the range of 2.0 to 5.0 m. The free board is the height (distance) from the bath surface of the hot metal 26 at rest to the loading port of a scouring container such as a converter.

When the value of (G / F) / (G / F) _st is less than 0.4 or exceeds 1.0, the fuel gas is burned out before reaching the bath surface of the hot metal 26 in the furnace body 2, The heat receiving efficiency to the powdery refining agent 29 is deteriorated. (G / F) / (G / F) If the value of _st is not less than 0.4 and not more than 1.0, the time until the powdery refining agent 29 reaches the bath surface of the hot metal 26 from the tip of the top blowing lance 3 It is possible to set the value (l / d) of the flame length l formed between the upper blowing lance height d which is the distance to be 0.8 or more and 1.2 or less. The ratio (l / d) of the top blowing lance height d to the flame length l is close to 1, and the flame length l is in the range of 0.8 to 1.2 with respect to the top blowing lance height d. For example, it can be said that the fuel consumed by the flame is efficiently consumed by the flame from the top blowing lance in view of the purpose of heat-up the powdery refining agent 29, and is confirmed also by Experiment 2 described later. The powdered smelting agent 29 is effectively heated by the flame from the top blowing lance, and it can be said that the heat receiving efficiency is good.

In addition to the above equation (1), it is preferable to maintain the discharge flow rate V _G (Nm / sec) of the oxidizing gas for combustion within a range satisfying the following equation (2).

0.2 ≦ V _G /C≦1.0 (2)
V _G : discharge velocity of oxidizing gas for combustion (Nm / sec)
C: Speed of sound (Nm / sec)
When the value of V _G / C is less than 0.2, the mixed state of the fuel gas and the oxidizing gas for combustion deteriorates, and the fuel in the space between the bath surface of the hot metal 26 and the tip of the top blowing lance 3 Gas is difficult to burn completely. On the other hand, if the value of V _G / C exceeds 1.0, the fuel gas is easily burned out before reaching the bath surface of the hot metal 26, and the efficiency of heat application to the powdery refining agent 29 is deteriorated. As a result, the heat receiving efficiency to the molten iron (molten iron) also deteriorates, and it becomes difficult to increase the blending ratio of cold iron sources such as iron scrap.

  By supplying the fuel gas and the oxidizing gas for combustion under conditions satisfying the above expression (1), the fuel is supplied from the fuel gas injection hole 17 and supplied from the combustion oxidizing gas injection hole 18. Since the oxidizing gas for combustion is close in all radial directions of the upper blow lance 3, they interfere with each other and the ambient temperature is high, and even within the combustion limit range without an ignition device. When the gas concentration reaches, combustion occurs, and a flame is formed below the upper blowing lance 3.

  Flame length matched to the lance height is formed by supplying fuel gas and oxidizing gas for combustion and adjusting the supply amount of oxidizing gas for combustion so as to satisfy the above equation (1) Experimented to be possible.

<Experiment 1>
Using the converter 1 shown in FIG. 1, the flame length when the supply amount of the oxidizing gas for combustion was changed was investigated. The furnace body 2 of the converter facility 1 can accommodate 350 tons of molten iron. 300 tons of molten iron was accommodated in the furnace body 2. The upper blowing lance 3 was disposed at a position where the upper blowing lance height d was in the range of 2.0 to 5.0 m. A plurality of lance bodies 14 having the same dimensions were prepared, and a plurality of lance tips 15 each having a design change were prepared. Fuel gas or an oxidizing gas for fuel gas combustion was supplied to form a flame at the lower end of the upper blowing lance 3.

  The plurality of lance tips 15 has a central hole having an inner diameter of 55 mm, a fuel gas injection hole having an annular slit gap of 6.5 mm, and a peripheral hole having a throat diameter of 50 mm and a 5-hole rubber nozzle with respect to the lance center axis. It is arranged at an angle of 15 °. On the other hand, with respect to the combustion oxidizing gas injection hole 18, each of the plurality of lance tips 15 has been changed in design. The combustion oxidizing gas injection hole 18 is a gap of an annular slit, and the plurality of lance tips 15 have arbitrary different dimensions within the range of the gaps of 16.4 mm to 25.4 mm. .

The plurality of lance tips 15 and the plurality of lance bodies 14 were respectively welded to prepare a plurality of upper blowing lances 3 having different gaps between the combustion oxidizing gas injection holes 18. In this way, when the flame is formed, it is possible to change the ejection speed (discharge speed (Nm / sec)) of the oxidizing gas for combustion even at the same flow rate (m ³ / sec) of the oxidizing gas for combustion. It became.

Propane gas (calorific value: 100.5 MJ / Nm ³ ) was used as the fuel gas, and the supply flow rate (supply speed) F of propane gas was 12 Nm ³ / min. Oxygen gas was used as the oxidizing gas for fuel gas combustion and the oxidizing gas for refining. The supply flow rate (supply rate) G of the oxidizing gas for fuel gas combustion is 0 Nm ³ / min to 75 Nm ³ / min, and the supply flow rate of the oxidizing gas for refining is 485 Nm ³ / min to 560 Nm ³ / min. The supply flow rate of all the oxygen blown was kept constant at 560 Nm ³ / min. The ratio value (G / F) _st of propane gas and the ratio of the stoichiometric coefficient of gas and the oxidizing property for combustion required for complete combustion of the propane gas was 5.0.

Also, after appropriately selecting one upper blowing lance 3 from among the plurality of upper blowing lances 3, the fuel gas and the oxidizing gas for combustion are blown from the selected upper blowing lance 3 to form a stable flame. The flame length in each condition was measured visually. The measurement results when the top blowing lance height d is 2.5 m are shown in FIG. The “flame length index” on the vertical axis in FIG. 3 is the stoichiometric ratio and the flame length l from the tip of the top blowing lance 3 to the tip of the flame formed when visually measured. It means “l / l _st ” which is a value of the ratio to the flame length l _st . “(G / F) / (G / F) _st ” on the horizontal axis in FIG. 3 is a flow ratio of propane gas and combustion oxidizing gas to (G / F) _st .

  As shown in FIG. 3, it has been found that the flame length is changed by changing the supply amount of the oxidizing gas for combustion. That is, it has been found that by adjusting the supply amount of the oxidizing gas for combustion, it is possible to form an appropriate flame length l that matches the upper blowing lance height d.

Next, under the condition of the theoretical combustion ratio “(G / F) / (G / F) _st = 1” in Experiment 1 above, the top blowing lance height d was changed and the heat deposition behavior on the hot metal was investigated. (Experiment 2).

<Experiment 2>
When the theoretical combustion ratio is 1, the fuel gas and the oxidation for fuel gas combustion are performed under the same conditions as in Experiment 1 except that the theoretical combustion ratio is “(G / F) / (G / F) _st = 1”. A gas of a sex gas was supplied to form a flame at the lower end of the upper blowing lance 3. The powdery refining agent was heated. The amount of heat applied to the molten iron under each condition where the top blowing lance height d was changed was calculated from the temperature rise of the molten iron.

The values (l / d) of the flame length l with respect to the lance height d and the values (l / d) with respect to the amount of heat applied on the basis of the case where the flame length l and the lance height d are equal (l / d = 1) FIG. 4 shows the relationship with the value of the amount of heat received (/ heat index) in / d). Assuming that heat is applied to the hot metal by the powdered smelting agent that has been heated by the flame, when the heat index exceeds 0.8, it is assumed that efficient heat is achieved. According to FIG. It is confirmed that the value of (l / d) is in the range of 0.8 to 1.2.
The powdery refining agent 29 injected together with the inert gas from the center hole 16 is heated or heated / melted by the heat of the formed flame, and is sprayed onto the bath surface of the hot metal 26 in the heated or molten state. Thereby, the heat of the powdery refining agent 29 is applied to the molten iron 26, the temperature of the molten iron 26 rises, and the dissolution of the added cold iron source is promoted. The powdery refining agent 29 preferably contains at least one of iron oxide, a lime-based medium solvent, and a combustible substance.

At that time, refining oxidizing gas such as oxygen gas is blown toward the bath surface of the hot metal 26 from the peripheral hole 19 of the upper blowing lance 3. In the dephosphorization reaction of the hot metal 26, phosphorus in the hot metal reacts with an oxidizing gas or iron oxide to form a phosphor oxide (P ₂ O ₅ ), and this phosphor oxide is formed by the incubation of the lime-based solvent. It progresses by being absorbed by the slag 27. In addition, the rate of dephosphorization increases as the hatching of the lime-based medium solvent is promoted. Therefore, as the powdery refining agent 29, it is preferable to use a lime-based medium solvent such as quick lime (CaO), limestone (CaCO ₃ ), slaked lime (Ca (OH) ₂ ). A mixture of quicklime with fluorite (CaF ₂ ) or alumina (Al ₂ O ₃ ) as a hatching accelerator can be used as the lime-based solvent. It is also possible to use converter slag produced in the decarburization blowing process of the molten iron 26 (CaO-SiO ₂ slag) as all or part of the lime-based medium solvent.

  The lime-based medium solvent sprayed on the bath surface of the hot metal 26 as the powdery refining agent 29 immediately hatches to form slag 27, and the supplied oxidizing gas for refining reacts with phosphorus in the hot metal. Phosphorus oxide is formed. Combined with the strong stirring of the hot metal 26 and the slag 27 by the stirring gas 28, the formed phosphorous oxide is rapidly absorbed by the hatched slag 27, and the dephosphorization reaction of the hot metal 26 proceeds promptly. When the lime-based medium solvent is not used as the powdery refining agent 29, the lime-based medium solvent is separately put on top from the furnace hopper.

  When iron oxide such as iron ore or mill scale is used as the powdery refining agent 29, the iron oxide functions as an oxygen source and reacts with phosphorus in the molten steel to advance a dephosphorization reaction. Further, the iron oxide reacts with the lime-based medium solvent to form a FeO-CaO compound on the surface of the lime-based medium solvent, which promotes the hatching of the lime-based medium solvent and promotes the dephosphorization reaction. When iron oxide containing combustible material such as blast furnace dust or converter dust is used, the combustible material is burned by the flame, and in addition to the above, the combustion heat of the combustible material is used to heat the hot metal 26. Contribute.

  Further, as the powdery refining agent 29, aluminum ash (30 to 50% by mass of metal Al produced by reaction of Al and oxygen in the air when Al ingot or scrap is melted in a melting furnace) is contained. When a flammable substance such as (Al oxide) or coke is used, the flammable substance is burned by the flame, and the combustion heat of the flammable substance contributes to the heating of the hot metal 26 in addition to the combustion heat of the fuel. In the case where a mixture of a lime-based solvent, iron oxide and a combustible substance is used as the powdery refining agent 29, the respective effects can be obtained in parallel.

  The heat of the powdery refining agent 29 heated by the flame from the upper blowing lance 3 or melted by the heating is transferred to the molten iron 26. Furthermore, the combustion heat of the flame at the tip of the upper blowing lance existing above the hot metal 26 is transmitted to the hot metal 26. In addition to the heat transmitted to the hot metal 26, the hot metal 26 is vigorously stirred, and the melting of the cold iron source in the hot metal is promoted. Dissolution of the charged cold iron source is completed during the dephosphorization process.

  Thereafter, when the phosphorus concentration in the hot metal 26 becomes the target value or less, all the supply from the top blowing lance 3 to the hot metal 26 is stopped, and the dephosphorization process is ended. After the dephosphorization process, the hot metal 26 subjected to the preliminary dephosphorization process by tilting the furnace body 2 is discharged into a hot metal holding container such as a ladle or a converter charging pot through the hot water outlet 6 and discharged. The hot metal 26 is transported to the next process equipment.

  As described above, according to the present invention, flames corresponding to various lance heights can be obtained by appropriately adjusting the supply amounts of fuel gas and oxygen gas for forming a burner flame below the top blowing lance tip. The length can be controlled. As a result, continuous and stable heating of the powdery refining agent 29 supplied into the furnace body 2 through the top blowing lance 3 until reaching the bath surface of the hot metal 26 is realized. Since the heat of the hot metal refining agent 29 surely reaches the hot metal 26, the heat margin of the hot metal 26 is improved, and in the oxidizing refining process of the hot metal 26 in the converter 1, the mixing ratio of the cold iron source such as iron scrap is changed. A significant increase is realized.

Using the converter equipment 1 and the top blowing lance 3 having the same dimensions as those in the experiments 1 and 2, the molten iron and iron scrap were charged into the converter equipment 1 and the lance height was set to 2.5 m. 3 was inserted into the furnace body 2, and dephosphorization blowing (preliminary dephosphorization of hot metal) was performed. Similarly to the above-described experiment, the top blow lance 3 was supplied with propane gas as the fuel and with oxygen gas as the oxidizing gas for combustion and the oxidizing gas for refining. The upper blow lance 3 has an inner diameter of 55 mm, a fuel gas injection hole with an annular slit gap of 6.5 mm, and a combustion oxidizing gas injection hole with an annular slit gap of 16.4-25. The peripheral hole is a 5-hole Laval nozzle with a throat diameter of 50 mm and is arranged at an angle of 15 ° with respect to the lance center axis. By changing the gap between the annular slits, the discharge flow rate can be changed even at the same supply speed. Propane supplied from the fuel gas supply channel so that the ratio (l / d) of the top blowing lance height d to the flame length l is 0.8 or more and 1.2 or less during dephosphorization blowing. and feed rate of the gas (Nm 3 ^/ min), flow ratio of feed rate of the combustion oxidizing gas supplied from the combustion oxidizing gas supply passage (Nm 3 ^/ min) (G / F) The ratio (G / F) _{st of the} stoichiometric coefficient between the fuel gas and the oxidizing gas for combustion required for complete combustion of the fuel gas is within the range of 0.4 to 1.0. Then, an oxidizing gas for combustion was supplied (Invention Examples 1 to 5). For comparison, the supply amount of the oxidizing gas for combustion is an amount required for complete combustion so that the value of (G / F) / (G / F) _st is outside the range of 0.4 to 1.0. The operation was also performed under conditions of less than 40% or more than 100% (Comparative Examples 1 and 2). Moreover, in Invention Examples 2-3, the discharge flow rate V _G (Nm / sec) of the oxidizing gas for combustion is adjusted so that V _G / C falls within the range of 0.2 to 1.0. An oxidizing gas for fuel gas combustion is supplied. On the other hand, in Invention Examples 4 to 5, V _G / C was out of the range of 0.2 to 1.0. Here, C is the speed of sound (Nm / sec), and is approximately 1150 m / sec around the hot metal at 1350 ° C.

  After charging iron scrap so that there is no unmelted iron scrap after dephosphorization, 300 tons of hot metal having a temperature of 1350 ° C. is charged. Next, argon gas is blown from the bottom blowing tuyere 7 while spraying mixed powder of quick lime, iron ore and steelmaking dust, fuel gas, oxidizing gas for combustion, and oxidizing gas for refining from the top blowing lance 3 toward the hot metal surface. Was blown into the hot metal as a stirring gas.

The amount of iron scrap charged was adjusted such that the preliminary dephosphorization end temperature was 1400 ° C. The amount of quicklime was adjusted so that the basicity (mass% CaO / mass% SiO ₂ ) of the slag in the furnace was 2.5.

  Table 1 shows the composition of the hot metal used in the preliminary dephosphorization treatment.

  Table 2 shows the composition of the steelmaking dust used.

The amount of powdered smelting agent blown in the preliminary dephosphorization treatment, the various gas flow rates to the top blowing lance, the bottom blown gas flow rate, and the flame length were set as shown in Table 3. By adjusting the supply amount of the oxidizing gas for fuel gas combustion, the value of (G / F) / (G / F) _{st and} the value of V _G / C were values shown in Table 3.

  Table 4 shows the results of the preliminary dephosphorization treatment under the operating conditions and operating methods shown above. The iron scrap blending ratio is variously changed, and the upper limit iron scrap blending ratio at which the charged iron scrap does not remain melted after the dephosphorization treatment is shown.

  As is clear from Table 4, when the blending ratio of the iron scraping time and the iron scrap is compared in Examples 1 to 5 of the present invention and Comparative Examples 1 and 2, according to the method of the present invention, it is necessary for the preliminary dephosphorization treatment of the hot metal. It can be seen that even when the blowing time is the same as 8 minutes, the operation can be performed with an increased ratio of iron scrap. From this, according to the present invention, it is predicted that the hot metal preliminary dephosphorization treatment can be performed with high efficiency.

Further, in Invention Examples 1 to 3 where the value of V _G / C satisfies 0.2 or more and 1.0 or less, the operation in which the mixing ratio of iron scrap is increased as compared with Invention Examples 4 and 5 which do not satisfy the present invention. You can see that it is possible. From this, it is predicted that when the value of V _G / C is 0.2 or more and 1.0 or less, the hot metal preliminary dephosphorization treatment can be performed with high efficiency.

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 Powder refining agent supply pipe 9A Refining agent conveyance gas supply pipe 10 Fuel gas supply pipe 11 Oxidizing gas supply pipe for combustion 12 Oxidizing gas supply pipe for refining 13 Dispenser 14 Lance body 15 Lance tip 16 Center hole 17 Fuel gas injection hole 18 Oxidizing gas injection hole for combustion 19 Peripheral hole 20 Innermost pipe 21 Partition pipe 22 Inner pipe 23 Middle pipe 24 Outer pipe 25 Outer pipe 26 Hot metal 27 Slag 28 Stirring gas 29 Powder refining agent 31 Powder refining agent supply flow path 32 Fuel gas supply flow path 33 Combustion oxidizing gas supply flow path 34 Refining Oxidizing gas supply flow path

Claims (6)

Using an upper blowing lance having a powdery refining agent supply channel, a fuel gas supply channel, an oxidizing gas supply channel for combustion of fuel gas, and an oxidizing gas supply channel for refining separately, The fuel gas is supplied from the fuel gas supply channel, and the combustion oxidizing gas is supplied from the combustion oxidizing gas supply channel, and the upper side is directed toward the molten iron bath surface accommodated in the converter. A flame is formed in front of the nozzle of the blowing lance,
Supplying the powdery refining agent from the powdery refining agent supply flow path, supplying the refining oxidizing gas while spraying the powdery refining agent toward the molten iron bath surface while heating with the flame. A method for refining molten iron that supplies oxidizing gas for refining toward a bath surface of molten iron from a flow path,
A method for refining molten iron, characterized in that the flame is formed while satisfying the following equation (1) for a flow rate ratio between a fuel gas and an oxidizing gas for combustion.
0.4 ≦ (G / F) / (G / F) _st ≦ 1.0 (1)
However, in the formula (1), G: Combustion oxidizing gas supply rate (Nm ³ / min),
F: Fuel gas supply rate (Nm ³ / min),
(G / F) _st : The ratio of the stoichiometric coefficient between the fuel gas and the oxidizing gas required for complete combustion of the fuel gas. The method for refining molten iron according to claim 1, wherein the height of the upper blow lance is in the range of 2.0 to 5.0 m. The method for refining molten iron according to claim 1 or 2, wherein a value of a free board of the converter is in a range of 2.0 to 5.0 m. 4. The combustion oxidizing gas supply rate G is adjusted so that the discharge flow rate V _G of the combustion oxidizing gas satisfies the following expression (2) : 4. The method for refining molten iron according to claim 1 .
0.2 ≦ V _G /C≦1.0 (2)
However, in the formula (2), V _G : discharge flow rate of combustion oxidizing gas (Nm / sec),
C: Sound velocity (Nm / sec). The powdery refining agent includes at least one of iron oxide, a lime-based solvent, and a flammable substance, and supplies the powdery refining agent together with an inert gas toward the molten iron bath surface. The method for refining molten iron according to any one of claims 1 to 4, wherein oxidation refining treatment is performed on molten iron to which a cold iron source is added. 6. The method for refining molten iron according to claim 5 , wherein the molten iron is hot metal, and the oxidative refining treatment is a preliminary dephosphorization treatment of hot metal.

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