Desiliconization and dephosphorization of hot metal in converter-type refining vessels

Abstract

To provide desiliconization and dephosphorization methods of hot metal in converter-type refining vessels capable of improving yield by suppressing generation of CO gas and reducing slopping generation frequency.SOLUTION: In a method for dephosphorizing hot metal by blowing gaseous oxygen gas into hot metal 2 charged in a converter type refining vessel 1 of an upper bottom blowing system from an upper blowing lance 4 and by injecting an iron oxide source which is solid oxygen from the top, a desiliconization reaction rate constant of the solid oxygen is determined in advance using the stirring power density obtained from a flow rate of the bottom blowing gas, and an amount of gaseous oxygen required for the desiliconization treatment is calculated using the determined desiliconization reaction rate constant and the target concentration [Si] in the hot metal. The gaseous oxygen gas of the calculated amount of gaseous oxygen is blown in from the top blowing lance, and after the [Si] concentration in the hot metal during the desiliconization treatment reaches the target concentration [Si] in the hot metal, the process shifts from the desiliconization treatment to the dephosphorization treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for desiliconizing and dephosphorizing molten iron charged into a top-bottom blowing converter-type refining vessel. [Background technology]

[0002] Molten pig iron produced in a blast furnace or the like contains Si, P, and other elements that reduce the performance of steel, and so dephosphorization is carried out at the molten pig iron stage. In converter operation, molten pig iron is charged into a converter-type refining vessel, and oxygen gas is blown toward the molten pig iron from a top blowing lance installed at the throat of the vessel, and bottom blowing gas is blown from a bottom blowing tuyeres installed at the bottom of the vessel to agitate the molten pig iron (dephosphorization treatment). Examples of dephosphorization treatment methods include those disclosed in Patent Documents 1 to 3.

[0003] Patent Document 1 aims to improve the controllability of the phosphorus concentration in converter blowing by performing an operation for adjusting the Si concentration in the molten iron at an appropriate timing. Specifically, the patent document discloses a converter blowing control device including: a desiliconization rate constant calculation unit that calculates an estimate of the primary desiliconization rate constant of the molten iron using a statistical model with molten iron data related to the molten iron being blown in the converter as explanatory variables; and a Si concentration estimation unit that estimates the Si concentration of the molten iron at a predetermined time during the blowing process based on the Si concentration of the molten iron before the blowing process and the primary desiliconization rate constant.

[0004] Patent Document 2 aims to accurately control the molten pig iron P concentration and improve production efficiency by appropriately adjusting the molten pig iron Si concentration. Specifically, the method discloses a method of acquiring initial molten pig iron data including the initial concentrations of molten pig iron components, sequentially estimating the molten pig iron Si concentration using a complex reaction model that combines a hot spot reaction, which is an oxidation reaction between the molten pig iron and oxygen injected from a top lance into the molten pig iron, and a slag-metal interface reaction, which is a reaction at the interface between the molten pig iron and slag that proceeds in a region different from the hot spot region where the hot spot reaction proceeds, and then performing an operation to adjust the molten pig iron Si concentration based on the difference between the estimated molten pig iron Si concentration and a target molten pig iron Si concentration.

[0005] Patent Document 3 aims to reduce the variation in the composition of desiliconization slag by appropriately estimating the amount of silicon removed and the amount of SiO2 generated in response to changes in the blowing conditions, such as gaseous oxygen, during the desiliconization treatment of molten iron. Specifically, when desiliconizing molten pig iron in a transport vessel by injecting gaseous oxygen or refining agent powder into the molten pig iron, the apparent desiliconization reaction rate constant K is calculated as a function equation containing as variables one or more of the refining agent powder injection rate per ton of molten pig iron, the immersion depth of the submerged lance discharge nozzle, and the gaseous oxygen injection rate per ton of molten pig iron. The apparent desiliconization reaction rate constant K is calculated using the obtained function equation. The silicon concentration in the molten pig iron after desiliconization is calculated using the calculated apparent desiliconization reaction rate constant K. The amount of silicon desiliconization is calculated from the difference between the calculated silicon concentration in the molten pig iron after desiliconization and the silicon concentration in the molten pig iron before desiliconization. The amount of CaO-based flux to be used is then determined based on the calculated amount of silicon desiliconization. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-031684 [Patent Document 2] Japanese Patent Application Publication No. 2018-095943 [Patent Document 3] Japanese Patent Application Publication No. 2019-173050 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, when performing desiliconization and dephosphorization treatments, the statistical model calculations must be performed based on exhaust gas data, slag data, etc., and there is a risk that the processing calculations will not be possible if the instrument that acquires the exhaust gas data is faulty. Furthermore, the desiliconization rate constant used in the statistical model is calculated based on the control of the phosphorus concentration in converter blowing, and the molten iron silicon concentration is not estimated based on the assumption of yield. In other words, there is a possibility that the method does not improve yield.

[0008] In Patent Document 2, when performing desiliconization and dephosphorization treatments, it is necessary to sequentially estimate the Si concentration in the molten iron using exhaust gas data, and if the instrument for acquiring the exhaust gas data is faulty, it may become very difficult to estimate the Si concentration in the molten iron.

[0009] Patent Document 3 is a technology related to the operation of a transfer vessel (torpedo car), and estimates the reaction rate constant based on desiliconization treatment operations in which gaseous oxygen or refining agent powder is injected. The technology described in Patent Document 3 cannot be used to perform desiliconization and dephosphorization treatments in a converter-type refining vessel, which is the subject of the present invention, due to differences in reaction efficiency and the method of adding the refining agent. Furthermore, Patent Document 3 primarily aims to reduce variation in the composition of desiliconization slag, and does not estimate the silicon concentration of the molten iron based on the assumption of yield. In other words, it may not improve yield.

[0010] The desiliconization reaction takes precedence over the dephosphorization reaction, followed by the decarbonization and dephosphorization reactions. This reaction can easily lead to slopping (the reaction between the carbon concentration in the molten iron and oxygen gas generates CO gas, which pushes the molten iron and slag out of the system). In other words, if a large amount of oxygen gas is injected into the molten iron, the decarbonization reaction begins during the desiliconization reaction, potentially generating CO gas, which can lead to slopping.

[0011] If this slopping phenomenon occurs, the molten iron in the furnace of the refining vessel will be discharged outside the system, resulting in a decrease in yield. Therefore, it is necessary to determine the target value of the [Si] concentration in the molten iron during desiliconization treatment and to determine in advance the amount of gaseous oxygen to be injected from the lance so that the target [Si] concentration in the molten iron is achieved.

[0012] In recent years, users have been demanding higher quality due to the trend toward higher added value steel products and environmental considerations, etc. Under these circumstances, there is a demand for the removal of Si, P, etc. from steel with low environmental impact while improving yield, in other words, the optimization of processing conditions.

[0013] In view of the above problems, an object of the present invention is to provide a method for desiliconizing and dephosphorizing molten pig iron in a converter-type refining vessel, which can improve yield by suppressing CO gas generation and reducing the frequency of slopping during desiliconizing and dephosphorizing treatment in a converter-type refining vessel. [Means for solving the problem]

[0014] In order to achieve the above object, the present invention provides the following technical means.

[0015] The method for desiliconizing and dephosphorizing molten pig iron in a converter-type refining vessel according to the present invention is a method for dephosphorizing molten pig iron by injecting gaseous oxygen from a top-blowing lance into the molten pig iron charged in a top-bottom blown converter-type refining vessel and adding an iron oxide source, which is solid oxygen, from above, and the desiliconizing reaction rate constant of the solid oxygen is calculated in advance using the stirring power density obtained from the flow rate of the bottom-blowing gas. From equation (1), The amount of gaseous oxygen required for desiliconization is calculated using the calculated desiliconization reaction rate constant and the target [Si] concentration in the molten iron. From equation (2) Calculate, The amount of gaseous oxygen (gas oxygen amount) blown from the top lance was adjusted so that the [Si] concentration in the molten iron was not less than 0.09 mass%. 2-gas decided and decidedThe method is characterized in that a certain amount of gaseous oxygen gas is injected from the top lance, and the desiliconization process is switched to the dephosphorization process after the [Si] concentration in the molten iron during the desiliconization process reaches the target [Si] concentration in the molten iron. TIFF0007744317000001.tif32170 ·k si-solid : Desiliconization reaction rate constant (1 / min.) ·a:Constant(t / (min.·W·Nm 3 ) ·ε: Stirring power density (W / t) ·O 2-solid : Amount of iron oxide source added from above (Nm 3 ) b: constant (1 / min.) TIFF0007744317000002.tif27170 however, ·O 2-gasblow : Top-blown oxygen flow rate during desiliconization (Nm 3 / min.) ·O 2-gas : The amount of gaseous oxygen (Nm) required for the estimated [Si] concentration (de-siliconization) at the end of the de-siliconization treatment 3 ) [Si] i : [Si] concentration in molten iron at the beginning of blowing (mass%) [Si] f : [Si] concentration in hot metal at estimated end point of desiliconization treatment (mass%) ·k Si-gas : Reaction rate constant of the amount of gaseous oxygen contributing to the desiliconization reaction (1 / min.) ·k Si-solid : Reaction rate constant of the amount of solid oxygen contributing to the desiliconization reaction (1 / min.) [Effects of the Invention]

[0016] According to the present invention, in the desiliconization treatment and dephosphorization treatment in a converter-type refining vessel, the generation of CO gas is suppressed and the frequency of slopping is reduced, thereby improving the yield. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a schematic overview of converter refining in a converter-type refining vessel. [Figure 2] This figure compares the yield when the [Si] concentration in the hot metal during desiliconization is predetermined and the yield when the [Si] concentration in the hot metal is not predetermined, taking into account the reaction rate constant of the amount of solid oxygen that contributes to the desiliconization reaction. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of a method for desiliconizing and dephosphorizing hot metal in a converter-type refining vessel according to the present invention will be described with reference to the drawings. Note that the embodiment described below is an example of a specific embodiment of the present invention, and the configuration of the present invention is not limited to this specific example.

[0019] The method for desiliconizing and dephosphorizing molten pig iron in a converter-type refining vessel according to the present invention involves blowing gaseous oxygen gas from a top-blowing lance 4 into molten pig iron 2 charged into a top-bottom blown converter-type refining vessel 1, and introducing an iron oxide source, which is solid oxygen, from an upper throat of the vessel to perform dephosphorization. In this method, the desiliconizing reaction rate constant k si-solid is calculated in advance using the stirring power density ε (from equation (1)), and the desiliconization reaction rate constant k si-solid The [Si] concentration in the hot metal during desiliconization treatment ([Si] f ) is calculated (using equation (2)), and once the predetermined [Si] concentration in the hot metal is reached, the process shifts from desiliconization to dephosphorization. In actual operation, the desiliconization reaction rate constant k si-solid and the target [Si] concentration in the hot metal, the amount of gaseous oxygen O required for the desiliconization reaction is calculated. 2-gas is calculated in advance.

[0020] FIG. 1 shows a schematic overview of converter refining in a converter-type refining vessel 1 (converter-type reaction vessel 1).

[0021] Generally, in the operation of a converter, lime containing a CaO source necessary for the dephosphorization reaction and an iron oxide source that contributes to the melting of the lime are added to the molten pig iron 2 charged into a converter-type refining vessel 1, and in order to uniformly mix the molten pig iron 2 and slag 3, gaseous oxygen is blown toward the molten pig iron 2 from a top blowing lance 4 inserted into the refining vessel 1 from the furnace throat at the top, and bottom blowing gas is sprayed from a bottom blowing tuyeres 5 located at the bottom of the converter-type refining vessel 1 to stir the molten pig iron 2, thereby performing a blowing (dephosphorization) process.

[0022] As shown in FIG. 1, in this embodiment, approximately 220 to 270 tons of molten pig iron 2 is charged into a converter-type refining vessel 1. Gaseous oxygen gas is blown onto the molten pig iron 2 from a top-blowing lance 4 inserted into the vessel from the upper throat, and lime and an iron oxide source (solid oxygen) are added from the throat of the vessel 1 to generate slag 3. While maintaining the molten pig iron temperature at 1300 to 1400°C, inert N2 gas is blown into the vessel from a bottom-blowing tuyeres 5 at the bottom of the furnace, stirring the molten pig iron 2 and slag 3 and promoting the dephosphorization reaction described below. 2[P]+5(FeO)+3(CaO)→3(CaO P2O5)+5[Fe]

[0023] When carrying out the above dephosphorization treatment, the temperature and the amount of oxygen required for dephosphorization, P _O2 It is necessary to derive the amount of gaseous oxygen required for the dephosphorization reaction, P _O2_gas and the amount of solid oxygen P _O2_solid is derived from simultaneous equations of the balance of the amount of oxygen required for the dephosphorization reaction and the heat balance of the heat input and output to the molten pig iron 2 in the converter-type refining vessel 1.

[0024] The following (1) to (3) show the temperature adjustment and the amount of oxygen required for dephosphorization, P _O2 The method of deriving is shown below.

[0025] (1) The amount of molten iron to be charged into the converter-type refining vessel 1, information on the molten iron 2 (such as the [Si] concentration in the molten iron, the [P] concentration in the molten iron, and the molten iron temperature) are obtained in advance.

[0026] (2) The amount of oxygen required for the dephosphorization reaction, P _O2is derived from the following formula: P _O2 ={(ln([P] i / [P] t )-β) / α} / W i however, P _O2 : Amount of oxygen required for dephosphorization reaction (Nm 3 ) ·W i : Amount of molten iron (t) [P] i :[P] concentration in hot metal (mass%) [P] t : Target [P] concentration after dephosphorization (mass%) ·α: Constant value α(t / Nm 3 ) β: constant value β(t)

[0027] The target [P] concentration after dephosphorization is set to an arbitrary value based on the steel specification conditions and the dephosphorization efficiency in the converter in the next process. The constants α and β are calculated based on the results of past experiments.

[0028] (3) The amount of gaseous oxygen required for the dephosphorization reaction, P _O2_gas and the amount of solid oxygen P _O2_solid is derived. The amount of oxygen in the dephosphorization reaction and the heat balance between heat input and heat output are calculated using the simultaneous equations shown below. P _O2_gas +P _O2_solid =P _O2 T i +H _P_O2_gas ×P _O2_gas +H _P_O2_solid ×P _O2_solid +H _Si ×[Si] i +ΔH=T t however, P _O2_gas : Amount of gaseous oxygen required for dephosphorization reaction (Nm 3 ) P _O2_solid : The amount of solid oxygen required for the dephosphorization reaction (Nm 3 ) T i :Hot metal temperature (℃) H _P_O2_gas : Thermal coefficient of dephosphorization in gaseous acid (°C / Nm 3 ) H _P_O2_solid : Thermal coefficient of dephosphorization in solid acid (℃ / Nm 3 ) H _Si : Desiliconization reaction heat coefficient (℃ / %) ΔH: Other reaction heat (slag sensible heat, secondary combustion heat, etc.) (℃) T t :Target temperature (℃)

[0029] First, the desiliconization reaction rate constant k si-solid is calculated in advance (using the following formula (1)) using the stirring power density ε obtained from the flow rate of the bottom-blowing gas blown from the bottom-blowing tuyeres 5 at the bottom of the refining vessel 1. In this embodiment, the desiliconization reaction rate constant k si-solid was calculated in advance (before blowing) as a function of the stirring power density ε.

[0030] Specifically, in the past, the contributions of the amount of gaseous oxygen and the amount of solid oxygen contributing to the desiliconization reaction were set to constant values. However, in this embodiment, in order to express the contribution of the amount of solid oxygen contributing to the desiliconization reaction, the desiliconization reaction rate constant k of solid oxygen, which is derived based on the stirring power density ε and the amount of solid oxygen introduced from above, is used. si-solid is expressed by the following formula (1).

[0031] The stirring power density ε and the amount of iron oxide source charged from above vary depending on the hot metal treatment conditions, so the desiliconization reaction rate of solid oxygen is calculated in advance for each treatment.

[0032]

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[0033] In addition, the desiliconization reaction rate constant k of solid oxygen before the dephosphorization treatment is shown in the following (4) to (6). si-solid The method of deriving is shown below.

[0034] (4) The stirring power density ε is calculated using the formula described in (Reference: Sano et al.'s formula: K. Mori and M. Sano: Tetsu-to-Hagane, 67 (1981), 672). ε=371×(Q bot / W i )×T i ×(ln(1+ρ L ×g×h / P)+(1-T bot / T l ) however, ·ε: Stirring power density (W / t) Q bot : Bottom blown gas flow rate (Nm 3 / s) ·W i : Amount of hot metal (t) T i :Hot metal temperature (K) ρ L : Hot metal density (kg / m 3 ) ·g: Gravitational acceleration (m / s 2 ) h: Bottom gas injection depth (m) P: Atmospheric pressure (Pa) T bot : Bottom blown gas temperature (℃)

[0035] (5) Amount of iron oxide source O added from above 2-solid Regarding P derived in (3) above, _O2_solid is used.

[0036] (6) The constants a and b are calculated based on the results of past experiments.

[0037] As mentioned above, the desiliconization rate constant k si-solid is calculated in advance (before blowing) as a function of the stirring power density ε, i.e., k si-solid By making it variable, the precision of the de-siliconization process has been improved.

[0038] The desiliconization reaction rate constant k obtained above si-solid The [Si] concentration in the hot metal during desiliconization is calculated using the following equation (2). In actual operation, the desiliconization reaction rate constant k si-solid and the target [Si] concentration in the hot metal, the amount of gaseous oxygen O required for the desiliconization reaction is calculated. 2-gas is calculated in advance. That is, the amount of gaseous oxygen O required for the desiliconization reaction is calculated as follows: 2-gas is the amount required to achieve the target [Si] concentration in the hot metal during desiliconization.

[0039] In detail, thermodynamically, the desiliconization reaction proceeds preferentially before the dephosphorization reaction proceeds, and in particular, the decarbonization reaction and the dephosphorization reaction begin to proceed when the [Si] concentration in the molten iron reaches about 0.10 mass%. This makes the slopping phenomenon (the reaction between the [C] concentration in the molten iron and oxygen gas generates CO gas, which pushes the molten iron 2 and slag 3 out of the system) more likely to occur. In other words, if a large amount of gaseous oxygen gas is injected into the molten iron 2, the de-C reaction starts during the de-Si reaction, which can generate CO gas, which leads to the slopping phenomenon.

[0040] If this slopping phenomenon occurs, the molten iron 2 in the furnace of the refining vessel 1 will be discharged outside the system, resulting in a decrease in yield. Therefore, it is necessary to determine in advance the target value of the [Si] concentration in the molten iron during the desiliconization process so that the [Si] concentration in the molten iron does not become ≦0.09 mass%. In other words, the amount of gaseous oxygen O injected from the top lance 4 is adjusted to achieve the target [Si] concentration in the molten iron. 2-gasIn this embodiment, the target value indicating the completion of the desiliconization reaction is determined by the [Si] concentration in the molten iron ([Si] f ) = 0.10 mass%.

[0041] The target [Si] concentration in the hot metal ([Si] f The amount of gaseous oxygen required to reach the temperature (°C) is calculated using the following formula (2).

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[0042] In the present invention, as described above, the amount of gaseous oxygen O necessary for proper desiliconization to achieve the target [Si] concentration in the molten iron in the desiliconization treatment is 2-gas By calculating in advance, it is possible to ensure that only the desiliconization reaction occurs during the desiliconization reaction, and that the decarbonization reaction starts during the dephosphorization reaction, thereby suppressing the generation of CO gas and preventing the slopping phenomenon.

[0043] Next, after the [Si] concentration in the hot metal in the desiliconization process reaches the calculated predetermined [Si] concentration in the hot metal, the process shifts from the desiliconization process to the dephosphorization process. That is, the calculated amount of gaseous oxygen O required for the desiliconization process is calculated.2-gas Gaseous oxygen gas is injected into the molten iron 2 from the top lance 4, and after the [Si] concentration in the molten iron during the desiliconization process reaches the target [Si] concentration in the molten iron, the process shifts from desiliconization to dephosphorization.

[0044] Specifically, in the treatment process, first, in order to reach a predetermined [Si] concentration in the molten iron, the amount of gaseous oxygen O necessary for the desiliconization reaction is determined. 2-gas is sprayed onto the molten iron 2. In the desiliconization process, a high gaseous oxygen flow rate is used to complete the process as quickly as possible within the limited processing time. After that, the desiliconization process is shifted to the dephosphorization process.

[0045] The dephosphorization process is carried out under soft blow conditions (lowering the top-blowing oxygen flow rate and increasing the height of the top-blowing lance 4, etc.), which delays the reaction between gaseous oxygen and the [C] concentration in the molten iron, suppresses the generation of CO gas, and reduces the frequency of slopping.

[0046] When the [Si] concentration in the hot metal during desiliconization is lower than the calculated predetermined (target) [Si] concentration in the hot metal, the gaseous oxygen flow rate O 2-gas If the temperature is high and the hot metal 2 is sprayed with the CO gas, the rate of CO gas generation increases, causing a slopping phenomenon and resulting in a decrease in yield.

[0047] On the other hand, when the [Si] concentration in the hot metal in the desiliconization process is higher than the calculated predetermined [Si] concentration in the hot metal, the process is shifted to the dephosphorization process and the gaseous oxygen flow rate O 2-gas If the level is lowered, the progress of the desiliconization reaction will be delayed, which will result in a longer treatment time and lead to a loss of steel production.

[0048] In other words, the amount of gaseous oxygen required for the desiliconization reaction is O 2-gas When this is injected into the molten iron 2, the target [Si] concentration in the molten iron is reached, and once this [Si] concentration is reached, the dephosphorization process begins.

[0049] In this way, by calculating the contribution of the gaseous oxygen amount and the solid oxygen amount that contribute to the desiliconization reaction, it is possible to perform deP blowing while suppressing the generation of CO gas and reducing the frequency of slopping, and also to improve the yield.

[0050] Here, the yield is defined as follows: Yield (%) = W f-Fe / W i-Fe ×100 however, ·W i-Fe : Fe source (t) charged into the furnace before treatment ·W f-Fe : amount of hot metal after treatment (t) ·W i-Fe =W i ×(100-[C] i -[Si] i -[P] i ) + Fe source in solid oxygen ·W f-Fe =W f ×(100-[C] f -[Si] f -[P] f )

[0051] Also, ·W i : Amount of hot metal before treatment (t) [C] i : [C] concentration in hot metal before treatment (mass%) [Si] i : [Si] concentration in hot metal before treatment (mass%) [P] i : [P] concentration in hot metal before treatment (mass%) ·W f : amount of hot metal after treatment (t) [C] f : [C] concentration in hot metal after treatment (mass%) [Si] f : [Si] concentration in hot metal after treatment (mass%) [P] f : [P] concentration in hot metal after treatment (mass%)

[0052] Table 1 shows a summary of the definitions of the parameters in this embodiment.

[0053] [Table 1] [Example] Below, examples carried out in accordance with the method for desiliconizing and dephosphorizing hot metal in a converter-type refining vessel of the present invention, as well as comparative examples carried out for comparison with the present invention, will be described.

[0054] The conditions for carrying out this example are as follows.

[0055] [Table 2] Table 3 shows examples of the desiliconization and dephosphorization treatment of hot metal in a converter-type refining vessel according to the present invention, as well as comparative examples carried out for comparison with the present invention. Table 3 is a continuous table, but is divided into two sections, one above the other, for ease of viewing.

[0056] [Table 3] In this Example 1, k si-solid = 0.40 (1 / min.), and the O calculated appropriately using equation (2) 2-gas =466Nm 3 In [Si] f =0.10 mass%, and the yield (W f-Fe / W i-Fe × 100) = 99.1% As a result, good results were obtained.

[0057] In this second embodiment, k si-solid = 0.61 (1 / min.), and the O calculated appropriately using equation (2) 2-gas =393Nm 3 In [Si] f =0.10 mass%, and the yield (W f-Fe / W i-Fe× 100) = 99.3%, which was a good result.

[0058] In this Example 3, k si-solid = 0.20 (1 / min.), and the O calculated appropriately from equation (2) 2-gas =650Nm 3 In [Si] f =0.10 mass%, and the yield (W f-Fe / W i-Fe × 100) = 99.0%, a good result.

[0059] In this Example 4, k si-solid = 0.06 (1 / min.), and the O calculated appropriately from equation (2) 2-gas =866Nm 3 In [Si] f =0.10 mass%, and the yield (W f-Fe / W i-Fe × 100) = 99.1%, which was a good result.

[0060] In this Example 5, k si-solid = 0.51 (1 / min.), and the O calculated appropriately from equation (2) 2-gas =493Nm 3 In [Si] f =0.10 mass%, and the yield (W f-Fe / W i-Fe × 100) = 99.1%, which was a good result.

[0061] In this Example 6, k si-solid = 0.77 (1 / min.), and the O calculated appropriately from equation (2) 2-gas =422Nm 3 In [Si] f =0.10 mass%, and the yield (W f-Fe / W i-Fe × 100) = 99.1%, which was a good result.

[0062] On the other hand, in Comparative Examples 7 to 12, k si-solid =0, [Si]f = 0.10 mass% O 2-gas (because more gaseous oxygen is blown in than necessary), f-Fe / W i-Fe × 100) = 98.5 to 98.8%, resulting in a decrease in yield.

[0063] Figure 2 compares the yield when the [Si] concentration in the hot metal during desiliconization is predetermined and the yield when the [Si] concentration in the hot metal is not predetermined, taking into account the reaction rate constant of the amount of solid oxygen that contributes to the desiliconization reaction.

[0064] As shown in Figure 2, Examples 1 to 6 had an average yield of 99.1%, which was a good result. On the other hand, Comparative Examples 7 to 12 had a yield significantly lower than the average, and a decrease in yield was observed. In this way, by taking into account the reaction rate constant of the solid oxygen amount, it is possible to reduce the frequency of slopping and improve the yield.

[0065] As described above, according to the method for desiliconization and dephosphorization of molten iron in a converter-type refining vessel of the present invention, the generation of CO gas is suppressed and the frequency of slopping is reduced during dephosphorization in a converter-type refining vessel, thereby improving yield.

[0066] It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. In particular, in the embodiments disclosed herein, matters not explicitly stated, such as operating conditions, operating conditions, various parameters, dimensions, weights, volumes of components, etc., do not deviate from the scope of ordinary practice by a person skilled in the art, and values ​​that can be easily assumed by a person skilled in the art are used. [Explanation of symbols]

[0067] 1 Converter-type refining vessel 2. Molten iron 3. Slug 4 Top-blowing lance 5 Bottom-blown tuyere

Claims

[Claim 1] A method for dephosphorizing molten pig iron by injecting gaseous oxygen gas from a top-blowing lance into molten pig iron charged in a top-bottom blown converter-type refining vessel and adding an iron oxide source, which is solid oxygen, from above, the desiliconization reaction rate constant of the solid oxygen is calculated in advance from Equation (1) using the stirring power density obtained from the flow rate of the bottom-blown gas; Using the obtained desiliconization reaction rate constant and the target [Si] concentration in the molten iron, the amount of gaseous oxygen required for the desiliconization treatment is calculated using equation (2), The amount of gaseous oxygen gas (gaseous oxygen amount) O2-gas to be blown from the top lance is determined so that the [Si] concentration in the molten iron does not become ≦0.09 mass%, and the determined amount of gaseous oxygen gas is blown from the top lance. After the [Si] concentration in the molten iron during the desiliconization process reaches the target [Si] concentration in the molten iron, the process shifts from desiliconization to dephosphorization. A method for desiliconizing and dephosphorizing molten iron in a converter-type refining vessel, comprising: ・k si-solid : Desiliconization reaction rate constant (1 / min.) ・a: Constant (t / (min.・W・Nm 3 ) ・ε: Stirring power density (W / t) ・O 2-solid: Amount of iron oxide source added from above (Nm 3 ) b: Constant (1 / min.) however, O 2-gasblow: Top-blown oxygen flow rate during desiliconization (Nm 3 / min.) · O 2-gas: Estimated [Si] concentration at the end of the desiliconization treatment (amount of gaseous oxygen required for desiliconization treatment) (Nm 3 ) [Si]i: [Si] concentration in hot metal at the beginning of blowing (mass%) [Si] f : [Si] concentration in hot metal at estimated end point of desiliconization treatment (mass%) ・k Si-gas : Reaction rate constant of the amount of gaseous oxygen contributing to the desiliconization reaction (1 / min.) ・k Si-solid: Reaction rate constant of the amount of solid oxygen contributing to the desiliconization reaction (1 / min.)

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