WO2024018783A1

WO2024018783A1 - Cold iron source solubility estimation device, cold iron source solubility estimation method, and refining treatment method for molten iron

Info

Publication number: WO2024018783A1
Application number: PCT/JP2023/021995
Authority: WO
Inventors: 雄大服部; 玲横森; 太小笠原; 涼川畑; 直樹菊池
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2022-07-19
Filing date: 2023-06-14
Publication date: 2024-01-25

Abstract

Provided is a cold iron source solubility estimation device that can calculate the solubility of a cold iron source by using high-versatility parameters.　This cold iron source solubility estimation device 30 estimates the solubility of a cold iron source in a refining process for molten iron that uses the cold iron source as the raw material, the device including: an acquisition unit 36 that acquires furnace information, including information about the molten iron and cold iron source; a computation unit 38 that uses the furnace information to calculate the interfacial carbon concentration between the cold iron source and the molten iron, the dissolution rate of the cold iron source, and the solubility of the cold iron source; and an output unit 40 that outputs the solubility, wherein, when the interfacial carbon concentration satisfies a prescribed condition, the computation unit uses the interfacial carbon concentration calculated one step previously to calculate a first dissolution rate from a heat transfer balance equation, and a second dissolution rate from a carbon material balance equation, and calculates the dissolution rate of the cold iron source by proportionally dividing the first dissolution rate and the second dissolution rate.

Description

Cold iron source dissolution rate estimation device, cold iron source dissolution rate estimation method, and molten iron refining processing method

The present invention provides a cold iron source dissolution rate estimating device, a cold iron source dissolution rate estimation method, and a molten iron refining method using the same for estimating the dissolution rate of a cold iron source in a molten iron refining process using a cold iron source as a raw material. Regarding.

In order to achieve carbon neutrality in 2050, the steel industry is also required to reduce the amount of _CO2 gas generated. The main cause of _CO2 emissions in the steel industry is the use of coal during the reduction of iron ore in the blast furnace process. Generally, in the blast furnace process, approximately 2 tons of CO ₂ is generated per 1 ton of crude steel during the production of steel products. On the other hand, if a cold iron source such as scrap or reduced iron is melted by electric power, heat transfer from molten iron, or carburization without using blast furnace pig iron, coal is not required. Therefore, the amount of _CO2 generated when using a cold iron source is approximately 500 kg per ton of crude steel (excluding the amount of _CO2 generated during reduced iron production), and compared to the blast furnace method, the amount of _CO2 generated per ton of crude steel is approximately 500 kg. Emissions can be reduced to about 1/4. Therefore, in order to reduce _CO2 emissions in the steel industry, it can be said that it is effective to reduce the amount of blast furnace pig iron used by reducing the hot metal content ratio in converters and to increase the amount of cold iron source used by introducing electric furnaces.

On the other hand, increasing the amount of cold iron source used increases the time required for complete melting of the cold iron source. If the time required to completely melt the cold iron source becomes longer and the cold iron source cannot be completely melted during the processing time, many disadvantages will occur in terms of operation and metallurgy. For example, in hot metal dephosphorization blowing in a converter, a sublance collides with an unmolten cold iron source, causing damage to the sublance. Furthermore, the undissolved cold iron source deposited on the bottom blowing tuyeres obstructs the stirring of the hot metal, resulting in poor dephosphorization.

In addition, in electric furnaces, cold iron sources are added continuously or intermittently, but if the loading speed is too high compared to the melting rate, the unmelted cold iron sources in the furnace will increase, and the cold iron sources will They can fuse together to form giant iron blocks. Since iron ingots have a small surface area to volume ratio and have a slow dissolution rate, the generation of iron ingots leads to a decrease in productivity and an increase in the required power. Therefore, in order to efficiently melt the cold iron source, it is important to know whether there is any unmelted cold iron source in the furnace.

The main method for determining the presence or absence of unmelted cold iron source is to use sensing to determine the timing of complete melting of the cold iron source. Many methods for determining the timing of complete melting of a cold iron source are targeted at electric furnaces, and these methods monitor temperature, pressure, vibration, light, etc. inside the furnace and determine whether the cold iron source is completely melted based on changes in the temperature, pressure, vibration, light, etc. Determine the timing.

For example, in Patent Document 1, the refractory temperature is measured at multiple points in the thickness direction using a temperature probe embedded in the side wall of the converter body, and the refractory surface temperature (molten iron temperature ) is disclosed. This method focuses on the fact that the temperature rise rate of molten iron increases after the cold iron source in the furnace is completely melted. According to Patent Document 1, it is possible to determine when the cold iron source is completely melted from the temperature change of the molten iron.

Additionally, although there are few examples of its application to actual operations, a one-dimensional heat transfer model (hereinafter referred to as "cold iron source melting model") that predicts the melting behavior of cold iron sources has been reported. Documents mentioning the dissolution model of cold iron sources include

Non-Patent Documents

1 and 2. According to the dissolution models of cold iron sources disclosed in

Non-Patent Documents

1 and 2, by assuming the heat transfer coefficient between molten iron and cold iron source and the mass transfer coefficient of molten iron, it is possible to accurately predict the melting behavior of cold iron source. It is said to be predictable. To apply the cold iron source dissolution model to actual operations, it is necessary to continuously or intermittently input information such as molten iron temperature and molten iron carbon concentration obtained by sensing etc. By using a cold iron source dissolution model, it is possible to predict not only the complete dissolution timing of the cold iron source but also the momentary dissolution rate of the cold iron source, which has the advantage of being able to predict the occurrence of undissolved cold iron sources during processing. be.

Japanese Patent Application Publication No. 8-3614

Patent Document 1 does not mention the threshold value of the temperature rise rate of molten iron, which is the standard for determining the complete melting timing of a cold iron source, and the determination is influenced by the subjectivity of the observer. In addition, in actual operation, the temperature transition of the molten iron changes due to factors such as changes in the top and bottom blowing flow rates, so there is a great concern that misjudgments or judgment delays may occur.

In addition, heat transfer and carburization (transfer of mass from molten iron to the surface layer of the cold iron source) are the driving forces for cold iron source melting, but the carbon concentration of the molten iron does not exceed the carbon concentration of the cold iron source, or the presence of solidification elements. Since carburization does not occur below and the driving force for melting the cold iron source is only heat transfer, the melting rate of the cold iron source can be calculated by considering the heat balance near the molten iron-cold iron source interface. On the other hand, if the molten iron carbon concentration exceeds the carbon concentration of the cold iron source, carburization will occur after the solidification elements are remelted, so when calculating the dissolution rate of the cold iron source, the carbon mass balance should be used instead of the heat balance near the interface. need to be considered. In this way, it is common to change the dissolution rate calculation formula depending on the driving force for melting the cold iron source, but in reality, the dissolution mechanism cannot be clearly distinguished.

For example, even if the molten iron carbon concentration exceeds the carbon concentration of the cold iron source and carburization occurs, heat transfer will not occur if the molten iron temperature is equal to or higher than the liquidus temperature of the cold iron source. It cannot be considered that it does not contribute to the melting of cold iron sources at all, and it is necessary to consider both carburization and heat transfer as melting mechanisms. However, conventional cold iron source melting models limit the driving force to carburization or heat transfer.

In the cold iron source melting models disclosed in

Non-Patent Documents

1 and 2, accuracy is ensured by using heat transfer coefficients and mass transfer coefficients as fitting parameters. However, the values of the fitting parameters are disclosed only for specific molten iron and cold iron source conditions mentioned in the literature, and there is a problem in that they lack general versatility. The present invention was made in view of these problems, and provides a cold iron source dissolution rate estimation device, a cold iron source dissolution rate estimation method, and a cold iron source dissolution rate estimation method that can calculate the dissolution rate of a cold iron source using highly versatile parameters. The purpose of the present invention is to provide a method for refining molten iron using the method.

The means for solving the above problems are as follows.
[1] A cold iron source melting rate estimating device for estimating the melting rate of the cold iron source in a molten iron refining process using a cold iron source as a raw material, which includes information on the molten iron and the cold iron source. an acquisition unit that acquires information; a calculation unit that uses the furnace information to calculate an interfacial carbon concentration between the cold iron source and the molten iron, a dissolution rate of the cold iron source, and a dissolution rate of the cold iron source; an output unit that outputs the dissolution rate, and when the interfacial carbon concentration satisfies at least one of the following formulas (1) and (2), the calculation unit outputs the dissolution rate calculated one step before. Using the interfacial carbon concentration, calculate the first dissolution rate from the heat transfer equation and the second dissolution rate from the carbon material balance equation, and divide the first dissolution rate and the second dissolution rate proportionally. By doing so, the dissolution rate of the cold iron source is calculated, and if the interfacial carbon concentration does not satisfy either of the following equations (1) and (2), the calculation unit uses the interfacial carbon concentration to calculate the dissolution rate of the cold iron source. A cold iron source dissolution rate estimating device that calculates a first dissolution rate or the second dissolution rate, and sets the calculated first dissolution rate or the second dissolution rate as the dissolution rate of the cold iron source.
C _i >C...(1)
C _i >C _i,t-1 ...(2)
In the above equations (1) and (2), C is the molten iron carbon concentration (mass%), C _i is the interfacial carbon concentration (mass%), and C _i,t-1 is the molten iron carbon concentration (mass%). Interfacial carbon concentration (mass%).
[2] When the carbon concentration of the cold iron source is lower than the carbon concentration of the molten iron, the calculation unit calculates the first dissolution rate based on the molten iron temperature, the molten iron carbon concentration, and the carbon concentration of the cold iron source. The cold iron source dissolution rate estimation device according to [1], which specifies an apportionment ratio for apportioning the second dissolution rate.
[3] The calculation unit estimates the dissolution rate of the cold iron source from time to time by repeatedly calculating the interfacial carbon concentration, the dissolution rate of the cold iron source, and the dissolution rate of the cold iron source. , the cold iron source dissolution rate estimation device according to [1] or [2].
[4] Estimate the dissolution rate of the cold iron source at the end of the refining process using the cold iron source dissolution rate estimating device according to any one of [1] to [3], and estimate the dissolution rate of the cold iron source at the end of the refining process. When the unmelted rate of the cold iron source calculated from the rate exceeds 5% by mass, a method for refining molten iron includes performing at least one of adding a heat raising material and extending the molten iron treatment.
[5] A cold iron source melting rate estimation method for estimating the melting rate of the cold iron source in a molten iron refining process using the cold iron source as a raw material, the method comprising: a method for estimating the melting rate of the cold iron source; an acquisition step of acquiring information; a calculation step of calculating an interfacial carbon concentration between the cold iron source and the molten iron, a dissolution rate of the cold iron source, and a dissolution rate of the cold iron source using the furnace information; an output step of outputting the dissolution rate, and when the interfacial carbon concentration satisfies at least one of the following formulas (1) and (2), the calculation step Using the interfacial carbon concentration, calculate the first dissolution rate from the heat transfer equation and the second dissolution rate from the carbon material balance equation, and divide the first dissolution rate and the second dissolution rate proportionally. By doing so, the dissolution rate of the cold iron source is calculated, and if the interfacial carbon concentration does not satisfy either of the following equations (1) or (2), in the calculation step, the interfacial carbon concentration is used to calculate the dissolution rate of the cold iron source. A cold iron source dissolution rate estimation method, comprising calculating a first dissolution rate or the second dissolution rate, and setting the calculated first dissolution rate or the second dissolution rate as the dissolution rate of the cold iron source.
C _i >C...(1)
C _i >C _i,t-1 ...(2)
In the above equations (1) and (2), C is the molten iron carbon concentration (mass%), C _{i is the interfacial carbon concentration (mass%), and C i} ,t-1 is the molten iron carbon concentration (mass%), and C _i,t-1 is the carbon concentration of the molten iron (mass%). Interfacial carbon concentration (mass%).
[6] When the carbon concentration of the cold iron source is lower than the carbon concentration of the molten iron, in the calculation step, the first dissolution rate is determined based on the molten iron temperature, the molten iron carbon concentration, and the carbon concentration of the cold iron source. The method for estimating a cold iron source dissolution rate according to [5], which specifies an apportionment ratio for apportioning the second dissolution rate.
[7] In the calculation step, the interfacial carbon concentration, the dissolution rate of the cold iron source, and the dissolution rate of the cold iron source are repeatedly calculated to estimate the dissolution rate of the cold iron source from time to time. The cold iron source dissolution rate estimation method according to [5] or [6].
[8] Estimating the dissolution rate of the cold iron source at the end of the refining process using the cold iron source dissolution rate estimation method according to any one of [5] to [7], When the unmelted rate of the cold iron source calculated from the rate exceeds 5% by mass, a method for refining molten iron includes performing at least one of adding a heat raising material and extending the molten iron treatment.

According to the present invention, the dissolution rate of a cold iron source can be calculated using an apportionment ratio that can be determined more easily than fitting parameters, so the method for estimating the dissolution rate of a cold iron source according to the present invention is more versatile than before. It can be said that this is a method for calculating the dissolution rate of a cold iron source with a high

FIG. 1 is a schematic diagram of a converter type refining furnace equipped with a cold iron source melting rate estimation device according to the present invention. FIG. 2 is a graph showing the proportional distribution ratio for hot metal temperatures of 1450 to 1480° C. in Table 1. FIG. 3 is a flowchart illustrating the flow of a cold iron source dissolution rate estimation method. FIG. 4 is a graph showing the estimated and actual measurement results of the dissolution rate of the square pure iron sample in Example 1. FIG. 5 is a graph showing the estimated and actual measurement results of the dissolution rate of the square pure iron sample in Example 2. FIG. 6 is a graph showing the estimated and actual measurement results of the dissolution rate of the square pure iron sample in Example 3.

Hereinafter, an example of an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of a converter type refining furnace equipped with a cold iron source melting rate estimation device according to the present invention. In FIG. 1, reference numeral 10 is a converter-type refining furnace, reference numeral 20 is a converter-type refining furnace control device, and reference numeral 50 is an operator. The converter type refining furnace control device 20 includes a process computer 22, an operation control computer 24, and a cold iron source melting rate estimation device 30.

In the converter type refining furnace 10, iron scrap is charged into the furnace as a cold iron source using a scrap chute, and then hot metal 11 is charged into the furnace using a charging pot. Oxygen gas (industrial pure oxygen) is supplied from a top blowing lance 14 to the hot metal 11 charged in the furnace, and stirring gas 13 is supplied from a tuyere (not shown) installed at the bottom of the furnace. It is configured to be blown into the hot metal 11 in the furnace. Hot metal 11 charged into the furnace is oxidized and refined by oxygen gas supplied from top blowing lance 14 while being stirred by stirring gas 13 . In the converter type refining furnace 1, preliminary dephosphorization treatment of the hot metal 11 and decarburization treatment of the hot metal 11 (hereinafter also referred to as "decarburization refining") are generally performed as refining treatment methods.

In the preliminary dephosphorization treatment of the hot metal 11, iron scrap is first charged as a source of cold iron into the converter-type smelting furnace 10 using a scrap chute (not shown), and then a charging pot (not shown) is charged into the converter type smelting furnace 10. Hot metal 11 is charged into the furnace using the method. After charging the hot metal 11, oxygen gas is supplied from the top blowing lance 14, nitrogen gas etc. is supplied as the stirring gas 13 from the tuyeres at the bottom of the furnace, and auxiliary raw materials such as heating materials and solvents are added to the hot metal. No. 11 is subjected to preliminary dephosphorization treatment.

In the preliminary dephosphorization treatment of the hot metal 11 in the converter type refining furnace 1, phosphorus in the hot metal is oxidized with oxygen gas to form phosphorus oxides (P ₂ O ₅ ), and the formed phosphorus oxides are treated with a CaO-based solvent. This is done by fixing 3CaO.P ₂ O ₅ (=Ca ₃ (PO ₄ ) ₂ ) in a stable form in the slag 12 produced by slag formation. In the preliminary dephosphorization treatment of the hot metal 11, when the phosphorus concentration of the hot metal 11 in the furnace reaches a predetermined value (for example, 0.050% by mass or less), the preliminary dephosphorization treatment is finished. After the preliminary dephosphorization treatment, dephosphorized hot metal is produced in the furnace.

After charging the hot metal 11 after the preliminary dephosphorization treatment, oxygen gas is supplied from the top blowing lance 14, and stirring gas 13 is supplied from the tuyere at the bottom of the furnace, and auxiliary materials such as coolant, heating material, solvent, etc. is added at appropriate times to decarburize the hot metal 11.

The decarburization treatment of the hot metal 11 proceeds by a decarburization reaction (C+O→CO) between oxygen gas and carbon in the molten iron, and the carbon concentration of the molten iron in the furnace reaches a predetermined value (for example, 0.05% by mass or less). The decarburization process is carried out until the After decarburization, decarburized molten steel is produced in the furnace. Here, "molten iron" is either hot metal or molten steel. In the decarburization treatment of the hot metal 11, the hot metal in the furnace changes into molten steel as the decarburization treatment progresses. Since it is difficult to distinguish and display the molten metal in the furnace during the decarburization process as molten pig iron and molten steel, molten pig iron and molten steel are collectively referred to as "molten iron."

The process computer 22 determines the hot metal temperature and hot metal component concentration at the end of the preliminary dephosphorization process, the amount of oxygen that should be supplied in order to set the molten iron temperature and the molten iron component concentration at the end of the decarburization process to target values, and This is a device that calculates the necessity and amount of input of coolant or heating material.

The operation control computer 24 determines the hot metal temperature, hot metal component concentration, and decarburization at the end of the preliminary dephosphorization treatment based on the amount of oxygen calculated by the process computer 22 and the input amount of the coolant or heating material. This is a device that controls operating conditions (oxygen gas supply amount, lance height, stirring gas supply amount, auxiliary material input amount, etc.) so that the molten steel temperature and molten steel component concentration at the end of treatment reach target values. Signals from the operational control computer 24 are fed back to the process computer 22 in order to control the refining even more precisely. Hereinafter, the cold iron source dissolution rate estimating device 30 according to the present embodiment will be used to estimate hot metal 11 using a converter type refining furnace 10 that uses iron scrap having a lower carbon concentration than the hot metal 11 as a cold iron source. This will be explained using an example in which it is applied to preliminary dephosphorization treatment. However, the cold iron source dissolution rate estimating device 30 is applicable not only to the converter type smelting furnace 10 but also to an electric furnace type smelting furnace, and also to decarburization treatment of the hot metal 11.

The cold iron source melting rate estimation device 30 is a calculation device that constitutes a part of the converter type smelting furnace control device 20. The cold iron source dissolution rate estimating device 30 includes a control section 32, a storage section 34, and an output section 40. The control unit 32 is, for example, a CPU or the like, and causes the control unit 32 to function as an acquisition unit 36 and a calculation unit 38 by executing a program read from the storage unit 34 .

The output unit 40 is, for example, an LCD or CRT display. The storage unit 34 is, for example, an information recording medium such as an update-recordable flash memory, a built-in hard disk or a hard disk connected via a data communication terminal, a memory card, and a read/write device thereof. The storage unit 34 records programs for executing the functions of the acquisition unit 36 and the calculation unit 38, as well as calculation formulas, data, etc. used in the programs.

Next, the processing executed by the acquisition unit 36 and the calculation unit 38 will be described. The acquisition unit 36 acquires in-furnace information through information input by the operator 50 or from an in-furnace sensor provided in the converter type refining furnace 10 via the process computer 22 . The furnace information includes information on the hot metal 11 and iron scrap. Specifically, the furnace information includes the charging amount of hot metal 11 charged into the furnace, the initial carbon concentration of hot metal 11, the charging amount of iron scrap, the initial carbon concentration of iron scrap, the density of iron scrap, and the iron This includes the latent heat of melting of scrap. In addition to these pieces of information, the acquisition unit 36 also acquires the momentary temperature of the hot metal 11, the bottom blowing flow rate of the stirring gas 13, and the furnace pressure as in-furnace information. The acquisition unit 36 outputs the acquired furnace information to the calculation unit 38.

The calculation unit 38 uses the in-furnace information to calculate the interfacial carbon concentration between the iron scrap charged into the converter type refining furnace 10 and the hot metal 11, the iron scrap dissolution rate, and the iron scrap dissolution rate. The calculation unit 38 first calculates the interfacial carbon concentration between the hot metal 11 and the iron scrap, and if the calculated interfacial carbon concentration satisfies at least one of the following equations (1) and (2), the calculation unit 38 calculates the interfacial carbon concentration between the hot metal 11 and the iron scrap. Using the calculated interfacial carbon concentration, the first dissolution rate is calculated from the heat transfer equation, and the second dissolution rate is calculated from the carbon mass balance equation, and the first dissolution rate and the second dissolution rate are calculated. The dissolution rate of iron scrap is calculated by proportionally dividing the dissolution rate. Note that if at least one of the following equations (1) and (2) is satisfied in the calculation one step before, the interfacial carbon concentration calculated one step before is used.

C _i >C...(1)
C _i >C _i,t-1 ...(2)
In the above equations (1) and (2), C is the carbon concentration (mass%) of the hot metal 11, C _i is the interfacial carbon concentration (mass%), and C _i,t-1 is calculated one step before. is the interfacial carbon concentration (mass%). In the following explanation, the subscript t-1 means a value calculated one step before.

In this way, the calculation unit 38 calculates the dissolution rate of iron scrap by proportionally dividing the first dissolution rate calculated from the heat balance formula and the second dissolution rate derived from the carbon material balance using the proportional division ratio. . As an example, the values of the proportion ratio when the carbon concentration of the cold iron source is 0.05% by mass are shown in Table 1 below.

A table of proportional division ratios for proportionally dividing the first dissolution rate and the second dissolution rate shown in Table 1 is created in advance for each carbon concentration of the cold iron source and stored in the storage unit 34.

FIG. 2 is a graph showing the proportional distribution ratio for hot metal temperatures of 1450 to 1480°C in Table 1. In FIG. 2, the horizontal axis is the molten iron carbon concentration (mass %), and the vertical axis is the proportion ratio (-). As shown in FIG. 2, the proportional distribution ratio for each molten iron carbon concentration is plotted on a predetermined curve. Therefore, for example, by determining the proportional distribution ratio of three different molten iron carbon concentrations and determining the curve (broken line in FIG. 2) using the three points, it is possible to determine the proportional distribution ratio of other molten iron carbon concentrations. As described above, since the apportionment ratio can be determined more easily than the conventional fitting parameters, the cold iron source dissolution rate estimation method according to the present embodiment using the apportionment ratio is a cold iron source dissolution rate estimation method that is more versatile than the conventional method. This can be said to be a method for calculating the dissolution rate of iron sources.

The calculation unit 38 reads out the table of apportionment ratios corresponding to the carbon concentration of the iron scrap from the storage unit 34, and specifies the values in the table corresponding to the temperature of the hot metal 11 and the carbon concentration of the molten iron as the apportionment ratio. That is, the calculation unit 38 specifies the proportional distribution ratio based on the molten iron temperature, the molten iron carbon concentration, and the carbon concentration of the cold iron source.

The calculation unit 38 calculates the dissolution rate of iron scrap by proportionally dividing the first dissolution rate and the second dissolution rate using the specified proportion ratio. On the other hand, when the calculated interfacial carbon concentration does not satisfy either of the above equations (1) and (2), the calculation unit 38 calculates the first dissolution rate or the second dissolution rate using the calculated interfacial carbon concentration. Calculate. In this case, since the first dissolution rate and the second dissolution rate are the same dissolution rate, the first dissolution rate or the second dissolution rate is taken as the dissolution rate of the iron scrap.

The calculation unit 38 uses the calculated iron scrap dissolution rate to calculate the iron scrap dissolution rate. In this way, the calculation unit 38 calculates the melting rate of iron scrap using the furnace information.

The calculation unit 38 outputs the calculated iron scrap dissolution rate to the output unit 40. The output unit 40 displays the calculation result of the melting rate of iron scrap so that the operator 50 who operates the converter type refining furnace 10 can visually check the result. Thereby, the operator 50 can confirm how much iron scrap is being melted during processing of the charge by looking at the display on the output unit 40, and can perform operations according to the melting rate of the iron scrap. For example, the dissolution rate of iron scrap at the end of the preliminary dephosphorization treatment of hot metal 11 is estimated, and if the undissolved rate of iron scrap calculated from the dissolution rate exceeds 5% by mass, the addition of a heating material It is preferable to carry out at least one operation of molten iron preliminary dephosphorization treatment extension. This makes it possible to reduce the amount of iron scrap that remains unmelted at the end of the preliminary dephosphorization process.

Next, a specific calculation method for calculating the dissolution rate of iron scrap in the calculation unit 38 will be explained. Note that formulas related to iron scrap, such as physical property values and dissolution rate, shall be calculated for each brand of iron scrap. The mass of the hot metal 11 and the carbon concentration of the hot metal 11 used in the calculation are calculated using the following formulas (3) and (4).

Here, W is the mass (ton) of hot metal 11 in the furnace, W ₀ is the charging amount (ton) of hot metal 11, W _SO is the charging amount (ton) of iron scrap, and S _m is the dissolution rate (mass %) of iron scrap, C is the carbon concentration (mass %) of hot metal 11, _C0 is the initial carbon concentration (mass %) of hot metal 11, and C _S0 is the initial carbon concentration of iron scrap (mass %). Carbon concentration (mass%).

In equation (4), it is assumed that the carbon concentration C of the hot metal 11 changes only depending on the iron scrap dissolution rate _Sm , and the influence of decarburization due to the reaction with blown oxygen or atmospheric oxygen is not considered. That is, in the presence of a solidified shell (dissolution rate S _m <0), the carbon concentration C of the hot metal 11 remains unchanged at the initial carbon concentration. Further, when the converter type refining furnace 10 has a means for measuring the carbon concentration C of the hot metal 11, the measured value of the carbon concentration C may be used without calculating the formula (4).

Furthermore, when applying the cold iron source dissolution rate estimating device 30 according to the present embodiment to decarburization treatment, the calculated carbon concentration C of molten steel deviates from the actual carbon concentration of molten steel at the final stage of treatment where decarburization progresses. It is expected that. However, since the molten steel temperature is high at the end of the decarburization process, the influence of the carbon concentration C of the molten steel on the dissolution rate of iron scrap is small, so the dissolution rate S _m of the cold iron source does not deviate greatly.

The physical property values of the hot metal 11 are calculated using the following formulas (5) to (12).

Here, ρ is the density of the hot metal 11 (ton/m ³ ), ε _B is the bottom-blowing stirring power (W/ton), Q _B is the bottom-blowing flow rate (Nm ³ /min), and T is the The temperature of the hot metal 11 (°C), g is the gravitational acceleration (m/s ² ), L is the bath depth (m), P is the furnace pressure (Pa), and h is the hot metal-iron scrap It is the interfacial heat transfer coefficient (W/(m ² ·K)), and D is the diffusion coefficient of the hot metal 11 (m ² /s).

Here, α is the thermal diffusivity of the hot metal 11 (m ² /s), C _P is the specific heat of the hot metal 11 (kcal/(kg・K)), and λ is the thermal conductivity of the hot metal 11 (W/(m・K) )), μ is the viscosity of the hot metal 11 (mPa·s), k is the mass transfer coefficient (m/s) of the hot metal 11, Sc is the Schmidt number (-), and Pr is the Prandtl number (-). Equation (5) is an empirical formula obtained from the scrap melting behavior in a top-blown 310 ton converter to a bottom-blown 240 ton converter described in Publication 1 below. Equation (10) is an equation derived from the Chilton-Colburn similarity law. Note that (-) means dimensionless.

Publication 1: H. Gaye, M. Wanin, P. Gugliermina and P. Schittly: 68th Steelmaking Conf. Proc. , ISS, Detroit, MI, USA, (1985), 91.

The carbon concentration at the interface between hot metal and scrap iron (hereinafter referred to as "interface carbon concentration") and the temperature at the interface between molten iron and cold iron source (hereinafter referred to as "interface temperature") are calculated by formulas (13) to (15) below. Calculate using. Equation (13) below is the heat transfer balance equation near the interface, Equation (14) below is the carbon material balance equation near the interface, and Equation (15) below is the relational equation between the temperature at the interface and the carbon concentration. . Using these three equations, the interfacial carbon concentration and interfacial temperature are calculated.

Here, T _i is the interface temperature (℃), T _S is the cold iron source temperature (℃), ρ _S is the density of iron scrap (ton/m ³ ), and Hs is the latent heat of melting of iron scrap. (MJ/ton), v is the dissolution rate (mm/s) of iron scrap (v>0: melting, v<0: growth (solidification shell formation), and λ _i is the heat of the hot metal-iron scrap interface. Conductivity (W/(m・K)) (hot metal side thermal conductivity at interface). _{T L,0} is the liquidus temperature (℃) of pure iron (carbon concentration 0 mass%), and a is It is a coefficient.

Further, the coefficient of the above equation (15) and the liquidus temperature of pure iron are calculated using the following equations (16) and (17). The coefficients calculated by the following equations (16) and (17) and the liquidus temperature of pure iron are used to calculate C _i in the next step.

Furthermore, the heat transfer coefficient of the hot metal-iron scrap interface (hereinafter referred to as "interface heat transfer coefficient") is calculated by the following equation (18). The interfacial heat transfer coefficient calculated by equation (18) is used to calculate the interfacial carbon concentration in the next step.

If the interfacial carbon concentration calculated here satisfies at least one of the following formulas (1) and (2), the interfacial carbon concentration calculated one step before is used instead of the calculated interfacial carbon concentration. , calculate the first dissolution rate from the above equation (13), calculate the second dissolution rate from the above equation (14), and divide the first dissolution rate and the second dissolution rate proportionally. Calculate the dissolution rate of scrap.

C _i >C...(1)
C _i >C _i,t-1 ...(2)

If the interfacial carbon concentration calculated one step before is used instead of the calculated interfacial carbon concentration, the first dissolution rate calculated from equation (13) and the first dissolution rate calculated from equation (14) The speed will be a different value. The calculation unit 38 calculates the dissolution rate of iron scrap by proportionally dividing the first dissolution rate and the second dissolution rate at a specific proportion.

As mentioned above, in calculating the dissolution rate of iron scrap, it is preferable to use equations (13) and (14) depending on the driving force for iron scrap melting, but in reality, the mechanism of iron scrap melting cannot be clearly distinguished. Therefore, if either equation (13) or equation (14) is used to calculate the dissolution rate of iron scrap, the dissolution rate of iron scrap that matches the actual phenomenon cannot be obtained.

Therefore, in order to increase the accuracy of estimating the dissolution rate of iron scrap, the calculation unit 38 specifies the first dissolution rate calculated from equation (13) and the second dissolution rate calculated from equation (14). Calculate the dissolution rate of iron scrap by apportioning it at the proportion of . Specifically, the dissolution rate of iron scrap is calculated using the following equation (19).

v _S = (first dissolution rate) x (1-Z) + (second dissolution rate) x Z... (19)
Here, v _S is the dissolution rate (m/min) of iron scrap, and Z is the proportionate ratio (-).

On the other hand, if the calculated interfacial carbon concentration does not satisfy either of the above equations (1) or (2), the dissolution rate of iron scrap is calculated using the interfacial carbon concentration. When using the calculated interfacial carbon concentration and interfacial temperature, the first dissolution rate calculated from equation (13) and the second dissolution rate calculated from equation (14) become equal. Therefore, in this case, the first dissolution rate or the second dissolution rate calculated using the interfacial carbon concentration is the dissolution rate of the iron scrap. In this way, the calculation unit 38 calculates the dissolution rate of iron scrap.

If the dissolution rate of iron scrap can be calculated, the dissolution rate of iron scrap can be calculated using the dissolution rate of iron scrap and the following formula (20).

Here, t _s0 is the initial thickness (mm) of the iron scrap, and Δt is the calculation time interval [s].

Finally, the temperature distribution of the iron scrap is determined using the following equations (21) and (22).

Here, α _S is the thermal diffusivity (m ² /s) of the iron scrap, x is the position in the thickness direction of the iron scrap, and one unit of x in this embodiment is t _S0 /100. Further, subscripts i+1 and i-1 represent the iron scrap temperatures of calculation elements adjacent to the molten iron element side and the iron scrap center side, respectively.

The temperature distribution of iron scrap is determined one-dimensionally using the above equation (21). To calculate this equation (21), it is necessary to discretize it as in the above equation (22). Therefore, the temperature distribution of iron scrap obtained from equation (22) becomes a discontinuous temperature distribution for each calculated thickness interval Δx.

Since the thickness interval Δx is set to 1/100 of t _S0 , there are 100 calculation elements representing iron scrap at the start of calculation (at the start of melting). One calculation element representing an interface is adjacent to the iron scrap element group, and a calculation element group representing molten iron is adjacent to the opposite side of the interface element. The initial number of molten iron elements is arbitrary, but it is preferably determined based on the allowable calculation cost. As the number of elements increases, the calculation cost increases, but the melting behavior when the solidified shell expands greatly in the initial stage of iron scrap melting can be calculated with higher accuracy.

The thickness of all calculation elements is Δx, and the calculation element thickness, the number of interface elements, and the total number of calculation elements are constant during calculation. However, the number of iron scrap elements and the number of molten iron elements during calculation change depending on the momentary iron scrap melting rate S _m determined from the above equation (20). For example, if the melting rate is 2% by mass at a certain time, the number of iron scrap elements at that time is 98, and the number of molten iron elements increases by two. Furthermore, since the interface element always exists between the iron scrap element group and the molten iron element group, it moves toward the iron scrap element side by a distance of 2×Δx from the initial position. On the other hand, if the melting rate is less than 0 (during solidification shell generation), the iron scrap elements increase and the molten iron elements decrease, so the interfacial elements move toward the molten iron elements.

Temperature distribution calculations first determine whether each calculation element corresponds to an iron scrap element, interface element, or molten iron element according to the iron scrap melting rate at that time, and then calculate the temperature distribution for each element as shown below. seek.
Iron scrap element: Calculated according to equation (22) above. However, the center of the steel scrap is treated as an adiabatic boundary (temperature is equal to that of adjacent elements).
Interface element: Interface temperature T _i calculated from the above equation (15).
Molten iron element: Molten iron temperature T, and temperature unevenness of the molten iron is not considered.

dT _S /dx used in equation (13) in the next step is calculated by dividing the temperature difference between the interface temperature Ti and the iron scrap element adjacent to the interface temperature by the thickness Δx of the calculation element. After calculating dT _S /dx used in equation (13) in the next step, obtain the furnace information again and use equations (3) to (21) above to calculate the steel scrap value after the calculation time interval Δt seconds. The dissolution rate may be calculated. By repeatedly calculating the dissolution rate of iron scrap in this manner, the dissolution rate of iron scrap at every moment during the preliminary dephosphorization process of the hot metal 11 can be calculated.

Note that the thermal diffusivity of iron scrap in the above equations (21) and (22) can be calculated using the following equations (23), (24), and (25).

Here, λ _S is the thermal conductivity of iron scrap (W/(m×K)), and C _PS is the specific heat of iron scrap (MJ/(t×K)).

FIG. 3 is a flow diagram illustrating the flow of the cold iron source dissolution rate estimation method. The processing of the cold iron source dissolution rate estimation method according to this embodiment will be explained using FIG. 3. The cold iron source dissolution rate estimation method according to the present embodiment is started, for example, by an instruction from the operator 50 at any time before and during the preliminary dephosphorization treatment of the hot metal 11.

The acquisition unit 36 of the cold iron source melting rate estimating device 30 executes the acquisition step and obtains the charging amount of the hot metal 11 charged into the furnace, the initial carbon concentration of the hot metal 11, and the iron scrap loading as furnace information. Information on the hot metal 11 and the iron scrap, such as the input amount, the initial carbon concentration of the iron scrap, the density of the iron scrap, and the latent heat of melting of the iron scrap, is acquired. In addition, the acquisition unit 36 acquires the bottom blowing flow rate of the stirring gas 13, the momentary temperature of the hot metal 11, and the furnace pressure as furnace information (step S101). The acquisition unit 36 outputs this in-furnace information to the calculation unit 38.

The calculation unit 38 executes the calculation step and calculates the interfacial carbon concentration C _i using the furnace information and the above equations (3) to (18) (step S102). When the calculated interfacial carbon concentration C _i satisfies at least one of the above equations (1) and (2), the calculation unit 38 replaces the calculated interfacial carbon concentration C _i with the one calculated one step earlier. The first dissolution rate and the second dissolution rate are calculated using the interfacial carbon concentration C _i,t-1 , and by proportionally dividing the first dissolution rate and the second dissolution rate, the Calculate the dissolution rate. In addition, if the calculated interfacial carbon concentration C _i does not satisfy either of the above equations (1) or (2), the first dissolution rate or the second dissolution rate is determined using the calculated interfacial carbon concentration C _i . The speed is calculated, and the calculated first dissolution rate or second dissolution rate is set as the dissolution rate of the iron scrap (step S103).

The calculation unit 38 executes a calculation step and calculates the iron scrap dissolution rate S _m using the iron scrap dissolution rate and the above equation (20) (step S104). Further, the calculation unit 38 executes a calculation step and calculates the temperature distribution of the iron scrap using the above equation (21) (step S105).

The calculation unit 38 outputs the dissolution rate S _m of iron scrap to the output unit 40 . The output unit 40 executes the output step and outputs the dissolution rate S _m (step S106).

The calculation unit 38 determines whether the calculated iron scrap dissolution rate S _m is 100 or more (step S107). If it is determined that the iron scrap melting rate S _m is 100 or more (step S107: Yes), the calculation unit 38 concludes that the iron scrap is completely melted and ends this process. On the other hand, if it is determined that the melting rate S _m of iron scrap is less than 100 (step S107: No), the calculation unit 38 returns the process to step S101 and again executes the processes of steps S101 to S107 to calculate the Calculate the dissolution rate S of iron scrap after a time interval Δt seconds. By repeatedly performing the processes of steps S101 to S107 in this way, the method for estimating the cold iron source dissolution rate according to the present embodiment can be performed at every moment until the iron scrap is completely melted in the preliminary dephosphorization process of the hot metal 11. The dissolution rate S _m of iron scrap can be calculated.

Next, an example will be described. In this example, a square pure iron sample (100 x 100 x 50 mm) imitating a cold iron source (iron scrap) was immersed 80 mm into 500 kg of molten iron produced using a cylindrical atmospheric furnace with an inner diameter of 430 mm. The dissolution rate of a square pure iron sample after a predetermined period of time was estimated using the method for estimating the dissolution rate of a cold iron source based on the morphology. The square pure iron sample was immersed in molten iron for a predetermined period of time, then collected and cooled in air, and the dissolution rate of the square pure iron sample was actually measured using the following equation (26).

Here, S _p is the dissolution rate (mass %) of the square pure iron sample, and L _S0 and L _S are the thicknesses (mm) of the square pure iron sample before and after immersion, respectively.

In order to measure the molten iron temperature and molten iron carbon concentration, temperature measurement with an immersion thermocouple and collection of molten iron samples for chemical analysis were performed before and after immersing a square pure iron sample in molten iron.

[Example 1]
In Example 1, the dissolution rate of a square pure iron sample was estimated using the cold iron source dissolution rate estimation method according to the present embodiment when the square pure iron sample was preheated to 1200°C and when it was not preheated. did. The conditions of Example 1 are shown in Table 2 below.

FIG. 4 is a graph showing the estimated and actual measurement results of the dissolution rate of the square pure iron sample in Example 1. In FIG. 4, the vertical axis is the dissolution rate (mass %) of the square pure iron sample, and the horizontal axis is the dissolution time (seconds). In Figure 4, each profile shows the dissolution rate estimated by the cold iron source dissolution rate estimation method, and each plot shows the dissolution rate of a square pure iron sample calculated using the above equation (26) after being collected after immersion and air-cooled. The actual measured value of the ratio (mass%) is shown.

As shown in FIG. 4, when the square pure iron sample was preheated, the estimated value of the dissolution rate and the experimental value almost matched regardless of whether it was not preheated. From this result, it was confirmed that the dissolution rate of a cold iron source can be estimated with high accuracy by using the cold iron source dissolution rate estimation method according to the present embodiment.

[Example 2]
In Example 2, the dissolution rate of a square pure iron sample when using molten iron whose initial temperature was varied in the range of 1430 to 1610°C was estimated using the cold iron source dissolution rate estimation method according to the present embodiment. The conditions of this Example 2 are shown in Table 3 below.

FIG. 5 is a graph showing the estimated and actual measurement results of the dissolution rate of the square pure iron sample in Example 2. In FIG. 5, the vertical axis is the dissolution rate (mass %) of the square pure iron sample, and the horizontal axis is the dissolution time (seconds). In Figure 5, each profile shows the dissolution rate estimated by the cold iron source dissolution rate estimation method, and each plot shows the square pure iron sample recovered after immersion and air-cooled, and calculated using the above equation (26). Measured values of dissolution rate (mass%) are shown.

As shown in FIG. 5, the estimated value of the dissolution rate and the experimental value almost matched under the conditions of Inventive Examples 11 to 16 in which the initial temperature of the molten iron was changed. From this result, it was confirmed that the dissolution rate of a cold iron source can be estimated with high accuracy by using the cold iron source dissolution rate estimation method according to the present embodiment.

[Example 3]
In Example 3, the dissolution rate of the cold iron source is estimated from the first dissolution rate obtained from equation (13) or the second dissolution rate obtained from equation (14), and the first dissolution rate obtained from equation (13). The dissolution rate estimated by estimating the dissolution rate of the cold iron source from the dissolution rate obtained by proportionally dividing the dissolution rate and the second dissolution rate obtained from equation (14) was confirmed. The conditions of this Example 3 are shown in Table 4 below.

FIG. 6 is a graph showing the estimated and actual measurement results of the dissolution rate of the square pure iron sample in Example 3. In FIG. 6, the vertical axis is the dissolution rate (mass %) of the square pure iron sample, and the horizontal axis is the dissolution time (seconds). In Figure 6, the profile shown by the solid line shows the dissolution rate estimated by the cold iron source dissolution rate estimation method, and the profile shown by the broken line shows the dissolution rate estimated using only equation (13) or equation (14). shows. Moreover, the circle plot shows the actual value of the dissolution rate (mass %) of the square pure iron sample, which was collected after immersion, air-cooled, and calculated using the above equation (26).

As shown in FIG. 6, when at least one of the above equations (1) and (2) is satisfied, the dissolution rate of the cold iron source is calculated from the dissolution rate obtained by proportionally dividing the first dissolution rate and the second dissolution rate. In Invention Example 31, in which the rate was estimated, the estimated value and the experimental value almost matched. On the other hand, even if at least one of the above equations (1) and (2) is satisfied, when the dissolution rate of the cold iron source is estimated from the dissolution rate determined only from equation (13) or equation (14), The estimated and experimental values did not match. From these results, in order to estimate the dissolution rate of cold iron sources with high accuracy, the first dissolution rate calculated from the heat transfer balance equation and the second dissolution rate calculated from the carbon mass balance equation should be appropriately adjusted. It was confirmed that it is important to determine the proportionate proportion and allocate the proportions.

10 Converter type smelting furnace 11 Hot metal 13 Stirring gas 14 Top blowing lance 20 Converter type smelting furnace control device 22 Process computer 24 Operation control computer 30 Cold iron source dissolution rate estimation device 32 Control section 34 Storage section 36 Acquisition section 38 Arithmetic unit 40 Output unit 50 Operator

Claims

A cold iron source dissolution rate estimation device for estimating the dissolution rate of the cold iron source in a molten iron refining process using the cold iron source as a raw material,
an acquisition unit that acquires furnace information including information on the molten iron and the cold iron source;
a calculation unit that calculates an interfacial carbon concentration between the cold iron source and the molten iron, a dissolution rate of the cold iron source, and a dissolution rate of the cold iron source using the furnace information;
an output unit that outputs the dissolution rate,
When the interfacial carbon concentration satisfies at least one of the following equations (1) and (2), the calculation unit calculates the first equation from the heat transfer balance equation using the interfacial carbon concentration calculated one step before. Calculate the dissolution rate of the cold iron source by calculating the second dissolution rate from the carbon material balance equation, and proportionally dividing the first dissolution rate and the second dissolution rate,
If the interfacial carbon concentration does not satisfy either equation (1) or (2) below, the calculation unit calculates the first dissolution rate or the second dissolution rate using the interfacial carbon concentration. A cold iron source dissolution rate estimating device, wherein the calculated first dissolution rate or the second dissolution rate is set as the dissolution rate of the cold iron source.
C i >C...(1)
C i >C i,t-1 ...(2)
In the above equations (1) and (2), C is the molten iron carbon concentration (mass%), C i is the interfacial carbon concentration (mass%), and C i,t-1 is the molten iron carbon concentration (mass%). Interfacial carbon concentration (mass%).
When the carbon concentration of the cold iron source is lower than the carbon concentration of the molten iron,
The calculation unit specifies an apportionment ratio for apportioning the first dissolution rate and the second dissolution rate based on molten iron temperature, molten iron carbon concentration, and cold iron source carbon concentration. Cold iron source dissolution rate estimation device.
The calculation unit estimates the dissolution rate of the cold iron source from time to time by repeatedly calculating the interfacial carbon concentration, the dissolution rate of the cold iron source, and the dissolution rate of the cold iron source. The cold iron source dissolution rate estimation device according to claim 1 or claim 2.
Estimating the dissolution rate of the cold iron source at the end of the refining process using the cold iron source dissolution rate estimation device according to claim 1 or 2,
If the unmelted rate of the cold iron source calculated from the melting rate at the end point exceeds 5% by mass, refining the molten iron by performing at least one of adding a heating material and extending the molten iron treatment. Processing method.
Estimating the dissolution rate of the cold iron source at the end of the refining process using the cold iron source dissolution rate estimation device according to claim 3,
If the unmelted rate of the cold iron source calculated from the melting rate at the end point exceeds 5% by mass, refining the molten iron by performing at least one of adding a heating material and extending the molten iron treatment. Processing method.
A cold iron source dissolution rate estimation method for estimating the dissolution rate of the cold iron source in a molten iron refining process using a cold iron source as a raw material, the method comprising:
an acquisition step of acquiring furnace information including information on the molten iron and the cold iron source;
a calculation step of calculating an interfacial carbon concentration between the cold iron source and the molten iron, a dissolution rate of the cold iron source, and a dissolution rate of the cold iron source using the furnace information;
an output step of outputting the dissolution rate,
If the interfacial carbon concentration satisfies at least one of the following equations (1) and (2), in the calculation step, the first calculation is performed from the heat transfer equation using the interfacial carbon concentration calculated one step before. Calculate the dissolution rate of the cold iron source by calculating the second dissolution rate from the carbon material balance equation, and proportionally dividing the first dissolution rate and the second dissolution rate,
If the interfacial carbon concentration does not satisfy either of the following equations (1) or (2), in the calculation step, the first dissolution rate or the second dissolution rate is calculated using the interfacial carbon concentration. A cold iron source dissolution rate estimation method, wherein the calculated first dissolution rate or the second dissolution rate is set as the dissolution rate of the cold iron source.
C i >C...(1)
C i >C i,t-1 ...(2)
In the above equations (1) and (2), C is the molten iron carbon concentration (mass%), C i is the interfacial carbon concentration (mass%), and C i,t-1 is the molten iron carbon concentration (mass%). Interfacial carbon concentration (mass%).
When the carbon concentration of the cold iron source is lower than the carbon concentration of the molten iron,
7. The method according to claim 6, wherein in the calculation step, a proportional division ratio is specified for proportionally dividing the first dissolution rate and the second dissolution rate based on the molten iron temperature, the molten iron carbon concentration, and the carbon concentration of the cold iron source. Cold iron source dissolution rate estimation method.
2. The calculation step estimates the dissolution rate of the cold iron source from time to time by repeatedly calculating the interfacial carbon concentration, the dissolution rate of the cold iron source, and the dissolution rate of the cold iron source. The cold iron source dissolution rate estimation method according to claim 6 or claim 7.
Estimating the dissolution rate of the cold iron source at the end of the refining process using the cold iron source dissolution rate estimation method according to claim 6 or 7,
If the unmelted rate of the cold iron source calculated from the melting rate at the end point exceeds 5% by mass, refining the molten iron by performing at least one of adding a heating material and extending the molten iron treatment. Processing method.
Estimating the dissolution rate of the cold iron source at the end of the refining process using the cold iron source dissolution rate estimation method according to claim 8,
If the unmelted rate of the cold iron source calculated from the melting rate at the end point exceeds 5% by mass, refining the molten iron by performing at least one of adding a heating material and extending the molten iron treatment. Processing method.