Cold iron source melting rate estimation device, cold iron source melting rate estimation method, and molten iron refining treatment method

Abstract

Provided is a device for estimating the melting rate of a cold iron source, said device being capable of calculating the melting rate of the cold iron source using highly versatile parameters. A cold iron source melting rate estimation device (30) for estimating the melting rate of a cold iron source in a refining process of molten iron using the cold iron source as a raw material, the cold iron source melting rate estimation device (30) comprising: an acquisition unit (36) for acquiring in-furnace information including information about the molten iron and the cold iron source; a calculation unit (38) that calculates the carbon concentration at the interface between the cold iron source and the molten iron, the melting rate of the cold iron source, and the melting rate of the cold iron source using the in-furnace information; when the interface carbon concentration satisfies a predetermined condition, the calculation unit calculates a first melting rate from a heat transfer equilibrium equation using the interface carbon concentration calculated in the previous step, calculates a second melting rate from a carbon mass equilibrium equation, and outputs the melting rate. And calculating the melting speed of the cold iron source by proportionally distributing the first melting speed and the second melting speed.

Description

Technical Field

[0001] The present invention relates to a cold iron source melting rate estimating device and method for estimating the melting rate of a cold iron source in a refining process of molten iron using the cold iron source as a raw material, and a molten iron refining process method using the same. Background Art

[0002] In order to achieve carbon neutrality by 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 method. Generally, in the blast furnace method, about 2 tons of CO2 are generated per ton of crude steel when manufacturing steel products. On the other hand, when cold iron sources such as scrap and reduced iron are melted by electricity or heat transfer and carburizing from molten iron without using blast furnace pig iron, coal is not required. Therefore, the amount of CO2 generated when using a cold iron source is about 500kg per ton of crude steel (excluding the amount of CO2 generated when reducing iron is manufactured), which can suppress CO2 emissions per ton of crude steel to about 1 / 4 compared to the blast furnace method. Therefore, it can be said that it is effective to reduce the use of blast furnace pig iron by reducing the molten pig iron blending ratio in the converter and to increase the use of cold iron sources by introducing electric furnaces in order to reduce CO2 emissions in the steel industry.

[0003] On the other hand, when the amount of cold iron source used increases, the time required for complete melting of the cold iron source increases. When the time required for complete melting of the cold iron source increases and the cold iron source is not completely melted within the processing time, a large number of disadvantages occur in terms of operation and metallurgy. For example, during the dephosphorization blowing of molten pig iron in a converter, the auxiliary spray gun collides with the unmelted cold iron source, causing the auxiliary spray gun to be damaged. In addition, the unmelted cold iron source accumulated on the bottom blowing tuyere hinders the stirring of the molten pig iron, resulting in poor dephosphorization.

[0004] In addition, the cold iron source is continuously or intermittently added to the electric furnace. However, if the additional loading speed is too fast relative to the melting speed, the unmelted cold iron source in the furnace increases, and sometimes the cold iron sources fuse together to form a huge iron block. Since the surface area of ​​the iron block is small relative to its volume and the melting speed is slow, the generation of the iron block leads to a decrease in productivity and an increase in the required electricity. Therefore, in order to melt the cold iron source efficiently, it is important to know whether there is an unmelted part of the cold iron source in the furnace.

[0005] As a method for determining whether there is an unmelted portion of the cold iron source, the timing of complete melting of the cold iron source is mainly determined by sensor detection. The method of determining the timing of complete melting of the cold iron source is mostly based on electric furnaces. In this method, the temperature, pressure, vibration, light, etc. in the furnace are monitored and the timing of complete melting of the cold iron source is determined based on the changes.

[0006] For example, Patent Document 1 discloses a method of measuring the refractory temperature at multiple points in the thickness direction using a temperature probe embedded in the side wall of the converter body, and continuously estimating the refractory surface temperature (molten iron temperature) from the obtained temperature gradient and the remaining thickness of the refractory. This method focuses on the complete melting of the cold iron source in the furnace and the subsequent increase in the temperature rise rate of the molten iron. According to Patent Document 1, the complete melting period of the cold iron source can be determined based on the temperature change of the molten iron.

[0007] In addition, although there is a lack of application examples to actual operations, a one-dimensional heat transfer model (hereinafter referred to as the "melting model of the cold iron source") for predicting the melting behavior of a cold iron source has been reported. As documents that mention the melting model of the cold iron source, non-patent documents 1 to 2 can be cited. According to the melting model of the cold iron source disclosed in non-patent documents 1 to 2, by assuming the heat transfer coefficient between molten iron and the cold iron source and the mass transfer coefficient of the molten iron, the melting behavior of the cold iron source can be predicted with good accuracy. In order to apply the melting model of the cold iron source to actual operations, it is necessary to continuously or intermittently input information such as the temperature of the molten iron, the carbon concentration of the molten iron, etc. obtained by sensor detection, etc. By using the melting model of the cold iron source, not only the timing of complete melting of the cold iron source can be predicted, but also the melting rate of the cold iron source at each moment can be predicted, so it has the advantage of being able to predict the occurrence of unmelted cold iron source during processing.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 8-3614

[0011] Non-patent literature

[0012] Non-patent document 1: Masahiro Kawakami and two others, "Analysis of heat and mass transfer of scrap melting in a steel bath", Iron and Steel, Vol. 85 (1999), P658-665

[0013] Non-patent document 2: Koichi Isobe and four others, "Analysis of the melting rate of scrap in high-carbon hot iron bath", Iron and Steel, 76th year (1990), p2033-2040 Summary of the invention

[0014] Problems to be solved by the invention

[0015] Patent Document 1 does not mention the threshold of the temperature rise rate of the molten iron as a criterion for determining the timing of complete melting of the cold iron source, and the determination is subject to the subjective influence of the observer. In addition, in actual operation, since the temperature change of the molten iron will also change due to major factors such as changes in the top and bottom blowing flow rates, there is a great concern about misjudgment and delay in determination.

[0016] In addition, as the driving force for the melting of the cold iron source, heat transfer and carburization (mass transfer from molten iron to the surface of the cold iron source) can be listed, but when the carbon concentration of the molten iron does not exceed the carbon concentration of the cold iron source, or when carburization does not occur in the presence of solidification elements, the driving force for the melting of the cold iron source is only heat transfer, so 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, when the carbon concentration of the molten iron exceeds the carbon concentration of the cold iron source, carburization occurs after the solidification elements are re-melted, so when calculating the melting rate of the cold iron source, it is necessary to consider the carbon mass balance equation instead of the heat balance near the interface. In this way, the melting rate calculation formula is usually changed according to the driving force for the melting of the cold iron source, but in fact the melting mechanism cannot be clearly distinguished.

[0017] For example, even when carburization occurs when the carbon concentration of molten iron exceeds the carbon concentration of the cold iron source, if the temperature of the molten iron is high, equal to or higher than the liquidus temperature of the cold iron source, it cannot be considered that heat transfer does not contribute to the melting of the cold iron source at all, and both carburization and heat transfer need to be considered as the melting mechanism. However, the existing cold iron source melting model is a model that limits the driving force to carburization or heat transfer.

[0018] In the cold iron source melting model disclosed in non-patent documents 1 and 2, the accuracy is ensured by using the heat transfer coefficient and the mass transfer coefficient as fitting parameters. However, the values ​​of the fitting parameters are only described for the specific molten iron and cold iron source conditions mentioned in the literature, and there is a problem of poor versatility. The present invention is completed in view of such problems, and its purpose is to provide a cold iron source melting rate estimation device and a cold iron source melting rate estimation method that can calculate the melting rate of the cold iron source using highly universal parameters, as well as a molten iron refining treatment method using the same.

[0019] Methods used to solve problems

[0020] Means for solving the above-mentioned problems are as follows.

[0021] [1] A cold iron source melting rate estimating device, which is a cold iron source melting rate estimating device for estimating the melting rate of the cold iron source in the refining process of molten iron using the cold iron source as a raw material, comprising: an acquisition unit for acquiring furnace information including information about the molten iron and the cold iron source; a calculation unit for calculating the interface carbon concentration between the cold iron source and the molten iron, the melting rate of the cold iron source and the melting rate of the cold iron source using the furnace information; and an output unit for outputting the melting rate, wherein the calculation unit outputs the melting rate when the interface carbon concentration satisfies at least one of the following equations (1) and (2). The first melting rate is calculated according to the heat transfer balance equation using the interface carbon concentration calculated in the previous step, and the second melting rate is calculated according to the carbon mass balance equation, and the melting rate of the cold iron source is calculated by allocating the first melting rate and the second melting rate in proportion. When the interface carbon concentration does not satisfy any of the following equations (1) and (2), the calculation unit calculates the first melting rate or the second melting rate using the interface carbon concentration, and uses the calculated first melting rate or the second melting rate as the melting rate of the cold iron source.

[0022] C i >C…(1)

[0023] C i >C i,t-1 …(2)

[0024] In the above formulas (1) and (2), C is the carbon concentration of molten iron (mass %), C i is the interface carbon concentration (mass %), C i,t-1 is the interfacial carbon concentration (mass %) calculated in the previous step.

[0025] [2] According to the cold iron source melting rate estimation device described in [1], wherein, when the carbon concentration of the cold iron source is lower than the carbon concentration of the molten iron, the calculation unit determines a proportional allocation ratio for proportionally allocating the first melting rate and the second melting rate based on the molten iron temperature, the molten iron carbon concentration and the carbon concentration of the cold iron source.

[0026] [3] A cold iron source melting rate estimating device according to [1] or [2], wherein the calculation unit estimates the melting rate of the cold iron source at each moment by repeatedly calculating the interface carbon concentration, the melting rate of the cold iron source and the melting rate of the cold iron source.

[0027] [4] A method for refining molten iron, wherein the melting rate of the cold iron source at the end of the refining treatment is estimated using the cold iron source melting rate estimation device described in any one of [1] to [3], and when the unmelted rate of the cold iron source calculated from the melting rate at the end exceeds 5 mass %, at least one of adding a heat-generating material and extending the molten iron treatment is performed.

[0028] [5] A method for estimating the melting rate of a cold iron source, which is a method for estimating the melting rate of a cold iron source in a refining process of molten iron using the cold iron source as a raw material, comprising: an acquisition step of in-furnace information including information about the molten iron and the cold iron source; a calculation step of using the in-furnace information to calculate the interface carbon concentration between the cold iron source and the molten iron, the melting rate of the cold iron source, and the melting rate of the cold iron source; and an output step of outputting the melting rate, wherein, in the calculation step, when the interface carbon concentration satisfies at least one of the following equations (1) and (2), Using the interface carbon concentration calculated in the previous step, the first melting rate is calculated according to the heat transfer balance equation, and the second melting rate is calculated according to the carbon mass balance equation, and the melting rate of the cold iron source is calculated by proportionally allocating the first melting rate and the second melting rate. When the interface carbon concentration does not satisfy any of the following (1) and (2), in the calculation step, the interface carbon concentration is used to calculate the first melting rate or the second melting rate, and the calculated first melting rate or the second melting rate is used as the melting rate of the cold iron source.

[0029] C i >C…(1)

[0030] C i >C i,t-1 …(2)

[0031] In the above formulas (1) and (2), C is the carbon concentration of molten iron (mass %), C i is the interface carbon concentration (mass %), C i,t-1 is the interfacial carbon concentration (mass %) calculated in the previous step.

[0032] [6] According to the cold iron source melting rate estimation method described in [5], when the carbon concentration of the cold iron source is lower than the carbon concentration of the molten iron, in the calculation step, the proportional allocation ratio of the first melting rate and the second melting rate is determined based on the molten iron temperature, the molten iron carbon concentration and the carbon concentration of the cold iron source.

[0033] [7] A method for estimating the melting rate of a cold iron source according to [5] or [6], wherein, in the calculation step, the melting rate of the cold iron source at each moment is estimated by repeatedly calculating the interface carbon concentration, the melting rate of the cold iron source and the melting rate of the cold iron source.

[0034] [8] A method for refining molten iron, wherein the melting rate of the cold iron source at the end of the refining treatment is estimated using the cold iron source melting rate estimation method described in any one of [5] to [7], and when the unmelted rate of the cold iron source calculated from the melting rate at the end exceeds 5 mass %, at least one of adding a heat-generating material and extending the molten iron treatment is performed.

[0035] Effects of the Invention

[0036] According to the present invention, the melting rate of the cold iron source can be calculated using the proportional distribution ratio which can be obtained more easily than the fitting parameters. Therefore, it can be said that the cold iron source melting rate estimation method of the present invention is a cold iron source melting rate calculation method with higher versatility than the conventional one. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of a converter type refining furnace equipped with the cold iron source melting rate estimation device of the present invention.

[0038] Figure 2 This is a diagram showing the proportional distribution ratio when the molten pig iron temperature in Table 1 is 1450 to 1480°C.

[0039] Figure 3 1 is a flowchart illustrating the flow of a method for estimating a cold iron source melting rate.

[0040] Figure 4 This is a graph showing the estimated results and the measured results of the melting rate of the square pure iron sample of Example 1.

[0041] Figure 5 This is a graph showing the estimated results and the measured results of the melting rate of the square pure iron sample of Example 2.

[0042] Figure 6 This is a graph showing the estimated results and the measured results of the melting rate of the square pure iron sample of Example 3. DETAILED DESCRIPTION

[0043] Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. Figure 1 It is a schematic diagram of a converter type refining furnace equipped with the cold iron source melting rate estimation device of the present invention. Figure 1In the figure, reference numeral 10 denotes a converter type refining furnace, reference numeral 20 denotes a converter type refining furnace control device, and reference numeral 50 denotes an operator. The converter type refining furnace control device 20 includes a process control computer 22 , a work control computer 24 , and a cold iron source melting rate estimation device 30 .

[0044] In the converter type refining furnace 10, scrap iron is charged into the furnace as a cold iron source using a scrap trough, and then molten pig iron 11 is charged into the furnace using a charging bucket. Oxygen (industrial pure oxygen) is supplied from a top-blowing lance 14 to the molten pig iron 11 charged into the furnace, and a stirring gas 13 is blown into the molten pig iron 11 in the furnace from a tuyere (not shown) provided at the bottom of the furnace. The molten pig iron 11 charged into the furnace is oxidatively refined by the oxygen supplied from the top-blowing lance 14 while being stirred by the stirring gas 13. In the converter type refining furnace 1, a preliminary dephosphorization treatment of the molten pig iron 11 and a decarburization treatment of the molten pig iron 11 (hereinafter also referred to as "decarburization refining") are generally performed as a refining treatment method.

[0045] In the pre-dephosphorization treatment of the molten pig iron 11, first, scrap iron is charged as a cold iron source into the converter type refining furnace 10 using a scrap tank (not shown), and then the molten pig iron 11 is charged into the furnace using a charging bucket (not shown). After the molten pig iron 11 is charged, oxygen is supplied from the top blowing lance 14, nitrogen gas as a stirring gas 13 is supplied from the tuyere at the bottom of the furnace, and auxiliary raw materials such as a heat-generating material and a medium solvent are added, thereby performing the pre-dephosphorization treatment on the molten pig iron 11.

[0046] The pre-dephosphorization treatment of the molten pig iron 11 in the converter type refining furnace 1 is performed as follows: phosphorus in the molten pig iron is oxidized by oxygen to form phosphorus oxide (P2O5), and the formed phosphorus oxide is fixed in the stable form of 3CaO·P2O5 (=Ca3(PO4)2) in the slag 12 generated by slagification of the CaO-based medium solvent. In the pre-dephosphorization treatment of the molten pig iron 11, when the phosphorus concentration of the molten pig iron 11 in the furnace reaches a predetermined value (for example, 0.050 mass % or less), the pre-dephosphorization treatment is terminated. After the pre-dephosphorization treatment, dephosphorized molten pig iron is generated in the furnace.

[0047] After the molten pig iron 11 after pre-dephosphorization treatment is loaded, oxygen is supplied from the top blowing lance 14, stirring gas 13 is supplied from the tuyere at the bottom of the furnace, and auxiliary materials such as cooling materials, heating materials, medium solvents, etc. are added in time to decarburize the molten pig iron 11.

[0048] The decarburization treatment of the molten pig iron 11 is carried out by a decarburization reaction (C+O→CO) between oxygen and carbon in the molten iron, and the decarburization treatment is carried out until the carbon concentration of the molten iron in the furnace reaches a specified value (for example, less than 0.05% by mass). After the decarburization treatment, molten steel after the decarburization treatment is generated in the furnace. Here, "molten iron" refers to either molten pig iron or molten steel. In the decarburization treatment of the molten pig iron 11, the molten pig iron in the furnace becomes molten steel as the decarburization treatment proceeds. Since it is difficult to distinguish the molten metal in the furnace during the decarburization treatment as molten pig iron and molten steel, the molten pig iron and molten steel are collectively referred to as "molten iron".

[0049] The process control computer 22 is a device that calculates the amount of oxygen to be supplied, as well as whether and how much cooling material or heat generating material should be added in order to make the molten pig iron temperature and molten pig iron component concentration at the end of the pre-dephosphorization treatment and the molten iron temperature and molten iron component concentration at the end of the decarburization treatment reach the target values.

[0050] The operation control computer 24 is a device that controls the operation conditions (oxygen supply amount, lance height, stirring gas supply amount, auxiliary raw material input amount, etc.) based on the oxygen amount and the input amount of the cooling material or the heat generating material calculated by the process control computer 22 so that the molten pig iron temperature and the molten pig iron component concentration at the end of the pre-dephosphorization treatment and the molten steel temperature and the molten steel component concentration at the end of the decarburization treatment reach the target values. In order to control the refining with better accuracy, the signal of the operation control computer 24 is fed back to the process control computer 22. Hereinafter, the cold iron source melting rate estimation device 30 of the present embodiment is applied to the pre-dephosphorization treatment of the molten pig iron 11 of the converter type refining furnace 10 using scrap iron having a lower carbon concentration than the carbon concentration of the molten pig iron 11 as the cold iron source as a raw material. However, the cold iron source melting rate estimation device 30 is not limited to the converter type refining furnace 10, and can also be applied to the electric furnace type refining furnace, and can also be applied to the decarburization treatment of the molten pig iron 11.

[0051] The cold iron source melting rate estimation device 30 is a computing device constituting a part of the converter type refining furnace control device 20. The cold iron source melting rate estimation device 30 includes a control unit 32, a storage unit 34, and an output unit 40. The control unit 32 is, for example, a CPU, and the control unit 32 functions as an acquisition unit 36 ​​and a computing unit 38 by executing a program read from the storage unit 34.

[0052] The output unit 40 is, for example, an LCD or CRT display. The storage unit 34 is, for example, an updateable flash memory, a hard disk built in or connected using a data communication terminal, a memory card or other information recording medium and its reading and writing device. The storage unit 34 records programs for executing the functions of the acquisition unit 36 ​​and the operation unit 38, and operation expressions and data used in the programs.

[0053] Next, the processing performed by the acquisition unit 36 ​​and the calculation unit 38 will be described. The acquisition unit 36 ​​acquires furnace information through the process control computer 22 by information input from the operator 50 or from the furnace sensor installed in the converter type refining furnace 10. The furnace information includes information on the molten pig iron 11 and scrap iron. Specifically, the furnace information includes the amount of molten pig iron 11 charged into the furnace, the initial carbon concentration of the molten pig iron 11, the amount of scrap iron charged, the initial carbon concentration of the scrap iron, the density of the scrap iron, and the melting latent heat of the scrap iron. In addition to this information, the acquisition unit 36 ​​also acquires the temperature of the molten pig iron 11 at every moment, the bottom blowing flow rate of the stirring gas 13, and the furnace pressure as furnace information. The acquisition unit 36 ​​outputs the acquired furnace information to the calculation unit 38.

[0054] The operation unit 38 uses the in-furnace information to calculate the interface carbon concentration between the scrap iron and the molten pig iron 11 charged into the converter type refining furnace 10, the melting rate of the scrap iron, and the melting rate of the scrap iron. The operation unit 38 first calculates the interface carbon concentration between the molten pig iron 11 and the scrap iron. When the calculated interface carbon concentration satisfies at least one of the following equations (1) and (2), the interface carbon concentration calculated in the previous step is used to calculate the first melting rate according to the heat transfer balance equation, and the second melting rate is calculated according to the carbon mass balance equation, and the melting rate of the scrap iron is calculated by proportionally allocating the first melting rate and the second melting rate. It should be noted that when the calculation in the previous step also satisfies at least one of the following equations (1) and (2), the interface carbon concentration calculated in the previous step is used.

[0055] C i >C…(1)

[0056] C i >C i,t-1 …(2)

[0057] In the above formulas (1) and (2), C is the carbon concentration (mass %) of the molten pig iron 11, C i is the interface carbon concentration (mass %), C i,t-1 is the interfacial carbon concentration (mass %) calculated in the previous step. In the following description, the subscript t-1 represents the value calculated in the previous step.

[0058] In this way, the calculation unit 38 calculates the melting rate of the scrap iron by proportionally allocating the first melting rate calculated from the heat balance equation and the second melting rate derived from the carbon mass balance equation at a proportional allocation ratio. As an example, the value of the proportional allocation ratio when the carbon concentration of the cold iron source is 0.05 mass % is shown in the following Table 1.

[0059]

[0060] The table of proportional distribution ratios in which the first melting rate and the second melting rate are proportionally distributed as shown in Table 1 is prepared in advance for each carbon concentration of the chill source and stored in the storage unit 34 .

[0061] Figure 2 This is a graph showing the proportional distribution ratio when the molten pig iron temperature is 1450 to 1480°C in Table 1. Figure 2 In the figure, the horizontal axis is the carbon concentration in molten iron (mass %), and the vertical axis is the proportional distribution ratio (-). Figure 2 As shown in FIG. 1 , the proportional distribution ratio at each molten iron carbon concentration is plotted on a predetermined curve. Therefore, for example, by finding the proportional distribution ratio at three different molten iron carbon concentrations and using these three points to find the curve ( Figure 2 The proportional distribution ratio of other molten iron carbon concentrations can be obtained by using the dotted line). Since the proportional distribution ratio can be obtained more easily than the existing fitting parameters, it can be said that the cold iron source melting rate estimation method of this embodiment using the proportional distribution ratio is a cold iron source melting rate calculation method with higher versatility than the existing method.

[0062] The calculation unit 38 reads out the table of proportional distribution ratios corresponding to the carbon concentration of the scrap iron from the storage unit 34, and determines the proportional distribution ratios as the values ​​in the table corresponding to the temperature of the molten pig iron 11 and the carbon concentration of the molten iron. That is, the calculation unit 38 determines the proportional distribution ratio based on the molten iron temperature, the molten iron carbon concentration, and the carbon concentration of the cold iron source.

[0063] The calculation unit 38 calculates the melting rate of the scrap iron by proportionally allocating the first melting rate and the second melting rate at the determined proportional allocation ratio. On the other hand, when the calculated interface carbon concentration does not satisfy any of the above formulas (1) and (2), the calculation unit 38 calculates the first melting rate or the second melting rate using the calculated interface carbon concentration. In this case, the first melting rate and the second melting rate are the same melting rate, so the first melting rate or the second melting rate is used as the melting rate of the scrap iron.

[0064] The calculation unit 38 calculates the melting rate of the scrap using the calculated melting rate of the scrap. In this way, the calculation unit 38 calculates the melting rate of the scrap using the in-furnace information.

[0065] The calculation unit 38 outputs the calculated melting rate of the scrap iron to the output unit 40. The output unit 40 displays the calculation result of the melting rate of the scrap iron in a manner that can be visually recognized by the operator 50 operating the converter type refining furnace 10. Thus, the operator 50 can observe the display of the output unit 40 to confirm to what extent the scrap iron is melted during the processing of the charge, and can perform operations corresponding to the melting rate of the scrap iron. For example, the melting rate of the scrap iron at the end of the pre-dephosphorization treatment of the molten pig iron 11 is estimated. When the unmelted rate of the scrap iron calculated from the melting rate exceeds 5% by mass, it is preferred to perform at least one of the addition of a heating material and the extension of the pre-dephosphorization treatment of the molten iron. Thus, the amount of unmelted scrap iron at the end of the pre-dephosphorization treatment can be reduced.

[0066] Next, the specific calculation method of calculating the melting rate of scrap iron by the calculation unit 38 is described. It should be noted that the formulas related to scrap iron, such as the physical property value and melting rate of scrap iron, are calculated for each brand of scrap iron. The mass of the molten pig iron 11 and the carbon concentration of the molten pig iron 11 used in the calculation are calculated using the following formulas (3) and (4).

[0067]

[0068] Here, W is the mass (tons) of the molten pig iron 11 in the furnace, W0 is the charge amount (tons) of the molten pig iron 11, and W S0 is the loading amount of scrap iron (tons), S m is the melting rate of scrap iron (mass %), C is the carbon concentration of molten pig iron 11 (mass %), C0 is the initial carbon concentration of molten pig iron 11 (mass %), C S0 is the initial carbon concentration of the scrap iron (mass %).

[0069] It should be noted that in formula (4), the carbon concentration C of the molten pig iron 11 only changes with the scrap iron melting rate S m The influence of decarburization caused by the reaction with the injected oxygen and the oxygen in the atmosphere is not considered. m <0), the carbon concentration C of the molten pig iron 11 is set to remain unchanged at the initial carbon concentration. In the case where the converter type refining furnace 10 has a device for measuring the carbon concentration C of the molten pig iron 11, the measured value of the carbon concentration C may be used without calculating the mathematical formula (4).

[0070] In addition, when the cold iron source melting rate estimation device 30 of the present embodiment is applied to the decarburization process, it is expected that the carbon concentration C of the molten steel calculated at the end of the decarburization process will deviate from the actual carbon concentration of the molten steel. However, at the end of the decarburization process, since the temperature of the molten steel is high, the carbon concentration C of the molten steel has little effect on the melting rate of the scrap iron, and therefore the melting rate S of the cold iron source is m Will not deviate significantly.

[0071] The physical properties of the molten pig iron 11 are calculated using the following equations (5) to (12).

[0072]

[0073] Here, ρ is the density of the molten pig iron 11 (tons / m 3 ), ε B is the bottom blowing stirring power (W / ton), Q B is the bottom blowing flow rate (Nm 3 / min), T is the temperature of the molten pig iron 11 (°C), g is the acceleration due to gravity (m / s 2 ), L is the bath depth (m), P is the furnace pressure (Pa), h is the molten pig iron-scrap interface heat transfer rate (W / (m 2 ·K)), D is the diffusion coefficient of molten pig iron 11 (m 2 / s).

[0074]

[0075] Here, α is the thermal diffusivity (m 2 / s), C P is the specific heat of molten pig iron 11 (kcal / (kg·K)), λ is the thermal conductivity of molten pig iron 11 (W / (m·K)), μ is the viscosity of molten pig iron 11 (mPa·s), k is the mass transfer coefficient of molten pig iron 11 (m / s), Sc is the Schmidt number (-), and Pr is the Prandtl number (-). Mathematical formula (5) is an empirical formula obtained from the scrap melting behavior in the top-blown 310-ton converter to the bottom-blown 240-ton converter described in the following publication 1. Mathematical formula (10) is a formula derived from the Chilton-Colburn similarity law. It should be noted that (-) represents dimensionless.

[0076] Publication 1: H. Gaye, M. Wanin, P. Gugliermina and P. Schittly: 68thSteelmaking Conf. Proc., ISS, Detroit, MI, USA, (1985), 91.

[0077] The carbon concentration at the molten pig iron-scrap interface (hereinafter referred to as "interface carbon concentration") and the temperature at the molten iron-chilled iron source interface (hereinafter referred to as "interface temperature") are calculated using the following equations (13) to (15). The following equation (13) is a heat transfer balance equation near the interface, the following equation (14) is a carbon mass balance equation near the interface, and the following equation (15) is a relationship between the temperature and the carbon concentration at the interface. The interface carbon concentration and the interface temperature are calculated using these three equations.

[0078]

[0079] Here, T i is the interface temperature (°C), T S is the temperature of the cold iron source (℃), ρ S is the density of scrap iron (tons / m 3 ), Hs is the latent heat of melting of scrap iron (MJ / ton), v is the melting speed of scrap iron (mm / s) (v>0: melting, v<0: growth (forming solidification shell), λ i T is the thermal conductivity of the molten pig iron-scrap iron interface (W / (m·K)) (thermal conductivity of the molten pig iron side of the interface). L,0 is the liquidus temperature (°C) of pure iron (carbon concentration 0 mass %), and a is a coefficient.

[0080] In addition, the coefficients of the above formula (15) and the liquidus temperature of pure iron are calculated by the following formulas (16) and (17). The coefficients and the liquidus temperature of pure iron calculated by the following formulas (16) and (17) are used for the next step C i Calculation.

[0081]

[0082] The heat transfer coefficient of the molten pig iron-scrap interface (hereinafter referred to as "interface heat transfer coefficient") is calculated by the following formula (18). The interface heat transfer coefficient calculated by formula (18) is used for the calculation of the interface carbon concentration in the next step.

[0083]

[0084] Here, when the calculated interface carbon concentration satisfies at least one of the following equations (1) and (2), the interface carbon concentration calculated in the previous step is used instead of the calculated interface carbon concentration, the first melting rate is calculated by the above equation (13), and the second melting rate is calculated by the above equation (14), and the melting rate of the scrap iron is calculated by allocating the first melting rate and the second melting rate in proportion.

[0085] C i >C…(1)

[0086] C i >C i,t-1 …(2)

[0087] When the interface carbon concentration calculated in the previous step is used instead of the calculated interface carbon concentration, the first melting rate calculated by equation (13) and the first melting rate calculated by equation (14) are different values. The calculation unit 38 calculates the melting rate of the scrap iron by proportionally allocating the first melting rate and the second melting rate at a specific proportional allocation ratio.

[0088] As described above, in calculating the melting rate of scrap iron, it is preferable to use equation (13) and equation (14) separately according to the driving force of scrap iron melting. However, in reality, the melting mechanism of scrap iron cannot be clearly distinguished. Therefore, when either equation (13) or equation (14) is used in calculating the melting rate of scrap iron, the melting rate of scrap iron consistent with the actual phenomenon cannot be obtained.

[0089] Therefore, in order to improve the estimation accuracy of the melting rate of the scrap iron, the calculation unit 38 calculates the melting rate of the scrap iron by proportionally allocating the first melting rate calculated by equation (13) and the second melting rate calculated by equation (14) at a specific proportional allocation ratio. Specifically, the melting rate of the scrap iron is calculated by the following equation (19).

[0090] v S =(first melting rate)×(1-Z)+(second melting rate)×Z…(19)

[0091] Here, v S is the melting speed of scrap iron (m / min), and Z is the proportional distribution ratio (-).

[0092] On the other hand, when the calculated interface carbon concentration does not satisfy any of the above formulas (1) and (2), the melting rate of the scrap iron is calculated using the interface carbon concentration. When the calculated interface carbon concentration and interface temperature are used, the first melting rate calculated by formula (13) is equal to the second melting rate calculated by formula (14). Therefore, in this case, the first melting rate or the second melting rate calculated using the interface carbon concentration is used as the melting rate of the scrap iron. In this way, the calculation unit 38 calculates the melting rate of the scrap iron.

[0093] If the melting rate of scrap iron can be calculated, the melting rate of scrap iron can be calculated using the melting rate of scrap iron and the following formula (20).

[0094]

[0095] Here, t s0 is the initial thickness of scrap iron (mm), Δt is the calculation time interval [s].

[0096] Finally, the temperature distribution of the scrap metal is determined using the following equations (21) and (22).

[0097]

[0098] Here, α S is the thermal diffusivity of scrap iron (m 2 / s), x is the position in the thickness direction of the scrap iron, and one unit of x in this embodiment is tS0 / 100. In addition, the subscripts i+1 and i-1 represent the scrap iron temperature of the calculation element adjacent to the molten iron element side and the scrap iron center side, respectively.

[0099] The temperature distribution of the scrap is obtained one-dimensionally using the above formula (21). In order to calculate the formula (21), it is necessary to discretize as in the above formula (22). Therefore, the temperature distribution of the scrap obtained by the formula (22) is a discontinuous temperature distribution for each calculation thickness interval Δx.

[0100] Since the thickness interval Δx is set to t S0 1 / 100 of the original number, so at the beginning of the calculation (when melting begins), there are 100 calculation elements representing scrap iron. One calculation element representing the interface is adjacent to the scrap iron element group, and the 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. Although the calculation cost increases with the number of elements, the melting behavior when the solidified shell expands greatly at the initial stage of scrap iron melting can be calculated with good accuracy.

[0101] The thickness of all calculation elements is Δx, and the thickness of the calculation elements, the number of interface elements, and the total number of calculation elements are constant in the calculation. However, the number of scrap iron elements and the number of molten iron elements in the calculation are calculated based on the scrap iron melting rate S at each moment obtained by the above formula (20) m For example, when the melting rate is 2 mass % at a certain moment, there are 98 scrap iron elements at that moment, and the number of molten iron elements increases by 2. In addition, since the interface element always exists between the scrap iron element group and the molten iron element group, it only moves 2×Δx to the scrap iron element side relative to the initial position. On the contrary, if the melting rate is less than 0 (solidification shell is being generated), the scrap iron element increases and the molten iron element decreases, so the interface element moves to the molten iron element side.

[0102] Regarding temperature distribution calculation, first, it is determined whether each calculation factor corresponds to any one of the scrap factor, interface factor, and molten iron factor based on the scrap melting rate at that time, and the temperature distribution of each factor is obtained as follows.

[0103] Scrap element: calculated by the above formula (22), where the scrap center is treated as an adiabatic boundary (temperature is equal to that of the adjacent elements).

[0104] Interface element: Interface temperature T calculated by equation (15) above i .

[0105] Molten iron elements: Molten iron temperature T, without considering the uneven temperature of the molten iron.

[0106] dT used in the next step (13) S / dx is calculated by dividing the difference between the interface temperature Ti and the temperature of the scrap element adjacent to the interface temperature by the thickness Δx of the element being calculated. S After / dx, the furnace information can be acquired again, and the melting rate of the scrap iron after the calculation time interval Δt seconds can be calculated using the above formulas (3) to (21). In this way, by repeatedly calculating the melting rate of the scrap iron, the melting rate of the scrap iron at every moment in the pre-dephosphorization treatment of the molten pig iron 11 can be calculated.

[0107] It should be noted that the thermal diffusivity of scrap iron in the above equations (21) and (22) can be calculated by the following equations (23), (24) and (25).

[0108]

[0109] Here, λ S is the thermal conductivity of scrap iron (W / (m×K)), C PS is the specific heat of scrap iron (MJ / (t×K)).

[0110] Figure 3 This is a flow chart that explains the process of the cold iron source melting rate estimation method. Figure 3 The process of the cold iron source melting rate estimation method of the present embodiment will be described. The cold iron source melting rate estimation method of the present embodiment is started at any time before or during the preliminary dephosphorization treatment of the molten pig iron 11 , for example, in accordance with an instruction from the operator 50 .

[0111] The acquisition unit 36 ​​of the cold iron source melting rate estimation device 30 performs an acquisition step to acquire information on the molten pig iron 11 and the scrap iron, such as the amount of the molten pig iron 11 charged into the furnace, the initial carbon concentration of the molten pig iron 11, the amount of the scrap iron charged, the initial carbon concentration of the scrap iron, the density of the scrap iron, and the melting latent heat of the scrap iron, as the furnace information. In addition, the acquisition unit 36 ​​acquires the bottom blowing flow rate of the stirring gas 13, the temperature of the molten pig iron 11 at every moment, and the furnace pressure as the furnace information together with this information (step S101). The acquisition unit 36 ​​outputs this furnace information to the calculation unit 38.

[0112] The calculation unit 38 executes the calculation step and calculates the interface carbon concentration C using the furnace information and the above equations (3) to (18). i (Step S102). The calculated interface carbon concentration C i When at least one of the above formulas (1) and (2) is satisfied, the calculation unit 38 replaces the calculated interface carbon concentration C with i The interfacial carbon concentration C calculated in the previous step is used i,t-1The first melting rate and the second melting rate are calculated, and these first melting rate and the second melting rate are proportionally distributed, thereby calculating the melting rate of the scrap iron. In addition, the calculated interface carbon concentration C i When neither of the above formulas (1) or (2) is satisfied, the calculated interface carbon concentration C i The first melting rate or the second melting rate is calculated, and the calculated first melting rate or the second melting rate is used as the melting rate of the scrap iron (step S103).

[0113] The calculation unit 38 performs the calculation step and calculates the melting rate S of the scrap iron using the melting rate of the scrap iron and the above formula (20). m (Step S104) In addition, the calculation unit 38 executes a calculation step to calculate the temperature distribution of the scrap using the above-mentioned equation (21) (Step S105).

[0114] The calculation unit 38 calculates the melting rate S of the scrap iron. m Output to the output unit 40. The output unit 40 performs an output step to output the melting rate S m (Step S106).

[0115] The calculation unit 38 determines the calculated melting rate S of the scrap iron. m Is it greater than 100 (step S107). m When the melting rate S of the scrap iron is greater than 100 (step S107: Yes), the calculation unit 38 determines that the scrap iron is completely melted and ends the process. m If the value is less than 100 (step S107: No), the calculation unit 38 returns the process to step S101, executes the process of steps S101 to S107 again, and calculates the melting rate S of the scrap iron after the calculation time interval Δt seconds. In this way, by repeatedly executing the process of steps S101 to S107, the cold iron source melting rate estimation method of this embodiment can calculate the melting rate S of the scrap iron at every moment until the scrap iron is completely melted during the pre-dephosphorization process of the molten pig iron 11. m .

[0116] Example

[0117] Next, an example is described. In this example, a square pure iron sample (100×100×50 mm) simulating a cold iron source (scrap iron) is immersed 80 mm in 500 kg of molten iron obtained by smelting in a cylindrical atmospheric furnace with an inner diameter of 430 mm, and the melting rate of the square pure iron sample after a specified time is estimated using the cold iron source melting rate estimation method of this embodiment. After the square pure iron sample is immersed in the molten iron for a specified time, it is recovered and air-cooled, and the melting rate of the square pure iron sample is measured using the following formula (26).

[0118]

[0119] Here, S p is the melting rate of the square pure iron sample (mass %), L S0 , L S Each of these is the thickness (mm) of the square pure iron sample before and after impregnation.

[0120] In order to measure the molten iron temperature and the carbon concentration of the molten iron, the temperature was measured by an embedded thermocouple before and after the square pure iron sample was immersed in the molten iron, and the molten iron sample for chemical analysis was collected.

[0121] [Example 1]

[0122] In Example 1, the melting rate of the square pure iron sample was estimated using the cold iron source melting rate estimation method of this embodiment when the square pure iron sample was preheated at 1200° C. and when it was not preheated. The conditions of Example 1 are shown in Table 2 below.

[0123]

[0124] Figure 4 : is a graph showing the estimated results and the measured results of the melting rate of the square pure iron sample in Example 1. Figure 4 In the figure, the vertical axis is the melting rate (mass %) of the square pure iron sample, and the horizontal axis is the melting time (seconds). Figure 4 In the figure, each curve represents the melting rate estimated by the cold iron source melting rate estimation method, and each plotted point represents the measured value of the melting rate (mass %) of the square pure iron sample recovered after impregnation and air-cooled and calculated using the above formula (26).

[0125] like Figure 4 As shown, the estimated value of the melting rate is roughly consistent with the experimental value regardless of whether the square pure iron sample is preheated or not. This result confirms that the melting rate of the cold iron source can be estimated with high accuracy by using the cold iron source melting rate estimation method of this embodiment.

[0126] [Example 2]

[0127] In Example 2, the cold iron source melting rate estimation method of this embodiment was used to estimate the melting rates of square pure iron samples using molten iron whose initial temperature was changed within the range of 1430 to 1610° C. The conditions of Example 2 are shown in Table 3 below.

[0128]

[0129] Figure 5: is a graph showing the estimated results and measured results of the melting rate of the square pure iron sample in Example 2. Figure 5 In the figure, the vertical axis is the melting rate (mass %) of the square pure iron sample, and the horizontal axis is the melting time (seconds). Figure 5 In the figure, each curve also represents the melting rate estimated by the cold iron source melting rate estimation method, and each plotted point also represents the measured value of the melting rate (mass %) of the square pure iron sample recovered after impregnation, air-cooled and calculated using the above formula (26).

[0130] like Figure 5 As shown, the estimated values ​​of the melting rate under the conditions of Invention Examples 11 to 16 in which the initial temperature of the molten iron was changed are substantially consistent with the experimental values. This result confirms that the melting rate of the cold iron source can be estimated with high accuracy by using the cold iron source melting rate estimation method of this embodiment.

[0131] [Example 3]

[0132] In Example 3, the estimated melting rates were confirmed when the melting rate of the cold iron source was estimated based on the first melting rate obtained by equation (13) or the second melting rate obtained by equation (14) and when the melting rate of the cold iron source was estimated based on the melting rate obtained by proportionally allocating the first melting rate obtained by equation (13) and the second melting rate obtained by equation (14). The conditions of Example 3 are shown in Table 4 below.

[0133]

[0134] Figure 6 : is a graph showing the estimated results and the measured results of the melting rate of the square pure iron sample in Example 3. Figure 6 In the figure, the vertical axis is the melting rate (mass %) of the square pure iron sample, and the horizontal axis is the melting time (seconds). Figure 6 In the figure, the curve represented by the solid line represents the melting rate estimated by the cold iron source melting rate estimation method, and the curve represented by the dotted line represents the melting rate estimated using only the formula (13) or the formula (14). In addition, the dots represent the measured values ​​of the melting rate (mass %) of the square pure iron sample recovered after immersion, air-cooled, and calculated using the above formula (26).

[0135] like Figure 6As shown, when at least one of the above-mentioned formulas (1) and (2) is satisfied, the estimated value of Invention Example 31, which estimates the melting rate of the cold iron source based on the melting rate obtained by proportionally allocating the first melting rate and the second melting rate, is roughly consistent with the experimental value. On the other hand, even when at least one of the above-mentioned formulas (1) and (2) is satisfied, when the melting rate of the cold iron source is estimated based on the melting rate obtained only by formula (13) or (14), the estimated value is inconsistent with the experimental value. These results confirm that in order to estimate the melting rate of the cold iron source with high accuracy, it is important to determine an appropriate proportional allocation ratio to proportionally allocate the first melting rate calculated by the heat transfer balance equation and the second melting rate calculated by the carbon mass balance equation.

[0136] Explanation of symbols

[0137] 10Converter type refining furnace

[0138] 11 Molten Pig Iron

[0139] 13 Stirring gas

[0140] 14 Top Blowing Spray Gun

[0141] 20 Converter type refining furnace control device

[0142] 22 Process Control Computer

[0143] 24Job control computer

[0144] 30 Cold iron source melting rate estimation device

[0145] 32. Control Unit

[0146] 34 Storage

[0147] 36 Acquisition Department

[0148] 38 Operation unit

[0149] 40 Output unit

[0150] 50 Operators

Claims

1. A cold iron source melting rate estimating device for estimating the melting rate of a cold iron source in a refining process of molten iron using the cold iron source as a raw material, It has: an acquisition unit for acquiring in-furnace information including information of the molten iron and the cold iron source; a calculation unit for calculating the carbon concentration at the interface between the cold iron source and the molten iron, the melting speed of the cold iron source, and the melting rate of the cold iron source using the in-furnace information; and an output unit for outputting the melting rate, When the interface carbon concentration satisfies at least one of the following equations (1) and (2), the operation unit uses the interface carbon concentration calculated in the previous step to calculate the first melting rate according to the heat transfer balance equation, calculates the melting rate of the cold iron source according to the calculated second melting rate, and distributes the first melting rate and the second melting rate in proportion. When the interface carbon concentration does not satisfy any one of the following equations (1) and (2), the calculation unit calculates the first melting rate or the second melting rate using the interface carbon concentration, and uses the calculated first melting rate or the second melting rate as the melting rate of the cold iron source. C i >C…(1) C i >C i,t-1 …(2) In the above formulas (1) and (2), C is the carbon concentration of molten iron (mass %), C i is the interface carbon concentration (mass %), C i,t-1 is the interfacial carbon concentration (mass %) calculated in the previous step.

2. The cold iron source melting rate estimation device according to claim 1, wherein: When the carbon concentration of the cold iron source is lower than the carbon concentration of the molten iron, the calculation unit determines a proportional allocation ratio for proportionally allocating the first melting rate and the second melting rate based on the molten iron temperature, the molten iron carbon concentration, and the carbon concentration of the cold iron source.

3. The cold iron source melting rate estimation device according to claim 1 or claim 2, wherein: The calculation unit estimates the melting rate of the chill source at each moment by repeatedly calculating the interface carbon concentration, the melting rate of the chill source, and the melting rate of the chill source.

4. A method for refining molten iron, wherein: The cold iron source melting rate estimation device according to claim 1 or claim 2 is used to estimate the melting 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 melting rate at the end time exceeds 5 mass %, at least one of adding a heat generating material and extending the molten iron treatment is performed.

5. A method for refining molten iron, wherein: The cold iron source melting rate estimation device according to claim 3 is used to estimate the melting 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 melting rate at the end time exceeds 5 mass %, at least one of adding a heat generating material and extending the molten iron treatment is performed.

6. A method for estimating a melting rate of a cold iron source, the method comprising estimating the melting rate of the cold iron source in a refining process of molten iron using the cold iron source as a raw material, It has: A step of acquiring furnace information including information of the molten iron and the cold iron source; The step of calculating the carbon concentration at the interface between the cold iron source and the molten iron, the melting speed of the cold iron source and the melting rate of the cold iron source by using the in-furnace information; as well as an outputting step of outputting the melting rate, When the interface carbon concentration satisfies at least one of the following equations (1) and (2), in the calculation step, the interface carbon concentration calculated in the previous step is used to calculate the first melting rate according to the heat transfer balance equation, the second melting rate is calculated according to the carbon mass balance equation, and the first melting rate and the second melting rate are proportionally distributed to calculate the melting rate of the cold iron source. When the interface carbon concentration does not satisfy any of the following equations (1) and (2), in the calculation step, the first melting rate or the second melting rate is calculated using the interface carbon concentration, and the calculated first melting rate or the second melting rate is used as the melting rate of the cold iron source. C i >C…(1) C i >C i,t-1 …(2) In the above formulas (1) and (2), C is the carbon concentration of molten iron (mass %), C i is the interface carbon concentration (mass %), C i,t-1 is the interfacial carbon concentration (mass %) calculated in the previous step.

7. The cold iron source melting rate estimation method according to claim 6, wherein: When the carbon concentration of the cold iron source is lower than the carbon concentration of the molten iron, in the calculation step, a proportional allocation ratio for proportionally allocating the first melting rate and the second melting rate is determined based on the molten iron temperature, the molten iron carbon concentration and the carbon concentration of the cold iron source.

8. The cold iron source melting rate estimation method according to claim 6 or claim 7, wherein: In the calculation step, the melting rate of the cold iron source at each moment is estimated by repeatedly calculating the interface carbon concentration, the melting speed of the cold iron source, and the melting rate of the cold iron source.

9. A method for refining molten iron, wherein: The cold iron source melting rate estimation method according to claim 6 or claim 7 is used to estimate the melting 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 melting rate at the end time exceeds 5 mass %, at least one of adding a heat generating material and extending the molten iron treatment is performed.

10. A method for refining molten iron, wherein: The cold iron source melting rate estimation method according to claim 8 is used to estimate the melting 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 melting rate at the end time exceeds 5 mass %, at least one of adding a heat generating material and extending the molten iron treatment is performed.

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