Furnace inside temperature measuring method for electric furnace, furnace inside temperature measuring device for electric furnace, control method for electric furnace, control device for electric furnace, furnace inside temperature measuring program for electric furnace, computer-readable storage medium that stores furnace inside temperature measuring program for electric furnace, and manufacturing method for metal material

Abstract

To provide a furnace inside temperature measuring method for an electric furnace that is capable of accurately measuring the furnace inside temperature of the electric furnace even in a case in which the electric furnace is enlarged; a furnace inside temperature measuring device; a furnace inside temperature measuring program; and a computer-readable storage medium that stores the furnace inside temperature measuring program.SOLUTION: A furnace inside temperature measuring method for an electric furnace is used for an electric furnace equipped with an electrode that melts a metal material inside the furnace through arc discharge and includes: an electromagnetic field calculating step of calculating a current density distribution and a magnetic field distribution inside the furnace using at least an amount of molten metal inside the furnace, a shape of a furnace body, and electric energy supplied to the electrode; a fluid calculation step of calculating the flow rates of molten metal and gas in the furnace using at least the magnetic field distribution inside the furnace calculated in the electromagnetic field calculation step; and a temperature calculation step of calculating a furnace inside temperature using at least the current density distribution inside the furnace calculated in the electromagnetic calculation step and the flow rates of molten metal and gas inside the furnace calculated in the fluid calculation step.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for measuring the temperature inside an electric furnace, an apparatus for measuring the temperature inside an electric furnace, a method for controlling an electric furnace, an apparatus for controlling an electric furnace, a program for measuring the temperature inside an electric furnace, a computer-readable storage medium storing a program for measuring the temperature inside an electric furnace, and a method for manufacturing a metal material. [Background technology]

[0002] In recent years, in order to reduce CO2 emissions, there has been a demand for the expanded use of electric furnaces, which are more effective in reducing CO2 emissions than blast furnaces, which use carbon sources such as coke to reduce iron ore. An electric furnace is equipped with a furnace that melts a cold iron source and stores the molten iron, and electrodes made of graphite or the like. In this electric furnace, high-voltage electricity is applied to the electrodes, causing an electric current to flow through an insulating layer with the air, generating an arc, which generates high temperatures (hereinafter, the high-temperature heat source generated by the current flowing through the air layer is called arc heat). It is said that the high temperatures caused by the arc heat reach temperatures of several thousand to tens of thousands of degrees, and the cold iron source is melted by transferring this heat to scrap or molten iron. In order to efficiently melt the cold iron source, it is necessary to create a high-temperature environment and transport heat evenly within the furnace to transfer heat to the scrap or molten iron.

[0003] Since arc heat is generated near the electrodes due to the structure, the heat may be unevenly distributed in the furnace. For this reason, a secondary heat source such as an auxiliary burner may be provided in the electric furnace. Also, if heat is not continuously supplied to the molten iron, the temperature of the molten iron may drop due to the heat radiated outside the furnace, and the molten iron may solidify, causing problems in the production of molten iron. For this reason, it is necessary to prevent cold spots from occurring in the molten iron by stirring the high-temperature molten iron near the electrodes and leveling the temperature of the molten iron in the furnace. Here, examples of molten iron stirring means include an electromagnetic stirrer that stirs the molten iron with electromagnetic force and a bottom blower that blows gas from the bottom of the furnace and stirs the molten iron by the upward force of bubbles rising in the molten iron. Thus, in an electric furnace, it is important to generate a high-temperature environment in the furnace and transport the generated heat throughout the furnace.

[0004] On the other hand, in order to expand the use and improve the efficiency of electric furnaces, it is necessary to enlarge the electric furnace. If the electric furnace is large, the contact area of ​​the molten iron with the external environment can be reduced compared to multiple small electric furnaces with the same production capacity, so the generated heat can be used efficiently. However, when the electric furnace is enlarged, the local arc heat generated near the electrodes needs to be transported into a large furnace, so the temperature inside the furnace is likely to become uneven. If the temperature inside the furnace drops and the molten iron solidifies, the production efficiency of the molten iron will deteriorate. In addition, if there are places where the temperature inside the furnace is likely to drop, it is necessary to level the temperature inside the furnace by using a secondary heat source, a molten iron stirring means, etc. Therefore, when enlarging the electric furnace to improve its efficiency, it becomes important to predict the temperature inside the furnace and identify places where the temperature inside the furnace is likely to be locally low.

[0005] In light of this background, Patent Document 1 proposes a method for predicting the temperature inside an electric furnace. The method described in Patent Document 1 predicts the near future temperature inside the furnace by inputting continuously measured temperatures inside the furnace and operational data such as the amount of electricity supplied and oxygen into a regression equation obtained by multiple regression analysis from past measurements of the temperature inside the furnace and operational data of the electric furnace. If the temperature inside the furnace and the temperature of molten iron can be investigated in advance by using this method, a regression equation can be created based on the temperature data and operational data, and the temperature near the area where the temperature inside the furnace is being measured can be predicted. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-181544 Summary of the Invention [Problem to be solved by the invention]

[0007] However, according to the method described in Patent Document 1, it is difficult to predict the temperature inside a large-sized electric furnace. Specifically, the method described in Patent Document 1 requires that the molten iron temperature be measured in advance, but in a large-sized electric furnace, the molten iron temperature has a distribution, and the molten iron temperature at a certain point does not necessarily represent the temperature of the entire molten iron. For this reason, when using the method described in Patent Document 1, the molten iron temperature needs to be measured at multiple points. However, since electric furnaces are high in temperature, it is essential to regularly update temperature measuring instruments. For this reason, when the molten iron temperature is measured at multiple points, the number of temperature measuring instruments that need to be regularly updated increases, and maintenance costs increase significantly.

[0008] In addition, since the scrap that is the source of cold iron has a sharp shape, if a temperature measuring instrument is installed at a location where the scrap may come into contact, the sensor part of the temperature measuring instrument is likely to be damaged by the scrap. If the temperature measuring instrument is damaged, it is not possible to measure the temperature sufficiently, and it becomes impossible to accurately predict the temperature inside the furnace. Furthermore, as the electric furnace becomes larger, the voltage applied to the electrodes becomes larger, and the interaction between phenomena such as the flow of molten iron and the gas flow inside the furnace becomes more pronounced, making it difficult to accurately predict the temperature inside the furnace using only data on the temperature of the molten iron at several points and operation data.

[0009] The present invention has been made to solve the above problems, and its object is to provide an electric furnace temperature measurement method, an electric furnace temperature measurement device, an electric furnace temperature measurement program, and a computer-readable storage medium storing the electric furnace temperature measurement program, which are capable of accurately measuring the temperature inside the electric furnace even when the electric furnace is large. Another object of the present invention is to provide an electric furnace control method and control device that can improve the operating efficiency of the electric furnace. Another object of the present invention is to provide a metal material manufacturing method that can manufacture metal materials with a good manufacturing yield. [Means for solving the problem]

[0010] (1) The method for measuring the temperature inside an electric furnace according to the present invention is a method for measuring the temperature inside an electric furnace equipped with electrodes that melt metal material inside the furnace by arc discharge, and includes: an electromagnetic field calculation step for calculating a current density distribution and a magnetic field distribution inside the furnace using at least the amount of molten metal in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes; a fluid calculation step for calculating the flow velocities of molten metal and gas in the furnace using at least the magnetic field distribution inside the furnace calculated in the electromagnetic field calculation step; and a temperature calculation step for calculating the temperature inside the furnace using at least the current density distribution inside the furnace calculated in the electromagnetic field calculation step and the flow velocities of molten metal and gas in the furnace calculated in the fluid calculation step.

[0011] (2) In the method for measuring the temperature inside an electric furnace described in (1) above, the fluid calculation step may further include a step of calculating a gas flow rate inside the furnace using a gas flow rate of a secondary heat source provided in the electric furnace, and the temperature calculation step may further include a step of calculating the temperature inside the furnace using the heat quantity of the secondary heat source.

[0012] (3) In the method for measuring the temperature inside an electric furnace described in (1) or (2) above, the temperature calculation step may further include a step of calculating the temperature inside the furnace using the amount of heat radiation from the furnace body.

[0013] (4) The electric furnace temperature measuring device of the present invention is an electric furnace temperature measuring device equipped with electrodes for melting metal material in the furnace by arc discharge, and includes an electromagnetic field calculation unit that calculates a current density distribution and a magnetic field distribution in the furnace using at least the amount of molten metal in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes, a fluid calculation unit that calculates the flow velocities of molten metal and gas in the furnace using at least the magnetic field distribution in the furnace calculated by the electromagnetic field calculation unit, and a temperature calculation unit that calculates the temperature in the furnace using at least the current density distribution in the furnace calculated by the electromagnetic field calculation unit and the flow velocities of molten metal and gas in the furnace calculated by the fluid calculation unit.

[0014] (5) The method for controlling an electric furnace according to the present invention includes a step of controlling the electric furnace according to a temperature inside the furnace calculated by the method for measuring temperature inside an electric furnace described in any one of (1) to (3) above.

[0015] (6) The electric furnace control device according to the present invention includes a control means for controlling the electric furnace in accordance with the temperature inside the furnace calculated by the electric furnace temperature measuring device described in (4) above.

[0016] (7) The electric furnace temperature measurement program of the present invention is a furnace temperature measurement program for an electric furnace equipped with electrodes for melting metal material in the furnace by arc discharge, which causes a computer to function as an electromagnetic field calculation unit that calculates a current density distribution and a magnetic field distribution in the furnace using at least the amount of molten metal in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes, a fluid calculation unit that calculates the flow velocities of molten metal and gas in the furnace using at least the magnetic field distribution in the furnace calculated by the electromagnetic field calculation unit, and a temperature calculation unit that calculates the temperature in the furnace using at least the current density distribution in the furnace calculated by the electromagnetic field calculation unit and the flow velocities of molten metal and gas in the furnace calculated by the fluid calculation unit.

[0017] (8) A computer-readable storage medium storing an electric furnace temperature measurement program according to the present invention is a computer-readable storage medium storing an electric furnace temperature measurement program having electrodes for melting metal material in the furnace by arc discharge, and causes a computer to function as an electromagnetic field calculation unit that calculates a current density distribution and a magnetic field distribution in the furnace using at least the amount of molten metal in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes, a fluid calculation unit that calculates the flow velocities of molten metal and gas in the furnace using at least the magnetic field distribution in the furnace calculated by the electromagnetic field calculation unit, and a temperature calculation unit that calculates the temperature in the furnace using at least the current density distribution in the furnace calculated by the electromagnetic field calculation unit and the flow velocities of molten metal and gas in the furnace calculated by the fluid calculation unit.

[0018] (9) A method for producing a metal material according to the present invention includes a step of producing a metal material by controlling an electric furnace in accordance with a temperature inside the furnace calculated by the method for measuring temperature inside an electric furnace described in any one of (1) to (3) above. Effect of the Invention

[0019] According to the electric furnace temperature measuring method, furnace temperature measuring device, furnace temperature measuring program, and computer-readable storage medium storing the furnace temperature measuring program of the present invention, the temperature inside the electric furnace can be measured with high accuracy even if the electric furnace is large. Furthermore, according to the electric furnace control method and control device of the present invention, the operating efficiency of the electric furnace can be improved. Furthermore, according to the metal material manufacturing method of the present invention, the metal material can be manufactured with a high manufacturing yield. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an AC electric furnace to which a method for measuring an internal temperature of an electric furnace according to an embodiment of the present invention is applied. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of a DC electric furnace to which the method for measuring the temperature inside an electric furnace according to one embodiment of the present invention is applied. [Diagram 3] FIG. 3 is a block diagram showing the configuration of a temperature measuring device to which a method for measuring the temperature inside an electric furnace according to an embodiment of the present invention is applied. [Figure 4] FIG. 4 is a flowchart showing the flow of a temperature measurement process according to an embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram illustrating an example of a computational grid. [Figure 6] FIG. 6 is a flowchart showing a flow of a modified example of the temperature measurement process shown in FIG. [Figure 7] FIG. 7 is a flowchart showing the flow of a modified example of the temperature measurement process shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Below, with reference to the drawings, an electric furnace internal temperature measuring method, an electric furnace internal temperature measuring device, an electric furnace control method, an electric furnace control device, an electric furnace internal temperature measuring program, a computer-readable storage medium storing an electric furnace internal temperature measuring program, and a metal material manufacturing method, which are one embodiment of the present invention, will be described.

[0022] [Configuration of electric furnace] First, with reference to Figs. 1 and 2, the configurations of an AC electric furnace and a DC electric furnace to which a method for measuring an internal temperature of an electric furnace according to an embodiment of the present invention is applied will be described.

[0023] FIG. 1 is a schematic diagram showing the configuration of an AC electric furnace to which a method for measuring the temperature inside an electric furnace according to one embodiment of the present invention is applied. As shown in FIG. 1, an AC electric furnace 1 to which a method for measuring the temperature inside an electric furnace according to one embodiment of the present invention is applied is a facility for producing molten iron S by melting a cold iron source such as scrap, which is a metal material, by arc discharge, and includes a furnace 2 and electrodes 3 (3a to 3c). The furnace 2 is a container for storing the molten iron S obtained by melting the cold iron source by arc discharge. The inner surface of the furnace 2 is covered with a refractory material 4 so as to be able to withstand high temperatures, and the upper part of the furnace 2 is covered with an upper lid 5. A molten iron port (not shown) for taking out the molten iron S to the outside is provided on the bottom or side of the furnace 2.

[0024] The furnace 2 is provided with an auxiliary raw material inlet (not shown) for feeding auxiliary raw materials such as lime and coke into the molten iron S to adjust the components of the molten iron S. The furnace 2 is provided with an auxiliary heat source 6 such as an auxiliary burner for supplementing the amount of heat when the temperature of the cold iron source cannot be adjusted by the arc discharge alone. A device having two functions of the auxiliary raw material inlet (not shown) and the auxiliary heat source 6 may be provided. The electrode 3 generates an arc discharge when a high-voltage three-phase AC current is supplied, and the cold iron source is melted by the arc heat. The electrode 3 is installed on the upper lid 5 and is often made of graphite. The AC electric furnace 1 is provided with three electrodes 3a to 3c to utilize the high-voltage three-phase AC current.

[0025] FIG. 2 is a schematic diagram showing the configuration of a DC electric furnace to which the method for measuring the temperature inside an electric furnace according to one embodiment of the present invention is applied. As shown in FIG. 2, a DC electric furnace 10 to which the method for measuring the temperature inside an electric furnace according to one embodiment of the present invention is applied is a facility for producing molten iron S by melting a cold iron source by arc discharge, and includes a furnace 2 and electrodes 3 (3d, 3e). The furnace 2 has a configuration similar to that of the furnace 2 of the AC electric furnace 1 shown in FIG. 1. The electrode 3 generates an arc discharge by being supplied with a high-voltage DC current, and melts the cold iron source by the arc heat. The electrodes 3d, 3e are installed on the top cover 5 and the bottom of the furnace 2, respectively, and are often made of graphite. When a DC power source is used to supply a DC current to the electrode 3, a conversion facility for converting the AC current to a DC current is provided. The upper electrode 3d may be one or more. When there are multiple electrodes 3d, the voltage of the DC current is increased to make it easier to diffuse the arc heat inside the furnace, and the melting speed of the cold iron source can be increased when the DC electric furnace 10 is enlarged.

[0026] [Configuration of temperature measuring device] Next, with reference to FIG. 3, a configuration of a temperature measuring device to which a method for measuring temperature inside an electric furnace according to an embodiment of the present invention is applied will be described.

[0027] Fig. 3 is a block diagram showing the configuration of a temperature measuring device to which the method for measuring temperature inside an electric furnace according to one embodiment of the present invention is applied. As shown in Fig. 3, a temperature measuring device 20 to which the method for measuring temperature inside an electric furnace according to one embodiment of the present invention is applied is configured with an information processing device such as a computer. A display device 21, an input device 22, and a measuring device 23 are connected to the temperature measuring device 20 via an electric communication line.

[0028] The display device 21 is composed of a known display device such as a liquid crystal display, and displays and outputs various information such as temperature calculation results output from the temperature measuring device 20. The input device 22 is composed of known input devices such as a keyboard and a mouse pointer, and inputs various information such as set values ​​to the temperature measuring device 20. The measuring device 23 is composed of a measuring device installed in the electric furnace, and inputs past and current measurement data to the temperature measuring device 20 in response to an acquisition request signal from the temperature measuring device 20. Examples of the measuring device include a measuring device that measures the surface level of molten iron S (the amount of molten iron S in the furnace 2) and a measuring device that measures the temperature of the furnace body.

[0029] The temperature measuring device 20 includes a calculation preparation unit 24, an electromagnetic field calculation unit 25, a fluid calculation unit 26, and a temperature calculation unit 27. The functions of these units are realized by an arithmetic processing unit such as a CPU in an information processing device executing a temperature measurement program 29 stored in a storage unit 28. The functions of these units will be described later. The storage unit 28 may be a storage medium fixed to a computer or the like, or a storage medium removable from a computer or the like. Examples of storage media fixed to a computer or the like include an EPROM (Erasable Programmable ROM) and a hard disk drive (HDD, Hard Disk Drive).

[0030] Examples of the recording medium removable from a computer include a universal serial bus (USB) memory, a flexible disk, a magneto-optical disk, a compact disc-read only memory (CD-ROM), a compact disc-rewritable (CD-RW), a digital versatile disc (DVD), a Blu-ray (registered trademark) disc (BD), a digital audio tape (DAT), an 8 mm tape, and a memory card. A solid state drive (SSD) can be used as a storage medium removable from a computer or fixed to a computer. The temperature measurement program 29 may be stored on a computer connected to a telecommunication line such as the Internet and provided by downloading the program via the telecommunication line. The temperature measurement program 29 may be provided or distributed via a telecommunication line such as the Internet.

[0031] [Temperature measurement processing] Next, with reference to FIG. 4, a flow of a process for measuring the temperature inside the electric furnaces (the AC electric furnace 1 and the DC electric furnace 10) by the temperature measuring device 20 (temperature measuring process) will be described.

[0032] Fig. 4 is a flowchart showing the flow of a temperature measurement process according to an embodiment of the present invention. The flowchart shown in Fig. 4 starts when an execution command for the temperature measurement process is input to the temperature measurement device 20, and the temperature measurement process proceeds to step S1.

[0033] In the process of step S1, the calculation preparation unit 24 acquires information on the shape of the electric furnace and the level of the molten iron S via the input device 22. Specifically, the calculation preparation unit 24 acquires two-dimensional or three-dimensional CAD data showing the shape of the electric furnace as information on the shape of the electric furnace. The file format of the CAD data may be any format that can be read by a computer, such as STEP, IGES, STL, etc. Information on the level of the molten iron S can be acquired from the measurement device 23. If information on the level of the molten iron S cannot be acquired from the measurement device 23, the calculation preparation unit 24 may estimate the amount of molten iron M in the furnace using, for example, the following formula (1), and calculate the level of the molten iron S from the amount of molten iron M and the bottom area of ​​the electric furnace. This completes the process of step S1, and the temperature measurement process proceeds to the process of step S2.

[0034]

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[0035] In the above formula (1), a and b are coefficients determined for each operating condition of the electric furnace, and are determined by conducting a test to measure the surface level of molten iron S at several points in the electric furnace under set operating conditions. Also, E is the average amount of electric power input to the electric furnace, and t is the elapsed time after the cold iron source is charged into the electric furnace.

[0036] In the process of step S2, the calculation preparation unit 24 creates a computational grid to be used in the subsequent processes from the information on the shape of the electric furnace acquired in the process of step S1. Specifically, the calculation preparation unit 24 divides the shape of the electric furnace containing the molten iron S into computational grids of polyhedrons such as tetrahedrons and hexahedrons. An example of the computational grid is shown in FIG. 5. In the example shown in FIG. 5, the electrode 3 and the electric furnace containing the molten iron S are divided into a plurality of computational grids M of rectangular shape. The calculation preparation unit 24 may improve the calculation accuracy by shortening the interval between adjacent computational grids, in other words, increasing the density of the computational grid, in the region where the change in physical quantities such as the magnetic field, the current, the speed, and the temperature is expected to be drastic. This completes the process of step S2, and the temperature measurement process proceeds to the process of step S3.

[0037] In the process of step S3, the calculation preparation unit 24 sets the boundary conditions and physical property values ​​of the calculation grid used by the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27 for calculation, on the premise that the operating conditions of the electric furnace do not change. Here, examples of the operating conditions of the electric furnace that may change include the current value (amount of power supplied) applied to the electrode 3, the heat amount (burner heat amount) and gas flow rate of the auxiliary heat source 6, the amount of molten iron S and slag, and the amount of heat released from the furnace body. Specifically, the calculation preparation unit 24 sets the region other than the electrodes as the insulating boundary condition for the calculation grid used by the electromagnetic field calculation unit 25 for calculation. In addition, the calculation preparation unit 24 sets the no-slip condition for the part corresponding to the wall surface of the furnace 2 in the calculation grid used by the fluid calculation unit 26 for calculation, and sets the pressure constant (generally set to 0, but any value is acceptable) for the part corresponding to the outlet.

[0038] Also, the boundary condition is set so that the furnace periphery dissipates heat to the outside air. In this case, the boundary condition may be set by giving a heat transfer coefficient with the outside air, or may be set by giving a fixed value of the heat transfer coefficient. Since the furnace is hot, heat is dissipated to the outside air by radiation, and if a boundary condition considering radiation is given, the prediction accuracy is improved. Since it may be difficult to calculate the amount of heat dissipated to the outside air under the operating conditions, a temperature sensor may be attached to the outer wall of the furnace and the outside air temperature may be measured at the same time, and the amount of heat dissipated from the furnace to the outside air may be measured in advance, and the amount of heat dissipated may be set as the boundary condition of the outer wall of the furnace. Also, the calculation preparation unit 24 sets, as physical property values ​​at the calculation points of the calculation grid, the electric conductivity and relative magnetic permeability of air and molten iron S for the electromagnetic field calculation unit 25, the density and viscosity of air and molten iron S for the fluid calculation unit 26, and the thermal conductivity and specific heat of air and molten iron S for the temperature calculation unit 27. The calculation preparation unit 24 may provide physical property values ​​to each vertex of the computational grid created in the processing of step S2, or may provide physical property values ​​at the center position of the computational grid. This completes the processing of step S3, and the temperature measurement processing proceeds to the processing of step S4.

[0039] In the process of step S4, the calculation preparation unit 24 acquires operation data of the electric furnace via the input device 22. Examples of the acquired operation data include the current value applied to the electrode 3, the heat quantity of the auxiliary heat source 6, and the gas flow rate. This completes the process of step S4, and the temperature measurement process proceeds to the process of step S5.

[0040] In the process of step S5, the calculation preparation unit 24 determines whether or not the measuring device 23 stores measurement data of the furnace body temperature. If the result of the determination is that the measuring device 23 stores measurement data of the furnace body temperature (step S5: Yes), the calculation preparation unit 24 advances the temperature measurement process to the process of step S6. On the other hand, if the measuring device 23 does not store measurement data of the furnace body temperature (step S5: No), the calculation preparation unit 24 advances the temperature measurement process to the process of step S7.

[0041] In the process of step S6, the calculation preparation unit 24 sets the measurement data (temperature boundary condition) of the furnace body temperature acquired from the measurement device 23 as the boundary condition of the portion corresponding to the furnace body of the computational grid used in the calculation by the temperature calculation unit 27. This completes the process of step S6, and the temperature measurement process proceeds to the process of step S8.

[0042] In the process of step S7, the calculation preparation unit 24 sets a fixed heat flux value as the boundary condition of the portion corresponding to the furnace body of the calculation grid used in the calculation by the temperature calculation unit 27. This completes the process of step S7, and the temperature measurement process proceeds to the process of step S8.

[0043] In the process of step S8, the electromagnetic field calculation unit 25 calculates the distribution of the current density and the magnetic field in the electric furnace using the computational grid created by the processes of steps S1 to S3 and the operation data acquired in the process of step S4. Specifically, the electromagnetic field calculation unit 25 calculates the current density J and the magnetic field B at each computation point of the computational grid by discretizing and numerically solving the following equation (5) based on Maxwell's equations shown in the following equations (2) to (4) according to the current value acquired in the process of step S4. This completes the process of step S8, and the temperature measurement process proceeds to the process of step S9.

[0044]

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[0045]

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[0046]

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[0047]

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[0048] In formulas (2) to (5), E is the electric field in the electric furnace, B is the magnetic field in the electric furnace, μ p is the magnetic permeability, J is the current density, σe is the electrical conductivity, and v is the flow velocity of the molten iron S and gas (fluid flow velocity).

[0049] In the process of step S9, the fluid calculation unit 26 calculates the flow velocity distribution of the gas and molten iron S in the electric furnace using the computational grid created by the processes of steps S1 to S3 and the magnetic field distribution in the electric furnace calculated in the process of step S8. Specifically, the fluid calculation unit 26 calculates the flow velocities of the gas and molten iron S at each computation point of the computational grid by discretizing and numerically solving the fluid equations shown in the following formulas (6) to (8) according to the magnetic field distribution in the electric furnace calculated in the process of step S8. By using the magnetic field distribution calculated in the process of step S8, the flow velocity distribution of the gas and molten iron S can be calculated with high accuracy, taking into account the Lorentz force generated by the movement of the molten iron S.

[0050]

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[0051]

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[0052]

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[0053] The above formula (6) is the continuity equation (law of conservation of mass), the above formula (7) is the Navier-Stokes equation (equation of motion), and the above formula (8) is the viscosity correction formula based on the turbulence model. In the above formulas (6) to (8), ρ is the fluid density, P is the stress, μ eff is the effective viscosity coefficient, μ l is the molecular viscosity, μ t denotes the turbulent viscosity.

[0054] When calculating the flow rate of molten iron S, a multiphase flow calculation method such as the VOF (Volume Of Fluid) method may be used to set the volume fraction of molten iron S for each calculation grid as shown in the following formulas (9) to (11), and calculate the advection of the fluid (gas and molten iron S) and the volume fraction, thereby considering the interaction between the flow of molten iron and the gas flow. In addition, when slag exists, the volume fraction of slag may be set, and the slag may be advected in the same way as molten iron, and the interaction between the gas flow, the flow of molten iron, and the slag flow may be considered. By considering the phases that actually exist, the calculation accuracy of the fluid flow rate can be improved. In addition, when slag exists, the amount of the auxiliary raw material charged is set as the slag amount, and the slag height is determined. In addition, when a secondary heat source 6 is installed, it is preferable to consider the flow rate or flow rate of the gas generated by the secondary heat source 6 based on the operation data. With this, the process of step S9 is completed, and the temperature measurement process proceeds to the process of step S10.

[0055]

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[0056]

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[0057]

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[0058] In the above formulas (9) to (11), α is the volume fraction of molten iron S, v a is the gas flow velocity, v m is the flow rate of molten iron S, ρ a is the density of the gas, ρ m is the density of molten iron S, μ effa is the effective viscosity coefficient of the gas, μ effm denotes the effective viscosity coefficient of molten iron S.

[0059] In the process of step S10, the temperature calculation unit 27 calculates the temperature distribution in the electric furnace by considering the heat generated by the current density distribution calculated in the process of step S8, the flow velocity distribution of the fluid calculated in the process of step S9, and the heat from the auxiliary heat source 6. Specifically, the temperature calculation unit 27 calculates the temperature distribution in the electric furnace by discretizing and numerically solving a physical equation based on the thermal advection-diffusion equation shown in the following formula (12). At this time, the heat generated by the current density distribution is given as a source term S0, and the heat from the auxiliary heat source 6 is given as a boundary condition or source term S0. The heat of the auxiliary heat source 6 may be calculated by solving a chemical reaction, or if the heat amount is known from past results, the heat amount from the past results may be given. With this, the process of step S10 is completed, and the temperature measurement process proceeds to the process of step S11.

[0060]

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[0061] In the process of step S11, the temperature calculation unit 27 outputs information on the temperature distribution of the electric furnace calculated in the process of step S10 to the display device 21. The operator refers to the information on the temperature distribution of the electric furnace displayed on the display device 21 and adjusts the current value applied to the electrodes, the heat amount of the auxiliary heat source 6, and the gas flow rate to prevent localized low temperatures from occurring in the furnace. For example, if a temperature below the minimum temperature of the molten iron S set in advance is displayed, the operator takes action to raise the temperature of the corresponding location. By displaying the temperature of the entire furnace, it is possible to improve the operating efficiency even in a large furnace where heat is likely to be unevenly distributed. In addition, it is possible to improve the production yield of the molten iron S. This completes the process of step S11, and the temperature measurement process proceeds to the process of step S12.

[0062] In the process of step S12, the temperature measuring device 20 determines whether or not to continue the temperature measurement process. If the result of the determination is that the temperature measurement process should be continued (step S12: Yes), the temperature measuring device 20 returns the temperature measurement process to the process of step S4. On the other hand, if the temperature measurement process should not be continued (step S12: No), the temperature measuring device 20 ends the series of temperature measurement processes.

[0063] As is clear from the above description, in the temperature measurement process according to one embodiment of the present invention, the electromagnetic field calculation unit 25 calculates the current density distribution and magnetic field distribution in the furnace using at least the surface level of the molten iron S in the furnace, the shape of the furnace body, and the amount of power supplied to the electrode 3, the fluid calculation unit 26 calculates the flow rate of the molten iron S and gas in the furnace using at least the magnetic field distribution in the furnace, and the temperature calculation unit 27 calculates the temperature in the furnace using at least the current density distribution in the furnace and the flow rate of the molten iron S and gas in the furnace. This makes it possible to accurately measure the temperature in the electric furnace even when the electric furnace is enlarged. In addition, by controlling the electric furnace according to the calculated temperature in the furnace, the operating efficiency of the electric furnace can be improved. In addition, by producing molten iron S by controlling the electric furnace according to the calculated temperature in the furnace, the molten iron S can be produced with a high production yield.

[0064] In this embodiment, in order to reduce the effort required for converting physical values, the same computational grid is used in the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27, but different computational grids may be used in the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27. In this case, the physical values ​​obtained in the electromagnetic field calculation unit 25 are used by interpolating them into the computational grids of the fluid calculation unit 26 and the temperature calculation unit 27. Examples of the interpolation method include linear interpolation and spline.

[0065] In the case of a large electric furnace, it is necessary to use not only arc heat but also multiple auxiliary heat sources. There are often multiple methods for keeping the temperature of the necessary points of the molten iron S above a threshold, but it is desirable to select the method that minimizes the operating cost. For this purpose, it is advisable to obtain the relationship between the input heat amount of each heat source and the operating cost, and to create an operating cost function with the input amount of each heat source as a variable. Since the operating cost varies depending on the electricity rate and the unit price of the fuel used for the auxiliary heat source, it is desirable to update the operating cost function periodically. In addition, it is advisable to set constraint conditions so that the temperature of multiple points of the molten iron S does not fall below the solidification temperature or a preset threshold value. In this case, the input amount of each heat source is set as a variable, and calculations are performed multiple times in the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27 to determine the input amount of each heat source that satisfies the constraint conditions and minimizes the operating cost. The input amount of each heat source that minimizes the operating cost is calculated using quadratic programming. As long as it can be calculated to minimize the operating cost, the calculation method for the minimum value does not matter. Alternatively, multiple input amount candidates may be set in advance, and each calculation unit may perform calculations to find the input amount that satisfies the constraints and minimizes the operating costs. By determining the heat source input amount that satisfies the necessary constraints and minimizes the operating costs, the operating efficiency of the electric furnace can be improved.

[0066] [Variation 1] FIG. 6 is a flow chart showing a flow of a modified example of the temperature measurement process shown in FIG. 4. The temperature measurement process shown in FIG. 4 is a process in which the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27 are not mutually coupled, but the temperature measurement process shown in FIG. 6 is a process in which the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27 are mutually coupled. Specifically, in the temperature measurement process shown in FIG. 6, the process after step S28 is different from the temperature measurement process shown in FIG. 4. In detail, when mutual coupling is performed, the electrical conductivity, the magnetic impermeability, the density, the viscosity, the specific heat, and the thermal conductivity, which are physical property values ​​with high temperature dependency, are repeatedly calculated in the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27. In the following, the description of the process of steps S21 to S27, which are the same as the process of steps S1 to S7 shown in FIG. 4, will be omitted, and the description will start from the process after step S28.

[0067] In the process of step S28, the calculation preparation unit 24 sets a certain physical property temperature, and calculates the electrical conductivity, magnetic permeability, density, viscosity, specific heat, and thermal conductivity according to the set physical property temperature. This completes the process of step S28, and the temperature measurement process proceeds to the process of step S29.

[0068] In the processes of steps S29 to S31, the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27 execute the same processes as the processes of steps S8 to S11 shown in Fig. 4 using the physical property values ​​calculated in the process of step S28. At this time, the electromagnetic field calculation unit 25 matches the surface level of the molten iron S and the slag height with the surface level of the molten iron S and the slag height calculated by the fluid calculation unit 26.

[0069] In the process of step S32, the temperature calculation unit 27 determines whether the temperature calculated in the process of step S31 is equal to or less than the convergence judgment threshold set in advance according to the required calculation accuracy. If the result of the determination is that the calculated temperature is equal to or less than the convergence judgment threshold (step S32: Yes), the temperature calculation unit 27 determines that the calculated temperature has converged, and advances the temperature measurement process to the process of step S33. On the other hand, if the calculated temperature is greater than the convergence judgment threshold (step S32: No), the temperature calculation unit 27 determines that the calculated temperature has not converged, and executes the processes of steps S28 to S31 again with the calculated temperature as the physical property temperature. The processes of steps S33 and S34 are the same as the processes of steps S11 and S12 shown in FIG. 4, and therefore will not be described below.

[0070] [Modification 2] FIG. 7 is a flowchart showing a flow of a modified example of the temperature measurement process shown in FIG. 4. As shown in FIG. 7, in this modified example, in the process of step S52, the calculation preparation unit 24 advances the calculation time. This makes it possible to predict the future furnace temperature and improve the operating efficiency of the electric furnace. For example, the temperature measurement device 20 predicts the furnace temperature 8 hours ahead at a predetermined time step, and displays a trend graph with the horizontal axis being time and the vertical axis being the furnace temperature on the display device 21. The trend graph may present the time course of the furnace temperature and the threshold value of the target temperature, and may present how the furnace temperature will be with respect to the future threshold value. In addition, a diagram of the furnace may be displayed to show which position of the furnace is likely to drop in temperature. The operator performs an operation to prevent the temperature from dropping based on the displayed future temperature prediction. At this time, the furnace may be locally heated using a secondary heat source, or the temperature may be adjusted by adjusting the charging interval, charging material, and charging method of the cold iron source without using a heat source. Adjusting the cold iron source takes time to change the temperature, but by checking the future predicted value, it is possible to grasp the problem in advance and take measures. If the operation method does not use a heat source, the energy consumption of the secondary heat source can be reduced and the operating efficiency of the electric furnace can be improved. Note that the processing of steps S41 to S51 shown in Fig. 7 is the same as the processing of steps S1 to S11 shown in Fig. 4.

[0071] Although the embodiments of the present invention have been described above, the present invention is not limited by the descriptions and drawings that form part of the disclosure of the present invention according to the present embodiments. In other words, other embodiments, examples, and operation techniques, etc., made by those skilled in the art based on the present embodiments are all included in the scope of the present invention. [Explanation of symbols]

[0072] 1 AC electric furnace 2 furnace 3,3a,3b,3c,3d,3e electrode 4 Refractories 5 Top lid 6 Secondary heat source 10 DC electric furnace 20 Temperature measuring device 21 Display device 22 Input Devices 23 Measuring Equipment 24 Calculation Preparation Department 25 Electromagnetic field calculation section 26 Fluid calculation section 27 Temperature calculation section 28 Memory section 29 Temperature Measurement Program S Molten iron

Claims

1. A method for measuring a temperature inside an electric furnace having electrodes for melting a metal material inside the furnace by arc discharge, comprising: an electromagnetic field calculation step of calculating a current density distribution and a magnetic field distribution in the furnace using at least the amount of molten metal in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes; a fluid calculation step of calculating flow velocities of molten metal and gas in the furnace using at least the magnetic field distribution in the furnace calculated in the electromagnetic field calculation step; a temperature calculation step of calculating a temperature in the furnace using at least the current density distribution in the furnace calculated in the electromagnetic field calculation step and the flow velocities of the molten metal and gas in the furnace calculated in the fluid calculation step; A method for measuring the temperature inside an electric furnace, comprising:

2. 2. The method for measuring temperature inside an electric furnace according to claim 1, wherein the fluid calculation step further includes a step of calculating a flow rate of gas inside the furnace using a gas flow rate of a secondary heat source equipped in the electric furnace, and the temperature calculation step further includes a step of calculating a temperature inside the furnace using a heat quantity of the secondary heat source.

3. 2. The method for measuring a temperature inside an electric furnace according to claim 1, wherein the temperature calculation step further comprises a step of calculating the temperature inside the furnace using an amount of heat radiation from a furnace body.

4. An apparatus for measuring temperature inside an electric furnace, the apparatus comprising: an electromagnetic field calculation unit that calculates a current density distribution and a magnetic field distribution in the furnace using at least the amount of molten metal in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes; a fluid calculation unit that calculates flow velocities of molten metal and gas in the furnace using at least the magnetic field distribution in the furnace calculated by the electromagnetic field calculation unit; a temperature calculation unit that calculates a temperature inside the furnace using at least the current density distribution inside the furnace calculated by the electromagnetic field calculation unit and the flow velocities of the molten metal and gas inside the furnace calculated by the fluid calculation unit; An electric furnace internal temperature measuring device.

5. A method for controlling an electric furnace, comprising the step of controlling the electric furnace according to a temperature inside the furnace calculated by the method for measuring temperature inside an electric furnace according to any one of claims 1 to 3.

6. 5. A control device for an electric furnace, comprising a control means for controlling the electric furnace in accordance with the temperature inside the furnace calculated by the furnace temperature measuring device of claim 4.

7. A program for measuring temperature inside an electric furnace having electrodes for melting a metal material inside the furnace by arc discharge, comprising: Computer, an electromagnetic field calculation unit that calculates a current density distribution and a magnetic field distribution in the furnace using at least the amount of molten metal in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes; a fluid calculation unit that calculates flow velocities of molten metal and gas in the furnace using at least the magnetic field distribution in the furnace calculated by the electromagnetic field calculation unit; a temperature calculation unit that calculates a temperature inside the furnace using at least the current density distribution inside the furnace calculated by the electromagnetic field calculation unit and the flow velocities of the molten metal and gas inside the furnace calculated by the fluid calculation unit; This is a program for measuring the temperature inside an electric furnace.

8. A computer-readable storage medium storing a program for measuring an internal temperature of an electric furnace having electrodes for melting a metal material in the furnace by arc discharge, Computer, an electromagnetic field calculation unit that calculates a current density distribution and a magnetic field distribution in the furnace using at least the amount of molten metal in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes; a fluid calculation unit that calculates flow velocities of molten metal and gas in the furnace using at least the magnetic field distribution in the furnace calculated by the electromagnetic field calculation unit; a temperature calculation unit that calculates a temperature inside the furnace using at least the current density distribution inside the furnace calculated by the electromagnetic field calculation unit and the flow velocities of the molten metal and gas inside the furnace calculated by the fluid calculation unit; A computer-readable storage medium storing a program for measuring the temperature inside an electric furnace.

9. A method for producing a metal material, comprising the step of producing a metal material by controlling an electric furnace according to a temperature inside the furnace calculated by the method for measuring temperature inside an electric furnace according to any one of claims 1 to 3.

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