Electric furnace temperature measuring method, electric furnace temperature measuring device, electric furnace control method, electric furnace control device, electric furnace temperature measuring program, computer-readable storage medium storing electric furnace temperature measuring program, and metal material manufacturing method

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, a device for measuring the temperature inside an electric furnace, a method for controlling an electric furnace, a device 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. Electric furnaces consist of a furnace that melts cold iron sources and stores the molten iron, and electrodes made of graphite or other materials. In electric furnaces, high-voltage electricity is applied to the electrodes, causing an electric current to flow through an insulating layer between the air and the furnace, generating an arc, which generates high temperatures (hereinafter, the high-temperature heat source generated by current flowing through the air layer is referred to as arc heat). The high temperatures generated by the arc heat are said to reach temperatures of several thousand to tens of thousands of degrees Celsius. This heat is then transferred to scrap or molten iron to melt the cold iron sources. To efficiently melt the cold iron sources, it is necessary to create a high-temperature environment and evenly transport heat within the furnace to transfer heat to the scrap or molten iron.

[0003] Because arc heat is generated near the electrodes due to its structure, heat distribution within the furnace can be uneven. For this reason, electric furnaces are sometimes equipped with auxiliary heat sources, such as auxiliary burners. Furthermore, if heat is not continuously supplied to the molten iron, the heat radiated outside the furnace can lower the temperature of the molten iron, causing it to solidify and causing problems in molten iron production. Therefore, it is necessary to agitate the high-temperature molten iron near the electrodes and equalize the temperature within the furnace to prevent cold spots from occurring within the molten iron. Examples of molten iron agitation methods include electromagnetic agitators that use electromagnetic force to stir the molten iron, and bottom blowers that inject gas from the bottom of the furnace and agitate the molten iron using the upward force of bubbles rising within the molten iron. Thus, in electric furnaces, it is important to generate a high-temperature environment within the furnace and transport the generated heat throughout the furnace.

[0004] On the other hand, expanding the use and efficiency of electric furnaces requires larger electric furnaces. A larger electric furnace reduces the contact area of ​​molten iron with the external environment compared to multiple small electric furnaces with the same production capacity, allowing for more efficient use of generated heat. However, when electric furnaces are enlarged, local arc heat generated near the electrodes must be transported throughout the large furnace, which can easily lead to uneven furnace temperatures. If the furnace temperature drops and the molten iron solidifies, the production efficiency of molten iron deteriorates. Furthermore, if there are areas where the furnace temperature is prone to drop, it is necessary to level the furnace temperature using a secondary heat source, a molten iron stirring device, or the like. Therefore, when enlarging electric furnaces to improve their efficiency, it is important to predict the furnace temperature and identify areas where the furnace temperature is likely to drop locally.

[0005] Against 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 temperature inside the furnace in the near future by inputting continuously measured temperatures inside the furnace and operational data such as the amount of electricity supplied and oxygen supply 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 determined 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, the method described in Patent Document 1 makes it difficult to predict the temperature inside a large-scale electric furnace. Specifically, the method described in Patent Document 1 requires that the temperature of molten iron be measured in advance. However, in a large-scale electric furnace, the temperature of the molten iron varies, and the temperature of the molten iron at a single point does not necessarily represent the temperature of the entire molten iron. Therefore, when using the method described in Patent Document 1, the temperature of the molten iron must be measured at multiple points. However, because electric furnaces are hot, it is essential to regularly update temperature measuring devices. Therefore, when measuring the temperature of molten iron at multiple points, the number of temperature measuring devices that must be regularly updated increases, significantly increasing maintenance costs.

[0008] Furthermore, because scrap, which is the source of cold iron, has a sharp shape, if a temperature measuring device is installed in a location where it may come into contact with the scrap, there is a high possibility that the sensor part of the temperature measuring device will be damaged by the scrap. If the temperature measuring device is damaged, it will be unable to measure the temperature sufficiently, making it impossible to accurately predict the temperature inside the furnace. Furthermore, as electric furnaces become larger, the voltage applied to the electrodes increases, 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 molten iron at a few points and operational data.

[0009] The present invention has been made to solve the above-mentioned 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 electric furnace temperature 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 high production 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 inside 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 inside 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 the gas flow rate inside the furnace using the 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 according to the present invention is an electric furnace temperature measuring device equipped with electrodes that melt metal material in the furnace by arc discharge, and includes an electromagnetic field calculation unit that calculates the current density distribution and 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 the temperature inside the furnace calculated by the method for measuring the 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 that melt metal material in the furnace by arc discharge, and causes a computer to function as an electromagnetic field calculation unit that calculates the current density distribution and 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 the current density distribution and 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) The method for manufacturing a metal material according to the present invention includes a step of manufacturing a metal material by controlling an electric furnace in accordance with the temperature inside the furnace calculated by the method for measuring the temperature inside an electric furnace described in any one of (1) to (3) above. [Effects of the Invention]

[0019] 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 according to the present invention enable accurate measurement of the electric furnace temperature even when the electric furnace is large. Furthermore, the electric furnace control method and control device according to the present invention enable improved operational efficiency of the electric furnace. Furthermore, the metal material manufacturing method according to the present invention enables metal materials to be manufactured with a high manufacturing yield. [Brief explanation 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 the temperature inside an electric furnace according to one embodiment of the present invention is applied. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a DC electric furnace to which a method for measuring the temperature inside an electric furnace according to one embodiment of the present invention is applied. [Figure 3] FIG. 3 is a block diagram showing the configuration of a temperature measurement device to which a method for measuring the temperature inside an electric furnace according to one embodiment of the present invention is applied. [Figure 4] FIG. 4 is a flowchart showing the flow of a temperature measurement process according to one embodiment of the present invention. [Figure 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 a flow of a modified example of the temperature measurement process shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

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

[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 the temperature inside an electric furnace according to one 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 metal, 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 to withstand high temperatures, and the top of the furnace 2 is covered with a top lid 5. A molten iron opening (not shown) for removing 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) through which auxiliary raw materials such as lime and coke are added to the molten iron S to adjust the composition of the molten iron S. The furnace 2 is provided with an auxiliary heat source 6, such as an auxiliary burner, to supplement the heat when the temperature of the cold iron source cannot be adjusted by arc discharge alone. A device having the dual functions of the auxiliary raw material inlet (not shown) and the auxiliary heat source 6 may be provided. The electrodes 3 generate arc discharge when supplied with high-voltage three-phase alternating current, and the arc heat melts the cold iron source. The electrodes 3 are attached to the upper lid 5 and are often made of graphite. The AC electric furnace 1 is provided with three electrodes 3a to 3c to utilize high-voltage three-phase alternating current.

[0025] FIG. 2 is a schematic diagram showing the configuration of a DC 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. 2, a DC electric furnace 10 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 by arc discharge, and includes a furnace 2 and electrodes 3 (3d, 3e). The furnace 2 has a configuration similar to that of the AC electric furnace 1 shown in FIG. 1. The electrode 3 generates an arc discharge when 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 lid 5 and the bottom of the furnace 2, respectively, and are often made of graphite. When a DC power source is used to supply DC current to the electrode 3, a conversion device for converting AC current to DC current is provided. The upper electrode 3d may be one or more. When there are multiple electrodes 3d, increasing the voltage of the DC current makes it easier to diffuse arc heat within the furnace, thereby increasing the melting rate of the cold iron source even when the DC electric furnace 10 is enlarged.

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

[0027] Fig. 3 is a block diagram showing the configuration of a temperature measurement device 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. 3, a temperature measurement device 20 to which a method for measuring the temperature inside an electric furnace according to one embodiment of the present invention is applied is configured by an information processing device such as a computer. A display device 21, an input device 22, and a measurement device 23 are connected to the temperature measurement 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 or 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 recording media removable from a computer include a USB (Universal Serial Bus) memory, a flexible disk, a magneto-optical disk, a CD-ROM (Compact Disc - Read Only Memory), a CD-RW (Compact Disc - Rewritable), a DVD (Digital Versatile Disc), a Blu-ray (registered trademark) Disc (BD), a DAT (Digital Audio Tape), an 8mm tape, and a memory card. A solid-state drive (SSD) can be used as both a removable storage medium and a fixed storage medium. The temperature measurement program 29 may be stored on a computer connected to a telecommunications line such as the Internet and provided by downloading it via the telecommunications line. The temperature measurement program 29 may also be provided or distributed via a telecommunications line such as the Internet.

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

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

[0033] In the processing of step S1, the calculation preparation unit 24 acquires information regarding 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 indicating the shape of the electric furnace as information regarding the shape of the electric furnace. The file format of the CAD data may be any format readable by a computer, such as STEP, IGES, or STL. Information regarding the level of the molten iron S can be acquired from the measurement device 23. If information regarding 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 processing of step S1, and the temperature measurement processing proceeds to the processing 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 tests to measure the surface level of molten iron S at several points inside 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 subsequent processes from information about 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 molten iron S into computational grids of polyhedrons, such as tetrahedrons and hexahedrons. An example of a computational grid is shown in FIG. 5. In the example shown in FIG. 5, the electric furnace containing the electrodes 3 and molten iron S is divided into multiple rectangular computational grids M. In areas where physical quantities such as the magnetic field, current, speed, and temperature are expected to change drastically, the calculation preparation unit 24 may shorten the spacing between adjacent computational grids, in other words, increase the density of the computational grids, thereby improving calculation accuracy. This completes the process of step S2, and the temperature measurement process proceeds to the process of step S3.

[0037] In the processing 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 calculations, assuming that the operating conditions of the electric furnace will not change. Examples of the operating conditions of the electric furnace that may change include the current value (amount of power supplied) applied to the electrodes 3, the heat quantity (burner heat quantity) and gas flow rate of the auxiliary heat source 6, the amount of molten iron S and slag, and the amount of heat radiation from the furnace body. Specifically, the calculation preparation unit 24 sets insulating boundary conditions in the regions other than the electrodes in the calculation grid used by the electromagnetic field calculation unit 25 for calculations. Furthermore, the calculation preparation unit 24 sets a no-slip condition in the portion of the calculation grid used by the fluid calculation unit 26 for calculations corresponding to the wall surface of the furnace 2, and a pressure constant (typically set to 0, but any value is acceptable) in the portion corresponding to the outlet.

[0038] Additionally, a boundary condition is set for the furnace periphery, allowing heat to radiate to the outside air. In this case, the boundary condition may be set by assigning a heat transfer coefficient to the outside air, or by assigning a fixed heat transfer coefficient. Because the furnace reaches high temperatures, heat is radiated to the outside air. Setting boundary conditions that take radiation into account improves prediction accuracy. Since it may be difficult to calculate the amount of heat radiated to the outside air under operating conditions, temperature sensors may be attached to the furnace exterior wall to simultaneously measure the outside air temperature. The amount of heat radiated from the furnace to the outside air may be measured in advance, and this heat radiated amount may be set as the boundary condition for the furnace exterior wall. Furthermore, the calculation preparation unit 24 sets the physical properties at the calculation points of the computational grid: the electrical conductivity and relative 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 assign physical property values ​​to each vertex of the computational grid created in the processing of step S2, or may assign physical property values ​​to 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 processing of step S4, the calculation preparation unit 24 acquires operational data of the electric furnace via the input device 22. Examples of the acquired operational 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 processing of step S4, and the temperature measurement processing proceeds to the processing of step S5.

[0040] In the process of step S5, the calculation preparation unit 24 determines whether or not the measurement device 23 stores measurement data of the furnace body temperature. If the result of the determination is that the measurement 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 measurement 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 processing of step S6, the calculation preparation unit 24 sets the measurement data (temperature boundary conditions) of the furnace body temperature acquired from the measurement device 23 as the boundary conditions of the location corresponding to the furnace body in the computational grid used for calculation by the temperature calculation unit 27. This completes the processing of step S6, and the temperature measurement processing proceeds to the processing of step S8.

[0042] In the processing of step S7, the calculation preparation unit 24 sets a fixed heat flux value as the boundary condition of the location corresponding to the furnace body in the computational grid used for calculation by the temperature calculation unit 27. This completes the processing of step S7, and the temperature measurement processing proceeds to the processing 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 Equation (5), which is based on Maxwell's equations shown in the following Equations (2) to (4), in accordance with 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 equations (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) in accordance with 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 equation of continuity (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 velocity of molten iron S, a multiphase flow calculation method such as the Volume of Fluid (VOF) method may be used. The volume fraction of molten iron S may be set for each computational grid, as shown in Equations (9) to (11), and the advection of fluids (gas and molten iron S) and their volume fractions may be calculated to account for the interaction between the molten iron flow and the gas flow. If slag is present, a slag volume fraction may be set and the slag may be advected in the same way as molten iron, thereby accounting for the interaction between the gas flow, molten iron flow, and slag flow. Accounting for the actual phases improves the accuracy of the fluid flow velocity calculation. If slag is present, the amount of auxiliary raw material input is used as the slag amount, and the slag height is determined. If a secondary heat source 6 is installed, the flow rate or velocity of the gas generated by the secondary heat source 6 may be considered based on operational data. This completes step S9, and the temperature measurement process proceeds to 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 step S10, the temperature calculation unit 27 calculates the temperature distribution in the electric furnace by taking into account the heat generated by the current density distribution calculated in step S8, the fluid flow velocity distribution calculated in step S9, and the heat from the secondary 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 equation (12). In this case, the heat generated by the current density distribution is given as a source term S0, and the heat from the secondary heat source 6 is given as a boundary condition or source term S0. The heat from the secondary heat source 6 may be calculated by solving a chemical reaction, or if the heat amount is known from past performance, the past performance heat amount may be used. This completes step S10, and the temperature measurement process proceeds to step S11.

[0060]

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[0061] In step S11, the temperature calculation unit 27 outputs information about the temperature distribution of the electric furnace calculated in step S10 to the display device 21. The operator refers to the information about the temperature distribution of the electric furnace displayed on the display device 21 and adjusts the current value applied to the electrodes, the heat quantity 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 a preset minimum temperature for molten iron S is displayed, the operator takes action to raise the temperature of the corresponding location. Displaying the temperature of the entire furnace can improve operational efficiency even in large furnaces where heat is likely to be unevenly distributed. It can also improve the production yield of molten iron S. This completes step S11, and the temperature measurement process proceeds to 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 molten iron S in the furnace, the shape of the furnace body, and the amount of power supplied to the electrodes 3; the fluid calculation unit 26 calculates the flow rate of 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 and the flow rate of molten iron S and gas in the furnace. This allows the temperature in the electric furnace to be measured accurately even when the electric furnace is large. Furthermore, by controlling the electric furnace according to the calculated temperature in the furnace, the operating efficiency of the electric furnace can be improved. Furthermore, 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, fluid calculation unit 26, and temperature calculation unit 27, but different computational grids may be used in the electromagnetic field calculation unit 25, fluid calculation unit 26, and temperature calculation unit 27. In this case, the physical values ​​determined in the electromagnetic field calculation unit 25 are interpolated into the computational grids of the fluid calculation unit 26 and temperature calculation unit 27 and then used. Examples of the interpolation method include linear interpolation and spline.

[0065] Large electric furnaces require the use of multiple secondary heat sources in addition to arc heat. While there are often multiple methods for maintaining the temperature of the required points of molten iron S above a threshold, it is desirable to select the method that minimizes operating costs. To achieve this, it is advisable to determine the relationship between the heat input of each heat source and operating costs and create an operating cost function with the input amount of each heat source as a variable. Because operating costs fluctuate depending on electricity rates and the unit price of fuel used for secondary heat sources, it is desirable to periodically update the operating cost function. It is also advisable to set constraints so that the temperatures of multiple points of molten iron S do not fall below the solidification temperature or a predetermined threshold. In this case, the input amount of each heat source is set as a variable, and multiple calculations are performed in the electromagnetic field calculation unit 25, fluid calculation unit 26, and temperature calculation unit 27 to determine the input amount of each heat source that satisfies the constraints and minimizes operating costs. The input amount of each heat source that minimizes operating costs is calculated using quadratic programming. As long as the calculation minimizes operating costs, any calculation method is acceptable. Alternatively, multiple input amount candidates can be set in advance, and each calculation unit can perform calculations to find the input amount that satisfies the constraints and minimizes the operating cost. By determining the heat source input amount that satisfies the necessary constraints and minimizes the operating cost, the operating efficiency of the electric furnace can be improved.

[0066] [Variation 1] FIG. 6 is a flowchart showing 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. However, 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 from step S28 onward differs from the temperature measurement process shown in FIG. 4. In more detail, when mutual coupling is performed, the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27 repeatedly calculate the electrical conductivity, magnetic impermeability, density, viscosity, specific heat, and thermal conductivity, which are physical properties that are highly temperature-dependent. In the following, a description of steps S21 to S27, which are the same as steps S1 to S7 shown in FIG. 4, will be omitted, and the description will begin with step S28 onward.

[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 processing of steps S29 to S31, the electromagnetic field calculation unit 25, the fluid calculation unit 26, and the temperature calculation unit 27 use the physical property values ​​calculated in the processing of step S28 to perform the same processing as the processing of steps S8 to S11 shown in Fig. 4. 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 a convergence determination 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 determination threshold (step S32: Yes), the temperature calculation unit 27 determines that the calculated temperature has converged, and proceeds with the temperature measurement process to the process of step S33. On the other hand, if the calculated temperature is greater than the convergence determination threshold (step S32: No), the temperature calculation unit 27 determines that the calculated temperature has not converged, and performs the processes of steps S28 to S31 again, assuming that the calculated temperature is 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] [Variation 2] FIG. 7 is a flowchart showing a modified example of the temperature measurement process shown in FIG. 4. As shown in FIG. 7, in this modified example, the calculation preparation unit 24 advances the calculation time in step S52. This allows for prediction of future furnace temperatures, which can be used to improve the operational efficiency of the electric furnace. For example, the temperature measurement device 20 predicts the furnace temperature for the next eight hours at a predetermined time interval and displays a trend graph on the display device 21, with the horizontal axis representing time and the vertical axis representing furnace temperature. The trend graph may display the furnace temperature over time and the target temperature threshold, and show how the furnace temperature will change relative to the future threshold. A diagram of the furnace may also be displayed, along with a diagram of the furnace. The operator performs operations to prevent the temperature from decreasing based on the displayed future temperature prediction. In this case, the furnace may be locally heated using a secondary heat source, or the temperature may be adjusted by adjusting the charging interval, material, and charging method of the cold iron source without using a heat source. While adjusting the cold iron source takes time to change the temperature, checking the future prediction allows for early identification of problems and appropriate countermeasures. 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 present invention has been described above as an embodiment, the present invention is not limited to the descriptions and drawings that form part of the disclosure of the present invention. In other words, other embodiments, examples, and operational techniques that can be made by those skilled in the art based on the present invention 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 equipped with electrodes that melt 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 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 the molten metal and gas inside the furnace calculated in the fluid calculation step; A method for measuring the temperature inside an electric furnace, including:

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 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 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 a heat radiation amount from the furnace body.

4. An apparatus for measuring temperature inside an electric furnace, the apparatus comprising: electrodes for melting a metal material inside the furnace by arc discharge; 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; a temperature calculation unit that calculates the 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 temperature measuring device equipped with the above.

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

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

7. A program for measuring the temperature inside an electric furnace equipped with electrodes that melt a metal material inside 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 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; a temperature calculation unit that calculates the 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 the temperature inside an electric furnace equipped with electrodes that melt a metal material inside 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 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; a temperature calculation unit that calculates the 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 manufacturing a metal material, comprising the step of manufacturing a metal material by controlling an electric furnace in accordance with the temperature inside the furnace calculated by the method for measuring the temperature inside an electric furnace according to any one of claims 1 to 3.

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