Electric arc furnace energization state determination device, electric arc furnace operation method, and electric arc furnace

Abstract

Provided is a technique with which it is possible to quickly determine the energization state in an electric arc furnace and to stably determine the furnace condition without being affected by dust. A power-on state determination device for an electric arc furnace is provided with: a detection means for detecting sound generated in the electric arc furnace; an output means for analyzing the frequency of the detected sound and outputting a frequency-sound pressure signal; and a determination means for determining the coverage state of an arc caused by slag formation on the basis of the signal strength of the detected sound in one predetermined frequency range selected from 500 Hz to 1500 Hz or in a plurality of frequencies. A method for producing molten steel by melting and refining waste material in an electric arc furnace controls any one of the oxygen-containing gas supply rate, the carbon material supply amount, and the slag-making material input amount, or a combination of a plurality thereof, on the basis of the energization state determined by the device.

Description

Technical Field

[0001] The present invention relates to an apparatus for determining an energized state based on sound generated inside an electric arc furnace, a method for operating an electric arc furnace using the apparatus, and an electric arc furnace equipped with the apparatus. Background Art

[0002] An electric arc furnace is an electric furnace that generates an arc between an electrode and a charge inside the furnace and heats and melts it. Generally, the temperature of the arc exceeds 2000°C, so the heat loss caused by radiation is large. In order to reduce the heat loss caused by this radiation, it is known that it is effective to shield the arc light by forming slag. Therefore, in order to improve the energization efficiency, it is important to detect the situation of slag formation inside the furnace. In addition, slag forming also has the effect of reducing the entrainment of the atmosphere into the molten steel and can also suppress the nitrogen absorption reaction into the molten steel. Therefore, in order to produce high-quality molten steel, it is also important to maintain the slag formation state.

[0003] Based on such a background, various techniques for detecting slag formation inside an electric furnace have been studied so far. In the technique described in Patent Document 1, a method for detecting the slag formation state during energization by monitoring the NOx concentration in the exhaust gas is disclosed. In addition, in the technique described in Patent Document 2, a method for directly monitoring the slag height inside the furnace by using microwaves is disclosed. In addition, in the technique described in Patent Document 3, a method for measuring the vibration and sound of the furnace body and indirectly estimating the slag formation state is disclosed.

[0004] [Prior Art Documents]

[0005] [Patent Documents]

[0006] Patent Document 1: Japanese Patent Laid-Open No. 10-226812

[0007] Patent Document 2: Japanese Patent Laid-Open No. 07-166222

[0008] Patent Document 3: Japanese Patent Laid-Open No. 2013-170748 Summary of the Invention

[0009] However, in the prior art, there are the following problems.

[0010] In the method described in Patent Document 1, since the components in the exhaust gas are used for determination, it takes time from the moment when the energization state inside the furnace changes to the detection of the exhaust gas components, and there is a problem that it is difficult to perform real-time slag formation control.

[0011] In the method described in Patent Document 2, when the amount of dust generated inside the furnace is large, noise is superimposed on the signal, and therefore there is a problem that it is impossible to stably detect the slag formation state.

[0012] In the method described in Patent Document 3, although detection can be performed relatively quickly and it is not easily affected by dust in the furnace, in frequency measurements below 500 Hz, the influence of sounds in the factory other than the arc sound is large, and there is a problem that stable determination of the furnace condition cannot be performed.

[0013] The present invention has been completed in view of the above circumstances, and an object thereof is to provide an energization state determination device for an electric arc furnace, an operation method for an electric arc furnace, and an electric arc furnace that can quickly determine the energization state in the furnace and can stably determine the furnace condition without being affected by dust.

[0014] [Means for Solving the Problem]

[0015] In order to solve the above problems, the inventor focused on the fact that the slag-making state cannot be maintained and an insulation breakdown sound of about 1000 Hz is generated when the energization state deteriorates, and conducted in-depth research repeatedly, and as a result, the present invention was completed.

[0016] The energization state determination device for an electric arc furnace of the present invention that effectively solves the above problems is characterized by including: a detection unit that detects sounds generated in the furnace of the electric arc furnace; an output unit that analyzes the frequency of the detected sound and outputs a frequency-sound pressure signal; and a determination unit that determines the covering state of the arc caused by slag-making based on the signal intensity of the detected sound in one specified frequency range or a plurality of frequencies selected from 500 Hz or more and 1500 Hz or less.

[0017] It should be noted that in the energization state determination device for an electric arc furnace of the present invention, the following (a), (b), etc. can be more preferable solutions.

[0018] (a) The determination unit determines the slag-making state in the furnace based on the sum or average of the signal intensities of the detected sounds in a specified frequency range or a plurality of frequencies selected from 500 Hz or more and 1500 Hz or less.

[0019] (b) The determination unit determines the slag-making state in the furnace excluding the implementation time of charging the main raw material and auxiliary raw material of the electric arc furnace.

[0020] The operation method for an electric arc furnace of the present invention that effectively solves the above problems, when melting and refining waste materials to produce molten steel in an electric arc furnace, controls any one of the supply rate of oxygen-containing gas, the supply amount of carbon material, and the input amount of slag-making material or controls a combination of a plurality of them based on the energization state determined using any of the above devices.

[0021] The electric arc furnace of the present invention that effectively solves the above problems is characterized by including any of the above devices.

[0022] [Effects of the Invention]

[0023] The energization state determination device for an electric arc furnace, the operation method for an electric arc furnace, and the electric arc furnace according to the present invention can quickly determine the energization condition inside the furnace and can stably determine the furnace condition without being affected by dust. Therefore, it is possible to reduce the power consumption rate of the electric arc furnace and is industrially useful. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a graph showing the sound pressure variation at 875 Hz when insulation breakdown occurs in the electric arc furnace according to an embodiment of the present invention.

[0025] Figure 2 It is a graph showing the sound pressure variation at 875 Hz when the main raw material is charged into the electric arc furnace according to the above embodiment.

[0026] Figure 3 It is a graph showing the relationship between the abnormal sound detection time rate where the average value of the specified sound pressure is 1 Pa or more and the index of the power consumption rate in the electric arc furnace according to the above embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] Hereinafter, embodiments of the present invention will be specifically described. The following embodiments illustrate devices and methods for embodying the technical idea of the present invention and do not specify the structure as the following structure. That is, various changes can be made to the technical concept of the present invention within the technical scope described in the claims.

[0028] The energization state determination device (hereinafter referred to as "this device") of the electric arc furnace according to this embodiment includes a sound collection microphone as a detection unit for detecting the sound generated inside the electric arc furnace. As the electric arc furnace, an AC type or a DC type can be used. In addition, this device includes an output unit that analyzes the frequency of the detected sound and outputs a frequency-intensity signal. This function can be achieved by hardware or software such as a computer. The microphone can be placed anywhere as long as it can hear the sound inside the electric furnace. It does not need to be placed near the electric furnace that becomes high temperature. In addition, this device includes a determination unit. This function can also be achieved by hardware or software such as a computer.

[0029] First, in order to exclude the influence of sounds generated inside the building that are not related to slag formation, the measured frequency is determined as a specified frequency value or a specified frequency width in the range of 500 Hz or more and 1500 Hz or less. Fourier transform can be performed on the measured sound, or a low-pass filter and a high-pass filter can be used. In the case of performing Fourier transform, the sum or average of the signal values of multiple frequencies in the range of 500 Hz or more and 1500 Hz or less can also be used for determination. In addition, in the above determination, by excluding the main raw material and the auxiliary raw material input implementation time from the determination, the furnace condition can be determined more stably.

[0030] The following is a detailed description.

[0031] Before the invention, the inventor measured the frequency of the insulation breakdown sound generated when the foaming was unstable and the energization state deteriorated. As a result, it was found that it occurred between 500 Hz and 1500 Hz. In addition, it was also found that the attenuation of the sound above 1500 Hz was large and it could not be measured stably. Therefore, by using the sum value of the electrical signals caused by the sound pressure of one frequency or a plurality of frequencies between 500 Hz and 1500 Hz, the furnace condition can be judged. In particular, the insulation breakdown sound is concentrated between 800 Hz and 1000 Hz, and preferably a part of the measurement frequencies is between 800 Hz and 1000 Hz. Figure 1 It shows the sound pressure change at 875 Hz when the insulation breakdown sound occurs. When the insulation breakdown sound is generated, a large sound pressure value is shown. For example, by taking 1 Pa of sound pressure as the threshold value, the insulation breakdown sound can be detected. This threshold value varies according to the input size and the microphone installation position.

[0032] On the other hand, the frequency of the charging sound generated when the main raw material and the auxiliary raw material are charged is measured, and the result is found to be around 1000 Hz. This frequency varies according to the type and size of the input material, etc., so it becomes a sound with a large frequency range. Therefore, it is difficult to separate the charging sound and the insulation breakdown sound only by frequency analysis. Figure 2 It shows the sound pressure at 875 Hz when the waste material as the main raw material is charged. However, since the charging time is determined in advance or manually determined, it can be easily grasped. For example, Figure 2 The main raw material is charged during the time period represented by SC in

[0033] [Embodiment]

[0034] Electric melting is carried out in an electric arc furnace with a tapping volume of 150 t to evaluate the effects of the above-mentioned embodiments. The electric furnace used in this embodiment is equipped with a water-cooled oxygen lance and a carbon injection lance, and oxygen and carbon materials can be blown into the furnace respectively.

[0035] The operation mode is carried out in the following steps. First, a iron source and auxiliary raw materials are charged into the furnace. In the electric furnace used in this embodiment, about 80 t of molten steel is left for the next charging operation, and the iron source and auxiliary raw materials are charged into this molten steel. Examples of the iron source include scrap, pig iron, reduced iron, etc. In addition, examples of the auxiliary raw materials include carbon addition materials, MgO sources for refractory protection, lime for adjusting the slag composition, etc. After charging the materials or during the charging process, power is supplied, and oxygen and carbon are blown in. Then, the iron source is successively charged. When the amount of molten steel in the furnace reaches approximately 230 t, the temperature of the molten steel is adjusted to about 1600 °C, and tapping is carried out. The tapping amount is targeted at 150 t, and about 80 t remains in the furnace and is transferred to the next charging again.

[0036] A microphone for sound collection is provided in the same building as the above-mentioned electric furnace. The microphone is provided at a distance of about 10 m from the electric furnace. The sound data measured by this microphone is Fourier-transformed using an FTT analyzer and decomposed into sound pressures for each frequency. At this time, the frequency width is set to 25 Hz, and the average value of the sound pressures at 850 Hz, 875 Hz, and 900 Hz is output to the monitor in the electric furnace operation room. The sound of this frequency is set as an abnormal sound. While monitoring this abnormal sound, the oxygen supply rate, carbon material blowing rate, and slag-making material addition rate are adjusted on a trial-and-error basis so that the sound pressure value does not exceed 1 Pa. Lime is used as the slag-making material. It should be noted that the same frequency sound is generated during the charging of the iron source. During this period, it is not determined as an abnormal sound and is not the object of the above adjustment.

[0037] The ratio of the time other than the iron source charging time to the energization time during operation when the sound pressure of the abnormal sound exceeds 1 Pa is defined as the abnormal sound detection time rate (%). The relationship between the index of the power consumption rate and the abnormal sound detection time rate is shown in Figure 3 . The power consumption rate is indexed with the average value of all data being 1.0. As the abnormal sound detection time rate decreases, the power consumption rate decreases. Thus, by operating while monitoring the abnormal sound, the energization efficiency is improved and the power consumption rate is reduced. This is because the slag-making state is maintained during energization, and the radiant heat from the arc can be shielded by the slag.

[0038] In this specification, the unit of mass [t] is 10 3 kg.

[0039] [Industrial Applicability]

[0040] The hot metal produced by the electric arc furnace and its operation method of the present invention is useful as a method for obtaining high-purity hot metal because it is not easily nitrogen-absorbing. In addition, according to the electric arc furnace and its operation method of the present invention, the unexpected arc energization to the furnace wall composed of refractory materials or water-cooled plates is reduced, so it also contributes to the improvement of the furnace body life.

Claims

1. An energization state determination device for an electric arc furnace, comprising: A detection unit that detects the sound generated inside the electric arc furnace; An output unit that analyzes the frequency of the detected sound and outputs a frequency-sound pressure signal; And A determination unit that determines the covering state of the arc caused by slag formation based on the signal intensity of the detected sound within one specified frequency range or multiple frequencies selected from 500 Hz or more and 1500 Hz or less.

2. The energization state determination device for an electric arc furnace according to claim 1, wherein The determination unit determines the slag formation state inside the furnace based on the sum or average of the signal intensities of the detected sound within the specified frequency range or multiple frequencies selected from 500 Hz or more and 1500 Hz or less.

3. The energization state determination device for an electric arc furnace according to claim 1, wherein The determination unit determines the slag formation state inside the furnace excluding the implementation time of charging the main raw material and auxiliary raw material of the electric arc furnace.

4. An operation method for an electric arc furnace, when melting and refining scrap to produce molten steel in the electric arc furnace, Based on the energization state determined by using the device according to any one of claims 1 to 3, control is performed on any one of the supply rate of the oxygen-containing gas, the supply amount of the carbon material, and the input amount of the slag-forming material, or multiple combinations thereof are controlled.

5. An electric arc furnace, comprising the device according to any one of claims 1 to 3.

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