Arc Electric Furnace Energization State Determination Device, Arc Electric Furnace Operation Method, and Arc Electric Furnace

Abstract

Provided is a technology that enables rapid determination of the energization status within an electric arc furnace and enables stable furnace condition assessment without being affected by dust. The present invention is an energization state determination device for an electric arc furnace, the device comprising: a detection means for detecting sound produced within the electric arc furnace; an output means for analyzing the frequency of the detected sound and outputting a frequency / acoustic pressure signal; and a determination means for determining the state of coverage of an arc formed by slag formation, on the basis of signal intensities for detected sounds of a frequency selected from a range 500-1500 Hz inclusive, a prescribed frequency range, or a plurality of frequencies. The present invention is also a method for producing molten steel by: controlling one of, or a combination of two or more of, a supply speed of an oxygen-containing gas, a carbon material supply quantity, and a slag formation material loading quantity, on the basis of the energization state determined using the energization state determination device; and melting and refining scrap by using the electric arc furnace.

Description

Technical Field

[0001] The present invention relates to an apparatus for determining an energization state from the in-furnace generated sound of an arc electric furnace, an operation method of an arc electric furnace using the apparatus, and an arc electric furnace equipped with the apparatus.

Background Art

[0002] An arc electric furnace is an electric furnace that generates an arc between an electrode and a charge in the furnace and heats and melts it. Generally, since the temperature of the arc exceeds 2000°C, the heat loss due to radiation is large. In order to reduce this heat loss due to 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 that slag is forming in the furnace. In addition, slag forming also has the effect of reducing the entrainment of air into the molten steel and can also suppress the nitriding reaction of the molten steel. Therefore, in order to produce high-quality molten steel, it is also important to maintain the slag forming state.

[0003] Against such a background, various in-furnace forming detection techniques have been studied so far. In the technique described in Patent Document 1, a method of detecting the forming 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 of directly monitoring the slag height in the furnace by using microwaves is disclosed. In addition, in the technique described in Patent Document 3, a method of measuring the vibration and sound of the furnace body and indirectly estimating the forming state is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the prior art has the following problems. In the method described in Patent Document 1, since the determination is made using the components in the exhaust gas, it takes time from the timing when the energization status in the furnace changes to the detection of the exhaust gas components, and there is a problem that real-time slag forming control is difficult.

[0006] In the method described in Patent Document 2, when the amount of dust generated in the furnace is large, noise is superimposed on the signal, and there is a problem that the forming status cannot be stably detected.

[0007] In the method described in Patent Document 3, it can be detected relatively quickly and is less affected by dust in the furnace. However, in the frequency measurement of 500 Hz or less, the influence of the sound in the factory other than the arc sound is large, and there is a problem that a stable furnace condition determination cannot be made.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide an energization state determination device for an arc electric furnace, an operation method for an arc electric furnace, and an arc electric furnace that can quickly determine the energization status in the furnace and stably determine the furnace condition without being affected by dust.

Means for Solving the Problems

[0009] In order to solve the above problems, the inventors focused on the fact that when the forming state cannot be maintained and the energization status deteriorates, an insulation breakdown sound at a high frequency of about 1000 Hz is generated, and as a result of repeated intensive studies, the present invention has been completed.

[0010] The energization state determination device for an arc electric furnace according to the present invention, which advantageously solves the above problems, comprises: a detection means for detecting the in-furnace generated sound of the arc electric 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 coating state of the arc by slag formation based on the signal intensity of the detected sound at one selected from 500 Hz or more and 1500 Hz or less, a predetermined frequency range, or a plurality of frequencies.

[0011] Note that the energization state determination device for an arc electric furnace according to the present invention (a) the determination means determines the in-furnace slag formation state based on the sum or average of the signal intensities of the detected sound in a predetermined frequency range selected from 500 Hz or more and 1500 Hz or less, or a plurality of frequencies; (b) the determination means determines the in-furnace slag formation state except for the main raw material and auxiliary raw material charging execution time of the arc electric furnace; etc. can be more preferable solution means.

[0012] The operation method of the arc electric furnace according to the present invention, which advantageously solves the above problems, when melting and refining scrap in an arc electric furnace to produce molten steel, controls any one or a combination of a plurality of the supply rate of the oxygen-containing gas, the carbon material supply amount, and the slag-forming material input amount based on the energization state determined using any of the above devices.

[0013] The arc electric furnace according to the present invention, which advantageously solves the above problems, is characterized by comprising any of the above devices.

Effects of the Invention

[0014] According to the energization state determination device, the operation method, and the arc electric furnace of the present invention, the energization situation in the furnace can be quickly determined, and the furnace condition can be stably determined without being affected by dust. Therefore, the power consumption per unit of the arc electric furnace can be reduced, which is industrially useful.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be specifically described. The following embodiments illustrate facilities and methods for embodying the technical idea of the present invention, and do not specify the configuration as the following. That is, the technical idea of the present invention can be variously modified within the technical scope described in the claims.

[0017] The energization state determination device of the arc electric furnace according to the present embodiment (hereinafter referred to as "the present device") includes a microphone for sound collection as a detection means for detecting the sound generated inside the arc electric furnace. As the arc electric furnace, an AC type or a DC type can be applied. Further, the present device includes output means for analyzing the frequency of the detected sound and outputting a frequency-intensity signal. This function can be realized by hardware or software such as a computer. The microphone can be placed anywhere as long as the sound inside the electric furnace can be heard. It is not necessary to place it near the high-temperature electric furnace. Further, the present device includes determination means. This function can also be realized by hardware or software such as a computer.

[0018] First, in order to eliminate the influence of sounds unrelated to forming that occur inside the building, the frequency to be measured is set to a predetermined frequency value or a predetermined frequency range within the range of 500 Hz or more and 1500 Hz or less. Fourier transform may be performed on the measured sound, or a low-pass filter and a high-pass filter may be used. When Fourier transform is performed, the sum or average of the signal values of a plurality of frequencies among the frequencies of 500 Hz or more and 1500 Hz or less may be used for determination. Also, in the above determination, by excluding the main raw material and auxiliary raw material input execution time from the determination, the furnace condition can be determined more stably.

[0019] The following will be described in detail. Prior to the invention, the inventors measured the frequency of the dielectric breakdown sound that occurs when forming is unstable and the energization state deteriorates. As a result, it was found that it occurs between 500 Hz and 1500 Hz. Also, it was found that the sound above 1500 Hz has a large attenuation and cannot be measured stably. Therefore, it is possible to determine the furnace condition by using the total value of the electrical signals caused by the sound pressure applied to one or a plurality of frequencies among 500 Hz or more and 1500 Hz or less. In particular, the dielectric breakdown sound is concentrated between 800 Hz and 1000 Hz, and it is preferable that a part of the measurement frequencies be between 800 Hz and 1000 Hz. FIG. 1 shows the sound pressure fluctuation at 875 Hz when the dielectric breakdown sound occurs. When the dielectric breakdown sound occurs, it shows a large sound pressure value. For example, by setting a sound pressure of 1 Pa as the threshold value, it is possible to detect the dielectric breakdown sound. This threshold value varies depending on the magnitude of the input and the installation position of the microphone.

[0020] On the one hand, when measuring the frequency of the charging sound generated when the main raw material and auxiliary raw materials are charged, it was found that it is around 1000 Hz. Since this frequency also varies depending on the type and size of the input materials, etc., it becomes a sound with a wide frequency range. Therefore, it is difficult to separate the charging sound and the insulation breakdown sound only by frequency analysis. Fig. 2 shows the sound pressure at 875 Hz when the scrap, which is 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, in Fig. 2, the main raw material was charged in the time zone indicated by SC. That is, it is easy to exclude only the timing when the charging sound occurs in advance and perform the determination, and the furnace condition determination accuracy can be improved.

Example

[0021] Electric melting was carried out in an arc furnace with a hot water output of 150 t scale to evaluate the effects of the above embodiment. The electric furnace used in this example 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.

[0022] The operation pattern is carried out in the following steps. First, the iron source and auxiliary raw materials are charged into the furnace. In the electric furnace used in this example, the operation is carried out leaving about 80 t of molten steel for the next charge, and the iron source and auxiliary raw materials are charged into the molten steel. Examples of the iron source include scrap, pig iron, and reduced iron. Also, examples of the auxiliary raw materials include carbonaceous materials, MgO sources for refractory protection, and lime for slag composition adjustment. After the materials are charged or during the charging process, power supply is started and oxygen and carbon are blown in. Then, the iron source is sequentially charged, and when the amount of molten steel in the furnace reaches approximately 230 t, the molten steel temperature is adjusted to about 1600 °C and tapping is carried out. The tapping amount is targeted at 150 t, leaving about 80 t in the furnace and shifting to the next charge again.

[0023] A microphone for sound collection was installed in the same building as the above electric furnace. This microphone is installed approximately 10 m away from the electric furnace. The acoustic data measured by this microphone was Fourier-transformed using an FTT analyzer and decomposed into sound pressure for each frequency. The frequency width at this time was set to 25 Hz, and the average values of the sound pressure at 850 Hz, 875 Hz, and 900 Hz were output to a monitor in the electric furnace operation room. The sound at this frequency was regarded as abnormal noise. While monitoring this abnormal noise, the oxygen supply rate, carbon material injection rate, and slag-forming material addition rate were adjusted through trial and error so that the sound pressure value did not exceed 1 Pa. Lime was used as the slag-forming material. Note that the same frequency sound is generated during the charging of the iron source. During that period, it was not determined as abnormal noise and was excluded from the above adjustments.

[0024] During operation, the ratio of the time excluding the iron source charging time to the time when the sound pressure of the abnormal noise exceeded 1 Pa with respect to the energization time was defined as the abnormal noise detection time rate (%), and the relationship between the index of the power consumption unit and the abnormal noise detection time rate is shown in Fig. 3. The power consumption unit is normalized with the average value of all data being 1.0. As the abnormal noise detection time rate decreases, the power consumption unit decreases. Thus, by operating while monitoring the abnormal noise, the energization efficiency was improved and the power consumption unit was reduced. This is because the slag-forming state was maintained during energization and the radiant heat from the arc was shielded by the slag.

[0025] In this specification, the mass unit "t" is 10 3 kg.

Industrial Applicability

[0026] The molten iron produced by the arc electric furnace and its operation method according to the present invention is less likely to absorb nitrogen, so it is also useful as a method for obtaining high-purity molten iron. Further, according to the arc electric furnace and its operation method according to the present invention, the unexpected energization of the arc to the furnace wall composed of refractories and water-cooled panels is reduced, which also contributes to improving the life of the furnace body.

Claims

1. detection means for detecting the in-furnace generated sound of an arc furnace; output means for analyzing the frequency of the detected sound and outputting a frequency-sound pressure signal; determination means for determining the coating state of the arc by slag formation based on the signal intensity of the detected sound of one selected from 800 Hz or more and 1000 Hz or less, a predetermined frequency range, or a plurality of frequencies; An energization state determination device for an arc furnace, comprising the above.

2. The determination means determines the slag formation state in the furnace based on the sum or average of the signal intensities of the detected sound in a predetermined frequency range selected from 800 Hz or more and 1000 Hz or less, or a plurality of frequencies. The energization state determination device for an arc furnace according to Claim 1.

3. The determination means determines the slag formation state in the furnace except for the main raw material and auxiliary raw material charging execution time of the arc furnace. The energization state determination device for an arc furnace according to Claim 1.

4. When melting and refining scrap in an arc furnace to produce molten steel, Based on the energization state determined using the device according to any one of Claims 1 to 3, any one of the supply rate of oxygen-containing gas, the amount of carbonaceous material supplied, and the amount of slag-forming material charged, or a combination of a plurality of them is controlled. An operation method for an arc furnace.

5. An arc furnace comprising the device according to any one of Claims 1 to 3.

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