Apparatus for determining energization state of alternating current arc furnace, operation method of alternating current arc furnace, and alternating current arc furnace

Abstract

Provided is a technology which can rapidly determine an energized state inside an alternating current arc electric furnace and stably determine a furnace condition without being affected by dust. This device for determining an energized state of an alternating current arc electric furnace comprises: a detection means which detects a generated in-furnace sound of the alternating current arc electric furnace; an output means which analyzes frequencies of the detected sound and outputs a frequency-sound pressure signal; and a determination means which, when a frequency of an integer multiple of a fundamental frequency F0 of the alternating current arc electric furnace is set as Fi, determines a coating state of the arc caused by slag foaming on the basis of the signal intensity in a range from Fi-0.5×F0 to Fi+0.5×F0. According to the present invention, with an operation method, a molten steel is manufactured by controlling, on the basis of the energized state determined by using the device, a combination of a supply speed of an oxygen-containing gas, and one or a plurality of a charcoal material supply amount, and a charging amount of a slag-making material, and dissolving and refining scraps in the alternating current arc electric furnace.

Description

Technical Field

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

Background Art

[0002] An arc-type electric furnace is a furnace that generates an arc between an electrode and a charge in the furnace to heat and melt 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. Further, slag formation 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. From this, in order to produce high-quality molten steel, it is also important to maintain the slag formation 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. Further, in the technique described in Patent Document 2, a method of directly monitoring the slag height in the furnace by using microwaves is disclosed. Further, 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 state 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 state cannot be stably detected.

[0007] In the method described in Patent Document 3, it can be detected relatively quickly and is not easily 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 energization state determination device for an alternating current arc electric furnace, an operation method for an alternating current arc electric furnace, and an alternating current arc type electric furnace that can quickly determine the energization state in the furnace and stably determine the furnace condition without being affected by dust are provided. The purpose is.

MEANS FOR SOLVING THE PROBLEMS

[0009] The energization state determination device for an alternating current arc electric furnace according to the present invention that advantageously solves the above problems includes a detection means for detecting the sound generated in the furnace of the alternating current arc electric furnace, an output means for analyzing the frequency of the detected sound and outputting a frequency-sound pressure signal, and when the frequency that is an integer multiple of the fundamental frequency F0 of the alternating current arc electric furnace is Fi, based on the signal intensity in the range from Fi - 0.5×F0 to Fi + 0.5×F0, and a determination means for determining the coating state of the arc due to slag forming, and is characterized by comprising.

[0010] Note that the energization state determination device for an AC arc furnace according to the present invention (a) When the determination means sets the frequency that is an integer multiple of the fundamental frequency F0 as Fi, the determination is made based on the signal intensity of the center frequency in the range from Fi - 0.5×F0 to Fi + 0.5×F0. (b) When the determination means sets the frequency that is an integer multiple of the fundamental frequency F0 as Fi, the determination is made based on the intensity ratio between the signal intensity of one of the higher frequencies and the signal intensity of one of the lower frequencies in the range from Fi - 0.5×F0 to Fi + 0.5×F0. (c) The difference between the two frequencies for obtaining the intensity ratio is 10 Hz or more and 40 Hz or less. etc. can be more preferable solution means.

[0011] The operation method of the AC arc furnace according to the present invention that advantageously solves the above problems is, when melting and refining scrap to produce molten steel in an AC arc furnace, based on the energization state determined using any of the above devices, controlling any one of, or a combination of, the supply rate of the oxygen-containing gas, the carbon material supply amount, and the slag-forming material input amount.

[0012] The AC arc furnace according to the present invention that advantageously solves the above problems is characterized by comprising any of the above devices.

Effects of the Invention

[0013] According to the energization state determination device, the operation method, and the AC arc furnace of the AC arc furnace according to 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 AC arc furnace can be reduced, which is industrially useful.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0015] 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.

[0016] The energization state determination device of the alternating current arc furnace according to this embodiment (hereinafter referred to as "this device") includes a microphone for sound collection as a detection means for detecting the sound generated inside the alternating current arc furnace. Further, this 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 such as a computer or software. 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, this device includes determination means for the energization state. This function can also be realized by hardware such as a computer or software.

[0017] First, measure the sound of the frequency caused by alternating current power. The intensity of the sound pressure of a predetermined frequency may be directly measured, or the sound pressure fluctuation may be measured and then Fourier-transformed, and the sound pressures of each frequency may be compared. The intensity ratio of the sound pressure signals of two different frequencies within a predetermined frequency range sandwiching the fundamental frequency may be compared. However, since the fundamental frequency itself may slightly fluctuate due to the electrical system on the supply side, it is preferable to select at intervals of 10 Hz or more. Generally, the sound at frequencies far from the fundamental frequency contains a lot of disturbances such as environmental noise. Therefore, when the frequency that is an integer multiple of the fundamental frequency F0 is Fi, it is preferable to use the signal intensity in the range from Fi - 0.5×F0 to Fi + 0.5×F0. In addition, it is preferable that the difference between the two frequencies is 40 Hz or less. Therefore, the difference is preferably 10 Hz or more and 40 Hz or less.

[0018] The following will be described in detail. Prior to the invention, the inventors confirmed that the sound generated from the AC arc is shielded by the forming slag, resulting in a lower sound. It is known that a liquid containing bubbles significantly reduces the transmittance of high-frequency sound. Due to this effect, when measuring the acoustic frequency outside the furnace when the slag is in the forming state, the center frequency decreases. This frequency decrease is on the order of several Hz and, although it can be perceived by humans with careful listening, it cannot be judged when it changes continuously. Therefore, it was considered that the slag forming state can be stably detected by mechanical measurement.

[0019] The inventors carried out energized melting of scrap and the like in an AC arc type electric furnace with a hot water output of 150 t scale and evaluated the effect. 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.

[0020] The operation pattern is carried out in the following steps. First, an iron source and auxiliary raw materials are charged into the furnace. In the electric furnace used in this embodiment, the operation is carried out while 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. Examples of the auxiliary raw materials include a carbonaceous material, an MgO source for refractory protection, and lime for adjusting the slag composition. After charging the raw materials or during the charging process, power supply is started and oxygen and carbon are blown in. Then, the iron source is sequentially 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 performed. The tapping amount is targeted at 150 t, and about 80 t is left in the furnace and the process proceeds to the next charge again.

[0021] A microphone for sound collection was installed in the same building as the above electric furnace. This microphone is 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 value obtained by dividing the sound pressure value at 75 Hz by the sound pressure value at 50 Hz was used as the sound pressure ratio (75 Hz / 50 Hz) and output to a monitor in the electric furnace operation room. This sound pressure ratio (75 Hz / 50 Hz) was used as an energization sound height index. Representative measurement results are shown in Fig. 1. At this time, a camera for observing the inside of the furnace was installed from the furnace wall, and the observation was carried out until the viewing angle was blocked by dust and slag. The electric furnace used in this embodiment has a fundamental frequency of 50 Hz. During operation, when forming was maintained and no arc was visible (solid line in Fig. 1), this energization sound height index changed between 0.4 and 1.0. However, when energization was carried out in an unstable forming state and arc light was confirmed by the camera (dotted line in Fig. 1), the energization sound height index changed between 0.5 and 3.0.

Example

[0022] Using the same alternating current arc furnace as in the above embodiment, while monitoring the energization sound height index, through trial and error, the oxygen supply rate, the carbon material blowing rate, and the slag-forming material addition rate were adjusted so that the energization sound height index did not exceed 1.0. Lime was used as the slag-forming material. The ratio of the time when the energization sound height index exceeded 1.0 to the energization time during operation was defined as the high-pitch detection time rate, and the relationship between the power unit index and the high-pitch detection time rate is shown in FIG. 2. The power unit index is normalized as a ratio with the one having the largest power unit being 1.0. From FIG. 2, as the high-pitch detection time rate decreases, the power unit decreases. When the energization sound height index (sound pressure ratio (75 Hz / 50 Hz)) could be kept below 1.0 for most periods, the power unit index became about 0.8. In this way, by operating while monitoring the energization sound height index, the energization efficiency was improved and the power unit was reduced. This is because the slag-forming state was maintained during energization and the radiant heat from the arc could be shielded by the slag.

[0023] In this specification, "t", which is a unit of mass, represents 10 3 kg.

Industrial Applicability

[0024] The molten iron produced by the alternating current arc 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 alternating current arc 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 AC arc electric furnace; output means for analyzing the frequency of the detected sound and outputting a frequency-sound pressure signal; when the frequency that is an integer multiple of the fundamental frequency F0 of the AC arc electric furnace is Fi, determination means for determining the coating state of the arc due to slag formation based on the signal intensity in the range from Fi - 0.5×F0 to Fi + 0.5×F0; comprising a power-on state determination device for an AC arc electric furnace, wherein the determination means determines based on the intensity ratio between the signal intensity of one of the higher frequencies and the signal intensity of one of the lower frequencies in the range from Fi - 0.5×F0 to Fi + 0.5×F0 when the frequency that is an integer multiple of the fundamental frequency F0 is Fi.

2. The difference between the two frequencies for obtaining the intensity ratio is 10 Hz or more and 40 Hz or less. The power-on state determination device for an AC arc electric furnace according to Claim 1.

3. In an AC arc electric furnace, when melting and refining scrap to produce molten steel, controlling any one or a combination of the supply rate of the oxygen-containing gas, the amount of carbon material supplied, and the amount of slag-forming material input based on the power-on state determined using the device according to Claim 1 or 2. An operation method for an AC arc electric furnace.

4. An AC arc electric furnace comprising the device according to Claim 1 or 2.

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