JPH1123157A - Evaluation method of arc burial in slag of arc melting furnace - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A method for accurately evaluating the state of burial of an arc into slag during the refining period of an arc melting furnace. SOLUTION: A furnace shell 6 generated from an arc 1 as a heat source.
In order to detect the vibration transmitted to the furnace, a vibration sensor 8 is attached to the furnace shell 6 or the furnace lid 7, and a detection signal of the vibration sensor 8 is converted into a measured vibration level by measuring means 9, 10, and 11. Device 12 for evaluating low-frequency change
Method to evaluate the burial condition of arc in slag.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the state of burial of an arc into slag in an arc furnace for producing molten steel by melting a cold iron source such as iron scrap and direct reduced iron.

[0002]

2. Description of the Related Art In recent years, an increasing number of processes for melting steel scrap generated by an arc furnace have been increasing due to resource and environmental problems. This arc furnace consumes a lot of electric power to melt the scrap,
It is desired to switch to setting of voltage and current suitable for the situation and to improve power use efficiency.

What is important here is to cover the arc by slag forming in order to efficiently transfer the heat of the arc to the molten steel. For this purpose, it is necessary to grasp the slag forming state in the furnace. Conventionally, a method of visually observing the inside of the furnace has been used to grasp the slag forming state.However, during arc generation, observation is difficult due to dust generation and flame, and the amount of oxygen and carbon injected and Since the forming condition differs depending on the blowing position, it has been necessary to check the number of times.

As a method other than visual observation, (a) a method of judging based on a change in the outlet temperature of cooling water for cooling the furnace body, and (b) a method of judging by sound, such as a sound level meter provided outside the furnace, have been put to practical use. Have been.

[0005]

However, these conventional methods have the following problems. The method (a) is
When a splash of molten steel generated by an arc or an acid lance accumulates on the inner wall of the furnace and a metal layer is formed, a heat insulating effect appears, and the outlet temperature of the cooling water cannot be correctly detected. Since this metal layer is not constant and cannot be evaluated under the same conditions, it is difficult to apply this method. In addition, temperature measurement errors occur due to the impact of oxygen from the lance on the inner wall and the flow of combustion gases in the furnace. In the above method (b), the detection level of the arc sound is greatly different depending on the opening and closing of the work box. If there is ancillary equipment near the detector installation position, it is affected by the noise. It is difficult to detect. Further, similarly, even when two melting furnaces are installed close to each other, the arc sound of the furnace to be detected cannot be correctly detected.

[0006]

According to a first aspect of the present invention, there is provided a method for evaluating burial of an arc into a slag of an arc melting furnace according to the first aspect of the present invention. In order to detect the vibration generated from the arc and transmitted to the furnace shell, a vibration sensor is attached to the furnace shell or the furnace lid, and the detection signal of this vibration sensor is converted into a measured vibration level by measuring means, and the measured vibration level is reduced and changed. It evaluates the state of burial of the arc into the slag based on the following.

According to a second aspect of the present invention, there is provided a method for evaluating burial of an arc into a slag of an arc melting furnace.
In order to detect the vibration generated from the arc that is the heat source and transmitted to the furnace shell, a vibration sensor was attached near the height position where the slag thickness was added to the upper surface of the molten steel at the end of melting of the furnace shell. The detection signal is converted into a measured vibration level by the measuring means, and the state of burial of the arc into the slag is evaluated based on the reduced change in the measured vibration level.

According to a third aspect of the present invention, there is provided a method for evaluating burial of an arc into a slag of an arc melting furnace according to the first aspect of the present invention.
Alternatively, in the method according to claim 2, only a signal in a specific frequency band unique to the arc is extracted from the detection signal of the vibration sensor and converted into a measured vibration level by a measuring unit. The burial state of the arc in the slag is evaluated based on this.

As a result, the state of burial of the arc in the slag can be accurately grasped by the vibration level measured from the vibration sensor attached to the outer wall of the furnace shell, and the arc can always be covered by the slag. Thus, wasteful power in the refining period can be suppressed, the power consumption can be reduced, and damage to the furnace wall refractory can be reduced.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the method for evaluating the burial of an arc into a slag of an arc melting furnace according to the present invention will be described. Vibration due to a strong thundering sound generated by an arc as a heating source is transmitted to the furnace shell by slag or air formed during the refining period (period in which the components of molten steel are adjusted after the scrap is melted). The vibration level shows a low value when the arc is covered by the slag, and shows a high value when the arc is exposed. Therefore, in the present invention, a vibration sensor is attached to the outer wall surface of the furnace shell of the arc furnace or the furnace lid, a detection signal of the vibration sensor is converted into a measurement vibration level, and the slag forming state is evaluated based on the measurement vibration level, and the measurement is performed. If the vibration level increases, it is determined that the arc has been exposed.

Further, in the present invention, since the injection of oxygen as auxiliary energy is performed at the time of melting the scrap, the jet sound of oxygen blown into the furnace is excluded while considering the frequency component of the measured vibration level. A band-pass filter that extracts only a signal in a specific frequency band specific to the arc, which is the source of vibration, from the detection signal of the vibration sensor, and determines the measured vibration level in this specific frequency band to determine whether the arc is buried in the slag. Is evaluated, a more accurate evaluation result can be obtained.

FIG. 1 is a configuration diagram for carrying out the method for evaluating the burial of an arc into a slag of an arc melting furnace according to the present invention. In FIG. 1, 1 is an arc, 2 is molten steel, 3 is a slag, 4 is a hearth, 5 is a graphite electrode, 6 is a furnace shell, 7 is a furnace lid, 8 is a vibration sensor (pickup), 9 is an amplifier, and 10 is an amplifier. filter,
11 is a vibration measuring device, 12 is an evaluation device, 13 is a voltage / current setting device, 14 is an electrode elevation control device, 15 is an arc current control device, 16 is an incidental equipment control device, 17 is an oxygen blowing control device, 18 is The coal powder blowing control device 19 is a chart display.

The configuration and operation of the present invention will be described with reference to FIG. The vibration sensor 8 is mounted near the position outside the furnace shell 6 of the arc furnace by the slag thickness from the upper surface level of the molten steel. The signal detected by the vibration sensor 8 and converted into an electric signal and output is amplified by the amplifier 9 with a predetermined gain. The signal amplified by the amplifier 9 is input to the filter 10.

The filter 10 is constituted by a band-pass filter, which removes unnecessary vibration signals in high and low frequency bands from an input signal and generates a frequency band unique to the arc (for example, a band of 100 Hz to 500 Hz described in the second embodiment). Or in the case of an AC arc furnace, twice the commercial power frequency and 6
Only the pass band centered on the double is passed, and the passed output is supplied to the vibration measuring device 11. The vibration measuring device 11 converts each input signal from the filter 10 into a measured vibration level (for example, a level of displacement or velocity, acceleration, or the like),
These converted signals are output to the evaluation device 12 and the chart display 19, respectively.

The evaluation device 12 determines whether or not the vibration level in the refining period measured by the vibration measuring device 11 exceeds a predetermined set level. If the level exceeds the predetermined level, the burial of the arc into the slag is incomplete. It is determined that there is, and this arc burial state determination signal is supplied to the voltage / current setting device 13 and the incidental equipment control device 16.

On the basis of the arc burial state determination signal supplied from the evaluation device 12, the incidental equipment control signal 16 controls the corresponding control devices 17 and 18 to finely adjust the blowing of coal powder and the blowing of oxygen into molten steel. And the voltage / current setting device 13 lowers the arc voltage, increases the current, lowers the electrode until the arc is submerged in the slag, and shortens the arc (to shorten the discharge distance to improve the heat transfer to the molten steel. It is possible to set the voltage and current according to the furnace conditions through the corresponding control devices 14 and 15, for example, by switching to operation. Thus, the arc heat can be effectively transmitted to the molten steel during the refining period. Further, the chart display 19 is a vibration measuring device 11.
Is recorded in a chart and displayed.

Hereinafter, specific first and second embodiments of the present invention will be described. Embodiment 1 In Embodiment 1, the furnace diameter is 7200 mm and the height is 60.
150 t of scrap was charged into a 00 mm arc furnace, and 30
Maximum 750V, 120kA by the inch graphite electrode 5
With a power capacity of. Further, 6000 Nm ³ / hr of acid was fed from a water-cooled oxygen lance through a working port provided on the furnace side wall. When the molten metal was accumulated in the furnace, coal powder was blown into the slag at a rate of 80 kg / min for refining. Note that the coal powder is used for refining molten steel components and forming flags during refining. Outside the furnace shell 6, a vibration sensor 8 was attached near the height where the slag thickness was added to the upper surface of the molten steel at the end of melting to detect the vibration of the furnace shell. This detection signal is measured as a vibration level via the amplifier 9, the filter 10 and the vibration measuring device 11, and the time transition of the measured vibration level is recorded by the chart display 19 in FIG. 2.

FIG. 2 is a diagram showing an example of measurement of the vibration level in the first embodiment of the present invention. At the same time, FIG. 2 shows the slag forming condition in the furnace observed from the working port, and the coal powder blowing, oxygen blowing and oxygen blowing. The timing of changing the applied voltage is also shown. As can be observed from FIG. 2, during the melting phase, the vibration level gradually decreases as the dissolution of the charge proceeds. The refining period starts when the end of melting ends and all the scrap is melted (Melt Down, MD).

In this refining period, when a good slag forming in which the arc is covered is observed, the vibration level is changing to a certain low value. here,
When the blowing of charcoal powder and oxygen is stopped for measuring or sampling the molten steel, that is, when the slag forming is insufficient and the arc is exposed, the vibration level becomes higher than the above value. Is shown. As a result, it was found that the furnace shell vibration level was very good and corresponded to the burial condition of the arc in the slag.

As described above, by grasping the burial state of the arc in the slag based on the value of the vibration level, the arc can always be covered by the slag, and as a result, the heat loss of the arc up to that time can be minimized. I can do things. Specifically, an improvement of 15 to 20 kWh / t per unit of electric power is achieved.
Also, in the measurement of the vibration level, it was found that there was no trouble due to dust, flame, and splash, and there was no problem in maintenance.

Embodiment 2 In the melting furnace of Embodiment 1 described above, a vibration sensor 8 having a high sensitivity even in a high frequency range of 2 kHz or more is used as a vibration sensor, and as a result of observation by changing a detection frequency band, It was found that the signal around 500 Hz best captured the slag forming situation. A signal in a high frequency region having a vibration frequency of 1 kHz or more is hardly changed, and the effect of the jet sound of the oxygen lance appears. Conversely, in a low frequency range, vibrations due to the movement of the electrode lifting / lowering system and equipment attached to the furnace are superimposed. Therefore, in a furnace having a small arc power, in order to eliminate these vibrations, an amplifier 9 (for example, an active filter) incorporating a band-pass filter that passes only a frequency band unique to the arc is used, or a band-pass filter is used. It is effective to provide a filter before the vibration measuring device 11. The frequency specific to the arc is in the range of about 100 Hz to 500 Hz. In particular, in an AC arc furnace, it is preferable to select the pass band of the band-pass filter around twice and six times the frequency of the commercial power supply.

Since the inside of the arc furnace is extremely high temperature and is affected by flame and dust, there has been no suitable sensor for detecting the state of burial of the arc in the foamed slag, so that it has been difficult to evaluate. However, according to the first and second embodiments described above, slag forming in the refining period, which is particularly important in the arc melting process, can be accurately grasped. Since there is no trouble due to splash or flame, there is no maintenance problem. Also, at the vibration detector mounting position (near the slag thickness added to the top surface of molten steel at the end of melting), there is almost no ingot adhesion, and vibrations corresponding to forming can be detected with good reproducibility without being affected by these. In addition, it is possible to set the appropriate injection of oxygen and coal powder and the setting of an arc in accordance with the slag forming condition, thereby improving the refining period efficiency.

[0023]

As described above, according to the present invention, in a method for evaluating the state of burial of an arc in a slag in an arc melting furnace, vibrations generated from an arc as a heat source and transmitted to a furnace shell are detected. A vibration sensor was attached to the furnace shell or furnace lid, and the detection signal of this vibration sensor was converted into a measured vibration level by a measuring means, and the state of burial of the arc into the slag was evaluated based on the reduced change in the measured vibration level. As a result, the state of burial of the arc in the slag during the refining period can be accurately grasped, and the arc can always be covered with the slag. And damage to the furnace wall refractory can be reduced.

According to the present invention, in the method for evaluating the state of burial of an arc in a slag in an arc melting furnace, in order to detect a vibration generated from the arc as a heat source and transmitted to the furnace shell, the melting of the furnace shell is completed. A vibration sensor is attached near the height position where the slag thickness is added to the upper surface of the molten steel at the time, and the detection signal of this vibration sensor is converted into a measured vibration level by the measuring means, and the arc is detected based on the reduced change in the measured vibration level. Of the burial of the slag in the slag was evaluated, and as a result, the burial of the arc in the slag during the refining period can be grasped very accurately, and the arc can always be covered by the slag. In addition, useless power in the refining period can be suppressed, the power consumption can be reduced, and damage to the furnace wall refractories can be reduced.

Further, according to the present invention, only a signal in a specific frequency band unique to the arc is extracted from the detection signal of the vibration sensor attached to the furnace shell and converted into a measured vibration level by the measuring means. Since the state of immersion of the arc in the slag is evaluated based on the reduced change in the measured vibration level, it is possible to obtain a more accurate evaluation result than when the frequency band of the measured vibration level is not limited.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for implementing a method for evaluating the burial of an arc into a slag of an arc melting furnace according to the present invention.

FIG. 2 is a diagram illustrating a measurement example of a vibration level according to the first embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc 2 Molten steel 3 Slag 4 Hearth 5 Graphite electrode 6 Furnace shell 7 Furnace lid 8 Vibration sensor 9 Amplifier 10 Filter 11 Vibration measuring device 12 Evaluation device 13 Voltage / current setting device 14 Electrode raising / lowering control device 15 Arc current control device 16 Attached Equipment control device 17 Oxygen blowing control device 18 Charcoal powder blowing control device 19 Chart display

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Ken Yao 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd.

Claims (3)

[Claims] In a method for evaluating the state of burial of an arc in an arc melting furnace, a vibration sensor is attached to a furnace shell or a furnace lid in order to detect vibration generated from an arc as a heat source and transmitted to the furnace shell. Converting the detection signal of the vibration sensor into a measured vibration level by measuring means, and evaluating the state of immersion of the arc in the slag based on the reduced change in the measured vibration level. Burial evaluation method. 2. A method for evaluating the state of burial of an arc in a slag in an arc melting furnace, comprising: detecting vibrations generated from an arc as a heat source and transmitted to a furnace shell; A vibration sensor is attached near the height position where the slag thickness is added to the slag, and the detection signal of this vibration sensor is converted into a measured vibration level by measuring means, and the arc is buried in the slag based on the reduced change in the measured vibration level. A method for evaluating burial of an arc into slag of an arc melting furnace, characterized by evaluating a situation. 3. A method for extracting only a signal in a specific frequency band unique to an arc from a detection signal of the vibration sensor, converting the signal into a measured vibration level by a measuring means, and detecting a slug of the arc based on a reduced change in the measured vibration level in the specific frequency band. The method for evaluating the burial of an arc into a slag of an arc melting furnace according to claim 1 or 2, wherein the state of burial in the slag is evaluated.