JP3387366B2 - Judging method of melting progress in arc furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining the progress of melting of a cold iron source in an arc furnace for manufacturing a molten steel by melting a cold iron source such as iron scrap or direct reduced iron.

[0002]

2. Description of the Related Art In recent years, an increasing number of processes have been used for melting steel scrap, which is frequently generated due to resource and environmental problems, by using an arc furnace. This arc furnace consumes a lot of electric power for melting scrap, so grasp the situation inside the furnace,
It is desired to switch the setting of voltage and current suitable for the situation to improve the power utilization efficiency. A particularly important time is the transition timing from the long melting period to the short arc and the subsequent melting period and the subsequent refining period.
It is important to accurately determine the timing of transition from the late melting stage to the refining stage. To this end, it is necessary to accurately grasp the progress of melting of the material in the furnace. In order to grasp this progress of melting, conventionally, the method of visually observing the inside of the furnace when the input power amount reached a predetermined amount was taken, but during arcing it is difficult to observe due to dust generation and flames. ,
In addition, there is a problem in that the degree of progress of melting differs depending on the material of the scrap and the like, so that it is necessary to repeatedly check.

In addition to this visual inspection, (a) a method of calculating the impedance from changes in the arc voltage and current or their elements, and judging by the transition of the changes (b) changes in the position of the electrode or per unit time Method to judge by transition of quantity (c) Method to judge by transition of outlet temperature of cooling water for cooling the furnace body (d) Place optical sensor on furnace lid to detect radiant light from molten steel in furnace Judgment method (Patent Fair 6-5
No. 0674) has been put to practical use.

[0004]

However, these conventional methods have the following problems. The methods (a) and (b) show changes when the arc is generated in the material before melting, but when the melting progresses and the arc becomes generated in the molten steel, a signal is output. No change is seen. For this reason, it is not possible to evaluate the situation of the late melting stage when the most important melting stage shifts to the refining stage. In the method of (C), if a splash of molten steel is generated on the inner wall of the furnace due to an arc or oxygen transfer lance and a metal layer is formed, a heat insulating effect appears and cannot be detected correctly. This metal layer is not constant, and therefore it cannot be evaluated under the same conditions, making it difficult to apply. In addition, oxygen from the oxygen transfer lance hits the inner wall, and the influence of the flow of combustion gas in the furnace causes further errors. The method (d) has a problem that it is affected by dust in the furnace and the effect of a flame by combustion, and that the light emitting hole is easily blocked by the splash, which requires maintenance.

The present invention has improved the conventional method for judging the progress of melting in an arc furnace, is easy to maintain, and is not affected by the splash or combustion gas generated in the furnace, and particularly from the latter stage of melting to the refining stage. The purpose is to provide a method for determining the progress of dissolution during a period of time.

[0006]

According to the method for determining the progress of melting in an arc furnace according to the present invention, a vibration sensor is attached to the outer surface of the side wall of the arc furnace, and the vibration sensor detects vibration of the furnace body during melting of the material. Then, by passing the output of the vibration sensor through a filter, the natural frequency of the arc is 100
Hz-500Hz frequency band or AC arc furnace
In the case of a frequency centered around 2 or 6 times the commercial frequency
A signal in a specific frequency band including several bands and its output signal
It is characterized in that the degree of progress of dissolution is determined by the change in the vibration level of the signal.

The vibration generated by the strong thundering sound generated by the arc, which is the heating source, is transmitted to the material such as residual scrap existing on the front surface of the furnace wall and further to the furnace shell. Then, the vibration level decreases as the melting progresses and the remaining material decreases. Therefore, in the present invention, a vibration sensor is attached to the outer wall surface or the column of the furnace shell of the arc furnace, preferably on the outer surface of the side wall near the molten steel upper surface level, and the vibration body detects vibration of the furnace body transmitted to the furnace shell. And
The amount of residual material is evaluated based on the detected vibration level, and the degree of progress of melting is evaluated. When the level of vibration is decreased, the degree of melting and the time of transition to the refining period are determined. Further, in the present invention, in order to exclude the vibration due to the jet noise of oxygen blown into the furnace, a filter is added to focus on the vibration peculiar to the arc, which is the source of the vibration. That is, the output of the vibration sensor is passed through a filter and used as a signal in a specific frequency band including the natural frequency of the arc for determining the melting progress.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a melting progress status judging device used in the method of the present invention. In FIG. 1, 1
Is a furnace shell of an arc furnace 10, 2 is a furnace lid, and 3 is a graphite electrode. When the graphite electrode 3 is energized, an arc 5 is generated between the scrap 4 or the molten steel 6 in the furnace, and the arc heat produces scrap. 4 is melted to produce molten steel 6 and slag 7. In order to detect the vibration of the furnace body transmitted to the furnace shell 2 with the strong thunder sound emitted by the arc 5 which is the heat source,
The vibration sensor 11 is attached to the outer wall surface of the furnace shell in the vicinity of the molten steel upper surface level, the output signal of the vibration sensor 11 is amplified by the amplifier 12, and the filter 13 that allows only a specific frequency band to pass.
Is input to the vibration measuring device 14 and converted into a vibration level by a converter (not shown). The progress of the dissolution is displayed on the chart display 15 according to the change of the vibration level and the decrease of the vibration level, and the dissolution progress evaluation device 16
Determine which stage the dissolution progress is at. Here, a reference value for determining the transition time from the late melting period to the refining period, which is particularly important, is set. When the vibration level drops below the set level, the evaluation device 16 causes the voltage / current setting device 17 to change. Send a setting change signal. Based on this setting change signal, the electrode lift control device 18 and the arc current control device 19 are respectively controlled, and the arc voltage is decreased and the current is increased to switch to the short arc.
The voltage and current settings are changed according to the conditions inside the furnace. Further, the output of the transition timing to the refining period starts the injection of carbon powder into the slag and the injection of oxygen into the molten steel.

Therefore, according to the present invention, it is possible to accurately grasp the particularly important transition time of the low voltage / high current to the short arc in the latter stage of the melting period, and the vibration sensor is arranged outside the furnace shell. Therefore, there is no trouble due to splash or flame, and there is no maintenance problem. In addition, since there is almost no metal adhesion at the molten steel upper surface level, there is no influence of these and vibrations according to the amount of remaining cold iron source can be detected with good reproducibility, so an appropriate arc according to the progress of melting can be obtained. It is possible to set and blow oxygen and carbon powder, improving the dissolution efficiency.

[0010]

EXAMPLES Examples of the present invention will be specifically described below. Example 1. Arc furnace (furnace diameter: 7200 mm, height: 60
Scrap 150 t was charged in (00 mm), and melted with a maximum power supply capacity of 750 V and 120 kA by a 30-inch graphite electrode. Further, from the water inlet provided on the side wall of the furnace, 6000 Nm ³ / hr of oxygen was fed from a water-cooled oxygen lance. When the molten metal had accumulated in the furnace, carbon powder was blown into the slag at 80 kg / min for refining. Outside the furnace shell, a vibration sensor was attached to the vicinity of the upper surface of the molten steel at the end of melting to detect the vibration of the furnace shell. FIG. 2 is a chart in which the vibration level is measured and charted through a receiver and a converter. As can be seen from this chart, the vibration level decreases as the amount of scrap before the furnace wall decreases in the latter stage of melting. Therefore, when the voltage dropped to 80 dB, the set voltage was lowered to 600 V and the current was increased to 130 kA. Further, when it dropped to 70 dB, carbon powder was blown into the slag and oxygen was blown into the molten steel.
At this time, the voltage was set to 550V. In addition, as a result of testing with a heat with a small scrap feed amount of 120 t,
After all, the timing when the vibration level dropped to 80 dB or less was about 20% faster than when the charging was carried out for about 150 t. As a result, it was found that the vibration level of the furnace shell corresponds to the progress of melting very well.

As described above, by grasping the progress of melting based on the vibration level, it has become possible to appropriately switch to the short arc or to shift to the refining period, and the amount of electric power that has been reached up to that point is reached. Then, compared with the operation by the pattern control which is switched, 10-20kW
An improvement in the power consumption rate of h / t was observed. Furthermore, it was found that there were no troubles due to dust, flame, or splash, and there was no problem in maintenance.

Example 2. In the above melting furnace, the vibration sensor was set to have a high sensitivity even in a high frequency region of 2 kHz or more, and the detection frequency band was changed and observed.
It was found that the signal near 0 Hz best captured the progress of dissolution. In addition to the fact that a signal in a high frequency region of 1 kHz or more is difficult to appear, the effect of the jet sound of the oxygen lance appears. At low frequencies, vibrations due to movements of the electrode lifting system and equipment attached to the furnace are superimposed. Therefore,
In a furnace with a small arc power, it is effective to install a bandpass filter in front of the receiver near the natural frequency of the arc in order to eliminate these vibrations. The frequency peculiar to the arc is in the range of about 100 Hz to 500 Hz, and particularly in the case of an AC arc furnace, it is good to select it at twice or six times the commercial frequency.

[0013]

As described above, according to the present invention,
A vibration sensor is attached to the outer surface of the side wall of the arc furnace to detect the vibration of the furnace body that is generated from the melting arc and transmitted to the furnace shell, so maintenance is easy and the effects of splash and combustion gas generated in the furnace are eliminated. The vibration level of the furnace vibration that is not received and is detected by the vibration sensor accurately indicates the situation of scrap remaining in the furnace from the late melting stage to the refining period, which is particularly important, and it is possible to switch to a short arc or The transition timing to the refining period can be properly performed. Furthermore, by passing the output of the vibration sensor through a filter, the natural frequency of the arc of 100 Hz to 500 Hz
Frequency band, or commercial frequency for AC arc furnaces
A signal in a specific frequency band including a frequency band centered around 2 times or 6 times is used, and the progress of dissolution is determined by the change in the vibration level of the output signal. Therefore, the progress of dissolution must be accurately determined. You can As a result, it is possible to suppress wasteful power in the latter stage of melting, reduce the power consumption rate, and reduce damage to the furnace wall refractory.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a dissolution progress status determination device used in a method of the present invention.

FIG. 2 is a diagram showing a measurement result of a vibration level in an example.

[Explanation of symbols]

1 furnace shell 2 furnace lid 3 Graphite electrode 4 scrap 5 arc 6 Molten steel 7 slag 10 arc furnace 11 Vibration sensor 12 amps 13 filters 14 Vibration measuring instrument 15 Chart display 16 Dissolution progress evaluation device 17 Voltage / current setting device 18-electrode lifting control device 19 Arc current control device

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Tanio, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Steel Pipe Co., Ltd. (56) Reference JP-A-63-263385 (JP, A) JP-A-2 -101381 (JP, A) JP-A-6-294587 (JP, A) JP-A-7-286218 (JP, A) JP-B-55-17314 (JP, B1) (58) Fields investigated (Int.Cl) . ⁷ , DB name) H05B 7/148 F27D 11/08

Claims (2)

(57) [Claims] 1. A vibration sensor is attached to an outer surface of a side wall of an arc furnace, a vibration of a furnace body generated during melting of a material is detected by the vibration sensor, and an output of the vibration sensor is passed through a filter to obtain a natural frequency of the arc of 100 Hz. ~ 500Hz
Frequency band, or commercial frequency for AC arc furnaces
A signal of a specific frequency band including a frequency band centering around 2 times or 6 times is used, and the progress of melting is judged by the change of the vibration level of the output signal . Judgment method. 2. The determination of the progress of melting in an arc furnace according to claim 1, wherein when the vibration level of the vibration of the furnace body becomes a predetermined value or less, it is determined that it is a transition time from the latter stage of melting to the refining stage. Method.