JPH1183330A - Melting progress evaluation method for arc melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate accurately the melting progress of raw materials with which an arc melting furnace is charged. SOLUTION: In this melting progress evaluation method for an arc melting furnace, oscillation sensors 1 are mounted on a furnace shell 12 at a plurality of places different in height, respectively, in order to detect respective oscillations generated from an arc 15, which works as a heat source, and transmitted to respective parts of the furnace shell 12. A detection signal from each of the plural sensors 1 is converted into a measured oscillation level by a measuring means consisting of an amplifier 2, a filter 3 and an oscillation measuring instrument 4, respectively. A low range transition of each of the plural measured oscillation levels is compared with one another and judged by a progress evaluation unit 5.

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 progress of melting of a cold iron source in an arc furnace for producing molten steel by melting a cold iron source such as iron scrap and direct reduced iron. It is.

[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. In an arc furnace, since a large amount of electric power is consumed to dissolve scrap, it is desired to grasp the conditions inside the furnace, switch to a setting of a voltage and a current suitable for the conditions, and improve the power use efficiency. . As a method for detecting the melting progress of a conventional general arc melting furnace, the transition of scrap melting is modeled as a transition of a plurality of scrap melting phases, and a voltage, which is considered appropriate for each of these phases,
Set the current as a power input pattern in advance,
Power was supplied according to this pattern.

For example, in a typical power input pattern, scrap melting ends in the following three phases in order. First phase (scrap boring) Here, scrap boring refers to the first state in which the scrap loaded in the furnace has begun to melt, in which the arc melts the lower scrap and the electrode descends. is there. In the first stage of the scrap melting, the voltage is set low from the viewpoint of thermal efficiency and facility protection of the furnace lid. Second phase (maximum power input) Also called kamakura melting or main melting, since the surroundings are covered with scrap, the power input efficiency is good and the maximum power is set. Third phase (transition to flat bath) A considerable part of the scrap in the furnace is in a molten state, and the high-temperature atmosphere by the arc is sucked out of the furnace without contributing to the melting of the scrap. High current.

[0004] These phases are switched when the input energy amount (input power amount, input oxygen amount) reaches a predetermined amount. And by tuning the set power for each phase set in the pattern and the input energy amount of switching, and also having multiple patterns and trying to change the applied pattern according to the loaded scrap, etc. Increasing the power input efficiency of scrap melting is a conventional method of improving power use efficiency.

[0005]

However, these conventional methods have the following problems. Scrap dissolution generally follows the average qualitative model described above, and power-up pattern control follows that qualitative model. However, the individual scrap melting does not completely match the model, but only roughly matches it.If the scrap is different in shape, quality, compounding, and how it is loaded in the furnace, the melting process will be different. Come. The timing of switching the melting phases may be appropriate for one scrap melting but inappropriate for another scrap melting. Therefore, even if control is performed using the same power input pattern, it is inevitable that the power input for individual scrap melting wastes. This is due to the fact that the power input pattern control is an open room according to an average and statistical model, and a control system with a feedback mechanism with a sensor that can estimate the furnace condition at the detection end must be constructed. If it is possible, the power can be switched according to the furnace condition, and the optimum power input control for individual scrap melting can be performed.

The prior art references provided with a sensor for estimating the condition of the arc furnace include, for example, Japanese Patent Publication No. Sho 5
JP-A-5-17313 entitled "Arc furnace capable of detecting the melting state" (hereinafter referred to as Reference 1). Reference 1 above
Converts the arc discharge sound during melting of the scrap into a current using a sonic converter such as a microphone installed in the furnace body, analyzes the waveform using an oscilloscope or other sonic analyzer, and analyzes the arc based on the results of analyzing the transition of the sonic waveform. This is for controlling the furnace. However, this method using the arc discharge sound has no relationship between the melting state of the charged material in the furnace wall portion where the arc column does not reach and the arc discharge sound, and cannot detect the melting state of the charged material in this portion. Was.

[0007] As a reference of the prior art in which the disadvantage of Reference 1 is improved, there is, for example, JP-A-2-101381 entitled "Method of detecting melting state in arc furnace" (hereinafter referred to as Reference 2). The above-mentioned Reference 2 is based on a power spectrum obtained by frequency analysis of the vibration of the furnace wall of the arc furnace during the melting process of the charged material in the arc furnace,
The time integrated value of the sum of the power frequency, its harmonics, and the remaining power spectrum components from which these nearby frequency components have been removed is determined, and the charging material dissolution state is detected based on the integrated value.

However, the method of detecting the impact generated due to the collapse of the charged material near the furnace wall in Reference 2 using a vibration sensor installed in the furnace body aims at detecting the collapse of the charged material. Therefore, in the embodiment, the commercial power supply frequency ± 10 Hz and a harmonic of this power supply frequency ± 10H
The power spectrum component of z is removed as a signal component having no correlation with the collapse of the charged material. As described above, in Reference 2, since the vibration frequency (including harmonics) inherent in the arc transmitted from the arc to the furnace wall via the peripheral unmelted scrap layer is not detected, melting in the arc furnace is not performed. The progress of the progress could not be evaluated correctly, and it was not satisfactory.

[0009]

According to a first aspect of the present invention, there is provided a method for evaluating the progress of melting of an arc melting furnace, comprising the steps of: In order to detect the vibration transmitted to each part of the furnace shell, vibration sensors are attached to a plurality of locations with different mounting heights to the furnace shell, and the detection signals of the plurality of vibration sensors are respectively converted to measurement vibration levels by measuring means. The melting progress of the charged material is evaluated by converting and comparing the reduction transition of each of the plurality of measured vibration levels.

According to a second aspect of the present invention, there is provided a method for evaluating a melting progress of an arc melting furnace according to the first aspect of the present invention, wherein a detection signal of each of the plurality of vibration sensors has a specific frequency band specific to an arc. Only the signal is taken out and converted into a measured vibration level by the measuring means, and the progress of dissolution of the charged material is evaluated by comparing and judging the low frequency transition of each of the plurality of measured vibration levels in this specific frequency band.

As a result, from the vibration level measured from the vibration sensor attached to the outer wall of the furnace shell, it is possible to accurately grasp the remaining state of the scrap in the furnace from the latter stage to the refining stage, which is particularly important in the arc melting process. Switching to the short arc and the timing of the transition to the refining period can be performed properly, so that wasteful electric power in the latter stage of melting can be suppressed, the power consumption unit is reduced, and damage to the furnace wall refractories is also reduced. be able to.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the method for evaluating the progress of melting in an arc melting furnace according to the present invention will be described.
Vibration transmitted to the furnace shell by a strong thundering sound generated by the arc as a heating source is transmitted by a material such as residual scrap present on the front surface of the furnace wall. Then, the vibration level decreases as the melting proceeds and the remaining material decreases. Therefore, in the present invention, in order to detect vibrations generated from an arc as a heat source and transmitted to each part of the furnace shell, vibration sensors are respectively provided at a plurality of locations having different mounting heights on an outer wall surface or a column of the furnace shell of the arc furnace. By converting the detection signals of each of the plurality of vibration sensors into a measured vibration level, and comparing and judging the reduction transition of each of the plurality of measured vibration levels, the remaining material in front of the furnace wall to which each of the vibration sensors is mounted is attached. The progress of melting and the transition to the refining period (period of adjusting the composition of molten steel after the melting of the scrap) due to the determination of the presence or absence of melting and evaluating the progress of melting and the vibration level dropping below a preset level Can be estimated in detail.

Furthermore, in the present invention, the frequency component of the measured vibration level is taken into consideration, and oxygen is blown as auxiliary energy during scrap melting, so that the jet sound of oxygen blown into the furnace is excluded. Along with
A band-pass filter is provided to extract only the signal in the specific frequency band unique to the arc, which is the source of vibration, from the detection signal of each vibration sensor, and the charging is performed by comparing and judging the transition of the measured vibration level in the low frequency band in this specific frequency band. Since the dissolution progress of the raw material is evaluated, a more accurate evaluation result can be obtained.

FIG. 1 is a block diagram for carrying out the method for evaluating the melting progress of an arc melting furnace according to the present invention. In FIG.
1 is a vibration sensor (pickup), 2 is an amplifier, 3 is a filter including three bandpass filters inside, 4 is a vibration measuring device, 5 is a progress evaluation device,
6 is a voltage / current setting device, 7 is an electrode elevation control device, 8 is an arc current control device, 9 is a chart display, 10 is a graphite electrode, 11 is a furnace lid, 12 is a furnace shell, 13 is a hearth, 14 is Scrap, 15 is an arc, 16 is slag, and 17 is molten steel.

The configuration and operation of the present invention will be described with reference to FIG. The vibration sensor 1 is attached to a plurality of locations on the outside of the furnace shell 12 of the arc furnace where the mounting heights to the furnace shell 12 are different. In FIG. 1, three vibration sensors 1 are attached to three places having different attachment heights to the furnace shell 12. The signals detected by the three vibration sensors 1 and converted into electric signals and output are amplified by the corresponding amplifiers 2 with a predetermined gain. Each signal amplified by each of the three amplifiers 2 is input to the filter 3.

The filter 3 includes three band-pass filters, each of which removes unnecessary vibration signals in high and low frequency bands from an input signal, and generates a frequency band unique to an arc (for example, 100 Hz to 500 Hz described in the second embodiment). Or, in the case of an AC arc furnace, a pass band centered on twice and six times the frequency of the commercial power supply).
The respective passing outputs are supplied to the vibration measuring device 4 respectively. The vibration measuring device 4 converts each of the three input signals into a measured vibration level (for example, a level of displacement or velocity, acceleration, or the like), and outputs the converted signals to the progress evaluation device 5 and the chart display 9, respectively. .

The progress evaluation device 5 detects three input signals, that is, three vibration sensors 1 attached to the furnace shell 12 and converts the three measured vibration levels, which are respectively converted, with time and decreases the vibration level. The progress of melting in the furnace is evaluated according to the
A control signal such as a current setting signal is output to the voltage / current setting device 6. The voltage / current setting device 6 outputs respective control signals to the electrode elevation control device 7 and the arc current control device 8 based on the control signal supplied from the progress evaluation device 5. Further, the chart display 9 records and displays the time transition of the three measured vibration levels output from the vibration measuring device 4 on a chart.

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, 130k by the inch graphite electrode 10
A was dissolved with the power capacity of A. 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. And 80kg / m when molten metal accumulates in the furnace
In, charcoal powder was blown into the slag for refining. The coal powder is used for refining molten steel components and forming slag during refining. Two vibration sensors 1 were mounted outside the furnace shell 12. One was mounted near the upper surface of the molten steel (hereinafter referred to as ML) at the time of completion of melting, and the other was mounted at a position of ML + 1500 mm, and the vibration of the furnace shell was detected. This detection signal is measured as a vibration level via the amplifier 2, the filter 3, and the vibration measuring device 4, and the time transition of the measured vibration level is recorded by the chart display 9 in FIG.

FIG. 2 is a diagram showing an example of measuring the vibration level in the first embodiment of the present invention. The vertical axis of the figure is the vibration level (unit: dB), and the horizontal axis is the time. As can be observed from the waveforms in FIG. 2, as the end of melting approaches and the amount of scrap in front of the furnace wall decreases, the two vibration levels detected at different heights both decrease. The vibration level near the ML largely decreases near the time when all the scrap is melted (Melt Down, hereinafter referred to as MD). This means that since the position where the vibration sensor was attached is near ML, the scrap on the front surface of the vibration sensor remains without melting until near MD, and when the vibration level is low, ML
It can be seen that the scrap on the front of the furnace wall in the vicinity melted and became a flat bath. Therefore, at this vibration level, MD
A determination can be made.

On the other hand, the vibration level detected at ML + 1500 gradually decreases as the end of lysis begins, and M
It becomes constant at a low value from a very early stage before D. This indicates that the scrap at the front of the vibration sensor melts earlier than the ML and the furnace wall is exposed because the position where the vibration sensor is mounted is high.

In the first embodiment, the following control is performed using these two vibration levels. (1) A period in which both the vibration level near the ML and the vibration level of the ML + 1500 are large (a period in which the vibration level of the ML + 1500 is 100 dB or more) Assuming that the scrap still remains sufficiently in the furnace, the maximum power (750 V, 130 KA) is supplied And cut the scrap with oxygen. (2) Vibration level near ML is still large, ML + 15
00 period (ML + 1500)
Scrap is melted up to the level of ML + 1500, but it is assumed that undissolved scrap still remains near the ML. Oxygen cutting is stopped and the power is reduced to a short arc (short discharge distance). (Operation to improve the heat transfer to molten steel) (600 V).

(3) Vibration level near ML, ML + 15
The period during which both the vibration levels of 00 and 00 were low (the period when the vibration level of ML was 65 dB or less and the vibration level of ML + 1500 was 90 dB or less) It was assumed that the scrap was completely melted into a flat bath, and oxygen was blown into the molten steel. , And the coal powder was put into the slag. The power is further reduced to a short arc and 55
0 V was applied.

In addition, the amount of scrap charged is 120 t.
As a result of a test with a small amount of heat, a change in the amplitude level similar to the above was observed at a time earlier by nearly 20% in proportion to the weight of the charged scrap as compared with the case where 150 t was charged. As described above, the switching to the short arc and the start of the refining operation can be appropriately performed by grasping the melting progress based on the amplitude level, and it is 25 to 30 kWh / t as compared with the operation by the power input pattern control up to that time. Per unit of power consumption was reduced. 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.

Second Embodiment In the melting furnace of the first embodiment, as the vibration sensor 1, a vibration sensor having a high sensitivity to a high frequency range of 2 kHz or more is used, and as a result of observation by changing a detection frequency band, It was found that the signal around 500 Hz best captured the progress of the dissolution. 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 with a small arc power, in order to eliminate these vibrations, an amplifier 2 (for example, an active filter) incorporating a band-pass filter that allows only a frequency band unique to the arc to be used, or It is effective to provide a bandpass filter before the vibration measuring device 4. Arc specific frequency is 10
It is in the range of about 0 Hz to 500 Hz, and particularly in an AC arc furnace, it is preferable to select the pass band of the band-pass filter around twice and six times the commercial power supply frequency.

Since the inside of the arc furnace is extremely high temperature and is affected by flame and dust, and the properties of the scrap are various, it has been difficult to correctly evaluate the progress of melting until now. However, according to the first and second embodiments described above, it is possible to accurately grasp the transition time to the short arc of low voltage and large current in the latter stage of the melting and the start time of the injection of the coal powder, which are particularly important in the arc melting process. Also, since the vibration sensor for detecting the vibration of the furnace shell is arranged outside the furnace shell, there is no trouble due to splash or flame, so that there is no maintenance problem. Also, since there is almost no ingot adhesion at the level of the molten steel upper surface, the vibration sensor attached in the vicinity is not affected by the ingot attachment, and the vibration according to the amount of the remaining cold iron source can be detected with good reproducibility. In addition, it is possible to set an appropriate arc in accordance with the progress of melting and to blow oxygen and coal powder, thereby improving melting efficiency.

[0026]

As described above, according to the present invention, in the method for evaluating the melting progress of the charged raw material in the arc melting furnace, the vibration generated from the arc as the heat source and transmitted to each part of the furnace shell is detected. Vibration sensors are attached to a plurality of locations with different mounting heights on the furnace shell, and the detection signals of the plurality of vibration sensors are converted into measurement vibration levels by measuring means, respectively, and the change in the plurality of measurement vibration levels is reduced. As a result, the progress of the melting of the charged raw materials was evaluated by comparing and judging the results.As a result, it is necessary to accurately grasp the remaining state of scrap in the furnace from the late melting stage to the refining stage, which is particularly important in the arc melting process. Switching to the short arc and the timing of the transition to the refining period can be performed properly, and wasteful power in the latter stage of melting can be suppressed, and power consumption can be reduced. There can also be reduced damage to the furnace wall refractories while being reduced.

According to the present invention, only a signal in a specific frequency band unique to the arc is extracted from the detection signals of the plurality of vibration sensors attached to the furnace shell, and converted into a measured vibration level by the measuring means. Since the dissolution progress of the charged material is evaluated by comparing and judging the low frequency transition of each of the plurality of measured vibration levels in the specific frequency band, the accuracy is higher than the case where the frequency band of the measured vibration level is not limited. Evaluation results can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for implementing a melting progress evaluation method for 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 Vibration sensor 2 Amplifier 3 Filter 4 Vibration measuring device 5 Progress evaluation device 6 Voltage / current setting device 7 Electrode up / down control device 8 Arc current control device 9 Chart display 10 Graphite electrode 11 Furnace lid 12 Furnace shell 13 Hearth 14 Scrap 15 Arc 16 Slag 17 Molten steel

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

Claims (2)

[Claims] 1. A method for evaluating the melting progress of a charged raw material in an arc melting furnace, wherein vibrations generated from an arc as a heat source and transmitted to respective parts of the furnace shell are respectively detected, so that mounting heights to the furnace shell are different. A vibration sensor is attached to each of a plurality of locations, the detection signals of each of the plurality of vibration sensors are converted into a measured vibration level by a measuring unit, and the reduction transition of each of the plurality of measured vibration levels is compared and determined to thereby determine a charge material. A melting progress evaluation method for an arc melting furnace, wherein the melting progress evaluation is performed. 2. Extracting only signals in a specific frequency band unique to an arc from detection signals of the plurality of vibration sensors and converting them into measurement vibration levels by measuring means, respectively. 2. The method for evaluating the melting progress of an arc melting furnace according to claim 1, wherein the melting progress of the charged raw material is evaluated by comparing and judging the transition of the low range.