JPS637616B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for predicting the escape phenomenon of slag and molten steel, so-called sloping, which occurs during steel refining.

Refining of molten steel in a refining furnace, such as a converter, involves inserting a lance vertically into the furnace from the mouth of the converter, spraying pure oxygen gas onto the molten steel from the lance, decarburizing the molten steel while stirring it, and then converting it. Dephosphorization and desulfurization are carried out through the reaction of the slag-forming agent put into the furnace with the molten slag that is generated.
During this slag formation process, slag forms depending on conditions such as slag composition, viscosity, oxygen potential, etc., and as this progresses, slag and molten steel escape phenomenon, so-called sloping, may occur. When this slopping occurs, it greatly affects the molten steel composition, steelmaking yield, etc., and also reduces blowing control efficiency.
This will lead to damage such as melting of the refractories of the slag line, so it is necessary to suppress this as much as possible.

Acoustic measurement method (Japanese Unexamined Patent Publication No. 45615, 1983) and vibration measurement method (Unexamined Japanese Patent Publication No. 1983-1983) are used to predict the occurrence of slag by determining the slag level during blowing in a converter.
77816), a furnace pressure measurement method, a microwave measurement method (Japanese Patent Application Laid-Open No. 118161/1983), etc. are known. The acoustic measurement method is a method to predict the occurrence of slag by estimating the slag level based on the degree of attenuation of the sound generated from inside the furnace during blowing. This is a method of measuring vibration and estimating the slag level or slag condition based on the degree of vibration to predict the occurrence of slopping. Furnace pressure measurement method measures fluctuations in furnace pressure during blowing and calculates the fluctuations. This is a method to predict the occurrence of slopping by estimating the slag level based on the degree of
The microwave measurement method is a method that projects microwaves directly into the furnace during blowing and directly measures the slag level using the principle of FM radar to predict the occurrence of sloping. The above-mentioned acoustic measurement method, vibration measurement method, and furnace pressure measurement method are all indirect measurement methods, and cannot quantitatively grasp the slag level and state of the slag, and the accuracy of predicting the occurrence of slopping is low. On the other hand, although the microwave measurement method described above, which is the basis of the method of the present invention, can directly and quantitatively grasp the slag level, subsequent research has shown that monitoring the slag level alone is not sufficient to predict the occurrence of slopping. It became clear. In other words, it has been found that even if the slag level is constant, there is a difference in the probability of slopping occurring if the slag properties, particularly fluidity and viscosity, differ.

The present invention has been made based on this knowledge, and an object of the present invention is to provide a method for accurately predicting the occurrence of sloping by monitoring the properties of the slag.

The sloping prediction method according to the present invention projects microwaves toward the slag from an antenna installed above the smelting furnace mouth, detects reflected waves from the slag, and calculates the slag level and the microwave reflectance on the slag surface. The method is characterized in that it measures the occurrence of sloping and predicts the occurrence of sloping based on the measurement results.
In other words, the slag properties are determined by the microwave reflectance.

The method of the present invention will be specifically explained below based on the drawings. FIG. 1 is a schematic diagram showing the implementation state of the method of the present invention. In the converter 1, a lance 2 for oxygen blowing is inserted vertically from the furnace mouth 1a at the upper opening, and the upper part of the furnace mouth is covered with a hood 5, and the waste gas generated in the converter refining is passed through the hood 5. The gas is guided and supplied to a waste gas recovery system or the like, or is disposed of through the hood 5. 4 is the molten steel that is being refined by the oxygen etc. from the lance 2 from the main raw materials such as hot metal and scrap charged into the converter at the start of the converter refining, and 3 is the molten steel that is being refined by the oxygen etc. from the lance 2 after the start of oxygen blowing. This is slag produced by the sludge from input sludge-forming agents such as limestone, quicklime, and fluorite.

In the method of the present invention, an antenna 6 is installed above the converter mouth 1a in order to project microwaves toward the slag 3 with the direction of transmission and reception being vertical. The antenna 6 is installed, for example, by inserting a cylindrical jacket 7 into the hood 5 with its axial direction vertical, and attaching the antenna 6 to the upper end of the jacket 7. In order to prevent damage to the antenna 6 due to fire, dust, and metal scattering from the converter 1, and to avoid deterioration of slag detection accuracy, the antenna 6 has a water-cooled structure, and the inside of the jacket 7 is equipped with N ₂ gas, etc. It is preferable to purge. The antenna 6 connects to the microwave generator 1 via a microwave circuit 9 including a waveguide (not shown), a reference reflector 8, and a circulator.
0, and the microwave circuit 9 is connected to a signal processing circuit 12 and a recorder 13. Frequency-modulated microwaves are emitted from the microwave generator 10, and this microwave signal passes through the microwave circuit 9 and the reference reflector 8, and is turned into microwaves from the antenna 6 toward the slag 3 in the converter 1. The microwaves projected by the slug 3 and reflected by the slug 3 are received by the antenna 6, inputted to the microwave circuit 9 via the reference reflector 8, and the circulator of the microwave circuit 9 generates a beat between the projected wave and the reflected wave. Waves (mixed waves) are obtained. A signal related to this beat wave is input to the signal processing circuit 12, and a signal corresponding to the slag level and the microwave reflectance on the slag surface is obtained as described later, and the occurrence of sloping is predicted based on these signals. Note that the signal is recorded on the recorder 13. FIG. 2 shows an example of the signal processing circuit 12, which includes a frequency counter section 1 that counts the frequency of the beat wave for each modulation period.
2a and a D/A converter 12b for D/A (digital/analog) conversion of the count signal, a rectifier circuit 12c for measuring the amplitude of the beat wave, and a rectified output smoothing circuit 12d.

Next, the principle of predicting the occurrence of slopping according to the method of the present invention will be explained. Microwaves generally projected onto an object and microwaves reflected from _the object
u ₂ as u ₁ = U ₁ cos (2πf ₁ t−φ ₁ ) …(1) u ₂ = U ₂ cos (2πf ₂ t−φ ₂ ) …(2) However, U ₁ : Projected wave amplitude f ₁ : Projected wave frequency φ ₁ : Projected wave phase angle U ₂ : Reflected wave amplitude f ₂ : Reflected wave frequency φ ₂ : Reflected wave phase angle t : When expressed as time, the beat wave P of the projected wave and reflected wave is expressed by the following formula. expressed.

P = 1/2 [U ₁ ² + U ₂ ² + 2U ₁ U ₂ cos {2π (f ₁ − f ₂ ) t − φ}] … (3) where, φ: beat wave phase angle or projected wave frequency f ₁ and the frequency of the reflected wave f ₂ is f ₂ = f ₁ −f〓 2x/C …(4) where x: distance from the antenna to the object surface C: microwave propagation speed f〓: frequency due to reflection Since there is a relationship between the rate of change, the frequency f _b of the beat wave P is f _b =f ₁ −f ₂ =f〓 2x/C (5), and is proportional to the distance x from the antenna to the object. Also, the amplitude U of the beat wave P is U = (U ₁ + U ₂ ) ² / 2 - (U ₁ - U ₂ ) ² / 2 = 2U ₁ U ₂ = 2ΓU ₁
² ...(6) However, Γ is the microwave reflectance on the slag surface, and is proportional to the microwave reflectance on the object.

Therefore, when microwaves are emitted toward the slag, the slag level and the microwave reflectance on the slag surface can be measured from the beat waves of the projected waves and the microwave reflected waves on the slag surface. That is, the frequency counter section 12a described above
Since it counts the frequency f _b of the beat wave, data regarding the slug level can be obtained from its output.
2d provides data regarding the microwave reflectance on the slag surface. The microwave reflectance on the slag surface is a value determined by the fluidity, viscosity, etc. of the slag, so by measuring the reflectance at the same time as the slag level and using this as data for predicting sloping, It is also possible to grasp changes in the occurrence of sloping that cannot be grasped by the level alone, and the accuracy of predicting the occurrence of sloping is increased.

Next, examples of the method of the present invention will be described. In Figures 3 and 4, the horizontal axis shows the blowing time as a percentage of the total blowing time, and the vertical axis shows the slag level and microwave reflectance with the furnace mouth level as 0. These are graphs showing changes in slag level (shown by the solid line) and changes in microwave reflectance (shown by the broken line) during the period. Each represents a case in which there is no problem. In Figure 3, slopping occurred in the area where the blowing time was around 50% (indicated by diagonal lines in the graph), but when the slag level was above a certain value (above S in the figure),
It has been found that sloping occurs when the microwave reflectance is below a certain value (below R in the figure). Figure 5 shows the relationship between these two conditions and the presence or absence of slopping, with the horizontal axis representing the microwave reflectance and the vertical axis representing the slag level.
In the figure, the case where sloping occurs is indicated by the black circle.
In addition, the white circles represent the cases in which sloping did not occur. By setting the condition that the slag level is above a certain value S and the microwave reflectance is below a certain value R (the shaded area in the figure) as the sloping occurrence prediction level, the occurrence of sloping can be predicted by 80% or more. I was able to do that.

Therefore, the conventional microwave measurement method (Japanese Unexamined Patent Publication No. 1983
118161), which predicts the occurrence of slopping by simply estimating the slag level, that is, determines that sloping has occurred when the slag level exceeds S. It is clear that the probability of prediction is significantly lower than 80% because there are many white circles that are included. In other words, according to the method of the present invention, the prediction rate is over 80%, whereas with the conventional microwave measurement method,
significantly lower than 80%.

On the other hand, the over-alarm rate is also used to evaluate the sloping prediction method. This over-alarm rate is defined as over-alarm rate = (number of opportunities without sloping)/(number of predicted opportunities) x 100%.

In the example shown in FIG. 5, the over-alarm rate is 15% or less in the present invention, whereas it is 45% or less in the conventional microwave measurement method, demonstrating that the prediction accuracy of the present invention is high.

This is considered to be due to the following reasons.

In other words, even if the slag level is constant, the possibility of slopping occurring varies depending on the Co gas bubbles trapped in the slag. When large bubbles of Co gas exist in the slag, the number of bubbles is small, and therefore there are few iron particles and slag around the bubbles, and in such a case, the reflectance is low. On the contrary, Co
When there are small gas bubbles, the number of bubbles is large;
In addition, there is a lot of granulated iron and slag around it, and in such cases the reflectance is high. This is because granular iron and slag have electrical properties that contribute to high reflectance.
This is because the ratio of the latter to bubbles having electrical properties that contribute to lowering the reflectance is higher than the former. Since larger bubbles have a larger impact force when they collapse, surrounding iron particles are more likely to be scattered, causing sloping. In short, there is a relationship in which sloping is more likely to occur as the reflectance is lower.

As detailed above, the method of the present invention predicts the occurrence of sloping based on both the slag level and the microwave reflectance on the slag surface, so even if the properties of the slag are different, the occurrence of sloping can be predicted with high accuracy. It has great effects on stabilizing molten steel components, improving steelmaking yield, improving blowing control efficiency, and preventing erosion of refractories in slag lines.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the implementation state of the present invention, Figure 2 is a schematic diagram showing the implementation state of the present invention.
The figure is a block diagram showing one example of a signal processing circuit.
Figures 5 to 5 are graphs showing the effects of the method of the present invention. DESCRIPTION OF SYMBOLS 1... Converter, 3... Slag, 4... Molten steel, 6... Antenna, 9... Microwave circuit, 10... Microwave generator, 12... Signal processing circuit.

Claims (1)

[Claims] 1. Project microwaves toward the slag from an antenna installed above the smelting furnace mouth, detect the reflected waves from the slag surface, measure the slag level and the microwave reflectance on the slag surface, and apply the measurement results to the slag. A sloping prediction method characterized by predicting the occurrence of sloping based on the following.