JPS6225727B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a blowing control method that controls the settings of, for example, the amount of oxygen fed, the height of the lance, the amount of auxiliary material input, etc., based on furnace condition data detected using a microwave slag level meter. Blowing in a converter involves, for example, blowing pure oxygen gas onto the molten steel from a lance inserted through the mouth of the converter to decarburize the molten steel while agitating it, or to cause de-adjacent and desulfurization reactions to occur. By the way, maintenance of an appropriate slag level and slag slag status is an important operational control item for stable blowing. An abnormality in the slag level indicates the precursor to so-called slopping, in which slag becomes foamy and blows out from the furnace mouth.Furthermore, poor slag slag formation affects the progress of deaggregation and desulfurization, both of which are important for steelmaking. It is known to have a significant impact on component quality and yield. For this reason, various methods for detecting the slag level and the state of slag slag have been proposed and put into practice. For example, one method of detecting the slag level is to detect the sound of a specific frequency in the converter, detect the forming state of the slag by analyzing the level, and predict the slag level accordingly ( (Japanese Patent Application Laid-Open No. 154517/1983). However, this method has problems such as low detection accuracy because the sound source position and intensity change, and the relationship between slug forming and sound is insufficient. In addition, the method of detecting the slag slag condition is to use a sublance to sample the slag intermittently during the blowing period and analyze the concentration of each component in the slag, especially the FeO concentration, to detect the slag condition. There is a method of detecting the vibration of the lance during smelting, capturing the kinetic energy of the slag as the vibration energy of the lance, and indirectly detecting the slag formation status. However, in the case of the former, these methods can only obtain indirect data, and sample collection and analysis require time, resulting in significant time delays in the detection data.
On the other hand, since the latter is an indirect detection method,
The detection accuracy was low, and when the amount of slag was small, the lance and slag did not come into contact, making detection impossible. The present inventors conducted experiments and research on a method for detecting the slag level and slag slag formation during the blowing process as described above, and as a result, they projected microwaves onto the slag surface and captured the microwaves reflected from the slag surface. , the frequency and slag level of the beat wave (hereinafter referred to as mixed wave) generated by mixing the projected microwave wave and the reflected wave, the microwave reflectance from the slag surface, the slag level, and the slag slag formation status,
Furthermore, we found that there is a close relationship with the occurrence of slopping. Incidentally, the relationship between the frequency of the mixed wave and the slag level is shown in FIG. 1A, and the relationship between the microwave reflectance and the state of slag formation is as shown in FIG. 1B. The graph shown in FIG. 1A shows the frequency (Hz) on the horizontal axis and the slug level on the vertical axis, and as is clear from this graph, the existence of a certain proportional relationship is recognized. In addition, the graph shown in Figure 1B shows the microwave reflectance on the horizontal axis and the T/Fe concentration in the slag, which is used to evaluate slag formation, on the vertical axis. It is recognized that there is a certain negative correlation. This means that the microwave reflectance is T・Fe
This is thought to be due to the fact that the degree of attenuation of the reflected waves increases in slag with a high slag, that is, in a good slag state. Note that this microwave reflectance also has a certain relationship with the slag level, as shown in FIG. 1C. The graph in Figure 1 C shows the blowing time on the horizontal axis, the slag level (m) on one side on the vertical axis, and the microwave reflectance (relative value) on the other side. The solid line shows the slag level, and the dashed line shows the microwave reflectance. As is clear from this graph, the microwave reflectance has a reciprocal relationship with the slag level, and from the graphs shown in FIG. It is permissible to show a relationship. Moreover, the occurrence of slopping, which is one of the main purposes of slag level detection, has been empirically shown to have a close relationship with the slag level and microwave reflectance, as shown in FIG. 1D. The graph shown in Figure 1D shows the microwave reflectance on the horizontal axis and the slag level detected based on the mixed wave frequency on the vertical axis, and the shaded area in the graph is the area where slopping occurs. It is. The present invention has been made based on this knowledge, and its purpose is to improve the mixed wave frequency of the projected wave and the reflected wave when microwaves are projected onto the slag surface, as well as the microwave frequency. The wave reflectance is detected, and based on this detection data, the slag level and slag slag formation situation are detected, and the system can predict the occurrence of slopping, inject sedatives to prevent slopping, adjust the lance height, adjust the oxygen supply amount, and more. The object of the present invention is to provide a blowing control method that allows accurate and rapid control of settings such as the timing and amount of slag injection. The blowing control method according to the present invention projects microwaves onto the slag surface in a converter, captures the microwaves reflected from the slag surface, and determines the frequency of the mixed wave of the projected waves and reflected waves and/or the slag surface. Calculate the microwave reflectance at It is characterized by setting control. First, the principle of the blowing control method according to the present invention will be explained below. Detection of the slag level based on the mixed wave frequency of the microwave projected onto the slag surface and the reflected wave from the microwave is performed as follows. That is, there exists a relationship between the two as shown in FIG. fb = 2L/C・f ₀ ...(1) However, fb: Mixed wave frequency (Hz) L: Distance between furnace mouth and slag surface f ₀ : Frequency change rate (Hz/sec) C: Microwave propagation speed ( (3×10 ⁸ m/sec) This slag level has a close relationship with the microwave reflectance as shown in Figure 1 C, and although it is not specifically shown, the microwave reflectance is multiplied by a predetermined coefficient. It is presumed that it can be easily obtained by this. Next, the state of slag slag formation based on the microwave reflectance is detected as follows. First, the microwave reflectance K is the projected microwave u ₁ to the object as shown below (2)
Expressed in the formula, the reflected microwave u ₂ from an object is as follows:
Since it is expressed as equation (3), its relative value u ₂ / u ₁
given as. u ₁ = U ₁ cos (ω ₁ t) ...(2) However, U ₁ : Amplitude ω ₁ : Angular frequency t: Time u ₂ = U ₂ cos (ω ₂ t) ...(3) However, U ₂ : Amplitude ω ₂ : Angular frequency As shown in Figure 1 (b), the microwave reflectance K given as above has a predetermined relationship with the T/Fe concentration in the slag, which represents the state of slag slag formation, and therefore, it is assumed that both The correspondence relationship is determined, and the quality of the slag slag formation can be determined by determining whether the microwave reflectance is the standard value (first
The determination may be made based on whether or not the temperature decreases by more than (shown by the dashed-dotted line in Figure B). Furthermore, as shown in Figure 1D, the occurrence of slopping can be determined by setting predetermined limit values for the slag level and microwave reflectance, respectively, and determining whether or not both exceed the limit values. . Therefore, in a steady state, the lance height, auxiliary material input, oxygen supply amount, etc. are controlled based on a reference pattern that changes over time depending on the blowing time, which has been determined empirically in advance. When an abnormality occurs in the level or slag formation condition, or when slopping conditions are reached, the operator manually monitors the display, etc. until the steady state is restored, or the above-mentioned example It is only necessary to automatically control the settings of each influencing factor, such as the lance height, the amount of oxygen to be fed, or the amount and timing of addition of auxiliary raw materials, slag-forming agents, etc. A specific configuration for carrying out the method of the present invention will be described below. FIG. 2 is a schematic diagram showing the implementation state of the present invention, in which 1 indicates a converter, 2 a hood for collecting waste gas, and 3 a lance for blowing oxygen, etc. The lance 3 is inserted into the converter 1 from the furnace mouth 1a through the hood 2, and its tip is positioned within the slag 1b in the converter 1, so as to blow oxygen into the slag 1b and the molten steel 1c below it. It's getting old. An antenna 5 constituting a microwave slag level meter 4 is installed in the hood 2 above the converter 1 at a position facing the converter mouth 1a. antenna 5
is installed in a water cooling jacket 45a, and is connected to the microwave generator 20 and the signal processing device 30 via a waveguide (not shown) and the microwave circuit 10, so that the microwave from the microwave generator 20 is Depending on the signal, microwaves are projected from the antenna 5 toward the slag surface in the converter 1, and microwaves reflected from the slag are received. FIG. 2 is a block diagram showing the electric circuit system of the microwave circuit 10, the microwave generation circuit 20, and the signal processing device 30. In response to the modulation signal from the frequency modulator 22, the microwave oscillator 21 generates an angular frequency ω. ₁ (ω ₁ /2π = 1 to 1000 GHz), this microwave signal is given to the antenna 5 via the magic T11 of the microwave circuit 10 and the circulator 12, and the microwave is emitted from the antenna 5. It will be done. The reflected wave from the slug 3 is received by the antenna 5, and the microwave signal related to this reflected wave is transmitted to the microwave circuit 1.
0 is input to the circulator 12. The microwave circuit 10 is configured to be able to detect weak reflected wave signals with high sensitivity.
11, a bridge circuit including a circulator 12, a mixer 13, and a variable attenuator 14. The mixer 13 mixes the projected wave signal and the reflected wave signal, and the mixed wave signal is sent to the preamplifier 31 of the signal processing device 30. is input. The mixed wave signal is amplified by the preamplifier 31 and then input to the filter 32, as well as to the frequency detection circuit 35, where the frequency of the mixed wave is detected and the detected frequency signal is input. Output to control circuit 6. On the other hand, the mixed wave signal input to the filter 32 is inputted to the waveform shaping circuit 33 after the DC component, ie, 1/2 (U ² ₁ +U ² ₂ ), etc. is removed.
A microwave modulation signal from the modulation oscillator 22 is also input to the waveform shaping circuit 33, and the mixed wave signal is rectified and smoothed by the waveform shaping circuit 33, and voltages corresponding to the amplitudes U ₁ and U ₂ are obtained. In addition to being output to the recorder 34 and recorded, it is also output to the reflectance detection circuit 36. The reflectance detection circuit 36 detects the reflectance K of the microwave slug by utilizing the fact that the amplitude voltage of the mixed wave signal is proportional to the reflectance K, and outputs this detection data to the control circuit 6. The reason why this reflectance K can be understood as a voltage proportional to the amplitude of the mixed wave is that the mixed wave P is expressed from the projected wave u ₁ and the reflected wave u ₂ as follows, and P = 1/2 { U ² ₁ +U ² ₂ +2U ₁ U ₂ cos(ω ₁ −ω ₂ )
t} When the amplitude U ₁ of the projected wave U ₁ is constant, the amplitudes U ₁ and U ₂ of the mixed wave P are proportional to the amplitude U ₂ of the reflected wave U ₂ , so the reflectance K is the amplitude of the mixed wave P. This is because it corresponds to The control circuit 6 operates according to the above equation (1) based on the frequency f _b of the mixed wave input from the frequency detection circuit 35, the frequency change rate (Hz/sec) input in advance, and the microwave propagation speed C. In addition to calculating the slag level L and outputting it to the display 7n, it is compared with the upper limit Lu and lower limit Ld of the slag level input in advance to determine whether the condition Ld≦L≦Lu is satisfied. If the slag level L exceeds this condition, the display 7n displays an alarm, and a signal is issued to emit an alarm sound. This is a slag level influencing factor. For example, lance height,
In order to control the amount of oxygen to be fed and the amount of auxiliary raw material input, control signals are output to the lance height setting device 7a, the amount of oxygen feed setting device 7b, the amount of auxiliary material input amount setting device 7c, etc., respectively. The control circuit 6 also controls the slag slag conversion based on the microwave reflectance K input from the reflectance detection circuit 36 and related data with the T/Fe concentration in the slag as shown in FIG. detect the situation,
This detected data is output to the display 7n, and the deviation is determined by comparing it with a standard pattern of slag slag formation that has been input in advance in relation to the blowing time, and when this deviation exceeds a certain level. In order to eliminate deviations, a slag agent input amount setting device is used to control factors that influence the slag slag formation status, such as the slag agent input amount.
It is designed to output a control signal at a distance of 7m. Furthermore, the control circuit 6 compares the slag level L obtained in the above process and the microwave reflectance K input from the reflectance detection circuit 36 with a pre-input limit value for preventing the occurrence of sloping, and determines the slag level L. , when the microwave reflectance K exceeds the limit value, it is directly determined that slopping has occurred and an alarm is displayed on the display 7n, and a control signal is sent to each setting device 7a etc. to set and control the aforementioned slag level influencing factors. is now output. Next, an example of blowing control by the method of the present invention will be explained using specific numerical values. The converter used was a 150-ton LD converter, and the blowing control during the process of melting high carbon ordinary steel, especially the slopping prevention control, is shown in Figure 4. The control pattern is shown. The graph in Figure 4 shows the blowing time (%) on the horizontal axis, and the level (m) relative to the furnace mouth, the amount of oxygen supplied (Nm ³ /min), and the microwave reflectance (relative value) on the vertical axis. In the graph, A is the slag level, B is the microwave reflectance,
Lu and Ld are the upper and lower limit values of the slag level, and a
is the lance height, b is the time of inputting the auxiliary material (iron ore),
c indicates the amount of oxygen supplied. As is clear from this graph, the slag level L exceeds the slag level upper limit Lu in the early and middle stages of blowing, but in the early stage of blowing, on the other hand, it is necessary to reduce the amount of oxygen supplied. Therefore, the slag level is lowered to prevent slopping, and in the middle stage of blowing, auxiliary materials are added to cool the slag, and the release of CO bubbles from the slag is improved, and the lance is raised. Reduces slag level,
Efforts were made to prevent slopping. As a result of such blowing control, the degree of occurrence of slopping was as shown in FIG. FIG. 5 is a graph showing the frequency of slopping when the method of the present invention is applied, as described above, in comparison with when the conventional method is applied, with the date of test implementation on the horizontal axis and the vertical axis. The sloping occurrence frequency index is shown in the graph, and in the graph, the line connecting the plot points of black circles shows the results of the method of the present invention, and the line connecting the plot points of white circles shows the results of the conventional method. As is clear from this graph, when the method of the present invention is used, the frequency of slopping occurrence is significantly reduced compared to when the conventional method is used. The results of melting in this test are as shown in Table 1.

[Table] The actual results in Table 1 above are before tapping in the LD converter. As is clear from Table 1, both the components and the temperature substantially matched the target values, indicating that the purification was carried out appropriately. In the above control example, when the slag level exceeds the upper limit, a configuration is shown in which different controls are performed separately at the early and middle stages of blowing, but this is not particularly limited. Influence factors that can most effectively control the slag level and slag slag condition may be determined in advance for each of various conditions, and may be set and controlled entirely, selectively, or arbitrarily depending on each condition. Of course. The control may be performed automatically as described above, but the operator may
This may be done manually depending on each situation while monitoring. As described above, in the method of the present invention, microwaves are projected onto the slag surface, the microwaves reflected from the surface are detected, and based on this detection signal, the mixed wave frequency of the projected microwave and the reflected microwave, as well as the We determined the microwave reflectance from the slag surface, detected the slag level and slag slag status based on these calculated data, and set and controlled each influencing factor accordingly. It is possible to accurately control the lance height adjustment, oxygen supply amount adjustment, auxiliary raw material input, slag forming agent input, etc. according to the furnace conditions, and the occurrence of slopping and poor slag slag formation can be significantly reduced. The present invention has excellent effects such as improved steel quality and yield.

[Brief explanation of the drawing]

Figure 1 A, B, C, and D show the mixed wave frequency, microwave reflectance, and slag level used in the method of the present invention.
A graph showing the relationship between the slag formation situation and the slopping occurrence area, etc., Fig. 2 is a schematic diagram showing the implementation state of the method of the present invention, Fig. 3 is a block diagram of the control system implementing the method of the present invention, and Fig. 4 5 is a graph showing an example of sloping prevention control using the method of the present invention, and FIG. 5 is a graph showing the results of a comparative test between the method of the present invention and the conventional method. 1...Converter, 2...Hood, 3...Lance, 4
...Microwave slag level meter, 5...Antenna, 6...Control circuit, 7a, 7b...7m...Setter, 10...Microwave circuit, 20...Microwave generator, 30...Signal processing circuit .

Claims (1)

[Claims] 1 Project microwaves onto the slag surface in the converter, capture the microwaves reflected from the slag surface, calculate the frequency of the mixed wave of the projected wave and reflected wave, and the microwave reflectance on the slag surface, and calculate these. A blowing control method characterized by detecting a slag level and a slag slag formation condition based on calculated values, and setting and controlling these influencing factors to maintain the slag level and slag slag formation condition at a predetermined reference state. .