JP5152050B2 - Method and apparatus for continuous monitoring of molten steel - Google Patents

Description

  The present invention relates to a continuous monitoring method and a continuous monitoring apparatus for continuously monitoring a metal, particularly a molten metal in a steel refining furnace, by a spectroscopic measurement method.

  In the refining process of a metal material, monitoring the concentration of component elements in the molten metal during the refining reaction in real time is very important for refining process optimization control. Hereinafter, steel will be described as an example of the metal material.

  In converter refining, where decarburization is performed by oxygen blowing in the steel manufacturing process, steelmaking such as an increase in total Fe concentration in slag due to excessive blowing, excessive free oxygen concentration in molten steel, and decrease in yield of Fe and Mn. In order to completely control the cost increase factor, it is not enough to perform point measurement with current sublances, and continuous monitoring of carbon concentration in molten steel is strongly required.

  Next, in the secondary refining technique, for example, a case of a mass production degassing apparatus RH will be described. The main goal of RH is decarburization, which requires continuous component measurements and two methods are commonly employed. It is important to understand the behavior of the C component in the degassing process. In particular, avoid the wasteful use of steam when evacuating by ending the process when the target C concentration is reached. Cost reduction is possible. In degassing, the inside of the tank is evacuated to remove C as CO gas. The C concentration during the treatment is measured by measuring the CO concentration in the exhaust gas and subtracting the amount of C discharged from the C concentration in the molten steel at the start of the treatment to estimate the C concentration in the molten steel during the treatment. The accuracy is not high. The other method is to take a sample of molten steel close to the surface of the ladle and quickly analyze it with an emission spectrometer. Component analysis such as C and other Mn is possible, but samples are collected in batches. In addition, since the processing is performed by an analysis device at a location away from the degassing apparatus, it is a drawback that it is impossible to quickly follow the component change in the degassing process.

  As a technique for continuously monitoring the concentration of chemical components in molten steel, a plasma state is generated by focusing a pulse laser with high peak power and irradiating the molten steel, and the light emission from this laser-generated plasma is analyzed spectroscopically. A laser emission analysis method is disclosed (for example, Patent Document 1).

  In the observation of the light emission from the laser-produced plasma, the light emission of all elements contained in the sample, such as the main component and the alloy component, is emitted at the same time. Therefore, in order to measure the light emission intensity of each element, these are separated. A large spectroscope with sufficient resolution is required. Such a large precision device needs to be installed in a place that is not affected by heat, vibration, dust, etc. of the refining equipment. Therefore, it is optimal to use a flexible optical fiber to transmit light emitted from the molten steel surface in the refining furnace to the spectroscope.

  Compared with the laser emission analysis method, the laser-induced fluorescence method, in which a vapor atom is irradiated with a laser tuned to one of the resonance wavelengths of the target element to induce fluorescence of this atom, is highly sensitive and selective. Known as an excellent analytical method, the present inventors have focused on this point and developed a technique for monitoring C and P in molten steel by a laser-induced fluorescence method. Details of this technique are disclosed in Patent Document 2. In analysis using laser-induced fluorescence, an ablation laser is first irradiated to evaporate and atomize a part of the sample. Then, after an appropriate delay time has elapsed from the ablation laser pulse, the selective excitation laser is irradiated. At this time, since only the fluorescence of the target element is selectively emitted, there is no need to use a large spectroscope, and the amount of signal emitted directly from the target element by a light quantity measuring device such as a photomultiplier tube or a photodiode is calculated. Can be measured.

  By the way, in the analysis of molten steel in the refining furnace, the ablation condition cannot always be constant due to various fluctuation factors. As such a variation factor, for example, the laser spot diameter at the molten metal surface irradiation point varies due to the variation in the molten steel molten metal surface height. Based on the method of statistically processing the ratio of the analytical element to the internal standard element (Patent Document 3) and the distance measurement by ultrasonic waves for the purpose of eliminating the variation in the measured value due to the fluctuation of the molten metal surface height. A method of adjusting the laser irradiation lance height and maintaining a constant distance from the molten metal surface (Patent Document 4) is disclosed.

Japanese Patent Laid-Open No. 60-231141 JP 2001-356096 A JP-A-8-15152 JP-A-8-15153

  However, in the molten steel analysis, it has become clear as a result of the examination by the present inventors that there are factors that affect the measurement results in addition to the molten steel surface level fluctuation. That is, in the molten steel analysis, it was found that the focal point of the signal light fluctuated with time, and the incident efficiency on the optical fiber fluctuated. For this reason, there has been a problem that a method of correcting the laser-induced fluorescence intensity fluctuation by the emission intensity of the element for internal standard observed by transmitting with an optical fiber cannot be applied. Although this factor is mentioned later, it is estimated that it is the influence of the heat | fever in the optical path until the signal light generate | occur | produced on the hot_water | molten_metal surface reaches an optical fiber.

  The present invention is based on the emission intensity of a main component measured by a spectroscopic analyzer or other specific element whose concentration can be regarded as constant by detecting a change in incidence efficiency of signal light emitted from laser-produced plasma into an optical fiber. The purpose of this is to make it possible to correct the laser-induced fluorescence intensity and thus improve the accuracy in element concentration measurement.

  The gist of the present invention for achieving the above object is as follows.

(1) A procedure of generating plasma by irradiating a molten steel with a laser beam using a first laser to evaporate a part of the molten steel, and irradiating the plasma with a laser beam using a second laser A step of generating laser-induced fluorescence by resonance-exciting a target element therein to generate fluorescence, condensing the laser-induced fluorescence, and measuring a laser-induced fluorescence intensity of the target element; The plasma emission from the plasma generated by laser light irradiation is collected, transmitted by an optical fiber cable, and then the intrinsic emission line intensity of iron plasma emission obtained by spectrum measurement using a spectroscope is used to determine the target element. A method for continuously monitoring molten steel, including a procedure for correcting laser-induced fluorescence intensity, wherein the plasma emission is collected by a lens and incident on an optical fiber receiving end face In a cross section perpendicular to the optical axis of the plasma emission branching light, an image obtained by branching a part of the plasma emission before detection and detecting the plasma emission branching light with an imaging device fixed at a fixed position is used. Continuous measurement of molten steel characterized by measuring the cross-sectional area S of the plasma emission branched light and correcting the laser-induced fluorescence intensity of the target element using a ratio S / S ₀ with a preset value S ₀ Method.
(2) A device for continuously monitoring molten steel by a spectroscopic measurement method, the first laser irradiation means for irradiating the molten steel with laser light to evaporate a part of the molten steel and generating plasma, and the purpose in the plasma Second laser irradiation means for inducing fluorescence by resonantly exciting elements to generate laser-induced fluorescence, a lens for condensing plasma emission from the plasma, an optical fiber cable for transmitting the plasma emission, and the laser induction Condensing means for condensing the fluorescence, means for detecting the amount of the collected laser-induced fluorescence, spectroscopic means for dispersing the plasma emission, and means for branching the plasma emission before entering the optical fiber light receiving end face If, based on an imaging device for detecting the branched plasma emission branched light, the information obtained by the imaging device, a laser induced in the target element Continuous monitoring apparatus molten steel characterized by having a an arithmetic unit for correcting the fluorescence intensity.

  According to the present invention, variation in laser-induced fluorescence intensity due to variation in ablation conditions can be correctly corrected with iron emission intensity, so that there is little variation in measurement sensitivity, and chemical component concentrations in molten steel can be measured with high accuracy. It greatly contributes to improving the controllability of steelmaking operations by monitoring the decarburization reaction in secondary refining.

It is a block diagram which shows an example of the molten steel continuous monitoring apparatus in connection with this invention. It is a block diagram explaining the mechanism of observation of the image of plasma luminescence condensed by a lens of Drawing 1, and the movement of a condensing lens holder. 2 is a graph showing the relationship between carbon concentration in molten steel and laser-induced fluorescence intensity of carbon according to Example 1. FIG. It is the graph which showed the measured value of the iron emission intensity by Example 1, and the correction value of the iron emission intensity corrected using the imaging spot area of plasma emission. It is the graph which showed the result of having correct | amended the laser-induced fluorescence intensity of carbon of FIG. 3 using the correction value of FIG. It is the graph which showed the relationship between the carbon concentration in molten steel and the laser-induced fluorescence intensity of carbon in a comparative example. It is a graph which shows the measurement result of the plasma luminescence intensity of iron in a comparative example. It is the graph which showed the result of having correct | amended the laser-induced fluorescence intensity of carbon of FIG. 6 using the iron emission intensity of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a molten steel continuous monitoring apparatus of the present invention. The ablation laser light a oscillated and output from the ablation laser oscillator 1 is reflected by the ablation laser light reflecting mirror 3, passes through the hollow tube 23 through the window member 20, and irradiates the analysis surface 25 which is the surface of the sample 24. Is done. Here, the ablation laser light a is condensed by a lens (not shown) so as to be focused in the vicinity of the analysis surface 25. The plasma emission c generated on the analysis surface 25 passes through the hollow tube 23, is reflected by the plasma emission reflection mirror 5, and is collected on the optical fiber light receiving end face 12 by the condenser lens 7. The plasma emission c is transmitted to the spectroscope 28 through the optical fiber cable 13 and the emission intensity of each element is measured by performing spectral analysis. An inert gas is supplied from the inert gas inlet 21 into the hollow tube 23.

  The selective excitation laser beam b is oscillated by the selective excitation laser beam 2 at a fixed time interval from the oscillation of the ablation laser beam a. Here, the wavelength of the selective excitation laser b is adjusted to the wavelength that is resonated with and absorbed by the element to be analyzed by the laser-induced fluorescence method. The selective excitation laser beam b is reflected by the selective excitation laser reflection mirror 4, passes through the hollow tube 23, and irradiates the analysis surface 25 that is the surface of the sample 24. The analysis target element present in the plasma generated by the irradiation of the ablation laser beam a is resonantly excited by the selective excitation laser beam b, induces fluorescence, and emits laser-induced fluorescence d. The laser-induced fluorescence d is reflected by the laser-induced fluorescence reflecting mirror 6, passes through the lens 16 and the optical filter 17, enters the light amount detector 18, and the light amount is converted into an electric current. It is sent to the device 29 and the laser-induced fluorescence intensity is measured.

A part of the plasma emission c is reflected by the plasma emission branch mirror 11 (plasma emission branch light c ₁ ) and enters the image sensor 14. As shown in the block diagram of FIG. 2, the image of the plasma emission branched light c ₁ obtained by the imaging device 14 is sent to the image analysis device 31 by the video signal transmission cable 15, and the image size (for example, diameter D) or The image area S is measured. Thus, the cross-sectional dimension or cross-sectional area of the plasma emission branched light c ₁ in a cross-section perpendicular to the optical axis of the plasma emission branched light c ₁ is measured. The image can also be observed by the monitor 30. Then, the control device 32 uses the preset image size D ₀ or image area S ₀ and the measured value D or S, and corrects the plasma emission intensity of iron by the ratio S / S ₀ thereof. For example, when the plasma emission intensity measurement value of iron sent from the spectroscope 28 is I and the image area at this time is S, the data analysis device 29 uses the correction value Ic = I × (S / S ₀ ). The measured laser-induced fluorescence intensity is corrected.

  Here, as the imaging device 14, an imaging device using a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor) is suitable. The plasma light emission branch mirror 11 is preferably capable of reflecting 1% or more of the plasma light emission c on the surface thereof. Those having a reflectance of 4 to 10% are more preferable. The back side should be anti-reflective coated to avoid double images. If the plasma emission branching light intensity is too strong to accurately measure the image size, a filter may be inserted on the incident surface of the image sensor 14 as necessary. The plasma emission branch mirror 11 and the image sensor 14 are arranged so that the optical path lengths from the condenser lens 7 to the optical fiber light receiving end face 12 and the image sensor 14 are equal. As shown in FIG. 1, the mirrors 3, 4, 5, 6, lenses 7, 16, the image sensor 14, the light amount detector 18 and the like are not affected by heat, vibration, dust, etc. from around the sample 24. In addition, it is arranged in the protective case 22.

  Here, the operation of the present invention will be further described. During continuous monitoring of molten steel, the hollow tube 23 is heated from the outside by molten steel radiation or the like. For this reason, Ar flowing through the hollow tube 23 has a higher temperature outside the center and is considered to have a slightly different refractive index in the radial direction. As a result of the distribution of the refractive index of the medium (Ar) in the direction perpendicular to the optical axis (the radial direction of the hollow tube), the inside of the hollow tube 23 is similar to the gradient index lens due to the thermal lens effect. It is thought that it has the effect of. The plasma emission c that has passed through the hollow tube 23 is affected by this lens. As a result, the image formation size at the optical fiber light receiving end face 12 is changed, and the incident efficiency to the optical fiber is changed. It is estimated that changes in intensity appear. The temporal change due to the temperature rise of the hollow tube 23 is independent of the fluctuation of the ablation condition due to the molten metal surface vibration or the like. Therefore, unless the influence of this change is separated, the laser induced by the emission intensity of Fe is induced. Correction of fluorescence intensity was not possible. In the present invention, by monitoring the imaging dimension of the plasma emission c and correcting the plasma emission intensity of iron based on this, it is possible to eliminate the above-mentioned temporal variation factors due to thermal effects.

  The measuring apparatus shown in FIG. 1 was brought close to the molten steel surface melted in the induction melting furnace, and the carbon concentration in the molten steel was measured by a laser induced fluorescence method. A Q switch pulse Nd: YAG laser was used as the ablation laser, and a titanium sapphire laser was used as the selective excitation laser. Ar gas was introduced from the inert gas inlet 21 and analyzed while blowing from the lower end of the hollow tube 23 onto the molten steel surface (analysis surface 25). Here, the wavelengths of the ablation laser beam a and the selective excitation laser beam b are 1064 nm and 248 nm, respectively, and the time interval (that is, the delay time) between the irradiation of the ablation laser beam a and the irradiation of the selective excitation laser beam b is 70 μs. Set to. The pulse time widths of the ablation laser beam a and the selective excitation laser beam b were about 10 ns and 25 ns, respectively. The molten steel irradiation pulse energy of the ablation laser beam a was 200 mJ. The carbon concentration in the molten steel was successively increased by melting extremely low carbon steel having a carbon content of about 10 ppm and then adding a high carbon content steel. Laser-induced fluorescence measurements were performed at each concentration level. As the carbon concentration in the molten steel to be referred to, a value obtained by sampling a part of the molten steel at each concentration level, solidifying, and quantified by the combustion infrared absorption method was used.

  As the image sensor 14, a 1.3 megapixel CMOS camera module was used. As the plasma emission branching mirror 11, a synthetic quartz substrate having a broadband (200 to 450 nm) antireflection coating on one side was used, and the plasma emission c was reflected and branched on the surface without the antireflection coating. As the optical fiber cable 13, a bundle fiber in which 12 strands having a fiber diameter of 230 μm were bundled was used. The bundle diameter was 1 mm. The exit end of the optical fiber cable 13 was disposed in front of the entrance slit of the spectrometer 28. The spectroscope 28 is a Czerny-Turner type having a focal length of 390 mm, and a diffraction grating having 2400 grooves / mm is used. A CCD with an intensifier was used as the light amount detector 18.

From the two-dimensional intensity profile of the image obtained by the image analyzer, the area S of the area of 13.5% or more with respect to the maximum intensity was obtained. Assuming that the plasma emission intensity of iron is I, the area measured at the start of the experiment is S ₀ , and the area measured at each concentration level is S, the correction value Ic of the plasma emission intensity of iron is Ic = I × (S / S ₀ ) was calculated, and the laser-induced fluorescence intensity was corrected by dividing the laser-induced fluorescence intensity by this correction value Ic. S ₀ was about 0.06 cm ² .

  3 and 4 show the laser-induced fluorescence intensity and the plasma emission intensity of iron, respectively. FIG. 4 shows the measured value I and the correction value Ic of the plasma emission intensity of iron. FIG. 5 shows the corrected laser-induced fluorescence intensity obtained by dividing the laser-induced fluorescence intensity by the correction value Ic. Comparing FIG. 3 and FIG. 5, it can be seen that the correlation with the carbon concentration [C] is improved by the correction with the correction value Ic of the plasma emission intensity of iron. Table 1 shows the relative standard deviation of the measured values (before correction) of the laser-induced fluorescence intensity for each carbon concentration and the relative standard deviation of the measured fluorescence intensity corrected using the plasma emission intensity of iron. Repeated measurement accuracy at each concentration level was also improved as shown in Table 1.

  As a comparative example, the laser-induced fluorescence intensity of carbon in molten steel was measured under the same conditions as in Example 1.

  FIG. 6 and FIG. 7 show the laser-induced fluorescence intensity and the plasma emission intensity of iron, respectively. FIG. 8 shows the corrected laser-induced fluorescence obtained by dividing the laser-induced fluorescence intensity of FIG. 6 by the iron plasma emission intensity of FIG. Indicates strength. Here, the iron emission intensity in FIG. 7 is not corrected as in the present invention. As seen in FIG. 8, the correlation between the carbon concentration [C] and the corrected laser-induced fluorescence intensity was not improved with respect to FIG.

  The present invention can be applied when continuously monitoring the component element concentrations in the molten metal in real time.

DESCRIPTION OF SYMBOLS 1 Ablation laser oscillator 2 Selective excitation laser oscillator 3 Ablation laser light reflection mirror 4 Selective excitation laser reflection mirror 5 Plasma emission reflection mirror 6 Laser-induced fluorescence reflection mirror 7 Condensing lens 8 Lens holder 11 Plasma emission branch mirror 12 Optical fiber light receiving end face 13 Optical fiber Cable 14 Image sensor 15 Video signal transmission cable 16 Lens 17 Optical filter 18 Light quantity detector 19 Transmission cable 20 Window material 21 Inert gas inlet 22 Protective case 23 Hollow tube 24 Sample 25 Analytical surface 28 Spectrometer 29 Data analysis device 30 Monitor 31 Image analysis device 32 Control device a Ablation laser light b Selective excitation laser light c Plasma emission c ₁ Plasma emission branched light d Laser induced fluorescence

Claims (2)

Irradiating the molten steel with laser light using a first laser to evaporate a part of the molten steel and generating plasma;
The second laser is used to irradiate the plasma with laser light, and the target element in the plasma is resonantly excited to induce fluorescence to generate laser-induced fluorescence. The laser-induced fluorescence is condensed and the target element is condensed. Measuring the laser-induced fluorescence intensity of
The plasma emission from the plasma generated by the laser beam irradiation by the first laser is collected, transmitted through an optical fiber cable, and the intrinsic emission line intensity of the plasma emission of iron obtained by spectrum measurement using a spectroscope is obtained. A method for correcting the laser-induced fluorescence intensity of the target element using, a continuous monitoring method for molten steel, comprising:
Obtained by condensing the plasma emission by a lens and branching a part of the plasma emission before entering the optical fiber light receiving end face, and detecting the plasma emission branched light with an imaging device fixed at a fixed position The cross-sectional area S of the plasma emission branch light in a cross section perpendicular to the optical axis of the plasma emission branch light is measured from an image, and the laser of the target element is used by using a ratio S / S ₀ with a preset value S _0. A method for continuously monitoring molten steel, wherein the induced fluorescence intensity is corrected. A continuous monitoring device for molten steel by spectroscopic measurement,
A first laser irradiation means for generating plasma by irradiating the molten steel with laser light to evaporate a part of the molten steel;
Second laser irradiation means for inducing fluorescence by resonantly exciting a target element in the plasma to generate laser-induced fluorescence;
A lens for condensing plasma emission from the plasma;
An optical fiber cable for transmitting the plasma emission;
Condensing means for condensing the laser-induced fluorescence;
Means for detecting the amount of the collected laser-induced fluorescence;
A spectroscopic means for splitting the plasma emission;
Means for branching the plasma emission before entering the optical fiber light receiving end surface;
An imaging device for detecting the branched plasma emission branched light;
An apparatus for continuously monitoring molten steel, comprising: a calculation unit that corrects the laser-induced fluorescence intensity of the target element based on information obtained by the imaging device.

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