JP5195664B2 - Lance for continuous monitoring of molten steel, continuous monitoring device and continuous monitoring method - Google Patents

Description

  The present invention relates to an apparatus and a continuous monitoring method 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 the steel manufacturing process, converter refining involves decarburization by oxygen blowing. In order to completely control the factors that increase steelmaking costs such as 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, it is necessary to use the current sublance as monitoring of the converter. Only point measurement of the carbon concentration in molten steel is insufficient, and continuous monitoring of the carbon concentration in molten steel in the converter is strongly required.

  Next, consider, for example, a mass production degasser RH in the secondary refining technology. The main goal of RH is decarburization. In degassing, the inside of the tank is evacuated to remove C as CO gas. At that time, it is important to grasp the behavior of the C component in the degassing process. In particular, by terminating the process when the target C concentration is reached, wasteful use of steam when evacuating can be avoided, and costs can be reduced. Decarburization and degassing require continuous component measurement, and two methods are generally employed. In the first method, the CO concentration in the exhaust gas is measured, and the C concentration in the molten steel being processed is estimated by subtracting the amount of C discharged from the C concentration in the molten steel at the start of processing. However, this method is not necessarily highly accurate. The second method is a method in which a sample of molten steel close to the surface of the ladle is collected and quickly analyzed with an emission analyzer. According to the second method, C and other components such as Mn can be analyzed. However, since samples are collected in batches, they are processed by an analyzer away from the degasser. The drawback is that it cannot quickly follow the component changes in the process.

  Therefore, as a technique for continuously monitoring the chemical component concentration in molten steel, a plasma state is generated by focusing pulsed laser light with a high peak output and irradiating the molten steel, and light emission from this laser-generated plasma For example, Patent Document 1 discloses a laser emission analysis method for spectroscopically analyzing the above.

  From the laser-produced plasma, light emission of all the elements contained in the sample such as the main component and the alloy component occurs simultaneously. Therefore, in order to measure the emission intensity of individual elements in the observation of plasma emission, a large spectroscope having a resolution sufficient to separate them 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.

  In contrast to the laser-generated plasma emission analysis method, the laser-induced fluorescence method irradiates vapor atoms with laser light having a wavelength tuned to one of the resonance wavelengths of the target element to induce fluorescence of the atoms. The laser-induced fluorescence method is known as an analytical method having high sensitivity and excellent selectivity. The inventor has paid attention to this point and has developed a monitoring technique for C and P in molten steel by a laser-induced fluorescence method. Details of these techniques are disclosed in Patent Document 2. In analysis using the laser-induced fluorescence method, an ablation laser beam, which is a pulse laser beam having a high peak value, 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, selective excitation laser light is irradiated. At this time, only the fluorescence of the target element is selectively emitted, so there is no need to use a large spectroscope, and the signal emitted from the target element directly by a light quantity measuring device such as a photomultiplier tube or a photodiode. The amount of light 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 the variation factor, for example, the laser spot diameter at the molten-metal surface irradiation point varies due to the variation in the molten steel 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 beam 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 inventor's examination that there are factors that affect the measurement results in addition to the molten steel level fluctuation. That is, in the molten steel analysis, it was found that the focal point of the laser beam and the signal beam was changed with time, and the power density of the laser on the molten steel surface and the incident efficiency of the signal beam to the optical fiber were changed. For this reason, the signal light generation intensity fluctuates, and the measured value of the light emission intensity of the internal standard element fluctuates independently of the fluctuation of the signal light generation intensity, so that there is a problem that the internal standard correction cannot be applied. Although this cause is mentioned later, it is estimated that it is the influence of the heat | fever with respect to propagation of the laser beam and signal light which generate | occur | produced on the molten steel surface until it reaches the molten steel surface.

  An object of the present invention is to solve the above problems and improve analysis accuracy even when the influence of heat is unavoidable as in molten steel analysis.

The gist of the present invention for achieving the above object is as follows.
(1) The first, second, and third hollow cylindrical tubes having different diameters, and the first, second, and third annular disks that are concentric with the outer circumference circle and the inner circumference circle are the respective centers. A lance having a three-layer structure in which axes are arranged coaxially, wherein the diameter of the first cylindrical tube is larger than the diameter of the second cylindrical tube, and the diameter of the second cylindrical tube is It is larger than the diameter of the third cylindrical tube, the second and third cylindrical tubes have a shorter dimension in the central axis direction than the first cylindrical tube, and the outer diameter and inner diameter of the first annular disc are , Respectively, equal to the inner diameter or outer diameter of the first cylindrical tube and the inner diameter or outer diameter of the third cylindrical tube, and one end of the first cylindrical tube is the outer periphery of the first annular disk One end of the third cylindrical tube is connected to the inner periphery of the first annular disk, and the outer and inner diameters of the second annular disk , Respectively, equal to the inner diameter of the first cylindrical tube and the inner diameter or outer diameter of the second cylindrical tube, and one end of the second cylindrical tube is connected to the inner periphery of the second annular disk The outer periphery of the second annular disc is connected to the inner wall of the first cylindrical tube, and the other end of the second cylindrical tube not connected to the second annular disc is: The first annular disk is disposed opposite to the first annular disk and spaced from the first annular disk, and the outer diameter of the third annular disk is equal to the inner diameter or outer diameter of the first cylindrical tube, The other end of the first cylindrical tube not connected to the first annular disk is connected to the outer periphery of the third annular disk, and is connected to the inner periphery of the third annular disk. Is attached with a window plate through which laser light is transmitted, in the vicinity of the connection point of the first cylindrical tube with the second annular disk and the first cylindrical tube. Lance for continuous monitoring of molten steel, characterized in that gas inlet connection side of the Jo disc is provided.
(2) A continuous monitoring device for molten steel by spectroscopic measurement, which is a continuous monitoring device for molten steel that measures the emission intensity of elements by irradiating the molten steel with laser light through the inside of a cylindrical hollow tube. A first laser beam irradiation means for irradiating the molten steel with a laser beam to evaporate a part of the molten steel to generate a plasma; and a laser-induced fluorescence is generated by resonantly exciting a target element in the plasma to induce fluorescence. Second laser light irradiation means for generating, a lens for condensing the plasma emission from the plasma, an optical fiber cable for transmitting the plasma emission, a condensing means for condensing the laser-induced fluorescence, and the condensing A means for detecting the amount of laser-induced fluorescence, a spectroscopic means for spectrally separating the plasma emission, a lance according to claim 1, and a gas introduced from a gas inlet of the lance. Continuous monitoring apparatus of the molten steel, characterized in that it comprises a means.
(3) A continuous monitoring method for molten steel in which laser light is irradiated to the molten steel through the inside of a cylindrical hollow tube and the emission line intensity specific to the element is measured, using the lance according to claim 1 The gas is introduced from the gas introduction port, the first space sandwiched between the first cylindrical tube and the second cylindrical tube, the first annular disk and the second cylindrical tube A second space between end portions, a third space sandwiched between the second cylindrical tube and the third cylindrical tube, an end portion of the third cylindrical tube and the third annular circle The third cylindrical tube is ejected from the opening of the first annular disk through the fourth space between the plate and the inside of the third cylindrical tube, and laser light is incident from the window plate. A method for continuous monitoring of molten steel, characterized in that the molten steel is irradiated through the interior of the steel.
(4) A step of irradiating the molten steel with laser light by the first laser light irradiating means to generate a plasma by evaporating a part of the molten steel, and irradiating the plasma with the laser light by the second laser light irradiating means. Resonantly exciting a target element in the plasma to induce fluorescence to generate laser-induced fluorescence, condensing the laser-induced fluorescence, and measuring the laser-induced fluorescence intensity of the target element; The method further comprises: condensing plasma emission from the plasma generated by laser light irradiation by laser light irradiation means, transmitting the light through an optical fiber cable, and measuring the spectrum using a spectroscope. The continuous monitoring method of the molten steel as described.

  According to the present invention, since fluctuations in measured values due to the influence of heat can be suppressed, the chemical component concentration in molten steel can be measured with high accuracy, and the controllability of steelmaking operations by monitoring the decarburization reaction in secondary refining, etc. It is a great place to contribute to improvement.

It is a block diagram explaining an example of the molten steel continuous monitoring apparatus in connection with this invention. It is sectional drawing showing the conventional lance used for the comparative example. 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 relationship between the carbon concentration in molten steel by the comparative example, and the laser-induced fluorescence intensity of carbon.

  In FIG. 1, the structure of the molten steel continuous monitoring apparatus of this invention is shown. The ablation laser beam a oscillated from the ablation laser oscillator 1 is reflected by the ablation laser beam reflecting mirror 3, passes through the inside 26 of the third cylindrical tube 25 of the lance 20 through the window plate 21, and is irradiated onto the analysis surface 27. (First laser light irradiation means). 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 27. The plasma emission c generated on the analysis surface 27 passes through the inside 26 of the third cylindrical tube 25, is reflected by the plasma emission reflection mirror 5, and is condensed by the plasma emission condensing lens 7 on the optical fiber light receiving end face 8. . The plasma emission is transmitted to the spectroscope 28 through the optical fiber cable 9, and the emission intensity of each element is measured by spectroscopic analysis.

  The selective excitation laser beam b is oscillated from 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 beam b is adjusted to the wavelength that resonates with 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 third cylindrical tube interior 26 via the window plate 21, and irradiates the analysis surface 27 (second laser light irradiation means). The analysis target element generated by irradiation with the ablation laser beam a is resonantly excited by the selective excitation laser beam b, 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 10 and the optical filter 11, enters the light amount detector 12, and the light amount is converted into current. It is sent to the analyzer 29 and the laser-induced fluorescence intensity is measured. As shown in FIG. 1, each of the mirrors 3, 4, 5, 6, lenses 7, 10 and the light amount detector 12 is protected from the influence of heat, vibration, dust, etc. from the surroundings. Placed in.

  During the molten steel continuous monitoring, the lance 20 is heated from the outside by molten steel radiation or the like. For this reason, for example, when the lance 50 as shown in FIG. 2 is used, the inert gas flowing through the hollow tube 53, such as Ar, has a higher temperature outside the center and has a slightly different refractive index in the radial direction. it is conceivable that. 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 hollow tube 53 has the same function as the gradient index lens. It is thought. Due to this thermal lens effect, the ablation laser light a changes its focal point in the interior 55 of the hollow tube 53, and the power density changes, thereby degrading the analysis accuracy. Further, the plasma emission c that has passed through the inside 55 of the hollow tube 53 is affected by this thermal lens effect, and as a result, the image formation dimension at the optical fiber light receiving end face 8 changes and the incidence efficiency on the optical fiber cable 9 changes. It was estimated that a change appears in the emission intensity of Fe, which should be constant. The temporal change due to the temperature rise of this hollow tube is independent of the fluctuation of the ablation condition due to the molten metal surface vibration and so on. Therefore, unless the influence by this change is separated, the laser-induced fluorescence due to the emission intensity of Fe Intensity correction was not possible.

  In order to avoid the influence of such molten steel radiant heat, it is conceivable to suppress the temperature increase of the hollow tube by air cooling or water cooling the hollow tube. However, in order to secure a flow rate that can sufficiently remove the radiant heat from the molten steel, a compressor and a pump are required, and the cost increases due to such additional devices and increased utility usage.

  Here, the configuration and operation of the lance of the present invention will be described.

  As shown in FIG. 1, the lance 20 has a three-layer structure including a first cylindrical tube 23 arranged on the outermost periphery and a second cylindrical tube and a third cylindrical tube 25 arranged coaxially with the central axis. Have. The second and third cylindrical tubes 24 and 25 have a shorter length in the central axis direction than the first cylindrical tube 23, and the upper ends thereof are arranged below the upper end of the first cylindrical tube 23. . The lower ends of the first cylindrical tube 23 and the third cylindrical tube 25 having the smallest diameter are connected by a first annular disk 31. The first annular disk 31 has an outer diameter equal to the inner diameter or outer diameter of the first cylindrical tube 23, and the inner diameter is equal to the inner diameter or outer diameter of the third cylindrical tube 25. The second cylindrical tube 24 is disposed away from the first annular disk 31 and slightly above in FIG. 1, and the upper end of the second cylindrical tube 24 and the inner wall of the first cylindrical tube 23 are the second They are connected by an annular disk 32. The second annular disk 32 has an outer diameter equal to the inner diameter of the first cylindrical tube 23 and an inner diameter equal to the inner diameter or the outer diameter of the second cylindrical tube 24. Furthermore, a third annular disk 33 is attached to the upper end of the first cylindrical tube 23. The outer diameter of the first annular disk 33 is equal to the inner diameter or the outer diameter of the first cylindrical tube 23, and a window plate 21 that transmits laser light is attached to the inner peripheral portion. In addition, as for each annular disc 31, 32, 33, the outer periphery circle | round | yen and the inner periphery circle | round | yen are formed concentrically, respectively. Furthermore, an inert gas inlet 22 is provided on the side wall of the first cylindrical tube 23 slightly below the position where the second annular disk 32 is disposed, that is, near the first annular disk 31. ing. In this way, the gas introduced from the inert gas inlet 22 passes through the first space 41, the first annular disk 31 and the second space between the first cylindrical tube 23 and the second cylindrical tube 24. The second space 42 between the lower end of the cylindrical tube 24, the third space 43 sandwiched between the second cylindrical tube 24 and the third cylindrical tube 25, the upper end of the third cylindrical tube 25 and the third space Passing through the fourth space 44 between the annular disk 33 and the interior 26 of the third cylindrical tube 25 in sequence, a passage is formed that is ejected from the opening 31a of the first annular disk.

  That is, as shown in FIG. 1, in the lance 20 of the present invention, an inert gas such as Ar flows in from the inert gas inlet 22 and passes through the first space 41 that is the outermost flow path. After flowing through the third space 43 that is the inner flow path toward the upper portion of the lance 20, the third cylindrical tube is formed at the upper portion of the lance 20. 23 flows into the interior 26 of the lance 23 and ejects from the opening 31a at the bottom of the lance 20. While passing through the first space 41, the inert gas is heated through the outer wall of the lance 20 that receives the molten steel radiation, and therefore flows into the interior 26 of the third cylindrical tube 23 in a state where the temperature has reached a sufficiently high temperature. To do. At this time, since the temperature difference between the inert gas passing through the interior 26 of the third cylindrical tube 23 and the third space 43 is small, the inert gas at room temperature is introduced into the interior 55 of the hollow tube 53 shown in FIG. Compared with direct blowing, the temperature distribution in the radial direction is less likely to occur, and the large thermal lens effect does not occur.

  The inert gas is originally used for the purpose of preventing oxidation of the molten steel surface, controlling the plasma generation atmosphere, and preventing absorption of plasma emission by oxygen. That is, according to the present invention, it is possible to suppress adverse effects on the analysis accuracy of molten steel radiant heat easily and inexpensively without increasing the amount of additional devices and utilities used.

  The 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 beam a, and a titanium sapphire laser was used as the selective excitation laser beam b. Ar gas is introduced from the inert gas introduction port 22 at a flow rate of 100 L / min, and is passed through the first space 41, the third space 43, and the interior 26 of the third cylindrical tube 25 in this order, and the third cylinder. Analysis was performed while spraying the molten steel surface from the opening 31a at the lower end of the tube 25. The material of the lance 20 was stainless steel.

  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 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 sequentially increased by melting an 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 used as a reference, a value obtained by sampling a part of the molten steel at each concentration level, solidifying and then quantifying by the combustion infrared absorption method was used.

  As a comparative example, the lance 50 shown in FIG. 2 was attached instead of the lance 20 of the apparatus shown in FIG. 1, and the laser-induced fluorescence intensity of carbon in molten steel was measured under the same conditions as in Example 1. . A lance 50 in FIG. 2 has a window plate 51 and an inert gas inlet 52 similar to those in the lance 20 in FIG. 1, and the outer periphery of a stainless steel hollow tube 53 is covered with a heat insulating material 54. That is, in the lance 50, the inert gas that has flowed from the inert gas inlet 52 moves down the hollow tube interior 55 as it is.

  FIG. 3 shows the laser-induced fluorescence intensity measured at each concentration level of carbon in the example. Moreover, the laser-induced fluorescence intensity measurement result of the comparative example is shown in FIG. As shown in FIG. 4, in the comparative example, a good correlation between the carbon concentration and the laser-induced fluorescence intensity cannot be obtained. As shown in FIG. 3, when the lance 20 of the present invention is used, the carbon concentration and the laser-induced fluorescence intensity are obtained. Correlation with fluorescence intensity was improved.

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

1 Ablation Laser Oscillator 2 Selective Excitation Laser Oscillator 3 Ablation Laser Light Reflection Mirror 4 Selective Excitation Laser Light Reflection Mirror 5 Plasma Emission Reflection Mirror 6 Laser Induced Fluorescence Reflection Mirror 7 Plasma Emission Condensing Lens 8 Optical Fiber Receiving End Face 9 Optical Fiber Cable 10 Lens 11 Optical Filter 12 Light quantity detector 13 Transmission cable 14 Protective case 20, 50 Lance 21, 51 Window plate 22, 52 Inert gas inlet 23 First cylindrical tube 24 Second cylindrical tube 25 Third cylindrical tube 26 Inside 27 Analysis Surface 28 Spectrometer 29 Data analysis device 31 First annular disk 31a Opening portion 32 Second annular disk 33 Third annular disk 41 First space 42 Second space 43 Third space 44 Fourth Space 53 hollow tube 54 heat insulating material 53 inside a ablation laser beam b selective excitation laser Light c plasma emission d laser induced fluorescence

Claims (4)

The first, second, and third hollow cylindrical tubes having different diameters, and the first, second, and third annular disks whose outer and inner circumferential circles are concentric are coaxial with each other. A lance having a three-layer structure arranged and arranged in a
The diameter of the first cylindrical tube is larger than the diameter of the second cylindrical tube, the diameter of the second cylindrical tube is larger than the diameter of the third cylindrical tube,
The second and third cylindrical tubes have a shorter dimension in the central axis direction than the first cylindrical tube,
The outer diameter and the inner diameter of the first annular disk are equal to the inner diameter or the outer diameter of the first cylindrical tube and the inner diameter or the outer diameter of the third cylindrical tube, respectively, and one of the first cylindrical tubes Is connected to the outer periphery of the first annular disk, one end of the third cylindrical tube is connected to the inner periphery of the first annular disk,
The outer diameter and the inner diameter of the second annular disk are equal to the inner diameter and the outer diameter of the first cylindrical tube, respectively, and one end portion of the second cylindrical tube. Is connected to the inner periphery of the second annular disk, the outer periphery of the second annular disk is connected to the inner wall of the first cylindrical tube,
The other end of the second cylindrical tube that is not connected to the second annular disc is disposed opposite the first annular disc and spaced from the first annular disc,
The outer diameter of the third annular disk is equal to the inner diameter or outer diameter of the first cylindrical tube, and the other end of the first cylindrical tube not connected to the first annular disk. Is connected to the outer periphery of the third annular disk, and a window plate through which laser light is transmitted is attached to the inner periphery of the third annular disk,
A continuous molten steel characterized in that a gas introduction port is provided in the vicinity of a connection portion of the first cylindrical tube with the second annular disk and on the connection side with the first annular disk. Monitoring lance. It is a continuous monitoring device for molten steel by spectroscopic measurement method, and it is a continuous monitoring device for molten steel that measures the intensity of the emission line specific to the element by irradiating the molten steel with laser light through the inside of a cylindrical hollow tube,
First laser light irradiation means for irradiating the molten steel with laser light to evaporate a part of the molten steel to generate plasma;
A second laser beam irradiation means for resonantly exciting a target element in the plasma to induce fluorescence 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;
A lance according to claim 1;
Means for introducing gas from the gas inlet of the lance;
A continuous monitoring apparatus for molten steel. A continuous monitoring method for molten steel in which laser light is irradiated to molten steel through the inside of a cylindrical hollow tube to measure the emission line intensity specific to the element,
Using the lance according to claim 1, gas is introduced from the gas introduction port, and a first space sandwiched between the first cylindrical tube and the second cylindrical tube, the first annular shape A second space between a disc and an end of the second cylindrical tube; a third space sandwiched between the second cylindrical tube and the third cylindrical tube; and the third cylindrical tube. Through the fourth space between the end of the first annular disk and the inside of the third cylindrical tube, and the laser beam is emitted from the opening of the first annular disk. The molten steel is irradiated from the inside of the third cylindrical tube and irradiated to the molten steel. Irradiating the molten steel with laser light by the first laser light irradiation means to evaporate a part of the molten steel to generate plasma;
The second laser light irradiation means irradiates the plasma with laser light, resonance-excites the target element in the plasma to induce fluorescence to generate laser-induced fluorescence, condenses the laser-induced fluorescence, and Measuring the laser-induced fluorescence intensity of the element;
And condensing plasma emission from the plasma generated by laser light irradiation by the first laser light irradiation means, transmitting the light through an optical fiber cable, and measuring the spectrum using a spectroscope. The continuous monitoring method of the molten steel of Claim 3.

Images