JPH0215817B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention collects fine particles generated from the surface of molten metal and transfers them to an emission spectrometer equipped with a plasma excitation source installed at a remote location. This relates to a method for analyzing the content of various components in molten metal online in real time using a flow of inert gas such as Ar.

In order to manage operations such as metal refining and steel manufacturing processes, it is necessary to analyze as quickly as possible to understand the component content, and to take appropriate measures based on the results. As described above, the present invention is a technology for directly analyzing molten metal, and is used in the fields of manufacturing process control analysis and quality control analysis in the steel industry, non-ferrous metal manufacturing industry, and the like.

(Prior Art) Spark emission spectroscopy, which targets block samples obtained by sampling and solidifying molten metal, is often used for manufacturing process control analysis in the metal manufacturing industry. However, in recent years, especially in the steel industry, online real-time technology that directly targets molten metals such as hot pig iron and molten steel has become available for faster manufacturing process control or operational management of new manufacturing processes such as multi-stage refining steelmaking. There is a strong need to develop analytical methods for this.

For the above purposes, molten metal has been used until now.
A method of pulverizing the powder using a special atomizer using Ar gas and performing emission spectroscopic analysis (BISRA Annual
Report: 78 (1966), 65, 78 (1967), 35 (1968))
Various methods have been studied. However, none of these methods have ever been actually put into practical use at manufacturing sites, and have only been attempted on a laboratory scale. The present inventors also applied a method of performing emission spectroscopic analysis by evaporating fine particles representative of the composition of the molten metal by irradiating the molten metal with electrical discharge such as a plasma arc or spark, or with a laser beam, etc. 201154
No. 1, patent application No. 58-30879), and filed a patent application. These inventions require a constant distance between the molten metal surface and the heating source device such as the tip of a spark discharge electrode, and are effective when the molten metal level fluctuates relatively slowly, but when the molten metal level fluctuates rapidly. In some cases, various measures must be taken to suppress fluctuations.

(Purpose of the invention) In developing a more practical direct analysis device for molten metal at actual manufacturing sites, it is important that the manufacturing site
Consideration must be given to the fact that the measurement environment is extremely poor, including high temperatures, vibrations, and dust. Therefore, precision measuring instruments such as spectrometers and detectors that can cause problems under adverse measurement environments must be installed in a building away from the location where molten metal is present. Molten metal can be evaporated as fine particles by electrical discharge, but if possible, it is necessary to evaporate the fine particles by a simple method, such as collecting fine particles that naturally evaporate due to the high heat of the molten metal itself. There is. Under these circumstances, the present invention aims at online real-time analysis in manufacturing process control analysis of molten metal, and collects fine particles that evaporate on the surface of molten metal.
The object of the present invention is to provide a practical analysis method for easily and quickly analyzing various components contained in molten metal by transporting the molten metal with an inert gas flow to an emission spectrometer having a plasma excitation source.

(Structure, operation, and embodiments of the invention) Based on the device example shown in FIG.
The effect will be explained. FIG. 1 shows an example in which the molten metal used is molten steel in a processing ladle in a steelmaking process. The apparatus of the present invention mainly includes a container 15 containing Ar gas, a particle collection tank 1 immersed in molten steel 2, a particle transport pipe 9, and a high frequency inductively coupled plasma emission spectrometer 10.
The particulate collection tank 1 is a cylinder made of a heat-shock-resistant refractory material such as boron nitride or graphite, and the Ar gas discharge port 5 at the tip is immersed in molten steel.
An Ar gas inlet pipe 3 and a particulate discharge pipe 6 are attached to the top, and the bottom is hollow to take in molten steel. Therefore, when the particulate collection tank 1 is immersed in the molten steel 2, it becomes a closed container having a space for the particulate evaporation chamber 8 inside. Ar gas container 15
Ar gas is introduced into the molten steel from the Ar gas introduction port into the Ar gas introduction pipe 3 at a constant flow rate measured by a flow meter, and from the discharge port 5 immersed in the molten steel at the tip of the introduction pipe 3. is supplied by bubbling.
In addition to Ar gas, inert gases such as N ₂ and He are suitable as the blowing gas. The type of gas is regulated in terms of the stability of the plasma flame of the analyzer, but
Currently, the development of a plasma flame that uses air is underway, and if this becomes possible, air may be used instead of an inert gas, and the fine particles will become oxides, but there will be no problem.

Fine particles of molten steel evaporate from the surface of the molten steel due to the high heat of the molten steel itself, but the amount of evaporation is much smaller than when strong external energy is applied, such as spark discharge or laser beam irradiation. Plasma emission spectroscopy is a highly sensitive analysis method, but in order to obtain better quantitative accuracy,
It is necessary to promote the evaporation of the particles in the particle evaporation chamber 8, to increase the recovery efficiency of the evaporated particles, and to obtain a stable recovery rate.

The present invention was created by conducting various studies on these points and devising a method for blowing Ar gas into the molten steel 2 and a method for collecting evaporated fine particles. Especially the place where Ar gas is blown,
It was revealed that the Ar gas temperature, the position of the particle exhaust port 7, etc. are important factors. Let us describe the blowing of Ar gas. Towards the hot water surface in the particulate evaporation chamber 8, so as to receive almost no preheating.
When Ar gas is supplied from Ar gas introduction pipe 3, Ar
As the distance between the tip of the gas introduction pipe 3 and the molten metal surface approaches, the evaporation of fine particles is suppressed, and the tip of the gas introduction pipe is connected to the molten steel 2.
Evaporation of fine particles was extremely suppressed when immersed in the liquid and bubbled with Ar gas. However,
The particulate introduction pipe 3 is made to receive sufficient heat conduction from the particulate collection tank 1 and radiant heat from the molten steel 2,
The evaporation of fine particles was greatly improved by lowering the flow rate of Ar gas introduced. The amount of evaporation of fine particles at this time is larger than that in the case where preheated Ar gas is supplied to the surface of the molten steel 2 and naturally evaporated fine particles are collected. The effect of promoting this is clear.

In addition, as mentioned above, Ar
Preheating the gas is very important. As a preheating method, there is also a method of heating with a heater etc. in the conduit between the Ar gas container 15 and the particulate collection tank 1, but since the molten steel 2 usually has an extremely large capacity, it is necessary to use the high heat contained in the molten steel. The method of using it as a heating source is convenient and practical. As shown in Fig. 1, the particulate collection tank 1 is immersed in molten steel 2 and heated to a red-hot state, and the Ar gas introduction pipe 3 is made of a material with heat resistance and good thermal conductivity. The structure has good heating efficiency due to heat conduction and radiant heat of the molten steel, and the introduction pipe 3
A suitable method is to preheat the Ar gas flowing inside. Furthermore, as shown in FIG. 2, a method of penetrating the Ar gas introduction pipe 3 into the side wall of the particulate collection tank 1 and blowing Ar gas into the molten steel 2 through the discharge port 5 is also effective. This is an efficient preheating method because it facilitates heat exchange with the particulate collection tank 1 which is heated to a high temperature by molten steel.

The installation position of the particulate discharge port 7 will now be described. In plasma emission spectroscopy, which analyzes fine particles, the finer the particle size and the narrower the particle size distribution range, the better the excitation efficiency in the plasma.
Since stable luminescence intensity is obtained, good quantitative accuracy and sensitivity can be obtained. Therefore, it is necessary to collect particles suitable for plasma emission spectroscopic analysis as the target of analysis, and for this reason, the installation position of the particle outlet 7 in the particle evaporation chamber 8 is limited.
Immediately near the molten steel surface, there are large particles caused by the agglomeration of scattered molten steel particles and evaporated fine particles, but the particles that evaporate and float several tens of millimeters above the molten steel surface are fine particles with a size of several hundred millimeters or less. and
It has excellent particle uniformity and quantitative accuracy.
However, if the distance from the hot water surface is too great, the collection efficiency of fine particles will decrease. For this reason, the particulate discharge port 7
must be installed at the upper part of the particulate evaporation chamber 8 at a predetermined distance from the surface of the molten steel 2. The distance from the molten metal surface is determined by the type of molten metal, the inner diameter of the particulate collection tank, the Ar gas flow rate, etc., but it is not appropriate to set it close to the surface of the molten metal, such as 10 mm or less.
Approximately 40 to 80 mm is appropriate.

The particulate discharge pipe 6 is connected to a plasma torch 11 of an analyzer 10 through a transport pipe 9 such as a stainless steel pipe. The particles in the particle evaporation chamber 8 are moved to the particle outlet 7 by the introduced Ar gas at a constant flow rate.
from there to the plasma torch 11. A stainless steel pipe with an inner diameter of 4 mmφ and a length of 40 m is used for the conveyance pipe.
When the Ar gas flow rate was set to 0.6/min, the internal pressure in the particle evaporation chamber 8 was approximately 150 mmH ₂ O, and the molten metal level fell by approximately 2 cm, but the molten steel particles reached the plasma torch 11 after approximately 18 seconds. By integrating the emission intensity for about 10 seconds, we were able to obtain analytical results with good reproducibility for each element. Although a small amount of fine particles remain on the inner wall of the transport tube, after one analysis, which takes about 30 seconds, is completed, the switching valve 14 installed just before the plasma torch 11 is switched.
By blowing Ar gas from the Ar gas container 8 at a flow rate of 10 to 20/min into the particle evaporation chamber 8 through the transport pipe 9, the remaining particles could be removed. At the same time, the molten steel in the particulate evaporation chamber 8 is removed from the same chamber,
By switching the switching valve 14 to return to the original analysis state, new molten steel in the ladle is taken into the evaporation chamber 8. By such a method, online analysis of the refining process of molten steel in the processing pot can be easily performed.

The fine particles introduced into the plasma torch 11 are excited and emit light at the high temperature of the plasma, and the emitted light is transmitted to the spectrometer 1.
2, the emission intensity of each element is simultaneously measured by a detector 13 such as a photomultiplier tube set at each wavelength position, and the emission intensity of multiple elements in the molten steel is simultaneously measured.
Rapid analysis can be performed. According to the present invention, C, P, S, Si, Mn, which are contained in trace amounts as impurities in molten steel,
Simultaneous analysis of most elements such as Ni and Cr, except for O, N, and H gas components, was possible. The emission spectrometer 10 is suitably an emission spectrometer having a plasma excitation source. Currently, a high-frequency inductively coupled plasma emission spectrometer that uses Ar plasma is most suitable from the viewpoint of good analysis accuracy and ease of handling.

Fine particles resulting from natural evaporation do not necessarily represent the chemical composition of the original molten metal due to the vapor pressure of each element. A notable example is Mn, which has a low vapor pressure, for example, when the Mn content in molten steel is 1.
%, the Mn content in naturally evaporated fine particles is approximately
20%. Therefore, it is difficult to directly determine the content of each element in the molten metal from the emission intensity of each element in the fine particles obtained by a plasma emission spectrometer. Therefore, we first prepared molten metal in which the content of each element was changed in stages,
Based on the content of each element in this molten metal, we investigated the correlation with the luminescence intensity of each element in the evaporated fine particles,
Create a calibration curve in advance. For the emission intensity of each element, the integrated intensity over a certain period of time may be used as is, but in the case of molten steel, which is the main component of molten metal, it is better to quantify it by using the ratio of the integrated emission intensity of Fe to the integrated emission intensity of the element of interest. Improves accuracy. Further, the temperature of the molten metal affects the amount of evaporation of the fine particles, and the higher the bath temperature, the easier the evaporation becomes, but the content ratio of each element in the fine particles also changes. Therefore, if the bath temperature changes in the manufacturing process of the target molten metal, the correlation between the content of each element and the luminescence intensity when the bath temperature is changed is investigated and created in advance. Use a standard calibration curve. That is, the content of each element can be determined with high accuracy by correcting the slope of a calibration curve created for molten metal at a certain temperature using the bath temperature. However, in the refining process of steelmaking, the fluctuation in molten steel temperature is very small, and it is around 10 degrees for molten steel at 1600 degrees Celsius, and in such cases, it is almost necessary to correct the analytical values of each element due to bath temperature. do not have.

(Effects of the Invention) As explained above, the present invention eliminates the complicated operations such as sampling, cooling solidification, cutting, and pretreatment such as polishing that have been conventionally performed when analyzing the components contained in molten metal samples. It is possible to perform direct analysis quickly and accurately without having to carry out the analysis, and it is extremely effective for operational management of metal refining and steelmaking processes.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an apparatus for implementing the present invention, and FIG. 2 is an explanatory diagram of a part of the particulate collection tank of the present invention. 1... Particulate collection tank, 2... Molten metal, 3...
Ar gas inlet pipe, 4...Ar gas inlet, 5...Ar
Gas discharge port, 6... Particulate discharge pipe, 7... Particulate discharge port, 8... Particulate evaporation chamber, 9... Particulate transport pipe, 10... High frequency inductively coupled plasma emission spectrometer, 11... Plasma torch, 12... Spectrometer, 13... Detector, 15, 15'... Ar gas container.

Claims (1)

[Claims] 1 The open bottom of the container is immersed in the molten metal, and an inert gas preheated using the heat of the molten metal is blown into the molten metal trapped inside the container, and the fine particles evaporated from the molten metal are removed together with the inert gas. Evaporated fine particle recovery molten metal characterized by discharging from the upper part of the container, conveying it to a plasma emission spectrometer, measuring the luminescence intensity of each element in the fine particles, and determining the concentration of each element contained in the molten metal. Analysis method.