JPH0731181B2 - Method and apparatus for hydrogen splitting in molten metal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for analyzing hydrogen in a refining process of molten metal. Analysis of hydrogen in molten metal during refining process is important for process control and quality control of refining process. For example, in the steel industry, in the vacuum degassing process, which is the next step of decarburization in a converter, hydrogen desorption in molten steel is analyzed to perform dehydrogenation process control and quality control.

(Prior Art) For the analysis of hydrogen in molten metal, a method of quantifying the hydrogen gas collected in a sampler in which the molten metal is collected is usually adopted by gas chromatography that detects thermal conductivity. In this method, molten metal is collected in a vacuum-sealed conduit, and hydrogen is diffused into a vacuum chamber of a sampler that has been decompressed in advance while being rapidly or slowly cooled, and an inert gas such as helium, nitrogen or argon is introduced into this vacuum chamber. As a carrier gas, hydrogen in the molten metal collected in the vacuum chamber is introduced into the separation column to separate hydrogen from other gas components, and then introduced into the thermal conductivity detector to quantify hydrogen. (Reference: New Experimental Chemistry Lecture 9, Analytical Chemistry (II), 3.1 Gas Chromatography, p60-71).

The thermal conductivity detector is as follows. When a sensitive element and a compensating element made of tungsten or the like are heated by a constant current and only a carrier gas such as helium is flowing, heat is removed from the two elements at a constant rate into the carrier gas. The element maintains a constant temperature. Next, when gas components with different thermal conductivities are mixed in the carrier gas, this steady state is broken, the temperature of the sensitivity element changes, and the resistance change of the sensitivity element is measured by the Wheatstone bridge circuit. The amount of hydrogen is determined (references p68-69 above).

(Problems to be Solved by the Invention) When the conventional gas chromatography using a thermal conductivity detector is applied to the object of the present invention, there are the following problems. (1) Since the thermal conductivity detector does not have selectivity, the gas sample collected in the molten metal sampler needs to be separated in advance through a separation column to separate hydrogen from other gas components. (2) This separation operation lengthens the time required for analysis. (3) Since the principle of the detector is to transfer heat, strict temperature control of about ± 0.1 ° C is essential. (4) Quantitative sensitivity and accuracy are insufficient for process control of degassing treatment of molten metal.

In addition, some molten metal samplers for hydrogen analysis have an unsuitable structure for immediate analysis after collection without rapid cooling, so it is important to select a sampler having an appropriate structure. It is also necessary to develop an analysis system for this sampler that does not cause any inconvenience even when heated.

Therefore, it is an object of the present invention to provide a method and apparatus for analyzing hydrogen in molten metal that overcomes these problems of the prior art. In particular, it is an object of the present invention to provide a novel analysis method and apparatus capable of performing analysis immediately in a heated state after collection at a metal refining site and quickly obtaining a hydrogen analysis value with high sensitivity and accuracy.

(Means and Actions for Solving Problems) In the present invention, as a result of repeated research to achieve these objects, a semiconductor hydrogen gas detector was adopted in place of the conventional thermal conductivity detector, and heating was performed. The present inventors have developed an analysis method and apparatus suitable for hydrogen analysis in a molten steel sampler in a state.

The present invention relates to an analysis method for quantifying hydrogen in a molten metal by using a sampler that collects the molten metal by diffusing and collecting the contained hydrogen. That is, without cooling the sampler from which the molten metal was collected, the inert gas of the carrier gas was immediately supplied in the heated state to introduce hydrogen and hydrogen contained in the molten metal which had been diffused and collected in the sampler vacuum chamber, A semiconductor-type hydrogen gas detection element is installed inside the tube and discharge tube, and it is sent at a constant flow rate into the measurement cell housed in a temperature-controlled room, and dehumidified oxygen is added from the middle of the path between the sampler and the measurement cell. Alternatively, a gas containing oxygen or air is added to the flow of the above inert gas so that the oxygen concentration is
It is mixed at a constant concentration of 10% to 21% and sent at a constant flow rate, and the hydrogen concentration in the molten metal is determined from the output signal of the detection element.

A semiconductor gas detector used as a hydrogen detector (reference: “Intelligence of semiconductor sensors” edited and published by Mimatsu Data System, p165-186) is an oxygen adsorbed on the surface of a metal oxide semiconductor such as SnO _2. However, the gas concentration is detected by utilizing the fact that it reacts with the reducing gas such as hydrogen supplied and is desorbed to change its electric conductivity. Therefore, as described above, the principle of the thermal conductivity detector that detects the gas concentration by utilizing the fact that the heat of the sensitive element heated by the supplied sample gas is taken away and the electrical resistance changes Are different. Usually, the hydrogen gas detector Among semiconductor type gas detectors, in order to have a molecular sieving function on the semiconductor surface of the metal oxide such as SnO _2, such as by depositing a SnO ₂ film, such as ethanol, carbon monoxide hydrogen It uses a semiconductor-type hydrogen gas sensing element that has selectivity by blocking reducing gas molecules larger than the molecule on the surface (reference document: the above reference document, p184). In addition, this semiconductor type hydrogen gas detection element needs to maintain a high temperature state of 300 to 400 ° C. and supply oxygen in order to accelerate adsorption / desorption of a target gas and obtain reproducibility.

Up to now, the gas detector has been used such as issuing an alarm when the preset border line of the target gas concentration is exceeded, and the purpose is to carry out a strict quantitative analysis of gas as in the present invention. I didn't. The present invention newly adopts the semiconductor type hydrogen gas detection element as described above for strict hydrogen analysis, and introduces a gas sample by a forcibly controlled carrier gas flow.
It achieves the improvement of accuracy, the omission of the separation column, the simplification of the device structure by relaxing the temperature control condition of the installation atmosphere of the detection element, the simplification of the analysis operation, and the great improvement of the practicality.

The structure and operation of the present invention will be described based on the measurement results of the characteristics of the detector used in the apparatus of the present invention shown in FIG. 1 and the apparatus of the present invention shown in FIGS. The apparatus of the present invention shown in FIG. 1 is mainly composed of a carrier gas supply unit, a standard gas introduction unit, an adsorption gas supply unit, a sampler storage unit, a measurement cell unit, an analysis result display unit and the like. The carrier gas supply unit includes an inert gas cylinder 1 and a gas flow rate controller 4. Argon, nitrogen, helium, etc. are used as the inert gas, but mixing of water and oxygen is not allowed. This is because the semiconductor-type hydrogen gas detection element 10 is sensitive to moisture and outputs an output signal, and the presence of oxygen reacts with hydrogen in the sampler in a heated state to change hydrogen into water. Use pure inert gas.

The reference gas introduction part is a part that supplies standard hydrogen gas from the cylinder 2 filled with standard hydrogen gas to the measuring device 7 and measures a fixed amount. When a fixed amount of standard hydrogen gas has been measured by a sampling coil or the like, the flow passage switch 6 is actuated so that the carrier gas sends the standard hydrogen gas to the measuring cell 9. Obtain the correlation between the output signal amount of the detected hydrogen 10 obtained at this time and the standard hydrogen amount introduced, and substitute the output signal amount of the gas sample collected by the actual molten metal sampler to substitute the hydrogen concentration in the sample. Ask for.

The adsorbed gas supply unit includes an air pump 3, a dehumidifier 5, and a flow rate controller 4 ″. The adsorbed gas is for adsorbing oxygen on the surface of the semiconductor detection element, and contains 10% or more by volume percentage of oxygen. A mixed gas of nitrogen, argon, etc. is suitable.It is easiest and convenient to supply air containing 20.9% oxygen by a pressure pump or a cylinder. It is thought that this is because the humidity adsorbs in a form that lowers the resistance value of the semiconductor, and it is necessary to dry by passing through the dehumidifier 5 consisting of a column packed with silica gel or molecular sieve. The semiconductor-type hydrogen gas sensing element used in the present invention is supplied with a constant flow rate of an argon-based gas containing oxygen up to several 10% and 500 ppm of hydrogen at a constant flow rate. Examine its concentration characteristics. In FIG. 2, showing a measurement chart by the recorder. Oxygen concentration 15
When it is%, the response speed of hydrogen detection by the detection element is also fast, it shows a constant output in a short time, oxygen is 15% without hydrogen.
Even when the gas was switched to an argon gas containing, the output quickly returned to the original baseline. When the oxygen concentration was 7.5%, the response was slightly reduced, and the speed at which the output returned to the baseline was also reduced. Furthermore, when the oxygen concentration is lowered to 3.3%, only a part of hydrogen can participate in desorption at the sensing element due to lack of oxygen concentration, so the response becomes faster, but a low value is shown and quantification is impossible. It also took a very long time for the output to return to the original baseline. Third
In the figure, the time required for the output once hydrogen was detected to return to the original base output from the time when the oxygen-mixed argon gas containing no hydrogen was supplied was plotted. Third
As shown in the figure, when the oxygen concentration was below 10%, it took an extremely long time below that. From these examination results, it is clear that the composition of the carrier gas for feeding the sample gas to the semiconductor-type hydrogen gas detector used in the present invention is preferably nitrogen, helium, argon or the like gas containing 10% or more of oxygen. . Of course, 100% oxygen gas does not cause any problems. However, as can be seen from the experimental results shown in FIG. 3, when the oxygen concentration in the carrier gas is set to 10% or more, the time to return to the base output becomes almost constant, so in practice carrier gases with these compositions are used. An atmosphere containing 20.9% oxygen by volume percentage is the most convenient, considering the time and effort required for preparation. Therefore, the oxygen concentration in the carrier gas should be from 10%
A range of 21% is appropriate. Further, when the oxygen concentration in the adsorbed gas changes, the resistance value of the detector changes even if hydrogen gas does not exist. This proves that the adsorption of oxygen to this sensing element directly controls the resistance value, and the oxygen concentration in the adsorbed gas is kept constant from 10% to 21%, and the flow rate controller 4 " Constantly supplies a constant flow rate.

The adsorbing gas supply place must be in front of the measuring cell 9 as shown in FIG. 1, but after the sampler housing. Since the purpose of the present invention is to perform an analysis immediately without collecting the molten metal after cooling with a sampler, naturally the sampler is in a heated state of 200 to 300 ° C. or more even when set in the sampler storage part, so that the sampler The collected hydrogen reacts with oxygen and burns, resulting in a low quantitative value.

The sampler storage part 8 is arranged between the carrier gas supply part and the standard gas introduction part and the measurement cell part, and is provided with a carrier gas introduction port for feeding the gas sample emitted from the molten metal collected in the sampler to the measurement cell part. And an outlet is provided. Although there are several types of molten metal hydrogen samplers, one example of molten steel hydrogen samplers is shown in FIG. A pipe 19 made of a thin steel pipe for solidifying molten steel into a rod shape is housed inside a cylindrical pipe 18, and a sealed tip 20 is immersed in the molten steel, and the molten steel is sucked into the pipe 19 by melting and destroying the tip 20. The hydrogen in the molten steel is released by slow cooling and is collected in the vacuum chamber 21. Cylindrical tube 18, tip 2
0, the part corresponding to the vacuum chamber 21 made of thin steel plate or quartz glass is used. The structure of the storage portion 8 is shown in FIG. 5 by taking the case of using the above sampler made of quartz glass as an example. The sampler 22 is put into the storage chamber 23, the lid 24 is closed, the carrier gas is introduced at a constant flow rate so as to be introduced from the direction of the arrow in FIG. 5 and discharged toward the measurement cell 9, and the drive screw 26 is rotated. By bellows
Hydrogen in the molten steel is sent to the measuring cell 9 by pressing down 27 and the metal rod 25 to crush the sampler.

Usually, a molten metal sampler is used in which a molten metal is sampled and then cooled to near room temperature by water cooling or cooling to be applied to an analyzer. Since the main purpose of hydrogen analysis in molten metal is to control the refining process of the metal, it is desirable to analyze the molten metal at the refining site immediately after collecting it and to see the result on the spot. Further, rather than cooling the collected molten metal to reduce the solubility of hydrogen and diffusing it in a vacuum chamber to collect it, it is more reliable in a short time to dissipate hydrogen under the flow of an inert gas in a high temperature state. Can be collected. However, in many samplers, a suction base portion 28 is provided, and the molten metal sucked into the sampler is first solidified to block the path leading to the hollow portion of the cylindrical tube 18 and the conduit 19. . In such a case, if the sample is immediately stored in the chamber 23 shown in FIG. 5 without being cooled rapidly and analyzed, the hydrogen released by the molten metal sucked by the wicking base 28 is added and the temperature is increased. It causes eye error. Therefore, a quartz glass sampler in which the cylindrical tube 18 and the conduit 19 are fused from the beginning and the amount of molten metal remaining in the wicking base 28 is small is suitable. All the sampler storage parts are made of heat-resistant stainless steel, etc., and it is necessary to purge the atmosphere by flowing a large amount of carrier gas consisting of an inert gas until just before the sampler storage.

The measurement cell unit is composed of a measurement cell 9 having a semiconductor hydrogen gas detection element 10 built-in and a temperature-controlled room 11 for accommodating the measurement cell. As described above, the semiconductor hydrogen gas detecting element 10 has a SiO ₂ film deposited on the surface of a metal oxide semiconductor, and a conductor such as an electrode and an iridium-palladium alloy for a heater is embedded therein. Although a sintered body of SnO ₂ is mainly used as a semiconductor, ZnO, TiO ₂ or the like may be used. This sensing element is originally intended to detect inorganic compounds such as hydrogen and CO, saturated chain hydrocarbons such as methane and ethane, unsaturated hydrocarbons such as ethylene and propylene, cyclic hydrocarbons such as benzene and toluene, and alcohols. Detects and has little selectivity.
However, the hydrogen gas detection element 10 manufactured by subjecting the SiO ₂ film to vapor deposition has excellent selectivity in hydrogen measurement. In the case of a molten steel hydrogen sampler, a slight amount of CO gas and the like coexist in the gas collected in the vacuum chamber 21 in addition to hydrogen. In the hydrogen gas detecting element 10, for example, CO needs to have a concentration of 500 times that of hydrogen in order to obtain the same output signal as hydrogen. If the amount of other components coexisting in the gas sample is large and the amount of hydrogen is affected, it is advisable to install a separation column in front of the measurement cell 9. Does not need The structure of the measurement cell 9 is such that the internal volume is as small as possible and the gas sample introduction tube 16 and the discharge tube are the same so that the gas sample carried by the carrier gas can pass through the hydrogen gas detection element 10 quickly without being overwhelmed. A cylindrical tube shape with 17 at both ends is suitable. As described above, the hydrogen gas detection element 10 is constantly heated to 300 to 400 ° C,
For example, the detection element in the measuring cell 9 which is a closed system under a constant condition of carrier gas having a constant flow rate of about several 100 ml / min at all times.
The temperature of the sensing element 10 is constant because it only passes through it. Normally, the thermal conductivity detector used as a hydrogen gas detector in gas chromatography is ± 0.
Compared to having to be installed under strict temperature control conditions such as 1 ° C, the semiconductor hydrogen gas detection element used in the present invention
In the case of 10, the temperature control of the measuring cell 9 installed may be remarkably gentle. However, since the object of the present invention is an accurate quantitative analysis of hydrogen, the measurement cell 9 is installed in a temperature-controlled room controlled with an accuracy of ± 2 to 3 ° C.

(Example) An example in which molten steel (5 g) was sampled with a molten metal sampler and hydrogen in the molten steel was quantified using the apparatus of the present invention shown in FIG. 1 will be described. 60 from the cylinder 1 with the flow controller 4
Argon adjusted to a flow rate of 0 ml / min is circulated to the measuring cell 9 as a carrier gas via the sampler housing part 8. A fixed amount of standard hydrogen gas measured from a standard hydrogen gas cylinder 2 through a flow controller 4'by a measuring device 7 such as a sampling coil is stored in the sampler housing 8 by the operation of the flow path switching device 6 using argon as a carrier gas. After that, it is sent to the measuring cell 9. At the same time, the dehumidifier 5 filled with silica gel and molecular sieve from the air pump 3
Air of the adsorbed gas is supplied to the pipe intermediate between the sampler housing 8 and the measurement cell 9 at a flow rate of 3 l / min via the flow controller 4 ″, mixed with the carrier gas and sent to the measurement cell 9. By supplying hydrogen gas, the relationship between the hydrogen concentration and the output signal of the detection element 10 is obtained.Next, the molten metal sampler 22 is stored in the sampler storage chamber 23, and the drive screw 26 is rotated while flowing the carrier gas. Then, the sampler 22 is crushed, and the hydrogen gas diffused from the molten steel collected in the conduit 19 of the sampler by the flow of the hydrogen gas and the carrier gas collected in the vacuum chamber 21 of the sampler,
The gas sample is introduced from the gas sample introducing pipe 16 into the measuring cell 9 installed in the temperature-controlled room 11 adjusted to about 50 ° C. The gas sample comes into contact with and passes through the detection element 10 connected to the power source 12, and is discharged from the system through the discharge pipe 17. After a few seconds, the output signal of the semiconductor hydrogen gas detection element 10 passes through the amplifier 13 or attenuator,
The integrated intensity of the detection peak is calculated by the data processor 14, and the standard hydrogen gas and the detection element stored in advance are stored.
The hydrogen concentration in the molten steel sample is calculated from the relational expression with the output signal of 10 and displayed on the analysis result display unit 15.

Table 1 shows an example of the results obtained by collecting and analyzing molten steel having a composition equivalent to JIS SS41 in a ladle for vacuum degassing in the steelmaking process. Table 1 shows the quantitative accuracy of molten steel at each hydrogen concentration level when repeated 5 times, and the thermal conductivity detection after conventional water cooling.
The quantitative value by gas chromatography is also shown. The quantitative value was in good agreement with the conventional method and the quantitative accuracy was good. Further, the quantitative sensitivity of the present invention is extremely high, and the gas sample is diluted and supplied to the detection element 10 with the adsorbed gas flow rate set to a large flow rate of 3 l / min as described above.

Therefore, the sensitivity can be improved by reducing the flow rate of the adsorbed gas. However, the oxygen concentration in the gas passing through the detection element 10 must be 10% or more. Therefore, the ratio of the carrier argon gas to the adsorbed gas air is set to 1: 5 so that the oxygen content rate is maintained at 17%, and the gas flow rate (hydrogen 1.
Fig. 6 shows a calibration curve measured by changing 0 ml corresponding to 18 ppm as hydrogen in steel when the amount of molten steel collected is 5 g. Further, FIG. 7 shows an example of a calibration curve measured when the hydrogen content in steel is 1.8 ppm or less. From FIG. 7, it can be seen that the quantitative sensitivity of the present invention is 10 times or more higher than that of the conventional thermal conductivity detector. Further, the analysis time required by the present invention is 30
Although it is a short time within seconds, it takes about 3 minutes in the conventional thermal conductivity detection-gas chromatography. Since the present invention can perform analysis immediately after collecting molten steel with a sampler, it takes less than 1 minute from collecting molten steel to obtaining hydrogen analysis results, and is more practical than conventional methods for process control of the steelmaking process. became.

(Effects of the Invention) As described above, the present invention makes the determination of hydrogen in a molten metal extremely simple and quick, as compared with the conventional thermal conductivity detection-gas chromatography. That is, compared to the conventional method, the molten metal sampler in the heated state can be immediately subjected to analysis, a separation column is not required in the measurement system, and the control conditions of the ambient temperature of the sensing element can be relaxed. Is small and simple, and the handling including maintenance is very easy.
The equipment cost has become significantly cheaper. In addition, the quantitative sensitivity and accuracy have improved and the reliability has increased. Further, the device is small and simple, and the restrictions such as the atmospheric temperature control are relaxed, so that the analyzer can be brought into the metal refining site. Since the present invention is characterized in that the molten metal can be analyzed immediately in a heated state, it takes less than 1 minute from the time when the molten metal is obtained until the hydrogen analysis value is obtained, which is significantly quicker than before. Improve and control the metal refining process and make a great contribution to quality control.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the overall configuration of an apparatus according to an embodiment of the present invention, and FIG.
3 and FIG. 3 are measurement results of the characteristics of the detector of the device of the present invention, FIG. 4 is an explanatory view of the hydrogen sampler in molten steel, which is the subject of the present invention, and FIG. Explanatory drawing, FIG. 6, and FIG. 7 are examples of calibration curves obtained by the present invention. 1 ... Inert gas cylinder, 2 ... Standard gas cylinder, 3 ... Air pump, 4, 4 ', 4 "... Gas flow controller, 5 ... Dehumidifier,
6 ... Flow path switching device, 7 ... Standard gas measuring device, 8 ... Sampler storage part, 9 ... Measuring cell, 10 ... Semiconductor type hydrogen gas detection element, 11 ... Constant temperature chamber, 12 ... Power supply device, 13 ... Amplifier, 14 ... Data processing device, 15 ... Analysis result display device, 16 ... Gas sample inlet port, 17 ... Gas sample outlet port, 18 ... Cylindrical tube, 19 ... Conduit, 20 ...
Tip, 21 ... Vacuum chamber, 22 ... Molten metal sampler, 23 ... Sampler storage chamber, 24 ... Lid, 25 ... Metal rod, 26 ... Drive screw, 27 ... Bellows, 28 ... Suction base.

Front Page Continuation (72) Inventor Yuuo Tozawa 1-6-6 Taito, Taito-ku, Tokyo Riken Industry Co., Ltd. (56) Reference JP-A-59-138956 (JP, A) JP-A-56-31642 ( JP, A) JP 58-158551 (JP, A) JP 49-29187 (JP, A) Actual development 59-113743 (JP, U)

Claims (3)

[Claims] 1. An analysis method for quantifying hydrogen in a molten metal by using a sampler for diffusing and collecting hydrogen contained after collecting the molten metal, without cooling the sampler from which the molten metal is collected. Immediately supplying an inert gas as a carrier gas, hydrogen in the molten metal and diffusible hydrogen trapped in the sampler vacuum chamber are equipped with a gas sample introduction pipe and a discharge pipe, and a semiconductor-type hydrogen gas detection element is provided inside. A constant flow rate is fed into the measuring cell installed in the temperature-controlled room, and the dehumidified oxygen or a gas or air containing a certain concentration of oxygen is added from the middle of the path between the sampler and the measuring cell. Oxygen concentration is 10%
Is mixed so as to have a constant concentration of 21% and sent at a constant flow rate, and the hydrogen concentration in the molten metal is obtained from the output signal of the detection element. 2. A carrier gas supply unit comprising an inert gas supply source and a gas flow controller, and a standard hydrogen gas supply unit comprising a standard hydrogen gas supply source and a standard hydrogen gas meter, a carrier gas inlet port and a carrier gas exhaust unit. An adsorption gas supply unit consisting of an adsorption gas supply source containing a 10% or more oxygen content, a gas dehumidifier, and a gas flow rate controller, connected to the sampler storage unit consisting of a sampler storage chamber with an outlet with a thin tube. And equipped with a diffusible hydrogen gas introduction pipe and the same outlet pipe, a semiconductor type hydrogen gas detection element is installed inside,
An apparatus for analyzing hydrogen in molten metal, characterized in that the measuring cell section housed in a thermostatic chamber is connected in this order by a thin tube, and the cell section is equipped with a power supply device and a data processing device. 3. An apparatus for analyzing hydrogen in molten metal according to claim 2, wherein the adsorbed gas supply unit comprises a pump for supplying air under pressure, a cylinder filled with air, an air dehumidifier, and an air flow controller. .