JP7327318B2 - Method for measuring molten steel temperature under reduced pressure - Google Patents

Description

The present invention relates to a method for continuously measuring the temperature of molten steel being refined in a vacuum chamber of a refining facility that refines molten steel under reduced pressure, such as an RH vacuum degasser.

In a secondary refining facility, which is the final process of iron and steel refining, conventionally, an immersion-type temperature measuring probe equipped with a thermocouple is immersed in molten steel in a ladle during refining to measure the molten steel temperature. Immersion-type temperature measuring probes exposed to high-temperature molten steel and slag are subject to severe erosion, and continuous measurement of molten steel temperature by immersion-type temperature-measuring probes is not possible. Therefore, the molten steel temperature is measured intermittently, and the temperature transition is predicted from the measurement result, and the temperature is adjusted.

Since the temperature is measured discontinuously in this way, if a phenomenon accompanied by a large temperature drop occurs, such as when bare metal adhering to the vacuum chamber falls into the molten steel, the temperature drop can be detected early. It was difficult to detect and respond to If the detection of the temperature drop is delayed, the amount of oxygen required to heat up the molten steel increases and the processing time is extended. As a result, continuous casting in a continuous casting machine is interrupted, resulting in a large operational impact.

Therefore, a method of continuously measuring the temperature of molten iron such as molten steel has been proposed. For example, Patent Document 1 proposes a method of continuously measuring the temperature of molten iron by penetrating a ceramic-coated continuous thermometer or immersion thermocouple through a measurement hole in the side wall of a cylindrical furnace and immersing it in molten iron in the furnace. It is Further, Patent Document 2 proposes a method of continuously measuring the temperature of molten steel by immersing a temperature measuring element in which a thermocouple is covered with a cermet protective tube through the side wall of a refining vessel into the molten steel.

However, in the above-described method of measuring temperature by immersing a thermometer with a thermocouple inside it in molten steel, it is necessary to use expensive refractories in order to suppress the wear of the protective tube due to slag and molten steel. There is In addition, even if the refractory performance is improved, the protection tube is still worn, and eventually the temperature measuring element must be replaced due to the wear of the protection tube, which inevitably increases the operating cost.

For these reasons, in recent years, non-contact temperature measurement methods for molten steel have been developed. For example, Patent Literature 3 proposes a method of continuously measuring the temperature of molten steel circulating in the vacuum chamber of an RH vacuum degasser with a radiation thermometer installed on the side wall of the vacuum chamber.

JP-A-5-39516 JP 2010-243171 A JP 2018-109633 A

However, Patent Document 3 mentioned above has the following problems.

Patent Document 3 uses a radiation thermometer as a thermometer that does not contact molten steel. It is a device that measures the temperature of the object, and there is a problem that the temperature measurement value has a large error due to the influence of the emissivity of the object.

On the other hand, a two-color thermometer is a method of measuring temperature using the infrared radiation intensity ratio of infrared rays of two different measurement wavelengths. , the influence of emissivity is cancelled, and measurement with higher accuracy is possible compared to a radiation thermometer that uses a single color. US Pat. No. 5,300,003 does not describe using a two-color thermometer.

However, as will be described later, according to the inventors' experiment of measuring molten steel temperature using a two-color thermometer in the vacuum chamber of the RH vacuum degassing apparatus, the atmospheric pressure in the vacuum chamber exceeded a certain value. It has been found that the accuracy of temperature measurements by a two-color thermometer decreases as the temperature increases. In addition, the surface of the molten steel is blocked by the ferroalloy that is introduced into the molten steel in the vacuum chamber through the raw material inlet, causing a phenomenon in which the temperature measured by the two-color thermometer is output lower than the actual temperature. I was able to confirm that.

The present invention has been made in view of the above circumstances, and its object is to continuously measure the temperature of molten steel in a vacuum chamber of a refining facility for refining molten steel under reduced pressure with a two-color thermometer. An object of the present invention is to provide a method for measuring the temperature of molten steel under reduced pressure, which can suppress a decrease in temperature measurement accuracy due to changes in the internal atmospheric pressure. Furthermore, it is possible to suppress a decrease in temperature measurement accuracy due to the presence of objects that block the surface of the molten steel, such as injected alloy iron and slag on the surface of the molten steel. The purpose is to provide a method for measuring molten steel temperature under

The gist of the present invention for solving the above problems is as follows.
[1] A method for measuring the temperature of molten steel under reduced pressure, in which the temperature of molten steel in a vacuum chamber of a refining facility for refining molten steel under reduced pressure is continuously measured with a two-color thermometer,
A method for measuring the temperature of molten steel under reduced pressure, wherein the wavelength used for temperature measurement by the two-color thermometer is changed according to the maximum atmospheric pressure in the vacuum chamber.
[2] When the maximum atmospheric pressure in the vacuum chamber is 0.67 kPa or more, the two wavelengths used for temperature measurement by the two-color thermometer are set within the range of the following formula (1). The method for measuring the temperature of molten steel under reduced pressure according to [1] above, wherein when the maximum value of the atmospheric pressure is less than 0.67 kPa, it is within the range of the following formula (2).
0.4≦wavelength (μm)≦0.7 (1)
0.4≦wavelength (μm)≦1.5 (2)
[3] The above [1] or [2], characterized in that the temperatures of the molten steel at multiple points in the vacuum chamber are measured, and the maximum temperature among the measured temperatures is taken as the representative temperature of the molten steel. A method of measuring the temperature of molten steel under reduced pressure.

According to the present invention, since the wavelength used for temperature measurement of the two-color thermometer is changed according to the atmospheric pressure in the vacuum chamber, the temperature of the molten steel being refined in the vacuum chamber under reduced pressure can be measured continuously with high accuracy. is realized. As a result, the accuracy of temperature control of molten steel being refined under reduced pressure has been improved, the operation has become more efficient by eliminating the need for excessive heating, and the refining time has been shortened, resulting in a reduction in manufacturing costs. be.

It is a schematic vertical cross-sectional view of an example of an RH vacuum degassing apparatus in which a two-color thermometer is installed. FIG. 4 is a diagram showing the relationship between the difference between the molten steel temperature measured value by a two-color thermometer and the molten steel temperature measured value by a thermocouple installed in an immersion type temperature measuring probe, and the atmospheric pressure in the vacuum chamber. It is a figure which shows the absorption spectrum of _H2O gas. FIG. 4 is a diagram showing the relationship between the difference between the molten steel temperature measured value by the two-color thermometer and the molten steel temperature measured value by the thermocouple installed in the immersion type temperature measuring probe, and the atmospheric pressure in the vacuum chamber in the example. Shows a comparison of the temperature measured by the thermocouple installed in the immersion type temperature measuring probe when the representative temperature of the molten steel is the average value of multiple temperature measurement points and the maximum temperature of multiple temperature measurement points. It is a diagram.

When the present inventors continuously measure the temperature of the molten steel in the vacuum chamber by concentrating the infrared rays radiated from the surface of the molten steel in the vacuum chamber of the refining equipment for refining the molten steel under reduced pressure with a two-color thermometer, , for the purpose of suppressing deterioration in temperature measurement accuracy due to changes in the atmospheric pressure in the vacuum chamber, the RH vacuum degassing equipment was selected as refining equipment for refining molten steel under reduced pressure. A test was conducted to measure the temperature of molten steel in a vacuum chamber with a two-color thermometer.

FIG. 1 shows a schematic longitudinal sectional view of an example of an RH vacuum degassing apparatus equipped with a two-color thermometer. In FIG. 1, 1 is a RH vacuum degassing device, 2 is a ladle, 3 is molten steel, 4 is slag, 5 is a vacuum tank, 6 is an upper tank, 7 is a lower tank, 8 is an ascending dip tube, and 9 is 10 is a circulating gas blowing pipe, 11 is a duct, 12 is a raw material inlet, 13 is a top blowing lance, 14 is a two-color thermometer, 15 is a computer for analysis, and 16 is a two-color thermometer. A communication cable 17 for connecting with the computer for analysis is a monitoring hole. The vacuum chamber 5 is composed of an upper chamber 6 and a lower chamber 7. A top blowing lance 13 is a device for blowing and adding oxygen gas or a solvent to the molten steel in the vacuum chamber. , and can move up and down inside the vacuum chamber 5 .

In the RH vacuum degassing apparatus 1, a ladle 2 containing molten steel 3 is raised by a lifting device (not shown), and an ascending immersion tube 8 and a descending immersion tube 9 are immersed in the molten steel 3 in the ladle. Then, the inside of the vacuum chamber 5 is evacuated by an exhaust device (not shown) connected to the duct 11 to decompress the inside of the vacuum chamber 5, and the inside of the rising side immersion pipe 8 from the reflux gas blowing pipe 10 is discharged. Reflux gas is blown into the When the pressure inside the vacuum chamber 5 is reduced, the molten steel 3 in the ladle rises in proportion to the difference between the atmospheric pressure and the atmospheric pressure in the vacuum chamber, and flows into the vacuum chamber. At the same time, due to the gas lift effect of the circulating gas blown from the circulating gas blowing pipe 10, the molten steel 3 in the ladle rises through the ascending immersion pipe 8 together with the circulating gas and flows into the vacuum chamber 5. , a flow returning to the ladle 2 via the descending dip pipe 9, a so-called reflux, is formed to perform RH vacuum degassing refining. The molten steel 3 is exposed to an atmosphere under reduced pressure in a vacuum chamber, and hydrogen and nitrogen in the molten steel move to the atmosphere in the vacuum chamber due to the difference in the equilibrium relationship based on the difference between the atmospheric pressure and the atmospheric pressure under reduced pressure. , the dehydrogenation reaction and denitrification reaction of the molten steel 3 proceed.

During this RH vacuum degassing refining, the interior of the vacuum chamber 5 is photographed by a two-color thermometer 14 through a monitoring hole 17 provided in the upper portion of the vacuum chamber 5 . The analyzing computer 15 continuously measures the temperature of the molten steel 3 in the vacuum chamber based on the data input from the two-color thermometer 14 .

Figure 2 shows the difference in temperature between the measured molten steel temperature measured with a two-color thermometer and the measured molten steel temperature measured with a thermocouple installed in an immersion type temperature probe during RH vacuum degassing refining. (thermocouple temperature - two-color thermometer temperature). FIG. 2 shows the relationship between the difference in temperature measurement values and the atmospheric pressure in the vacuum chamber, with the horizontal axis representing the atmospheric pressure in the vacuum chamber.

The two-color thermometer 14 used has two wavelengths of 0.90 μm and 1.05 μm for temperature measurement. In addition, the measurement of the molten steel temperature with a thermocouple is performed by intermittently immersing the immersion type temperature measuring probe in the molten steel 3 in the ladle to measure the temperature of the molten steel. is the difference between the temperature measurement value of the thermocouple and the temperature measurement value of the two-color thermometer when the immersion type temperature measuring probe is immersed in the molten steel 3 .

Here, the molten steel temperature in the ladle measured by a thermocouple was 1580 to 1620°C. In the RH vacuum degasser 1, the molten steel 3 is circulated through the ladle 2 and the vacuum tank 5, and the temperature of the molten steel in the vacuum tank is considered to be the same as the temperature of the molten steel in the ladle.

As shown in FIG. 2, when the atmospheric pressure in the vacuum chamber is less than 0.67 kPa (≈5.0 torr), the temperature measurement difference between the thermocouple and the two-color thermometer is 90° C. or less. It is not affected by the atmospheric pressure in the vacuum chamber, but when the atmospheric pressure in the vacuum chamber rises to 0.67 kPa or more, the temperature measurement with the thermocouple and the two-color thermometer will occur as the atmospheric pressure in the vacuum chamber rises. value difference increases. In other words, it was found that the temperature measurement accuracy of the two-color thermometer 14 deteriorated when the atmospheric pressure in the vacuum chamber was 0.67 kPa or higher.

The inventors investigated the reason why the temperature measurement accuracy of the two-color thermometer 14 decreases when the atmospheric pressure in the vacuum chamber increases. As a result, the inventors have found that the reason for this is the influence of gases present in the atmosphere within the vacuum chamber. In other words, the inventors have found that the infrared radiation emitted from the surface of the molten steel is absorbed by the gas present in the atmosphere within the vacuum chamber.

Various types of gas are present in the vacuum chamber of a refining facility for refining molten steel under reduced pressure, and the wavelengths absorbed by each type of gas are different. Therefore, depending on the type of gas present in the vacuum chamber, infrared radiation of only one of the two wavelengths used in the two-color thermometer 14 is absorbed, and the value of the original infrared radiation intensity ratio is Different values are printed. In other words, a value different from the original value of the infrared radiation intensity ratio is displayed, resulting in a decrease in temperature measurement accuracy. Such deterioration in temperature measurement accuracy due to gas absorption is caused by an increase in atmospheric pressure in the vacuum chamber, as shown in FIG.

Therefore, in the method of measuring the molten steel temperature under reduced pressure according to the present invention, the wavelength used in the two-color thermometer 14 is changed and set according to the atmospheric pressure in the vacuum chamber. By doing so, regardless of the atmospheric pressure in the vacuum chamber, the influence of the gas present in the vacuum chamber can be eliminated, and the accuracy of temperature measurement can be improved.

In choosing the wavelengths to be used for temperature measurement with the two-color thermometer 14, one should take into consideration the possible atmospheric pressure within the vacuum chamber. Based on the test results of the RH vacuum degassing apparatus 1, the method of determining the wavelength to be used and the results thereof will be described below.

In the RH vacuum degassing apparatus 1, when the two-color thermometer 14 continuously measures the molten steel temperature in the vacuum chamber, it is necessary to consider the gas species in the vacuum chamber. In the RH vacuum degassing apparatus 1, the atmospheric pressure in the vacuum chamber changes greatly during operation. Under extremely low pressure, almost no gas exists in the vacuum chamber, and it is thought that the temperature measurement by the two-color thermometer 14 is not greatly affected. , the appearance of gas in the vacuum chamber is foreseen.

Gas species that may appear include H ₂ O gas (water vapor). The vacuum chamber 5 of the RH vacuum degassing apparatus 1 has a structure in which the outer shell is made of steel and the inside of the steel shell is covered with a refractory material. Inclusions are used. As a result, when the refractories forming the vacuum chamber 5 are exposed to high temperatures, H ₂ O gas is generated within the vacuum chamber.

FIG. 3 shows the absorption spectrum of H ₂ O gas. As shown in FIG. 3, there are many absorption peaks in the wavelength band of 0.7 μm or longer. In FIG. 3, when the vertical axis is "0", the wavelength is not absorbed, and when the vertical axis is "1", the wavelength is almost completely absorbed. For example, about half of infrared radiation with a wavelength of 0.90 μm is absorbed, and almost no infrared radiation with a wavelength of 1.05 μm is absorbed.

In the example shown in FIG. 2, in which the temperature measurement accuracy decreased as the atmospheric pressure in the vacuum chamber increased, the wavelengths used in the two-color thermometer 14 were 0.90 μm and 1.05 μm. A peak of the absorption spectrum of H ₂ O gas exists in the vicinity of 0.9 μm. That is, the reason why the accuracy of temperature measurement decreased as the atmospheric pressure in the vacuum chamber increased was that of the wavelengths of 0.90 μm and 1.05 μm used for temperature measurement by the two-color thermometer 14, 0.90 μm was absorbed by the H ₂ O gas in the vacuum chamber, and a value different from the original value of the infrared radiation intensity ratio was output.

As is clear from FIG. 2, the temperature measurement accuracy of the two-color thermometer 14 is lowered when the atmospheric pressure in the vacuum chamber reaches 0.67 kPa or higher. Therefore, in the present invention, the maximum value of the atmospheric pressure in the vacuum chamber is divided into cases of 0.67 kPa or more and cases of less than 0.67 kPa, and the wavelengths used in the two-color thermometer 14 are set respectively. is preferred. Specifically, when the maximum value of the atmospheric pressure in the vacuum chamber is 0.67 kPa or more, the two wavelengths used for temperature measurement by the two-color thermometer 14 are set within the range of the following formula (1). When the maximum value of the atmospheric pressure in the vacuum chamber is less than 0.67 kPa, the two wavelengths used for temperature measurement by the two-color thermometer 14 are set within the range of the following formula (2) is preferred.

0.4≦wavelength (μm)≦0.7 (1)
0.4≦wavelength (μm)≦1.5 (2)
When the maximum value of the atmospheric pressure in the vacuum chamber is 0.67 kPa or more, the influence of the H ₂ O gas present in the vacuum chamber increases, so the peak of the absorption spectrum of the H ₂ O gas is less than 0.7 μm. Select two wavelengths in the range of If the wavelength is 0.7 μm or less, there is a disadvantage that the radiation intensity is weak, but absorption by H ₂ O gas can be prevented. On the other hand, the lower limit wavelength is 0.3×10 ¹⁶ (J×s/m ³ ) at 2000 K (assuming the temperature of molten steel) to ensure the infrared radiation intensity used for temperature measurement. was set to 0.4 μm based on Planck's law.

Planck's law indicates the wavelength distribution of infrared radiation intensity emitted from a black body, and the infrared radiation intensity (E) is expressed by the following equation (3).

E(λ,T)=(2hc ² /λ ⁵ )×(1/e ^hc/λkT −1) (3)
Here, in the equation (3), h is Planck's constant (J × s), c is the speed of light (m / s), λ is the wavelength (m), k is the Boltzmann constant (J / K), T is the temperature (K ).

When the maximum value of the atmospheric pressure in the vacuum chamber is less than 0.67 kPa, as can be seen from FIG. 2, the influence of the H ₂ O gas present in the vacuum chamber is small, so there is no need to limit the upper limit wavelength. . Therefore, in order to secure the infrared radiation intensity used for temperature measurement, the infrared radiation intensity of a black body at 2000 K (assuming the temperature of molten steel) was set to 0.3 × 10 ¹⁶ (J × s/m ³ ). Second, two wavelengths are set within the range of 0.4 μm to 1.5 μm based on Planck's law.

As described above, the surface of the molten steel is obstructed by the ferroalloy or the like introduced through the raw material inlet 12, so that the temperature measured by the two-color thermometer 14 is output lower than the actual temperature. Therefore, in order to prevent this phenomenon, a method for determining the representative temperature of molten steel was investigated.

Generally, the ferroalloy is charged from the raw material inlet 12 during RH vacuum degassing refining. Therefore, when the ferroalloy reaches the surface of the molten steel, the grains of the ferroalloy scatter and fall to the surface of the molten steel. In other words, the ferroalloy blocks part of the surface of the molten steel that can be confirmed through the monitoring hole 17 . Therefore, the temperatures of the molten steel 3 in the vacuum chamber are measured at multiple points at the same time, and the highest temperature among them is taken as the representative temperature.

By doing so, even if part of the surface of the molten steel is blocked by the alloy iron and the temperature measurement value is lowered, the temperature of the molten steel 3 can be accurately measured as long as the other measurement points are not blocked. . In addition, since it is assumed that the molten steel surface is blocked by the ferroalloy, the measurement points by the two-color thermometer 14 should be separated by at least the maximum diameter of the ferroalloy to be used, and more points should be measured. is preferred. In addition, in measuring the temperature at multiple points, multifaceted temperature measurement using one two-color thermometer 14 is essentially the same as the case of measuring using a plurality of two-color thermometers. means that

As described above, according to the present invention, the wavelength used for temperature measurement by the two-color thermometer 14 is changed according to the atmospheric pressure in the vacuum chamber. It is possible to continuously measure the temperature of 3 with high accuracy.

Although the above description exemplifies the RH vacuum degasser 1 as refining equipment for refining molten steel under reduced pressure, the application of the present invention is not limited to the RH vacuum degasser 1 . That is, as long as the refining equipment can collect infrared radiation emitted from the molten steel surface in the vacuum tank with a two-color thermometer, DH vacuum degassing equipment, REDA vacuum degassing equipment, VAD vacuum refining equipment, etc. The present invention can be applied to various refining facilities.

The present invention was applied to an RH vacuum degassing apparatus, and continuous temperature measurement of molten steel in a vacuum chamber was performed using a two-color thermometer. In addition, in order to confirm the temperature measurement accuracy of the two-color thermometer, the temperature of the molten steel in the ladle was intermittently measured using an immersion type temperature measuring probe. Since the maximum atmospheric pressure in the vacuum chamber in the RH vacuum degassing refining this time is 10 kPa, the wavelengths used for temperature measurement with a two-color thermometer were set to 0.5 μm and 0.6 μm according to formula (1). .

FIG. 4 shows the relationship between the difference between the molten steel temperature measured by the two-color thermometer and the molten steel temperature measured by the thermocouple installed in the immersion type temperature measuring probe, and the atmospheric pressure in the vacuum chamber. As shown in FIG. 4, even when the atmospheric pressure in the vacuum chamber increased to 0.67 kPa or higher, no drop in temperature measurement accuracy was observed with the two-color thermometer.

In addition, in FIG. 5, the representative temperature of the molten steel is set to the immersion type temperature measuring probe for the case where the average value of the multiple temperature measurement points by the two-color thermometer and the maximum temperature of the multiple temperature measurement points are set. A comparison with thermocouple temperature measurements is shown. As is clear from FIG. 5, it was confirmed that the temperature measurement accuracy was improved by setting the maximum temperature of the plurality of temperature measurement points to the representative temperature of the molten steel being refined in the vacuum chamber under reduced pressure.

Reference Signs List 1 RH vacuum degassing device 2 ladle 3 molten steel 4 slag 5 vacuum tank 6 upper tank 7 lower tank 8 ascending dip pipe 9 descending dip pipe 10 reflux gas blowing pipe 11 duct 12 raw material inlet 13 top blowing lance 14 2 Color thermometer 15 Computer for analysis 16 Communication cable 17 Monitoring hole

Claims (2)

A method for measuring the temperature of molten steel under reduced pressure, wherein the temperature of molten steel in a vacuum chamber of a refining facility for refining molten steel under reduced pressure is continuously measured with a two-color thermometer,
The wavelength used for temperature measurement by the two-color thermometer is changed according to the maximum value of the atmospheric pressure in the vacuum chamber,
The two wavelengths used for temperature measurement by the two-color thermometer are within the range of the following formula (1) when the maximum value of the atmospheric pressure in the vacuum chamber is 0.67 kPa or more, and the atmosphere in the vacuum chamber is A method for measuring the temperature of molten steel under reduced pressure, wherein when the maximum pressure is less than 0.67 kPa, the range of the following formula (2) is satisfied.
0.4≦wavelength (μm)≦0.7 (1)
0.4≦wavelength (μm)≦1.5 (2) 2. The method for measuring the temperature of molten steel under reduced pressure according to claim 1 , wherein temperatures of the molten steel at multiple points in the vacuum chamber are measured, and the highest temperature among the measured temperatures is used as the representative temperature of the molten steel. .

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