JPH10306312A - Method for observing hydrogen concentration in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly detect a rapid change in hydrogen concn. in exhaust gas in a vacuum degassing apparatus by constantly measuring the sound velocity propagated in the exhaust gas and detecting the change in hydrogen concn. contained in the exhaust gas with a change in the sound velocity. SOLUTION: The exhaust gas produced in the vacuum degassing treatment of molten steel, is mainly constituted with CO, CO2 and H2 . Since the sound velocity propagated in the exhaust gas of H2 gas only is three to five times as high as that in only CO gas or CO2 gas, the sound velocity of the above exhaust gas is affected most sensitively to the hydrogen gas concn. Based on this, a speaker 3 as the sound wave transmitter and an ultrasonic microphone 2 for receiver mutually faced in the radius direction, are arranged on the inner wall of a duct 1 for exhaust gas to measure the variation of sound volume per unit time between the transmitter and the receiver. In such a way, the hydrogen concn. in the exhaust gas is observed and the adding quantity of flux is adjusted and the vacuum degree is lowered, and thereby, the exhaust gas composition can be made not to reach the explosion limit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for monitoring the concentration of hydrogen gas in exhaust gas, and more particularly to a method for monitoring the concentration of hydrogen gas contained in exhaust gas in a vacuum degassing apparatus used for steel refining without using a gas analyzer. This is a technique for easily detecting an increase or decrease in density.

[0002]

2. Description of the Related Art Since carbon contained in steel has a great effect on the quality and mechanical strength of the steel, in recent steelmaking processes, molten steel decarburized and refined in a converter or the like is further subjected to a vacuum degassing apparatus. , And may be decarbonized to a so-called extremely low carbon region. At that time, in order to set the carbon content to a target value, the exhaust gas component of the vacuum degassing device is analyzed, and dynamic control based on the analysis value is performed.

[0003] The exhaust gas component of this vacuum degassing device is under vacuum of about several tens torr because the vacuum degassing device is under vacuum.
It is difficult to sample near that point, and usually
Analyzed under normal pressure. That is, JP-A-6-8102
As disclosed in Japanese Patent Publication No. 7, a vacuum pump is installed at a place far away from the vacuum degassing device, exhaust gas at normal pressure is collected at the outlet of the pump, and a mass spectrometer or an infrared spectrometer is used. Is used to analyze the components in the exhaust gas. In this method, since the exhaust gas is directly introduced into the analyzer, a sampling device for removing dust and dehumidifying was required. In addition, the sampling device requires frequent maintenance because dust in exhaust gas combines with moisture to cause clogging of the filter. Also, since the installation position of the analyzer is far from the vacuum degassing device, it takes time for the gas to pass through the sampling device and reach the analyzer, which hinders rapid component analysis.

[0004] Even in the conventional exhaust gas analysis which cannot perform such rapid analysis, ordinary vacuum smelting has functioned as a reaction monitor in a degassing apparatus. However, in recent years, with the diversification of steel types processed under vacuum, an unexpected change in gas components at the time of feeding auxiliary materials into the furnace has become a problem. For example, when elements having high hydrogen storage properties such as Ti, Zr, and Hf are added to molten steel in a vacuum degassing apparatus in order to adjust to an effective amount in steel, hydrogen stored in these metals is suddenly released. It was observed that they were mixed into the exhaust gas and rapidly changed the hydrogen concentration. Similar problems were also found when choppers (scrap scraps) or the like were introduced as a cold material during refining, or when a lime-based flux containing a large amount of moisture was introduced as a refining flux. This hydrogen is a gas species that causes a gas explosion together with CO. Therefore, from the viewpoint of safety, it must be absolutely avoided that the exhaust gas exceeds the explosion limit due to the rapid increase in the hydrogen concentration in the exhaust gas.

However, in the above-described conventional analysis using gas sampling, rapid analysis cannot be performed. Therefore, even if the amount of hydrogen gas rapidly increases in the exhaust gas passing through the duct, the situation cannot be detected quickly, and preventive measures are delayed. There is a risk that it will. Therefore, there has been a problem that the vacuum degassing of molten steel cannot be performed with security.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a method and an apparatus for monitoring the concentration of hydrogen in exhaust gas which can rapidly detect a rapid change in the concentration of hydrogen in exhaust gas of a vacuum degassing apparatus. It is an object.

[0007]

Means for Solving the Problems In order to achieve the above object, the inventor has made an intensive effort to find a hydrogen concentration monitoring means capable of performing rapid processing, instead of collecting and analyzing exhaust gas. And the propagation speed of the sound passing through the exhaust gas (hereinafter, referred to as
The present invention has been completed by focusing on the fact that the sound velocity is affected by the hydrogen concentration in the exhaust gas.

That is, the present invention relates to a method for monitoring the concentration of hydrogen gas in exhaust gas, which constantly measures the speed of sound propagating in the exhaust gas and detects a change in the concentration of hydrogen contained in the exhaust gas based on the change in the sound speed. is there. Further, the present invention is a method for monitoring the concentration of hydrogen gas in exhaust gas, wherein a threshold value is set for the sound speed, and an alarm is issued when the measured sound speed exceeds the threshold value.

Further, the present invention is characterized in that a speaker for generating a sound wave and an ultrasonic microphone for receiving the sound wave are provided opposite to each other on the inner wall of the exhaust gas duct of the vacuum degassing apparatus. It is also a hydrogen gas concentration monitoring device. 4. The apparatus according to claim 3, wherein the speaker and the ultrasonic microphone are provided so as to face each other in a radial direction of the inner wall.

In the present invention, since the speed of sound propagating in the exhaust gas is constantly measured and the amount of change is detected, the rapid concentration of hydrogen in the exhaust gas can be easily detected. As a result, the operator can accurately manage the hydrogen concentration of the exhaust gas, and can quickly perform the measure (reduction of the hydrogen content).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described. Speed of sound propagating in gas
Is 337.1 (m / sec) when the gas is all CO.
c), CO_Two 258.0 (m / sec), H_Two 
Is 1269.5 (m / sec). True of molten steel
Exhaust gas generated by the empty degassing process is almost CO, CO _Two , H
_Two Because of the above facts, the vacuum degassing device
These exhaust gases react most sensitively depending on the hydrogen gas concentration.
It is thought that.

The present invention embodies this idea, and FIG. 1 shows an example of an apparatus used. FIG. 1 shows a cross section of an exhaust gas duct 1, and a speaker 3 for transmitting a sound wave and an ultrasonic microphone 2 for receiving are provided on the inner wall of the duct 1 so as to face each other in the radial direction. In the present invention, the installation position is not limited to the radial direction of the duct 1, but may be any relationship as long as they are opposed to each other in the longitudinal direction. by this,
The change in volume per time between transmission and reception can be measured.

[0013] In addition, a cold material such as a chopper to be added to the molten steel at the time of the above-mentioned vacuum degassing treatment may include CO, C in exhaust gas.
The O ₂ amount is hardly changed, or even if it is changed, the change speed is small. Therefore, CO, CO in exhaust gas
Regarding the _two concentrations, analysis using a conventional exhaust gas analyzer (not shown) is sufficient. Further, if the hydrogen gas concentration estimated from the sound speed of the exhaust gas according to the present invention is corrected with those analysis values, more accurate monitoring of the hydrogen gas concentration in the exhaust gas becomes possible.

Based on the change in the hydrogen concentration in the exhaust gas monitored in this manner, the composition of the exhaust gas can be adjusted to the explosion limit by adjusting the amount of the flux added such as alloy components and calcined lime, or by reducing the degree of vacuum. It is possible to avoid entering. At that time, a threshold value is set for the sound velocity, and if it exceeds the value, a warning is issued to alert the operator, and the degree of vacuum is temporarily reduced to reduce the amount of generated gas, thereby preventing delay in treatment. it can. Note that the threshold may be the lower explosive limit concentration of hydrogen.

[0015]

EXAMPLE A so-called VOD was used as a vacuum degassing device, and an ultrasonic microphone 2 and a speaker 3 were installed on the inner wall of an exhaust duct 1 so as to face each other in the radial direction as shown in FIG. Then, a sound speed measurement test was performed under the following conditions.
When performing degassing treatment of the molten steel in VOD, the conventional exhaust gas _{composition, CO: 60vol%, CO 2} : a 40 vol%, the speed of sound passing through the waste gas is about as measured by the apparatus according to the present invention 307 (m / sec).

Next, the composition of the molten steel was adjusted by adding a Ti alloy to the molten steel, and during that time, the measurement of the sound velocity was continued with the apparatus according to the present invention. The changes in the hydrogen concentration and the speed of sound in the exhaust gas are shown in FIGS. 2 and 3, respectively. From these figures, it can be seen that the hydrogen concentration and the sound speed start increasing immediately after the addition of Ti. The composition of the exhaust gas finally becomes CO: 60
_{vol%, CO 2: 30vol%} , H 2: 10vol%
And the sound speed was 408 (m / sec).

According to the test results, it was possible to quickly detect a change in the hydrogen concentration by measuring the speed of sound in the exhaust gas, and it was confirmed that the present invention was effective for the safety of vacuum degassing of molten steel.

[0018]

As described above, according to the present invention, the change in the composition of the exhaust gas can be grasped by the change in the sound propagation speed. This is particularly effective when monitoring the increase or decrease of the hydrogen concentration without using an analyzer or a sampling device that requires initial costs and maintenance costs.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a device for monitoring the concentration of hydrogen in exhaust gas according to the present invention.

FIG. 2 is a diagram showing a change with time of the hydrogen concentration obtained by implementing the method for monitoring the hydrogen concentration in exhaust gas according to the present invention.

FIG. 3 is a diagram showing a change over time in sound speed obtained by implementing the method for monitoring hydrogen concentration in exhaust gas according to the present invention.

[Explanation of symbols]

 1 Duct for exhaust gas 2 Ultrasonic microphone 3 Speaker 4 Sound wave

Claims (4)

[Claims] 1. A sound velocity that propagates in exhaust gas is constantly measured,
A method for monitoring the concentration of hydrogen gas in exhaust gas, wherein the change in the concentration of hydrogen contained in the exhaust gas is detected based on the change in the speed of sound. 2. A method for monitoring the concentration of hydrogen gas in exhaust gas according to claim 1, wherein a threshold value is set for the sound speed, and an alarm is issued when the measured value exceeds the threshold value. 3. A hydrogen gas concentration monitor in an exhaust gas, wherein a speaker for generating a sound wave and an ultrasonic microphone for receiving the sound wave are provided on the inner wall of the exhaust gas duct of the vacuum degassing device so as to face each other. apparatus. 4. The exhaust gas hydrogen concentration monitoring apparatus according to claim 3, wherein the speaker and the ultrasonic microphone are provided to face each other in a radial direction of an inner wall.