JPH073399B2 - Method and device for detecting gas leak from underground pipe of city gas - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas leak detection method and apparatus for detecting gas leak from a underground gas pipe of city gas such as natural gas or manufactured gas near the surface of the earth. It is a thing.

[Conventional technology]

It is extremely important for gas safety to detect city gas leaking from the gas pipe buried in the ground near the surface of the gas pipe burial section.

Traditionally, FID has been used exclusively to detect such gas leaks.
(Hydrogen flame ionization method) was used.

The FID is a detector that utilizes the fact that an organic compound is ionized in a high-temperature hydrogen flame and the electrical conductivity between the electrodes in the flame is increased. This FID is CO, H ₂
It is sensitive to almost all organic gases containing carbon other than gas and has no gas selectivity. In addition, the conventional combustible gas sensor using a metal oxide semiconductor has low gas sensitivity and low gas selectivity to detect gas leakage from underground gas pipes of city gas in the vicinity of the surface of the earth. Dependence and stability were also bad, and I could not pay attention to it at all.

[Problems to be solved by the invention]

The above FID has high sensitivity, but since it is necessary to burn hydrogen gas at all times during measurement, the operation is complicated and workable, such as mounting a hydrogen cylinder, checking the hydrogen pressure, and checking the ignition of the hydrogen flame. Is also bad. Moreover, the running cost is very high because the hydrogen gas of the hydrogen cylinder is consumed.
Furthermore, it is highly sensitive to alcohols, unsaturated hydrocarbons, and aromatic hydrocarbons, and therefore, gases other than lower saturated hydrocarbon gas, which is a component of city gas, such as exhaust gas from automobiles and various gas such as organic solvent gas such as paints. However, there was a problem that it was sensitive and led to misinformation.

Further, the conventional flammable gas sensor using a metal oxide semiconductor is equally sensitive to gases other than saturated hydrocarbons such as methane and butane. For example, unsaturated hydrocarbons such as acetylene and ethylene, aromatic hydrocarbons such as benzene and toluene,
I also feel vapors of alcohol, aldehydes, and ketones.
Therefore, when detecting gas leaks from underground pipes on the road surface, let alone carbon monoxide in the exhaust gas of automobiles,
It is also sensitive to organic gases such as aldehydes and acetylene, which are generally called CH components, leading to false alarms. Further, since the conventional saturated hydrocarbon selectivity S _n O ₂ sintered thick-film 4 terminal sensor is intended exclusively for preventing explosion, the warning level is 1000
The sensitivity is low at ~ 5000ppm, and the sensitivity is insufficient to detect the dilute city gas (~ 20ppm) diffused on the surface of the earth due to leakage from the underground pipe. Also, the response speed also requires about 10 seconds,
It is impossible to detect a gas leak by a scanning method which passes the leak point in a few seconds. In addition, the conventional metal oxide semiconductor gas sensor is easily affected by humidity due to water pools on the surface of the earth, and therefore stable measurement cannot be expected at all times. Also, S _n
Since the size of the O ₂ sintered body is as large as 4 × 2 × 1 mm and the power consumption is large, there are many problems that it is not suitable for battery operation.

The present invention has been made to solve the above problems, and provides a detection method and device capable of simply and surely detecting leak of city gas from an underground pipe, and a leak point The purpose is to improve the efficiency of discovery.

(Means for Solving Problems) The gas leak detection method for city gas according to the present invention has a specific surface area of 50 to 300 m ² / g when detecting gas leak from an underground pipe of city gas in the vicinity of the ground surface. Using a highly sensitive saturated hydrocarbon-selective hot-wire type semiconductor gas sensor prepared by adding antimony pentoxide to tin oxide, controlling the valence, and adding an appropriate amount of a stabilizer over time and 0.05% or less with a white silver catalyst as pt The city gas is estimated by detecting the lower saturated hydrocarbon gas in the city gas, and the city gas is detected by separating the combustible gas containing no lower saturated hydrocarbon gas.

Further, a gas leakage detecting device for burying underground gas of city gas according to the present invention is a saturated hydrocarbon selective hot wire type semiconductor gas sensor according to claim 1, and a gas near the surface of the earth is sucked from a gas suction port to saturate the saturated carbon. A pump for discharging the gas from the gas outlet after contacting the hydrogen-selective hot wire semiconductor gas sensor, an indicator for indicating the output of the saturated hydrocarbon-selective hot wire semiconductor gas sensor, and the saturated hydrocarbon-selective hot wire sensor And a display for issuing an alarm when the output of the semiconductor gas sensor exceeds a predetermined value.

[Action]

In a method for detecting gas leakage from a buried underground pipe of city gas according to the present invention, attention is paid to lower saturated hydrocarbon gas such as methane gas contained in city gas, and a highly sensitive saturated hydrocarbon selective hot-wire semiconductor By detecting the lower saturated hydrocarbon gas using a gas sensor, it is estimated that the gas leaks from the underground pipe of city gas.

Further, the gas leak detection device from the underground pipe of city gas according to the present invention, since the gas near the surface of the ground is sucked by the pump and brought into contact with the saturated hydrocarbon selective hot-wire semiconductor gas sensor, if gas leak occurs. If there is a saturated hydrocarbon gas, the saturated hydrocarbon-selective hot-wire semiconductor gas sensor outputs an output, which is displayed by the indicator as the concentration of city gas, and an alarm is output if the concentration is equal to or higher than a predetermined value.

〔Example〕

First, the city gas that is the detection target of the present invention will be described.

City gas can be roughly divided into natural gas (LNG) and manufactured gas.
Production gas can be classified into coal gas (coke gas), petroleum gas (naphtha gas) and LPG metamorphic gas. The composition of gas differs depending on each gas company, but in the case of using natural gas, CH ₄ is about 88% and other hydrocarbons containing 2 to 4 carbon atoms are about 10%. There are many. The calorific value of the produced gas is different, and its composition varies depending on the coal gas, petroleum gas, etc.
As a standard gas composition of al / m ³ , H ₂ 32 to 46%, CH ₄ 18 to
_{20%, CO5~10%, C n} H n ( Medium hydrocarbon) 4% to 10% remaining
_{They are} N ₂ , O ₂ and CO ₂ . The present invention is intended to efficiently detect gas leakage of city gas by detecting lower saturated hydrocarbon gas such as methane gas in the city gas.

Next, an embodiment of the present invention will be described. An example of a saturated hydrocarbon selective hot-wire semiconductor gas sensor (hereinafter simply referred to as a gas sensor) used in an embodiment of the present invention
Shown in Figures (a) and (b).

FIG. 1 (a) shows an example of a case where the gas sensor is formed into a spherical shape, and the outer diameter using a platinum wire 1 of 20 μmφ is 0.25.
In mm [phi], by sintering coil 2 in length 0.25mm outer diameter of 1mmφ less, for example, S _n O ₂ spherical less in diameter 1mm was embedded in a fine powder mass in 0.85Mmfai, forming a metal oxide semiconductor 3 It was done. The platinum wire 1 has a function of detecting a change in electric resistance of the metal oxide semiconductor 3 due to adsorption of a combustible gas and also serving as a heater for heating the metal oxide semiconductor 3 to a predetermined temperature. This sensor is also known as a two-terminal type semiconductor gas sensor.

FIG. 1 (b) is a side sectional view showing a substrate type gas sensor.
For example, a platinum film resistor 5 is formed on one surface of an alumina substrate 4 having a thickness of 0.4 mm in a meandering manner, and a paste similar to the above is applied thereon to a thickness of 0.3 mm, for example, and dried and fired to form a metal. The oxide semiconductor 6 is formed.

A saturated hydrocarbon-selective hot-wire semiconductor gas sensor used in the present invention is disclosed in Japanese Patent Publication No. 61-55062 and Japanese Unexamined Patent Publication No. 59-142.
Although those disclosed in Japanese Patent No. 445 and Japanese Utility Model Laid-Open No. 60-7062) are known, the sensitivity is still insufficient with these characteristics. Therefore, in the present invention, a more sensitive methane selective sensor is used. As an example of the metal oxide semiconductor 3,
Qs added over time stabilizer S _n O ₂ in fine powder, 0.5% Sb _n O ₅ as Sb, dispersing the fine powder of platinum catalyst was supported below 0.05% as Pt ethylene glycol to obtain paste After that, use a platinum wire with a diameter of 20 μm and an outer diameter of 250 μm and a length of 250.
Coat the coil 2 with a diameter of 0.8 μm into a spherical shape with a diameter of 0.8 to 0.9 mm.
Dry and sinter and use at a sensor temperature of 450 ℃. In this way, by adjusting the specific surface area of S _n O _{2 and} the amount of platinum catalyst and Sb ₂ O ₅ supported, the combustion activity of the metal oxide semiconductor 3 and the sensitivity to methane are adjusted, and a high sensitivity response is obtained. The property is extremely fast, and the selectivity for miscellaneous gas can be obtained.

FIG. 2 is a diagram showing an example of the measuring circuit. In this figure, a gas sensor R _s is installed in the gas passage, R ₀ , R ₁ and R ₂ are resistors, E is a power source, VR is a variable resistor, and V is a voltmeter.

In this way, the gas sensor R _s and the three resistors R ₀ , R ₁ , and R ₂ form a bridge circuit, and the output voltage is taken out by the change in the resistance value of the detection side due to the gas adsorption to the gas sensor R _s ,
Indicate with voltmeter V.

FIG. 3 is an example of a block diagram of a measuring apparatus embodying the present invention, in which the output from the gas sensor R _s is amplified by the amplifier AMP, displayed as the concentration of city gas by the indicator M, and passed through the comparator COM. A warning such as flashing lamp or buzzer or intermittent buzzer sound can be issued from the display DP. In addition, PW is a power supply, PS is a constant voltage circuit,
Gi is a gas inlet, Go is a gas outlet, and P is a pump.

FIG. 4 shows the ratio of the output of each gas when the output of 100 ppm of methane in the case of the present invention is 100% in the case of the FID method, and FIG. It can be seen that the saturated hydrocarbon selectivity is excellent.

That is, in Fig. 4, when the output of 100 ppm of methane is 100%, toluene, benzene, propane, and ethylene are 100% at a gas concentration of 20 to 70 ppm, and therefore malfunction may occur when trying to detect methane. However, in Fig. 5, ethylene, hydrogen, benzene, alcohol, toluene, propylene, acetone, carbon monoxide, acetylene, etc. are much lower than methane, so the detection of trace methane is highly reliable and malfunctions are detected. It hardly happens.

〔The invention's effect〕

As described above, in the gas leakage detection method from the underground buried pipe of city gas according to the present invention, when detecting the gas leakage from the underground buried pipe of city gas in the vicinity of the ground surface, the specific surface area 50 to 300 m. High-sensitivity saturated hydrocarbon-selective hot-wire semiconductor gas sensor made by adding antimony pentoxide to ² / g tin oxide, controlling the valence, and adding an appropriate amount of time-dependent stabilizer and 0.05% or less with platinum catalyst as pt It is presumed to be city gas by detecting lower saturated hydrocarbon gas in city gas using, and the city gas is detected by separating it from combustible gas that does not contain lower saturated hydrocarbon gas.
Gas leak of city gas near the surface layer where gas pipes are buried,
It can be detected with high sensitivity and high reliability.

Further, in the gas leak detection device from the underground pipe of city gas according to the present invention, the conventional FID must always be equipped with a hydrogen cylinder and always ignite a hydrogen flame at the time of measurement, therefore, Compared to running costs that are expensive, complicated operations, large equipment, and poor workability, the saturated hydrocarbon selective hot-wire semiconductor gas sensor of the present invention is used, and gas near the surface of the earth is discharged from the gas inlet. A pump for sucking and contacting the saturated hydrocarbon-selective hot-wire semiconductor gas sensor and then discharging it from a gas outlet, an indicator for indicating the output of the saturated hydrocarbon-selective hot-wire semiconductor gas sensor, and the saturated carbonization sensor With a display that issues an alarm when the output of the hydrogen-selective hot-wire semiconductor gas sensor exceeds a predetermined value, you can simply turn the switch on and off. Work is extremely simple, also running cost since it does not require hydrogen gas is 1 or less 20 minutes compared with FID. In addition, it is small and lightweight, has good workability, has a small output with a large output, and has a fast response speed. Therefore, it is a very excellent device for detecting gas leaks of city gas from underground pipes for mobile use, which can be displayed with a simple amplification circuit, is small and convenient to carry, and can be operated with one hand. In addition, it has extremely excellent features such that the detection speed can be increased.

[Brief description of drawings]

1 (a) and 1 (b) are cross-sectional views of a saturated hydrocarbon selective hot wire type semiconductor gas sensor used in the present invention, FIG. 2 is a diagram showing an example of a circuit used in the practice of the present invention, and FIG. FIG. 4 is a block diagram of a measuring apparatus for carrying out the invention, FIG. 4 is a detection characteristic diagram of the FID method, and FIG. 5 is a detection characteristic diagram of the present invention. In the figure, 1 is a platinum wire, 2 is a coil, 3 is a metal oxide semiconductor, R _s is a saturated hydrocarbon selective hot wire semiconductor gas sensor,
P is a pump, Gi is a gas inlet, Go is a gas outlet, PW is a power source, PS is a constant voltage circuit, AMP is an amplifier, COM is a comparator, M is an indicator, and DP is a display.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Koji Komatsu Inventor, Koji Komatsu 2-5-5 Mitsuyanaka, Yodogawa-ku, Osaka, Japan (56) References Japanese Patent Publication No. 61-55062 (JP, B2)

Claims (2)

[Claims] 1. A specific surface area of 50 to 300 m ² / g when detecting a gas leak from a buried underground pipe of city gas near the ground surface.
Antimony pentoxide is added to the tin oxide of to control the valence,
By detecting a lower saturated hydrocarbon gas in the city gas using a highly sensitive saturated hydrocarbon selective hot wire type semiconductor gas sensor created by adding an appropriate amount of a time stabilizer and 0.05% or less using platinum catalyst as pt A method for detecting gas leakage from a buried underground pipe of city gas, which is presumed to be city gas and is separated from combustible gas that does not contain lower saturated hydrocarbon gas to detect the city gas. 2. A highly sensitive material prepared by adding antimony pentoxide to tin oxide having a specific surface area of 50 to 300 m ² / g, controlling the valence, and adding an appropriate amount of a temporal stabilizer and 0.05% or less of platinum catalyst as pt. A saturated hydrocarbon-selective hot-wire semiconductor gas sensor,
Instruct the output of the saturated hydrocarbon-selective hot-wire semiconductor gas sensor and the pump that sucks gas near the surface of the earth from the gas inlet to contact the saturated hydrocarbon-selective hot-wire semiconductor gas sensor and then discharges it from the gas outlet And a display for issuing an alarm when the output of the saturated hydrocarbon-selective hot-wire semiconductor gas sensor is equal to or higher than a predetermined value. Detection device.