City gas leak detection method and gas detector

Abstract

To provide a city gas leak inspection method and a gas detector that can easily and accurately detect city gas leaks. [Solution] The city gas leak detection method measures the butane gas concentration and the flammable gas concentration in the gas under test and determines whether or not city gas is leaking based on the proportion of butane gas in the flammable gas in the gas under test. The gas detector includes a control unit 140 that has the function of determining whether or not city gas is leaking based on the proportion of butane gas in the flammable gas in the gas under test. In a configuration that includes a butane gas detection sensor 120, a photoionization type gas sensor equipped with an ultraviolet light source 125 that emits ultraviolet light having a photon energy smaller than the ionization energy of propane gas is used as the butane gas detection sensor 120.

Description

Technical Field

[0001] The present invention relates to a method for inspecting urban gas leakage capable of identifying and detecting urban gas leakage, for example, as gushing methane gas, and a gas detector used in the method for inspecting urban gas leakage.

Background Art

[0002] Gas pipes for urban gas supply buried underground may gradually corrode over time due to the influence of the underground environment, or may be damaged by earthquakes or the like, resulting in leakage of urban gas from a part of the gas pipe. In such cases, it is necessary to quickly locate and repair the gas leakage point of the gas pipe. Also, after the repair work of the gas pipe is completed, it is necessary to inspect for the presence or absence of gas leakage before flowing urban gas.

[0003] Since urban gas is a mixed gas mainly composed of methane gas and containing ethane gas, propane gas, butane gas, etc., for urban gas detection, usually, for example, a so-called methane-specification gas detector calibrated with a combustible gas sensor such that the concentration indication value when introducing methane gas at a concentration of 100 vol% becomes 100 vol% is used.

[0004] On the other hand, methane gas is also generated during the decomposition process of organic matter by microorganisms. Therefore, for detecting urban gas leakage, it is necessary to distinguish between urban gas and naturally generated methane gas. However, in a methane-specification gas detector, methane gas not derived from urban gas may also be detected, so there is a risk of false detection of urban gas leakage.

[0005] To address this problem, a method is known in which, for sample gases that may contain city gas, LPG, and naturally occurring methane, concentration detectors are used to measure the concentrations of methane gas z1 and ethane gas x1 in the sample gas. Based on the ratio c of the ethane concentration x1 to the methane concentration z1 of the city gas that may be present in the sample gas, and the proportion α of other gases in the city gas that may be present in the sample gas, the concentration Ct of city gas in the sample gas is calculated using the formula Ct = x1(1 + 1 / a + 1 / c) / (1 - α) (see Patent Document 1).

[0006] Furthermore, a method is known in which a semiconductor gas sensor has different detection sensitivities for methane gas and ethane gas depending on the temperature, and methane gas is detected at a first temperature at predetermined time intervals. If methane gas is detected, gas detection is performed at a second temperature in the low-temperature range, thereby determining whether the detected gas is a first gas, such as natural gas, which has a low ethane gas content, or a second gas, such as city gas, which has an ethane gas content of a predetermined percentage or more (see Patent Document 2). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2018-169264 [Patent Document 2] Patent No. 7559275 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in the method described in Patent Document 1, gas components other than the three gas components of methane, ethane, and propane are treated as "miscellaneous gases (other gases)" and the concentration of city gas is determined. However, it has become clear that if other paraffinic hydrocarbon gases such as butane and pentane are included in city gas, even if the composition ratio of these paraffinic hydrocarbon gases is only a few percent, it will affect the concentration indication value. Furthermore, city gas often contains butane and pentane gases, and the city gas detection method described in Patent Document 1 has the problem that it is difficult to detect the concentration with high accuracy depending on the type of city gas. Furthermore, the method described in Patent Document 2 has a problem in that, when the concentration of city gas is low, the difference in sensitivity between city gas and methane gas of the gas sensor is small, making it difficult to accurately distinguish between leaked city gas and naturally occurring methane gas unless the concentration of city gas is several thousand ppm or higher.

[0009] The inventors focused on the butane gas component contained in city gas and discovered that by selectively detecting butane gas, it becomes possible to distinguish between leaked city gas and naturally occurring methane gas, thereby enabling highly accurate detection of city gas. This led to the completion of the present invention. This invention was completed in view of these circumstances, and aims to provide a method for easily detecting city gas leaks with high accuracy, and a gas detector suitable for use in the city gas leak detection method. [Means for solving the problem]

[0010] The present invention provides a method for inspecting city gas leaks, which includes a butane gas measurement step for measuring the concentration of butane gas contained in a test gas, a combustible gas measurement step for measuring the concentration of combustible gas containing butane gas contained in the test gas, and a city gas leak determination step for determining whether or not city gas is leaking based on the proportion of butane gas in the combustible gas in the test gas.

[0011] The present invention provides a gas detector comprising at least one of a butane gas detection sensor and a flammable gas detection sensor, and includes a control unit that has the function of determining whether or not city gas is leaking based on the proportion of butane gas in the flammable gas in the gas being tested, thereby solving the above problem. [Effects of the Invention]

[0012] According to the inventions of claim 1 and claim 6, by comparing the proportion of butane gas in the combustible gas in the gas under test with the proportion of butane gas components contained in city gas, it becomes possible to easily detect city gas leaks with high accuracy, even if the concentration of the leaked city gas is as low as, for example, 100 ppm.

[0013] The paraffinic hydrocarbon gases contained in city gas have higher ionization energy as the number of carbon atoms decreases. Therefore, by using a photoionization gas sensor equipped with an ultraviolet light source that emits ultraviolet light having a photon energy lower than that of propane gas, the inventions of claim 2 and claim 7 become capable of selectively detecting butane gas without sensitivity to methane gas, thus enabling detection of city gas leaks with even higher accuracy. According to the inventions of claim 3 and claim 8, the concentrations of flammable gas and butane gas can be detected for the test gas under the same measurement conditions, thereby improving the reliability of the measurement results. According to the inventions of claim 4 and claim 9, it becomes possible to accurately distinguish between city gas and naturally occurring methane gas. According to the invention according to claim 5 and the invention according to claim 10, since low-concentration flammable gas can be detected, even if the leaked city gas is at a low concentration, by selectively detecting butane gas with a butane detection sensor, it becomes possible to reliably detect city gas. Further, since a hot-wire type semiconductor gas sensor can achieve power saving and miniaturization, it is extremely useful when configuring a gas detector as a portable type.

Brief Description of Drawings

[0014] [Figure 1] It is a flowchart showing an example of a city gas leakage determination process. [Figure 2] It is a diagram showing the sensor sensitivity of a butane gas detection sensor to city gas and methane gas. [Figure 3] It is a block diagram schematically showing the configuration of a gas detector according to an embodiment of the present invention. [Figure 4] It is a schematic diagram showing an example of the configuration of a butane gas detection sensor. [Figure 5] It is a schematic diagram showing an example of the configuration of a flammable gas sensor.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described in detail.

[0016] 〔City Gas Leakage Inspection Method〕 The city gas leakage inspection method according to the present invention is, for example, a method for identifying and detecting the leakage of city gas from a gas pipe buried in the ground from naturally occurring methane gas or the like, and includes a butane gas measurement step of measuring the concentration of butane gas contained in the test gas, a flammable gas measurement step of measuring the concentration of flammable gas containing butane gas contained in the test gas, and a city gas leakage determination step of determining whether or not city gas is leaking based on the ratio of butane gas in the flammable gas in the test gas. Here, city gas usually has methane (CH4) as the main component, and contains at least one or more gas components selected from paraffinic hydrocarbon gases such as ethane (C2H6), propane (C3H8), normal butane (n-C4H 10 ), isobutane (i-C4H 10 ), isopentane (i-C5H 12 ), normal pentane (n-C5H 12 ) and other gas components other than paraffinic hydrocarbon gases.

[0017] For the butane gas measurement step and the flammable gas measurement step, as long as the butane gas concentration and the flammable gas concentration in the test gas can be measured, the means for measuring the butane gas concentration and the flammable gas concentration is not particularly limited. Specifically, the butane gas measurement step and the flammable gas measurement step may be performed by a gas detector equipped with two types of gas sensors, namely a first gas sensor for detecting butane gas and a second gas sensor for detecting flammable gas, or may be performed by each of two types of gas detectors, namely a first gas detector equipped with a sensor for detecting butane gas and a second gas detector equipped with a sensor for detecting flammable gas. In any case, it is acceptable. When the butane gas measurement step and the flammable gas measurement step are performed by a gas detector equipped with two types of gas sensors, the butane gas concentration and the flammable gas concentration in the test gas according to the actual situation can be measured, so that the leakage of city gas can be accurately detected.

[0018] The butane gas measurement step is performed by a gas detector equipped with a photoionization type gas sensor that irradiates the test gas with ultraviolet light to ionize it and detects the gas concentration from the ion current generated at this time as a sensor for detecting butane gas$.

[0019] As the photoionization type gas sensor, it is preferable to use a photoionization type gas sensor equipped with an ultraviolet light source that irradiates ultraviolet light having a photon energy smaller than the ionization energy of propane gas. As an ultraviolet light source, for example, an ultraviolet lamp filled with krypton gas (photon energy: approximately 10.6 eV), an ultraviolet lamp filled with argon gas (photon energy: 11.7 eV), etc., can be used, and LED light sources or laser light sources may also be used.

[0020] The paraffinic hydrocarbon gases contained in city gas tend to have higher ionization energies as the number of carbon atoms decreases, and the ionization energy of hydrogen gas is higher than that of methane gas. Therefore, by using such an ultraviolet light source, it is possible to reliably ionize butane gas without ionizing methane gas, including naturally occurring seepage methane gas, as well as ethane gas and hydrogen gas. As a result, the butane gas detection sensor can selectively detect butane gas at low concentrations on the ppb order. Figure 2 shows the sensor sensitivity of the butane detection sensor for city gas and methane gas. In Figure 2, the solid line shows the relationship between sensor output and gas concentration for city gas, and the dashed line shows the relationship between sensor output and gas concentration for methane gas.

[0021] The flammable gas measurement process is performed using a gas detector equipped with a flammable gas detection sensor capable of detecting flammable gases. For detecting flammable gases, solid-state sensors such as hot-wire semiconductor gas sensors, catalytic combustion gas sensors, new ceramic gas sensors, semiconductor gas sensors, or thermal conduction gas sensors, as well as optical sensors such as infrared gas sensors and optical interference gas sensors, can be used. Among these, it is preferable to use a hot-wire semiconductor gas sensor. Hot-wire semiconductor gas sensors can detect low concentrations of flammable gases. Therefore, even if the leaked city gas is at a low concentration, it is possible to reliably detect city gas by selectively detecting butane gas with a butane detection sensor. Furthermore, hot-wire semiconductor gas sensors can be made more energy-efficient and smaller, making them extremely useful when configuring gas detectors as portable devices.

[0022] In the urban gas leakage determination process, the identification process for identifying whether the combustible gas is naturally generated, such as methane gas or hydrogen gas, or the leaking urban gas, is performed according to the following procedures (1) and (2). (1) Procedure for determining the presence or absence of combustible gas. (2) Procedure for identifying the type of combustible gas.

[0023] (1) In the procedure for determining the presence or absence of combustible gas, as shown in FIG. 1, for example, by performing a determination process S1 of comparing the combustible gas concentration with a preset gas leakage determination threshold value T0, the presence or absence of combustible gas leakage is determined. Specifically, for example, when the combustible gas concentration value Cf is less than the preset gas leakage determination threshold value T0, it can be determined that no combustible gas leakage has occurred. On the other hand, when the combustible gas concentration value Cf is greater than or equal to the gas leakage determination threshold value T0, it can be determined that some combustible gas exists. Here, the gas leakage determination threshold value T0 is set to a value within a concentration range of, for example, 0 to 500 ppm, for example, 10 ppm.

[0024] (2) In the procedure for identifying the type of combustible gas, for example, based on the combustible gas concentration and the butane gas concentration, the presence or absence of urban gas leakage is determined by identifying between urban gas and combustible gas other than urban gas. Specifically, first, when it is confirmed that the combustible gas concentration Cf is greater than or equal to the preset gas leakage determination threshold value T0, an identification process S2 of comparing the combustible gas concentration Cf with a preset first threshold value T1 (>T0) is performed. In this identification process S2, when it is confirmed that the combustible gas concentration Cf is greater than or equal to the first threshold value T1, an identification process S3 of comparing the butane concentration value Cb with a second threshold value T2 is performed, and when it is confirmed that the combustible gas concentration Cf is less than the first threshold value T1, an identification process S4 of comparing the butane concentration value Cb with a third threshold value T3 (<T2) set to a value smaller than the second threshold value T2 is performed. Here, the first threshold T1 is set to a value within the concentration range of 100 to 5000 ppm, for example, 500 ppm. The second threshold T2 and the third threshold T3 are set in relation to the first threshold T1 based on the proportion of butane gas contained in the city gas (0.2 to 2.8 vol%), with the second threshold T2 being set to a value within the concentration range of 0.2 to 150 ppm, for example, 40 ppm, and the third threshold T3 being set to a value within the concentration range of 0.001 to 50 ppm, for example, 4 ppm.

[0025] In the identification process S3, if the butane gas concentration Cb [ppb] is equal to or greater than the second threshold T2, it can be determined that the flammable gas is city gas. If the butane gas concentration Cb is less than the second threshold T2, it can be determined that the flammable gas is a flammable gas other than city gas (for example, methane gas).

[0026] In the identification process S4, if the butane gas concentration Cb is equal to or greater than the third threshold T3, it can be determined that the flammable gas is city gas. If the butane concentration indicator Cb is less than the third threshold T3, it can be determined that the flammable gas is a flammable gas other than city gas (for example, methane gas).

[0027] In the above, each step (1) and (2) in the city gas leak detection process may be performed based on the respective sensor outputs of the flammable gas detection sensor and the butane gas detection sensor, rather than the gas concentration value. In such cases, the gas leak detection threshold T0 and the first threshold T1 to the third threshold T3 should each be set to values ​​within the output range corresponding to the gas concentration range set for the gas concentration value.

[0028] The following describes a gas detector according to the present invention that can be suitably used in the above-described method for inspecting city gas leaks.

[0029] The gas detector according to the present invention is configured as a portable type used by workers to distinguish and detect, for example, a leak of city gas from a gas pipe buried underground from naturally occurring methane gas.

[0030] Figure 3 is a block diagram schematically showing the configuration of a gas detector according to one embodiment of the present invention. The gas detector 100 according to this embodiment includes a gas detection unit 110 and a control unit 140 that controls the operation of the gas detector 100.

[0031] In this embodiment, the gas detection unit 110 includes a butane gas detection sensor 120 for detecting butane gas and a combustible gas detection sensor 130 for detecting combustible gas.

[0032] In this embodiment, the butane gas detection sensor 120 is composed of a photoionization gas sensor that irradiates the gas to be tested with ultraviolet light to ionize it and detects the gas concentration from the ion current generated at this time. As shown in Figure 4, the butane gas detection sensor 120 comprises an ionization chamber 121 into which the test gas (indicated by the filled-in arrow in Figure 2) is introduced, a cathode 122 and an anode 123 positioned opposite each other and spaced apart within the ionization chamber 121, an ultraviolet light source 125 that irradiates the test gas introduced into the ionization chamber 121 with ultraviolet light (indicated by the open-circle arrow in Figure 2) through a window member 126, a power supply 127 that applies a voltage controlled to a constant magnitude between the cathode 122 and the anode 123, and a current detection means 128 that detects the ionization current I flowing between the cathode 122 and the anode 123.

[0033] The ultraviolet light source 125 used emits ultraviolet light with a wavelength having a photon energy lower than the ionization energy of propane gas. As the ultraviolet light source 125, as described above, for example, an ultraviolet lamp filled with krypton gas (photon energy: approximately 10.6 eV), an ultraviolet lamp filled with argon gas (photon energy: 11.7 eV), etc., can be used, or an LED light source or a laser light source may also be used. The window member 126 can be made of, for example, magnesium fluoride, lithium fluoride, calcium fluoride, or quartz.

[0034] In this embodiment, the flammable gas detection sensor 130 is composed of, for example, a hot-wire semiconductor gas sensor that detects the change in resistance value that occurs when a metal oxide semiconductor comes into contact with the gas to be detected as the gas concentration. In this embodiment, the flammable gas detection sensor 130 has a power-saving configuration by not having a compensation element that is insensitive to the flammable gas to be detected. As shown in Figure 5, a gas detection element 131, in which a gas-sensitive part 132 is formed around a resistive heating element 133 that generates heat when energized, and a current detection resistor 135 are connected in series with a power supply 136 that applies a voltage controlled to a constant magnitude to the resistive heating element 133 in the gas detection element 131. In addition, a voltage detection means 137 is connected in parallel with the gas detection element 131, and a current detection means 138 is connected in parallel with the current detection resistor 135. The gas sensing portion 132 of the gas detection element 131 is made of a sintered metal oxide semiconductor. The resistance heating element 133 is made of a heater having a coil portion in which metal wires, for example, made of platinum or an alloy thereof, are wound in a coil shape.

[0035] The control unit 140 is composed of a CPU, which is a central processing unit, and includes a combustible gas concentration calculation unit 141 that calculates the concentration of combustible gas in the test gas based on the sensor output of the combustible gas detection sensor 130, a butane gas concentration calculation unit 142 that calculates the concentration of butane gas in the test gas based on the sensor output of the butane gas detection sensor 120, and a determination unit 143 that determines whether or not city gas is leaking based on the proportion of butane gas contained in the combustible gas in the test gas.

[0036] The determination unit 143 first determines whether or not a flammable gas is present in the gas being tested, and if the presence of a flammable gas is confirmed, it has the function of identifying whether the flammable gas is naturally occurring methane gas or hydrogen gas, or whether it is leaking city gas.

[0037] In the gas detector according to this embodiment, the butane gas concentration and the combustible gas concentration in the gas to be tested are measured by the butane gas detection sensor 120 and the combustible gas detection sensor 130 (the butane gas measurement step and the combustible gas measurement step), and the determination unit 143 performs an identification process including the above steps (1) and (2) to determine whether the combustible gas is naturally occurring methane gas or hydrogen gas, or leaked city gas (the city gas leak determination step).

[0038] Therefore, with the gas detector 100 described above, by comparing the proportion of butane gas in the combustible gas in the gas being tested with the proportion of butane gas components contained in city gas, it becomes possible to easily detect city gas leaks with high accuracy, even if the concentration of the leaked city gas is as low as, for example, 100 ppm.

[0039] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications can be made. For example, the gas detector according to the above embodiment is configured to include both a butane gas detection sensor and a flammable gas detection sensor, but it may also be configured to include only one of the gas sensors, either the butane gas detection sensor or the flammable gas detection sensor. In a gas detector equipped only with a butane gas detection sensor, it may be configured to allow input of the flammable gas concentration or sensor output value measured by a separate gas detector equipped with a flammable gas detection sensor. Similarly, in a gas detector equipped only with a flammable gas detection sensor, it may be configured to allow input of the butane gas concentration or sensor output value measured by a separate gas detector equipped with a butane gas detection sensor. [Explanation of Symbols]

[0040] 100... Gas detector 110... Gas detection unit 120 ··· Butane gas detection sensor 121 ··· Ionization Chamber 122... cathode 123 ··· Anode 125... UV light source 126... Window components 127... power supply 128 ··· Current detection means 130... Sensor for detecting flammable gases 131... Gas detection element 132... Gas-sensitive section 133 ··· Resistive heating element 135 ··· Current sensing resistor 136... power supply 137... Voltage detection means 138 ··· Current detection means 140 ··· Control Unit 141... Flammable gas concentration calculation unit 142 ··· Butane gas concentration calculation unit 143 ... Judgment section

Claims

1. A butane gas measurement process for measuring the concentration of butane gas contained in the test gas, A combustible gas measurement step for measuring the concentration of combustible gases, including butane gas, contained in the test gas, A city gas leak detection process that determines whether or not city gas is leaking based on the proportion of butane gas in the combustible gas in the gas being tested. A method for inspecting city gas leaks, characterized by including [a specific element].

2. The method for inspecting a city gas leak according to claim 1, characterized in that the butane gas measurement step is performed using a gas detector equipped with a photoionization type gas sensor as a butane gas detection sensor, which is equipped with an ultraviolet light source that irradiates ultraviolet light having a photon energy smaller than the ionization energy of propane gas.

3. The method for inspecting a city gas leak according to claim 1, characterized in that the butane gas measurement step and the combustible gas measurement step are performed using a gas detector equipped with two types of gas sensors: a butane gas detection sensor and a combustible gas detection sensor, each having a different detection principle.

4. The method for testing for city gas leaks according to claim 1, characterized in that, in the city gas leak determination step, it is determined that city gas is leaking when the concentration of flammable gas in the gas to be tested is equal to or greater than a first threshold and the concentration of butane gas in the gas to be tested is equal to or greater than a second threshold, or when the concentration of flammable gas in the gas to be tested is less than the first threshold and the concentration of butane gas in the gas to be tested is equal to or greater than a third threshold set to a value smaller than the second threshold.

5. The method for inspecting a city gas leak according to claim 3, characterized in that the gas detector used is equipped with a hot-wire semiconductor gas sensor as the sensor for detecting flammable gas.

6. A gas detector comprising at least one of a butane gas detection sensor and a flammable gas detection sensor, A gas detector characterized by having a control unit that has a function to determine whether or not city gas is leaking based on the proportion of butane gas in the combustible gas in the gas being tested.

7. Equipped with a butane gas detection sensor, The gas detector according to claim 6, characterized in that the butane gas detection sensor is a photoionization type gas sensor equipped with an ultraviolet light source that irradiates ultraviolet light having a photon energy smaller than the ionization energy of propane gas.

8. The gas detector according to claim 7, further comprising a sensor for detecting flammable gases in a test gas.

9. The gas detector according to claim 1, characterized in that the control unit determines that city gas is leaking when the concentration of flammable gas in the gas to be tested is equal to or greater than a first threshold and the concentration of butane gas in the gas to be tested is equal to or greater than a second threshold, or when the concentration of flammable gas in the gas to be tested is less than the first threshold and the concentration of butane gas in the gas to be tested is equal to or greater than a third threshold set to a value smaller than the second threshold.

10. The gas detector according to claim 8, characterized in that the aforementioned sensor for detecting flammable gas is a hot-wire type semiconductor gas sensor.

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