WO2019186794A1 - Gas detecting method and gas detecting device - Google Patents

Abstract

The purpose of the present invention is to provide a gas detecting method and a gas detecting device that make it possible to obtain, with a certain accuracy, the total concentration of paraffinic hydrocarbon components in a subject gas and the lower explosion limit concentration of the subject gas. In the present invention, a mixed gas containing two or more kinds of paraffinic hydrocarbon components is used as a subject gas, the refractive index and specific gravity of the subject gas are measured, and either one of or both the total concentration of the paraffinic hydrocarbon components in the subject gas and the lower explosion limit concentration of the subject gas are calculated on the basis of the ratio (Δs/Δn) of the difference in specific gravity (Δs) between the subject gas and a base gas in the subject gas to the difference in refractive index (Δn) between the subject gas and the base gas.

Description

Gas detection method and gas detection apparatus

The present invention relates to a gas detection method and a gas detection device.

For example, when unloading LNG from a carrier ship that transports liquefied natural gas (LNG) to land facilities, a loading arm is usually used. After unloading, LNG vaporized gas remains in the loading arm. Therefore, when disconnecting the loading arm, it is required to purge the LNG vaporized gas in the loading arm with an inert gas and confirm that the concentration of the LNG vaporized gas discharged from the loading arm is below the lower explosion limit concentration. It has been. In particular, nitrogen is used as an inert gas when purging for the purpose of discharging LNG vaporized gas. Here, the reason why nitrogen is used as the inert gas is that if moisture or carbon dioxide is contained, the moisture or carbon dioxide is solidified at the temperature of LNG, which may damage the inside of the pipe or equipment.

Generally, for detecting a combustible gas, for example, a contact combustion type gas sensor, a semiconductor type gas sensor, a non-dispersion type infrared sensor or the like is used. For example, Patent Document 1 describes that an LNG vaporized gas or an LPG vaporized gas is detected by a catalytic combustion gas detector.

JP 2013-234773 A

Thus, although the main component of LNG is methane, paraffinic hydrocarbon components such as ethane, propane, and butane are also included, and the composition of LNG varies depending on the place of production.
The gas discharged by purging the LNG vaporized gas in the loading arm with an inert gas contains a large amount of methane that is easily vaporized at the initial stage. However, with the passage of time, the boiling point of ethane, propane, butane, etc. is high. The ratio of paraffinic hydrocarbon components is high. The tendency of the composition of the LNG vaporized gas to change with time varies depending on the place where the LNG is produced, and it is difficult to predict the tendency of the composition to change with time. For this reason, in the case of measuring the lower explosion limit percentage concentration indicating the percentage of the total concentration of paraffinic hydrocarbon components with respect to the lower explosion limit concentration of the LNG vaporized gas using the inert gas as a base gas, it is included in the LNG vaporized gas. A gas sensor having an equivalent sensitivity level is required for any paraffinic hydrocarbon component.

However, the catalytic combustion type sensor and the semiconductor type sensor cannot detect the concentration of the paraffinic hydrocarbon component in the inert gas such as nitrogen gas because oxygen is indispensable from the detection principle. On the other hand, a non-dispersive infrared sensor cannot detect a plurality of types of paraffinic hydrocarbon components contained in LNG at the same sensitivity level.
As described above, for example, there is no gas sensor having an equivalent sensitivity level with respect to all paraffinic hydrocarbon components contained in the LNG vaporized gas having an inert gas as a base gas.

The present invention has been made based on the above circumstances, and even for a test gas containing an inert gas as a base gas, the total concentration of paraffinic hydrocarbon components in the test gas and the test It is an object of the present invention to provide a gas detection method and a gas detection device that can obtain the lower explosion limit concentration of gas with a certain accuracy.

The gas detection method of the present invention uses a mixed gas containing two or more paraffinic hydrocarbon components as a test gas,
Measure the refractive index and specific gravity of the test gas,
Based on the ratio (Δs / Δn) of the specific gravity difference (Δs) between the test gas and the base gas in the test gas to the refractive index difference (Δn) between the test gas and the base gas. One or both of the total concentration of the paraffinic hydrocarbon components in the detected gas and the lower explosion limit concentration of the detected gas are calculated.

In the gas detection method of the present invention, the total concentration of paraffinic hydrocarbon components in the test gas and the lower explosive limit concentration of the test gas are calculated,
It is preferable to calculate a lower explosion limit percentage concentration indicating a percentage of the total concentration of paraffinic hydrocarbon components of the test gas with respect to the lower explosion limit concentration of the test gas.

Furthermore, in the gas detection method of the present invention, the test gas is preferably an LNG vaporized gas or an LPG vaporized gas containing an inert gas as a base gas, and the inert gas is preferably a nitrogen gas.

Furthermore, in the gas detection method of the present invention, the specific gravity difference (Δs) between the test gas and the nitrogen gas that is the base gas of the test gas is determined by the specific gravity difference between the specific hydrocarbon component and the nitrogen gas ( specific gravity difference normalized value normalized by Delta] s _H) calculates a (Δs / Δs _H), the refractive index difference between the test gas and nitrogen gas ([Delta] n), and nitrogen gas that particular hydrocarbon component refractive index difference refractive index difference normalized value normalized by _{(Δn H) (Δn / Δn} H) calculated for,
It is preferable to calculate a ratio of the specific gravity difference normalized value (Δs / Δs _H ) to the refractive index difference normalized value (Δn / Δn _H ).

Furthermore, in the gas detection method of the present invention, the specific hydrocarbon component is methane gas, and the ratio of the specific gravity difference normalized value normalized based on methane gas to the refractive index difference normalized value is taken as the X axis, In an XY coordinate system with the explosion lower limit concentration as the Y axis, a curve included in a region between a curve represented by the following formula (1-a) and a curve represented by the following formula (1-b) or It is preferable to calculate the lower explosion limit concentration of the test gas based on a calibration curve indicated by a broken line.

In the above formulas (1-a) and (1-b), y is the lower explosion limit concentration [vol%], and x is the ratio of the specific gravity difference normalized value based on methane gas to the refractive index difference normalized value. It is.

Furthermore, in the gas detection method of the present invention, the ratio of the specific gravity difference normalized value normalized with respect to methane gas to the refractive index difference normalized value is x, the refractive index difference between the test gas and nitrogen gas is Δn, When the refractive index difference between methane gas and nitrogen gas is Δn _CH4 , it is preferable to calculate the total concentration y ′ of hydrocarbon components in the test gas based on the following mathematical formula (2).

The gas detection apparatus of the present invention uses a mixed gas containing two or more paraffinic hydrocarbon components as a test gas,
A refractive index measuring means for measuring the refractive index of the test gas;
Specific gravity measuring means for measuring the specific gravity of the test gas;
The ratio (Δs / Δn) of the specific gravity difference (Δs) between the test gas and the base gas in the test gas to the refractive index difference (Δn) between the test gas and the base gas in the test gas is calculated. A ratio calculating means for
One or both of HC component concentration calculating means for calculating the total concentration of paraffinic hydrocarbon components in the test gas based on the ratio and LEL calculating means for calculating the lower explosion limit concentration of the test gas are provided. It is characterized by.

The gas detection device of the present invention comprises both the HC component concentration calculating means and the LEL calculating means,
The lower explosive limit percentage concentration calculating means for calculating the lower explosive limit percentage concentration indicating the percentage of the total concentration of the paraffinic hydrocarbon components of the detected gas with respect to the explosive lower limit concentration of the detected gas is provided. It is preferable.

In the gas detection apparatus of the present invention, the test gas is preferably an LNG vaporized gas or an LPG vaporized gas containing an inert gas as a base gas, and the inert gas is preferably a nitrogen gas.

According to the gas detection method and the gas detection apparatus of the present invention, regardless of the composition ratio of the paraffinic hydrocarbon component, the total concentration of the paraffinic hydrocarbon component contained in the test gas, the lower explosive limit concentration of the test gas , And the lower explosion limit percentage concentration can be obtained with a certain accuracy.

It is a block diagram which shows roughly the structure in an example of the gas detection apparatus of this invention. It is a graph which shows an example of the correlation with the ratio with respect to the refractive index difference normalized value of a specific gravity difference normalized value, and an explosion lower limit density | concentration. For each of a plurality of types of test gases used in Experimental Examples 1 to 3, the value of the lower explosion limit percentage concentration obtained by the gas detection method according to the present invention and the explosion lower limit obtained in accordance with the IEC standard. It is a graph which shows the relationship with the value of a limit percentage density | concentration.

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

In the gas detection method of the present invention and the gas detection device of the present invention in which the gas detection method is executed, a mixed gas containing two or more paraffinic hydrocarbon components is used as a test gas.
Examples of the test gas include LNG vaporized gas and LPG vaporized gas mainly containing paraffinic hydrocarbons containing inert gas such as nitrogen gas or air as a base gas. Specifically, for example, gas discharged from the loading arm by purging the LNG vaporized gas or LPG vaporized gas remaining in the loading arm after completion of the LNG or LPG landing work with an inert gas, etc. it can.

FIG. 1 is a block diagram schematically showing the configuration of an example of the gas detection apparatus of the present invention.
The gas detection apparatus includes a gas detection unit 10 that measures a physical property value of a test gas, and an arithmetic processing unit 20 that processes data output from the gas detection unit 10.

The gas detection unit 10 includes a sound speed measuring unit 11 that measures the sound speed V _d of the test gas, and a refractive index measurement unit 15 that measures the refractive index n _d of the test gas. In this gas detection device, the test gas is sequentially supplied to the sound velocity measuring means 11 and the refractive index measuring means 15 as indicated by white arrows in FIG.

As the sound speed measuring means 11, for example, an ultrasonic sensor can be used. The ultrasonic sensor has a measurement tube in which a sound wave transmission source is provided at one end and a sound wave reception source is provided at the other end. In the ultrasonic sensor, the time (propagation time) required for the sound wave from the sound wave source to propagate through the test gas and reach the sound wave receiving source is measured in the state where the test gas is circulated in the measuring tube. The sound velocity V _{d of the} test gas is obtained from the value of the propagation time.

As the refractive index measuring means 15, for example, a difference in refractive index of light between a test gas and a reference gas such as air is detected as a displacement of interference fringes, and the refraction of the test gas is based on the amount of displacement. A light wave interferometer that measures the rate n _d can be used.

The arithmetic processing unit 20 includes a specific gravity measuring mechanism 25 that obtains the specific gravity S _d of the test gas based on the value of the sound velocity V _d of the test gas and the refractive index n _d of the test gas.

The specific gravity measuring mechanism 25 is measured by a sound speed-specific gravity conversion processing means 26 for obtaining _a sound speed converted specific gravity S _a based on the value of the sound speed V _d of the test gas measured by the sound speed measuring means 11 and the refractive index measuring means 15. refractive index determine the refractive index in terms of the specific gravity S _b based on the value of the refractive index n _d of the test gas - relative density conversion processing means 27, the gas to be detected on the basis of the sound speed in terms of the specific gravity S _a and refractive index in terms of the specific gravity S _b Specific gravity calculating means 28 for obtaining the specific gravity S _d of

The sound velocity-specific gravity conversion processing means 26 uses, for example, the correlation between the sound speed and specific gravity of the specific gas that has been acquired in advance for the specific gas consisting only of the paraffinic hydrocarbon component, and the sound velocity conversion specific gravity of the test gas. _Sa is calculated. Specifically, assuming that the test gas is a specific gas, the sound speed conversion specific gravity _Sa is calculated by comparing the value of the sound speed V _d acquired for the test gas with the correlation.

The refractive index-specific gravity conversion processing means 27 uses, for example, the correlation between the refractive index and specific gravity of the specific gas acquired in advance for the specific gas consisting only of the paraffinic hydrocarbon component, to refract the test gas. The rate conversion specific gravity _Sb is calculated. Specifically, assuming that the test gas is a specific gas, the refractive index conversion specific gravity S _b is calculated by comparing the value of the refractive index n _d acquired for the test gas with the correlation.

The specific gravity calculating means 28 is based on the sound speed converted specific gravity S _a obtained by the sound speed-specific gravity conversion processing means 26 and the refractive index converted specific gravity S _b obtained by the refractive index-specific gravity conversion processing means 27, as shown in the following formula (3). Thus, the specific gravity S _{d of the} test gas is calculated. Here, the specific gravity S _d , the sound velocity converted specific gravity S _a , and the refractive index converted specific gravity S _b of the test gas are all values when the specific gravity of air is 1.

In the above formula (3), α is a correction factor. The correction factor α is preferably a value within a numerical range of, for example, 2.4 or more and 9.3 or less, and more preferably a value within a numerical range of 3.0 or more and 6.2 or less.
Since the correction factor α is a value within the above numerical range, even if the sample gas contains a mixed gas, the correction factor α is obtained regardless of the composition of the mixed gas and the sample gas. The difference between the specific gravity S _d of the test gas and the true value of the specific gravity of the test gas is small.

Thus, the arithmetic processing unit 20 in the gas detection device includes a ratio calculation unit 30 that calculates a ratio between data related to the specific gravity S _d of the test gas and data related to the refractive index n _d of the test gas. The LEL calculating means 35 for calculating the lower explosion limit concentration y of the test gas based on the ratio, and the HC component for calculating the total concentration y ′ of paraffinic hydrocarbon components in the test gas based on the ratio The concentration calculation means 40 and the lower explosion limit percentage concentration y _L of the test gas are calculated based on the lower explosion limit concentration y of the test gas and the total concentration y ′ of paraffinic hydrocarbon components in the test gas. Explosive lower limit percentage concentration calculation means 45 is provided.

The ratio calculating means 30 is configured to calculate a ratio (Δs) of a specific gravity difference (Δs) between the test gas and the base gas in the test gas to a refractive index difference (Δn) between the test gas and the base gas in the test gas. / Δn).

Further, the ratio calculation means 30 normalizes the specific gravity difference (Δs) between the test gas and the base gas and the refractive index difference (Δn) between the test gas and the base gas, and the respective normalized values obtained thereby are normalized. It is preferable to have a function of calculating the ratio using the data relating to the specific gravity S _{d of the} test gas and the data relating to the refractive index n _d of the test gas.
Specifically, the specific gravity difference (Δs) between the test gas and the base gas is normalized by the specific gravity difference (Δs _H ) between the specific hydrocarbon component and the base gas, and the specific gravity difference normalized value (Δs / Δs) _H ) is calculated. Further, the refractive index difference (Δn) between the test gas and the base gas is normalized based on the refractive index difference (Δn _H ) between the specific hydrocarbon component and the base gas, and the refractive index difference normalized value (Δn) / Δn _H ) is calculated.
By using the normalized value to calculate the ratio of the data related to the specific gravity of the test gas to the data related to the refractive index of the test gas, the evaluation can be performed on a constant basis regardless of the composition of the test gas. Can do. Here, the specific hydrocarbon component is preferably methane gas. This is because the ratio x obtained by the ratio calculation means 30 can be normalized (normalized) so that the maximum value is 1.

The ratio x of the specific gravity difference normalized value normalized with respect to methane gas to the refractive index difference normalized value is calculated by, for example, the following formula (4). In the following mathematical formula (4), Δn is the difference in refractive index between the test gas and nitrogen gas (n−n _N2 ), Δn _CH4 is the difference in refractive index between methane gas and nitrogen gas (n _CH4 −n _N2 ), Δs Is the specific gravity difference (s−s _N2 ) between the test gas and nitrogen gas, and Δs _CH4 is the specific gravity difference between the methane gas and nitrogen gas (s _CH4 −s _N2 ).
In the following formula (4), when the base gas in the test gas is, for example, air, the refractive index and specific gravity of air may be used instead of the refractive index n _N2 and specific gravity s _N2 of nitrogen gas. In addition, when standardizing data based on a specific hydrocarbon component other than methane gas, the refractive index and specific gravity of the specific hydrocarbon component used as a reference instead of the refractive index n _CH4 and specific gravity s _CH4 of _methane gas are used. Use it.

The LEL calculation means 35 calculates the lower explosion limit concentration y [vol%] of the test gas based on the calibration curve indicating the correlation between the ratio x obtained by the ratio calculation means 30 and the lower explosion limit concentration y. To do.
The calibration curve is, for example, the ratio x of the specific gravity difference normalized value (Δs / Δs _CH4 ) normalized with respect to methane gas to the refractive index difference normalized value (Δn / Δn _CH4 ) as the X axis, and the lower explosion limit concentration In the XY coordinate system with Y as the Y axis, the curve is approximated by a curve or a broken line included in a region between the curve represented by the equation (1-a) and the curve represented by the equation (1-b). Is. The reason why the calibration curve is set in this way is as follows.

First of all, the specific gravity and refractive index of each of a plurality of kinds of test gases having a paraffinic hydrocarbon component as the main component and different compositions are actually measured, and the refractive index difference of the specific gravity difference normalized value based on methane gas. A ratio x to the normalized value is calculated. Further, the lower explosion limit concentration (theoretical value) is calculated based on the composition of each test gas, and the actually measured values thus obtained are represented by the ratio x as the X axis and the lower explosion limit concentration as the Y axis. And plotted in an XY coordinate system. As a result, as indicated by a solid line in FIG. 2, the relationship between the ratio x and the lower explosion limit concentration y is drawn by a single curve (hereinafter referred to as “reference calibration curve”) Cs, regardless of the composition of the test gas. It was confirmed that it was possible. Here, the reference calibration curve Cs is a curve represented by the following mathematical formula (5).

On the other hand, the value of the lower explosive limit concentration of various paraffinic hydrocarbon components is shown in, for example, IEC standard, ISO standard, or ICSC (International Chemical Safety Card, International Chemical Safety Card). However, there are some values that are different from each other as the value of the lower explosion limit concentration y. For example, the lower explosion limit value for isobutane gas (x = −0.35) is 1.3 vol% in the IEC standard (circled plot in FIG. 2) and 1.5 vol% in the ISO standard (in FIG. 2). (Triangle mark plot), in ICSC, it is 1.8 vol% (square mark plot in FIG. 2). In FIG. 2, the values of methane gas (x = 1.00), ethane gas (x = −0.06), and propane gas (x = −0.26) are also shown. The values based on the standard, the triangle marks are values based on the ISO standard, and the square marks are values based on the ICSC.
For this reason, in the present invention, the allowable range β for the value of the lower explosion limit concentration y obtained from the reference calibration curve Cs is set based on the lower explosion limit concentration values of various hydrocarbon components according to the respective standards. The The allowable range β is preferably in the range of −0.2 vol% or more and 0.7 vol% or less with respect to the value of the lower explosion limit concentration y obtained from the reference calibration curve Cs. That is, the curve (a) indicated by a broken line in FIG. 2 is a curve indicating the upper limit of the allowable range, and the curve (b) is a curve indicating the lower limit of the allowable range. Therefore, if a curve or a broken line set in the region between the curves (a) and (b) is set as a calibration curve, the lower explosion limit concentration y can be obtained with a certain accuracy.

The HC component concentration calculation means 40 calculates the total concentration y ′ [vol%] of the paraffinic hydrocarbon component contained in the test gas based on the value of the ratio x obtained by the ratio calculation means 30. Calculated by
In addition, when the base gas is air, or when a specific hydrocarbon component that is used as a standard when standardizing data on the refractive index and specific gravity of the test gas is set to a hydrocarbon component other than methane gas For this purpose, the values of the coefficients in the equations (1-a) and (1-b) and the equation (2) may be appropriately changed.

The lower explosion limit percentage calculating means 45 converts the value of the lower explosion limit concentration y obtained by the LEL calculating means 35 and the value of the total concentration y ′ of the paraffinic hydrocarbon components obtained by the HC component concentration calculating means 40. Based on this, the lower explosion limit percentage concentration y _L [% LEL] is calculated. The lower explosion limit percentage concentration y _L is a value indicating the percentage of the total concentration y ′ of paraffinic hydrocarbon components with respect to the lower explosion limit concentration y, and is obtained by y _L = (y ′ / y) × 100.

Hereinafter, the gas detection operation by the above gas detection device will be described by taking as an example the case where the test gas contains nitrogen gas as the base gas.

In the above gas detection device, a test gas is supplied to each of the sound velocity measuring means 11 and the refractive index measuring means 15, and a reference gas such as air is supplied to the refractive index measuring means 15. Thereby, the sound velocity V _{d of the} test gas is measured by the sound velocity measuring means 11 and the refractive index n _{d of the} test gas is measured by the refractive index measuring means 15. In the specific gravity measuring mechanism 25, based on the value of the acoustic velocity V _d of the measured test gas, the acoustic velocity in terms of the specific gravity S _a of the test gas to sonic velocity - is determined by the specific gravity conversion processing unit 26. Further, based on the measured value of the refractive index n _d of the test gas, the refractive index conversion specific gravity S _{b of the} test gas is obtained by the refractive index-specific gravity conversion processing means 27. Based on the sound velocity converted specific gravity S _a and the refractive index converted specific gravity S _b thus obtained, the specific gravity S _{d of the} test gas is calculated by the specific gravity calculating means 28.

In the ratio calculation means 30, first, the specific gravity difference Δs between the test gas and nitrogen gas is normalized by, for example, the specific gravity difference Δs _CH4 between methane gas and nitrogen gas, so that the specific gravity difference normalized value (Δs / Δs) is obtained. _CH4 ) is calculated. Also, the refractive index difference normalized value (Δn / Δn _CH4 ) is calculated by normalizing the refractive index difference Δn between the test gas and nitrogen gas, for example, with the refractive index difference Δn _CH4 between methane gas and nitrogen gas. Is done. Next, based on the specific gravity difference normalized value (Δs / Δs _CH4 ) and the refractive index difference normalized value (Δn / Δn _CH4 ), the specific gravity difference normalized value (Δs / Δs _CH4 ) is A ratio x to the refractive index difference normalized value (Δn / Δn _CH4 ) is calculated.

Based on the ratio x obtained as described above, in the LEL calculating means 35, the lower explosion limit concentration y of the test gas is calculated by, for example, the reference calibration curve Cs represented by the above formula (5). Further, based on the ratio x, the total concentration y ′ of the paraffinic hydrocarbon components contained in the test gas is calculated by the HC component concentration calculating means 40 by the above formula (2).
Further, based on the value of the lower explosion limit concentration y of the test gas and the total concentration y ′ of the paraffinic hydrocarbon component, the lower explosion limit percentage concentration y _{L of the} test gas is calculated as the lower explosion limit percentage concentration calculation means. 45.

Thus, according to the above gas detection method, even if the base gas in the test gas is an inert gas such as nitrogen gas, the lower explosion limit of the test gas regardless of the composition ratio of the paraffinic hydrocarbon component The concentration y, the total concentration y ′ of the paraffinic hydrocarbon components contained in the test gas, and the lower explosion limit percentage concentration y _L can be obtained with a certain degree of accuracy.
In calculating these characteristic values, the refractive index value and the sound velocity value obtained by the sound velocity measuring means 11 and the refractive index measuring means 15 each made of a physical sensor are used, so that a high response speed is obtained. Continuous measurement can be performed. In addition, since the physical sensor is less susceptible to sensitivity deterioration, highly reliable gas detection can be performed.

The above gas detection apparatus in which such a gas detection method is executed includes, for example, the loading arm by purging the gas in which the fuel gas remaining in the loading arm after the landing operation of the fuel gas is vaporized with nitrogen gas This is suitable for detecting the gas discharged from the inside.
For example, the gas discharged from the loading arm used in the LNG ship is a gas containing a large amount of methane, which is a hydrocarbon component that easily vaporizes, at the initial stage when the purge of nitrogen gas is started. , Propane, butane and other high boiling hydrocarbon components are discharged. In addition, the degree of composition change with the passage of time of the gas discharged from the loading arm varies depending on the production area of the LNG and is difficult to predict. However, according to the above-described gas detection device, it is highly reliable that the gas remaining in the loading arm is below the lower explosion limit concentration regardless of the composition ratio of the paraffinic hydrocarbon component contained in the test gas. Can be detected by sex. Moreover, the purge work by nitrogen gas can be performed efficiently.

Hereinafter, experimental examples of the present invention will be described.

[Experimental Example 1]
Plural kinds of paraffinic hydrocarbon components having different total concentrations obtained by diluting a mixed gas (CH ₄ : C ₂ H ₆ = 50: 50) composed of methane gas (CH ₄ ) and ethane gas (C ₂ H ₆ ) with nitrogen gas The test gas was prepared.
Using the gas detection apparatus having the configuration shown in FIG. 1, the lower explosion limit percentage concentration [% LEL] (hereinafter referred to as “actual measurement value”) in each test gas was obtained. Here, the specific gravity of the test gas was calculated by the above equation (3) under the condition that the value of the correction factor α was 3.32. Further, the lower explosion limit concentration of the test gas was calculated based on the reference calibration curve expressed by the above mathematical formula (5). Furthermore, the total concentration of paraffinic hydrocarbon components contained in the test gas was calculated by the above formula (2).
Further, the lower explosion limit percentage concentration [% LEL] (hereinafter referred to as “theoretical value”) of each test gas was calculated by a method based on the IEC standard.
The data obtained as described above was plotted on a graph with the horizontal axis representing the theoretical value and the vertical axis representing the measured value. The results are shown by the diamond-shaped plots in FIG. A straight line indicated by a broken line in FIG. 3 is an ideal straight line in which a theoretical value and a measured value coincide with each other.

[Experimental example 2]
Mixed gas (CH ₄ : C ₂ H ₆ : C ₃ H ₈ ) consisting of methane gas (CH ₄ ), ethane gas (C ₂ H ₆ ) and propane gas (C ₃ H ₈ ) = 33.3: 33.3: 33. A plurality of types of test gases having different total concentrations of paraffinic hydrocarbon components were prepared by diluting 3) with nitrogen gas.
In the same manner as in Experimental Example 1, the actual measurement value and the theoretical value of the lower explosion limit percentage concentration of each test gas were obtained. The results are shown as circled plots in FIG.

[Experimental Example 3]
Mixed gas (C ₂ H ₆ : C ₃ H ₈ : i-C ₄ H ₁₀₎ = 33 consisting of ethane gas (C ₂ H ₆ ), propane gas (C ₃ H ₈ ) and isobutane gas (i-C ₄ H ₁₀ ) .3: 33.3: 33.3) diluted with nitrogen gas, a plurality of types of test gases having different total concentrations of paraffinic hydrocarbon components were prepared.
In the same manner as in Experimental Example 1, the actual measurement value and the theoretical value of the lower explosion limit percentage concentration of each test gas were obtained. The results are shown by the square marks in FIG.

As is clear from the above results, according to the present invention, it was confirmed that the lower explosion limit percentage concentration can be obtained within a certain error range with respect to the theoretical value regardless of the gas composition.

It was also confirmed that the lower explosion limit percentage concentration can be obtained within a certain error range even for theoretical values based on ISO standards and ICSC.
Furthermore, for a single gas mainly composed of one hydrocarbon component, such as methane, ethane, butane or isobutane, the lower explosion limit unit concentration was determined in the same manner as in Experimental Example 1, and the theoretical value according to any standard. However, it was confirmed that the lower explosion limit unit concentration can be obtained within a certain error range.

The present invention can specify the concentration of the paraffinic hydrocarbon component of the mixed gas in terms of the lower explosion limit percentage concentration for the mixed gas containing a plurality of types of paraffinic hydrocarbon components using the inert gas as a base gas. It is expected to be extremely useful when detecting the gas remaining in the loading arm after the completion of the landing operation of the fuel gas.

DESCRIPTION OF SYMBOLS 10 Gas detection part 11 Sound speed measurement means 15 Refractive index measurement means 20 Arithmetic processing part 25 Specific gravity measurement mechanism 26 Sonic-specific gravity conversion processing means 27 Refractive index-specific gravity conversion processing means 28 Specific gravity calculation means 30 Ratio calculation means 35 LEL calculation means 40 HC Component concentration calculation means 45 Explosive lower limit percentage concentration calculation means

Claims (11)

A mixed gas containing two or more paraffinic hydrocarbon components is used as a test gas.
Measure the refractive index and specific gravity of the test gas,
Based on the ratio (Δs / Δn) of the specific gravity difference (Δs) between the test gas and the base gas in the test gas to the refractive index difference (Δn) between the test gas and the base gas. A gas detection method comprising calculating one or both of a total concentration of paraffinic hydrocarbon components in a detected gas and a lower explosion limit concentration of the detected gas. Calculate the total concentration of paraffinic hydrocarbon components in the test gas and the lower explosive limit concentration of the test gas,
2. The gas detection method according to claim 1, wherein a lower explosion limit percentage concentration indicating a percentage of a total concentration of paraffinic hydrocarbon components of the test gas with respect to a lower explosion limit concentration of the test gas is calculated. 3. The gas detection method according to claim 1, wherein the test gas is an LNG vaporized gas or an LPG vaporized gas containing an inert gas as a base gas. The gas detection method according to claim 3, wherein the inert gas is nitrogen gas. The specific gravity difference (Δs) between the test gas and the nitrogen gas that is the base gas of the test gas is normalized by the specific gravity difference (Δs _H ) between the specific hydrocarbon component and the nitrogen gas, and the specific gravity difference normalized value (Δs / Δs _H ) is calculated, and the refractive index difference (Δn) between the test gas and nitrogen gas is normalized by the refractive index difference (Δn _H ) between the specific hydrocarbon component and nitrogen gas. Calculate the refractive index difference normalized value (Δn / Δn _H ),
The gas detection method according to claim 4, wherein a ratio of the specific gravity difference normalized value (Δs / Δs _H ) to the refractive index difference normalized value (Δn / Δn _H ) is calculated. The specific hydrocarbon component is methane gas,
In the XY coordinate system in which the ratio of the specific gravity difference normalized value normalized with respect to methane gas to the refractive index difference normalized value is the X axis and the lower explosion limit concentration is the Y axis, The lower explosive limit concentration of the test gas is calculated based on a calibration curve indicated by a curve or a broken line included in a region between the indicated curve and the curve indicated by the following mathematical formula (1-b) The gas detection method according to claim 5.

[In the above formulas (1-a) and (1-b), y is the lower explosive limit concentration [vol%], x is the specific gravity difference normalized value normalized with respect to methane gas as a standard, and the refractive index difference normalized value. It is a ratio. ] The ratio of the specific gravity difference normalized value normalized with respect to methane gas to the refractive index difference normalized value is x, the refractive index difference between the test gas and nitrogen gas is Δn, and the refractive index difference between methane gas and nitrogen gas is Δn _CH4 The gas detection method according to claim 6, wherein the total concentration y ′ of hydrocarbon components in the test gas is calculated based on the following mathematical formula (2).

A mixed gas containing two or more paraffinic hydrocarbon components is used as a test gas.
A refractive index measuring means for measuring the refractive index of the test gas;
Specific gravity measuring means for measuring the specific gravity of the test gas;
The ratio (Δs / Δn) of the specific gravity difference (Δs) between the test gas and the base gas in the test gas to the refractive index difference (Δn) between the test gas and the base gas in the test gas is calculated. A ratio calculating means for
One or both of HC component concentration calculating means for calculating the total concentration of paraffinic hydrocarbon components in the test gas based on the ratio and LEL calculating means for calculating the lower explosion limit concentration of the test gas are provided. A gas detection device characterized by comprising: Both the HC component concentration calculating means and the LEL calculating means,
It further comprises a lower explosion limit percentage concentration calculating means for calculating a lower explosion limit percentage concentration indicating a percentage of the total concentration of paraffinic hydrocarbon components of the test gas with respect to the lower explosion limit concentration of the test gas. The gas detection device according to claim 8. The gas detection apparatus according to claim 8 or 9, wherein the test gas is an LNG vaporized gas or an LPG vaporized gas containing an inert gas as a base gas. The gas detection device according to claim 10, wherein the inert gas is nitrogen gas.

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