JP7523301B2 - Methane concentration measuring device and methane concentration measuring method - Google Patents
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims description 483
- 238000000034 method Methods 0.000 title claims description 25
- 239000007789 gas Substances 0.000 claims description 421
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 190
- 238000005259 measurement Methods 0.000 claims description 162
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 95
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 85
- 229910001873 dinitrogen Inorganic materials 0.000 claims description 82
- 239000001569 carbon dioxide Substances 0.000 claims description 81
- 238000004364 calculation method Methods 0.000 claims description 74
- 239000003345 natural gas Substances 0.000 claims description 41
- 239000000203 mixture Substances 0.000 claims description 13
- 238000002485 combustion reaction Methods 0.000 claims description 5
- 238000010521 absorption reaction Methods 0.000 claims description 4
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 10
- 229910001882 dioxygen Inorganic materials 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 8
- 230000000704 physical effect Effects 0.000 description 8
- 238000012545 processing Methods 0.000 description 8
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 7
- 238000012937 correction Methods 0.000 description 6
- 239000004215 Carbon black (E152) Substances 0.000 description 5
- 229930195733 hydrocarbon Natural products 0.000 description 5
- 150000002430 hydrocarbons Chemical class 0.000 description 5
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 description 4
- 239000000446 fuel Substances 0.000 description 4
- 238000000691 measurement method Methods 0.000 description 4
- 239000001273 butane Substances 0.000 description 3
- 238000004817 gas chromatography Methods 0.000 description 3
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 3
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 3
- 239000001294 propane Substances 0.000 description 3
- YYAVXASAKUOZJJ-UHFFFAOYSA-N 4-(4-butylcyclohexyl)benzonitrile Chemical compound C1CC(CCCC)CCC1C1=CC=C(C#N)C=C1 YYAVXASAKUOZJJ-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000002737 fuel gas Substances 0.000 description 2
- 201000003034 pontocerebellar hypoplasia type 4 Diseases 0.000 description 2
- 238000010276 construction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
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Description
本発明は、メタン濃度測定装置およびメタン濃度測定方法に関する。 The present invention relates to a methane concentration measuring device and a methane concentration measuring method.
近年、天然ガスを電力・都市ガスなど以外の燃料（例えばエンジンの燃料など）として利用する技術の開発が進んでいる。 In recent years, there has been progress in the development of technology to use natural gas as a fuel other than electricity and city gas (for example, as engine fuel).
天然ガスを燃料として利用する場合、その品質を確認する指標としては例えば、熱量や天然ガス中の燃焼性ガス成分の組成（濃度）などがある。天然ガスなどの燃料ガスの熱量を測定する方法としては、例えば熱量と特定の対応関係を有する物性値を測定し、測定値に基づいて熱量の値（換算熱量）を求める方法などが、本件出願人によって提案されている（例えば特許文献１参照。）。 When natural gas is used as fuel, indicators for confirming its quality include, for example, calorific value and the composition (concentration) of combustible gas components in the natural gas. As a method for measuring the calorific value of fuel gases such as natural gas, the present applicant has proposed, for example, a method for measuring a physical property value that has a specific correspondence with the calorific value and determining the value of the calorific value (equivalent calorific value) based on the measured value (see, for example, Patent Document 1).
また、天然ガス中の燃焼性ガスの組成分析（例えば、メタン（ＣＨ４）の濃度の測定など）については、ガスクロマトグラフィなどを用いることが一般的である。 Furthermore, for the composition analysis of combustible gases in natural gas (for example, measurement of the concentration of methane (CH 4 )), gas chromatography or the like is generally used.
しかしながら、天然ガスの組成、主に天然ガス中のメタン（ＣＨ４）の濃度を簡易な構成でありながら信頼性の高い値で得ることができる装置および手法は知られていなかった。 However, no device or method has been known that can obtain the composition of natural gas, mainly the concentration of methane (CH 4 ) in natural gas, with high reliability while having a simple configuration.
本発明は、以上のような事情に基づいてなされたものであって、測定対象ガスである天然ガス中のメタン（ＣＨ４）の濃度を簡易な構成でありながら信頼性の高い値で得ることができるメタン濃度測定装置およびメタン濃度測定方法を提供することを目的とする。 The present invention has been made in light of the above circumstances, and aims to provide a methane concentration measuring device and a methane concentration measuring method that can obtain a highly reliable value for the concentration of methane ( CH4 ) in natural gas, which is the gas to be measured, while having a simple configuration.
本発明は、基礎熱量を用いて測定ガス中のメタン濃度を算出するメタン濃度測定装置であって、前記基礎熱量は、対象となるガスにおいて不燃ガスの成分を除いた燃焼性ガス成分の燃焼熱量であり、前記測定ガスは天然ガスであり、前記不燃ガスは二酸化炭素ガス及び窒素ガスを少なくとも含み、前記測定ガス中の二酸化炭素ガス濃度および窒素ガス濃度を取得する不燃ガス濃度取得手段と、前記測定ガスの屈折率を測定し屈折率換算熱量を算出する屈折率換算熱量測定手段と、前記測定ガスの音速を測定し音速換算熱量を算出する音速換算熱量測定手段と、熱量計算手段と、メタン濃度算出手段と、を有し、前記不燃ガス濃度取得手段は、前記二酸化炭素ガス濃度を測定し、前記窒素ガス濃度を測定し、あるいは前記屈折率換算熱量、前記音速換算熱量および前記二酸化炭素ガス濃度を用いて第１算出式により該窒素ガス濃度を算出する手段であり、前記熱量計算手段は、前記屈折率換算熱量と前記音速換算熱量を用いる第２算出式により前記測定ガスの換算熱量を算出し、前記窒素ガス濃度、前記二酸化炭素ガス濃度および前記換算熱量を用いる第３算出式により、前記測定ガスの前記基礎熱量（以下「測定ガス基礎熱量」）を算出する手段であり、前記メタン濃度算出手段は、組成が既知の天然ガスを基準ガスとした場合の該基準ガスの基礎熱量と、該基準ガス中のメタン含有率の相関を示す第４算出式と、前記窒素ガス濃度と前記二酸化炭素ガス濃度と前記測定ガス中のメタン含有率（以下「測定ガスメタン含有率」）を用いて該測定ガス中のメタン濃度を算出する第５算出式を有し、前記第４算出式に、前記測定ガス基礎熱量を代入して前記測定ガスメタン含有率を算出し、前記測定ガスメタン含有率、前記窒素ガス濃度および前記二酸化炭素ガス濃度を用いて前記第５算出式により前記メタン濃度を算出する手段である、ことを特徴とするメタン濃度測定装置に係るものである。 The present invention provides a methane concentration measuring device that calculates a methane concentration in a measurement gas using a basic calorific value, the basic calorific value being a heat value of combustion of combustible gas components in a target gas excluding non-combustible gas components, the measurement gas being natural gas, the non-combustible gas including at least carbon dioxide gas and nitrogen gas, the device having a non-combustible gas concentration acquiring means for acquiring a carbon dioxide gas concentration and a nitrogen gas concentration in the measurement gas, a refractive index converted calorific value measuring means for measuring a refractive index of the measurement gas and calculating a refractive index converted calorific value, a sound speed converted calorific value measuring means for measuring a speed of sound in the measurement gas and calculating a sound speed converted calorific value, a calorific value calculation means, and a methane concentration calculating means, the non-combustible gas concentration acquiring means being a means for measuring the carbon dioxide gas concentration, measuring the nitrogen gas concentration, or calculating the nitrogen gas concentration by a first calculation formula using the refractive index converted calorific value, the sound speed converted calorific value, and the carbon dioxide gas concentration, the calorific value calculation means being a means for calculating the refractive index converted calorific value and the methane concentration measuring means is a means for calculating the converted calorific value of the measurement gas by a second calculation formula using the sonic converted calorific value, and for calculating the basic calorific value of the measurement gas (hereinafter "measurement gas basic calorific value") by a third calculation formula using the nitrogen gas concentration, the carbon dioxide gas concentration, and the converted calorific value, the methane concentration calculating means having a fourth calculation formula showing a correlation between the basic calorific value of a reference gas and the methane content in the reference gas when a natural gas having a known composition is used as the reference gas, and a fifth calculation formula for calculating the methane concentration in the measurement gas using the nitrogen gas concentration, the carbon dioxide gas concentration, and the methane content in the measurement gas (hereinafter "measurement gas methane content"), the methane concentration calculating means is a means for calculating the measurement gas methane content by substituting the measurement gas basic calorific value into the fourth calculation formula, and for calculating the methane concentration by the fifth calculation formula using the measurement gas methane content, the nitrogen gas concentration, and the carbon dioxide gas concentration.
また、本発明は、基礎熱量を用いて測定ガス中のメタン濃度を算出するメタン濃度測定方法であって、前記基礎熱量は、対象となるガスにおいて不燃ガスの成分を除いた燃焼性ガス成分の燃焼熱量であり、前記測定ガスは天然ガスであり、前記不燃ガスは二酸化炭素ガス及び窒素ガスを少なくとも含み、前記測定ガス中の二酸化炭素ガス濃度および窒素ガス濃度を取得する不燃ガス濃度取得ステップと、前記測定ガスの屈折率を測定し屈折率換算熱量を算出するステップと、前記測定ガスの音速を測定し音速換算熱量を算出するステップと、熱量計算ステップと、メタン濃度算出ステップと、を有し、前記不燃ガス濃度取得ステップでは、前記二酸化炭素ガス濃度を測定し、前記窒素ガス濃度を測定し、あるいは前記屈折率換算熱量、前記音速換算熱量および前記二酸化炭素ガス濃度を用いて第１算出式により該窒素ガス濃度を算出し、前記熱量計算ステップでは、前記屈折率換算熱量と前記音速換算熱量を用いる第２算出式により前記測定ガスの換算熱量を算出し、前記窒素ガス濃度、前記二酸化炭素ガス濃度および前記換算熱量を用いる第３算出式により、前記測定ガスの前記基礎熱量（以下「測定ガス基礎熱量」）を算出し、前記メタン濃度算出ステップでは、組成が既知の天然ガスを基準ガスとした場合の該基準ガスの基礎熱量と、該基準ガス中のメタン含有率の相関を示す第４算出式に前記測定ガス基礎熱量を代入して前記測定ガス中のメタン含有率（以下「測定ガスメタン含有率」）を算出し、前記窒素ガス濃度と前記二酸化炭素ガス濃度と前記測定ガスメタン含有率を用いる第５算出式により前記測定ガス中のメタン濃度を算出する、ことを特徴とするメタン濃度測定方法に係るものである。
The present invention also provides a methane concentration measurement method for calculating a methane concentration in a measurement gas using a basic calorific value , the basic calorific value being a heat value of combustion of combustible gas components in a target gas excluding non-combustible gas components, the measurement gas being natural gas, the non-combustible gas containing at least carbon dioxide gas and nitrogen gas, the method comprising : an incombustible gas concentration acquisition step of acquiring a carbon dioxide gas concentration and a nitrogen gas concentration in the measurement gas; a step of measuring a refractive index of the measurement gas and calculating a refractive index converted calorific value; a step of measuring a speed of sound in the measurement gas and calculating a speed of sound converted calorific value; a calorific value calculation step; and a methane concentration calculation step, the incombustible gas concentration acquisition step measuring the carbon dioxide gas concentration, measuring the nitrogen gas concentration, or calculating a methane concentration by a first calculation formula using the refractive index converted calorific value, the speed of sound converted calorific value, and the carbon dioxide gas concentration. the calorific value calculation step calculates the converted calorific value of the measurement gas by a second calculation formula using the refractive index converted calorific value and the sonic speed converted calorific value; the basic calorific value of the measurement gas (hereinafter "measurement gas basic calorific value") is calculated by a third calculation formula using the nitrogen gas concentration, the carbon dioxide gas concentration, and the converted calorific value; the methane concentration calculation step calculates the methane content in the measurement gas (hereinafter "measurement gas methane content") by substituting the measurement gas basic calorific value into a fourth calculation formula showing a correlation between the basic calorific value of a reference gas, when a natural gas having a known composition is used as the reference gas, and the methane content in the reference gas; and the methane concentration in the measurement gas is calculated by a fifth calculation formula using the nitrogen gas concentration, the carbon dioxide gas concentration, and the methane content in the measurement gas .
本発明によれば、、測定対象ガスである天然ガス中のメタン（ＣＨ４）の濃度を簡易な構成でありながら信頼性の高い値で得ることができるメタン濃度測定装置およびメタン濃度測定方法を提供することができる。 According to the present invention, it is possible to provide a methane concentration measuring device and a methane concentration measuring method that can obtain a highly reliable value of the concentration of methane (CH 4 ) in natural gas, which is a gas to be measured, while having a simple configuration.
以下、本発明の実施の形態について添付図面を参照して説明する。図１は、本発明のメタン濃度測定装置１の一例における構成の概略を示すブロック図である。本実施形態のメタン濃度測定装置１は、測定対象ガスに含まれるメタン（メタンガス）濃度を測定する。測定対象ガスは、一例として天然ガスである。天然ガスは、一般的にはパラフィン系炭化水素ガス（例えば、メタン（ＣＨ４），エタン（Ｃ２Ｈ６）、プロパン（Ｃ３Ｈ８），ブタン（ｎ－Ｃ４Ｈ１０）など）を主成分とする。本実施形態の測定対象ガスは、特にメタン（メタンガス）を少なくとも含むガス（天然ガス）である。 Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an outline of the configuration of an example of a methane concentration measuring device 1 of the present invention. The methane concentration measuring device 1 of this embodiment measures the concentration of methane (methane gas) contained in a gas to be measured. The gas to be measured is, for example, natural gas. Natural gas generally contains paraffin-based hydrocarbon gas (e.g., methane (CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), butane (n-C 4 H 10 ), etc.) as a main component. The gas to be measured in this embodiment is a gas (natural gas) that contains at least methane (methane gas) in particular.
メタン濃度測定装置１は、例えば、測定対象ガスの基礎熱量Ｑ´を算出する熱量測定手段２０と、基礎熱量Ｑ´に基づき、測定対象ガスに含まれるメタン濃度ＸＣＨ４を算出するメタン濃度算出手段４０と、測定対象ガスのメタン濃度ＸＣＨ４などの情報を表示する出力手段４５とが、例えば外装容器１０内に配設されて構成されている。 The methane concentration measuring device 1 is configured by, for example, arranging in an outer container 10 a calorific value measuring means 20 that calculates a basic calorific value Q' of a measurement target gas, a methane concentration calculating means 40 that calculates a methane concentration XCH4 contained in the measurement target gas based on the basic calorific value Q', and an output means 45 that displays information such as the methane concentration XCH4 of the measurement target gas.
熱量測定手段２０は、測定対象ガスの熱量と特定の対応関係を有する物性値を測定する測定手段を有し、測定した該物性値に基づき測定対象ガスの熱量ＱＯＳおよび基礎熱量Ｑ´を算出する。物性値は例えば、屈折率および音速である。より詳細に、熱量測定手段２０は例えば、測定対象ガスである天然ガスの屈折率の値から求められる屈折率換算熱量ＱＯを得るための屈折率換算熱量測定手段２１と、当該測定対象ガスの音速の値から求められる音速換算熱量ＱＳを得るための音速換算熱量測定手段２５と、当該測定対象ガスに含まれる干渉ガスの濃度を取得する干渉ガス濃度取得手段５０を有する。一般的に流通している天然ガスは、燃焼性ガスとしてパラフィン系炭化水素ガスを主成分とし、熱量測定において誤差成分となる窒素（Ｎ２）、二酸化炭素（ＣＯ２）などの干渉ガス（雑ガス）を含んでいる。本実施形態の干渉ガス濃度取得手段５０は、例えば、干渉ガスのうち一般的に割合の多い二酸化炭素ガスの濃度（二酸化炭素ガス濃度ＸＣＯ２）を測定する二酸化炭素ガス濃度測定手段５１と、窒素ガスの濃度（窒素ガス濃度ＸＮ２）を算出する窒素ガス濃度計算手段３０とを含む。 The calorific value measuring means 20 has a measuring means for measuring a physical property value having a specific correspondence with the calorific value of the measurement target gas, and calculates the calorific value QOS and basic calorific value Q' of the measurement target gas based on the measured physical property value. The physical property value is, for example, a refractive index and a sound speed. More specifically, the calorific value measuring means 20 has, for example, a refractive index converted calorific value measuring means 21 for obtaining a refractive index converted calorific value QO obtained from the value of the refractive index of the measurement target gas, natural gas, a sound speed converted calorific value measuring means 25 for obtaining a sound speed converted calorific value QS obtained from the value of the sound speed of the measurement target gas, and an interference gas concentration acquiring means 50 for acquiring the concentration of an interference gas contained in the measurement target gas. Generally, natural gas in circulation is mainly composed of paraffinic hydrocarbon gas as a combustible gas, and contains interference gases (miscellaneous gases) such as nitrogen (N 2 ) and carbon dioxide (CO 2 ) that become error components in calorific value measurement. The interference gas concentration acquisition means 50 of this embodiment includes, for example, a carbon dioxide gas concentration measurement means 51 that measures the concentration of carbon dioxide gas (carbon dioxide gas concentration XCO2 ), which generally accounts for a large proportion of interference gases, and a nitrogen gas concentration calculation means 30 that calculates the concentration of nitrogen gas (nitrogen gas concentration XN2 ).
屈折率換算熱量測定手段２１は、例えば、測定対象ガスの屈折率を測定する屈折率測定手段２２と、屈折率測定手段２２によって測定された屈折率の値に基づいて屈折率換算熱量ＱＯを求める機能を有する屈折率－熱量換算処理手段２３とを備えている。 The refractive index converted calorific value measuring means 21 includes, for example, a refractive index measuring means 22 that measures the refractive index of the measurement target gas, and a refractive index-to-calorific value conversion processing means 23 that has a function of calculating the refractive index converted calorific value QO based on the value of the refractive index measured by the refractive index measuring means 22.
屈折率－熱量換算処理手段２３は、測定対象ガスである天然ガスにおいて不燃ガス成分（例えば窒素（Ｎ２）ガスや二酸化炭素（ＣＯ２）ガスなど）を含まない燃焼性ガス成分（パラフィン系炭化水素ガス）のみからなる特定ガスについて、例えばグラフ化することなどによって予め取得された屈折率と熱量との相関関係を利用し、当該相関関係に対して、測定対象ガスについて得られた屈折率の値が特定ガスの屈折率であると仮定して対照することにより屈折率換算熱量ＱＯを算出する。 The refractive index-calorific value conversion processing means 23 uses the correlation between the refractive index and calorific value, which has been obtained in advance, for example by graphing, for a specific gas consisting only of combustible gas components (paraffinic hydrocarbon gas) that does not contain non-combustible gas components (e.g., nitrogen (N 2 ) gas or carbon dioxide (CO 2 ) gas) in the natural gas gas to be measured, and calculates the refractive index converted calorific value Q O by comparing the refractive index value obtained for the gas to be measured with the correlation, assuming that it is the refractive index of the specific gas.
音速換算熱量測定手段２５は、測定対象ガス中における音波の伝播速度（測定対象ガスの音速）を測定する音速測定手段２６と、音速測定手段２６によって測定された音速の値に基づいて音速換算熱量ＱＳの値を求める機能を有する音速－熱量換算処理手段２７とを備えている。 The sonic speed converted calorific value measuring means 25 includes a sonic speed measuring means 26 that measures the propagation speed of sound waves in the gas to be measured (the sonic speed of the gas to be measured), and a sonic speed-to-calorific value conversion processing means 27 that has a function of calculating the value of the sonic speed converted calorific value QS based on the value of the sonic speed measured by the sonic speed measuring means 26.
音速－熱量換算処理手段２７は、測定対象ガスである天然ガスにおいて不燃ガス成分（例えばＮ２ガスやＣＯ２ガスなど）を含まない燃焼性ガス成分（パラフィン系炭化水素ガス）のみからなる特定ガスについて、例えばグラフ化することなどによって予め取得された音速と熱量との相関関係を利用し、当該相関関係に対して、測定対象ガスについて得られた音速の値が特定ガスの音速である仮定して対照することにより音速換算熱量ＱＳを算出する。 The sonic speed-calorific value conversion processing means 27 uses a correlation between the sonic speed and the calorific value, which is obtained in advance, for example, by graphing, for a specific gas consisting only of combustible gas components (paraffinic hydrocarbon gas) that does not contain non-combustible gas components (e.g., N2 gas or CO2 gas) in the natural gas that is the sample gas, and calculates the sonic speed converted calorific value QS by comparing the sonic speed value obtained for the sample gas with the correlation, assuming that it is the sonic speed of the specific gas.
二酸化炭素ガス濃度測定手段５１は、特に限定されるものではないが、例えば、赤外線が検知対象ガスである二酸化炭素ガスによって吸収されることによる赤外線光量の減衰の程度に応じて二酸化炭素ガス濃度ＸＣＯ２を検出する赤外式センサを備えたものにより構成することが好ましい。二酸化炭素ガス濃度測定手段５１として、いわゆる非分散型赤外線吸収法を利用したものが用いられることにより、測定対象ガスに含まれる他の雑ガスの影響を可及的に小さくすることができ、二酸化炭素ガス濃度ＸＣＯ２を高い精度で検出することができる。 The carbon dioxide gas concentration measuring means 51 is not particularly limited, but is preferably configured with an infrared sensor that detects the carbon dioxide gas concentration X CO2 according to the degree of attenuation of the amount of infrared light caused by absorption of infrared light by the carbon dioxide gas, which is the gas to be detected. By using a so-called non-dispersive infrared absorption method as the carbon dioxide gas concentration measuring means 51, the influence of other miscellaneous gases contained in the gas to be measured can be minimized as much as possible, and the carbon dioxide gas concentration X CO2 can be detected with high accuracy.
窒素ガス濃度計算手段３０は、屈折率換算熱量測定手段２１によって得られた屈折率換算熱量ＱＯの値と、音速換算熱量測定手段２５によって得られた音速換算熱量ＱＳの値と、二酸化炭素ガス濃度測定手段５１によって得られた二酸化炭素ガス濃度ＸＣＯ２の値とに基づいて、測定対象ガスに含まれる窒素ガス濃度ＸＮ２を算出する。窒素ガス濃度の算出方法は、後述する。 The nitrogen gas concentration calculation means 30 calculates the nitrogen gas concentration XN2 contained in the measurement target gas based on the value of the refractive index converted calorific value QO obtained by the refractive index converted calorific value measurement means 21, the value of the sonic speed converted calorific value QS obtained by the sonic speed converted calorific value measurement means 25, and the value of the carbon dioxide gas concentration XCO2 obtained by the carbon dioxide gas concentration measurement means 51. The method of calculating the nitrogen gas concentration will be described later.
また、熱量測定手段２０は、測定対象ガスの熱量ＱＯＳの値および基礎熱量Ｑ´の値を算出する熱量計算手段３５を備えている。測定対象ガスの熱量ＱＯＳとは、測定対象ガスの屈折率および音速の値に基づく換算熱量であり、熱量計算手段３５は、屈折率換算熱量ＱＯ、音速換算熱量ＱＳ、測定された二酸化炭素ガス濃度ＸＣＯ２および算出された窒素ガス濃度ＸＮ２により、屈折率および音速の値に基づく測定対象ガスの熱量（換算熱量）ＱＯＳを算出する。また、本実施形態の「基礎熱量Ｑ´」とは、天然ガスから不燃ガス（干渉ガス）成分を除いたときの燃焼性ガス成分の燃焼熱量をいい、熱量計算手段３５は、測定対象ガスの換算熱量ＱＯＳ、二酸化炭素ガス濃度ＸＣＯ２および窒素ガス濃度ＸＮ２に基づき、測定対象ガスの基礎熱量Ｑ´を算出する。これらの算出方法については、後述する。 The calorific value measuring means 20 is provided with a calorific value calculation means 35 for calculating the value of the calorific value QOS and the basic calorific value Q' of the gas to be measured. The calorific value QOS of the gas to be measured is a converted calorific value based on the refractive index and the sound speed of the gas to be measured, and the calorific value calculation means 35 calculates the calorific value (converted calorific value) QOS of the gas to be measured based on the refractive index and the sound speed using the refractive index converted calorific value QO, the sound speed converted calorific value QS , the measured carbon dioxide gas concentration XCO2 , and the calculated nitrogen gas concentration XN2 . In addition, the "basic calorific value Q'" in this embodiment refers to the combustion heat value of the combustible gas component when the non-combustible gas (interference gas) component is removed from the natural gas, and the calorific value calculation means 35 calculates the basic calorific value Q ' of the gas to be measured based on the converted calorific value QOS of the gas to be measured, the carbon dioxide gas concentration XCO2 , and the nitrogen gas concentration XN2 . The calculation method will be described later.
メタン濃度算出手段４０は、測定対象ガスに含有されるメタン濃度を算出可能である。より詳細には、メタン濃度算出手段４０は、基準となる天然ガス中の燃焼性ガス（ここではパラフィン系炭化水素ガス）におけるメタン含有率と、基準となる天然ガスの基礎熱量との関係を示す所定の相関式を有する。ここで、本実施形態における「メタン含有率」とは燃焼性ガスに含有されるメタンの割合（メタンの体積百分率）である。この相関式の詳細については後述する。そしてメタン濃度算出手段４０は、熱量計算手段３５によって算出された基礎熱量Ｑ´および干渉ガス濃度取得手段５０（二酸化炭素ガス濃度測定手段５１、窒素ガス濃度計算手段３０）によって取得した二酸化炭素ガス濃度ＸＣＯ２、窒素ガス濃度ＸＮ２と、上述の相関式により、測定対象ガスに含まれるメタン含有率を求め、当該メタン含有率に基づき測定対象ガスに含まれるメタン濃度ＸＣＨ４を算出可能である。 The methane concentration calculation means 40 can calculate the methane concentration contained in the measurement target gas. More specifically, the methane concentration calculation means 40 has a predetermined correlation equation showing the relationship between the methane content in the combustible gas (here, paraffinic hydrocarbon gas) in the reference natural gas and the basic calorific value of the reference natural gas. Here, the "methane content" in this embodiment is the ratio of methane contained in the combustible gas (volume percentage of methane). Details of this correlation equation will be described later. The methane concentration calculation means 40 can calculate the methane content contained in the measurement target gas by the basic calorific value Q' calculated by the calorific value calculation means 35, the carbon dioxide gas concentration X CO2 and the nitrogen gas concentration X N2 acquired by the interference gas concentration acquisition means 50 (carbon dioxide gas concentration measurement means 51, nitrogen gas concentration calculation means 30), and the above-mentioned correlation equation, and can calculate the methane concentration X CH4 contained in the measurement target gas based on the methane content.
＜窒素ガス濃度算出方法＞
次に、窒素ガス濃度計算手段３０における窒素ガス濃度ＸＮ２算出方法について説明する。窒素ガス濃度計算手段３０は、屈折率換算熱量測定手段２１によって得られた屈折率換算熱量ＱＯの値と、音速換算熱量測定手段２５によって得られた音速換算熱量ＱＳの値と、二酸化炭素ガス濃度測定手段５１によって得られた二酸化炭素ガスの濃度ＸＣＯ２の値とに基づいて、下記式（１）により、窒素ガス濃度ＸＮ２を算出する。
Next, a method for calculating the nitrogen gas concentration XN2 in the nitrogen gas concentration calculation means 30 will be described. The nitrogen gas concentration calculation means 30 calculates the nitrogen gas concentration XN2 by the following formula (1) based on the value of the refractive index converted calorific value QO obtained by the refractive index converted calorific value measurement means 21, the value of the sonic speed converted calorific value QS obtained by the sonic speed converted calorific value measurement means 25 , and the value of the carbon dioxide gas concentration XCO2 obtained by the carbon dioxide gas concentration measurement means 51.
上記式（１）における窒素ガス濃度ＸＮ２は、体積百分率で表される〔ｖｏｌ％〕。ｋＮ２は、窒素ガスについての誤差係数であって、雑ガス成分としてのＮ２が屈折率測定手段２２に及ぼす誤差の影響の大きさを表す。ｋＣＯ２は、二酸化炭素ガスについての誤差係数であって、雑ガス成分としてのＣＯ２が屈折率測定手段２２に及ぼす誤差の影響の大きさを表す。 The nitrogen gas concentration XN2 in the above formula (1) is expressed as a volume percentage [vol%]. kN2 is an error coefficient for nitrogen gas, and represents the magnitude of the error influence of N2 as an interference gas component on the refractive index measurement means 22. kCO2 is an error coefficient for carbon dioxide gas, and represents the magnitude of the error influence of CO2 as an interference gas component on the refractive index measurement means 22.
測定対象ガスは干渉ガス（雑ガス）として窒素ガスおよび二酸化炭素ガスを含み、干渉ガスは、屈折率換算熱量測定手段２１および音速換算熱量測定手段２５における測定対象ガスの測定誤差の要因となる。 The measurement target gas contains nitrogen gas and carbon dioxide gas as interference gases (miscellaneous gases), and the interference gases are a cause of measurement errors of the measurement target gas in the refractive index converted calorific value measuring means 21 and the sound speed converted calorific value measuring means 25.
そこで、本実施形態では、屈折率換算熱量測定手段２１にて測定・換算された屈折率換算熱量ＱＯ、および音速換算熱量測定手段２５により測定・換算された音速換算熱量ＱＳに対して、補正因子α、窒素ガスについての誤差係数ｋＮ２、二酸化炭素ガスについての誤差係数ｋＣＯ２により補正を行う。 Therefore, in this embodiment, the refractive index converted calorific value Q O measured and converted by the refractive index converted calorific value measuring means 21 and the sonic speed converted calorific value Q S measured and converted by the sonic speed converted calorific value measuring means 25 are corrected using the correction factor α, the error coefficient k N2 for nitrogen gas, and the error coefficient k CO2 for carbon dioxide gas.
補正因子αの値は、例えば、測定対象ガスに含まれる雑ガス成分（例えば窒素ガスおよび二酸化炭素ガスなど）の各々について、屈折率換算熱量ＱＯおよび音速換算熱量ＱＳを実際に測定し、得られた屈折率換算熱量ＱＯおよび音速換算熱量ＱＳの、例えばガスクロマトグラフィを用いた分析によって得られた熱量に対する誤差の比に基づいて設定することができる。ここに、補正因子αは、例えば、１．１～４．２の範囲内、好ましくは２．００～２．６０の範囲内において選択される値である。補正因子αの値は、測定対象ガスに含まれる雑ガス成分の種類によって異なる値をとるが、上記数値範囲内から選択された値であることにより、屈折率換算熱量ＱＯおよび音速換算熱量ＱＳに生じる測定誤差を適正に補正することができる。 The value of the correction factor α can be set, for example, based on the ratio of error of the refractive index converted calorific value QO and the sonic speed converted calorific value QS to the calorific value obtained by analysis using, for example, gas chromatography, by actually measuring the refractive index converted calorific value QO and the sonic speed converted calorific value QS for each of the miscellaneous gas components (e.g., nitrogen gas and carbon dioxide gas) contained in the measurement target gas. Here, the correction factor α is, for example, a value selected within the range of 1.1 to 4.2, preferably within the range of 2.00 to 2.60. The value of the correction factor α varies depending on the type of miscellaneous gas component contained in the measurement target gas, but by selecting a value within the above numerical range, the measurement error occurring in the refractive index converted calorific value QO and the sonic speed converted calorific value QS can be appropriately corrected.
窒素ガスについての誤差係数ｋＮ２は、例えば２０．００～３０．００の範囲内において選択される値である。また、二酸化炭素ガスについての誤差係数ｋＣＯ２は、例えば３５．００～４５．００の範囲内において選択される値である。窒素ガスについての誤差係数ｋＮ２および二酸化炭素ガスについての誤差係数ｋＣＯ２が上記数値範囲内において選択された値であることにより、屈折率換算熱量ＱＯに生じる測定誤差を適正に補正することができる。 The error coefficient kN2 for nitrogen gas is a value selected, for example, within the range of 20.00 to 30.00. The error coefficient kCO2 for carbon dioxide gas is a value selected, for example, within the range of 35.00 to 45.00. By selecting the error coefficient kN2 for nitrogen gas and the error coefficient kCO2 for carbon dioxide gas within the above numerical ranges, the measurement error occurring in the refractive index converted calorific value QO can be appropriately corrected.
具体的には、窒素ガスについての誤差係数ｋＮ２の値は、例えば窒素ガス（１００ｖｏｌ％）について実際に屈折率換算熱量測定手段２１によって屈折率換算熱量ＱＯを測定し、得られた値に基づいて設定することができる。また、二酸化炭素ガスについての誤差係数ｋＣＯ２の値についても同様に、例えば二酸化炭素ガス（１００ｖｏｌ％）について実際に屈折率換算熱量測定手段２１によって屈折率換算熱量ＱＯを測定し、得られた値に基づいて設定することができる。 Specifically, the value of the error coefficient kN2 for nitrogen gas can be set based on the refractive index converted calorific value QO obtained by actually measuring the refractive index converted calorific value QO for nitrogen gas (100 vol%) using the refractive index converted calorific value measuring means 21. Similarly, the value of the error coefficient kCO2 for carbon dioxide gas can be set based on the refractive index converted calorific value QO obtained by actually measuring the refractive index converted calorific value QO for carbon dioxide gas (100 vol%) using the refractive index converted calorific value measuring means 21.
このように上記式（１）によれば干渉ガスによる誤差成分を排除した、測定対象ガス中の窒素ガス濃度ＸＮ２を算出できる。 In this way, according to the above formula (1), it is possible to calculate the nitrogen gas concentration XN2 in the gas to be measured, with error components due to interference gases eliminated.
＜測定対象ガスの換算熱量ＱＯＳの算出方法＞
次に、測定対象ガスの換算熱量ＱＯＳの算出方法について説明する。熱量計算手段３５は、屈折率換算熱量測定手段２１によって得られた屈折率換算熱量ＱＯの値と、音速換算熱量測定手段２５によって得られた音速換算熱量ＱＳの値とに基づいて、測定対象ガスである天然ガスの換算熱量ＱＯＳの値を算出する。具体的には、屈折率換算熱量ＱＯが音速換算熱量ＱＳ以下の大きさである場合（ＱＯ≦ＱＳ）には、下記式（２）により、補正因子αとして１．１～４．２の範囲内、好ましくは２．００～２．６０の範囲内において選択される値を用いる条件にて、熱量ＱＯＳの値を算出する。一方、屈折率換算熱量ＱＯの値が音速換算熱量ＱＳの値より大きい場合（ＱＯ＞ＱＳ）には、熱量ＱＯＳの値として、屈折率換算熱量ＱＯの値が用いられる。
Next, a method for calculating the converted calorific value QOS of the measurement target gas will be described. The calorific value calculation means 35 calculates the value of the converted calorific value QOS of the natural gas, which is the measurement target gas, based on the value of the refractive index converted calorific value QO obtained by the refractive index converted calorific value measurement means 21 and the value of the sonic speed converted calorific value QS obtained by the sonic speed converted calorific value measurement means 25. Specifically, when the refractive index converted calorific value QO is equal to or smaller than the sonic speed converted calorific value QS ( QO ≦ QS ), the value of the calorific value QOS is calculated using the following formula (2) under the condition that a value selected from the range of 1.1 to 4.2, preferably the range of 2.00 to 2.60 is used as the correction factor α. On the other hand, when the value of the refractive index converted calorific value QO is larger than the sonic speed converted calorific value QS ( QO > QS ), the value of the refractive index converted calorific value QO is used as the value of the calorific value QOS .
また、熱量計算手段３５は、このようにして得られた熱量ＱＯＳの値と、二酸化炭素ガス濃度測定手段５１によって得られた二酸化炭素ガスの濃度ＸＣＯ２の値と、窒素ガス濃度計算手段３０によって得られた窒素ガスの濃度ＸＮ２の値とに基づいて、下記式（３）により、測定対象ガスの基礎熱量Ｑ´の値〔ＭＪ／Ｎｍ３〕を算出する。
このように、測定対象ガスの基礎熱量Ｑ´は、測定対象ガス中の窒素ガス濃度ＸＮ２および二酸化炭素ガス濃度ＸＣＯ２の関数（ｆ（ＸＣＯ２, ＸＮ２））となる。 In this way, the basic calorific value Q' of the measurement object gas is a function (f( XCO2 , XN2 )) of the nitrogen gas concentration XN2 and the carbon dioxide gas concentration XCO2 in the measurement object gas.
＜メタン濃度算出方法＞
次に、メタン濃度算出手段４０におけるメタン濃度算出方法について説明する。本願出願人は、鋭意研究を重ねた結果、天然ガスの基礎熱量の値と、当該天然ガスのうち燃焼性ガスにおけるメタン含有率との間には特定の相関関係が成立することを見出した。より詳細には、ＩＳＯ／ＴＲ ２２３０２：２０１４に記載のメタン価算出方法で用いられる、組成が既知の複数種の天然ガスを基準ガスとし、当該基準ガスの基礎熱量（文献値：以下「基準基礎熱量ＱＲ」という。）と、当該基準ガスのうち干渉ガス(不燃性ガス)成分を除いた、燃焼性ガス中のメタンの含有率（以下、「基準メタン含有率ＰＣＨ４」という。」との関係性を検討した。この場合の基準ガスは、燃焼性ガスの成分として、メタン（ＣＨ４），エタン（Ｃ２Ｈ６）、プロパン（Ｃ３Ｈ８），ブタン（Ｃ４Ｈ１０）を含み、干渉ガスの成分として、窒素（Ｎ２）ガスおよび二酸化炭素（ＣＯ２）ガスを少なくとも含んでいる。
<Calculation method for methane concentration>
Next, a description will be given of a method for calculating the methane concentration in the methane concentration calculation means 40. As a result of extensive research, the applicant of the present application has found that a specific correlation exists between the value of the basic calorific value of natural gas and the methane content in the combustible gas of the natural gas. More specifically, a plurality of types of natural gas with known composition used in the methane number calculation method described in ISO/TR 22302:2014 was used as the reference gas, and the relationship between the basic calorific value of the reference gas (literature value: hereinafter referred to as "reference basic calorific value Q R ") and the methane content in the combustible gas excluding interference gas (non-combustible gas) components of the reference gas (hereinafter referred to as "reference methane content P CH4 ") was examined. In this case, the reference gas contains methane (CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), and butane (C 4 H 10 ) as combustible gas components, and at least nitrogen (N 2 ) gas and carbon dioxide (CO 2 ) gas as interference gas components.
つまり基準メタン含有率ＰＣＨ４は、基準ガスのうち燃焼性ガス（メタン（ＣＨ４），エタン（Ｃ２Ｈ６）、プロパン（Ｃ３Ｈ８）およびブタン（Ｃ４Ｈ１０）の合計値（文献値））を１００とした場合の、メタン（文献値）の体積百分率である。 That is, the standard methane content P CH4 is the volume percentage of methane (literature value) when the combustible gas (the total value (literature value) of methane (CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), and butane (C 4 H 10 )) in the standard gas is taken as 100.
図２は、複数種の基準ガスの各々について、基準基礎熱量ＱＲ〔ＭＪ／Ｎｍ３〕を横軸、基準メタン含有率ＰＣＨ４〔ｖｏｌ％〕を縦軸とする座標系においてプロットしたグラフである。同図において、実線は、２種類の燃焼性ガスを含む混合ガス（ＣＨ４－Ｃ４Ｈ１０、ＣＨ４－Ｃ３Ｈ８、ＣＨ４－Ｃ２Ｈ６）について、それぞれ２種類の燃焼性ガスの濃度の和が１００％となるように調整した基準ガスの場合の相関を示す。また、破線は、複数種類の燃焼性ガス（ＣＨ４，Ｃ２Ｈ６，Ｃ３Ｈ８，ｉ－Ｃ４Ｈ１０，ｎ－Ｃ４Ｈ１０，ｉ－Ｃ５Ｈ１２，ｎ－Ｃ５Ｈ１２，Ｃ６＋）の混合ガスについて、複数種類の燃焼性ガスの濃度の総和が１００％となるように調整した基準ガスの場合の相関を直線近似したものである。 2 is a graph plotting a number of reference gases in a coordinate system with the horizontal axis representing the reference basic calorific value Q R [MJ/Nm 3 ] and the vertical axis representing the reference methane content P CH4 [vol %]. In the figure, the solid line indicates the correlation for the reference gases (CH 4 -C 4 H 10 , CH 4 -C 3 H 8 , CH 4 -C 2 H 6 ) that contain two types of combustible gases and are adjusted so that the sum of the concentrations of the two types of combustible gases is 100%. The dashed line is a linear approximation of the correlation for a standard gas containing a mixture of multiple types of combustible gases ( CH4 , C2H6 , C3H8 , i- C4H10 , n- C4H10 , i- C5H12 , n- C5H12 , C6 + ) adjusted so that the sum of the concentrations of the multiple types of combustible gases is 100%.
そしてこの破線の直線近似から、基準基礎熱量ＱＲと燃焼性ガスにおける基準メタン含有率ＰＣＨ４との関係を近似的に示す相関式（以下式（４）で示す）を取得した。 From the linear approximation of this dashed line, a correlation equation (shown below as equation (4)) approximately showing the relationship between the reference basic calorific value Q R and the reference methane content P CH4 in the combustible gas was obtained.
ＰＣＨ４＝－２．１ＱＲ＋１８３．８７ 式（４）
ここで、ＰＣＨ４：基準メタン含有率〔ｖｏｌ％〕
ＱＲ ：基準基礎熱量〔ＭＪ／Ｎｍ３〕
P CH4 =-2.1Q R +183.87 Formula (4)
Where, P CH4 : Reference methane content [vol%]
Q R : Standard basal calorific value [MJ/ Nm3 ]
すなわち、測定対象ガスの基礎熱量Ｑ´が取得できれば、上式（４）により、当該測定対象ガスに含まれる燃焼性ガスにおける（燃焼性ガスを１００とした場合の）メタン含有率Ｐ´ＣＨ４が算出可能となる。 In other words, if the basic calorific value Q' of the sample gas can be obtained, the methane content P'CH4 in the combustible gas contained in the sample gas (when the combustible gas is 100) can be calculated using the above formula (4).
更に、干渉ガスとなる窒素ガスおよび二酸化炭素ガスの濃度が取得できれば、測定対象ガス中のメタン濃度ＸＣＨ４は、以下の式（５）により算出できる。 Furthermore, if the concentrations of the interference gases nitrogen gas and carbon dioxide gas can be obtained, the methane concentration XCH4 in the measurement target gas can be calculated by the following formula (5).
ＸＣＨ４＝Ｐ´ＣＨ４
×｛１－（０．０１ＸＮ２＋０．０１ＸＣＯ２）｝ 式（５）
ここで、ＸＣＨ４ ：測定対象ガス中のメタン濃度
Ｐ´ＣＨ４：測定対象ガスに含まれる燃焼性ガスにおけるメタン含有率
ＸＣＯ２ ：二酸化炭素ガス濃度測定手段５１により測定した二酸化炭素ガス濃度
ＸＮ２ ：窒素ガス濃度計算手段３０により算出した窒素ガス濃度
X CH4 =P' CH4 × {1-(0.01X N2 +0.01X CO2 ) } Equation (5)
Where, XCH4 : methane concentration in the measurement target gas
P ' CH4 : methane content in combustible gas contained in the measurement target gas
X CO2 : Carbon dioxide gas concentration measured by the carbon dioxide gas concentration measuring means 51
X N2 : Nitrogen gas concentration calculated by the nitrogen gas concentration calculation means 30
すなわち本実施形態のメタン濃度算出手段４０は、基準基礎熱量ＱＲと基準メタン含有率ＰＣＨ４の特定の関係式（上述の式（４））、および測定対象ガス中の燃焼性ガスにおけるメタン含有率Ｐ´ＣＨ４と、二酸化炭素ガス濃度および窒素ガス濃度に基づくメタン濃度の算出式（上述の式（５））を有している。そして、測定対象ガスを本実施形態のメタン濃度測定装置１に供給し、測定対象ガスの基礎熱量Ｑ´を算出して、式（４）の基準基礎熱量ＱＲに代入することにより、当該測定対象ガスに含まれる燃焼性ガスにおけるメタン含有率Ｐ´ＣＨ４を算出する。また、算出された当該メタン含有率Ｐ´ＣＨ４と二酸化炭素ガス濃度測定手段５１により測定した二酸化炭素ガス濃度、および窒素ガス濃度計算手段３０により算出した窒素ガス濃度ＸＮ２に基づき、測定対象ガス中のメタン濃度ＸＣＨ４を算出（測定）する。このように本実施形態によれば、測定対象ガス中の主な干渉ガス（二酸化炭素ガスおよび窒素ガス）による測定誤差を低減して当該測定対象ガス中のメタン濃度を算出（測定）できる。 That is, the methane concentration calculation means 40 of this embodiment has a specific relational expression (the above-mentioned formula (4)) between the reference basic calorific value Q R and the reference methane content P CH4 , and a calculation formula (the above-mentioned formula (5)) for the methane content P' CH4 in the combustible gas in the sample gas, and the methane concentration based on the carbon dioxide gas concentration and the nitrogen gas concentration. Then, the sample gas is supplied to the methane concentration measurement device 1 of this embodiment, the basic calorific value Q' of the sample gas is calculated, and the methane content P' CH4 in the combustible gas contained in the sample gas is calculated by substituting the reference basic calorific value Q R in formula (4). In addition, the methane concentration X CH4 in the sample gas is calculated (measured) based on the calculated methane content P' CH4 , the carbon dioxide gas concentration measured by the carbon dioxide gas concentration measurement means 51, and the nitrogen gas concentration X N2 calculated by the nitrogen gas concentration calculation means 30. As described above, according to this embodiment, the methane concentration in the measurement target gas can be calculated (measured) while reducing measurement errors caused by the main interfering gases (carbon dioxide gas and nitrogen gas) in the measurement target gas.
以上において、測定対象ガスである天然ガスには、干渉ガス（雑ガス）成分として、例えば酸素ガスが含まれていることがある。しかし、天然ガスに含まれる酸素ガスはごく微量であるため、酸素ガスについては、メタン濃度に対する影響を実質的に無視することができる。なお、酸素ガスについても二酸化炭素ガスおよび窒素ガスと同様に、酸素ガスが含まれることによる誤差を排除してもよい。具体的には例えば酸素ガスの測定手段を設けて測定対象ガスに含まれる酸素ガスを測定し（あるいは、他の干渉ガスの測定・算出結果に基づき酸素ガスを算出し）、上述の式（１）、式（３）および式（５）などにおいて、酸素ガスの濃度、および酸素ガスが含まれることによる誤差成分を排除して、測定対象ガス中のメタン濃度ＸＣＨ４を算出するようにしてもよい。 In the above, the natural gas as the measurement target gas may contain, for example, oxygen gas as an interference gas (miscellaneous gas). However, since the amount of oxygen gas contained in natural gas is very small, the effect of oxygen gas on the methane concentration can be substantially ignored. Note that, as with carbon dioxide gas and nitrogen gas, the error due to the inclusion of oxygen gas may also be eliminated for oxygen gas. Specifically, for example, an oxygen gas measuring means may be provided to measure the oxygen gas contained in the measurement target gas (or the oxygen gas may be calculated based on the measurement and calculation results of other interference gases), and the concentration of oxygen gas and the error components due to the inclusion of oxygen gas may be eliminated in the above-mentioned formulas (1), (3), and (5), to calculate the methane concentration XCH4 in the measurement target gas.
図１を参照してメタン濃度測定装置１におけるメタン濃度測定方法について改めて説明する。図１においてメタン濃度測定装置１は、測定対象ガスを屈折率測定手段２２、音速測定手段２６および二酸化炭素ガス濃度測定手段５１の各々に供給するための測定対象ガス導入部１１と、屈折率測定手段２２において検知原理上必要とされる参照ガスを導入するための参照ガス導入部１２および、ガス排出部１３を有する。また、図１における二点鎖線は、ガス配管を示す。 The methane concentration measurement method in the methane concentration measurement device 1 will be explained again with reference to Figure 1. In Figure 1, the methane concentration measurement device 1 has a measurement target gas inlet 11 for supplying the measurement target gas to each of the refractive index measurement means 22, the sound speed measurement means 26, and the carbon dioxide gas concentration measurement means 51, a reference gas inlet 12 for introducing a reference gas required for the detection principle in the refractive index measurement means 22, and a gas exhaust section 13. The two-dot chain line in Figure 1 indicates the gas piping.
上記のメタン濃度測定装置１においては、例えば、適宜のガスサンプリング装置を介してガスパイプラインに配管接続され、ガスパイプライン内を流通する測定対象ガス（天然ガス）の一部が測定対象ガスとして測定対象ガス導入部１１から音速換算熱量測定手段２５の音速測定手段２６および屈折率換算熱量測定手段２１の屈折率測定手段２２の各々に順次に供給される。また、例えば空気などの参照ガスが参照ガス導入部１２から屈折率換算熱量測定手段２１の屈折率測定手段２２に供給される。これにより、屈折率換算熱量測定手段２１においては、測定対象ガスの屈折率が屈折率測定手段２２によって測定され、その結果に基づいて屈折率換算熱量ＱＯが屈折率－熱量換算処理手段２３によって求められる。また、音速換算熱量測定手段２５においては、測定対象ガスの音速が音速測定手段２６によって測定され、その結果に基づいて音速換算熱量ＱＳの値が音速－熱量換算処理手段２７によって求められる。一方、測定対象ガス導入部１１から導入された測定対象ガスの他の全部が、干渉ガス濃度取得手段５０の二酸化炭素ガス濃度測定手段５１に供給される。これにより、二酸化炭素ガス濃度測定手段５１において、測定対象ガスに含まれる二酸化炭素ガスの濃度ＸＣＯ２〔ｖｏｌ％（体積百分率）〕が二酸化炭素ガス濃度測定手段５１によって測定される。 In the above methane concentration measuring device 1, for example, the device is connected to a gas pipeline via an appropriate gas sampling device, and a part of the measurement target gas (natural gas) flowing through the gas pipeline is sequentially supplied as the measurement target gas from the measurement target gas inlet 11 to each of the sonic speed measuring means 26 of the sonic speed converted calorific value measuring means 25 and the refractive index measuring means 22 of the refractive index converted calorific value measuring means 21. Also, a reference gas such as air is supplied from the reference gas inlet 12 to the refractive index measuring means 22 of the refractive index converted calorific value measuring means 21. As a result, in the refractive index converted calorific value measuring means 21, the refractive index of the measurement target gas is measured by the refractive index measuring means 22, and the refractive index converted calorific value Q O is calculated by the refractive index-calorific value conversion processing means 23 based on the result. Also, in the sonic speed converted calorific value measuring means 25, the sonic speed of the measurement target gas is measured by the sonic speed measuring means 26, and the value of the sonic speed converted calorific value Q S is calculated by the sonic speed-calorific value conversion processing means 27 based on the result. Meanwhile, the rest of the sample gas introduced from the sample gas inlet 11 is supplied to a carbon dioxide gas concentration measuring means 51 of the interference gas concentration acquiring means 50. As a result, the carbon dioxide gas concentration measuring means 51 measures the concentration X CO2 [vol % (volume percentage)] of carbon dioxide gas contained in the sample gas.
以上のようにして得られた、屈折率換算熱量ＱＯの値と、音速換算熱量ＱＳの値とに基づいて、上記式（１）および上記式（２）により、補正因子αとして特定の範囲内において選択された値を用いて、測定対象ガス中の窒素ガス濃度ＸＮ２および換算熱量ＱＯＳが算出される。そして、換算熱量ＱＯＳの値と、二酸化炭素ガス濃度ＸＣＯ２の値と、窒素ガス濃度ＸＮ２の値とに基づいて、上記式（３）により、測定対象ガスの基礎熱量Ｑ´が算出される。 Based on the thus obtained values of the refractive index converted calorific value QO and the sonic speed converted calorific value QS , the nitrogen gas concentration XN2 and the converted calorific value QOS in the measurement target gas are calculated using a value selected within a specific range as the correction factor α by the above formula (1) and the above formula (2).Then, based on the value of the converted calorific value QOS , the value of the carbon dioxide gas concentration XCO2 , and the value of the nitrogen gas concentration XN2 , the basic calorific value Q ' of the measurement target gas is calculated by the above formula (3).
次いで、メタン濃度算出手段４０によって、熱量測定手段２０によって得られた基礎熱量Ｑ´の値と式（４）に基づいて、測定対象ガス中の燃焼性ガスにおけるメタン含有率Ｐ´ＣＨ４が算出される。また、当該メタン含有率Ｐ´ＣＨ４と、干渉ガス濃度取得手段５０による二酸化炭素ガス濃度ＸＣＯ２および窒素ガス濃度ＸＮ２と、式（５）により測定対象ガス中のメタン濃度ＸＣＨ４が算出され、その結果が出力手段４５に表示される。なお、測定対象ガスおよび参照ガスは、ガス排出部１３を介して装置外部に排出される。 Next, the methane concentration calculation means 40 calculates the methane content P'CH4 in the combustible gas in the sample gas based on the value of the basic calorific value Q' obtained by the calorific value measurement means 20 and formula (4). The methane concentration XCH4 in the sample gas is calculated using the methane content P'CH4 , the carbon dioxide gas concentration XCO2 and the nitrogen gas concentration XN2 obtained by the interference gas concentration acquisition means 50, and formula (5), and the result is displayed on the output means 45. The sample gas and the reference gas are exhausted to the outside of the device via the gas exhaust section 13.
以上説明したように本実施形態のメタン濃度測定装置１は、測定対象ガスの基礎熱量Ｑ´を算出する熱量測定手段２０と、基礎熱量Ｑ´に基づき、測定対象ガスに含まれるメタン濃度ＸＣＨ４を算出するメタン濃度算出手段４０と、を有する。メタン濃度算出手段４０は、測定対象ガスの基礎熱量Ｑ´に基づき、測定対象ガスに含まれる燃焼性ガス中のメタン含有率Ｐ´ＣＨ４を算出し、そのメタン含有率Ｐ´ＣＨ４と、二酸化炭素ガス濃度ＸＣＯ２および窒素ガス濃度ＸＮ２から測定対象ガス中のメタン濃度ＸＣＨ４を算出する。 As described above, the methane concentration measuring device 1 of this embodiment has the calorific value measuring means 20 that calculates the basic calorific value Q' of the measurement target gas, and the methane concentration calculating means 40 that calculates the methane concentration XCH4 contained in the measurement target gas based on the basic calorific value Q'. The methane concentration calculating means 40 calculates the methane content P'CH4 in the combustible gas contained in the measurement target gas based on the basic calorific value Q' of the measurement target gas, and calculates the methane concentration XCH4 in the measurement target gas from the methane content P'CH4 , the carbon dioxide gas concentration XCO2 , and the nitrogen gas concentration XN2 .
また、メタン濃度測定装置１は、測定対象ガスの屈折率から得られる屈折率換算熱量ＱＯと、測定対象ガスの音速から得られる音速換算熱量ＱＳとに基づいて測定対象ガスの換算熱量ＱＯＳを算出する熱量計算手段３５と、測定対象ガスに含まれる干渉ガスの濃度を取得する干渉ガス濃度取得手段５０とを有し、熱量測定手段２０は、換算熱量ＱＯＳと干渉ガスの濃度（ここでは窒素ガス濃度ＸＮ２、二酸化炭素ガス濃度ＸＣＯ２）に基づき、基礎熱量Ｑ´を算出する。 The methane concentration measuring device 1 also has a calorific value calculation means 35 that calculates the converted calorific value QOS of the sample gas based on the refractive index converted calorific value QO obtained from the refractive index of the sample gas and the sonic speed converted calorific value QS obtained from the sonic speed of the sample gas, and an interference gas concentration acquisition means 50 that acquires the concentration of an interference gas contained in the sample gas, and the calorific value measurement means 20 calculates the basic calorific value Q' based on the converted calorific value QOS and the concentrations of the interference gases (here, nitrogen gas concentration XN2 and carbon dioxide gas concentration XCO2 ).
また、メタン濃度算出手段４０は、それぞれに既知の異なる濃度のメタンを含む複数種の基準ガスについての基準基礎熱量ＱＲとその燃焼性ガスにおける基準メタン含有率ＰＣＨ４との関係を示す相関式（式４）を有し、測定対象ガスの基礎熱量Ｑ´に基づく（実際の）メタン含有率Ｐ´ＣＨ４を算出可能である。さらにメタン濃度算出手段４０は、測定対象ガスのメタン含有率Ｐ´ＣＨ４に基づく測定対象ガス（干渉ガス成分を含む）中のメタン濃度の算出式（式５）を有し、メタン含有率Ｐ´ＣＨ４と、ガス濃度ＸＣＯ２および窒素ガス濃度ＸＮ２から測定対象ガス中のメタン濃度ＸＣＨ４を算出可能である。 The methane concentration calculation means 40 has a correlation equation (equation 4) showing the relationship between the reference basic calorific value Q R for a plurality of reference gases each containing a known different concentration of methane and the reference methane content P CH4 in the combustible gas, and can calculate the (actual) methane content P' CH4 based on the basic calorific value Q' of the measurement target gas. Furthermore, the methane concentration calculation means 40 has a calculation equation (equation 5) for the methane concentration in the measurement target gas (including interference gas components) based on the methane content P' CH4 of the measurement target gas, and can calculate the methane concentration X CH4 in the measurement target gas from the methane content P' CH4 , the gas concentration X CO2 , and the nitrogen gas concentration X N2 .
また、干渉ガス濃度取得手段５０は、例えば赤外式センサを有し、少なくとも二酸化炭素ガス濃度ＸＣＯ２を測定可能である。また、本実施形態では、窒素ガス濃度ＸＮ２を窒素ガス濃度計算手段３０により算出した。しかしこれに限らず、干渉ガス濃度取得手段５０は、窒素ガス濃度ＸＮ２を測定可能な測定手段を備え、窒素ガス濃度ＸＮ２を実測してもよい。 The interference gas concentration acquisition means 50 has, for example, an infrared sensor and can measure at least the carbon dioxide gas concentration X CO2 . In the present embodiment, the nitrogen gas concentration X N2 is calculated by the nitrogen gas concentration calculation means 30. However, the present invention is not limited to this, and the interference gas concentration acquisition means 50 may have a measurement means capable of measuring the nitrogen gas concentration X N2 and may actually measure the nitrogen gas concentration X N2 .
また、本実施形態のメタン濃度測定方法は、燃焼性ガスを含む測定対象ガスの基礎熱量Ｑ´を算出するステップと、基礎熱量Ｑ´に基づいて測定対象ガスに含まれるメタン濃度ＸＣＨ４を算出するステップと、を有する。すなわち、基礎熱量Ｑ´に基づいて測定対象ガスに含まれるメタン濃度ＸＣＨ４を算出するものであれば、上記の構成を備えていなくてもよく、上記の例に限らない。 The methane concentration measurement method of the present embodiment includes a step of calculating a basic calorific value Q' of a measurement target gas containing a combustible gas, and a step of calculating a methane concentration XCH4 contained in the measurement target gas based on the basic calorific value Q'. In other words, as long as the method calculates a methane concentration XCH4 contained in the measurement target gas based on the basic calorific value Q', it does not need to have the above configuration and is not limited to the above example.
例えば、上記の例では、基礎熱量Ｑ´は、測定対象ガスの熱量と特定の対応関係を有する物性値を測定し、該物性値に基づき算出する場合を例示したが、これに限らず、他の方法により基礎熱量Ｑ´を算出してもよい。 For example, in the above example, the basic calorific value Q' is calculated based on a measured physical property value that has a specific correspondence with the calorific value of the gas to be measured, but the basic calorific value Q' may be calculated by other methods.
また、上記の例では、測定対象ガスの熱量と特定の対応関係を有する物性値として、測定対象ガスの屈折率と音速を測定する場合を説明したが、測定対象ガスの熱量と特定の対応関係を有する物性値であれば上記の例に限らない。 In the above example, the refractive index and sound speed of the gas to be measured are measured as physical property values that have a specific correspondence with the calorific value of the gas to be measured. However, the present invention is not limited to the above example, and any physical property value that has a specific correspondence with the calorific value of the gas to be measured may be used.
また、メタン濃度ＸＣＨ４を算出するステップでは、算出した基礎熱量Ｑ´に基づき測定対象ガスの、燃焼性ガス中のメタン含有率Ｐ´ＣＨ４を算出し、該メタン含有率Ｐ´ＣＨ４に基づきメタン濃度ＸＣＨ４を算出する。この方法により測定対象ガス中のメタン濃度ＸＣＨ４を算出するものであれば、上記の構成を備えていなくてもよく、上記の例に限らない。 In addition, in the step of calculating the methane concentration XCH4 , the methane content P'CH4 in the combustible gas of the measurement target gas is calculated based on the calculated basic calorific value Q', and the methane concentration XCH4 is calculated based on the methane content P'CH4 . As long as the method calculates the methane concentration XCH4 in the measurement target gas, it is not necessary to have the above configuration, and is not limited to the above example.
また、メタン濃度測定方法は、測定対象ガスの屈折率から得られる屈折率換算熱量ＱＯと、測定対象ガスの音速から得られる音速換算熱量ＱＳとに基づいて測定対象ガスの換算熱量ＱＯＳを算出するステップと、測定対象ガスに含まれる干渉ガスの濃度を取得するステップと、換算熱量ＱＯＳと干渉ガスの濃度に基づき、測定対象ガスの基礎熱量Ｑ´を算出するステップを有する。 The methane concentration measurement method further includes a step of calculating a converted calorific value Q of the sample gas based on a refractive index converted calorific value Q obtained from the refractive index of the sample gas and a sonic speed converted calorific value Q obtained from the sonic speed of the sample gas , a step of acquiring a concentration of an interference gas contained in the sample gas, and a step of calculating a basic calorific value Q of the sample gas based on the converted calorific value Q and the concentration of the interference gas.
また、メタン濃度ＸＣＨ４を算出するステップでは、それぞれに既知の異なる濃度のメタンを含む複数種の基準ガスについてその燃焼性ガス中の基準メタン含有率ＰＣＨ４と当該基準ガスの基準基礎熱量ＱＲの関係を示す相関式（式（４））を用いる場合を例示した。しかし式（４）に限らず、基準メタン含有率ＰＣＨ４と基準基礎熱量ＱＲの関係を示す他の相関式を有する構成であってもよい。また、測定対象ガス中のメタン濃度ＸＣＨ４は、例えば、上式（５）により求める構成に限らない。 In addition, in the step of calculating the methane concentration XCH4 , a correlation equation (equation (4)) showing the relationship between the reference methane content PCH4 in the combustible gas and the reference basic calorific value QR of a plurality of reference gases each containing a known different concentration of methane is used as an example. However, the present invention is not limited to equation (4), and may have another correlation equation showing the relationship between the reference methane content PCH4 and the reference basic calorific value QR . In addition, the methane concentration XCH4 in the measurement target gas is not limited to the configuration obtained by, for example, the above equation (5).
また、干渉ガスの濃度を取得するステップでは、例えば赤外線吸収法により少なくとも二酸化炭素ガス濃度ＸＣＯ２を測定し、窒素ガス濃度ＸＮ２を算出して基礎熱量Ｑ´を算出する。なお、窒素ガス濃度ＸＮ２を実測してもよい。 In the step of acquiring the concentration of the interference gas, for example, at least the carbon dioxide gas concentration X CO2 is measured by an infrared absorption method, and the nitrogen gas concentration X N2 is calculated to calculate the basic calorific value Q'. The nitrogen gas concentration X N2 may be actually measured.
上記のメタン濃度測定装置１およびメタン濃度算出方法によれば、基準基礎熱量ＱＲの値と燃焼性ガス中のメタン含有率ＰＣＨ４との相関関係（式（４））は、含有するメタン濃度がそれぞれ異なる基準となる天然ガス（文献値）に基づき取得される。そして、この相関関係に測定対象ガスの基礎熱量Ｑ´を対応させて実際の測定対象ガスにおけるメタン含有率Ｐ´ＣＨ４を取得する。また、測定対象ガスの干渉ガス（二酸化炭素ガス濃度ＸＣＯ２、窒素ガス濃度ＸＮ２）の濃度を取得し、測定対象ガスにおけるメタン含有率Ｐ´ＣＨ４（干渉ガスを含まない値）と、実測または算出された干渉ガスの濃度に基づき、メタン濃度を算出する。このとき、算出される窒素ガス濃度ＸＮ２は、干渉ガスとして窒素ガスおよび二酸化炭素ガスが含まれることによる影響（誤差）を実験による裏づけにより定量的に明らかにし、干渉ガスによる誤差が補正された値となっている。また、窒素ガス濃度ＸＮ２を用いて取得される測定対象ガスの基礎熱量Ｑ´についても、ひいては干渉ガスによる誤差が補正された値となっている。したがって本実施形態によって得られる（測定される）メタン濃度ＸＣＨ４は所定の信頼性を有するものとなる。 According to the above methane concentration measuring device 1 and methane concentration calculation method, the correlation (Equation (4)) between the value of the standard basic calorific value Q R and the methane content P CH4 in the combustible gas is obtained based on natural gas (literature value) which is a standard having different methane concentrations. Then, the basic calorific value Q' of the measurement target gas is made to correspond to this correlation to obtain the methane content P' CH4 in the actual measurement target gas. In addition, the concentration of interference gases (carbon dioxide gas concentration X CO2 , nitrogen gas concentration X N2 ) of the measurement target gas is obtained, and the methane concentration is calculated based on the methane content P' CH4 (value not including interference gas) in the measurement target gas and the actually measured or calculated concentration of the interference gas. At this time, the calculated nitrogen gas concentration X N2 is a value in which the influence (error) due to the inclusion of nitrogen gas and carbon dioxide gas as interference gases is quantitatively clarified by experimental support, and the error due to the interference gas is corrected. In addition, the basic calorific value Q' of the measurement target gas obtained using the nitrogen gas concentration X N2 is also a value in which errors due to interference gases have been corrected. Therefore, the methane concentration X CH4 obtained (measured) by this embodiment has a certain degree of reliability.
また、メタン濃度測定装置１によれば、熱量測定手段２０によって測定対象ガスの基礎熱量Ｑ´を連続的に測定することにより、実際の状況に即した測定対象ガスのメタン濃度ＸＣＨ４を連続的に取得することができる。このため、例えば、燃料ガスとしての天然ガスの実際の燃料性状の監視を行うことができる。従って、ガス組成の変動が生じた場合には、ガス組成の変動に伴うメタン濃度ＸＣＨ４の変動を速やかに検出することができる。 Furthermore, according to the methane concentration measuring device 1, the basic calorific value Q' of the sample gas is continuously measured by the calorific value measuring means 20, so that the methane concentration XCH4 of the sample gas that corresponds to the actual situation can be continuously obtained. Therefore, for example, the actual fuel properties of natural gas as a fuel gas can be monitored. Therefore, when a change in the gas composition occurs, the change in the methane concentration XCH4 accompanying the change in the gas composition can be quickly detected.
また、本実施形態における測定機器は、例えば、二酸化炭素ガス濃度ＸＣＯ２を検出する赤外式センサ、屈折率測定手段（例えば、屈折率計）２２および、音速測定手段２６（例えば超音波音速計など）である。したがって、ガスクロマトグラフィと比較して、小型・軽量且つシンプルな構成でありながら高精度に、測定対象ガス（天然ガス）中のメタン濃度を測定することができる。 The measuring device in this embodiment is, for example, an infrared sensor for detecting the carbon dioxide gas concentration X CO2 , a refractive index measuring means (for example, a refractometer) 22, and a sound speed measuring means (for example, an ultrasonic sound speed meter, etc.). Therefore, compared to gas chromatography, it is possible to measure the methane concentration in the measurement target gas (natural gas) with high accuracy while being small, lightweight, and having a simple configuration.
また、測定に際しては、相当の時間を要することがなく、しかも基礎熱量Ｑ´の算出処理とメタン濃度ＸＣＨ４の算出処理との間にタイムラグが生じることがないため、メタン濃度ＸＣＨ４をリアルタイムに測定することができる。 In addition, the measurement does not require a significant amount of time, and no time lag occurs between the calculation process of the basic calorific value Q' and the calculation process of the methane concentration X CH4 , so the methane concentration X CH4 can be measured in real time.
さらにまた、熱量測定手段２０が、測定対象ガスの熱量を屈折率換算熱量ＱＯおよび音速換算熱量ＱＳの２種に基づいて算出する構成のものであることにより、得られる換算熱量ＱＯＳは、測定対象ガスのガス組成によらずに当該測定対象ガスの熱量の真値との差の小さい値となるので、算出されるメタン濃度ＸＣＨ４の値の信頼性が一層高いものなる。 Furthermore, since the calorific value measuring means 20 is configured to calculate the calorific value of the sample gas based on two types of values, the refractive index converted calorific value QO and the sonic speed converted calorific value QS , the obtained converted calorific value QOS has a small difference from the true value of the calorific value of the sample gas regardless of the gas composition of the sample gas, so that the calculated methane concentration XCH4 has higher reliability.
なお、上記のメタン濃度測定装置１においては、一例として、熱量測定手段２０およびメタン濃度算出手段４０が外装容器１０内に配設されてなる場合を示した。これにより、測定システムの構築および操作が簡便となる。しかしながら、熱量測定手段２０およびメタン濃度算出手段４０が外装容器１０内に配設されない構成であってもよく、外装容器１０は不要としてもよい。 In the above methane concentration measuring device 1, as an example, the calorific value measuring means 20 and the methane concentration calculating means 40 are disposed inside the outer container 10. This simplifies the construction and operation of the measurement system. However, the calorific value measuring means 20 and the methane concentration calculating means 40 may not be disposed inside the outer container 10, and the outer container 10 may not be necessary.
以上、本発明の実施の形態について説明したが、本発明は上記の実施の形態に限定されるものではなく、種々の変更を加えることができる。 The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment and various modifications can be made.
例えば、本実施形態に示した各数式は一例であり、各数式に用いた係数や数値等は上記の値に限定されるものではない。 For example, the formulas shown in this embodiment are merely examples, and the coefficients and numerical values used in each formula are not limited to the values described above.
また、熱量測定手段２０は、上記構成のものに限定されるものではなく、熱伝導率換算熱量の値と、屈折率換算熱量の値とに基づいて熱量の値を求める構成を有する装置が用いられていてもよい。また、熱量と特定の対応関係を有する物性値の１つ、例えば屈折率、熱伝導率、音速のうちから選ばれる１つを測定し、その測定値に基づいて熱量を求める構成のものであってもよい。このようにして得られた測定対象ガスの熱量に基づいて算出される基礎熱量の値を利用しても、メタン濃度ＸＣＨ４を得ることができる。 The calorific value measuring means 20 is not limited to the above configuration, and may be a device having a configuration for calculating the value of the calorific value based on the value of the thermal conductivity converted calorific value and the value of the refractive index converted calorific value. Alternatively, it may be a device having a configuration for measuring one of the physical property values having a specific correspondence relationship with the calorific value, for example, one selected from the refractive index, thermal conductivity, and sound speed, and calculating the calorific value based on the measured value. The methane concentration XCH4 can also be obtained by using the value of the basic calorific value calculated based on the calorific value of the measurement target gas obtained in this way.
また、干渉ガス濃度取得手段５０は、干渉ガスの濃度を取得可能な手段であれば上記の構成に限らない。例えば、窒素ガス濃度を測定可能な窒素ガス濃度測定手段を有し、二酸化炭素ガス濃度測定手段５１と窒素ガス濃度測定手段によりそれぞれの干渉ガス濃度を測定する構成であってもよい。また、測定対象ガスは、二酸化炭素ガスおよび窒素ガス以外の干渉ガスが含まれるガスであってもよく、その場合は、干渉ガス濃度取得手段５０は、測定対象ガスに含まれる全ての干渉ガスのそれぞれの濃度を測定可能な測定手段を備える構成であってもよいし、一部の干渉ガスについては演算により算出する構成であってもよい。 The interference gas concentration acquisition means 50 is not limited to the above configuration as long as it is a means capable of acquiring the concentration of the interference gas. For example, it may have a nitrogen gas concentration measurement means capable of measuring the nitrogen gas concentration, and may be configured to measure the respective interference gas concentrations using the carbon dioxide gas concentration measurement means 51 and the nitrogen gas concentration measurement means. The measurement target gas may also be a gas containing interference gases other than carbon dioxide gas and nitrogen gas. In that case, the interference gas concentration acquisition means 50 may be configured to include a measurement means capable of measuring the respective concentrations of all interference gases contained in the measurement target gas, or may be configured to calculate the concentrations of some interference gases by calculation.
またメタン濃度測定装置１は、その構成（上述した各手段）の少なくとも一部がハードウェアにより実現されていてもよいし、ソフトウェアにより実現されていてもよい。 In addition, at least a part of the configuration (each of the above-mentioned means) of the methane concentration measuring device 1 may be realized by hardware or software.
＜実験例＞
以下、本発明の実験例について説明する。
図３は、本実施形態のメタン濃度測定装置１およびメタン濃度測定方法によって得られた測定対象ガス中に含まれるメタン濃度ＸＣＨ４の値（測定結果）と、基準ガスに含まれるメタン濃度の値との誤差率を示すグラフである。具体的には、上記の式（４）を導いた各種基準ガス（ＩＳＯ／ＴＲ ２２３０２：２０１４に記載の複数の天然ガス（組成が既知である天然ガス）を測定対象ガスとして、上述の本実施形態の手法によりメタン濃度ＸＣＨ４を測定（算出）し、基準ガス（測定対象ガス）の既知のメタン濃度（文献値）との誤差を求めた。その結果について、横軸を算出したメタン濃度ＸＣＨ４〔ｖｏｌ％〕、縦軸を誤差〔ｖｏｌ％〕とする座標系にプロットした。同図に示すように、算出されたメタン濃度ＸＣＨ４の誤差率は±６．０％以内となり、実用される一般的なメタン含有量の測定対象ガスにおいて高い信頼度が得られることが分かった。特にメタン濃度が高い場合（９０％以上の場合）となり、非常に高い信頼度が得られることが分かった。
<Experimental Example>
Experimental examples of the present invention will now be described.
3 is a graph showing the error rate between the value (measurement result) of the methane concentration X CH4 contained in the measurement target gas obtained by the methane concentration measuring device 1 and the methane concentration measuring method of this embodiment and the value of the methane concentration contained in the reference gas. Specifically, the methane concentration X CH4 was measured (calculated) by the method of this embodiment using various reference gases (plural natural gases (natural gases with known compositions) described in ISO/TR 22302:2014) from which the above formula ( 4 ) was derived as the measurement target gas, and the error from the known methane concentration (literature value) of the reference gas (measurement target gas) was obtained. The results were plotted in a coordinate system with the calculated methane concentration X CH4 [vol%] on the horizontal axis and the error [vol%] on the vertical axis. As shown in the figure, the error rate of the calculated methane concentration X CH4 was within ±6.0%, and it was found that a high reliability could be obtained in a measurement target gas with a general methane content that is used in practice. In particular, when the methane concentration is high (90% or more), it was found that a very high reliability could be obtained.
１ メタン濃度測定装置
１０ 外装容器
１１ 測定対象ガス導入部
１２ 参照ガス導入部
１３ ガス排出部
２０ 熱量測定手段
２１ 屈折率換算熱量測定手段
２２ 屈折率測定手段
２３ 屈折率－熱量換算処理手段
２５ 音速換算熱量測定手段
２６ 音速測定手段
２７ 音速－熱量換算処理手段
３０ 窒素ガス濃度計算手段
３５ 熱量計算手段
４０ メタン濃度算出手段
４５ 表示手段
５０ 干渉ガス濃度取得手段
５１ 二酸化炭素ガス濃度測定手段
Ｑ´ 基礎熱量
ＱＯ 屈折率換算熱量
ＱＳ 音速換算熱量
ＱＯＳ 熱量（換算熱量）
ＱＲ 基準基礎熱量
1 Methane concentration measuring device 10 Outer container 11 Measurement target gas inlet 12 Reference gas inlet 13 Gas outlet 20 Calorific value measuring means 21 Refractive index converted calorific value measuring means 22 Refractive index measuring means 23 Refractive index-calorific value conversion processing means 25 Sonic speed converted calorific value measuring means 26 Sonic speed measuring means 27 Sonic speed-calorific value conversion processing means 30 Nitrogen gas concentration calculating means 35 Calorific value calculating means 40 Methane concentration calculating means 45 Display means 50 Interference gas concentration acquiring means 51 Carbon dioxide gas concentration measuring means Q' Basic calorific value Q O Refractive index converted calorific value Q S Sonic speed converted calorific value Q OS calorific value (converted calorific value)
Q R standard basic heat quantity
Claims (4)
前記基礎熱量は、対象となるガスにおいて不燃ガスの成分を除いた燃焼性ガス成分の燃焼熱量であり、
前記測定ガスは天然ガスであり、
前記不燃ガスは二酸化炭素ガス及び窒素ガスを少なくとも含み、
前記測定ガス中の二酸化炭素ガス濃度および窒素ガス濃度を取得する不燃ガス濃度取得手段と、
前記測定ガスの屈折率を測定し屈折率換算熱量を算出する屈折率換算熱量測定手段と、
前記測定ガスの音速を測定し音速換算熱量を算出する音速換算熱量測定手段と、
熱量計算手段と、
メタン濃度算出手段と、を有し、
前記不燃ガス濃度取得手段は、
前記二酸化炭素ガス濃度を測定し、
前記窒素ガス濃度を測定し、あるいは前記屈折率換算熱量、前記音速換算熱量および前記二酸化炭素ガス濃度を用いて第１算出式により該窒素ガス濃度を算出する手段であり、
前記熱量計算手段は、前記屈折率換算熱量と前記音速換算熱量を用いる第２算出式により前記測定ガスの換算熱量を算出し、
前記窒素ガス濃度、前記二酸化炭素ガス濃度および前記換算熱量を用いる第３算出式により、前記測定ガスの前記基礎熱量（以下「測定ガス基礎熱量」）を算出する手段であり、
前記メタン濃度算出手段は、
組成が既知の天然ガスを基準ガスとした場合の該基準ガスの基礎熱量と、該基準ガス中のメタン含有率の相関を示す第４算出式と、
前記窒素ガス濃度と前記二酸化炭素ガス濃度と前記測定ガス中のメタン含有率（以下「測定ガスメタン含有率」）を用いて該測定ガス中のメタン濃度を算出する第５算出式を有し、
前記第４算出式に、前記測定ガス基礎熱量を代入して前記測定ガスメタン含有率を算出し、
前記測定ガスメタン含有率、前記窒素ガス濃度および前記二酸化炭素ガス濃度を用いて前記第５算出式により前記メタン濃度を算出する手段である、
ことを特徴とするメタン濃度測定装置。 A methane concentration measuring device that calculates a methane concentration in a measurement gas using a basic calorific value,
The basic calorific value is the combustion heat value of combustible gas components in the target gas, excluding non-combustible gas components ,
the measurement gas is natural gas;
The non-combustible gas includes at least carbon dioxide gas and nitrogen gas,
a non-combustible gas concentration acquisition means for acquiring a carbon dioxide gas concentration and a nitrogen gas concentration in the measurement gas;
a refractive index converted calorific value measuring means for measuring the refractive index of the measurement gas and calculating a refractive index converted calorific value;
a sonic velocity converted calorific value measuring means for measuring the sonic velocity of the measurement gas and calculating a sonic velocity converted calorific value;
A heat calculation means;
A methane concentration calculation means,
The non-combustible gas concentration acquisition means
Measure the carbon dioxide gas concentration;
a means for measuring the nitrogen gas concentration, or for calculating the nitrogen gas concentration by a first calculation formula using the refractive index converted calorific value, the sound speed converted calorific value, and the carbon dioxide gas concentration,
the calorific value calculation means calculates the converted calorific value of the measurement gas by a second calculation formula using the refractive index converted calorific value and the sound speed converted calorific value;
a means for calculating the basic calorific value of the measurement gas (hereinafter referred to as "measurement gas basic calorific value") by a third calculation formula using the nitrogen gas concentration, the carbon dioxide gas concentration, and the converted calorific value;
The methane concentration calculation means
a fourth calculation formula showing a correlation between a basic calorific value of a reference gas and a methane content in the reference gas when the reference gas is a natural gas having a known composition;
a fifth calculation formula for calculating a methane concentration in the measurement gas using the nitrogen gas concentration, the carbon dioxide gas concentration, and the methane content in the measurement gas (hereinafter referred to as "measurement gas methane content");
Calculating the methane content of the measurement gas by substituting the basic calorific value of the measurement gas into the fourth calculation formula;
a means for calculating the methane concentration by the fifth calculation formula using the methane content of the measurement gas, the nitrogen gas concentration, and the carbon dioxide gas concentration;
A methane concentration measuring device characterized by:
ことを特徴とする請求項１に記載のメタン濃度測定装置。 The non-combustible gas concentration acquisition means has an infrared sensor.
2. The methane concentration measuring device according to claim 1 .
前記基礎熱量は、対象となるガスにおいて不燃ガスの成分を除いた燃焼性ガス成分の燃焼熱量であり、
前記測定ガスは天然ガスであり、
前記不燃ガスは二酸化炭素ガス及び窒素ガスを少なくとも含み、
前記測定ガス中の二酸化炭素ガス濃度および窒素ガス濃度を取得する不燃ガス濃度取得ステップと、
前記測定ガスの屈折率を測定し屈折率換算熱量を算出するステップと、
前記測定ガスの音速を測定し音速換算熱量を算出するステップと、
熱量計算ステップと、
メタン濃度算出ステップと、を有し、
前記不燃ガス濃度取得ステップでは、
前記二酸化炭素ガス濃度を測定し、
前記窒素ガス濃度を測定し、あるいは前記屈折率換算熱量、前記音速換算熱量および前記二酸化炭素ガス濃度を用いて第１算出式により該窒素ガス濃度を算出し、
前記熱量計算ステップでは、前記屈折率換算熱量と前記音速換算熱量を用いる第２算出式により前記測定ガスの換算熱量を算出し、
前記窒素ガス濃度、前記二酸化炭素ガス濃度および前記換算熱量を用いる第３算出式により、前記測定ガスの前記基礎熱量（以下「測定ガス基礎熱量」）を算出し、
前記メタン濃度算出ステップでは、
組成が既知の天然ガスを基準ガスとした場合の該基準ガスの基礎熱量と、該基準ガス中のメタン含有率の相関を示す第４算出式に前記測定ガス基礎熱量を代入して前記測定ガス中のメタン含有率（以下「測定ガスメタン含有率」）を算出し、
前記窒素ガス濃度と前記二酸化炭素ガス濃度と前記測定ガスメタン含有率を用いる第５算出式により前記測定ガス中のメタン濃度を算出する、
ことを特徴とするメタン濃度測定方法。 A method for measuring a methane concentration in a measurement gas by using a basic calorific value , comprising:
The basic calorific value is the combustion heat value of combustible gas components in the target gas, excluding non-combustible gas components,
the measurement gas is natural gas;
The non-combustible gas includes at least carbon dioxide gas and nitrogen gas,
a non-combustible gas concentration acquisition step of acquiring a carbon dioxide gas concentration and a nitrogen gas concentration in the measurement gas;
measuring the refractive index of the measurement gas and calculating the refractive index converted calorific value;
measuring the sound velocity of the measurement gas and calculating the sound velocity converted calorific value;
A heat calculation step;
A methane concentration calculation step,
In the non-combustible gas concentration acquisition step,
Measure the carbon dioxide gas concentration;
measuring the nitrogen gas concentration, or calculating the nitrogen gas concentration by a first calculation formula using the refractive index converted calorific value, the sound speed converted calorific value, and the carbon dioxide gas concentration;
In the calorific value calculation step, a converted calorific value of the measurement gas is calculated by a second calculation formula using the refractive index converted calorific value and the sonic speed converted calorific value;
Calculating the basic calorific value of the measurement gas (hereinafter referred to as "measurement gas basic calorific value") by a third calculation formula using the nitrogen gas concentration, the carbon dioxide gas concentration, and the converted calorific value;
In the methane concentration calculation step,
calculating the methane content in the measurement gas (hereinafter referred to as "measurement gas methane content") by substituting the measurement gas basic calorific value into a fourth calculation formula showing a correlation between the basic calorific value of the reference gas and the methane content in the reference gas when a natural gas having a known composition is used as the reference gas;
Calculating the methane concentration in the measurement gas by a fifth calculation formula using the nitrogen gas concentration, the carbon dioxide gas concentration, and the methane content of the measurement gas.
A method for measuring methane concentration.
ことを特徴とする請求項３に記載のメタン濃度測定方法。 The carbon dioxide gas concentration is measured by an infrared absorption method.
4. The method for measuring methane concentration according to claim 3 .
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| WO2017013897A1 (en) | 2015-07-22 | 2017-01-26 | 理研計器株式会社 | Methane number calculation method and methane number measurement device |
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