JP2016133194A - Boil-off gas release preventing controlling method of liquefied natural gas (lng) vehicle - Google Patents

Boil-off gas release preventing controlling method of liquefied natural gas (lng) vehicle Download PDF

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JP2016133194A
JP2016133194A JP2015009467A JP2015009467A JP2016133194A JP 2016133194 A JP2016133194 A JP 2016133194A JP 2015009467 A JP2015009467 A JP 2015009467A JP 2015009467 A JP2015009467 A JP 2015009467A JP 2016133194 A JP2016133194 A JP 2016133194A
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gas
boil
lng
pressure
recovery container
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JP6519194B2 (en
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原　裕一
Yuichi Hara
裕一 原
正義 田沼
Masayoshi Tanuma
正義 田沼
和彦 城田
Kazuhiko Shirota
和彦 城田
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Isuzu Motors Ltd
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Abstract

PROBLEM TO BE SOLVED: To provide a boil-off gas release preventing controlling method of a liquefied natural gas (LNG) vehicle capable of preventing release of a boil-off gas (BOG) even when the vehicle is left to stand for a long period.SOLUTION: A boil-off gas release preventing controlling method of an LNG vehicle includes an LNG fuel tank 10 for storing an LNG fuel, a fuel supply circuit 16 for vaporizing LNG in the LNG fuel tank 10 and supplying the same to an engine, a safety valve 15 releasing a boil-off gas to the atmospheric air when a pressure in the LNG fuel tank 10 reaches a limit pressure, and a boil-off gas recovery container 25 for recovering the boil-off gas in the LNG fuel tank 10 as an accumulation gas. Before stopping the driving of the LNG vehicle, the accumulation gas in the boil-off gas recovery container 25 is supplied to the fuel supply circuit 16 to reduce a pressure, and the boil-off gas is recovered to the boil-off gas recovery container 25 when the pressure of the boil-off gas in the LNG fuel tank 10 rises in stopping the driving of the LNG vehicle.SELECTED DRAWING: Figure 1

Description

本発明は、ＬＮＧを燃料とするＬＮＧ車に係り、特に、ＬＮＧタンクで発生するボイルオフガスを大気に放出するのを防止できるＬＮＧ車のボイルオフガス放出防止制御方法に関するものである。   The present invention relates to an LNG vehicle using LNG as fuel, and more particularly to a boil-off gas emission prevention control method for an LNG vehicle that can prevent release of boil-off gas generated in an LNG tank to the atmosphere.

ＬＮＧ（液化天然ガス）を燃料とする大型車については、シェールガス供給拡大に伴う燃料の低価格化により今後のニーズが高まるとともに、海外におけるＬＮＧ車の普及が進んでいる。   With regard to large vehicles that use LNG (liquefied natural gas) as fuel, future needs are increasing due to lower fuel prices associated with the expansion of shale gas supply, and LNG vehicles are spreading overseas.

ＬＮＧ車は、ＬＮＧを燃料として用いるため、圧縮天然ガス（ＣＮＧ）を用いるＣＮＧ車に対して、エネルギー密度が単位体積当たり約３倍と高く、燃料の一充填当たりの航続距離が長く、長距離大型トラックなどに適している。   Since LNG vehicles use LNG as fuel, the energy density is about three times higher per unit volume than CNG vehicles that use compressed natural gas (CNG), and the cruising distance per filling of fuel is long. Suitable for large trucks.

ＬＮＧ車のＬＮＧ燃料タンクは断熱二重構造で形成されているものの、入熱によりタンク内圧が上昇することは避けられない。ＬＮＧ車の運転中は、燃料蒸発ガス（ボイルオフガス）の気化潜熱でＬＮＧ燃料タンクが冷却されるためにタンク内圧力の上昇は防止できるものの、ＬＮＧ車を数日間も運転停車したままにするとボイルオフガスの取り扱いが課題となっている。   Although the LNG fuel tank of the LNG vehicle is formed with a heat insulating double structure, it is inevitable that the tank internal pressure rises due to heat input. While the LNG vehicle is in operation, the LNG fuel tank is cooled by the latent heat of vaporization of the fuel evaporative gas (boil-off gas), so that the pressure inside the tank can be prevented from rising, but if the LNG vehicle is left operating for several days, the boil-off occurs. The handling of gas is an issue.

特開２０１１−０８９５９６号公報JP 2011-089596 A 特開２０１４−１４９０５９号公報JP 2014-149059 A 特開平０６−００２６２９号公報JP-A-06-002629

すなわち、長期間放置時には、ＬＮＧ燃料タンク内部の圧力が上昇し、タンクの破裂防止のため、安全弁よりボイルオフガスが大気へ放出するようにしている。しかし、ボイルオフガスは、メタンが主成分であり、温室効果ガスであるため、車外に放出しないことが望ましい。   That is, when left standing for a long period of time, the pressure inside the LNG fuel tank rises, and the boil-off gas is discharged from the safety valve to the atmosphere to prevent the tank from bursting. However, since boil-off gas is mainly composed of methane and is a greenhouse gas, it is desirable that the boil-off gas is not released outside the vehicle.

そこで、本発明の目的は、上記課題を解決し、長期間放置してもボイルオフガスの放出を防止できるＬＮＧ車のボイルオフガス放出防止制御方法を提供することにある。   Accordingly, an object of the present invention is to provide a boil-off gas release prevention control method for an LNG vehicle that can solve the above-described problems and prevent the release of boil-off gas even when left for a long period of time.

上記目的を達成するために本発明は、ＬＮＧ燃料を貯蔵するＬＮＧ燃料タンクと、該ＬＮＧ燃料タンク内のＬＮＧを気化させてエンジンに供給する燃料供給回路と、前記ＬＮＧ燃料タンク内の圧力が限界圧になったときにボイルオフガスを大気に放出する安全弁と、前記ＬＮＧ燃料タンク内のボイルオフガスを蓄ガスとして回収するボイルオフガス回収容器とを備え、前記ＬＮＧ車の運転停止前に、前記ボイルオフガス回収容器内の蓄ガスを前記燃料供給回路に供給して前記ボイルオフガス回収容器を落圧し、前記ＬＮＧ車の運転停車時に、前記ＬＮＧ燃料タンク内のボイルオフガスの圧力が上昇したとき、そのボイルオフガスをボイルオフガス回収容器に回収することを特徴とするＬＮＧ車のボイルオフガス放出制御方法である。   In order to achieve the above object, the present invention provides an LNG fuel tank that stores LNG fuel, a fuel supply circuit that vaporizes LNG in the LNG fuel tank and supplies the LNG fuel to an engine, and a pressure in the LNG fuel tank is limited. And a boil-off gas recovery container for recovering the boil-off gas in the LNG fuel tank as a stored gas, and before the operation of the LNG vehicle is stopped, the boil-off gas is provided. When the stored gas in the recovery container is supplied to the fuel supply circuit to lower the pressure of the boil-off gas recovery container and the pressure of the boil-off gas in the LNG fuel tank rises when the LNG vehicle is stopped, the boil-off gas Is a boil-off gas release control method for an LNG vehicle.

前記ＬＮＧ車がアイドル回転のとき、前記ボイルオフガス回収容器内の蓄ガスを前記燃料供給回路に供給して、前記ボイルオフガス回収容器内を落圧するのが好ましい。   When the LNG vehicle is idling, it is preferable that the stored gas in the boil-off gas recovery container is supplied to the fuel supply circuit to reduce the pressure in the boil-off gas recovery container.

前記ＬＮＧ車の停止時に、前記ボイルオフガス回収容器内の蓄ガスの圧力が高いとき、前記ボイルオフガス回収容器内の蓄ガスを前記燃料供給回路に供給して、前記ボイルオフガス回収容器内を落圧するのが好ましい。   When the pressure of the stored gas in the boil-off gas recovery container is high when the LNG vehicle is stopped, the stored gas in the boil-off gas recovery container is supplied to the fuel supply circuit to reduce the pressure in the boil-off gas recovery container. Is preferred.

前記燃料供給回路に消費ガス切替弁が接続され、前記ボイルオフガス回収容器の出口側に蓄ガス消費切替弁が接続され、前記ボイルオフガス回収容器の蓄ガス圧力が前記燃料供給回路側の圧力より高いとき、前記消費ガス切替弁を閉じ、前記蓄ガス消費切替弁を開とするのが好ましい。   A consumption gas switching valve is connected to the fuel supply circuit, a storage gas consumption switching valve is connected to an outlet side of the boil-off gas recovery container, and a stored gas pressure in the boil-off gas recovery container is higher than a pressure on the fuel supply circuit side It is preferable that the consumption gas switching valve is closed and the stored gas consumption switching valve is opened.

前記ボイルオフガス回収容器には、メタン吸着材が充填されるのが好ましい。   The boil-off gas recovery container is preferably filled with a methane adsorbent.

本発明は、ＬＮＧ車の運転中にボイスオフガス回収容器の蓄ガスをエンジン側に供給して落圧しておくことで、ＬＮＧ車を長期間停止する際に、ＬＮＧ燃料タンク内で発生するボイルオフガスをボイスオフガス回収容器に回収させることができ、ＬＮＧ燃料タンクの圧力上昇を極力抑えてボイルオフガスの大気放出を防止できるという優れた効果を発揮する。   The present invention supplies boil-off gas generated in the LNG fuel tank when the LNG vehicle is stopped for a long time by supplying the stored gas in the voice-off gas recovery container to the engine side and reducing the pressure during operation of the LNG vehicle. Can be recovered in the voice-off gas recovery container, and an excellent effect of preventing the boil-off gas from being released into the atmosphere by suppressing the pressure increase of the LNG fuel tank as much as possible.

本発明の一実施の形態を示す図である。It is a figure which shows one embodiment of this invention. 本発明の他の実施の形態を示す図である。It is a figure which shows other embodiment of this invention. 本発明において、ＬＮＧ車のエンジン稼働後、長期間停止したときのＬＮＧ燃料タンクの圧力経時変化を示すものである。In the present invention, the change with time of pressure of the LNG fuel tank when the engine of the LNG vehicle is stopped for a long time after the engine is operated is shown. 比較例として、ＬＮＧ車のエンジン稼働後、長期間停止したときのＬＮＧ燃料タンクの圧力経時変化を示すものである。As a comparative example, the pressure aging change of the LNG fuel tank when the engine is stopped for a long time after the engine of the LNG vehicle is operated is shown. 比較例としてのＬＮＧ車のＬＮＧ燃料供給系を示す図である。It is a figure which shows the LNG fuel supply system of the LNG vehicle as a comparative example.

以下、本発明の好適な一実施の形態を添付図面に基づいて詳述する。   A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

図１は、ＬＮＧ車のＬＮＧ燃料供給系に本発明のボイルオフガス放出防止構造を組み込み、これを制御するための実施の形態を示したもので、図において、ＬＮＧ１１を貯蔵するＬＮＧ燃料タンク１０は、内槽と外槽からなる断熱二重構造で形成される。このＬＮＧ燃料タンク１０は、例えば、耐圧３ＭＰａのタンクで、車両に１基又は２基搭載される。   FIG. 1 shows an embodiment for incorporating and controlling the boil-off gas emission preventing structure of the present invention in an LNG fuel supply system of an LNG vehicle. In the figure, an LNG fuel tank 10 for storing LNG 11 is shown. It is formed with a heat insulating double structure consisting of an inner tank and an outer tank. The LNG fuel tank 10 is, for example, a tank with a withstand pressure of 3 MPa, and one or two are mounted on the vehicle.

ＬＮＧ燃料タンク１０には、ＬＮＧ１１を充填する充填ライン１２が接続されると共にＬＮＧ燃料タンク１０内が限界圧に達したときにタンク内のボイルオフガスを放出するボイルオフガス放出回路１３が接続される。   The LNG fuel tank 10 is connected to a filling line 12 for filling the LNG 11, and to a boil-off gas discharge circuit 13 for discharging the boil-off gas in the tank when the inside of the LNG fuel tank 10 reaches a limit pressure.

ボイルオフガス放出回路１３は、ＬＮＧ燃料タンク１０の気相部１０ｇに臨んで接続されるボイルオフガス放出ライン１４が接続され、そのボイルオフガス放出ライン１４に安全弁１５が接続されて構成される。この安全弁１５は、ＬＮＧ燃料タンク１０内の気相部１０ｇの圧力が、限界圧（例えば１．４〜１．６ＭＰａの間で設定）に達したときに開いてボイルオフガスを大気に放出する。   The boil-off gas discharge circuit 13 is configured such that a boil-off gas discharge line 14 connected to the gas phase portion 10g of the LNG fuel tank 10 is connected, and a safety valve 15 is connected to the boil-off gas discharge line 14. The safety valve 15 opens to release the boil-off gas to the atmosphere when the pressure of the gas phase portion 10g in the LNG fuel tank 10 reaches a limit pressure (for example, set between 1.4 to 1.6 MPa).

ＬＮＧ燃料タンク１０には、エンジンにＬＮＧ燃料タンク１０内のＬＮＧ１１を気化させてエンジンに供給する燃料供給回路１６が接続される。   Connected to the LNG fuel tank 10 is a fuel supply circuit 16 that vaporizes the LNG 11 in the LNG fuel tank 10 and supplies it to the engine.

この燃料供給回路１６は、ＬＮＧ燃料タンク１０の液相部１０ｌに臨んで接続される燃料供給ライン１７に、ＬＮＧを気化してＮＧとする熱交換器１８、脈動を防止する緩衝容器１９、消費ガス切替弁２０、エンジンへ供給するＮＧの圧力を、例えば０．４ＭＰａに調整するレギュレータ２１が接続されて構成される。   This fuel supply circuit 16 is connected to a fuel supply line 17 connected to the liquid phase portion 10l of the LNG fuel tank 10, a heat exchanger 18 that vaporizes LNG to NG, a buffer container 19 that prevents pulsation, A gas switching valve 20 and a regulator 21 that adjusts the pressure of NG supplied to the engine to 0.4 MPa, for example, are connected.

２基のＬＮＧ燃料タンク１０を搭載する場合、各ＬＮＧ燃料タンク１０の燃料供給ライン１７を共用し、充填ライン１２を共用する等を行い、燃料タンク内圧力と２つの容器間のＬＮＧ液面の平均化を図るように構成するのがよい。   When two LNG fuel tanks 10 are mounted, the fuel supply line 17 of each LNG fuel tank 10 is shared, the filling line 12 is shared, etc., and the pressure inside the fuel tank and the LNG liquid level between the two containers are It is preferable to configure so as to achieve averaging.

熱交換器１８の上流側の燃料供給ライン１７とボイルオフガス放出ライン１４を結んでＬＮＧ戻す或いはボイルオフガスを供給するライン２２が接続されると共にそのライン２２に、ＬＮＧ燃料タンク１０内の圧力を保圧する保圧弁２３が接続される。   A line 22 is connected to the fuel supply line 17 on the upstream side of the heat exchanger 18 and the boil-off gas discharge line 14 to return LNG or supply boil-off gas, and the pressure in the LNG fuel tank 10 is maintained in the line 22. A pressure keeping valve 23 is connected.

本発明においては、ボイルオフガス放出ライン１４に、回収ライン２４を介してボイルオフガス回収容器２５を接続してなり、ボイルオフガス回収容器２５で、ＬＮＧ車の運転停車時に、ＬＮＧ燃料タンク１０内のボイルオフガスを蓄ガスとして回収するようにしたものである。   In the present invention, a boil-off gas recovery container 25 is connected to the boil-off gas discharge line 14 via a recovery line 24, and the boil-off in the LNG fuel tank 10 is stopped in the boil-off gas recovery container 25 when the operation of the LNG vehicle is stopped. The gas is recovered as stored gas.

このボイルオフガス回収容器２５は、ライン２２の接続位置と安全弁１５間のボイルオフガス放出ライン１４に回収ライン２４を介して接続され、その回収ライン２４に、圧力制御弁２６が接続される。圧力制御弁２６は、例えば出入口ポートの差圧が設定圧（例えば０．３ＭＰａ）以上のときに開き、差圧がゼロ近くになったときに閉じるようになっている。   The boil-off gas recovery container 25 is connected to a boil-off gas discharge line 14 between the connection position of the line 22 and the safety valve 15 via a recovery line 24, and a pressure control valve 26 is connected to the recovery line 24. For example, the pressure control valve 26 opens when the differential pressure at the inlet / outlet port is equal to or higher than a set pressure (for example, 0.3 MPa), and closes when the differential pressure becomes close to zero.

またボイルオフガス回収容器２５の出口側は、排出ライン３０を介して、蓄ガス消費切替弁３３とレギュレータ２１間の燃料供給ライン１７に接続される。排出ライン３０には、圧力計３２、蓄ガス消費切替弁３３、逆止弁３４が順次接続される。   The outlet side of the boil-off gas recovery container 25 is connected to the fuel supply line 17 between the stored gas consumption switching valve 33 and the regulator 21 via the discharge line 30. A pressure gauge 32, a gas storage consumption switching valve 33, and a check valve 34 are sequentially connected to the discharge line 30.

ボイルオフガス回収容器２５で、ＬＮＧ燃料タンク１０内で発生するボイルオフガスを回収するためには、ボイルオフガス回収容器２５内を落圧する必要がある。   In order to recover the boil-off gas generated in the LNG fuel tank 10 by the boil-off gas recovery container 25, it is necessary to reduce the pressure in the boil-off gas recovery container 25.

このため、ＬＮＧ車を運転中に、ボイルオフガス回収容器２５内に回収された蓄ガスを燃料供給回路１６を介してエンジンに供給することで落圧する。   For this reason, during operation of the LNG vehicle, the stored gas recovered in the boil-off gas recovery container 25 is supplied to the engine via the fuel supply circuit 16 to reduce the pressure.

この際、圧力計３２の検出圧力が、ＥＣＵ３５に入力され、ＥＣＵ３５がボイルオフガス回収容器２５内の圧力を基に、消費ガス切替弁２０と蓄ガス消費切替弁３３を開閉制御する。   At this time, the detected pressure of the pressure gauge 32 is input to the ECU 35, and the ECU 35 controls the opening and closing of the consumption gas switching valve 20 and the stored gas consumption switching valve 33 based on the pressure in the boil-off gas recovery container 25.

このようにエンジン運転中に、ボイルオフガス回収容器２５内の蓄ガスを蓄ガス消費切替弁３３、逆止弁３４を介してエンジン側に供給することで、ボイルオフガス回収容器２５内の圧力は減少するので、車両を停止する際に、ＬＮＧ燃料タンク１０内の圧力が上昇したときにボイルオフガスを回収することが可能となる。   Thus, during operation of the engine, the pressure in the boil-off gas recovery container 25 is reduced by supplying the stored gas in the boil-off gas recovery container 25 to the engine side via the storage gas consumption switching valve 33 and the check valve 34. Thus, when the vehicle is stopped, the boil-off gas can be recovered when the pressure in the LNG fuel tank 10 increases.

特に低温始動時等のＬＮＧの気化促進が期待できない環境下で、ボイルオフガス回収容器２５内の蓄ガスを安定したＣＮＧ（気化されたＬＮＧ）をエンジンに供給することも可能となる。   It is also possible to supply CNG (vaporized LNG) with stable stored gas in the boil-off gas recovery container 25 to the engine, particularly in an environment where LNG vaporization promotion cannot be expected, such as at low temperature startup.

このボイルオフガス回収容器２５内の蓄ガスを供給する場合、運転可能な圧力（予め設定された蓄ガス圧力）まで気体で安定している蓄ガスのみをエンジンに供給する。水温が設定された温度へ到達し、かつ蓄ガス圧力が予め設定された圧力まで到達するとＬＮＧの燃料供給回路１６に切り替える。また、場合によっては蓄ガスで燃料供給している間は、エンジン回転数制限や吸入空気量制限など運転制限をかけるようにしてもよい。   When the stored gas in the boil-off gas recovery container 25 is supplied, only the stored gas that is stable in gas up to the operable pressure (prestored stored gas pressure) is supplied to the engine. When the water temperature reaches the set temperature and the stored gas pressure reaches the preset pressure, the LNG fuel supply circuit 16 is switched. In some cases, while fuel is supplied with stored gas, operation restrictions such as engine speed restriction and intake air quantity restriction may be applied.

図２は、本発明の他の実施の形態を示したものである。   FIG. 2 shows another embodiment of the present invention.

図２の実施の形態においては、基本構成は図１と同じであるが、ボイルオフガス回収容器２５Ａ内にメタンを吸蔵するための吸着剤３１を充填して構成したものである。   In the embodiment of FIG. 2, the basic configuration is the same as that of FIG. 1, but the boil-off gas recovery container 25A is filled with an adsorbent 31 for storing methane.

次に、本実施の形態におけるボイルオフガス放出防止を説明する。   Next, prevention of boil-off gas emission in the present embodiment will be described.

先ず図５は、従来のＬＮＧ車のＬＮＧ燃料供給系を示し、図１、図２で説明した本発明のＬＮＧ車のボイルオフガス放出防止構造で、部材符号が同じものは同じ番号で示してある。   First, FIG. 5 shows a LNG fuel supply system of a conventional LNG vehicle. In the LNG vehicle boil-off gas emission preventing structure of the present invention described in FIGS. 1 and 2, the same reference numerals are used to denote the same member codes. .

従来においては、図４に示すようにエンジン稼働中は、ＬＮＧ燃料タンク１０内の圧力は、低く保たれ（例えば０．４ＭＰａ以下）、エンジン停止後は、ＬＮＧ燃料タンク１０内のＬＮＧ１１は、大気からの入熱を受けて徐々にその温度が上昇して蒸発してボイルオフガスとなり、そのボイルオフガスで気相部１０ｇの圧力が上昇する。この気相部１０ｇの圧力が安全弁１５の限界圧（１．４ＭＰａ）に達すると安全弁１５が開いてオイルオフガスを大気に放出され、その放出で、気相部１０ｇの圧力が下がるため、安全弁１５が閉じ、その後の入熱で、気相部１０ｇの圧力が上昇して安全弁１５が開いてオイルオフガスを大気に放出され、これを繰り返すことになる。   Conventionally, as shown in FIG. 4, the pressure in the LNG fuel tank 10 is kept low (for example, 0.4 MPa or less) while the engine is running, and the LNG 11 in the LNG fuel tank 10 is In response to the heat input, the temperature gradually rises and evaporates to form a boil-off gas, and the pressure in the gas phase portion 10g increases with the boil-off gas. When the pressure in the gas phase portion 10g reaches the limit pressure (1.4 MPa) of the safety valve 15, the safety valve 15 is opened and the oil-off gas is released to the atmosphere. Is closed, and with the subsequent heat input, the pressure in the gas phase portion 10g rises, the safety valve 15 is opened, and the oil-off gas is released to the atmosphere, and this is repeated.

本発明においては、ＬＮＧ車が運転停止する前に、ボイルオフガス回収容器２５内に貯留されている蓄ガスを、ＬＮＧ車の運転中にＬＮＧ燃料タンク１０内の気相部１０ｇの圧力と同じか、それより低い圧力に保持されるように制御しておく。この制御は運転始動時や運転中或いは停止中で、エンジンがアイドル回転のときに行うのがよい。   In the present invention, before the operation of the LNG vehicle is stopped, whether the stored gas stored in the boil-off gas recovery container 25 is the same as the pressure of the gas phase portion 10g in the LNG fuel tank 10 during operation of the LNG vehicle. , And keep the pressure lower than that. This control is preferably performed when the engine is idling, during operation start, during operation, or during stoppage.

ＬＮＧ車の停止後は、図３に示すように、ＬＮＧ燃料タンク１０内のＬＮＧ１１が、大気からの入熱を受けて徐々にその温度が上昇し、気相部１０ｇの圧力が上昇するが、圧力制御弁２６の出入口の圧力差Δｐ（気相部１０ｇの圧力とボイルオフガス回収容器２５の圧力差）が、例えば０．３ＭＰａ以上となると圧力制御弁２６が開き、気相部１０ｇのボイルオフガスは、ボイルオフガス放出ライン１４、圧力制御弁２６、回収ライン２４を介してボイルオフガス回収容器２５に回収される。   After the LNG vehicle is stopped, as shown in FIG. 3, the LNG 11 in the LNG fuel tank 10 receives heat from the atmosphere and gradually rises in temperature, and the pressure in the gas phase portion 10g rises. When the pressure difference Δp at the inlet / outlet of the pressure control valve 26 (pressure difference between the gas phase portion 10g and the pressure difference between the boil-off gas recovery container 25) becomes, for example, 0.3 MPa or more, the pressure control valve 26 opens and the boil-off gas in the gas phase portion 10g. Is recovered in the boil-off gas recovery container 25 via the boil-off gas discharge line 14, the pressure control valve 26, and the recovery line 24.

これにより、ＬＮＧ燃料タンク１０内の気相部１０ｇの圧力が下がり、従来のような圧力上昇を防止できる。   Thereby, the pressure of the gas phase part 10g in the LNG fuel tank 10 is lowered, and the pressure increase as in the conventional case can be prevented.

次に、この下がった圧力から、再度気相部１０ｇの圧力が上昇し、気相部１０ｇとボイルオフガス回収容器２５の圧力差がΔｐとなったとき、再度圧力制御弁２６が開いて、気相部１０ｇのボイルオフガスをボイルオフガス回収容器２５内に回収する。   Next, when the pressure in the gas phase part 10g rises again from this reduced pressure and the pressure difference between the gas phase part 10g and the boil-off gas recovery container 25 becomes Δp, the pressure control valve 26 opens again, The boil-off gas of the phase part 10 g is recovered in the boil-off gas recovery container 25.

このようにして、気相部１０ｇで発生したボイルオフガスを、圧力制御弁２６を介してボイルオフガス回収容器２５内に回収し、これを蓄ガスとすることで、安全弁１５が動作する限界圧（例えば１．４ＭＰａ）に達してボイルオフガスの大気放出する時間を、拡大することができる。   In this way, the boil-off gas generated in the gas phase portion 10g is recovered in the boil-off gas recovery container 25 via the pressure control valve 26, and this is used as a stored gas, whereby the limit pressure (at which the safety valve 15 operates) For example, the time during which the boil-off gas is released to the atmosphere after reaching 1.4 MPa can be extended.

また、図２のようにボイルオフガス回収容器２５Ａに吸着剤３１を充填した場合には、内容積は１／８程度とすることができる。   Further, when the boil-off gas recovery container 25A is filled with the adsorbent 31 as shown in FIG. 2, the internal volume can be reduced to about 1/8.

本発明では、ＬＮＧ燃料タンク１０から放出されるボイルオフガスをボイルオフガス回収容器２５に回収する際に、ボイルオフガス回収容器２５内に回収し、蓄積された蓄ガスをＬＮＧ車の運転中にエンジン側に供給して、ボイルオフガス回収容器２５内の圧力をＬＮＧ燃料タンク１０内の運転中の圧力（例えば０．４ＭＰａに落圧しておく。この落圧運転は、ＬＮＧ車がアイドル回転のときなど、ＥＣＵ３５が圧力計３２で検出した圧力に基づいて適宜消費ガス切替弁２０と蓄ガス消費切替弁３３を開閉制御する。   In the present invention, when the boil-off gas discharged from the LNG fuel tank 10 is collected in the boil-off gas collection container 25, the boil-off gas collection container 25 collects the accumulated gas and stores the accumulated gas during the operation of the LNG vehicle. The pressure in the boil-off gas recovery container 25 is reduced to a pressure during operation in the LNG fuel tank 10 (for example, to 0.4 MPa. This pressure reduction operation is performed when the LNG vehicle is in idle rotation, etc. Based on the pressure detected by the pressure gauge 32, the ECU 35 appropriately controls the opening and closing of the consumption gas switching valve 20 and the stored gas consumption switching valve 33.

このようにして、ボイルオフガス回収容器２５内を落圧し、ＬＮＧ車が長期間停車する際には、ＬＮＧ燃料タンク１０から放出されるボイルオフガスをボイルオフガス回収容器２５に回収し、併せてその際に放出されるＬＮＧ気化潜熱によりＬＮＧ燃料タンク１０を冷やすことで、ボイルオフガスの大気放出に至るまでの時間を延長させることができる。   In this way, when the pressure in the boil-off gas recovery container 25 is reduced and the LNG vehicle stops for a long time, the boil-off gas released from the LNG fuel tank 10 is recovered in the boil-off gas recovery container 25, and at that time By cooling the LNG fuel tank 10 with the LNG vaporization latent heat released to the air, the time until the boil-off gas is released to the atmosphere can be extended.

１０ ＬＮＧ燃料タンク
１５ 安全弁
１６ 燃料供給回路
２５ ボイルオフガス回収容器 10 LNG fuel tank 15 Safety valve 16 Fuel supply circuit 25 Boil-off gas recovery container

Claims (5)

ＬＮＧ燃料を貯蔵するＬＮＧ燃料タンクと、該ＬＮＧ燃料タンク内のＬＮＧを気化させてエンジンに供給する燃料供給回路と、前記ＬＮＧ燃料タンク内の圧力が限界圧になったときにボイルオフガスを大気に放出する安全弁と、前記ＬＮＧ燃料タンク内のボイルオフガスを蓄ガスとして回収するボイルオフガス回収容器とを備え、前記ＬＮＧ車の運転停止前に、前記ボイルオフガス回収容器内の蓄ガスを前記燃料供給回路に供給して前記ボイルオフガス回収容器を落圧し、前記ＬＮＧ車の運転停車時に、前記ＬＮＧ燃料タンク内のボイルオフガスの圧力が上昇したとき、そのボイルオフガスをボイルオフガス回収容器に回収することを特徴とするＬＮＧ車のボイルオフガス放出制御方法。   An LNG fuel tank for storing LNG fuel, a fuel supply circuit for vaporizing the LNG in the LNG fuel tank and supplying it to the engine, and boil-off gas to the atmosphere when the pressure in the LNG fuel tank reaches a limit pressure A safety valve for discharging, and a boil-off gas recovery container for recovering the boil-off gas in the LNG fuel tank as a stored gas, and before the operation of the LNG vehicle is stopped, the stored gas in the boil-off gas recovery container is stored in the fuel supply circuit. And the pressure of the boil-off gas recovery container is reduced, and when the pressure of the boil-off gas in the LNG fuel tank rises when the LNG vehicle is stopped, the boil-off gas is recovered in the boil-off gas recovery container. A boil-off gas emission control method for an LNG vehicle. 前記ＬＮＧ車がアイドル回転のとき、前記ボイルオフガス回収容器内の蓄ガスを前記燃料供給回路に供給して、前記ボイルオフガス回収容器内を落圧する請求項１記載のＬＮＧ車のボイルオフガス放出制御方法。   2. The boil-off gas discharge control method for an LNG vehicle according to claim 1, wherein when the LNG vehicle is idling, the stored gas in the boil-off gas recovery container is supplied to the fuel supply circuit to reduce the pressure in the boil-off gas recovery container. . 前記ＬＮＧ車の停止時に、前記ボイルオフガス回収容器内の蓄ガスの圧力が高いとき、前記ボイルオフガス回収容器内の蓄ガスを前記燃料供給回路に供給して、前記ボイルオフガス回収容器内を落圧する請求項１記載のＬＮＧ車のボイルオフガス放出制御方法。   When the pressure of the stored gas in the boil-off gas recovery container is high when the LNG vehicle is stopped, the stored gas in the boil-off gas recovery container is supplied to the fuel supply circuit to reduce the pressure in the boil-off gas recovery container. The boil-off gas emission control method of the LNG vehicle according to claim 1. 前記燃料供給回路に消費ガス切替弁が接続され、前記ボイルオフガス回収容器の出口側に蓄ガス消費切替弁が接続され、前記ボイルオフガス回収容器の蓄ガス圧力が前記燃料供給回路側の圧力より高いとき、前記消費ガス切替弁を閉じ、前記蓄ガス消費切替弁を開とする請求項１〜３のいずれかに記載のＬＮＧ車のボイルオフガス放出制御方法。   A consumption gas switching valve is connected to the fuel supply circuit, a storage gas consumption switching valve is connected to an outlet side of the boil-off gas recovery container, and a stored gas pressure in the boil-off gas recovery container is higher than a pressure on the fuel supply circuit side The boil-off gas discharge control method for an LNG vehicle according to any one of claims 1 to 3, wherein the consumption gas switching valve is closed and the stored gas consumption switching valve is opened. 前記ボイルオフガス回収容器には、メタン吸着材が充填される請求項１〜４いずれかに記載のＬＮＧ車のボイルオフガス放出制御方法。   The boil-off gas release control method for an LNG vehicle according to any one of claims 1 to 4, wherein the boil-off gas recovery container is filled with a methane adsorbent.
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