JP5769445B2 - Surplus gas generation suppression method for liquefied natural gas storage / transport ship and liquefied natural gas storage / transport ship - Google Patents

Surplus gas generation suppression method for liquefied natural gas storage / transport ship and liquefied natural gas storage / transport ship Download PDF

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JP5769445B2
JP5769445B2 JP2011040369A JP2011040369A JP5769445B2 JP 5769445 B2 JP5769445 B2 JP 5769445B2 JP 2011040369 A JP2011040369 A JP 2011040369A JP 2011040369 A JP2011040369 A JP 2011040369A JP 5769445 B2 JP5769445 B2 JP 5769445B2
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natural gas
liquefied natural
lng
tank
loaded
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JP2012177419A (en
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石田　聡成
聡成 石田
俊夫 小形
俊夫 小形
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Mitsubishi Heavy Industries Ltd
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Mitsubishi Heavy Industries Ltd
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Priority to CN201280010359.6A priority patent/CN103403435B/en
Priority to PCT/JP2012/052516 priority patent/WO2012114851A1/en
Priority to KR1020137022029A priority patent/KR20130117859A/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C6/00—Methods and apparatus for filling vessels not under pressure with liquefied or solidified gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C9/00—Methods or apparatus for discharging liquefied or solidified gases from vessels not under pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2201/00—Vessel construction, in particular geometry, arrangement or size
    • F17C2201/01—Shape
    • F17C2201/0128—Shape spherical or elliptical
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2201/00—Vessel construction, in particular geometry, arrangement or size
    • F17C2201/05—Size
    • F17C2201/052—Size large (>1000 m3)
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2221/00—Handled fluid, in particular type of fluid
    • F17C2221/03—Mixtures
    • F17C2221/032—Hydrocarbons
    • F17C2221/033—Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
    • F17C2223/0146—Two-phase
    • F17C2223/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2223/0161—Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
    • F17C2223/0146—Two-phase
    • F17C2223/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2223/0169—Liquefied gas, e.g. LPG, GPL subcooled
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/03—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the pressure level
    • F17C2223/033—Small pressure, e.g. for liquefied gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/03—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the pressure level
    • F17C2223/035—High pressure (>10 bar)
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/04—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by other properties of handled fluid before transfer
    • F17C2223/042—Localisation of the removal point
    • F17C2223/046—Localisation of the removal point in the liquid
    • F17C2223/047—Localisation of the removal point in the liquid with a dip tube
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/01—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the phase
    • F17C2225/0146—Two-phase
    • F17C2225/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2225/0161—Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/01—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the phase
    • F17C2225/0146—Two-phase
    • F17C2225/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2225/0169—Liquefied gas, e.g. LPG, GPL subcooled
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/03—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the pressure level
    • F17C2225/033—Small pressure, e.g. for liquefied gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/03—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by the pressure level
    • F17C2225/035—High pressure, i.e. between 10 and 80 bars
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/04—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by other properties of handled fluid after transfer
    • F17C2225/042—Localisation of the filling point
    • F17C2225/043—Localisation of the filling point in the gas
    • F17C2225/044—Localisation of the filling point in the gas at several points, e.g. with a device for recondensing gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/04—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by other properties of handled fluid after transfer
    • F17C2225/042—Localisation of the filling point
    • F17C2225/046—Localisation of the filling point in the liquid
    • F17C2225/047—Localisation of the filling point in the liquid with a dip tube
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2260/00—Purposes of gas storage and gas handling
    • F17C2260/03—Dealing with losses
    • F17C2260/031—Dealing with losses due to heat transfer
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2270/00—Applications
    • F17C2270/01—Applications for fluid transport or storage
    • F17C2270/0102—Applications for fluid transport or storage on or in the water
    • F17C2270/0105—Ships
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2270/00—Applications
    • F17C2270/01—Applications for fluid transport or storage
    • F17C2270/0102—Applications for fluid transport or storage on or in the water
    • F17C2270/011—Barges

Description

本発明は、液化天然ガスの貯蔵・運搬等に用いられる液化天然ガス貯蔵・運搬船及び液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法に係り、特に、液化天然ガス貯蔵・運搬船に対する液化天然ガス積込時に発生する余剰ガスを抑制する技術に関する。   The present invention relates to a liquefied natural gas storage / transport ship used for liquefied natural gas storage / transport and the like, and a method for suppressing excessive gas generation in a liquefied natural gas storage / transport ship, and more particularly to a liquefied natural gas product for a liquefied natural gas storage / transport ship. The present invention relates to a technique for suppressing surplus gas generated during charging.

従来、液化天然ガス（以下、「ＬＮＧ」と呼ぶ）の運搬に使用される液化天然ガス運搬船（ＬＮＧＣ，ＳＲＶ）や、再ガス化装置を備えた浮体式液化天然ガス貯蔵船（ＦＳＲＵ）のように、ＬＮＧを取り扱う液化天然ガス貯蔵・運搬船が知られている。
既存の液化天然ガス運搬船では、ＬＮＧ貯蔵タンクへのＬＮＧ積込時にＬＮＧが気化して大量の天然ガスを発生するので、運搬船側で消費できない大半の余剰ガスについては、たとえば図４に示すように、陸上基地へ返送して基地側で処理（通常は焼却処理）することが行われている。 Conventionally, liquefied natural gas carriers (LNGC, SRV) used for transporting liquefied natural gas (hereinafter referred to as “LNG”) and floating liquefied natural gas storage vessels (FSRU) equipped with a regasifier In addition, a liquefied natural gas storage / transport ship that handles LNG is known.
In an existing liquefied natural gas carrier, LNG is vaporized when LNG is loaded into the LNG storage tank, and a large amount of natural gas is generated. Therefore, as shown in FIG. It is returned to the land base and processed on the base side (usually incineration processing).

図４に示す液化天然ガス運搬船１は、球形のＬＮＧ船内貯蔵タンク２を備えている。各ＬＮＧ船内貯蔵タンク２は、陸上基地側のＬＮＧ陸上貯蔵タンク１０等からＬＮＧポンプ１１により送出されるＬＮＧを積み込む際に使用する実線表示のＬＮＧ積込配管系統１２と、各ＬＮＧ貯蔵タンク２から気化した天然ガスを払い出す際に使用する破線表示のガス払出配管系統１３とを備えている。
ガス払出配管系統１３は、各ＬＮＧ船内貯蔵タンク２内の天然ガスを機関部３に供給するとともに、陸上基地側のフレアスタック１４に導いて燃焼させる。 A liquefied natural gas carrier 1 shown in FIG. 4 includes a spherical LNG inboard storage tank 2. Each LNG inboard storage tank 2 includes an LNG loading piping system 12 indicated by a solid line used when loading LNG sent from the LNG land storage tank 10 on the land base side by the LNG pump 11, and each LNG storage tank 2. And a gas delivery pipe system 13 indicated by a broken line used when delivering the vaporized natural gas.
The gas discharge piping system 13 supplies the natural gas in each LNG inboard storage tank 2 to the engine unit 3 and guides it to the flare stack 14 on the land base side for combustion.

液化天然ガス運搬船１において、ＬＮＧ船内貯蔵タンク２へのＬＮＧ積込時に大量の余剰ガスが発生する主な理由としては、下記の２点があげられる。
１）ＬＮＧ船内貯蔵タンク２を予冷してからＬＮＧ積込を開始するが、ＬＮＧ船内貯蔵タンク２は積込ＬＮＧの飽和温度まで冷却されていない。このため、ＬＮＧ船内貯蔵タンク２内に極低温のＬＮＧを積み込むことにより、図５に矢印で示すような熱の移動が生じ、積込ＬＮＧはＬＮＧ船内貯蔵タンク２や天然ガスとの接触面で飽和温度まで昇温する。この結果、ＬＮＧ船内貯蔵タンク２の内部では、大量の天然ガスが発生する。
２）積込オペレーション前にＬＮＧ船内貯蔵タンク２内に残留しているＬＮＧは、長期間放置されて重質化（メタン成分の揮発）が進んでおり、この結果、液温が上昇した状態にある。このため、残留ＬＮＧよりも液温の低い新たなＬＮＧが流入することにより、ＬＮＧ船内貯蔵タンク２の内部では突沸現象が生じるので、特に積込初期において大量の天然ガスが発生する。 In the liquefied natural gas carrier 1, there are the following two main reasons why a large amount of surplus gas is generated when LNG is loaded into the LNG inboard storage tank 2.
1) LNG loading is started after the LNG inboard storage tank 2 is pre-cooled, but the LNG inboard storage tank 2 is not cooled to the saturation temperature of the loaded LNG. For this reason, by loading cryogenic LNG into the LNG inboard storage tank 2, heat transfer as indicated by arrows in FIG. 5 occurs, and the loaded LNG is in contact with the LNG inboard storage tank 2 and natural gas. The temperature is raised to the saturation temperature. As a result, a large amount of natural gas is generated inside the LNG inboard storage tank 2.
2) The LNG remaining in the LNG inboard storage tank 2 before the loading operation has been left for a long period of time and has become heavier (the volatilization of the methane component). As a result, the liquid temperature has increased. is there. For this reason, since a new LNG whose liquid temperature is lower than the residual LNG flows in, a bumping phenomenon occurs inside the LNG inboard storage tank 2, and thus a large amount of natural gas is generated particularly at the initial stage of loading.

浮体式液化天然ガス貯蔵船の場合、ＬＮＧ積込時に発生する余剰ガスの処理は、より一層困難になる。すなわち、図３に示すように、液化天然ガスシャトル運搬船（ＳＨＵＴＴＬＥ ＬＮＧＣ）１Ｓから浮体式液化天然ガス貯蔵船１ＦへのＬＮＧ積込オペレーション時には、液化天然ガスシャトル運搬船１Ｓ側への返送可能ガス量は、基本的に液化天然ガスシャトル運搬船１Ｓから供給したＬＮＧ容積と同一の容量に制約される。
このため、大気放出が許可されない状況では、浮体式液化天然ガス貯蔵船１Ｆの船上適所に再液化装置（不図示）を装備し、余剰ガスを液化して再度ＬＮＧ船内貯蔵タンク２へ戻すしかない。なお、図中の符号４はＬＮＧポンプ、５は船上再ガス化装置、１２はＬＮＧ積込配管系統、１３はガス払出配管系統、１５は船上再ガス化装置５でガス化した高圧の天然ガス（ＣＮＧ）を陸上施設等へ供給する高圧ガス払出配管系統である。 In the case of a floating liquefied natural gas storage ship, it becomes even more difficult to treat surplus gas generated during LNG loading. That is, as shown in FIG. 3, during the LNG loading operation from the liquefied natural gas shuttle carrier (SHUTTLE LNGC) 1S to the floating liquefied natural gas storage vessel 1F, the amount of gas that can be returned to the liquefied natural gas shuttle carrier 1S side is Basically, the capacity is limited to the same volume as the LNG volume supplied from the liquefied natural gas shuttle carrier 1S.
For this reason, in a situation where release into the atmosphere is not permitted, there is no choice but to equip a suitable place on the floating liquefied natural gas storage ship 1F with a reliquefaction device (not shown), liquefy excess gas and return it to the LNG inboard storage tank 2 again. . In the figure, reference numeral 4 is an LNG pump, 5 is an onboard regasifier, 12 is an LNG loading piping system, 13 is a gas discharge piping system, and 15 is high-pressure natural gas gasified by the onboard regasifier 5. This is a high-pressure gas discharge piping system that supplies (CNG) to land facilities and the like.

ＬＮＧ船に関する従来技術としては、運送中にＬＮＧ貯蔵タンクから発生する蒸発ガス（ＢＯＧ）を低減するため、常圧付近の圧力範囲内で調節されるタンク内蒸気圧力の上昇を許容するタンク強度とする技術が知られている。（たとえば、特許文献１参照）
また、低温液化ガス貯蔵タンクにおいては、層状化防止運転中の急激なＢＯＧ発生を防止するロールオーバー発生防止方法が提案されている。（たとえば、特許文献２参照） The conventional technology related to the LNG ship includes a tank strength that allows an increase in the vapor pressure in the tank that is adjusted within a pressure range near normal pressure in order to reduce evaporative gas (BOG) generated from the LNG storage tank during transportation. The technology to do is known. (For example, see Patent Document 1)
Moreover, in the low temperature liquefied gas storage tank, the rollover generation | occurrence | production prevention method which prevents rapid BOG generation | occurrence | production during the stratification prevention operation is proposed. (For example, see Patent Document 2)

特開２００８−１９６６８５号公報JP 2008-196685 A 特開２０００−１７９７９８号公報JP 2000-179798 A

上述したように、ＬＮＧ積込時に発生する余剰ガスの処理については、陸上基地側での処理ができない浮体式液化天然ガス貯蔵船において特に困難となる。この余剰ガスは、再液化装置による処理も可能ではあるが、余剰ガス量が多いほど再液化装置も大型化するので、船上の設置スペース確保やコストの面で不利になる。
このため、ＬＮＧ積込時に気化して発生する天然ガス量を減少させることができれば、余剰ガスとなる天然ガス量も減少して少なくなるので、余剰ガスの処理が容易または不要となる。 As described above, the processing of surplus gas generated during LNG loading is particularly difficult in a floating liquefied natural gas storage ship that cannot be processed on the land base side. Although this surplus gas can be processed by the reliquefaction device, the reliquefaction device becomes larger as the surplus gas amount increases, which is disadvantageous in terms of securing installation space on the ship and cost.
For this reason, if the amount of natural gas generated by vaporization at the time of LNG loading can be reduced, the amount of natural gas that becomes surplus gas also decreases and decreases, so that the processing of surplus gas becomes easy or unnecessary.

このような背景から、液化天然ガス貯蔵・運搬船の液化天然ガス船内貯蔵タンクに液化天然ガスを積み込むＬＮＧ積込時において、タンク内での気化を抑制して発生する天然ガス量の低減が可能な液化天然ガス貯蔵・運搬船及び液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法が望まれる。
本発明は、上記の事情に鑑みてなされたものであり、その目的とするところは、液化天然ガスを液化天然ガス船内貯蔵タンクに積み込むＬＮＧ積込時に発生する天然ガス量を低減し、ＬＮＧ積込により発生する余剰ガス量を最小限に抑えた液化天然ガス貯蔵・運搬船及び液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法を提供することにある。 From such a background, it is possible to reduce the amount of natural gas generated by suppressing vaporization in the tank when LNG is loaded into the liquefied natural gas ship storage tank of the liquefied natural gas storage / transport ship. There is a demand for a method for suppressing excessive gas generation in a liquefied natural gas storage / transport ship and a liquefied natural gas storage / transport ship.
The present invention has been made in view of the above circumstances, and the object of the present invention is to reduce the amount of natural gas generated when LNG is loaded into a liquefied natural gas inboard storage tank, An object of the present invention is to provide a liquefied natural gas storage / transport ship that minimizes the amount of surplus gas generated by stagnation, and a method for suppressing excessive gas generation in a liquefied natural gas storage / transport ship.

本発明は、上記の課題を解決するため、下記の手段を採用した。
本発明に係る液化天然ガス貯蔵・運搬船は、極低温状態の液化天然ガスを貯蔵する液化天然ガス貯蔵タンクを備えている液化天然ガス貯蔵・運搬船であって、前記液化天然ガス貯蔵タンクに前記液化天然ガスを積み込む際、積込液化天然ガスが過冷却状態となるように、前記積込液化天然ガスが気化した天然ガスでタンク内圧を上げて沸点を上昇させるとともに、前記積込液化天然ガスをタンク底部付近まで導いて積み込む液化天然ガス積込配管系統から分岐して、前記積込液化天然ガスをタンク頂部近傍からタンク内に投入して積み込むための頂部液化天然ガス投入系統を設けたことを特徴とするものである。 In order to solve the above problems, the present invention employs the following means.
The liquefied natural gas storage / transport ship according to the present invention is a liquefied natural gas storage / transport ship equipped with a liquefied natural gas storage tank for storing liquefied natural gas in a cryogenic state, wherein the liquefied natural gas storage tank is provided with the liquefied natural gas storage tank. when loading the natural gas, as loading liquefied natural gas is supercooled state, together with increasing the boiling point by increasing the tank pressure natural gas the loading liquefied natural gas is vaporized, the loading liquefied natural gas A top liquefied natural gas charging system was provided for branching from the liquefied natural gas loading piping system that leads to the vicinity of the bottom of the tank for loading, and for loading the loaded liquefied natural gas into the tank from near the top of the tank and loading it. It is a feature.

このような本発明の液化天然ガス貯蔵・運搬船によれば、液化天然ガス貯蔵タンクに液化天然ガスを積み込む際、積込液化天然ガスが過冷却状態となるように、積込液化天然ガスが気化した天然ガスでタンク内圧を上げて沸点を上昇させるとともに、積込液化天然ガスをタンク底部付近まで導いて積み込む液化天然ガス積込配管系統から分岐して、積込液化天然ガスをタンク頂部近傍からタンク内に投入して積み込むための頂部液化天然ガス投入系統を設けたので、タンク内の天然ガスを再凝縮させる冷熱源として過冷却状態にある積込液化天然ガスを有効利用し、かつ、頂部液化天然ガス投入系統からタンク内に投入した積込液化天然ガスがタンク内の上部から液面まで自然落下することで、効率のよい熱交換が可能になる。 According to such a liquefied natural gas storage / transport ship of the present invention, when the liquefied natural gas is loaded into the liquefied natural gas storage tank, the loaded liquefied natural gas is vaporized so that the loaded liquefied natural gas is supercooled. The internal pressure of the tank is increased by increasing the internal pressure of the tank, and the boiling liquefied natural gas is branched from the liquefied natural gas loading piping system for introducing and loading the loaded liquefied natural gas to the vicinity of the bottom of the tank. Since the top liquefied natural gas charging system for loading and loading into the tank is provided, the liquefied natural gas in the supercooled state is effectively used as a cooling heat source for recondensing the natural gas in the tank, and the top The loaded liquefied natural gas charged into the tank from the liquefied natural gas charging system naturally falls from the upper part of the tank to the liquid level, thereby enabling efficient heat exchange.

上記の発明において、前記頂部液化天然ガス投入系統は、前記積込液化天然ガスを頂部液化天然ガス流路からカーテン状に自然落下させるもの、前記積込液化天然ガスを頂部液化天然ガス流路に穿設したひとつまたは複数の噴射穴から自然落下させるもの、前記積込液化天然ガスを頂部液化天然ガス流路に取り付けたひとつまたは複数のスプレーノズルから噴霧状に自然落下させるもののいずれでもよいが、頂部液化天然ガス流路の管端から自然落下させる等、頂部液化天然ガス流路を設け、積込液化天然ガスを自然落下させるものであればこの限りではない。
このように、頂部液化天然ガス投入系統から液化天然ガスを重力により自然落下させてタンク内に投入すれば、積込液化天然ガスとタンク内天然ガスとの間は、接触面積が増すとともに接触時間も長くなる。このため、積込液化天然ガスとタンク内天然ガスとの間では熱交換が促進され、効率のよい熱交換を行うことができる。 In the above invention, the top liquefied natural gas charging system is configured to drop the loaded liquefied natural gas in a curtain form from the top liquefied natural gas flow path, and the loaded liquefied natural gas to the top liquefied natural gas flow path. Either one that spontaneously drops from one or a plurality of injection holes that are drilled, one that spontaneously falls in the form of a spray from one or more spray nozzles attached to the top liquefied natural gas flow path may be, This is not limited as long as the top liquefied natural gas flow path is provided such that the top liquefied natural gas flow path is provided to drop naturally from the pipe end of the top liquefied natural gas flow path.
In this way, if the liquefied natural gas is naturally dropped by gravity from the top liquefied natural gas input system and is introduced into the tank, the contact area increases between the loaded liquefied natural gas and the natural gas in the tank and the contact time. Also gets longer. For this reason, heat exchange is accelerated | stimulated between loading liquefied natural gas and the natural gas in a tank, and efficient heat exchange can be performed.

本発明に係る液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法は、極低温状態の液化天然ガスを貯蔵する液化天然ガス貯蔵タンクを備えている液化天然ガス貯蔵・運搬船に適用され、積込液化天然ガスの前記液化天然ガス貯蔵タンクへの積込時に気化する天然ガスの発生量を抑制する液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法であって、前記積込液化天然ガスが過冷却状態となるように、前記積込液化天然ガスが気化した天然ガスでタンク内圧を上げて沸点を上昇させた状態とし、液化天然ガス積込配管系統により前記積込液化天然ガスをタンク底部付近まで導いて積み込むとともに、前記液化天然ガス積込配管系統から分岐させた頂部液化天然ガス投入系統により前記積込液化天然ガスをタンク頂部近傍からタンク内へ自然落下させて積み込むことを特徴とするものである。 The method for suppressing surplus gas generation of a liquefied natural gas storage / transport ship according to the present invention is applied to a liquefied natural gas storage / transport ship equipped with a liquefied natural gas storage tank for storing liquefied natural gas in a cryogenic state, and is loaded liquefaction. A method for suppressing excess gas generation in a liquefied natural gas storage / transport ship that suppresses the generation amount of natural gas that is vaporized when loading the natural gas into the liquefied natural gas storage tank, wherein the loaded liquefied natural gas is in a supercooled state The liquefied natural gas is brought into a state where the internal pressure of the tank is increased by raising the internal pressure of the tank with the natural gas vaporized , and the liquefied natural gas loading piping system guides the loaded liquefied natural gas to the vicinity of the bottom of the tank. loading with, gravity into the liquefied natural gas loading pipe apex is branched from the grid liquefied natural gas input line by the loading LNG tank top tank from the vicinity Te Was and is characterized in that the loading and.

このような液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法によれば、積込液化天然ガスが過冷却状態となるように、積込液化天然ガスが気化した天然ガスでタンク内圧を上げて沸点を上昇させた状態とし、液化天然ガス積込配管系統により積込液化天然ガスをタンク底部付近まで導いて積み込むとともに、液化天然ガス積込配管系統から分岐させた頂部液化天然ガス投入系統により積込液化天然ガスをタンク頂部近傍からタンク内へ自然落下させて積み込むので、タンク内の天然ガスを再凝縮させる冷熱源として過冷却状態の積込液化天然ガスを用い、しかも、積込液化天然ガスがタンク頂部から重力により自然落下して投入されるため、効率のよい熱交換が可能になる。 According to the surplus gas generation suppression method of such a liquefied natural gas storage and transportation ship, the boiling point is increased by increasing the tank internal pressure with the natural gas vaporized from the loaded liquefied natural gas so that the loaded liquefied natural gas becomes supercooled. The liquefied natural gas loading piping system leads the loaded liquefied natural gas to near the bottom of the tank and loads it, and the liquefied natural gas loading piping system branches off from the liquefied natural gas loading piping system. Since liquefied natural gas is naturally dropped from near the top of the tank and loaded into the tank, supercooled loaded liquefied natural gas is used as a cooling heat source for recondensing the natural gas in the tank. Since it falls from the top of the tank and falls by gravity, it is possible to exchange heat efficiently.

上述した本発明によれば、液化天然ガスを液化天然ガス船内貯蔵タンクに積み込むＬＮＧ積込時において、液化天然ガスを加圧すれば過冷却状態になるという低温物質の挙動を応用することにより、気化によりタンク内で発生する天然ガス量を低減し、ＬＮＧ積込により発生する余剰ガス量を最小限に抑えた液化天然ガス貯蔵・運搬船及び液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法を提供するという顕著な効果が得られる。   According to the above-described present invention, by applying the behavior of a low-temperature substance in which liquefied natural gas is supercooled when pressurized, when LNG is loaded into a liquefied natural gas inboard storage tank. Providing a liquefied natural gas storage / transport ship and a method for suppressing excess gas generation in a liquefied natural gas storage / transport ship that reduces the amount of natural gas generated in the tank by vaporization and minimizes the surplus gas generated by LNG loading. A remarkable effect is obtained.

本発明に係る液化天然ガス貯蔵・運搬船及び液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法に関する一実施形態を示しており、（ａ）は積込液化天然ガスを液化天然ガス貯蔵タンクのタンク頂部近傍からタンク内に投入して積み込むための頂部液化天然ガス投入系統を示す図、（ｂ）は液化天然ガス貯蔵タンクに積込液化天然ガスを投入して積み込む際、積込液化天然ガスが過冷却状態となるようにタンク内圧を上げて沸点を上昇させることを示す説明図である。1 shows an embodiment of a liquefied natural gas storage / transport ship and a method for suppressing excessive gas generation in a liquefied natural gas storage / transport ship according to the present invention, wherein (a) shows a tank top portion of a liquefied natural gas storage tank that is loaded with liquefied natural gas. The top liquefied natural gas charging system for loading into the tank from the vicinity and loading, (b) is a diagram showing the excess of the loaded liquefied natural gas when loading and loading the loaded liquefied natural gas into the liquefied natural gas storage tank. It is explanatory drawing which shows raising a tank internal pressure so that it may be in a cooling state, and raising a boiling point. 本発明に係る頂部液化天然ガス投入系統の具体例を示す図であり、（ａ）はカーテン方式、（ｂ）は噴射方式、（ｃ）はスプレー方式である。It is a figure which shows the specific example of the top liquefied natural gas injection | throwing-in system which concerns on this invention, (a) is a curtain system, (b) is an injection system, (c) is a spray system. 浮体式液化天然ガス貯蔵船（ＦＳＲＵ）に液化天然ガスシャトル運搬船から液化天然ガスを積み込むＬＮＧ積込オペレーションを示す説明図である。It is explanatory drawing which shows LNG loading operation which loads liquefied natural gas from a liquefied natural gas shuttle carrier ship to a floating body type liquefied natural gas storage ship (FSRU). 液化天然ガス運搬船（ＬＮＧＣ，ＳＲＶ）に陸上基地から液化天然ガスを積み込むＬＮＧ積込オペレーションを示す説明図である。It is explanatory drawing which shows LNG loading operation which loads liquefied natural gas from a land base into a liquefied natural gas carrier ship (LNGC, SRV). 液化天然ガス貯蔵タンクにおける熱移動を示す説明図である。It is explanatory drawing which shows the heat transfer in a liquefied natural gas storage tank.

以下、本発明に係る液化天然ガス貯蔵・運搬船及び液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法の一実施形態を図面に基づいて説明する。
図３は、浮体式液化天然ガス貯蔵船１Ｆに対し、液化天然ガスシャトル運搬船１Ｓから液化天然ガス（ＬＮＧ）を積み込むＬＮＧ積込オペレーションを示す説明図である。浮体式液化天然ガス貯蔵船１Ｆは、ＬＮＧを貯蔵可能な球形のＬＮＧ船内貯蔵タンク２とともに船上再ガス化装置５を備えたＬＮＧ船であり、洋上に固定して液化天然ガスシャトル船１ＳからＬＮＧを受け入れる。ＬＮＧ船内貯蔵タンク２内のＬＮＧは、必要に応じて船上再ガス化装置５でガス化されて高圧の天然ガス（ＣＮＧ）となり、海底等に敷設された高圧ガス払出配管系統１５を介して、浮体式液化天然ガス貯蔵船１Ｆから陸上施設等へ送出される。 DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of a liquefied natural gas storage / transport ship and a method for suppressing excessive gas generation in a liquefied natural gas storage / transport ship according to the present invention will be described with reference to the drawings.
FIG. 3 is an explanatory diagram showing an LNG loading operation for loading liquefied natural gas (LNG) from the liquefied natural gas shuttle carrier 1S to the floating liquefied natural gas storage ship 1F. The floating liquefied natural gas storage ship 1F is an LNG ship equipped with an onboard regasification device 5 together with a spherical LNG inboard storage tank 2 capable of storing LNG, and is fixed on the ocean to the LNG LNG shuttle ship 1S to LNG. Accept. The LNG in the LNG inboard storage tank 2 is gasified by the on-board regasifier 5 as necessary to become high-pressure natural gas (CNG), and through a high-pressure gas discharge piping system 15 laid on the seabed or the like, It is sent from the floating liquefied natural gas storage ship 1F to land facilities.

一方、液化天然ガスシャトル運搬船１Ｓには、液化基地で球形のＬＮＧ船内貯蔵タンク２に搭載したＬＮＧを受入地点まで輸送し、上述した浮体式液化天然ガス貯蔵船１Ｆに送出するタイプのＬＮＧ船、あるいは、船上で再ガス化した天然ガスをパイプライン等により陸上施設（貯蔵施設や再液化施設等）に送出するタイプのＬＮＧ船がある。図示の液化天然ガスシャトル船１Ｓは、ＬＮＧ船内貯蔵タンク２に搭載したＬＮＧを、タンク内に配設されたＬＮＧポンプ４を用いて、浮体式液化天然ガス貯蔵船１Ｆに送出するタイプのＬＮＧ船である。   On the other hand, in the liquefied natural gas shuttle carrier 1S, the LNG ship of the type that transports the LNG mounted in the spherical LNG inboard storage tank 2 to the receiving point at the liquefaction base and sends it to the floating liquefied natural gas storage ship 1F described above, Alternatively, there is a type of LNG ship that sends natural gas regasified on board to an onshore facility (storage facility, reliquefaction facility, etc.) by a pipeline or the like. The illustrated liquefied natural gas shuttle ship 1S is an LNG ship of a type that sends LNG mounted in an LNG inboard storage tank 2 to a floating liquefied natural gas storage ship 1F using an LNG pump 4 disposed in the tank. It is.

図３において、液化天然ガスシャトル運搬船１Ｓと浮体式液化天然ガス貯蔵船１Ｆとの間は、実線表示のＬＮＧ積込配管系統１２と破線表示のガス払出配管系統１３とにより連結されている。
一方のＬＮＧ積込配管系統１２は、液化天然ガスシャトル運搬船１Ｓから浮体式液化天然ガス貯蔵船１ＦへＬＮＧを送出するために使用され、他方のガス払出配管系統１３は、ＬＮＧ積込時に浮体式液化天然ガス貯蔵船１Ｆ側のＬＮＧ船内貯蔵タンク２で発生する余剰ガスの返送に使用される。
なお、ＬＮＧ積込配管系統１２及びガス払出配管系統１３は、ＬＮＧの荷役（送出）を行う液化天然ガスシャトル運搬船１Ｓ毎に分離及び連結が可能となっている。 In FIG. 3, the liquefied natural gas shuttle carrier 1 </ b> S and the floating liquefied natural gas storage ship 1 </ b> F are connected by an LNG loading piping system 12 indicated by a solid line and a gas discharge piping system 13 indicated by a broken line.
One LNG loading piping system 12 is used to send LNG from the liquefied natural gas shuttle carrier 1S to the floating liquefied natural gas storage ship 1F, and the other gas discharge piping system 13 is a floating type at the time of LNG loading. Used to return surplus gas generated in the LNG inboard storage tank 2 on the liquefied natural gas storage ship 1F side.
In addition, the LNG loading piping system 12 and the gas discharge piping system 13 can be separated and connected for each liquefied natural gas shuttle carrier 1S that handles (sends) LNG.

上述したように、液化天然ガス貯蔵船１Ｆや液化天然ガスシャトル運搬船１Ｓのような液化天然ガス貯蔵・運搬船（以下、ＬＮＧ船）は、極低温状態のＬＮＧを貯蔵する球形のＬＮＧ船内貯蔵タンク２を備えている。
このため、本実施形態では、ＬＮＧ船に搭載されたＬＮＧ船内貯蔵タンク２にＬＮＧを積み込む際、積込液化天然ガス（積込ＬＮＧ）が過冷却状態となるようにタンク内圧を上げて沸点を上昇させるとともに、たとえば図１（ａ）に示すように、積込ＬＮＧをＬＮＧ船内貯蔵タンク２の頂部近傍からタンク内に投入して積み込むための頂部液化天然ガス投入系統（頂部ＬＮＧ投入系統）２０を設けてある。 As described above, a liquefied natural gas storage / transport ship (hereinafter, LNG ship) such as the liquefied natural gas storage ship 1F and the liquefied natural gas shuttle transport ship 1S is a spherical LNG inboard storage tank 2 that stores LNG in a cryogenic state. It has.
For this reason, in this embodiment, when LNG is loaded into the LNG inboard storage tank 2 mounted on the LNG ship, the tank internal pressure is raised so that the loaded liquefied natural gas (loaded LNG) is in a supercooled state, thereby increasing the boiling point. As shown in FIG. 1A, for example, a top liquefied natural gas charging system (top LNG charging system) 20 for loading and loading the loaded LNG from the vicinity of the top of the LNG inboard storage tank 2 into the tank. Is provided.

すなわち、ＬＮＧ船内貯蔵タンク２にＬＮＧを積み込む際には、ＬＮＧ船内貯蔵タンク２を従来の運転圧力（最大０．２５ｂａｒＧ以下）より高い圧力に加圧すると、積込ＬＮＧの沸点がタンク内で上昇して過冷却状態となる。このため、ＬＮＧ船内貯蔵タンク２の内部では、タンク内の天然ガス（残存ガス及び発生ガス）を再凝縮させるための冷熱源として、積込ＬＮＧの顕熱を利用することができる。
この場合、ＬＮＧ船内貯蔵タンク２を球形とすれば、構造上メンブレンタイプのものより高い圧力まで加圧することが可能であるから、積込ＬＮＧの沸点をより高い温度に設定して大きな冷熱量を得ることができる。なお、メンブレンタイプの場合には、加圧の上限が０．６ＢａｒＧ程度と推測されるが、球形の場合には、０．６ＢａｒＧ以上に加圧することは容易である。 That is, when LNG is loaded into the LNG inboard storage tank 2, if the LNG inboard storage tank 2 is pressurized to a pressure higher than the conventional operating pressure (maximum 0.25 barG or less), the boiling point of the loaded LNG increases in the tank. And it becomes a supercooled state. For this reason, inside the LNG ship storage tank 2, the sensible heat of the loaded LNG can be used as a cold heat source for recondensing the natural gas (residual gas and generated gas) in the tank.
In this case, if the LNG inboard storage tank 2 is made spherical, it is possible to pressurize to a higher pressure than that of the membrane type structurally, so the boiling point of the loaded LNG is set to a higher temperature and a large amount of cold heat is generated. Can be obtained. In the case of the membrane type, the upper limit of pressurization is estimated to be about 0.6 BarG, but in the case of a spherical shape, it is easy to pressurize to 0.6 BarG or more.

換言すれば、図１（ｂ）に示すように、ＬＮＧ船内貯蔵タンク２内に投入された積込ＬＮＧは、０．２５ＢａｒＧ以上に加圧されて温度Ｔ１の過冷却状態にあり、従って、天然ガスの温度Ｔ２よりも低温の状態（Ｔ１＜Ｔ２）になっているので、相対的に温度が低い過冷却状態の積込ＬＮＧは、図中に白抜矢印Ｈで示すように、タンク内の天然ガスから吸熱して冷却するので、天然ガスを凝縮させて液体のＬＮＧに状態変化させる冷熱源として利用可能になる。   In other words, as shown in FIG. 1 (b), the loaded LNG charged into the LNG inboard storage tank 2 is pressurized to 0.25 BarG or more and is in a supercooled state at the temperature T1. Since the temperature is lower than the gas temperature T2 (T1 <T2), the supercooled loading LNG in the tank has a relatively low temperature, as indicated by the white arrow H in the figure. Since it absorbs heat from natural gas and cools it, it can be used as a cold heat source that condenses natural gas and changes its state to liquid LNG.

このとき、ＬＮＧ船内貯蔵タンク２の内部加圧は、積込ＬＮＧの自己蒸発を利用することで容易に達成できる。
すなわち、ＬＮＧの積込作業を開始することにより、ＬＮＧ船内貯蔵タンク２の内部に投入された積込ＬＮＧが気化して天然ガスとなり、この天然ガスがタンク内圧を上昇させることにより、タンク内に投入された積込ＬＮＧの沸点が上昇して過冷却状態となる。従って、過冷却状態の積込ＬＮＧは、タンク内に存在して余剰ガスの原因となる天然ガスを冷却する冷熱源となり、天然ガスから吸熱することにより凝縮させてＬＮＧとすることができる。なお、上述した内部加圧を行う場合、ガス払出配管系統１３に設けた図示省略の開閉弁は閉じられる。 At this time, the internal pressurization of the LNG inboard storage tank 2 can be easily achieved by utilizing the self-evaporation of the loaded LNG.
That is, by starting the loading operation of LNG, the loading LNG charged into the LNG inboard storage tank 2 is vaporized to become natural gas, and this natural gas raises the tank internal pressure, thereby The boiling point of the loaded LNG is increased and the supercooled state is reached. Therefore, the supercooled loading LNG serves as a cooling source for cooling the natural gas that is present in the tank and causes excess gas, and can be condensed into LNG by absorbing heat from the natural gas. In addition, when performing the internal pressurization mentioned above, the on-off valve not shown provided in the gas discharge piping system 13 is closed.

頂部ＬＮＧ投入系統２０は、たとえば図１（ａ）に示すように、ＬＮＧ積込配管系統１２から分岐して設けられた配管系統であり、ＬＮＧ船内貯蔵タンク２の頂部付近には、頂部液化天然ガス流路（頂部ＬＮＧ流路）２１を備えている。
すなわち、既存のＬＮＧ積込配管系統１２は、ＬＮＧ船内貯蔵タンク２のタンク底部付近まで導かれており、従って、顕熱差による熱交換は、図１（ｂ）に示した白抜矢印Ｈのように、タンク内のＬＮＧ液面において液相とガス相との間で局所的に行われるのみであり、凝縮量は充分でない。 The top LNG charging system 20 is a piping system provided by branching from the LNG loading piping system 12, for example, as shown in FIG. 1 (a). In the vicinity of the top of the LNG inboard storage tank 2, the top liquefied natural A gas flow path (top LNG flow path) 21 is provided.
In other words, the existing LNG loading piping system 12 is led to the vicinity of the tank bottom of the LNG inboard storage tank 2, and therefore heat exchange due to the sensible heat difference is indicated by the white arrow H shown in FIG. Thus, it is only performed locally between the liquid phase and the gas phase on the LNG liquid level in the tank, and the amount of condensation is not sufficient.

しかし、上述した頂部ＬＮＧ投入系統２０を設けることにより、頂部ＬＮＧ投入系統２０から投入される積込ＬＮＧとタンク内に存在している天然ガスとは、積込ＬＮＧがタンク内の上部からＬＮＧ液面まで自然落下することにより、図１（ａ）に白抜矢印Ｈａで示すような熱交換が行われるので、接触面積が増大することに加えて長い接触時間を確保できるようになる。この結果、積込ＬＮＧとタンク内に存在している天然ガスとの間では、互いの熱交換が促進されて熱交換効率が向上する。なお、図中の白抜矢印Ｈｂは、ＬＮＧ船内貯蔵タンク２と外気との熱交換を示している。   However, by providing the top LNG charging system 20 described above, the loading LNG charged from the top LNG charging system 20 and the natural gas present in the tank are the same as the loading LNG from the upper part in the tank. By naturally falling to the surface, heat exchange as indicated by the white arrow Ha in FIG. 1A is performed, so that a long contact time can be secured in addition to an increase in the contact area. As a result, mutual heat exchange is promoted between the loading LNG and the natural gas present in the tank, and the heat exchange efficiency is improved. The white arrow Hb in the figure indicates heat exchange between the LNG inboard storage tank 2 and the outside air.

頂部ＬＮＧ投入系統２０の具体的な構成例としては、たとえば図２（ａ）に示す頂部ＬＮＧ投入系統２０Ａのように、タンク内において積込ＬＮＧをカーテン状に自由落下させるように構成されたものがある。この場合の頂部ＬＮＧ流路２１Ａは、上部を開放した樋状のＬＮＧ流路２２とされ、内周側壁面２２ａより低く設定した外周側壁面２２ｂから積込ＬＮＧを略全周にわたって溢流させることにより、重力により積込ＬＮＧをカーテン状に自然落下させるものである。   As a specific configuration example of the top LNG charging system 20, for example, the top LNG charging system 20A shown in FIG. 2A is configured to freely drop the loading LNG in a curtain shape in the tank. There is. The top LNG flow path 21A in this case is a bowl-shaped LNG flow path 22 having an open upper portion, and overflows the loaded LNG from the outer peripheral side wall face 22b set lower than the inner peripheral side wall face 22a over substantially the entire circumference. Thus, the loaded LNG is naturally dropped into a curtain shape by gravity.

このように、積込ＬＮＧがＬＮＧ船内貯蔵タンク２の内部で頂部ＬＮＧ流路２１Ａからカーテン状に自然落下すると、カーテン状の積込ＬＮＧとタンク内の天然ガスとの接触面積は、図１（ｂ）に示したタンク内底部付近から投入される場合のように、ＬＮＧ液面のみと接触する場合の接触面積と比較して、カーテン状の面積分だけ増大する。また、頂部ＬＮＧ流路２１Ａから投入される積込ＬＮＧは自然落下であるため、比較的長い接触時間を確保することもできる。
すなわち、頂部ＬＮＧ投入系統２０Ａから投入される積込ＬＮＧとタンク内に存在している天然ガスとは、接触面積の増大に加えて長い接触時間を確保できるようになるので、互いの熱交換が促進されて熱交換効率が向上する。 Thus, when the loading LNG naturally falls like a curtain from the top LNG flow path 21A inside the LNG inboard storage tank 2, the contact area between the curtain-shaped loading LNG and the natural gas in the tank is as shown in FIG. Compared with the contact area when contacting only the LNG liquid level as in the case where the tank is introduced from the vicinity of the bottom in the tank shown in b), it is increased by the curtain-like area. Moreover, since the loading LNG thrown in from the top part LNG flow path 21A is a natural fall, it can also ensure comparatively long contact time.
That is, the loading LNG charged from the top LNG charging system 20A and the natural gas existing in the tank can secure a long contact time in addition to an increase in the contact area. It is promoted to improve the heat exchange efficiency.

ところで、上述した頂部ＬＮＧ投入系統２０は、積込ＬＮＧを頂部ＬＮＧ流路２１Ａからカーテン状に自然落下させる頂部ＬＮＧ投入系統２０Ａに限定されることはなく、たとえば下記の変形例が可能である。
図２（ｂ）に示す第１変形例の頂部ＬＮＧ投入系統２０Ｂは、配管材料を頂部ＬＮＧ流路２１Ｂに、積込ＬＮＧを噴射する１または複数の噴射穴２３を穿設したものである。この噴射穴２３は、噴射した積込ＬＮＧを各噴射穴２３から略円錐状に拡散させるとともに、噴射した積込ＬＮＧをタンク内のＬＮＧ液面まで重力により自然落下させる噴射方式となる。この場合の噴射穴２３は、熱交換効率を向上させるため、頂部ＬＮＧ流路２１Ｂの全面にわたって等ピッチに配置することが望ましい。 By the way, the top LNG charging system 20 described above is not limited to the top LNG charging system 20A that naturally drops the loading LNG from the top LNG flow path 21A in a curtain shape, and for example, the following modifications are possible.
The top LNG charging system 20B of the first modification shown in FIG. 2 (b) is one in which one or a plurality of injection holes 23 for injecting the loading LNG are formed in the top LNG flow path 21B. The injection hole 23 is an injection method in which the injected loading LNG is diffused in a substantially conical shape from each of the injection holes 23 and the injected loading LNG is naturally dropped by gravity to the LNG liquid level in the tank. The injection holes 23 in this case are desirably arranged at an equal pitch over the entire surface of the top LNG flow path 21B in order to improve heat exchange efficiency.

図２（ｃ）に示す第２変形例の頂部ＬＮＧ投入系統２０Ｃは、配管材料を頂部ＬＮＧ流路２１Ｃに、積込ＬＮＧを噴霧状に噴射する１または複数のスプレーノズル２４を取り付けたものであり、各スプレーノズル２４から積込ＬＮＧを噴霧状に噴射して自然落下させるスプレー方式となる。この場合のスプレーノズル２４についても、熱交換効率を向上させるため、頂部ＬＮＧ流路２１Ｃの全面にわたって等ピッチに配置することが望ましい。   The top LNG charging system 20C of the second modification shown in FIG. 2 (c) is one in which one or a plurality of spray nozzles 24 for injecting the loaded LNG in a spray form are attached to the top LNG flow path 21C. There is a spray method in which the loaded LNG is sprayed from each spray nozzle 24 in a spray form and is naturally dropped. The spray nozzles 24 in this case are also desirably arranged at an equal pitch over the entire surface of the top LNG flow path 21C in order to improve heat exchange efficiency.

このように、カーテン方式、噴射方式及びスプレー方式のいずれかを採用し、頂部ＬＮＧ投入系統２０から積込ＬＮＧを自然落下させてタンク内に投入することにより、積込ＬＮＧとタンク内天然ガスとの間に大きな接触面積や接触時間を確保できるので、効率のよい熱交換が可能になる。また、たとえばスプレー方式のように、タンク内を自然落下する積込ＬＮＧを径の小さい粒子にすることは、タンク内天然ガスとの接触面積がより一層大きくなるので、熱交換の効率向上に有効である。
なお、カーテン方式、噴射方式及びスプレー方式については、単独採用に限定されることはなく、複数の方式を適宜組み合わせたものでもよい。 In this way, any one of the curtain system, the injection system, and the spray system is adopted, and the loaded LNG is naturally dropped from the top LNG charging system 20 and is introduced into the tank, so that the loaded LNG and the natural gas in the tank are Since a large contact area and contact time can be ensured during this period, efficient heat exchange becomes possible. In addition, for example, as in the spray method, it is effective to improve the efficiency of heat exchange by making the loaded LNG that naturally falls in the tank into particles with a small diameter because the contact area with the natural gas in the tank is further increased. It is.
In addition, about a curtain system, an injection system, and a spray system, it is not limited to single adoption, What combined several systems suitably may be used.

このように、上述した本実施形態のＬＮＧ船では、ＬＮＧ船内貯蔵タンク２に積込ＬＮＧを投入して積み込む際、積込ＬＮＧが過冷却状態となるようにタンク内圧を上げて沸点を上昇させるとともに、積込ＬＮＧをタンク頂部近傍からタンク内に投入して積み込むための頂部ＬＮＧ投入系統２０を設けたので、タンク内の天然ガスを再凝縮させる冷熱源として過冷却状態にある積込ＬＮＧが保有する冷熱を有効利用することができる。さらに、頂部ＬＮＧ投入系統２０からタンク内に投入した積込ＬＮＧは、カーテン状、噴射による略円錐形状、及び／または噴霧状に自然落下させるようにしたので、タンク内天然ガスとの接触時間や接触面積が増すことにより、熱交換の効率を向上させることができる。   As described above, in the LNG ship according to the present embodiment described above, when the LNG is loaded into the LNG inboard storage tank 2 and loaded, the tank internal pressure is increased so that the loaded LNG is in a supercooled state to raise the boiling point. In addition, since the top LNG charging system 20 for loading and loading the loaded LNG into the tank from the vicinity of the top of the tank is provided, the loaded LNG in a supercooled state is used as a cooling heat source for recondensing the natural gas in the tank. It is possible to effectively use the cold energy that is held. Furthermore, since the loading LNG introduced into the tank from the top LNG introduction system 20 is allowed to fall naturally into a curtain shape, a substantially conical shape by injection, and / or a spray shape, the contact time with the natural gas in the tank, By increasing the contact area, the efficiency of heat exchange can be improved.

そして、上述した構成のＬＮＧ船では、すなわち、極低温状態のＬＮＧを貯蔵するＬＮＧ船内貯蔵タンク２を備えているＬＮＧ船では、積込ＬＮＧをＬＮＧ船内貯蔵タンク２へ積み込む際に気化する天然ガスの発生量について、以下に説明する方法で積込ＬＮＧを投入することにより、抑制が可能となる。
すなわち、ＬＮＧ船の余剰ガス発生抑制方法は、積込ＬＮＧが過冷却状態となるようにＬＮＧ船内貯蔵タンク２のタンク内圧を上げて沸点を上昇させた状態とし、積込ＬＮＧをタンク頂部近傍からタンク内のＬＮＧ液面まで重力により自然落下させて積み込むものであり、この結果、タンク内の天然ガスを再凝縮させる冷熱源として、過冷却状態にある積込ＬＮＧが保有する冷熱を有効入り用することができる。しかも、タンク内の上部から投入される積込ＬＮＧは、タンク頂部から重力により自然落下するので、タンク内天然ガスとの接触時間や接触面積を増して効率のよい熱交換が可能になる。 And in the LNG ship of the structure mentioned above, ie, the LNG ship provided with the LNG ship storage tank 2 which stores LNG of a cryogenic state, the natural gas vaporized when loading LNG into the LNG ship storage tank 2 It is possible to suppress the amount of generated by introducing the loading LNG by the method described below.
That is, the method for suppressing excessive gas generation in the LNG ship is to increase the boiling point by raising the tank internal pressure of the LNG inboard storage tank 2 so that the loaded LNG becomes supercooled, and the loaded LNG from the vicinity of the top of the tank. As a result, the LNG liquid in the tank is naturally dropped by gravity and loaded, and as a result, the cold heat stored in the supercooled LNG is effectively used as a cold heat source for recondensing the natural gas in the tank. can do. Moreover, since the loading LNG introduced from the upper part of the tank naturally falls by gravity from the top of the tank, the contact time with the natural gas in the tank and the contact area can be increased, thereby enabling efficient heat exchange.

そして、上述した液化天然ガス貯蔵・運搬船及び液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法は、より冗長性のある貨物オペレーション、すなわち、ＬＮＧ船内貯蔵タンク２のタンク内圧を減圧することによる天然ガス生成を可能にする。
具体的に説明すると、十分に加圧されたＬＮＧ船内貯蔵タンク２内のＬＮＧは、沸点が高く過冷却状態になっている。このため、ＬＮＧ船内貯蔵タンク２内のＬＮＧが入熱を受けても、その沸点に到達するまでは液温が上がるだけでガスは発生しない。このことは、熱をＬＮＧ内に溜めた状態と言い換えることができる。 The above-described liquefied natural gas storage / transport ship and the surplus gas generation suppression method for the liquefied natural gas storage / transport ship are more redundant cargo operations, that is, natural gas by reducing the tank internal pressure of the LNG inboard storage tank 2. Enable generation.
More specifically, the LNG in the LNG inboard storage tank 2 that is sufficiently pressurized has a high boiling point and is in a supercooled state. For this reason, even if the LNG in the LNG inboard storage tank 2 receives heat, the liquid temperature only rises and no gas is generated until the boiling point is reached. This can be paraphrased as a state where heat is accumulated in the LNG.

逆に、ガス払出配管系統１３に設けた図示省略の開閉弁を開くなどしてＬＮＧ船内貯蔵タンク２のタンク内圧を下げると、ＬＮＧの飽和温度が下がるため、一部のＬＮＧがガス化することになる。この原理を利用すれば、ＬＮＧ積込後のオペレーションにおいて、たとえばＬＮＧ船機関部３等のようなガス消費先の必要に応じて、ＬＮＧ船内貯蔵タンク２のタンク内圧をコントロールすれば、天然ガスを自由に生成できるようになる。   On the contrary, if the tank internal pressure of the LNG inboard storage tank 2 is lowered by opening an on-off valve (not shown) provided in the gas discharge piping system 13, the saturation temperature of the LNG is lowered, so that a part of the LNG is gasified. become. If this principle is used, in the operation after LNG loading, if the tank internal pressure of the LNG inboard storage tank 2 is controlled according to the needs of the gas consuming destination such as the LNG ship engine section 3, etc., natural gas is supplied. It can be generated freely.

上述した本実施形態によれば、ＬＮＧをＬＮＧ船内貯蔵タンク２に積み込むＬＮＧ積込時において、ＬＮＧを加圧すれば過冷却状態になるという低温物質の挙動を応用することにより、気化によりタンク内で発生する天然ガス量を低減し、ＬＮＧ積込により発生する余剰ガス量を最小限に抑えることができる。
従って、ＬＮＧ船内貯蔵タンク２にＬＮＧを積み込む際には余剰の天然ガスが発生しないため、従来のように船上の圧縮機にて天然ガスを陸上基地へ返送し、焼却処理をする必要がない。すなわち、天然ガスを返送する圧縮機の運転に必要な動力や、天然ガスを無駄に消費するガス焼却処理が不要となる。また、浮体式液化天然ガス貯蔵船１ＦのようなＬＮＧ船では、再液化処理装置のような余剰ガスの処理装置について、不要または小型化することが可能になる。 According to the above-described embodiment, when LNG is loaded into the LNG inboard storage tank 2, by applying the behavior of a low-temperature substance that is supercooled if LNG is pressurized, It is possible to reduce the amount of natural gas generated in the above and minimize the amount of surplus gas generated by LNG loading.
Accordingly, when LNG is loaded into the LNG inboard storage tank 2, no surplus natural gas is generated, so that it is not necessary to return the natural gas to the land base by the on-board compressor and to incinerate it as in the prior art. That is, the power necessary for the operation of the compressor that returns the natural gas and the gas incineration process that wastes the natural gas are unnecessary. Further, in an LNG ship such as a floating liquefied natural gas storage ship 1F, a surplus gas processing device such as a reliquefaction processing device can be unnecessary or downsized.

また、ＬＮＧ船内貯蔵タンク２の内圧を減圧すれば、減圧に応じたガス化量の調整が可能になり、従って、天然ガスを意図的に生成することができる。このようなガス化量調整は、たとえば再ガス化装置５のように、従来のＬＮＧ船で一般的に設置されている強制ガス化装置（ベーパライザー）でガス化量を調整する手法と比較して、蒸気等の熱源が不要であるなど効率的かつ簡易な手法となる。
このように、上述した本実施形態は、ＬＮＧ船内貯蔵タンク２を備えたＬＮＧ船等の船舶において、ＬＮＧ船内貯蔵タンク２にＬＮＧを積み込む場合に適用されるものであり、船舶の種類等について上述した実施形態に限定されることはなく、その要旨を逸脱しない範囲内において適宜変更することができる。 Further, if the internal pressure of the LNG inboard storage tank 2 is reduced, the gasification amount can be adjusted according to the reduced pressure, and therefore natural gas can be intentionally generated. Such gasification amount adjustment is compared with a method of adjusting the gasification amount with a forced gasifier (vaporizer) generally installed in a conventional LNG ship, such as the regasification device 5. Thus, it is an efficient and simple method such that a heat source such as steam is unnecessary.
As described above, the above-described embodiment is applied to the case where the LNG is loaded into the LNG inboard storage tank 2 in a ship such as an LNG ship provided with the LNG inboard storage tank 2. The present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the scope of the invention.

１ 液化天然ガス運搬船
１Ｓ 液化天然ガスシャトル運搬船
１Ｆ 浮体式液化天然ガス貯蔵船
２ 液化天然ガス（ＬＮＧ）船内貯蔵タンク
１２ 液化天然ガス（ＬＮＧ）積込配管系統
１３ ガス払出配管系統
２０，２０Ａ〜２０Ｃ 頂部液化天然ガス投入系統（頂部ＬＮＧ投入系統）
２１，２１Ａ〜２１Ｃ 頂部液化天然ガス流路（頂部ＬＮＧ流路）
２２ 液化天然ガス（ＬＮＧ）流路
２３ 噴射穴
２４ スプレーノズル
1 liquefied natural gas carrier 1S liquefied natural gas shuttle carrier 1F floating liquefied natural gas storage ship 2 liquefied natural gas (LNG) inboard storage tank 12 liquefied natural gas (LNG) loading piping system 13 gas discharge piping system 20, 20A-20C Top liquefied natural gas input system (top LNG input system)
21, 21A-21C Top liquefied natural gas flow path (top LNG flow path)
22 liquefied natural gas (LNG) flow path 23 spray hole 24 spray nozzle

Claims (5)

極低温状態の液化天然ガスを貯蔵する液化天然ガス貯蔵タンクを備えている液化天然ガス貯蔵・運搬船であって、
前記液化天然ガス貯蔵タンクに前記液化天然ガスを積み込む際、積込液化天然ガスが過冷却状態となるように、前記積込液化天然ガスが気化した天然ガスでタンク内圧を上げて沸点を上昇させるとともに、
前記積込液化天然ガスをタンク底部付近まで導いて積み込む液化天然ガス積込配管系統から分岐して、前記積込液化天然ガスをタンク頂部近傍からタンク内に投入して積み込むための頂部液化天然ガス投入系統を設けたことを特徴とする液化天然ガス貯蔵・運搬船。 A liquefied natural gas storage / transport ship equipped with a liquefied natural gas storage tank for storing liquefied natural gas in a cryogenic state,
When loading the liquefied natural gas into the liquefied natural gas storage tank, the internal pressure of the tank is increased by the natural gas vaporized from the loaded liquefied natural gas so that the boiling point is raised so that the loaded liquefied natural gas becomes supercooled. With
The top liquefied natural gas is branched from the liquefied natural gas loading piping system that guides and loads the loaded liquefied natural gas to the vicinity of the bottom of the tank, and the loaded liquefied natural gas is loaded into the tank from near the tank top. A liquefied natural gas storage / transport ship, characterized by the introduction of an input system. 前記頂部液化天然ガス投入系統は、前記積込液化天然ガスを頂部液化天然ガス流路からカーテン状に自然落下させることを特徴とする請求項１に記載の液化天然ガス貯蔵・運搬船。   2. The liquefied natural gas storage / transport ship according to claim 1, wherein the top liquefied natural gas charging system naturally drops the loaded liquefied natural gas in a curtain shape from the top liquefied natural gas flow path. 3. 前記頂部液化天然ガス投入系統は、前記積込液化天然ガスを頂部液化天然ガス流路に穿設したひとつまたは複数の噴射穴から自然落下させることを特徴とする請求項１に記載の液化天然ガス貯蔵・運搬船。   2. The liquefied natural gas according to claim 1, wherein the top liquefied natural gas charging system spontaneously drops the loaded liquefied natural gas from one or a plurality of injection holes formed in the top liquefied natural gas flow path. Storage and transport ship. 前記頂部液化天然ガス投入系統は、前記積込液化天然ガスを頂部液化天然ガス流路に取り付けたひとつまたは複数のスプレーノズルから噴霧状に自然落下させることを特徴とする請求項１に記載の液化天然ガス貯蔵・運搬船。   2. The liquefaction according to claim 1, wherein the top liquefied natural gas charging system spontaneously drops the loaded liquefied natural gas in a spray form from one or a plurality of spray nozzles attached to the top liquefied natural gas flow path. Natural gas storage and transport ship. 極低温状態の液化天然ガスを貯蔵する液化天然ガス貯蔵タンクを備えている液化天然ガス貯蔵・運搬船に適用され、積込液化天然ガスの前記液化天然ガス貯蔵タンクへの積込時に気化する天然ガスの発生量を抑制する液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法であって、
前記積込液化天然ガスが過冷却状態となるように、前記積込液化天然ガスが気化した天然ガスでタンク内圧を上げて沸点を上昇させた状態とし、液化天然ガス積込配管系統により前記積込液化天然ガスをタンク底部付近まで導いて積み込むとともに、前記液化天然ガス積込配管系統から分岐させた頂部液化天然ガス投入系統により前記積込液化天然ガスをタンク頂部近傍からタンク内へ自然落下させて積み込むことを特徴とする液化天然ガス貯蔵・運搬船の余剰ガス発生抑制方法。 Natural gas applied to a liquefied natural gas storage / transport ship equipped with a liquefied natural gas storage tank for storing liquefied natural gas in a cryogenic state and vaporized when the loaded liquefied natural gas is loaded into the liquefied natural gas storage tank A method for suppressing excess gas generation in a liquefied natural gas storage / transport ship that suppresses the generation amount of
As the loading liquefied natural gas is supercooled state, wherein the loading liquefied natural gas to raise the tank pressure in natural gas vaporized in a state of increasing the boiling point, the product by liquefied natural gas loading pipe system The liquefied natural gas is led to near the bottom of the tank and loaded, and the loaded liquefied natural gas is naturally dropped from the vicinity of the tank top into the tank by the top liquefied natural gas charging system branched from the liquefied natural gas loading piping system. A method for suppressing excessive gas generation in a liquefied natural gas storage / transport ship, characterized by being loaded.
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