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JP3673127B2 - Boil-off gas reliquefaction method - Google Patents

Boil-off gas reliquefaction method Download PDF

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Publication number
JP3673127B2
JP3673127B2 JP31718299A JP31718299A JP3673127B2 JP 3673127 B2 JP3673127 B2 JP 3673127B2 JP 31718299 A JP31718299 A JP 31718299A JP 31718299 A JP31718299 A JP 31718299A JP 3673127 B2 JP3673127 B2 JP 3673127B2
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Prior art keywords
gas
boil
liquid
drum
nitrogen
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JP31718299A
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Japanese (ja)
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JP2001132896A (en
Inventor
俊和 入江
宣夫 幡中
孝司 三橋
栄治 富永
和彦 大竹
勝 岡
守孝 中村
元裕 大森
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Chiyoda Corp
Mitsubishi Heavy Industries Ltd
Nippon Yusen KK
Osaka Gas Co Ltd
Original Assignee
Chiyoda Corp
Mitsubishi Heavy Industries Ltd
Nippon Yusen KK
Osaka Gas Co Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F25J1/0025—Boil-off gases "BOG" from storages
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/0045—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by vaporising a liquid return stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/005—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by expansion of a gaseous refrigerant stream with extraction of work
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/007—Primary atmospheric gases, mixtures thereof
    • F25J1/0072—Nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0203—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle
    • F25J1/0208—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0285—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings
    • F25J1/0288—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0292—Refrigerant compression by cold or cryogenic suction of the refrigerant gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/04—Mixing or blending of fluids with the feed stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/62—Details of storing a fluid in a tank

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、液化ガスの貯蔵・運搬において貯槽から発生するボイルオフガスを再液化するための再液化方法に関し、特に液化手段にて液化した後に気液分離を行い、ここで得られた液のみを貯槽に戻すようにした再液化方法に関するものである。
【０００２】
【従来の技術】
ＬＮＧの貯槽から発生するボイルオフガス（以下、ＢＯＧと呼称する）の再液化を行う際に、ＢＯＧを熱交換器で飽和状態まで冷却して液化した後、一旦気液分離ドラムに導き、ここで分離された液のみを貯槽に戻す方法が知られている（特開平７−１５７７８２号公報参照）。
【０００３】
【発明が解決しようとする課題】
この方法では、気液分離ドラム内のガス体に、メタン等の炭化水素の未凝縮分と、不純物としての窒素を主体とした非凝縮分とが含まれ、その取り扱いが問題となる。すなわち、単に廃ガスとしてボイラー等で処理したのでは、有用な炭化水素を放出することになり、経済性の面で望ましくなく、他方、炭化水素の回収を優先させて圧縮機の上流等へ合流させるようにすると、不純物としての窒素により圧縮機や冷却器での処理量を徒に増加させる不都合が生じる。
【０００４】
本発明は、このような従来技術の問題点を解消するべく案出されたものであり、その主な目的は、メタン等の有用分の排出を抑えつつ、不純物としての窒素を効率的に除去することが可能なＢＯＧの再液化方法を提供することにある。
【０００５】
【課題を解決するための手段】
このような目的を果たすために、本発明においては、窒素を不純物として含む液化ガスの貯槽から発生するＢＯＧを、液化手段にて液化した後に気液分離を行い、ここで得られた液を貯槽に戻すようにしたＢＯＧの再液化方法において、気液分離により得られた液を、貯槽から液化手段に向かうＢＯＧを流通させるドラムに環流し、ここで液中に含まれる窒素を減圧によりＢＯＧ中にフラッシュさせた上で、その液を当該ドラムから引き抜いて貯槽に戻し、ドラムに環流された液が当該ドラムにおいてＢＯＧと接触することにより、ＢＯＧの温度を液化手段の入口で一定に保持するようにしたものとした。
【０００６】
これによると、ＢＯＧ中にフラッシュした窒素は、ＢＯＧと共に圧縮機や冷却器等からなる液化手段に送られ、この液化手段や気液分離用のドラムとこれらの連絡配管等で構成される再液化装置内に窒素が濃縮される。そして、気液分離により得られたガス体はボイラーで燃焼させることによって系外に排出され、これによりメタン等の有用分の排出を抑えつつ、不純物としての窒素を効率的に除去することが可能となる。しかも、液化手段上流のドラムに環流された液が貯槽からのＢＯＧと接触することにより、ＢＯＧ温度を液化手段の入口で一定に保持することができるため、ＢＯＧ発生量の増減による負荷変動に対するＢＯＧ液化装置内の温度制御が容易になる。なお、窒素分をフラッシュさせるためのドラムは、貯槽からのＢＯＧに同伴する液滴を除去するために液化手段上流に設けられるミスト分離用ドラムと兼用することが構成を簡略化する上で望ましい。
【０００７】
【発明の実施の形態】
以下に添付の図面を参照して本発明の構成を詳細に説明する。
【０００８】
図１は、本発明が適用されたＢＯＧの再液化を行う冷却システムの概略構成を示している。ここでは、液化ガスとしてのＬＮＧの貯蔵・運搬においてＬＮＧタンク１から発生するＢＯＧが、ＢＯＧコンプレッサ２により圧縮された後、熱交換器３により冷却されて再液化するようになっている。
【０００９】
ＢＯＧコンプレッサ２の上流には、ドラム内にデミスタを備えた構造のミスト分離用ドラム５が設けられており、ＬＮＧタンク１から送られてくるＢＯＧに含まれる液滴が除去され、これによりＢＯＧコンプレッサ２への液滴の同伴を防止している。
【００１０】
熱交換器３の下流側には、気液分離用ドラム６が設けられている。この気液分離用ドラム６では、熱交換器３にてＢＯＧを飽和状態まで冷却して得られた液から、炭化水素の未凝縮分、並びに不純物としての窒素を主体とした非凝縮分を含むガス体が分離され、適宜にバルブ７を開放させることでガス体を抜き出すことができる。
【００１１】
他方、気液分離用ドラム６内の飽和状態の液は、バルブ８を開放させてＬＮＧタンク１に戻される他、制御バルブ１０にて気液分離用ドラム６内の液面を一定に保持しながら連絡配管９を経てミスト分離用ドラム５に環流される。ここで、飽和液は減圧され、その中に含まれる窒素が、ＬＮＧタンク１から送られてきたＢＯＧ中にフラッシュして液から分離される。ＢＯＧ中にフラッシュした窒素は、ＢＯＧと共にＢＯＧコンプレッサ２に送られる。ミスト分離用ドラム５に残留する液は、返送ポンプ１１により引き抜かれてＬＮＧタンク１へ圧送される。
【００１２】
これにより、ＢＯＧコンプレッサ２、熱交換器３、ミスト分離用ドラム５、気液分離用ドラム６、並びにこれらの連絡配管で構成される再液化装置内に窒素分が濃縮され、気液分離用ドラム６内のガス体をバルブ７の開放によりボイラーで燃焼させて系外に排出することで、メタン等の有用分の排出を抑えつつ、不純物としての窒素を効率的に除去することができる。他方、液体は不純物量が減少して濃縮された状態でＬＮＧタンク１ヘ戻される。そして、ミスト分離用ドラム５に環流された液がＬＮＧタンク１からのＢＯＧと接触することにより、ＢＯＧ温度をＢＯＧコンプレッサ２の入口で一定に保持することができるため、ＢＯＧ発生量の増減による負荷変動に対してＢＯＧ再液化装置内の温度制御が容易になる。
【００１３】
熱交換器３においてＢＯＧを液化するための冷熱は、窒素を冷媒としたクローズドエキスパンダサイクルによる窒素冷凍サイクル１３により供給される。この窒素冷凍サイクル１３では、熱交換器３を出た冷媒窒素が、窒素コンプレッサ１４〜１６、並びにインタクーラ１７・１８及びアフタクーラ１９により冷却されながら圧縮される。
【００１４】
アフタクーラ１９を出た冷媒窒素は、さらにブースタコンプレッサ２０で圧縮され、ついでアフタクーラ２１で冷却された後、熱交換器３へ送られる。熱交換器３では、窒素冷却部２２において冷媒窒素が低温窒素との熱交換により冷却される。熱交換器３を出た冷媒窒素は、エキスパンダ２３に送られ、ここで減圧により膨張してＢＯＧ再液化に要する冷熱を生成し、熱交換器３に送られる。エキスパンダ２３での冷媒窒素を減圧する際の仕事でブースタコンプレッサ２０が駆動される。
【００１５】
なお、本実施形態においては、ＬＮＧを例に説明を行ったが、本発明はこれに限定されるものではなく、この他の液化ガス、例えばＬＰＧにも適用することができる。
【００１６】
【実施例】
以下に、本発明による方法をＬＮＧのボイルオフガスの再液化に適用した際の非凝縮ガス中の窒素含有量に関する算出結果を示す。また比較のために従来の方法による値も併記する。なお、ここでは、ボイルオフガス中の窒素濃度を２．５％、５％、１０％とした３ケースに分け、各ケース毎に非凝縮ガス量を５０ｋｇｍｏｌ／ｈ、１００ｋｇｍｏｌ／ｈ、１５０ｋｇｍｏｌ／ｈとした例を示す。
【００１７】
まず、ボイルオフガス中の窒素濃度が２．５％の場合の例を次の表１、表２及び表３に示す。
【００１８】
【表１】

Figure 0003673127
【００１９】
【表２】
Figure 0003673127
【００２０】
【表３】
Figure 0003673127
【００２１】
次に、ボイルオフガス中の窒素濃度が５％の場合の例を、次の表４、表５及び表６に示す。
【００２２】
【表４】
Figure 0003673127
【００２３】
【表５】
Figure 0003673127
【００２４】
【表６】
Figure 0003673127
【００２５】
さらに、ボイルオフガス中の窒素濃度が１０％の場合の例を、次の表７、表８及び表９に示す。
【００２６】
【表７】
Figure 0003673127
【００２７】
【表８】
Figure 0003673127
【００２８】
【表９】
Figure 0003673127
【００２９】
以上の例から明らかなように、本発明による方法によれば、従来方法に比較して非凝縮ガス中の窒素濃度が高まり、本発明の有効性が確認された。
【００３０】
【発明の効果】
このように本発明によれば、ＢＯＧを液化した後に気液分離を行って得られた液中の窒素分を液化手段上流のドラムでフラッシュさせることにより、再液化装置内に窒素分を濃縮させることができ、これによりメタン等の有用分の排出を抑えつつ、不純物としての窒素を効率的に除去することが可能となる。しかも、ＢＯＧ温度を液化手段の入口で一定に保持することができるため、ＢＯＧ液化装置内の温度制御が容易になるので、制御システムを簡略化することができる。
【図面の簡単な説明】
【図１】本発明が適用されたボイルオフガスの再液化システムの概略構成を示すブロック図である。
【符号の説明】
１ ＬＮＧタンク
２ ＢＯＧコンプレッサ
３ 熱交換器
５ ミスト分離用ドラム
６ 気液分離用ドラム
７・８ バルブ
９ 連絡配管
１０ 制御バルブ
１１ 返送ポンプ
１３ 窒素冷凍サイクル
１４〜１６ 窒素コンプレッサ
１７・１８ インタクーラ
１９ アフタクーラ
２０ ブースタコンプレッサ
２１ アフタクーラ
２２ 窒素冷却部
２３ エキスパンダ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a re-liquefaction method for re-liquefying boil-off gas generated from a storage tank in storage / transport of liquefied gas, and in particular, gas-liquid separation is performed after liquefaction by liquefaction means, and only the liquid obtained here The present invention relates to a re-liquefaction method that returns to a storage tank.
[0002]
[Prior art]
When re-liquefying the boil-off gas (hereinafter referred to as BOG) generated from the LNG storage tank, the BOG is cooled to a saturated state with a heat exchanger and liquefied, and then led to a gas-liquid separation drum. A method is known in which only the separated liquid is returned to the storage tank (see JP-A-7-157782).
[0003]
[Problems to be solved by the invention]
In this method, the gas body in the gas-liquid separation drum includes an uncondensed portion of hydrocarbon such as methane and a non-condensed portion mainly composed of nitrogen as an impurity, and handling thereof becomes a problem. In other words, if the waste gas is simply treated with a boiler or the like, useful hydrocarbons will be released, which is undesirable in terms of economy. On the other hand, priority is given to the recovery of hydrocarbons and the upstream of the compressor. In this case, there arises a problem that the amount of processing in the compressor and the cooler is increased by nitrogen as an impurity.
[0004]
The present invention has been devised to solve such problems of the prior art, and its main purpose is to efficiently remove nitrogen as an impurity while suppressing emission of useful components such as methane. An object of the present invention is to provide a BOG reliquefaction method that can be used.
[0005]
[Means for Solving the Problems]
In order to achieve such an object, in the present invention, BOG generated from a storage tank of liquefied gas containing nitrogen as an impurity is liquefied by a liquefying means, and then gas-liquid separation is performed, and the liquid obtained here is stored in the storage tank. In the BOG re-liquefaction method, the liquid obtained by gas-liquid separation is circulated to a drum through which the BOG is directed from the storage tank to the liquefaction means, where nitrogen contained in the liquid is reduced in the BOG after having flashed on, to return to the reservoir by pulling out the liquid from the drum, by the liquid that is circulated in the drum is in contact with the BOG in the drum, kept constant at the inlet of the liquefying means the temperature of the BOG It was supposed to be.
[0006]
According to this, the nitrogen flushed in the BOG is sent together with the BOG to the liquefaction means consisting of a compressor, a cooler, etc., and the reliquefaction composed of the liquefaction means, the gas-liquid separation drum and their connecting pipes, etc. Nitrogen is concentrated in the apparatus. And the gas body obtained by gas-liquid separation is discharged out of the system by burning with a boiler, and this makes it possible to efficiently remove nitrogen as impurities while suppressing the discharge of useful components such as methane. It becomes. In addition, since the liquid recirculated to the drum upstream of the liquefaction means comes into contact with the BOG from the storage tank, the BOG temperature can be kept constant at the inlet of the liquefaction means. Temperature control in the liquefaction device is facilitated. In order to simplify the structure, it is desirable that the drum for flushing the nitrogen content is also used as a mist separation drum provided upstream of the liquefaction means in order to remove droplets accompanying the BOG from the storage tank.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
[0008]
FIG. 1 shows a schematic configuration of a cooling system for reliquefying BOG to which the present invention is applied. Here, BOG generated from the LNG tank 1 in storing and transporting LNG as liquefied gas is compressed by the BOG compressor 2 and then cooled by the heat exchanger 3 to be liquefied again.
[0009]
A mist separation drum 5 having a demister in the drum is provided upstream of the BOG compressor 2, and droplets contained in the BOG sent from the LNG tank 1 are removed, whereby the BOG compressor 2 is prevented from being accompanied by droplets.
[0010]
A gas-liquid separation drum 6 is provided on the downstream side of the heat exchanger 3. The gas-liquid separation drum 6 includes an uncondensed portion of hydrocarbons and a non-condensed portion mainly composed of nitrogen as an impurity from a liquid obtained by cooling the BOG to a saturated state in the heat exchanger 3. The gas body is separated, and the gas body can be extracted by opening the valve 7 as appropriate.
[0011]
On the other hand, the saturated liquid in the gas-liquid separation drum 6 is returned to the LNG tank 1 by opening the valve 8, and the liquid level in the gas-liquid separation drum 6 is held constant by the control valve 10. However, it is circulated to the mist separating drum 5 through the connecting pipe 9. Here, the saturated liquid is decompressed, and nitrogen contained therein is separated from the liquid by flushing into the BOG sent from the LNG tank 1. The nitrogen flushed into the BOG is sent to the BOG compressor 2 along with the BOG. The liquid remaining in the mist separation drum 5 is drawn out by the return pump 11 and is pumped to the LNG tank 1.
[0012]
As a result, the nitrogen content is concentrated in the BOG compressor 2, the heat exchanger 3, the mist separation drum 5, the gas-liquid separation drum 6, and the reliquefaction apparatus constituted by these connecting pipes, and the gas-liquid separation drum The gas body in 6 is burned by a boiler by opening the valve 7 and discharged out of the system, so that nitrogen as an impurity can be efficiently removed while suppressing discharge of useful components such as methane. On the other hand, the liquid is returned to the LNG tank 1 in a state where the amount of impurities is reduced and concentrated. Since the liquid recirculated to the mist separation drum 5 comes into contact with the BOG from the LNG tank 1, the BOG temperature can be kept constant at the inlet of the BOG compressor 2. Temperature control in the BOG reliquefaction device is facilitated against fluctuations.
[0013]
Cold heat for liquefying BOG in the heat exchanger 3 is supplied by a nitrogen refrigeration cycle 13 by a closed expander cycle using nitrogen as a refrigerant. In the nitrogen refrigeration cycle 13, the refrigerant nitrogen exiting the heat exchanger 3 is compressed while being cooled by the nitrogen compressors 14 to 16, the intercoolers 17 and 18, and the aftercooler 19.
[0014]
The refrigerant nitrogen that has exited the aftercooler 19 is further compressed by the booster compressor 20, then cooled by the aftercooler 21, and then sent to the heat exchanger 3. In the heat exchanger 3, the refrigerant nitrogen is cooled in the nitrogen cooling unit 22 by heat exchange with low-temperature nitrogen. The refrigerant nitrogen exiting the heat exchanger 3 is sent to the expander 23, where it expands due to decompression to generate cold heat required for BOG reliquefaction, and is sent to the heat exchanger 3. The booster compressor 20 is driven by the work when decompressing the refrigerant nitrogen in the expander 23.
[0015]
In the present embodiment, LNG has been described as an example. However, the present invention is not limited to this, and can be applied to other liquefied gases such as LPG.
[0016]
【Example】
Below, the calculation result regarding the nitrogen content in non-condensable gas at the time of applying the method by this invention to reliquefaction of the boil-off gas of LNG is shown. For comparison, the values according to the conventional method are also shown. Here, the nitrogen concentration in the boil-off gas is divided into three cases of 2.5%, 5%, and 10%, and the amount of non-condensable gas is 50 kgmol / h, 100 kgmol / h, and 150 kgmol / h for each case. An example is shown.
[0017]
First, the following Table 1, Table 2, and Table 3 show examples when the nitrogen concentration in the boil-off gas is 2.5%.
[0018]
[Table 1]
Figure 0003673127
[0019]
[Table 2]
Figure 0003673127
[0020]
[Table 3]
Figure 0003673127
[0021]
Next, examples where the nitrogen concentration in the boil-off gas is 5% are shown in the following Table 4, Table 5 and Table 6.
[0022]
[Table 4]
Figure 0003673127
[0023]
[Table 5]
Figure 0003673127
[0024]
[Table 6]
Figure 0003673127
[0025]
Furthermore, the following Table 7, Table 8 and Table 9 show examples when the nitrogen concentration in the boil-off gas is 10%.
[0026]
[Table 7]
Figure 0003673127
[0027]
[Table 8]
Figure 0003673127
[0028]
[Table 9]
Figure 0003673127
[0029]
As apparent from the above examples, according to the method of the present invention, the nitrogen concentration in the non-condensed gas is increased as compared with the conventional method, and the effectiveness of the present invention has been confirmed.
[0030]
【The invention's effect】
As described above, according to the present invention, the nitrogen content in the liquid obtained by gas-liquid separation after liquefying BOG is flushed with the drum upstream of the liquefaction means, thereby concentrating the nitrogen content in the reliquefaction apparatus. This makes it possible to efficiently remove nitrogen as an impurity while suppressing discharge of useful components such as methane. In addition, since the BOG temperature can be kept constant at the inlet of the liquefaction means, temperature control in the BOG liquefaction apparatus is facilitated, and the control system can be simplified.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a boil-off gas reliquefaction system to which the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 LNG tank 2 BOG compressor 3 Heat exchanger 5 Drum for mist separation 6 Drum for gas-liquid separation 7 and 8 Valve 9 Connection pipe 10 Control valve 11 Return pump 13 Nitrogen refrigeration cycle 14-16 Nitrogen compressor 17 and 18 Intercooler 19 After cooler 20 Booster compressor 21 Aftercooler 22 Nitrogen cooling part 23 Expander

Claims (2)

窒素を不純物として含む液化ガスの貯槽から発生するボイルオフガスを、液化手段にて液化した後に気液分離を行い、ここで得られた液を前記貯槽に戻すボイルオフガスの再液化方法であって、
前記気液分離により得られた液を、前記貯槽から前記液化手段に向かうボイルオフガスを流通させるドラムに環流し、ここで液中に含まれる窒素を減圧によりボイルオフガス中にフラッシュさせた上で、その液を当該ドラムから引き抜いて前記貯槽に戻し、前記ドラムに環流された液が当該ドラムにおいてボイルオフガスと接触することにより、ボイルオフガスの温度を前記液化手段の入口で一定に保持するようにしたことを特徴とするボイルオフガスの再液化方法。A boil-off gas re-liquefaction method in which boil-off gas generated from a storage tank of liquefied gas containing nitrogen as an impurity is gas-liquid separated after liquefying by liquefaction means, and the liquid obtained here is returned to the storage tank,
The liquid obtained by the gas-liquid separation is circulated to a drum through which the boil-off gas from the storage tank toward the liquefaction means is circulated, where nitrogen contained in the liquid is flushed into the boil-off gas by decompression, it returns the liquid to the reservoir is withdrawn from the drum, by the liquid that is circulated in the drum is in contact with the BOG in the drum, so as to maintain the temperature of the boil-off gas constant at the inlet of said liquefied means A method for re-liquefying boil-off gas. 前記液中の窒素をフラッシュさせるためのドラムが、前記貯槽からのボイルオフガスに同伴する液滴を除去するために前記液化手段の上流に設けられるミスト分離用のドラムであることを特徴とする請求項１に記載のボイルオフガスの再液化方法。    The drum for flushing nitrogen in the liquid is a mist separation drum provided upstream of the liquefying means in order to remove droplets accompanying the boil-off gas from the storage tank. Item 2. The boil-off gas reliquefaction method according to Item 1.
JP31718299A 1999-11-08 1999-11-08 Boil-off gas reliquefaction method Expired - Fee Related JP3673127B2 (en)

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JP2008064213A (en) * 2006-09-08 2008-03-21 Chugoku Electric Power Co Inc:The Compressor with bog warmer and power generation system having the same
KR100804954B1 (en) 2007-02-13 2008-02-20 대우조선해양 주식회사 Apparatus and method for reliquefying boil-off gas capable of stabilizing operation start-up
KR100804953B1 (en) 2007-02-13 2008-02-20 대우조선해양 주식회사 Apparatus and method for reliquefying boil-off gas capable of refrigeration load variable operation
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US9003828B2 (en) 2007-07-09 2015-04-14 Lng Technology Pty Ltd Method and system for production of liquid natural gas
JP5132452B2 (en) * 2008-07-07 2013-01-30 東京瓦斯株式会社 BOG reliquefaction equipment
KR101386543B1 (en) 2012-10-24 2014-04-18 대우조선해양 주식회사 System for treating boil-off gas for a ship
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JP6501527B2 (en) * 2015-01-09 2019-04-17 大阪瓦斯株式会社 Boil-off gas reliquefaction plant
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