KR20220080445A - Bog reliquefaction system and method - Google Patents

Bog reliquefaction system and method Download PDF

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KR20220080445A
KR20220080445A KR1020200169556A KR20200169556A KR20220080445A KR 20220080445 A KR20220080445 A KR 20220080445A KR 1020200169556 A KR1020200169556 A KR 1020200169556A KR 20200169556 A KR20200169556 A KR 20200169556A KR 20220080445 A KR20220080445 A KR 20220080445A
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gas
boil
liquid nitrogen
storage tank
unit
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KR1020200169556A
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임문채
권혁
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대우조선해양 주식회사
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • 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
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
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    • F17C9/00—Methods or apparatus for discharging liquefied or solidified gases from vessels not under pressure
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    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/42—Nitrogen
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Abstract

본 발명은, LNG 증발가스의 재액화 시스템 및 방법에 관한 것으로서, 보다 상세하게는, 액체질소와 액화천연가스 저장 시 필연적으로 발생하는 증발가스를 열교환시켜 응축시킬 수 있는 LNG 증발가스의 재액화 시스템 및 방법에 관한 것이다.
LNG 증발가스의 재액화 시스템 및 방법이 개시된다. 본 발명의 LNG 증발가스의 재액화 시스템은, 액화천연가스 저장탱크로부터 공급되는 증발가스를 압축하는 압축부; 압축부에서 압축된 증발가스를 액체질소 공급부에서 공급되는 액체 질소와 열교환을 시키는 열교환부; 및 열교환부에서 열교환된 증발가스를 액화시키는 액화부를 포함한다.The present invention relates to a system and method for re-liquefaction of LNG BOG, and more particularly, to a re-liquefaction system for LNG BOG that can be condensed by heat-exchanging BOG inevitably generated when liquid nitrogen and liquefied natural gas are stored. and methods.
A system and method for reliquefying LNG boil-off gas are disclosed. The LNG boil-off gas re-liquefaction system of the present invention includes: a compression unit for compressing the boil-off gas supplied from a liquefied natural gas storage tank; a heat exchange unit for exchanging the boil-off gas compressed in the compression unit with liquid nitrogen supplied from the liquid nitrogen supply unit; and a liquefaction unit for liquefying the boil-off gas heat-exchanged in the heat exchange unit.

Figure P1020200169556
Figure P1020200169556

Description

LNG 증발가스의 재액화 시스템 및 방법{BOG RELIQUEFACTION SYSTEM AND METHOD}Reliquefaction system and method of LNG boil-off gas {BOG RELIQUEFACTION SYSTEM AND METHOD}

본 발명은, LNG 증발가스의 재액화 시스템 및 방법에 관한 것으로서, 보다 상세하게는, 액체질소와 액화천연가스 저장 시 필연적으로 발생하는 증발가스를 열교환시켜 응축시킬 수 있는 LNG 증발가스의 재액화 시스템 및 방법에 관한 것이다.The present invention relates to a system and method for re-liquefaction of LNG boil-off gas, and more particularly, a re-liquefaction system for LNG boil-off gas that can be condensed by heat-exchanging boil-off gas inevitably generated when liquid nitrogen and liquefied natural gas are stored. and methods.

액화천연가스(LNG)의 저장(상압에서 -163℃)은 외기온도의 차이와 운전조건 - LNG 적재, 하역, 해상조건, 운전상태 등 -의 변화로 인해 증발가스(BOG; Boil Off Gas)가 항상 발생하므로, 상압에 근접한 설계조건을 갖는 액화천연가스 화물창이나 육상의 저장탱크는 증발가스 처리설비(BOGTU, Boil Off Gas Treatment Unit)가 필수적으로 요구된다.Storage of liquefied natural gas (LNG) (-163 ℃ at normal pressure) causes boil-off gas (BOG) Since it always occurs, a BOGTU (Boil Off Gas Treatment Unit) is essential for a liquefied natural gas cargo hold or onshore storage tank having design conditions close to atmospheric pressure.

액화천연가스 운반선의 경우 발생된 증발가스는, 항해 중에는 추진엔진이나 보조엔진의 연료로 사용되지만, 여분은 BOGTU에서 액화되어 LNG 화물창으로 회수되고, 처리설비용량을 초과하여 발생한 경우 가스연소장치(GCU)에서 연소시켜 소모된다.In the case of liquefied natural gas carriers, the BOG generated is used as fuel for propulsion engines or auxiliary engines during voyage, but the excess is liquefied at BOGTU and recovered to the LNG cargo hold. ) is burned and consumed.

기체인 증발가스(대략 -100℃, 대기압 수준)를 -163℃의 액체(LNG)로 상변화시키기 위해 증발잠열(대략 510kJ/kg)을 제거해야 하므로 액화 과정에서 막대한 에너지가 필요하다.In order to phase change the gaseous boil-off gas (about -100℃, atmospheric pressure level) to liquid (LNG) at -163℃, the latent heat of evaporation (about 510kJ/kg) must be removed, so enormous energy is required in the liquefaction process.

이로 인해 현재 액화천연가스 운반선의 경우 크게 아래의 두 가지 방법으로 증발가스를 냉동하여 응축시켜 회수 하나 필요에 따라 혼합형을 사용하기도 한다.For this reason, in the case of current liquefied natural gas carriers, the boil-off gas is frozen and condensed by the following two methods to recover it, but a mixed type is sometimes used if necessary.

① 폐쇄형 냉동사이클(Closed loop refrigeration cycle): 별도의 냉매를 사용한 폐쇄형 냉동사이클(압축기 - 응축기 - JT 밸브 - 압력분리조)을 이용해 발생시킨 저온의 냉매와 증발가스를 열교환시켜 응축시키는 방법① Closed loop refrigeration cycle: A method of heat-exchanging and condensing low-temperature refrigerant and boil-off gas generated using a closed refrigeration cycle (compressor - condenser - JT valve - pressure separation tank) using a separate refrigerant.

② 개방형 냉동사이클(Open loop refrigeration cycle): 증발가스(BOG) 자체를 냉매로 사용하여 압축기와 응축기를 거친 후 JT밸브에서 감압시켜 온도를 강하시킨 후 압력분리조에서 응축된 액화천연가스를 회수하는 방법② Open loop refrigeration cycle: It uses boil-off gas (BOG) itself as a refrigerant, passes through a compressor and a condenser, and then reduces the temperature by reducing the pressure at the JT valve and recovering the condensed liquefied natural gas in the pressure separation tank. Way

하지만, 상기 방법은 그 과정상 복잡한 장치를 사용하여, 초기 투자비용이 매우 높고, 압축된 천연가스의 누설 시 화재 위험성 뿐 아니라 주성분인 메탄이 오존층 파괴의 주범이므로 환경오염 문제도 제기되며, LNG 운반선의 경우 운항과정에서 처리설비에 정비소요가 발생 시 증발가스의 액화가 정지될 수 밖에 없는 문제점이 지적된다.However, the method uses a complicated device in the process, the initial investment cost is very high, and the risk of fire in case of leakage of compressed natural gas, as well as the environmental pollution problem is raised because methane, the main component, is the main culprit of ozone layer destruction, and LNG carrier In the case of the case, the problem is pointed out that the liquefaction of BOG must be stopped when maintenance is required for treatment facilities during operation.

한편, 액체질소(증발잠열, 199kJ/KG)는 비등점이 -196℃로 액화천연가스(-163℃) 보다 낮으므로 증발가스의 응축에 냉매로 사용할 수 있고, 가격이 LNG 대비 1/3로 저렴하며 연소되지 않을 뿐 아니라 대기로 방출 시에도 환경오염에서 자유롭다.On the other hand, liquid nitrogen (latent heat of evaporation, 199kJ/KG) has a boiling point of -196℃, which is lower than liquefied natural gas (-163℃), so it can be used as a refrigerant for the condensation of BOG, and its price is 1/3 cheaper than LNG. It is not combusted and is free from environmental pollution even when released to the atmosphere.

이로 인해 액체질소를 이용한 증발가스의 액화는 소규모 설비의 경우 다양하게 사용되나, 증발잠열이 천연가스의 증발잠열대비 39%에 불과한 단점이 있다. For this reason, liquefaction of boil-off gas using liquid nitrogen is used in various ways in the case of small-scale facilities, but has a disadvantage in that the latent heat of evaporation is only 39% of the latent heat of evaporation of natural gas.

전술한 기술구성은 본 발명의 이해를 돕기 위한 배경기술로서, 본 발명이 속하는 기술분야에서 널리 알려진 종래 기술을 의미하는 것은 아니다.The above-described technical configuration is a background for helping understanding of the present invention, and does not mean a conventional technique widely known in the technical field to which the present invention pertains.

한국등록특허공보 제10-1996288호(대우조선해양 주식회사) 2019. 06. 28.Korea Patent Publication No. 10-1996288 (Daewoo Shipbuilding & Marine Engineering Co., Ltd.) 2019. 06. 28.

따라서 본 발명이 이루고자 하는 기술적 과제는, 액체질소와 액화천연가스 저장 시 필연적으로 발생하는 증발가스를 열교환시켜 응축시킴으로써 종래의 증발가스 액화방법에 따른 투자비 및 운영비를 절감할 수 있는 LNG 증발가스의 재액화 시스템 및 방법을 제공하는 것이다.Therefore, the technical task to be achieved by the present invention is to heat-exchange and condense BOG, which is inevitably generated when liquid nitrogen and liquefied natural gas are stored, thereby reducing investment and operating costs according to the conventional BOG liquefaction method. To provide a liquefaction system and method.

또한, 액체질소가 기체로 변화될 때 부피가 증가(20℃ 기준 649배)하는 것을 이용해 축동력을 회수하여 추가 전력을 생산할 수 있는 LNG 증발가스의 재액화 시스템 및 방법을 제공하는 것이다.Another object of the present invention is to provide a system and method for reliquefying LNG boil-off gas that can generate additional power by recovering shaft power by using an increase in volume (649 times based on 20°C) when liquid nitrogen is changed to gas.

본 발명의 일 측면에 따르면, 액화천연가스 저장탱크로부터 공급되는 증발가스를 압축하는 압축부; 상기 압축부에서 압축된 상기 증발가스를 액체질소 공급부에서 공급되는 액체 질소와 열교환을 시키는 열교환부; 및 상기 열교환부에서 열교환된 상기 증발가스를 액화시키는 액화부를 포함하는 LNG 증발가스의 재액화 시스템이 제공될 수 있다.According to an aspect of the present invention, a compression unit for compressing the boil-off gas supplied from the liquefied natural gas storage tank; a heat exchange unit for exchanging the boil-off gas compressed in the compression unit with liquid nitrogen supplied from the liquid nitrogen supply unit; and a liquefaction unit configured to liquefy the boil-off gas heat-exchanged in the heat exchange unit may be provided.

상기 액체질소 공급부는, 상기 액체 질소가 저장되는 액체질소 저장탱크; 및 상기 액체질소 저장탱크에 저장된 상기 액체 질소를 상기 열교환부로 펌핑시키는 펌프를 포함할 수 있다.The liquid nitrogen supply unit may include: a liquid nitrogen storage tank in which the liquid nitrogen is stored; and a pump for pumping the liquid nitrogen stored in the liquid nitrogen storage tank to the heat exchange unit.

상기 액체질소 저장탱크는 단일벽 또는 진공 이중벽 압력용기로 마련될 수 있다.The liquid nitrogen storage tank may be provided as a single-walled or vacuum double-walled pressure vessel.

상기 압력용기는 보냉재로 감싸질 수 있다.The pressure vessel may be wrapped with an insulating material.

상기 액체질소 저장탱크에서 발생되는 증발 질소는 허용 압력 초과 시 터보 익스팬더로 공급될 수 있다.Evaporated nitrogen generated in the liquid nitrogen storage tank may be supplied to the turbo expander when the allowable pressure is exceeded.

상기 터보 익스팬더에 연결되어 발전되는 발전기를 더 포함할 수 있다.It may further include a generator connected to the turbo expander to generate electricity.

상기 액체질소 저장탱크와 연결되며 상기 액체질소 저장탱크에서 배출되는 질소 가스가 저장되는 질소 가스 저장조를 더 포함할 수 있다.It may further include a nitrogen gas storage tank connected to the liquid nitrogen storage tank and storing nitrogen gas discharged from the liquid nitrogen storage tank.

상기 압축부는, 상기 액화천연가스 저장탱크에서 공급되는 상기 증발가스를 압축시키는 제1 압축기; 및 상기 제1 압축기에서 압축된 상기 증발가스를 압축시키는 제2 압축기를 포함할 수 있다.The compression unit, a first compressor for compressing the boil-off gas supplied from the liquefied natural gas storage tank; and a second compressor for compressing the boil-off gas compressed in the first compressor.

상기 제1 압축기와 상기 제2 압축기를 연결하는 라인에서 분기되며 상기 제2 압축기를 바이패스하여 상기 제2 압축기의 후방 라인에 합류되는 분기부를 더 포함할 수 있다.A branching part branching from a line connecting the first compressor and the second compressor to bypass the second compressor and joining a rear line of the second compressor may be further included.

상기 액화부는, 상기 열교환부에서 응축된 상기 응축 가스를 감압시키는 증발가스 감압밸브; 및 상기 감압밸브에서 감압된 상기 응축 가스를 기체와 액체로 분리하는 플래쉬 드럼을 포함할 수 있다.The liquefaction unit may include: a boil-off gas pressure reducing valve for reducing the pressure of the condensed gas condensed in the heat exchange unit; and a flash drum configured to separate the condensed gas decompressed by the pressure reducing valve into a gas and a liquid.

상기 플래쉬 드럼에서 분리된 기체는 상기 액체천연가스 저장탱크와 상기 압축부를 연결하는 라인으로 공급될 수 있다.The gas separated from the flash drum may be supplied to a line connecting the liquid natural gas storage tank and the compression unit.

상기 압축부에서 압축되어 증발가스 사용처로 공급되는 상기 증발가스를 압축시키는 냉각기를 더 포함할 수 있다.It may further include a cooler for compressing the boil-off gas compressed by the compression unit and supplied to a place where the boil-off gas is used.

상기 압축부와 상기 열교환부를 연결하는 라인에 마련되어 상기 열교환부에서 열교환된 상기 액체 질소의 온도를 상승시켜 체적 유량을 증가시키는 제1 열교환기를 더 포함할 수 있다.It may further include a first heat exchanger provided on a line connecting the compression unit and the heat exchange unit to increase the volumetric flow rate by increasing the temperature of the liquid nitrogen heat-exchanged in the heat exchange unit.

상기 제1 열교환기의 후방에 배치되도록 상기 압축부와 상기 열교환부를 연결하는 라인에 마련되며 상기 제1 열교환기에서 열교환된 상기 증발가스를 냉각시키는 제2 열교환기를 더 포함할 수 있다.A second heat exchanger provided on a line connecting the compression unit and the heat exchange unit to be disposed at the rear of the first heat exchanger to cool the boil-off gas heat-exchanged in the first heat exchanger may be further included.

또한, 본 발명의 다른 측면에 따르면, 액화천연가스 저장탱크에서 발생되는 증발가스를 액체질소 공급부에서 공급되는 액체 질소와 열교환한 후 액화부에서 액화시키는 LNG 증발가스의 재액화 방법이 제공될 수 있다.Further, according to another aspect of the present invention, there may be provided a method for re-liquefying LNG boil-off gas in which the boil-off gas generated in the liquefied natural gas storage tank is liquefied in the liquefaction unit after heat exchange with liquid nitrogen supplied from the liquid nitrogen supply unit. .

본 발명의 실시예들은, 액화를 위한 복잡하고 고가인 장비의 상당부분을 생략할 수 있어 초기투자비를 절감할 수 있고, 선체 내 질소 공급 시스템 등 이너트 시스템(inert system)을 대체할 수 있다.Embodiments of the present invention, it is possible to omit a significant part of the complicated and expensive equipment for liquefaction, thereby reducing the initial investment cost, and can replace an inert system such as a nitrogen supply system in the hull.

또한, 증발가스(BOG) 처리를 위한 설비의 초기 투자비 및 운영비 절감에 따른 수주 경쟁력을 강화할 수 있다.In addition, it is possible to strengthen the competitiveness of winning orders by reducing the initial investment and operating costs of facilities for BOG treatment.

또한, 고순도 질소는 대기방출에 국제 환경법적 제약이 없으며 액체 질소의 비용이 액화천연가스 대비 저렴하므로, 운전비용을 절감할 수 있다.In addition, high-purity nitrogen does not have international environmental restrictions on air emission, and since the cost of liquid nitrogen is cheaper than liquefied natural gas, operating costs can be reduced.

나아가, 천연가스는 고도의 인화성 물질이자 누수 시 오존층을 파괴하는 대표적인 물질이므로, 유사한 목적의 공정장치와 비교 시 탑재량(inventory)을 줄일 수 있어 안전성을 향상시킬 수 있고, 증발가스 액화설비 내 압축기 압력을 낮출 수 있어 누수 가능성을 감소시킴으로써 친환경적인 설비를 구축할 수 있다.Furthermore, since natural gas is a highly flammable material and a representative material that destroys the ozone layer in case of leakage, it is possible to reduce the inventory and improve safety when compared with process equipment for similar purposes, and the pressure of the compressor in the boil-off gas liquefaction facility By reducing the possibility of leakage, eco-friendly facilities can be built.

도 1은 본 발명의 일 실시예에 따른 LNG 증발가스의 재액화 시스템을 개략적으로 도시한 도면이다.
도 2는 본 실시예의 개략적인 작동도이다.1 is a diagram schematically illustrating a system for reliquefying LNG boil-off gas according to an embodiment of the present invention.
2 is a schematic operation diagram of the present embodiment.

본 발명과 본 발명의 동작상의 이점 및 본 발명의 실시에 의하여 달성되는 목적을 충분히 이해하기 위해서는 본 발명의 바람직한 실시예를 예시하는 첨부 도면 및 첨부 도면에 기재된 내용을 참조하여야만 한다.In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

이하, 첨부된 도면을 참조하여 본 발명의 바람직한 실시예를 설명함으로써, 본 발명을 상세히 설명한다. 각 도면에 제시된 동일한 참조부호는 동일한 부재를 나타낸다.Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention with reference to the accompanying drawings. Like reference numerals in each figure indicate like elements.

도 1은 본 발명의 일 실시예에 따른 LNG 증발가스의 재액화 시스템을 개략적으로 도시한 도면이고, 도 2는 본 실시예의 개략적인 작동도이다.1 is a diagram schematically illustrating a system for reliquefying LNG boil-off gas according to an embodiment of the present invention, and FIG. 2 is a schematic operation diagram of this embodiment.

이들 도면에 도시된 바와 같이, 본 실시예에 따른 LNG 증발가스의 재액화 시스템은, 액화천연가스 저장탱크(T)로부터 공급되는 증발가스를 압축하는 압축부(10)와, 액화천연가스와 열교환되는 액체 질소를 저장 및 공급하는 액체질소 공급부(20)와, 압축부(10)에서 압축된 증발가스를 액체질소 공급부(20)에서 공급되는 액체 질소와 열교환시켜 응축시키는 열교환부(30)를 포함한다.As shown in these drawings, the LNG BOG re-liquefaction system according to the present embodiment includes a compression unit 10 for compressing BOG supplied from a liquefied natural gas storage tank T, and heat exchange with liquefied natural gas. It includes a liquid nitrogen supply unit 20 for storing and supplying liquid nitrogen to be used, and a heat exchange unit 30 for condensing the boil-off gas compressed in the compression unit 10 by heat exchange with liquid nitrogen supplied from the liquid nitrogen supply unit 20 . do.

또한, 본 실시예에 따른 LNG 증발가스의 재액화 시스템은, 열교환부(30)에서 열교환된 증발가스를 액화시키는 액화부(40)와, 열교환부(30)에서 열교환에 의해 기체로 상변화된 질소 및/또는 액체질소 공급부(20)에서 발생되는 증발 질소가 허용 압력을 초과 시 제1 밸브(23)를 통해 토출된 증발 질소를 공급받아 작동되는 터보 익스팬더(50)와, 터보 익스팬더(50)에 연결되어 발전되는 발전기(60)를 포함한다. In addition, the LNG boil-off gas re-liquefaction system according to the present embodiment includes a liquefaction unit 40 for liquefying the boil-off gas heat-exchanged in the heat exchange unit 30 , and nitrogen phase-changed into gas by heat exchange in the heat exchange unit 30 . and/or the turbo expander 50 which is operated by receiving the evaporated nitrogen discharged through the first valve 23 when the evaporated nitrogen generated from the liquid nitrogen supply unit 20 exceeds the allowable pressure, and the turbo expander 50 It includes a generator 60 that is connected to generate electricity.

또한, 본 실시예에 따른 LNG 증발가스의 재액화 시스템은, 액체질소 저장탱크(21)와 연결되며 액체질소 저장탱크(21)에서 배출되는 질소 가스가 저장되는 질소 가스 저장조(70)와, 압축부(10)의 제1 압축기(11)와 제2 압축기(12)를 연결하는 라인에서 분기되며 제2 압축기(12)를 바이패스하여 제2 압축기(12)의 후방 라인에 합류되는 분기부(80)를 포함한다. In addition, the LNG boil-off gas reliquefaction system according to this embodiment includes a nitrogen gas storage tank 70 connected to the liquid nitrogen storage tank 21 and storing nitrogen gas discharged from the liquid nitrogen storage tank 21 , and the compression A branching part ( 80).

또한, 본 실시예에 따른 LNG 증발가스의 재액화 시스템은, 압축부(10)와 열교환부(30)를 연결하는 라인에 마련되어 열교환부(30)에서 열교환된 액체 질소의 온도를 상승시켜 체적 유량을 증가시키는 제1 열교환기(90)와, 제1 열교환기(90)의 후방에 배치되도록 압축부(10)와 열교환부(30)를 연결하는 라인에 마련되며 제1 열교환기(90)에서 열교환에 의해 냉각된 증발가스를 선내에서 공급되는 냉각수(C1)와 열교환시켜 추가 냉각시키는 제2 열교환기(100)와, 압축부(10)와 증발가스 사용처를 연결하는 라인에 마련되어 증발가스 사용처로 공급되는 증발가스를 냉각시키는 냉각기(110)를 구비한다.In addition, in the LNG boil-off gas reliquefaction system according to the present embodiment, a volume flow rate is provided in a line connecting the compression unit 10 and the heat exchange unit 30 to increase the temperature of liquid nitrogen heat-exchanged in the heat exchange unit 30 . It is provided in a line connecting the first heat exchanger 90 to increase The second heat exchanger 100 for additional cooling by heat-exchanging the BOG cooled by heat exchange with the cooling water C1 supplied in the ship, and the line connecting the compression unit 10 and the BOG usage point are provided to the BOG usage point. A cooler 110 for cooling the supplied boil-off gas is provided.

본 실시예의 압축부(10)는, 액화천연가스 저장탱크(T)에서 발생된 증발가스를 압축시켜, 유량의 일부는 증발가스 사용처 예를 들어 LNG 선박의 메인엔진이나 보조엔진으로 보내고, 나머지는 열교환부(30)로 보낼 수 있다.The compression unit 10 of this embodiment compresses the BOG generated in the liquefied natural gas storage tank (T), and a portion of the flow rate is sent to the BOG usage place, for example, the main engine or auxiliary engine of the LNG ship, and the rest is It can be sent to the heat exchange unit (30).

본 실시예에서 압축부(10)는, 도 1에 도시된 바와 같이, 액화천연가스 저장탱크(T)에서 공급되는 증발가스를 압축시키는 저단의 제1 압축기(11)와, 제1 압축기(11)에서 압축된 증발가스를 더 높은 압력으로 압축시키는 고단의 제2 압축기(12)를 포함한다. In this embodiment, the compression unit 10, as shown in FIG. 1, a first compressor 11 of a lower stage for compressing the boil-off gas supplied from the liquefied natural gas storage tank T, and the first compressor 11 ) includes a high-stage second compressor 12 for compressing the compressed boil-off gas to a higher pressure.

본 실시예의 압축부(10)는, 증발가스 사용처의 요구 압력에 따라 2단 이상의 압축기를 더 구비할 수 있다. The compression unit 10 of the present embodiment may further include a compressor of two or more stages according to the required pressure of the place of use of the boil-off gas.

본 실시예에서 제1 압축기(11)에서 압축된 증발가스는, 도 1에 도시된 바와 같이, 분기부(80)를 통해 제2 압축기(12)를 바이패스하여 제1 열교환기(90)로 공급될 수 있다. In this embodiment, the BOG compressed in the first compressor 11 bypasses the second compressor 12 through the branch 80 to the first heat exchanger 90 as shown in FIG. 1 . can be supplied.

구체적으로, 본 실시예에서 제1 압축기(11)의 토출압력이 높은 경우에는 분기부(80)를 통해 제2 압축기(12)를 거치지 않고 바로 제1 열교환기(90)로 증발가스를 보낼 수 있다. Specifically, in the present embodiment, when the discharge pressure of the first compressor 11 is high, the boil-off gas can be directly sent to the first heat exchanger 90 through the branch 80 without going through the second compressor 12 . have.

예를 들어, 수요처가 ME-GI 엔진의 경우 소요 압력이 300 bar로, 액화공정의 설계압력이 초과되므로, 압축기의 최종단인 제2 압축기(12)가 아닌 적절한 중간단인 제1 압축기(11)에서 분기시킬 수 있다.For example, in the case of a ME-GI engine, the required pressure is 300 bar and the design pressure of the liquefaction process is exceeded. ) can be branched from.

본 실시예의 액체질소 공급부(20)는, 액화천연가스 저장탱크(T)에서 발생되는 증발가스를 열교환시키는 액체 질소를 공급하는 것으로서, 액체 질소(증발잠열, 199kJ/KG)는 비등점이 -196℃로 액화천연가스(-163℃) 보다 낮으므로 증발가스의 응축에 냉매로 사용할 수 있다.The liquid nitrogen supply unit 20 of this embodiment supplies liquid nitrogen that heat-exchanges the boil-off gas generated in the liquefied natural gas storage tank T, and the liquid nitrogen (latent heat of evaporation, 199 kJ/KG) has a boiling point of -196 ° C. As it is lower than liquefied natural gas (-163℃), it can be used as a refrigerant for condensing BOG.

본 실시예에서 액체질소 공급부(20)는, 도 1에 도시된 바와 같이, 액체 질소가 저장되는 액체질소 저장탱크(21)와, 액체질소 저장탱크(21)에 저장된 액체 질소를 열교환부(30)로 펌핑시키는 펌프(22)와, 액체질소 저장탱크(21)와 터보 익스팬더(50)를 연결하는 라인에 마련되어 이 라인을 개폐시키는 제1 밸브(23)를 포함한다.In this embodiment, the liquid nitrogen supply unit 20, as shown in FIG. 1, transfers the liquid nitrogen storage tank 21 in which liquid nitrogen is stored and the liquid nitrogen stored in the liquid nitrogen storage tank 21 to the heat exchange unit 30 ) and a first valve 23 provided in a line connecting the liquid nitrogen storage tank 21 and the turbo expander 50 to open and close this line.

본 실시예는 매 항해 전, 액체 질소를 액체질소 저장탱크(21)에 충진할 수 있다.In this embodiment, before every voyage, liquid nitrogen may be filled in the liquid nitrogen storage tank 21 .

또한, 본 실시예에서 액체질소 저장탱크(21)는 보냉재로 감싼 압력용기로 마련될 수 있으며, 단일벽 압력용기 또는 진공 이중벽 압력용기일 수 있다. In addition, in this embodiment, the liquid nitrogen storage tank 21 may be provided as a pressure vessel wrapped with an insulating material, and may be a single-wall pressure vessel or a vacuum double-wall pressure vessel.

나아가, 본 실시예에서 액체질소 저장탱크(21)에서 발생되는 증발 질소는, 별도로 처리하지 않고 허용압력 초과 시, 열교환부(30)에서 토출되는 기체 질소 흐름에 합류시켜 터보 익스팬더(50)로 보낼 수 있다. 이 때, 증발 질소의 토출을 위해 제1 밸브(23)가 개방될 수 있다.Furthermore, in the present embodiment, the evaporated nitrogen generated in the liquid nitrogen storage tank 21 is not separately treated and when the allowable pressure is exceeded, it is sent to the turbo expander 50 by joining the gas nitrogen flow discharged from the heat exchange unit 30 . can At this time, the first valve 23 may be opened to discharge the evaporative nitrogen.

본 실시예의 열교환부(30)는, 액화천연가스 저장탱크(T)에서 공급되는 증발가스를 액체질소 공급부(20)에서 공급되는 액체 질소와 열교환시켜, 증발가스를 응축시킬 수 있다. 이 때 액체 질소는 액체에서 기체 상태로 상변화될 수 있다.The heat exchange unit 30 of this embodiment may heat-exchange the boil-off gas supplied from the liquefied natural gas storage tank T with the liquid nitrogen supplied from the liquid nitrogen supply unit 20 to condense the boil-off gas. At this time, liquid nitrogen may be phase-changed from a liquid to a gaseous state.

본 실시예에서 열교환부(30)로 공급되는 증발가스는 제1 열교환기(90)와 제2 열교환기(100)를 차례로 거쳐 온도가 강하된 후 열교환부(30)로 공급될 수 있다.In this embodiment, the boil-off gas supplied to the heat exchange unit 30 may pass through the first heat exchanger 90 and the second heat exchanger 100 in sequence, and after the temperature is lowered, may be supplied to the heat exchange unit 30 .

또한, 본 실시예에서 열교환부(30)는 다수의 유체가 입출입되는 브레이즈드 알미늄 열교환기(brazed aluminum and multiple stream type heat exchanger) 또는 프린티드 서킷 열교환기(printed circuit heat exchanger)일 수 있다.In addition, in this embodiment, the heat exchange unit 30 may be a brazed aluminum heat exchanger (brazed aluminum and multiple stream type heat exchanger) or a printed circuit heat exchanger (printed circuit heat exchanger) to which a plurality of fluids enter and exit.

본 실시예의 액화부(40)는, 열교환부(30)에서 열교환되어 응축된 증발가스를 액화시킬 수 있다.The liquefaction unit 40 of the present embodiment may liquefy the boil-off gas condensed by heat exchange in the heat exchange unit 30 .

본 실시예에서 액화부(40)는, 도 1에 도시된 바와 같이, 열교환부(30)에서 응축된 증발가스를 감압시키는 증발가스 감압밸브(41)와, 증발가스 감압밸브(41)에서 감압된 응축가스를 기체와 액체로 분리하는 플래쉬 드럼(42)과, 액화천연가스 저장탱크(T)와 제1 압축기(11)를 연결하는 라인과 플래쉬 드럼(42)을 연결하는 라인에 마련되어 플래쉬 드럼(42)에서 분리된 증발가스를 전술한 연결하는 라인으로 공급되도록 전술한 연결하는 라인을 개폐시키는 제2 밸브(43)를 포함한다.In this embodiment, as shown in FIG. 1 , the liquefaction unit 40 includes a boil-off gas pressure reducing valve 41 for decompressing the boil-off gas condensed in the heat exchange unit 30 , and a pressure reduction at the boil-off gas pressure reducing valve 41 . The flash drum 42 for separating the condensed gas into gas and liquid, and the line connecting the liquefied natural gas storage tank T and the first compressor 11 and the line connecting the flash drum 42 are provided in the flash drum and a second valve 43 for opening and closing the above-mentioned connecting line so that the boil-off gas separated in (42) is supplied to the above-mentioned connecting line.

증발가스 감압밸브(41)는 줄-톰슨 밸브일 수 있다. The boil-off gas pressure reducing valve 41 may be a Joule-Thompson valve.

본 실시예는 열교환부(30)에서 응축된 증발가스를 플래쉬 드럼(42)에서 플래쉬시켜, 액체(LNG)는 액화천연가스 저장탱크(T)로 회수하고, 기체 상태의 미응축 증발가스는 액화천연가스 저장탱크(T)에서 발생되는 증발가스 흐름에 합류시켜 냉각기(110)를 거친 후 증발가스 사용처로 공급할 수 있다. In this embodiment, the BOG condensed in the heat exchange unit 30 is flashed in the flash drum 42, the liquid (LNG) is recovered to the liquefied natural gas storage tank T, and the non-condensed BOG in a gaseous state is liquefied. It can be supplied to a place where the boil-off gas is used after passing through the cooler 110 by joining the boil-off gas flow generated in the natural gas storage tank (T).

본 실시예의 터보 익스팬더(50)는, 도 1에 도시된 바와 같이, 기본적으로 열교환부(30)에서 증발가스와 열교환하여 기체로 상변화된 질소를 공급받을 수 있다. As shown in FIG. 1 , the turbo expander 50 of the present embodiment may receive nitrogen phase-changed into gas by exchanging heat with boil-off gas in the heat exchange unit 30 .

또한, 본 실시예의 터보 익스팬더(50)는, 추가로, 액체질소 저장탱크(21)에 연결되어, 액체질소 저장탱크(21)로부터 증발질소를 공급받을 수도 있다. In addition, the turbo expander 50 of the present embodiment may be further connected to the liquid nitrogen storage tank 21 to receive evaporated nitrogen from the liquid nitrogen storage tank 21 .

기체 상태의 질소는 부피유량이 액체 상태일 때보다 수백 배로 증가하므로 이를 터보 익스팬더(50)의 축동력으로 이용할 수 있다. 회수된 축동력은 직접적으로 펌프부를 돌리거나 발전기(60)에 연결되어 발전기(60)를 작동시킬 수 있다.Since the volume flow rate of nitrogen in the gaseous state is increased several hundred times compared to that in the liquid state, it can be used as a shaft power of the turbo expander 50 . The recovered shaft power may directly turn the pump unit or be connected to the generator 60 to operate the generator 60 .

본 실시예의 질소 가스 저장조(70)는, 제1 열교환기(90)에서 배출되는 질소 가스의 압력을 조절하는 역할과 질소 가스를 저장하는 역할을 가지며, 따라서, 질소 가스를 선박 내 수요처에 공급하기 위한 저장조로 사용될 수 있다.The nitrogen gas storage tank 70 of this embodiment has a role of regulating the pressure of nitrogen gas discharged from the first heat exchanger 90 and a role of storing nitrogen gas, and thus supplying nitrogen gas to demand in the ship It can be used as a storage tank for

도 1에 도시된 바와 같이, 본 실시예에서 제1 열교환기(90)와 질소 가스 저장조(70)를 연결하는 라인에는 압력 제어 밸브(71)가 마련되어, 질소 가스 저장조(70)로 공급되는 질소 가스를 압축시킬 수 있다.As shown in FIG. 1 , a pressure control valve 71 is provided on the line connecting the first heat exchanger 90 and the nitrogen gas storage tank 70 in this embodiment, and nitrogen supplied to the nitrogen gas storage tank 70 is provided. Gas can be compressed.

본 실시예의 분기부(80)는, 전술한 바와 같이 제1 압축기(11)의 토출압력이 높은 경우 제2 압축기(12)를 거치지 않고 바로 제1 열교환기(90)로 증발가스를 보내 열교환부(30)와 액화부(40)를 거쳐 액화시키도록 할 수 있다.As described above, the branch unit 80 of this embodiment sends boil-off gas directly to the first heat exchanger 90 without going through the second compressor 12 when the discharge pressure of the first compressor 11 is high. It can be liquefied through (30) and the liquefaction unit (40).

본 실시예에서 분기부(80)는, 도 1에 도시된 바와 같이, 제1 압축기(11)와 제2 압축기(12)를 연결하는 라인에서 분기되어 제2 압축기(12)의 후방 라인에 합류되는 분기 라인(81)과, 분기 라인(81)에 마련되어 분기 라인(81)을 개폐시키는 개폐 밸브(82)를 포함한다.In this embodiment, the branch 80 is branched from the line connecting the first compressor 11 and the second compressor 12 to join the rear line of the second compressor 12 as shown in FIG. 1 . and a branch line 81 to be used, and an on/off valve 82 provided on the branch line 81 to open and close the branch line 81 .

본 실시예의 제1 열교환기(90)는, 도 1에 도시된 바와 같이, 압축부(10)와 제2 열교환기(100)를 연결하는 라인에 마련되며 열교환부(30)에서 열교환되어 기화된 질소 가스의 온도를 상승시켜 체적 유량을 증가시킬 수 있다. 체적 유량이 증가된 질소 가스는 터보 익스팬더(50)로 공급되어 터보 익스팬더(50)의 구동축을 회전시키는 동력으로 제공될 수 있다.The first heat exchanger 90 of this embodiment is provided in a line connecting the compression unit 10 and the second heat exchanger 100, as shown in FIG. The volumetric flow rate can be increased by increasing the temperature of the nitrogen gas. The nitrogen gas having an increased volume flow rate may be supplied to the turbo expander 50 to provide power for rotating a driving shaft of the turbo expander 50 .

본 실시예에서 제1 열교환기(90)는 제2 열교환기(100)로 대체될 수 있고, 이때 제1 열교환기(90)는 마련되지 않을 수 있다.In this embodiment, the first heat exchanger 90 may be replaced with the second heat exchanger 100 , and in this case, the first heat exchanger 90 may not be provided.

본 실시예의 제2 열교환기(100)는, 도 1에 도시된 바와 같이, 제1 열교환기(90)와 열교환부(30)를 연결하는 라인에 마련되며, 제1 열교환기(90)에서 열교환된 증발가스를 선내에서 공급할 수 있는 냉각수(C1)를 이용하여 냉각시킬 수 있다.As shown in FIG. 1 , the second heat exchanger 100 of this embodiment is provided on a line connecting the first heat exchanger 90 and the heat exchange unit 30 , and heat exchanges in the first heat exchanger 90 . The evaporated gas can be cooled by using the cooling water (C1) that can be supplied in the ship.

본 실시예에서 제2 열교환기(100)는 압축부(10)에서 토출되는 증발가스를 냉매를 사용하여 40℃로 냉각시킬 수 있다.In the present embodiment, the second heat exchanger 100 may cool the boil-off gas discharged from the compression unit 10 to 40° C. using a refrigerant.

이와 같이 본 발명은 기재된 실시예에 한정되는 것이 아니고, 본 발명의 사상 및 범위를 벗어나지 않고 다양하게 수정 및 변형할 수 있음은 이 기술의 분야에서 통상의 지식을 가진 자에게 자명하다. 따라서 그러한 수정 예 또는 변형 예들은 본 발명의 특허청구범위에 속한다 하여야 할 것이다.As such, the present invention is not limited to the described embodiments, and it is apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the present invention. Accordingly, it should be said that such modifications or variations are included in the claims of the present invention.

10 : 압축부 11 : 제1 압축기
12 : 제2 압축기 20 : 액체질소 공급부
21 : 액체질소 저장탱크 22 : 펌프
23 : 제1 밸브 30 : 열교환부
40 : 액화부 41 : 감압밸브
42 : 플래쉬 드럼 43 : 제2 밸브
50 : 터보 익스팬더 51 : 소음 저감기
60 : 발전기 70 : 질소 가스 저장조
71 : 압력 제어 밸브 80 : 분기부
81 : 분기 라인 82 : 개폐 밸브
90 : 제1 열교환기 100 : 제2 열교환기
110 : 냉각기 T : 액화천연가스 저장탱크10: compression unit 11: first compressor
12: second compressor 20: liquid nitrogen supply unit
21: liquid nitrogen storage tank 22: pump
23: first valve 30: heat exchange unit
40: liquefied part 41: pressure reducing valve
42: flash drum 43: second valve
50: turbo expander 51: noise reducer
60: generator 70: nitrogen gas storage tank
71: pressure control valve 80: branch
81: branch line 82: on-off valve
90: first heat exchanger 100: second heat exchanger
110: cooler T: liquefied natural gas storage tank

Claims (15)

액화천연가스 저장탱크로부터 공급되는 증발가스를 압축하는 압축부;
상기 압축부에서 압축된 상기 증발가스를 액체질소 공급부에서 공급되는 액체 질소와 열교환시키는 열교환부; 및
상기 열교환부에서 열교환된 상기 증발가스를 액화시키는 액화부를 포함하는, LNG 증발가스의 재액화 시스템.a compression unit for compressing the boil-off gas supplied from the liquefied natural gas storage tank;
a heat exchange unit for heat-exchanging the boil-off gas compressed in the compression unit with liquid nitrogen supplied from the liquid nitrogen supply unit; and
Re-liquefaction system of LNG boil-off gas comprising a liquefaction unit for liquefying the boil-off gas heat-exchanged in the heat exchange unit. 청구항 1에 있어서,
상기 액체질소 공급부는,
상기 액체 질소가 저장되는 액체질소 저장탱크; 및
상기 액체질소 저장탱크에 저장된 상기 액체 질소를 상기 열교환부로 펌핑시키는 펌프를 포함하는, LNG 증발가스의 재액화 시스템.The method according to claim 1,
The liquid nitrogen supply unit,
a liquid nitrogen storage tank in which the liquid nitrogen is stored; and
Reliquefaction system of LNG boil-off gas comprising a pump for pumping the liquid nitrogen stored in the liquid nitrogen storage tank to the heat exchange unit. 청구항 2에 있어서,
상기 액체질소 저장탱크는 단일벽 또는 진공 이중벽 압력용기로 마련되는, LNG 증발가스의 재액화 시스템.3. The method according to claim 2,
The liquid nitrogen storage tank is provided as a single-wall or vacuum double-wall pressure vessel, the LNG boil-off gas reliquefaction system. 청구항 3에 있어서,
상기 압력용기는 보냉재로 감싸지는, LNG 증발가스의 재액화 시스템.4. The method according to claim 3,
The pressure vessel is wrapped with an insulating material, LNG boil-off gas reliquefaction system. 청구항 2에 있어서,
상기 액체질소 저장탱크에서 발생되는 증발 질소는 허용 압력 초과 시 터보 익스팬더로 공급되는, LNG 증발가스의 재액화 시스템.3. The method according to claim 2,
Evaporative nitrogen generated in the liquid nitrogen storage tank is supplied to the turbo expander when the allowable pressure is exceeded, the LNG boil-off gas reliquefaction system. 청구항 5에 있어서,
상기 터보 익스팬더에 연결되어 발전되는 발전기를 더 포함하는, LNG 증발가스의 재액화 시스템.6. The method of claim 5,
Reliquefaction system of LNG boil-off gas further comprising a generator connected to the turbo expander to generate electricity. 청구항 2에 있어서,
상기 액체질소 저장탱크와 연결되며 상기 액체질소 저장탱크에서 배출되는 질소 가스가 저장되는 질소 가스 저장조를 더 포함하는, LNG 증발가스의 재액화 시스템.3. The method according to claim 2,
The reliquefaction system of LNG boil-off gas, which is connected to the liquid nitrogen storage tank and further includes a nitrogen gas storage tank in which nitrogen gas discharged from the liquid nitrogen storage tank is stored. 청구항 1에 있어서,
상기 압축부는,
상기 액화천연가스 저장탱크에서 공급되는 상기 증발가스를 압축시키는 제1 압축기; 및
상기 제1 압축기에서 압축된 상기 증발가스를 압축시키는 제2 압축기를 포함하는, LNG 증발가스의 재액화 시스템.The method according to claim 1,
The compression unit,
a first compressor for compressing the boil-off gas supplied from the liquefied natural gas storage tank; and
Reliquefaction system of LNG boil-off gas comprising a second compressor for compressing the boil-off gas compressed in the first compressor. 청구항 8에 있어서,
상기 제1 압축기와 상기 제2 압축기를 연결하는 라인에서 분기되며, 상기 제2 압축기를 바이패스하여 상기 제2 압축기의 후방 라인에 합류되는 분기부를 더 포함하는, LNG 증발가스의 재액화 시스템.9. The method of claim 8,
The reliquefaction system of LNG boil-off gas, further comprising a branch branched from a line connecting the first compressor and the second compressor, and joined to a rear line of the second compressor by bypassing the second compressor. 청구항 1에 있어서,
상기 액화부는,
상기 열교환부에서 응축된 상기 증발가스를 감압시키는 증발가스 감압밸브; 및
상기 증발가스 감압밸브에서 감압된 상기 응축 가스를 기체와 액체로 분리하는 플래쉬 드럼을 포함하는, LNG 증발가스의 재액화 시스템.The method according to claim 1,
The liquefaction unit,
a boil-off gas pressure reducing valve for reducing the boil-off gas condensed in the heat exchange unit; and
and a flash drum for separating the condensed gas pressure-reduced by the boil-off gas pressure reducing valve into gas and liquid. 청구항 10에 있어서,
상기 플래쉬 드럼에서 분리된 기체는 상기 액화천연가스 저장탱크와 상기 압축부를 연결하는 라인으로 공급되는, LNG 증발가스의 재액화 시스템.11. The method of claim 10,
The gas separated from the flash drum is supplied to a line connecting the liquefied natural gas storage tank and the compression unit. 청구항 1에 있어서,
상기 압축부에서 압축되어 증발가스 사용처로 공급되는 상기 증발가스를 압축시키는 냉각기를 더 포함하는, LNG 증발가스의 재액화 시스템.The method according to claim 1,
The re-liquefaction system of LNG boil-off gas, further comprising a cooler for compressing the boil-off gas compressed in the compression unit and supplied to a place where the boil-off gas is used. 청구항 1에 있어서,
상기 압축부와 상기 열교환부를 연결하는 라인에 마련되어 상기 열교환부에서 열교환된 상기 액체 질소의 온도를 상승시켜 체적 유량을 증가시키는 제1 열교환기를 더 포함하는, LNG 증발가스의 재액화 시스템.The method according to claim 1,
The reliquefaction system of LNG boil-off gas, further comprising a first heat exchanger provided in a line connecting the compression unit and the heat exchange unit to increase the volume flow rate by increasing the temperature of the liquid nitrogen heat-exchanged in the heat exchange unit. 청구항 13에 있어서,
상기 제1 열교환기의 후방에 배치되도록 상기 압축부와 상기 열교환부를 연결하는 라인에 마련되며, 상기 제1 열교환기에서 열교환된 상기 증발가스를 냉각시키는 제2 열교환기를 더 포함하는, LNG 증발가스의 재액화 시스템.14. The method of claim 13,
The LNG boil-off gas, which is provided on a line connecting the compression unit and the heat exchange unit to be disposed at the rear of the first heat exchanger, further comprising a second heat exchanger for cooling the boil-off gas heat-exchanged in the first heat exchanger reliquefaction system. 액화천연가스 저장탱크에서 발생되는 증발가스를 액체질소 공급부에서 공급되는 액체 질소와 열교환한 후 액화부에서 액화시키는, LNG 증발가스의 재액화 방법.A method of re-liquefying LNG boil-off gas, in which BOG generated in a liquefied natural gas storage tank is liquefied in the liquefaction unit after exchanging heat with liquid nitrogen supplied from a liquid nitrogen supply unit.
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