Carbon dioxide re-liquefaction system and carbon dioxide re-liquefaction method utilizing closed cycle

Abstract

The present invention relates to a carbon dioxide evaporation gas re-liquefaction method. The carbon dioxide evaporation gas re-liquefaction method according to the present invention is characterized by comprising: a step for forming compressed evaporation gas by supplying carbon dioxide evaporation gas evaporated in a storage tank to a compressor in a carbon dioxide carrier using a dual-fuel engine; a cooling step for supplying the compressed evaporation gas to a first evaporation gas heat exchanger and cooling same through heat exchange with a refrigerant circulating in a refrigeration cycle; and a recovery step for spraying the re-liquefied carbon dioxide cooled through the cooling step into the storage tank and recovering same, wherein a second cooling step or a third cooling step is additionally performed during the cooling step according to the operation mode of the carbon dioxide carrier.

Description

Carbon dioxide reliquefaction system and carbon dioxide reliquefaction method using a closed cycle

[0001] The present invention relates to a carbon dioxide liquefaction system and a carbon dioxide liquefaction method utilizing a closed cycle for re-liquefying and processing evaporated gas of liquefied carbon dioxide in a liquefied carbon dioxide carrier using liquefied gas as fuel.

[0002] When energy is obtained from fossil fuels, the combustion reaction produces carbon dioxide. Carbon dioxide, emitted in large quantities due to the increased use of fossil fuels, is designated as a greenhouse gas (GHG) that contributes to global warming.

[0003] Although the global warming potential of carbon dioxide is low compared to other greenhouse gases, it is classified as a very important greenhouse gas because it accounts for approximately 80% of total greenhouse gas emissions and its emissions can be regulated.

[0004] Through various international agreements, each country is regulating the reduction of carbon dioxide emissions, and as a result, the development of carbon dioxide treatment technologies such as carbon capture, utilization, and storage (CCUS) technology, which reduces the amount of carbon dioxide emitted into the atmosphere by collecting carbon dioxide generated at various industrial sites and storing it in a separate location, is required.

[0005] The above CCUS technology liquefies and transports post-processed carbon dioxide for separate processing. At this time, various processing methods are being proposed, such as injecting the liquefied carbon dioxide into the remaining space after oil extraction to store it in a stable state, or using it by spraying it at high pressure instead of water when extracting oil.

[0006] At this time, in order to liquefy carbon dioxide, there is an open cycle method that performs its own heat exchange through depressurization of the Joule-Thomson valve after pressurization, and a closed cycle method that uses a separate refrigerant with a lower saturation temperature than CO2.

[0007] The closed cycle method allows for higher efficiency with less refrigerant than the open cycle, but requires a separate refrigeration system.

[0008] Accordingly, the development of an optimal system that takes into account not only system efficiency but also price is required.

[0009] In order to solve the above problems, the present invention aims to provide a carbon dioxide liquefaction system and a carbon dioxide liquefaction method utilizing a closed cycle.

[0010] Specifically, the purpose of the present invention is to provide a carbon dioxide liquefaction system and a carbon dioxide liquefaction method utilizing a closed cycle capable of re-liquefying and recovering liquefied carbon dioxide vaporized gas by utilizing the cold heat of the liquefied natural gas (LNG) in a liquefied carbon dioxide carrier using liquefied natural gas (LNG) as fuel.

[0011] In addition, the purpose is to lower the pressure inside the tank by recovering the re-liquefied carbon dioxide into a carbon dioxide cargo tank (storage tank) and lowering the temperature of the vapor inside the cargo tank.

[0012] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0013] According to one aspect of the present invention for achieving the above-described object, a method for re-liquefying carbon dioxide evaporation gas is provided, comprising a step of supplying carbon dioxide evaporation gas evaporated in a storage tank to a compressor to form compressed evaporation gas, a cooling step of supplying the compressed evaporation gas to a first evaporation gas heat exchanger to cool it by heat exchange with a refrigerant circulating in a refrigeration cycle, and a recovery step of injecting the re-liquefied carbon dioxide cooled through the cooling step into the storage tank to recover it, wherein the cooling step additionally performs a second cooling step or a third cooling step depending on the operation mode of the carbon dioxide carrier.

[0014] Preferably, the cooling step further includes a refrigeration cycle circulation step for circulating and cooling the refrigerant, and the refrigeration cycle circulation step may be such that the refrigerant heated by heat exchange with the compressed evaporation gas passes through a refrigerant compressor and is compressed, and the compressed refrigerant passes through a refrigerant control valve and is expanded and cooled.

[0015] Preferably, when the carbon dioxide carrier is operated in gas mode, a second cooling step is additionally performed, and the second cooling step can perform secondary cooling by supplying the compressed evaporation gas cooled primarily through the cooling step to a second evaporation gas heat exchanger and exchanging heat with the liquefied gas supplied to the engine.

[0016] Preferably, the secondarily cooled compressed evaporation gas can be expanded to form a supercooled reliquefied evaporation gas in a liquid state.

[0017] Preferably, the secondarily cooled compressed evaporation gas is supplied to a first evaporation gas control valve, and the first evaporation gas control valve may expand the secondarily cooled compressed evaporation gas to form a supercooled reliquefied evaporation gas in a liquid state.

[0018] Preferably, the liquid-state supercooled reliquefied evaporation gas is recovered to the storage tank through one recovery line selected from the first reliquefied recovery line and the second reliquefied recovery line, and when the reliquefied recovery line is closed by dry ice, it may be recovered by bypassing the unclosed reliquefied recovery line.

[0019] Preferably, when the carbon dioxide carrier is operated in oil mode, a third cooling step may be additionally performed, wherein the third cooling step may include a gas-liquid mixed evaporation gas generation step of expanding the first-cooled compressed evaporation gas to generate a gas-liquid mixed evaporation gas, and a evaporation gas separation step of separating the gas-liquid mixed evaporation gas into a liquid-state re-liquefied evaporation gas and a gas-state evaporation gas.

[0020] Preferably, the liquid-state re-liquefied evaporation gas is recovered by spraying it into the storage tank, and a recirculation step is included to recirculate the separated gaseous evaporation gas to a evaporation gas compressor to re-liquefy it, and the recirculation step may be such that the gaseous evaporation gas passes through a first evaporation gas heat exchanger and is recirculated to the evaporation gas compressor, the gaseous evaporation gas is heated while cooling the compressed evaporation gas, and the heated gaseous evaporation gas is re-supplied to the compressor through the recirculation line.

[0021] According to another aspect of the present invention for achieving the above object, a carbon dioxide evaporation gas re-liquefaction system is provided, which includes an engine using liquefied gas as fuel, a storage tank for storing liquefied carbon dioxide, a evaporation gas compressor for generating compressed evaporation gas by compressing evaporation gas of the liquefied carbon dioxide generated in the storage tank, a first evaporation gas heat exchanger for cooling the compressed evaporation gas, a second evaporation gas heat exchanger for secondarily cooling the primarily cooled evaporation gas supplied from the first evaporation gas heat exchanger by heat exchange with liquefied gas supplied to the engine, and a refrigeration cycle in which a refrigerant circulates to supply cold heat to the first evaporation gas heat exchanger.

[0022] Preferably, the second evaporation gas heat exchanger and storage tank are connected to a re-liquefaction recovery line, and a first evaporation gas control valve that expands and supercools the evaporation gas that has been secondarily cooled through the second evaporation gas heat exchanger may be disposed on the re-liquefaction recovery line.

[0023] Preferably, a spray nozzle line is arranged at the upper portion of the storage tank, and the spray nozzle line may be connected to the re-liquefaction recovery line to spray the supercooled evaporated gas within the storage tank.

[0024] Preferably, the second evaporation gas heat exchanger and storage tank are connected to a recirculation line, so that the evaporation gas that has not been secondarily cooled through the second evaporation gas heat exchanger can be recirculated to the evaporation gas compressor.

[0025] Preferably, a second evaporation gas control valve that expands the evaporation gas that has not been secondary cooled in the second evaporation gas heat exchanger to generate a gas-liquid mixed evaporation gas and an evaporation gas separator that separates the gas-liquid mixed evaporation gas into a liquid-state re-liquefied evaporation gas and a gas-state evaporation gas may be disposed on the recirculation line.

[0026] Preferably, the lower part of the evaporation gas separator is connected to a re-liquefaction recovery line, and the upper part of the evaporation gas separator is connected to a recirculation line, so that the liquid-state re-liquefied evaporation gas is supplied to a storage tank through the re-liquefaction recovery line, and the gaseous evaporation gas is supplied to the first evaporation gas heat exchanger through the recirculation line, and the gaseous evaporation gas supplied to the first evaporation gas heat exchanger is heated through heat exchange and recirculated to the evaporation gas compressor.

[0027] Preferably, the second evaporation gas heat exchanger and storage tank are connected to a first re-liquefaction recovery line, and a first evaporation gas control valve that expands and supercools the evaporation gas that has been secondarily cooled through the second evaporation gas heat exchanger may be disposed on the first evaporation gas recovery line.

[0028] Preferably, the second evaporation gas heat exchanger and storage tank are connected to a second re-liquefaction recovery line, and a second evaporation gas control valve may be arranged on the second re-liquefaction recovery line.

[0029] Preferably, a vaporization gas separator is disposed on the second re-liquefaction recovery line to separate the gas-liquid mixed vaporization gas into a liquid-state re-liquefied vaporization gas and a gas-state vaporization gas, and a valve for branching the flow of vaporization gas may be disposed between the second vaporization gas control valve and the vaporization gas separator.

[0030] Preferably, the lower part of the evaporation gas separator is connected to a third re-liquefaction recovery line, and the upper part of the evaporation gas separator is connected to a recirculation line, so that the liquid-state re-liquefied evaporation gas is supplied to a storage tank through the re-liquefaction recovery line, and the gaseous evaporation gas is supplied to the first evaporation gas heat exchanger through the recirculation line, and the gaseous evaporation gas supplied to the first evaporation gas heat exchanger is heated through heat exchange and recirculated to the evaporation gas compressor.

[0031] Preferably, the refrigeration cycle may further include a refrigerant compressor that compresses the refrigerant heated while exchanging heat in the first evaporative gas heat exchanger, and a refrigerant control valve that expands the compressed refrigerant and supplies it to the first evaporative gas heat exchanger.

[0032] According to the present invention, which is achieved as described above, there is an effect of providing a carbon dioxide re-liquefaction system and a carbon dioxide re-liquefaction method utilizing a closed cycle.

[0033] Specifically, in a liquefied carbon dioxide carrier using liquefied natural gas (LNG) as fuel, there is provided a carbon dioxide re-liquefaction system and a carbon dioxide re-liquefaction method utilizing a closed cycle capable of re-liquefying and recovering liquefied carbon dioxide vaporized gas by utilizing the cold heat of the liquefied natural gas.

[0034] Additionally, by recovering the liquefied carbon dioxide into the carbon dioxide cargo tank, the temperature of the vapor inside the cargo tank is lowered, thereby lowering the pressure inside the tank.

[0035] In addition, since there is no steam returned through the separator (evaporation gas separator), the flow rate of carbon dioxide evaporation gas flowing into the evaporation gas compressor (carbon dioxide compressor) is reduced, which has the effect of reducing power consumption.

[0036] In addition, when there is no or insufficient cooling of the liquefied gas, it has the effect of being able to operate selectively depending on the situation by using the existing Joule-Thompson valve and separator (evaporation gas separator).

[0037] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0038] FIG. 1 and FIG. 2 are schematic diagrams illustrating a carbon dioxide evaporation gas re-liquefaction system according to one embodiment of the present invention.

[0039] The purpose and technical configuration of the present invention and the resulting operation and effects will be more clearly understood through a detailed description based on the drawings attached to the specification of the present invention.

[0040] The terminology used herein is merely used to describe specific embodiments and is not intended to limit the present invention. For example, when a component is referred to as "including" herein, unless specifically stated otherwise, it does not exclude other components but rather implies that other components may be included. Furthermore, when a component is referred to as "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to the other component, other components may also be present in between.

[0041] Hereinafter, the present invention will be described in detail by describing preferred embodiments thereof with reference to the attached drawings. The embodiments described below are provided to facilitate the technical concept of the present invention for those skilled in the art to understand, and should not be construed as limiting the present invention. It should be understood that the embodiments of the present invention can have various applications to those skilled in the art.

[0042] In the present invention described below, the transportation means may be equipped with a liquefied carbon dioxide storage tank and capable of being transported via land or sea routes. In describing one embodiment of the present invention, the transportation means will be described as a ship navigating the sea.

[0043] Additionally, in some embodiments of the present invention, the vessel may be a liquefied carbon dioxide carrier (LCO2Carrier). However, this is not limited to this, and the embodiments described below may be applied equally to any vessel equipped with a liquefied carbon dioxide storage tank.

[0044] Additionally, the term “ship” in this specification may include a ship with self-propulsion capability, as well as a marine structure floating on the sea but without propulsion capability.

[0045] In addition, a liquefied carbon dioxide carrier according to an embodiment of the present invention described below may be provided with one or more dual-fuel engines that can selectively use gas fuel and fuel oil or a mixture thereof as fuel, as a propulsion engine or a power generation engine.

[0046] Here, the gaseous fuel may be stored in the fuel tank on board in a liquefied state, that is, in the form of liquefied gas, and may be supplied to the engine in a gaseous state or in a liquid state by vaporizing. For example, the liquefied gas may be selected from among hydrocarbon series such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), LPG (Liquefied Ethylene Gas), and LPG (Liquefied Propylene Gas), as well as non-hydrocarbon series liquefied gases such as liquefied ammonia (NH3) and liquefied hydrogen.

[0047] In one embodiment of the present invention described below, the gas fuel is explained as an example of natural gas, and therefore, liquefied natural gas may be stored in the fuel tank.

[0048] In addition, the engine here is a dual fuel engine, which is one of the engines used in ships and can use natural gas as fuel. For example, the engine may include one or more of the ME-GI (MAN Electronic Gas Injection) engine, the X-DF (eXtra long stroke Dual Fuel) engine, and the DF engine (DFDE (Dual Fuel Diesel Electric), DFDG (Dual Fuel Diesel Generator)). However, the present invention is not limited thereto.

[0049] Hereinafter, a carbon dioxide evaporation gas re-liquefaction system according to one embodiment of the present invention will be described with reference to FIGS. 1 and 2.

[0050] A liquefied carbon dioxide carrier according to the present embodiment may be configured to include a liquefied carbon dioxide system, a liquefied carbon dioxide storage unit, an evaporation gas treatment unit, and a fuel supply unit (not shown).

[0051] The liquefied carbon dioxide storage unit includes one or more storage tanks (100) for storing liquefied carbon dioxide, and the storage tanks (100) are pressurized tanks that can be operated in a state where the carbon dioxide is pressurized above a certain pressure to maintain a liquid state.

[0052] The evaporation gas treatment unit may include an evaporation gas compressor (210) that compresses evaporation gas discharged from a storage tank (100), and a first evaporation gas heat exchanger (220) that cools the compressed evaporation gas by the evaporation gas compressor (210).

[0053] In detail, the carbon dioxide evaporation gas generated in the carbon dioxide storage tank (100) is introduced into the evaporation gas compressor (210) through the evaporation gas supply line (BL), and is compressed in the evaporation gas compressor (210) to generate compressed evaporation gas. At this time, it is preferable that the compressed evaporation gas be compressed to a pressure at which at least a portion thereof can be liquefied during the cooling process in the first evaporation gas heat exchanger (220).

[0054] Furthermore, the evaporation gas treatment unit may further include an intermediate cooler (211) for cooling the evaporation gas, the temperature of which has increased during the process of being compressed in the evaporation gas compressor (210), before supplying it to the first evaporation gas heat exchanger (220), and a buffer tank (212) for buffering the evaporation gas cooled in the intermediate cooler (211) before supplying it to the first evaporation gas heat exchanger (220). The compressed evaporation gas discharged from the evaporation gas compressor (210) may be cooled in the intermediate cooler (211) through the evaporation gas supply line (BL), and then may be introduced into the high-temperature fluid path of the first evaporation gas heat exchanger (220).

[0055] The first evaporation gas heat exchanger (220) cools compressed evaporation gas, and can generate compressed cooled evaporation gas by exchanging heat with compressed evaporation gas introduced through the evaporation gas supply line (BL).

[0056] For example, compressed evaporation gas introduced through the evaporation gas supply line (BL) can be heat-exchanged with a low-temperature refrigerant circulating in a refrigeration cycle (500) described later, and the compressed evaporation gas can be cooled by the heat exchange to generate compressed cooled evaporation gas.

[0057] Alternatively, the compressed evaporation gas introduced through the evaporation gas supply line (BL) may be heat-exchanged with the low-temperature refrigerant circulating in the refrigeration cycle (500) described later and the gaseous evaporation gas separated from the liquid in the evaporation gas separator (260), and the compressed evaporation gas may be cooled by the heat exchange to generate the compressed cooled evaporation gas.

[0058] Meanwhile, a second evaporation gas heat exchanger (230) may be further included on the evaporation gas supply line (BL), and the second evaporation gas heat exchanger (230) may be configured to be placed at the rear end of the first evaporation gas heat exchanger (220).

[0059] In detail, it is preferable that the second evaporation gas heat exchanger (230) performs secondary cooling by exchanging heat between the primary cooled compressed cooled evaporation gas supplied from the first evaporation gas heat exchanger and the liquefied gas supplied to the engine (400).

[0060] For example, when a carbon dioxide carrier operates in gas mode, the second evaporation gas heat exchanger (230) receives the compressed cooled evaporation gas that has been primarily cooled from the first evaporation gas heat exchanger (220) and performs heat exchange with liquefied gas (LNG), which is fuel supplied from a fuel tank (300) to an engine (400) along a fuel supply line (FL). Through the heat exchange, the LNG is heated and supplied to the engine (400), and the compressed cooled evaporation gas can be supplied after being secondarily cooled.

[0061] Accordingly, the second evaporation gas heat exchanger (230) may be a vaporizer that vaporizes LNG supplied from the fuel tank (300) to the engine (400).

[0062] Alternatively, a vaporizer (not shown) for vaporizing LNG supplied as fuel for the engine (400) may be further provided downstream of the second vaporization gas heat exchanger (230), so that the second vaporization gas heat exchanger (250) may be utilized as a preheater for preheating LNG before supplying LNG from the fuel tank (300) to the vaporizer.

[0063] In addition, the second evaporation gas heat exchanger (230) is connected to the storage tank (100) and the re-liquefaction recovery line (RL), so that the compressed refrigerated evaporation gas that passes through the second evaporation gas heat exchanger (230) and is secondarily cooled can be recovered to the storage tank (100).

[0064] In detail, the first evaporation gas control valve (240) is arranged on the re-liquefaction recovery line (RL), and the secondarily cooled compressed evaporation gas can be supplied to the storage tank (100) by passing through the first evaporation gas control valve (240).

[0065] Alternatively, the second evaporation gas heat exchanger (230) may be connected to the storage tank (100) and the first re-liquefaction recovery line (RL1), and a first evaporation gas control valve (240) may be disposed on the first re-liquefaction recovery line (RL1), and the secondarily cooled compressed cooled evaporation gas may be supplied to the storage tank (100) by passing through the first evaporation gas control valve (240).

[0066] At this time, the first evaporation gas control valve (240) expands the secondarily cooled compressed cooled evaporation gas to generate a liquid-state re-liquefied evaporation gas, and the liquid-state re-liquefied evaporation gas is in a supercooled state. It is preferable that the first evaporation gas control valve (240) uses a Joule-Thomson valve that expands the evaporation gas cooled by an isenthalpic process.

[0067] In addition, the re-liquefaction recovery line (RL) is connected to the upper spray nozzle line (110) within the storage tank (100), and the re-liquefaction vaporization gas in a supercooled liquid state passing through the first vaporization gas control valve (240) can be sprayed within the storage tank. At this time, by spraying the re-liquefaction vaporization gas in a supercooled liquid state, there is an effect of effectively lowering the pressure within the storage tank (100).

[0068] Meanwhile, the second evaporation gas heat exchanger (230) and the storage tank (100) are connected to a recirculation line (GL), so that the evaporation gas that has not been secondary cooled can be recirculated to the evaporation gas compressor (210) through the second evaporation gas heat exchanger (230).

[0069] Alternatively, the secondary cooled compressed evaporation gas formed by performing heat exchange in the second evaporation gas heat exchanger (230) may pass through the first evaporation gas control valve (240) and be generated as dry ice to block the first re-liquefaction recovery line (RL1).

[0070] Accordingly, the re-liquefaction system according to the present invention may further include a second re-liquefaction recovery line (RL2) connecting the second evaporation gas heat exchanger (230) and the storage tank (100), and it is preferable that a second evaporation gas control valve (250) is arranged on the second evaporation gas recovery line (RL2).

[0071] At this time, the second evaporation gas control valve (250) expands the secondary cooled compressed cooled evaporation gas supplied from the second evaporation gas heat exchanger (230) to generate a liquid-state re-liquefied evaporation gas, and the liquid-state re-liquefied evaporation gas is in a supercooled state. Accordingly, it is preferable that the second evaporation gas control valve (250) use a Joule-Thomson valve that expands the evaporation gas cooled by an isenthalpic process, like the first evaporation gas control valve (240).

[0072] In addition, the second evaporation gas heat exchanger (230) and the storage tank (100) are connected to a recirculation line (GL), so that the evaporation gas that has not been secondary cooled can be recirculated to the evaporation gas compressor (210) through the second evaporation gas heat exchanger (230).

[0073] In detail, when the carbon dioxide carrier is operated in oil mode and the second evaporation gas heat exchanger does not have or has insufficient cooling heat and thus is not secondary cooled, it is preferable that a second evaporation gas control valve (250) and an evaporation gas separator (260) are arranged on the recirculation line (GL) to recirculate the evaporation gas through the recirculation line (GL).

[0074] At this time, the primary cooled compressed evaporation gas that has not been secondary cooled in the second evaporation gas heat exchanger (230) passes through the second evaporation gas control valve (250), and generates a gas-liquid mixed evaporation gas that is a mixture of a liquid-state re-liquefied evaporation gas and a gas-state evaporation gas, and it is preferable to supply the generated gas-liquid mixed evaporation gas to an evaporation gas separator (260).

[0075] Alternatively, the evaporation gas separator (260) may be placed on the second re-liquefaction recovery line (RL2), the upper portion of the evaporation gas separator (260) may be connected to the recirculation line (GL), and the lower portion of the evaporation gas separator (260) may be connected to the third re-liquefaction recovery line (RL3).

[0076] At this time, a valve (251) is further included to supply the flow of evaporation gas to the evaporation gas separator (260) on the second re-liquefaction recovery line (RL2), and it is preferable that the valve (251) be arranged between the second evaporation gas control valve (250) and the evaporation gas separator (260). Accordingly, it is preferable that the valve (251) be a control valve or a 3-way on-off valve.

[0077] That is, the primary cooled compressed evaporation gas that is not secondary cooled in the second evaporation gas heat exchanger (230) passes through the second evaporation gas control valve (250), and generates a gas-liquid mixed evaporation gas that is a mixture of a liquid-state reliquefied evaporation gas and a gas-state evaporation gas, and the generated gas-liquid mixed evaporation gas is supplied to the evaporation gas separator (260).

[0078] It is preferable that the above-mentioned evaporation gas separator (260) separates the gas-liquid mixed evaporation gas into a liquid-state re-liquefied evaporation gas and a gas-state evaporation gas. Specifically, the lower part of the evaporation gas separator (260) is connected to the storage tank (100) and the re-liquefied recovery line (RL) or the third re-liquefied recovery line (RL3), and it is preferable that the liquid-state re-liquefied evaporation gas obtained by separating the gas-liquid mixed evaporation gas in the evaporation gas separator (260) is recovered to the storage tank (100) through the re-liquefied recovery line (RL) or the third re-liquefied recovery line (RL3).

[0079] In addition, the evaporation gas separator (260) is connected to the storage tank (100) and the recirculation line (GL), so that the gaseous evaporation gas obtained by separating the gas and liquid mixed evaporation gas in the evaporation gas separator (260) can be recirculated through the recirculation line (GL).

[0080] In detail, the recirculation line (GL) is connected to the evaporation gas compressor (210), and it is preferable that the evaporation gas in a gaseous state be recirculated by joining the evaporation gas flow from the storage tank (100) to the evaporation gas compressor (210).

[0081] At this time, it is preferable that the gaseous evaporation gas recycled to the evaporation gas compressor (210) through the recirculation line (GL) be heated while recovering cold heat through heat exchange in the first evaporation gas heat exchanger (220) and then supplied to the evaporation gas compressor (210).

[0082] In addition, the first evaporation gas heat exchanger (220) may apply a three-stream heat exchanger so that the gaseous evaporation gas recycled to the evaporation gas compressor (210) through the recirculation line (GL) and the low-temperature refrigerant circulating through the refrigerant circulation line (ML) can exchange heat with the compressed evaporation gas transferred from the evaporation gas compressor (210) through the evaporation gas supply line (BL).

[0083] That is, the gaseous evaporation gas supplied from the evaporation gas separator (260) and the refrigerant circulating in the refrigeration cycle (500) cool the compressed evaporation gas, and the gaseous evaporation gas can be heated and recycled to the evaporation gas compressor (210).

[0084] The refrigeration cycle (500) may be configured to include a refrigerant compressor (510) for compressing refrigerant and a refrigerant control valve (520) for controlling the flow of refrigerant supplied to the first evaporative gas heat exchanger (220).

[0085] In addition, the refrigeration cycle (500) further includes a refrigerant cooler (511) that cools the refrigerant whose temperature has risen during the process of being compressed in the refrigerant compressor (510). The refrigerant introduced into the refrigerant compressor (510) through the refrigerant circulation line (ML) is compressed in the refrigerant compressor (510) to generate compressed refrigerant, and the compressed refrigerant can be cooled in the refrigerant cooler (511) and then supplied to the first evaporative gas heat exchanger (220) through the refrigerant circulation line (ML).

[0086] At this time, the refrigerant control valve (520) may be a flow rate control valve that controls the flow rate of the cooled compressed refrigerant, i.e., the low-temperature refrigerant, supplied from the refrigerant cooler (511) to the first evaporative gas heat exchanger (220) through the refrigerant circulation line (ML), and may have a function of expanding the compressed refrigerant cooled in the refrigerant cooler (511) through an isenthalpic process.

[0087] Accordingly, the low-temperature refrigerant that has passed through the refrigerant cooler (511) and the refrigerant control valve (520) is introduced into the first evaporative gas heat exchanger (220) in a liquid state, and is vaporized through heat exchange to be introduced into the refrigerant compressor (510) in a gaseous state.

[0088] That is, the low-temperature refrigerant circulating in the refrigerant circulation line (ML) is heated while exchanging heat with the compressed evaporation gas supplied through the evaporation gas compressor (210), and the low-temperature refrigerant becomes a high-temperature refrigerant while cooling the carbon dioxide evaporation gas in the first evaporation gas heat exchanger (220), and it is preferable that the high-temperature refrigerant is introduced into the refrigerant compressor (510) through the refrigerant circulation line (ML) and circulates through the refrigeration cycle (500). At this time, the refrigerant circulating in the refrigeration cycle (500) may be a hydrocarbon-based refrigerant such as ammonia or propane. However, it is not limited thereto, and it is preferable to select and apply a refrigerant suitable for re-liquefying the carbon dioxide evaporation gas by circulating in the refrigeration cycle (500).

[0089] Hereinafter, a method for re-liquefying carbon dioxide vaporization gas according to an embodiment of the present invention will be described with reference to a carbon dioxide vaporization gas re-liquefaction system according to an embodiment of the present invention described above.

[0090] In a carbon dioxide carrier using a dual-fuel engine, the carbon dioxide evaporation gas re-liquefaction method may be configured to include a compressed evaporation gas formation step, a cooling step, and a recovery step.

[0091] The above-mentioned compressed evaporation gas formation step supplies the carbon dioxide evaporation gas evaporated in the storage tank (100) to the evaporation gas compressor (210), and is compressed while passing through the evaporation gas compressor (210). At this time, the compressed evaporation gas is cooled in an intermediate cooler (211) through the evaporation gas supply line (BL), and then remains in the buffer tank (210) and can be introduced into the high-temperature fluid path of the first evaporation gas heat exchanger (220).

[0092] The cooling step further includes a refrigeration cycle circulation step by supplying the compressed evaporation gas to the first evaporation gas heat exchanger (220) and cooling it by heat exchange with the refrigerant circulating in the refrigeration cycle.

[0093] The above refrigeration cycle circulation step is such that the heated refrigerant exchanges heat with the compressed evaporation gas and is compressed while passing through the refrigerant compressor, and the compressed refrigerant is expanded and cooled while passing through the refrigerant control valve, and the cooled refrigerant passes through the first evaporation gas heat exchanger (220) to cool the compressed evaporation gas supplied from the storage tank (100).

[0094] Meanwhile, the cooling step may include a second cooling step depending on the operation mode of the carbon dioxide carrier.

[0095] In detail, when the vessel is operated in gas mode, the compressed evaporation gas cooled primarily through the cooling step is supplied to the second evaporation gas heat exchanger to perform the second cooling step.

[0096] The second cooling step is preferably performed by supplying the first-cooled compressed refrigerated evaporation gas to the second refrigerated gas heat exchanger (230), and performing secondary cooling by heat-exchanging the first-cooled compressed refrigerated evaporation gas with the liquefied gas supplied to the engine (400).

[0097] For example, the second evaporation gas heat exchanger (230) receives the compressed cooled evaporation gas that has been primarily cooled from the first evaporation gas heat exchanger (220) and performs heat exchange with liquefied gas (LNG), which is fuel supplied from a fuel tank (300) to an engine (400) along a fuel supply line (FL). Through the heat exchange, the LNG is heated and supplied to the engine (400), and the compressed cooled evaporation gas can be supplied after being secondarily cooled.

[0098] In detail, as disclosed in FIG. 1, the compressed evaporation gas secondarily cooled through the second cooling step can be supplied to the first evaporation gas control valve (240). It is preferable that the re-liquefied evaporation gas in a supercooled liquid state passing through the second evaporation gas control valve (240) be sprayed and recovered within the storage tank. At this time, by spraying and recovering the re-liquefied evaporation gas in a supercooled liquid state, there is an effect of effectively lowering the pressure within the storage tank (100).

[0099] Alternatively, as disclosed in FIG. 2, it is preferable that the compressed evaporated gas secondarily cooled through the second cooling step is recovered to the storage tank through one recovery line selected from among the first re-liquefaction recovery line (RL1) and the second re-liquefaction recovery line (RL2).

[0100] For example, when the secondary cooled compressed evaporation gas is recovered through the first re-liquefaction recovery line (RL1), the secondary cooled compressed evaporation gas passes through the first evaporation gas control valve (240) and a supercooled liquid-state re-liquefaction evaporation gas is formed, and the supercooled liquid-state re-liquefaction evaporation gas can be recovered by being injected into the storage tank. At this time, by injecting and recovering the supercooled liquid-state re-liquefaction evaporation gas, there is an effect of effectively lowering the pressure within the storage tank (100).

[0101] Meanwhile, if the cold energy of LNG is excessively used during the second cooling step, the temperature of carbon dioxide may drop below the triple point, causing dry ice to be generated. As dry ice is generated, the first re-liquefaction recovery line (RL1) or the second re-liquefaction recovery line (RL2) may be closed, preventing carbon dioxide from being recovered to the storage tank (100). Therefore, it is desirable to control the supply amount of LNG so that dry ice is not generated.

[0102] However, if the temperature of carbon dioxide drops below the triple point during the second cooling step and dry ice is generated, causing the first re-liquefaction recovery line (RL1) or the second re-liquefaction recovery line (RL2) to be closed, it is preferable to recover the carbon dioxide by bypassing the re-liquefaction recovery line (RL) that is not closed.

[0103] For example, if the temperature of carbon dioxide drops below the triple point during the second cooling step, dry ice is generated, and the first re-liquefaction recovery line (RL1) is closed, the LNG can be recovered by bypassing the second re-liquefaction recovery line (RL2) without performing heat exchange with the cold heat of the LNG in the second evaporation gas heat exchanger (230).

[0104] At this time, a second evaporation gas control valve (250) is arranged on the second re-liquefaction recovery line (RL2), so that the first cooled compressed evaporation gas that has passed through the second evaporation gas control valve (250) expands to form a liquid-state re-liquefaction evaporation gas, and the formed liquid-state re-liquefaction evaporation gas can be recovered to the storage tank (100) along the second re-liquefaction recovery line (RL2).

[0105] Alternatively, when dry ice is generated and the first re-liquefaction recovery line (RL1) is closed, the amount of cold heat of LNG supplied to the second boil-off gas heat exchanger (230) is controlled and supplied to perform heat exchange, and the secondary cooled compressed boil-off gas formed through the heat exchange can be recovered by bypassing it to the second re-liquefaction recovery line (RL2).

[0106] At this time, the second-cooled compressed evaporation gas passes through the second evaporation gas control valve (250) on the second re-liquefaction recovery line (RL2), and can be formed as a supercooled re-liquefied evaporation gas while passing through the second evaporation gas control valve (250), and the formed liquid-state supercooled re-liquefied evaporation gas can be recovered by being injected into the storage tank (100) along the second re-liquefaction recovery line (RL2).

[0107] At this time, it is preferable to control the valve (251) so that the supercooled reliquefied evaporation gas in a liquid state can be supplied to the storage tank (100) by placing the valve (251) on the second reliquefaction recovery line (RL2).

[0108] That is, when the vessel is operated in gas mode, the carbon dioxide boil-off gas is recovered through the first re-liquefaction recovery line (RL1) or the second re-liquefaction recovery line (RL2). If the carbon dioxide boil-off gas cannot be recovered through the first re-liquefaction recovery line (RL1), it is preferable to recover and store the carbon dioxide boil-off gas through the second re-liquefaction recovery line (RL2). If the carbon dioxide boil-off gas cannot be recovered through the second re-liquefaction recovery line (RL2), it is preferable to recover and store the carbon dioxide boil-off gas through the first re-liquefaction recovery line (RL1).

[0109] The above cooling step may further include a third cooling step when the vessel is operated in oil mode.

[0110] In detail, it is preferable that the third cooling step further include a gas-liquid mixed evaporation gas generation step of expanding the first cooled compressed evaporation gas to generate a gas-liquid mixed evaporation gas, and a evaporation gas separation step of separating the gas-liquid mixed evaporation gas into a liquid-state reliquefied evaporation gas and a gas-state evaporation gas.

[0111] In addition, the above-mentioned evaporation gas separation step separates the evaporation gas in a gaseous state and the re-liquefied evaporation gas in a liquid state, and includes a recovery step of injecting the separated re-liquefied evaporation gas into a storage tank (100) and recovering it, and a recirculation step of recirculating the separated evaporation gas in a gaseous state to the evaporation gas compressor (210) to re-liquefy it.

[0112] That is, it is preferable to perform the third cooling step when secondary cooling is not performed due to lack of or insufficient cooling heat in the second evaporation gas heat exchanger.

[0113] In addition, the recirculation step is preferably such that the vaporization gas passes through the first vaporization gas heat exchanger (220) and is recirculated to the vaporization gas compressor (210), so that the vaporization gas in the gaseous state is heated while cooling the compressed vaporization gas, and the heated vaporization gas in the gaseous state is resupplied to the vaporization gas compressor (210) through the recirculation line (GL), and is recirculated by joining the vaporization gas flow from the storage tank (100) to the vaporization gas compressor (210).

[0114] As seen above, there is an effect of providing a carbon dioxide re-liquefaction system and carbon dioxide re-liquefaction method utilizing a closed cycle.

[0115] Specifically, in a liquefied carbon dioxide carrier using liquefied natural gas (LNG) as fuel, there is provided a carbon dioxide re-liquefaction system and a carbon dioxide re-liquefaction method utilizing a closed cycle capable of re-liquefying and recovering liquefied carbon dioxide vaporized gas by utilizing the cold heat of the liquefied natural gas.

[0116] Additionally, by recovering the re-liquefied carbon dioxide into the carbon dioxide cargo tank, the temperature of the vapor inside the cargo tank is lowered, thereby lowering the pressure inside the tank.

[0117] In addition, since there is no steam returned through the separator (evaporation gas separator), the flow rate of carbon dioxide evaporation gas flowing into the evaporation gas compressor (carbon dioxide compressor) is reduced, which has the effect of reducing power consumption.

[0118] In addition, when there is no or insufficient cooling of the liquefied gas, it has the effect of being able to operate selectively depending on the situation by using the existing Joule-Thompson valve and separator (evaporation gas separator).

[0119] The above description is merely an example of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications, changes, and substitutions may be made without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical idea of ​​the present invention, but rather to explain it, and the scope of the technical idea of ​​the present invention is not limited by these embodiments and the accompanying drawings. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

Claims

1. For carbon dioxide carriers using dual fuel engines, A step of forming compressed evaporative gas by supplying carbon dioxide evaporative gas evaporated in a storage tank to a compressor; A cooling step for supplying the compressed evaporation gas to a first evaporation gas heat exchanger and cooling it by heat exchange with a refrigerant circulating in a refrigeration cycle; and It includes a recovery step for recovering the re-liquefied carbon dioxide cooled through the cooling step by spraying it into the storage tank; The above cooling step additionally performs a second cooling step or a third cooling step depending on the operation mode of the carbon dioxide carrier. Method for re-liquefying carbon dioxide vaporized gas.

2. In paragraph 1, The above cooling step further includes a refrigeration cycle circulation step for cooling by circulating the refrigerant; The above refrigeration cycle circulation step is performed by exchanging heat with the compressed evaporated gas and the heated refrigerant passes through the refrigerant compressor and is compressed. The compressed refrigerant passes through the refrigerant control valve and expands and is cooled. Method for re-liquefying carbon dioxide vaporized gas.

3. In paragraph 1, When the above carbon dioxide carrier is operated in gas mode, a second cooling step is additionally performed. The second cooling step is to perform secondary cooling by supplying the compressed evaporation gas cooled primarily through the cooling step to the second evaporation gas heat exchanger and exchanging heat with the liquefied gas supplied to the engine. Method for re-liquefying carbon dioxide vaporized gas.

4. In paragraph 3, The second cooled compressed evaporation gas is expanded to form a supercooled reliquefied evaporation gas in a liquid state. Method for re-liquefying carbon dioxide vaporized gas.

5. In paragraph 3, The above secondary cooled compressed evaporation gas is supplied to the first evaporation gas control valve, The above first evaporation gas control valve expands the secondarily cooled compressed evaporation gas to form a supercooled reliquefied evaporation gas in a liquid state. Method for re-liquefying carbon dioxide vaporized gas.

6. In paragraph 5, The above liquid-state supercooled reliquefied evaporated gas is recovered to the storage tank through one recovery line selected from the first reliquefied recovery line and the second reliquefied recovery line. When the above re-liquefaction recovery line is closed by dry ice, the liquid is recovered by bypassing the unclosed re-liquefaction recovery line. Method for re-liquefying carbon dioxide vaporized gas.

7. In paragraph 1, When the above carbon dioxide carrier is operated in oil mode, a third cooling stage is additionally performed. The third cooling step is a gas-liquid mixed evaporation gas generation step that expands the first cooled compressed evaporation gas to generate a gas-liquid mixed evaporation gas; and A vaporization gas separation step for separating a vaporization gas mixture into a liquid-state re-liquefied vaporization gas and a gaseous vaporization gas; comprising: Method for re-liquefying carbon dioxide vaporized gas.

8. In paragraph 7, The above liquid-state re-liquefied evaporated gas is recovered by spraying it into the storage tank, It includes a recirculation step for recirculating the separated gaseous vaporized gas to a vaporized gas compressor to re-liquefy it; The above recirculation step is to recirculate the vaporized gas through the first vaporized gas heat exchanger to the vaporized gas compressor. The above gaseous evaporation gas is heated while cooling the compressed evaporation gas, The heated gaseous evaporation gas is resupplied to the compressor through the recirculation line. Method for re-liquefying carbon dioxide vaporized gas.

9. Engines that use liquefied gas as fuel; A storage tank for storing liquefied carbon dioxide; A vaporization gas compressor that compresses vaporization gas of liquefied carbon dioxide generated in the above storage tank to generate compressed vaporization gas; A first evaporative gas heat exchanger for cooling the compressed evaporative gas; A second evaporative gas heat exchanger that performs heat exchange with the liquefied gas supplied to the engine to cool the first cooled evaporative gas supplied from the first evaporative gas heat exchanger; and A refrigeration cycle including a refrigerant circulating to supply cold heat to the first evaporative gas heat exchanger; Carbon dioxide evaporation gas reliquefaction system.

10. In paragraph 9, The above second evaporation gas heat exchanger and storage tank are connected to a re-liquefaction recovery line. A first evaporation gas control valve is arranged on the above re-liquefaction recovery line to expand and supercool the evaporation gas that has been secondarily cooled through the second evaporation gas heat exchanger. Carbon dioxide evaporation gas reliquefaction system.

11. In paragraph 10, A spray nozzle line is arranged at the top of the above storage tank. The above spray nozzle line is connected to the above re-liquefaction recovery line and sprays the supercooled evaporated gas in the storage tank. Carbon dioxide evaporation gas reliquefaction system.

12. In paragraph 9, The above second evaporation gas heat exchanger and storage tank are connected to a recirculation line. The second non-cooled evaporation gas is recirculated to the evaporation gas compressor through the second evaporation gas heat exchanger. Carbon dioxide evaporation gas reliquefaction system.

13. In paragraph 12, A second evaporation gas control valve that expands the evaporation gas that has not been secondarily cooled in the second evaporation gas heat exchanger on the recirculation line to generate a gas-liquid mixed evaporation gas; and A vaporization gas separator is arranged to separate the above-mentioned vaporization gas mixture into a liquid-state re-liquefied vaporization gas and a gaseous vaporization gas. Carbon dioxide evaporation gas reliquefaction system.

14. In paragraph 13, The lower part of the above evaporated gas separator is connected to a re-liquefaction recovery line, The upper part of the above evaporated gas separator is connected to a recirculation line, The liquid-state reliquefied evaporated gas is supplied to the storage tank through the reliquefied recovery line. Through the above recirculation line, the vaporized gas is supplied to the first vaporized gas heat exchanger, The vaporization gas supplied to the first vaporization gas heat exchanger is heated through heat exchange and recirculated to the vaporization gas compressor. Carbon dioxide evaporation gas reliquefaction system.

15. In paragraph 9, The above second evaporation gas heat exchanger and storage tank are connected to the first re-liquefaction recovery line. A first evaporation gas control valve is arranged on the first re-liquefaction recovery line to expand and supercool the evaporation gas that has been secondarily cooled through the second evaporation gas heat exchanger. Carbon dioxide evaporation gas reliquefaction system.

16. In paragraph 15, The above second evaporation gas heat exchanger and storage tank are connected to the second re-liquefaction recovery line. A second evaporation gas control valve is disposed on the second re-liquefaction recovery line; Carbon dioxide evaporation gas reliquefaction system.

17. In paragraph 16, An evaporation gas separator is arranged on the second re-liquefaction recovery line to separate the gas-liquid mixed evaporation gas into a liquid-state re-liquefaction evaporation gas and a gas-state evaporation gas. A valve for branching the flow of evaporation gas is arranged between the second evaporation gas control valve and the evaporation gas separation valve. Carbon dioxide evaporation gas reliquefaction system.

18. In paragraph 17, The lower part of the above evaporation gas separator is connected to the third re-liquefaction recovery line, The upper part of the above evaporated gas separator is connected to a recirculation line, The liquid-state reliquefied evaporated gas is supplied to the storage tank through the reliquefied recovery line. Through the above recirculation line, the vaporized gas is supplied to the first vaporized gas heat exchanger, The vaporization gas supplied to the first vaporization gas heat exchanger is heated through heat exchange and recirculated to the vaporization gas compressor. Carbon dioxide evaporation gas reliquefaction system.

19. In paragraph 9, The above refrigeration cycle comprises a refrigerant compressor that compresses refrigerant heated through heat exchange in a first evaporative gas heat exchanger; and Further comprising a refrigerant control valve for expanding the compressed refrigerant and supplying it to the first evaporative gas heat exchanger; Carbon dioxide evaporation gas reliquefaction system.

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