A closed-cycle carbon dioxide reliquefaction system and a carbon dioxide reliquefaction method.

Abstract

The present invention relates to a method for reliquefying evaporated carbon dioxide gas. The method for reliquefying evaporated carbon dioxide gas according to the present invention, in a carbon dioxide transport ship using a dual-fuel engine, comprises: a step of supplying evaporated carbon dioxide gas evaporated in a storage tank to a compressor to generate compressed evaporated gas; a cooling step of supplying the compressed evaporated gas to a first evaporated gas heat exchanger and cooling it by heat exchange with a refrigerant circulating in a refrigeration cycle; and a recovery step of injecting the reliquefied carbon dioxide cooled in the cooling step into the storage tank for recovery, wherein the cooling step is further characterized by performing a second cooling step or a third cooling step depending on the operating mode of the carbon dioxide transport ship.

Description

Technical Field

[0002]

[0001] The present invention relates to a carbon dioxide liquefaction system and a carbon dioxide liquefaction method that utilize a closed cycle for re-liquefying and treating evaporation gas of liquefied carbon dioxide in a transport ship for liquefied carbon dioxide using liquefied gas as fuel.

Background Art

[0002] When obtaining energy from fossil fuels, carbon dioxide is generated by combustion reactions. Carbon dioxide, which is emitted in large quantities with the increasing use of fossil fuels, is designated as one of the greenhouse gases (GHG; Greenhouse Gas) that cause the global warming phenomenon.

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

[0004] Based on various international agreements regarding the reduction of carbon dioxide emissions, many countries regulate the reduction of carbon dioxide emissions. As one of the derivative technologies, carbon dioxide generated from various industrial sites is recovered and stored separately in another place for isolation, so as to reduce the amount of carbon dioxide released into the atmosphere. The development of carbon dioxide treatment technologies such as carbon capture, utilization, and storage (CCUS) is required.

[0005] The above CCUS technology liquefies and transports the treated carbon dioxide and performs separate treatment. At this time, various treatment methods have been proposed, such as injecting the liquefied carbon dioxide into the space remaining after oil extraction and storing it in a stable state, or injecting it at high pressure as a substitute for water during oil extraction and using it.

[0006] There are two main methods for liquefying carbon dioxide: the open cycle method, which involves self-heat exchange through depressurization using a Joule-Thomson valve after pressurization, and the closed cycle method, which uses a different refrigerant with a lower saturation temperature than carbon dioxide.

[0007] While closed-loop systems offer higher efficiency with smaller refrigerant usage compared to open-loop systems, they require a separate refrigeration system.

[0008] Therefore, there is a need to develop an optimal system that takes into account not only system efficiency but also cost-effectiveness. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] To solve the above-mentioned problems, the present invention aims to provide a carbon dioxide liquefaction system and a carbon dioxide liquefaction method using a closed cycle.

[0010] Specifically, the objective is to provide a carbon dioxide liquefaction system and method that utilize a closed-loop cycle in a liquefied carbon dioxide transport vessel using liquefied natural gas (LNG) as fuel, which reliquefies and recovers evaporated liquefied carbon dioxide.

[0011] Furthermore, the aim is to recover the reliquefied carbon dioxide in a carbon dioxide cargo tank (storage tank) to lower the temperature of the steam inside the cargo tank and reduce the pressure inside the tank.

[0012] The technical problems of the present invention are not limited to those described above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the following description. Means for solving the invention

[0013] To achieve the above objective, one embodiment of the present invention provides a method for reliquefying carbon dioxide vapor in a carbon dioxide transport ship using a dual-fuel engine, comprising: a step of supplying carbon dioxide vapor evaporated in a storage tank to a compressor to generate compressed vapor; a cooling step of supplying the compressed vapor to a first vapor gas heat exchanger and cooling it by heat exchange with a refrigerant circulating in a refrigeration cycle; and a recovery step of injecting the reliquefied carbon dioxide cooled in the cooling step into the storage tank for recovery, wherein the cooling step is further performed by adding a second cooling step or a third cooling step depending on the operating mode of the carbon dioxide transport ship.

[0014] Preferably, the cooling step further comprises a refrigeration cycle circulation step of circulating a refrigerant for cooling, wherein in the refrigeration cycle circulation step, the refrigerant heated by heat exchange with the compressed evaporated gas passes through a refrigerant compressor and is compressed, and the compressed refrigerant passes through a refrigerant control valve and expands for cooling.

[0015] Preferably, when the carbon dioxide transport vessel is operated in gas mode, a second cooling step is added, in which the compressed evaporative gas that has been primary cooled in the first cooling step is supplied to a second evaporative gas heat exchanger, and secondary cooling can be performed by heat exchange with the liquefied gas supplied to the engine.

[0016] Preferably, the secondary cooled compressed evaporative gas can be expanded to generate a liquid supercooled reliquefied evaporative gas.

[0017] Preferably, the secondary cooled compressed evaporative gas is supplied to a first evaporative gas control valve, and the first evaporative gas control valve can expand the secondary cooled compressed evaporative gas to generate a re-liquefied evaporative gas in a supercooled liquid state.

[0018] Preferably, the re-liquefied evaporated gas in the supercooled liquid state is recovered to the storage tank via a recovery line selected from a first re-liquefaction recovery line and a second re-liquefaction recovery line. If the re-liquefaction recovery line is blocked by dry ice, the re-liquefied evaporated gas in the supercooled liquid state is recovered by diverting to an unblocked re-liquefaction recovery line.

[0019] Preferably, when the carbon dioxide transport vessel is operated in oil mode, a third cooling step is additionally performed, the third cooling step further comprising: a gas-liquid mixed evaporated gas generation step, which expands the primary cooled compressed evaporated gas to generate a gas-liquid mixed evaporated gas; and an evaporated gas separation step, which separates the gas-liquid mixed evaporated gas into a liquid reliquefied evaporated gas and a gaseous evaporated gas.

[0020] Preferably, the system includes a recirculation step in which the liquid reliquefied evaporative gas is injected into the storage tank for recovery and the separated gaseous evaporative gas is recirculated to an evaporative gas compressor for reliquefaction; in the recirculation step, the gaseous evaporative gas passes through a first evaporative gas heat exchanger and is recirculated to an evaporative gas compressor, where the gaseous evaporative gas is heated while cooling the compressed evaporative gas, and the heated gaseous evaporative gas is resupplied to the compressor via the recirculation line.

[0021] To achieve the above-mentioned objectives, another embodiment of the present invention provides a carbon dioxide vapor reliquefaction system comprising: an engine that uses liquefied gas as fuel; a storage tank for storing liquefied carbon dioxide; an evaporative gas compressor that compresses the liquefied carbon dioxide vapor produced in the storage tank to generate compressed evaporative gas; a first evaporative gas heat exchanger for cooling the compressed evaporative gas; a second evaporative gas heat exchanger that secondarily cools the primary cooled evaporative gas supplied from the first evaporative gas heat exchanger by exchanging heat with liquefied gas supplied to the engine; and a refrigeration cycle in which a refrigerant circulates to supply cooling to the first evaporative gas heat exchanger.

[0022] Preferably, the second evaporation gas heat exchanger and the storage tank are connected to a re-liquefaction recovery line, and a first evaporation gas control valve for expanding and subcooling the evaporation gas secondarily cooled by the second evaporation gas heat exchanger is provided in the re-liquefaction recovery line.

[0023] Preferably, a spray nozzle line is provided at the upper part inside the storage tank, and the spray nozzle line is connected to the re-liquefaction recovery line to inject the subcooled evaporation gas into the storage tank.

[0024] Preferably, the second evaporation gas heat exchanger and the storage tank are connected to a recirculation line, and the evaporation gas not secondarily cooled by the second evaporation gas heat exchanger is recirculated to the evaporation gas compressor.

[0025] Preferably, a second evaporation gas control valve for expanding the evaporation gas not secondarily cooled by the second evaporation gas heat exchanger to generate a gas-liquid mixed evaporation gas; and an evaporation gas separator for separating the gas-liquid mixed evaporation gas into a liquid re-liquefied evaporation gas and a gaseous evaporation gas; are provided in the recirculation line.

[0026] Preferably, the evaporation gas separator is connected to the re-liquefaction recovery line at its lower part and to the recirculation line at its upper part. The liquid re-liquefied evaporation gas is supplied to the storage tank via the re-liquefaction recovery line, and the gaseous evaporation gas is supplied to the first evaporation gas heat exchanger via the recirculation line. The gaseous evaporation gas supplied to the first evaporation gas heat exchanger is heated by heat exchange and recirculated to the evaporation gas compressor.

[0027] Preferably, the second evaporation gas heat exchanger and the storage tank are connected to the first re-liquefaction recovery line, and a first evaporation gas control valve for expanding and subcooling the evaporation gas secondarily cooled by the second evaporation gas heat exchanger is provided in the first re-liquefaction recovery line.

[0028] Preferably, the second evaporation gas heat exchanger and the storage tank are connected to a second re-liquefaction recovery line, and a second evaporation gas control valve is provided in the second re-liquefaction recovery line.

[0029] Preferably, an evaporation gas separator for separating the evaporation gas in a gas-liquid mixture into liquid re-liquefied evaporation gas and gaseous evaporation gas is provided in the second re-liquefaction recovery line, and a valve for branching the flow of the evaporation gas is provided between the second evaporation gas control valve and the evaporation gas separator.

[0030] Preferably, the evaporation gas separator is connected to a third re-liquefaction recovery line at its lower part and to a recirculation line at its upper part. The liquid re-liquefied evaporation gas is supplied to the storage tank via the re-liquefaction recovery line, and the gaseous evaporation gas is supplied to the first evaporation gas heat exchanger via the recirculation line. The gaseous evaporation gas supplied to the first evaporation gas heat exchanger is heated by heat exchange and recirculated to the evaporation gas compressor.

[0031] Preferably, the refrigeration cycle further includes a refrigerant compressor that compresses the refrigerant heated by heat exchange in the first evaporation gas heat exchanger; and a refrigerant control valve that expands the compressed refrigerant and supplies it to the first evaporation gas heat exchanger.

Advantages of the Invention

[0032] The present invention configured as described above has the effect of providing a carbon dioxide re-liquefaction system and a carbon dioxide re-liquefaction method using a closed cycle.

[0033] Specifically, in a liquefied carbon dioxide transport ship using liquefied natural gas (LNG) as fuel, it has the effect of providing a carbon dioxide re-liquefaction system and a carbon dioxide re-liquefaction method that utilize a closed cycle to re-liquefy and recover liquefied carbon dioxide evaporation gas by making use of the cold heat of the liquefied natural gas.

[0034] Also, it has the effect of recovering the re-liquefied carbon dioxide into a carbon dioxide cargo tank, lowering the temperature of the vapor in the cargo tank, and reducing the pressure in the tank.

[0035] Furthermore, since there is no steam returned via a separator (evaporative gas separator), the flow rate of carbon dioxide evaporative gas flowing into the evaporative gas compressor (carbon dioxide compressor) is reduced, which has the effect of reducing power consumption.

[0036] Furthermore, if there is insufficient or no cooling capacity for the liquefied gas, the conventional Joule-Thomson valve and separator (evaporative gas separator) can be used to selectively operate the system according to the situation.

[0037] The technical problems of the present invention are not limited to those described above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the following description. [Brief explanation of the drawing]

[0038] [Figure 1] Figure 1 is a schematic diagram illustrating a carbon dioxide evaporative reliquefaction system according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram illustrating a carbon dioxide evaporative reliquefaction system according to one embodiment of the present invention. [Modes for carrying out the invention]

[0039] The objectives and technical configuration of the present invention, as well as its operation and effects, can be clearly understood from the detailed description based on the drawings attached to the specification of the present invention.

[0040] The terminology used herein is used solely to describe specific embodiments and is not intended to limit the invention. For example, in this specification, "includes" or "complements" a component means, unless otherwise stated, that it may include or provide other components, rather than excluding them. Furthermore, where it is stated that a component "connects" or "bonds" to another component, it should be understood that while direct connection or bonding with other components is possible, other components may be present in between.

[0041] The present invention will now be described in detail using preferred embodiments with reference to the attached drawings. The embodiments described below are provided so that those skilled in the art can easily understand the technical concept of the present invention, and should not be construed as limiting the present invention. It is natural that embodiments of the present invention can be applied in various ways by ordinary artisans in the relevant field.

[0042] In this invention, the transport means refers to a system equipped with a storage tank for liquefied carbon dioxide and capable of transporting it by land or sea. In the following description, a vessel operating on the sea will be used as an example of the transport means.

[0043] Furthermore, in one embodiment of the present invention, the vessel is a liquefied carbon dioxide carrier (LCO2 carrier). However, it is not limited to this and can be applied to any type of vessel equipped with a liquefied carbon dioxide storage tank.

[0044] Furthermore, the term "vessel" in this invention includes not only vessels with self-propulsion capabilities, but also floating offshore structures that do not possess self-propulsion capabilities.

[0045] Furthermore, the liquefied carbon dioxide transport vessel according to one embodiment of the present invention, described later, is equipped with one or more dual-fuel engines that selectively or mixed gaseous fuel and fuel oil as fuel for propulsion or power generation.

[0046] Gas fuels are stored in fuel tanks on board the ship in a liquefied state, i.e., as liquefied gas, and supplied to the engine either as a vaporized gas or in liquid form. For example, liquefied gases can be selected from hydrocarbon-based liquefied gases such as liquefied natural gas (LNG), liquefied ethane gas (LEG), liquefied petroleum gas (LPG), liquefied ethylene gas (LEG), and liquefied propylene gas (LPG), as well as non-hydrocarbon-based liquefied gases such as liquefied ammonia (NH3) and liquefied hydrogen.

[0047] In the following embodiment of the present invention, natural gas is used as the gaseous fuel, and liquefied natural gas is stored in the fuel tank.

[0048] Here, the engine is a dual-fuel engine that can use natural gas as fuel. The engine may include, for example, one or more of the following: ME-GI (MAN Electronic Gas Injection) engine, X-DF (extra-long stroke Dual Fuel) engine, DF engine (DFDE (Dual Fuel Diesel Electric), DFDG (Dual Fuel Diesel Generator)), but is not limited to these.

[0049] A carbon dioxide evaporative gas reliquefaction system according to one embodiment of the present invention will be described below with reference to Figures 1 and 2.

[0050] The liquefied carbon dioxide transport vessel according to this embodiment is equipped with a liquefied carbon dioxide system and comprises a liquefied carbon dioxide storage unit, an evaporative gas processing unit, and a fuel supply unit (not shown).

[0051] The liquefied carbon dioxide storage unit comprises one or more storage tanks 100 for storing liquefied carbon dioxide. The storage tanks 100 are pressurized tanks and are operated under a pressurized state above a predetermined pressure in order to maintain the liquid state of carbon dioxide.

[0052] The evaporative gas processing unit includes an evaporative gas compressor 210 that compresses the evaporative gas discharged from the storage tank 100, and a first evaporative gas heat exchanger 220 that cools the evaporative gas compressed by the evaporative gas compressor 210.

[0053] Specifically, the carbon dioxide evaporative gas generated in the carbon dioxide storage tank 100 flows into the evaporative gas compressor 210 via the evaporative gas supply line BL, where it is compressed to produce compressed evaporative gas. At this time, it is preferable that the compressed evaporative gas is compressed to a pressure at which at least a portion of it is liquefied during the cooling process in the first evaporative gas heat exchanger 220.

[0054] Furthermore, the evaporative gas processing unit further includes an intermediate cooler 211 that cools the evaporative gas, which has been heated during the compression process in the evaporative gas compressor 210, before supplying it to the first evaporative gas heat exchanger 220, and a buffer tank 212 that buffers the evaporative gas cooled in the intermediate cooler 211 before supplying it to the first evaporative gas heat exchanger 220. The compressed evaporative gas discharged from the evaporative gas compressor 210 passes through the evaporative gas supply line BL, is cooled in the intermediate cooler 211, then remains in the buffer tank 212, and is introduced into the high-temperature fluid flow path of the first evaporative gas heat exchanger 220.

[0055] The first evaporative gas heat exchanger 220 cools the compressed evaporative gas and exchanges heat with the compressed evaporative gas that flows in through the evaporative gas supply line BL to generate compressed cooled evaporative gas.

[0056] For example, compressed evaporative gas that flows into the first evaporative gas heat exchanger 220 via the evaporative gas supply line BL is subjected to heat exchange with the low-temperature refrigerant circulating in the refrigeration cycle 500 (described later), and the compressed evaporative gas is cooled by the heat exchange, generating compressed cooled evaporative gas.

[0057] Alternatively, the compressed evaporative gas that flows into the first evaporative gas heat exchanger 220 via the evaporative gas supply line BL undergoes heat exchange with the low-temperature refrigerant circulating in the refrigeration cycle 500 (described later) and the gaseous evaporative gas separated into liquid and gaseous states in the evaporative gas separator 260. This heat exchange cools the compressed evaporative gas, generating compressed cooled evaporative gas.

[0058] The evaporative gas processing unit further includes a second evaporative gas heat exchanger 230 in the evaporative gas supply line BL, with the second evaporative gas heat exchanger 230 located downstream of the first evaporative gas heat exchanger 220.

[0059] Specifically, the second evaporative gas heat exchanger 230 preferably performs secondary cooling by exchanging heat with the liquefied gas supplied to the engine 400 for the primary cooled compressed evaporative gas supplied from the first evaporative gas heat exchanger.

[0060] For example, when a carbon dioxide carrier is operating in gas mode, the second evaporative gas heat exchanger 230 is supplied with compressed cooled evaporative gas that has been primary cooled from the first evaporative gas heat exchanger 220. This gas exchanges heat with LNG, which is the fuel supplied from the fuel tank 300 to the engine 400 along the fuel supply line FL. The LNG is heated by the heat exchange and supplied to the engine 400, while the compressed cooled evaporative gas is secondary cooled and supplied.

[0061] Therefore, the second evaporative gas heat exchanger 230 may also function as a vaporizer that vaporizes the LNG supplied from the fuel tank 300 to the engine 400.

[0062] Alternatively, the second evaporative gas heat exchanger 230 may further include a vaporizer (not shown) downstream for vaporizing LNG supplied as fuel to the engine 400, and the second evaporative gas heat exchanger 230 may be used as a preheater to preheat the LNG before supplying it from the fuel tank 300 to the vaporizer.

[0063] Furthermore, the second evaporative gas heat exchanger 230 is connected to the storage tank 100 via the reliquefaction recovery line RL, allowing the compressed cooled evaporative gas that has passed through the second evaporative gas heat exchanger 230 and been secondarily cooled to be recovered into the storage tank 100.

[0064] Specifically, the reliquefaction and recovery line RL is equipped with a first evaporative gas control valve 240, and the secondary cooled compressed evaporative gas passes through the first evaporative gas control valve 240 and is supplied to the storage tank 100.

[0065] Alternatively, the second evaporative gas heat exchanger 230 is connected to the storage tank 100 and the first re-liquefaction and recovery line RL1, and the first re-liquefaction and recovery line RL1 is provided with a first evaporative gas control valve 240, and the secondary cooled compressed evaporative gas passes through the first evaporative gas control valve 240 and is supplied to the storage tank 100.

[0066] The first evaporative gas control valve 240 expands the secondary cooled compressed evaporative gas to generate a re-liquefied evaporative gas in a supercooled liquid state. The first evaporative gas control valve 240 preferably uses a Joule-Thomson valve that expands the evaporative gas cooled by an isenthalpic process.

[0067] Furthermore, the re-liquefaction recovery line RL is connected to the upper spray nozzle line 110 inside the storage tank 100, and the re-liquefied evaporated gas in a supercooled liquid state is injected into the storage tank 100 after passing through the first evaporated gas control valve 240. At this time, injecting the re-liquefied evaporated gas in a supercooled liquid state efficiently lowers the pressure inside the storage tank 100.

[0068] Meanwhile, the second evaporative gas heat exchanger 230 and the storage tank 100 are connected to a recirculation line GL, and the evaporative gas that was not secondarily cooled in the second evaporative gas heat exchanger 230 passes through the recirculation line GL and is recirculated to the evaporative gas compressor 210.

[0069] Alternatively, the secondary cooled compressed evaporative gas generated by heat exchange in the second evaporative gas heat exchanger 230 may be generated as dry ice as it passes through the first evaporative gas control valve 240, potentially blocking the first reliquefaction and recovery line RL1.

[0070] Therefore, the reliquefaction system of the present invention may further include a second reliquefaction recovery line RL2 connecting the second evaporative gas heat exchanger 230 and the storage tank 100, and it is preferable to provide a second evaporative gas control valve 250 in the second reliquefaction recovery line RL2.

[0071] The second evaporative gas control valve 250 expands the secondary cooled compressed evaporative gas supplied from the second evaporative gas heat exchanger 230, generating a re-liquefied evaporative gas in a supercooled liquid state. The second evaporative gas control valve 250, like the first evaporative gas control valve 240, preferably uses a Joule-Thomson valve that expands the evaporative gas cooled by an isenthalpic process.

[0072] Furthermore, the second evaporative gas heat exchanger 230 and the storage tank 100 are connected to a recirculation line GL, and the evaporative gas that was not secondarily cooled in the second evaporative gas heat exchanger 230 is recirculated to the evaporative gas compressor 210.

[0073] Specifically, when a carbon dioxide transport vessel operates in oil mode and there is no or insufficient cooling in the second evaporative gas heat exchanger, resulting in no secondary cooling, it is preferable to recirculate the gas through the recirculation line GL, and to provide the recirculation line GL with a second evaporative gas control valve 250 and an evaporative gas separator 260.

[0074] In this case, the primary cooled compressed evaporative gas that has not been secondary cooled in the second evaporative gas heat exchanger 230 preferably passes through the second evaporative gas control valve 250, generating a gas-liquid mixed evaporative gas in which liquid reliquefied evaporative gas and gaseous evaporative gas are mixed, and this generated gas-liquid mixed evaporative gas is supplied to the evaporative gas separator 260.

[0075] Alternatively, the evaporative gas separator 260 can be installed in the second re-liquefaction and recovery line RL2, with the upper part of the evaporative gas separator 260 connected to the recirculation line GL and the lower part of the evaporative gas separator 260 connected to the third re-liquefaction and recovery line RL3.

[0076] In this case, a valve 251 is further provided in the second re-liquefaction recovery line RL2 to supply the flow of evaporated gas to the evaporated gas separator 260, and it is preferable that the valve 251 is provided between the second evaporated gas control valve 250 and the evaporated gas separator 260. It is preferable that the valve 251 be a control valve or a three-way on-off valve.

[0077] In other words, the primary-cooled compressed evaporative gas that has not been secondary-cooled in the second evaporative gas heat exchanger 230 passes through the second evaporative gas control valve 250, generating a gas-liquid mixed evaporative gas in which liquid reliquefied evaporative gas and gaseous evaporative gas are mixed. This generated gas-liquid mixed evaporative gas is then supplied to the evaporative gas separator 260.

[0078] Preferably, the evaporative gas separator 260 separates the gas-liquid mixed evaporative gas into liquid reliquefied evaporative gas and gaseous evaporative gas. Specifically, it is preferable that the lower part of the evaporative gas separator 260 is connected to the storage tank 100 and the reliquefied recovery line RL or the third reliquefied recovery line RL3, and that the liquid reliquefied evaporative gas obtained by gas-liquid separation of the gas-liquid mixed evaporative gas in the evaporative gas separator 260 is recovered to the storage tank 100 via the reliquefied recovery line RL or the third reliquefied recovery line RL3.

[0079] Furthermore, the evaporative gas separator 260 is connected to the storage tank 100 and the recirculation line GL. The gaseous evaporative gas obtained by separating the gas-liquid mixture of evaporative gas in the evaporative gas separator 260 is recirculated via the recirculation line GL.

[0080] Specifically, it is preferable that the recirculation line GL is connected to the evaporative gas compressor 210, and that the gaseous evaporative gas merges with the flow of evaporative gas from the storage tank 100 to the evaporative gas compressor 210 and is recirculated.

[0081] In this case, it is preferable that the gaseous evaporated gas recirculated to the evaporative gas compressor 210 via the recirculation line GL is heated in the first evaporative gas heat exchanger 220 while recovering cold energy through heat exchange, and then supplied to the evaporative gas compressor 210.

[0082] Furthermore, the first evaporative gas heat exchanger 220 can be a three-stream heat exchanger in order to exchange heat between the gaseous evaporative gas recirculated to the evaporative gas compressor 210 via the recirculation line GL and the low-temperature refrigerant circulating in the refrigerant circulation line ML and the compressed evaporative gas transferred from the evaporative gas compressor 210 via the evaporative gas supply line BL.

[0083] In other words, the gaseous evaporated gas supplied from the evaporative gas separator 260 and the refrigerant circulating in the refrigeration cycle 500 cool the compressed evaporated gas, and the gaseous evaporated gas is heated and recirculated to the evaporative gas compressor 210.

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

[0085] Furthermore, the refrigeration cycle 500 further includes a refrigerant cooler 511 that cools the refrigerant which has been heated during the compression process in the refrigerant compressor 510. The refrigerant that flows into the refrigerant compressor 510 via the refrigerant circulation line ML is compressed in the refrigerant compressor 510 to produce compressed refrigerant, which is then cooled in the refrigerant cooler 511 and then supplied to the first evaporative gas heat exchanger 220 via the refrigerant circulation line ML.

[0086] In this case, the refrigerant control valve 520 is a flow rate adjustment valve that adjusts the flow rate of the cooling compressed refrigerant, i.e., the low-temperature refrigerant, supplied from the refrigerant cooler 511 to the first evaporative gas heat exchanger 220 via the refrigerant circulation line ML, and has the function of expanding the compressed refrigerant cooled in the refrigerant cooler 511 in an isenthalpic process.

[0087] As a result, the low-temperature refrigerant, after passing through the refrigerant cooler 511 and the refrigerant control valve 520, flows into the first evaporative gas heat exchanger 220 in liquid form, vaporizes due to heat exchange, and flows into the refrigerant compressor 510 in gaseous form.

[0088] In other words, it is preferable that the low-temperature refrigerant circulating in the refrigerant circulation line ML is heated by the evaporative gas compressor 210 while exchanging heat with the compressed evaporative gas supplied by the compressor, and that the low-temperature refrigerant becomes a high-temperature refrigerant while cooling the carbon dioxide evaporative gas in the first evaporative gas heat exchanger 220, and that the high-temperature refrigerant flows into the refrigerant compressor 510 via the refrigerant circulation line ML and circulates in 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 to these, and it is preferable to select and apply a refrigerant that is suitable for circulating in the refrigeration cycle 500 and for the reliquefaction of carbon dioxide evaporative gas.

[0089] Hereinafter, a method for reliquefying carbon dioxide evaporated gas according to one embodiment of the present invention will be described with reference to the carbon dioxide evaporated gas reliquefaction system according to one embodiment of the present invention described above.

[0090] In a carbon dioxide transport vessel using a dual-fuel engine, the method for reliquefying carbon dioxide vapor comprises a step for forming compressed vapor gas, a cooling step, and a recovery step.

[0091] In the compressed evaporative gas formation process, the carbon dioxide evaporative gas evaporated in the storage tank 100 is supplied to the evaporative gas compressor 210 and compressed as it passes through the evaporative gas compressor 210. At this time, the compressed evaporative gas is cooled in the intercooler 211 via the evaporative gas supply line BL and can be stored in the buffer tank 210 before flowing into the high-temperature fluid flow path of the first evaporative gas heat exchanger 220.

[0092] The cooling process further comprises a refrigeration cycle circulation process in which compressed evaporative gas is supplied to a first evaporative gas heat exchanger 220 and cooled by heat exchange with the refrigerant circulating in the refrigeration cycle.

[0093] In the refrigeration cycle circulation process, the refrigerant heated by heat exchange with the compressed evaporative gas passes through the refrigerant compressor and is compressed. This compressed refrigerant then passes through the refrigerant control valve and is expanded and cooled. This cooled refrigerant then passes through the first evaporative gas heat exchanger 220 to cool the compressed evaporative gas supplied from the storage tank 100.

[0094] Furthermore, the cooling process may include a second cooling process depending on the operating mode of the carbon dioxide transport vessel.

[0095] Specifically, when operating a ship in gas mode, the second cooling process may be carried out by supplying the compressed evaporative gas, which has been primarily cooled in the cooling process, to the second evaporative gas heat exchanger.

[0096] In the second cooling step, it is preferable that the primary cooled compressed evaporative gas is supplied to the second evaporative gas heat exchanger 230, and the primary cooled compressed evaporative gas exchanges heat with the liquefied gas supplied to the engine 400 to perform secondary cooling.

[0097] For example, the second evaporative gas heat exchanger 230 receives compressed cooled evaporative gas that has been primary cooled from the first evaporative gas heat exchanger 220, and performs heat exchange with liquefied gas (LNG), which is fuel supplied from the fuel tank 300 to the engine 400 along the fuel supply line FL. Through heat exchange, the LNG is heated and supplied to the engine 400, and the compressed cooled evaporative gas is secondary cooled and supplied.

[0098] Specifically, as shown in Figure 1, the compressed evaporative gas that has been secondarily cooled in the second cooling step is supplied to the first evaporative gas control valve 240. It is preferable that the re-liquefied evaporative gas, which has passed through the evaporative gas control valve 240 and is in a supercooled liquid state, is injected and recovered in the storage tank. At this time, by injecting and recovering the re-liquefied evaporative gas in a supercooled liquid state, the pressure inside the storage tank 100 can be efficiently reduced.

[0099] Alternatively, as shown in Figure 2, it is preferable that the compressed evaporated gas, which has been secondarily cooled in the second cooling step, is recovered into a storage tank via one of the recovery lines selected from the first reliquefaction recovery line RL1 and the second reliquefaction recovery line RL2.

[0100] For example, when secondary-cooled compressed evaporative gas is recovered via the first reliquefaction recovery line RL1, the secondary-cooled compressed evaporative gas passes through the first evaporative gas control valve 240 to generate reliquefied evaporative gas in a supercooled liquid state, and this reliquefied evaporative gas in a supercooled liquid state is injected and recovered in the storage tank. In this case, by injecting and recovering the reliquefied evaporative gas in a supercooled liquid state, the pressure inside the storage tank 100 can be efficiently reduced.

[0101] On the other hand, if the cold energy of the LNG is used excessively during the execution of the second cooling process, the temperature of carbon dioxide may drop below the triple point, generating dry ice. This dry ice generation may block the first reliquefaction and recovery line RL1 or the second reliquefaction and recovery line RL2, preventing the recovery of carbon dioxide into the storage tank 100. Therefore, it is preferable to control the amount of LNG supplied to prevent the generation of dry ice.

[0102] However, if the temperature of carbon dioxide drops below the triple point during the execution of the second cooling process, generating dry ice and blocking the first re-liquefaction and recovery line RL1 or the second re-liquefaction and recovery line RL2, it is preferable to divert the carbon dioxide to the unblocked re-liquefaction and recovery line RL for recovery.

[0103] For example, if the temperature of carbon dioxide drops below the triple point during the execution of the second cooling process and the first re-liquefaction and recovery line RL1 becomes blocked due to the generation of dry ice, the second evaporative gas heat exchanger 230 will not perform heat exchange with the cold energy of LNG, and the carbon dioxide will be diverted to the second re-liquefaction and recovery line RL2 for recovery.

[0104] At this time, a second evaporative gas control valve 250 is provided on the second reliquefaction recovery line RL2, and the compressed evaporative gas that has been primarily cooled after passing through the second evaporative gas control valve 250 expands to generate liquid reliquefied evaporative gas, and this generated liquid reliquefied evaporative gas is recovered in the storage tank 100 along the second reliquefaction recovery line RL2.

[0105] Alternatively, if the first re-liquefaction and recovery line RL1 is blocked by the generation of dry ice, the amount of cold energy supplied to the second evaporative gas heat exchanger 230 is controlled and supplied while heat exchange is performed, and the secondary cooled compressed evaporative gas generated by the heat exchange is diverted to the second re-liquefaction and recovery line RL2 for recovery.

[0106] At this time, the secondary cooled compressed evaporative gas passes through the second evaporative gas control valve 250 of the second reliquefaction and recovery line RL2, generating supercooled reliquefied evaporative gas as it passes through the second evaporative gas control valve 250. This generated liquid supercooled reliquefied evaporative gas is then injected along the reliquefaction and recovery line RL2 into the storage tank 100 for recovery.

[0107] In this case, it is preferable to provide a valve 251 in the second reliquefaction recovery line RL2 and to control the valve 251 so that liquid supercooled reliquefaction evaporated gas is supplied to the storage tank 100.

[0108] In other words, when operating a vessel in gas mode, it is preferable to recover the evaporated carbon dioxide gas via the first reliquefaction and recovery line RL1 or the second reliquefaction and recovery line RL2. If it is not possible to recover the evaporated carbon dioxide gas via the first reliquefaction and recovery line RL1, it is preferable to recover and store the evaporated carbon dioxide gas via the second reliquefaction and recovery line RL2. If it is not possible to recover the evaporated carbon dioxide gas via the second reliquefaction and recovery line RL2, it is preferable to recover and store the evaporated carbon dioxide gas via the first reliquefaction and recovery line RL1.

[0109] The cooling process may further include a third cooling process when the vessel is operating in oil mode.

[0110] Specifically, the third cooling step preferably further comprises a gas-liquid mixed evaporated gas generation step, which expands the primary cooled compressed evaporated gas to generate a gas-liquid mixed evaporated gas, and an evaporated gas separation step, which separates the gas-liquid mixed evaporated gas into a liquid reliquefied evaporated gas and a gaseous evaporated gas.

[0111] Furthermore, the evaporative gas separation process includes a recovery process in which gaseous evaporative gas and liquid reliquefied evaporative gas are separated, and the separated reliquefied evaporative gas is injected into a storage tank 100 for recovery, and a recirculation process in which the separated gaseous evaporative gas is recirculated to an evaporative gas compressor 210 for reliquefaction.

[0112] In other words, the third cooling step is preferably performed when there is no or insufficient cooling in the second evaporative gas heat exchanger and secondary cooling has not occurred.

[0113] Furthermore, the recirculation process involves passing the first evaporative gas heat exchanger 220 and recirculating it to the evaporative gas compressor 210. Preferably, the gaseous evaporative gas is heated while cooling the compressed evaporative gas, and the heated gaseous evaporative gas is resupplied to the evaporative gas compressor 210 via the recirculation line GL, where it joins the flow of evaporative gas from the storage tank 100 to the evaporative gas compressor 210 and is recirculated.

[0114] As described above, a carbon dioxide reliquefaction system and a carbon dioxide reliquefaction method utilizing a closed-loop cycle are provided.

[0115] Specifically, the present invention provides a carbon dioxide reliquefaction system and method that utilize a closed-loop cycle in a liquefied carbon dioxide transport vessel fueled by liquefied natural gas (LNG), which uses the cold energy of liquefied natural gas to reliquefy and recover evaporated liquefied carbon dioxide.

[0116] Furthermore, by recovering the reliquefied carbon dioxide in the carbon dioxide cargo tank, the temperature of the steam inside the cargo tank is lowered, which has the effect of reducing the pressure inside the tank.

[0117] Furthermore, because there is no steam returned via the separator (evaporative gas separator), the flow rate of carbon dioxide evaporative gas into the evaporative gas compressor (carbon dioxide compressor) decreases, resulting in a reduction in power consumption.

[0118] Furthermore, if there is no or insufficient cooling of the liquefied gas, the conventional Joule-Thomson valve and separator (evaporative gas separator) can be used to selectively operate the system according to the situation.

[0119] The above description is merely illustrative of the technical concept of the present invention, and those skilled in the art to which the present invention belongs can make various modifications, changes, and substitutions within the bounds of the essence of the present invention. Therefore, the embodiments and accompanying drawings disclosed herein are explanatory, not limiting, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by the embodiments and accompanying drawings. The scope of protection of the present invention shall be interpreted by the following claims, and all technical concepts within the same scope shall be interpreted as being included within the scope of the rights of the present invention.

Claims

1. In a method for reliquefying evaporated carbon dioxide gas in a carbon dioxide transport ship using a dual-fuel engine, A process of supplying the evaporated carbon dioxide gas from the storage tank to a compressor to produce compressed evaporated gas; and, A cooling step in which the compressed evaporative gas is supplied to a first evaporative gas heat exchanger and cooled by heat exchange with the refrigerant circulating in the refrigeration cycle; A recovery step is to inject the re-liquefied carbon dioxide cooled in the cooling step into the storage tank for recovery; The cooling process may be further modified by adding a second or third cooling process depending on the operating mode of the carbon dioxide transport vessel. A method for reliquefying evaporated carbon dioxide gas.

2. The cooling step further comprises a refrigeration cycle circulation step of circulating a refrigerant to cool; In the refrigeration cycle circulation process, the refrigerant heated by heat exchange with the compressed evaporated gas passes through a refrigerant compressor and is compressed, and the compressed refrigerant passes through a refrigerant control valve and is expanded and cooled. The method for reliquefying evaporated carbon dioxide gas according to claim 1.

3. When the aforementioned carbon dioxide transport vessel is operated in gas mode, a second cooling process is added. In the second cooling step, the compressed evaporative gas that has been primarily cooled in the first cooling step is supplied to a second evaporative gas heat exchanger, and secondary cooling is performed by heat exchange with the liquefied gas supplied to the engine. The method for reliquefying evaporated carbon dioxide gas according to claim 1.

4. The secondary cooled compressed evaporative gas is expanded to generate a liquid supercooled reliquefied evaporative gas. The method for reliquefying evaporated carbon dioxide gas according to claim 3.

5. The secondary cooled compressed evaporative gas is supplied to the first evaporative gas control valve. The first evaporative gas control valve expands the secondary cooled compressed evaporative gas to generate a re-liquefied evaporative gas in a supercooled liquid state. The method for reliquefying evaporated carbon dioxide gas according to claim 3.

6. The re-liquefied evaporated gas in the supercooled liquid state is recovered into the storage tank via one recovery line selected from the first re-liquefaction recovery line and the second re-liquefaction recovery line. If the aforementioned re-liquefaction and recovery line becomes blocked by dry ice, the supercooled liquid state of the re-liquefied evaporated gas is recovered by diverting to an unblocked re-liquefaction and recovery line. The method for reliquefying evaporated carbon dioxide gas according to claim 5.

7. When the aforementioned carbon dioxide transport vessel is operated in oil mode, a third cooling process is added. The third cooling step is a gas-liquid mixed evaporative gas generation step, which involves expanding the primary cooled compressed evaporative gas to generate a gas-liquid mixed evaporative gas; The system further comprises: an evaporation gas separation step for separating a gas-liquid mixture of evaporated gas into a liquid re-liquefied evaporated gas and a gaseous evaporated gas; The method for reliquefying evaporated carbon dioxide gas according to claim 1.

8. The aforementioned liquid reliquefied evaporated gas is injected into the storage tank and recovered. The separated gaseous evaporated gas is recirculated to an evaporative gas compressor for reliquefaction; a recirculation step is provided. In the aforementioned recirculation process, the gaseous evaporative gas passes through the first evaporative gas heat exchanger and is recirculated to the evaporative gas compressor. The aforementioned gaseous evaporated gas is heated while the compressed evaporated gas is cooled. The heated vaporized gas is resupplied to the compressor via the recirculation line. The method for reliquefying evaporated carbon dioxide gas according to claim 7.

9. An engine that uses liquefied gas as fuel; and, Storage tanks for storing liquefied carbon dioxide; and, An evaporative gas compressor that compresses the liquefied carbon dioxide evaporative gas produced in the storage tank to produce compressed evaporative gas; A first evaporative gas heat exchanger for cooling the compressed evaporative gas; and A second evaporative gas heat exchanger that performs secondary cooling by exchanging heat between the primary cooled evaporative gas supplied from the first evaporative gas heat exchanger and the liquefied gas supplied to the engine; A refrigeration cycle comprising: a refrigerant circulating to supply cooling energy to the first evaporative gas heat exchanger; A system for reliquefying evaporated carbon dioxide gas.

10. The second evaporative gas heat exchanger and the storage tank are connected to a re-liquefaction recovery line. The re-liquefaction and recovery line is provided with a first evaporative gas control valve that expands and supercools the evaporative gas that has been secondarily cooled in the second evaporative gas heat exchanger. The carbon dioxide vapor reliquefaction system according to claim 9.

11. A spray nozzle line is provided at the top of the storage tank. The spray nozzle line is connected to the re-liquefaction and recovery line, and the supercooled evaporated gas is injected into the storage tank. The carbon dioxide evaporation gas reliquefaction system according to claim 10.

12. The second evaporative gas heat exchanger and the storage tank are connected to a recirculation line. The evaporated gas that was not secondarily cooled in the second evaporated gas heat exchanger is recirculated to the evaporated gas compressor. The carbon dioxide vapor reliquefaction system according to claim 9.

13. The recirculation line includes a second evaporative gas control valve that expands the evaporative gas that was not secondarily cooled in the second evaporative gas heat exchanger to generate a gas-liquid mixed evaporative gas; An evaporative gas separator is provided to separate the aforementioned gas-liquid mixture of evaporated gas into a liquid re-liquefied evaporated gas and a gaseous evaporated gas; The carbon dioxide evaporation gas reliquefaction system according to claim 12.

14. The aforementioned evaporative gas separator is connected to a re-liquefaction recovery line at its lower end and to a recirculation line at its upper end. The liquid reliquefied evaporated gas is supplied to the storage tank via the reliquefaction recovery line. The gaseous evaporative gas is supplied to the first evaporative gas heat exchanger via the aforementioned recirculation line. The gaseous evaporative gas supplied to the first evaporative gas heat exchanger is heated by heat exchange and recirculated to the evaporative gas compressor. The carbon dioxide evaporation gas reliquefaction system according to claim 13.

15. The second evaporative gas heat exchanger and the storage tank are connected to the first re-liquefaction and recovery line. The first re-liquefaction and recovery line is provided with a first evaporative gas control valve that expands and supercools the evaporative gas that has been secondarily cooled in the second evaporative gas heat exchanger. The carbon dioxide vapor reliquefaction system according to claim 9.

16. The second evaporative gas heat exchanger and the storage tank are connected to the second re-liquefaction and recovery line. A second evaporation gas control valve is provided in the second reliquefaction and recovery line. The carbon dioxide evaporation gas reliquefaction system according to claim 15.

17. The second reliquefaction and recovery line is provided with an evaporative gas separator that separates the gas-liquid mixed evaporative gas into liquid reliquefied evaporative gas and gaseous evaporative gas. A valve is provided between the second evaporative gas control valve and the evaporative gas separator to divert the flow of evaporative gas. The carbon dioxide evaporation gas reliquefaction system according to claim 16.

18. The aforementioned evaporative gas separator is connected to the third re-liquefaction recovery line at its lower end and to the recirculation line at its upper end. The liquid reliquefied evaporated gas is supplied to the storage tank via the reliquefaction recovery line. The gaseous evaporative gas is supplied to the first evaporative gas heat exchanger via the aforementioned recirculation line. The gaseous evaporative gas supplied to the first evaporative gas heat exchanger is heated by heat exchange and recirculated to the evaporative gas compressor. The carbon dioxide evaporation gas reliquefaction system according to claim 17.

19. The aforementioned refrigeration cycle is A refrigerant compressor that compresses the refrigerant heated by heat exchange in the first evaporative gas heat exchanger; A refrigerant control valve that expands the compressed refrigerant and supplies it to the first evaporative gas heat exchanger; further comprising The carbon dioxide vapor reliquefaction system according to claim 9.

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