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

Abstract

The present invention relates to a carbon dioxide reliquefaction system and a carbon dioxide reliquefaction method utilizing a closed cycle. The carbon dioxide evaporative reliquefaction system according to the present invention includes an engine that uses liquefied gas as fuel, a storage tank for storing liquefied carbon dioxide, an evaporative gas compressor that compresses the carbon dioxide evaporative gas evaporated in the storage tank to produce compressed evaporative gas, a first evaporative gas heat exchanger for cooling the compressed evaporative gas, and a refrigeration cycle in which a refrigerant circulates to supply cooling to the first evaporative gas heat exchanger, wherein the refrigeration cycle includes a refrigerant compressor for compressing the refrigerant heated by heat exchange in the first evaporative gas heat exchanger, a refrigerant control valve for supplying the compressed refrigerant to the first evaporative gas heat exchanger after it has expanded, and a second evaporative gas heat exchanger for cooling the refrigerant that has passed through the refrigerant control valve by heat exchange with the carbon dioxide evaporative gas evaporated in the storage tank.

Description

Technical Field

[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 liquefied carbon dioxide carrier that uses liquefied gas as fuel.

Background Art

[0002] When obtaining energy from fossil fuels, carbon dioxide is generated by combustion reactions. Carbon dioxide emitted in large quantities due to 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 the global warming index of carbon dioxide is lower than that of other greenhouse gases, it is classified as a very important greenhouse gas in terms of accounting for about 80% of the total greenhouse gas emissions and being able to regulate the emissions.

[0004] Through various international agreements, each country regulates the reduction of carbon dioxide emissions. As one of the technologies derived therefrom, after collecting carbon dioxide generated at various industrial sites and storing it separately in a different location, carbon dioxide treatment technologies such as carbon capture, utilization, and storage technology (CCUS: Carbon Capture Utilization & Storage) that reduce the amount of carbon dioxide released into the atmosphere are required to be developed.

[0005] The CCUS technology liquefies and transports the post-treated carbon dioxide and then processes it separately. At this time, various treatment options are presented, such as storing the liquefied carbon dioxide in a stable state by injecting it into the space remaining after oil extraction, or injecting it at a high pressure to use it instead of water when extracting oil.

[0006] In this process, to liquefy carbon dioxide, two methods are used: an open-cycle method, which performs heat exchange through depressurization via a Joule-Thomson valve after pressurization, and a closed-cycle method, which uses a separate refrigerant with a lower saturation temperature than carbon dioxide. (See, for example, Patent Document 1) .

[0007] While closed-cycle systems can achieve high efficiency with less refrigerant compared to open-cycle systems, they require a separate refrigeration system.

[0008] Therefore, there is a need to develop an optimal system that takes into account system efficiency and cost aspects. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International release WO2013 / 055115A1 [Overview of the project] [Problems that the invention aims to solve]

[0010] To solve the above-mentioned problems, the present invention aims to provide a carbon dioxide liquefaction system and a carbon dioxide liquefaction method utilizing a closed cycle.

[0011] More specifically, in liquefied carbon dioxide carriers that use liquefied natural gas (LNG) as fuel, the objective is to reduce the amount of refrigerant circulating in the refrigeration cycle by utilizing the cold energy of evaporated carbon dioxide gas from the liquefied carbon dioxide storage tank to cool the refrigerant circulating in the refrigeration cycle.

[0012] Furthermore, after recovering the reliquefied carbon dioxide in a carbon dioxide cargo tank (storage tank), the objective is to reduce the pressure inside the tank by lowering the temperature of the steam inside the cargo tank.

[0013] The technical problems of the present invention are not limited to those mentioned above, and other technical problems not mentioned can be clearly understood by an ordinary person from the following description. [Means for solving the problem]

[0014] According to one aspect of the present invention for achieving the above-mentioned objectives, a carbon dioxide vapor reliquefaction system is provided, comprising: an engine that uses liquefied gas as fuel; a storage tank for storing liquefied carbon dioxide; an evaporative gas compressor that compresses the carbon dioxide vapor evaporated in the storage tank to produce compressed evaporative gas; a first evaporative gas heat exchanger for cooling the compressed evaporative gas; and a refrigeration cycle in which a refrigerant circulates to supply cooling to the first evaporative gas heat exchanger, wherein the refrigeration cycle includes a refrigerant compressor for compressing the refrigerant heated by heat exchange in the first evaporative gas heat exchanger; a refrigerant control valve for expanding the compressed refrigerant and then supplying it to the first evaporative gas heat exchanger; and a second evaporative gas heat exchanger for cooling the refrigerant that has passed through the refrigerant control valve by heat exchange with the carbon dioxide vapor evaporated in the storage tank.

[0015] Preferably, the second evaporative gas heat exchanger can supply the carbon dioxide evaporative gas, which has been heated by heat exchange with the refrigerant, to the evaporative gas compressor.

[0016] Preferably, the refrigeration cycle further includes a refrigerant heat exchanger, the second evaporative gas heat exchanger primarily cools the refrigerant that has passed through the refrigerant control valve by exchanging heat with carbon dioxide evaporative gas evaporated in the storage tank, the refrigerant heat exchanger primarily cools the primarily cooled refrigerant by exchanging heat with liquefied gas supplied to the engine, and the carbon dioxide evaporative gas heated by heat exchange with the refrigerant can be supplied to an evaporative gas compressor.

[0017] Preferably, the system includes a re-liquefaction and recovery line connecting the first evaporative gas heat exchanger to a storage tank, and a first evaporative gas control valve located in the re-liquefaction and recovery line.

[0018] Preferably, a spray nozzle line is located in the upper part of the storage tank, and the spray nozzle line is connected to the re-liquefaction and recovery line, allowing the supercooled evaporated gas to be injected into the storage tank.

[0019] Preferably, the system includes a recirculation line connecting the first evaporative gas heat exchanger to a storage tank, allowing the evaporative gas that has not been cooled through the first evaporative gas heat exchanger to be recirculated to the evaporative gas compressor via the recirculation line.

[0020] Preferably, the recirculation line may include a second evaporative gas control valve that expands the evaporative gas that has not been cooled by the first evaporative gas heat exchanger to generate a gas-liquid mixed evaporative gas, and an evaporative gas separator that separates the gas-liquid mixed evaporative gas into a liquid reliquefied evaporative gas and a gaseous evaporative gas.

[0021] Preferably, the lower part of the evaporative gas separator is connected to a reliquefaction and recovery line, and the upper part of the evaporative gas separator is connected to a recirculation line, wherein the reliquefied evaporative gas in liquid state is supplied to a storage tank via the reliquefaction and recovery line, and the evaporative gas in gaseous state is supplied to a first evaporative gas heat exchanger via the recirculation line, and the evaporative gas in gaseous state supplied to the first evaporative gas heat exchanger is heated through heat exchange and then recirculated to the evaporative gas compressor.

[0022] According to another aspect of the present invention for achieving the above objective, the carbon dioxide evaporated gas in the storage tank Evaporated gasA compressed evaporation gas forming step of supplying to a compressor to form a compressed evaporation gas, a cooling step of cooling the compressed evaporation gas by heat exchange with a refrigerant circulating in a refrigeration cycle, and a recovery step of recovering the re-liquefied carbon dioxide cooled through the cooling step, wherein the cooling step includes a refrigerant circulation step in which the refrigerant circulates in the refrigeration cycle, and the refrigerant circulation step includes a refrigerant cooling step of cooling the refrigerant, and the refrigerant cooling step cools the refrigerant by heat exchange with carbon dioxide evaporation gas, and the carbon dioxide evaporation gas heated by the heat exchange is Evaporated gas Provided is a method for re-liquefying carbon dioxide evaporation gas, which is supplied to a compressor.

[0023] Preferably, the compressed evaporation gas forming step may further include a first heat exchange step of primarily heat-exchanging the carbon dioxide evaporation gas evaporated in a storage tank.

[0024] Preferably, the refrigerant cooling step may include a first refrigerant cooling step of primarily cooling the refrigerant while heat-exchanging the refrigerant with carbon dioxide evaporation gas, and a second refrigerant cooling step of secondarily cooling the primarily cooled refrigerant while heat-exchanging the refrigerant with liquefied gas supplied to an engine.

[0025] Preferably, the cooling step may further include a gas-liquid mixed evaporation gas generating step of expanding the compressed evaporation gas to generate a gas-liquid mixed evaporation gas, and an evaporation gas separating step of separating the gas-liquid mixed evaporation gas into a re-liquefied evaporation gas in a liquid state and an evaporation gas in a gaseous state.

[0026] Preferably, the re-liquefied evaporation gas in the liquid state may include a recycling step of injecting and recovering the re-liquefied evaporation gas into the storage tank and recycling the separated evaporation gas in the gaseous state to an evaporation gas compressor to re-liquefy the evaporation gas.

[0027] Preferably, the recycling step is a step in which the evaporation gas in the gaseous state passes through a first evaporation gas heat exchanger and is recycled to the evaporation gas compressor, and the evaporation gas in the gaseous state is heated while cooling the compressed evaporation gas, and the heated evaporation gas in the gaseous state is , re Via a circulation line Evaporated gas It can be resupplied to the compressor. [Effects of the Invention]

[0028] According to the present invention configured as described above, there is an effect of providing a carbon dioxide reliquefaction system and a carbon dioxide reliquefaction method that utilize a closed cycle.

[0029] More specifically, in liquefied carbon dioxide carriers that use liquefied natural gas (LNG) as fuel, utilizing the cold energy of evaporated carbon dioxide gas from liquefied carbon dioxide storage tanks to cool the refrigerant circulating in the refrigeration cycle has the effect of reducing the amount of refrigerant circulating in the refrigeration cycle.

[0030] Furthermore, the heat exchange of the evaporated carbon dioxide gas raises its temperature, and the recirculating gaseous carbon dioxide and the evaporated carbon dioxide gas are mixed before flowing into the compressor, eliminating the need to install a separate cryogenic compressor.

[0031] Furthermore, after recovering the reliquefied carbon dioxide in a carbon dioxide cargo tank (storage tank), lowering the temperature of the steam inside the cargo tank has the effect of reducing the pressure inside the tank.

[0032] Since evaporated gas is constantly generated from the liquefied carbon dioxide storage tank, continuous operation is possible.

[0033] The technical problems of the present invention are not limited to those mentioned above, and other technical problems not mentioned can be clearly understood by an ordinary person from the following description. [Brief explanation of the drawing]

[0034] [Figure 1] This is a simplified diagram illustrating a carbon dioxide evaporative reliquefaction system according to one embodiment of the present invention. [Figure 2] This is a simplified diagram showing a carbon dioxide evaporative reliquefaction system according to another embodiment of the present invention. [Modes for carrying out the invention]

[0035] The objectives, technical configuration, and detailed aspects of the present invention, as well as its operation and effects, will be better understood through a detailed description based on the drawings attached to the specification of the present invention.

[0036] The terms used herein are for illustrative purposes only to describe specific embodiments and are not intended to limit the invention. For example, the term "includes" a component in this specification means that it may include other components, rather than excluding them, unless otherwise stated. Furthermore, when it is mentioned that one component is "linked" or "connected" to another component, it should be understood that this may mean that it is directly linked to or connected to the other component, or that other components may be present in between.

[0037] The present invention will be described in detail below by referring to the attached drawings to describe preferred embodiments of the present invention. Each embodiment described below is provided so that the technical concept of the present invention can be easily understood by those skilled in the art, and should not be construed as limiting the present invention, and it is obvious that each embodiment of the present invention can be applied in various ways by those ordinary in the art.

[0038] In the present invention described later, 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 below, the transportation means will be described as a ship operating at sea as an example.

[0039] Furthermore, in one embodiment of the present invention, the vessel may be a liquefied carbon dioxide carrier (LCO2 Carrier), but is not limited thereto. Any vessel equipped with a liquefied carbon dioxide storage tank can be similarly fitted with the embodiments described later.

[0040] Furthermore, in this specification, the term "ship" can include not only ships that have propulsion capabilities themselves, but also floating structures on the sea that do not have propulsion capabilities.

[0041] Furthermore, a liquefied carbon dioxide carrier according to one embodiment of the present invention, described later, may be equipped with one or more dual-fuel engines that can use gaseous fuel and fuel oil as fuel by selectively or by mixing them, as propulsion engines or power generation engines.

[0042] Here, the gaseous fuel may be stored in the ship's fuel tanks in a liquefied state, i.e., in the form of liquefied gas, or it may be supplied to the engine in a gaseous or liquid state by vaporization. For example, the liquefied gas may be selected from hydrocarbon series such as liquefied natural gas (LNG), liquefied ethane gas (LEG), liquefied petroleum gas (LPG), liquefied ethylene gas, and liquefied propylene gas, as well as from non-hydrocarbon series liquefied gases such as liquefied ammonia (NH3) and liquefied hydrogen.

[0043] In the embodiment described later, the case in which the gaseous fuel is natural gas will be used as an example, and therefore, liquefied natural gas may be stored in the fuel tank.

[0044] Here, the engine is a dual-fuel engine, and engines used in ships can use natural gas as fuel. For example, the engine may include, but is not limited to, 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), and DFDG (Dual Fuel Diesel Generator)).

[0045] The carbon dioxide vapor reliquefaction system according to one embodiment of the present invention will be described below with reference to Figures 1 and 2.

[0046] The liquefied carbon dioxide carrier according to this embodiment includes a liquefied carbon dioxide system and may be equipped with a liquefied carbon dioxide storage unit, an evaporative gas processing unit, and a fuel supply unit (not shown).

[0047] The liquefied carbon dioxide storage unit includes one or more storage tanks 100 for storing liquefied carbon dioxide, and the storage tanks 100 can be operated as pressurized tanks under a pressure above a certain level so as to maintain the carbon dioxide in a liquid state.

[0048] 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. The carbon dioxide evaporative gas generated in the carbon dioxide storage tank 100 can flow into the evaporative gas compressor 210 via the evaporative gas supply line BL.

[0049] More specifically, the evaporative gas processing unit further includes a second evaporative gas heat exchanger 120 in the evaporative gas supply line BL, and the evaporative gas discharged from the storage tank 100 undergoes heat exchange as it passes through the second evaporative gas heat exchanger 120, and compressed evaporative gas can be generated when the heat-exchanged carbon dioxide evaporative gas flows into the evaporative gas compressor 210.

[0050] At this time, the carbon dioxide evaporative gas flowing in through the evaporative gas supply line BL exchanges heat with the low-temperature refrigerant circulating in the refrigeration cycle 500, which will be described later. This heat exchange can heat the carbon dioxide evaporative gas, and the carbon dioxide whose temperature has risen due to the heating can flow into the evaporative gas compressor.

[0051] Furthermore, it is preferable that the compressed evaporative gas is compressed to a pressure such that at least a portion of it is liquefied during the cooling process in the first evaporative gas heat exchanger 220.

[0052] Furthermore, the evaporative gas processing unit may further include an intermediate cooler 211 for cooling the evaporative gas, whose temperature has risen 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 for buffering 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 is cooled in the intermediate cooler 211 via the evaporative gas supply line BL, and then supplied to the buffer tank 212 It can remain there before being introduced into the high-temperature fluid flow path of the first evaporative gas heat exchanger 220.

[0053] The first evaporative gas heat exchanger 220 cools the compressed evaporative gas and can generate compressed cooled evaporative gas by exchanging heat with the compressed evaporative gas that flows in through the evaporative gas supply line BL.

[0054] For example, the compressed evaporative gas flowing into the first evaporative gas heat exchanger 220 via the evaporative gas supply line BL may exchange heat with the low-temperature refrigerant circulating in the refrigeration cycle 500 described later, so that the compressed evaporative gas is cooled by the heat exchange.

[0055] Alternatively, the compressed evaporated gas flowing in via the evaporated gas supply line BL may undergo heat exchange with the low-temperature refrigerant circulating in the refrigeration cycle 500 (described later) and the gaseous evaporated gas separated in the evaporated gas separator 260, thereby cooling the compressed evaporated gas.

[0056] The evaporative gas processing unit further includes a reliquefied evaporative gas recovery line RL that connects the first evaporative gas heat exchanger 220 to the storage tank 100, and the cooled compressed evaporative gas from the first evaporative gas heat exchanger 210 is recovered to the storage tank 100 via the reliquefied evaporative gas recovery line RL.

[0057] More specifically, a first evaporative gas control valve 240 is located in the reliquefaction and recovery line RL, and the cooled compressed evaporative gas can be supplied to the storage tank 100 by passing through the first evaporative gas control valve 240.

[0058] In this case, the first evaporative gas control valve 240 expands the cooled compressed evaporative gas to generate a re-liquefied evaporative gas in a liquid state, and the re-liquefied evaporative gas in a liquid state may be supercooled. For this reason, it is preferable to use a Joule-Thomson valve that expands the evaporative gas cooled by an isentropic process as the first evaporative gas control valve 240.

[0059] Furthermore, the re-liquefaction recovery line RL is connected to the upper spray nozzle line 110 in the storage tank 100, and the re-liquefied evaporated gas in a supercooled liquid state that has passed through the first evaporated gas control valve 240 can be injected into the storage tank. At this time, injecting the supercooled re-liquefied evaporated gas in a liquid state has the effect of effectively lowering the pressure inside the storage tank 100.

[0060] Furthermore, the evaporative gas processing unit includes a recirculation line GL that connects the first evaporative gas heat exchanger 220 to the storage tank 100, allowing the compressed evaporative gas to be recirculated to the evaporative gas compressor 210 after heat exchange has been performed through the first evaporative gas heat exchanger 220.

[0061] More specifically, a second evaporative gas control valve 250 and an evaporative gas separator 260 are arranged in the recirculation line GL, and a liquid compressed cooled evaporative gas is formed by heat exchange through the first evaporative gas heat exchanger 220. The compressed cooled evaporative gas passes through the second evaporative gas control valve 250, generating a gas-liquid mixed evaporative gas in which the liquid reliquefied evaporative gas and the gaseous evaporative gas are mixed, and the generated gas-liquid mixed evaporative gas can be supplied to the evaporative gas separator 260.

[0062] The evaporative gas separator 260 separates the gas-liquid mixed evaporative gas into a liquid reliquefied evaporative gas and a gaseous evaporative gas. The evaporative gas separator 260 and the storage tank 100 may be connected via both a reliquefied recovery line RL and a recirculation line GL.

[0063] More specifically, the lower part of the evaporative gas separator 260 is connected to the storage tank 100 via a re-liquefaction recovery line RL, and it is preferable that the re-liquefied evaporative gas in a liquid state obtained by separating the gas-liquid mixed evaporative gas in the evaporative gas separator 260 is recovered to the storage tank 100 via the re-liquefaction recovery line RL.

[0064] In other words, the reliquefied evaporated gas in liquid state can be recovered and stored in the storage tank 100 via the reliquefied recovery line RL or the recirculation line GL, and can be selectively recovered depending on the system conditions. For example, if ice (dry ice) is generated in the operating line of the reliquefied recovery line RL and the recirculation line GL, the reliquefied evaporated gas can be recovered by diverting it to the line where no ice is being generated.

[0065] On the other hand, the evaporative gas separator 260 is connected to the storage tank 100 via a recirculation line GL, and the gaseous evaporative gas obtained by separating the gas-liquid mixed evaporative gas in the evaporative gas separator 260 can be recirculated via the recirculation line GL.

[0066] More specifically, the recirculation line GL is connected to the evaporative gas compressor 210, and it is preferable that the gaseous evaporative gas recirculated to the evaporative gas compressor 210 via the recirculation line GL is heated while recovering cold energy through heat exchange in the first evaporative gas heat exchanger 220, and then supplied to the evaporative gas compressor 210.

[0067] In this case, it is preferable that the evaporated gas, from which the cooling energy has been recovered, is heated after passing from the storage tank 100 through the second evaporated gas heat exchanger 120 and then recirculated by joining the flow of evaporated gas toward the evaporated gas compressor 210. By mixing the evaporated carbon dioxide gas evaporated in the storage tank 100 with the flow of recirculated evaporated gas, the temperature can rise to above room temperature (approximately 35°C).

[0068] In other words, the carbon dioxide vapor, whose temperature has risen, is resupplied to the evaporative gas compressor 210, which has the effect of eliminating the need to consider a cryogenic compressor when arranging the evaporative gas compressor 210.

[0069] Furthermore, a 3-stream heat exchanger can be applied as the first evaporative gas heat exchanger 220 so that 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 can exchange heat with the compressed evaporative gas transferred from the evaporative gas compressor 210 via the evaporative gas supply line BL.

[0070] 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 can be heated and then recirculated to the evaporative gas compressor 210.

[0071] The refrigeration cycle 500 may be configured to 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.

[0072] Furthermore, the refrigeration cycle 500 includes a refrigerant cooler 511 for cooling the refrigerant whose temperature has risen during the compression process in the refrigerant compressor 510. The refrigerant introduced 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 supplied to the first evaporative gas heat exchanger 220 via the refrigerant circulation line ML.

[0073] Furthermore, the refrigeration cycle 500 preferably further includes a second evaporative gas heat exchanger 120. More specifically, the second evaporative gas heat exchanger 120 is located in the refrigerant circulation line ML, preferably downstream of the refrigerant cooler 511. That is, the refrigerant that has passed through the refrigerant cooler 511 passes through the second evaporative gas heat exchanger 120 and is cooled by heat exchange with the carbon dioxide evaporative gas evaporated from the storage tank 100.

[0074] Alternatively, as shown in Figure 2, the refrigeration cycle 500 preferably further includes a second evaporative gas heat exchanger 120 and a refrigerant heat exchanger 310, and more specifically, the second evaporative gas heat exchanger 120 and the refrigerant heat exchanger 310 are arranged in the refrigerant circulation line ML, and preferably downstream of the refrigerant cooler 511.

[0075] In other words, the refrigerant that has passed through the refrigerant cooler 511 passes through the second evaporative gas heat exchanger 120 and is first cooled by heat exchange with carbon dioxide evaporative gas evaporated from the storage tank 100. The first cooled refrigerant then passes through the refrigerant heat exchanger 310 and is secondarily cooled by heat exchange with liquefied gas (LNG), which is fuel supplied from the fuel tank 300 to the engine 400.

[0076] In this configuration, the LNG is heated through heat exchange in the refrigerant heat exchanger 310 before being supplied to the engine 400, and the refrigerant can be secondarily cooled and circulated. Therefore, the refrigerant heat exchanger 310 can function as a vaporizer that vaporizes the LNG supplied from the fuel tank 300 to the engine 400.

[0077] or ,cold The refrigerant heat exchanger 310 is further equipped with a vaporizer (not shown) downstream for vaporizing LNG supplied as fuel to the engine 400, and the refrigerant heat exchanger 310 can also be used as a preheater to preheat the LNG before supplying it from the fuel tank 300 to the vaporizer.

[0078] On the other hand, a refrigerant control valve 520 may be located downstream of the refrigerant heat exchanger 310.

[0079] The refrigerant control valve 520 may also be a flow control valve that adjusts the flow rate of the cooling compressed refrigerant, i.e., the low-temperature refrigerant, supplied from the refrigerant heat exchanger 310 to the first evaporative gas heat exchanger 220 via the refrigerant circulation line ML, and may have the function of expanding the compressed refrigerant cooled in the refrigerant heat exchanger 310 by an isentropic process.

[0080] Therefore, the low-temperature refrigerant that has passed through the second evaporative gas heat exchanger 120 and the refrigerant control valve 520 flows into the first evaporative gas heat exchanger 220 in a liquid state, is vaporized by heat exchange, and then flows into the refrigerant compressor 510 in a gaseous state.

[0081] In other words, the low-temperature refrigerant circulating in the refrigerant circulation line ML is heated while exchanging heat with the compressed evaporative gas supplied by the evaporative gas compressor 210. 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 the high-temperature refrigerant is introduced to the refrigerant compressor 510 via the refrigerant circulation line ML and preferably circulates in the refrigeration cycle 500.

[0082] In this case, the refrigerant circulating in the refrigeration cycle 500 may be a hydrocarbon-based refrigerant such as ammonia or propane, but is not limited to these. It is preferable to select and apply a refrigerant that is suitable for circulating in the refrigeration cycle 500 and reliquefying the evaporated carbon dioxide gas.

[0083] The following describes a method for reliquefying carbon dioxide evaporated gas according to one embodiment of the present invention, with reference to the carbon dioxide evaporated gas reliquefaction system according to one embodiment of the present invention described above.

[0084] In a carbon dioxide carrier using a dual-fuel engine, the method for reliquefying the carbon dioxide vapor may be configured to include a compressed vapor gas formation step, a cooling step, and a recovery step.

[0085] The compressed evaporative gas formation step involves supplying the carbon dioxide evaporative gas evaporated in the storage tank 100 to the evaporative gas compressor 210, so that the carbon dioxide evaporative gas can be compressed as it passes through the carbon dioxide evaporative gas compressor 210.

[0086] More specifically, the carbon dioxide evaporative gas evaporated from the storage tank 100 undergoes heat exchange as it passes through the second evaporative gas heat exchanger 120, and compressed evaporative gas can be generated when the heat-exchanged carbon dioxide evaporative gas flows into the evaporative gas compressor 210.

[0087] At this time, the carbon dioxide evaporative gas flowing into the second evaporative gas heat exchanger via the evaporative gas supply line BL exchanges heat with the low-temperature refrigerant circulating in the refrigeration cycle 500, thereby heating the carbon dioxide evaporative gas, and the carbon dioxide whose temperature has risen due to the heating can flow into the evaporative gas compressor.

[0088] Furthermore, the compressed evaporated gas that has passed through the evaporated gas compressor 210 is cooled in the intermediate cooler 211 via the evaporated gas supply line BL, and then in the buffer tank 212 It can remain there before being introduced into the high-temperature fluid flow path of the first evaporative gas heat exchanger 220.

[0089] The cooling process involves supplying the compressed evaporative gas to the first evaporative gas heat exchanger 220 and cooling it by heat exchange with the refrigerant circulating in the refrigeration cycle, and may include a refrigerant circulation process in which the refrigerant circulates in the refrigeration cycle.

[0090] Furthermore, the refrigerant circulation process may further include a refrigerant cooling process for cooling the heated refrigerant. In the refrigerant cooling process, the refrigerant heated by heat exchange with the compressed evaporative gas passes through a refrigerant compressor and is compressed, and the compressed refrigerant expands and is cooled as it passes through a refrigerant control valve, and the cooled refrigerant passes through the first evaporative gas heat exchanger 220 and cools the compressed evaporative gas supplied from the storage tank 100.

[0091] More specifically, in the refrigerant cooling process, it is preferable that the refrigerant that has passed through the refrigerant compressor 510 and the refrigerant cooler 511 passes through the second evaporative gas heat exchanger 120 and performs heat exchange with the carbon dioxide evaporative gas evaporated from the storage tank 100.

[0092] Subsequently, the cooled refrigerant passes through a refrigerant control valve 520 located downstream of the refrigerant heat exchanger 310. As the cooled compressed refrigerant passes through the refrigerant control valve 520, it expands, and the temperature of the refrigerant may decrease further.

[0093] Alternatively, the refrigerant cooling process preferably comprises a first refrigerant cooling process in which the refrigerant that has passed through the refrigerant compressor 510 and the refrigerant cooler 511 passes through the second evaporative gas heat exchanger 120 and is primarily cooled while exchanging heat with carbon dioxide evaporative gas evaporated from the storage tank 100, and a second refrigerant cooling process in which the refrigerant that has been primarily cooled passes through the refrigerant heat exchanger 310 and is primarily cooled while exchanging heat with liquefied gas (LNG), which is fuel supplied from the fuel tank 300 to the engine 400.

[0094] At this time, the refrigerant cooled through the second refrigerant cooling process passes through a refrigerant control valve 520 located downstream of the refrigerant heat exchanger 310. As the cooled compressed refrigerant passes through the refrigerant control valve 520, it expands, and the temperature of the refrigerant can decrease further.

[0095] Subsequently, the refrigerant, whose temperature has been lowered by cooling, passes through the first evaporative gas heat exchanger 220 and exchanges heat with the compressed evaporative gas. This heat exchange cools the compressed evaporative gas, and the cooled compressed evaporative gas can be supplied to the first evaporative gas control valve 240.

[0096] At this time, the cooled compressed evaporative gas passing through the first evaporative gas control valve 240 is formed into a liquid re-liquefied evaporative gas after expansion, and this liquid re-liquefied evaporative gas can be recovered into the storage tank 100.

[0097] More specifically, the re-liquefied evaporated gas in liquid state is in a supercooled state, and it is preferable to inject the supercooled re-liquefied evaporated gas in liquid state into the storage tank for recovery. In this case, injecting and recovering the re-liquefied evaporated gas in liquid state can effectively reduce the pressure inside the storage tank 100.

[0098] A method for reliquefying carbon dioxide evaporative gas may further include a gas-liquid mixed evaporative gas generation step, in which the compressed evaporative gas compressed in the cooling step is expanded to generate a gas-liquid mixed evaporative gas, and an evaporative gas separation step, in which the gas-liquid mixed evaporative gas is separated into a reliquefied evaporative gas in a liquid state and an evaporative gas in a gaseous state.

[0099] Furthermore, the evaporative gas separation step may further include a recovery step of injecting the separated liquid reliquefied evaporative gas into a storage tank 100 for recovery, and a recirculation step of recirculating the separated gaseous evaporative gas to an evaporative gas compressor 210 for reliquefaction.

[0100] More specifically, if the refrigerant is not sufficiently cooled, the compressed evaporative gas that has passed through the first evaporative gas heat exchanger 220 is supplied to the second evaporative gas control valve 250, and the compressed evaporative gas that has passed through the second evaporative gas control valve 250 expands to form a gas-liquid mixed evaporative gas.

[0101] Subsequently, the gas-liquid mixed evaporative gas is supplied to the evaporative gas separator 260, where it is separated into a gaseous evaporative gas and a liquid evaporative gas. Preferably, the liquid evaporative gas is injected into the storage tank 100 for recovery, and the separated gaseous evaporative gas is recirculated to the evaporative gas compressor 210 for reliquefaction.

[0102] In other words, when heat exchange is performed in the first evaporative gas heat exchanger 220, if there is no or insufficient cooling, it is preferable to supply the compressed evaporative gas to the second evaporative gas control valve 250 for recovery.

[0103] On the other hand, the recirculation process involves recirculating the evaporative gas to the evaporative gas compressor 210 while passing through the first evaporative gas heat exchanger 220. Preferably, the evaporative gas in a gaseous state from which cooling energy has been recovered while passing through the first evaporative gas heat exchanger 220 is heated after passing through the second evaporative gas heat exchanger 120 from the storage tank 100, and then recirculated by joining the flow of evaporative gas toward the evaporative gas compressor 210.

[0104] As explained above, this system has the effect of providing a carbon dioxide reliquefaction system and a carbon dioxide reliquefaction method that utilize a closed cycle.

[0105] More specifically, in liquefied carbon dioxide carriers that use liquefied natural gas (LNG) as fuel, utilizing the cold energy of evaporated carbon dioxide gas from liquefied carbon dioxide storage tanks to cool the refrigerant circulating in the refrigeration cycle has the effect of reducing the amount of refrigerant circulating in the refrigeration cycle.

[0106] Furthermore, the heat exchange of the evaporated carbon dioxide gas raises its temperature, and the recirculating gaseous carbon dioxide and the evaporated carbon dioxide gas are mixed before flowing into the compressor, eliminating the need to install a separate cryogenic compressor.

[0107] Furthermore, after recovering the reliquefied carbon dioxide in a carbon dioxide cargo tank (storage tank), lowering the temperature of the steam inside the cargo tank has the effect of reducing the pressure inside the tank.

[0108] Since evaporated gas is constantly generated from the liquefied carbon dioxide storage tank, continuous operation is possible.

[0109] The above description is merely illustrative of the technical concept of the present invention, and a person with ordinary skill in the art to which the present invention pertains will be able to make various modifications, changes, and substitutions without departing from the essential characteristics of the present invention. Therefore, the embodiments and accompanying drawings disclosed herein are for illustrative purposes only, not to limit the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments and accompanying drawings. The scope of protection of the present invention must be interpreted in accordance with the following claims, and all technical concepts within an equivalent scope should be interpreted as being included in the scope of rights of the present invention.

Claims

1. An engine that uses liquefied gas as fuel; Storage tanks for storing liquefied carbon dioxide; An evaporative gas compressor that compresses the carbon dioxide evaporated gas in the aforementioned storage tank to produce compressed evaporative gas; A first evaporative gas heat exchanger for cooling the compressed evaporative gas; and A refrigeration cycle comprising a refrigerant circulating to supply cooling energy to the first evaporative gas heat exchanger; The aforementioned refrigeration cycle includes a refrigerant compressor that compresses the refrigerant heated by heat exchange in a first evaporative gas heat exchanger; A refrigerant control valve that expands the compressed refrigerant and then supplies it to the first evaporative gas heat exchanger; and A carbon dioxide vapor reliquefaction system comprising: a second vapor gas heat exchanger that cools the refrigerant that has passed through the refrigerant control valve by heat exchange with carbon dioxide vapor gas evaporated in the storage tank;

2. The carbon dioxide evaporative gas reliquefaction system according to claim 1, wherein the second evaporative gas heat exchanger supplies the carbon dioxide evaporative gas, which has been heated by heat exchange with the refrigerant, to the evaporative gas compressor.

3. The refrigeration cycle further includes a refrigerant heat exchanger; The second evaporative gas heat exchanger first cools the refrigerant that has passed through the refrigerant control valve by exchanging heat with the carbon dioxide evaporative gas evaporated in the storage tank. The refrigerant heat exchanger secondarily cools the refrigerant that has been first cooled by exchanging heat with the liquefied gas supplied to the engine. The carbon dioxide evaporative gas reliquefaction system according to claim 1, wherein the carbon dioxide evaporative gas heated by heat exchange with the refrigerant is supplied to an evaporative gas compressor.

4. A re-liquefaction and recovery line connecting the first evaporative gas heat exchanger to the storage tank, The carbon dioxide evaporative gas reliquefaction system according to claim 1, further comprising a first evaporative gas control valve disposed in the reliquefaction recovery line.

5. The spray nozzle line is positioned at the top of the storage tank, The carbon dioxide evaporative gas reliquefaction system according to claim 4, wherein the spray nozzle line is connected to the reliquefaction and recovery line and injects the supercooled evaporative gas into the storage tank.

6. The system includes a recirculation line connecting the first evaporative gas heat exchanger to a storage tank, The carbon dioxide evaporative gas reliquefaction system according to claim 1, wherein the evaporative gas that has not been cooled through the first evaporative gas heat exchanger is recirculated to the evaporative gas compressor via a recirculation line.

7. The recirculation line includes a second evaporative gas control valve that expands the evaporative gas that has not been cooled by the first evaporative gas heat exchanger to generate a gas-liquid mixed evaporative gas; and The carbon dioxide evaporative gas reliquefaction system according to claim 6, further comprising an evaporative gas separator for separating the gas-liquid mixed evaporative gas into a reliquefied evaporative gas in a liquid state and an evaporative gas in a gaseous state.

8. The lower part of the aforementioned evaporative gas separator is connected to the re-liquefaction recovery line. The upper part of the aforementioned evaporative gas separator is connected to the recirculation line, The re-liquefied evaporated gas in liquid state is supplied to the storage tank via the re-liquefaction recovery line. The evaporated gas in a gaseous state is supplied to the first evaporated gas heat exchanger via the aforementioned recirculation line. The carbon dioxide evaporative gas reliquefaction system according to claim 7, wherein the evaporative gas in a gaseous state supplied to the first evaporative gas heat exchanger is heated through heat exchange and then recirculated to the evaporative gas compressor.

9. A compressed evaporative gas formation process in which the carbon dioxide evaporated in the storage tank is supplied to a compressor to form compressed evaporative gas; A cooling step in which the compressed evaporated gas is cooled by heat exchange with a refrigerant circulating in a refrigeration cycle; A recovery step for recovering the re-liquefied carbon dioxide cooled through the aforementioned cooling step; The cooling step includes a refrigerant circulation step in which the refrigerant circulates through the refrigeration cycle; The refrigerant circulation step includes a refrigerant cooling step for cooling the refrigerant; A method for reliquefying carbon dioxide vapor, wherein the refrigerant cooling step involves cooling the refrigerant by heat exchange with carbon dioxide vapor, and supplying the heat-heated carbon dioxide vapor to a compressor.

10. The method for reliquefying carbon dioxide vapor gas according to claim 9, wherein the compressed vapor gas formation step further includes a first heat exchange step of firstly exchanging heat with carbon dioxide vapor gas evaporated in a storage tank.

11. The method for reliquefying carbon dioxide vapor gas according to claim 9, wherein the compressed vapor gas formation step further includes a first heat exchange step of firstly exchanging heat with carbon dioxide vapor gas evaporated in a storage tank.

12. The cooling step includes a gas-liquid mixed evaporative gas generation step in which the compressed evaporative gas is expanded to generate a gas-liquid mixed evaporative gas; and A method for reliquefying carbon dioxide evaporative gas according to claim 9, further comprising an evaporation gas separation step of separating a gas-liquid mixed evaporation gas into a reliquefied evaporation gas in a liquid state and an evaporation gas in a gaseous state.

13. The re-liquefied evaporated gas in the liquid state is injected into the storage tank and recovered. A method for reliquefying carbon dioxide evaporative gas according to claim 12, comprising a recirculation step of recirculating the separated gaseous evaporative gas back to an evaporative gas compressor in order to reliquefy it.

14. The aforementioned recirculation process involves the evaporated gas in a gaseous state passing through the first evaporated gas heat exchanger and being recirculated to the evaporated gas compressor. The aforementioned gaseous evaporated gas is heated while the compressed evaporated gas is cooled. The method for reliquefying carbon dioxide evaporative gas according to claim 13, wherein the heated gaseous evaporated gas is resupplied to the compressor via the recirculation line.

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