Ship evaporative gas treatment system and evaporative gas treatment method

Abstract

A marine evaporative emission control system and method are disclosed. [Solution] The ship evaporative gas treatment system of the present invention comprises a first compressor that compresses evaporated gas generated from liquefied gas stored in a storage tank of the ship, a second compressor that compresses evaporated gas generated from the liquefied gas stored in the storage tank, a heat exchanger that cools the evaporated gas compressed by the first compressor or the second compressor, and a refrigerant circulation line that circulates refrigerant supplied to the heat exchanger. The first compressor is a multi-stage compressor having multiple compression sections and compresses evaporated gas to a fuel supply pressure of a propulsion engine, and the second compressor compresses evaporated gas to a fuel supply pressure of a power generation engine to which fuel of a lower pressure than the propulsion engine is supplied, and the evaporated gas compressed in some of the compression sections of the first compressor is cooled by the heat exchanger or supplied to the power generation engine.

Description

Technical Field

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[0001] The present invention relates to a ship's evaporation gas treatment system and an evaporation gas treatment method. More specifically, in a ship provided with a propulsion engine and a power generation engine to which fuel at a lower pressure than the propulsion engine is supplied, evaporation gas (BOG, Boil-Off Gas) generated from liquefied gas stored in a storage tank in the ship is supplied as fuel to the engine, and the evaporation gas not used as fuel is re-liquefied and recovered into the storage tank. The present invention relates to a ship's evaporation gas treatment system and an evaporation gas treatment method.

Background Art

[0002] In recent years, the consumption of liquefied gas such as liquefied natural gas (LNG) has been increasing rapidly worldwide. Liquefied gas obtained by liquefying natural gas at a low temperature has the advantage of improving storage and transportation efficiency because its volume is greatly reduced compared to the gaseous state. In addition, liquefied gas such as liquefied natural gas can remove or reduce air pollutants during the liquefaction process and is an environmentally friendly fuel with low emissions of air pollutants during combustion.

[0003] Liquefied natural gas is a colorless and transparent liquid obtained by cooling natural gas mainly composed of methane to about -163°C for liquefaction, and its volume is about 1 / 600 that of natural gas. Therefore, liquefying natural gas enables very efficient transportation.

[0004] However, since the liquefaction temperature of natural gas is extremely low at -162°C under atmospheric pressure, liquefied natural gas is sensitive to temperature changes and easily evaporates. Therefore, the storage tank in which liquefied natural gas is stored is heat-insulated, but due to the continuous transfer of external heat to the storage tank, during the transportation process of liquefied natural gas, liquefied natural gas continuously vaporizes naturally in the storage tank and evaporation gas is generated.

[0005] Evaporative gases represent a loss of LNG, making them a significant issue in terms of transportation efficiency. Furthermore, the accumulation of evaporated gases in storage tanks can lead to excessive pressure increases, potentially causing the tanks to rupture. Therefore, various methods are being studied to treat evaporated gases generated in storage tanks. Recently, methods such as reliquefying the evaporated gases and returning them to the storage tank, or using the evaporated gases as an energy source at fuel demand sites such as ship engines, are being employed.

[0006] Methods for reliquefying evaporated gases include those that utilize a refrigeration cycle with other refrigerants and reliquefy the evaporated gas through heat exchange with the refrigerant, and those that use the evaporated gas itself as a refrigerant without using other refrigerants to reliquefy it.

[0007] On the other hand, among the engines commonly used in ships, those that can use natural gas as fuel include gas-fueled engines such as DFDE, X-DF, and ME-GI engines.

[0008] The DFDE consists of four stages and employs the Otto Cycle, in which natural gas at a relatively low pressure of about 5.5 barg is injected into the combustion air inlet and compressed as the piston rises.

[0009] The X-DF engine consists of two strokes, uses approximately 15 barg of natural gas as fuel, and employs the Otto cycle. Furthermore, the ME-GI engine consists of two strokes and employs a diesel cycle that directly injects high-pressure natural gas at around 300 barg into the combustion chamber near the top dead center of the piston. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Korean Registered Patent Publication No. 10-1386543 [Patent Document 2] Korean Registered Patent Publication No. 10-1751854 [Overview of the project] [Problems that the invention aims to solve]

[0011] The applicant of this application has invented a method for reliquefying evaporated gas without using other refrigerants by using the evaporated gas itself as a refrigerant. This method involves cooling the evaporated gas compressed by a compressor through heat exchange with the evaporated gas before compression, and then expanding it using a Joule-Thomson valve or the like to reliquefy a portion of the evaporated gas. Such a system is called a PRS (Partial Re-liquefaction System).

[0012] When the amount of liquefied gas in the storage tank is large, the amount of evaporated gas generated is also large. In cases where a large amount of evaporated gas needs to be reliquefied, such as when a ship is at anchor or when the amount of evaporated gas used by the engine is small due to low-speed operation, PRS alone may not be able to reach the required amount of reliquefaction. Therefore, the applicant of this application has invented an improved PRS technology to enable the reliquefaction of a larger amount of evaporated gas.

[0013] As an improved technology of PRS, a system that can further cool the evaporated gas by using the evaporated gas itself as a refrigerant in a refrigerant cycle is called MRS (Methane Refrigeration System).

[0014] Furthermore, other refrigerants, such as mixed refrigerants or nitrogen, can be used separately to cool the evaporated gas that is reliquefied.

[0015] On the other hand, in ships equipped with engines that use evaporated gas as fuel, the compressor that supplies fuel to the engine can be used to reliquefy the evaporated gas.

[0016] Figure 1 shows a ship equipped with engines E1 and E2 that are supplied with evaporated gas generated from LNG as fuel. This ship is equipped with an evaporated gas treatment system, in which the evaporated gas, compressed to high pressure by fuel supply compressors 10A and 10B, is supplied as fuel to engines E1 and E2. The compressed evaporated gas that is not used as fuel is cooled by the cold energy of the evaporated gas in a heat exchanger 20, then depressurized in a depressurization device 30, separated into gas and liquid in a gas-liquid separator 40, and recovered in a storage tank T.

[0017] The compressors 10A and 10B, installed for this fuel supply, are provided according to the fuel supply conditions required by the engine, and two compressors are installed, including a redundant compressor required by the classification society (Korean Register) to prepare for compressor failure. In cases such as anchoring, when the engine's fuel consumption is low and the amount of evaporated gas to be reliquefied is large, both compressors may be operated. However, in this case, the cooling of the heat exchanger 20 becomes insufficient, resulting in low reliquefaction efficiency, while the electricity consumption to drive the two high-pressure compressors is high, reducing energy efficiency, and the cost of installing the two high-pressure compressors is also high.

[0018] The present invention solves these problems and provides an evaporative gas treatment system and an evaporative gas treatment method that can improve reliquefaction efficiency and reduce installation and operating costs. [Means for solving the problem]

[0019] To solve the above problems, the present invention provides a ship's evaporative gas treatment system comprising: a first compressor for compressing evaporated gas generated from liquefied gas stored in a ship's storage tank; a second compressor for compressing evaporated gas generated from liquefied gas stored in the storage tank; a heat exchanger for cooling the evaporated gas compressed by the first or second compressor; and a refrigerant circulation line for circulating a refrigerant supplied to the heat exchanger. The first compressor is a multi-stage compressor having a plurality of compression sections, and compresses the evaporated gas to the fuel supply pressure of the propulsion engine. The second compressor compresses the evaporated gas to the fuel supply pressure of a power generation engine, which is supplied with fuel at a lower pressure than the propulsion engine. The evaporated gas compressed by a portion of the compression section of the first compressor is cooled by the heat exchanger or supplied to the power generation engine.

[0020] Furthermore, it is preferable that the refrigerant circulation line is provided with a refrigerant compression section that compresses the refrigerant discharged from the heat exchanger after heat exchange in the heat exchanger, and a refrigerant expansion section that expands and cools the refrigerant that has been compressed in the refrigerant compression section and cooled in the heat exchanger, before supplying it to the heat exchanger.

[0021] Furthermore, in the present invention, it is preferable to further include an evaporated gas supply line that supplies evaporated gas generated in the storage tank to the heat exchanger and then to the first compressor or the second compressor; a first fuel supply line that connects the downstream of the first compressor to the propulsion engine; a reliquefaction line that cools the evaporated gas compressed by a part of the compression section of the first compressor or the second compressor in the heat exchanger and recovers it in the storage tank; and a second fuel supply line that supplies the evaporated gas compressed by a part of the compression section of the first compressor or the second compressor to the power generation engine.

[0022] In the present invention, a branch line that branches from the evaporation gas supply line, bypasses the heat exchanger, and supplies evaporation gas to the first compressor or the second compressor, and a preheater provided in the branch line for heating the evaporation gas are further provided. When the re-liquefaction system for re-liquefying the evaporation gas is not operating or when the load on the re-liquefaction system is small, it is preferable to supply all or part of the evaporation gas generated in the storage tank, after bypassing the heat exchanger, through the branch line to the preheater for heating and then supply it to the first compressor or the second compressor.

[0023] In the present invention, a decompression device for decompressing the compressed evaporation gas cooled by the heat exchanger, and a gas-liquid separator for gas-liquid separating the evaporation gas decompressed by the decompression device are further provided. It is preferable to merge the flash gas separated by the gas-liquid separator with the flow of uncompressed evaporation gas supplied to the first compressor or the second compressor upstream of the heat exchanger, and recover the liquefied gas separated by the gas-liquid separator into the storage tank.

[0024] In the present invention, a liquefied gas supply line for supplying the liquefied gas stored in the storage tank as fuel to the propulsion engine, a pressurizing pump provided in the liquefied gas supply line for pressurizing the liquefied gas to the fuel supply pressure of the propulsion engine, and a vaporizer for heating the liquefied gas pressurized by the pressurizing pump are further preferably provided.

[0025] In the present invention, a liquefied gas branch line that branches from the liquefied gas supply line downstream of the vaporizer and is connected to the power generation engine, a pressure regulating valve provided in the liquefied gas branch line for regulating the pressure of the liquefied gas according to the fuel supply pressure of the power generation engine, and a heater provided in the liquefied gas branch line for additionally heating the liquefied gas passing through the pressure regulating valve according to the fuel supply temperature of the power generation engine are further preferably provided.

[0026] Further, in the present invention, in the ship speed generation section, the first compressor is driven to compress the evaporated gas generated in the storage tank by the first compressor, and supply it to the propulsion engine and the power generation engine. At the same time, the excess compressed evaporated gas is cooled by the heat exchanger. When the ship is at anchor, it is preferable to drive the second compressor to compress the evaporated gas generated in the storage tank by the second compressor, supply it to the power generation engine, and cool the excess compressed evaporated gas by the heat exchanger.

[0027] Further, in the present invention, it is preferable that the refrigerant circulating in the refrigerant circulation line is nitrogen.

[0028] Also, in the present invention, in a method for treating evaporated gas of a ship provided with a propulsion engine and a power generation engine to which fuel at a pressure lower than that of the propulsion engine is supplied, after compressing the evaporated gas generated from the liquefied gas stored in the storage tank with a first compressor or a second compressor, the compressed evaporated gas not supplied as fuel to the propulsion engine and the power generation engine is cooled and reliquefied by a heat exchanger to which a refrigerant circulated through a refrigerant circulation line is supplied. The first compressor is a multistage compressor having a plurality of compression parts, compresses the evaporated gas to the fuel supply pressure of the propulsion engine, the second compressor compresses the evaporated gas to the fuel supply pressure of the power generation engine, and the evaporated gas compressed by a part of the compression parts of the first compressor is cooled by the heat exchanger or supplied to the power generation engine. A method for treating evaporated gas of a ship is provided.

[0029] Further, in the present invention, in the ship speed generation section, the first compressor is driven to compress the evaporated gas generated in the storage tank by the first compressor, and then supply it to the propulsion engine and the power generation engine. At the same time, the excess compressed evaporated gas is cooled by the heat exchanger. When the ship is at anchor, the second compressor is driven to compress the evaporated gas generated in the storage tank by the second compressor, and then supply it to the power generation engine. At the same time, it is preferable to cool the excess compressed evaporated gas by the heat exchanger.

[0030] Furthermore, in the present invention, it is preferable that the refrigerant circulating in the refrigerant circulation line is compressed in the refrigerant compression section, cooled in the heat exchanger, then expanded and cooled in the refrigerant expansion section, and supplied to the heat exchanger as a cooling source, and that the refrigerant compression section is connected to the refrigerant expansion section, and that the expansion energy of the refrigerant is transmitted from the refrigerant expansion section to compress the refrigerant. [Effects of the Invention]

[0031] The present invention relates to a ship equipped with a propulsion engine and a power generation engine supplied with fuel at a lower pressure than that of the propulsion engine, comprising a first compressor that compresses the evaporated gas to the fuel supply pressure of the propulsion engine and a second compressor that compresses the evaporated gas to the fuel supply pressure of the power generation engine, wherein the evaporated gas compressed by a part of the compression section of the first compressor is supplied to a heat exchanger for cooling or supplied to the power generation engine.

[0032] By equipping the ship with a multi-stage compressor capable of compressing evaporated gas to high pressure and another compressor capable of compressing it to lower pressure, and by operating them separately according to the ship's operating conditions, redundancy requirements are met, electricity consumption is reduced, and the ship can be operated efficiently by utilizing evaporated gas as fuel.

[0033] Furthermore, by utilizing the cold energy of the evaporated gas itself and the cold energy of the refrigerant cycle to improve the cooling efficiency of the heat exchanger, the reliquefaction rate can be increased without the need to install additional equipment such as boost compressors. In addition, by reliquefying only the residual evaporated gas after fuel consumption, the load on the refrigerant cycle can be adjusted according to the amount of residual evaporated gas, thereby reducing fuel consumption. [Brief explanation of the drawing]

[0034] [Figure 1] A schematic example of a conventional evaporative gas treatment system is shown below. [Figure 2] A schematic diagram of the evaporation gas treatment system according to the first embodiment of the present invention is shown. [Figure 3] A schematic diagram of the evaporation gas treatment system according to a second embodiment of the present invention is shown. [Modes for carrying out the invention]

[0035] The operational advantages of the present invention and the objectives achieved by embodiments of the present invention will be explained with reference to the drawings and the contents described in the drawings, using embodiments of the present invention as examples.

[0036] Hereinafter, embodiments of the present invention will be described with reference to the drawings, explaining their configuration and operation. Furthermore, the reference numerals for the components in each drawing will be the same as, to the extent possible, for the same component as shown in other drawings.

[0037] Hereinafter, the vessels of the present invention include vessels equipped with engines that can use liquefied gas and evaporated gas generated from liquefied gas as fuel for propulsion or power generation, and all types of vessels that use liquefied gas or evaporated gas as fuel for onboard engines. Typical examples include self-propelled vessels such as LNG carriers, liquid hydrogen carriers, and LNG RVs (Regasification Vessels), as well as floating offshore structures without propulsion capabilities, such as LNG FPSOs (Floating Production Storage Offloading) and LNG FSRUs (Floating Storage Regasification Units).

[0038] Furthermore, the liquefied gas of the present invention includes all types of liquefied gases that can be liquefied and transported at low temperatures, and whose evaporated gas generated during storage can be used as fuel for engines and the like. Examples of such liquefied gases include liquefied petroleum gases such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), liquefied ethylene gas, and liquefied propylene gas. However, in the embodiments described later, LNG, one of the representative liquefied gases, will be used as an example.

[0039] On the other hand, the fluid flowing through each line of this embodiment may be in a liquid state, a gas-liquid mixture state, a gas state, or a supercritical fluid state, depending on the operating conditions of the system.

[0040] Figure 2 schematically shows a ship's evaporative gas treatment system according to the first embodiment of the present invention.

[0041] As shown in Figure 2, the reliquefaction system of this embodiment is for reliquefying evaporated gas generated from liquefied gas stored in a storage tank T provided on a ship. This system includes compressors 100a and 100b that compress the evaporated gas generated in the storage tank T, and a heat exchanger 200 to which all or part of the evaporated gas compressed by the compressors 100a and 100b is supplied, and which cools the compressed evaporated gas by heat exchange with the uncompressed evaporated gas and refrigerant before it is supplied to the compressors 100a and 100b. For this reason, an evaporated gas supply line GL is provided that connects the storage tank T and the compressors 100a and 100b via the heat exchanger 200, and a reliquefaction line RL is provided downstream of the compressors 100a and 100b to supply the reliquefied evaporated gas to the storage tank T.

[0042] Furthermore, a refrigerant circulation line NL is provided through which the refrigerant supplied to the heat exchanger 200 circulates. The refrigerant circulation line NL includes a refrigerant expansion section 310 that expands and cools the refrigerant supplied to the heat exchanger 200, and a refrigerant compression section 320 that compresses the refrigerant that is discharged from the heat exchanger 200 after heat exchange has taken place in the heat exchanger 200.

[0043] The refrigerant compression section 320 is equipped with a compander-type compressor, and the compressor and the refrigerant expansion section 310 are axially connected so that the expansion energy of the refrigerant is transmitted and drives the compander-type compressor. In this embodiment, the refrigerant compression section 320 is described as being driven by a motor M, but the motor M may also be connected to the refrigerant expansion section 310 so that the expansion energy of the refrigerant is transmitted and drives the motor M to compress the refrigerant.

[0044] The refrigerant compressed in the refrigerant compression section 320 is supplied to the heat exchanger 200 for cooling, then supplied to the refrigerant expansion section 310 via the refrigerant circulation line NL, where it is cooled by expansion, and then supplied again to the heat exchanger 200 as refrigerant.

[0045] Therefore, in the heat exchanger 200 of this embodiment, heat is exchanged between four flows: all or part of the compressed evaporated gas, the uncompressed evaporated gas before being supplied to the compressors 100a and 100b, the refrigerant cooled by expansion in the refrigerant expansion section 310, and the refrigerant compressed in the refrigerant compression section 320.

[0046] For example, nitrogen (N2) can be used as the refrigerant circulated through the refrigerant circulation line NL and supplied to the heat exchanger 200. When a refrigerant cycle is configured in which compressed refrigerant is supplied to the heat exchanger 200, cooled by the cold energy of the refrigerant itself, then expanded and supplied back to the heat exchanger 200 for circulation, and the evaporated gas is cooled by heat exchange, a large amount of nitrogen refrigerant is required to cool the evaporated gas to its liquefaction temperature because there is a difference in heat capacity between the evaporated gas, which is mainly composed of methane, and nitrogen. For this reason, a large portion of the cold energy of the refrigerant cycle must be used to cool the nitrogen refrigerant itself, which leads to problems such as an increase in the capacity of the compressor that compresses the refrigerant and the expansion device that expands the refrigerant, and an increase in power consumption due to these capacity increases. To solve these problems, in this embodiment, the cryogenic uncompressed evaporated gas discharged from the storage tank T is supplied to the heat exchanger 200 and then supplied to the compressors 100a and 100b. This reduces the refrigerant flow rate required for the refrigerant cycle, which in turn reduces the capacity of the equipment needed for refrigerant compression and expansion, lowers power consumption, and further reduces installation and operating costs.

[0047] In the system of this embodiment, during the process of processing the evaporated gas generated from the liquefied gas in the storage tank T, the evaporated gas generated in the storage tank T is supplied to the heat exchanger 200 and then to the compressors 100a and 100b.

[0048] In compressors 100a and 100b, the evaporated gas is compressed, for example, to the fuel supply pressure of the ship's engine. In the case of a ship, as in this embodiment, where the cold energy of the refrigerant circulating in the refrigerant circulation line NL is utilized in the heat exchanger 200, and where a propulsion engine and a power generation engine with a lower fuel supply pressure are provided, the evaporated gas is compressed in compressors 100a and 100b to the fuel supply pressure of the power generation engine and supplied to the power generation engine E2 as fuel, and the residual evaporated gas remaining after fuel supply is reliquefied. In the case of a DFGE engine, for example, the evaporated gas is compressed in compressors 100a and 100b to a pressure of 5 to 10 bara.

[0049] Regarding regulations concerning ships, the compressor that supplies fuel to the engines must be designed with redundancy to prepare for emergencies. Redundancy means that if one device becomes unusable due to failure, maintenance, or other reasons, another device can be used as a substitute. For this purpose, the compressor is configured with a main compressor 100a and a backup compressor 100b. During normal operation, only the main compressor 100a, i.e., one compressor, is operated to supply fuel to the propulsion engine, power generation engine, etc., and the remaining compressed gas is reliquefied in the reliquefaction line RL.

[0050] Regarding fuel supply to the propulsion engine, liquefied gas pumped and discharged from storage tank T is supplied via liquefied gas supply line LL to a pressurizing pump 600 that pressurizes the liquefied gas to the fuel supply pressure of the propulsion engine, and to a vaporizer 610 that heats the pressurized liquefied gas according to the fuel supply temperature, before being supplied to the propulsion engine. A liquefied gas branch line LL2 is provided, branching downstream of the vaporizer 610 in the liquefied gas supply line LL and connecting to a power generation engine E2. The liquefied gas branch line LL2 is equipped with a pressure regulating valve 620 that adjusts the pressure of the liquefied gas according to the fuel supply pressure of the power generation engine E2, and a heater 630 that further heats the liquefied gas that has passed through the pressure regulating valve 620 according to the fuel supply temperature of the power generation engine E2. The pressurized liquefied gas may be supplied to these devices before being supplied to the power generation engine E2.

[0051] Meanwhile, the evaporated gas compressed by compressors 100a and 100b is supplied to the heat exchanger 200 via the reliquefaction line RL for cooling. The compressed and reliquefied evaporated gas and the refrigerant compressed in the refrigerant compression section 320 form a hot stream in the heat exchanger 200, while the uncompressed evaporated gas and the refrigerant cooled by expansion in the refrigerant expansion section 310 form a cold stream.

[0052] In the heat exchanger 200, four flows exchange heat, and the hot stream is cooled by heat exchange with the cold stream. The heat exchanger 200 is, for example, a BAHE (Brazed Aluminum Heat Exchanger).

[0053] The supply and discharge positions of each flow within the heat exchanger 200 can be changed to more effectively exchange heat between the hot stream and the cold stream, thereby cooling the compressed gas being reliquefied.

[0054] Of the cold streams of the heat exchanger 200, the nitrogen refrigerant supplied to the heat exchanger 200 after being cooled by expansion has a temperature of approximately -167°C at a pressure of approximately 10 bar, which is lower than the temperature of the other cold stream of the heat exchanger 200, the incompressible evaporated gas (approximately -50°C). Therefore, if these are supplied together to the heat exchanger 200, not all of the cooling energy of the nitrogen refrigerant will be used to cool the compressed gas that is reliquefied, and some of the cooling energy may be absorbed by the other cold stream (i.e., the incompressible evaporated gas). For this reason, although not specifically illustrated in the diagram, the lower-temperature nitrogen refrigerant flow (flow via NL in Figure 2) is supplied from downstream of the heat exchanger 200 and configured to pass through the entire length of the heat exchanger 200, while the higher-temperature incompressible evaporated gas flow (flow via GL in Figure 2) is supplied from the middle section of the heat exchanger 200.

[0055] Therefore, the compressed gas in the reliquefaction line RL is sequentially cooled by passing through the high-temperature region to the low-temperature region of the heat exchanger 200. In the high-temperature region, it is cooled by the supply of cooling energy from two cold streams: the refrigerant in the refrigerant circulation line NL and the uncompressed evaporated gas in the evaporated gas supply line GL. In the low-temperature region, it is sequentially cooled by heat exchange with one cold stream: the refrigerant in the refrigerant circulation line NL immediately after being supplied to the heat exchanger 200.

[0056] By performing heat exchange in this manner, the compressed gas being reliquefied can be cooled more effectively, increasing the reliquefaction rate, preventing thermal fatigue of the heat exchanger 200, and thus preventing damage to the equipment.

[0057] Meanwhile, the evaporated gas (compressed gas) cooled by heat exchange in the heat exchanger 200 is supplied to the depressurization device 400 of the reliquefaction line RL, where it is depressurized, and the evaporated gas depressurized in the depressurization device 400 is supplied to the gas-liquid separator 500.

[0058] The depressurization device 400 consists of an expander or an expansion valve such as a Joule-Thomson valve that depressurizes the evaporated gas that has been cooled after compression. The depressurization cools the evaporated gas by adiabatic expansion or isentropic expansion.

[0059] The evaporated gas, which has been depressurized and further cooled by the depressurization device 400, is supplied to the gas-liquid separator 500. The liquid separated in the gas-liquid separator 500 is supplied to the storage tank T via the re-liquefaction line RL for re-storage. However, in this embodiment, even after passing through the gas-liquid separator 500, the gaseous flash gas and the liquid liquefied gas may not be completely phase-separated, and the separated liquid or liquefied gas may contain unseparated flash gas.

[0060] The flash gas separated in the gas-liquid separator 500 is joined from the top of the gas-liquid separator 500 to the flow of uncompressed evaporated gas upstream of the heat exchanger 200 and the preheater 700 described later, and is supplied to the heat exchanger 200 or the preheater 700, and then supplied to the compressors 100a and 100b.

[0061] The system of this embodiment improves the cooling efficiency of the heat exchanger 200 by utilizing the cold energy of the evaporated gas itself and the cold energy of the refrigerant cycle. This eliminates the need to install and operate additional equipment such as a boost compressor that compresses the evaporated gas to high pressure to increase the reliquefaction rate, thereby reducing CAPEX (Capital Expenditure) and OPEX (Operating Expenditure).

[0062] On the other hand, the evaporated gas generated in the storage tank T is discharged from the storage tank T at an extremely low temperature in the range of -140°C to -100°C, depending on the storage tank operation. At this time, depending on the type of compressor installed for fuel supply to the engine, the temperature of the evaporated gas supplied to the compressor is required to be within a predetermined temperature range. In particular, a room-temperature compressor is installed for fuel supply to the engine. In this case, when the reliquefaction system is in operation and the amount of evaporated gas to be reliquefied is large and the load on the reliquefaction system is above a predetermined range, the low-temperature evaporated gas generated in the storage tank T is supplied to the heat exchanger 200, where it is sufficiently heated by heat exchange and supplied to the compressors 100a and 100b. However, when the amount of evaporated gas consumed by the engine is large and the reliquefaction system is not in operation, or when the load on the reliquefaction system is small, even if the evaporated gas is supplied to the heat exchanger 200, the evaporated gas is not sufficiently heated to the appropriate intake temperature required by the compressors 100a and 100b.

[0063] In the system of this embodiment, to solve these problems, a branch line BL is provided that bypasses the heat exchanger 200 from the storage tank T and can supply the gas directly to the compressors 100a and 100b. A preheater 700 capable of heating the evaporated gas is provided in this branch line BL.

[0064] When the reliquefaction system is in operation, the evaporated gas generated in the storage tank T is heated by heat exchange in the heat exchanger 200 before being supplied to the compressors 100a and 100b. However, when the reliquefaction system is not in operation or when the load on the reliquefaction system is low, all or part of the evaporated gas generated in the storage tank T bypasses the heat exchanger 200 and is heated in the preheater 700 via the branch line BL before being supplied to the compressors 100a and 100b.

[0065] In this embodiment, the evaporated gas is compressed by compressors 100a and 100b for fuel supply to the power generation engine E2, then supplied to the power generation engine E2 as fuel, and any excess compressed gas is reliquefied. On the other hand, the liquefied gas in the storage tank T is pressurized by the pressure pump 600 and then supplied to the propulsion engine E1 as fuel via the vaporizer 610. However, in the above embodiment, even when the ship speed is high and the fuel consumption of the propulsion engine E1 is high, the evaporated gas is not supplied to the propulsion engine E1 as fuel. Instead, the evaporated gas that remains after being compressed by compressors 100a and 100b and not supplied to the power generation engine E2 as fuel is reliquefied, and the reliquefied gas is supplied to the propulsion engine E1 as fuel. Therefore, there is a problem that energy efficiency decreases due to the need to pressurize and vaporize again by the pressure pump 600 and the vaporizer 610. Therefore, in the second embodiment described below, this problem can be solved and energy efficiency can be improved.

[0066] Figure 3 schematically shows an evaporation gas treatment system according to a second embodiment of the present invention.

[0067] In this embodiment, we will omit the explanation of the configurations common to the first embodiment described above, and instead focus on explaining the differences from the first embodiment.

[0068] This embodiment differs from the first embodiment in the configuration of the compressor that compresses the evaporated gas. In this embodiment, the first compressor 100A is a multi-stage compressor equipped with a plurality of compression sections 110, 120, and the evaporated gas is compressed in the first compressor 100A to the fuel supply pressure of the propulsion engine E1. The second compressor 100B is a compressor that compresses the evaporated gas to the fuel supply pressure of the power generation engine E2, which is supplied with fuel at a lower pressure than the propulsion engine E1. In this embodiment, the first compressor 100A and the auxiliary second compressor 100B are configured to be able to compress to different pressures.

[0069] In this embodiment, the first compressor 100A compresses the evaporated gas through multiple compression sections 110, 120 and an intercooler to the fuel supply pressure of the propulsion engine E1, and supplies the evaporated gas generated in the storage tank T to the propulsion engine E1 as fuel. The power generation engine E2 is supplied with evaporated gas compressed by only a portion of the compression section 110 of the first compressor 100A or evaporated gas compressed by the second compressor 100B. In addition, the evaporated gas compressed by only a portion of the compression section 110 of the first compressor 100A is supplied to the heat exchanger 200 for cooling.

[0070] Therefore, in this embodiment, an evaporative gas supply line GL is provided to supply evaporative gas from the storage tank T to the first compressor 100A or the second compressor 100B via the heat exchanger 200, and a first fuel supply line FL1 connected to the propulsion engine E1 is provided downstream of the first compressor 100A.

[0071] A reliquefaction line RL is provided to recover the evaporated gas compressed by only a portion of the compression section 110 of the first compressor 100A or by the second compressor 100B, after cooling it in a heat exchanger 200, into a storage tank T. A second fuel supply line FL2 is also provided to supply the evaporated gas compressed by only a portion of the compression section 110 of the first compressor 100A or by the second compressor 100B to the power generation engine E2. The first compressor 100A consists of an upstream compression section 110 that compresses the evaporated gas to a pressure that can be supplied to the heat exchanger 200 or the power generation engine E2, and a downstream compression section 120 that further compresses the evaporated gas compressed in the upstream compression section 110 to the fuel supply pressure of the propulsion engine E1. For example, if an ME-GI engine is provided as the propulsion engine and a DFGE engine as the power generation engine, the upstream compression section 110 of the first compressor 100A compresses the evaporated gas to a pressure of 5 to 12 bara, and the downstream compression section 120 compresses it to a pressure of 250 to 400 bara.

[0072] In the system of this embodiment, the first compressor 100A or the second compressor 100B can be operated individually according to the operation of the ship.

[0073] First, in the section where the propulsion engine E1 consumes a large amount of fuel and generates ship speed, the first compressor 100A is driven. The evaporated gas generated in the storage tank T is supplied to the heat exchanger 200 via the evaporated gas supply line GL, and then supplied to the first compressor 100A via the first line GLA where it is compressed. The evaporated gas compressed by the first compressor 100A is supplied as fuel to the propulsion engine E1 via the first fuel supply line FL1. In this case, the evaporated gas compressed in the upstream compression section 110 of the first compressor 100A is supplied as fuel to the power generation engine E2 via the second fuel supply line FL2. The excess compressed gas that is not supplied as fuel to the propulsion engine E1 and the power generation engine E2 is supplied to the heat exchanger 200 via the reliquefaction line RL, cooled by heat exchange with the refrigerant circulating in the refrigerant circulation line NL and the uncompressed evaporated gas, reliquefied in the depressurization device 400 and the gas-liquid separator 500, and recovered in the storage tank T. If there is no surplus compressed gas to be reliquefied after fuel supply, it is not necessary to operate the reliquefaction system, and the evaporated gas discharged from the storage tank T may be supplied directly to the first compressor 100A via the branch line BL, bypassing the heat exchanger 200.

[0074] When the propulsion engine E1 has little to no fuel consumption, such as when the ship is anchored, the second compressor 100B is driven. The evaporated gas generated in the storage tank T is supplied to the heat exchanger 200, then to the second compressor 100B where it is compressed, and the compressed gas from the second compressor 100B is supplied as fuel to the power generation engine E2. The excess compressed gas remaining after fuel supply is supplied to the heat exchanger 200 via the reliquefaction line RL where it is cooled, reliquefied in the depressurization device 400 and the gas-liquid separator 500, and recovered in the storage tank T.

[0075] In this embodiment, a multi-stage compressor 100A capable of compressing evaporated gas to a high pressure for supplying it as fuel to the propulsion engine E1, and a compressor 100B that compresses the evaporated gas to the pressure of the power generation engine E2, which has a lower fuel supply pressure than the propulsion engine E1, are provided. By operating these compressors separately according to the operating conditions of the ship, redundancy requirements are met, and evaporated gas is used as fuel, reducing the consumption of electrical energy for fuel supply and reliquefaction, thereby enabling efficient operation of the ship.

[0076] Furthermore, by utilizing the cold energy of the evaporated gas itself and the cold energy of the refrigerant cycle to improve the cooling efficiency and reliquefaction rate of the heat exchanger 200, the evaporated gas generated in the storage tank T is preferentially consumed as fuel, and only the residual evaporated gas is reliquefied. This reduces the load on the refrigerant cycle and the amount of liquefied gas consumed as fuel.

[0077] The present invention is not limited to the embodiments described above, and it will be obvious to those skilled in the art that various modifications or variations can be made without exceeding the technical essence of the invention.

Claims

1. A first compressor for compressing evaporated gas generated from liquefied gas stored in a ship's storage tank; and, A second compressor for compressing the evaporated gas generated from the liquefied gas stored in the aforementioned storage tank; A heat exchanger for cooling the evaporated gas compressed by the first compressor or the second compressor; The heat exchanger is supplied with a refrigerant circulation line: and The first compressor is a multi-stage compressor equipped with multiple compression sections, which compresses the evaporated gas to the fuel supply pressure of the propulsion engine, The second compressor compresses the evaporated gas to the fuel supply pressure of the power generation engine, which is supplied with fuel at a lower pressure than the propulsion engine. The evaporated gas compressed in a part of the compression section of the first compressor is cooled by the heat exchanger or supplied to the power generation engine. The system further comprises: an evaporated gas supply line that supplies evaporated gas generated in the storage tank to the heat exchanger and then to the first compressor or the second compressor; a first fuel supply line that connects the downstream of the first compressor to the propulsion engine; a reliquefaction line that cools the evaporated gas compressed by a part of the compression section of the first compressor or the second compressor in the heat exchanger and recovers it in the storage tank; and a second fuel supply line that supplies the evaporated gas compressed by a part of the compression section of the first compressor or the second compressor to the power generation engine. A branch line that branches off from the aforementioned evaporative gas supply line and bypasses the heat exchanger to supply evaporative gas to the first compressor or the second compressor; and a preheater provided in the branch line for heating the evaporative gas: When the reliquefaction system for reliquefying the evaporated gas is not in operation or when the load on the reliquefaction system is low, all or part of the evaporated gas generated in the storage tank is bypassed by the heat exchanger, heated by the preheater via the branch line, and supplied to the first or second compressor. Shipboard evaporative gas treatment system.

2. The aforementioned refrigerant circulation line includes: A refrigerant compression unit that compresses the refrigerant discharged from the heat exchanger after heat exchange in the heat exchanger; A refrigerant expansion unit is provided which expands and cools the refrigerant that has been compressed in the refrigerant compression unit and then cooled in the heat exchanger, and then supplies it to the heat exchanger; The ship's evaporative gas treatment system according to claim 1.

3. A depressurizing device for reducing the pressure of the compressed evaporated gas cooled by the heat exchanger; A gas-liquid separator for separating the evaporated gas, which has been depressurized by the aforementioned depressurization device, into gas-liquid and gas-liquid components; further comprising The flash gas separated in the gas-liquid separator is merged upstream of the heat exchanger with the flow of uncompressible evaporated gas supplied to the first or second compressor, thereby recovering the liquefied gas separated in the gas-liquid separator into the storage tank. The ship's evaporative gas treatment system according to claim 1.

4. A liquefied gas supply line that supplies the liquefied gas stored in the storage tank to the propulsion engine as fuel; A pressurizing pump provided in the liquefied gas supply line for pressurizing the liquefied gas to the fuel supply pressure of the propulsion engine; The present invention further comprises: a vaporizer for heating the liquefied gas pressurized by the aforementioned pressure pump; The ship's evaporative gas treatment system according to claim 3.

5. A liquefied gas branch line that branches off from the liquefied gas supply line downstream of the vaporizer and connects to the power generation engine; A pressure regulating valve provided in the liquefied gas branch line adjusts the pressure of the liquefied gas according to the fuel supply pressure of the power generation engine; The invention further comprises: a heater provided in the liquefied gas branch line for additionally heating the liquefied gas that has passed through the pressure control valve in accordance with the fuel supply temperature of the power generation engine; The ship's evaporative gas treatment system according to claim 4.

6. In the ship speed generation section, the first compressor is driven to compress the evaporated gas generated in the storage tank and supply it to the propulsion engine and the power generation engine, while the excess compressed evaporated gas is cooled by the heat exchanger. When the ship is at anchor, the second compressor is driven to compress the evaporated gas generated in the storage tank and supply it to the power generation engine, while the excess compressed evaporated gas is cooled by the heat exchanger. A ship evaporative gas treatment system according to any one of claims 1 to 5.

7. The refrigerant circulating in the aforementioned refrigerant circulation line is nitrogen. The ship's evaporative gas treatment system according to claim 6.

8. In a method for treating evaporated gases in a ship equipped with a propulsion engine and a power generation engine supplied with fuel at a lower pressure than the propulsion engine, The evaporated gas generated from the liquefied gas stored in the storage tank is supplied to a heat exchanger via an evaporated gas supply line, and then to a first or second compressor. After being compressed by the first or second compressor, the compressed evaporated gas that was not supplied as fuel to the propulsion engine and the power generation engine is reliquefied in a reliquefaction system that cools the heat exchanger with a refrigerant circulated via a refrigerant circulation line. The first compressor is a multi-stage compressor having multiple compression sections, and compresses the evaporated gas to the fuel supply pressure of the propulsion engine, and the second compressor compresses the evaporated gas to the fuel supply pressure of the power generation engine, The evaporated gas compressed in a part of the compression section of the first compressor is cooled by the heat exchanger or supplied to the power generation engine. When the reliquefaction system is not in operation or when the load on the reliquefaction system is low, all or part of the evaporated gas generated in the storage tank is diverted from the evaporated gas supply line to bypass the heat exchanger, heated by a preheater installed in the branch line, and supplied to the first or second compressor. A method for treating evaporated gases from ships.

9. In the ship speed generation section, the first compressor is driven to compress the evaporated gas generated in the storage tank, and then supply it to the propulsion engine and the power generation engine, while the excess compressed evaporated gas is cooled by the heat exchanger. When the ship is at anchor, the second compressor is driven to compress the evaporated gas generated in the storage tank, and then supply it to the power generation engine, while the excess compressed evaporated gas is cooled by the heat exchanger. The method for treating evaporated gases from a ship according to claim 8.

10. The refrigerant circulating in the aforementioned refrigerant circulation line is compressed in the refrigerant compression section, cooled in the heat exchanger, then expanded and cooled in the refrigerant expansion section, and supplied to the heat exchanger as a cooling source. The refrigerant compression unit is connected to the refrigerant expansion unit, and the expansion energy of the refrigerant is transmitted from the refrigerant expansion unit to compress the refrigerant. The method for treating evaporated gases from a ship according to claim 9.

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