Ship comprising gas treatment system

Abstract

The present invention relates to a ship, which may comprise: a liquefied gas storage tank for storing liquefied gas; a main compressor that compresses the boil-off gas generated in the liquefied gas storage tank and supplies the boil-off gas to a demand end; a first heat exchanger that recovers the heat and cold of the boil-off gas supplied from the liquefied gas storage tank to the main compressor; a second heat exchanger for cooling the boil-off gas circulating from the main compressor to the liquefied gas storage tank; and a first liquefied gas supply unit for supplying liquefied gas to the boil-off gas at the front end of the main compressor.

Description

Technical Field

[0001] The invention relates to a vessel comprising a gas processing system. Background Art

[0002] A ship is a means of transport that sails on the ocean carrying a large amount of minerals, crude oil, natural gas or thousands of containers. It is made of steel and moves by the thrust generated by the rotation of the propeller while floating on the water with the help of buoyancy.

[0003] Generally, such ships generate thrust by driving an engine. In this case, the engine uses gasoline or diesel to move a piston, and the reciprocating motion of the piston rotates a crankshaft, thereby rotating a shaft connected to the crankshaft to drive a propeller.

[0004] However, when heavy oil such as HFO or MFO is used as propulsion fuel, various harmful substances included in the exhaust gas seriously pollute the environment, so regulations on the use of heavy oil as fuel oil are being strengthened, and the cost for meeting such regulations is gradually increasing.

[0005] Therefore, technology is being developed to use liquefied gas such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) as fuel for ships instead of gasoline or diesel.

[0006] Such liquefied gas is stored in a liquefied gas storage tank in liquid phase. The volume of liquefied natural gas is reduced to 1 / 600 through liquefaction, the volume of liquefied petroleum gas is reduced to 1 / 260 of propane through liquefaction, and the volume of butane is reduced to 1 / 230, thereby having the advantage of high storage efficiency.

[0007] However, since such liquefied gas is stored at an extremely low temperature of -50°C or lower, there is a problem of generating boil-off gas due to external heat penetration, and therefore research and development of technology for stably storing and handling liquefied gas is being continued. Summary of the invention

[0008] Problems to be solved by the invention

[0009] The present invention is proposed to solve the problems of the above-mentioned prior art. The purpose of the present invention is to prevent the load from being concentrated on the refrigerant heat exchange part by considering the temperature of the boil-off gas supplied to the main compressor and using the boil-off gas to cool the refrigerant in the process of supplying boil-off gas to the demand end in a liquefied gas propelled ship.

[0010] The problems of the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by a person skilled in the art from the following description.

[0011] Technical solutions to the problem

[0012] A ship according to one aspect of the present invention may include: a liquefied gas storage tank for storing liquefied gas; a main compressor for compressing boil-off gas generated in the liquefied gas storage tank and supplying it to a demand side; a first heat exchanger for recovering the cold and heat of the boil-off gas supplied from the liquefied gas storage tank to the main compressor; a second heat exchanger for cooling the boil-off gas circulating from the main compressor to the liquefied gas storage tank; and a first liquefied gas supply unit for supplying liquefied gas to the boil-off gas at the front end of the main compressor.

[0013] Specifically, it can also include a second liquefied gas supply unit that supplies liquefied gas to the evaporated gas at the rear end of the main compressor, and can determine whether to operate the pump arranged in the liquefied gas storage tank based on whether the temperature of the evaporated gas supplied to the front end of the main compressor is higher than a preset temperature.

[0014] Specifically, the preset temperature may be determined within a range of -70°C to -50°C.

[0015] Specifically, the ship according to one aspect of the present invention may supply liquefied gas to the first liquefied gas supply unit by operating the pump when the temperature of the boil-off gas supplied to the front end of the main compressor is equal to or higher than a preset temperature.

[0016] Specifically, a portion of the liquefied gas supplied to the first liquefied gas supply part may be supplied to the second liquefied gas supply part.

[0017] Specifically, a ship according to one aspect of the present invention can supply a portion of the liquefied gas circulating from the second heat exchanger to the liquefied gas storage tank to the first liquefied gas supply unit without operating the pump when the temperature of the evaporating gas supplied to the front end of the main compressor is lower than a predetermined temperature.

[0018] Specifically, in the first heat exchanger, heat exchange may be performed between boil-off gas transferred from the liquefied gas storage tank to the main compressor and refrigerant discharged from the refrigerant compressor.

[0019] Effects of the Invention

[0020] The ship of the present invention can supply boil-off gas to the demand side at an appropriate temperature, and can prevent an excessive load from being applied to a specific heat exchanger or a specific compressor.

[0021] The effects of the present invention are not limited to the above-mentioned effects, and a person skilled in the art can clearly understand other effects not mentioned through the description of the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a diagram showing a ship according to a first embodiment of the present invention.

[0023] Figure 2 It is a diagram showing a ship according to a second embodiment of the present invention.

[0024] Figure 3 It is a diagram showing a ship according to a third embodiment of the present invention.

[0025] Figure 4 It is a diagram showing a ship according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0026] Hereinafter, when a certain part is described as “including” or “having” a certain constituent element, this means that other constituent elements may also be included, rather than excluding other constituent elements, unless there is a specific description to the contrary.

[0027] In the following, liquefied gas may be used to mean all gaseous fuels that are usually stored in a liquid state, such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG), ethylene, and ammonia. For the sake of convenience, a gas that is no longer in a liquid state due to being heated or pressurized may also be referred to as a liquefied gas. The same may also apply to boil-off gas. In addition, for the sake of convenience, LNG may be used to mean NG (Natural Gas) in a liquid state and natural gas (NG) in a supercritical state, and boil-off gas may be used to mean boil-off gas in a gaseous state and liquefied boil-off gas.

[0028] Hereinafter, high pressure (HP: High pressure), low pressure (LP: Low pressure), high temperature and low temperature are relative and do not represent absolute values.

[0029] Hereinafter, expressions such as first, second, etc. are used in the present invention to indicate that a particular configuration is provided in plural, and each expression may refer to any one of the plural configurations. In the absence of the addition of the first, second, etc. expressions, the corresponding configuration may be a concept including all configurations to which the first, second, etc. expressions are added.

[0030] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0031] Figure 1 It is a diagram showing a ship according to a first embodiment of the present invention.

[0032] Reference Figure 1 The ship 1 according to the first embodiment of the present invention may include a liquefied gas storage tank 10 , a first heat exchanger 20 , a second heat exchanger 30 , a main compressor 40 , and a demand end 50 .

[0033] The ship 1 can be anchored or sailing. When the ship 1 is anchored, the power generation engine 51 can be operated. When the ship 1 is sailing, the power generation engine 51 and the propulsion engine can be operated.

[0034] When the ship 1 is moored, the pressure required by the main compressor 40 may be 6 to 10 bar, and the inlet temperature of the main compressor 40 may be -50°C. When the ship 1 is sailing, the pressure required by the main compressor 40 may be about 13 bar, and the inlet temperature of the main compressor 40 may be -70°C. The liquefied gas storage tank 10 stores liquefied gas to be supplied to the demand end 50. At this time, the liquefied gas storage tank 10 can store liquefied gas in a liquid state and can have a pressure tank form. A plurality of liquefied gas storage tanks 10 may be provided, and more than a plurality of liquefied gas storage tanks 10 may be arranged side by side.

[0035] The liquefied gas storage tank 10 has a heat-insulating structure, but if heat enters the liquefied gas storage tank 10 from the outside, the liquefied gas stored in the liquefied gas storage tank 10 becomes warm, and a part of it evaporates. The evaporated liquefied gas is stored as boil-off gas (BOG; Boil off gas) in the space above the liquid level of the liquefied gas in the liquid phase stored in the liquefied gas storage tank 10.

[0036] In the liquefied gas storage tank 10, a boil-off gas supply line L1 capable of discharging boil-off gas stored in the upper space of the liquefied gas storage tank 10 to the outside of the liquefied gas storage tank 10 may be provided at the upper portion of the liquefied gas storage tank 10. The boil-off gas may be delivered to the demand end 50 via the boil-off gas supply line L1.

[0037] When the boil-off gas is delivered to the demand side 50 via the boil-off gas supply line L1, the boil-off gas may pass through the main compressor 40. The boil-off gas may be increased in pressure when passing through the main compressor 40 and may be in a pressure state required by the demand side 50.

[0038] The demand side 50 may be a dual fuel combustion (DF) engine as the main propulsion device. In this specification, when it is recorded that liquefied gas is delivered to the demand side 50, this may include the delivery of liquefied gas to the power generation engine 51 that generates the electricity required in the ship or the GCU (Gas Combustion Unit) 52 that burns boil-off gas.

[0039] The BOG supply line L1 may be provided with a first heat exchanger 20. When the BOG passes through the first heat exchanger 20, the refrigerant in the BOG cold and heat recovery line L31 may be cooled, and in this process, the BOG transferred to the demand end 50 may be heated.

[0040] The refrigerant compressor 60 can branch into an evaporative gas heat recovery line L31 and a first refrigerant line L32 from the rear end. The control unit (not shown) can adjust the amount of refrigerant supplied to the first heat exchanger 20 or the second heat exchanger 30 by adjusting the opening of the first control valve V1 provided on the evaporative gas heat recovery line L31 and the second control valve V2 provided on the first refrigerant line L32.

[0041] Since a portion of the refrigerant discharged from the refrigerant compressor 60 is supplied to the first heat exchanger 20 via the evaporation gas cold and heat recovery line L31, the flow rate of the refrigerant supplied to the second heat exchanger 30 is relatively reduced, thereby reducing the load required for cooling the refrigerant in the second heat exchanger 30. That is, the first heat exchanger 20 cools a portion of the refrigerant discharged from the refrigerant compressor 60, thereby reducing the flow rate of the refrigerant cooled in the second heat exchanger 30, thereby reducing the load required for cooling the refrigerant in the second heat exchanger 30.

[0042] The evaporation gas supply line L1 is provided with a circuit for allowing the evaporation gas to bypass the first heat exchanger 20, so that the evaporation gas can be controlled to bypass the first heat exchanger 20 before the temperature of the evaporation gas at the front end of the main compressor 40 reaches a predetermined level or above.

[0043] The boil-off gas supply line L1 may be partially branched at the rear end of the main compressor 40 so that the boil-off gas may circulate to the liquefied gas storage tank 10 via the boil-off gas circulation line L2 .

[0044] The boil-off gas circulating from the rear end of the main compressor 40 to the liquefied gas storage tank 10 may pass through the second heat exchanger 30. The boil-off gas having a temperature increased by the main compressor 40 exchanges heat with the refrigerant in the second heat exchanger 30, and may be cooled and liquefied in the process.

[0045] The second heat exchanger 30 may include three or more heat exchange parts. The second heat exchanger 30 may include a first evaporation gas heat exchange part 31, a second evaporation gas heat exchange part 32, and a refrigerant heat exchange part 33. In this specification, the first evaporation gas heat exchange part 31, the second evaporation gas heat exchange part 32, and the refrigerant heat exchange part 33 provided in the second heat exchanger 30 may refer to a region provided in a device called the second heat exchanger 30 or a flow path provided in the second heat exchanger 30.

[0046] Specifically, the first evaporation gas heat exchange part 31 and the second evaporation gas heat exchange part 32 can enable the refrigerant passing through the expander 70 to exchange heat with the evaporation gas circulated from the main compressor 40 to the liquefied gas storage tank 10, and the refrigerant heat exchange part 33 can enable the refrigerant passing through the expander 70 to exchange heat with the refrigerant passing through the refrigerant compressor 60.

[0047] At this time, the refrigerant may be nitrogen, a mixed refrigerant, or the like, and the ship 1 may include various components such as a refrigerant supply unit 80 , a booster pump 81 , and an expansion tank 82 , depending on the composition of the refrigerant.

[0048] Reference Figure 1 , a gas treatment system provided in a ship 1 according to an embodiment of the present invention is described. Figure 1 , the refrigerant passes through the refrigerant compressor 60 and the temperature is relatively increased. At this time, the refrigerant is transferred to the first heat exchanger 20 or the second heat exchanger 30. In the first heat exchanger 20, the refrigerant exchanges heat with the boil-off gas discharged from the liquefied gas storage tank 10, and in the second heat exchanger 30, the refrigerant exchanges heat with the refrigerant discharged from the expander 70.

[0049] That is, in the first heat exchanger 20, the boil-off gas discharged from the liquefied gas storage tank 10 is heat-exchanged with the refrigerant discharged from the refrigerant compressor 60, so that the refrigerant discharged from the refrigerant compressor 60 can be cooled. In addition, in the refrigerant heat exchange portion 33 in the second heat exchanger 30, the refrigerant that has passed through the expander 70 and the refrigerant that has passed through the refrigerant compressor 60 are heat-exchanged with each other, so that the refrigerant that has passed through the refrigerant compressor 60 can be cooled.

[0050] The boil-off gas delivered to the demand side 50 via the main compressor 40 increases in volume as the temperature increases, and as the volume of the boil-off gas increases, the load applied to the main compressor 40 increases. Therefore, in order to reduce the volume of the boil-off gas delivered to the main compressor 40 and reduce the load applied to the main compressor 40, preferably, the temperature of the boil-off gas passing through the main compressor 40 is lower than -50°C.

[0051] It should be noted that the refrigerant is cooled by repeatedly performing compression and expansion, and the heat and cold generated at this time are used to cool the evaporated gas. However, since the cooling of the refrigerant requires a large load, in order to reduce the load required for cooling the refrigerant, it is necessary to use the evaporated gas transmitted to the main compressor 40 to pre-cool the refrigerant.

[0052] Therefore, in a ship 1 according to an embodiment of the present invention, the temperature of the evaporating gas passing through the main compressor 40 can be maintained in a range below -50°C, and the load applied to the main compressor 40 can be reduced by transferring the refrigerant passing through the refrigerant compressor 60 to the first heat exchanger 20, thereby maximizing the use of the heat and cold of the evaporating gas to cool the refrigerant.

[0053] As described above, in a ship 1 according to an embodiment of the present invention, in order to meet the required pressure or temperature conditions of the demand end 50 of the ship, boil-off gas is supplied to the demand end 50 through the main compressor 40, and in order to maximize the use of the cold and heat of the boil-off gas to reliquefy the boil-off gas, a line for transferring the refrigerant to the first heat exchanger 20 and a line for transferring the refrigerant to the second heat exchanger 30 are branched from the rear end of the refrigerant compressor 60.

[0054] The boil-off gas cold heat recovery line L31 and the first refrigerant line L32 are integrated at the expander line L4 , and the refrigerant in the boil-off gas cold heat recovery line L31 and the first refrigerant line L32 is expanded and cooled in the expander 70 .

[0055] The refrigerant discharged from the expander 70 is a refrigerant with a relatively low temperature, and the refrigerant flow line branches at the rear end of the first evaporation gas heat exchange section 31 in the second heat exchanger 30. A part of the refrigerant can be heat-exchanged with the evaporation gas circulating from the rear end of the main compressor 40 to the liquefied gas storage tank 10 in the second evaporation gas heat exchange section 32, and the rest of the refrigerant can be heat-exchanged with the refrigerant discharged from the refrigerant compressor 60 in the refrigerant heat exchange section 33.

[0056] The amount of refrigerant flowing from the first evaporation gas heat exchange section 31 to the second evaporation gas heat exchange section 32 and the amount of refrigerant flowing from the first evaporation gas heat exchange section 31 to the refrigerant heat exchange section 33 can be adjusted according to the temperature of the evaporation gas circulating from the rear end of the main compressor 40 to the liquefied gas storage tank 10, or the temperature of the refrigerant discharged from the refrigerant heat exchange section 33.

[0057] The boil-off gas circulating to the liquefied gas storage tank 10 can be cooled for the first time in the second boil-off gas heat exchange section 32. The temperature of the refrigerant transferred from the rear end of the first boil-off gas heat exchange section 31 to the second boil-off gas heat exchange section 32 can be lower than the temperature at the front end of the expander 70. In the second boil-off gas heat exchange section 32, the refrigerant lowers the temperature of the boil-off gas circulating to the liquefied gas storage tank 10, thereby reducing the load applied to the first boil-off gas heat exchange section 31 to liquefy the boil-off gas.

[0058] The first evaporation gas heat exchanger 31 may cool the evaporation gas discharged from the second evaporation gas heat exchanger 32 for the second time. Since the evaporation gas is cooled for the first time in the second evaporation gas heat exchanger 32, the load applied to the first evaporation gas heat exchanger 31 for liquefying the evaporation gas may be reduced.

[0059] In the refrigerant heat exchange section 33, the refrigerant discharged from the refrigerant compressor 60 can be cooled using the refrigerant discharged from the first evaporation gas heat exchange section 31. Since the second evaporation gas heat exchange section 32 partially shares the evaporation gas cooling of the first evaporation gas heat exchange section 31, the temperature of the refrigerant passing through the first evaporation gas heat exchange section 31 can be relatively low compared to a case where the second evaporation gas heat exchange section 32 is not provided. Therefore, in order to cool the refrigerant discharged from the refrigerant compressor 60, the temperature of the refrigerant transferred to the refrigerant heat exchange section 33 can be lowered to improve the cooling efficiency in the refrigerant heat exchange section 33, and the amount of refrigerant transferred to the refrigerant heat exchange section 33 can also be reduced, so that the size of the refrigerant heat exchange section 33 can be reduced, thereby reducing the cost and space required for the system configuration in the ship.

[0060] That is, after the evaporation gas is cooled for the first time in the second evaporation gas heat exchange section 32, the evaporation gas is cooled for the second time in the first evaporation gas heat exchange section 31, and thus the temperature drop of the refrigerant in the first evaporation gas heat exchange section 31 can be reduced compared to the case where the second evaporation gas heat exchange section 32 is not provided when cooling of the evaporation gas is performed in the first evaporation gas heat exchange section 31. Thus, in the case where the refrigerant discharged from the first evaporation gas heat exchange section 31 is used to cool the refrigerant discharged from the refrigerant compressor 60 in the refrigerant heat exchange section 33, the cooling efficiency of the refrigerant can be improved, and the size of the refrigerant heat exchange section 33 can be reduced.

[0061] In order to adjust the temperature of the boil-off gas injected into the main compressor 40, the liquefied gas may be supplied to the first liquefied gas supply part S1 or the second liquefied gas supply part S2. For details related to this, please refer to the following description. Figure 2 Provide explanation.

[0062] In this specification, it is described that the gas treatment system is operated based on the temperature of the evaporated gas passing through the main compressor 40 being -50°C. However, the case where the benchmark of the evaporated gas temperature passing through the main compressor 40 is set to -50°C refers to a case where the power generation engine 51 is running and the propulsion engine is not running in the ship 1, so that the pressure required by the main compressor 40 is low and the inlet temperature of the main compressor 40 is high. When the propulsion engine is running and the pressure required by the main compressor 40 is relatively high, the benchmark of the temperature of the evaporated gas passing through the main compressor 40 can be made lower to -70°C.

[0063] As described above, the reference of the boil-off gas temperature passing through the main compressor 40 may be changed depending on whether the ship 1 is sailing or not, and the reference of the boil-off gas temperature may be set at about -70°C to -50°C.

[0064] Figure 2 It is a diagram showing a ship according to a second embodiment of the present invention.

[0065] The following, for Figure 1 The description of the common structures of the parts described in the above description may be omitted.

[0066] Reference Figure 2 , a ship 1 according to an embodiment of the present invention may include a liquefied gas storage tank 10, a first heat exchanger 20, a second heat exchanger 30, a main compressor 40, and a demand end 50. In the first heat exchanger 20, heat exchange can be performed between the boil-off gas in the boil-off gas supply line L1 and the refrigerant in the boil-off gas cold and heat recovery line L31. In the second heat exchanger 30, heat exchange can be performed between the refrigerant in the expander line L4 and the refrigerant in the first refrigerant line L32, and heat exchange can be performed between the refrigerant in the expander line L4 and the liquefied gas or boil-off gas in the boil-off gas circulation line L2.

[0067] The first heat exchanger 20 can recover the heat of the boil-off gas in the liquefied gas storage tank 10. The refrigerant passing through the first heat exchanger 20 along the boil-off gas heat recovery line L31 is pre-cooled, and is further cooled by passing through the expander 70.

[0068] The refrigerant having passed through the expander 70 is supplied to the second heat exchanger 30 , and the refrigerant having passed through the expander 70 can cool the refrigerant in the first refrigerant line L32 and the liquefied gas or the boil-off gas in the boil-off gas circulation line L2 .

[0069] The liquefied gas or boil-off gas circulating along the boil-off gas circulation line L2 may be completely reliquefied in the second heat exchanger 30 .

[0070] On the other hand, Figure 1 As shown, the boil-off gas delivered to the demand side 50 via the main compressor 40 increases in volume as the temperature increases, and as the volume of the boil-off gas increases, the load applied to the main compressor 40 may increase. In addition, as the temperature of the boil-off gas passing through the main compressor 40 increases, the cold and heat recovered in the first heat exchanger 20 may be insufficient, and the reliquefaction efficiency of the boil-off gas in the second heat exchanger 30 may decrease. Therefore, in order to reduce the load applied to the main compressor 40 and improve the reliquefaction efficiency, it is preferred that the temperature of the boil-off gas passing through the main compressor 40 is lower than -50°C.

[0071] When the temperature of the boil-off gas passing through the main compressor 40 is above -50°C, the liquefied gas in the liquefied gas storage tank 10 can be supplied to the first liquefied gas supply part S1 by using a pump provided in the liquefied gas storage tank 10. By supplying low-temperature liquefied gas to the first liquefied gas supply part S1, the boil-off gas in the boil-off gas supply line L1 can be cooled.

[0072] However, as long as liquefied gas is supplied from the liquefied gas storage tank 1 to the first liquefied gas supply part S1 and the liquefied gas circulates to the liquefied gas storage tank 1, heat is injected into the liquefied gas storage tank 1, and the boil-off gas reliquefaction efficiency may be reduced. In order to avoid this, the liquefied gas in the liquefied gas storage tank 10 can be transferred to the second liquefied gas supply part S2 along the second liquefied gas supply line L6 branched from the first liquefied gas supply line L5 and connected to the second liquefied gas supply part S2. By supplying liquefied gas to the second liquefied gas supply part S2, the boil-off gas reliquefaction efficiency can be improved by about 7%.

[0073] At this time, the third control valve V3 may be opened to transfer liquefied gas to the second liquefied gas supply part S2 according to the temperature of the boil-off gas supplied to the main compressor 40. By supplying low-temperature liquefied gas to the second liquefied gas supply part S2, the reliquefaction efficiency in the second heat exchanger 30 may be improved.

[0074] On the other hand, when the temperature of the boil-off gas supplied to the main compressor 40 and the temperature of the boil-off gas passing through the main compressor 40 are sufficiently low, in order to lower the temperature of the boil-off gas, it is necessary to supply liquefied gas to the first liquefied gas supply part S1, but even if the temperature of the boil-off gas changes, the amount of boil-off gas generated will not increase sharply, and the reliquefaction efficiency will not decrease sharply.

[0075] On the contrary, in a state where the temperature of the boil-off gas supplied to the main compressor 40 and the temperature of the boil-off gas passing through the main compressor 40 are sufficiently low, the reliquefaction efficiency may be reduced due to the heat injected into the liquefied gas storage tank 10 when a pump is used in the process of supplying the liquefied gas in the liquefied gas storage tank 10.

[0076] When the pump is operated while the liquefied gas in the liquefied gas storage tank 10 is supplied to the first liquefied gas supply unit S1, there is a problem that the power used by the pump is wasted, and heat penetrates along the piping through which the liquefied gas flows, thereby increasing the amount of evaporated gas generated in the liquefied gas storage tank. Furthermore, if the process of stopping and operating the pump is frequently repeated depending on the temperature of the evaporated gas, there is a problem that power is wasted in the preparation process for the pump operation, such as cooling down the piping, and additional time is required for the preparation process.

[0077] That is, if liquefied gas is supplied to the first liquefied gas supply part S1 by operating a pump provided in the liquefied gas storage tank 10 to cool the boil-off gas when the boil-off gas temperature is sufficiently low, the reliquefaction efficiency may decrease and the energy consumption may increase during the reliquefaction process.

[0078] Nevertheless, in order to smoothly supply fuel to the demand side 50 and reduce the load imposed on the main compressor 40, it is necessary to adjust the temperature of the boil-off gas delivered to the main compressor 40. Therefore, when the pump is not operated, the boil-off gas can be cooled by delivering the low-temperature liquefied gas that has passed through the second heat exchanger 30 to the first liquefied gas supply part S1 along the liquefied gas branch line L7. In this case, the reliquefaction efficiency can be improved by about 9% compared with the case of supplying liquefied gas by operating the pump.

[0079] As described above, whether to operate the pump provided to the liquefied gas storage tank 10 may be determined according to the temperature of the boil-off gas supplied to the front end of the main compressor 40 .

[0080] Preferably, it is determined whether the temperature of the boil-off gas at the front end of the main compressor 40 of the operating pump is -50°C. When the temperature of the boil-off gas is above -50°C, the pump needs to be operated to quickly cool the boil-off gas, and in order to improve the reliquefaction efficiency, a portion of the liquefied gas transferred to the first liquefied gas supply part S1 can be supplied to the second liquefied gas supply part S2.

[0081] On the contrary, when the temperature of the boil-off gas is lower than -50°C, the operation of the pump may be interrupted, and a portion of the low-temperature liquefied gas that has passed through the second heat exchanger 30 may be supplied to the first liquefied gas supply unit S1. As described above, the temperature of the boil-off gas may be adjusted by supplying the low-temperature liquefied gas supplied through the boil-off gas circulation line L2 to the first liquefied gas supply unit S1 without operating the pump provided in the liquefied gas storage tank 10. Here, the temperature of the boil-off gas that may interrupt the operation of the pump may be higher than -90°C and lower than -50°C.

[0082] When the temperature of the evaporated gas passing through the main compressor 40 is above -50°C, the pump is running. At this time, the liquefied gas can be delivered to the second liquefied gas supply part S2 by opening the third control valve V3. When the temperature of the evaporated gas passing through the main compressor 40 is lower than -50°C, the operation of the pump is interrupted. At this time, a part of the liquefied gas circulating from the second heat exchanger to the liquefied gas storage tank can be delivered to the first liquefied gas supply part S1 by opening the fourth control valve V4.

[0083] In the above, whether to operate the pump is determined based on the temperature of the evaporated gas being -50°C. However, this is the case when the propulsion engine of the ship 1 is not running and the ship 1 is anchored. When the propulsion engine of the ship 1 is running and the ship 1 is sailing, whether to operate the pump can also be determined based on the temperature of the evaporated gas being -70°C.

[0084] That is, when the ship 1 is sailing, when the temperature of the boil-off gas is above -70°C, the pump can be operated to transfer liquefied gas to the first liquefied gas supply part S1, and a portion of the liquefied gas transferred to the first liquefied gas supply part S1 can be supplied to the second liquefied gas supply part S2.

[0085] On the contrary, when the ship 1 is sailing, when the temperature of the boil-off gas is lower than -70°C, the operation of the pump can be interrupted, and a part of the low-temperature liquefied gas that has passed through the second heat exchanger 30 can be supplied to the first liquefied gas supply unit S1. Here, the temperature of the boil-off gas that can interrupt the operation of the pump can be higher than -90°C and lower than -70°C.

[0086] Figure 3 It is a diagram showing a ship according to a third embodiment of the present invention.

[0087] Figure 4 It is a diagram showing a ship according to a fourth embodiment of the present invention.

[0088] The following, for Figure 1 and Figure 2 The description of the common structures of the parts described in the above description may be omitted.

[0089] Reference Figure 3 A ship 1 according to an embodiment of the present invention may include a liquefied gas storage tank 10 , a second heat exchanger 30 , a main compressor 40 , a demand end 50 , and a third heat exchanger 90 .

[0090] In the second heat exchanger 30, since the line of the first refrigerant line L32 crosses each other, heat exchange can be performed between the refrigerant in the expander line L4 and the refrigerant in the first refrigerant line L32, and heat exchange can be performed between the refrigerant in the expander line L4 and the liquefied gas or evaporated gas in the evaporative gas circulation line L2.

[0091] In the third heat exchanger 90, the boil-off gas in the boil-off gas supply line L1 and the liquefied gas or boil-off gas in the boil-off gas circulation line L2 can exchange heat. The third heat exchanger 90 can recover cold and heat from the boil-off gas in the boil-off gas supply line L1. At this time, the boil-off gas in the boil-off gas supply line L1 can be preheated and supplied to the main compressor 40, and conversely, the boil-off gas in the boil-off gas circulation line L2 can be precooled and supplied to the second heat exchanger 30.

[0092] The boil-off gas having passed through the main compressor 40 may exchange heat with the boil-off gas discharged from the liquefied gas storage tank 10 in the third heat exchanger 90 , and then exchange heat with the refrigerant in the expander line L4 in the second heat exchanger 90 to be completely reliquefied.

[0093] As in Figure 2 As described above with respect to the first liquefied gas supply part S1 or the second liquefied gas supply part S2, when the temperature of the boil-off gas passing through the main compressor 40 is above -50°C, the liquefied gas in the liquefied gas storage tank 10 can be supplied to the first liquefied gas supply part S1 by using a pump provided in the liquefied gas storage tank 10. By supplying low-temperature liquefied gas to the first liquefied gas supply part S1, the boil-off gas in the boil-off gas supply line L1 can be cooled.

[0094] At this time, part of the liquefied gas transferred to the first liquefied gas supply part S1 can be transferred to the second liquefied gas supply part S2 along the second liquefied gas supply line L6 branched from the first liquefied gas supply line L5 and connected to the second liquefied gas supply part S2. By lowering the temperature of the boil-off gas in the boil-off gas circulation line L2 supplied to the third heat exchanger 90, the reliquefaction efficiency in the third heat exchanger 90 can be improved.

[0095] On the contrary, when the temperature of the evaporated gas passing through the main compressor 40 is lower than -50°C, the operation of the pump arranged in the liquefied gas storage tank 10 can be interrupted, and a portion of the low-temperature liquefied gas that has passed through the third heat exchanger 90 can be supplied to the first liquefied gas supply part S1 along the liquefied gas branch line L7 to control the temperature of the evaporated gas.

[0096] When the temperature of the evaporated gas passing through the main compressor 40 is above -50°C, the pump is running. At this time, the liquefied gas can be delivered to the second liquefied gas supply part S2 by opening the fifth control valve V5. When the temperature of the evaporated gas passing through the main compressor 40 is lower than -50°C, the operation of the pump is interrupted. At this time, a part of the liquefied gas circulating from the second heat exchanger to the liquefied gas storage tank can be delivered to the first liquefied gas supply part S1 by opening the sixth control valve V6.

[0097] In the above, whether to operate the pump is determined based on the temperature of the evaporated gas being -50°C. However, this is the case when the propulsion engine of the ship 1 is not running and the ship 1 is anchored. When the propulsion engine of the ship 1 is running and the ship 1 is sailing, whether to operate the pump can also be determined based on the temperature of the evaporated gas being -70°C.

[0098] That is, when the ship 1 is sailing, when the temperature of the boil-off gas is above -70°C, the pump can be operated to transfer liquefied gas to the first liquefied gas supply part S1, and a portion of the liquefied gas transferred to the first liquefied gas supply part S1 can be supplied to the second liquefied gas supply part S2.

[0099] On the contrary, when the ship 1 is sailing, when the temperature of the boil-off gas is lower than -70°C, the operation of the pump can be interrupted, and a part of the low-temperature liquefied gas that has passed through the second heat exchanger 30 can be supplied to the first liquefied gas supply unit S1. Here, the temperature of the boil-off gas that can interrupt the operation of the pump can be higher than -90°C and lower than -70°C.

[0100] like Figure 3 As shown, the second liquefied gas supply part S2 can be arranged at the front end of the third heat exchanger 90, such as Figure 4 As shown, the second liquefied gas supply part S2 may be disposed at the rear end of the third heat exchanger 90 .

[0101] As described above, in the ship 1 of the present invention, in the process of supplying boil-off gas to the demand end 50 in the liquefied gas propelled ship, the temperature of the boil-off gas supplied to the main compressor 40 is considered and the boil-off gas is used to cool the refrigerant, thereby preventing the load from being concentrated on the refrigerant heat exchange part 33.

[0102] In addition, in the ship 1 of the present invention, it can be divided into a first evaporation gas heat exchange section 31 and a second evaporation gas heat exchange section 32 to cool the evaporation gas, and a refrigerant heat exchange section 33 is arranged at the rear end of the first evaporation gas heat exchange section 31, so as to improve the cooling efficiency in the refrigerant heat exchange section 33 and reduce the size of the refrigerant heat exchange section 33.

[0103] In addition, in the ship 1 of the present invention, the temperature of the evaporated gas can be controlled by operating the pump to supply the liquefied gas in the liquefied gas storage tank 10 to the front end of the main compressor 40, or the liquefied gas circulating from the main compressor 40 can be reliquefied and supplied to the front end of the main compressor 40 to control the temperature of the evaporated gas at the front end of the main compressor 40.

[0104] Furthermore, in the ship 1 of the present invention, the load applied to the main compressor 40 can be reduced by adjusting the temperature of the boil-off gas at the front end of the main compressor 40 .

[0105] In addition, in the ship 1 of the present invention, the refrigerant can be pre-cooled by exchanging heat between the evaporated gas transmitted to the main compressor 40 and the refrigerant discharged from the refrigerant compressor 60, and the evaporated gas circulating from the main compressor 40 can be pre-cooled by exchanging heat between the evaporated gas transmitted to the main compressor 40 and the evaporated gas circulating from the main compressor 40.

[0106] Obviously, the present invention is not limited to the above-mentioned embodiments, and the present invention may include a combination of the embodiments or a combination of at least one of the embodiments and another embodiment of the known technology.

[0107] Although the present invention has been described in detail above through specific embodiments, this is for the purpose of specifically illustrating the present invention. The present invention is not limited thereto, and those skilled in the art may make modifications or improvements within the technical concept of the present invention.

[0108] Simple variations or modifications of the present invention all belong to the present invention, and the specific protection scope of the present invention will become clear from the attached claims.

Claims

1. A ship, characterized in that: include: Liquefied gas storage tanks, which store liquefied gas; A main compressor, compressing boil-off gas generated in the liquefied gas storage tank and supplying it to a demand side; a first heat exchanger for recovering cold and heat of boil-off gas supplied from the liquefied gas storage tank to the main compressor; a second heat exchanger for cooling boil-off gas circulated from the main compressor to the liquefied gas storage tank; and The first liquefied gas supply unit supplies liquefied gas to boil-off gas at the front end of the main compressor.

2. The ship according to claim 1, characterized in that: Also included is a second liquefied gas supply unit for supplying liquefied gas to boil-off gas at the rear end of the main compressor; Whether to operate the pump provided in the liquefied gas storage tank is determined according to whether the temperature of the boil-off gas supplied to the front end of the main compressor is higher than a preset temperature.

3. The ship according to claim 2, characterized in that: The preset temperature is determined within a range of -70°C to -50°C.

4. The ship according to claim 2, characterized in that: When the temperature of the boil-off gas supplied to the front end of the main compressor is equal to or higher than a preset temperature, the pump is operated to supply the liquefied gas to the first liquefied gas supply unit.

5. The ship according to claim 4, characterized in that: A portion of the liquefied gas supplied to the first liquefied gas supply part is supplied to the second liquefied gas supply part.

6. The ship according to claim 2, characterized in that: When the temperature of boil-off gas supplied to the front end of the main compressor is lower than a preset temperature, the pump is not operated and part of the liquefied gas circulating from the second heat exchanger to the liquefied gas storage tank is supplied to the first liquefied gas supply unit.

7. The ship according to claim 1, characterized in that: In the first heat exchanger, heat is exchanged between boil-off gas supplied from the liquefied gas storage tank to the main compressor and refrigerant discharged from the refrigerant compressor.

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