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KR-20260065092-A - SUBCOOLING SYSTEM OF LIQUEFIED NATURAL GAS, VESSEL INCLUDING THE SAME, AND MANUFACTURING METHOD OF MIXED REFRIGERANT FOR SUBCOOLING SYSTEM OF LIQUEFIED NATURAL GAS

KR20260065092AKR 20260065092 AKR20260065092 AKR 20260065092AKR-20260065092-A

Abstract

One embodiment of the present invention comprises a liquefied natural gas circulation pipe (100) installed on a hull (S) and providing a path for circulating liquefied natural gas inside a liquefied natural gas storage tank (TK) and resupplying it to the liquefied natural gas storage tank (TK), and a cooling unit (200) installed on the liquefied natural gas circulation pipe (100) and supercooling the liquefied natural gas, wherein the cooling unit (200) comprises a first heat exchanger (210) that supercools the liquefied natural gas to a first cooling temperature by exchanging heat with the liquefied natural gas moving along the liquefied natural gas circulation pipe (100), a refrigerant circulation pipe (220) connected to the first heat exchanger and providing a path for circulating a mixed refrigerant that exchanges heat with the liquefied natural gas, and a refrigerant cooling unit (230) installed on the refrigerant circulation pipe (220) that cools the mixed refrigerant to a second cooling temperature lower than the first cooling temperature and supplies it to the first heat exchanger (210). The mixed refrigerant located in the cooling section (200) provides a supercooling system for liquefied natural gas that maintains a gaseous state.

Inventors

  • 유진열
  • 배재류
  • 황윤호

Assignees

  • 사단법인 오션플랫폼

Dates

Publication Date
20260508
Application Date
20241031

Claims (17)

  1. A liquefied natural gas circulation pipe (100) installed on the hull (S) and providing a path to circulate liquefied natural gas inside a liquefied gas storage tank (TK) and resupply it to the liquefied natural gas storage tank (TK); and It includes a cooling unit (200) installed on the above liquefied natural gas circulation pipe (100) and supercooling the liquefied natural gas; The above cooling unit (200) is, A first heat exchanger (210) that exchanges heat with the liquefied natural gas moving along the liquefied natural gas circulation pipe (100) to supercool the liquefied natural gas to a first cooling temperature, and A refrigerant circulation pipe (220) connected to the first heat exchanger and providing a path for a mixed refrigerant to circulate and exchange heat with the liquefied natural gas, and, It includes a refrigerant cooling unit (230) installed on the refrigerant circulation pipe (220) and cooling the mixed refrigerant to a second cooling temperature lower than the first cooling temperature and supplying it to the first heat exchanger (210). The mixed refrigerant located in the cooling unit (200) maintains a gaseous state. liquefied natural gas supercooling system.
  2. In Article 1, The above refrigerant cooling unit (230) is, A first compressor (231) that compresses the mixed refrigerant that has passed through the first heat exchanger (210), and A first cooler (232) that cools the mixed refrigerant that has passed through the first compressor (231), and A second compressor (233) that compresses the mixed refrigerant that has passed through the first cooler (232), and A second cooler (234) that cools the mixed refrigerant that has passed through the second compressor (233), and A second heat exchanger (235) for cooling the mixed refrigerant that has passed through the second cooler (234), and Characterized by including an expansion unit (236) that cools the mixed refrigerant passing through the second heat exchanger (235) to the second cooling temperature and supplies it to the first heat exchanger (210). liquefied natural gas supercooling system.
  3. In Article 2, The first heat exchanger (210) and the second heat exchanger (235) are installed adjacent to each other, and The mixed refrigerant that has passed through the first heat exchanger (210) passes through the second heat exchanger (235), characterized in that liquefied natural gas supercooling system.
  4. In Paragraph 3, The mixed refrigerant that passed through the second cooler (234) is, Characterized by the mixed refrigerant passing through the first heat exchanger (210) and heat exchange in the second heat exchanger (235). liquefied natural gas supercooling system.
  5. In Article 2, The above refrigerant cooling unit (230) is, It further includes a motor (237) connecting the second compressor (233) and the expander (236), and The rotor of the above motor (237) is, Characterized by directly connecting the impeller of the second compressor (233) and the impeller of the expander (236). liquefied natural gas supercooling system.
  6. In Article 1, The apparatus further comprises a circulation pump (300) installed at the front end of the cooling section (200) on the above liquefied natural gas circulation pipe (100) and providing pressure to circulate the liquefied natural gas. liquefied natural gas supercooling system.
  7. In Article 6, The apparatus further comprises a flow control unit (400) installed at the rear end of the cooling unit (200) on the liquefied natural gas circulation pipe (100) and controlling the flow rate of the liquefied natural gas. liquefied natural gas supercooling system.
  8. In Article 1, The apparatus further comprises a heater (500) installed at the front end of the cooling section (200) on the above liquefied natural gas circulation pipe (100) and heating the liquefied natural gas. liquefied natural gas supercooling system.
  9. In Article 8, The heater (500) includes a glycol heat exchange heater that uses glycol water, and Characterized by the fact that the proportion of glycol contained in the above glycol water is higher than the proportion of water, liquefied natural gas supercooling system.
  10. In Article 9, The apparatus further comprises a temperature measuring device (600) installed between the heater (500) and the first heat exchanger (210) and measuring the temperature of the liquefied natural gas that has passed through the heater (500). liquefied natural gas supercooling system.
  11. In Article 1, The apparatus further comprises an injection nozzle (700) installed at one end of the above-mentioned liquefied natural gas circulation pipe (100) for injecting the supercooled liquefied natural gas into the interior of the liquefied gas storage tank (TK). liquefied natural gas supercooling system.
  12. A supercooling system for liquefied natural gas according to any one of claims 1 to 11, shipping.
  13. In Article 12, The above vessel is, Characterized as being a liquefied natural gas carrier or a liquefied natural gas fuel propulsion vessel, shipping.
  14. A first step of measuring the amount of a first sample mixed refrigerant containing helium and nitrogen and having a first composition ratio with the highest proportion of helium, and the amounts of helium and nitrogen constituting the first sample mixed refrigerant; A second step of injecting the above-mentioned first sample mixed refrigerant into a liquefied natural gas supercooling system to conduct a first test and measure the first cooling efficiency; A third step of partially extracting the first sample mixed refrigerant from the supercooling system of the liquefied natural gas and measuring the amount extracted after the first test; Step 4: Using the extraction amount of the first sample mixed refrigerant, additionally injecting nitrogen into the liquefied natural gas supercooling system to produce a second sample mixed refrigerant having a second composition ratio; Step 5, measuring the second cooling efficiency by performing a second test using the second sample mixed refrigerant having the second composition ratio; and A sixth step of detecting the composition ratio of a sample mixed refrigerant having an optimal cooling efficiency by comparing the first cooling efficiency and the second cooling efficiency; comprising Method for manufacturing a mixed refrigerant for a liquefied natural gas supercooling system.
  15. In Article 14, The amount of the first sample mixed refrigerant extracted above is, Characterized by the amount of helium of the second composition ratio above being an amount remaining in the supercooling system of the liquefied natural gas, Method for manufacturing a mixed refrigerant for a liquefied natural gas supercooling system.
  16. In Article 15, The amount of nitrogen additionally injected in the above second test is, Characterized by being an amount that creates the above second composition ratio, Method for manufacturing a mixed refrigerant for a liquefied natural gas supercooling system.
  17. In Article 14, The above-mentioned liquefied natural gas supercooling system is, Characterized as a supercooling system for liquefied natural gas according to any one of claims 1 to 11, Method for manufacturing a mixed refrigerant for a liquefied natural gas supercooling system.

Description

SUBCOOLING SYSTEM OF LIQUEFIED NATURAL GAS, VESSEL INCLUDING THE SAME, AND MANUFACTURING METHOD OF MIXED REFRIGERANT FOR SUBCOOLING SYSTEM OF LIQUEFIED NATURAL GAS The present invention relates to a liquefied natural gas supercooling system, a ship equipped with said system, and a method for manufacturing a mixed refrigerant for a liquefied natural gas supercooling system. More specifically, the invention relates to a liquefied natural gas supercooling system for minimizing evaporative gas generated in a fuel storage tank, a ship equipped with said system, and a method for manufacturing a mixed refrigerant for a liquefied natural gas supercooling system. Generally, natural gas is transported in a gaseous state through onshore or offshore gas pipelines, or transported to distant destinations in the form of liquefied natural gas (LNG) stored on LNG carriers. This LNG is obtained by cooling natural gas to cryogenic temperatures (approximately -163°C), and since its volume is reduced to approximately 1/600 of that of natural gas in its gaseous state, it is very suitable for long-distance transportation by sea. LNG carriers that carry LNG and sail the sea to unload it at an onshore destination, or LNG regasification vessels (RVs) that carry LNG and sail the sea to an onshore destination to regasify the stored LNG and unload it in the form of natural gas, include storage tanks (commonly referred to as 'cargo tanks') capable of withstanding the cryogenic temperatures of liquefied natural gas. LNG in such storage tanks is prone to evaporation due to the influence of the external environment, and the boil-off gas (BOG) can increase the pressure inside the storage tank and damage the tank. To prevent this, methods of re-liquefying evaporated gas and supercooling liquefied natural gas to an ultra-low temperature of about -177°C are used. In particular, the liquefied natural gas supercooling system includes a cooling section in which a refrigerant circulates and supercools the liquefied natural gas, and the cooling section can increase heat exchange efficiency by using a mixed refrigerant rather than a single refrigerant as the refrigerant. However, if the mixed refrigerant contains heavy elements such as pentane, the temperature of the cooling section may drop excessively during the heat exchange process, causing freezing to occur in the cooling section and potentially leading to the cooling section's failure. In addition, to supercool liquefied natural gas, non-explosive refrigerants such as helium or nitrogen must be used. However, helium is too light to be compressed, and while nitrogen has a boiling point of -196 degrees, some of it begins to turn into a liquid state at -170 degrees, so liquid nitrogen can damage the impeller of the expander. In addition, to change the composition ratio of a mixed refrigerant containing helium and nitrogen, the existing mixed refrigerant must be completely extracted from the cooling section, the entire cooling section must be vacuumed again, and then the mixed refrigerant with the changed composition ratio must be injected into the cooling section. In this case, expensive helium is wasted, increasing the consumption of helium, and the vacuuming process takes a long time, leading to increased costs. FIG. 1 is a schematic drawing illustrating a vessel including a supercooling system for liquefied natural gas according to one embodiment of the present invention. FIG. 2 is a drawing specifically illustrating a supercooling system for liquefied natural gas according to one embodiment of the present invention. FIG. 3 is a flowchart of a method for manufacturing a mixed refrigerant for a supercooling system of liquefied natural gas according to another embodiment of the present invention. Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic drawing illustrating a vessel including a supercooling system for liquefied natural gas according to one embodiment of the present invention. As illustrated in FIG. 1, a vessel according to one embodiment of the present invention includes a hull (S), an engine (E), a liquefied gas storage tank (TK), and a supercooling system (SOS) for liquefied natural gas. The hull (S) may include various types of hulls, such as the hull of a liquefied gas carrier or the hull of a liquefied gas fuel propulsion vessel. However, although the present embodiment is described based on the hull (S), it is not necessarily limited thereto and can be applied to marine structures such as offshore plants. The engine (E) is installed in the hull (S) and may include a main engine that propels the hu