| 摘要 |
PROBLEM TO BE SOLVED: To reduce the pressure raising in an LNG tank during transportation by providing a heat exchanger in a paper layer in the upper part of the LNG tank and connecting a refrigerant feed mechanism to the heat exchanger to feed and circulate liquefied gas having a boiling point lower than that of the LNG as a refrigerant. SOLUTION: A heat exchanger 8 is provided in a paper layer 7 in the upper part of an LNG tank 2 and a refrigerant feed mechanism 9 is provided in the heat exchanger 8 so as to feed and circulate liquefied gas having a boiling point lower than that of the LNG as refrigerant. If the temperature of the paper layer 7 of the LNG tank increases higher than the set value during transportation, a controller 15 starts the feeding of liquid nitrogen. Then, extruded liquid nitrogen is fed and circulated in the heat exchanger 8 to absorb the heat from the paper layer 7 and be vaporized. The temperature of the paper layer 7 decreases along with it so as to liquefy boiloff gas, reduce the total amount of the boiloff gas, and reduce the pressure of the LNG tank 2.
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