Ship

A boil-off gas reliquefaction method for use in a ship having a storage tank storing liquefied gas, the boil-off gas reliquefaction method comprising:

• compressing, by a multi-stage compressor comprising a plurality of compressors connected in series, boil-off gas (BOG) discharged from the storage tank to provide compressed BOG;
• cooling and liquefying, by a first heat exchanger, at least part of the compressed BOG to provide a first flow of cooled compressed BOG;
• further cooling, at a second heat exchanger, the first flow of the cooled compressed BOG;
• expanding and further cooling, by a first decompressor, a first portion of the first flow to provide an expanded flow;
• heat-exchanging, at a third heat exchanger, a second portion of the first flow with the expanded flow from the first decompressor for further cooling the second portion;
• and
• expanding, at a second decompressor, the cooled second portion to provide a liquefied flow to a liquefied gas return line connecting between the second decompressor and the storage tank,
• wherein the second heat exchanger is on the liquefied gas return line and interposed between the second decompressor and the storage tank,
• wherein the method further comprises heat-exchanging, at the second heat exchanger, the liquefied flow returning to the storage tank in the liquefied gas return line with the first flow of cooled compressed BOG from the first heat exchanger such that the liquefied flow flowing back to the storage tank from the second decompressor is heated in the liquefied gas return line prior to arriving at the storage tank and such that the first flow of cooled compressed BOG is further cooled prior to arriving the first decompressor and the second decompressor.