Method of cooling boil off gas and an apparatus therefor

A method of cooling a boil off gas (BOG) stream from a liquefied cargo in a floating transportation vessel, said liquefied cargo having a boiling point of greater than −110° ° C. at 1 atmosphere, said method comprising the steps of:

• compressing a BOG stream from said liquefied cargo in at least two stages of compression comprising a first stage and a final stage to provide a compressed BOG discharge stream, wherein said first stage of compression has a first stage discharge pressure and said final stage of compression has a final stage suction pressure, and at least one intermediate compressed BOG streams is provided between consecutive stages of compression;
• cooling the compressed BOG discharge stream against at least one first coolant streams to provide a first cooled compressed BOG stream;
• cooling the first cooled compressed BOG stream against at least one second coolant stream to provide a second cooled compressed BOG stream;
• cooling the second cooled compressed BOG stream against a third coolant stream to provide a third cooled compressed BOG stream;
• providing a vessel fuel stream from the liquefied cargo;
• using the vessel fuel stream as a coolant stream to cool both the compressed BOG discharge stream and the first cooled compressed BOG stream;
• and
• using at least an expanded portion of the third cooled compressed BOG stream as at least a portion of the vessel fuel stream.