Reliquefaction of boil off gas

Claim 2

A method as claimed in claim 1 in which combustion aiar to the ship''s propulsion engine is pre-heated by hot exhaust gas from the gas turbine.

Claim 3

A method as claimed in claim 1 in which the said first coolant means includes said first and second low pressure refrigerant streams.

Claim 4

A method as claimed in claim 1 in which the said first low pressure refrigerant stream is combined with said second low pressure refrigerant stream to form a combined low pressure refrigerant stream which provides at least part of each of said first and second coolant means, said combined stream being thereafter passed to said compressor means for recompression and said first and second streams of compressed refrigerant being derived from the recompressed combined stream after said recompressed combined stream has been cooled by said heat exchange with said second coolant means.

Claim 5

A method as claimed in claim 1 in which said first and second coolant means each further include a stream of gas resulting from evaporation of the cargo.

Claim 6

A method as claimed in claim 1 in which at least said second stream of compressed refrigerant is derived from said gas evaporated from the cargo, and wherein step (iv) is effected by indirect heat exchange between said condensed second stream of compressed refrigerant and said second low pressure refrigerant stream prior to effecting Joule-Thomson expansion of said condensed second stream, said condensate being recovered from said condensed second stream after said Joule-Thomson expansion, and the remainder of said expanded second stream providing said second low pressure refrigerant stream.

Claim 7

A method as claimed in claim 7 in which the said first low pressure refrigerant stream is combined with said second low pressure refrigerant stream to form a combined low pressure refrigerant stream which provides at least part of each of said first and second coolant means, said combined stream being thereafter passed to said compressor means for recompression and said first and second streams of compressed refrigerant being derived from the recompressed combined stream after said recompressed combined stream has been cooled by said heat exchange with said second coolant means.

Claim 8

A method as claimed in claim 8 in which said gas evaporated from the cargo is injected into said combined low pressure refrigerant stream and is contained in said first and second coolant means.

Claim 9

A method as claimed in claim 7 in which said gas evaporated from the cargo has a fuel value, a portion of said gas is used to fuel said gas turbine and said condensate is recovered from said condensed second stream and returned to the cargo at a rate which is equal to the rate of evaporation of gas from the cargo less the rate of consumption of the evaporated cargo as fuel.

Claim 10

A method as claimed in claim 10 in which said portion is derived from at least partially recompressed refrigerant.

Claim 11

A method as claimed in claim 1 in which said second stream of low pressure refrigerant consists of said expanded condensed second stream of compressed refrigerant and said gas evaporated from the cargo is reliquefied by indirect heat exchange with said second low pressure refrigerant stream.

Claim 12

A method as claimed in claim 12 in which the liquefied gas and the refrigerant is nitrogen.

Claim 13

A method as claimed in claim 12 in which said first low pressure refrigerant stream is combined with said second low pressure refrigerant stream to form a combined low pressure refrigerant stream which provides at least part of each of said first and second coolant means, said combined stream being thereafter passed to said compressor means for recompression and said first and second streams of compressed refrigerant being derived from the recompressed combined stream after said recompressed combined stream has been cooled by said heat exchange with said second coolant means.

Claim 14

A method as claimed in claim 12 in which said Joule-Thomson expansion is effected in at least two steps whereby said second stream of low pressure refrigerant is provided in the form of a plurality of separate flows at different pressures.

Claim 15

A method as claimed in claim 15 in which at least one of said flows is at substantially the same pressure as said first low pressure refrigerant stream and is combined therewith to form a combined low pressure refrigerant stream which provides part of each of said first and second coolant means, the remainder of said second low pressure refrigerant stream is at lower pressure and provides another part of each of said first and second coolant means, said remainder being thereafter compressed to substantially the pressure of said combined low pressure refrigerant stream and then combined therewith and the stream so produced being recompressed to form a stream from which said first and second streams of compressed refrigerant are derived after said recompressed stream has been cooled by said heat exchange with said second coolant means.

Claim 16

A method as claimed in claim 12 in which said first and second coolant means each further include a stream of gas resulting from evaporation of the cargo, said gas stream being separate from the gas to be reliquefied.

Claim 17

A method as claimed in claim 12 in which the gas resulting from the evaporation of the ship''s cargo has a fuel value and a portion of said gas is used to fuel the gas turbine, said portion being separate from the gas to be reliquefied.

Claim 18

A method as claimed in claim 18 in which said portion provides a part of each of asid first and second coolant means before it is supplied to said gas turbine.

Claim 19

A method as claimed in claim 7 in which the liquefied gas is liquefied natural gas.

Claim 20

Ship-board apparatus for the reliquefaction of gas resulting from evaporation of a ship''s cargo of liquefied gas, said apparatus including: refrigerant compressing means comprising first and second compressor means arranged for passage of gaseous refrigerant therethrough in series; expansion turbine means operatively connected to one of said first and second compressor means to drive same; hydrocarbon fueled gas turbine means operatively connected to the other of said first and second compressor meaNs to drive same; expansion valve means; and first, second and third heat exchange means; and further including: first conduit means for passing a first stream of compressed refrigerant from said first and second compression means through said first heat exchange means to cool it and then through said turbine expansion means to work expand it to provide a first low pressure refrigerant stream; second conduit means for passing a second stream of compressed refrigerant through said first, second and third heat exchange means in series to cool and condense the stream and then through said expansion valve means whereby to cause partial vaporization of the condensed stream; means for recovering at least a part of the unvaporized portion of the partially vaporized stream; third conduit means for passing a second low pressure refrigerant stream comprising the unrecovered part of the partially vaporized stream in counter-current indirect heat exchange relationship with said second stream of compressed refrigerant in said third heat exchange means; fourth conduit means for passing both said second low pressure refrigerant stream leaving said third heat exchange means and said first low pressure refrigerant stream in counter-current indirect heat exchange relationship with said second stream of compressed refrigerant in said second heat exchange means and thereafter in counter-current indirect heat exchange relationship with said second and first streams of compressed refrigerant in said first heat exchange means and thereafter returning said first and second low pressure refrigerant streams to said refrigerant compressing means; fifth conduit means for feeding gas evaporated from the liquefied gas cargo into admixture with low pressure refrigerant; and sixth conduit means for passing the recovered part of the unvaporized portion of the partially vaporized stream for return to the liquefied gas cargo.

Claim 21

Apparatus as claimed in claim 21 in which said gas turbine is adapted to be fueled by gas evaporated from the liquid gas cargo, said apparatus also including means for feeding a portion of refrigerant recovered from said first compressor means to said gas turbine means as fuel.

Claim 22

Apparatus as claimed in claim 21 in which the expansion valve means is adapted to provide said second low pressure refrigerant stream as a plurality of flows at different pressures.

Claim 23

Apparatus as claimed in claim 21 arranged in three separable modules, the first of which contains one compressor means and the gas turbine means operatively connected to said compressor means to drive same, the second of which includes the second compressor means and the expansion turbine means operatively connected to said second compressor means to drive same, and the third of which includes a cold box containing said heat exchange means and said expansion valve means.

Claim 24

Ship-board apparatus for the reliquefaction of gas resulting from evaporation of a ship''s cargo of liquefied gas, said apparatus comprising: refrigerant compressing means comprising first and second compressor means arranged for passage of gaseous refrigerant therethrough in series; expansion turbine means operatively connected to one of said first and second compressor means to drive same; hydrocarbon fuel gas turbine means operatively connected to the other of said first and second compressor means to drive same; expansion valve means; and first, second and third heat exchange means; and further including: first conduit means for passing a first stream of compressed refrigerant from said first and second compression means through said first heat exchange means to cool it and then through said turbine expansion means to work expand it to provide a first low pressure refrigerant stream; second conduit means for passing a second stream of compressed refrigerant through said first, second and third heat exchange means in series to cool and condense the partiAl vaporization of said condensed stream to form a second low pressure refrigerant stream; third conduit means for passing said second low pressure refrigerant stream through said third heat exchange means; fourth conduit means for passing gas evaporated from the liquefied gas cargo through said third heat exchange means in indirect heat exchange relationship with said second low pressure refrigerant stream and to pass liquid so formed for return to said liquefied gas cargo; and fifth conduit means for passing both said second low pressure refrigerant stream leaving said third heat exchange means and said first low pressure refrigerant stream in counter-current heat exchange relationship with said second stream of compressed refrigerant in said second heat exchange means and thereafter in counter-current indirect heat exchange relationship with said second and first streams of compressed refrigerant in said first heat exchange means and thereafter returning said first and second low pressure refrigerant streams to said refrigerant compressing means.

Claim 25

Apparatus as claimed in claim 25 in which said gas turbine means is adapted to be fueled by gas evaporated from the liquid gas cargo, said apparatus further including conduit means for passing a portion of the evaporated gas from the cargo in indirect counter-current heat exchange with said compressed refrigerant to warm said portion and then to said gas turbine means as fuel.

Claim 26

Apparatus as claimed in claim 25 in which the expansion valve means is adapted to provide said second low pressure refrigerant stream as a plurality of flows at different pressures.

Claim 27

Apparatus as claimed in claim 25 arranged in three separable modules, the first of which contains one compressor means and the gas turbine means operatively connected to said compressor means to drive same, the second of which includes the second compressor means and the expansion turbine means operatively connected to said second compressor means to drive same, and the third of which includes a cold box containing said heat exchange means and said expansion valve means.