A ship includes: a boil-off gas heat exchanger which is installed on a downstream of a storage tank and heat-exchanges a compressed boil-off gas (a first fluid) by a boil-off gas discharged from the storage tank as a refrigerant to cool the boil-off gas; a compressor installed on a downstream of the boil-off gas heat exchanger and compresses a part of the boil-off gas from the storage tank; an extra compressor which is installed on a downstream of the boil-off gas heat exchanger and in parallel with the compressor and compresses the other part of the boil-off gas from the storage tank; a refrigerant heat exchanger which additionally cools the first fluid; and a refrigerant decompressing device which expands a second fluid, which is sent to the refrigerant heat exchanger, and then sends the second fluid back to the refrigerant heat exchanger.

Disclosed is a boil-off gas reliquefaction system for vessels. The BOG reliquefaction system for vessels includes: a multistage compressor compressing BOG; a heat exchanger cooling the BOG compressed by the multistage compressor through heat exchange using BOG not compressed by the multistage compressor as a refrigerant; a pressure reducer disposed downstream of the heat exchanger and decompressing a fluid cooled by the heat exchanger; and a bypass line through which BOG is supplied to the multistage compressor after bypassing the heat exchanger.

A ship including a liquefied gas storage tank includes: first and second compressors which compresse a boil-off gas discharged from a storage tank; a boost compressor which compresses one part of the boil-off gas that is compressed by at least any one of the first compressor and/or the second compressor; a first heat exchanger which heat exchanges the boil-off gas compressed by the boost compressor and the boil-off gas discharged from the storage tank; a refrigerant decompressing device which expands the other part of the boil-off gas that is compressed by at least any one of the first compressor and/or the second compressor; a second heat exchanger which cools, by a fluid expanded by the refrigerant decompressing device as a refrigerant; and an additional compressor which is compresses the refrigerant that passes through the refrigerant decompressing device and second heat exchanger.

A method of cooling a boil-off gas (BOG) stream from a liquefied gas tank comprising at least the step of heat exchanging the BOG stream with a first refrigerant in a heat exchanger, the heat exchanger having an entry port and a warmer exit port, and comprising at least the steps of: (a) passing the first refrigerant into the entry port of the heat exchanger and into a first zone of the heat exchanger to exchange heat with the BOG stream, to provide a first warmer refrigerant stream; (b) withdrawing the first warmer refrigerant stream from the heat exchanger at an intermediate exit port between the entry port and the warmer exit port; (c) admixing the first warmer refrigerant stream with an oil-containing refrigerant stream to provide a combined refrigerant stream; (d) passing the combined refrigerant stream into the heat exchanger through an entry port located in a second zone of the heat exchanger that is warmer than the first zone; (e) passing the combined refrigerant stream out of the heat exchanger through the warmer exit port. The present invention is a modification of a refrigerant cycle for BOG cooling, and LNG re-liquefaction in particular, that allows the use of a cost-efficient oil-injected screw compressor in the refrigerant system. The present invention is also able to accommodate the possibility of different flows or flow rates of the first refrigerant stream and the oil-containing refrigerant stream, such that there is reduced or no concern by the user of the process in relation to possible oil freezing and clogging of the heat exchanger caused by variation of the flow or flow rate of the oil-containing refrigerant stream.

An apparatus, system and method for capture, utilization and sendout of latent heat in boil off gas (BOG) onboard a cryogenic storage vessel is described. A liquefied gas vessel comprises a cryogenic cargo tank onboard a liquefied gas vessel, the cargo tank comprising a liquefied gas and a BOG, a latent heat exchanger fluidly coupled to a stream of the liquefied gas and a stream of the BOG, wherein the latent heat exchanger transfers a heat between the BOG stream and the liquefied gas stream to produce a condensed BOG, means for combining the condensed BOG and the liquefied gas stream to obtain a combined stream, the means for combining the condensed BOG and the liquefied gas stream fluidly coupled to the latent heat exchanger, and a liquefied gas regasifier onboard the vessel and fluidly coupled to the combined stream, wherein the liquefied gas regasifier regasifies the combined stream.

A system for reliquefying a boil off gas generated in a storage tank includes a first compressor compressing a partial amount (hereinafter, referred to as fluid a) of boil off gas discharged from the storage tank, a second compressor compressing another partial amount (hereinafter, referred to as fluid b) of boil off gas discharged from the storage tank, a second expanding unit expanding a partial amount (hereinafter, referred to as fluid c) of a flow formed as the fluid a and the fluid b join, a heat-exchanger cooling another partial amount (hereinafter, referred to as fluid d) of the flow formed as the fluid a and the fluid b join, and a first expanding unit expanding the fluid d cooled by the heat-exchanger, wherein the heat-exchanger heat-exchanges the fluid d with the fluid c as a coolant expanded by the second expanding unit to cool the fluid d.

An apparatus, system and method for capture, utilization and sendout of latent heat in boil off gas (BOG) onboard a cryogenic storage vessel is described. A liquefied gas vessel comprises a cryogenic cargo tank onboard a liquefied gas vessel, the cargo tank comprising a liquefied gas and a BOG, a latent heat exchanger fluidly coupled to a stream of the liquefied gas and a stream of the BOG, wherein the latent heat exchanger transfers a heat between the BOG stream and the liquefied gas stream to produce a condensed BOG, means for combining the condensed BOG and the liquefied gas stream to obtain a combined stream, the means for combining the condensed BOG and the liquefied gas stream fluidly coupled to the latent heat exchanger, and a liquefied gas regasifier onboard the vessel and fluidly coupled to the combined stream, wherein the liquefied gas regasifier regasifies the combined stream.

A method for liquefying a feed gas stream. A refrigerant stream is cooled and expanded to produce an expanded, cooled refrigerant stream. Part or all of the expanded, cooled refrigerant stream is mixed with a make-up refrigerant stream in a separator, thereby condensing heavy hydrocarbon components from the make-up refrigerant stream and forming a gaseous expanded, cooled refrigerant stream. The gaseous expanded, cooled refrigerant stream passes through a heat exchanger zone to form a warm refrigerant stream. The feed gas stream is passed through the heat exchanger zone to cool at least part of the feed gas stream by indirect heat exchange with the expanded, cooled refrigerant stream, thereby forming a liquefied gas stream. The warm refrigerant stream is compressed to produce the compressed refrigerant stream.

An LNG production system including a boil off gas recondenser that can recondense boil off gas without using a BOG compressor and without depending on an LNG liquefaction process is provided.

A method of recycling liquefied natural gas (LNG) boil-off gas (BOG) in natural gas liquefaction plants can include: supplying a feed gas to a liquefaction subsystem; liquefying the feed gas to produce LNG and end-flash gas (EFG); compressing the EFG to compressed EFG; using the compressed EFG as fuel gas; storing the LNG in one or more LNG tanks; compressing LNG BOG from the one or more LNG tanks to produce compressed LNG BOG; and either (1) operating in a recycle mode by supplying at least a portion of the compressed LNG BOG to the feed gas via a bidirectional line, or (2) operating in a fuel mode by (a) supplying a portion of the feed gas to the fuel gas via the bidirectional line and (b) supplying the compressed LNG BOG to the fuel gas.