A natural gas liquefaction method and system having integrated nitrogen removal. Recycled LNG gas is cooled in a separate and parallel circuit from the natural gas stream in the main heat exchanger. Cooled recycled gas and natural gas streams are directed to a nitrogen rectifier column after the warm bundle. The recycle stream is introduced to the rectifier column above the natural gas stream and at least one separation stage is located in the rectifier column between the recycle stream inlet and the natural gas inlet. The bottom stream from the rectifier column is directed to a cold bundle of the main heat exchanger where it is subcooled.

Liquefied natural gas (LNG) boil off gas (BOG) and/or end flash gas (EFG) can be used to recondense refrigerant vent gas. For example, a method can include: passing LNG BOG through a first condensing heat exchanger and/or passing an EFG from liquefaction system through a second condensing heat exchanger; and condensing the refrigerant vent gas in the first and/or second condensing heat exchangers, wherein (when using the first condensing heat exchanger) the LNG BOG is the coolant in the first condensing heat exchanger and (when using the second condensing heat exchanger) the EFG is the coolant in the second condensing heat exchanger, and wherein (when using both condensing heat exchangers) the first and second condensing heat exchangers are in parallel and not in series.

A system for supplying compressed gas to several gas-fed devices is based on a liquid piston gas multistage compressor (100). Gas pressure measurements performed at a gas intake (10), an intermediate gas outlet (20) and at an end gas outlet (30) of the system allow controlling respective gas capacities of the compressor stages. Easy and reliable control can thus be obtained for the system operation. Varying the number of the compressor stages allows matching any pressure requirements for the gas delivery to all the gas-fed devices, and varying the gas capacities of the compressor stages allows easy adaptation to variable gas consumptions of the gas-fed devices.

The invention relates to a liquid natural gas plant for producing liquefied natural gas. The liquid natural gas plant comprises two or more parallel treatment and liquefaction trains, each train comprising a cooling stage arranged to receive a cleaned natural gas stream from a gas treatment stage, an NGL-extraction unit for extracting natural gas liquids, thereby generating a light natural gas stream. The liquid natural gas plant comprises an additional liquefaction train, comprising an additional cooling stage arranged to receive an additional feed stream for generating additional liquefied natural gas. The additional feed stream comprises two or more side streams taken from the light natural gas taken from the respective light natural gas streams of the one or more parallel treatment and liquefaction trains.

In a BOG treatment system, boil-off gas (BOG) discharged from a storage tank is compressed, most of the BOG is used as the fuel of vessel engines, and a remaining part of the BOG is liquefied by cold energy of BOG newly discharged from the storage tank and is returned to the storage tank, thereby efficiently utilizing the BOG. The BOG treatment system for a vessel includes a compressor compressing the BOG discharged from the storage tank; a medium pressure gas engine receiving at least a part of the BOG compressed by the compressor, as fuel; a heat exchanger exchanging heat between the remaining part of the BOG, which is not supplied to the medium pressure gas engine as fuel, and the BOG, which is discharged from the storage tank and is not compressed; and an expander decompressing the remaining part of the BOG cooled by the heat exchanger.

A power supply and cooling system for a floating structure having a tank, includes a supply circuit having at least one compression device, the supply circuit being configured to supply gas to a gas-consuming device, and a cooling circuit having a heat exchanger configured to participate in managing the internal pressure of the tank, the cooling circuit being connected to the supply circuit on either side of the compression device. The compression device includes two compression stages, and the power supply and cooling system includes a control device configured to connect the compression stages in series or in parallel.

A refrigerant cycle pressure control system includes: a heat exchanger cooling boil-off gas received from a storage tank; a refrigerant cycle including a refrigerant circulation line, a refrigerant compressor, and an expander; an inventory tank storing the refrigerant to be charged to the refrigerant cycle; a refrigerant supply line connecting the inventory tank to an upstream side of the refrigerant compressor to replenish the refrigerant cycle with the refrigerant; a refrigerant discharge line connecting a downstream side of the refrigerant compressor to the inventory tank to discharge the refrigerant from the refrigerant cycle to the inventory tank; and a pressure regulation line branched off of the refrigerant discharge line. The refrigerant cycle is depressurized by discharging the refrigerant from the refrigerant cycle through the refrigerant discharge line or the pressure regulation line.

Disclosed herein is a BOG reliquefaction method for LNG ships. The BOG reliquefaction method for LNG ships includes: 1) compressing BOG; 2) cooling the BOG compressed in Step 1) through heat exchange between the compressed BOG and a refrigerant using a heat exchanger; 3) expanding the BOG cooled in Step 2); and 4) stably maintaining reliquefaction performance regardless of change in flow rate of the BOG compressed in Step 1) and supplied to the heat exchanger to be used as a reliquefaction target.

Described herein are methods and systems for liquefying natural gas by: cooling and liquefying a natural gas feed stream via indirect heat exchange with at least a first cold refrigerant stream to form a first liquefied natural gas stream and a warmed gaseous refrigerant stream; flashing and separating the first liquefied natural gas stream to form a liquefied natural gas product stream and at least a first flash gas stream; combining and compressing the first flash gas stream and the warmed gaseous refrigerant stream to form a compressed refrigerant stream; and expanding at least a first portion of the compressed refrigerant stream to form the first cold refrigerant stream; wherein the natural gas feed stream is kept separate from and is not combined with either the first flash gas stream or the compressed refrigerant stream.

A vessel for the transport of liquefied gas has a hull, a cargo storage tank arranged in the hull for storing liquefied gas and an engine to propel the ship. A compressor has a compressor inlet connected to a vapour space of the at least one cargo storage tank for receiving boil-off gas at a first pressure and a compressor outlet for supplying pressurized boil-off gas to the at least one engine at a second pressure exceeding the first pressure. A boil-off gas recovery system is provided for recovery of boil off gas. The boil-off gas recovery system has a cooling section with a cooling section inlet connected to the compressor outlet to recondense at least part of the pressurized boil-off gas and a boil-off gas storage tank having a boil-off gas storage tank inlet connected to the cooling section outlet for storing the recondensed pressurized boil-off gas.