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.

An embodiment of a method for supplying refrigerants to a liquefied natural gas (LNG) facility includes: advancing a first refrigerant from a first storage device to a heat exchanger, the first refrigerant having a first temperature; advancing a second refrigerant from a second storage device to the heat exchanger, the second refrigerant having a second temperature different than the first temperature; flowing the first refrigerant and the second refrigerant through the heat exchanger; adjusting the second temperature based on at least a transfer of heat between the first refrigerant and the second refrigerant in the heat exchanger; and transferring the first refrigerant and the second refrigerant to the LNG facility.

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.

Systems and methods are provided for adjusting a composition, pressure, and/or flow rate of a mixed refrigerant (MR) fluid in a liquefaction system to provide refrigeration to natural gas (NG) feedstock to produce liquefied natural gas (LNG). The MR fluid that is in circulation within a liquefaction system can include heavy components and light components. During LNG production, heavy components and/or light components of the MR fluid can be selectively removed from, and reintroduce into the MR fluid, thereby altering the composition of the remaining MR fluid in circulation. Adjusting the composition of the MR fluid in circulation within a liquefaction system can allow the system to be optimized to maximize efficiency, LNG production, and or profitability while the system is in operation.

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 operating, during an at least partial shutdown of a refrigerant distribution subsystem in a natural gas liquefaction facility, can include: draining down at least a portion of a mixed refrigerant in one or more components of the refrigerant distribution subsystem into a high-pressure holding tank of a drain down subsystem, wherein draining down to the high-pressure holding tank is achieved by pumping the mixed refrigerant from the refrigerant distribution subsystem to the high-pressure holding tank or backfilling the refrigerant distribution subsystem with a backfill gas; and optionally, transferring at least a portion of the mixed refrigerant into a low-pressure drum from the high-pressure holding tank.

The invention relates to compression refrigerator control systems, viz. to refrigerant composition control in premixed refrigerant cycle of liquefied natural gas (LNG) production. The method for controlling the refrigerant composition in the pre-cooled mixed refrigerant (PMR) cycle for LNG production comprises controlling in view of the weather forecast temperatures. The method comprises measuring the concentration of each PMR component and measuring the ambient temperature. Further, it comprises calculating the required concentration of each component for each of the measured and weather forecast temperatures on the basis of the predetermined relationship between the optimum concentration of each component and ambient temperature; calculating the time period required to change appropriately each component concentration in transition to the following of the weather forecast temperatures by using the highest possible change (increase or decrease) rate of each component concentration for the said cycle; and comparing the measured and required concentration of each component in view of the calculated time periods and direction of change in the component concentrations during these periods. The invention allows a higher efficiency of the pre-cooling cycle due to maintaining the optimum PMR composition thus minimizing the cooled product temperature in LNG production.

An embodiment of a method for supplying refrigerants to a liquefied natural gas (LNG) facility includes: advancing a first refrigerant from a first storage device to a heat exchanger, the first refrigerant having a first temperature; advancing a second refrigerant from a second storage device to the heat exchanger, the second refrigerant having a second temperature different than the first temperature; flowing the first refrigerant and the second refrigerant through the heat exchanger; adjusting the second temperature based on at least a transfer of heat between the first refrigerant and the second refrigerant in the heat exchanger; and transferring the first refrigerant and the second refrigerant to the LNG facility.

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.