KR20180095870A - Method for producing inflator-based LNG reinforced with liquid nitrogen - Google Patents

Abstract

Method of producing liquefied natural gas (LNG). The natural gas stream is sent to a mechanical refrigeration unit to liquefy the natural gas stream to form a pressurized liquefied natural gas (LNG) stream having a pressure of greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa). A liquid refrigerant supercooling unit is provided in the first position. The liquid phase refrigerant is produced in a second location that is geographically remote from the first location. The generated liquid refrigerant is delivered to the first position. The LNG stream is produced by subcooling the pressurized LNG stream in the liquid refrigerant subcooling unit by heat exchange between the pressurized LNG stream and at least one stream of liquid coolant.

Description

Method for producing inflator-based LNG reinforced with liquid nitrogen

Cross-reference to related patent sources

This application claims the benefit of U.S. Provisional Patent Application No. 62 / 266,979, filed on December 14, 2015, entitled Method of Producing Expander-Based LNG Reinforced with Liquid Nitrogen, the title of which is incorporated herein by reference. .

This application claims priority from US Provisional Patent Application No. 62 / 266,976 entitled " Method and System for Separating Nitrogen from Liquefied Natural Gas Using Liquefied Nitrogen ", entitled "LNG Carrier US 62 / 266,983, entitled " Natural Gas Liquefaction Method in High Pressure Compression and Expansion, " US 62 / 622,985, entitled " All of which have common inventors and assigns and are filed on the same date, the disclosures of which are incorporated herein by reference in their entirety.

Technical field

Field of the Invention The present invention relates generally to the field of liquefied natural gas (LNG) formation. More particularly, the present invention relates to the production and transport of LNG from coastal and / or remote sources of natural gas.

This section is intended to introduce various aspects of the art that may be related to the present invention. This discussion is intended to provide a framework for a better understanding of certain aspects of the present invention. Therefore, it should be understood that this section should be read in this light, and not necessarily read as accepting prior art.

LNG is a fast-growing means of supplying natural gas from areas rich in natural gas to remote areas where demand for natural gas is high. Conventional LNG cycles include a) initial treatment of natural gas resources to remove contaminants such as water, sulfur compounds and carbon dioxide; b) separating various heavy hydrocarbon gases such as propane, butane, pentane and the like by various possible methods including self-refrigeration, external refrigeration, lean oil, and the like; c) substantially freezing the natural gas by external refrigeration to form liquefied natural gas at about -160 DEG C at atmospheric pressure or near atmospheric pressure; d) transporting the LNG product in the vessel or tanker designed for this purpose to a market location; And e) repressurizing and re-gasifying the LNG in a regasification plant to form a pressurized natural gas stream that can be dispensed to natural gas consumers. Step (c) of a conventional LNG cycle typically requires the use of a large refrigeration compressor powered by a large gas turbine driver that emits substantial carbon and other emissions. Large capital investments of billions of US dollars and extensive infrastructure are required as part of the liquefaction plant. Step (e) of the conventional LNG cycle generally involves repressurizing the LNG with the required pressure using a cryogenic pump and then re-gasifying the LNG to effect heat exchange with the seawater but ultimately through the intermediate fluid Or burning a portion of the natural gas to heat and vaporize the LNG to form pressurized natural gas. Generally, the available exergy of cryogenic LNG is not utilized.

A relatively new technology for producing LNG is known as floating LNG (FLNG). FLNG technology involves the construction of gas treatment and liquefaction facilities in floating structures such as barges or ships. FLNG is a technology solution for monetizing coastal stranded gas, which makes it economically impossible to construct a gas pipeline on the coast. FLNG is also increasingly being considered for land and offshore gas fields located in distant and / or environmentally sensitive and / or politically difficult areas. This technology has a clear advantage over conventional land-based LNG in that it has less environmental footprint at the production site. In addition, because most of the LNG installations are built at the shipyards with lower labor rates and reduced execution risk, this technology can provide projects at a faster and cheaper cost.

While FLNG has several advantages over conventional land-based LNGs, there remains a significant technical challenge to the application of this technology. For example, the FLNG structure should provide the same level of gas treatment and liquefaction in areas that are less than one-quarter of the area available on land LNG plants. For this reason, it is necessary to develop a technology that reduces the footprint of the FLNG plant while maintaining the capacity of the liquefaction plant, thereby reducing the overall project cost. One promising means of reducing footprint is to modify the liquefaction technology used in FLNG plants. Known liquefaction techniques include single mixed refrigerant (SMR) processes, dual mixed refrigerant (DMR) processes, and expander-based (or expansion) processes. Inflator-based processes have several advantages that are appropriate for FLNG projects. The most important advantage is that this technology provides liquefaction without the need for external hydrocarbon refrigerants. Elimination of liquid hydrocarbon refrigerant inventory, such as propane storage, significantly reduces serious safety problems, especially in the FLNG project. A further advantage of the inflator-based process compared to the mixed refrigerant process is that the inflator-based process is less susceptible to coastal movement because the main refrigerant remains predominantly in the gas phase.

Although expander-based processes are beneficial, applying this technology to FLNG projects with LNG production of more than 2 million tonnes per year (MTA) has proven to be less attractive than using mixed refrigerant processes. The capacity of known expander-based process trains is typically less than 1.5 MTA. On the other hand, mixed refrigerant process trains such as the propane-pre-cooling process or the dual-mix refrigerant process may have a train capacity in excess of 5 MTA. The size of the inflator-based process train is limited because the refrigerant is kept in a steady state throughout the process and the refrigerant absorbs energy through its sensible heat. For this reason, the refrigerant volumetric flow rate is large throughout the process and the size of the heat exchanger and piping is proportionally larger than that used in the mixed refrigerant process. In addition, the limit on the size of the compander horsepower results in a parallel rotating machine as the capacity of the inflator-based process train increases. The production rate of an FLNG project using an expander-based process may exceed 2 MTA if multiple expander-based trains are allowed. For example, for a 6MTA FLNG project, six or more parallel inflator-based process trains may be sufficient to achieve the required production. However, the number of equipments, complexity and cost are both increased by the multi-inflator train. Also, compared to the mixed refrigerant process, the assumed process simplification of the inflator-based process doubles the need for multiple trains for the inflator-based process, while the mixed refrigerant process can achieve the required production rate with one or two trains It starts to raise. For this reason, there is a need to develop an FLNG liquefaction process that achieves high LNG production capacity while still having the advantages of an expander-based process. In addition, there is a need to develop FLNG technology solutions that can better handle the difficulties experienced by ship movements in gas processing.

US Pat. No. 3,400,547 to Williams et al. Discloses a process in an LNG production facility in which liquid nitrogen (LIN) produced at different locations is used as a refrigerant for natural gas liquefaction. This process uses a propane chiller to cool the natural gas before condensing the natural gas by indirect heat exchange with the vaporized LIN. British Patent No. 1,596,330 to Thompson discloses a process in an LNG production facility in which LIN produced at different locations is used as a refrigerant for natural gas liquefaction. This process uses propane and ethylene cooler with LIN to liquefy natural gas with LNG. The processes disclosed in these two patents have the disadvantage of requiring a significant amount of LIN to produce LNG while using a mechanical refrigeration system. It is estimated that both processes require a LIN of approximately 1 ton or more per ton of LNG produced. In FLNG applications, the space for storing LIN at the top or in the hull of a floating structure may be limited. It is advantageous to apply LNG production technology to FLNG using LNG because it greatly reduces the top space required for the liquefaction process. It would also be advantageous to have LNG production techniques that use less than 1 ton of LIN per tonne of LNG produced, more preferably less than 0.75 ton of LIN, and more preferably less than 0.5 ton of LIN.

U.S. Patent No. 6,412,302 to Foglietta discloses a feed gas expander-based process in which two independent closed refrigeration loops are used to cool feed gas to form LNG. The first closed refrigeration loop uses the components of the feed gas or feed gas as the refrigerant. Nitrogen gas is used as the refrigerant for the second closed freezing loop. This technique has the advantage of requiring smaller equipment and top space than a dual loop nitrogen expander-based process. For example, in this technique, the volumetric flow rate of the refrigerant in the low pressure compressor may be 20 to 50% smaller than the double loop nitrogen expander-based process. However, this technology is still limited to capacities less than 1.5 MTA.

US Patent No. 8,616,012 to Minta discloses a feed gas expander-based process in which the feed gas is used as a refrigerant in a closed refrigeration loop. Within this closed refrigeration loop, the refrigerant is compressed to a pressure of at least 1500 psia or, more preferably, greater than 2500 psia. The refrigerant is then cooled and expanded to achieve cryogenic temperatures. This cooled refrigerant is then used in a heat exchanger to cool the feed gas from warm to cryogenic temperatures. The feed gas is then further cooled using a subcooling refrigeration loop to form LNG. In one embodiment, the supercooled refrigeration loop is a closed loop in which the flash gas is used as the refrigerant. This feed gas expander-based process has the advantage that it is not limited to a train capacity range of less than 1 MTA. A train size of approximately 6 MTA was considered. However, this technique has the disadvantage that the number of equipment is increased and the complexity is increased due to the requirements for the compression of the two independent refrigeration loops and the feed gas. Also, high pressure operation means that equipment and piping will be much heavier than other inflator-based processes.

British Patent No. 2,486,036 to Maunder et al. Discloses a feed gas expander-based process which is an open loop refrigeration cycle comprising a precooling expander loop and a liquefied expander loop that uses a gas phase after expansion to liquefy natural gas . According to Maunder, the inclusion of the inflator liquefaction stage in this process significantly reduces the recycle gas velocity and the overall refrigeration power required. This technique is simpler than that described by Foglietta and Minta, since only one type of refrigerant with a single compression string is used. However, this technology is still limited to capacities less than 1.5 MTA and requires the use of liquefied inflators, not standard equipment for LNG production. This technique has also been shown to be less efficient than the technology described by Foglietta and Minta for the liquefaction of lean natural gas.

There is a need to develop an LNG production process that has a high LNG production capacity while reducing facility footprint while also having the advantage of an expander-based process. There is a need to develop LNG technology solutions that can better handle the difficulties that ship movement has on gas treatment. This high capacity inflator-based liquefaction process is particularly suitable for FLNG applications where the inherent safety and simplicity of the inflator-based liquefaction process is greatly appreciated.

The present invention provides a method for producing liquefied natural gas (LNG). The natural gas stream is sent to a mechanical refrigeration unit to liquefy the natural gas stream to form a pressurized liquefied natural gas (LNG) stream having a pressure of greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa). A liquid refrigerant subcooling unit is provided in the first position. The liquid phase refrigerant is produced in a second location that is geographically remote from the first location. The generated liquid refrigerant is delivered to the first position. The LNG stream is produced by subcooling the pressurized LNG stream in the liquid refrigerant subcooling unit by heat exchange between the pressurized LNG stream and at least one stream of liquid coolant.

The present invention also provides a system for producing liquefied natural gas (LNG). The mechanical refrigeration unit liquefies the natural gas stream using a feed gas expander-based process to form a pressurized liquefied natural gas (LNG) stream having a pressure of greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa). The liquid nitrogen (LIN) supercooling unit is located in the first position. A liquid nitrogen (LIN) stream is produced at a second location that is geographically remote from the first location. The LIN stream is transferred to the LIN and the cooling unit. The LIN and subcooling units subcool the pressurized LNG stream by heat exchange between the pressurized LNG stream and at least one stream of the LIN stream to produce an LNG stream and at least one vaporized LIN stream.

The foregoing has broadly outlined the features of the invention in order that the detailed description that follows may be better understood. Additional features will also be described herein.

These and other features, aspects and advantages of the present invention will become apparent from the following description, appended claims, and accompanying drawings.
1 is a graph showing a temperature cooling curve for an expander-based heat exchanger process.
Figure 2a is a simplified diagram of the value chain of the known FLNG technique.
2B is a simplified diagram of a value chain according to an embodiment described herein.
3 is a schematic diagram of a system according to an embodiment described herein.
4 is a schematic view of a mechanical refrigeration unit according to an embodiment described herein.
5 is a schematic diagram of a liquid nitrogen (LIN) and cooling unit according to an embodiment described herein.
6 is a schematic diagram of a LIN subcooling unit according to an embodiment described herein.
7 is a flow chart illustrating a method according to an embodiment described herein.
It should be noted that the drawings are only examples, and are not intended to limit the scope of the present invention. In addition, the drawings are not drawn to scale in general, but are made for convenience and clarity in illustrating various aspects of the present invention.

To facilitate an understanding of the principles of the present disclosure, reference will now be made to the features shown in the drawings and specific language will be used for the description. Nevertheless, it will be understood that it is not intended to limit the scope of the invention. Any alterations and further modifications and any additional applications, as described herein, are contemplated as would occur to those skilled in the art to which the invention relates. For clarity, some features not relevant to the present invention may not be shown in the figures.

DETAILED DESCRIPTION OF THE INVENTION Initially, for ease of reference, certain terms used herein and their meaning as used in this context are disclosed. Unless the terminology used herein is defined below, one of ordinary skill in the relevant arts should be accorded the broadest definition of at least one printed matter or given term reflected in the issued patent. Furthermore, all equivalents, synonyms, novel developments and terms or descriptions which, while they are within the scope of the claims, are not to be construed as limitations of the use of the following terms.

As one of ordinary skill in the art will recognize, different persons may refer to the same features or elements with different names. These documents do not distinguish between components and features that differ only in name. The drawings are not necessarily to scale. Some features and elements of the present disclosure may be exaggerated in scale or approximate form and some details of conventional components may not be shown for clarity and brevity. Referring to the drawings described herein, the same reference numerals may be referred to in the several figures for the sake of simplicity. In the following description and the claims, the terms " including "and" comprising "are to be interpreted as meaning" including, but not limited to, "

The articles "the "," a "and" an "do not necessarily denote a single entity, but are inclusive and open to include a plurality of such elements.

As used herein, the terms "about," "about, "" substantially, "and like terms are intended to have a broad meaning in concert with the uses generally accepted by those skilled in the art to which the subject matter of the present disclosure relates. It is to be understood that those skilled in the art, upon review of this specification, will appreciate that these terms are intended to be illustrative and allow explanation of the specific features claimed without limiting the scope of these features to the exact numerical range provided. Accordingly, these terms are to be construed as being considered to be within the scope of the invention, either as a non-essential or non-essential change or alternative to the described subject matter.

The term "heat exchanger" means a device designed to efficiently transfer or "exchange" heat from one material to another. Exemplary heat exchanger types include, but are not limited to, cocurrent or countercurrent heat exchangers, indirect heat exchangers (e.g., spiral wound heat exchangers, plate-like, brazed aluminum plate fin types, fin heat exchangers, shell and tube heat exchangers, etc.), direct contact heat exchangers, or any combination thereof.

The term "dual purpose carrier" means: (a) capable of transporting LIN to an export terminal for natural gas and / or LNG; and (b) transporting the LNG to an LNG import terminal Means a vessel that can be used.

As described above, conventional LNG cycles include (a) initial treatment of natural gas resources to remove contaminants such as water, sulfur compounds, and carbon dioxide; (b) separating various heavy hydrocarbon gases such as propane, butane, pentane, and the like by a variety of methods including self-cooling, external refrigeration, lean oil, and the like; (c) substantially freezing the natural gas by external refrigeration to form LNG at about -160 < 0 > C at atmospheric pressure or near atmospheric pressure; (d) transporting the LNG product in the vessel or tanker designed for this purpose to a market location; And (e) repressurizing and re-gasifying the LNG in the regasification plant to form a pressurized natural gas stream that can be dispensed to natural gas consumers. The present invention generally involves liquefying natural gas using liquid nitrogen (LIN). In general, producing LNG using LIN is an unusual LNG cycle, where step (c) is replaced by a natural gas liquefaction process using a significant amount of LIN as an open loop source of refrigeration , Step (e) can be modified to use cryogenic LNG exergy to promote liquefaction of nitrogen gas to form LIN, which in turn can be used to transport LNG to a source location and serve as a refrigeration source for LNG production . The LIN-to-LNG concept described may further include the transfer of the LNG from the resource location (export terminal) to the market location (import terminal) in the ship or tanker and the reverse transfer of the LIN from the market location to the resource location.

The embodiments described herein provide a method of enhancing a mechanical cooling process for producing LNG using liquid refrigerant produced at different locations to subcool the liquefied natural gas resulting from the mechanical cooling process. More specifically, a process is disclosed wherein treated natural gas can be sent to a mechanical cooling process. The natural gas may be fully liquefied in a mechanical cooling process to produce a pressurized LNG stream wherein the pressure of the pressurized LNG stream is greater than 50 psia (or 345 kPa) and less than 500 psia (or 3445 kPa), or more specifically 100 psia (or 690 kPa ) And less than 400 psia (or 2758 kPa), or, more specifically, greater than 200 psia (or 1379 kPa) and less than 300 psia (or 2068 kPa). The pressurized LNG stream may then be subcooled by heat exchange with at least one liquid coolant stream to form an LNG stream. A liquid refrigerant stream is produced at a geographic location different from where the natural gas is liquefied and may be 50 miles, or 100 miles, or 200 miles, or 500 miles, or 1,000 miles, or 1,000 miles or more from this location. The mechanical cooling process may be a single mixed refrigerant process, a pure component cascade refrigerant process, a dual mixed refrigerant process, an inflator-based refrigeration process, or any other commonly known refrigeration process capable of liquefying a natural gas stream to produce a pressurized LNG stream Lt; / RTI >

In one embodiment, the inflator-based process for LNG production may be enhanced using LIN generated at different locations to subcool the pressurized LNG from the inflator-based process. Natural gas, if present, can be treated to remove impurities such as water, heavy hydrocarbons, and sour gas to produce natural gas suitable for liquefaction. The treated natural gas may be fully liquefied in an expander-based process to produce a pressurized LNG stream wherein the pressure of the pressurized LNG stream is greater than 50 psia (or 345 kPa) and less than 500 psia (or 3445 kPa) (Or 690 kPa) and less than 400 psia (or 2758 kPa), or, more specifically, greater than 200 psia (or 1379 kPa) and less than 300 psia (or 2068 kPa). The pressurized LNG stream may then be subcooled by heat exchange with at least one LIN stream to form an LNG stream. The expander-based process may be a nitrogen gas expander-based process or may be a feed gas expander-based process.

Figure 1 shows a typical temperature cooling curve 100 for an expander-based liquefaction process. The high temperature curve 104 is a temperature curve for the natural gas stream. The low temperature curve 102 is a composite temperature curve of a cold cooling stream and a warm cooling stream. As illustrated, the cooling curve is indicated by three temperature pinch-points. The lowest temperature pinch-point 106 occurs where the cooler of the two cooling streams, typically the cold cooling stream, enters the heat exchanger. The intermediate temperature pinch-point 108 occurs where a second cooling stream, typically an on-cooling stream, enters the heat exchanger. The on-temperature pinch-point 110 occurs where the cold and warm cooling streams exit the heat exchanger. Minimum temperature pinch-point 106 constitutes the required flow rate of the cold cooling stream. Since the cold cooling stream is first cooled by the on-cooling stream before it is expanded to low temperature, the flow rate of the cold-cooling stream also affects the required flow rate of the on-cooling stream. One way to increase the capacity of an expander-based process without significantly increasing equipment size and required power is to increase the temperature at the lowest temperature pinch point. In this case, to produce LNG, additional refrigeration is needed to subcool the pressurized LNG from the expander-based process. Subcooling the pressurized LNG by another mechanical refrigeration cycle would not be advantageous and efficient. For this reason, the embodiments described herein propose the use of liquid refrigerants produced at different locations to subcool the pressurized LNG. The liquid refrigerant may be LIN.

Under certain circumstances, the liquid phase refrigerant can be produced with an amount of energy that allows the entire process of producing pressurized LNG and liquefied refrigerant to be thermodynamically more efficient than conventional LNG production processes. For example, the refrigerant may be nitrogen produced from an air separation plant, where the nitrogen is liquefied using cool air available in the gasification of the LNG. Typically, in the process of gasification of LNG, all available exergy from LNG gasification is lost to the environment. Using such exergy, the LIN can be produced with a sufficiently low energy cost to bring the total energy requirement of the embodiments described herein to be close to, or much lower than, the energy cost of a conventional LNG production process.

In accordance with an embodiment described herein, the expander-based process may be a feed-gas expander-based process. The feed-gas expander-based process may be an open loop feed gas process wherein the recycling loop includes a warm-end inflator loop and a cold-end inflator loop. The on-end inflator can discharge the first cooling stream and the cold-end inflator can discharge the second cooling stream. The temperature of the first cooling stream may be higher than the temperature of the second cooling stream. The pressure of the first cooling stream may be the same as or similar to the pressure of the second cooling stream. The cold-end inflator can discharge the two-phase stream separated into the second cooling stream and the second pressurized LNG stream. Natural gas, if present, can be treated to remove impurities such as water, heavy hydrocarbons, and sour gases to produce natural gas suitable for liquefaction. The treated natural gas may be fully liquefied by indirect heat exchange with the first and second cooling streams to produce a first pressurized LNG stream. The first pressurized LNG stream may be mixed with the second pressurized LNG stream to form a pressurized LNG stream. The pressure of the pressurized LNG stream is greater than 50 psia (or 345 kPa) and less than 500 psia (or 3445 kPa), or more specifically greater than 100 psia (or 690 kPa) and less than 400 psia (or 2758 kPa), or more specifically greater than 200 psia (or 1379 kPa) And 300 psia (or 2068 kPa). The pressurized LNG stream can be subcooled by heat exchange with at least one LIN stream to form an LNG stream. The subcooling process includes using at least one heat exchanger to allow indirect heat exchange between the vaporized LIN stream and the pressurized LNG stream. The supercooling process may further include other commonly known equipment to enable cooling of other equipment, such as compressors, expanders, separators, and / or pressurized LNG streams. The vaporized LIN stream may be used to liquefy the second stream of treated natural gas after heat exchange with the pressurized LNG stream to produce an additional pressurized LNG stream. An additional pressurized LNG stream may be mixed with the pressurized LNG stream prior to subcooling the pressurized LNG stream with LIN.

In one described embodiment, the produced LNG can be shipped on the LNG carrier and / or the dual purpose carrier at the LNG production location and transferred to a different location where the LNG is unloaded and re-gasified. The cold energy from the LNG gasification can liquefy the nitrogen which is then shipped to the LIN carrier and / or the dual purpose carrier and redirected to the LNG production location where LIN is used to liquefy the treated natural gas do.

FIGS. 2A and 2B are simplified diagrams that highlight the differences between the value chain of the embodiment described herein and the value chain of conventional FLNG technology, wherein the FLNG facility contains all or nearly all the equipment needed to process and liquefy natural gas do. As shown in FIG. 2A, the LNG cargo ship 200a transports the LNG from the FLNG facility 202 to the offshore import terminal 204, where the LNG is unloaded and regasified. The LNG carrier 200b without cargo and ballast is recovered to the FLNG facility 202 and re-shipped. On the other hand, the embodiment described herein and shown in FIG. 2B provides a floating processing unit (FPU) 206 having a much smaller footprint than the FLNG facility 202 (FIG. 2A). 2B, an LIN cargo ship or dual purpose ship 208a with LIN loaded at the import terminal 204 arrives at the FPU 206 and transfers its LIN cargo to the FPU 206 and / Lt; / RTI > On the FPU 206, the mechanical refrigeration unit cools the natural gas into a pressurized LNG stream. The pressurized LNG stream is then subcooled within the LIN < RTI ID = 0.0 > subcooling < / RTI > unit on FPU 206 to produce LNG. The produced LNG is transferred to the LNG cargo ship or dual purpose ship 208b. The LNG cargo ship or dual purpose vessel 208b now loaded with LNG sails to the import terminal 204 where the LNG is unloaded and regasified. The liquefied nitrogen is liquefied at the import terminal 204 using cold energy from re-gasification of the LNG. The liquefied nitrogen in the import terminal 204 can be produced in the air separation unit 210. The air separation unit 210 may be a part of the import terminal 204 or a part in the import terminal 204 or may be a facility separate from the import terminal 204. The LIN may then be shipped to a LIN cargo ship or dual purpose vessel returning to the FPU 206 to repeat the liquefaction process.

In another aspect of the invention, LIN can be used to liquefy LNG boil-off gas from the tank during LNG production, transfer and / or unloading. In another aspect of the invention, the LIN from the supercooling process and / or the vaporized LIN can be used to cool the inlet air to the gas turbine of the mechanical cooling process. In another aspect of the invention, LIN and / or LIN evaporation gas can be used to keep the liquefier cool during the turn down or shutdown of the liquefaction process. In another aspect of the invention, nitrogen vapor may be used to deriminate the cryogenic heat exchanger during periods between LNG production. Nitrogen vapors with contaminants can be vented to the atmosphere.

3 is a schematic diagram of a system 300 according to an embodiment described herein. Natural gas, if present, can be treated to remove impurities such as water, heavy hydrocarbons, and sour gases to produce a natural gas stream 302 suitable for liquefaction. The treated natural gas stream 302 may be sent to a mechanical refrigeration unit 304 where the treated natural gas 302 is fully liquefied and produces a pressurized LNG stream 306. The pressure of the pressurized LNG stream 306 may be greater than 50 psia (or 345 kPa) and less than 500 psia (or 3445 kPa), or more specifically greater than 100 psia (or 690 kPa) and less than 400 psia (or 2758 kPa) 1379 kPa) and less than 300 psia (or 2068 kPa). The mechanical refrigeration unit 304 may be a single mixed cooling process, a pure component cascade cooling process, a dual mixed cooling process, an inflator-based refrigeration process, or a process that can liquefy the treated natural gas stream 302 into the pressurized LNG stream 306 Any other commonly known refrigeration process may be included. The mechanical refrigeration unit 304 may include a gas turbine that is used to provide mechanical power to drive the compressor in the mechanical refrigeration unit 304. The pressurized LNG stream 306 may be sent to the liquid coolant and supercooling unit 308 where the pressurized LNG stream 306 is supercooled by heat exchange with the liquid coolant stream 310 to form the LNG stream 312. The liquid refrigerant stream 310 is generated at a position different from the positions of the mechanical refrigeration unit 304 and the liquid refrigerant subcooling unit 308. [ The liquid-phase refrigerant stream 310 is vaporized and warmed in the liquid-phase refrigerant supercooling unit 308, and then exits the liquid-phase refrigerant supercooling unit 308 as a refrigerant gas outlet 314. The liquid refrigerant subcooling unit 308 includes at least one heat exchanger to permit indirect heat exchange between the liquid refrigerant stream 310 and the pressurized LNG stream 306. The liquid refrigerant subcooling unit 308 may further include other commonly known equipment for enabling cooling of other equipment, such as a compressor, an expander, a separator, and / or a pressurized LNG stream 306. The vaporized liquid coolant stream 310 may be used to liquefy the second stream of treated natural gas 316 after heat exchange with the pressurized LNG stream 306 to produce an additional pressurized LNG stream. The additional pressurized LNG stream may be combined with the pressurized LNG stream 306 to form an LNG stream 312 prior to subcooling the pressurized LNG stream 306 with the liquid coolant stream 310.

4 is a schematic view of a mechanical refrigeration unit 400 according to an embodiment described herein. The mechanical refrigeration unit 400 includes a feed gas expander-based process. The natural gas liquefied by the mechanical refrigeration unit 400, if present, can be processed to remove impurities such as water, heavy hydrocarbons, and sour gas, to produce a natural gas stream 402 suitable for liquefaction . With the coupling device 403, the treated natural gas stream 402 is mixed with the recovered refrigerant stream 404. The combined natural gas stream 405 is then separated by one or more manifolds, a splitter, or other type of separator 406, 408, 409, , A first refrigerant stream (412), a second refrigerant stream (414), and a liquid coolant to produce a small amount of treated natural gas stream (415), as described herein. The first refrigerant stream (412) is expanded in a first inflator (417) to produce a first cooling stream (416). The first cooling stream 416 flows into at least one heat exchanger 418 where it exchanges heat with the treated second natural gas stream 410 and the second refrigerant stream 414 to cool the two streams . The heated first cooling stream 416 now exits the at least one heat exchanger 418 as a first warm stream 420. The second refrigerant stream 414 is cooled in at least one heat exchanger 418 and then expanded in a second inflator 422 to produce a two-phase stream 424. The pressure of the two-phase stream 424 may be the same or substantially the same as the pressure of the first cooling stream 416. The two-phase stream 424 can be separated into its vapor component and its liquid component in the two-phase separator 426 to form a second cooling stream 428 and a second pressurized LNG stream 430. The temperature of the first cooling stream 416 may be higher than the temperature of the second cooling stream 428. The second pressurized LNG stream 430 may be pumped to a higher pressure after exiting the two phase separator 426, using the pump 432. The second cooling stream 428 may be introduced into at least one heat exchanger 418 where it is heat exchanged with the treated second natural gas stream 410 and the second refrigerant stream 414 to cool the stream . The heated second cooling stream exits the at least one heat exchanger 418 as a second warm stream 434. The treated second natural gas stream 410 may undergo heat exchange with the first cooling stream 416 and the second cooling stream 428 to produce a first pressurized LNG stream 436. After the first pressurized LNG stream 436 exits the at least one heat exchanger 418, the first pressurized LNG stream 436 may be depressurized in a hydraulic turbine 437 or other decompressor. The first pressurized LNG stream 436 may be mixed with the second pressurized LNG stream 430 to form a combined pressurized LNG stream 438. The pressure of the combined pressurized LNG stream 438 is greater than 50 psia (or 345 kPa) and less than 500 psia (or 3445 kPa), or more specifically greater than 100 psia (or 690 kPa) and less than 400 psia (or 2758 kPa) Or 1379 kPa) and less than 300 psia (or 2068 kPa). As described further herein, the pressurized LNG stream 438 may be sent to the LIN < RTI ID = 0.0 > and / or < / RTI >

The first warm stream 420 may combine with the second warm stream 434 in the combining device 440 to form a combined warm refrigerant stream 442. The combined warm refrigerant stream 442 may be compressed in a number of compressor stages to form a recirculated refrigerant stream 404. The compressor stage may include a first compressor stage 444, a second compressor stage 446, and a third compressor stage 448. The first compressor stage 444 may be driven by a gas turbine (not shown). The second compressor stage 446 may be driven solely by shaft power generated by the first inflator 417. [ The third compressor stage 448 may be solely driven by the shaft force generated by the second inflator 422. Coolers 450, 452 and 454 may cool the combined warm refrigerant stream 442 after each of the first, second and third compressor stages 444, 446 and 448.

5 is a schematic diagram of a LIN subcooling unit 500 according to an embodiment described herein. The LIN supercooling unit 500 may be used with the mechanical refrigeration unit 400 shown in FIG. The LIN produced at a location different from the location of the LIN subcooling unit 500 is transferred to the location of the LIN subcooling unit 500 and sent to the at least one heat exchanger 502 as a LIN stream 504. In at least one heat exchanger 502, the LIN stream 504 is vaporized by a subcooling of the pressurized LNG stream 506 (which may be the same as the combined pressurized LNG stream 438 of FIG. 4) Nitrogen stream < RTI ID = 0.0 > 508 < / RTI > The vaporized nitrogen stream 508 is sent to a second heat exchanger 512 to liquefy the treated natural gas stream 514 which may be the same as the small treated natural gas stream 415 to produce additional pressurized LNG Stream 516 can be formed. Additional pressurized LNG stream 516 may be combined with pressurized LNG stream 506 at the coupling device 518 prior to entering the at least one heat exchanger 502. The additional pressurized LNG stream 516 may be depressurized in the hydraulic turbine 520 or other decompressor before being combined with the pressurized LNG stream 506. The vaporized nitrogen stream 508 in the second heat exchanger 512 is heated by the treated natural gas stream 514 and used in other areas of the gas treatment facility where the LIN and the cooling unit 500 are located, Thereby forming a nitrogen gas 522 that can be discharged.

6 is a schematic diagram of a LIN supercooling unit 600 according to an embodiment described herein. The LIN supercooling unit 600 can be used with the mechanical refrigeration unit 400 shown in Fig. The LIN produced at a location different from the location of the LIN subcooling unit 560 is transferred from a different location and sent to the LIN and cooling unit 600 as a LIN stream 602. The pump 604 may pump the LIN stream 602 at a pressure greater than 400 psi to form the high pressure LIN stream 606. The high pressure LIN stream 606 in the at least one heat exchanger 610 is heat exchanged with the pressurized LNG stream 608 (which may be the same as the combined pressurized LNG stream 438 of FIG. 4) Stream 612 is formed. The first warmed nitrogen gas stream 612 may be expanded in the first expander 614 to form a first further cooled nitrogen gas stream 616. The first further cooled nitrogen gas stream 616 in the at least one heat exchanger 610 is heat exchanged with the pressurized LNG stream 608 to form a second warmed nitrogen gas stream 618.

The second warmed nitrogen gas stream 618 may be introduced into the second warmed nitrogen gas stream 618 such that in the second heat exchanger 619 a second warmed nitrogen gas stream 618 is compressed in the one or more compressor stages to form a compressed nitrogen gas stream 620, It is possible to perform indirect heat exchange with another process stream. 6, one or more compressor stages may include two compression stages, including a first compressor stage 622 and a second compressor stage 624. The second compressor stage 624 may be driven solely by the shaft force generated by the first inflator 614. The first compressor stage 622 can be driven solely by the shaft force generated by the second inflator 626. [ After each compression stage, the compressed nitrogen gas stream 620 can be indirectly heat exchanged with the environment in each of the coolers 628, 630. The compressed nitrogen gas stream 620 may be expanded at the second expander 626 to form a second further cooled nitrogen gas stream 632. A second further cooled nitrogen gas stream 632 in the at least one heat exchanger 610 is heat exchanged with the pressurized LNG stream 608 to form a third warmed nitrogen gas stream 634. The pressurized LNG stream 608 is subcooled by heat exchange with a high pressure LIN stream 606, a first further cooled nitrogen gas stream 616, and a second further cooled nitrogen gas stream 632, (636). The third warmed nitrogen gas stream 634 is sent to a third heat exchanger 638 to produce a treated natural gas stream 640 which may be the same as the small processed natural gas stream 415 of FIG. May be liquefied to form additional pressurized LNG stream 642. [ Additional pressurized LNG stream 642 may be combined with pressurized LNG stream 608 at the combining device 644 prior to subcooling pressurized LNG stream 608 in at least one heat exchanger 610. [ The additional pressurized LNG stream 642 may be depressurized in the hydraulic turbine 646 before being combined with the pressurized LNG stream 608. The third warmed nitrogen gas stream 634 can be heated by the treated natural gas stream 640 to be used in other areas of the gas treatment facility where the LIN and / Gas 648 may be formed. The LIN subcooling unit 600 shown in FIG. 6 reduces the LIN requirement for subcooling the pressurized LNG stream to about 20 to 25% compared to the LIN subcooling unit 500 shown in FIG. However, the choice of the subcooling unit may depend on criteria such as the LIN cost and the top space available for LIN storage and / or LIN < RTI ID = 0.0 > and / or < / RTI >

7 is a flow diagram of a method 700 of producing liquefied natural gas (LNG). At block 702, the natural gas stream is sent to the mechanical refrigeration unit to liquefy the natural gas stream and form a pressurized liquefied natural gas (LNG) stream having a pressure of greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa) . At block 704, a liquid refrigerant supercooling unit is provided in a first position. At block 706, liquid refrigerant is generated at a second location that is geographically remote from the first location. At block 708, the resulting liquid refrigerant is delivered to the first location. At block 710, the pressurized LNG stream is heat exchanged between at least one stream of liquid phase refrigerant to subcool the pressurized LNG stream in the liquid refrigerant subcooling unit to produce an LNG stream.

The steps shown in Figure 7 are provided for illustrative purposes only, and the specific steps may not be required to perform the disclosed method. Moreover, FIG. 7 does not show all steps that may be performed. The claims, and the claims and the claims.

The embodiments described herein have several advantages over known techniques. For example, the embodiments described herein can significantly increase the capacity of conventional mechanical cooling processes without significantly increasing the required power and footprint of the mechanical cooling process. For example, as compared to known feed gas expander-based processes, feed gas expander-based processes coupled with the LIN cooldown described herein can produce greater than about 50% LNG in equivalent mechanical refrigeration power. The amount of LIN required is about 0.26 ton LIN per ton of LNG produced. As the amount of LIN is reduced, this technology is particularly suitable for FLNG applications. Using the embodiments described herein, an additional throughput of 50% through a feed gas expander-based process can increase the volumetric flow rate required for the low pressure compressor and the cryogenic heat exchanger load by only about 10%, respectively, as compared to the known feed gas expander technology .

Embodiments described herein may include any combination of the methods and systems described in the paragraphs below. This is not to be considered as a complete listing of all possible aspects, as any number of variations may be implemented from the foregoing description.

One. As a production method of liquefied natural gas (LNG)

Sending a natural gas stream to a mechanical refrigeration unit to liquefy the natural gas stream to form a pressurized liquefied natural gas (LNG) stream having a pressure of greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa);

Providing a liquid refrigerant subcooling unit at a first location;

Generating liquid refrigerant at a second location that is geographically remote from the first location;

Transferring the generated liquid refrigerant to the first position; And

Cooling the pressurized LNG stream in the liquid coolant subcooling unit by heat exchange between the pressurized LNG stream and at least one stream of the liquid coolant to produce an LNG stream

/ RTI >

2. The method of item 1, wherein the mechanical refrigeration unit comprises an inflator-based refrigeration process.

3. The method of claim 2, wherein the expander-based refrigeration process is a feed gas expander-based process.

4. The method of claim 3, wherein the feed gas expander-based process is an open loop feed gas expander-based process.

5. Item 3, wherein the feed gas expander-based process is a closed loop feed gas expander-based process.

6. Item 3, wherein the feed gas expander-based process

Withdrawing the first cooling stream from the on-end inflator; And

Discharging the two-phase stream from the cold-end inflator

Wherein the temperature of the first cooling stream is higher than the temperature of the two-phase stream.

7. The method of claim 3 further comprising the step of separating said pressurized LNG stream into a first pressurized LNG stream and said second stream into a second cooled stream and a second pressurized LNG stream.

8. Item 3, wherein the feed gas expander-based process

Withdrawing the first cooling stream from the on-end inflator; And

Withdrawing the second cooling stream from the cold-end inflator

Wherein the temperature of the first cooling stream is higher than the temperature of the second cooling stream.

9. Item 7 or Item 8, wherein the pressure of the first cooling stream is equal to or substantially equal to the pressure of the second cooling stream.

10. The method of claim 9, further comprising mixing the second pressurized LNG stream with the first pressurized LNG stream before sending the second pressurized LNG stream to the liquid coolant subcooling unit.

11. The method according to any one of items 1 to 10, wherein the liquid refrigerant supercooling unit includes at least one heat exchanger.

12. The method according to any one of items 1 to 11, wherein the liquid refrigerant supercooling unit includes at least one compressor and / or an expander.

13. The method of any of items 1 to 12, wherein the vaporized liquid refrigerant stream is used to liquefy the treated second natural gas stream to produce an additional pressurized LNG stream.

14. 13. The method of claim 13, wherein the further pressurized LNG stream is mixed with the pressurized LNG stream prior to subcooling the further pressurized LNG stream with liquid coolant.

15. The method according to any of items 1 to 14, further comprising the step of placing the mechanical refrigeration unit and the liquid refrigerant subcooling unit on a floating LNG facility.

16. The method according to any one of items 1 to 15, further comprising the step of re-liquefying the LNG vapor using the liquid refrigerant.

17. The method of any one of items 1 to 16, wherein the mechanical refrigerating unit and / or the liquid refrigerant supercooling unit and / or the liquid refrigerant supercooling unit are used during the turndown and / or shutdown period of the mechanical refrigeration unit by using the liquid refrigerant and / How to keep the equipment cool.

18. The method according to any one of items 1 to 17, wherein warm liquid refrigerant vapor is used for deriming the heat exchanger used for heat exchange.

19. In any one of Items 1 to 18,

Transporting the LNG stream from a first location to a second location on a dual purpose vehicle; And

Transferring said liquid refrigerant from said second location to said first location in said dual purpose carrier after said LNG stream is unloaded from said dual purpose carrier,

≪ / RTI >

20. The method of any one of items 1 to 19, wherein the mechanical refrigeration unit comprises one of a single mixed refrigerant process, a pure component cascade refrigerant process, or a dual mixed refrigerant process.

21. Item 20. The method of any one of items 1 to 20, wherein the pressurized LNG stream has a pressure of greater than 100 psia and less than 400 psia (2758 kPa).

22. Item 21. The method of any one of items 1 to 21, wherein the pressurized LNG stream has a pressure of greater than 200 psia and less than 300 psia (2068 kPa).

23. The method according to any one of items 1 to 22, wherein the liquid refrigerant comprises liquid nitrogen (LIN).

24. 23. The method of claim 23, further comprising the step of heat exchanging with LNG during LNG regasification to produce LIN.

25. 23. The method of claim 23, further comprising pressurizing LIN to a pressure of greater than 400 psia (2758 kPa) to form a high pressure liquid nitrogen stream.

26. Item 25. The method of item 25 further comprising the step of forming a warm nitrogen gas stream by heat exchange between the high pressure liquid nitrogen stream and the pressurized LNG stream.

27. Item 23, wherein in the liquid refrigerant subcooling unit, the pressure of the at least one warmed natural gas stream in the at least one expander service is lowered to lower the pressure of the at least one warmed nitrogen gas stream, Further comprising the step of producing a cooled nitrogen gas stream.

28. Item 27. The method of Item 27, wherein at least one further cooled nitrogen gas stream is heat exchanged with the pressurized LNG stream to form a warmed nitrogen gas stream.

29. 27. The method of claim 27, further comprising coupling at least one inflator service with at least one generator for generating power.

30. 27. The method of claim 27, further comprising coupling at least one inflator service with at least one compressor used to compress the warmed nitrogen gas stream.

31. The method of any of items 1 to 30, further comprising the step of sending pressurized LNG streams from a plurality of mechanical refrigeration units to a liquid refrigerant subcooling unit to produce at least one LNG stream.

32. A system for producing liquefied natural gas (LNG)

A mechanical refrigeration unit configured to liquefy the natural gas stream using a feed gas expander-based process to form a pressurized liquefied natural gas (LNG) stream having a pressure of greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa);

A liquid nitrogen (LIN) and cooling unit located in a first location;

A liquid nitrogen (LIN) stream generated at a second location that is geographically remote from the first location and transferred to the LIN and the cooling unit

/ RTI >

Wherein the LIN subcooling unit is configured to subcool the pressurized LNG stream by heat exchange between the pressurized LNG stream and at least one stream of the LIN stream thereby producing an LNG stream and at least one vaporized LIN stream. system.

33. Item 32, wherein the mechanical freezing unit

An on-inflator configured to discharge a first cooling stream; And

A cold-end inflator configured to discharge a two-phase stream,

Wherein the temperature of the first cooling stream is higher than the temperature of the two-phase stream, the pressurized LNG stream is a first pressurized LNG stream, and the two-phase stream is configured to be divided into a second cooling stream and a second pressurized LNG stream. system.

34. Item 32, wherein the mechanical freezing unit

An on-inflator configured to discharge a first cooling stream; And

A cold-end inflator configured to discharge a second cooling stream,

Wherein the temperature of the first cooling stream is higher than the temperature of the second cooling stream.

35. Item 33 or item 34, wherein the pressure of the first cooling stream is equal to or substantially equal to the pressure of the second cooling stream.

36. Item 35. The system of claim 35, wherein the second pressurized LNG stream is mixed with the first pressurized LNG stream prior to sending the pressurized LNG stream to the LIN subcooling unit.

37. 33. The system of any of items 32 to 35, wherein at least one vaporized liquid refrigerant stream is used to liquefy the treated second natural gas stream to produce an additional pressurized LNG stream.

38. Item (32) to (36), wherein the mechanical refrigeration unit and the liquid refrigerant supercooling unit are located on a floating LNG facility.

39. Item 32. Item 37. The method of any one of items 32-37, wherein the LNG stream is transferred from a first location to a second location, and after the supercooled LNG stream is unloaded from the dual purpose carrier, 2 < / RTI > position to a first position.

It is to be understood that the foregoing description is susceptible of numerous changes, modifications, and alternative constructions without departing from the scope of the invention. Accordingly, the foregoing description is not intended to limit the scope of the invention. Rather, the scope of the present invention is determined only by the claims and their equivalents. It is also contemplated that structures and features in this embodiment may be altered, rearranged, substituted, removed, duplicated, combined, or added to one another.

Claims (28)

As a production method of liquefied natural gas (LNG)
Sending a natural gas stream to a mechanical refrigeration unit to liquefy the natural gas stream to form a pressurized liquefied natural gas (LNG) stream having a pressure of greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa);
Providing a liquid refrigerant subcooling unit at a first location;
Generating liquid refrigerant at a second location that is geographically remote from the first location;
Transferring the generated liquid refrigerant to the first position; And
Subcooling the pressurized LNG stream in the liquid refrigerant subcooling unit by heat exchange between the pressurized LNG stream and at least one stream of the liquid coolant to produce an LNG stream
/ RTI > The method of claim 1, wherein the mechanical refrigeration unit comprises an inflator-based refrigeration process. 3. The method of claim 2, wherein the inflator-based refrigeration process is one of an open loop feed gas inflator-based process and a closed loop feed gas inflator-based process. 3. The method of claim 2, wherein the inflator-based refrigeration process
Evacuating the first cooling stream from a warm-end inflator; And
Draining the two-phase stream from the cold-end inflator
Wherein the temperature of the first cooling stream is higher than the temperature of the two-phase stream. 5. The method of claim 4, wherein the pressurized LNG stream is a first pressurized LNG stream, and the step of separating the two-phase stream into a second cooled stream and a second pressurized LNG stream. 4. The method of claim 3, wherein the inflator-based refrigeration process
Withdrawing the first cooling stream from the on-end inflator; And
Withdrawing the second cooling stream from the cold-end inflator
Wherein the temperature of the first cooling stream is higher than the temperature of the second cooling stream. 7. The method of claim 5 or 6, wherein the pressure of the first cooling stream is equal to or substantially equal to the pressure of the second cooling stream. 8. The method of claim 7, further comprising mixing the second pressurized LNG stream with the first pressurized LNG stream prior to sending the second pressurized LNG stream to the liquid coolant subcooling unit. 9. The refrigerating machine according to any one of claims 1 to 8, wherein the liquid refrigerant supercooling unit
At least one heat exchanger, or
At least one compressor and / or an expander. 10. The method according to any one of claims 1 to 9,
Liquefying the treated second natural gas stream using the vaporized liquid refrigerant stream to produce a further pressurized LNG stream; And
Mixing said additional pressurized LNG stream with said pressurized LNG stream prior to subcooling said further pressurized LNG stream with said liquid coolant;
≪ / RTI > 11. The method according to any one of claims 1 to 10, further comprising the step of placing the mechanical refrigeration unit and the liquid refrigerant subcooling unit on a floating LNG facility. 12. The method of any one of claims 1 to 11, further comprising re-liquefying the LNG boil-off gas using the liquid refrigerant. 13. A method according to any one of claims 1 to 12, characterized in that the liquid refrigerant and / or the liquid phase refrigerant vapor is used for the mechanical refrigeration unit and / or the liquid phase refrigerant during the turndown and / A method of keeping a supercooling unit device cool. 14. The method according to any one of claims 1 to 13, wherein the warm liquid refrigerant vapor is used to deriminate the heat exchanger used for heat exchange. 15. The method according to any one of claims 1 to 14,
Transporting the LNG stream from a first location to a second location on a dual purpose vehicle; And
Transferring said liquid refrigerant from said second location to said first location in said dual purpose carrier after said LNG stream is unloaded from said dual purpose carrier,
≪ / RTI > 16. The method according to any one of claims 1 to 15, wherein the mechanical refrigeration unit comprises one of a single mixed refrigerant process, a pure component cascade refrigerant process, or a dual mixed refrigerant process. 17. The process of any preceding claim, wherein the pressurized LNG stream has a pressure of greater than 100 psia (690 kPa) and less than 400 psia (2758 kPa). 18. The process according to any one of claims 1 to 17, wherein the pressurized LNG stream has a pressure of greater than 200 psia and less than 300 psia (2068 kPa). 19. The process according to any one of claims 1 to 18, wherein the liquid refrigerant comprises liquid nitrogen (LIN) and further comprising the step of heat exchanging with LNG during LNG regasification to produce LIN. 20. The process according to any one of claims 1 to 19, wherein the liquid refrigerant comprises liquid nitrogen,
Pressurizing LIN to a pressure greater than 400 psia (2758 kPa) to form a high pressure liquid nitrogen stream;
Exchanging heat between the high pressure liquid nitrogen stream and the pressurized LNG stream to form a warm nitrogen gas stream; And
In the liquid refrigerant subcooling unit, the pressure of the at least one warmed natural gas stream in the at least one inflator service is lowered to lower the pressure of the at least one warmed nitrogen gas stream, thereby providing at least one further cooled Step of producing a nitrogen gas stream
≪ / RTI > 21. The method of claim 20, wherein at least one further cooled nitrogen gas stream is heat exchanged with the pressurized LNG stream to form a warmed nitrogen gas stream. 21. The method of claim 20, further comprising combining at least one inflator service with at least one generator to generate power, or at least one compressor to compress the warmed nitrogen gas stream. 23. The method of any one of claims 1 to 22, further comprising the step of sending pressurized LNG streams from a plurality of mechanical refrigeration units to said liquid refrigerant subcooling unit to produce at least one LNG stream. A system for producing liquefied natural gas (LNG)
A mechanical refrigeration unit configured to liquefy the natural gas stream using a feed gas expander-based process to form a pressurized liquefied natural gas (LNG) stream having a pressure of greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa);
A liquid nitrogen (LIN) and cooling unit located in a first location;
A liquid nitrogen (LIN) stream generated at a second location that is geographically remote from the first location and transferred to the LIN and the cooling unit
/ RTI >
Wherein the LIN subcooling unit is configured to subcool the pressurized LNG stream by heat exchange between the pressurized LNG stream and at least one stream of the LIN stream and thereby produce an LNG stream and at least one vaporized LIN stream. system. 26. The refrigeration system of claim 24, wherein the mechanical refrigeration unit
An on-inflator configured to discharge a first cooling stream; And
A cold-end inflator configured to discharge a two-phase stream,
Wherein the temperature of the first cooling stream is higher than the temperature of the two-phase stream, the pressurized LNG stream is a first pressurized LNG stream, and the two-phase stream is configured to be divided into a second cooling stream and a second pressurized LNG stream. system. 26. The refrigeration system of claim 24, wherein the mechanical refrigeration unit
An on-inflator configured to discharge a first cooling stream; And
A cold-end inflator configured to discharge a second cooling stream,
Wherein the temperature of the first cooling stream is higher than the temperature of the second cooling stream. 27. The system according to any one of claims 24 to 26, wherein the mechanical refrigeration unit and the liquid refrigerant subcooling unit are located on a floating LNG facility. 28. The method of any of claims 24 to 27, further comprising: transferring the LNG stream from a first location to a second location, and after the supercooled LNG stream is unloaded from a dual-purpose carrier, Further comprising a dual purpose carrier configured to transfer the liquid refrigerant from the second location to the first location within the carrier.

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