LNG production from methane-containing synthesis gas

Abstract

To provide methods and systems for producing liquefied natural gas (LNG) from a methane-containing synthetic gas (MCSG).SOLUTION: Described herein are methods and systems for producing liquefied natural gas (LNG) from a methane-containing synthetic gas (MCSG). An MCSG feed stream may be cooled and partially liquefied using one or more heat exchanger units. A first phase separator and a second phase separator in downstream fluid flow communication with the first phase separator may be used to separate the partially liquefied MCSG stream into a first residue gas stream and first and second feed streams, and the first and second feed streams are then fed into a distillation column to produce an LNG stream and a second residue gas stream.SELECTED DRAWING: Figure 1

Description

Background Art

[0001] The present invention relates to a method and system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG).

[0002] With the evolution of environmentally friendly fuel technologies, gasification and natural gas liquefaction processes have been integrated to produce LNG from MCSG. MCSG is a light hydrocarbon-containing gas that includes methane and impurities lighter than methane, which can be produced from the gasification of coal or oil residues. Making MCSG from gasification products is a clean way of using conventional solid and low-value heavy liquid fuels by enabling unitary carbon capture and sequestration while clean, low-carbon-containing methane is being produced and distributed. Further, the co-production of LNG from the gasification process provides an attractive option for diversifying the product portfolio and improving the overall economics of the project.

[0003] An exemplary prior art process for producing LNG from MCSG is shown and described in U.S. Patent No. 10,436,505. In the process shown herein, a hydrocarbon-containing feed gas stream, such as a synthesis gas stream, is cooled to a relatively warm temperature of -30 to -130 °C in a main heat exchanger that provides cooling using a vaporizing mixed refrigerant. The cooled feed gas stream exiting the main heat exchanger is further cooled in a reboiler that provides heat for boiling in a secondary distillation column (at a lower operating pressure). The cooled feed gas stream exiting the reboiler is then further cooled to a temperature of -120 to -200 °C, at least partially liquefied in the main heat exchanger, flashed, and separated in a drum to form a flashed vapor stream and a liquid stream. The flashed vapor stream is expanded in the expander portion of a compressor and sent to the rectifying portion (at a higher operating pressure) of a primary distillation column. The liquid stream is depressurized through a valve and sent to the bottom of the primary distillation column.

[0004] The bottom liquid flow from the primary distillation column is sent to a secondary distillation column to further improve methane recovery. The bottom liquid flow from the secondary distillation column is cooled to a final temperature of -120 to -200°C in the main heat exchanger to form an LNG product flow. The overhead steam flow from the secondary distillation column is condensed in the main heat exchanger and flushed in the reflux drum. The reflux drum liquid is used as reflux for both the primary and secondary distillation columns. The reflux drum steam is compressed in the compression section of the compander and combined with the overhead steam from the primary distillation column to form a residual gas flow that is heated in the main heat exchanger and recompressed in the residual gas compressor before being discharged from the facility.

[0005] A standard heat pump configuration using a two-stage compressor and JT valves is used to supply a cooling refrigerant, and therefore cooling, to the main heat exchanger.

[0006] The configuration described in U.S. Patent No. 10,436,505 can produce LNG rich in high-purity methane, but it has certain drawbacks. One challenge is that the mixed refrigerant flow is introduced into the main heat exchanger as a two-phase mixture. This complicates the piping design and can lead to undesirable unstable operation due to slugging. Also, two-phase flow requires special design features of the main heat exchanger to ensure that the liquid and vapor phases are evenly distributed. For example, if the main heat exchanger is a plate-fin exchanger, special devices such as separators and injection pipes must be provided to ensure that the phases are evenly distributed throughout all passages. Using these devices can increase costs and reduce operational stability. In addition, two-phase flow can be unstable at low flow rates, causing phase separation, resulting in large internal temperature gradients and potentially damaging the main heat exchanger.

[0007] Another drawback is that the main exchanger utilizes two different low-pressure flows (i.e., a cooling vaporized refrigerant mixture flow and a residual gas flow) to provide the heat exchanger with cooling duty, which effectively eliminates the use of coil-wound heat exchangers as the main heat exchanger. Coil-wound heat exchangers have proven to be efficient, reliable, and robust for natural gas liquefaction and end-flush gas heat exchange applications. The design and manufacturing techniques of coil-wound heat exchangers allow for much higher unit handling capacity (heat exchange efficiency achieved per coil-wound heat exchanger unit) while avoiding the use of multiple heat exchanger units (in the case of plate-fin heat exchangers) in parallel up to very large capacities. A coil-wound heat exchanger unit includes one or more tube bundles enclosed in a shell casing, with the tube side of the unit designed to receive one or more heat flows that require cooling, and the shell side of the unit designed to receive either a single flow of cooling refrigerant or two or more cold flows that are mixed on the shell side and exit as a single flow of heated refrigerant. The only way a coil-wound heat exchanger can be adapted to the use of two or more cold flows that must remain separated is to pass at least one of the cold flows through one of the tube-side passages of the heat exchanger. However, designing a coil-wound heat exchanger would be challenging given the low available pressure drop and the relatively high typical resistance in the tube-side passages of the heat exchanger.

[0008] A further drawback of the process is that all of the residual gas is produced at relatively low pressure. This increases the operating and capital costs of the process, as a larger amount of residual gas produced at low pressure requires more power to recompress the gas and a larger residual gas compressor to accommodate it. [Overview of the Initiative]

[0009] This specification discloses a method and system for producing LNG from MCSG, which offers several advantages over the prior art described above. The method and system can use a single distillation column (instead of two or more columns). A coil-wound heat exchanger unit can be used, which is separate from a heat exchanger unit used to recover refrigeration from the residual gas stream, and which can receive, cool, and partially liquefy a portion of the MCSG feed stream, and / or which can receive and cool a refrigerant (such as a mixed refrigerant or other vaporized refrigerant), which is then used to cool and partially liquefy the MCSG feed stream. A portion of the residual gas can be discharged at substantially the same pressure as the MCSG feed stream, and recompression is relatively little or no.

[0010] Several preferred embodiments of the systems and methods according to the present invention are outlined below.

[0011] Embodiment 1: A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the method is (a) Cooling the MCSG supply flow and partially liquefying it to produce a partially liquefied MCSG supply flow, (b) Separating the partially liquefied MCSG feed flow into at least three flows, including a liquid flow and two vapor flows, using a first phase separator and a second phase separator arranged in series, the second phase separator being in fluid communication downstream with the first phase separator, the liquid flow forming a first feed flow, one of the vapor flows forming a second feed flow, and the other of the vapor flows forming a first residual gas flow. (c) Introducing the first supply flow into the distillation column at the first position, (d) Introducing the second feed stream into the distillation column at a second position above the first position, wherein there is at least one separation step between the first position and the second position. (e) Extracting the LNG flow from the distillation column containing the bottom liquid of the distillation column, (f) Extracting a second residual gas stream from the distillation column containing the distillation column overhead vapor, Methods that include...

[0012] Embodiment 2: Step (b) is, (i) The first phase separator separates the partially liquefied MCSG supply flow into the liquid flow that forms the first supply flow and the vapor flow, (ii) Dividing the steam flow from the first phase separator to form a steam flow that forms the second supply flow and a steam flow that forms the third supply flow, (iii) Cooling the third supply flow and partially liquefying it, and then separating the third supply flow in the second phase separator into a vapor flow that forms the first residual gas flow and a liquid flow that forms the fourth supply flow, Includes, Step (c) includes reducing the pressure of the first feed stream and then introducing the first feed stream into the distillation column at the first position, Step (d) includes reducing the pressure of the second feed stream and then introducing the second feed stream into the distillation column at the second location, The method according to embodiment 1, further comprising reducing the pressure of the fourth feed stream and then introducing the fourth feed stream into the distillation column at a third position above the second position, wherein there is at least one separation step between the second position and the third position.

[0013] Embodiment 3: The method according to Embodiment 2, wherein the third position is located at the top of the distillation column.

[0014] Embodiment 4: The method according to Embodiment 2 or 3, wherein one or both of the first residual gas flow and the second residual gas flow are heated via indirect heat exchange with the third supply flow in order to provide cooling efficiency for cooling and partial liquefaction of the third supply flow in step (b)(iii).

[0015] Appearance 5: Step (b) is, (i) The first phase separator separates the partially liquefied MCSG flow into a vapor flow that forms the first residual gas flow and a liquid flow that forms the third supply flow, (ii) reducing the pressure of the third supply flow, partially vaporizing the third supply flow, and separating the flow in the second phase separator into the liquid flow that forms the first supply flow and the vapor flow that forms the second supply flow, Includes, The method according to embodiment 1, wherein step (c) includes heating the first feed stream and then introducing the first feed stream into the distillation column at the first position.

[0016] Embodiment 6: The method according to Embodiment 5, wherein there is at least one separation step between the second position and the top of the column, and the method further comprises compressing, cooling and expanding the second residual gas stream or portion of the distillation column overhead vapor, thereby at least partially liquefying it to form a reflux stream, and introducing the reflux stream into the distillation column at a third position at the top of the distillation column.

[0017] Embodiment 7: The method according to Embodiment 5 or 6, wherein in step (c), the first supply flow is heated via indirect heat exchange with the MCSG supply flow in order to provide the cooling efficiency for the cooling and partial liquefaction of the MCSG supply flow in step (a).

[0018] Aspect 8: The method according to any one of Aspects 1 to 7, wherein one or both of the first residual gas stream and the second residual gas stream are heated via indirect heat exchange with the supply stream of the MCSG in order to provide a cooling efficiency for cooling and partially liquefying the supply stream of the MCSG in step (a).

[0019] Aspect 9: The method according to any one of Aspects 1 to 8, wherein there is at least one separation stage between the first position and the bottom of the column, and the method further includes heating a part of the LNG stream or the distillation column bottom liquid, thereby at least partially vaporizing it to form a boil-up stream, and introducing the boil-up stream into the distillation column at the bottom of the distillation column.

[0020] Aspect 10: The method according to any one of Aspects 1 to 9, wherein at least a part of the second residual gas stream is compressed and combined with the first residual gas stream.

[0021] Aspect 11: The method according to any one of Aspects 1 to 10, wherein the method further includes subcooling the LNG stream.

[0022] Aspect 12: Step (a) is (i) dividing the MCSG supply stream into at least two parts including a first part and a second part; (ii) cooling and partially liquefying the first part of the MCSG supply stream in a first heat exchanger unit or a set of units via indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or the set of units is a coil-wound heat exchanger unit or a set of units; (iii) cooling and partially liquefying the second part of the MCSG supply stream in a second heat exchanger unit or a set of units via indirect heat exchange with one or more process streams. (iv) Combining the cooled and partially liquefied first portion with the cooled and partially liquefied second portion to form the partially liquefied MCSG feed stream; The method according to any one of aspects 1 to 11, comprising.

[0023] Aspect 13: The method according to aspect 12, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units.

[0024] Aspect 14: The method according to aspect 12 or 13, wherein in step (a)(iii), the one or more process streams include one or more streams selected from the first residual gas stream, the second residual gas stream, and a portion of the LNG stream or distillation column bottoms liquid.

[0025] Aspect 15: The method according to any one of aspects 12 to 14, wherein the first refrigerant is a refrigerant that vaporizes when heated in the first heat exchanger unit or set of units.

[0026] Aspect 16: The method according to any one of aspects 12 to 15, further comprising subcooling the LNG stream in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant.

[0027] Aspect 17: Step (a)(ii) includes cooling and partially liquefying the first portion of the MCSG feed stream in the first heat exchanger unit or set of units via indirect heat exchange with one or more streams of cooled first refrigerant, the first heat exchanger unit or set of units being a coil wound heat exchanger unit or set of units, and the one or more streams of cooled first refrigerant being produced by also cooling the first refrigerant in the first heat exchanger unit or set of units. The method according to any one of aspects 12 to 16.

[0028] Aspect 18: Step (a) is (i) manufacturing a cooled first refrigerant by cooling a first refrigerant in a first heat exchanger unit or set of units, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units. (ii) Cooling and partially liquefying the MCSG supply flow in a second heat exchanger unit or set of units through indirect heat exchange with one or more flows and one or more process flows of the cooled first refrigerant, thereby forming the partially liquefied MCSG supply flow, The method according to any one of embodiments 1 to 11, including the method described above.

[0029] Embodiment 19: The method according to Embodiment 18, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units.

[0030] Embodiment 20: The method according to Embodiment 18 or 19, wherein in step (a)(ii), the one or more process flows include one or more of the first residual gas flow, the second residual gas flow, and the LNG flow or a portion of the distillation column bottom liquid.

[0031] Embodiment 21: The method according to any one of Embodiments 18 to 20, wherein in step (a)(i), the first refrigerant is cooled in the first heat exchanger unit or set of units through indirect heat exchange with a portion of the cooled first refrigerant produced in step (a)(i).

[0032] Embodiment 22: The method according to any one of Embodiments 18 to 21, further comprising supercooling the LNG flow in the first heat exchanger unit or set of units.

[0033] Embodiment 23: A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the method is (a) (i) Dividing the MCSG supply flow into at least two parts, including a first part and a second part, (ii) Cooling and partially liquefying a first portion of a first heat exchanger unit or set of units through indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, (iii) Cooling and partially liquefying a second portion of a second heat exchanger unit or set of units through indirect heat exchange with one or more process flows, (iv) Combining the cooled and partially liquefied first portion with the cooled and partially liquefied second portion to form the partially liquefied MCSG supply flow, This involves cooling and partially liquefying the MCSG supply flow to produce a partially liquefied MCSG supply flow. (b) Separating the partially liquefied MCSG supply flow into an LNG flow and one or more residual gas flows, Methods that include...

[0034] Embodiment 24: The method according to Embodiment 23, wherein in step (b), the partially liquefied MCSG feed stream is separated into an LNG stream and one or more residual gas streams using one or more phase separators and / or one or more distillation columns.

[0035] Embodiment 25: The method according to Embodiment 23 or 24, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units.

[0036] Embodiment 26: The method according to any one of Embodiments 23 to 25, wherein in step (a)(iii), the one or more process flows include one or more flows selected from one or more of the residual gas flow, a portion of the LNG flow, or a portion of the bottom liquid of the distillation column.

[0037] Embodiment 27: The method according to any one of Embodiments 23 to 26, wherein the first refrigerant is a refrigerant that vaporizes when heated in the first heat exchanger unit or set of units.

[0038] Embodiment 28: The method according to any one of embodiments 23 to 27, further comprising supercooling the LNG flow in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant.

[0039] Embodiment 29: The method according to any one of Embodiments 23 to 28, wherein step (a)(ii) comprises cooling and partially liquefying the first portion of the MCSG supply flow in a first heat exchanger unit or set of units via indirect heat exchange with one or more flows of a cooled first refrigerant, the first heat exchanger unit or set of units being a coil-wound heat exchanger unit or set of units, and the one or more flows of the cooled first refrigerant being produced by also cooling the first refrigerant in the first heat exchanger unit or set of units.

[0040] Embodiment 30: A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the method is (a) (i) manufacturing a cooled first refrigerant by cooling a first refrigerant in a first heat exchanger unit or set of units, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units. (ii) Cooling the MCSG supply flow in a second heat exchanger unit or set of units through indirect heat exchange with one or more flows of cooled first refrigerant and one or more process flows, partially liquefying it to form a partially liquefied MCSG supply flow, This involves cooling and partially liquefying the MCSG supply flow to produce a partially liquefied MCSG supply flow. (b) Separating the partially liquefied MCSG supply flow into an LNG flow and one or more residual gas flows, Methods that include...

[0041] Embodiment 31: The method according to Embodiment 30, wherein in step (b), the partially liquefied MCSG feed stream is separated into an LNG stream and one or more residual gas streams using one or more phase separators and / or one or more distillation columns.

[0042] Embodiment 32: The method according to Embodiment 30 or 31, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units.

[0043] Embodiment 33: The method according to any one of Embodiments 30 to 32, wherein in step (a)(ii), the one or more process flows include one or more of the first residual gas flow, the second residual gas flow, and a portion of the LNG flow or distillation column bottom liquid.

[0044] Embodiment 34: The method according to any one of Embodiments 30 to 33, wherein in step (a)(i), the first refrigerant is cooled in the first heat exchanger unit or set of units through indirect heat exchange with a portion of the cooled first refrigerant produced in step (a)(i).

[0045] Embodiment 35: The method according to any one of embodiments 30 to 34, further comprising supercooling the LNG flow in the first heat exchanger unit or set of units.

[0046] Embodiment 36: A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the system is One or more heat exchanger units for receiving, cooling, and partially liquefying the MCSG feed flow to produce a partially liquefied MCSG feed flow, A first phase separator and a second phase separator, which are fluid-connected to one or more heat exchanger units and arranged in series, wherein the second phase separator is fluid-connected downstream to the first phase separator to separate the partially liquefied MCSG feed flow into at least three flows, including a liquid flow and two vapor flows, the liquid flow forming a first feed flow, one of the vapor flows forming a second feed flow, and the other of the vapor flows forming a first residual gas flow, A distillation column having a first inlet at a first position for receiving the first feed flow, a second inlet at a second position for receiving the second feed flow, the second position being above the first position, and at least one separation step between the first position and the second position, an outlet at the bottom of the distillation column for taking out an LNG flow formed from the bottom liquid of the distillation column, and an outlet at the top of the distillation column for taking out a second residual gas flow formed from the overhead vapor of the distillation column, A system that includes this.

[0047] Embodiment 37: A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the system is A set of conduits for dividing the MCSG supply flow into at least two parts, including a first part and a second part, A first heat exchanger unit or set of units for receiving the first portion and cooling and partially liquefying the first portion through indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, A second heat exchanger unit or set of units for receiving the second portion and cooling and partially liquefying the second portion through indirect heat exchange with one or more process flows, A set of conduits for receiving and combining the cooled and partially liquefied first portion and the cooled and partially liquefied second portion to form a partially liquefied MCSG supply flow, One or more phase separators and / or one or more distillation columns for receiving the partially liquefied MCSG feed stream and separating it into an LNG stream and one or more residual gas streams, A system that includes this.

[0048] Embodiment 38: A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the system is A first heat exchanger unit or set of units for cooling a first refrigerant and producing a cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, A second heat exchanger unit or set of units for receiving one or more process flows, and for receiving an MCSG supply flow, and for cooling and partially liquefying the MCSG supply flow through indirect heat exchange between the one or more flows of the cooled first refrigerant and the one or more process flows, to form a partially liquefied MCSG supply flow. One or more phase separators and / or one or more distillation columns for receiving the partially liquefied MCSG feed stream and separating it into an LNG stream and one or more residual gas streams, A system that includes this. [Brief explanation of the drawing]

[0049] [Figure 1] Figure 1 is a schematic flowchart illustrating a method and system for producing LNG from MCSG according to one embodiment of the present invention.

[0050] [Figure 1A]Figure 1A is a schematic flowchart showing a suitable refrigeration system for use with the method and system shown in Figure 1.

[0051] [Figure 2] Figure 2 is a schematic flowchart showing a method and system for producing LNG from MCSG according to another embodiment of the present invention.

[0052] [Figure 3] Figure 3 is a schematic flowchart showing a method and system for producing LNG from MCSG according to another embodiment of the present invention.

[0053] [Figure 3A] Figure 3A is a schematic flowchart showing a suitable refrigeration system for use with the method and system shown in Figure 3.

[0054] [Figure 4] Figure 4 is a schematic flowchart showing a method and system for producing LNG from MCSG according to another embodiment of the present invention. [Modes for carrying out the invention]

[0055] This specification describes a method and system for producing LNG from MCSG.

[0056] As used herein, and unless otherwise stated, the articles “a” and “an” mean one or more when applied to any feature in the embodiments of the invention described herein and in the claims. The use of “a” and “an” does not limit its meaning to a single feature unless such limitation is specifically stated. The article “the” preceding a singular or plural noun or noun phrase refers to a particular specific feature or a particular specific feature, and may have a singular or plural meaning depending on the context in which it is used.

[0057] Where letters are used in this specification to identify enumerated steps of a method (e.g., (a), (b), and (c)), these letters are used solely to aid in referring to the steps of the method and are not intended to indicate a specific order in which the claimed steps are performed, except to the extent that such an order is specifically enumerated.

[0058] Where used herein to identify enumerated features of a method or system, terms such as “first,” “second,” and “third” are used solely to aid in referring to and distinguishing the features in question, and are not intended to indicate any particular order of features unless such order is specifically enumerated, and only to that extent.

[0059] As used herein, the term “methane-containing synthesis gas,” also referred to herein as “MCSG,” refers to a gas containing methane and lighter components than methane (i.e., components having higher volatility and lower boiling points than methane), particularly hydrogen and / or carbon monoxide. As used herein, the term includes gasification synthesis gas product streams containing methane molecules and synthetic natural gas streams produced from a methanation process containing impurities such as hydrogen and carbon monoxide. In preferred embodiments, the methane-containing synthesis gas feed stream may contain 10 to 60 mol% methane, with the remainder being a mixture of carbon monoxide and hydrogen, and optionally containing small amounts of carbon dioxide, water, and / or other impurities.

[0060] As used herein, the term residual gas refers to a gas removed from the MCSG feedstream that is lighter than methane, particularly a gas primarily consisting of hydrogen and / or carbon monoxide, etc. In a preferred embodiment, the residual gas stream may contain less than 10 mol% methane, more preferably less than 2 mol%, with the remainder consisting of or substantially of lighter than methane components, such as a mixture of hydrogen and carbon monoxide, and optionally including small amounts of other components, such as nitrogen and / or argon.

[0061] As used herein, the terms “liquefied natural gas” or “LNG” refer to a liquefied gas stream, primarily methane-containing, preferably comprising at least 85 mol%, more preferably at least 90 mol%, and most preferably at least about 95 mol% of the feed stream. The LNG stream may still contain small amounts of other components that may be present in the MCSG feed stream and have not been removed by the process, such as small amounts of other components heavier than methane (i.e., less volatile and with higher boiling points), such as carbon dioxide or heavier hydrocarbons than methane (e.g., methane, propane, butane, pentane), and / or small amounts of lighter components than methane, such as nitrogen, hydrogen, or carbon monoxide.

[0062] As used herein, the term “distillation column” refers to a column containing one or more separation stages, comprising devices such as packings or trays that increase contact and thus increase mass transfer between the upward-flowing rising vapor and the downward-flowing liquid within the column. In this way, the concentration of lighter components (i.e., more volatile and with lower boiling points) increases at the top of the column, in the rising vapor which is collected as overhead vapor, and the concentration of heavier components (i.e., less volatile and with higher boiling points) increases at the bottom of the column, in the falling liquid which is collected as bottom liquid. The “top” of a distillation column refers to the portion of the column that is at or above the uppermost separation stage. The “bottom” of the column refers to the portion of the column that is at or below the lowermost separation stage. The “intermediate position” of the column refers to the position between the top and bottom of the column, i.e., the position between two separation stages.

[0063] As used herein, the term “phase separator” refers to a drum or other form of vessel into which two phase flows can be introduced to separate a flow into its constituent vapor phase and liquid phase, with the liquid and vapor flows exiting the vessel in equilibrium. In contrast to a distillation column (where the liquid and vapor flows exiting the column are not in equilibrium), a phase separator does not contain any separation stage (i.e., packing or tray) within the vessel to bring the upward-rising vapor and downward-flowing liquid into contact.

[0064] As used herein, the term “fluid communication” refers to the property of connectivity between two or more components that allows liquids, vapors, and / or two-phase mixtures to be transported between them, either directly or indirectly, in a controlled manner (i.e., without leakage). Joining two or more components to fluid communication with one another can include any preferred method known in the art, such as the use of welding, flanged conduits, gaskets, and bolts. The two or more components can also be joined together via other components of a system that can separate them, for example, via valves, gates, or other devices that can selectively restrict or direct the flow of fluid.

[0065] In this specification, the statement that a second device or component is in fluid communication "downstream" with a first device or component means that the second device or component is positioned to receive fluid directly or indirectly from the first device or component.

[0066] As used herein, the term “indirect heat exchange” refers to heat exchange between two fluids that remain separated from each other by some form of physical barrier.

[0067] As used herein, the term “coil-wound heat exchanger unit” refers to a type of heat exchanger unit known in the art, comprising one or more tube bundles enclosed in a shell casing. Each tube bundle comprises several tubes, and the inside of the tubes, which define one or more flow paths (also referred to as tube circuits) for one or more fluid flows to pass through the heat exchanger unit, is referred herein to as the “tube side” of the heat exchanger unit. The space inside the shell casing and outside the tubes defines a single flow path for fluid flows to pass through the heat exchanger unit, and this space inside the shell casing and outside the tubes is referred herein to as the “shell side” of the heat exchanger unit. In this way, the fluid passing through the shell side of the heat exchanger can undergo indirect heat exchange with the fluid passing through the tube side of the heat exchanger. When a coil-wound heat exchanger unit is used to cool one or more "hot" fluid flows via indirect heat exchange with a "cold" refrigerant, the cooling refrigerant almost always passes through the shell side of the heat exchanger because the shell side offers much lower flow resistance and allows for a much larger pressure drop than the tube side, thus making it far more effective and efficient to pass the cooling refrigerant through the shell side (the cooling refrigerant is typically a vaporizing or expanding fluid at relatively low pressure). Coil-wound heat exchangers are a compact design of heat exchangers known for their robustness, safety, and heat transfer efficiency, and thus have the advantage of providing a very efficient level of heat exchange relative to their footprint. However, since the shell side defines only a single flow path through the heat exchanger, it is not practical to use two or more flows of cooling refrigerant to provide cooling efficiency in a coil-wound heat exchanger when mixing of the refrigerant flows is not permitted.

[0068] Herein, for illustrative purposes only, various exemplary embodiments of the present invention will be described with reference to the figures.

[0069] Referring now to Figure 1, a method and system for producing LNG from MCSG according to a first embodiment of the present invention are shown.

[0070] For example, an MCSG feed stream 100, such as a synthesis gas stream 100 containing a mixture of hydrogen, carbon monoxide, carbon dioxide, nitrogen, water, methane, ethane, and other hydrocarbons, at ambient temperature and high pressure, typically 20–80 bara, may first be sent to a pretreatment system 105. Depending on the composition of the MCSG feed stream, the pretreatment system may include an acid gas removal unit for removing hydrogen sulfide and carbon dioxide impurities, a dehydration unit for removing water, and a mercury removal unit for removing mercury. There may also be a heavy component removal step where LPG (liquefied petroleum gas) components, freezeable pentane, and heavier components are removed. Thus, the flow rate and composition of the MCSG feed stream 111 leaving the pretreatment section 105 may differ significantly from the flow rate and composition of the MCSG feed stream 100 entering the pretreatment section 105, although the MCSG feed stream still contains methane and lighter components than methane, particularly hydrogen and carbon monoxide.

[0071] The MCSG supply flow 111, exiting the pretreatment section 105, is typically at ambient temperature and is divided into two flows, namely a first flow 113 and a second flow 115. Preferably, a small portion of the MCSG supply flow 111, for example, a first flow 113 consisting of 10 to 40 percent, more preferably 20 to 30 percent of the flow of the MCSG supply flow 111, is sent to a first heat exchanger unit or set of units 114. The second flow 115, consisting of the remainder of the flow of the MCSG supply flow 111 and therefore preferably the majority of that flow, is sent to a second heat exchanger unit or set of units 116. The second heat exchanger unit or set of units 116 may include, for example, a plate fin heat exchanger unit or a plurality of plate fin heat exchanger units arranged in parallel. The first flow 113 and the second flow 115 are cooled and partially liquefied in the first heat exchanger unit 114 and the second heat exchanger unit 116, respectively, to form a first cooled and partially liquefied flow 120 and a second cooled and partially liquefied flow 117, respectively, at temperatures of -130°C to -160°C, more preferably -140°C to -150°C. The first and second cooled and partially liquefied flows 120 and 117 are then combined (the pressure of the second cooled and partially liquefied flow 117 is first adjusted as needed, for example, via a pressure regulator valve 117A to control the flow of said flow 117) to form a partially liquefied MCSG supply flow 130, separated using a first phase separator 140 and a second phase separator 135 arranged in series, the second phase separator being in flow communication downstream with the first phase separator.

[0072] More specifically, the partially liquefied MCSG feed stream 130 is first introduced into a first phase separator 140, in which case the first phase separator 140 is a flash drum, where the partially liquefied MCSG feed stream is flashed and separated into liquid steam, which forms a first feed stream 152, and a vapor stream 141. The vapor stream 141 is divided to form a second feed stream 143 (preferably consisting of 60-90 percent or more preferably 70-80 percent of the flow of the vapor stream 141) and a third feed stream 142 (the remainder of the vapor stream 141, i.e., preferably consisting of 10-40 percent, more preferably 20-30 percent of the flow of that stream). The third feed stream 142 is further cooled to a temperature of -170°C to -200°C, more preferably -180°C to -190°C, and partially liquefied to form a partially liquefied third feed stream 133. The partially liquefied third feed stream 133 is then introduced into a second phase separator 135, which is a flash drum, where the partially liquefied third feed stream is flashed and separated into a liquid stream that forms a fourth feed stream 150 and a vapor stream that forms a first residual gas stream 137.

[0073] The third supply flow 142 can be further cooled and partially liquefied by passing the third supply flow 142 through a third heat exchanger unit or set of units 131, as shown in Figure 1, to form a partially liquefied third supply flow 133, which may include, for example, a plate fin exchanger unit or a plurality of plate fin exchanger units arranged in parallel. Alternatively, the third heat exchanger unit can be combined with the second heat exchanger unit to form a single unit or a set of units arranged in parallel, with the flow 115 being cooled in the warmer section of the unit and the flow 142 being cooled in the colder section of the unit.

[0074] The first supply flow 152 and the fourth supply flow 150 are pressure-reduced, for example, by passing flow 152 through a JT valve 152A and flow 150 through a JT valve 150A, after which each of the flows becomes two-phase. The second supply flow 143 is pressure-reduced, for example, by expanding the flow in an expander 179, after which the second supply flow 143 may become steam or two-phase. The expansion work from the expander 179 can be recovered, for example, by coupling the expander to a compressor that compresses the supply gas or residual gas, or, for example, in a generator. Next, the first feed stream 152, the second feed stream 151, and the fourth feed stream 150 are introduced, respectively, into different positions in the distillation column 145, as will be further described below, and the distillation column 145 operates at a pressure of 1.0 to 5.0 bara, more preferably 1.5 to 3.5 bara.

[0075] A first feed stream 152 is introduced into the distillation column 145 at a first position in Figure 1, above one or more separation stages of the column represented by section 145C of the column and below one or more separation stages of the column represented by section 145B of the column. A second feed stream 151 is introduced into the distillation column at a second position in Figure 1, above one or more separation stages of the column represented by section 145B of the column and below one or more separation stages of the column represented by section 145A of the column. A fourth feed stream 150 is introduced into the distillation column at a third position at the top of the column, above one or more separation stages of the column represented by section 145A of the column, thereby providing a reflux source to the column.

[0076] The reboiler efficiency of the distillation column 145 is provided by heating the flow of distillation column bottom liquid 153 in a second heat exchanger unit or set of units 116, via indirect heat exchange with a second flow 115 (obtained from splitting the MCSG feed flow), thereby at least partially vaporizing it and forming a boiling flow 154 (formed from the partially vaporized distillation column bottom liquid) that is reintroduced to the bottom of the distillation column.

[0077] The LNG stream 180 formed from the bottom liquid of the distillation column is taken from the bottom of the distillation column 145 at a temperature of -130°C to -160°C, more preferably -140°C to -150°C, and is preferably pressurized by a pump 181 and sent (as stream 183) to and through a first heat exchanger unit or set of units 114 to be supercooled and form a supercooled LNG product stream 187 that can be stored on-site in an LNG storage container or directly transported off-site (e.g., via a pipeline or transport container). The LNG streams 180 and 187 typically contain less than 1 mol% nitrogen, preferably less than 0.5 mol%, and also preferably have a carbon monoxide content of less than 10 ppm. The proportion of methane recovered in the LNG streams 180 and 187 from the MCSG feed stream 111 may exceed 95%.

[0078] The second residual gas stream 160, formed by the overhead vapor of the distillation column, is withdrawn from the top of the distillation column 145 at a temperature of -170°C to -200°C, more preferably -180°C to -190°C, and typically contains more than 95 mol%, preferably more than 98 mol%, of hydrogen and carbon monoxide.

[0079] The first residual gas flow 137 and the second residual gas flow 160 each pass through the third heat exchange unit or set of units 131 via indirect heat exchange with the third supply flow 142, are heated, and then each (see flows 138 and 161) passes through the second heat exchanger unit or set of units 116 via indirect heat exchange with the second flow 115 obtained from splitting the MCSG supply flow, are further heated (or, in an alternative embodiment in which the third heat exchanger unit is combined with the second heat exchanger unit, the first residual gas flow 137 and the second residual gas flow 160 are heated in the colder section of the combined unit, and then further heated in the warmer section of the combined unit). Next, the resulting heated second residual gas flow 162 is compressed and cooled in the compressor 163 and aftercooler 165, and then mixed with the resulting heated first residual gas flow 139 to form a combined residual gas flow 173. The residual gas flow 173 can be used as fuel for the plant or sent to downstream units for further purification, separation, and / or chemical synthesis. Optionally, part or all of the flow 139 can be purified to produce hydrogen products and combined with the residual gas flow 170.

[0080] The first heat exchanger unit or set of units 114 is preferably a coil-wound unit or set of units, for example, as shown in Figure 1A. Any type of refrigeration process known in the art for the liquefaction of natural gas (including synthetic or alternative natural gases) may be used in the first heat exchanger unit or set of units 114, for example, in a single-mix refrigerant process, a double-mix refrigerant process, a propane, ammonia or HFC pre-cooled mixed refrigerant process, a reverse Brayton cycle using nitrogen, methane or ethane, or a multi-fluid cascade cycle. However, in exemplary embodiments, a single-mix refrigerant (SMR) process, as shown in Figure 1A, may be used.

[0081] As shown in Figure 1A, the coil-wound heat exchanger unit 114 includes a hot section containing a hot tube bundle 114A and a cold section containing a cold tube bundle 114B (the terms "hot" and "cold" are relative). The first flow 113 obtained by splitting the MCSG supply flow passes through the hot tube bundle 114A, is cooled, and partially liquefied to form a first cooled, partially liquefied flow 120. The LNG vapor 183 passes through the cold tube bundle 114B, is supercooled, and forms a supercooled LNG product flow 187. Cooling efficiency is imparted to the hot and cold tube bundles of the coil-wound heat exchanger unit by vaporizing the mixed refrigerant passing through the shell side of the heat exchanger unit. The SMR cycle shown in Figure 1A, used to supply the vaporized low-temperature mixed refrigerant to the shell side of the heat exchanger unit, is well known in the art and is therefore described only broadly here for the sake of brevity. In very simple terms, the heated vaporized refrigerant mixture taken from the shell side at the bottom of the heat exchanger unit is compressed, cooled, and separated into one or more MRL (liquid refrigerant mixture) flows (two shown in the figure) and one or more MRV (vaporized refrigerant mixture) flows (one shown in the figure) in a compression train including one or more compressor stages 115A, 115B, an aftercooler, and a phase separator. The MRL flows are cooled as they pass through the hot tube bundle, expanded as they pass through the JT valve, combined, and introduced to the shell side of the heat exchanger unit at the top of the hot tube bundle, providing vaporized refrigerant that flows downward through the shell side around the tubes of the hot tube bundle. The MRV flows are cooled as they pass through the cold and hot tube bundles, at least partially liquefied, expanded as they pass through the JT valve, and introduced to the shell side of the heat exchanger unit at the top of the cold tube bundle, providing vaporized refrigerant that flows downward through the shell side around the tubes of the cold and hot tube bundles.

[0082] The method and system shown in Figure 1 produce a high-purity, methane-rich LNG product with a high methane recovery rate. Because it requires only a single distillation column and recompression of only a portion of the residual gas produced (i.e., only the residual gas contained in the second residual gas stream), the capital and operating costs of the system are reduced, as is the installation area, compared to a system requiring multiple distillation columns, recompression of all the produced residual gas, and a compressor capable of compressing all the produced residual gas. This allows for the use of coil-wound heat exchanger units, thereby taking advantage of the benefits provided by such units in terms of their compact design, robustness, safety, and heat transfer efficiency, further reducing the installation area and improving system and process efficiency. Furthermore, the use of two-phase refrigerants in the second and third heat exchanger units is avoided, which can be, for example, plate-fin exchanger units, as considered, thereby avoiding the operational difficulties that can arise from the use of such refrigerants in such types of heat exchangers.

[0083] Figure 2 shows a method and system for producing LNG from MCSG according to a second embodiment of the present invention. The embodiment shown in Figure 2 differs from that shown in Figure 1 in that the partially liquefied MCSG feed stream is separated by first and second phase separators, and the reflux is supplied to the distillation column.

[0084] For example, an MCSG feed stream 200, such as a synthesis gas stream 200 containing a mixture of hydrogen, carbon monoxide, carbon dioxide, nitrogen, water, methane, ethane, and other hydrocarbons at ambient temperature and pressure, typically 20–80 bara, may first be sent to a pretreatment system 205. Depending on the composition of the MCSG feed stream, the pretreatment system may include an acidic gas removal unit to remove hydrogen sulfide and carbon dioxide impurities, a dehydration unit to remove water, and a mercury removal unit to remove mercury. There may also be a heavy component removal step to remove LPG (liquefied petroleum gas) components, freezeable pentane, and heavier components. Thus, the flow rate and composition of the MCSG feed stream 211 leaving the pretreatment section 205 may differ significantly from the flow rate and composition of the MCSG feed stream 200 entering the pretreatment section 205, although the MCSG feed stream still contains methane and lighter components than methane, particularly hydrogen and carbon monoxide.

[0085] The MCSG supply flow 211 exiting the pretreatment section 205 is typically at ambient temperature and is divided into two flows, namely a first flow 213 and a second flow 215. Preferably, a small portion of the MCSG supply flow 211, for example, a first flow 213 consisting of 10 to 40 percent, more preferably 20 to 30 percent of the flow of the MCSG supply flow 211, is sent to a first heat exchanger unit or set of units 214. The second flow 215, consisting of the remainder of the flow of the MCSG supply flow 211, and therefore preferably the majority of that flow, is sent to a second heat exchanger unit or set of units 216. The second heat exchanger unit or set of units 216 may include, for example, a plate fin heat exchanger unit or a plurality of plate fin heat exchanger units arranged in parallel. The first flow 213 and the second flow 215 are cooled and partially liquefied in the first heat exchanger unit 214 and the second heat exchanger unit 216, respectively, to form a first cooled, partially liquefied flow 220 and a second cooled, partially liquefied flow 217, respectively, at temperatures of -120°C to -150°C, more preferably -130°C to -140°C. The first and second cooled, partially liquefied flows 220 and 217 are then combined (the pressure of the second cooled, partially liquefied flow 217 is first adjusted as needed, for example, via valve 217A to control the flow of flow 217) to form a partially liquefied MCSG supply flow 230.

[0086] The partially liquefied MCSG feed stream 230 is then further cooled (and further partially liquefied) in a third heat exchanger unit or set of units 231 to form a partially liquefied MCSG feed stream 233 at a temperature of -155°C to -185°C, and more preferably -165°C to -175°C. The third heat exchanger unit or set of units 231 may include, for example, a plate fin exchanger unit or a plurality of plate fin exchanger units arranged in parallel. In another embodiment (not shown), the third heat exchanger unit may be combined with the second heat exchanger unit to form a single unit or a set of units arranged in parallel, with the flow 215 being cooled in the warmer section of the unit and the flow 230 being cooled in the colder section of the unit.

[0087] Next, the partially liquefied MCSG feed stream 233 is separated using a first phase separator 235 and a second phase separator 240 arranged in series, the second phase separator being in flow communication downstream with the first phase separator. More specifically, the partially liquefied MCSG feed stream 233 is first introduced into the first phase separator 235, in this case the first phase separator 235 is a flash drum, where the partially liquefied MCSG feed stream is flashed and separated into liquid steam forming a third feed stream 236 and a vapor stream forming a first residual gas stream 237. The third supply flow 236 is pressure-reduced and partially vaporized, for example, by passing the flow through the JT valve 237A, and the flow is then two-phase. The partially vaporized two-phase third supply flow is then introduced into the second phase separator 240, which is a flash drum, where the partially liquefied third supply flow is flashed and separated into a liquid flow forming the first supply flow 242 and a vapor flow forming the second supply flow 251.

[0088] A first feed flow 242, which is a flow controlled by valve 242A to control the liquid level in a second phase separator 240, passes through a third heat exchanger unit or set of units 231 via indirect heat exchange with a partially liquefied MCSG feed flow 230, is heated, and then the flow becomes two-phase (or, in an alternative embodiment where the third heat exchanger unit is combined with the second heat exchanger unit, the third feed flow 242 is heated in the colder section of the combined unit). The first feed flow 252 and the second feed flow 251 are then introduced, respectively, into different locations in the distillation column 245, as will be further described below, and the distillation column 245 operates at a pressure of 3.0 to 7.0 bara, more preferably 4.5 to 5.5 bara.

[0089] The first feed stream 252 is introduced into the distillation column 245 at a first position, above one or more separation stages of the column represented by section 245C of the column in Figure 2, and below one or more separation stages of the column represented by section 245B of the column in Figure 1. The second feed stream 251 is introduced into the distillation column at a second position, above one or more separation stages of the column represented by section 245B of the column, and below one or more separation stages of the column represented by section 245A of the column in Figure 2.

[0090] The reboiler efficiency of the distillation column 245 is provided by heating the flow of distillation column bottom liquid 253 in a second heat exchanger unit or set of units 116, via indirect heat exchange with a second flow 215 (obtained from splitting the MCSG feed flow), thereby at least partially vaporizing it and forming a boiling flow 254 (formed from the partially vaporized distillation column bottom liquid) that is reintroduced to the bottom of the distillation column.

[0091] The LNG stream 280 formed from the bottom liquid of the distillation column is taken out from the bottom of the distillation column 245 at a temperature of -125°C to -155°C, more preferably -135°C to -145°C, and is preferably pressurized by pump 181 and sent (as stream 283) through the first heat exchanger unit or set of units 214 to be supercooled and form a supercooled LNG product stream 287 that can be stored on-site in an LNG storage container or directly transported off-site (e.g., via pipeline or transport container). The LNG streams 280 and 287 typically contain 1 mol% or less of nitrogen, preferably less than 0.5 mol%, and also preferably have a carbon monoxide content of 10 ppm or less. The proportion of methane recovered in the LNG streams 280 and 287 from the MCSG feed stream 211 may exceed 95%.

[0092] The second residual gas stream 260, formed by the overhead vapor of the distillation column, is withdrawn from the top of the distillation column 245 at a temperature of -160°C to -190°C, more preferably -170°C to -180°C, and typically contains more than 95 mol%, preferably more than 98 mol%, of hydrogen and carbon monoxide.

[0093] The first residual gas flow 237 and the second residual gas flow 260 each pass through the third heat exchange unit or set of units 231, are heated, and then each (see flows 238 and 261) passes through the second heat exchanger unit or set of units 216, where they are further heated, resulting in a heated first residual gas flow 239 and a heated second residual gas flow 262 (or, in an alternative embodiment where the third heat exchanger unit is combined with the second heat exchanger unit, the first residual gas flow 237 and the second residual gas flow 260 are heated in the colder section of the combined unit and then further heated in the warmer section of the combined unit). Next, the heated second residual gas flow 262 is compressed and cooled by the compressor 263 and aftercooler 265 to form a compressed second residual gas flow 270, which is then divided into two parts 271 and 275.

[0094] Preferably, a first portion 271 of the compressed second residual gas flow, consisting of a small portion of the compressed second residual gas flow 270, for example, 10% to 30%, more preferably 15% to 25% of the flow, is mixed with the heated first residual gas flow 239 to form a combined residual gas flow 273. The residual gas flow 273 can be used as fuel for the plant or sent to downstream units for further purification, separation, and / or chemical synthesis. Optionally, a portion or all of the flow 239 can be purified to produce a hydrogen product and combined with the residual gas flow 271.

[0095] A second portion 275 of the compressed second residual gas flow, consisting of the remainder of the flow of the compressed second residual gas flow 270, and therefore preferably the majority of the flow, passes through the second heat exchanger unit or set of units 216 and is cooled (or, in an alternative embodiment in which a third heat exchanger unit is combined with the second heat exchanger unit, the second portion 275 is cooled in the warmer section of the combined unit) to form a cooling flow 277 at a temperature of -120°C to -150°C, more preferably -130°C to -140°C. The cooling flow 277 is then expanded in the expander 279 to form a reflux flow 250 having a temperature of -160°C to -190°C, more preferably -170°C to -180°C, which is at least partially liquefied and introduced into the distillation column 245 at a third position above one or more separation stages of the distillation column represented by section 245A and at the top of the distillation column, thereby providing a reflux source to the distillation column. The expanded material from the expander 279 can be recovered, for example, by coupling the expander to a compressor that compresses the feed gas or residual gas, or, for example, in a generator.

[0096] The first heat exchanger unit or set of units 214 is preferably a coil-wound unit or set of units, for example, as shown in Figure 1A. Any type of refrigeration process known in the art for the liquefaction of natural gas (including synthetic or alternative natural gases) may be used in the first heat exchanger unit or set of units 214, for example, in a single-mix refrigerant process, a double-mix refrigerant process, a propane, ammonia or HFC pre-cooled mixed refrigerant process, a reverse Brayton cycle using nitrogen, methane or ethane, or a multi-fluid cascade cycle. However, in exemplary embodiments, an SMR (single-mix refrigerant) process as shown in Figure 1A and described above may be used.

[0097] The method and system shown in Figure 2 have the same advantages and benefits as the method and system shown in Figure 1. Compared to the embodiment shown in Figure 1, the embodiment shown in Figure 2 can achieve an even higher methane recovery rate by using reflux with a very low methane content, and thus can further improve the methane recovery rate of the process. However, the embodiment shown in Figure 1 has a better specific power output compared to the embodiment shown in Figure 2.

[0098] Figure 3 shows a method and system for producing LNG from MCSG according to a third embodiment of the present invention. In Figure 3, features shared with the first embodiment shown in Figure 1 are assigned the same reference numerals, but increased by 200. For example, the partially liquefied MCSG feed stream 330 in Figure 3 corresponds to the partially liquefied MCSG feed stream 130 in Figure 1, and the distillation column 345 in Figure 3 corresponds to the distillation column 145 shown in Figure 1. Unless a feature in Figure 3 is specifically described as being different from the corresponding feature in Figure 1, it can be assumed that the feature has the same structure and function as the corresponding feature in Figure 1 described above. Furthermore, if a feature does not have a different structure or function, it may not be specifically mentioned in the further description of Figure 3 below.

[0099] The embodiment shown in Figure 3 differs from that shown in Figure 1 in that the MCSG supply flow is cooled to form a partially liquefied MCSG supply flow, and in that a first heat exchanger unit or set of units is used, and the first heat exchanger unit or set of units is used to supply refrigerant, thereby supplying additional refrigerant to a third heat exchanger unit or set of units and a second heat exchanger unit or set of units.

[0100] More specifically, in Figure 3, the entire MCSG feed stream 311 leaving the pretreatment section 305 is sent to a second heat exchanger unit or set of units 316, through which the MCSG feed stream 311 is cooled to a temperature of -130°C to -160°C, more preferably -140°C to -150°C, to form a partially liquefied MCSG feed stream 330, which is then separated using a first phase separator 340 and a second phase separator 335 arranged in series (as described above with respect to Figure 1). As described above with respect to Figure 1, the second heat exchanger unit or set of units 316 may include, for example, a plate fin heat exchanger unit or a plurality of plate fin heat exchanger units arranged in parallel.

[0101] The first heat exchanger unit or set of units 314 is not used to accept and cool any portion of the MCSG supply flow. Instead, in the arrangement shown in Figure 3, the first heat exchanger unit or set of units 314 is used to cool the first refrigerant, producing a flow of cooled first refrigerant 390, which is, The first refrigerant 392 is taken out of the first heat exchanger unit or set of units 314, passes through the third heat exchanger unit or set of units 331, and is heated through indirect heat exchange with the third supply flow 342, thereby providing additional refrigeration (along with the first residual gas flow 337 and the second residual gas flow 360) to the unit. The resulting flow of the first refrigerant 392 exiting the third heat exchanger unit or set of units 331 then passes through the second heat exchanger unit or set of units 316, and is further heated through indirect heat exchange with the MCSG supply flow 311, thereby providing additional refrigeration (along with the first residual gas flow 338, the second residual gas flow 361, and the flow of the distillation column bottom liquid 353) to the unit. The resulting heated flow of the first refrigerant 395 is then returned to the first heat exchanger unit or set of units 314, where it is cooled again. In those alternative embodiments in which the third heat exchanger unit is combined with the second heat exchanger unit, the cooled flow of the first refrigerant 390 is instead heated in the colder section of the combined unit and then further heated in the warmer section of the combined unit.

[0102] The first heat exchanger unit or set of units 314 is preferably a coil-wound unit or set of units, for example, as shown in Figure 3A. Any type of refrigeration process known in the art for the liquefaction of natural gas (including synthetic or alternative natural gases) may be used in the first heat exchanger unit or set of units 314, for example, in a single mixed refrigerant process, a double mixed refrigerant process, a propane, ammonia or HFC pre-cooled mixed refrigerant process, a reverse Brayton cycle using nitrogen, methane or ethane, or a multi-fluid cascade cycle. However, in exemplary embodiments, an SMR (single mixed refrigerant) process may be used, as depicted in Figure 3A, where the first refrigerant is a mixed refrigerant.

[0103] As shown in Figure 3A, the coil-wound heat exchanger unit 314 includes a hot section containing a hot tube bundle 314A and a cold section containing a cold tube bundle 314B (the terms "hot" and "cold" are relative). LNG vapor 383 passes through the cold tube bundle 114B, is supercooled, and forms a supercooled LNG product flow 387. Cooling efficiency is imparted to the hot and cold tube bundles of the coil-wound heat exchanger unit by a cooled first refrigerant that passes through the shell side of the heat exchanger unit, is heated, and vaporizes. The SMR cycle shown in Figure 3A, used to cool the first refrigerant, is well known in the art and is therefore described only broadly herein for the sake of brevity. In very simple terms, a heated and vaporized first refrigerant, taken from the shell side at the bottom of the heat exchanger unit, is combined with a flow of heated and vaporized first refrigerant 395 (returning from the first heat exchanger unit or set of units 314) and compressed, cooled, and separated into one or more MRL (mixed refrigerant liquid) flows (two shown in the figure) and one or more MRV (mixed refrigerant vapor) flows (one shown in the figure) in a compression train including one or more compressors, aftercoolers, and phase separators. The MRL flows are cooled as they pass through the heated tube bundle, expanded through the JT valve, and combined with and introduced to the shell side of the heat exchanger unit at the top of the heated tube bundle, providing a vaporized first refrigerant that flows downward through the shell side around the tubes of the heated tube bundle.

[0104] The MRV flow passes through the hot and cold tube bundles, where it is cooled and at least partially liquefied to form a flow of cooled first refrigerant, which is taken out from the top of the cold tube bundle, expanded and divided to form a flow of cooled first refrigerant 390 (which is heated and, in this case vaporized, as described above in the third heat exchanger unit or set of units 331 and the second heat exchanger unit or set of units 316) and a flow of cooled first refrigerant which is introduced into the shell side of the first heat exchanger unit 314 at the top of the cold tube bundle and provides a vaporized first refrigerant that flows downward through the shell side around the tubes of the hot and cold tube bundles. The cooled first refrigerant flow taken out from the top of the cold tube bundle can be expanded, for example, by passing the flow through a JT valve, and then divided to form a flow of cooled first refrigerant 390 and a flow of cooled first refrigerant introduced into the shell side of the first heat exchanger unit 314 at the top of the cold tube bundle, as shown in Figure 3A. Alternatively, the cooled first refrigerant flow taken out from the top of the cold tube bundle can be divided first, and the resulting divided flows can then be expanded separately (for example, using separate JT valves).

[0105] The method and system shown in Figure 3 have similar advantages and benefits to the method and system shown in Figure 1 described above. Compared to the embodiment shown in Figure 1, the embodiment shown in Figure 3 avoids the need to split and distribute the MCSG supply flow between the first and second heat exchanger units, but has the potential disadvantage of requiring the use of a two-phase refrigerant in the second and / or third heat exchanger units (i.e., the first refrigerant used in the second and / or third heat exchanger units is two-phase).

[0106] Figure 4 shows a method and system for producing LNG from MCSG according to a fourth embodiment of the present invention. In Figure 4, features shared with the second embodiment shown in Figure 2 are assigned the same reference numerals, but increased by 200. For example, the partially liquefied MCSG feed stream 430 in Figure 4 corresponds to the partially liquefied MCSG feed stream 230 in Figure 2, and the distillation column 445 in Figure 4 corresponds to the distillation column 445 in Figure 1. Unless a feature in Figure 4 is specifically described as being different from the corresponding feature in Figure 2, it can be assumed that the feature has the same structure and function as the corresponding feature in Figure 2 described above. Furthermore, if a feature does not have a different structure or function, it may not be specifically mentioned in the further description of Figure 4 below.

[0107] The embodiment shown in Figure 4 differs from that shown in Figure 1 in that a configuration in which the MCSG supply flow is cooled to form a partially liquefied MCSG supply flow, and a configuration in which a second heat exchanger unit or set of units is used, and the first heat exchanger unit or set of units is used to supply refrigerant, thereby supplying additional refrigerant to a third heat exchanger unit or set of units and the second heat exchanger unit or set of units.

[0108] More specifically, in Figure 4, the entire MCSG feed stream 411 leaving the pretreatment section 405 is sent to a second heat exchanger unit or set of units 416, through which the MCSG feed stream 411 is cooled to a temperature of -120°C to -150°C, more preferably -130°C to -140°C, to form a partially liquefied MCSG feed stream 430, which is then separated using a first phase separator 435 and a second phase separator 440 arranged in series (as described above with respect to Figure 2). As described above with respect to Figure 2, the second heat exchanger unit or set of units 416 may include, for example, a plate fin heat exchanger unit or a plurality of plate fin heat exchanger units arranged in parallel.

[0109] The first heat exchanger unit or set of units 414 is not used to accept and cool any portion of the MCSG supply flow. Instead, in the arrangement shown in Figure 4, the first heat exchanger unit or set of units 414 is used to cool the first refrigerant and produce a flow of cooled first refrigerant 490, which is, The first refrigerant 492 is taken out of the first heat exchanger unit or set of units 414, passes through the third heat exchanger unit or set of units 431, where it is heated via indirect heat exchange with the partially liquefied MCSG feed stream 430, thereby providing additional refrigeration (along with the first residual gas stream 437, the second residual gas stream 460, and the first feed stream 442) to the unit. The resulting flow of the first refrigerant 492 exiting the third heat exchanger unit or set of units 431 then passes through the second heat exchanger unit or set of units 416, where it is further heated via indirect heat exchange with the MCSG feed stream 411, thereby providing additional refrigeration (along with the first residual gas stream 438, the second residual gas stream 461, and the distillation column bottom liquid stream 453) to the unit. The resulting heated flow of the first refrigerant 495 is then returned to the first heat exchanger unit or set of units 414, where it is cooled again. In those alternative embodiments in which the third heat exchanger unit is combined with the second heat exchanger unit, the cooled flow of the first refrigerant 490 is instead heated in the colder section of the combined unit and then further heated in the warmer section of the combined unit.

[0110] The first heat exchanger unit or set of units 414 is preferably a coil-wound unit or set of units, for example, as shown in Figure 3A. Any type of refrigeration process known in the art for the liquefaction of natural gas (including synthetic or alternative natural gases) may be used in the first heat exchanger unit or set of units 414, for example, in a single-mix refrigerant process, a double-mix refrigerant process, a propane, ammonia or HFC pre-cooled mixed refrigerant process, a reverse Brayton cycle using nitrogen, methane or ethane, or a multi-fluid cascade cycle. However, in exemplary embodiments, an SMR (single-mix refrigerant) process as shown in Figure 3A and described above may be used.

[0111] The method and system shown in Figure 4 have the same advantages and benefits as the method and system shown in Figure 3. Compared to the embodiment shown in Figure 3, the embodiment shown in Figure 4 can achieve an even higher methane recovery rate by using reflux with a very low methane content, and thus can further improve the methane recovery rate of the process. However, the embodiment shown in Figure 3 has a better specific power output compared to the embodiment shown in Figure 4.

[0112] Example 1 In this embodiment, a method and system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG) as shown in Figure 1 was simulated using Aspen version 10. Table 1 below shows the flow data from the simulation. In this embodiment, the residual gas compressor 163 has four stages with a breaking horsepower of approximately 61.8 MW, the mixed refrigerant compressors 115A and 115B have a breaking horsepower of approximately 30.3 MW, the expander 179 extracts 10.5 MW of work, and the process has a methane recovery rate of 95%. Table 1: Thermal and material equilibrium [Table 1]

[0113] Example 2 In this example, a method and system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), as shown in Figure 2, was simulated using Aspen version 10. Table 2 below shows the flow data from the simulation. Table 2: Thermal and material equilibrium [Table 2]

[0114] The method and system of this embodiment utilize a heat pump (expander 279) to enable extremely high product recovery. This produces a high-purity reflux with an extremely low methane content, improving the methane recovery rate of the process compared to the process of Example 1. However, the process of Example 1 has a better specific power output of 922.6 kW-hr / ton compared to the process of Example 2, at 848.5 kW-hr / ton.

[0115] It will be understood that the present invention is not limited to the details described above with respect to preferred embodiments, and that numerous modifications and changes can be made without departing from the spirit or scope of the invention as defined in the following claims. The following embodiments can be cited as examples of the present invention. (Note 1) A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the method is (a) Cooling the MCSG supply flow and partially liquefying it to produce a partially liquefied MCSG supply flow, (b) Separating the partially liquefied MCSG feed flow into at least three flows, including a liquid flow and two vapor flows, using a first phase separator and a second phase separator arranged in series, wherein the second phase separator is in fluid communication downstream with the first phase separator, the liquid flow forming a first feed flow, one of the vapor flows forming a second feed flow, and the other of the vapor flows forming a first residual gas flow. (c) Introducing the first feed stream into the distillation column at the first position, (d) Introducing the second feed stream into the distillation column at a second position above the first position, wherein there is at least one separation step between the first and second positions. (e) Extracting the LNG flow from the distillation column formed by the bottom liquid of the distillation column, (f) Extracting a second residual gas stream from the distillation column formed by the distillation column overhead vapor, Methods that include... (Note 2) Step (b) is, (i) The first phase separator separates the partially liquefied MCSG supply flow into the liquid flow forming the first supply flow and the vapor flow, (ii) Dividing the steam flow from the first phase separator to form the steam flow that forms the second supply flow and the steam flow that forms the third supply flow, (iii) Cooling the third supply flow and partially liquefying it, and then separating the third supply flow in the second phase separator into the vapor flow that forms the first residual gas flow and the liquid flow that forms the fourth supply flow, Includes, Step (c) includes reducing the pressure of the first feed stream and then introducing the first feed stream into the distillation column at the first position, Step (d) includes reducing the pressure of the second feed stream and then introducing the second feed stream into the distillation column at the second position, The method according to Appendix 1, further comprising reducing the pressure of the fourth feed stream and then introducing the fourth feed stream into the distillation column at a third position above the second position, wherein there is at least one separation step between the second position and the third position. (Note 3) The method according to Appendix 2, wherein the third position is at the top of the distillation column. (Note 4) The method according to Appendix 2, wherein one or both of the first residual gas flow and the second residual gas flow are heated via indirect heat exchange with the third supply flow in order to provide the cooling duty for the cooling and partial liquefaction of the third supply flow in step (b)(iii). (Note 5) Step (b) is, (i) Separating the partially liquefied MCSG flow in the first phase separator into the vapor flow that forms the first residual gas flow and the liquid flow that forms the third supply flow, (ii) reducing the pressure of the third supply flow, partially vaporizing the third supply flow, and separating the flow in the second phase separator into the liquid flow forming the first supply flow and the vapor flow forming the second supply flow, Includes, The method according to Appendix 1, wherein step (c) includes heating the first feed stream and then introducing the first feed stream into the distillation column at the first position. (Note 6) The method according to Appendix 5, wherein there is at least one separation step between the second position and the top of the column, and the method further comprises compressing, cooling and expanding the second residual gas stream or portion of the distillation column overhead vapor, thereby at least partially liquefying it to form a reflux stream, and introducing the reflux stream into the distillation column at a third position at the top of the distillation column. (Note 7) The method according to Appendix 5, wherein in step (c), the first feed stream is heated via indirect heat exchange with the MCSG feed stream in order to provide the cooling efficiency for the cooling and partial liquefaction of the MCSG feed stream in step (a). (Note 8) The method according to Appendix 1, wherein, in order to provide the cooling efficiency for the cooling and partial liquefaction of the MCSG supply flow in step (a), one or both of the first residual gas flow and the second residual gas flow are heated via indirect heat exchange with the MCSG supply flow. (Note 9) The method according to Appendix 1, wherein there is at least one separation step between the first position and the bottom of the column, and the method further comprises heating a portion of the LNG flow or distillation column bottom liquid, thereby at least partially vaporizing it to form a boiling flow, and introducing the boiling flow into the distillation column at the bottom of the distillation column. (Note 10) The method according to Appendix 1, wherein at least a portion of the second residual gas flow is compressed and combined with the first residual gas flow. (Note 11) The method according to Appendix 1, further comprising supercooling the LNG flow. (Note 12) Step (a) is, (i) Dividing the MCSG supply flow into at least two parts, including a first part and a second part, (ii) Cooling and partially liquefying the first portion of the MCSG supply flow in a first heat exchanger unit or set of units via indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, (iii) Cooling and partially liquefying the second portion of the MCSG supply flow in a second heat exchanger unit or set of units through indirect heat exchange with one or more process flows, (iv) Combining the cooled and partially liquefied first portion of the MCSG supply flow with the cooled and partially liquefied second portion of the MCSG supply flow to form the partially liquefied MCSG supply flow, The method described in Appendix 1, including the method described in Appendix 1. (Note 13) The method according to Appendix 12, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. (Note 14) The method according to Appendix 12, wherein in step (a)(iii), the one or more process flows include one or more flows selected from the first residual gas flow, the second residual gas flow, and the LNG flow or a portion of the distillation column bottom liquid. (Note 15) The method according to Appendix 12, wherein the first refrigerant is a refrigerant that vaporizes when heated in the first heat exchanger unit or set of units. (Note 16) The method according to Appendix 12, further comprising supercooling the LNG flow in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant. (Note 17) The method according to Appendix 12, wherein step (a)(ii) comprises cooling and partially liquefying the first portion of the MCSG supply flow in the first heat exchanger unit or set of units through indirect heat exchange with one or more flows of cooled first refrigerant, the first heat exchanger unit or set of units being a coil-wound heat exchanger unit or set of units, and the one or more flows of cooled first refrigerant are also produced by cooling the first refrigerant in the first heat exchanger unit or set of units. (Note 18) Step (a) is, (i) manufacturing a cooled first refrigerant by cooling a first refrigerant in a first heat exchanger unit or set of units, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units. (ii) Cooling and partially liquefying the MCSG supply flow in a second heat exchanger unit or set of units through indirect heat exchange with one or more flows and one or more process flows of the cooled first refrigerant to form the partially liquefied MCSG supply flow, The method described in Appendix 1, including the method described in Appendix 1. (Note 19) The method according to Appendix 18, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. (Note 20) The method according to Appendix 18, wherein in step (a)(ii), the one or more process flows include one or more of the first residual gas flow, the second residual gas flow, and the LNG flow or a portion of the distillation column bottom liquid. (Note 21) The method according to Appendix 18, wherein in step (a)(i), the first refrigerant is cooled in the first heat exchanger unit or set of units through indirect heat exchange with the portion of the cooled first refrigerant produced in step (a)(i). (Note 22) The method according to Appendix 18, further comprising supercooling the LNG flow in the first heat exchanger unit or set of units. (Note 23) A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the method is (a) (i) Dividing the MCSG supply flow into at least two parts, including a first part and a second part, (ii) Cooling and partially liquefying the first portion of a first heat exchanger unit or set of units through indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, (iii) Cooling and partially liquefying the second portion in a second heat exchanger unit or set of units through indirect heat exchange with one or more process flows, (iv) Combining the cooled and partially liquefied first portion and the cooled and partially liquefied second portion to form the partially liquefied MCSG supply flow, This involves cooling and partially liquefying the MCSG supply flow to produce a partially liquefied MCSG supply flow. (b) Separating the partially liquefied MCSG supply flow into an LNG flow and one or more residual gas flows, Methods that include... (Note 24) The method according to Appendix 23, wherein in step (b), the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residual gas streams using one or more phase separators and / or one or more distillation columns. (Note 25) The method according to Appendix 23, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. (Note 26) The method according to Appendix 23, wherein in step (a)(iii), the one or more process flows include one or more flows selected from one or more of the residual gas flow, a portion of the LNG flow, or a portion of the distillation column bottom liquid. (Note 27) The method according to Appendix 23, wherein the first refrigerant is a refrigerant that vaporizes when heated in the first heat exchanger unit or set of units. (Note 28) The method according to Appendix 23, further comprising supercooling the LNG flow in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant. (Note 29) The method according to Appendix 23, wherein step (a)(ii) comprises cooling and partially liquefying the first portion of the MCSG supply flow in the first heat exchanger unit or set of units through indirect heat exchange with one or more flows of cooled first refrigerant, the first heat exchanger unit or set of units being a coil-wound heat exchanger unit or set of units, and the one or more flows of cooled first refrigerant are also produced by cooling the first refrigerant in the first heat exchanger unit or set of units. (Note 30) A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the method is (a) (i) manufacturing a cooled first refrigerant by cooling a first refrigerant in a first heat exchanger unit or set of units, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units. (ii) Cooling and partially liquefying the MCSG supply flow in a second heat exchanger unit or set of units through indirect heat exchange with one or more flows and one or more process flows of the cooled first refrigerant, to form a partially liquefied MCSG supply flow, This involves cooling and partially liquefying the MCSG supply flow to produce the partially liquefied MCSG supply flow, (b) Separating the partially liquefied MCSG supply flow into an LNG flow and one or more residual gas flows, Methods that include... (Note 31) The method according to Appendix 30, wherein in step (b), the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residual gas streams using one or more phase separators and / or one or more distillation columns. (Note 32) The method according to Appendix 30, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. (Note 33) The method according to Appendix 30, wherein in step (a)(ii), the one or more process flows include one or more of the first residual gas flow, the second residual gas flow, and the LNG flow or a portion of the distillation column bottom liquid. (Note 34) The method according to Appendix 30, wherein in step (a)(i), the first refrigerant is cooled in the first heat exchanger unit or set of units through indirect heat exchange with a portion of the cooled first refrigerant produced in step (a)(i). (Note 35) The method according to Appendix 30, further comprising supercooling the LNG flow in the first heat exchanger unit or set of units. (Note 36) A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the system is One or more heat exchanger units for receiving, cooling, and partially liquefying the MCSG feed flow to produce a partially liquefied MCSG feed flow, A first phase separator and a second phase separator, which are fluid-connected to one or more heat exchanger units and arranged in series, wherein the second phase separator is fluid-connected downstream to the first phase separator to separate the partially liquefied MCSG feed flow into at least three flows, including a liquid flow and two vapor flows, the liquid flow forming a first feed flow, one of the vapor flows forming a second feed flow, and the other of the vapor flows forming a first residual gas flow, A distillation column having: a first inlet at a first position for receiving the first feed flow; a second inlet at a second position for receiving the second feed flow, the second position being above the first position; at least one separation step between the first position and the second position; an outlet at the bottom of the distillation column for taking out an LNG flow formed from the bottom liquid of the distillation column; and an outlet at the top of the distillation column for taking out a second residual gas flow formed from the overhead vapor of the distillation column. A system that includes this. (Note 37) A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the system is A set of conduits for dividing the MCSG supply flow into at least two parts, including a first part and a second part, A first heat exchanger unit or set of units for receiving the first portion and cooling and partially liquefying the first portion through indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, A second heat exchanger unit or set of units for receiving the second portion and cooling and partially liquefying the second portion through indirect heat exchange with one or more process flows, A set of conduits for receiving and combining the cooled and partially liquefied first portion and the cooled and partially liquefied second portion to form a partially liquefied MCSG supply flow, One or more phase separators and / or one or more distillation columns for receiving the partially liquefied MCSG feed stream and separating it into an LNG stream and one or more residual gas streams, A system that includes this. (Note 38) A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the system is A first heat exchanger unit or set of units for cooling a first refrigerant to produce a cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, A second heat exchanger unit or set of units for receiving one or more process flows, and for receiving an MCSG supply flow, and for cooling and partially liquefying the MCSG supply flow through indirect heat exchange with the one or more flows of the cooled first refrigerant and the one or more process flows to form a partially liquefied MCSG supply flow, One or more phase separators and / or one or more distillation columns for receiving the partially liquefied MCSG feed stream and separating it into an LNG stream and one or more residual gas streams, A system that includes this.

Claims

1. A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the method is (a) (i) Dividing the MCSG supply flow into at least two parts, including a first part and a second part, (ii) Cooling and partially liquefying a first portion of a first heat exchanger unit or set of units through indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, (iii) Cooling and partially liquefying the second portion in a second heat exchanger unit or set of units through indirect heat exchange with one or more process flows, (iv) Combining the cooled and partially liquefied first portion and the cooled and partially liquefied second portion to form the partially liquefied MCSG supply flow, This involves cooling the aforementioned MCSG supply flow, partially liquefying it, and producing a partially liquefied MCSG supply flow. (b) Separating the partially liquefied MCSG supply stream into an LNG stream and one or more residual gas streams, Includes, The method further includes subcooling the LNG flow in the first heat exchanger unit or set of units through indirect heat exchange with the first refrigerant. method.

2. The method according to claim 1, wherein in step (b), the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residual gas streams using one or more phase separators and / or one or more distillation columns.

3. The method according to claim 1, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units.

4. The method according to claim 1, wherein in step (a)(iii), the one or more process flows include one or more flows selected from one or more of the residual gas flow, a portion of the LNG flow, or a portion of the bottom liquid of the distillation column.

5. The method according to claim 1, wherein the first refrigerant is a refrigerant that vaporizes when heated in the first heat exchanger unit or set of units.

6. The method according to claim 1, wherein step (a)(ii) comprises cooling and partially liquefying the first portion of the MCSG supply flow in the first heat exchanger unit or set of units via indirect heat exchange with one or more flows of cooled first refrigerant, the first heat exchanger unit or set of units being a coil-wound heat exchanger unit or set of units, and the one or more flows of cooled first refrigerant also being produced by cooling the first refrigerant in the first heat exchanger unit or set of units.

7. A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), wherein the method is (a) (i) manufacturing a cooled first refrigerant by cooling a first refrigerant in a first heat exchanger unit or set of units, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units. (ii) Cooling and partially liquefying the MCSG supply flow in a second heat exchanger unit or set of units through indirect heat exchange with one or more flows and one or more process flows of the cooled first refrigerant, to form a partially liquefied MCSG supply flow, This involves cooling and partially liquefying the MCSG supply flow to produce the partially liquefied MCSG supply flow, (b) Separating the partially liquefied MCSG supply stream into an LNG stream and one or more residual gas streams, Includes, The method further includes supercooling the LNG flow in the first heat exchanger unit or set of units. method.

8. The method according to claim 7, wherein in step (b), the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residual gas streams using one or more phase separators and / or one or more distillation columns.

9. The method according to claim 7, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units.

10. The method according to claim 7, wherein in step (a)(ii), the one or more process flows include one or more of the first residual gas flow, the second residual gas flow, and the LNG flow or a portion of the distillation column bottom liquid.

11. The method according to claim 7, wherein in step (a)(i), the first refrigerant is cooled in the first heat exchanger unit or set of units through indirect heat exchange with a portion of the cooled first refrigerant produced in step (a)(i).

12. A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG) by the method described in Claim 1, wherein the system is A set of conduits for dividing the MCSG supply flow into at least two parts, including the first part and the second part, A first heat exchanger unit or set of units for receiving the first portion and cooling and partially liquefying the first portion through indirect heat exchange with the first refrigerant, A second heat exchanger unit or set of units for receiving the second portion and cooling and partially liquefying the second portion through indirect heat exchange with one or more process flows, A set of conduits for receiving and combining the cooled and partially liquefied first portion and the cooled and partially liquefied second portion to form the partially liquefied MCSG supply flow, One or more phase separators and / or one or more distillation columns for receiving the partially liquefied MCSG feed stream and separating it into the LNG stream and one or more residual gas streams, A system that includes this.

13. A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG) by the method of Claim 7, wherein the system is A first heat exchanger unit or set of units for cooling the first refrigerant to produce the cooled first refrigerant, A second heat exchanger unit or set of units for receiving the one or more flows of the cooled first refrigerant from the first heat exchanger unit, for receiving the one or more process flows, and for receiving the MCSG supply flow, and for cooling and partially liquefying the MCSG supply flow through indirect heat exchange with the one or more flows of the cooled first refrigerant and the one or more process flows to form the partially liquefied MCSG supply flow, One or more phase separators and / or one or more distillation columns for receiving the partially liquefied MCSG feed stream and separating it into the LNG stream and the one or more residual gas streams, A system that includes this.

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