Producing LNG from methane-containing synthetic 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 technology]

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

[0002] The evolution of green fuel technology has led to the integration of gasification and natural gas liquefaction processes to produce LNG from MCSG. MCSG is a light hydrocarbon-containing gas containing methane and lighter impurities than methane that can be produced from the gasification of coal or oil residues. Making MCSG from gasification products is a clean method of using traditional solid and low-value heavy liquid fuels by enabling centralized carbon capture and sequestration while clean, low-carbon-containing methane is produced and distributed. Additionally, the co-production of LNG from the gasification process provides an attractive option to diversify the product portfolio and improves the overall economics of the project.

[0003] An exemplary prior art process for producing LNG from MCSG is shown and described in U.S. Pat. No. 10,436,505. In the process shown therein, 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 utilizes a vaporizing mixed refrigerant to provide cooling. 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 (lower operating pressure). The cooled feed gas stream exiting the reboiler is then further cooled to a temperature of −120 to −200° C. and at least partially liquefied in the main heat exchanger before being flashed and separated in drums to form a flashed vapor stream and a liquid stream. The flashed vapor stream is expanded in an expander section of a compander and sent to the rectification section of the primary distillation column (higher operating pressure). The liquid stream is reduced in pressure through a valve and sent to the bottom of the primary distillation column.

[0004] A bottoms stream removed from the primary column is sent to a secondary column for further improved methane recovery. The bottoms stream removed from the secondary column is cooled in the main heat exchanger to a final temperature of -120 to -200 °C to form an LNG product stream. An overhead vapor stream from the secondary column is condensed in the main heat exchanger and flashed in a reflux drum. The reflux drum liquid is used as reflux for both the primary and secondary columns. The reflux drum vapor is compressed in the compression section of the compander and combined with overhead vapor from the primary column to form a residue gas stream that is warmed in the main heat exchanger and recompressed in the residue gas compressor and sent out of the facility.

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

[0006] The configuration shown in U.S. Pat. No. 10,436,505, while capable of producing high purity methane-rich LNG, has certain drawbacks. One challenge is that the mixed refrigerant stream is introduced into the main heat exchanger as a two-phase mixture. This complicates the design of the piping and can cause undesirable unstable operation due to slugging. Two-phase flow also 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 tubes must be provided to ensure that the phases are evenly distributed across all the passages. The use of these devices can increase costs and reduce operational stability. In addition, two-phase flow can become unstable at low flow rates, causing phase separation and resulting in large internal temperature gradients, resulting in potential damage to the main heat exchanger.

[0007] Another drawback is that the main exchanger utilizes two different low pressure streams (i.e., a cooled vaporized mixed refrigerant stream and a residue gas stream) to provide the cooling duty for the heat exchanger, which essentially precludes the use of coil-wound type 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 flash gas heat exchange applications. The design and manufacturing techniques of coil-wound heat exchangers allow for much higher unit throughput (heat exchange duty achieved per coil-wound heat exchanger unit) while avoiding the use of multiple heat exchanger units in parallel (in the case of plate-fin heat exchangers) up to very large volumes. Coil-wound heat exchanger units include one or more tube bundles encased in a shell casing, the tube side of the unit is designed to accept one or more hot streams requiring cooling, and the shell side of the unit is designed to accept a single stream of cooled refrigerant or two or more cold streams that are mixed in the shell side and exit as a single stream of warmed refrigerant. The only way that a coil-wound heat exchanger can accommodate the use of two or more cold streams that are to be kept separate is by passing at least one of the cold streams through one of the tube-side flow paths of the heat exchanger. However, designing a coil-wound exchanger can be difficult given the low pressure drop available and the relatively high typical resistance in the tube-side flow paths of the heat exchanger.

[0008] A further disadvantage of the process shown is that all of the residual gas is produced at relatively low pressure, which increases the operating and capital costs of the process since the greater the amount of residual gas produced at low pressure, the greater the power requirements to recompress the gas and the larger the residual gas compressor must be to accommodate the gas. Summary of the Invention

[0009] Disclosed herein are methods and systems for producing LNG from MCSG that offer several advantages over the prior art discussed above. The methods and systems can use a single distillation column (instead of two or more columns). A coiled heat exchanger unit can be used that is separate from the heat exchanger unit used to recover refrigeration from the residue gas stream, and that can receive, cool, and partially liquefy a portion of the MCSG feed stream, and / or that can receive and cool a refrigerant (such as a mixed refrigerant or other vaporizable refrigerant) that is then used to cool and partially liquefy the MCSG feed stream. The residue gas portion can be discharged at substantially the same pressure as the MCSG feed stream, with relatively little or no recompression required.

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

[0011] Aspect 1: A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the method comprising: (a) cooling and partially liquefying an MCSG feed stream to produce a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams using a first phase separator and a second phase separator arranged in series, the second phase separator being in downstream flow communication with the first phase separator, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; (c) introducing the first feed stream into a distillation column at a first location; (d) introducing the second feed stream into the distillation column at a second location above the first location, wherein there is at least one separation stage between the first location and the second location; (e) removing an LNG stream from the distillation column comprising a distillation column bottoms; (f) removing a second residue gas stream from the distillation column comprising distillation column overhead vapor; A method comprising:

[0012] Aspect 2: Step (b) comprises: (i) separating the partially liquefied MCSG feed stream in the first phase separator into the liquid stream forming the first feed stream and a vapor stream; (ii) splitting the vapor stream from the first phase separator to form a vapor stream that forms the second feed stream and a vapor stream that forms a third feed stream; (iii) cooling and partially liquefying the third feed stream and then separating the third feed stream in the second phase separator into the vapor stream forming the first residue gas stream and a liquid stream forming a fourth feed stream; Including, step (c) comprises reducing the pressure of the first feed stream and then introducing the first feed stream into the distillation column at the first location; step (d) comprises reducing the pressure of the second feed stream and then introducing the second feed stream into the distillation column at the second location; 2. The method of claim 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 location above the second location, wherein there is at least one separation stage between the second location and the third location.

[0013] Aspect 3. The method of aspect 2, wherein the third location is at the top of the distillation column.

[0014] Aspect 4. The method of aspect 2 or 3, wherein one or both of the first and second residue gas streams are warmed via indirect heat exchange with a third feed stream to provide cooling capacity for the cooling and partial liquefaction of said third feed stream in step (b)(iii).

[0015] Aspect 5: Step (b) comprises: (i) separating the partially liquefied MCSG stream in the first phase separator into the vapor stream forming the first residue gas stream and a liquid stream forming a third feed stream; (ii) reducing the pressure of the third feed stream to partially vaporize the third feed stream and separate it in the second phase separator into the liquid stream forming the first feed stream and the vapor stream forming the second feed stream; Including, 2. The method of embodiment 1, wherein step (c) comprises warming the first feed stream and then introducing the first feed stream into a distillation column at the first location.

[0016] Aspect 6: The method of aspect 5, wherein there is at least one separation stage between the second location and the top of the column, the method further comprising compressing, cooling, and expanding the second residue gas stream or a 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 location at the top of the distillation column.

[0017] Aspect 7. The method of aspect 5 or 6, wherein in step (c), the first feed stream is warmed via indirect heat exchange with the MCSG feed stream to provide cooling capacity for the cooling and partial liquefaction of the MCSG feed stream in step (a).

[0018] Aspect 8. The method of any one of Aspects 1-7, wherein one or both of the first residue gas stream and the second residue gas stream are warmed via indirect heat exchange with the MCSG feed stream to provide cooling capacity for the cooling and partial liquefaction of the MCSG feed stream in step (a).

[0019] Aspect 9: The method of any one of aspects 1-8, wherein there is at least one separation stage between the first location and a bottom of the tower, and the method further comprises warming and thereby at least partially vaporizing a portion of the LNG stream or distillation tower bottoms liquid to form a boil-up stream, and introducing the boil-up stream into the distillation tower at a bottom of the distillation tower.

[0020] Embodiment 10. The method of any one of embodiments 1 to 9, wherein at least a portion of the second residual gas stream is compressed and combined with the first residual gas stream.

[0021]

[0023] Embodiment 11: The method of any one of embodiments 1-10, wherein the method further comprises subcooling the LNG stream.

[0022] Aspect 12: Step (a) comprises: (i) dividing the MCSG feedstream into at least two portions, including a first portion and a second portion; (ii) cooling and partially liquefying the first portion of the MCSG feed stream in a first heat exchanger unit or set of units via indirect heat exchange with a first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; (iii) cooling and partially liquefying the second portion of the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more process streams; (iv) combining the cooled, partially liquefied first portion with the cooled, 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 of 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 of aspect 12 or 13, wherein in step (a)(iii), the one or more process streams comprise one or more streams selected from the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or a distillation column bottoms liquid.

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

[0026] Aspect 16: The method of any one of aspects 12-15, wherein the method further comprises 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: The method of any one of Aspects 12-16, wherein step (a)(ii) comprises cooling and partially liquefying the first portion of the MCSG feed stream in a first heat exchanger unit or set of units via indirect heat exchange with one or more streams of cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coiled heat exchanger unit or set of units, and wherein the one or more streams of cooled first refrigerant are produced by also cooling the first refrigerant in the first heat exchanger unit or set of units.

[0028] Aspect 18: Step (a) comprises: (i) cooling a first refrigerant in a first heat exchanger unit or set of units to produce a cooled first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; (ii) cooling and partially liquefying the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more streams of the cooled first refrigerant and one or more process streams to form the partially liquefied MCSG feed stream; The method according to any one of aspects 1 to 11, comprising:

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

[0030] Aspect 20: The method of aspect 18 or 19, wherein in step (a)(ii), the one or more process streams comprise one or more of the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or a distillation column bottoms liquid.

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

[0032]

[0041] Aspect 22. The method of any one of aspects 18-21, wherein the method further comprises subcooling the LNG stream in the first heat exchanger unit or set of units.

[0033] Aspect 23: A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the method comprising: (a) (i) dividing the MCSG feedstream into at least two portions, including a first portion and a second portion; (ii) cooling and partially liquefying the first portion in a first heat exchanger unit or set of units via indirect heat exchange with a first refrigerant, the first heat exchanger unit or set of units being a coiled 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 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; cooling and partially liquefying the MCSG feed stream by producing a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into an LNG stream and one or more residue gas streams; A method comprising:

[0034] Aspect 24. The method of aspect 23, wherein in step (b), the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residue gas streams using one or more phase separators and / or one or more distillation columns.

[0035] Example 25: The method of example 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] Aspect 26. The method of any one of aspects 23 to 25, wherein in step (a)(iii), the one or more process streams comprise one or more streams selected from one or more of the residue gas stream, a portion of the LNG stream, or a portion of a distillation column bottoms.

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

[0038] Aspect 28: The method of any one of aspects 23 to 27, wherein the method further comprises subcooling the LNG stream in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant.

[0039] Aspect 29: The method of any one of Aspects 23-28, wherein step (a)(ii) comprises cooling and partially liquefying the first portion of the MCSG feed stream in a first heat exchanger unit or set of units via indirect heat exchange with one or more streams of cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coiled heat exchanger unit or set of units, and wherein the one or more streams of cooled first refrigerant are produced by also cooling the first refrigerant in the first heat exchanger unit or set of units.

[0040] Aspect 30: A method for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the method comprising: (a) (i) cooling a first refrigerant in a first heat exchanger unit or set of units to produce a cooled first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; (ii) cooling and partially liquefying the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more streams of cooled first refrigerant and one or more process streams to form a partially liquefied MCSG feed stream; cooling and partially liquefying the MCSG feed stream by producing a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into an LNG stream and one or more residue gas streams; A method comprising:

[0041] Aspect 31. The method of aspect 30, wherein in step (b), the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residue gas streams using one or more phase separators and / or one or more distillation columns.

[0042] Aspect 32: The method of aspect 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] Aspect 33: The method of any one of aspects 30-32, wherein in step (a)(ii), the one or more process streams comprise one or more of the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or a distillation column bottoms liquid.

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

[0045] Embodiment 35: The method of any one of embodiments 30-34, wherein the method further comprises subcooling the LNG stream in the first heat exchanger unit or set of units.

[0046] Aspect 36: A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the system comprising: one or more heat exchanger units for receiving, cooling, and partially liquefying the MCSG feed stream to produce a partially liquefied MCSG feed stream; a first phase separator and a second phase separator in flow communication with the one or more heat exchanger units and arranged in series, the second phase separator in downstream flow communication with the first phase separator for separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; a distillation column having a first inlet at a first location for receiving said first feed stream and a second inlet at a second location for receiving said second feed stream, said second location being above said first location, and having at least one separation stage between said first location and said second location, an outlet at the bottom of said distillation column for removing an LNG stream formed from a distillation column bottoms liquid, and an outlet at the top of said distillation column for removing a second residue gas stream formed from a distillation column overhead vapor; Including, the system.

[0047] Aspect 37: A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the system comprising: a set of conduits for dividing the MCSG feed stream into at least two portions, including a first portion and a second portion; 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, the first heat exchanger unit or set of units being a coiled 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 via indirect heat exchange with one or more process streams; a set of conduits for receiving and combining the cooled, partially liquefied first portion and the cooled, partially liquefied second portion to form a partially liquefied MCSG feed stream; one or more phase separators and / or one or more distillation columns for receiving and separating the partially liquefied MCSG feed stream into an LNG stream and one or more residue gas streams; Including, the system.

[0048] Aspect 38: A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the system comprising: a first heat exchanger unit or set of units for cooling a first refrigerant to produce a cooled first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; a second heat exchanger unit or set of units for receiving one or more streams of the cooled first refrigerant from the first heat exchanger unit, for receiving one or more process streams, and for receiving an MCSG feed stream and cooling and partially liquefying the MCSG feed stream via indirect heat exchange between the one or more streams of the cooled first refrigerant and the one or more process streams to form a partially liquefied MCSG feed stream; one or more phase separators and / or one or more distillation columns for receiving and separating the partially liquefied MCSG feed stream into an LNG stream and one or more residue gas streams; Including, the system. [Brief description of the drawings]

[0049] [Figure 1] FIG. 1 is a schematic flow diagram illustrating a method and system for producing LNG from MCSG in accordance with one embodiment of the present invention.

[0050] [Figure 1A]FIG. 1A is a schematic flow diagram illustrating a refrigeration system suitable for use in the method and system of FIG.

[0051] [Diagram 2] FIG. 2 is a schematic flow diagram illustrating a method and system for producing LNG from MCSG in accordance with another embodiment of the present invention.

[0052] [Diagram 3] FIG. 3 is a schematic flow diagram illustrating a method and system for producing LNG from MCSG in accordance with another embodiment of the present invention.

[0053] [Figure 3A] FIG. 3A is a schematic flow diagram illustrating a refrigeration system suitable for use in the method and system of FIG.

[0054] [Figure 4] FIG. 4 is a schematic flow diagram illustrating a method and system for producing LNG from MCSG in accordance with another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Described herein are methods and systems for producing LNG from MCSG.

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

[0057] When letters are used herein to identify recited steps of a method (e.g., (a), (b), and (c)), these letters are used only to aid in referencing the method steps and are not intended to indicate a particular order in which the claimed steps are performed, unless and only to the extent that such order is specifically recited.

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

[0059] As used herein, the term "methane-containing syngas", also referred to herein as "MCSG", refers to a gas containing methane and components lighter than methane (i.e., components having a higher volatility and lower boiling point than methane), such as, in particular, hydrogen and / or carbon monoxide. The term as used herein includes gasification syngas product streams containing methane molecules and synthetic natural gas streams produced from methanation processes containing impurities such as hydrogen and carbon monoxide. In a preferred embodiment, the methane-containing syngas feed stream may contain 10-60 mol% methane, with the remaining content being a mixture of carbon monoxide and hydrogen, and optionally small amounts of carbon dioxide, water, and / or other impurities.

[0060] As used herein, the term residue gas refers to gas comprising primarily components lighter than methane that have been removed from the MCSG feed stream, in particular hydrogen and / or carbon monoxide. In a preferred embodiment, the residue gas stream may comprise less than 10 mol% methane, more preferably less than 2 mol% methane, with the remainder consisting or consisting essentially of components lighter than methane, such as, for example, a mixture of hydrogen and carbon monoxide, optionally with minor amounts of other components, such as nitrogen and / or argon.

[0061] The term "liquefied natural gas" or "LNG" as used herein refers to a liquefied gas stream comprising primarily methane, preferably comprising at least 85 mole%, more preferably at least 90 mole%, and most preferably at least about 95 mole% 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, higher boiling point), such as carbon dioxide or hydrocarbons heavier than methane (e.g., methane, propane, butane, pentane), and / or small amounts of components lighter 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 composed of devices such as packings or trays that increase the contact and thus the mass transfer between the upwardly ascending vapor and the downwardly flowing liquid flowing through the column. In this way, the concentration of the lighter (i.e., more volatile, lower boiling point) components increases in the ascending vapor that is collected as overhead vapor at the top of the column, and the concentration of the heavier (i.e., less volatile, higher boiling point) components increases in the descending liquid that is collected as bottoms at the bottom of the column. The "top" of a distillation column refers to the portion of the column at or above the uppermost separation stage. The "bottom" of the column refers to the portion of the column 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., between two separation stages.

[0063] As used herein, the term "phase separator" refers to a drum or other form of vessel into which a two-phase stream may be introduced in order to separate the stream into its constituent vapor and liquid phases, with the liquid and vapor streams exiting the vessel being in equilibrium. In contrast to a distillation column (where the liquid and vapor streams exiting the column are not in equilibrium), a phase separator does not contain any separation stages (i.e., packing or trays) within the vessel to contact the upwardly rising vapor and downwardly flowing liquid.

[0064] As used herein, the term "flow communication" refers to a property of connectivity between two or more components that allows liquids, vapors, and / or two-phase mixtures to be transported between the components in a controlled manner (i.e., without leakage), either directly or indirectly. Coupling two or more components so that they are in flow communication with each other can include any suitable method known in the art, such as the use of welding, flanged conduits, gaskets, and bolts. Two or more components can also be coupled together through other components of the system that can separate them, for example, through valves, gates, or other devices that can selectively restrict or direct the flow of fluids.

[0065] As used herein, a second device or component is in "downstream" flow communication 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 the exchange of heat between two fluids, where the two fluids 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 that includes one or more tube bundles encased in a shell casing. Each tube bundle includes a plurality of tubes, the interior of the tubes defining one or more flow paths (also referred to as tube circuits) for passing one or more fluid streams through the heat exchanger unit, referred to herein 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 passing fluid streams through the heat exchanger unit, and the space inside the shell casing and outside the tubes is referred to herein as the "shell side" of the heat exchanger unit. In this manner, fluid passing through the shell side of the heat exchanger can undergo indirect heat exchange with 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 streams through indirect heat exchange with a "cold" refrigerant, the cooling refrigerant almost always passes through the shell side of the heat exchanger since the shell side offers a much lower flow resistance and allows a much larger pressure drop than the tube side, making passing the cooling refrigerant through the shell side much more effective and efficient (the cooling refrigerant is typically a vaporizing or expanding fluid at a relatively low pressure). Coil-wound heat exchangers are a compact design of heat exchanger known for their robustness, safety, and heat transfer efficiency, and thus have the advantage of providing a very efficient level of heat exchange compared 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 streams of cooling refrigerant to provide cooling capacity in a coil-wound heat exchanger if mixing of the refrigerant streams is not permitted.

[0068] Various exemplary embodiments of the present invention will now be described, by way of example only, with reference to the figures.

[0069] Referring now to FIG. 1, there is shown a method and system for producing LNG from an MCSG in accordance with a first embodiment of the present invention.

[0070] For example, an MCSG feed stream 100, such as a synthesis gas stream 100 comprising 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 be first 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 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 components removal step in which LPG (liquefied petroleum gas) components, freezeable pentane, and heavier components are removed. Thus, although the flow rate and composition of the MCSG feed stream 111 exiting the pretreatment section 105 may be significantly different from the flow rate and composition of the MCSG feed stream 100 entering said pretreatment section 105, the MCSG feed stream still comprises methane and components lighter than methane, in particular hydrogen and carbon monoxide.

[0071] The MCSG feed stream 111 leaving the pretreatment section 105 is then split into two streams, a first stream 113 and a second stream 115. The first stream 113, preferably comprising a minor portion of the MCSG feed stream 111, for example 10-40 percent, more preferably 20-30 percent of the MCSG feed stream 111 stream, is sent to a first exchanger unit or set of units 114. The second stream 115, comprising the remainder of the MCSG feed stream 111 stream, and thus preferably the majority of said stream, is sent to a second heat exchanger unit or set of units 116. The second heat exchanger unit or set of units 116 may, for example, comprise a plate-fin heat exchanger unit or a plurality of plate-fin heat exchanger units arranged in parallel. First stream 113 and second stream 115 are cooled and partially liquefied in first heat exchanger unit 114 and second heat exchanger unit 116, respectively, to form first cooled and partially liquefied stream 120 and second cooled and partially liquefied stream 117, respectively, each at a temperature between −130° C. and −160° C., more preferably between −140° C. and −150° C. The first and second cooled and partially liquefied streams 120, 117 are then combined (the pressure of second cooled and partially liquefied stream 117 is initially adjusted as necessary, e.g., via pressure regulator valve 117A, to control the flow of said stream 117) to form partially liquefied MCSG feed stream 130 that is separated using first phase separator 140 and second phase separator 135 arranged in series, the second phase separator being in downstream flow communication with the first phase separator.

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

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

[0074] The first and fourth feed streams 152, 150 are reduced in pressure, for example, by passing stream 152 through JT valve 152A and stream 150 through JT valve 150A, after which each of the streams becomes two-phase. The second feed stream 143 is reduced in pressure, for example, by expanding the stream in expander 179, after which the second feed stream 151 can become vapor or two-phase. The expansion work from expander 179 can be recovered, for example, by coupling the expander to a compressor that compresses the feed gas or residue gas, or can be recovered, for example, in a generator. The first feed stream 152, the second feed stream 151, and the fourth feed stream 150 are then each introduced into a different location of the distillation column 145, as further described below, which 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 location above one or more separation stages of the column represented in Figure 1 by column section 145C and below one or more separation stages of the column represented in Figure 1 by column section 145B. A second feed stream 151 is introduced into the distillation column at a second location above one or more separation stages of the column represented in Figure 1 by column section 145B and below one or more separation stages of the column represented in Figure 1 by column section 145A. A fourth feed stream 150 is introduced into the distillation column at a third location at the top of the column, above one or more separation stages of the column represented by column section 145A, thereby providing a source of reflux for the column.

[0076] Reboiler capacity for distillation column 145 is provided by warming and thereby at least partially vaporizing a stream of distillation column bottoms 153 in a second heat exchanger unit or set of units 116 via indirect heat exchange with a second stream 115 (obtained from splitting the MCSG feed stream), thereby forming a boil-up stream 154 (formed from said partially vaporized distillation column bottoms) that is reintroduced into the bottom of the distillation column.

[0077] LNG stream 180 formed from the distillation column bottoms is removed from the bottom of distillation column 145 at a temperature between -130°C and -160°C, more preferably between -140°C and -150°C, preferably increased in pressure with pump 181, sent (as stream 183) to and passed through the first heat exchanger unit or set of units 114 to be subcooled to form subcooled LNG product stream 187 which can be stored onsite in an LNG storage vessel or directly transported offsite (e.g. via a pipeline or transport vessel). LNG streams 180, 187 typically contain 1 mole % or less nitrogen, preferably less than 0.5 mole % nitrogen, and also preferably have a carbon monoxide content of 10 ppm or less. The percentage of methane recovered in LNG streams 180, 187 from the MCSG feed stream 111 may be greater than 95%.

[0078] A second residue gas stream 160 formed by the distillation column overhead vapor is removed from the top of distillation column 145 at a temperature between −170° C. and −200° C., more preferably between −180° C. and −190° C., and typically contains greater than 95 mole %, preferably greater than 98 mole %, of hydrogen and carbon monoxide.

[0079] The first residual gas stream 137 and the second residual gas stream 160 each pass through a third heat exchange unit or set of units 131 via indirect heat exchange with a third feed stream 142 and are warmed, and then each (see streams 138 and 161) passes through a second heat exchanger unit or set of units 116 via indirect heat exchange with a second stream 115 obtained from splitting the MCSG feed stream and are further warmed (or, in an alternative embodiment where the third heat exchanger unit is combined with the second heat exchanger unit, the first residual gas stream 137 and the second residual gas stream 160 are warmed in a cooler section of the combined unit and then further warmed in a warmer section of the combined unit). The resulting warmed second residue gas stream 162 is then compressed and cooled in compressor 163 and aftercooler 165 before being mixed with the resulting warmed first residue gas stream 139 to form a combined residue gas stream 173. Residual gas stream 173 can be used as fuel for the plant or sent to downstream units for further purification, separation, and / or chemical synthesis. Optionally, some or all of stream 139 can be purified to make hydrogen product and can be combined with residue gas stream 170.

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

[0081] As shown in FIG. 1A, the coiled heat exchanger unit 114 includes a warm section including a warm tube bundle 114A and a cold section including a cold tube bundle 114B (the terms warm and cold are relative). A first stream 113 resulting from the split of the MCSG feed stream passes through the warm tube bundle 114A and is cooled and partially liquefied to form a first cooled, partially liquefied stream 120. LNG vapor 183 passes through the cold tube bundle 114B and is subcooled to form a subcooled LNG product stream 187. Cooling capacity is provided to the warm and cold tube bundles of the coiled heat exchanger unit by vaporizing the mixed refrigerant passing through the shell side of the heat exchanger unit. The SMR cycle shown in FIG. 1A used to supply the vaporized cold mixed refrigerant to the shell side of the heat exchanger unit is well known in the art and will only be generally described herein for brevity. Very simply, the warmed vaporized mixed refrigerant removed from the shell side at the bottom of the heat exchanger unit is compressed, cooled, and separated in a compression train including one or more compressor stages 115A, 115B, an aftercooler, and a phase separator into one or more MRL (mixed refrigerant liquid) streams (two shown in the figure) and one or more MRV (mixed refrigerant vapor) streams (one shown in the figure). The MRL streams are cooled through a hot tube bundle, expanded through a JT valve, combined, and introduced into the shell side of the heat exchanger unit at the top of the hot tube bundle to provide vaporized refrigerant that flows down through the shell side around the tubes of the hot tube bundle. The MRV streams are cooled through a cold and hot tube bundle, at least partially liquefied, expanded through a JT valve, and introduced into the shell side of the heat exchanger unit at the top of the cold tube bundle to provide vaporized refrigerant that flows down through the shell side around the tubes of the cold and hot tube bundle.

[0082] The method and system of FIG. 1 produces a high purity methane-rich LNG product with high methane recovery. Because it requires a single distillation column and recompression of only a portion of the produced residual gas (i.e., only the residual gas contained in the second residual gas stream), the capital and operating costs of the system are reduced, as well as the footprint, 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 the use of coil-wound heat exchanger units, thereby also taking advantage of the advantages offered by such units in terms of their compact design, robustness, safety, and heat transfer efficiency, further reducing the footprint and improving the efficiency of the system and process. Also, the use of a two-phase refrigerant in the second and third heat exchanger units, which can be, for example, plate-fin exchanger units as discussed, can be avoided, thereby avoiding operational difficulties that may arise from the use of such refrigerants in such types of heat exchangers.

[0083] Figure 2 illustrates a method and system for producing LNG from MCSG in accordance with a second embodiment of the present invention. The embodiment illustrated in Figure 2 differs from that illustrated in Figure 1 with respect to the manner in which the partially liquefied MCSG feed stream is separated by the first and second phase separators and the manner in which reflux is provided to the distillation column.

[0084] For example, an MCSG feed stream 200, such as a synthesis gas stream 200 comprising 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 be first sent to a pretreatment system 205. Depending on the composition of the MCSG feed stream, the pretreatment system may include an acid 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 in which LPG (liquefied petroleum gas) components, freezeable pentane, and heavier components are removed. Thus, although the flow rate and composition of the MCSG feed stream 211 exiting the pretreatment section 205 may be significantly different from the flow rate and composition of the MCSG feed stream 200 entering said pretreatment section 205, the MCSG feed stream still includes methane and components lighter than methane, in particular hydrogen and carbon monoxide.

[0085] The MCSG feed stream 211 leaving the pretreatment section 205 is then split into two streams, a first stream 213 and a second stream 215. The first stream 213, preferably comprising a minor portion of the MCSG feed stream 211, for example 10-40 percent, more preferably 20-30 percent of the MCSG feed stream 211 stream, is sent to a first exchanger unit or set of units 214. The second stream 215, comprising the remainder of the MCSG feed stream 211 stream, and thus preferably comprising the majority of said stream, is sent to a second heat exchanger unit or set of units 216. The second heat exchanger unit or set of units 216 may, for example, comprise a plate-fin heat exchanger unit or a plurality of plate-fin heat exchanger units arranged in parallel. First stream 213 and second stream 215 are cooled and partially liquefied in first heat exchanger unit 214 and second heat exchanger unit 216, respectively, to form first cooled, partially liquefied stream 220 and second cooled, partially liquefied stream 217, each at a temperature between −120° C. and −150° C., more preferably between −130° C. and −140° C. The first and second cooled, partially liquefied streams 220, 217 are then combined (the pressure of second cooled, partially liquefied stream 217 is initially adjusted as necessary, e.g., via valve 217A, to control the flow of stream 217) to form partially liquefied MCSG feed stream 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 between −155° C. and −185° C., and more preferably between −165° C. and −175° C. The third heat exchanger unit or set of units 231 may include, for example, a plate fin exchanger unit or multiple 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 into a single unit or set of parallel units, with stream 215 being cooled in a warmer section of the unit and stream 230 being cooled in a cooler section of the unit.

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

[0088] The first feed stream 242, whose flow is controlled by valve 242A to control the liquid level in the second phase separator 240, passes through a third heat exchanger unit or set of units 231 and is warmed via indirect heat exchange with the partially liquefied MCSG feed stream 230, after which the stream 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 stream 242 is warmed in the cooler section of the combined unit). The first feed stream 252 and the second feed stream 251 are then each introduced into different positions of a distillation column 245, as further described below, which operates at a pressure of 3.0 to 7.0 bara, more preferably 4.5 to 5.5 bara.

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

[0090] Reboiler capacity for distillation column 245 is provided by warming and thereby at least partially vaporizing a stream of distillation column bottoms 253 in a second heat exchanger unit or set of units 116 via indirect heat exchange with a second stream 215 (obtained from splitting the MCSG feed stream), thereby forming a boil-up stream 254 (formed from said partially vaporized distillation column bottoms) that is reintroduced into the bottom of the distillation column.

[0091] LNG stream 280 formed from the distillation column bottoms is removed from the bottom of distillation column 245 at a temperature between −125° C. and −155° C., more preferably −135° C. and −145° C., preferably increased in pressure with pump 181, sent (as stream 283) and passed through a first heat exchanger unit or set of units 214 to be subcooled to form a subcooled LNG product stream 287 which can be stored onsite in an LNG storage vessel or directly transported offsite (e.g., via a pipeline or transport vessel). LNG streams 280, 287 typically contain 1 mol % or less nitrogen, preferably less than 0.5 mol % nitrogen, and also preferably have a carbon monoxide content of 10 ppm or less. The percentage of methane recovered in LNG streams 280, 287 from MCSG feed stream 211 may be greater than 95%.

[0092] A second residue gas stream 260 formed by the distillation column overhead vapor is removed from the top of distillation column 245 at a temperature between −160° C. and −190° C., more preferably between −170° C. and −180° C., and typically contains greater than 95 mole %, preferably greater than 98 mole %, of hydrogen and carbon monoxide.

[0093] The first residual gas stream 237 and the second residual gas stream 260 each pass through the third heat exchange unit or set of units 231 and are warmed, and then each (see streams 238 and 261) passes through the second heat exchanger unit or set of units 216 and is further warmed there, resulting in a warmed first residual gas stream 239 and a warmed second residual gas stream 262 (or, in an alternative embodiment where the third heat exchanger unit is combined with the second heat exchanger unit, the first residual gas stream 237 and the second residual gas stream 260 are warmed in a cooler section of the combined unit and then further warmed in a warmer section of the combined unit). The warmed second residue gas stream 262 is then compressed and cooled in compressor 263 and aftercooler 265 to form a compressed second residue gas stream 270 which is then split into two portions 271 , 275 .

[0094] A first portion 271 of the compressed second residue gas stream, preferably consisting of a minor portion of the compressed second residue gas stream 270, for example consisting of 10% to 30%, more preferably 15% to 25% of the flow of that stream, is mixed with the warmed first residue gas stream 239 to form a combined residue gas stream 273. The residue gas stream 273 can be used as fuel for the plant or can be sent to downstream units for further purification, separation, and / or chemical synthesis. Optionally, some or all of stream 239 can be purified to make hydrogen products and can be combined with the residue gas stream 271.

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

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

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

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

[0099] The embodiment shown in FIG. 3 differs from that shown in FIG. 1 with respect to the manner in which the MCSG feed stream is cooled to form a partially liquefied MCSG feed stream and with respect to the manner in which a first heat exchanger unit or set of units is used to supply refrigerant and thereby 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 exiting pre-treatment section 305 is sent to and passes through a second heat exchanger unit or set of units 316 where it is cooled and partially liquefied to form a partially liquefied MCSG feed stream 330 at a temperature between -130°C and -160°C, more preferably between -140°C and -150°C, and then separated using first phase separator 340 and 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 multiple plate fin heat exchanger units arranged in parallel.

[0101] The first heat exchanger unit or set of units 314 is not used to receive and cool any portion of the MCSG feed stream. Instead, in the arrangement shown in FIG. 3, the first heat exchanger unit or set of units 314 is used to cool a first refrigerant to produce a stream of cooled first refrigerant 390, which is The resulting stream of first refrigerant 392 exiting the third heat exchanger unit or set of units 331 is then passed through the second heat exchanger unit or set of units 316 and is further warmed through indirect heat exchange with the MCSG feed stream 311, thereby providing additional refrigeration (together with the first residue gas stream 338, the second residue gas stream 361, and the distillation column bottoms stream 353) to the unit. The resulting warmed stream of 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 a third heat exchanger unit is combined with a second heat exchanger unit, the cooled first refrigerant 390 stream is instead warmed in a colder section of the combined unit and then further warmed in a warmer section of the combined unit.

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

[0103] As shown in Figure 3A, the coiled heat exchanger unit 314 includes a warm section including a warm tube bundle 314A and a cold section including a cold tube bundle 314B (the terms "warm" and "cold" are relative). LNG vapor 383 passes through the cold tube bundle 114B and is subcooled to form a subcooled LNG product stream 387. Cooling power is provided to the warm and cold tube bundles of the coiled heat exchanger unit by a cooled first refrigerant which passes through the shell side of the heat exchanger unit, warms and vaporizes. The SMR cycle shown in Figure 3A used to cool the first refrigerant is well known in the art and will be only broadly described herein for brevity. Very simply, the warmed vaporized first refrigerant removed from the bottom shell side of the heat exchanger unit is combined with a warmed vaporized first refrigerant 395 stream (returning from the first heat exchanger unit or set of units 314) and compressed, cooled, and separated in a compression train including one or more compressors, aftercoolers, and phase separators into one or more MRL (mixed refrigerant liquid) streams (two shown in the figure) and one or more MRV (mixed refrigerant vapor) streams (one shown in the figure). The MRL streams are passed through a warm tube bundle where they are cooled, expanded through a JT valve, and combined and introduced into the shell side of the heat exchanger unit at the top of the warm tube bundle to provide a vaporized first refrigerant that flows down through the shell side around the tubes of the warm tube bundle.

[0104] The MRV stream passes through the hot and cold tube bundles where it is cooled and at least partially liquefied to form a cooled first refrigerant stream which is removed from the top of the cold tube bundle, expanded and split to form a cooled first refrigerant stream 390 (which is warmed, 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 cooled first refrigerant stream which is introduced into the shell side of the first heat exchanger unit 314 at the top of the cold tube bundle to provide a vaporizing first refrigerant that flows downward through the shell side around the tubes of the hot and cold tube bundles. The cooled first refrigerant stream removed from the top of the cold tube bundle can be expanded, for example, by passing it through a JT valve and then split to form a cooled first refrigerant stream 390 and a cooled first refrigerant stream that is 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 stream removed from the top of the cold tube bundle can first be split and then the resulting split streams can be expanded separately (e.g., using separate JT valves).

[0105] The method and system of Figure 3 have similar advantages and benefits as the method and system of Figure 1 described above. In comparison to the embodiment shown in Figure 1, the embodiment shown in Figure 3 avoids these needs to split and distribute the MCSG feed stream 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] FIG. 4 illustrates a method and system for producing LNG from MCSG according to a fourth embodiment of the present invention. In FIG. 4, features shared with the second embodiment illustrated in FIG. 2 are assigned the same reference numbers, increased by a factor of 200. Thus, for example, partially liquefied MCSG feed stream 430 in FIG. 4 corresponds to partially liquefied MCSG feed stream 230 in FIG. 2, and distillation column 445 in FIG. 4 corresponds to distillation column 445 in FIG. 1. Unless a feature in FIG. 4 is specifically described as being different from the corresponding feature in FIG. 2, that feature can be assumed to have the same structure and function as the corresponding feature in FIG. 2 described above. Moreover, if that feature does not have a different structure or function, it may not be specifically mentioned in the further description of FIG. 4 below.

[0107] The embodiment shown in FIG. 4 differs from that shown in FIG. 1 with respect to the manner in which the MCSG feed stream is cooled to form a partially liquefied MCSG feed stream and with respect to the manner 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 and thereby additional refrigerant to the 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 exiting pre-treatment section 405 is sent to and passes through a second heat exchanger unit or set of units 416 where it is cooled and partially liquefied to form a partially liquefied MCSG feed stream 430 at a temperature between -120°C and -150°C, more preferably between -130°C and -140°C, and then separated using first phase separator 435 and 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 multiple plate fin heat exchanger units arranged in parallel.

[0109] The first heat exchanger unit or set of units 414 is not used to receive and cool any portion of the MCSG feed stream. Instead, in the arrangement shown in FIG. 4, the first heat exchanger unit or set of units 414 is used to cool a first refrigerant to produce a stream of cooled first refrigerant 490, which is The resulting stream of first refrigerant 492 exiting the third heat exchanger unit or set of units 431 is then passed through the second heat exchanger unit or set of units 416 where it is further warmed through indirect heat exchange with the MCSG feed stream 411, thereby providing additional refrigeration to the unit (along with the first residue gas stream 438, the second residue gas stream 461, and the distillation column bottoms liquid stream 453). The resulting warmed stream of 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 a third heat exchanger unit is combined with a second heat exchanger unit, the cooled first refrigerant 490 stream is instead warmed in a colder section of the combined unit and then further warmed in a warmer section of the combined unit.

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

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

[0112] Example 1 In this example, 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 flow data from the simulation. In this example, the residue gas compressor 163 has four stages with approximately 61.8 MW break horsepower, the mixed refrigerant compressors 115A and 115B have approximately 30.3 MW break horsepower, the expander 179 extracts 10.5 MW of work, and the process has a methane recovery of 95%. Table 1: Thermal and material balance [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 balance [Table 2]

[0114] The method and system of this example allows for very high product recovery using a heat pump (expander 279), which produces a high purity reflux with very low methane content, improving the methane recovery of the process compared to the process of Example 1. However, the process of Example 1 has a better specific power output compared to the process of Example 2, 848.5 kW-hr / ton vs. 922.6 kW-hr / ton.

[0115] It will be understood that the invention is not limited to the details set forth above in relation to the preferred embodiments, but that numerous modifications and variations may be made without departing from the spirit or scope of the invention as defined in the following claims. The present invention can be embodied in the following manner. (Appendix 1) 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) cooling and partially liquefying an MCSG feed stream to produce a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams using a first phase separator and a second phase separator arranged in series, the second phase separator being in downstream flow communication with the first phase separator, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; (c) introducing the first feed stream into a distillation column at a first location; (d) introducing the second feed stream into the distillation column at a second location above the first location, wherein there is at least one separation stage between the first location and the second location; (e) removing an LNG stream from the distillation column formed of distillation column bottoms; (f) removing a second residue gas stream from the distillation column formed with distillation column overhead vapor; A method comprising: (Appendix 2) Step (b) (i) separating the partially liquefied MCSG feed stream in the first phase separator into the liquid stream forming the first feed stream and a vapor stream; (ii) splitting the vapor stream from the first phase separator to form a vapor stream that forms the second feed stream and a vapor stream that forms a third feed stream; (iii) cooling and partially liquefying the third feed stream and then separating the third feed stream in the second phase separator into the vapor stream forming the first residue gas stream and a liquid stream forming a fourth feed stream; Including, step (c) comprises reducing the pressure of the first feed stream and then introducing the first feed stream into the distillation column at the first location; step (d) comprises reducing the pressure of the second feed stream and then introducing the second feed stream into the distillation column at the second location; 2. The method of claim 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 location above the second location, wherein there is at least one separation stage between the second location and the third location. (Appendix 3) 3. The method of claim 2, wherein the third location is at the top of the distillation column. (Appendix 4) 3. The method of claim 2, wherein one or both of the first and second residue gas streams are warmed via indirect heat exchange with the third feed stream to provide a cooling duty for the cooling and partial liquefaction of the third feed stream in step (b)(iii). (Appendix 5) Step (b) (i) separating the partially liquefied MCSG stream in the first phase separator into the vapor stream forming the first residue gas stream and a liquid stream forming a third feed stream; (ii) reducing the pressure of the third feed stream to partially vaporize the third feed stream and separate said stream in the second phase separator into the liquid stream forming the first feed stream and the vapor stream forming the second feed stream; Including, 2. The method of claim 1, wherein step (c) comprises warming the first feed stream and then introducing the first feed stream into a distillation column at the first location. (Appendix 6) 6. The method of claim 5, wherein there is at least one separation stage between the second location and the top of the column, the method further comprising compressing, cooling, and expanding, thereby at least partially liquefying, a portion of the second residue gas stream or distillation column overhead vapor to form a reflux stream, and introducing the reflux stream into the distillation column at a third location at the top of the distillation column. (Appendix 7) 6. The method of claim 5, wherein in step (c), the first feed stream is warmed via indirect heat exchange with the MCSG feed stream to provide cooling capacity for the cooling and partial liquefaction of the MCSG feed stream in step (a). (Appendix 8) 2. The method of claim 1, wherein one or both of the first residue gas stream and the second residue gas stream are warmed via indirect heat exchange with the MCSG feed stream to provide cooling capacity for the cooling and partial liquefaction of the MCSG feed stream in step (a). (Appendix 9) 2. The method of claim 1, wherein there is at least one separation stage between the first location and a bottom of the column, the method further comprising warming and thereby at least partially vaporizing a portion of the LNG stream or distillation column bottoms liquid to form a boiling stream and introducing the boiling stream into the distillation column at the bottom of the distillation column. (Appendix 10) 2. The method of claim 1, wherein at least a portion of the second residue gas stream is compressed and combined with the first residue gas stream. (Appendix 11) 2. The method of claim 1, further comprising subcooling the LNG stream. (Appendix 12) Step (a) (i) dividing the MCSG feed stream into at least two portions, including a first portion and a second portion; (ii) cooling and partially liquefying the first portion of the MCSG feed stream in a first heat exchanger unit or set of units via indirect heat exchange with a first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; (iii) cooling and partially liquefying the second portion of the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more process streams; (iv) combining the cooled, partially liquefied first portion of the MCSG feed stream with the cooled, partially liquefied second portion of the MCSG feed stream to form the partially liquefied MCSG feed stream; The method of claim 1, comprising: (Appendix 13) 13. The method of claim 12, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. (Appendix 14) 13. The method of claim 12, wherein in step (a)(iii), the one or more process streams comprise one or more streams selected from the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or a distillation column bottoms liquid. (Appendix 15) 13. The method of claim 12, wherein the first refrigerant is a refrigerant that vaporizes when warmed in the first heat exchanger unit or set of units. (Appendix 16) 13. The method of claim 12, further comprising subcooling the LNG stream in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant. (Appendix 17) 13. The method of claim 12, wherein step (a)(ii) comprises 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 coiled heat exchanger unit or set of units, and the one or more streams of cooled first refrigerant are also produced by cooling the first refrigerant in the first heat exchanger unit or set of units. (Appendix 18) Step (a) (i) cooling a first refrigerant in a first heat exchanger unit or set of units to produce a cooled first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; (ii) cooling and partially liquefying the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more streams of the cooled first refrigerant and one or more process streams to form the partially liquefied MCSG feed stream; The method of claim 1, comprising: (Appendix 19) 19. The method of claim 18, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. (Appendix 20) 19. The method of claim 18, wherein in step (a)(ii), the one or more process streams comprise one or more of the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or a distillation column bottoms liquid. (Appendix 21) 19. The method of claim 18, wherein in step (a)(i), the first refrigerant is cooled in the first heat exchanger unit or set of units via indirect heat exchange with a portion of the cooled first refrigerant produced in step (a)(i). (Appendix 22) 19. The method of claim 18, further comprising subcooling the LNG stream in the first heat exchanger unit or set of units. (Appendix 23) 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) (i) dividing an MCSG feed stream into at least two portions, including a first portion and a second portion; (ii) cooling and partially liquefying the first portion in a first heat exchanger unit or set of units via indirect heat exchange with a first refrigerant, the first heat exchanger unit or set of units being a coiled 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 via indirect heat exchange with one or more process streams; (iv) combining the cooled, partially liquefied first portion with the cooled, partially liquefied second portion to form the partially liquefied MCSG feed stream; cooling and partially liquefying the MCSG feed stream by producing a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into an LNG stream and one or more residue gas streams; A method comprising: (Appendix 24) 24. The method of claim 23, wherein in step (b), the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residue gas streams using one or more phase separators and / or one or more distillation columns. (Appendix 25) 24. The method of claim 23, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. (Appendix 26) 24. The method of claim 23, wherein in step (a)(iii), the one or more process streams comprise one or more streams selected from one or more of the residue gas stream, a portion of the LNG stream, or a portion of a distillation column bottoms liquid. (Appendix 27) 24. The method of claim 23, wherein the first refrigerant is a refrigerant that vaporizes when warmed in the first heat exchanger unit or set of units. (Appendix 28) 24. The method of claim 23, further comprising subcooling the LNG stream in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant. (Appendix 29) 24. The method of claim 23, wherein step (a)(ii) comprises 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 coiled heat exchanger unit or set of units, and the one or more streams of cooled first refrigerant are also produced by cooling the first refrigerant in the first heat exchanger unit or set of units. (Appendix 30) 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) (i) cooling a first refrigerant in a first heat exchanger unit or set of units to produce a cooled first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; (ii) cooling and partially liquefying the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more streams of the cooled first refrigerant and one or more process streams to form a partially liquefied MCSG feed stream; cooling and partially liquefying the MCSG feed stream by producing the partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into an LNG stream and one or more residue gas streams; A method comprising: (Appendix 31) 31. The method of claim 30, wherein in step (b), the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residue gas streams using one or more phase separators and / or one or more distillation columns. (Appendix 32) 31. The method of claim 30, wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. (Appendix 33) 31. The method of claim 30, wherein in step (a)(ii), the one or more process streams comprise one or more of the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or a distillation column bottoms liquid. (Appendix 34) 31. The method of claim 30, wherein in step (a)(i), the first refrigerant is cooled in the first heat exchanger unit or set of units via indirect heat exchange with a portion of the cooled first refrigerant produced in step (a)(i). (Appendix 35) 31. The method of claim 30, further comprising subcooling the LNG stream in the first heat exchanger unit or set of units. (Appendix 36) 1. A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the system comprising: one or more heat exchanger units for receiving, cooling, and partially liquefying the MCSG feed stream to produce a partially liquefied MCSG feed stream; a first phase separator and a second phase separator in flow communication with the one or more heat exchanger units and arranged in series, the second phase separator in downstream flow communication with the first phase separator for separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; a distillation column having a first inlet at a first location for receiving said first feed stream, a second inlet at a second location for receiving said second feed stream, said second location being above said first location, at least one separation stage between said first location and said second location, an outlet at the bottom of said distillation column for removing an LNG stream formed from a distillation column bottoms liquid, and an outlet at the top of said distillation column for removing a second residue gas stream formed from a distillation column overhead vapor; Including, the system. (Appendix 37) 1. A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the system comprising: a set of conduits for dividing the MCSG feed stream into at least two portions, including a first portion and a second portion; 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, the first heat exchanger unit or set of units being a coiled 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 via indirect heat exchange with one or more process streams; a set of conduits for receiving and combining the cooled, partially liquefied first portion and the cooled, partially liquefied second portion to form a partially liquefied MCSG feed stream; one or more phase separators and / or one or more distillation columns for receiving and separating the partially liquefied MCSG feed stream into an LNG stream and one or more residue gas streams; Including, the system. (Appendix 38) 1. A system for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the system comprising: a first heat exchanger unit or set of units for cooling a first refrigerant to produce a cooled first refrigerant, said first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; a second heat exchanger unit or set of units for receiving one or more streams of the cooled first refrigerant from the first heat exchanger unit, for receiving one or more process streams, and for receiving an MCSG feed stream and cooling and partially liquefying the MCSG feed stream via indirect heat exchange with the one or more streams of the cooled first refrigerant and the one or more process streams to form a partially liquefied MCSG feed stream; one or more phase separators and / or one or more distillation columns for receiving and separating the partially liquefied MCSG feed stream into an LNG stream and one or more residue gas streams; Including, the system.

Claims

1. 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) cooling and partially liquefying an MCSG feed stream to produce a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams using a first phase separator and a second phase separator arranged in series, the second phase separator being in downstream flow communication with the first phase separator, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; (c) introducing the first feed stream into a distillation column at a first location; (d) introducing the second feed stream into the distillation column at a second location above the first location, wherein there is at least one separation stage between the first location and the second location; (e) removing an LNG stream from the distillation column formed of distillation column bottoms; (f) removing a second residue gas stream from the distillation column formed of distillation column overhead vapor; Including, Step (b) (i) separating the partially liquefied MCSG feed stream in the first phase separator into the liquid stream forming the first feed stream and a vapor stream; (ii) splitting the vapor stream from the first phase separator to form a vapor stream that forms the second feed stream and a vapor stream that forms a third feed stream; (iii) cooling and partially liquefying said third feed stream and then separating said third feed stream in said second phase separator into said vapor stream forming said first residue gas stream and a liquid stream forming a fourth feed stream; Including, step (c) comprises reducing the pressure of the first feed stream and then introducing the first feed stream into the distillation column at the first location; step (d) comprises 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 further comprising reducing the pressure of the fourth feed stream and then introducing the fourth feed stream into the distillation column at a third location above the second location, wherein there is at least one separation stage between the second location and the third location.

2. 2. The method of claim 1, wherein the third location is at the top of the distillation column.

3. 2. The method of claim 1, wherein one or both of the first and second residue gas streams are warmed via indirect heat exchange with the third feed stream to provide a cooling duty for the cooling and partial liquefaction of the third feed stream in step (b)(iii).

4. 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) cooling and partially liquefying an MCSG feed stream to produce a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams using a first phase separator and a second phase separator arranged in series, the second phase separator being in downstream flow communication with the first phase separator, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; (c) introducing the first feed stream into a distillation column at a first location; (d) introducing the second feed stream into the distillation column at a second location above the first location, wherein there is at least one separation stage between the first location and the second location; (e) removing an LNG stream from the distillation column formed of distillation column bottoms; (f) removing a second residue gas stream from the distillation column formed of distillation column overhead vapor; Including, Step (b) (i) separating the partially liquefied MCSG stream in the first phase separator into the vapor stream forming the first residue gas stream and a liquid stream forming a third feed stream; (ii) reducing the pressure of said third feed stream to partially vaporize said third feed stream and separate said stream in said second phase separator into said liquid stream forming said first feed stream and said vapor stream forming said second feed stream; Including, The method of claim 1, wherein step (c) comprises warming said first feed stream and then introducing said first feed stream into a distillation column at said first location.

5. 5. The method of claim 4, wherein there is at least one separation stage between said second location and the top of said column, said method further comprising compressing, cooling and expanding, thereby at least partially liquefying, a portion of said second residue gas stream or distillation column overhead vapor to form a reflux stream, and introducing said reflux stream into said distillation column at a third location at said top of said distillation column.

6. 5. The method of claim 4, wherein in step (c), the first feed stream is warmed via indirect heat exchange with the MCSG feed stream to provide cooling capacity for the cooling and partial liquefaction of the MCSG feed stream in step (a).

7. 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) cooling and partially liquefying an MCSG feed stream to produce a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams using a first phase separator and a second phase separator arranged in series, the second phase separator being in downstream flow communication with the first phase separator, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; (c) introducing the first feed stream into a distillation column at a first location; (d) introducing the second feed stream into the distillation column at a second location above the first location, wherein there is at least one separation stage between the first location and the second location; (e) removing an LNG stream from the distillation column formed of distillation column bottoms; (f) removing a second residue gas stream from the distillation column formed of distillation column overhead vapor; Including, There is at least one separation stage between the first location and a bottom of the column, the method further comprising warming and thereby at least partially vaporizing a portion of the LNG stream or distillation column bottoms liquid to form a boiling stream and introducing the boiling stream into the distillation column at the bottom of the distillation column.

8. 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) cooling and partially liquefying an MCSG feed stream to produce a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams using a first phase separator and a second phase separator arranged in series, the second phase separator being in downstream flow communication with the first phase separator, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; (c) introducing the first feed stream into a distillation column at a first location; (d) introducing the second feed stream into the distillation column at a second location above the first location, wherein there is at least one separation stage between the first location and the second location; (e) removing an LNG stream from the distillation column formed of distillation column bottoms; (f) removing a second residue gas stream from the distillation column formed of distillation column overhead vapor; Including, wherein at least a portion of the second residual gas stream is compressed and combined with the first residual gas stream.

9. 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) cooling and partially liquefying an MCSG feed stream to produce a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams using a first phase separator and a second phase separator arranged in series, the second phase separator being in downstream flow communication with the first phase separator, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; (c) introducing the first feed stream into a distillation column at a first location; (d) introducing the second feed stream into the distillation column at a second location above the first location, wherein there is at least one separation stage between the first location and the second location; (e) removing an LNG stream from the distillation column formed of distillation column bottoms; (f) removing a second residue gas stream from the distillation column formed of distillation column overhead vapor; Including, Step (a) (i) splitting the MCSG feed stream into at least two portions including a first portion and a second portion; (ii) cooling and partially liquefying the first portion of the MCSG feed stream in a first heat exchanger unit or set of units via indirect heat exchange with a first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; (iii) cooling and partially liquefying the second portion of the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more process streams; (iv) combining the cooled, partially liquefied first portion of the MCSG feed stream with the cooled, partially liquefied second portion of the MCSG feed stream to form the partially liquefied MCSG feed stream; A method comprising:

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

11. 10. The method of claim 9, wherein in step (a)(iii), the one or more process streams comprise one or more streams selected from the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or a distillation column bottoms liquid.

12. 10. The method of claim 9, wherein the first refrigerant is a refrigerant that vaporizes when warmed in the first heat exchanger unit or set of units.

13. 10. The method of claim 9, further comprising subcooling the LNG stream in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant.

14. 10. The method of claim 9, wherein step (a)(ii) comprises 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 a cooled first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units, and the one or more streams of cooled first refrigerant are also produced by cooling the first refrigerant in the first heat exchanger unit or set of units.

15. 1. A process for producing liquefied natural gas (LNG) from methane-containing synthesis gas (MCSG), the process comprising: (a) cooling and partially liquefying an MCSG feed stream to produce a partially liquefied MCSG feed stream; (b) separating the partially liquefied MCSG feed stream into at least three streams including a liquid stream and two vapor streams using a first phase separator and a second phase separator arranged in series, the second phase separator being in downstream flow communication with the first phase separator, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; (c) introducing the first feed stream into a distillation column at a first location; (d) introducing the second feed stream into the distillation column at a second location above the first location, wherein there is at least one separation stage between the first location and the second location; (e) removing an LNG stream from the distillation column formed of distillation column bottoms; (f) removing a second residue gas stream from the distillation column formed of distillation column overhead vapor; Including, Step (a) (i) cooling a first refrigerant in a first heat exchanger unit or set of units to produce a cooled first refrigerant, the first heat exchanger unit or set of units being a coiled heat exchanger unit or set of units; (ii) cooling and partially liquefying the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more streams of the cooled first refrigerant and one or more process streams to form the partially liquefied MCSG feed stream; A method comprising:

16. The method of claim 15 , wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units.

17. 16. The method of claim 15, wherein in step (a)(ii), the one or more process streams comprise one or more of the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or a distillation column bottoms liquid.

18. 16. The method of claim 15, wherein in step (a)(i), the first refrigerant is cooled in the first heat exchanger unit or set of units via indirect heat exchange with a portion of the cooled first refrigerant produced in step (a)(i).

19. The method of claim 15 , further comprising subcooling the LNG stream in the first heat exchanger unit or set of units.

20. 16. The method of any one of claims 1, 4, 7-9 and 15, wherein one or both of the first residue gas stream and the second residue gas stream are warmed via indirect heat exchange with the MCSG feed stream to provide cooling capacity for the cooling and partial liquefaction of the MCSG feed stream in step (a).

21. The method of any one of claims 1, 4, 7-9 and 15, wherein the method further comprises subcooling the LNG stream.

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