Open-loop liquefaction process by NGL recovery

Abstract

To provide an open loop liquefaction process with natural gas liquid (NGL) recovery.SOLUTION: Described herein are methods and systems for removing natural gas liquids from a natural gas feed stream and for liquefying the natural gas feed stream so as to produce a liquefied natural gas (LNG) stream and a natural gas liquid (NGL) stream.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method and a system for removing liquefied natural gas (NGL) from a natural gas feed stream and liquefying the natural gas feed stream to produce a liquefied natural gas (LNG) stream and a liquefied natural gas (NGL) stream.

Background Art

[0002] Before liquefying natural gas, it is often desirable to remove heavy hydrocarbons (also referred to herein as "HHC") such as C6+ hydrocarbons (hydrocarbons having 6 or more carbon atoms) and aromatic compounds (e.g., benzene, toluene, ethylbenzene, and xylene) from the natural gas to avoid freezing of these components in the heat exchangers used to liquefy the natural gas. C2-C5+ hydrocarbons (hydrocarbons having 2-5 or more carbon atoms), also referred to in the art as liquefied natural gas (or "NGL"), are also typically separated from natural gas because they have a relatively high market value.

[0003] Conventionally, removing NGL (and HHC) from a rich natural gas feed stream (a natural gas feed stream rich in these components) has involved the use of a stand-alone front-end NGL extraction operating at low to medium pressure. Additional equipment is then required to increase the feed pressure in order to efficiently liquefy the natural gas.

[0004] U.S. Patent Application No. US2018 / 0180354(A1) describes a method and system for liquefying natural gas in which the compressed refrigerant stream exiting the refrigerant compressor is split into first and second portions. The first portion of the compressed refrigerant is combined with the natural gas feed stream before the natural gas feed stream is pre-cooled in a pre-cooler, expanded in an expander, and introduced into a phase separator (or the upper part of a demethanizer column), where it is separated into vapor and liquid fractions. The vapor fraction is removed from the phase separator and heated in a first heat exchanger before being sent to the refrigerant compressor. The second portion of the refrigerant stream is cooled in a first heat exchanger section before being further split into third and fourth portions. The third portion is further cooled and liquefied in a second heat exchanger to provide the LNG product, and the fourth portion is expanded in an expander and separated into vapor and liquid fractions in the phase separator. The vapor fraction is removed from the phase separator, heated in the second heat exchanger, and then further heated in the first heat exchanger before being sent to the refrigerant compressor. SUMMARY OF THE INVENTION

[0005] Disclosed herein are a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream, in which a front-end liquid natural gas (NGL) unit is integrated with a natural gas liquefaction unit that uses an open-loop cooling cycle. The integrated approach disclosed herein eliminates the need for supply compression equipment while still achieving a level of liquid natural gas recovery and aromatic compound extraction similar to that achievable using a stand-alone front-end NGL unit. The open-loop cooling cycle also eliminates the need for equipment, piping, and instrumentation related to refrigerant storage and injection within the liquefaction unit (since in an open-loop refrigerant cycle, the supply functions as a continuous source of refrigerant). Such equipment reduction and operational complexity lead to a reduction in capital costs and an increase in operational efficiency.

[0006] Some preferred embodiments of the method and system according to the present invention are outlined below.

[0007] Aspect 1: A method for removing liquefied natural gas from a natural gas feed stream and liquefying the natural gas feed stream, comprising: (a) expanding and / or cooling the natural gas feed stream and introducing the stream into a distillation column having one or more separation sections, wherein the natural gas feed stream is introduced into the distillation column below at least one of the separation sections; (b) withdrawing a liquefied natural gas stream from the bottom of the distillation column; (c) withdrawing a natural gas vapor stream from the top of the distillation column; (d) heating the natural gas vapor stream and a first expanded refrigerant stream in one or more heat exchanger sections, compressing the resulting heated stream, and combining the streams to form a compressed refrigerant, wherein the natural gas vapor stream and the first expanded refrigerant stream can be combined before, during, or after being heated and compressed; (e) cooling at least a first portion of the compressed refrigerant via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream that are heated in step (d) to form a first cryogenic refrigerant stream; (f) expanding the first cryogenic refrigerant stream, separating the stream into a vapor phase and a liquid phase, and forming a first liquefied natural gas stream from the liquid phase and a first expanded refrigerant stream from the vapor phase; (g) forming a reflux stream, expanding the reflux stream, and introducing the reflux stream into the top of the distillation column to provide reflux to the distillation column, wherein the reflux stream is formed from a portion of the first liquefied natural gas stream, a portion of the liquid phase separated in step (f), a portion of the first cryogenic refrigerant stream withdrawn from the stream before the stream is separated in step (f), a further portion of the compressed refrigerant cooled via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream that are heated in step (d), and / or a portion of the liquefied natural gas product derived from the liquefied natural gas stream or the first liquefied natural gas stream.

[0008] Aspect 2: The method according to aspect 1, wherein in step (a), the natural gas feed stream is introduced into a distillation column having two or more separation sections, and the expanded natural gas feed stream is introduced into the distillation column below at least one of the separation sections and above at least another one of the separation sections.

[0009] Aspect 3: The method further includes (h) a step of providing boiling up to the distillation column by reboiling a part of the liquid at the bottom of the distillation column, the method according to aspect 2.

[0010] Aspect 4: The method according to any one of aspects 1 to 3, wherein in step (a), the natural gas feed stream is expanded before being introduced into the distillation column.

[0011] Aspect 5: The method according to aspect 4, wherein in step (a), the natural gas feed stream is cooled and then expanded before being introduced into the distillation column. After the natural gas feed stream is cooled, it is separated into a vapor phase and a liquid phase. The vapor phase is expanded and introduced into the distillation column at a first location below at least one separation section of the column, and the liquid phase is expanded and introduced into the distillation column at a second location below the first location, and there is at least one separation section between the first location and the second location.

[0012] Aspect 6: The method according to any one of aspects 1 to 5, wherein in step (a), the natural gas feed stream is cooled before being introduced into the distillation column, and at least a part of the natural gas feed stream is cooled through indirect heat exchange with a natural gas vapor stream and a first expanded refrigerant stream that is heated in step (d).

[0013] Aspect 7: The method according to any one of aspects 1 to 6, wherein in step (g), the reflux stream is formed from a part of the first liquefied natural gas stream separated in step (f) and / or a part of the liquid phase.

[0014] Aspect 8: The first expanded refrigerant stream is formed at a temperature lower than the vapor stream of natural gas, and in step (e), at least a first portion of the compressed refrigerant is cooled via indirect heat exchange with the vapor stream of natural gas and the first expanded refrigerant stream, and then further cooled via indirect heat exchange with the first expanded refrigerant stream to form a first low-temperature refrigerant stream, the method according to any one of aspects 1 to 7.

[0015] Aspect 9: Step (e) includes cooling a first portion of the compressed refrigerant and a second portion of the compressed refrigerant via indirect heat exchange with the natural gas vapor stream heated in step (d) and the first expanded refrigerant stream to form a first low-temperature refrigerant stream and a second low-temperature refrigerant stream respectively, the first and second portions of the compressed refrigerant being cooled with respect to the natural gas vapor stream and the first expanded refrigerant stream, the first portion of the compressed refrigerant then being further cooled with respect to the natural gas vapor stream and the first expanded refrigerant stream, so that the first low-temperature refrigerant stream is formed at a temperature lower than the second low-temperature refrigerant stream. Step (f) includes expanding the first low-temperature refrigerant stream, expanding the second low-temperature refrigerant stream, combining the streams, separating them into a vapor phase and a liquid phase, forming a first liquefied natural gas stream from the liquid phase, and forming a first expanded refrigerant stream from the vapor phase, the method according to any one of aspects 1 to 8.

[0016] Aspect 10: The method (i) further includes a step of expanding a third portion of the compressed refrigerant to form a second expanded refrigerant stream, the second expanded refrigerant stream being formed at a temperature higher than the first expanded refrigerant stream or the natural gas vapor stream. Step (d) includes heating the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream in one or more heat exchanger sections, compressing the resulting heated stream, and combining the streams to form a compressed refrigerant, the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream being combinable before, during, or after being heated and compressed. Step (e) includes cooling at least a first portion of the compressed refrigerant via indirect heat exchange with a natural gas vapor stream, a first expanded refrigerant stream, and a second expanded refrigerant stream that are heated in step (d) to form a first low-temperature refrigerant stream, wherein at least the first portion of the compressed refrigerant is cooled against the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream and then further cooled against the natural gas vapor stream and the first expanded refrigerant stream, the method according to any one of aspects 1-9.

[0017] Aspect 11: Step (e) includes cooling a first portion of the compressed refrigerant and a second portion of the compressed refrigerant via indirect heat exchange with a natural gas vapor stream, a first expanded refrigerant stream, and a second expanded refrigerant stream that are heated in step (d) to form a first low-temperature refrigerant stream and a second low-temperature refrigerant stream, respectively, wherein the first and second portions of the compressed refrigerant are cooled against the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream, and the first portion of the compressed refrigerant is then further cooled against the natural gas vapor stream and the first expanded refrigerant stream, such that the first low-temperature refrigerant stream is formed at a lower temperature than the second low-temperature refrigerant stream. Step (f) of the method according to aspect 10 includes expanding the first low-temperature refrigerant stream, expanding the second low-temperature refrigerant stream, combining the streams, separating them into a vapor phase and a liquid phase, and forming a first liquefied natural gas stream from the liquid and a first expanded refrigerant stream from the vapor phase.

[0018] Aspect 12: The second low-temperature refrigerant stream is expanded in an expander portion of a compression expander having a compressor portion used to compress at least a portion of the natural gas vapor stream and / or the first expanded refrigerant stream in step (d), and / or A third portion of the compressed refrigerant is expanded in an expander portion of a compression expander having a compressor portion used to compress at least a portion of the natural gas vapor stream and / or the first expanded refrigerant stream in step (d), the method according to any one of aspects 9-11.

[0019] Aspect 13: The method according to any one of Aspects 1 to 12, wherein in step (f), the first low-temperature refrigerant stream is separated into a vapor phase and a liquid phase in a phase separator.

[0020] Aspect 14: The method further includes (j) further cooling at least a portion of the first liquefied natural gas stream to form a liquefied natural gas product stream, the method according to any one of Aspects 1 to 13.

[0021] Aspect 15: The method according to Aspect 14, wherein step (j) includes flashing at least a portion of the first liquefied natural gas stream to form a liquefied natural gas product stream and one or more flash gas streams.

[0022] Aspect 16: The method further includes (k) cooling and liquefying a fourth portion of the compressed refrigerant through indirect heat exchange with one or more flash gas streams to form a second liquefied natural gas stream or a set of liquefied natural gas streams, and step (j) includes flashing at least a portion of the first liquefied natural gas stream and the second liquefied natural gas stream or the set of liquefied natural gas streams to form a liquefied natural gas product stream and one or more flash gas streams, the method according to Aspect 15.

[0023] Aspect 17: The method further includes (l) cooling a fifth portion of the compressed refrigerant through indirect heat exchange with one or more flash gas streams, and then combining the fifth portion of the compressed refrigerant with the first portion of the compressed refrigerant during cooling of at least the first portion of the compressed refrigerant in step (e) to form a first low-temperature refrigerant stream, the method according to Aspect 16.

[0024] Aspect 18: The method further includes (m) compressing one or more flash gas streams to form a compressed flash gas stream, and cooling and liquefying the compressed flash gas stream through indirect heat exchange with the natural gas vapor stream being heated in step (d) and the first expanded refrigerant stream to form a third liquefied natural gas stream. The method according to any one of aspects 15 to 17, wherein step (j) comprises flashing at least a portion of the first liquefied natural gas stream and the third liquefied natural gas stream to form a liquefied natural gas product stream and one or more flash gas streams.

[0025] Aspect 19: The method (m) further comprises compressing one or more flash gas streams and combining them with the natural gas vapor stream and the first expanded refrigerant stream to form a compressed refrigerant, the method according to any one of aspects 15 to 17.

[0026] Aspect 20: A system for removing liquid natural gas from a natural gas feed stream and liquefying the natural gas feed stream, the system comprising one or more expansion devices and / or heat exchanger sections arranged and configured to expand and / or cool the natural gas feed stream to form an expanded and / or cooled natural gas feed stream; a distillation column having one or more separation sections, the distillation column being arranged and configured to receive the expanded and / or cooled natural gas feed stream in at least one lower distillation column of the separation sections, and to separate the expanded and / or cooled natural gas feed stream into a liquid natural gas stream extracted from the bottom of the distillation column and a natural gas vapor stream extracted from the top of the distillation column; one or more conduits, heat exchanger sections, and compression stages arranged and configured to receive and warm the natural gas vapor stream and the first expanded refrigerant stream, and to compress the resulting warmed stream and combine the streams to form a compressed refrigerant, wherein the one or more conduits, heat exchanger sections, and compression stages can be arranged and configured such that the natural gas vapor stream and the first expanded refrigerant stream are combined before, during, or after being warmed and compressed. Pass at least a first portion of the compressed refrigerant through one or more heat exchanger sections to cool at least the first portion of the compressed refrigerant via indirect heat exchange with a natural gas vapor stream and a first expanded refrigerant stream to form a first low-temperature refrigerant stream, and one or more conduits arranged and configured as such; Expand the first low-temperature refrigerant stream, separate the stream into a vapor phase and a liquid phase, and from the liquid phase, a first liquefied natural gas stream, and from the vapor phase, one or more expansion and separation devices for forming a first expanded refrigerant stream; Receiving a reflux stream, expanding the reflux stream, and introducing the reflux stream into the upper part of a distillation column to provide reflux to the distillation column, and one or more conduits and expansion devices arranged and configured to perform such, wherein the reflux stream is a portion of the first liquefied natural gas stream, a portion of the liquid phase separated in step (f), a portion of the first low-temperature refrigerant stream withdrawn from the stream before the stream is separated in step (f), a further portion of the compressed refrigerant cooled via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream heated in step (d), and / or a portion of the liquefied natural gas product derived from the liquefied natural gas stream or the first liquefied natural gas stream, one or more conduits and expansion devices formed therefrom.

Brief Description of the Drawings

[0027] [Figure 1] Figure 1 is a schematic flow diagram depicting a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a first embodiment of the present invention.

[0028] [Figure 1A] Figure 1A is a schematic flow diagram depicting a coil-wound heat exchanger unit suitable for use in the method and system of Figure 1.

[0029] [Figure 1B] Figure 1B is a schematic flow diagram depicting an integrated heat exchanger and phase separator unit suitable for use in the method and system of Figure 1.

[0030] [Figure 1C] Figure 1C is a schematic flow diagram depicting the arrangement of a flash gas compressor suitable for use in the method and system of Figure 1.

[0031] [Figure 1D] Figure 1D is a schematic flow diagram depicting another arrangement of a flash gas compressor suitable for use in the method and system of Figure 1.

[0032] [Figure 2] Figure 2 is a schematic flow diagram depicting a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a second embodiment of the present invention.

[0033] [Figure 3] Figure 3 is a schematic flow diagram depicting a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a third embodiment of the present invention.

[0034] [Figure 4] Figure 4 is a schematic flow diagram depicting a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a fourth embodiment of the present invention.

[0035] [Figure 5] Figure 5 is a schematic flow diagram depicting a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a fifth embodiment of the present invention.

[0036] [Figure 6] Figure 6 is a schematic flow diagram depicting a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a sixth embodiment of the present invention.

[0037] [Figure 7]FIG. 7 is a schematic flow diagram depicting a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a seventh embodiment of the present invention.

[0038] [Figure 8] FIG. 8 is a schematic flow diagram depicting a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to an eighth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0039] Methods and systems for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream to produce an LNG stream and an NGL stream are described herein.

[0040] As used herein, unless otherwise indicated, the articles "a" and "an" mean one or more when applied to any feature of the embodiments of the invention described herein and within the scope of the specification and claims. 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 indicates a particular specified feature or a plurality of particular specified features and may have a singular or plural implication depending on the context in which it is used.

[0041] When letters are used herein to identify the recited steps of a method (e.g., (a), (b), and (c)), these letters are used merely to assist in referring to the method steps and are not intended to indicate the specific order in which the claimed steps are to be performed, except where such order is specifically recited and only to the extent that such order is specifically recited.

[0042] When terms such as "first," "second," "third," etc. are used herein to identify recited features of a method or system, they are used only to reference and assist in distinguishing the features in question, and are not intended to indicate any specific order of the features, except where such order is specifically recited and only to the extent that such order is specifically recited.

[0043] As used herein, the term "natural gas" includes synthetic natural gas and / or substitute natural gas. The main component of natural gas is methane (typically including at least 85 mol% of the feed stream, more often at least 90 mol%, and on average about 95 mol%). Other typical components of raw natural gas that may be present in lesser amounts include one or more "light components" (i.e., components having a lower boiling point than methane) such as nitrogen, helium, and hydrogen, and / or one or more "heavy components" (i.e., components having a higher boiling point than methane) such as carbon dioxide and other acid gases, moisture, mercury, and heavier hydrocarbons such as ethane, propane, butane, and pentane. However, prior to liquefaction, the raw natural gas feed stream is optionally processed to reduce the level of any heavy components to a level required to avoid freezing or other operational problems in the heat exchanger section where the natural gas is cooled and liquefied.

[0044] As used herein, the term "liquefied natural gas" refers to natural gas in the liquid phase, or natural gas at a temperature and pressure above its critical point (i.e., a supercritical fluid), having a density greater than its critical point density. Similarly, reference to the "liquefaction" of natural gas refers to the conversion of natural gas from its vapor to a liquid (i.e., from the gaseous phase to the liquid phase), typically by cooling, or, in relation to natural gas at a temperature and pressure above its critical point, the act of increasing the density of the natural gas to a density greater than its critical point density, typically by cooling.

[0045] As used herein, the term "indirect heat exchange" refers to heat exchange between two fluids maintained in a state separated from each other by some form of physical barrier.

[0046] As used herein, the term "heat exchanger section" refers to a unit or portion of a unit in which indirect heat exchange occurs between one or more flows of a fluid flowing through the low temperature side of the heat exchanger section and one or more flows of a fluid flowing through the heating side of the heat exchanger section, the flow of fluid flowing through the low temperature side being thereby heated and the flow of fluid flowing through the heating side being thereby cooled (the terms "heating side" and "low temperature side" are purely relative). Unless otherwise indicated, the heat exchanger section can be of any suitable type of heat exchanger section, including but not limited to, a shell and tube heat exchanger section, a coil wound, or a plate and fin type heat exchanger.

[0047] As used herein, the terms "coil wound heat exchanger" and "coil wound heat exchanger unit" refer to a type of heat exchanger known in the art that includes one or more tube bundles enclosed within a shell casing. A "coil wound heat exchanger section" represents one or more of said tube bundles, the "tube side" of said bundle, i.e., typically the heating side of the section, the interior of the tubes within the bundle that define one or more passages (also referred to as tube circuits) through the section, and the "shell side" of said bundle, i.e., typically the cooler side of the section, which comprises the space defined between the interior of the shell casing and the exterior of the tubes and is defined by the interior of the shell casing and the exterior of the tubes. The shell side provides a much lower flow resistance than the tube side, allows for a much larger pressure drop than the tube side, and is much more effective and efficient for the expanded flow of the cooler refrigerant passing through the shell side. Therefore, the shell side is almost always used as the cooler side of the section, and the refrigerant provides a cooling duty to the section passing through the shell side. Coil wound heat exchangers are heat exchangers with a compact design known for their robustness, safety, and heat transfer efficiency, and thus have the advantage of providing a very efficient level of heat exchange relative to their installation area. However, since the shell side defines only a single passage through the heat exchanger section, it is not possible to use the flow of two or more refrigerants in the shell side of the coil wound heat exchanger section without said flow of the refrigerant being mixed in the shell side of the heat exchanger section.

[0048] As used herein, the term "flash" (also referred to in the art as "flash evaporation") refers to the process of reducing the pressure of a liquid (or supercritical or two-phase) stream to cool the stream and evaporate a portion of the liquid, resulting in a cooler, lower pressure two-phase mixture of vapor and liquid, and the vapor present in this mixture is also referred to as "flash gas". As used herein, the phrase "flash and separation" refers to the process of flashing a stream and separating the flash gas from the remaining liquid.

[0049] As used herein, the terms "gaseous flow of refrigerant" and "gaseous refrigerant flow" refer to a flow of refrigerant in which substantially all, and more preferably all, of the flow is vapor (i.e., in the gaseous phase). Preferably, the flow is at least 80 mol% vapor (i.e., has a vapor fraction of at least 0.8). More preferably, the flow is at least 90 mol%, at least 95 mol%, or at least 99 mol% vapor.

[0050] As used herein, the term "expansion device" refers to any device or set of devices suitable for expanding and thereby reducing the pressure of a fluid. Suitable types of expansion devices for expanding a fluid include "isentropic" expansion devices such as expanders (i.e., turboexpanders) or hydraulic turbines, in which the fluid is expanded and thereby the pressure and temperature of the fluid are reduced in a substantially isentropic manner (i.e., in a manner that generates work), and "isenthalpic" expansion devices such as valves or other throttle devices, in which the fluid is expanded and thereby the pressure and temperature of the fluid are reduced without generating work.

[0051] As used herein, the term "separation device" refers to any device or set of devices suitable for separating a two-phase (vapor and liquid) flow or mixture into separate vapor (gas) and liquid flows. Examples of separation devices include phase separators and distillation columns.

[0052] As used herein, the term "distillation column" refers to a column that includes one or more separation sections, each separation section being composed of one or more separation stages (composed of devices such as packing or trays) that increase contact and thus enhance mass transfer between the upward flowing vapor and the downward flowing liquid within the column, such that the liquid and vapor streams exiting the column are not in equilibrium (the concentration of the more volatile components increases in the upward flowing vapor and the concentration of the less volatile components increases in the downward flowing liquid). The term "overhead vapor" refers to the vapor that accumulates at the top of the column. The term "bottom liquid" refers to the liquid that accumulates at the bottom of the column. The "top" of the column refers to the portion of the column above the separation section (i.e., above the uppermost separation stage or above that). The "bottom" of the column refers to the portion of the column below the separation section (i.e., below the lowermost separation stage or below that). The "midpoint" of the column refers to the location between two separation sections, between the top and bottom of the column. The term "reflux" refers to the source of the liquid flowing downward from the top of the column. The term "boilup" refers to the source of the vapor flowing upward from the bottom of the column, typically generated by boiling ( "reboiling") a portion of the bottom liquid.

[0053] The term "phase separator" refers to a drum or other form of container in which a two-phase flow can be separated into its vapor and liquid phase components, and the liquid and vapor streams exiting the container are in equilibrium (there are no separation stages within the phase separator).

[0054] By way of example, various exemplary embodiments of the present invention will be described with reference to the drawings. In the figures, where a feature is common to two or more figures, the feature is assigned the same reference number. Unless a feature is specifically described as being different from other embodiments shown in the drawings, it can be assumed that the feature has the same structure and function as the corresponding feature in the embodiment in which it is described. Further, in the embodiments described below, if the feature does not have a different structure or function, it may not be specifically mentioned in the specification.

[0055] Referring to FIG. 1, a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a first embodiment of the present invention are shown.

[0056] A mixture of NGL and HHC (including aromatic compounds) is also included. Typically, the natural gas feed stream 100 at ambient temperature and high pressure, typically 50 - 100 bar, more preferably 70 - 95 bar, is sent to the pretreatment section 101. Depending on the composition of the natural gas feed, the pretreatment of the natural gas feed stream 100 in the pretreatment section 101 can include treating the natural gas feed stream in an acid gas removal unit for removing H2S and CO2, a dehydration unit for removing water, and / or a mercury removal unit.

[0057] Next, the pretreated natural gas feed stream 102 exiting the pretreatment section 101 is precooled by passing at least a portion of the natural gas feed stream through the warming side of the first heat exchanger section 106A of the main heat exchanger, and the at least a portion of the natural gas feed stream is precooled via indirect heat exchange with the combined natural gas vapor, the first expansion refrigerant, and the second expansion refrigerant stream 152 (described in more detail below) passing through the cold side of the first heat exchanger section 106A. In the illustrated embodiment, this is done by splitting the pretreated natural gas feed stream 102 exiting the pretreatment section 101 into two streams: a bypass stream 108 consisting of 20 - 60%, more preferably 30 - 50% of the flow rate of the pretreated natural gas feed stream 102 that bypasses the first heat exchanger section 106A, and a feed stream 104 consisting of the remaining flow rate of the pretreated natural gas feed stream 102 that passes through the circuit (i.e., one or more passages) on the warming side of the first heat exchanger section 106A, is cooled from - 40°C to - 20°C, more preferably from - 35°C to - 25°C, and then recombined with the bypass stream 108 and introduced into the high - pressure (HP) phase separator 110.

[0058] The HP phase separator 110 operates at a pressure of 50 to 100 bar, more preferably 70 to 95 bar. In the HP phase separator 110, the pre-treated and pre-cooled natural gas feed stream is separated into a vapor phase and a liquid phase. The vapor phase of the natural gas feed stream is taken out of the HP phase separator 110 as stream 111, expanded in the first expander 112A to form an expanded stream 114, which is introduced into the distillation column 117 at a first intermediate location of the column below the separation section 117A of the column and above the separation section 117B of the column. The liquid phase of the natural gas feed stream is taken out of the HP phase separator 110 as stream 115, expanded across a J-T valve, and introduced into the distillation column 117 at a second intermediate location below the separation section 117B of the column (thus, this section is positioned between the first intermediate location and the second intermediate location) and above the separation section 117C of the column.

[0059] The distillation column 117 preferably operates at a pressure of 20 to 40 bar, more preferably 25 to 30 bar. The reflux to the distillation column 117 is provided by a reflux stream 162 (described in more detail below) that is expanded across a J-T valve and introduced into the upper part of the distillation column 117 above the separation section 117A. The boil-up for the distillation column 117 is provided by re-boiling a portion of the liquid at the bottom of the distillation column in the re-boiler 118. The heating duty for re-boiling a portion of the bottom liquid in the re-boiler 118 can be provided by a heat transfer fluid that passes through the re-boiler via a vapor stream or indirect heat exchange with a portion of the bottom liquid and is cooled. In an alternative embodiment, for a particular feed composition, the re-boiler 118 can be integrated with the first heat exchanger section 106A in a state where a portion of the bottom liquid is heated as it passes through a circuit (i.e., one or more passages) on the low-temperature side of the heat exchanger section 106A, and the heating duty for re-boiling a portion of the bottom liquid is provided in this case by one or more streams passing through the heating side of the first heat exchanger section 106A. In yet another embodiment, the re-boiler 118 can be replaced or supplemented by injecting a heating process stream into the bottom of the distillation column 117.

[0060] Within distillation column 117, the upwardly rising vapor from the natural gas feed stream (i.e., streams 114 and 115) is contacted with the downwardly flowing liquid from the reflux stream as they pass through the separation stage within distillation column 117, thereby "scrubbing" components heavier than methane from the upwardly rising vapor (i.e., removing at least a portion of those components less volatile than methane from the vapor). Similarly, the downwardly flowing liquid from the natural gas feed stream is contacted with the upwardly rising vapor from the bottom of the column as it passes through the separation stage within distillation column 117, thereby "stripping" methane and components lighter than methane from the downwardly flowing liquid (i.e., removing at least a portion of those components more volatile than methane and methane from the liquid). Thus, the natural gas feed stream is separated within distillation column 117 into a vapor fraction rich in methane collected as distillation column overhead vapor and a liquid fraction concentrated in hydrocarbons heavier than methane collected as distillation column bottom liquid.

[0061] The NGL stream 119 formed from the distillation column bottom liquid is withdrawn from the bottom of the distillation column. The NGL stream 119 has a high aromatic compound content together with NGL and HHC and is at a temperature of 80 °C to 40 °C, more preferably 70 °C to 50 °C. The percentage of C3+ components from the natural gas feed stream 102 recovered within the NGL stream 119 can be higher than 90 mol% (calculated as the total molar flow rate of all C3+ components within the NGL stream 119 divided by the total molar flow rate of all C3+ components within the natural gas feed stream 102).

[0062] The natural gas vapor stream 120 formed from the distillation column overhead vapor is withdrawn from the upper part of the distillation column. The natural gas vapor stream 120 has a temperature of -90°C to -60°C, more preferably -80°C to -70°C, and typically contains less than 0.1 mol% C5+ hydrocarbons (i.e., the total of all C5+ hydrocarbons in the natural gas vapor stream 120 is less than 0.1 mol% of the stream) and less than 1 mol ppm of aromatic compounds (i.e., the total of all aromatic compounds in the natural gas vapor stream 120 is less than 1 mol ppm of the stream).

[0063] The first expanded refrigerant stream 148 passes through the low-temperature side of the third heat exchanger section 106C of the main heat exchanger, where it is heated to a temperature of -100°C to -60°C, more preferably -90°C to -70°C. Then, the first expanded refrigerant stream 149 exiting the low-temperature side of the third heat exchanger section 106c is combined with the natural gas vapor stream 120 to form a combined natural gas vapor and first expanded refrigerant stream 150. The combined natural gas vapor and first expanded refrigerant stream 150 passes through the low-temperature side of the second heat exchanger section 106B of the main heat exchanger, where it is heated to a temperature of -60°C to -20°C, more preferably -50°C to -30°C. Then, the combined natural gas vapor and first expanded refrigerant stream 151 exiting the low-temperature side of the second heat exchanger section 106B is combined with the second expanded refrigerant stream 144 to form a combined natural gas vapor, first expanded refrigerant, and second expanded refrigerant stream 152. Then, the combined natural gas vapor, first expanded refrigerant, and second expanded refrigerant stream 152 passes through the low-temperature side of the first heat exchanger section 106A of the main heat exchanger, where it is heated to within a few degrees Celsius of the temperature of the pre-treated natural gas feed stream 104 entering the heat exchanger section.

[0064] Then, the combined natural gas vapor, first expanded refrigerant, and second expanded refrigerant stream 122 exiting the low-temperature side of the first heat exchanger section 106A is sent to a compression system including a plurality of compression stages to be compressed to form the compressed refrigerant 142.

[0065] More specifically, the combined natural gas vapor, first expansion refrigerant, and second expansion refrigerant stream 122 exiting the low temperature side of the first heat exchanger section 106A is first compressed by the multi-stage refrigerant compressor 124 to produce, for example, a head of 15,000 to 10,000 meters. In the illustrated embodiment, the multi-stage refrigerant compressor 124 has an intercooler 125 (to improve compression efficiency), which may be omitted depending on the equipment design and total head across the refrigerant compressor 124. The compressed stream 126 exiting the multi-stage refrigerant compressor is then cooled in the aftercooler 127, cooled in three associated aftercoolers 130, 135, and 139, and split among three parallel compression stages 112B, 134B, and 138B before being further compressed, forming three further compressed streams 131, 140, and 136, which are then recombined to form the compressed refrigerant 142. The parallel compression stages 112B, 134B, 138B, the associated aftercoolers 130, 135, and 139, the multi-stage refrigerant compressor 124, and the associated intercooler 125 and aftercooler 127 can all be implemented in multiple strings.

[0066] The compressed refrigerant 142 at a pressure of 100 to 80 bar is then split into several refrigerant streams 155, 143, 173, 182.

[0067] The stream 155, representing the first and second portions of the compressed refrigerant 142, passes through the circuit on the heating side (i.e., one or more passages) of the first heat exchanger section 106A (separate from the circuit through which the natural gas supply stream 104 passes), and is cooled to a temperature of -40°C to -20°C, more preferably -35°C to -25°C, via indirect heat exchange with the combined natural gas vapor, the first expansion refrigerant, and the second expansion refrigerant stream 152 passing through the low-temperature side of the heat exchanger section. The resulting cooled stream 156 is then split into the first and second portions of the compressed refrigerant. The second portion of the compressed refrigerant forms a second low-temperature refrigerant stream 164 consisting of 90 to 70 percent, more preferably 85 to 75 percent, of the flow rate of stream 156, and the first portion of the formed stream 158 of the compressed refrigerant consists of the remaining portion of the flow rate of stream 156. In an alternative embodiment, instead of passing through and being cooled as a single stream on the heating side of the first heat exchanger section 106A, the first and second portions of the compressed refrigerant can pass through and be cooled in separate circuits on the heating side of the first heat exchanger section and be taken as separate streams forming streams 158 and 164.

[0068] The stream 158, which includes the first portion of the compressed refrigerant, passes through the circuit on the heating side of the second heat exchanger section 106B, where it is further cooled via indirect heat exchange with the combined natural gas vapor and the first expansion refrigerant stream 150 passing through the low-temperature side of the heat exchanger section. Then it passes through the circuit on the heating side of the third heat exchanger section 106C, where it is further cooled via indirect heat exchange with the first expansion refrigerant stream 148 passing through the low-temperature side of the heat exchanger section, to form a first low-temperature refrigerant stream 159 taken from the heating side of the third heat exchanger section 106C at a temperature of -105°C to -80°C, more preferably -100°C to -90°C.

[0069] The first low-temperature refrigerant stream 159 and the second low-temperature refrigerant stream 164 are then expanded, combined, separated into a vapor phase and a liquid phase, with the first liquefied natural gas stream 160 formed from the liquid phase and the first expansion refrigerant stream 148 formed from the vapor phase.

[0070] More specifically, in the embodiment illustrated in FIG. 1, the first low-temperature refrigerant stream 159 is expanded across a J-T valve, the second low-temperature refrigerant stream 164 is expanded within the second expander 134A, and then the two streams are introduced into and combined within a low-pressure (LP) phase separator 147, where they are separated into a vapor phase and a liquid phase. The vapor phase is taken out of the LP phase separator 147 to form a first expanded refrigerant stream 148 (and then sent to the cold side of the third heat exchange section 106c of the main heat exchanger), and the liquid phase is taken out of the LP phase separator 147 to form a first liquefied natural gas stream 160. In the described embodiment, the first and second low-temperature refrigerant streams are introduced separately into the LP phase separator 147, but alternatively, they can be combined after being expanded and before being introduced into the LP phase separator 147. Alternatively, more than two LP phase separators can be used, and the first and second low-temperature refrigerant streams are introduced into and separated in different LP phase separators, and the vapor phases of the separators are then taken out and combined, and the liquid phases of the separators are then taken out and combined.

[0071] The stream 143 representing the third portion of the compressed refrigerant 142 is expanded in the third expander 138A to form a second expanded refrigerant stream 144, and then (as described above) combined with the combined natural gas vapor and the first expanded refrigerant stream 151 to form a combined natural gas vapor, first expanded refrigerant, and second expanded refrigerant stream 152.

[0072] In the embodiment illustrated in FIG. 1, the first expander 112A is the expander portion of the first compression-expansion machine, and its compressor portion is formed by the first compression stage 112B of three parallel compression stages. The second expander 134A is the expander portion of the second compression-expansion machine, and its compressor portion is formed by the second compression stage 134B of three parallel compression stages. The third expander 138A is the expander portion of the third compression-expansion machine, and its compressor portion is formed by the third compression stage 138B of three parallel compression stages. In an alternative embodiment, the expansion work from the first, second, and / or third expanders can instead be recovered by a generator. However, in such an arrangement, any one of the first compression stage 112B, the second compression stage 134B, and / or the third compression stage 138B must be driven by a different power source, or when distributing one or more of the compression stages, the head generated in the compression stage needs to be constituted by the multistage refrigerant compressor 124.

[0073] The first liquefied natural gas stream 160 is split such that a first portion of the stream forms a reflux stream 162, which is pumped by the reflux pump 163 into the distillation column 117, then expands across the J-T valve as described above and is introduced into the upper part of the distillation column 117 to provide reflux to the distillation column. The reflux stream 162 is at a temperature of -105°C to -80°C, more preferably -100°C to -90°C, and consists of 5 to 20 percent, more preferably 10 to 15 percent, of the flow rate of the first liquefied natural gas stream 160. In an alternative embodiment, instead of (or in addition to) forming the reflux stream 162 from a portion of the first liquefied natural gas stream 160 in the manner described above, the reflux stream can be from a portion of the liquid phase separated within the LP phase separator 147 by taking out the first portion of the liquid phase as the first liquefied natural gas stream 160 from the LP phase separator 147 and taking out the second portion of the liquid phase from the LP phase separator 147 as the reflux stream 162 (thus, the first liquefied natural gas stream 160 and the reflux stream 162 are taken out from the LP phase separator 147 as separate streams).

[0074] The second portion 166 of the first liquefied natural gas stream 160, which consists of the remaining portion of the stream, is flashed together with the second set of liquefied natural gas streams 177, 186 and the third liquefied natural gas stream 199 to form the LNG product stream 192 and the flash gas streams 171 and 181.

[0075] More specifically, the second portion of the first liquefied natural gas stream 160 is flashed across a J-T valve to form a stream 166 that is introduced into the HP flash gas phase separator 167, where it is separated into a vapor phase and a liquid phase. The HP flash gas phase separator 167 operates at a pressure of 20 - 10 bar. A hydraulic turbine (not shown) can be used to extract work from the stream 166 before the stream 166 is flashed and introduced into the HP flash gas phase separator 167. The vapor phase taken out from the HP flash gas phase separator 167 forms the first flash gas stream 169, and the liquid phase taken out from the HP flash gas phase separator 167 is flashed across a J-T valve to form a liquid stream 168 that is introduced into the LP flash gas phase separator 178, where it is separated into a vapor phase and a liquid phase. The LP flash gas phase separator 178 operates at a pressure of 10 - 2 bar. The vapor phase taken out from the LP flash gas phase separator 178 forms the second flash gas stream 179, and the liquid phase taken out from the LP flash gas phase separator 178 forms the LNG product stream 192, which is sent to and stored in the LNG storage tank 193. If the pressure in the LP flash gas phase separator 178 does not provide sufficient driving force, an LNG pump (not shown) can be used to transfer the LNG product stream 192 to the LNG storage tank 193.

[0076] The first flash gas stream 169 passes through the low temperature sides of the first 170A heat exchanger section and the second 170B heat exchanger section of the first flash gas heat exchanger, is heated, and forms a heated first flash gas stream 171. The second flash gas stream 179 passes through the low temperature sides of the first 180A heat exchanger section and the second 180B heat exchanger section of the second flash gas heat exchanger, is heated, and forms a heated second flash gas stream 181.

[0077] The heated first flash gas stream 171 and the second flash gas stream 181 are combined and compressed to form a compressed flash gas stream 189. In the embodiment illustrated in FIG. 1, the heated first flash gas stream 171 and the second flash gas stream 181 are compressed in a multi-stage flash gas compressor 187 and an associated aftercooler 188. In the illustrated embodiment, the multi-stage flash gas compressor 187 has five stages with four intercoolers, although the number of stages can be reduced (or increased) depending on the compressor design. The heated second flash gas stream 181 is sent to the inlet of stage 1 of the multi-stage flash gas compressor 187. The heated first flash gas stream 171 is sent to the inlet of stage 3 of the multi-stage flash gas compressor 187 in the illustrated embodiment, although this stream can be sent to an earlier or later stage of the flash gas compressor 187 depending on where it is most efficient. The stages of the multi-stage flash gas compressor 187 can be arranged in any suitable arrangement, two such arrangements being illustrated in FIGS. 1C and 1D.

[0078] The boil-off gas (BOG) stream 194, consisting of tank flash, boil-off gas, and vapor displacement, is withdrawn from the head space of the LNG storage tank 193 and compressed and cooled in the BOG compressor 195 and the associated aftercooler 196 to form a compressed BOG gas stream 197. Alternatively, depending on the preferred operation, the LNG storage tank 193 can be operated at the bubble point. In this case, the BOG stream 194 and the associated BOG compressor 195 and the associated aftercooler 196 may be omitted, or the BOG stream 194 may consist only of vapor displacement with the BOG compressor 195 and the associated aftercooler 196 sized accordingly.

[0079] The compressed flash gas streams 189, 191 are combined with the compressed BOG gas stream 197 (if present) to form a recycle stream 198, which passes through the heating sides of the first heat exchanger section 106A, the second heat exchanger section 106B, and the third heat exchanger section 106C of the main heat exchanger, is cooled, and is liquefied to form a third liquefied natural gas stream 199, which is flashed across a J-T valve and introduced into the HP flash gas phase separator 167, where it is separated into a vapor phase and a liquid phase.

[0080] In an alternative embodiment, instead of being combined and then passing through the heating sides of the first heat exchanger section 106A, the second heat exchanger section 106B, and the third heat exchanger section 106C as the combined recycle stream 198, the compressed flash gas streams 189, 191 and the compressed BOG gas stream 197 can pass through separate circuits on the heating sides of the first heat exchanger section 106A, the second heat exchanger section 106B, and the third heat exchanger section 106C and be cooled and liquefied separately before being combined. Additionally or alternatively, the cooled and liquefied compressed flash gas streams and compressed BOG gas streams (whether separately cooled and liquefied or combined streams) can be sent to and introduced into the LP phase separator 147 instead of being sent to the HP flash gas phase separator 167 for separation (for this purpose, they can be combined with the first low-temperature refrigerant stream 159 and the second low-temperature refrigerant stream 164 and separated).

[0081] The refrigerant compressor 124, the flash gas compressor 187, and (if present) the BOG compressor 197 can be powered via any suitable means. In the embodiment illustrated in FIG. 1, a portion of the compressed flash gas taken from the compressed flash gas stream 189 is taken out to form the fuel stream 190 (before the compressed flash gas stream 189 is combined with the compressed BOG stream 197), and that fuel stream can be used to power a gas turbine to directly drive the compressor(s) and / or for the generation of electricity used to drive the compressor(s). Alternatively, if power is available from off-site (e.g., from the electrical grid), this can be used to power the compressor(s), in which case there may be no need for additional fuel and the fuel stream 190 may be omitted.

[0082] The streams 173 and 182, which together represent the fourth and fifth portions of the compressed refrigerant 142, are cooled in the first and second flash gas heat exchangers via indirect heat exchange with the first and second flash gas streams.

[0083] More specifically, the stream 173 representing a part of the fourth and fifth portions of the compressed refrigerant passes through the heating side of the first heat exchanger section 170A of the first flash gas heat exchanger and is cooled to form a pre-cooled stream 174, which is then split into stream 175 and stream 176. The stream 182 representing a part of the fourth and fifth portions of the compressed refrigerant passes through the heating side of the first heat exchanger section 180A of the second flash gas heat exchanger and is cooled to form a pre-cooled stream 183, which is then split into stream 184 and stream 185.

[0084] Both streams 176 and 185 represent the fourth portion of the compressed refrigerant. Stream 176 passes through the heating side of the second heat exchanger section 170B of the first flash gas heat exchanger, is further cooled and liquefied to form a second set of streams 177 of liquefied natural gas stream at a temperature of -130°C to -100°C, more preferably -120°C to -110°C, is flashed across a J-T valve and introduced into the HP flash gas phase separator 167, where it is separated into a vapor phase and a liquid phase. Stream 185 passes through the heating side of the second heat exchanger section 180B of the second flash gas heat exchanger, is further cooled and liquefied to form a second set of streams 186 of liquefied natural gas stream at a temperature of -160°C to -120°C, more preferably -150°C to -130°C, is flashed across a J-T valve and introduced into the LP flash gas phase separator 178, where it is separated into a vapor phase and a liquid phase.

[0085] Flows 175 and 184, which both represent the fifth portion of the compressed refrigerant, are introduced to the heating side of the second heat exchanger section 106B of the main heat exchanger and combined with flow 158, which contains the first portion of the compressed refrigerant, before passing through. In an alternative embodiment, flows 175 and 184 can be combined with flow 158 after flow 158 has passed through and been cooled on the heating side of the second heat exchanger section 106B and the flows are introduced to the heating side of the third heat exchanger section 106C of the main heat exchanger before passing through. Flow 175 consists of 60 to 20 percent, more preferably 50 to 30 percent, of the flow rate of the pre-cooled flow 174 exiting heat exchanger section 170A. Flow 184 consists of 60 to 20 percent, more preferably 50 to 30 percent, of the pre-cooled flow 183 exiting exchanger 180A.

[0086] Flow 155, which represents the first and second portions of the compressed refrigerant 142, preferably consists of 50 to 60 percent of the flow rate of the compressed refrigerant 142. Flow 143, which represents the third portion of the compressed refrigerant 142, preferably consists of 30 to 40 percent of the flow rate of the compressed refrigerant 142. Flows 173 and 182, each of which represents a part of the fourth and fifth portions of the compressed refrigerant 142, preferably each consists of 2 to 10 percent of the flow rate of the compressed refrigerant 142.

[0087] The first heat exchanger sections of the primary heat exchanger 106A, 106B, and 106C can be any type of heat exchanger section. In a preferred arrangement, all three heat exchanger sections can be, for example, coil-wound heat exchanger sections as illustrated in FIG. 1A. However, one, two, or all three sections can also be another type of heat exchanger section, such as a shell and tube or plate fin type heat exchanger section. The first heat exchanger sections of the primary heat exchanger 106A, 106B, and 106C may be housed in separate units (e.g., as illustrated in FIG. 1A, the first heat exchanger sections of the primary heat exchanger 106A, 106B, and 106C are each coil-wound heat exchanger sections housed within their own shell casing), or alternatively, one, two, or all three sections can be housed in the same unit (e.g., the first heat exchanger sections of the primary heat exchanger 106A, 106B, and 106C are each coil-wound heat exchanger sections, and two or all three sections are housed in the same shell casing). Additionally, in alternative embodiments, the primary heat exchanger can include additional heat exchanger sections arranged in series or parallel with the first heat exchanger sections of the primary heat exchanger 106A, 106B, and 106C, and can include more (or fewer) heat exchanger sections. For example, in one embodiment, the first heat exchanger section 106A can be replaced with a set (i.e., two or more) of first heat exchanger sections arranged in parallel, all of which are connected in series to the second heat exchanger section 106B, and the flow heated and cooled in the set of first heat exchanger sections is split between the sections before being recombined again.

[0088] In embodiments where the first 106A, second 106B, and third 106C heat exchanger sections of the main heat exchanger are of a type of heat exchanger section that can easily regulate separate flows (e.g., plate fin type heat exchanger sections, etc.) on the low temperature side of the heat exchanger section, the natural gas vapor flow, the first expanded refrigerant flow, and / or the second expanded refrigerant flow do not need to be combined before being cooled. Instead, they can be cooled in separate circuits on the low temperature side of the heat exchanger section of the main heat exchanger before, during, or after combination and before compression to form the compressed refrigerant 142.

[0089] The first 170A and second 170B heat exchanger sections of the first flash gas heat exchanger, and the first 180A and second 180B heat exchanger sections of the second flash gas heat exchanger can be of any type of heat exchanger section. In a preferred arrangement, the heat exchanger section can be a coil wound heat exchanger section, and some or all of the heat exchanger sections can be of another type of heat exchanger section, such as a shell and tube or plate fin type heat exchanger section. The first 170A and second 170B heat exchanger sections of the first flash gas heat exchanger can be housed within a single unit (e.g., within the same shell casing if they are coil wound heat exchanger sections) or separate units. Similarly, the first 180A and second 180B heat exchanger sections of the second flash gas heat exchanger can be housed within a single unit or separate units. In alternative embodiments, the first flash gas heat exchanger and / or the second flash gas heat exchanger can consist of more (or fewer) heat exchanger sections.

[0090] When the flash gas heat exchanger and the second flash gas heat exchanger are coil wound heat exchangers, as shown and illustrated in Figure 1B, it is also possible to integrate these heat exchangers with the HP and LP flash gas phase separators. In this arrangement, the first flash gas heat exchanger unit includes a shell casing that includes both a first heat exchanger section 170A and a second heat exchanger section 170B that are pre-cooled, and a liquefaction section and a phase separator section that are positioned below the heat exchanger sections and function as an HP flash gas phase separator. The second flash gas heat exchanger unit includes a shell casing that includes both a first heat exchanger section 180A and a second heat exchanger section 180B that are pre-cooled, and a liquefaction section and a phase separator section that are positioned below the heat exchanger sections and function as an LP flash gas phase separator. The first liquefied natural gas stream 166, the flow of the second set of liquefied natural gas streams 177, and the third liquefied natural gas stream 199 are all introduced (after being flashed across the J-T valve) into the phase separation section of the first flash gas heat exchanger unit, where they are separated into a liquid phase and a vapor phase. The liquid phase is withdrawn from the bottom of the first flash gas heat exchanger unit to form a liquid stream 168, and the vapor phase forms a first flash gas stream that rises through the shell sides of the second heat exchanger section 170B and the first heat exchanger section 170A, providing a cooling duty to the heat exchanger sections. The liquid stream 168 from the HP flash gas phase separator and the flow of the second set of liquefied natural gas streams 186 are introduced into the phase separator of the second flash gas heat exchanger unit after being flashed across the J-T valve, where they are separated into a liquid phase and a vapor phase. The liquid phase is withdrawn from the bottom of the first flash gas heat exchanger unit to form an LNG product stream 192, and the vapor phase forms a second flash gas stream that rises through the shell sides of the second 180B and the first heat exchanger section 180A, providing a cooling duty to the heat exchanger sections.

[0091] In the embodiment shown in FIG. 1, the first liquefied natural gas stream 166, the second set of liquefied natural gas stream flows 177, and the third liquefied natural gas stream 199 are all introduced into the HP flash gas phase separator 167, where they are combined and separated into a vapor phase and a liquid phase as described above. However, in an alternative embodiment, one, two, or all three of the streams can be combined after being expanded and before being introduced into the HP flash gas phase separator 167. Alternatively, two or more HP flash gas phase separators can be used, and two or all three of the streams are introduced into different HP flash gas phase separators, separated, then the vapor phases of the separators are withdrawn and combined, and then the liquid phases of the separators are withdrawn and combined.

[0092] Similarly, in the embodiment shown in FIG. 1, the liquid stream 168 from the HP flash gas phase separator and the second set of liquefied natural gas stream flows 186 are introduced into the LP flash gas phase separator 178, where they are combined and separated into a vapor phase and a liquid phase as described above. However, in an alternative embodiment, these streams can be combined after being expanded and before being introduced into the LP flash gas phase separator 178, or two LP flash gas phase separators can be used, and the two streams are introduced into different LP flash gas phase separators, separated, then the vapor phases of the separators are withdrawn and combined, and then the liquid phases of the separators can be withdrawn and combined.

[0093] As described above, in the arrangement shown in FIG. 1, the reflux stream 162 is formed from a portion of the first liquefied natural gas stream 160 by splitting the first liquefied natural gas stream 160 (or, alternatively, can be formed from a portion of the liquid phase separated within the LP phase separator 147 by taking out a portion of the liquid phase from the LP phase separator 147 as the reflux stream 162). However, in an alternative embodiment, the reflux stream 162 can alternatively (or additionally) be the following: (i) A portion of the first cryogenic refrigerant stream 159 taken from the stream before the stream is expanded and introduced into the LP phase separator 147, (ii) A portion of stream 158 (including the first part of the compressed refrigerant), taken from the stream after it has passed through and been cooled on the heating side of the second heat exchanger section 106B of the main heat exchanger and before the stream has passed through and been further cooled on the heating side of the third heat exchanger section 106C of the main heat exchanger. (iii) A portion of the liquid separated in the HP flash gas phase separator 167 (this portion is taken out as a separate stream from the liquid stream 168 taken out from the separator). (iv) A portion of the liquid stream 168 exiting the HP flash gas phase separator 167, where a portion of the liquid stream 168 is taken out before the remainder of the stream is flashed and introduced into the LP flash gas separator 178. (v) A portion of the liquid separated in the LP flash gas phase separator 178 (this portion is taken out as a separate stream from the LNG product stream 192 taken out from the separator). (vi) A portion of the LNG product stream 192 taken out before the remaining portion of the stream is transferred to the LNG storage tank 193, and / or (vii) Can be formed from the LNG product taken out from the LNG storage tank 193.

[0094] In an alternative arrangement to that shown in FIG. 1, instead of being expanded as shown in FIG. 1 and introduced into the LP phase separator 147, the first low-temperature refrigerant stream 159 can be flashed and introduced into the HP flash gas phase separator 167.

[0095] In an alternative arrangement to that shown in FIG. 1, instead of being combined with the first expanded refrigerant stream 149 exiting the low-temperature side of the third heat exchanger section 106C of the main heat exchanger, the natural gas vapor stream 120 formed from the distillation column overhead vapor taken out from the top of the distillation column can be combined with the first expanded refrigerant stream 148 and then pass through the low-temperature side of the third heat exchanger section 106C of the main heat exchanger.

[0096] In an alternative arrangement to the arrangement shown in FIG. 1, instead of or in addition to further cooling the first liquefied natural gas stream 166 by flashing the stream to form an LNG product stream 192, the first liquefied natural gas stream 166 can be further cooled against another refrigerant such as a refrigerant circulating within a closed loop cycle.

[0097] The method and system according to the first embodiment of the invention depicted in FIG. 1 provide various advantages over the method and system depicted in U.S. Patent Application Publication No. 2018 / 0180354 (A1).

[0098] Specifically, the use of a distillation column 117 for separating a natural gas feed stream provides improved recovery of NGLs and aromatic compounds compared to the use of only a phase separator or a stripping column (i.e., a distillation column without a reflux stream and without a separation stage above the location where the natural gas feed stream is introduced into the distillation column). The use of only a phase separator results in a decrease in the recovery rate of NGLs and aromatic compounds from the natural gas feed. Since NGLs are valuable commodities, their loss to the LNG product is financially inefficient, and when the natural gas feed has a high aromatic compound content, insufficient removal of these compounds can cause them to freeze in the main heat exchanger, resulting in a shutdown of operation. The use of only a stripping column can achieve higher NGL recovery than the use of a phase separator, but can still leave a high content of aromatic compounds in the natural gas feed. Conversely, by using a distillation column 117 having at least one separation section (117A) above the location where the natural gas feed is introduced, in the manner shown in FIG. 1, it is possible to achieve high NGL recovery (i.e., recovery of more than 90 mole% of the C3+ components) while reducing the content of aromatic compounds in the LNG product to less than 1 ppm mole (thus providing a level of performance similar to that achievable using a stand-alone front-end NGL unit).

[0099] Using a main heat exchanger having second and third heat exchanger sections 106B and 106C, which mix the natural gas vapor stream 120 from the top of the distillation column with the expanded refrigerant stream 149 exiting the low temperature side of the third heat exchanger section 106C (in the manner illustrated in FIG. 1), reduces the specific output of the process.

[0100] Manufacturing LNG products by flashing the liquefied natural gas stream 166 obtained from the LP phase separator 147 improves the efficiency of the process (by reducing the amount of cooling that needs to be provided to the main heat exchanger), together with the associated recovery of cold from the flash gas and recycle of the flash gas in the flash gas heat exchanger.

[0101] Pre-cooling the natural gas feed stream 102 using the first heat exchanger section 106A of the main heat exchanger before the stream is expanded and separated eliminates the need for a separate heat exchanger unit for pre-cooling the natural gas feed stream, thereby simplifying the design and reducing plot space. Additionally, using the HP phase separator 110 to separate the pre-cooled natural gas feed stream into a liquid phase and a vapor phase, with the vapor phase expanding in the first expander 112A and the liquid phase expanding across a J-T valve before introducing the pre-cooled natural gas feed stream into the distillation column 117, improves expander efficiency and simplifies the expander design compared to using expanders designed to expand or create a stream having both a liquid phase and a vapor phase (the use of the HP phase separator 110 also adds another theoretical stage of separation and thus further improves NGL recovery).

[0102] Combining the natural gas vapor stream 120 with the first expanded refrigerant stream 149 to form a combined stream 150 that is heated on the low temperature side of the second heat exchanger section 106B of the main heat exchanger, and further combining the combined stream 150 with the second expanded refrigerant stream 144 to form a combined stream 152 that is further heated on the low temperature side of the first heat exchanger 106A of the main heat exchanger means that the refrigerant compressor 124 has to handle only one inlet stream 122 (formed from the combined, heated natural gas vapor, first expanded refrigerant, and second expanded refrigerant streams), thereby making it possible to significantly simplify the design of the refrigerant compressor 124. Further, since they do not need to receive the streams that need to be kept separate on the low temperature side of the heat exchanger section, it is possible for the first heat exchanger section 106A and the second heat exchanger section 106B to be coil wound heat exchanger sections. As described above, the coil wound heat exchanger is a heat exchanger with a compact design known for its robustness, safety, and heat transfer efficiency, and thus has the advantage of providing a very efficient level of heat exchange with respect to their installation area. However, since the shell side defines only a single passage through the heat exchanger section, on the shell side of the coil wound heat exchanger section, it is not possible to use more than one refrigerant stream without the said stream of refrigerant being mixed on the shell side of the heat exchanger section.

[0103] The operation of the expansion machine part and the compressor part of the first compression expander as the first expander 112A and the first compression stage 112B, the expansion machine part and the compressor part of the second compression expander as the second expander 134A and the second compression stage 134B, and the expansion machine part and the compressor part of the third compression expander as the third expander 138A and the third compression stage 138B also provides additional efficiency by connecting and supplying the outlet of the multistage refrigerant compressor 124 to the inlet of the compressor part.

[0104] Referring now to FIG. 2, there is shown a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a second embodiment of the present invention. In FIG. 2, the equipment and flows downstream of the LP phase separator 247 are not shown since they are the same as those in FIG. 1. Also, for simplicity, in the arrangement depicted in FIG. 2, the first, second, and third expanders 212A, 234A, 238A are not the expander portions of the compression expanders, and the parallel compression stages 112B, 134B, and 138B are omitted, and all compression for the production of the compressed refrigerant 242 is provided by the multi-stage refrigerant compressor 224.

[0105] The method and system depicted in FIG. 2 differ from the method and system depicted in FIG. 1 in that not all of the pre-cooled feed stream 207 exiting the first heat exchanger section 206A is recombined with the bypass stream 208 and introduced into the HP phase separator 210. Rather, in the arrangement depicted in FIG. 2, a portion of the pre-cooled feed stream 207 exiting the first heat exchanger section 206A (representing 25 to 2 percent, more preferably 15 to 5 percent of the flow of the pre-cooled feed stream 207) is further cooled by passing through the warming side circuit of the second heat exchanger section 206A, cooled from the stream 213 at a temperature of -90°C to -60°C, more preferably -80°C to -70°C, and then expanded at a third intermediate location above the first intermediate location where the expanded stream 214 is introduced into the distillation column 217, and introduced into the distillation column, and a separation section 217B exists between the third intermediate location and the first intermediate location.

[0106] The use of this additional feed stream 213 to the distillation column 217 cooled in the manner described above can further improve NGL recovery and reduce the specific output of the process.

[0107] All of the variations, alternative embodiments, and alternative arrangements described with reference to the embodiment depicted in FIG. 1 are similarly applicable to the embodiment depicted in FIG. 2 and the embodiments depicted in the further figures described below.

[0108] Referring now to FIG. 3, there is shown a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a third embodiment of the present invention. In FIG. 3, the equipment and flows downstream of the LP phase separator 347 are not shown since they are the same as those in FIG. 1. Also, for simplicity, in the arrangement depicted in FIG. 3, the first, second, and third expanders 312A, 334A, 338A are not the expander portions of the compression-expanders, and the parallel compression stages 112B, 134B, and 138B are omitted, and all compression for the production of the compressed refrigerant 342 is provided by the multi-stage refrigerant compressor 324.

[0109] The method and system depicted in FIG. 3 differ from the method and system depicted in FIG. 2 in that the third heat exchanger section 206C of the main heat exchanger is removed and not used. This reduces the number of equipment, but has an adverse effect on the specific output of the process.

[0110] Referring now to FIG. 4, there is shown a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a third embodiment of the present invention. In FIG. 4, the equipment and flows downstream of the LP phase separator 447 are not shown since they are the same as the equipment and flows in FIG. 1, except as otherwise described below. Also, for simplicity, in the arrangement depicted in FIG. 4, the first and second expanders 412A, 434A are not the expander portions of the compression-expanders, and the parallel compression stages 112B and 134B are omitted, and all compression for the production of the compressed refrigerant 442 is provided by the multi-stage refrigerant compressor 424.

[0111] The method and system depicted in FIG. 4 differ from the method and system depicted in FIG. 1 in that the third expander 138A is removed (and thus the second expanded refrigerant stream 144 also does not exist), the second heat exchanger section 106B of the main heat exchanger is removed and replaced with the economizer heat exchanger section 406B, the natural gas vapor stream 420 taken from the upper part of the distillation column 417 is cooled separately from the first expanded refrigerant stream 449 exiting the low-temperature side of the third heat exchanger section 406C, the reflux streams 462, 463 to the distillation column 417 are from different sources, and the HP phase separator 110 is also removed. This reduces the number of devices but has an adverse effect on the specific output of the process.

[0112] More specifically, in the method and system of FIG. 4, the pre-treated natural gas feed stream 402 is expanded in the first expander 412A and introduced into the distillation column 417 at an intermediate location below the separation section 417A of the column and above the separation section 417D of the column. The natural gas vapor stream 420 taken from the upper part of the distillation column passes through and is heated on the low-temperature side of the economizer heat exchanger section 406B and further heated on the low-temperature side of the first heat exchanger section 406A. The natural gas vapor stream 421 passes through a separate circuit on the low-temperature side of the first heat exchanger section 406A rather than through the circuit on the low-temperature side of the first heat exchanger section 406A through which the first expanded refrigerant stream 449 passes. The heated first expanded refrigerant stream 422 exiting the low-temperature side of the first heat exchanger section 406A is sent to the low-pressure inlet of the multistage refrigerant compressor 424, and the heated natural gas vapor stream 415 exiting the low-temperature side of the first heat exchanger section 406A is sent to the medium-pressure inlet of the multistage refrigerant compressor 424, where it is combined with the first expanded refrigerant and further compressed. A portion of the cooled stream 456 (including the first and second portions of the compressed refrigerant) exiting the heating side of the first heat exchanger section 406 is taken out to form the reflux stream 462, which passes through the heating side of the economizer heat exchanger section 406B and is further cooled before being expanded and introduced into the upper part of the distillation column 417.

[0113] Referring now to FIG. 5, there is shown a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a fifth embodiment of the present invention. In FIG. 5, the equipment and flows downstream of the LP phase separator 547 are not shown since they are the same as the equipment and flows of FIG. 1, except where otherwise described below. Also, for simplicity, in the arrangement depicted in FIG. 5, the first and second expanders 512A, 534A are not the expander portions of the compression-expanders and the parallel compression stages 112B and 134B are omitted, and all compression for the production of the compressed refrigerant 542 is provided by the multi-stage refrigerant compressor 524.

[0114] The method and system depicted in FIG. 5 differ from the method and system shown in FIG. 1 in that the third expander 138A has been removed (and thus the second expanded refrigerant stream 144 also does not exist), the third heat exchanger section 106C of the main heat exchanger has been removed, and the HP phase separator 110 has also been removed. This reduces the number of pieces of equipment but has an adverse effect on the specific output of the process.

[0115] More specifically, in the method and system of FIG. 5, the pre-treated natural gas feed stream 502 is expanded in a first expander 512A and introduced into a distillation column 517 at an intermediate location below the separation section 517A of the column and above the separation section 517D of the column. In the illustrated embodiment, the natural gas vapor stream 520 withdrawn from the top of the distillation column passes through the low temperature side of a second heat exchanger section 506B and is heated before passing through the low temperature side of a first heat exchanger section 506A where it is further heated. The natural gas vapor stream 520 passes through separate circuits on the low temperature sides of the second and first heat exchanger sections 506B and 506A rather than through the circuit on the low temperature side of the heat exchanger section through which the first expanded refrigerant stream 548 passes. The heated first expanded refrigerant stream 522 exiting the low temperature side of the first heat exchanger section 506A is sent to the low pressure inlet of a multi-stage refrigerant compressor 524, and the heated natural gas vapor stream 515 exiting the low temperature side of the first heat exchanger section 506A is sent to the intermediate pressure inlet of the multi-stage refrigerant compressor 524 where it is combined with and further compressed by the first expanded refrigerant. In an alternative embodiment, the natural gas vapor stream 520 can be combined with the first expanded refrigerant stream 548 in the same manner as shown in FIG. 1 prior to heating and compression of the combined stream. This approach allows for the use of a coiled heat exchanger section for the first and second heat exchanger sections 506A and 506B and simplifies the design of the multi-stage refrigerant compressor 524, although it may result in a slight further increase in specific output.

[0116] Referring now to FIG. 6, a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a sixth embodiment of the present invention are shown. In FIG. 6, equipment and streams downstream of the LP phase separator 647 are not shown since they are identical to the equipment and streams of FIG. 1 except as otherwise described below. Also, for simplicity, in the arrangement depicted in FIG. 6, the first and second expanders 612A, 634A are not the expander portions of compression expanders, and the parallel compression stages 112B and 134B are omitted, and all compression for the production of compressed refrigerant 642 is provided by a multi-stage refrigerant compressor 624.

[0117] The method and system depicted in FIG. 6 differ from the method and system depicted in FIG. 5 in that a third heat exchanger section 606C of the main heat exchanger is reintroduced and the natural gas vapor stream 620 is combined with the first expanded refrigerant stream 649 before being heated and compressed in the same manner as shown in FIG. 1 for the combined stream. This approach has a better specific output than that shown in FIG. 5.

[0118] Referring now to FIG. 7, there is shown a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to a seventh embodiment of the present invention. In FIG. 7, the equipment and flows downstream of the LP phase separator 747 are not shown as they are the same as those in FIG. 1. Also, for simplicity, in the arrangement depicted in FIG. 7, the second and third expanders 734A and 738A are not the expander portions of the compression-expanders, the parallel compression stages 712B, 734B, and 738B are omitted, and all compression for the production of the compressed refrigerant 742 is provided by the multistage refrigerant compressor 724.

[0119] The method and system depicted in FIG. 7 differ from the method and system depicted in FIG. 1 in that the HP phase separator 110 is removed, and the first expander 712B is the expander portion of the compression-expander, where the compressor portion of the compressor is used to compress the natural gas feed before expansion.

[0120] More specifically, in the method and system of FIG. 7, the pretreated natural gas feed stream 702 is first compressed in the supply compression stage 712B that constitutes the compressor portion of the first compression-expander, cooled in the associated aftercooler 707, then expanded in the first expander 712A that forms the expansion portion of the first compression-expander, and introduced into the distillation column 717 at an intermediate location below the separation section 717A of the column and above the separation section 717D of the column.

[0121] By compressing the natural gas feed stream prior to expansion, the arrangement depicted in FIG. 7 eliminates the need to precool the natural gas feed stream in one or more of the main heat exchangers, thus simplifying the design of the exchanger. Compared to the arrangement shown in FIG. 2, the possibility of freezing heavy feed components in the second heat exchanger 706B is also eliminated. Further, removing the HP feed separator 110 and reducing the number of feed streams to the distillation column simplifies the system design. Compared to the arrangement shown in FIG. 2, the arrangement shown in FIG. 7 has a better specific output.

[0122] Referring now to FIG. 8, a method and system for removing NGL from a natural gas feed stream and liquefying the natural gas feed stream according to an eighth embodiment of the present invention are shown.

[0123] The method and system depicted in FIG. 8 differ in that the compressed BOG gas stream 897 and the compressed flash gas stream 889 do not combine to form a recycle stream 198 that passes through the warming sides of the first heat exchanger section 106A, the second heat exchanger section 106B, and the third heat exchanger section 106C of the main heat exchanger, is cooled and liquefied, flashed across a J-T valve, and introduced into the HP flash gas phase separator 167 to form a third liquefied natural gas stream 199. Instead, in the arrangement shown in FIG. 8, the compressed BOG gas stream 897 and the compressed flash gas stream 889 are combined with the combined natural gas vapor, first expansion refrigerant, and second expansion refrigerant stream 822 exiting the cold side of the first heat exchanger section 806A, and the combined stream 899 of natural gas vapor, first expansion refrigerant, second expansion refrigerant, flash gas, and BOG is then sent to the inlet of a multistage refrigerant compressor 824.

[0124] Similar to the embodiment shown in FIG. 7, in the method and system of FIG. 8, the HP phase separator 110 is also removed, and the first expander 812B is the expander part of the compression expander, and its compressor part is such that the supply is expanded within the first expander 812B and introduced into the distillation column 817 at an intermediate location below the separation section 817A and above the separation section 817B of the column before being compressed by the natural gas supply 802. As a result, in the arrangement shown in FIG. 8, the parallel compression stage consists of only two stages 834B and 838B, and the first stage 112B is omitted.

[0125] In the specific arrangement shown in FIG. 8, the first, second, and third heat exchanger sections 806A, 806B, 806C of the main heat exchanger are all coil-wound heat exchanger sections, and the third heat exchanger section 806C is positioned below the second heat exchanger section 806B (similarly, positioned below the first heat exchanger section 806A).

[0126] In such an arrangement, in an alternative embodiment, it would be possible to integrate the LP phase separator 847 with a coil-wound heat exchanger unit that includes the third heat exchanger section 806C (in the specific embodiment illustrated in FIG. 8, the coil-wound heat exchanger unit that includes the third heat exchanger section also includes the second heat exchanger section 806B). More specifically, in such an arrangement, the coil-wound heat exchanger unit has a shell casing that includes the third heat exchanger section (and optionally, the second heat exchanger section above it, or the second and first heat exchanger sections), and a phase separation section positioned below the third heat exchanger section. The first low-temperature refrigerant flow and the second low-temperature refrigerant flow are expanded and introduced into the phase separation section of the coil-wound heat exchanger unit, where they are separated into a liquid phase and a vapor phase. The liquid phase is taken out from the bottom of the coil-wound heat exchanger unit to form a first liquefied natural gas flow, and the vapor phase forms a first expanded refrigerant flow that rises through the shell side of the third heat exchanger section.

Example

[0127] Example 1 In this example, Aspen simulation software, version 10, available from Aspen Technologies, Inc. was used to simulate a method and system for cooling and liquefying natural gas as depicted in FIG. 1.

[0128] Table 1 shows the flow data from the simulation example. In this example, the multistage refrigerant compressor 124 has two stages and operates in two strings, each string having an approximate gas horsepower of 48.8 MW. The flash gas compressor 187 and the BOG compressor 195 had approximate gas horsepowers of 36.6 MW and 12.0 MW, respectively. In the simulated process, 90 mol% of the C3+ components from the natural gas feed were recovered in the NGL stream 119 withdrawn from the bottom of the distillation column 117. Table 1:

Table 1A

Table 1B

Table 1C

Table 1D

Table 1E

Table 1F

Table 1G

Table 1H

Table 1I

[0129] The present invention is not limited to the details described above with reference to the preferred embodiments, and it will be understood that numerous modifications and variations can be made without departing from the spirit or scope of the invention as defined in the following claims. Examples of embodiments of the present invention are listed in the following items [Aspect 1] to [Aspect 20]. [Aspect 1] A method for removing liquefied natural gas from a natural gas supply stream and liquefying the natural gas supply stream, comprising: (a) expanding and / or cooling the natural gas supply stream and introducing the stream into a distillation column having one or more separation sections, wherein the natural gas supply stream is introduced into the distillation column below at least one of the separation sections; (b) withdrawing a liquefied natural gas stream from the bottom of the distillation column; (c) withdrawing a natural gas vapor stream from the top of the distillation column; (d) heating the natural gas vapor stream and a first expanded refrigerant stream in one or more heat exchanger sections, compressing the resulting heated stream, and combining the streams to form a compressed refrigerant, wherein the natural gas vapor stream and the first expanded refrigerant stream can be combined before, during, or after being heated and compressed; (e) cooling at least a first portion of the compressed refrigerant via indirect heat exchange between the natural gas vapor stream and the first expanded refrigerant stream that are heated in step (d) to form a first low-temperature refrigerant stream; (f) expanding the first low-temperature refrigerant stream, separating the stream into a vapor phase and a liquid phase, and forming a first liquefied natural gas stream from the liquid phase and a first expanded refrigerant stream from the vapor phase; (g) forming a reflux stream, expanding the reflux stream, and introducing the reflux stream into the top of the distillation column to provide reflux to the distillation column, wherein the reflux stream is formed from a portion of the first liquefied natural gas stream, a portion of the liquid phase separated in step (f), a portion of the first low-temperature refrigerant stream withdrawn from the stream before the stream is separated in step (f), a further portion of the compressed refrigerant cooled via indirect heat exchange between the natural gas vapor stream and the first expanded refrigerant stream that are heated in step (d), and / or a portion of a liquefied natural gas stream or a liquefied natural gas product derived from the first liquefied natural gas stream. [Aspect 2] In process (a), the natural gas feed stream is introduced into a distillation column having two or more separation sections, and the expanded natural gas feed stream is introduced into the distillation column below at least one of the separation sections and above at least another one of the separation sections, the method according to aspect 1. [Aspect 3] The method being (h) further comprising the step of providing boil-up to the distillation column by reboiling a portion of the liquid at the bottom of the distillation column, the method according to aspect 2. [Aspect 4] In process (a), the natural gas feed stream is expanded before being introduced into the distillation column, the method according to aspect 1. [Aspect 5] In process (a), the natural gas feed stream is cooled before being introduced into the distillation column and then expanded, the natural gas feed stream is separated into a vapor phase and a liquid phase after being cooled, the vapor phase is expanded and introduced into the distillation column at a first location below at least one separation section of the column, the liquid phase is expanded and introduced into the distillation column at a second location below the first location, and at least one separation section is present between the first location and the second location, the method according to aspect 4. [Aspect 6] In process (a), the natural gas feed stream is cooled before being introduced into the distillation column, and at least a portion of the natural gas feed stream is cooled via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream that is being heated in process (d), the method according to aspect 1. [Aspect 7] In process (g), the reflux stream is formed from a portion of the first liquefied natural gas stream separated in process (f) and / or a portion of the liquid phase, the method according to aspect 1. [Aspect 8] The first expanded refrigerant stream is formed at a temperature lower than the natural gas vapor stream, and in process (e), at least the first portion of the compressed refrigerant is cooled via indirect heat exchange with the vapor stream of the natural gas and the first expanded refrigerant stream and then further cooled via indirect heat exchange with the first expanded refrigerant stream to form the first low-temperature refrigerant stream, the method according to aspect 1. [Aspect 9] Step (e) includes cooling the first portion of the compressed refrigerant and the second portion of the compressed refrigerant through indirect heat exchange between the natural gas vapor stream and the first expanded refrigerant stream that are heated in step (d), to form the first low-temperature refrigerant stream and the second low-temperature refrigerant stream respectively, wherein the first and second portions of the compressed refrigerant are cooled with respect to the natural gas vapor stream and the first expanded refrigerant stream, and the first portion of the compressed refrigerant is then further cooled with respect to the natural gas vapor stream and the first expanded refrigerant stream, so that the first low-temperature refrigerant stream is formed at a temperature lower than the second low-temperature refrigerant stream. The method according to aspect 1, wherein step (f) includes expanding the first low-temperature refrigerant stream, expanding the second low-temperature refrigerant stream, combining the streams, separating them into a vapor phase and a liquid phase, and forming the first liquefied natural gas stream from the liquid phase and the first expanded refrigerant stream from the vapor phase. [Aspect 10] The method is (i) further including a step of expanding a third portion of the compressed refrigerant to form a second expanded refrigerant stream, wherein the second expanded refrigerant stream is formed at a temperature higher than the first expanded refrigerant stream or the natural gas vapor stream. Step (d) includes heating the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream in one or more heat exchanger sections, compressing the resulting heated stream, and combining the streams to form a compressed refrigerant, wherein the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream can be combined before, during, or after being heated and compressed. The method according to aspect 1, wherein step (e) includes cooling at least the first portion of the compressed refrigerant through indirect heat exchange with the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream that are heated in step (d), to form the first low-temperature refrigerant stream, wherein at least the first portion of the compressed refrigerant is cooled with respect to the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream, and then further cooled with respect to the natural gas vapor stream and the first expanded refrigerant stream. [Aspect 11] Step (e) includes indirectly cooling the first portion of the compressed refrigerant and the second portion of the compressed refrigerant via indirect heat exchange with the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream that are heated in step (d), to form the first low-temperature refrigerant stream and the second low-temperature refrigerant stream, respectively, wherein the first and second portions of the compressed refrigerant are cooled with respect to the natural gas vapor stream, the first expanded refrigerant stream, and the second expanded refrigerant stream, and the first portion of the compressed refrigerant is then further cooled with respect to the natural gas vapor stream and the first expanded refrigerant stream, such that the first low-temperature refrigerant stream is formed at a lower temperature than the second low-temperature refrigerant stream, The method according to aspect 10, wherein step (f) includes expanding the first low-temperature refrigerant stream, expanding the second low-temperature refrigerant stream, combining the streams, separating them into a vapor phase and a liquid phase, and forming the first liquefied natural gas stream from the liquid phase and the first expanded refrigerant stream from the vapor phase. [Aspect 12] The second low-temperature refrigerant stream is expanded in an expander portion of a compression-expander having a compressor portion used to compress at least a portion of the natural gas vapor stream and / or the first expanded refrigerant stream in step (d), and / or The method according to aspect 9, wherein the third portion of the compressed refrigerant is expanded in an expander portion of a compression-expander having a compressor portion used to compress at least a portion of the natural gas vapor stream and / or the first expanded refrigerant stream in step (d). [Aspect 13] The method according to aspect 1, wherein in step (f), the first low-temperature refrigerant stream is separated into a vapor phase and a liquid phase in a phase separator. [Aspect 14] The method is (j) further comprising the step of further cooling at least a portion of the first liquefied natural gas stream to form a liquefied natural gas product stream, according to the method of aspect 1. [Aspect 15] The method according to aspect 14, wherein step (j) includes flashing at least a portion of the first liquefied natural gas stream to form the liquefied natural gas product stream and one or more flash gas streams. [Aspect 16] The method is (k) further comprising the step of cooling and liquefying a fourth portion of the compressed refrigerant via indirect heat exchange with the one or more flash gas streams to form a second liquefied natural gas stream or a set of liquefied natural gas streams, The method according to aspect 15, wherein step (j) comprises flashing at least a portion of the first liquefied natural gas stream and the second liquefied natural gas stream or set of liquefied natural gas streams to form the liquefied natural gas product stream and the one or more flash gas streams. [Aspect 17] The method further comprises: (l) cooling a fifth portion of the compressed refrigerant via indirect heat exchange with the one or more flash gas streams, and then combining the fifth portion of the compressed refrigerant with the at least first portion of the compressed refrigerant during the cooling of the at least first portion of the compressed refrigerant in step (e) to form the first low temperature refrigerant stream, as described in aspect 16. [Aspect 18] The method further comprises: (m) compressing the one or more flash gas streams to form a compressed flash gas stream, and cooling and liquefying the compressed flash gas stream via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream that are being heated in step (d) to form a third liquefied natural gas stream, and step (j) comprises flashing at least a portion of the first liquefied natural gas stream and the third liquefied natural gas stream to form the liquefied natural gas product stream and the one or more flash gas streams, as described in aspect 15. [Aspect 19] The method further comprises: (m) compressing the one or more flash gas streams and combining them with the natural gas vapor stream and the first expanded refrigerant stream to form the compressed refrigerant, as described in aspect 15. [Aspect 20] A system for removing liquid natural gas from a natural gas feed stream and liquefying the natural gas feed stream, comprising: one or more expansion devices and / or heat exchanger sections arranged and configured to expand and / or cool the natural gas feed stream to form an expanded and / or cooled natural gas feed stream; and a distillation column having one or more separation sections, the distillation column being arranged and configured to receive the expanded and / or cooled natural gas feed stream in the distillation column below at least one of the separation sections and to separate the expanded and / or cooled natural gas feed stream into a liquid natural gas stream withdrawn from the bottom of the distillation column and a natural gas vapor stream withdrawn from the top of the distillation column. One or more conduits, heat exchanger sections, and compression stages that are arranged and configured to receive and heat the natural gas vapor stream and the first expanded refrigerant stream, and to compress the resulting heated stream and combine the streams to form a compressed refrigerant, where the one or more conduits, heat exchanger sections, and compression stages can be arranged and configured such that the natural gas vapor stream and the first expanded refrigerant stream are combined before, during, or after being heated and compressed, one or more conduits, heat exchanger sections, and compression stages One or more conduits arranged and configured to pass at least a first portion of the compressed refrigerant through the one or more heat exchanger sections to cool the at least first portion of the compressed refrigerant via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream to form a first low-temperature refrigerant stream One or more expansion and separation devices for expanding the first low-temperature refrigerant stream, separating the stream into a vapor phase and a liquid phase, and forming the first liquefied natural gas stream from the liquid phase and the first expanded refrigerant stream from the vapor phase One or more conduits and expansion devices arranged and configured to receive a reflux stream, expand the reflux stream, and introduce the reflux stream into the upper portion of the distillation column to provide reflux to the distillation column, where the reflux stream is a portion of the first liquefied natural gas stream, a portion of the liquid phase separated in step (f), a portion of the first low-temperature refrigerant stream withdrawn from the stream before the stream is separated in step (f), a further portion of the compressed refrigerant cooled via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream heated in step (d), and / or a portion of the liquefied natural gas stream or a liquefied natural gas product derived from the first liquefied natural gas stream, one or more conduits and expansion devices, a system

Claims

Claim 1 A method for removing liquefied natural gas from a natural gas feed stream and liquefying the natural gas feed stream, comprising: (a) expanding and / or cooling the natural gas feed stream and introducing the stream into a distillation column having one or more separation sections, wherein the natural gas feed stream is introduced into the distillation column below at least one of the separation sections; (b) withdrawing a liquefied natural gas stream from the bottom of the distillation column; (c) withdrawing a natural gas vapor stream from the top of the distillation column; (d) heating the natural gas vapor stream and a first expanded refrigerant stream in one or more heat exchanger sections, compressing the resulting heated stream, and combining the streams to form a compressed refrigerant, wherein the natural gas vapor stream and the first expanded refrigerant stream are combined before, during, or after being heated and compressed; (e) cooling a first portion and a second portion of the compressed refrigerant via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream that are heated in step (d) to form a first cryogenic refrigerant stream and a second cryogenic refrigerant stream, respectively; wherein the first and second portions of the compressed refrigerant are cooled against the natural gas vapor stream and the first expanded refrigerant stream, and the first portion of the compressed refrigerant is then further cooled against the natural gas vapor stream and the first expanded refrigerant stream, such that the first cryogenic refrigerant stream is formed at a lower temperature than the second cryogenic refrigerant stream; (f) expanding the first cryogenic refrigerant stream, expanding the second cryogenic refrigerant stream, combining the resulting expanded streams, separating the combined streams into a vapor phase and a liquid phase, and withdrawing a first liquefied natural gas stream from the liquid phase and a first expanded refrigerant stream from the vapor phase; (g) forming a reflux stream, expanding the reflux stream, and introducing the reflux stream into an upper portion of the distillation column to provide reflux to the distillation column, wherein the reflux stream is formed from a portion of the first liquefied natural gas stream, a portion of the liquid phase separated in step (f), a portion of the first cryogenic refrigerant stream withdrawn from the stream before the stream is separated in step (f), a further portion of the compressed refrigerant cooled via indirect heat exchange between the natural gas vapor stream heated in step (d) and the first expansion refrigerant stream, and / or a portion of a liquefied natural gas stream or liquefied natural gas product derived from the first liquefied natural gas stream; and providing; and a method comprising the steps of. **Claim 2** The method according to claim 1, wherein in step (a), the natural gas feed stream is introduced into a distillation column having two or more separation sections, and the expanded natural gas feed stream is introduced into the distillation column below at least one of the separation sections and above at least another one of the separation sections. **Claim 3** The method is The method according to claim 2, further comprising the step of (h) providing boil-up to the distillation column by reboiling a portion of the liquid at the bottom of the distillation column. **Claim 4** The method according to claim 1, wherein in step (a), the natural gas feed stream is expanded before being introduced into the distillation column. **Claim 5** The method according to claim 4, wherein in step (a), the natural gas feed stream is cooled and then expanded before being introduced into the distillation column, the natural gas feed stream is separated into a vapor phase and a liquid phase after being cooled, the vapor phase is expanded and introduced into the distillation column at a first location below at least one separation section of the distillation column, the liquid phase is expanded and introduced into the distillation column at a second location below the first location, and at least one separation section is present between the first location and the second location. **Claim 6** The method according to claim 1, wherein in step (a), the natural gas feed stream is cooled before being introduced into the distillation column, and at least a portion of the natural gas feed stream is cooled via indirect heat exchange with the natural gas vapor stream and the first expansion refrigerant stream heated in step (d). **Claim 7** The method according to claim 1, wherein in step (g), the reflux flow is formed from a portion of the first liquefied natural gas flow separated in step (f) and / or a portion of the liquid phase.

8. The method according to claim 1, wherein the first expanded refrigerant flow is formed at a temperature lower than the natural gas vapor flow, and in step (e), the first portion of the compressed refrigerant is cooled through indirect heat exchange with the natural gas vapor flow and the first expanded refrigerant flow, and then further cooled through indirect heat exchange with the first expanded refrigerant flow to form the first low-temperature refrigerant flow.

9. The method comprises (i) a step of expanding a third portion of the compressed refrigerant to form a second expanded refrigerant flow, wherein the second expanded refrigerant flow is formed at a temperature higher than the first expanded refrigerant flow or the natural gas vapor flow. Step (d) includes heating the natural gas vapor flow, the first expanded refrigerant flow, and the second expanded refrigerant flow in one or more heat exchanger sections, compressing the resulting heated flow, and combining the flows to form a compressed refrigerant, wherein the natural gas vapor flow, the first expanded refrigerant flow, and the second expanded refrigerant flow are combined before, during, or after being heated and compressed. Step (e) includes cooling the first portion of the compressed refrigerant and the second portion of the compressed refrigerant through indirect heat exchange with the natural gas vapor flow, the first expanded refrigerant flow, and the second expanded refrigerant flow heated in step (d) to form the first low-temperature refrigerant flow and the second low-temperature refrigerant flow respectively, wherein the first and second portions of the compressed refrigerant are cooled with respect to the natural gas vapor flow, the first expanded refrigerant flow, and the second expanded refrigerant flow, and the first portion of the compressed refrigerant is then further cooled with respect to the natural gas vapor flow and the first expanded refrigerant flow, so that the first low-temperature refrigerant flow is formed at a temperature lower than the second low-temperature refrigerant flow. The method according to claim 1.

10. The second low-temperature refrigerant flow is expanded in the expansion portion of a compression expander having a compressor portion used to compress at least a portion of the natural gas vapor flow and / or the first expanded refrigerant flow in step (d), and / or The method according to claim 9, wherein the third portion of the compressed refrigerant is expanded in an expander portion of a compression expander having a compressor portion used to compress at least a portion of the natural gas vapor stream and / or the first expanded refrigerant stream in step (d).

11. The method according to claim 1, wherein in step (f), the obtained expanded stream is separated into a vapor phase and a liquid phase in one or more phase separators.

12. The method is (j) further comprising the step of further cooling at least a portion of the first liquefied natural gas stream to form a liquefied natural gas product stream, according to claim 1 of the method.

13. The method according to claim 12, wherein step (j) comprises flashing at least a portion of the first liquefied natural gas stream to form the liquefied natural gas product stream and one or more flash gas streams.

14. The method is (k) further comprising the step of cooling and liquefying a fourth portion of the compressed refrigerant via indirect heat exchange with the one or more flash gas streams to form a second liquefied natural gas stream or a set of liquefied natural gas streams, The method according to claim 13, wherein step (j) comprises flashing at least a portion of the first liquefied natural gas stream and the second liquefied natural gas stream or the set of liquefied natural gas streams to form the liquefied natural gas product stream and the one or more flash gas streams.

15. The method is (l) further comprising the step of cooling a fifth portion of the compressed refrigerant via indirect heat exchange with the one or more flash gas streams, and then combining the fifth portion of the compressed refrigerant with the first portion of the compressed refrigerant during the cooling of the at least first portion of the compressed refrigerant in step (e) to form the first low-temperature refrigerant stream, according to claim 14 of the method.

16. The method is (m) further comprising the step of compressing the one or more flash gas streams to form a compressed flash gas stream, and cooling and liquefying the compressed flash gas stream via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream heated in step (d) to form a third liquefied natural gas stream, The method of claim 13, wherein step (j) comprises flashing at least a portion of the first liquefied natural gas stream and the third liquefied natural gas stream to form the liquefied natural gas product stream and the one or more flash gas streams.

17. The method further comprises: (m) compressing the one or more flash gas streams and combining them with the natural gas vapor stream and the first expanded refrigerant stream to form the compressed refrigerant, as claimed in claim 13.

18. A system for removing liquid natural gas from a natural gas feed stream and liquefying the natural gas feed stream, comprising: one or more expansion devices and / or heat exchanger sections arranged and configured to expand and / or cool the natural gas feed stream to form an expanded and / or cooled natural gas feed stream; a distillation column having one or more separation sections, the distillation column being arranged and configured to receive the expanded and / or cooled natural gas feed stream in at least one of the separation sections below the distillation column and to separate the expanded and / or cooled natural gas feed stream into a liquid natural gas stream withdrawn from the bottom of the distillation column and a natural gas vapor stream withdrawn from the top of the distillation column; one or more conduits, heat exchanger sections, and compression stages arranged and configured to receive and warm the natural gas vapor stream and the first expanded refrigerant stream, and to compress the resulting warmed stream and combine the streams to form the compressed refrigerant, the one or more conduits, heat exchanger sections, and compression stages being arranged and configured such that the natural gas vapor stream and the first expanded refrigerant stream are combined before, during, or after being warmed and compressed. Pass the first portion of the compressed refrigerant and the second portion of the compressed refrigerant through the one or more heat exchanger sections to cool the first portion of the compressed refrigerant and the second portion of the compressed refrigerant via indirect heat exchange between the natural gas vapor stream and the first expanded refrigerant stream, respectively forming a first low-temperature refrigerant stream and a second low-temperature refrigerant stream, wherein the first and second portions of the compressed refrigerant are cooled with respect to the natural gas vapor stream and the first expanded refrigerant stream, and the first portion of the compressed refrigerant is then further cooled with respect to the natural gas vapor stream and the first expanded refrigerant stream, so that the first low-temperature refrigerant stream is formed at a lower temperature than the second low-temperature refrigerant stream, and one or more conduits arranged and configured as such; One or more expansion and separation devices arranged and configured to expand the first low-temperature refrigerant stream, expand the second low-temperature refrigerant stream, combine the resulting expanded streams, separate them into a vapor phase and a liquid phase, and form a first liquefied natural gas stream from the liquid phase and the first expanded refrigerant stream from the vapor phase; One or more conduits and expansion devices arranged and configured to receive a reflux stream, expand the reflux stream, and introduce the reflux stream into the upper part of the distillation column to provide reflux to the distillation column, wherein the reflux stream is a part of the first liquefied natural gas stream, a part of the liquid phase separated in step (f), a part of the first low-temperature refrigerant stream withdrawn from the stream before the stream is separated in step (f), a further portion of the compressed refrigerant cooled via indirect heat exchange with the natural gas vapor stream and the first expanded refrigerant stream heated in step (d), and / or a liquefied natural gas stream or a part of a liquefied natural gas product derived from the first liquefied natural gas stream, and a system comprising one or more conduits and expansion devices formed therefrom.

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