Integrated process for NGL (natural gas liquids recovery) and LNG (liquefaction of natural gas)

Abstract

The invention relates to an integrated process and apparatus for liquefaction of natural gas and recovery of natural gas liquids. In particular, the improved process and apparatus reduces the energy consumption of a Liquefied Natural Gas (LNG) unit by using a portion of the already cooled overhead vapor from a fractionation column from an NGL (natural gas liquefaction) unit to, depending upon composition, provide, for example, reflux for fractionation in the NGL unit and/or a cold feed for the LNG unit, or by cooling, within the NGL unit, a residue gas originating from a fractionation column of the NGL unit and using the resultant cooled residue gas to, depending upon composition, provide, for example, reflux/feed for fractionation in the NGL and/or a cold feed for the LNG unit, thereby reducing the energy consumption of the LNG unit and rendering the process more energy-efficient.

Claims

1. A process for integrated liquefaction of natural gas and recovery of natural gas liquids, said process comprising: cooling a feed stream containing light hydrocarbons in one or more heat exchangers, wherein said feed stream is cooled and partially condensed by indirect heat exchange; introducing the partially condensed feed stream into a gas/liquid cold separator producing an overhead gaseous stream and bottoms liquid stream which are to be introduced into a fractionation system, said fractionation system comprising a light ends fractionation column and a heavy ends fractionation column; expanding at least a portion of the overhead gaseous stream from the gas/liquid cold separator and introducing said expanded overhead gaseous stream into a lower region of said light ends fractionation column; introducing at least a portion of the bottoms liquid stream from gas/liquid cold separator into said heavy ends fractionation column at an intermediate point thereof; removing a first liquid product stream from the bottom of said heavy ends fractionation column; removing a overhead gaseous stream from the top of said light ends fractionation column, and said process further comprising: (i) subjecting a first portion of the light ends fractionation column overhead gaseous stream to indirect heat exchange with an overhead gaseous stream removed from the top of said heavy ends fractionation column, whereby said overhead gaseous stream from the top of said heavy ends fractionation column is cooled and partially condensed, and introducing the cooled and partially condensed overhead gaseous stream from the top of said heavy ends fractionation column into the light ends fractionation column; (ii) removing a second portion of the overhead gaseous stream from said light ends fractionation column as a side stream, and subjecting said side stream to indirect heat exchange for further cooling, partially liquefying said side stream via indirect heat exchange, wherein said side stream of the overhead gaseous stream from the light ends fractionation column is split off from the overhead gaseous stream prior to the indirect heat exchange between said first portion of the light ends fractionation column overhead gaseous stream and the overhead gaseous stream removed from the top of said heavy ends fractionation column; (iii) introducing the partially liquefied side stream into a further separation means, recovering a liquid stream from said further separation means and introducing the recovered liquid stream into the light ends fractionation column as a liquid reflux stream and/or the heavy ends fractionation column as a liquid reflux stream, and (iv) recovering an overhead vapor stream from said further separation means, subjecting said overhead vapor stream from said further separation means to indirect heat exchange for additional cooling and partial condensation, and feeding the resultant vapor and condensate to an LNG separator wherein a final LNG liquid product is produced.

2. A process according to claim 1, further comprising cooling said feed stream containing light hydrocarbons in a main heat exchanger wherein the feed stream partially condensed by indirect heat exchange; introducing said first liquid product stream from said heavy ends fractionation column into said main heat exchanger for indirect heat exchanger with said feed stream; wherein after subjecting said first portion of said overhead gaseous stream from the top of said light ends fractionation column to indirect heat with said overhead gaseous stream removed from the top of said heavy ends fractionation column, removing said first portion of the overhead gaseous stream from said light ends fractionation column as residue gas; wherein, before said side stream is subjected to said indirect heat exchange for further cooling, said side stream is partially liquefying across a flow-control valve.

3. A process according to claim 1, further comprising: introducing said feed stream containing light hydrocarbons into a main heat exchanger wherein said feed stream is cooled and partially condensed by indirect heat exchange; introducing the liquid product stream from the bottom of said heavy ends fractionation column into said main heat exchanger where it undergoes indirect heat exchanger with said feed stream; and wherein the liquid stream recovered from said further separation means is introduced into said light ends fractionation column as reflux.

4. A process according to claim 2, wherein said liquid stream recovered from said further separation means is introduced into said light ends fractionation column as said liquid reflux stream.

5. A process according to claim 1, wherein said liquid stream recovered from the further separation means is introduced into the heavy ends fractionation column as liquid reflux.

6. A process according to claim 1, wherein a portion of said bottoms liquid stream from the gas/liquid cold separator is delivered to a liquid/liquid heat exchanger for indirect heat exchange with said bottom liquid stream removed from the light ends fractionation column, and then said portion of bottoms liquid stream from the gas/liquid cold separator is fed to an intermediate region of the light ends fractionation column as a liquid reflux.

7. A process according to claim 1, wherein a a portion of the gaseous overhead stream removed from the top of cold separator and a portion of bottoms liquid stream from cold separator are combined and the resultant combined stream is subjected to indirect heat exchange with the overhead vapor from the light ends fractionation column, wherein the combined stream is cooled and partially liquefied, and the resultant cooled and partially liquefied combined stream is introduced into the top region of the light ends fractionation column to provide additional reflux.

8. An apparatus for integration of liquefaction of natural gas and recovery of natural gas liquids, said apparatus comprising: one or more heat exchangers for cooling and partially condensing by indirect heat exchange a feed stream containing light hydrocarbons; a gas/liquid cold separator and means for introducing a partially condensed feed stream from the one or more heat exchangers into the gas/liquid cold separator, the gas/liquid cold separator having upper outlet means for removing an overhead gaseous stream and lower outlet means for removing a bottoms liquid stream; means for introducing the overhead gaseous stream and the bottoms liquid stream from the gas/liquid cold separator into a fractionation system comprising a light ends fractionation column and a heavy ends fractionation column, the means comprising an expansion device for expanding at least a portion of overhead gaseous stream from the gas/liquid cold separator and means for introducing expanded overhead gaseous stream into a lower region of said light ends fractionation column, and means for introducing at least a portion of the bottoms liquid stream from the gas/liquid cold separator into said heavy ends fractionation column at an intermediate point thereof; means for removing a first liquid product stream from the bottom of the heavy ends fractionation column; means for removing an overhead gaseous stream from the top of the light ends fractionation column, and means for removing a bottoms liquid stream from a lower region of the light ends fractionation column, and introducing this bottoms liquid stream from the light ends fractionation column into an upper region of the heavy ends fractionation column; said apparatus further comprising: (i) a first heat exchanger for subjecting a first portion of the light ends fractionation column overhead gaseous stream to indirect heat exchange with an overhead gaseous stream removed from the top of the heavy ends fractionation column, whereby the overhead gaseous stream from the top of the heavy ends fractionation column is cooled and partially condensed, means for removing the cooled and partially condensed overhead gaseous stream from said first heat exchanger, and means for introducing this cooled and partially condensed overhead gaseous stream from the top of the heavy ends fractionation column into the light ends fractionation column; (ii) means for removing a second portion of the overhead gaseous stream from the light ends fractionation column as a side stream, and a further heat exchanger for subjecting the side stream to indirect heat exchange to further cool, and partially liquefy the side stream, wherein said side stream of the overhead gaseous stream from the light ends fractionation column is split off from the overhead gaseous stream from the light ends fractionation column prior to the indirect heat exchange between said first portion of the light ends fractionation column overhead gaseous stream and the overhead gaseous stream removed from the top of said heavy ends fractionation column in said first heat exchanger; (iii) means for introducing the partially liquefied side stream into a further separation means, means for recovering a liquid stream from the further separation means and means for introducing the recovered liquid stream into the light ends fractionation column as a liquid reflux stream and/or the heavy ends fractionation column as a liquid reflux stream, (iv) means for recovering an overhead vapor stream from the further separation means, a further heat exchanger for subjecting this overhead vapor stream to indirect heat exchange for additional cooling and partial condensation, means for feeding the resultant vapor and condensate to an LNG separator, and means for recovering LNG liquid product from the LNG separator, and (v) means for recovering an overhead vapor stream from the further separation means, a compressor for compressing this overhead vapor stream to form a residue gas.

9. An apparatus according to claim 8, said apparatus further comprising: a main heat exchanger for cooling and partially condensing the feed stream by indirect heat exchange; means for introducing the first liquid product stream from the bottom of the heavy ends fractionation column into the main heat exchanger for indirect heat exchange with the feed stream; and a flow-control valve for partially liquefying the side stream before introducing said side stream into said further heat exchanger.

10. A process for integrated liquefaction of natural gas and recovery of natural gas liquids, said process comprising: cooling a feed stream containing light hydrocarbons by indirect heat exchange in a feed heat exchanger; introducing the cooled feed stream into a gas/liquid cold separator, removing from said gas/liquid cold separator an overhead gaseous stream and bottoms liquid stream, and introducing said overhead gaseous stream and bottoms liquid stream into a fractionation system, said fractionation system comprising a light ends fractionation column and a heavy ends fractionation column; removing a liquid product stream from said fractionation system; removing an overhead gaseous stream from said fractionation system; generating a residue gas stream from said overhead gaseous stream from said fractionation system; introducing said residue gas stream into a further separation means, and recovering from said further separation means a liquid product stream and an overhead vapor stream; introducing either said liquid product stream or said overhead vapor stream to an LNG exchanger/separator; subjecting either said liquid product stream or said overhead vapor stream to liquefaction in said LNG exchanger/separator; and removing LNG liquid product from said LNG exchanger/separator, wherein an overhead gaseous stream is removed from the top of said light ends fractionation column as said overhead gaseous stream from said fractionation system; said overhead gaseous stream from said light ends fractionation column is split into a first portion and a second portion; after said overhead gaseous stream from said light ends fractionation column is split into a first portion and a second portion, said first portion is heated by indirect heat exchange with an overhead gaseous stream removed from the top of said heavy ends fractionation column, whereby said overhead gaseous stream from the top of said heavy ends fractionation column is cooled by said indirect heat exchange; said second portion of overhead gaseous stream is cooled by indirect heat exchange; and the cooled second portion of overhead gaseous stream is introduced into said further separation means as said residue gas.

11. A process according to claim 10, said process further comprising: introducing the cooled overhead gaseous stream from the top of said heavy ends fractionation column into said light ends fractionation column; introducing said liquid product stream from said further separation means into said light ends fractionation column and/or said heavy ends fractionation column as a liquid reflux stream; and introducing said overhead vapor stream from said further separation means into said LNG exchanger/separator.

12. A process according to claim 10, said process further comprising: heating said overhead gaseous stream by indirect heat exchange with an overhead gaseous stream removed from the top of said heavy ends fractionation column, and said overhead gaseous stream from the top of said heavy ends fractionation column is cooled by said indirect heat exchange; introducing the cooled overhead gaseous stream from the top of said heavy ends fractionation column into said light ends fractionation column; heating and compressing the heated overhead gaseous stream from the light ends fractionation column; cooling and expanding said overhead gaseous stream from the light ends fractionation column; splitting the cooled and expanded overhead gaseous stream from the light ends fractionation column into a first expanded stream and a second expanded stream; introducing said first expanded stream into said light ends fractionation column; introducing said second expanded stream into further separation means as said residue gas; and introducing said liquid product stream from said further separation means into said LNG exchanger/separator.

13. A process according to claim 10, wherein said process further comprises introducing said liquid product stream recovered from said further separation means into said light ends fractionation column as said liquid reflux stream.

14. A process according to claim 10, wherein said process further comprises introducing said liquid product stream recovered from said further separation means into said heavy ends fractionation column as said liquid reflux stream.

15. A process according to claim 10, wherein said process further comprises removing a bottoms liquid stream from a lower region of said heavy ends fractionation column, heating said bottoms liquid stream from said heavy ends fractionation column in said feed heat exchanger, and returning said bottoms liquid stream from said heavy ends fractionation column to the lower region of said heavy ends fractionation column.

16. A process according to claim 10, wherein said process further comprises removing a liquid stream from a first intermediate point of said heavy ends fractionation column, heating said liquid stream removed from said heavy ends fractionation column by indirect heat exchange with the feed stream in said feed heat exchanger, and introducing said liquid stream into said heavy ends fractionation column at another intermediate point below said first intermediate point.

17. A process according to claim 10, wherein said process further comprises splitting said bottoms liquid stream from the gas/liquid cold separator in to a first bottom liquid stream and a second bottoms liquid stream, introducing said first bottom liquid stream into said heavy ends fractionation column, delivering said second bottoms liquid stream is delivered to a liquid/liquid heat exchanger for indirect heat exchange with bottom liquid stream removed from said light ends fractionation column, and then introducing said second bottoms liquid stream into an intermediate region of said light ends fractionation column as a liquid reflux.

18. A process according to claim 10, wherein said process further comprises: splitting said overhead gaseous stream from said gas/liquid cold separator into a first cold separator overhead gaseous stream and a second cold separator overhead gaseous stream; splitting said bottoms liquid stream from said gas/liquid cold separator into a first cold separator bottoms liquid stream and a second cold separator bottoms liquid stream; combining said second cold separator overhead gaseous stream and said second cold separator bottoms liquid stream; cooling the resultant combined stream by indirect heat exchange with an overhead vapor from said light ends fractionation column, and introducing the cooled combined stream into the top region of said light ends fractionation column to provide reflux.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention as well as further advantages, features and examples of the present invention are explained in more detail by the following descriptions of embodiments based on the Figures, wherein:

(2) FIGS. 1-27 each schematically show shows exemplary embodiments in accordance with the invention.

(3) The embodiments of FIGS. 1-16 are modifications of the CRYO-PLUS™ process. The embodiments of FIGS. 17-21, on the other hand, are modifications of the so-called Gas Subcooled Process (GSP), and the embodiments of FIGS. 22-26 are modifications of the so-called Recycle Split Vapor (RSV) process.

(4) In FIG. 1, gas feed stream (1), containing, for example, helium, nitrogen methane, ethane, ethylene, and C3+ hydrocarbons (e.g., a natural gas feed stream) is introduced into the system at a temperature of, e.g., 10 to 50° C. and a pressure of, e.g., 250 to 1400 psig. The gas feed stream (1) is cooled and partially condensed by indirect heat exchange in a main heat exchanger (2) against process streams (15, 16, 18) and then introduced into a gas/liquid cold separator (3). The gaseous overhead stream (4) removed from the top of the cold separator (3) is expanded, for example, in a turboexpander (5), and then introduced (6) into the lower region of the light ends fractionation column (7) (LEFC). The bottoms liquid stream (8) from the cold separator (3) is introduced into the heavy ends fractionation column (9) (HEFC) at an intermediate point thereof. The light ends fractionation column typically operates at a temperature of −70 to −135° C. and a pressure of 60 to 500 psig. The heavy ends fractionation column typically operates at a temperature of −135 to +70° C. and a pressure of 60 to 500 psig.

(5) A liquid stream (10) is removed from the bottom of the LEFC (7) and delivered, via pump (11), to the top of the HEFC (9). An overhead vapor product (12), also called a residue gas, is removed from the top of the LEFC (7), undergoes indirect heat exchange in a subcooler (13) with a gas stream (14) discharged from the top of the HEFC (9), before being heated in the main heat exchanger (2) and then discharged from the system. A portion of this overhead vapor product can be used as fuel gas. Another portion of the overhead vapor product can be further compressed before being sent to a gas pipeline.

(6) In a typical system, the warm overhead product from the LEFC can be sent to a gas pipeline for delivery to the consumer, or it can be 100% liquefied in an LNG unit, or a portion can flow to the gas pipeline while the remainder can be liquefied by the LNG unit. Liquefying the overhead gas product after warming the gas requires energy. However, as described further below, the inventive process uses overhead gas product from the top of the LEFC as the LNG unit feed, thereby preserving cooling of the overhead gas product and reducing energy consumption.

(7) A liquid product stream (15) is removed from the bottom of the HEFC (9) and passed through the main heat exchanger (2) where it undergoes indirect heat exchanger with the gas feed stream (1). In addition, a further liquid stream (16) is removed from a first intermediate point of the HEFC (9). This further liquid stream (16) is heated by indirect heat exchange with the gas feed stream (1) (e.g., in main heat exchanger (2)), and then reintroduced (17) into the HEFC (9) at a second intermediate point below the first intermediate point. An additional liquid stream (18) is removed from the lower region of the HEFC (9), heated in an indirect heat exchanger (e.g., in main heat exchanger (2) acting as a reboiler for the HEFC (9), and returned (19) to the lower region of the HEFC (9). Further, as noted above, a gas stream (14) is removed from the top of the HEFC (9).

(8) Additional structural elements shown in FIG. 1 are a product surge tank (20) which allows for recycling of a portion of the liquid product stream (15) back to the bottom of the HEFC (9). There also can be a trim reboiler (21) in the reboiler system of the HEFC (9) to supplement the heating provided by the reboiler for the HEFC. Also, in addition to the cooling provided in the main heat exchanger, the refrigeration needed for the cooling and partially condensation of the gas feed stream (1) can be partially provided by passing the gas feed stream (1) through a chiller (22), wherein it undergoes indirect heat exchange with an external refrigerant stream.

(9) In accordance with the invention, a side stream (23) is taken from the overhead vapor product of the LEFC and partially liquefied, via Joule-Thomson effect cooling, across a flow-control valve (24). The partially liquefied vapor stream is then delivered to a refrigerant system wherein it undergoes indirect heat exchange with a refrigerant fluid for further cooling. The resultant stream (25) is then fed into a further separation means (26), such as a further gas/liquid separator or a further distillation column, where the majority of ethane as well as heavier hydrocarbon components are recovered as liquid product (27) and returned to the LEFC as a liquid reflux stream. If a further distillation column is desired as the separation means, it can be integrated into the LNG unit. If the further distillation column requires a reboiler, the reboiler can be integrated into the LNG exchanger.

(10) The overhead vapor stream (28) from the further separation means, rich in methane, undergoes indirect heat exchange with the refrigerant fluid of the refrigerant system for additional cooling. The resultant cooled stream (29) is then fed into the LNG exchanger where it is subjected to liquefaction to form the LNG product. This cooled stream (29) can then be sent to a gas/liquid separator for separating light components, such as nitrogen, before being introduced into the LNG unit.

(11) At an intermediate point in the LNG exchanger, a vapor-liquid stream can be removed and introduced into an intermediate separator to separate heavier hydrocarbons (C.sub.2+) and return a lighter (essentially nitrogen, methane and ethane) stream to the LNG exchanger for final liquefaction, to allow the LNG product to meet desired specifications. The resulting liquids are increased in pressure via a pump and can be introduced into the LEFC as an additional reflux stream to further improve the C.sub.2+ recovery. The vapor stream from the intermediate separator reenters the LNG exchanger and proceeds, via additional cooling, to liquefy.

(12) This integration of the NGL and LNG processes allows for a significant reduction of energy consumption in the LNG unit without compromising the NGL recovery process. The utilization of a portion of the cold overhead vapor from the LEFC of the NGL process reduces refrigeration requirements, allowing the processes to take place in a more efficient manner that not only reduces overall energy consumption, but also provides improved recoveries for both processes.

(13) FIG. 2 illustrates an alternative embodiment of the invention. As in FIG. 1, a side stream (23) is taken from the overhead vapor product (12) of the LEFC and partially liquefied across a flow-control valve (24). The partially liquefied vapor undergoes indirect heat exchange with a refrigerant fluid for further cooling and is then fed into a further separation means (e.g., a further gas/liquid separator or further distillation column) where the majority of ethane as well as heavier hydrocarbon components are recovered as liquid product (27) and returned to the LEFC (7) as a liquid reflux stream. The methane-rich overhead vapor stream (28) from the further separation means undergoes indirect heat exchange with the refrigerant fluid for additional cooling, and is then fed as into the LNG exchanger, where liquefaction occurs.

(14) In FIG. 2, however, additional reflux streams are provided for the LEFC (7). Prior to expansion of the gaseous overhead stream (4), obtained from cold separator (3), in the turboexpander (5), a portion (30) of the gaseous overhead stream (4) is fed to the subcooler (13) where it undergoes indirect heat exchange with the overhead vapor from LEFC (7). In the subcooler (13), portion (30) of the gaseous overhead stream (4) is cooled further and partially liquefied, and then is introduced into the top region of the LEFC (7) to thereby provide additional reflux (31).

(15) In addition, a portion (32) of bottoms liquid stream (8) from cold separator (3) is delivered to a liquid/liquid heat exchanger (33), where it undergoes indirect heat exchange with bottom liquid (10) removed from the bottom of the LEFC (7). The resultant stream (34) is then fed to an intermediate region of the LEFC (7) as a liquid reflux. These two additional reflux streams for the LEFC (7) improve recovery of the ethane and heavier hydrocarbon components.

(16) A further embodiment is illustrated in FIG. 3. As in FIGS. 1 and 2, a side stream (23) is taken from the overhead vapor product (12) of the LEFC and partially liquefied across a flow-control valve (24). The partially liquefied vapor undergoes indirect heat exchange with a refrigerant fluid for further cooling and is then fed into a further separation means (e.g., a further gas/liquid separator or further distillation column) where the majority of ethane as well as heavier hydrocarbon components are recovered in as liquid product (27) and returned to the LEFC (7) as a liquid reflux stream. The methane-rich overhead vapor stream (28) from the further separation means undergoes indirect heat exchange with the refrigerant fluid for additional cooling, and is then fed as into the LNG exchanger, where liquefaction occurs.

(17) As in FIG. 2, FIG. 3 provides additional reflux for the LEFC (7). Here again, prior to expansion in the turboexpander (5), a portion (30) is branched off from the gaseous overhead stream (4) removed from the top of cold separator (3) (4). In this case, however, the portion (30) is combined with a portion (32) of bottoms liquid stream (8) removed from the bottom of the cold separator (3). The relative proportions of the liquid and vapor removed provide the mechanism to allow the generation of additional reflux in the indirect heat exchanger (subcooler) that follows. For example, in the combined stream the proportion of the gaseous overhead stream is up to 80%, and the proportion of the bottoms liquid stream is up to 99%

(18) The combined stream (35) is fed to the subcooler (13) where it undergoes indirect heat exchange with the overhead vapor from LEFC (7). Stream (35) is cooled and partially liquefied in the subcooler (13) and introduced into the top region of the LEFC (7) to provide additional reflux. This additional reflux stream for the LEFC (7) improves recovery of the ethane and heavier hydrocarbon components.

(19) FIG. 4 illustrates a modification of the embodiment of FIG. 3. As in FIGS. 1-3, a side stream (23) is taken from the overhead vapor product (12) of the LEFC and partially liquefied across a flow-control valve (24). In FIG. 4, this partially liquefied stream is treated in the same manner as in FIG. 3. A portion (30) of the gaseous overhead stream (4) removed from the top of cold separator (3) is combined with a portion (32) of bottoms liquid stream (8) removed from the bottom of the cold separator (3). The combined stream (35) is fed to the subcooler (13), where it undergoes indirect heat exchange with the overhead vapor from LEFC (7). The cooled and partially liquefied stream (35) is introduced into the top region of the LEFC (7) to provide additional reflux.

(20) As in FIGS. 1-3, in FIG. 4 a side stream (23) is taken from the overhead vapor product (12) of the LEFC and partially liquefied across a flow-control valve (24). However, in FIG. 4, this side stream (23) taken from the overhead vapor product (12) of the LEFC is treated differently. The partially liquefied vapor undergoes indirect heat exchange with a refrigerant fluid for further cooling and is then fed into a further separation means (e.g., a further gas/liquid separator or further distillation column). The methane-rich overhead vapor stream (28) from the further separation means undergoes indirect heat exchange with the refrigerant fluid for additional cooling, and is then fed as stream 29 into the LNG exchanger, where liquefaction occurs. The majority of ethane as well as heavier hydrocarbon components are recovered from the bottom of the further separation means as liquid product (27). But, instead of being sent to the LEFC (7), in the embodiment of FIG. 4 this liquid product (27) is introduced into the top of the HEFC (9) as a liquid reflux stream.

(21) FIG. 5 illustrates a modification of the embodiment of FIG. 2. As in FIG. 2, a side stream (23) is taken from the overhead vapor product (12) of the LEFC and partially liquefied across a flow-control valve (24). The partially liquefied vapor undergoes indirect heat exchange with a refrigerant fluid for further cooling and is then fed into a further separation means (26) where the majority of ethane as well as heavier hydrocarbon components are recovered as liquid product (27) and returned to the LEFC (7) as a liquid reflux stream. The methane-rich overhead vapor stream (28) from the further separation means (26) undergoes indirect heat exchange with the refrigerant fluid for additional cooling, and is then fed as stream 29 into the LNG exchanger, where liquefaction occurs.

(22) Further, as in FIG. 2, additional reflux streams are provided for the LEFC (7). Prior to expansion of the gaseous overhead stream (4), obtained from cold separator (3), in the turboexpander (5), portion (30) of the gaseous overhead stream (4) removed from the top of cold separator (3) is fed to the subcooler (13), where it undergoes indirect heat exchange with the overhead vapor (12) from LEFC (7). In the subcooler (13), portion (30) of the gaseous overhead stream (4) is cooled further and partially liquefied in the subcooler (13) and introduced into the top region of the LEFC (7) to thereby provide additional reflux. In addition, a portion (32) of bottoms liquid stream (8) removed from the bottom of the cold separator (3) is delivered to a liquid/liquid heat exchanger (33), where it undergoes indirect heat exchange with the bottom liquid stream (10) removed from the bottom of the LEFC (7). The resultant stream (34) is then fed to an intermediate region of the LEFC (7) as a liquid reflux.

(23) FIG. 5, however, incorporates a refrigeration loop through the NGL process which results in a reduction in energy consumption. Specifically, a stream of refrigerant fluid (36) from the refrigerant system is fed through the main heat exchanger (2) (e.g., a plate-fin heat exchanger) where it undergoes indirect heat exchange with the gas feed stream (1), the liquid product stream (15) from the bottom of the HEFC (9), the further liquid stream (16) from an intermediate point of the HEFC (9), the reboiler stream (18) removed from the bottom region of the HEFC (9), and the overhead vapor product stream (12) removed from the top of the LEFC (7). The refrigerant stream, cooled and partially liquefied, leaves the main heat exchanger as stream (37). Thereafter, the refrigerant stream is introduced into the subcooler (13) where it is further cooled and liquefied. This stream is then flashed across a valve (38), causing the fluid to reach even colder temperatures and is then fed back to the subcooler (13) to provide cooling to the reflux streams of the LEFC (7). The refrigerant stream (39) then returns to the main heat exchanger (2), where it serves as a coolant to the NGL process streams. The refrigerant stream is then returned to the refrigeration system for compression.

(24) FIG. 6 illustrates an embodiment which is similar to that shown in FIG. 5, but with a modified refrigeration loop. A stream of refrigerant fluid (36) from the refrigerant system is fed through the main heat exchanger (2) where it undergoes indirect heat exchange with the gas feed stream (1), the liquid product stream (15) from the bottom of the HEFC (9), the further liquid stream (16) from an intermediate point of the HEFC (9), the reboiler stream (18) removed from the bottom region of the HEFC (9), and the overhead vapor product stream (12) removed from the top of the LEFC (7). The refrigerant stream, cooled and partially liquefied, leaves the main heat exchanger (2) as stream (37). Thereafter, the refrigerant stream is introduced into the subcooler (13) where it is further cooled and liquefied. This stream is then introduced into a heat exchanger (40) for cooling the side stream (23) from the LEFC overhead vapor product stream (12). The refrigerant stream exits heat exchanger (40) and is flashed across a valve (41), causing the fluid to reach even colder temperatures. The resultant stream is then fed back to the same heat exchanger (40) to provide further cooling. Thereafter, the refrigerant passes through the subcooler (13) and the main heat exchanger (2), and then flows to the refrigeration system for compression.

(25) FIG. 7 shows a further embodiment of the invention. In this embodiment, a side stream is not removed from the overhead vapor product of the LEFC. Moreover, a residual gas stream is utilized in the main heat exchanger (2) (and the subcooler (13) and then treated in the further separation means (26). This embodiment allows for a reduction in utility consumption when compared to a standalone LNG unit, thereby rendering the process more energy efficient.

(26) Thus, in FIG. 7, a portion of the high pressure residue gas (42) is introduced into the cryogenic process and passes through the main heat exchanger (2). In main heat exchanger (2), this high pressure residue gas is cooled by heat exchange against various process stream (e.g., residue gas from the top of the LEFC, the feed stream, product stream from the bottom of the HEFC, and side streams from the HEFC). Thereafter, the cooled high pressure residue gas (43) is further cooled in the subcooler (13) by heat exchange with overhead vapor product (12), also called a residue gas, removed from the top of the LEFC (7), and overhead vapor product (12) removed from the top of the HEFC (9).

(27) A portion of the cooled high pressure reside gas stream (44) is then flashed expanded (e.g., via an expansion valve) to the operating pressure of the LEFC (7) and combined with the overhead vapor product (14) removed from the top of the HEFC, after the latter is subcooled in subcooler (13). The combined stream serves as reflux to the LEFC and is considered the top feed to the column. The remaining portion of the cooled high pressure residue gas stream (45) is flashed (e.g., via an expansion valve to a lower pressure then the other portion and is fed to the further separation means (26) (e.g., a LNGL separator). The liquid (27) removed from the bottom of the further separation means is a methane-rich liquid which is sent to an LNG storage vessel (46) before being sent to the LNG production unit. The vapor stream removed from the top of the further separation means (26) is compressed in a boil-off gas (BOG) compressor (47) and removed as a residue gas stream. The BOG compressor, compresses the potentially nitrogen rich stream from the low pressure of the liquefaction temperature to the final discharge pressure of the residue gas compressor. This boil off gas is combined with other residue gas at a point downstream of the removal of any portion of residue gas that is to be used in the system. The potentially high nitrogen concentration in the boil off gas renders it less suitable for use in the system for cooling purposes.

(28) FIG. 8 shows a further embodiment of the invention. In this embodiment, a side stream (23) is removed from the overhead vapor product (12) of the LEFC (7) is used as feed for the LNG production unit. The LEFC overhead vapor side stream, before being used as feed for the LNG production unit, is cooled and liquefied by a standalone refrigeration source (REF). By using a cooled portion of the LEFC overhead vapor as a feed to the LNG unit, the utility consumption of the refrigeration unit is decreased and thereby the process is rendered more energy efficient when compared to a standalone LNG production unit. Additionally, using a portion of the cold liquid from the LNG production unit as reflux for the LEFC increases the efficiency and product recovery.

(29) As shown in FIG. 8, prior to delivery to the subcooler (13) a portion (23) of the LEFC overhead vapor is removed and introduced as feed to the LNG production unit. In particular, this portion of the LEFC overhead vapor is partially liquefied by heat exchange in an LNGL heat exchanger (48) (i.e., a heat exchanger that combines functions of the NGL LNG units) with refrigerant and with a residue gas from the LNG production unit. The resulting stream partially liquefied is fed to a further separation means such as a reflux separator (26), where the majority of ethane as well as heavier hydrocarbon components are separated as liquid, removed as bottom liquid from the reflux separator (26), and returned to the LEFC as reflux (27).

(30) The methane-rich vapors (28) from the top of the reflux separator (26) are further cooled by heat exchange in LNGL heat exchanger (48) against refrigerant and boil off gas from the LNG production unit. The resultant partially liquefied methane-rich stream (29) is then flashed (e.g., by expansion in an expansion valve) to a lower pressure and the resultant stream (49) is fed into a further separator (50), i.e., a LNGL separator. The methane-rich liquid removed the bottom of the further separator (50) is optionally sent to an LNG storage vessel (46) before being sent to further processing, if desired. The vapor 51 (i.e., boil off gas) removed from the top of the further separator (50) is subjected to heat exchange in the LNGL exchanger (48) to provide additional cooling for the portion of the LEFC overhead vapor (23), and is then compressed in a BOG compressor (47) and combined with residue gas from NGL recovery unit.

(31) FIG. 9 shows a modification of the embodiment of FIG. 8. In FIG. 8, the vapor (51), i.e., boil off gas, removed from the top of the further separator (50) is subjected to heat exchange in the LNGL exchanger (48) to provide additional cooling for the portion of the LEFC overhead vapor (23), and is then compressed in the BOG compressor (47) and combined with residue gas from NGL recovery unit. However, in FIG. 9, this vapor (51) removed from the top of the further separator (50) is compressed in the BOG compressor (47) without previously being used in the LNGL exchanger (48) to provide additional cooling for the portion of the LEFC overhead vapor (23). Additionally, a residue gas (52) is introduced into the LNGL heat exchanger (48), where it is cooled and liquefied. After exiting the LNGL exchanger (48), the liquefied residue gas is flashed across a valve, causing the fluid to reach even colder temperatures, and is then fed back to LNGL heat exchanger (48) to provide further cooling for the LNG production unit.

(32) FIG. 10 shows an embodiment that is very similar to the embodiment of FIG. 1, except that the treatment of the overhead vapor stream (28) from the further separation means (26) differs. Thus, as in FIG. 1, in the embodiment of FIG. 10 a side stream (23) is taken from the overhead vapor product of the LEFC (7). The side stream (23) is delivered to a refrigerant system where it undergoes indirect heat exchange with a refrigerant fluid (REF). The resultant stream (25) is then fed into a further separation means (26), such as a further gas/liquid separator or a further distillation column. The majority of ethane and heavier hydrocarbon components are recovered from the bottom of the further separation means (26) as a liquid product stream (27) and returned to the LEFC as a liquid reflux.

(33) The overhead vapor stream (28) from the further separation means (26), rich in methane, undergoes indirect heat exchange in an LNGL heat exchanger with the refrigerant fluid of the refrigerant system for additional cooling. This methane rich stream leaves the LNGL exchanger as a cooled partially liquefied stream (29) and is then flashed (e.g., by expansion in an expansion valve) to a lower pressure. The resultant stream (41) is fed into a further separator (50), i.e., a LNGL separator. The methane-rich liquid removed the bottom of the further separator (50) is optionally sent to an LNG storage vessel (46) before being sent to the LNG production unit. The vapor removed from the top of the further separator (50) is compressed in BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.

(34) FIG. 11 shows an embodiment which combines the embodiment of FIG. 2 with that of FIG. 10. By using a portion of the cooled LEFC overhead (23) as a feed to the LNG production unit, the utility consumption of the refrigeration unit is decreased and thereby the process is rendered more energy efficient when compared to a standalone LNG production unit. Additionally, returning a portion of the cold liquid from the LNG unit as well as streams from the cold separator as reflux streams to the LEFC increases efficiency and product recovery of the NGL recovery unit.

(35) Thus, as in FIG. 2, additional reflux streams are provided for the LEFC in the embodiment of FIG. 11. Prior to expansion, a portion (30) of the gaseous overhead stream (4) from the cold separator (3) is fed to the subcooler (13) where it undergoes indirect heat exchange with the overhead vapor from LEFC (7). In the subcooler (13), this portion (30) is further cooled and partially liquefied, and then expanded and introduced into the top region of the LEFC (7) to thereby provide additional reflux (31).

(36) In addition, a portion (32) of bottoms liquid stream (8) from cold separator (3) is delivered to a liquid/liquid heat exchanger (33), where it undergoes indirect heat exchange with bottom liquid (10) removed from the bottom of the LEFC (7). The resultant stream (34) is then expanded and fed into an intermediate region of the LEFC (7) as a liquid reflux.

(37) Also, as in FIG. 10, in the embodiment of FIG. 11, the methane-rich vapor stream that leaves LNGL exchanger (48) as a partially liquefied stream (29) is flashed (e.g., by expansion in an expansion valve) to a lower pressure. The resultant stream (41) is fed into a further separator (50), i.e., a LNGL separator. The methane-rich liquid removed the bottom of the further separator (50) is optionally sent to an LNG storage vessel (46) before being sent to the LNG production unit. The vapor (boil off gas) (51) removed from the top of the further separator (50) is compressed in a BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.

(38) FIG. 12 illustrates a system that combines the embodiment of FIG. 3 with that of FIG. 10. As with the embodiment of FIG. 10, the use of a portion (23) of the cooled LEFC overhead as a feed to the LNG production unit decreases utility consumption of the refrigeration unit and thereby renders the process more energy efficient. Additionally, returning a portion of the cold liquid from the LNG unit as well as streams from the cold separator as reflux streams to the LEFC increases efficiency and product recovery of the NGL recovery unit.

(39) In FIG. 12, as in FIGS. 10 and 11, the methane rich stream that leaves LNGL exchanger (48) as a cooled partially liquefied stream (29) is flashed (e.g., by expansion in an expansion valve) to a lower pressure. The resultant stream (41) is fed into a further separator (50), i.e., a LNGL separator. The methane-rich liquid removed the bottom of the further separator (50) is optionally sent to an LNG storage vessel (46) before being sent to the LNG production unit. The vapor (boil off gas) (51) removed from the top of the further separator (50) is compressed in a BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.

(40) As in FIG. 3, the system of FIG. 12 provides additional reflux streams for the LEFC (7). Prior to expansion in turboexpander (5), a portion (30) is branched off from the gaseous overhead stream (4) removed from the top of cold separator (3). This portion (30) is combined with a portion of bottoms liquid stream (32) removed from the bottom of the cold separator (3). The combined stream (35) is fed to subcooler (13) where it undergoes indirect heat exchange with the overhead vapor from LEFC (7). Stream (35) is cooled and partially liquefied in the subcooler (13), and then expanded and introduced into the top region of the LEFC (7) to provide additional reflux. This additional reflux stream for the LEFC (7) improves recovery of the ethane and heavier hydrocarbon components.

(41) FIG. 13 illustrates a system that combines the embodiments of FIGS. 4 and 10. As with the embodiment of FIG. 10, the use of a portion (23) of the cooled LEFC overhead as a feed to the LNG production unit decreases utility consumption of the refrigeration unit and thereby renders the process more energy efficient. Additionally, returning a portion of the cold liquid from the LNG unit as a reflux stream to the HEFC (see, e.g., FIG. 4), as well as using streams from the cold separator as reflux streams for the LEFC, increases efficiency and product recovery of the NGL recovery unit.

(42) As in FIG. 4, in the system of FIG. 13 the side stream (23) taken from the overhead vapor product (12) of the LEFC undergoes indirect heat exchange in the LNGL exchanger (48) with a refrigerant fluid for cooling and is then fed into a further separation means (26) (e.g., a further gas/liquid separator or further distillation column). The methane-rich overhead vapor stream (28) from the further separation means (26) undergoes indirect heat exchange with the refrigerant fluid for additional cooling in the LNGL exchanger (48). As in FIGS. 10 and 11, the methane rich stream that leaves LNGL exchanger as a cooled partially liquefied stream (29) is flashed (e.g., by expansion in an expansion valve) to a lower pressure. The resultant stream (41) is fed into a further separator (50), i.e., a LNGL separator. The methane-rich liquid removed the bottom of the further separator (50) is optionally sent to an LNG storage vessel (46) before being sent to the LNG production unit. The vapor (boil off gas) (51) removed from the top of the further separator (50) is compressed in BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.

(43) As in FIG. 4, the system of FIG. 13 provides additional reflux streams for both the LEFC (7) and the HEFC (9). The ethane and heavier hydrocarbon components recovered from the bottom of the further separation means (26) as liquid product (27) are introduced into the top of the HEFC (9) as a liquid reflux stream, rather than being sent to the LEFC (7). Also, prior to expansion in turboexpander (5), a portion (30) is branched off from the gaseous overhead stream (4) removed from the top of cold separator (3). This portion (30) is combined with a portion of bottoms liquid stream (32) removed from the bottom of the cold separator (3). The combined stream (35) is fed to subcooler (13) where it undergoes indirect heat exchange with the overhead vapor (12) from LEFC (7). Stream (35) is cooled and partially liquefied in the subcooler (13), and then expanded and introduced into the top region of the LEFC (7) to provide additional reflux.

(44) FIG. 14 illustrates a system that combines the embodiments of FIGS. 5 and 10. As with the embodiment of FIG. 10, the use of a portion (23) of the LEFC overhead as a feed to the LNG production unit decreases utility consumption of the refrigeration unit and thereby renders the process more energy efficient. Additionally, returning a portion of the cold liquid from the LNG unit as a reflux stream to the LEFC (see, e.g., FIG. 5), as well as using streams from the cold separator as reflux streams for the LEFC, increases efficiency and product recovery of the NGL recovery unit. Further, the incorporation of a refrigeration loop through the NGL process results in further reduction in energy consumption.

(45) As in FIGS. 2 and 5, in FIG. 14 a side stream (23) is taken from the overhead vapor product (12) of the LEFC and subjected to indirect heat exchange (48) with a refrigerant fluid for further cooling. This stream is then fed to a further separation means (26) where the majority of ethane as well as heavier hydrocarbon components are recovered as liquid product (27) and returned to the LEFC (7) as a liquid reflux stream. The methane-rich overhead vapor stream (28) from the further separation means (26) undergoes indirect heat exchange with the refrigerant fluid for additional cooling in the LNGL exchanger (48).

(46) As in FIGS. 10-12, the methane rich stream that leaves LNGL exchanger as a cooled partially liquefied stream (29) is flashed (e.g., by expansion in an expansion valve) to a lower pressure. The resultant stream (41) is fed into a further separator (50), i.e., a LNGL separator. The methane-rich liquid removed the bottom of the further separator (50) is optionally sent to an LNG storage vessel (46) before being sent to the LNG production unit. The vapor (boil off gas) (51) removed from the top of the further separator (50) is compressed in a BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.

(47) Further, as in FIGS. 2 and 5, additional reflux streams are provided for the LEFC (7). Prior to expansion of the gaseous overhead stream (4), obtained from cold separator (3) in the turboexpander (5), a portion (30) of the gaseous overhead stream (4) is fed to the subcooler (13), where it undergoes indirect heat exchange with the overhead vapor (12) from LEFC (7). In the subcooler (13), portion (30) is cooled further and partially liquefied, and then expanded and introduced into the top region of the LEFC (7) to provide additional reflux. In addition, a portion of bottoms liquid stream (32) removed from the bottom of the cold separator (3) is delivered to a liquid/liquid heat exchanger (33), where it undergoes indirect heat exchange with the bottom liquid stream (10) removed from the bottom of the LEFC (7). The resultant stream (34) is then fed to an intermediate region of the LEFC (7) as a liquid reflux.

(48) FIG. 14, however, further incorporates a refrigeration loop through the NGL process which results in a reduction in energy consumption. Specifically, a stream of refrigerant fluid (52) from the refrigerant system is fed through the main heat exchanger (2) (e.g., a plate-fin heat exchanger) where it undergoes indirect heat exchange with the liquid product stream (15) from the bottom of the HEFC (9), the further liquid stream (16) from an intermediate point of the HEFC (9), the reboiler stream (18) removed from the bottom region of the HEFC (9), and the overhead vapor product stream (12) removed from the top of the LEFC (7). The refrigerant stream, cooled and partially liquefied, leaves the main heat exchanger as stream (53). Thereafter, the refrigerant stream is introduced into the subcooler (13) where it is further cooled and liquefied. This stream is then flashed across a valve causing the fluid to reach even colder temperatures and is then fed (54) back to the subcooler (13) to provide cooling to the reflux streams of the LEFC (7). The refrigerant stream (55) then returns to the main heat exchanger (2), where it serves as a coolant to the NGL process streams. The refrigerant stream (56) is then returned to the refrigeration system for compression. The incorporation of this refrigeration loop through the NGL process results in a reduction in energy consumption.

(49) FIG. 15 shows a system that is a modification of the system of FIG. 14 that combines features of the embodiments of FIGS. 6 and 10. Thus, FIG. 15 illustrates an embodiment which is similar to that shown in FIG. 14, but with a modified refrigeration loop. A stream of refrigerant fluid (52) from the refrigerant system is fed through the main heat exchanger (2) where it undergoes indirect heat exchange with the liquid product stream (15) from the bottom of the HEFC (9), the further liquid stream (16) from an intermediate point of the HEFC (9), the reboiler stream (18) removed from the bottom region of the HEFC (9), and the overhead vapor product stream (12) removed from the top of the LEFC (7). The refrigerant stream, cooled and partially liquefied, leaves the main heat exchanger (2) as stream (53). Thereafter, the refrigerant stream is introduced into the subcooler (13) where it is further cooled and liquefied. This stream is then introduced into a heat exchanger (48) for cooling the side stream (23) from the LEFC overhead vapor product stream (12). The refrigerant stream exits heat exchanger (48) and is flashed across a valve, causing the fluid to reach even colder temperatures. The resultant stream (54) is then fed back to the same heat exchanger (48) to provide further cooling. Thereafter, the refrigerant stream passes through the subcooler (13) and exits therefrom as stream (55). Refrigerant stream (55) passes through the main heat exchanger (2), and then flows to the refrigeration system for compression. Here again, the incorporation of a refrigeration loop through the NGL process results in a reduction in energy consumption.

(50) FIG. 16 shows a further embodiment of the invention. In this embodiment, like in the embodiment of FIG. 7, a side stream is not removed from the overhead vapor product (12) of the LEFC before the latter is sent to the subcooler (13). Instead, after the overhead vapor product of the LEFC passes through the subcooler (13), it is sent to the main heat exchanger, and then at least portion thereof is compressed. At least a portion of this compressed residue gas is used as feed for the LNG production unit and to provide a reflux stream for the LEFC. Using the residue gas as a feed to the LNG unit reduces the utility consumption of the refrigeration unit thereby rendering the process more energy efficient when compared to a standalone LNG unit. Also, returning a portion of the cold liquid from the LNG production unit as reflux for the LEFC increases the efficiency and product recovery of the NGL recovery unit.

(51) As shown in FIG. 16, overhead vapor (12) obtained from the top of the LEFC, passes through the subcooler (13) and the main heat exchanger (2). The resultant stream (57) is compressed in compressor (58), and then recycled (59) to a LNGL heat exchanger (48) wherein it is cooled and partially liquefied by heat exchange with refrigerant. The resulting stream is fed to a further separation means such as a reflux separator (26). The majority of ethane and heavier hydrocarbon components are removed as a liquid stream (27) from the bottom of the reflux separator (26) and returned to the LEFC as reflux. The methane-rich vapor stream (28) removed from the top of the reflux separator (26) is sent to the LNGL heat exchanger (48) where it undergoes heat exchange with the refrigerant for additional cooling. The resultant partially liquefied stream (29) exits the LNGL heat exchanger (48) and is flashed (e.g., by expansion in an expansion valve) to a lower pressure, and fed as stream (41) to an LNGL separator (50). A methane-rich liquid is recovered from the LNGL separator (50) and optionally sent to an LNG storage vessel (46). The vapor (boil off gas) (51) from the LNGL separator is compressed in a BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.

(52) As noted above, FIGS. 17-21 are modifications of the Gas Subcooled Process (GSP). In FIG. 17, gas feed stream (1), containing, for example, helium, nitrogen methane, ethane, ethylene, and C3+ hydrocarbons (e.g., a natural gas feed stream) is introduced into the system at a temperature of, e.g., 4 to 60° C. and a pressure of, e.g., 300 to 1500 psig. The gas feed stream (1) is split into two partial feed streams, first partial feed stream (1A) and second partial feed stream (1B). The first partial feed stream (1A) is cooled and partially condensed by indirect heat exchange in a main heat exchanger (2) against process streams (16, 18, 15), e.g., streams originating from a demethanizer. The second partial feed stream (1B) is cooled and partially condensed by indirect heat exchange in another heat exchanger (60) against a process stream (12), e.g., an overhead stream from a demethanizer (this heat exchanger can share a common core with another heat exchanger, e.g., the subcooler described below). These two partial feed streams are then recombined (1C), optionally further cooled (61) (e.g., by indirect heat exchange against a refrigerant), and then introduced into a gas/liquid cold separator (3).

(53) The gaseous overhead stream (4) removed from the top of the cold separator (3) is split into two potions (30, 30A). Similarly, the bottoms liquid stream (8) from the cold separator (3) is also split into two potions (32, 32A).

(54) A first portion of the gaseous overhead stream (30A) is expanded, for example, in a turboexpander (5), which can be optionally coupled to a compressor (63), and then introduced as stream (6) into an intermediate region of a demethanizer column (62) at a first intermediate point. A first portion of the bottoms liquid stream (32A) from the cold separator (3) is also introduced and expanded into an intermediate region of the demethanizer column (62) at a second intermediate point which is below the first intermediate point, i.e., the point of introduction of the first portion of the gaseous overhead stream (6). The second portion of the gaseous overhead stream (30) is combined with the second portion of the bottoms liquid stream (32) to form a combined cold separator stream (35), which is then cooled in a subcooler (13) by indirect heat exchange with an overhead vapor stream (12) from the top of the demethanizer (62). Stream (35) is then introduced and expanded into the upper region of the demethanizer. The demethanizer column (62) typically operates at a temperature of −70 to −115° C. and a pressure of 100 to 500 psig.

(55) A liquid product stream is removed from the bottom of the demethanizer (62) and sent to a product surge vessel (20). Liquid from the product surge vessel (20) can be recycled to the bottom region of the demethanizer (62). The liquid product stream (15) from the product surge vessel (20) is heated by heat exchange, for example, by passage through the main heat exchanger (2) where it can undergo indirect heat exchange with the first partial feed stream (1A). In addition, a further liquid stream (16) is removed from a third intermediate point of the demethanizer, i.e., below the second intermediate point. This further liquid stream (16) is heated by indirect heat exchange, e.g., in the main heat exchanger (2) against first partial feed stream (1A), and then reintroduced (17) into the demethanizer at a fourth intermediate point i.e., below the third intermediate point. An additional liquid stream (18) is removed from the lower region of the demethanizer, i.e., below the fourth intermediate point. This additional liquid stream (18) is heated by indirect heat exchange, e.g., in the main heat exchanger (2), acting here as a reboiler, against first partial feed stream (1A), and then reintroduced (19) into the lower region of the demethanizer. Further, as noted above, an overhead vapor stream (12) is removed from the top of the demethanizer (62).

(56) A high pressure (e.g., 300 to 1500 psig) residue gas stream (64) is introduced into the system and cooled by indirect heat exchange in heat exchanger (60) against a process stream (12), e.g., an overhead stream from the demethanizer, further cooled in the subcooler (13), and optionally further cooled in a further heat exchanger (e.g., an LNGL exchanger). A portion (65) of this cooled high pressure reside gas stream is expanded (e.g., via an expansion valve) to the operating pressure of the demethanizer (62), combined with the combined cold separator stream (35) and then introduced into the upper region of the demethanizer (62) as the top feed thereof. The remaining portion of the cooled high pressure residue gas stream is expanded (e.g., via an expansion valve) to a pressure below the operating pressure of the demethanizer and fed to a further separation means, e.g., an LNGL separator (50). A methane rich liquid stream is removed from the further separation means (50), optionally stored in an LNG storage vessel (46), before being sent to the LNG production unit. The overhead vapor (boil off gas) (51) from the further separation means is compressed in a BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.

(57) The embodiment of FIG. 18 involves the use of a side stream from the overhead vapor stream of the demethanizer, rather than the high pressure residue gas stream of the embodiment of FIG. 17. Thus, in FIG. 18, a portion of the cooled overhead vapor (12) from the demethanizer (62) is used as feed for the LNG production unit.

(58) Before being cooled in the subcooler (13), a side stream (23) is separated from the overhead vapor stream (12) of the demethanizer and is partially liquefied by heat exchange in an LNGL heat exchanger (48) against a refrigerant. The resulting stream is fed to a further separation means such as a reflux separator (26). In the reflux separator the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger, is flashed-expanded via an expansion valve to a lower pressure and fed into a further separation means (50) (e.g., an LNGL separator). A methane-rich liquid is recovered from the bottom of the further separation means (50) and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (51) (boil off gas) is removed from the top of the further separation means (50) and used in the LNGL heat exchanger (48) to provide additional cooling for the side stream (23) from the demethanizer overhead vapor stream (12) and the methane-rich vapor stream (28) removed from the top of the reflux separator (26). The vapor stream (51) from the top of the further separation means is then compressed in a BOG compressor (47) and combined with other residue gas from the GSP unit.

(59) The embodiment of FIG. 19 is similar to the embodiment of FIG. 18, except that additional cooling in the LNGL heat exchanger (48) is achieved by the initially cooling and liquefying a residue gas stream which is then expanded and sent back to the LNGL heat exchanger (48) as a cooling medium.

(60) Thus, in FIG. 19 the side stream (23) from the overhead vapor stream (12) of the demethanizer is partially liquefied by heat exchange in an LNGL heat exchanger (48) against a refrigerant. The resulting stream is fed to a further separation means such as a reflux separator (26). The bottom liquid stream (27) (mostly ethane and higher hydrocarbon components) is returned to the demethanizer as reflux. The methane-rich vapor stream (28) is cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger (48), is flashed-expanded via an expansion valve to a lower pressure and fed (41) into a further separation means (50) (e.g., an LNGL separator). A methane-rich liquid is recovered from the bottom of the further separation means (50) and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (51) (boil off gas) is removed from the top of the further separation means (50), compressed in a BOG compressor (47), and combined with other residue gas from the GSP unit.

(61) A residue gas (67) is introduced into the LNGL exchanger (48), where it is cooled and liquefied. The residue gas exits the LNGL exchanger and is flashed across a valve, causing the fluid to reach even colder temperatures. The resultant stream (68) is then fed back to the LNGL exchanger (48) to provide additional cooling for the side stream (23) from the demethanizer overhead vapor stream (12) and the methane-rich vapor stream (28) removed from the top of the reflux separator (26).

(62) FIG. 20 illustrates an embodiment similar to that of FIGS. 18 and 19. However, in the embodiment of FIG. 20 no additional cooling, such as from residue gas (67) or the vapor stream from the top of the further separation means (50), is used in the LNGL heat exchanger (48).

(63) Like FIGS. 18-20, the embodiment of FIG. 21 involves the use of a side stream originating from the overhead vapor stream of the demethanizer. However, in this case, the side stream is separated from the overhead vapor stream of the demethanizer after the latter has undergone further cooling (i.e., in subcooler (13) and heat exchanger (60)). Also, the side stream is compressed before it is introduced into the LNGL exchanger (48).

(64) As shown in FIG. 21, the overhead vapor stream (12) from the top of the demethanizer passes through the subcooler (13) and through the heat exchanger (60) that cools the second partial feed stream (1B). Thereafter, at least a portion of the overhead vapor stream is compressed in compressor (63) (which is coupled to expander (5)) to form a residue gas. Then, a portion (59) of this residue gas is cooled and partially liquefied by heat exchange in an LNGL heat exchanger (48) against a refrigerant. The resulting stream is fed to a further separation means such as a reflux separator (26).

(65) In the reflux separator (26) the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer (62) as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger, is flashed-expanded via an expansion valve to a lower pressure and fed (41) into a further separation means (50) (e.g., an LNGL separator). A methane-rich rich liquid is recovered from the bottom of the further separation means (50) and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (boil off gas) (51) is removed from the top of the further separation means (50), compressed in a BOG compressor (47), and combined with other residue gas from the GSP unit.

(66) As noted above, FIGS. 22-26 are modifications of the Recycle Split Vapor (RSV) Process. As shown in FIG. 22, gas feed stream (1), containing, for example, helium, nitrogen methane, ethane, ethylene, and C3+ hydrocarbons (e.g., a natural gas feed stream) is introduced into the system at a temperature of, e.g., 4 to 60° C. and a pressure of, e.g., 300 to 1500 psig. The gas feed stream (1) is split into two partial feed streams, a first partial feed stream (1A) and a second partial feed stream (1B). The first partial feed stream (1A) is cooled and partially condensed by indirect heat exchange in a main heat exchanger (2) against process streams (16, 18, 15). The second partial feed stream (1B) is cooled and partially condensed by indirect heat exchange in another heat exchanger (60) against a process stream (12), e.g., an overhead stream from a demethanizer (62) (this heat exchanger can share a common core with another heat exchanger, e.g., the subcooler described below). These two partial feed streams are then recombined (1C), optionally further cooled (61) (e.g., by indirect heat exchange against a refrigerant), and then introduced into a gas/liquid cold separator (3).

(67) The gaseous overhead stream (4) removed from the top of the cold separator (3) is split into two potions (30, 30A). Similarly, the liquid bottom stream (8) removed from the cold separator (3) is also split into two potions (32, 32A).

(68) A first portion of the gaseous overhead stream (30A) is expanded, for example, in a turboexpander (5), which can be optionally coupled to a compressor (63) and then introduced as stream (6) into an intermediate region of a demethanizer column (62) at a first intermediate point. A first portion of the bottoms liquid stream (32A) from the cold separator (3) is also expanded and introduced into an intermediate region of the demethanizer column (62) at a second intermediate point which is below the first intermediate point, i.e., the point of introduction of the first portion of the gaseous overhead stream (6). The second portion of the gaseous overhead stream (30) is combined with the second portion of the bottoms liquid stream (32) to form a combined cold separator stream (35), which is then cooled in a subcooler (13) by indirect heat exchange with an overhead vapor stream (12) from the top of the demethanizer (62), and expanded and introduced into the upper region of the demethanizer as a top feed thereof. The demethanizer column (62) typically operates at a temperature of −70 to −115° C. and a pressure of 100 to 500 psig.

(69) A liquid product stream is removed from the bottom of the demethanizer (62) and sent to a product surge vessel (20). Liquid from the product surge vessel can be recycled to the bottom region of the demethanizer (62). The liquid product stream (15) from the product surge vessel (2) is heated by heat exchange, for example, by passage through the main heat exchanger (2) where it can undergo indirect heat exchange with the first partial feed stream (1A). In addition, a further liquid stream (16) is removed from a third intermediate point of the demethanizer, i.e., below the second intermediate point. This further liquid stream (16) is heated by indirect heat exchange, e.g., in the main heat exchanger (2) against first partial feed stream (1A), and then reintroduced (17) into the demethanizer at a fourth intermediate point i.e., below the third intermediate point. An additional liquid stream (18) is removed from the lower region of the demethanizer, i.e., below the fourth intermediate point. This additional liquid stream (18) is heated by indirect heat exchange, e.g., in the main heat exchanger (2) (in this case acting as a reboiler) against first partial feed stream (1A), and then reintroduced (19) into the lower region of the demethanizer. Further, as noted above, an overhead vapor stream (12) is removed from the top of the demethanizer (62).

(70) A high pressure (e.g., 300 to 1500 psig) residue gas stream (69) is introduced into the system and cooled by indirect heat exchange in the subcooler (13). At least a portion of this residue gas stream (69) is then expanded (e.g., via an expansion valve) to the operating pressure of the demethanizer and introduced (70) into the upper region of the demethanizer as another top feed thereof.

(71) Another portion (23) of the residue gas stream (69) is expanded (e.g., via an expansion valve) to a pressure below the operating pressure of the demethanizer and fed to a further separation means (50), e.g., an LNGL separator. A methane rich liquid stream is removed from the further separation means (50) and optionally stored in an LNG storage vessel (46), before being sent to the LNG production unit. The overhead vapor stream (boil off gas) (51) removed from the further separation means (50) is compressed in a BOG compressor (47) and combined with other residue gas from the RSV unit.

(72) FIG. 23 shows an embodiment which is the same as the embodiment of FIG. 22, except that the subcooler (13) is split into two separate exchangers (13A) and (13B). Thus, in subcooler (13A) the residue gas stream (69) is cooled by heat exchange with a portion of the demethanizer overhead stream (12), and in subcooler (13B) the combined cold separator stream (35) is cooled by heat exchange with another portion (12A) of the demethanizer overhead stream.

(73) The embodiment of FIG. 24 is similar to the embodiment of FIG. 23, except that the side stream (23) from the residue gas stream (69) is treated in a manner similar to the treatment of side stream (23) in FIG. 18. Thus, after residue gas stream (69) is cooled in the subcooler (13), a side stream (23) is separated therefrom and is partially liquefied by heat exchange in an LNGL heat exchanger (48) against a refrigerant. The resulting stream is fed to a further separation means such as a reflux separator (26). In the reflux separator the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger, is flashed-expanded via an expansion valve to a lower pressure and fed into a further separation means (50) (e.g., an LNGL separator). A methane-rich liquid is recovered from the bottom of the further separation means (50) and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (51) (boil off gas) is removed from the top of the further separation means (50) and used in the LNGL heat exchanger (48) to provide additional cooling for the side stream (23) from the demethanizer overhead vapor stream (12) and the methane-rich vapor stream (28) removed from the top of the reflux separator (26). The vapor stream (51) from the top of the further separation means is then compressed in a BOG compressor (47) and combined with other residue gas from the RSV unit.

(74) The embodiment of FIG. 25 treats the high pressure residue gas stream, which is cooled by indirect heat exchange in the subcooler, in a manner similar to the way that the side stream from the overhead vapor stream of the demethanizer is treated in FIG. 19. As shown in FIG. 25, the high pressure residue gas stream (69) is cooled by indirect heat exchange in the subcooler (13), and then divided into a first portion (70) and a second portion (23). The first portion (70) of the residue gas stream is expanded (e.g., via an expansion valve) to the operating pressure of the demethanizer and introduced into the upper region of the demethanizer as a top feed thereof. The second portion (23) of the residue gas stream is cooled and partially liquefied by heat exchange in an LNGL heat exchanger (48) against a refrigerant. The resulting stream is fed to a further separation means such as a reflux separator (26).

(75) In the reflux separator, the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger, is flashed-expanded via an expansion valve to a lower pressure and fed (41) into a further separation means (50) (e.g., an LNGL separator). A methane-rich liquid is recovered from the bottom of the further separation means and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (boil off gas) (51) is removed from the top of the further separation means, compressed in a BOG compressor (47) and combined with other residue gas from the RSV unit.

(76) A residue gas (67) is introduced into the LNGL exchanger (48), where it is cooled and liquefied. The residue gas exits the LNGL exchanger (48) and is flashed across a valve, causing the fluid to reach even colder temperatures. The resultant stream (68) is then fed back to the LNGL exchanger to provide additional cooling for the second portion of the residue gas stream (23) and the methane-rich vapor stream (28) removed from the top of the reflux separator (26).

(77) FIG. 26 illustrates an embodiment similar to that of FIGS. 24 and 25. However, in the embodiment of FIG. 26 no additional cooling is used in the LNGL heat exchanger (48). Compare FIG. 20.

(78) The embodiment of FIG. 27 is similar to the embodiments of FIGS. 23-25, except that the residue gas that is cooled in the LNGL heat exchanger originates from the overhead vapor stream of the demethanizer. See FIG. 21.

(79) As shown in FIG. 27, a high pressure residue gas stream (69) is cooled by indirect heat exchange in the subcooler (13), and then expanded (e.g., via an expansion valve) to the operating pressure of the demethanizer and introduced into the upper region of the demethanizer as a top feed (70) thereof. Thus, unlike the embodiments of FIGS. 24-26, the high pressure residue gas stream that exits the subcooler is not divided into a first portion and a second portion.

(80) As shown in FIG. 27, the overhead vapor stream 12 from the top of the demethanizer (62) passes through the subcooler (13) and the heat exchanger (60) that cools the second partial feed stream (1B). Thereafter, at least a portion of the overhead vapor stream is compressed in compressor (63) (which is shown as being coupled to expander (5)) to form a residue gas. Then, a portion of this residue gas (59) is cooled and partially liquefied by heat exchange in an LNGL heat exchanger (48) against a refrigerant. The resulting stream is fed to a further separation means such as a reflux separator (26).

(81) In the reflux separator (26) the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger (48), is flashed-expanded via an expansion valve to a lower pressure and fed (41) into a further separation means (50) (e.g., an LNGL separator). A methane-rich liquid is recovered from the bottom of the further separation means and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (boil off gas) (51) is removed from the top of the further separation means from the top of the further separation means, compressed in a BOG compressor (47) and combined with other residue gas from the RSV unit.

(82) Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

(83) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(84) The entire disclosure[s] of all applications, patents and publications, cited herein and of priority U.S. provisional Application No. 61/746,727, filed Dec. 28, 2012 are incorporated by reference herein.

(85) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.