GAS PROCESSING METHODOLOGY UTILIZING REFLUX AND ADDITIONALLY SYNTHESIZED STREAM OPTIMIZATION

Abstract

Gas processing methodology for high efficiency recovery of propane and/or ethane from a natural gas feed stream. The method is conducted without turboexpansion, and in some embodiments, without the use of a refrigeration system. A natural gas stream is processed to have gas and liquid portions. The gas portions are cooled and flow to a refluxed absorber column and the liquid portions flow to a lower pressure distillation column. Bottoms of the absorber column are depressurized into a separator, with the separator overhead vapor being used as a source of absorber column reflux. The separator liquids are fed into the lower pressure distillation column and the distillation column overhead vapor stream is used to cool the feed and/or reflux streams. The overhead vapour stream from the lower pressure distillation can be recycled to the absorber, either as a recycle or a source of reflux.

Claims

1. A method of processing natural gas to recover selected hydrocarbons contained therein, comprising: cooling and partially condensing a natural gas feed stream; separating the cooled and partially condensed stream into a plurality of liquid streams and gas streams; passing said gas streams into a fractionator column and said liquid streams into a distillation column; recovering an overheads stream from said distillation column; treating said overheads stream to form at least one overhead stream; passing said at least one overhead stream into said fractionator column as a recycle stream or source of reflux liquids; contacting said source of reflux liquids as a reflux stream with said natural gas feed stream in said fractionator column to liquefy hydrocarbon components present in said natural gas feed stream or recycling said recycle stream; and recovering a bottoms stream from said fractionator column.

2. The method as set forth in claim 1, wherein said overheads stream is treated to form a plurality of overhead streams.

3. The method as set forth in claim 1, wherein said bottoms stream from said fractionator are depressurized in a separator.

4. The method as set forth in claim 3, further including the step of utilizing an intermediate pressure vessel as said separator.

5. The method as set forth in claim 4, further including treating an intermediate pressure vessel overheads stream to form at least one reflux stream.

6. The method as set forth in claim 5, further including the step of passing at least one reflux stream into said fractionator column as a source of reflux.

7. The method as set forth in claim 3, further including the step of depressurizing the separator bottoms into said distillation column and recovering selected hydrocarbon components from said bottoms stream.

8. The method as set forth in claim 1, wherein said method is conducted absent the use of turboexpansion as a unit operation.

9. The method as set forth in claim 1, wherein said treating said at least one overheads stream to form a plurality of overhead streams includes forming a plurality of reflux streams at different pressures.

10. The method as set forth in claim 1, further including the step of varying fluid flow rates at least between said fractionator column and said distillation column.

11. The method as set forth in claim 1, wherein said method has a turndown range between 30% and 100% of flowrate in said method where 99% recovery is maintained.

12. The method as set forth in claim 1, wherein said method utilizes at least cooling, heat exchange, depressurization and separation unit operations, said method further including initially determining the composition of the natural gas; and selecting a sequence of said unit operations based on said composition of said natural gas for energy optimization in effecting said method.

13. A gas processing plant, comprising: a separator for receiving a cooled and partially condensed natural gas feed stream to separate said feed stream into a liquid stream and a gas stream; a fractionator column for receiving said gas stream and reflux streams produced from a distillation column; an intermediate pressure vessel in fluid communication with said fractionator column for producing an overheads stream, said overheads stream being utilized in said fractionator column as said reflux streams to liquefy hydrocarbons present in said feed stream, said fractionator column producing a bottoms stream which is depressurized into a distillation column to recover selected hydrocarbons; and a distillation column in fluid communication with said intermediate pressure vessel, said intermediate pressure vessel producing a bottoms stream for feeding into said distillation column.

14. The gas processing plant as set forth in claim 13, further including a network of heat exchangers positioned to recover and distribute heat from all streams of said streams during processing.

15. The gas processing plant as set forth in claim 13, wherein said overheads stream is compressed, cooled and divided into a plurality of overhead streams.

16. The gas processing plant as set forth in claim 13, wherein at least one of said overhead streams is compressed, cooled and depressurized for use in said fractionator column as a reflux stream.

17. The gas processing plant as set forth in claim 13, wherein said overhead streams are pressurized at a different pressure relative to one another.

18. The gas processing plant as set forth in claim 13, wherein said overhead streams may exist in a gas, partially condensed, or liquid state.

19. A method of processing natural gas with a fractionator column and distillation column in fluid communication to recover selected hydrocarbons contained therein, comprising a plurality of operations, comprising: a separation operation where a natural gas stream is processed to form a liquid stream and a gas stream which are separated; an intermediate pressurization operation fluid communication with said fractionator column for producing an overheads stream; an overheads processing and distribution operation where an overheads stream is recovered from said distillation column and processed into a plurality of overhead streams distributed into predetermined locations in said fractionator column; a distillation operation in said fractionator column where said natural gas feed stream contacts said overhead streams to liquefy hydrocarbon components present in said natural gas stream; and a bottoms recovery and processing operation where a bottoms stream is recovered from said fractionator column and processed by depressurization directly in said distillation column in the absence of turboexpansion to recover selected hydrocarbons.

20. The method as set forth in claim 19, wherein said method further includes heat exchange operations between each of the separation, overheads processing and distribution, refrigeration and bottoms recovery operations to recover and distribute heat between all streams associated with said operations.

21. The method as set forth in claim 19, wherein said distillation column is operated as a deethanizer.

22. The method as set forth in claim 19, wherein said distillation column is operated as a demethanizer.

23. The method as set forth in claim 19, wherein said operations are modifiable to recover ethane, propane, hydrocarbons, or a combination thereof.

24. The method as set forth in claim 19, wherein said separation operation includes cooling and partially condensing said natural gas feed stream.

25. The method as set forth in claim 19, wherein said bottoms recovery and processing operation includes introducing said bottoms stream at a pressure of between 500 kPag and 2000 kPag into said distillation column relative to a pressure of between 2000 and 7000 kPag prior to introduction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] FIG. 1 is a process flow diagram in accordance with a first embodiment of the present invention;

[0077] FIG. 2 is a process flow diagram in accordance with a second embodiment of the present invention;

[0078] FIG. 3 is a is a process flow diagram in accordance with a third embodiment of the present invention;

[0079] FIG. 4 is a is a process flow diagram in accordance with a fourth embodiment of the present invention;

[0080] FIG. 5 is a process flow diagram in accordance with a fifth embodiment of the present invention;

[0081] FIG. 6 is a process flow diagram in accordance with a further embodiment of the present invention;

[0082] FIG. 7 is a process flow diagram in accordance with another embodiment of the present invention;

[0083] FIG. 8 is a process flow diagram in accordance with yet another embodiment of the present invention;

[0084] FIG. 9 is a process flow diagram in accordance with yet another embodiment of the present invention;

[0085] FIG. 10 a process flow diagram in accordance with yet a still further embodiment of the present invention; and

[0086] FIG. 11 a process flow diagram in accordance with yet another embodiment of the present invention.

[0087] Similar numerals employed in the Figures denote similar elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0088] Referring now to FIG. 1, shown is a process flow diagram for a first embodiment of the present invention for propane recovery and ethane rejection.

[0089] A natural gas feed stream 10 at a pressure above, for example, approximately 5000 kPag flows through heat exchanger 12 cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 16 leaving exchanger 12 is then passed through a chiller 18, which partially condenses the natural gas stream. The chiller 18 may operate at, for example, approximately −40° C. and may use common refrigerants such as propane, or ammonia. Other suitable refrigerant examples are well within the purview of one skilled in the art.

[0090] The partially condensed natural gas stream 20 is then separated in separator 22 and the gas portion 24 leaving separator 22 is further cooled by heat exchange at 26 with a sales gas stream 28 and a reflux stream 30, discussed in greater detail herein after. The gas stream 32 is then depressurized across a valve 34 entering, as stream 36, to the bottom of a refluxed fractionator tower 38 at, for example, approximately 3500 kPag. The gas flows upwardly through tower 38 where it is contacted with the downwardly flowing reflux liquids. The fractionator tower 38 bottoms liquids 40 exit the bottom of tower 38 as illustrated and are depressurized across a valve 42 directly into the top of a second distillation column 44, operating in the example as a deethanizer at approximately 1000 kPag. The deethanizer (second distillation column 44) is also fed the condensed liquids 46 from the separator 22. Liquids 46 are depressurized via valve 48 into the deethanizer 44.

[0091] Distillation of these liquids occurs in the deethanizer 44, with the bottoms product reboiled in circuit 50 to produce a low ethane content C3+ liquid product 52. The deethanizer reboiler circuit can be heated using a heat medium, or by heat exchange with a hot compressor discharge stream.

[0092] The deethanizer overheads 54 flow to a heat exchanger 56, which is used to further cool the stream after compression in compressor 58 to a pressure above the fractionator operating pressure followed by cooling in an air exchanger 60. The overheads stream 62 is then chilled and partially condensed in a chiller 64, and further condensed in an exchanger 66 with the sales gas, prior to being separated in separator 68.

[0093] The liquid stream 70 from the separator 68 is used as a medium quality source of reflux, with a composition that is approximately half methane and half ethane. The medium quality reflux stream 70 is fed into a mid-point of the fractionator tower 38 as illustrated in the Figure.

[0094] The gas stream 72 from the separator 68 can optionally be split into two streams 30 (referenced herein previously) and 73, with the ratio of the split determining the degree of propane recovery versus the refrigeration and reflux compression energy requirement. For the highest propane recovery, all of the gas stream from separator 68 can be used to generate high quality reflux liquids. The stream 30 is used to cool the feed to the fractionator 38 in a heat exchanger 76. The stream 74 then flows to another heat exchanger 78 which is used to further cool the stream after compression in compressor 80 and cooling in an air exchanger 82.

[0095] The stream 84 is compressed to approximately 7000 kPag, and then chilled in chiller 86 and cooled with heat exchanger 88 with the sales gas stream 90 from fractionator tower 38. Depressurization of this stream 92 is achieved by valve 94 to the fractionator tower 38 and this depressurization condenses a portion of the stream into high quality liquefied natural gas reflux, composed mainly of liquid methane. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the propane and heavier components from the upwardly flowing natural gas into the liquid phase. The fractionator overheads 90 have propane and heavier components effectively absorbed by the reflux and this exits the fractionator 38 as sales gas. The sales gas is used to cool the reflux streams, fractionator feed, and inlet natural gas in heat exchangers 88, 66, 26, and 12 and then the sales gas exits the process for further compression, if required.

[0096] Turning now to FIG. 2, shown is a process flow diagram in another embodiment of the invention for ethane recovery.

[0097] In this embodiment, natural gas stream 10 at a pressure above approximately 7000 kPag flows through a heat exchanger 12, cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 16 is then passed through a series of heat exchangers and a chiller, 18, 100 and 102, respectively, which partially condenses the natural gas stream. The chiller 100 may operate at approximately −40° C., and may use common refrigerants such as propane, or ammonia. The partially condensed natural gas stream 104 is then separated in separator 22 and the gas portion 24 is then depressurized across a valve 34, entering the bottom of fractionator tower 38 at approximately 3500 kPag.

[0098] The gas flows upwards through the refluxed fractionator tower 38 where it is contacted with the downwards flowing reflux liquids. The fractionator tower 38 bottoms liquids 40 exit the bottom of the tower 38 and are depressurized across a valve 42 directly into the top of second distillation column 44 operating as a demethanizer at approximately 1000 kPag. The demethanizer 44 is also fed the condensed liquids 46 from the separator 22 which are depressurized across a valve 48 into the demethanizer.

[0099] Distillation of these liquids occurs in the demethanizer 44 with the bottoms product reboiled in a reboiler circuit 50 to produce a low methane content C2+ liquid product 52. The demethanizer reboiler circuit 50 can be heated by heat exchange with the feed gas stream, another process stream of appropriate temperature, or a heat medium stream. The demethanizer overheads 54 flows to a series of heat exchangers 102, 18 which are used to cool the feed gas stream.

[0100] The demethanizer overheads then flow to a compressor 58 which compresses the gas stream 106 to a pressure above the fractionator operating pressure, and then the gas is cooled in an air exchanger 60. This gas is then split into two streams 108,110 with the ratio of the split determining the degree of ethane recovery versus the refrigeration and reflux compression energy requirement.

[0101] One of these two streams 108 can be chilled and depressurized into a mid-point of the fractionator tower 38. The other of these two split streams, can be further compressed to approximately 9000 kPag in compressor 111, cooled with an air cooler 112, chilled with chiller 114, cooled by heat exchangers 116, 118 with the fractionator tower overheads 120 and depressurized across a valve 122 into the fractionator tower 38 to generate high quality reflux liquids.

[0102] Depressurization of this stream 124 to the fractionator tower 38 pressure condenses a portion of the stream into high quality liquefied natural gas reflux, consisting primarily of liquid methane. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the ethane and heavier components from the upwards flowing natural gas, into the liquid phase. The fractionator overheads 120 have had ethane and heavier components effectively absorbed by the reflux, and exits the fractionator 38 as sales gas. The sales gas is used to cool the reflux stream, and inlet natural gas in heat exchangers (118, 116, 12), and then the sales gas exits the process for further compression, if required.

[0103] FIG. 3 illustrates yet another variation of the present invention for switchable ethane recovery.

[0104] The process may be arranged so that the ethane recovery can be switched on and off. The figure illustrates the ethane rejection mode. Generally speaking, the process is very similar to that discussed regarding FIG. 1, with the exception of the following:

[0105] The feed gas pressure for high ethane recovery is desirably above approximately 7000 kPag. The distillation column 44 operates as a demethanizer as opposed to a deethanizer. Overheads stream 54 from the demethanizer 44 is redirected from the exchanger 56 to the exchanger 76.

[0106] The gaseous stream 72 from the separator 68 is redirected from exchanger 76 to exchanger 78.

[0107] Stream 74 from the exchanger 76 is redirected from the exchanger 76 to the exchanger 56. The demethanizer reboiler 44 can instead be heated using a heat medium, or by heat exchange with process streams such as the feed gas stream 16.

[0108] Turning now to FIG. 4, shown is a propane recovery, ethane rejection process flow diagram.

[0109] Natural gas stream 10 at a pressure above approximately 5000 kPag flows through heat exchanger 12, cooling the gas by exchanging heat with the cold sales gas leaving the process at 14.

[0110] The natural gas stream 16 is then passed through a heat exchanger 126 which partially condenses the natural gas stream. The partially condensed natural gas stream 128 is then separated in separator 22 and the gas portion 24 is further cooled in a chiller 27. The chiller 27 may operate at approximately −40° C., and may use common refrigerants such as propane, or ammonia.

[0111] The partially condensed gas stream is then depressurized across valve 34, entering the bottom of a fractionator tower 38 at approximately 3500 kPag. The gas flows upwardly through the refluxed fractionator tower 38 where it is contacted with the downwardly flowing reflux liquids.

[0112] The fractionator tower 38 bottoms liquid 40 exit the bottom of the tower 38 and are depressurized across valve 42 directly into the top of a second distillation column 44 operating as a deethanizer at approximately 1000 kPag.

[0113] The deethanizer 44 is also fed the condensed liquids 46 from separator 22, which are depressurized across valve 48 into the deethanizer 44.

[0114] Distillation of these liquids occurs in the deethanizer 44 with the bottoms product reboiled in circuit 50 to produce a liquid product 52, in this example, a low ethane content C3+.

[0115] The deethanizer reboiler circuit 50 can be heated using a heat medium, or by heat exchange with a hot compressor discharge stream.

[0116] The deethanizer overheads 54 flow to heat exchanger 126 which uses the overheads to cool the feed gas. The overheads then flow to another heat exchanger 56 which is used to further cool the stream after compression with compressor 58 to a pressure above the fractionator operating pressure, and cooling in air exchanger 60.

[0117] The overheads stream is then split into two streams 108 and 110 each to be used as a source of reflux in the absorber.

[0118] Reflux stream 108 is cooled by heat exchange 56 with the deethanizer overheads stream, then chilled with chiller 132, partially condensed and depressurized across valve 134 into a midpoint of the fractionator tower 38 as a source of medium quality reflux.

[0119] The other split reflux stream 110 is further compressed at 111, cooled with air exchanger 112, heat exchange at 116, chilled at 114, and further cooled and condensed by heat exchange at 118 with the sales gas. Depressurization of this stream across valve 122 to the fractionator tower 38 pressure condenses a portion of the stream into high quality reflux. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the propane and heavier components from the upwardly flowing natural gas, into the liquid phase.

[0120] The fractionator overheads 120 at this point in the process have had propane and heavier components effectively absorbed by the reflux and the exit the fractionator 38 as sales gas.

[0121] The sales gas is used to cool the reflux streams, fractionator feed, and inlet natural gas in heat exchangers and then the sales gas exits the process for further compression, if required.

[0122] FIG. 5 is a process flow diagram depicting propane recovery with ethane rejection).

[0123] Similar to the previous embodiments, natural gas stream 10 at a pressure above approximately 5000 kPag flows through heat exchanger 12, cooling the gas by exchanging heat with the cold sales gas leaving the process at 14.

[0124] The natural gas stream 16 is then passed through heat exchanger 126, which partially condenses the natural gas stream. The partially condensed natural gas stream 128 is then separated with separator 22 with gas portion 24 further cooled in chiller 27.

[0125] Chiller 27 may operate at approximately −40° C.

[0126] The partially condensed gas stream (9) is further cooled by heat exchange with the sales gas stream as shown and depressurized across valve 34, entering the bottom of a fractionator tower 38 at a pressure of approximately 3500 kPag.

[0127] The gas flows upwardly through the refluxed fractionator tower 38 where it is contacted with the downwardly flowing reflux liquids.

[0128] The fractionator tower 38 bottoms liquids 40 exit the bottom of the tower 38. and are depressurized across valve 42 directly into the top of distillation column 44, operating as a deethanizer at approximately 1000 kPag.

[0129] The deethanizer 44 is also fed the condensed liquids 46 from the separator 22, which are depressurized across valve 48 into the deethanizer 44. Distillation of these liquids occurs in the deethanizer 44, with the bottoms product reboiled in circuit 50 to produce liquid product 52 which in this example is a low ethane content C3+ product.

[0130] The deethanizer reboiler circuit 50 can be heated using a heat medium, or by heat exchange with a hot compressor discharge stream.

[0131] The deethanizer overheads 54 flow to heat exchanger 126 which uses the overheads to cool the feed gas. The overheads then flow to another heat exchanger 56, which is used to further cool the stream after compression at 58 to a pressure above the fractionator operating pressure, and cooling in air exchanger 60.

[0132] The overheads stream is then split into two streams 108 and 110 each to be used as a source of reflux in the absorber.

[0133] Reflux stream 108 is cooled by heat exchanger 56 with the deethanizer overheads stream, then chilled at 132, further cooled and condensed by heat exchange at 138 with the sales gas, and depressurized across valve 134 into a mid-point of the fractionator tower 38 as a source of medium quality reflux.

[0134] The other split reflux stream 110 is further compressed at 111, cooled with air exchanger 112, heat exchange at 116, chilled at 114 and further cooled and condensed by heat exchange 118 with the sales gas.

[0135] Depressurization of this stream across a valve 122 to the fractionator tower pressure condenses a portion of the stream into high quality reflux. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the propane and heavier components from the upwards flowing natural gas, into the liquid phase.

[0136] The fractionator overheads 120 at this point have had propane and heavier components effectively absorbed by the reflux, and the exits the fractionator 38 as sales gas. The sales gas is used to cool the reflux streams, fractionator feed, and inlet natural gas in heat exchangers and then the sales gas exits the process for further compression, if required.

[0137] These processes can economically achieve higher ethane and/or propane recoveries than the traditional turbo-expander processes with lower plant inlet pressures. Generally, depending upon gas composition, it is desired to have a plant inlet pressure of approximately 7000 kPa to achieve 99% ethane recovery. When inlet pressures are higher, energy, capital cost, and operating cost can be saved by having lower refrigerant temperatures than −40° C. Depending upon markets conditions for ethane sales and energy purchase, some scenarios may favor lower ethane recovery for reasons of economics. Lower ethane recovery can be easily achieved with warmer refrigerant temperatures, but raising the demethanizer pressure and/or the gas fractionator pressure can also be considered.

[0138] Similarly, an inlet pressure of approximately 5000 kPa is generally desired for 99% propane recovery, but with higher inlet pressures, lower refrigerant temperatures can save capital cost, energy cost, and operating cost and still achieve an economical 99% propane recovery.

[0139] Referring now to FIG. 6, shown is a process flow diagram for a first embodiment of the present invention for propane recovery and ethane rejection, without the use of a refrigeration system for chilling.

[0140] A natural gas feed stream 10 at a pressure above, for example, approximately 6500 kPag flows through heat exchanger 12 cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 16 leaving exchanger 12 is then passed through heat exchanger 18′, which further cools and may partially condense the natural gas stream, by exchanging heat with the deethanizer (distillation column 44) overheads stream 54. The natural gas stream is then further cooled by exchanging heat with the cold liquids leaving process separators 22 and 140, in heat exchangers 100 and 102, further partially condensing gas. The partially condensed natural gas stream 20 is then separated in separator 22 and the gas portion 24 leaving separator 22 is depressurized across a valve 34 entering, as stream 36, to the bottom of a refluxed fractionator tower 38 at, for example, approximately 3500 kPag. The gas flows upwardly through tower 38 where it is contacted with the downwardly flowing reflux liquids. The fractionator tower 38 bottoms liquids 40 exit the bottom of tower 38 as illustrated and are depressurized across a valve 42 into the intermediate pressure vessel 140 operating at approximately 1000 kPag. The liquids stream 142 leaving the intermediate pressure vessel 140 are then used to cool the reflux stream entering the top of the fractionator 38, and the natural gas feed stream, with heat exchangers 88 and 102. The fractionator bottoms liquids are then fed into the deethanizer 44. The condensed liquids 46 from the separator 22 are depressurized across valve 48 through heat exchanger 100 in order to cool the natural gas feed stream, and then the stream is also fed into the deethanizer 44.

[0141] Distillation of these liquids occurs in the deethanizer 44, with the bottoms product reboiled in circuit 50 to produce a low ethane content C3+ liquid product 52. The deethanizer reboiler circuit can be heated using a heat medium, or by heat exchange with a hot compressor discharge stream.

[0142] The deethanizer overheads 54 flow to heat exchanger 18′ which is used to cool natural gas feed stream 16. The deethanizer overheads 106 then flow to heat exchanger 56 which is used to cool the stream after compression in compressor 58 to a pressure above the fractionator operating pressure followed by cooling in air exchanger 60.

[0143] The overheads stream 336 is then further cooled with fractionator overheads gas in exchanger 66, and fed into the fractionator 38 at a mid-point of the fractionator tower as a source of medium quality reflux.

[0144] The gas stream 154 leaving the intermediate pressure vessel 140, can be split into two streams 156 and 158, in order to provide an appropriate volume of reflux liquids to the fractionator 38. The stream 158 that is not required for fractionator reflux, is fed to the deethanizer 44. The stream 156 intended for fractionator 38 reflux then flows to another heat exchanger 178 which is used to further cool the stream after compression in compressor 111 and cooling in an air exchanger 112.

[0145] The stream has been compressed to approximately 7000 kPag, and is then cooled in exchanger 88 by heat transfer with the depressurized liquids stream 142 leaving the intermediate pressure vessel. Depressurization of this stream 124 is achieved by valve 122 to the fractionator tower 38 and this depressurization condenses a portion of the stream into high quality liquefied natural gas reflux, composed mainly of liquid methane. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the propane and heavier components from the upwardly flowing natural gas into the liquid phase.

[0146] The fractionator overheads 120 have propane and heavier components effectively absorbed by the reflux and this exits the fractionator 38 as sales gas. The sales gas is used to cool the reflux, and inlet natural gas in heat exchangers 66 and 12, and then the sales gas exits the process for further compression, if required.

[0147] Turning now to FIG. 7, shown is a process flow diagram in another embodiment of the invention for propane recovery, requiring a refrigeration system for chilling.

[0148] Natural gas feed stream 10 at a pressure above, for example, approximately 5000 kPag flows through heat exchanger 12 cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 16 leaving exchanger 12 is then passed through heat exchanger 18′, which further cools and may partially condense the natural gas stream, by exchanging heat with the deethanizer (distillation column 44) overheads stream 54. The natural gas stream is then further cooled with chiller 100′. The chiller 100′ may operate at approximately −40° C., and may use common refrigerants such as propane, or ammonia. The partially condensed natural gas stream 20 is then separated in separator 22 and the gas portion 24 leaving separator 22 is depressurized across a valve 34 entering, as stream 36, to the bottom of a refluxed fractionator tower 38 at, for example, approximately 3500 kPag. The gas flows upwardly through tower 38 where it is contacted with the downwardly flowing reflux liquids. The fractionator tower 38 bottoms liquids 40 exit the bottom of tower 38 as illustrated and are depressurized across a valve 42 into intermediate pressure vessel 140 operating at approximately 1000 kPag. The liquids stream 142 leaving the intermediate pressure vessel 140 are then used to cool the reflux stream entering the top of the fractionator 38. The fractionator bottoms liquid stream is then fed into the deethanizer 44. The condensed liquids 46 from the separator 22 are depressurized across valve 48, and then the stream is also fed into the deethanizer 44.

[0149] Distillation of these liquids occurs in the deethanizer 44, with the bottoms product reboiled in circuit 50 to produce a low ethane content C3+ liquid product 52. The deethanizer reboiler circuit 50 can be heated using a heat medium, or by heat exchange with a hot compressor discharge stream.

[0150] The deethanizer overheads 54 flow to a heat exchanger 18, which is used to cool natural gas feed stream 16. The deethanizer overheads 106 then flow to heat exchanger 56 which is used to cool the stream after compression in compressor 58 to a pressure above the fractionator operating pressure followed by cooling in air exchanger 60.

[0151] The overheads stream 62 is then further cooled by heat exchange with the sales gas in heat exchangers 64′ and 66, and is then fed into the fractionator 38 at a mid-point of the fractionator tower as a source of medium quality reflux.

[0152] The gas stream 154 leaving the intermediate pressure vessel 140, can be split into two streams 156 and 158, in order to provide an appropriate volume of reflux liquids to the fractionator 38. The stream 158 that is not required for fractionator reflux, is fed to the deethanizer. The stream 156 intended for fractionator 38 reflux then flows to heat exchanger 178 which is used to further cool the stream after compression in compressor 111 and cooling in an air exchanger 112.

[0153] The stream 84′ has been compressed to approximately 7000 kPag, and is then cooled by heat exchange with the sales gas in exchangers 116 and 118, and is also chilled in chiller 114. The stream 86 is then cooled in exchanger 88 by heat transfer with the depressurized liquids stream 142 leaving the intermediate pressure vessel. Depressurization of this stream 124 is achieved by valve 122 into the fractionator tower 38 and this depressurization condenses a portion of the stream into high quality liquefied natural gas reflux, composed mainly of liquid methane. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the propane and heavier components from the upwardly flowing natural gas into the liquid phase. The fractionator overheads 120 have propane and heavier components effectively absorbed by the reflux and this exits the fractionator 38 as sales gas. The sales gas is used to cool the reflux streams, and inlet natural gas in heat exchangers 118, 66, 116, 64′ and 12, and then the sales gas exits the process for further compression, if required.

[0154] FIG. 8 illustrates yet another variation of the present invention for ethane recovery.

[0155] In this embodiment, natural gas stream 10 at a pressure above approximately 7000 kPag flows through a heat exchanger 12, cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 16 is then passed through a chiller 100′, which partially condenses the natural gas stream. The chiller 100′ may operate at approximately −40° C., and may use common refrigerants such as propane, or ammonia. The natural gas stream is then split, such that appropriate reflux stream cooling and tower temperature profiles can be achieved. One of the split streams 170 is depressurized across valve 172, into separator 176 at approximately 3500 kPag. The gas stream leaving the separator 176 is fed into fractionator 38, and the liquid stream 180 leaving the separator 176 is depressurized across valve 184 into the demethanizer 44. The other portion of the partially condensed natural gas feed stream 101 is further cooled and condensed by heat exchange with sales gas and the demethanizer overheads in exchangers 102 and 18′. The stream is then depressurized and separated into gas and liquid streams in separator 22, with the gas portion 24 being fed into the fractionator tower 38 at approximately 3500 kPag.

[0156] The gas flows upwards through the refluxed fractionator tower 38 where it is contacted with the downwards flowing reflux liquids. The fractionator tower 38 bottoms liquids 40 exit the bottom of the tower 38 and are depressurized across valve 42 directly into the top of second distillation column 44 operating as a demethanizer at approximately 1000 kPag. The demethanizer 44 is also fed the condensed liquids 46 from the separator 22 which are depressurized across a valve 48 into the demethanizer. The demethanizer 44 is also fed the condensed liquids 180 from the separator 176 which are depressurized across a valve 184 into the demethanizer 44.

[0157] Distillation of these liquids occurs in the demethanizer 44 with the bottoms product reboiled in a reboiler circuit 50 to produce a low methane content C2+ liquid product 106. The demethanizer reboiler circuit 50 can be heated by heat exchange with the feed gas stream, another process stream of appropriate temperature, or a heat medium stream. The demethanizer overheads 54 is used to cool and further condense the feed gas stream 104 using heat exchanger 18′.

[0158] The demethanizer overheads then flow to heat exchanger 116, which further cools the overheads after compression and air cooling (58, 60, 111, 112). The overheads stream is then chilled at 114, and further cooled by heat exchange with the fractionator overheads stream 120, in heat exchanger 118. The stream is then depressurized across valve 122 into the fractionator tower 38, which condenses a portion of the stream into high quality liquefied natural gas reflux, consisting primarily of liquid methane. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the ethane and heavier components from the upwards flowing natural gas, into the liquid phase. The fractionator overheads 120 have had ethane and heavier components effectively absorbed by the reflux, and exits the fractionator 38 as sales gas. The sales gas is used to cool the reflux stream, and inlet natural gas in heat exchangers 18′, 102, 12), and then the sales gas exits the process for further compression, if required.

[0159] FIG. 9 illustrates yet another variation of the present invention, configured such that ethane recovery can be switched on and off using a single apparatus.

[0160] In this embodiment, in ethane recovery mode, natural gas stream 10 at a pressure above approximately 7000 kPag flows through a heat exchanger 12, cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 16 is then passed through a chiller 100′, which partially condenses the natural gas stream. The chiller 100′ may operate at approximately −40° C., and may use common refrigerants such as propane, or ammonia. The natural gas stream is then split, such that appropriate reflux stream cooling and tower temperature profiles can be achieved. One of the split streams 170 is depressurized across valve 172, into separator 176 at approximately 3500 kPag. The gas stream 188 leaving the separator 176 is fed into fractionator 38, and the liquid 180 stream leaving the separator 176 is depressurized across valve 184 into the demethanizer 44. The other portion of the partially condensed natural gas feed stream 101 is further cooled and condensed by heat exchange with sales gas and the demethanizer overheads in exchangers 102 and 18. The stream is then depressurized and separated into gas and liquid streams in separator 22, with the gas portion 24 being fed into the fractionator tower 38 at approximately 3500 kPag.

[0161] The gas stream 24 flows upwards through the refluxed fractionator tower 38 where it is contacted with the downwards flowing reflux liquids. The fractionator tower 38 bottoms liquids 40 exit the bottom of the tower 38 and are depressurized across a valve 42 directly into the top of second distillation column 44 operating as a demethanizer at approximately 1000 kPag. The demethanizer 44 is also fed the condensed liquids 46 from the separator 22 which are depressurized across a valve 48 into the demethanizer. The demethanizer 44 is also fed the condensed liquids 180 from the separator 176 which are depressurized across a valve 184 into the demethanizer.

[0162] Distillation of these liquids occurs in the demethanizer 44 with the bottoms product reboiled in a reboiler circuit 50 to produce a low methane content C2+ liquid product 106. The demethanizer reboiler circuit 50 can be heated by heat exchange with the feed gas stream, another process stream of appropriate temperature, or a heat medium stream. The demethanizer overheads 54 is used to cool and further condense the feed gas stream 104 using heat exchanger 18.

[0163] The demethanizer overheads 76 then flow to heat exchanger 116, which further cools the overheads after compression and air cooling (58, 60, 111, 112). The overheads stream is then chilled, and further cooled by heat exchange with the fractionator overheads stream 120, in heat exchanger 118. The stream 124 is then depressurized across valve 122 into the fractionator tower 38, which condenses a portion of the stream into high quality liquefied natural gas reflux, consisting primarily of liquid methane. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the ethane and heavier components from the upwards flowing natural gas, into the liquid phase. The fractionator overheads 120 have had ethane and heavier components effectively absorbed by the reflux, and exits the fractionator 38 as sales gas. The sales gas is used to cool the reflux stream, and inlet natural gas in heat exchangers (118, 102, 12), and then the sales gas exits the process for further compression, if required.

[0164] In order to switch the system from ethane recovery mode, to ethane rejection mode, a number of valves must be changed in position to appropriately redirect stream flows. Changing the positions of valves 300, 304, 308, 312, 316, 320, 324, 328, 332, 336, 340, and 344, and operating the distillation tower 44 as a deethanizer, instead of a demethanizer, allows the process to operate in ethane rejection mode. In this mode, a natural gas feed stream 10 at a pressure above, for example, approximately 5000 kPag flows through heat exchanger 12 cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 16 leaving exchanger 12 is then passed through a chiller 100′, which partially condenses the natural gas stream. The chiller 100′ may operate at, for example, approximately −40° C. and may use common refrigerants such as propane, or ammonia. Other suitable refrigerant examples are well within the purview of one skilled in the art.

[0165] The partially condensed natural gas stream 20 is then further cooled by heat exchange at 102 and 18 with a sales gas stream 28 and a reflux stream 30, then depressurized across valve 172 into separator 176. The order of this chilling, heat exchange, depressurization, and separation can occur in a different order, as most advantageous from an energy standpoint for the particular gas composition. The gas portion 188 leaving separator 176 is discussed in greater detail herein after. The gas stream 188 then enters the bottom of a refluxed fractionator tower 38 at, for example, approximately 3500 kPag. The gas flows upwardly through tower 38 where it is contacted with the downwardly flowing reflux liquids. The fractionator tower 38 bottoms liquids 40 exit the bottom of tower 38 as illustrated and are depressurized across a valve 42 directly into the top of a second distillation column 44, operating in the example as a deethanizer at approximately 1000 kPag. The deethanizer (second distillation column 44) is also fed the condensed liquids 180 from the separator 176. Liquids 180 are depressurized via valve 184 into the deethanizer 44.

[0166] Distillation of these liquids occurs in the deethanizer 44, with the bottoms product reboiled in circuit 50 to produce a low ethane content C3+ liquid product 52. The deethanizer reboiler circuit can be heated using a heat medium, or by heat exchange with a hot compressor discharge stream.

[0167] The deethanizer overheads 54 flow to a heat exchanger 200, which is used to further cool the stream after compression in compressor 58 to a pressure above the fractionator operating pressure followed by cooling in an air exchanger 60. The overheads stream 62 is then chilled and partially condensed in a chiller 206, and further condensed in an exchanger 210 with the sales gas, prior to being separated in separator 22.

[0168] The liquid stream 46 from the separator 22 is used as a medium quality source of reflux, with a composition that is approximately half methane and half ethane. The medium quality reflux stream is fed into a mid-point of the fractionator tower 38 as illustrated in the Figure.

[0169] The gas stream from the separator 22 can optionally be split into two streams 24 (referenced herein previously) and 74, with the ratio of the split determining the degree of propane recovery versus the refrigeration and reflux compression energy requirement. For the highest propane recovery, all of the gas stream from separator 22 can be used to generate high quality reflux liquids. The stream 74 is used to cool the feed to the fractionator 38 in a heat exchanger 18. The stream 76 then flows to another heat exchanger 116 which is used to further cool the stream after compression in compressor 111 and cooling in an air exchanger 112.

[0170] The stream 115 is compressed to approximately 7000 kPag, and then chilled in chiller 114 and cooled with heat exchanger 118 with the sales gas stream 120 from fractionator tower 38. Depressurization of this stream 124 is achieved by valve 122 to the fractionator tower 38 and this depressurization condenses a portion of the stream into high quality liquefied natural gas reflux, composed mainly of liquid methane. This reflux stream flows downwardly through the fractionator tower 38, effectively absorbing the propane and heavier components from the upwardly flowing natural gas into the liquid phase.

[0171] The fractionator overheads 120 have propane and heavier components effectively absorbed by the reflux and this exits the fractionator 38 as sales gas. The sales gas is used to cool the reflux streams, fractionator feed, and inlet natural gas in heat exchangers 118, 102, 210 and 12 and then the sales gas exits the process for further compression, if required.

[0172] Turning now to FIG. 10, shown is a process flow diagram in another embodiment of the invention for ethane recovery, that does not require a refrigeration system or turboexpander for cooling.

[0173] A natural gas feed stream 10 at a pressure above, for example, approximately 6500 kPag flows through heat exchanger 12 cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 15 leaving exchanger 12 is then passed through heat exchangers 400, 402, 404, and 406, which further cools the natural gas stream by heat exchange with the sales liquids, demethanizer 44 overheads, condensed feed liquids, and intermediate liquids streams 408, 410, 412, and 414 which further cools partially condenses the natural gas stream for separation in separator 416. The order of these heat exchangers, depressurization, and separation can occur in a different order, as most advantageous from an energy standpoint for the particular gas composition. The liquids outlet from separator 416 is depressurized across valve 418, then is used to cool the gas outlet of separator 404, and also cool the feed gas stream, and is fed into the demethanizer tower 44 operating at approximately 1000 kPag. The gas outlet from separator 416 is then cooled by the depressurized liquids from separator 416, and the gas stream is then depressurized to approximately 3500 kPag, forming more liquids which are separated in separator 420. The liquids stream leaving separator 420 are depressurized through valve 422 into an intermediate pressure distillation tower 424. The gas stream 426 leaving separator is fed to a refluxed fractionator tower 428. The gas flows upwardly through fractionator tower 428 where it is contacted with the downwardly flowing reflux liquids. The fractionator tower 428 bottoms liquids 430 exit the bottom of tower 428 as illustrated and are depressurized across a valve 432 into intermediate pressure distillation tower 424. The intermediate pressure distillation tower 424 accepts several sources of heavier, primarily liquid streams, and distills them, with the overheads of this column being the lean stream used for reflux in the fractionator column.

[0174] The liquids stream 432 leaving the intermediate pressure distillation column 424 are then used to cool the reflux stream in exchanger 434, and the partially condensed natural gas feed stream in exchanger 406, before being fed to the demethanizer 44

[0175] Distillation of the liquid streams occurs in the demethanizer 44, with the bottoms product reboiled in circuit 436 to produce a low methane content C2+ liquid product 438. The demethanizer reboiler circuit 436 can be heated using an appropriate temperature process stream within the process, such as the natural gas feed stream, or an appropriate heat medium.

[0176] The demethanizer overheads 410 flow to heat exchanger 402, which is used to cool natural gas feed stream 18. The demethanizer overheads 440 then flow to a heat exchanger 442 which is used to cool the stream after compression in compressor 446 to a pressure above the fractionator operating pressure followed by cooling in an air exchanger 448.

[0177] The overheads stream 450 is then further cooled by heat exchange with the sales gas in heat exchanger 452, and is then depressurized across valve 454 into separator 456. The gas portion of this stream is fed into the fractionator 428, and the liquid portion is further fed into the intermediate pressure distillation tower 424.

[0178] The gas stream 37 leaving the intermediate pressure fractionation tower 424 can be split into two streams 458 and 460, in order to provide an appropriate volume of reflux liquids to the fractionator 428. The stream 460 that is not required for fractionator reflux, is fed to the demethanizer. The stream 462 intended for fractionator 428 reflux then flows to another heat exchanger 464 which is used to further cool the stream after compression in compressor 466 and cooling in an air exchanger 468.

[0179] The stream 470 has been compressed to approximately 7000 kPag, and is then cooled by heat exchange with the sales gas in exchanger 434. Depressurization of this stream is achieved by valve 472 into the fractionator tower 428 and this depressurization condenses a portion of the stream into high quality liquefied natural gas reflux, composed mainly of liquid methane. This reflux stream flows downwardly through the fractionator tower 428, effectively absorbing the propane and heavier components from the upwardly flowing natural gas into the liquid phase.

[0180] The fractionator overheads 474 have ethane and heavier components effectively absorbed by the reflux and this exits the fractionator 428 as sales gas. The sales gas is used to cool the feed and recycle streams in heat exchangers 452 and 12, and then the sales gas exits the process for further compression, if required.

[0181] Turning now to FIG. 11, shown is a process flow diagram in another embodiment of the invention for ethane recovery, using refrigeration for cooling.

[0182] In this embodiment, natural gas stream 10 at a pressure above approximately 7000 kPag flows through a heat exchanger 12, cooling the gas by exchanging heat with the cold sales gas leaving the process, generally denoted by numeral 14. The natural gas stream 16 is then passed through a chiller 100′, which partially condenses the natural gas stream. The chiller 100′ may operate at approximately −40° C., and may use common refrigerants such as propane, or ammonia. The natural gas stream is then split, such that appropriate reflux stream cooling and tower temperature profiles can be achieved. One of the split streams 500 is depressurized across valve 502, into separator 504 at approximately 3500 kPag. The gas stream 504 leaving the separator 504 is fed into fractionator 508, and the liquid stream 510 leaving the separator 504 is depressurized into intermediate pressure distillation tower 512. The other portion of the partially condensed natural gas feed stream 514 is further cooled and condensed by heat exchange with sales gas and the intermediate pressure distillation tower overheads in exchangers 516 and 518. The stream is then depressurized and separated into gas and liquid streams in separator 520, with the gas portion 522 being fed into the fractionator tower 506 at approximately 3500 kPag.

[0183] The gas flows upwards through the refluxed fractionator tower 506 where it is contacted with the downwards flowing reflux liquids. The fractionator tower 506 bottoms liquids 524 exit the bottom of the tower 506 and are depressurized across a valve 526 directly into the top of intermediate pressure distillation tower 512. The intermediate pressure distillation tower 512 is also fed the condensed liquids 528 from the separator 520 which are depressurized across a valve 530 into the intermediate pressure distillation tower 512. The intermediate pressure distillation tower 512 is also fed the condensed liquids 510 from the separator 504 which are depressurized across a valve 532 into the intermediate pressure distillation tower 512.

[0184] Distillation of these liquids occurs in the intermediate pressure distillation tower 512 with the bottoms product reboiled in a reboiler circuit 534. The reboiler circuit 534 can be heated by heat exchange with another process stream of appropriate temperature, or a heat medium stream. The intermediate pressure overheads then flow to heat exchanger 536, which further cools the overheads after compression at 538, air cooling at 540, and cooling by heat exchange at 542 with the demethanizer overheads. The overheads stream further cooled by heat exchange with the fractionator overheads stream 544, in heat exchanger 546. The stream is then depressurized across valve 548 into the fractionator tower 506, which condenses a portion of the stream into high quality liquefied natural gas reflux, consisting primarily of liquid methane. This reflux stream flows downwardly through the fractionator tower 506, effectively absorbing the ethane and heavier components from the upwards flowing natural gas, into the liquid phase. At this point, the fractionator overheads 544 have had ethane and heavier components effectively absorbed by the reflux, and exit the fractionator 506 as sales gas. The sales gas is used to cool the reflux stream, and inlet natural gas in heat exchangers (550, 516, 12), and then the sales gas exits the process for further compression, if required.

[0185] The intermediate distillation column liquids are depressurized into a demethanizer column operating at approximately 1000 kPag. Distillation of these liquids occurs in the demethanizer 552 with the bottoms product reboiled in a reboiler circuit 554 to produce a low methane content C2+ liquid product 556. The demethanizer reboiler circuit 554 can be heated by heat exchange with the feed gas stream, another process stream of appropriate temperature, or a heat medium stream. The demethanizer overheads 558 are used to cool and further condense the feed gas stream 104 using heat exchanger 518, and to cool the high quality reflux stream using exchanger 542. The demethanizer overheads are then compressed, cooled, chilled, and depressurized (560,562,564,566) into the intermediate pressure distillation tower