Multiple reflux flow hydrocarbon recovery method

Abstract

To provide a system and process for recovering ethane and heavier components from a hydrocarbon gas flow.SOLUTION: Provided is a system for separating an introduction gas flow containing methane, C2 components, and C3 components into a volatile gas fraction containing methane, and a less volatile hydrocarbon fraction containing C2+ components. The system may comprise pipes, valves, and a control device configured to flexibly operate the system in a high ethane recovery mode, a high throughput mode, or, in some embodiments, a high propane recovery mode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments herein relate to the recovery of ethane and heavier components from hydrocarbon gas streams. In particular, embodiments herein relate to the flexible recovery of ethane and heavier components from hydrocarbon streams that allows the process to be easily transitioned from high throughput to high recovery modes. [Background technology]

[0002] Valuable hydrocarbon components, such as ethane, ethylene, propane, propylene, and heavier hydrocarbon components, are present in various gas streams. Some gas streams are natural gas streams, refinery off-gas streams, coal seam gas streams, etc. These components may also be present in other hydrocarbon sources, such as coal, tar sands, and crude oil, to name a few. The amount of valuable hydrocarbons varies depending on the source, and some of these streams may contain more than 50% methane and lighter components (i.e., nitrogen, carbon monoxide (CO), hydrogen, etc.), ethane, and carbon dioxide (CO2). Propane, propylene, and heavier hydrocarbon components generally constitute a small portion of the total supply. Due to the cost of natural gas, there is a need for processes that can achieve high recoveries of ethane, ethylene, and heavier components while reducing the operating and capital costs associated with the process. These processes also need to be easy and efficient to operate in order to maximize the revenues obtained.

[0003] Several processes are available for recovering hydrocarbon components from natural gas. These processes include the chilled, lean oil, chilled lean oil, and cryogenic processes. Recently, cryogenic processes have become increasingly popular due to their reliability, efficiency, and ease of operation compared to other processes. Cryogenic processes vary depending on the hydrocarbon components recovered: ethane and heavier components, or propane and heavier components. Typically, ethane recovery processes employ a single column with a reflux stream, as shown in U.S. Patent Nos. 5,629,995, 5,729,965, 5,733,975, and 5,829,975, to increase recovery and make the process efficient. Depending on the source of the reflux stream, the maximum recovery possible from the scheme may be limited. For example, if the reflux stream is derived from a hydrocarbon gas feed stream, a cryogenic separator vapor stream, or a first vapor stream, as in U.S. Patent No. 5,629,995, the reflux stream contains ethane, limiting the maximum recovery possible from the scheme.

[0004] Patent Document 4, which is a residue recycling method, discloses recycling the residue to the top of the column as a first feed from the top. The overhead of the low-temperature separator is divided into two streams, and a portion is condensed, subcooled, and introduced into the column as a second feed from the top. The second stream from the low-temperature separator overhead is expanded in a turbo expander or JT valve and then introduced as a third feed from the top.

[0005] In Patent Document 5, Figure 6, a configuration is used in which the remainder recycle and / or feed gas can be fed to the reflux separator. In Figures 5-7 of Patent Document 6, the feed gas is introduced as a second feed at the top of the column. Other patents and publications relating to the treatment of light hydrocarbon streams include, among others, Patent Documents 7, 8, 9, 10, 11, 12, 13, and 14. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 4,519,824 (hereinafter referred to as the '824 patent) [Patent Document 2] U.S. Patent No. 4,278,457 [Patent Document 3] U.S. Patent No. 4,157,904 [Patent Document 4] U.S. Patent No. 5,568,737 [Patent Document 5] U.S. Patent No. 7,793,517 [Patent Document 6] U.S. Patent Application Publication No. 2019 / 0170435 [Patent Document 7] US Patent Application Publication No. 2014 / 0260420 [Patent Document 8] US Patent Application Publication No. 2014 / 0075987 [Patent Document 9] US Patent Application Publication No. 2013 / 0014390 [Patent Document 10] US Patent Application Publication No. 2010 / 0043488 [Patent Document 11] US Patent Application Publication No. 2005 / 0204774 [Patent Document 12] US Patent Application Publication No. 2004 / 0172967 [Patent Document 13] US Patent Application Publication No. 2004 / 0159122 [Patent Document 14] U.S. Patent No. 6,244,070 Summary of the Invention [Means for solving the problem]

[0007] In one aspect, embodiments herein relate to a system for separating an input gas stream containing methane, C2 components, C3 components, and optionally heavier hydrocarbons into a volatile gas fraction containing methane and a less volatile hydrocarbon fraction containing C2+ components. The system may include a flow divider that divides the input gas stream into a first feed stream and a second feed stream. A first heat exchanger may be provided to cool the first feed stream, and a second heat exchanger may be provided to cool the second feed stream. The system may include a separator that separates the cooled first and second feed streams into a first vapor stream and a first liquid stream, as well as flow lines that feed the first vapor stream to a demethanizer and flow lines that feed the first liquid stream to the demethanizer. The demethanizer may separate the feed stream into a demethanizer overhead stream and a demethanizer bottoms stream. One or more compressors may be provided to compress the demethanizer overhead stream to form a remainder gas stream, and a demethanizer reflux line may supply a reflux stream to an upper portion of the demethanizer. A portion of the remainder gas stream may be supplied to the demethanizer reflux line via a flow line, and a flow line may supply a third portion of the input gas stream to the demethanizer reflux line. The system further includes a first valve for allowing or preventing flow of a portion of the remainder gas stream to the demethanizer reflux line, and a second valve for allowing or preventing flow of the third portion of the input gas stream to the demethanizer reflux line.

[0008] In some embodiments, the system may further include a control system configured to control the position of the first and second valves.

[0009] The first heat exchanger may be a gas-gas heat exchanger configured to exchange heat between one or more of the first feed stream, the demethanizer overhead stream, and the reflux stream, and the second heat exchanger may be a reboiler configured to exchange heat between one or more side draws from the demethanizer and the second feed stream.

[0010] In another aspect, embodiments herein may relate to a method of operating the system described above, which may include closing the first valve and opening the second valve to operate the system in a high throughput mode for a predetermined time, and closing the second valve and opening the first valve to operate the system in a high ethane recovery mode for a predetermined time.

[0011] In yet another aspect, embodiments herein relate to a process for separating an input gas stream comprising methane, C2 components, C3 components, and optionally heavier hydrocarbons into a volatile gas fraction comprising methane and a less volatile hydrocarbon fraction comprising C2+ components, the process comprising: a. In the first period, i. dividing an input gas stream into a first feed stream and a second feed stream, and cooling said first feed stream and said second feed stream; ii. separating the cooled first and second feed streams into a first vapor stream and a first liquid stream; iii. expanding said first liquid stream, thereby forming a first demethanizer feed stream; iv. expanding the first gas stream to a lower pressure, thereby forming a second demethanizer feed stream; v. feeding the first demethanizer feed stream and the second demethanizer feed stream to a demethanizer and separating the first demethanizer feed stream and the second demethanizer feed stream into a demethanizer overhead stream and a demethanizer bottoms stream; vi. warming and compressing said demethanizer overhead stream to form a remainder gas stream; and vii. recovering a first portion of said residual gas stream as a product stream and recycling a second portion of said residual gas stream to said demethanizer as a reflux stream. operating the process in a high ethane recovery mode comprising: b. ceasing to recycle the second portion of the remaining gas as reflux; c. In the second period, i. dividing the input gas stream into the first feed stream, the second feed stream, and a third feed stream, and cooling the first feed stream, the second feed stream, and the third feed stream; ii. separating the cooled first and second feed streams into a first vapor stream and a first liquid stream; iii. expanding said first liquid stream, thereby forming a first demethanizer feed stream; iv. expanding the first gas stream to a lower pressure, thereby forming a second demethanizer feed stream; v. feeding the first demethanizer feed stream and the second demethanizer feed stream to a demethanizer and separating the first demethanizer feed stream and the second demethanizer feed stream into a demethanizer overhead stream and a demethanizer bottoms stream; vi. warming and compressing the demethanizer overhead stream to form a remainder gas stream that is recovered as product; and vii. feeding the third feed stream to the demethanizer as reflux. operating the process in a high throughput mode including:

[0012] In other embodiments, the process may further include operating the process in a C3+ recovery mode of operation while recovering less than 90% of the ethane during a third period of time.

[0013] In yet another aspect, embodiments disclosed herein relate to a system for separating an input gas stream containing methane, C2 components, C3 components, and optionally heavier hydrocarbons into a volatile gas fraction containing methane and a less volatile hydrocarbon fraction containing C2+ components. The system may include a flow divider that divides the input gas stream into a first feed stream and a second feed stream. A gas-gas heat exchanger may be provided to cool the first feed stream and produce a cooled first feed stream. A second heat exchanger may be provided to cool the second feed stream and produce a cooled second feed stream. The system may also include a first separator that separates the cooled first and second feed streams into a first vapor stream and a first liquid stream. The flow divider may divide the first vapor stream into a first portion and a second portion, and an expander may be provided to expand the first portion of the first vapor stream and extract work from the first portion of the first vapor stream. A flow line may be provided to cool a second portion of the first vapor stream in the gas-gas heat exchanger, and a second separator may be provided to separate the cooled second portion of the first vapor stream into a second vapor stream and a second liquid stream. The system may also include a flow line to supply the first liquid stream to a demethanizer as a first tower feed stream, a flow line to supply the expanded first portion of the first vapor stream to the demethanizer as a second tower feed stream, a flow line to supply the second liquid stream to the demethanizer as a third feed stream, and a flow line to supply the second vapor stream to the demethanizer as a fourth feed stream. The demethanizer may be configured to receive feeds provided by the first, second, third, and fourth feed streams and separate the feeds into a demethanizer overhead stream and a demethanizer bottoms stream. A flow line may be provided to warm the demethanizer overhead stream in the gas-gas exchanger, and one or more compressors may be provided to compress the warmed demethanizer overhead stream to form a remainder gas stream, at least one compressor being driven by work extracted in the expander.The fifth tower feed stream may be configured to receive (i) a portion of the remainder gas stream, (ii) a third portion of the input gas stream, or (iii) a mixture of (i) and (ii), and to cool (i), (ii), or (ii) in the gas-gas exchanger. The system may further include a reflux flow line providing a reflux stream to an upper portion of the demethanizer tower, the reflux flow line being configured with valves and piping such that the reflux stream contains either (i), (ii), or (ii) or the second vapor stream provided from the fifth tower feed stream. A first valve may be provided to control or stop the flow of the portion of the remainder gas stream into the fifth tower feed line, and a second valve may be provided to control or stop the flow of the third portion of the input gas stream into the fifth tower feed line.

[0014] Other aspects and advantages will be apparent from the following description and appended claims. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a simplified process flow diagram of a C2+ recovery process according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a simplified process flow diagram of a C2+ recovery process according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] Embodiments herein relate to separating an inlet gas into a light fraction and a heavy fraction. As used herein, inlet gas refers to a hydrocarbon gas, typically received from a high-pressure gas line, consisting essentially of methane, with the remainder being ethane, ethylene, propane, propylene, and heavier components, as well as carbon dioxide, nitrogen, and other trace gases. The term "C2+ components" refers to all organic components having at least two carbon atoms, including alkanes, olefins, and alkynes, especially aliphatic species such as ethane, ethylene, and acetylene.

[0017] Systems according to embodiments herein for separating an input gas stream containing methane, C2 components, C3 components, and optionally heavier hydrocarbons into a volatile gas fraction containing methane and a less volatile hydrocarbon fraction containing C2+ components provide operators with the flexibility to operate in a first, high throughput mode and a second, high ethane recovery mode. Market demands and other factors may make it desirable to operate in either the high throughput mode or the high ethane recovery mode, and systems herein allow operators to easily transition between operating modes.

[0018] The system may include a flow divider that divides the input gas stream into a first feed stream and a second feed stream. A first heat exchanger may be provided to cool the first feed stream and a second heat exchanger may be provided to cool the second feed stream. A separator may receive the cooled first and second feed streams and then separate the cooled first and second feed streams into a first vapor stream and a first liquid stream.

[0019] A flow line may be provided to feed the first vapor stream to a demethanizer. Similarly, a flow line may be provided to feed the first liquid stream to the demethanizer. In the demethanizer, the feed gas may be separated into a demethanizer overhead stream comprising methane and a demethanizer bottoms stream comprising C2+ components. One or more compressors may be provided to compress the demethanizer overhead stream to form a remaining gas stream.

[0020] A demethanizer reflux line may be used to supply a reflux stream to an upper portion of the demethanizer. The system may also include a flow line that supplies a portion of the remainder gas stream to the demethanizer reflux line. A flow line may be configured to supply a third portion of the input gas stream to the demethanizer reflux line. A first valve may be used to allow or stop the flow of a portion of the remainder gas stream to the demethanizer reflux line, and a second valve may be used to allow or stop the flow of the third portion of the input gas stream to the demethanizer reflux line. A control system may be configured to control the positions of the first and second valves. Using the feed gas as reflux, closing the first valve and opening the second valve operates the system in a high throughput mode. Using the remainder gas as reflux, closing the second valve and opening the first valve operates the system in a high ethane recovery mode.

[0021] 1 and 2 illustrate embodiments of the C2+ recovery system herein, with like numerals representing like parts. Additionally, while the following description relating to FIGS. 1 and 2 provides exemplary temperatures, pressures, or ranges thereof, it should be understood that when a range is given for a pressure or temperature, even if only one exemplary temperature or pressure is given, the associated temperature or pressure may also be a range. Additionally, it should be understood that the temperatures and pressures given may vary depending on the compositional makeup of each stream.

[0022] Referring now to Figures 1 and 2, the raw feed gas to a C2+ recovery system may contain certain impurities, such as water, CO2, and H2S, which are detrimental to cryogenic processing. If CO2 and H2S are present in significant amounts, the raw feed gas stream may be treated to remove the CO2 and H2S. This treated gas is then dried and filtered before being sent to the cryogenic section of the C2+ recovery system as input feed gas stream 20. Input feed gas stream 20 is split into a first input stream 20a, which may contain a portion of the input feed gas stream, and a second input stream 20b, which contains the remainder of the input feed gas stream. First input stream 20a and second input stream 20b may be of equivalent composition.

[0023] First inlet stream 20a may be cooled in gas-gas heat exchanger 30 to a temperature in the range of 0°F to -60°F, e.g., -5°F to -35°F, -20°F, etc., by heat exchange contact with a cold stream to partially condense the heavy hydrocarbons. Second inlet stream 20b may be cooled in demethanizer reboiler 40 to a temperature in the range of 0°F to -60°F, e.g., -5°F to -35°F, -20°F, etc., by heat exchange contact with reboiler streams 71, 73 to partially condense the heavy hydrocarbons. In all embodiments herein, gas-gas heat exchanger 30 and demethanizer reboiler 40 may be a single multi-pass exchanger, a plurality of individual heat exchangers, or combinations or variations thereof.

[0024] The cooled inlet streams 20a', 20b' are then combined and sent to low-temperature separator 50, which operates, for example, at approximately -20°F (e.g., -10 to -30°F). Depending on the composition and feed pressure of inlet feed gas stream 20, some external cooling in the form of propane refrigeration may be required to sufficiently cool inlet gas streams 20a', 20b', such as propane refrigeration provided as needed via exchanger 21. While propane refrigeration is shown, other refrigerants can be used in place of propane. Separator 50 may be, for example, a flash drum or a low-temperature absorber, and in some embodiments, may include at least one mass transfer zone. In some embodiments, the mass transfer zone may be a tray or similar equilibrium separation stage, or a flash zone.

[0025] Cryogenic separator 50 produces separator bottoms stream 52 and separator overhead stream 54. Separator bottoms stream 52 is expanded through first expansion valve 130 to a pressure of, for example, about 330 psia (e.g., in the range of 275 psia to 500 psia), thereby cooling the stream to, for example, about −70° F. This cooled and expanded stream is sent to demethanizer 70 as first demethanizer (i.e., tower) feed stream 53.

[0026] Separator overhead stream 54 may be expanded essentially isentropically in expander 100, for example, to a pressure of about 325 psia. By reducing the pressure and extracting work from the stream, the resulting expanded stream 56 may be cooled, for example, to a temperature of about −91° F. (−80 to −100° F.). The cooled expanded stream 56 may then be sent to demethanizer 70. In some embodiments, stream 56 may be fed, for example, as a second tower feed stream below third tower feed stream 64, e.g., above first tower feed stream 53 and below third tower feed stream 64. This work is subsequently recovered in booster compressor 102 driven by expander 100 to partially boost the pressure of demethanizer overhead stream 78. In some embodiments, a booster compressor (not shown) driven by expander 100 may be used to partially boost the pressure of input stream 20.

[0027] In some embodiments, a portion 20c of overhead stream 54 may be withdrawn upstream of expander 100 and optionally supplied to reflux separator 60. Third input vapor stream 20c may be cooled in gas-gas heat exchanger 30, for example, to a temperature of about −30°F to −70°F, and partially condensed by heat exchange contact with a cold stream. The partially condensed stream may then be supplied to reflux separator 60 as intermediate reflux stream 55, which produces reflux separator bottoms stream 62 and reflux separator overhead stream 66. Reflux separator bottoms stream 62 may be expanded by second expansion valve 140 and supplied to demethanizer 70 as third column feed stream 64, for example, below fourth column feed stream 68. Alternatively, reflux separator overhead stream 66 may be further cooled in gas-gas heat exchanger 30 by heat exchange contact with a cold stream and expanded through third expansion valve 150, for example, to a pressure in the range of about 300-500 psia (e.g., a pressure of about 325 psia), thereby cooling the stream, for example, to −148° F. The cooled, expanded stream may be fed to demethanizer 70 as fourth tower feed stream 68. Fourth tower feed stream 68 may be introduced below demethanizer reflux stream 126. In some embodiments, expanded reflux separator bottoms stream 64 may be combined with stream 56 and fed to demethanizer 70 as a combined second tower feed stream. In other embodiments, as shown in FIG. 2, the system may be configured for additional flexibility by providing valves and flow lines to switch the feed points of fourth tower feed stream 68 and reflux stream 126 and feed stream 68 as reflux.

[0028] Thus, demethanizer 70 may be supplied with second tower feed stream 56, third tower feed stream 64, fourth tower feed stream 68, and demethanizer reflux stream 126, thereby providing demethanizer overhead stream 78, demethanizer bottoms stream 77, and one or more reboiler side streams 71, 73.

[0029] In demethanizer 70, rising vapor from first tower feed stream 53 is at least partially condensed by intimate contact with liquids falling from second tower feed stream 56, third tower feed stream 64, fourth tower feed stream 68, and demethanizer reflux stream 126, thereby producing a demethanizer overhead stream 78 containing a substantial amount of methane and lighter components from input feed gas stream 20. The condensed liquid descends down demethanizer 70 and is removed as demethanizer bottoms stream 77 containing a substantial amount of ethane, ethylene, propane, propylene, and heavier components from input feed gas stream 20. As used herein, ethane recovery refers to the amount of ethane recovered via demethanizer bottoms stream 77 compared to the amount of ethane in feed 20.

[0030] Reboiler streams 71, 73 may be taken from the bottom half of the vessel of demethanizer 70. Additionally, reboiler streams 71, 73 may be warmed in demethanizer reboiler 40 and returned to the demethanizer as reboiler reflux streams 72, 74, respectively. This side reboiler design allows for the recovery of refrigeration from demethanizer 70.

[0031] Demethanizer overhead stream 78 is warmed in gas-gas heat exchanger 30, for example, to a temperature of about 90°F (e.g., 80-100°F). After warming, demethanizer overhead stream 78 is compressed in booster compressor 102, for example, to a pressure of about 380 psia (e.g., 350 psia-400 psia), using power generated by expander 100. The intermediate-pressure residue gas is then sent to residue compressor 110, where the pressure is increased, for example, to above 800 psia or to pipeline specifications, to form residue gas stream 120. Residual gas stream 120 is then cooled by residue aftercooler 112 to release the heat generated during compression. Residual gas stream 120 may be, for example, a pipeline sales gas containing a significant amount of methane and lighter components from input feed gas stream 20, and minor amounts of C2+ and heavier components.

[0032] Additionally, embodiments herein provide operational flexibility, allowing operators to operate in high recovery and high plant throughput modes.

[0033] In the high recovery mode, at least a portion of the remainder gas stream 120 may be returned to the process to produce a remainder gas reflux stream 122. This remainder gas reflux stream 122 may be cooled by heat exchange contact with a cold stream in gas-gas heat exchanger 30 to a temperature in the range of, for example, −80 to −150° F., substantially condensing the stream. This cooled remainder gas reflux stream 124 may then be expanded through fourth expansion valve 160 to a pressure of, for example, about 325 psia (275 to 500 psia), thereby cooling to a temperature of, for example, about −157° F., and sent to demethanizer 70 as demethanizer reflux stream 126. In some embodiments, demethanizer reflux stream 126 is sent above fourth column feed stream 68 of demethanizer 70 as an overhead feed stream to demethanizer 70.

[0034] In the high throughput mode, the remainder recycle 122 may be discontinued, for example, by closing valve 170. As reflux to the demethanizer 70, the fourth portion 20d of the input feed gas may be provided by opening valve 180 and providing input gas to the reflux line, where it may be cooled by heat exchange contact with a cold stream in gas-to-gas heat exchanger 30. This cooled feed gas reflux stream 124 may then be expanded through fourth expansion valve 160, whereby the feed gas reflux is cooled and provided to the demethanizer 70 as demethanizer reflux stream 126. The reflux in such an embodiment has the same composition as the feed.

[0035] In high recovery mode, a portion of the residual gas after compression may be recycled as an overhead reflux / feed stream in the recovery process to enhance ethane and propane recovery. The recycled residual gas (stream 122) may be, for example, about 10% to over 30% of the residual gas exiting the compressors (102, 110).

[0036] In the high throughput mode, the advantage is that the retentate recycle can be eliminated, allowing the unit to process more gas. Excess dry feed gas is sent to the retentate recycle flow path, using the same reflux feed configuration. This configuration allows this option to use the same equipment (reflux line, expansion valve, expander, heat exchanger, and compressor) while simultaneously processing more gas overall through the unit.

[0037] In some embodiments, a control system 200 may be provided to control the position of valves 170, 180. When operation in a high throughput mode is desired, valve 170 may be closed and valve 180 may be open, thereby providing a portion of the feed gas as reflux to the demethanizer. When operation in a high ethane recovery mode is desired, valve 180 may be closed and valve 170 may be open, thereby providing a portion of the remaining gas as reflux to the demethanizer. In this manner, the system allows for easy transitions between operating modes.

[0038] If it is desired to operate the system in a high ethane recovery mode, the system (e.g., valves, controllers, etc.) may be configured to use the remaining gas as reflux to the demethanizer. Thus, a high ethane recovery mode for a separation process may include splitting an input gas stream into a first feed stream and a second feed stream, and cooling the first and second feed streams. The cooled first and second feed streams may then be separated into a first vapor stream and a first liquid stream. The first liquid stream may be expanded to thereby form a first demethanizer feed stream, and the first gas stream may be expanded to a lower pressure to thereby form a second demethanizer feed stream. The first and second demethanizer feed streams may then be fed to a demethanizer, which separates the feed streams into a demethanizer overhead stream and a demethanizer bottoms stream. The demethanizer overhead stream may be warmed and compressed to form a remainder gas stream, a first portion of which may be recovered as a product stream, and a second portion of which may be provided as reflux to the demethanizer tower.

[0039] If it is desired to operate the system in a high throughput mode, the system (e.g., valves, controls, etc.) may be configured to use the feed gas as reflux to the demethanizer. Thus, a high throughput mode for a separation process may include splitting the input gas stream into a first feed stream, a second feed stream, and a third feed stream, and cooling the first feed stream, the second feed stream, and the third feed stream. Similar to the high ethane recovery mode, the first feed stream and the second feed stream may be separated into a first vapor stream and a first liquid stream, which may each be expanded and fed as feeds to the demethanizer, where the feeds may be split into a demethanizer overhead stream and a demethanizer bottoms stream. The demethanizer overhead stream may be warmed and compressed to form a remaining gas stream that is recovered as product. Instead of using the remainder gas as reflux, the third feed stream may be fed as reflux to the demethanizer, thereby allowing the system to operate in a high throughput mode.

[0040] In other embodiments where it is desirable to increase throughput while achieving relatively high ethane recovery, control system 200 may also be configured to operate valves 170 and 180 such that the combined feed of remainder gas 122 and feed 20d is fed to the demethanizer as reflux.

[0041] In yet another embodiment, the system may be configured to operate in a C3+ recovery mode of operation. In the C3+ recovery mode, valve 130 may be partially or fully closed and valve 132 may be at least partially or fully opened, thereby providing at least a portion or all of the liquid feed from separator 50 to reboiler 40. Valve 200 may be closed, thereby eliminating the need to withdraw a side draw via flow line 71, but providing liquid hydrocarbons via flow line 52 as feed to the lower portion of the column. Valve 201 may be opened or closed depending on the desired ethane recovery, although valve 201 may be opened to achieve ethane recoveries greater than 20%. Additional heat may be provided by trim reboiler 210, which may use remainder recycle 122, an external heat source (steam or hot oil), or other suitable process streams as heat sources. Such flow schemes may offer the ability to recover significant amounts of the C3+ components in the feed, e.g., greater than 95% or greater than 98% of the C3+ hydrocarbons, although ethane recovery may be reduced, e.g., to less than 90% ethane recovery.

[0042] As described above, embodiments herein allow gas plant operators to choose between high ethane recovery and high plant throughput. It is not obvious to feed enriched feed gas as overhead reflux, as this would reduce recovery. However, this offers the advantage of operational flexibility. With minimal capital investment, an additional 15-20% of the feed gas can be processed. Even at lower recovery rates, more total natural gas liquids products are recovered. This offers significant advantages to gas plant operators seeking to maximize plant throughput.

[0043] Two operating modes were simulated, one using the remainder gas recycle as reflux to the demethanizer, and the other using a portion of the feed gas as reflux to the demethanizer. The results of the simulations are shown in Table 1.

[0044] [Table 1]

[0045] When used as the upper reflux, the more enriched feed gas results in a lower ethane recovery (92% vs. 97%). However, using the more enriched feed gas as the upper reflux can significantly increase throughput (200 million standard cubic feet per day vs. 240 million standard cubic feet per day, a 20% increase in throughput under simulated conditions).

[0046] Unless otherwise defined, all technical and scientific terms used have the same meaning as commonly understood by one of ordinary skill in the art to which these systems, devices, methods, processes, and compositions of matter belong.

[0047] The singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise.

[0048] As used in this specification and the appended claims, the words "comprise," "has," "include," and all grammatical variations thereof are each intended to have an open, non-limiting meaning such that they do not exclude additional elements or steps.

[0049] "Optionally" means that the described event or circumstance may or may not occur. The description includes instances in which the event or circumstance occurs and instances in which it does not occur.

[0050] When the term "approximately" or "about" is used, it can mean that a value can vary by ±10%, 5%, 2%, 1%, 0.5%, 0.1%, or 0.01%.

[0051] Ranges may be expressed as from about one particular value to about another particular value, inclusive. When such a range is expressed, it is to be understood that another embodiment is from the one particular value to the other particular value, along with all particular values ​​and combinations thereof within that range.

[0052] While the present disclosure includes a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will recognize that other embodiments may be devised without departing from the scope of the present disclosure, which scope, therefore, should be limited only by the appended claims.

Claims

1. 1. A system for separating an input gas stream comprising methane, C2 components, C3 components, and optionally heavier hydrocarbons, into a volatile gas fraction comprising methane and a less volatile hydrocarbon fraction comprising C2+ components, the system comprising: a flow divider that divides the input gas stream into a first feed stream and a second feed stream; a first heat exchanger for cooling the first feed stream; a second heat exchanger for cooling the second feed stream; a separator for separating the cooled first and second feed streams into a first vapor stream and a first liquid stream; a flow line supplying the first vapor stream to a demethanizer; a flow line supplying said first liquid stream to said demethanizer; said demethanizer column separating said feed stream into a demethanizer overhead stream and a demethanizer bottoms stream; one or more compressors for compressing the demethanizer overhead stream to form a remainder gas stream; a demethanizer reflux line for supplying a reflux stream to an upper portion of the demethanizer; a flow line supplying a portion of the remainder gas stream to the demethanizer reflux line; a flow line supplying a third portion of the input gas stream to the demethanizer reflux line; a first valve for permitting or preventing flow of a portion of the remainder gas stream to the demethanizer reflux line; and a second valve for permitting or stopping flow of a third portion of said input gas stream to said demethanizer reflux line;

2. The system of claim 1 , further comprising a control system configured to control the position of the first valve and the second valve.

3. 2. The system of claim 1, wherein the first heat exchanger comprises a gas-to-gas heat exchanger exchanging heat between one or more of the first feed stream, the demethanizer overhead stream, and the reflux stream.

4. 2. The system of claim 1, wherein the second heat exchanger comprises a reboiler that exchanges heat between one or more side draws from the demethanizer and the second feed stream.

5. closing the first valve and opening the second valve and operating the system in a high throughput mode for a predetermined period of time; and 10. A method of operating a system as recited in claim 1, comprising closing said second valve and opening said first valve and operating said system in a high ethane recovery mode for a predetermined period of time.

6. 1. A process for separating an input gas stream comprising methane, C2 components, C3 components, and optionally heavier hydrocarbons, into a volatile gas fraction comprising methane and a less volatile hydrocarbon fraction comprising C2+ components, comprising: In the first period, (a) dividing an input gas stream into a first feed stream and a second feed stream, and cooling the first feed stream and the second feed stream; (b) separating the cooled first and second feed streams into a first vapor stream and a first liquid stream; (c) expanding the first liquid stream, thereby forming a first demethanizer feed stream; (d) expanding the first gas stream to a lower pressure, thereby forming a second demethanizer feed stream; (e) feeding the first demethanizer feed stream and the second demethanizer feed stream to a demethanizer and separating them into a demethanizer overhead stream and a demethanizer bottoms stream; (f) warming and compressing the demethanizer overhead stream to form a remainder gas stream; and (g) recovering a first portion of the remainder gas stream as a product stream and recycling a second portion of the remainder gas stream to the demethanizer column as a reflux stream. operating the process in a high ethane recovery mode comprising: ceasing to recycle the second portion of the remaining gas as reflux; In the second period, (aa) dividing the input gas stream into the first feed stream, the second feed stream, and a third feed stream, and cooling the first feed stream, the second feed stream, and the third feed stream; (bb) separating the cooled first and second feed streams into a first vapor stream and a first liquid stream; (cc) expanding the first liquid stream, thereby forming a first demethanizer feed stream; (dd) expanding the first gas stream to a lower pressure, thereby forming a second demethanizer feed stream; (ee) feeding the first demethanizer feed stream and the second demethanizer feed stream to a demethanizer and separating the first demethanizer feed stream and the second demethanizer feed stream into a demethanizer overhead stream and a demethanizer bottoms stream; (ff) warming and compressing the demethanizer overhead stream to form a remainder gas stream that is recovered as product; and (gg) feeding the third feed stream to the demethanizer as reflux. operating the process in a high throughput mode comprising: A process involving:

7. 10. The process of claim 6, further comprising operating the process in a C3+ recovery mode of operation during a third period of time while recovering less than 90% of the ethane.

8. 7. The process of claim 6, further comprising: during a third time period, mixing a portion of the remaining gas with the third feed stream to form a mixed reflux stream; and feeding the mixed reflux stream as reflux to the demethanizer tower.

9. 1. A system for separating an input gas stream comprising methane, C2 components, C3 components, and optionally heavier hydrocarbons, into a volatile gas fraction comprising methane and a less volatile hydrocarbon fraction comprising C2+ components, the system comprising: a flow divider that divides the input gas stream into a first feed stream and a second feed stream; a gas-to-gas heat exchanger for cooling the first feed stream to produce a cooled first feed stream; a second heat exchanger for cooling the second feed stream to produce a cooled second feed stream; a first separator for separating the cooled first and second feed streams into a first vapor stream and a first liquid stream; a flow divider that divides the first vapor stream into a first portion and a second portion; an expander for expanding a first portion of the first vapor stream and extracting work from the first portion of the first vapor stream; a flow line for cooling a second portion of said first vapor stream in said gas-to-gas heat exchanger; a second separator for separating the cooled second portion of the first vapor stream into a second vapor stream and a second liquid stream; a flow line supplying the first liquid stream to a demethanizer tower as a first tower feed stream; a flow line supplying the expanded first portion of the first vapor stream to the demethanizer tower as a second tower feed stream; a flow line supplying the second liquid stream as a third feed stream to the demethanizer; a flow line supplying the second vapor stream as a fourth feed stream to the demethanizer; said demethanizer column separating said first, second, third, and fourth feed streams into a demethanizer overhead stream and a demethanizer bottoms stream; a flow line for warming said demethanizer overhead stream in said gas-gas exchanger; one or more compressors for compressing the warmed demethanizer overhead stream to form a remainder gas stream, at least one compressor being driven by work extracted in the expander; (i) a portion of the remaining gas stream, (ii) a third portion of the input gas stream, or (iii) a fifth tower feed stream configured to receive a mixture of (i) and (ii) and to cool the received (i), (ii), or (ii) in the gas-gas exchanger; a reflux flow line supplying a reflux stream to an upper portion of the demethanizer tower, the valves and piping configured such that the reflux stream contains either (i), (ii), or (ii) supplied from the fifth tower feed stream or the second vapor stream; a first valve for controlling or stopping the flow of a portion of the remainder gas stream to the fifth column feed line; and a system including a second valve for controlling or stopping the flow of a third portion of said inlet gas stream to said fifth column feed line;

10. The system of claim 9 further comprising a flow line for cooling a portion of the second vapor in the gas-gas exchanger.

11. 10. The system of claim 9, wherein the first tower feed stream is fed to a lower portion of the demethanizer than the second tower feed stream, the second tower feed stream is fed to a lower portion of the demethanizer than the third tower feed stream, and the third tower feed stream is fed to a lower portion of the demethanizer than the fourth tower feed stream.

12. 12. The system of claim 11, wherein in a first configuration, the fourth tower feed stream is the reflux stream and the fifth tower feed stream is fed to a portion of the demethanizer tower above the third tower feed stream and below the reflux stream, and in a second configuration, the fifth tower feed stream is the reflux stream and the fourth tower feed stream is fed to a portion of the demethanizer tower below the reflux stream.

13. The system of claim 9 , further comprising a flow line configured to supply at least a portion of the first liquid stream to the second heat exchanger.

14. 10. The system of claim 9, wherein the second heat exchanger comprises a reboiler that exchanges heat between one or more side draws from the demethanizer and the second feed stream.

15. 10. The system of claim 9, further comprising a mixer upstream of the first separator for mixing the cooled first and second feed streams to produce a mixed cooled feed stream, and an exchanger for further cooling the mixed cooled feed stream.

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