Methods for separating hydrocarbons

Abstract

According to embodiments, a method for separating a mixed feed stream includes compressing and cooling the mixed feed stream and separating the mixed feed stream in a first separator to form at least a first light fraction and a first heavy fraction. The method includes cooling the first light fraction and separating the cooled first light fraction to form at least a second light fraction and a second heavy fraction. The method includes passing a first portion of the second heavy fraction to the first separator and separating a first portion of the first heavy fraction in a second separator to form at least a third light fraction and a third heavy fraction. The method includes cooling the third light fraction, separating the cooled third light fraction to form at least a fourth light fraction and a fourth heavy fraction, and passing the fourth heavy fraction to the second separator.

Description

METHODS FOR SEPARATING HYDROCARBONSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 621,305 filed January 16, 2024, the contents of which are incorporated in their entirety herein.TECHNICAL FIELD

[0002] Embodiments described herein generally relate to separation of chemicals, such as methods and systems for separating hydrocarbons.BACKGROUND

[0003] Various hydrocarbons, such as ethylene, ethane, propylene, propane, and heavier hydrocarbons, may be recovered from a variety of streams obtained from chemical reactors. Cryogenic separation processes may be used to recover more one or more chemical species. However, such separations may be costly and utilize relatively cold temperatures.SUMMARY

[0004] According to one or more embodiments described herein, in cryogenic separation processes, a mixed feed stream comprising C2, C3, and C4 hydrocarbons may be compressed and cooled by heat exchange with other process streams and / or external sources of refrigeration in one or more heat exchangers positioned within a cold box. As the mixed feed stream is cooled, the mixed feed stream may be separated into various light and heavy fractions. C2, C3, and C4 hydrocarbons have relatively low boiling points, and they are generally separated at relatively low temperatures, such as temperatures from 0 °C to -150 °C. Separating C2, C3, and C4 hydrocarbons at such low temperatures is generally an energy intensive process. There is a need for improved cryogenic separation methods that reduce energy consumption by improving the separation efficiency of C2, C3, and C4 hydrocarbons and using fewer external sources of refrigeration.

[0005] According to one or more embodiments, one or more of the heat exchangers positioned within a cold box may be used to cool the mixed feed stream and fractions of the mixed feed stream. Some fractions of the mixed feed stream may undergo pressure reduction and be used as coolant streams in the heat exchangers. This may reduce the need for the use of externalcoolants in the cryogenic separation process. Additionally, one or more of the heat exchangers in the cold box may be used as a condenser for a fractionation system that is used to form some of the light and heavy fractions. For example, the one or more heat exchangers in the cold box may be used to cool a light fraction from a fractionation system and condense a portion of that light fraction. Then, the condensed portion of the light fraction may be passed back to the fractionation system as a reflux stream. Using a heat exchanger positioned within the cold box as a condenser may reduce the capital cost of the fractionation system as a separate condenser in the fractionation system may not be necessary. Furthermore, some fractions of the mixed feed stream may be used as reflux streams to improve the separation of various fractions in one or more of the separators. For example, the mixed feed stream may be separated into a first light fraction and a first heavy fraction in a first separator. The first light fraction may be separated into a second light fraction and a second heavy fraction, and a portion of the second heavy fraction may be passed to the first separator as a reflux. This may improve the recovery of C3 hydrocarbons in the first separator.

[0006] According to one or more embodiments of the present disclosure, a method for separating a mixed feed stream comprises compressing the mixed feed stream to form a compressed mixed feed stream. The mixed feed stream comprises one or more of C2, C3, and C4+ hydrocarbons. The method further comprises cooling the compressed mixed feed stream to form a cooled mixed feed stream and separating the cooled mixed feed stream in a first separator to form at least a first light fraction and a first heavy fraction. The method further comprises cooling the first light fraction to form a cooled first light fraction and separating the cooled first light fraction to form at least a second light fraction and a second heavy fraction. The method further comprises passing a first portion of the second heavy fraction to the first separator and separating a first portion of the first heavy fraction in a second separator to form at least a third light fraction and a third heavy fraction. The method further comprises cooling the third light fraction in one or more heat exchangers positioned within a cold box to form a cooled third light fraction, separating the cooled third light fraction to form at least a fourth light fraction and a fourth heavy fraction, and passing the fourth heavy fraction to the second separator.

[0007] Additional features and advantages of the technology disclosed herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the technology as described herein, including the detailed description which follows, the claims, as well as the appended drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0009] FIG. 1 schematically depicts a system for separating hydrocarbons, according to one or more embodiments disclosed herein.

[0010] It should be understood that the drawings are schematic in nature, and do not include some components of a separation system commonly employed in the art, such as, without limitation, temperature transmitters, pressure transmitters, flow meters, pumps, valves, and the like. It would be known that these components are within the spirit and scope of the present embodiments disclosed. However, operational components, such as those described in the present disclosure, may be added to the embodiments described in this disclosure.

[0011] Reference will now be made in greater detail to various embodiments, some embodiments of which are illustrated in the accompanying drawings.DETAILED DESCRIPTION

[0012] One or more non-limiting embodiments of methods for separating a mixed feed stream are described herein. Referring now to FIG. 1 , a method for separating a mixed feed stream 100 may comprise compressing the mixed feed stream 100 to form a compressed mixed feed stream 101. The mixed feed stream 100 may be compressed in one or more compressors. For example, in the embodiment depicted in FIG. 1, the mixed feed stream 100 may be compressed in compressor 406. In one or more embodiments, the mixed feed stream 100 may be compressed in multiple compressor arranged in series. For example, the mixed feed stream 100 may be compressed in 1, 2, 3, 4, or even 5 or more compressors arranged in series.

[0013] In one or more embodiments, the mixed feed stream 100 may comprise one or more of C2, C3, or C4+ hydrocarbons. In some embodiments, the mixed feed stream may comprise at least 70 wt.% of the one or more of C2, C3, or C4+ hydrocarbons. For example, the mixed feed stream 100 may comprise at least 70 wt.%, 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.%, or 95 wt.% of the one or more of C2, C3, or C4+ hydrocarbons. In one or more embodiments, the one or more ofC2, C3, or C4+ hydrocarbons may comprise olefins and paraffins, including but not limited to ethane, ethylene, propane, propylene, butane, and butene. In one or more embodiments, the mixed feed stream 100 may further comprise one or more of nitrogen, hydrogen, methane, carbon monoxide, and carbon dioxide. In some embodiments, the mixed feed stream may comprise from 0.1 wt.% to 15 wt.% N2, from 0.01 wt.% to 10 wt.% H2, from 0.01 wt.% to 10 wt.% methane, and from 70 wt.% to 99 wt.% one or more of C2, C3, or C4+ hydrocarbons.

[0014] In one or more embodiments, the compressed mixed feed stream 101 may have a temperature from 10 °C to 75 °C. For example, the compressed mixed feed stream 101 may have a temperature from 10 °C to 75 °C, from 20 °C to 75 °C, from 30 °C to 75 °C, from 40 °C to 75 °C, from 50 °C to 75 °C, from 60 °C to 75 °C, from 70 °C to 75 °C, from 10 °C to 65 °C, from 10 °C to 55 °C, from 10 °C to 45 °C, from 10 °C to 35 °C, from 10 °C to 25 °C, from 10 °C to 20 °C, from 10 °C to 15 °C, or any range or combination of ranges formed from these endpoints. In one or more embodiments, the compressed mixed feed stream 101 may have a pressure from 250 psig to 500 psig. For example, the compressed mixed feed stream 101 may have a pressure from 250 psig to 500 psig, from 300 psig to 500 psig, from 350 psig to 500 psig, from 400 psig to 500 psig, from 450 psig to 500 psig, from 250 psig to 450 psig, from 250 psig to 400 psig, from 250 psig to 350 psig, from 250 psig to 300 psig, or any range or combination of ranges formed from these endpoints.

[0015] In one or more embodiments, the method for separating the mixed feed stream 100 may comprise cooling the compressed mixed feed stream 101 to form a cooled mixed feed stream 102. The compressed mixed feed stream 101 may be cooled in any suitable heat exchanger. The compressed mixed feed stream 101 may occur in one or more heat exchangers. In some embodiments, the compressed mixed feed stream 101 may be cooled in a heat exchanger positioned within cold box 220. In one or more embodiments, as depicted in FIG. 1, cooling the compressed mixed feed stream 101 may occur in the second heat exchanger 202. In one or more embodiments, cooling the compressed mixed feed stream 101 may condense at least a portion of the compressed mixed feed stream 101.

[0016] As used in this disclosure, a “cold box” refers to an insulated enclosure that may house one or more system components. The cold box may be insulated to minimize heat transfer between the system components and the environment. In one or more embodiments, one or moreheat exchangers may be positioned within a cold box. In some embodiments, multiple heat exchangers may be positioned in series within a cold box. The heat exchangers may include a brazed heat exchanger, a shell and tube heat exchanger, double pipe heat exchanger, plate heat exchanger, tubular heat exchanger, fin type heat exchanger, condensers, evaporators, boilers, or combinations thereof.

[0017] In one or more embodiments, the cooled mixed feed stream 102 may be separated in a first separator 300 to form at least a first light fraction 104 and a first heavy fraction 106. In one or more embodiments, the first separator 300 may be a distillation column. Using a distillation column as the first separator 300 may improve the separation of C3 hydrocarbons from C2 hydrocarbons and lighter chemicals in the first separator 300. For example, in one or more embodiments, the first light fraction may comprise at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, or even at least 90 wt.% C2 hydrocarbons and lighter components, such as N2 and H2. It should be noted that lighter components other than N2 and H2 may be included in the first light fraction in one or more embodiments.

[0018] As used in this disclosure, a “separator” refers to any separation device or system of separation devices that at least partially separates one or more chemicals that are mixed in a process stream from one another. For example, a separator may selectively separate differing chemical species or phases from one another, forming one or more chemical fractions. Examples of separators include, without limitation, distillation columns, flash drums, knock-out drums, knock-out pots, traps, scrubbers, expansion devices, membranes, solvent extraction devices, and the like. It should be understood that separation processes described in this disclosure may not completely separate all of one chemical constituent from all of another chemical constituent. It should be understood that the separation processes described in this disclosure “at least partially” separate different chemical components from one another, and that even if not explicitly stated, it should be understood that separation may include only partial separation. As used in this disclosure, one or more chemical constituents may be “separated” from a process stream to form a new process stream. Generally, a process stream may enter a separator and be divided, or separated, into two or more process streams of desired composition.

[0019] The first light fraction 104 may be cooled to form a cooled first light fraction 108. In some embodiments, the cooled first light fraction 108 may be partially condensed, and in someembodiments, the cooled first light fraction 108 may be fully condensed. The first light fraction 104 may be cooled in one or more heat exchangers. In some embodiments, the first light fraction 104 may be cooled in one or more heat exchangers positioned within cold box 220. In one or more embodiments, the first light fraction 104 may be cooled in the first heat exchanger 200.

[0020] Still referring to FIG. 1, the cooled first light fraction 108 may be separated to form at least a second light fraction 110 and a second heavy fraction 112. The cooled first light fraction 108 may be separated into the second light fraction 110 and the second heavy fraction 112 in separator 302. Separator 302 may be any suitable separator. For example, without limitation, separator 302 may be a vapor / liquid separator, such as a flash drum.

[0021] In one or more embodiments, the second heavy fraction 112 may comprise one or more of C2, C3, and C4+ hydrocarbons. In some embodiments, the second heavy fraction 112 may comprise greater than or equal to 30 wt.%, greater than or equal to 40 wt.%, greater than or equal to 50 wt.% C2 hydrocarbons. For example, the second heavy fraction 112 may comprise greater than or equal to 50 wt.%, greater than or equal to 60 wt.%, greater than or equal to 70 wt.%, greater than or equal to 80 wt.%, or even greater than or equal to 85 wt.% C2 hydrocarbons.

[0022] The second light fraction 110 may comprise one or more of hydrogen, nitrogen, methane, carbon monoxide, and carbon dioxide. In one or more embodiments, the second light fraction 110 may comprise greater than or equal to 50 wt.% of one or more of hydrogen, nitrogen, methane, carbon monoxide, and carbon dioxide. For example, the second light fraction 110 may comprise greater than or equal to 30 wt.%, greater than or equal to 40 wt.%, greater than or equal to 50 wt.%, greater than or equal to 60 wt.%, greater than or equal to 70 wt.%, greater than or equal to 80 wt.%, or even greater than or equal to 85 wt.% of one or more of hydrogen, nitrogen, methane, carbon monoxide, and carbon dioxide.

[0023] In one or more embodiments, a first portion of the second heavy fraction 114 may be passed to the first separator 300. In such embodiments, the first portion of the second heavy fraction 114 may be passed to the first separator 300 as a reflux stream. Without intending to be bound by theory, passing the first portion of the second heavy fraction 114 back to the first separator 300 may improve the separation between C2 hydrocarbons and C3 hydrocarbons in the first separator 300. This may allow for increased recovery of C3 hydrocarbons and increased concentration of C2 hydrocarbons in the first light fraction 104.

[0024] Still referring to FIG. 1, the first heavy fraction 106 may comprise one or more of C2, C3, and C4 hydrocarbons. In some embodiments, the first heavy fraction 106 may comprise greater than or equal to 50 wt.% C3 hydrocarbons. For example, the first heavy fraction 106 may comprise greater than or equal to 50 wt.%, greater than or equal to 55 wt.%, greater than or equal to 60 wt.%, greater than or equal to 65 wt.%, greater than or equal to 70 wt.%, greater than or equal to 75 wt.%, or even greater than or equal to 80 wt.% C3 hydrocarbons.

[0025] In one or more embodiments, the pressure of the first heavy fraction 106 may be reduced to form a cooled first heavy fraction 107. Reducing the pressure of the first heavy fraction 106 may at least partially vaporize the first heavy fraction 106 and may reduce the temperature of the first heavy fraction 106. In one or more embodiments, the pressure of the first heavy fraction 106 may be reduced by passing the first heavy fraction 106 through a valve 504. Valve 504 may be any suitable valve.

[0026] The cooled first heavy fraction 107 may be passed through one or more heat exchangers to provide cooling in the one or more heat exchangers. Passing the cooled first heavy fraction 107 through the one or more heat exchangers may warm the cooled first heavy fraction 107. In one or more embodiments, the one or more heat exchangers may be positioned within cold box 220. Still referring to FIG. 1, in one or more embodiments, the cooled first heavy fraction 107 may be passed through the second heat exchanger 202 to provide cooling in the second heat exchanger 202. Without intending to be bound by theory, using the cooled first heavy fraction 107 as a coolant in one or more of the heat exchangers may reduce, or even eliminate, the need for the use of an external refrigerant in the one or more heat exchangers.

[0027] In one or more embodiments, a first portion of the first heavy fraction 132 may be passed to a second separator 304. In one or more embodiments, the second separator 304 may be a fractionation system. As used in this disclosure, a “fractionation system” refers to any fractionation device or system of fractionation devices that at least partially divide a certain quantity of a mixture (gas, solid, liquid, or combinations thereof), during a phase transition, into a number of smaller fractions in which the composition varies according to a gradient. In one or more embodiments, the second separator 304 may be a multi-stage fractionation system. In such embodiments, the second separator 304 may comprise multiple fractionation devices in series. Forexample, the second separator 304 may comprise multiple separators and may include reflux or recycle streams between the separators.

[0028] In one or more embodiments, the first portion of the first heavy fraction 132 may be separated into at least a third light fraction 136 and a third heavy fraction 134. In one or more embodiments, the third light fraction 136 may comprise C2 and C3 hydrocarbons. For example, the third light fraction 136 may comprise at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, or even at least 90 wt.% C2 and C3 hydrocarbons. In one or more embodiments, the third heavy fraction 134 may comprise at least 50 wt.% C3 hydrocarbons. For example, the third heavy fraction 134 may comprise at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, or even at least 90 wt.% C3 hydrocarbons.

[0029] In one or more embodiments, the third light fraction 136 may be cooled in one or more heat exchangers within the cold box 220 to form a cooled third light fraction 138. Cooling the third light fraction 136 may at least partially condense the third light fraction 136. For example, in the embodiment depicted in FIG. 1, the third light fraction 136 may be passed to the second heat exchanger 202 positioned within cold box 220. The third light fraction 136 may be cooled in the second heat exchanger 202 to form cooled third light fraction 138.

[0030] Still referring to FIG. 1, the cooled third light fraction 138 may be separated to form at least a fourth light fraction 142 and a fourth heavy fraction 140. The cooled third light fraction 138 may be separated into the fourth light fraction 142 and the fourth heavy fraction 140 in separator 306. Separator 306 may be any suitable separator. In one or more embodiments, separator 306 may be a vapor / liquid separator, such as a flash drum.

[0031] In one or more embodiments, the fourth light fraction 142 may comprise greater than or equal to 50 wt.% C2 hydrocarbons. For example, the fourth light fraction 142 may comprise greater than or equal to 30 wt.%, 35 wt.%, 40 wt.%, 45 wt.%, 50 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, 70 wt.%, or even 75 wt.% C2 hydrocarbons. In one or more embodiments, the fourth heavy fraction 140 may comprise greater than or equal to 75 wt.% C2 and C3 hydrocarbons. For example, the fourth heavy fraction 140 may comprise greater than or equal to 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.%, or even 95 wt.% C2 and C3 hydrocarbons.

[0032] In one or more embodiments, the fourth heavy fraction 140 may be passed from separator 306 to the second separator 304. In such embodiments, the one or more heat exchangers within the cold box 220 may serve as a condenser for separator 304. Without intending to be bound by theory, using one or more of the heat exchangers positioned within the cold box 220 as a condenser for the fractionation system (separator 304), may improve the efficiency of the cooling within the system and may reduce the capital costs and cooling requirement of the fractionation system, as a separate condenser may not be necessary in the fractionation system. This may also reduce the need for the use of external refrigerants in the fractionation system and help eliminate external refrigeration loops.

[0033] Still referring to FIG. 1, in one or more embodiments, the pressure of the fourth light fraction 142 may be reduced to form a cooled fourth light fraction 144. Reducing the pressure of the fourth light fraction 142 may reduce the temperature of the fourth light fraction 142 to form the cooled fourth light fraction 144. The pressure of the fourth light fraction 142 may be reduced by passing the fourth light fraction 142 though a valve 502. Valve 502 may be any suitable valve.

[0034] The cooled fourth light fraction 144 may be passed through one or more heat exchangers as a coolant to provide cooling in the one or more heat exchangers. Passing the cooled fourth light fraction 144 through the one or more heat exchangers may warm the cooled fourth light fraction 144 to form a warmed fourth light fraction 146. In one or more embodiments, the one or more heat exchangers may be positioned within cold box 220. Still referring to FIG. 1, in one or more embodiments, the cooled fourth light fraction 144 may be passed through the second heat exchanger 202 to provide cooling the second heat exchanger 202 and form a warmed fourth light fraction 146. Without intending to be bound by theory, using the cooled fourth light fraction 144 as a coolant in one or more of the heat exchangers may improve the cooling efficiency and reduce the need for external refrigeration in the one or more heat exchangers.

[0035] In one or more embodiments, the warmed fourth light fraction 146 may be passed to compressor 406. As previously described, the mixed feed stream 100 may be compressed in compressor 406. In such embodiments, the warmed fourth light fraction 146 may be combined with the mixed feed stream 100 and compressed in compressor 406 to form the compressed mixed feed stream 101. Without intending to be bound by theory, recycling the warmed fourth lightfraction 146 to the compressor 406 to be included in the compressed mixed feed stream 101 may allow for the recovery of desired hydrocarbon products from the warmed fourth light fraction 146.

[0036] In one or more embodiments, the pressure of a second portion of the second heavy fraction 116 may be reduced to form a cooled second portion of the second heavy fraction 118. Reducing the pressure of the second portion of the second heavy fraction 116 may at least partially vaporize the second portion of the second heavy fraction 116 and may cool the second portion of the second heavy fraction 116. In one or more embodiments, the pressure of the second portion of the second heavy fraction 116 may be reduced by passing the second portion of the second heavy fraction 116 through a valve 500. Valve 500 may be any suitable valve.

[0037] Still referring to FIG. 1, the cooled second portion of the second heavy fraction 118 may be passed through one or more heat exchangers to form a warmed second portion of the second heavy fraction 130. Passing the cooled second portion of the second heavy fraction 118 through one or more heat exchangers may provide cooling in the one or more heat exchangers. In one or more embodiments, the one or more heat exchangers may be positioned within cold box 220. For example, in the embodiment depicted in FIG. 1, the cooled second portion of the second heavy fraction 118 may be passed through the first heat exchanger 200 to form stream 128 and stream 128 may be passed through the second heat exchanger 202 to form the warmed second portion of the second heavy fraction 130. First heat exchanger 200 and second heat exchanger 202 may be positioned within cold box 220. In one or more embodiments, the warmed second portion of the second heavy fraction 130 may exit the system. Without intending to be bound by theory, using the cooled second portion of the second heavy fraction 118 as a coolant in the one or more heat exchangers may reduce the need for the use of external refrigerants in the one or more heat exchangers.

[0038] Still referring to FIG. 1, the second light fraction 110 may be passed through one or more heat exchangers to provide cooling in the one or more heat exchangers and to produce a warmed second light fraction 120. The one or more heat exchangers may be positioned in the cold box 220. In one or more embodiments, as depicted in FIG. 1, the second light fraction 110 may be passed from separator 302 to the first heat exchanger 200 to provide cooling in the first heat exchanger 200 and produced warmed second light fraction 120.

[0039] In one or more embodiments, a pressure of the warmed second light fraction 120 may be reduced in a turbo-expander 402 to form a cooled second light fraction 122. The turboexpander 402 may extract work from the warmed second light fraction 120 when the pressure of the warmed second light fraction 120 is reduced. Reducing the pressure of the warmed second light fraction 120 and extracting work from the warmed second light fraction 120 in the turboexpander may reduce the temperature of the warmed second light fraction 120.

[0040] As described herein, a “turbo-expander” may be a system component or multiple system components suitable for reducing the pressure of a process stream and extracting work from that process stream. In some embodiments, a turbo-expander may be mechanically linked to a turbo-compressor such that work extracted by the turbo-expander may at least partially drive the turbo-compressor.

[0041] As described herein, “work” refers to energy transferred to or from an object by the application of force along a displacement. For example, work may be extracted from the warmed second light fraction 120 when the warmed second light fraction 120 causes a component of the turbo-expander 402 to move, such as causing a turbine in the turbo -expander 402 to spin. Power refers to the amount of work performed over a period of time. For example, the rate at which work is extracted from the warmed second light fraction 120 may be expressed in terms of power.

[0042] In one or more embodiments, the cooled second light fraction 122 may be passed through one or more heat exchangers to provide cooling in the one or more heat exchangers. The one or more heat exchangers may be positioned within the cold box 220. In some embodiments, passing the cooled second light fraction 122 through the one or more heat exchangers may produce an off-gas stream 126, which may exit the system. Referring still to FIG. 1, in one or more embodiments, the cooled second light fraction 122 may be passed through the first heat exchanger 200 to provide cooling in the first heat exchanger 200 and produce stream 124. Stream 124 may be passed through the second heat exchanger 202 to provide cooling to the second heat exchanger 202 and form off-gas stream 126.

[0043] Still referring to FIG. 1, the work extracted from the warmed second light fraction 120 by the turbo-expander 402 may be used to drive a turbo-compressor 404. In one or more embodiments, a second portion of the first heavy fraction 148 may be compressed in turbocompressor 404 to form a compressed recycle stream 150. In one or more embodiments, thecompressed recycle stream 150 may be passed from the turbo-compressor 404 to compressor 406. As previously described, the mixed feed stream 100 may be compressed in compressor 406. In such embodiments, the compressed recycle stream 150 may be combined with the mixed feed stream 100 and compressed in compressor 406 to form the compressed mixed feed stream 101. In one or more embodiments, as depicted in FIG. 1, the compressed recycle stream 150 and the warmed fourth light fraction 146 may be combined with the mixed feed stream 100 and compressed in compressor 406 to form the compressed mixed feed stream 101. In embodiments where multiple compressors are used in series to compress the mixed feed stream 100, as previously described, the compressed recycle stream 150, the warmed fourth light fraction 146, or both may be passed to a compressor downstream of the first compressor in the series of compressors used to form the compressed mixed feed stream 101. Without intending to be bound by theory, recycling the compressed recycle stream 150 to the compressor 406 to be included in the compressed mixed feed stream 101 may allow for the recovery of desired hydrocarbon products from the compressed recycle stream 150.

[0044] As described herein, a “turbo-compressor” may be a system component or multiple system components suitable for increasing the pressure of a process stream. A turbo-compressor may be mechanically linked to a turbo-expander. Work extracted by the turbo-expander may be used to compress one or more process streams in the turbo-compressor. In some embodiments, the turbo-compressor may make use of other sources of energy or work, such as energy or work from an electric motor, in addition to work extracted by the turbo -expander.

[0045] In some embodiments described herein, and as depicted in FIG. 1, the first heat exchanger 200 and second heat exchanger 202 may each be positioned within cold box 220. In one or more embodiments, not depicted, the first and second heat exchangers may be positioned within separate cold boxes, based on the cooling needs of the system.

[0046] In one or more embodiments, a stream comprising alkanes 152 may be passed through the one or more heat exchangers to provide cooling in the one or more heat exchangers. The stream comprising alkanes may comprise greater than 25 wt.%, 50 wt.%, 75 wt.% or even 95 wt.% alkanes. In one or more embodiments, the stream comprising alkanes may comprise one or more of C2, C3, and C4 alkanes. Passing the stream comprising alkanes 152 through the one or more heat exchangers may warm the stream comprising alkanes 152 to form a warmed alkanestream 154. In one or more embodiments, the one or more heat exchangers may be positioned within cold box 220. Passing the stream comprising alkanes 152 may provide cooling to the one or more heat exchangers. Without intending to be bound by theory, passing the stream comprising alkanes 152 through the one or more heat exchangers to provide cooling in the one or more heat exchangers may reduce the need to use external refrigerants or coolants in the one or more heat exchangers. In one or more embodiments, at least a portion of the warmed alkane stream 154 may be passed to a reactor. For example, at least a portion of the warmed alkane stream 154 may be passed to a dehydrogenation reactor to be used a feedstock for the dehydrogenation reaction.EXAMPLES

[0047] Various embodiments of the processes and systems for separating a mixed feed stream will be further clarified in the following Examples. The Examples are illustrative in nature, and should not be understood to limit the subject matter of the present disclosure.

[0048] Example 1

[0049] Example 1 was conducted using an integrated separation train process model in Aspen plus for the recovery system depicted in FIG. 1. Table 1 shows temperatures, pressures, and mass fractions ratios of streams depicted in FIG. 1. The numbering of the streams included in Table 1 is consistent with the numbering of the streams in FIG. 1 and the numbering used throughout the detailed description.Table 1.Table 1. Cont.Table 1. Cont.

[0050] As shown in Example 1, passing the first portion of the second heavy fraction 114 back to the first separator 300 as a reflux stream may improve the separation of C3 hydrocarbons from C2 hydrocarbons. Specifically, the first light fraction 104 included only 2 wt.% C3 hydrocarbons and 86 wt.% of the combination of C2 hydrocarbons, H2, and N2. Furthermore, the cold box 220 was suitable for use as a condenser for the second separator 304. Additionally, there was no need for an external refrigeration loop to provide additional cooling to the separation system.

[0051] It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present technology, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”

[0052] It should be understood that where a first component is described as “comprising” a second component, it is contemplated that, in some embodiments, the first component “consists of’ or “consists essentially of’ that second component. Additionally, the term “consisting essentially of’ is used in this disclosure to refer to quantitative values that do not materially affect the basic and novel characteristic(s) of the disclosure. For example, a chemical composition “consisting essentially of’ a particular chemical constituent or group of chemical constituents should be understood to mean that the composition includes at least about 99.5% of a that particular chemical constituent or group of chemical constituents.

[0053] It should be understood that any two quantitative values assigned to a property may constitute a range of that property, and all combinations of ranges formed from all stated quantitative values of a given property are contemplated in this disclosure.

[0054] The subject matter of the present disclosure has been described in detail and by reference to specific embodiments. It should be understood that any detailed description of a component or feature of an embodiment does not necessarily imply that the component or feature is essential to the particular embodiment or to any other embodiment. Further, it should be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter.

Claims

CLAIMS1. A method for separating a mixed feed stream, the method comprising: compressing the mixed feed stream to form a compressed mixed feed stream, wherein the mixed feed stream comprises one or more of C2, C3, and C4+ hydrocarbons; cooling the compressed mixed feed stream to form a cooled mixed feed stream; separating the cooled mixed feed stream in a first separator to form at least a first light fraction and a first heavy fraction; cooling the first light fraction to form a cooled first light fraction; separating the cooled first light fraction to form at least a second light fraction and a second heavy fraction; passing a first portion of the second heavy fraction to the first separator; separating a first portion of the first heavy fraction in a second separator to form at least a third light fraction and a third heavy fraction; cooling the third light fraction in one or more heat exchangers positioned within a cold box to form a cooled third light fraction; separating the cooled third light fraction to form at least a fourth light fraction and a fourth heavy fraction; and passing the fourth heavy fraction to the second separator.

2. The method of claim 1, the method further comprising: reducing a pressure of the fourth light fraction to form a cooled fourth light fraction; passing the cooled fourth light fraction through one or more heat exchangers as a coolant to form a warmed fourth light fraction; andpassing the warmed fourth light fraction to a compressor, wherein the compressing the mixed feed stream to form the compressed mixed feed stream occurs in the compressor.

3. The method of claim 1 or 2, wherein the mixed feed stream comprises greater than or equal to 70 wt.% of one or more of C2, C3, and C4+ hydrocarbons.

4. The method of any one of claims 1 to 3, wherein the second heavy fraction comprises greater than or equal to 30 wt.% C2 hydrocarbons.

5. The method of any one of claims 1 to 4, wherein the second light fraction comprises greater than or equal to 30 wt.% of one or more of hydrogen, nitrogen, methane, carbon monoxide, and carbon dioxide.

6. The method of any one of claims 1 to 5, wherein the first heavy fraction comprises greater than or equal to 30 wt.% C3 hydrocarbons.

7. The method of any one of claims 1 to 6, wherein the third heavy fraction comprises greater than or equal to 75 wt.% C3 hydrocarbons.

8. The method of any one of claims 1 to 7, wherein the fourth light fraction comprises greater than or equal to 30 wt.%. C2 hydrocarbons.

9. The method of any one of claims 1 to 8, wherein the fourth heavy fraction comprises greater than or equal to 75 wt.% C2 and C3 hydrocarbons.

10. The method of any one of claims 1 to 9, the method further comprising passing the first heavy fraction through one or more heat exchangers before separating the first portion of the first heavy fraction to form at least the third light fraction and the third heavy fraction.

11. The method of any one of claims 1 to 10, the method further comprising: reducing a pressure of a second portion of the second heavy fraction to form a cooled second portion of the second heavy fraction; and passing the cooled second portion of the second heavy fraction through one or more heat exchangers to form a warmed second portion of the second heavy fraction.

12. The method of any one of claims 1 to 11, the method further comprising: passing the second light fraction through one or more heat exchangers to form a warmed second light fraction; reducing a pressure of the warmed second light fraction in a turbo-expander, wherein work is extracted from the warmed second light fraction to form a cooled second light fraction; and passing the cooled second light fraction through one or more heat exchangers to provide cooling in the one or more heat exchangers.

13. The method of claim 12, the method further comprising: using the work from the turbo expander to drive a turbo-compressor; compressing a second portion of the first heavy fraction in the turbo-compressor to form a compressed recycle stream; andpassing the compressed recycle stream to a compressor, wherein the compressing the mixed feed stream to form the compressed mixed feed stream occurs in the compressor.

14. The method of any one of claims 1 to 13, the method further comprising passing a stream comprising alkanes through the one or more heat exchangers to provide cooling in the one or more heat exchangers.

15. The method of any one of claims 1 to 14, wherein the compressed mixed feed stream has a pressure from 250 psig to 500 psig.

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