Single column nitrogen rejection unit

Abstract

A system for removing nitrogen from a hydrocarbon feed stream has a heat exchanger system that cools the hydrocarbon feed stream. A feed separator separates a cooled feed stream from the heat exchanger system into a methane-enriched fluid and a first nitrogen-enriched fluid. A helium separator receives cooled first nitrogen-enriched fluid from the heat exchanger system and produces a first helium-enriched fluid and a helium separator bottoms fluid and directs the first helium-enriched fluid to the heat exchanger system. A warm helium stripper receives the helium separator bottoms fluid from the helium separator and first nitrogen-enriched fluid from the feed separator as a stripping fluid and produces a second helium-enriched fluid and a warm helium stripper bottoms fluid and directs the warm helium stripper bottoms fluid to the distillation column. A cold helium stripper receives the cooled first helium-enriched fluid from the heat exchanger system and second helium-enriched fluid from the warm helium stripper as a stripping fluid and produces a crude helium fluid and a cold helium stripper bottoms fluid and directs the cold helium stripper bottoms fluid to the distillation column. A reflux compressor compresses at least a portion of the warmed nitrogen-enriched vapor stream from the heat exchanger system. A reflux accumulator receives the cooled nitrogen-enriched fluid stream from the heat exchanger system and produces an overhead reflux-drum vapor stream and a reflux fluid stream and directs the reflux fluid stream to the distillation column. The distillation column produces a nitrogen-enriched vapor stream and a column bottoms liquid stream.

Description

SINGLE COLUMN NITROGEN REJECTION UNITCLAIM OF PRIORITY

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 507,880, filed June 13, 2023, the contents of which are hereby incorporated by reference.FIELD OF THE DISCLOSURE

[0002] The present invention relates generally to a system and method for removing nitrogen from a hydrocarbon gas stream and, more particularly, to a system and method for removing nitrogen from a hydrocarbon gas stream which can be vented to the atmosphere. The system and method may also produce a recyclable crude helium stream.BACKGROUND

[0003] In prior art hydrocarbon gas liquefaction processes, such as natural gas liquefaction, it is often necessary to remove nitrogen from a feed stream of the hydrocarbon gas. This may be done due to purification or nitrogen recovery requirements. The nitrogen removed from the feed stream may be used as fuel or in other applications or vented to atmosphere. Use of a nitrogen rejection unit (NRU) for such processing of natural gas or other hydrocarbon gas feed streams is known in the art, but increases in efficiency and systems and effectively separating a mixed gas stream into multiple single gas streams is highly desirable.SUMMARY

[0004] There are several aspects of the present subject matter which may be embodied separately or together in the devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.

[0005] In one aspect, a system for removing nitrogen from a hydrocarbon feed stream includes a heat exchanger system that receives and cools the feed stream. A distillation column includes a number of inlet ports, a top vapor outlet, and a bottom liquid outlet. Afeed separator is in fluid communication with the heat exchanger system and receives a cooled feed steam and separates the stream into a methane-enriched liquid and a nitrogen- enriched vapor. The heat exchanger system receives and cools nitrogen-enriched vapor and methane-enriched liquid from the feed separator and directs cooled methane-enriched liquid to the distillation column. A helium separator receives cooled nitrogen-enriched fluid from the heat exchanger system and produces a first helium enriched vapor and a first nitrogen- enriched liquid and directs the first helium enriched vapor to the heat exchanger system. A warm helium stripper receives the first nitrogen-enriched liquid from the helium separator and nitrogen-enriched vapor from the feed separator as a stripping gas and produces a second helium enriched vapor and a second nitrogen-enriched liquid and directs the nitrogen- enriched liquid to the distillation column. A cold helium stripper receives the cooled first helium enriched fluid from the heat exchanger system and second helium enriched vapor from the warm helium stripper as a stripping gas and produces a helium vapor and a helium and nitrogen liquid and directs the helium and nitrogen liquid to the distillation column. The heat exchanger system receives helium vapor from the cold helium stripper to provide cooling within the heat exchanger system. The heat exchanger system receives a nitrogen- enriched vapor stream from the top vapor outlet of the distillation column to provide cooling within the heat exchanger system and to create a warmed nitrogen-enriched vapor stream. A reflux compressor receives and compresses at least a portion of the warmed nitrogen-enriched vapor stream from the heat exchanger system. The heat exchanger system receives and cools a compressed nitrogen-enriched vapor stream from the reflux compressor to produce a cooled nitrogen-enriched fluid stream. A reflux accumulator receives the cooled nitrogen-enriched fluid stream from the heat exchanger system and produces an overhead reflux-drum vapor stream and a reflux liquid stream and directs the reflux liquid stream to the distillation column. The distillation column produces a nitrogen-enriched vapor stream that exits the distillation column through the top vapor outlet and a column bottoms liquid stream that exits the distillation column through the bottom liquid outlet.

[0006] In another aspect, a method of removing nitrogen from a hydrocarbon feed stream includes the steps of cooling the feed stream in a heat exchanger system; directing the cooled feed stream to a feed separator; separating the cooled gas into a nitrogen-enriched vapor and a methane-enriched liquid; directing the methane-enriched liquid through the heat exchanger system and to a distillation column; cooling and condensing the nitrogen-enriched vapor inthe heat exchanger system and directing cooled nitrogen-enriched fluid to a helium separator; separating the cooled nitrogen-enriched fluid into a first helium-enriched vapor and a helium separator bottoms fluid in the helium separator; directing the helium separator bottoms fluid from the helium separator to a warm helium stripper and first nitrogen-enriched fluid from the feed separator as a stripping gas to the warm helium stripper; forming a second helium- enriched fluid and a warm helium stripper bottoms fluid in the warm helium stripper; directing the warm helium stripper bottoms fluid to the distillation column; cooling the first helium-enriched fluid in the heat exchanger system and directing cooled first helium-enriched fluid to a cold helium stripper; sending the second helium-enriched fluid to the cold helium stripper as a stripping gas; forming a crude helium vapor and a cold helium stripper bottoms fluid in the cold helium stripper; refrigerating the heat exchanger system by directing the crude helium vapor through the heat exchanger system; directing the cold helium stripper bottoms fluid to the distillation column; producing a nitrogen-enriched vapor stream out of a top outlet of the distillation column; refrigerating the heat exchanger system by directing the nitrogen-enriched vapor stream through the heat exchanger system to form a warmed nitrogen-enriched vapor stream and compressing at least a portion of the warmed nitrogen- enriched vapor stream to form a compressed nitrogen-enriched vapor stream; directing the compressed nitrogen-enriched vapor stream through the heat exchanger system to a reflux accumulator so that an overhead reflux-drum vapor stream and a reflux liquid stream are formed; directing the reflux liquid stream to the distillation column; and withdrawing a column bottoms liquid stream from a bottom of the distillation column.

[0007] In a further aspect, a system for removing nitrogen from a hydrocarbon feed stream includes a heat exchanger system configured to receive and cool the hydrocarbon feed stream. A distillation column includes inlet ports, a top vapor outlet, and a bottom liquid outlet. A feed separator is in fluid communication with the heat exchanger system and is configured to receive a cooled feed stream and separate the cooled feed stream into a methane-enriched fluid and a first nitrogen-enriched fluid. The heat exchanger system is configured to receive and cool first nitrogen-enriched fluid from the feed separator and methane-enriched fluid from the feed separator and to direct cooled methane-enriched fluid to the distillation column. A middle-feed separator is configured to receive cooled first nitrogen-enriched fluid from the heat exchanger system and produce a first helium-enriched fluid and a middle-feed separator bottoms fluid and to direct the first helium-enriched fluid tothe heat exchanger system. A middle-feed separator bottoms expansion device is configured to receive the middle-feed separator bottoms fluid from the middle-feed separator and to direct expanded middle-feed separator bottoms fluid to the distillation column. The heat exchanger system is configured to receive and cool the first helium-enriched fluid from the middle-feed separator and to direct cooled first helium-enriched fluid to the distillation column. The heat exchanger system is configured to receive a nitrogen-enriched vapor stream from the top vapor outlet of the distillation column to provide cooling within the heat exchanger system and to create a warmed nitrogen-enriched vapor stream. A reflux compressor is configured to receive and compress at least a portion of the warmed nitrogen- enriched vapor stream from the heat exchanger system. The heat exchanger system configured to receive and cool a compressed nitrogen-enriched vapor stream from the reflux compressor to produce a cooled nitrogen-enriched fluid stream. A reflux accumulator is configured to receive the cooled nitrogen-enriched fluid stream from the heat exchanger system and to produce an overhead reflux-drum vapor stream and a reflux fluid stream and to direct the reflux fluid stream to the distillation column. The distillation column configured to produce a nitrogen-enriched vapor stream that exits the distillation column through the top vapor outlet and a column bottoms liquid stream that exits the distillation column through the bottom liquid outlet.

[0008] In a still further aspect, a method of removing nitrogen from a hydrocarbon feed stream includes the steps of cooling the hydrocarbon feed stream in a heat exchanger system; directing the cooled gas fluid feed stream to a feed separator; separating the cooled gas into a nitrogen-enriched vapor and a methane-enriched liquid; directing the methane-enriched liquid through the heat exchanger and to a distillation column; cooling and condensing the nitrogen- enriched vapor in the heat exchanger and directing cooled nitrogen-enriched fluid to a middle-feed separator; separating the cooled nitrogen-enriched fluid into a first helium- enriched vapor and a middle-feed separator bottoms fluid in the middle-feed separator; directing the first helium-enriched vapor from the middle-feed separator to the heat exchanger system; cooling the first helium-enriched vapor in the heat exchanger system and directing a cooled first helium-enriched fluid to the distillation column; sending the middlefeed separator bottoms fluid to a middle-feed separator bottoms expansion device; expanding the middle feed separator bottoms fluid in the middle-feed separator bottoms fluid expansion device and directing an expanded middle feed separator bottoms fluid to the distillationcolumn; producing a nitrogen-enriched vapor stream out of a top outlet of the distillation column; refrigerating the heat exchanger system by directing the nitrogen-enriched vapor stream through the heat exchanger system to form a warmed nitrogen-enriched vapor stream and compressing at least a portion of the warmed nitrogen-enriched vapor stream to form a compressed nitrogen-enriched vapor stream; directing the compressed nitrogen-enriched vapor stream through the heat exchanger system to a reflux accumulator so that an overhead reflux-drum vapor stream and a reflux liquid stream are formed; directing the reflux liquid stream to the distillation column; and withdrawing a column bottoms liquid stream from a bottom of the distillation column.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 is a process flow and schematic illustrating a first embodiment of the system and method of the disclosure.

[0010] Fig. 2 is a process flow and schematic illustrating a second embodiment of the system and method of the disclosure.DETAILED DESCRIPTION OF EMBODIMENTS

[0011] Disclosed herein is a nitrogen rejection unit (NRU) system and method for the removal of nitrogen from a hydrocarbon feed stream. While natural gas is described as the feed stream, the system and method may accommodate alternative hydrocarbon feed streams. The system and method may also include separation of helium to use outside of the system. Embodiments of the system and method of the disclosure are illustrated in Figs. 1 and 2 and described below.

[0012] It should be noted herein that the passages and streams are sometimes both referred to by the same element number set out in the figures. Also, as used herein, and as known in the art, a heat exchanger is that device or an area in the device wherein indirect heat exchange occurs between two or more streams at different temperatures, or between a stream and the environment. As used herein, the terms “communication”, “communicating”, and the like generally refer to fluid communication unless otherwise specified. Furthermore, although two fluids in communication may exchange heat upon mixing, such an exchange would not be considered to be the same as heat exchange in a heat exchanger, although such an exchangecan take place in a heat exchanger. As used herein, the term “reducing the pressure of’ (or variations thereof) does not involve a phase change, while the term “flashing” (or variations thereof) involves a phase change, including even a partial phase change. As used herein, the terms, “high”, “middle”, “mid”, “warm”, “cold” and the like are relative to comparable streams, as is customary in the art.

[0013] An embodiment of the system of the present disclosure may include at least one of each of the following components: a warm heat exchanger 10, a feed separator 12, a cold heat exchanger 14, a helium separator 16, a warm helium stripper column 18, a cold helium stripper column 20, a reflux accumulator 24, a reflux compressor 64 and a NRU distillation column 26. The separators 12 and 16 may each be a separation drum or any other separation device known in the art. These components may all be placed within a cold box which may provide protection (such as from weather elements) and insulation to the inside components. As is known in the art, the cold box may be comprised of steel and may include an insulating material. The system may also include a methane pump 28, which can be placed outside of the cold box. The warm and cold heat exchangers 10 and 14 are part of a heat exchanger system. In alternative embodiments, the heat exchanger system may include a single heat exchanger in place of warm and cold heat exchangers 10 and 14 or may include more than two heat exchangers.

[0014] A first embodiment of the system and method of the disclosure, illustrated in Fig. 1, receives a feed stream 32, which may be a natural gas fluid stream, which is compressed to be at the required pressure so that the energy is balanced. This stream is a mixture of gases which, as an example only, consists of nitrogen, methane and helium. In some embodiments, the stream 32 is predominantly methane and nitrogen. Stream 32 enters the system and is fed to the warm heat exchanger 10 where it is cooled and partially condensed. A bypass stream 33 based on control valve 29 may ensure that the feed gas separator 12 is at required temperature. As an example only, the warm heat exchanger 10 (and all main heat exchangers in the further embodiments discussed below) may be a brazed aluminum heat exchanger (BAHX) or other heat exchanger type. The cooled and condensed stream from the warm heat exchanger is then expanded via feed expansion device 35 and directed to the feed separator drum 12. As an example only, expansion device 35, and any other expansion devicereferenced below, may be a Joule-Thomson valve or any other fluid expansion device known in the art.

[0015] The feed separator drum 12 separates most of the methane from the nitrogen. The feed separator drum 12 produces a first nitrogen-enriched fluid (which may be an overhead vapor) 34 and a methane-enriched fluid (which may be a bottom liquid) 36. The methane- enriched fluid 36 from the bottom of the feed separator drum 12 is directed through the cold heat exchanger 14. A bypass stream 37, under the control of bypass valve 39, may be used to ensure that liquid in the NRU column 26 is at an adequate temperature. This methane- enriched fluid 36 is subcooled in the cold heat exchanger 14. After it is subcooled, and expanded via expansion device 41, this stream is directed to a inlet of the NRU column 26. The NRU column 26 separates methane from the nitrogen. The NRU column 26 can be trayed and / or provided with packing. The NRU column 26 includes a plurality of inlets for receiving streams from various components of the system. The NRU column 26 also includes a top vapor outlet for removing nitrogen vapor from the system. The NRU column further includes a bottom liquid outlet.

[0016] The majority of the first nitrogen-enriched fluid 34 from the feed separator drum 12 is directed to the cold heat exchanger 14 where it is cooled and partially condensed. This cooled and partially condensed vapor is then expanded via expansion device 43 and sent to the helium separator 16. This produces a first helium-enriched fluid (which may be overhead vapor) 42 and a helium separator bottoms fluid (which may be a nitrogen-enriched bottoms liquid) 44. The first helium-enriched fluid 42 is then directed back through the cold heat exchanger 14 where it is cooled, and partially condensed and is then expanded via expansion device 45 and sent to the cold helium stripper 20 producing a crude helium fluid (which may be vapor overhead) 46 and a cold helium stripper bottoms fluid (which may be liquid) 48 (which may be enriched in nitrogen) at the bottom. The cold helium stripper 20 separates the helium from the nitrogen. The overhead 46 is crude helium, which is a mixture of helium and nitrogen. The crude helium fluid 46 is then directed through the cold heat exchanger 14, and then through the warm heat exchanger 10 to recover energy / refrigeration by providing cooling within the cold and warm heat exchangers. Crude helium product (which may be vapor) 52 then exits the NRU system for helium handling. This helium vapor can be from about 20% to about 80% helium. Additionally, the balance of the vapor can be nitrogen. Thecold helium stripper bottoms fluid (which may be enriched in nitrogen) 48 from the cold helium stripper 20 is then expanded via expansion device 49 and directed to an inlet of the NRU column 26.

[0017] The helium separator bottoms fluid (which may be nitrogen-enriched) 44 from the bottom of the helium separator 16 is directed to the warm helium stripper 18 after expansion in expansion device 51. Stream 54, after expansion in expansion device 53, provides a stripping gas to separate helium from the streams entering the warm and cold helium strippers 18 and 20. The warm helium stripper 18 separates the helium from the nitrogen. More specifically, at the warm helium stripper 18, a mass transfer occurs against the bypass vapor 54 originating from the overhead vapor of the feed separator drum 12 producing second helium-enriched fluid (which may be overhead vapor) 56 and warm helium stripper bottoms fluid (which may be a nitrogen-enriched bottoms liquid) 58. The second helium-enriched overhead vapor 56 of the warm helium stripper 18 is then, after expansion in expansion device 55, used as the stripping gas for the cold helium stripper 20. The warm helium stripper bottoms fluid 58 from the warm helium stripper 18, after expansion in expansion device 57, is then directed to an inlet of the NRU column 26. In alternative embodiments, there may be fewer helium stripper steps or additional helium stripper steps to increase or reduce the helium content in the crude helium stream.

[0018] NRU column 26 produces nitrogen-enriched vapor 62. This overhead nitrogen- enriched vapor 62 from the NRU column 26 is sent through the cold exchanger 14 and then the warm exchanger 10 to recover energy / refrigeration by providing refrigeration therein and to produce high purity warm nitrogen-enriched vapor 61. In some embodiments, this high purity nitrogen-enriched vapor includes less than 0.1% hydrocarbons. A portion of this high purity warm nitrogen-enriched vapor 61, which may be mostly nitrogen with the balance being methane, is then vented to atmosphere, and another portion is sent to the reflux compressor 64 to generate the nitrogen reflux required to achieve the high nitrogen purity within the NRU system, and to provide a portion of the refrigeration requirements of the NRU system. The reflux compressor 64 provides adequate reflux. In one embodiment, the reflux compressor 64 is a multistage compressor with interstage cooling.

[0019] Compressor 64 produces compressed nitrogen-enriched vapor 63 which is cooled in recycle after-cooler 67 to form cooled stream 65. Recycle after cooler 67 may be a heat exchanger that uses ambient air or another fluid as the cooling fluid, or any other type of heat exchanger known in the art. The cooled compressed nitrogen-enriched vapor 65 originating from the reflux compressor 64 is then sent to the warm exchanger 10 and the cold exchanger 14 where it is cooled so as to be de-superheated, fully condensed, and subcooled to form cooled nitrogen-enriched fluid stream 69. The small bypass of stream 72 around the cold exchanger 14 under the control of valve 77 is provided for control purposes. This bypass ensures that the differential temperature between feed to reflex drum and return from NRU column is controlled. Stream 69 is then flashed across an expansion device 74 and sent to the reflux accumulator 24 which, as an example only, may be a reflux drum. The reflux accumulator ensures that there is a steady reflux flow to the NRU column 26. The reflux accumulator vapor stream 68 of reflux accumulator 24, under the control of valve 79, is combined with the overhead vapor of column 62 at a junction and is then directed through the cold exchanger 14. The liquid bottoms of the reflux accumulator 24 is directed under the control of valve 81 as the reflux fluid 66 to an inlet of the NRU column 26 to ensure that there is a steady reflux flow thereto.

[0020] NRU distillation column 26 may include both a side or first reboiler 76 and a bottoms or second reboiler 78. Distillation column 26 may include a first reboiler inlet port and a second reboiler inlet port and a first side liquid outlet and second side liquid outlet corresponding to each reboiler. Both of these reboilers provide refrigeration duty to the cold exchanger 14. The cold heat exchanger 14 may include a first and second reboiler passage. In the illustrated embodiment, these reboilers operate using a gravity / thermosyphon flow arrangement, and do not require pumps.

[0021] NRU column 26 provides a column bottom liquid (which may be methane liquid or purified liquid natural gas) stream 82. The column bottom liquid stream 82 may exit from the bottom outlet of NRU column 26 and travel to the pump 28. At the pump, the pressure is increased to provide the correct methane boiling temperature required in the warm exchanger 10. The liquid stream discharged from the pump 28 is then sent through the warm exchanger 10 where the methane liquid is boiled and superheated. The resulting methane vapor stream 71 is then directed out of the system. Methane vapor stream 71 has low nitrogen content andmay optionally be compressed and further processed. A small bypass stream 73 may be directed to an LNG tank (not shown) under control of valve 75 to ensure that the NRU column 26 does not get too cold.

[0022] In a second embodiment of the system and method of the disclosure, which will now be described with reference to Fig. 2, helium recovery has been omitted. The remaining aspects of the system of Fig. 2 are similar to those of Fig. 1.

[0023] The system of Fig. 2 receives a natural gas fluid stream 132, which is compressed to be at the required pressure so that the energy is balanced. This stream is a mixture of gases which, as an example only, consists of nitrogen, methane and helium. In some embodiments, the stream 132 is predominantly methane and nitrogen. Stream 132 enters the system and is fed to the warm heat exchanger 110 where it is cooled and partially condensed. A bypass stream 133 based on control valve 129 may ensure that the feed gas separator 112 is at required temperature. The cooled and condensed stream from the warm heat exchanger is then expanded via feed expansion device 135 and directed to the feed separator drum 112.

[0024] The feed separator drum 112 separates most of the methane from the nitrogen. The feed separator drum 112 produces a first nitrogen-enriched fluid 134 and a methane-enriched fluid 136. The methane-enriched fluid 136 from the bottom of the feed separator drum 112 is directed through the cold heat exchanger 114. A bypass stream 137, under the control of bypass valve 139, may be used to ensure that liquid in the NRU column 126 is at an adequate temperature. This methane-enriched fluid 136 is subcooled in the cold heat exchanger 114. After it is subcooled, and expanded via expansion device 141, this stream is directed to a inlet of the NRU column 126. The NRU column 126 separates methane from the nitrogen. The NRU column 126 can be trayed and / or provided with packing. The NRU column 126 includes a plurality of inlets for receiving streams from various components of the system. The NRU column 126 also includes a top vapor outlet for removing nitrogen-enriched vapor from the system. The NRU column further includes a bottom liquid outlet.

[0025] The majority of the nitrogen-enriched fluid 134 from the feed separator drum 112 is directed to the cold heat exchanger 114 where it is cooled and partially condensed. This cooled and partially condensed vapor is then expanded via expansion device 143 and sent to the middle-feed separator 116. This produces a heliumenriched fluid 142 and a nitrogen-enriched fluid 144. The helium-enriched fluid 142 is then directed back through the cold heat exchanger 114 where it is cooled, and partially condensed and is then expanded via helium expansion device 145 and sent to the distillation column 126. The nitrogen-enriched fluid 144 from the bottom of the middle-feed separator 116 is directed to the distillation column 126 after expansion in expansion device 151.

[0026] NRU column 126 produces nitrogen-enriched vapor 162. This nitrogen-enriched vapor 162 from the NRU column 126 is sent through the cold exchanger 114 and then the warm exchanger 110 to recover energy / refrigeration by providing refrigeration therein and to produce high purity warm nitrogen-enriched vapor 161. In some embodiments, this high purity nitrogen-enriched vapor includes less than 0.1% hydrocarbons. A portion of this high purity warm nitrogen vapor 161, which may be mostly nitrogen with the balance being methane, is then vented to atmosphere, and another portion is sent to the reflux compressor 164 to generate the nitrogen reflux required to achieve the high nitrogen purity within the NRU system, and to provide a portion of the refrigeration requirements of the NRU system. The reflux compressor 164 provides adequate reflux. In one embodiment, the reflux compressor 164 is a multistage compressor with interstage cooling.

[0027] Compressor 164 produces high compressed nitrogen-enriched vapor 163 which is cooled in recycle after-cooler 167. Recycle after cooler 167 may be a heat exchanger that uses ambient air or another fluid as the cooling fluid, or any other type of heat exchanger known in the art. The cooled compressed nitrogen-enriched vapor 165 originating from the reflux compressor 164 is then sent to the warm exchanger 110 and the cold exchanger 114 where it is cooled so as to be de-superheated, fully condensed, and subcooled to form cooled nitrogen-enriched fluid 169. The small bypass stream 172 around the cold exchanger 114 under the control of valve 177 is provided for control purposes. This bypass ensures that the differential temperature between feed to reflex drum and return from NRU column is controlled. Stream 169 is then flashed across an expansion device 174 and sent to the optional reflux accumulator 124 which, as an example only, may be a reflux drum. The reflux accumulator ensures that there is a steady reflux flow to the NRU column 126. The overhead vapor 168 of reflux accumulator 124, under the control of valve 179, is combined with the overhead vapor of column 162 at a junction and is then directed through the cold exchanger 114. The liquid bottoms of the reflux accumulator 124 is directed under the controlof valve 181 as the reflux fluid 166 to an inlet of the NRU column 126 to ensure that there is a steady reflux flow thereto.

[0028] As in the embodiment of Fig. 1, NRU distillation column 126 may optionally include a side or first reboiler 176 and / or a bottoms or second reboiler 178. Distillation column 126 may include a first reboiler inlet port and a second reboiler inlet port and a first side liquid outlet and second side liquid outlet corresponding to each reboiler. Both of these reboilers provide refrigeration duty to the cold exchanger 114. The cold heat exchanger 114 may include a first and second reboiler passage. In the illustrated embodiment, these reboilers operate using a gravity / thermosyphon flow arrangement, and do not require pumps.

[0029] NRU column 126 provides a column bottoms liquid stream 182 (which may be methane liquid or purified liquid natural gas). The column bottoms liquid stream 182 may exit from the bottom outlet of NRU column 126 and travel to the pump 128. At the pump, the pressure is increased to provide the correct methane boiling temperature required in the warm exchanger 110. The liquid stream discharged from the pump 128 is then sent through the warm exchanger 110 where the methane liquid is boiled and superheated. The resulting methane vapor stream 171 is then directed out of the system. Methane vapor stream 171 has low nitrogen content and may optionally be compressed and further processed. A small bypass stream 173 may be directed to an LNG tank (not shown) under control of valve 175 to ensure that the NRU column 126 does not get too cold.

[0030] There are several aspects of the present subject matter which may be embodied separately or together in the methods, devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.

[0031] While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A system for removing nitrogen from a hydrocarbon feed stream comprising: a. a heat exchanger system configured to receive and cool the hydrocarbon feed stream; b. a distillation column including a plurality of inlet ports, a top vapor outlet, and a bottom liquid outlet; c. a feed separator in fluid communication with the heat exchanger system and configured to receive a cooled feed stream and separate the cooled feed stream into a methane-enriched fluid and a first nitrogen-enriched fluid; d. the heat exchanger system configured to receive and cool first nitrogen- enriched fluid from the feed separator and methane-enriched fluid from the feed separator and to direct cooled methane-enriched fluid to the distillation column; e. a helium separator configured to receive cooled first nitrogen-enriched fluid from the heat exchanger system and produce a first helium-enriched fluid and a helium separator bottoms fluid and to direct the first helium-enriched fluid to the heat exchanger system; f. a warm helium stripper configured to receive the helium separator bottoms fluid from the helium separator and first nitrogen-enriched fluid from the feed separator as a stripping fluid and to produce a second helium-enriched fluid and a warm helium stripper bottoms fluid and to direct the warm helium stripper bottoms fluid to the distillation column; g. a cold helium stripper configured to receive the cooled first helium-enriched fluid from the heat exchanger system and second helium-enriched fluid from the warm helium stripper as a stripping fluid and to produce a crude helium fluid and a cold helium stripper bottoms fluid and to direct the cold helium stripper bottoms fluid to the distillation column; h. said heat exchanger system configured to receive crude helium fluid from the cold helium stripper to provide cooling within the heat exchanger system; i. said heat exchanger system configured to receive a nitrogen-enriched vapor stream from the top vapor outlet of the distillation column to provide coolingwithin the heat exchanger system and to create a warmed nitrogen-enriched vapor stream; j . a reflux compressor configured to receive and compress at least a portion of the warmed nitrogen-enriched vapor stream from the heat exchanger system; k. said heat exchanger system configured to receive and cool a compressed nitrogen-enriched vapor stream from the reflux compressor to produce a cooled nitrogen-enriched fluid stream; l. a reflux accumulator configured to receive the cooled nitrogen-enriched fluid stream from the heat exchanger system and to produce an overhead refluxdrum vapor stream and a reflux fluid stream and to direct the reflux fluid stream to the distillation column; m. said distillation column configured to produce a nitrogen-enriched vapor stream that exits the distillation column through the top vapor outlet and a column bottoms liquid stream that exits the distillation column through the bottom liquid outlet.

2. The system of claim 1 further comprising a junction configured so that the overhead reflux-drum vapor stream from the reflux accumulator is joined with the nitrogen- enriched vapor stream from the distillation column to form a combined nitrogen-enriched vapor stream that is directed to the heat exchange system to provide cooling within the heat exchanger system.

3. The system of claim 1, wherein the heat exchanger system, the distillation column, the helium separator, the warm and cold helium strippers and the reflux accumulator are within a cold box.

4. The system of claim 1 further comprising a recycle after cooler configured to receive and cool fluid compressed by the compressor and to direct cooled fluid to the heat exchanger system.

5. The system of claim 1 further comprising a pump configured to receive the column bottoms liquid stream that exits the distillation column through the bottom liquid outlet.

6. The system of claim 1 further comprising a feed expansion device configured to receive and expand the feed stream and to direct the expanded stream to the heat exchanger system.

7. The system of claim 1 wherein the distillation column includes a first side liquid outlet and a first reboiler inlet port and the heat exchanger system includes a first reboiler passage configured to receive and at least partially vaporize a first reboiler liquid stream from the first side liquid outlet of the distillation column so that cooling is provided in the heat exchanger system, said reboiler passage also configured to return a first reboiler fluid stream to the first reboiler inlet port of the distillation column.

8. The system of claim 7 wherein the distillation column includes a second side liquid outlet and a second reboiler inlet port and the heat exchanger system includes a second reboiler passage configured to receive and at least partially vaporize a second reboiler liquid stream from the second side liquid outlet of the distillation column so that cooling is provided in the heat exchanger system, said second reboiler passage also configured to return a second reboiler fluid stream to the second reboiler inlet port of the distillation column.

9. The system of claim 1 wherein the column bottoms liquid stream includes methane.

10. The system of claim 1 wherein the heat exchanger system includes a warm heat exchanger and a cold heat exchanger and wherein: i) the heat exchanger is configured to receive and cool the hydrocarbon feed stream; ii) a feed separator in fluid communication with the warm heat exchanger and configured to receive a cooled feed stream and separate the cooledfeed stream into a methane-enriched fluid and a first nitrogen-enriched fluid; iii) a cold heat exchanger configured to receive and cool first nitrogen- enriched fluid from the feed separator and methane-enriched fluid from the feed separator and to direct cooled methane-enriched fluid to the distillation column; iv) a helium separator configured to receive cooled first nitrogen-enriched fluid from the cold heat exchanger and produce a first helium-enriched fluid and a helium separator bottoms fluid and to direct the first helium-enriched fluid to the heat exchanger system; v) a cold helium stripper configured to receive the cooled first helium- enriched fluid from the cold heat exchanger and second helium- enriched fluid from the warm helium stripper as a stripping fluid and to produce a crude helium fluid and a cold helium stripper bottoms fluid and to direct the cold helium stripper bottoms fluid to the distillation column; vi) said cold and warm heat exchangers configured to receive crude helium fluid from the cold helium stripper to provide cooling within the heat exchanger system; vii) said cold and warm heat exchangers configured to receive a nitrogen- enriched vapor stream from the top vapor outlet of the distillation column to provide cooling within the heat exchanger system and to create a warmed nitrogen-enriched vapor stream; viij) a reflux compressor configured to receive and compress at least a portion of the warmed nitrogen-enriched vapor stream from the warm heat exchanger; ix) said warm and cold heat exchangers configured to receive and cool a compressed nitrogen- enriched vapor stream from the reflux compressor to produce a cooled nitrogen- enriched fluid stream; x) a reflux accumulator configured to receive the cooled nitrogen- enriched fluid stream from the cold heat exchanger and to produce areflux drum vapor stream and a reflux fluid stream and to direct the reflux fluid stream to the distillation column.

11. A method of removing nitrogen from a hydrocarbon feed stream comprising the steps of: a. cooling the hydrocarbon feed stream in a heat exchanger system; b. directing the cooled gas fluid feed stream to a feed separator; c. separating the cooled gas into a first nitrogen-enriched fluid and a methane- enriched fluid; d. directing the methane-enriched fluid through the heat exchanger system and to a distillation column; e. cooling and condensing the first nitrogen-enriched fluid in the heat exchanger system and directing cooled nitrogen-enriched fluid to a helium separator; f. separating the cooled nitrogen-enriched fluid into a first helium -enriched vapor and a helium separator bottoms fluid in the helium separator; g. directing the helium separator bottoms fluid from the helium separator to a warm helium stripper and first nitrogen-enriched fluid from the feed separator as a stripping gas to the warm helium stripper; h. forming a second helium-enriched fluid and a warm helium stripper bottoms fluid in the warm helium stripper; i. directing the warm helium stripper bottoms fluid to the distillation column; j. cooling the first helium-enriched fluid in the heat exchanger system and directing cooled first helium-enriched fluid to a cold helium stripper; k. sending the second helium-enriched fluid to the cold helium stripper as a stripping gas; l. forming a crude helium vapor and a cold helium stripper bottoms fluid in the cold helium stripper; m. refrigerating the heat exchanger system by directing the crude helium vapor through the heat exchanger system; n. directing the cold helium stripper bottoms fluid to the distillation column;o. producing a nitrogen-enriched vapor stream out of a top outlet of the distillation column; p. refrigerating the heat exchanger system by directing the nitrogen-enriched vapor stream through the heat exchanger system to form a warmed nitrogen- enriched vapor stream and compressing at least a portion of the warmed nitrogen-enriched vapor stream to form a compressed nitrogen-enriched vapor stream; q. directing the compressed nitrogen-enriched vapor stream through the heat exchanger system to a reflux accumulator so that an overhead reflux-drum vapor stream and a reflux liquid stream are formed; r. directing the reflux liquid stream to the distillation column; and s. withdrawing a column bottoms liquid stream from a bottom of the distillation column.

12. The method of claim 11 wherein the column bottoms liquid stream includes methane.

13. The method of claim 11 further comprising the step of cooling the compressed nitrogen-enriched vapor stream in a recycle after cooler before directing the compressed nitrogen-enriched vapor stream through the heat exchanger system.

14. The method of claim 11 further comprising the step of joining the overhead reflux-drum vapor stream from the reflux accumulator with the nitrogen-enriched vapor stream from the distillation column to form a combined nitrogen-enriched vapor stream that is directed to the heat exchanger system to provide refrigeration within the heat exchanger system.

15. The method of claim 11 further comprising the step of pumping the column bottoms liquid stream.

16. The method of claim 11 further comprising the step of venting the helium vapor after it is directed through the heat exchanger system.

17. A system for removing nitrogen from a hydrocarbon feed stream comprising: a. a heat exchanger system configured to receive and cool the hydrocarbon feed stream; b. a distillation column including a plurality of inlet ports, a top vapor outlet, and a bottom liquid outlet; c. a feed separator in fluid communication with the heat exchanger system and configured to receive a cooled feed stream and separate the cooled feed stream into a methane-enriched fluid and a first nitrogen-enriched fluid; d. the heat exchanger system configured to receive and cool first nitrogen- enriched fluid from the feed separator and methane-enriched fluid from the feed separator and to direct cooled methane-enriched fluid to the distillation column; e. a middle-feed separator configured to receive cooled first nitrogen-enriched fluid from the heat exchanger system and produce a second nitrogen-enriched fluid and a middle-feed separator bottoms fluid and to direct the second nitrogen-enriched fluid to the heat exchanger system; f. a middle-feed separator bottoms expansion device configured to receive the middle-feed separator bottoms fluid from the middle-feed separator and to direct expanded middle-feed separator bottoms fluid to the distillation column; g. said heat exchanger system configured to receive and cool the second nitrogen-enriched fluid from the middle-feed separator and to direct cooled second nitrogen- enriched fluid to the distillation column; h. said heat exchanger system configured to receive a nitrogen-enriched vapor stream from the top vapor outlet of the distillation column to provide cooling within the heat exchanger system and to create a warmed nitrogen-enriched vapor stream; i. a reflux compressor configured to receive and compress at least a portion of the warmed nitrogen-enriched vapor stream from the heat exchanger system; j. said heat exchanger system configured to receive and cool a compressed nitrogen-enriched vapor stream from the reflux compressor to produce a cooled nitrogen-enriched fluid stream;k. a reflux accumulator configured to receive the cooled nitrogen-enriched fluid stream from the heat exchanger system and to produce an overhead refluxdrum vapor stream and a reflux fluid stream and to direct the reflux fluid stream to the distillation column; l. said distillation column configured to produce a nitrogen-enriched vapor stream that exits the distillation column through the top vapor outlet and a column bottoms liquid stream that exits the distillation column through the bottom liquid outlet.

18. The system of claim 17 further comprising a second nitrogen-enriched fluid expansion device configured to receive and expand cooled second nitrogen-enriched fluid from the heat exchanger system and to direct expanded cooled second nitrogen-enriched fluid to the distillation column.

19. A method of removing nitrogen from a hydrocarbon feed stream comprising the steps of a. cooling the hydrocarbon feed stream in a heat exchanger system; b. directing the cooled gas fluid feed stream to a feed separator; c. separating the cooled gas into a nitrogen-enriched vapor and a methane- enriched liquid; d. directing the methane-enriched liquid through the heat exchanger and to a distillation column; e. cooling and condensing the nitrogen-enriched vapor in the heat exchanger and directing cooled nitrogen-enriched fluid to a middle-feed separator; f. separating the cooled nitrogen-enriched fluid into a first helium-enriched vapor and a middle-feed separator bottoms fluid in the middle-feed separator; g. directing the first helium-enriched vapor from the middle-feed separator to the heat exchanger system; h. cooling the first helium-enriched vapor in the heat exchanger system and directing a cooled first helium-enriched fluid to the distillation column; i. sending the middle-feed separator bottoms fluid to a middle-feed separator bottoms expansion device;j. expanding the middle feed separator bottoms fluid in the middle-feed separator bottoms fluid expansion device and directing an expanded middle feed separator bottoms fluid to the distillation column; k. producing a nitrogen-enriched vapor stream out of a top outlet of the distillation column; l. refrigerating the heat exchanger system by directing the nitrogen-enriched vapor stream through the heat exchanger system to form a warmed nitrogen- enriched vapor stream and compressing at least a portion of the warmed nitrogen-enriched vapor stream to form a compressed nitrogen-enriched vapor stream; m. directing the compressed nitrogen-enriched vapor stream through the heat exchanger system to a reflux accumulator so that an overhead reflux-drum vapor stream and a reflux liquid stream are formed; n. directing the reflux liquid stream to the distillation column; and o. withdrawing a column bottoms liquid stream from a bottom of the distillation column.

20. The method of claim 19 further comprising the step of receiving and expanding the cooled first helium-enriched fluid of step h. from the heat exchanger system in a helium expansion device and directing expanded cooled first helium-enriched fluid to the distillation column.

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