Nitrogen removal unit system and method for supplying low nitrogen concentrations
A two-column system with low-pressure operation and efficient nitrogen-methane separation addresses inefficiencies in existing nitrogen removal systems, achieving reduced power consumption and cost-effective nitrogen recovery.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- CHART ENERGY & CHEMICALS INC
- Filing Date
- 2024-05-30
- Publication Date
- 2026-06-05
AI Technical Summary
Existing nitrogen removal systems for natural gas streams are inefficient and require high power consumption, lacking in terms of both energy efficiency and cost-effectiveness.
A two-column system is employed, where the first column operates at a relatively low pressure to generate nitrogen-enriched vapor, followed by compression and subsequent separation in a second column at a higher pressure, utilizing heat exchangers and expansion devices to minimize energy consumption and reduce capital and operational expenses.
The system achieves efficient nitrogen-methane separation with reduced power requirements, lower capital and operational expenditures, and offers compact packaging, producing a final gas product suitable for discharge with low nitrogen content.
Smart Images
Figure 2026518359000001_ABST
Abstract
Description
Technical Field
[0001]
[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 505,316, filed May 31, 2023, the content of which is incorporated by reference.
[0002]
[0002] This disclosure generally relates to systems and methods for removing nitrogen from natural gas streams. More particularly, this disclosure relates to two-column systems and methods for removing nitrogen from natural gas or liquefied natural gas streams.
Background Art
[0003]
[0003] It is often necessary to remove nitrogen from a natural gas feed stream. This can be done for purification or nitrogen recovery requirements. The nitrogen removed from the feed stream may be used as fuel or in other applications or may be discharged to the atmosphere. The use of nitrogen rejection units (NRUs) for such treatment of natural gas or liquefied natural gas feed streams is known in the art, but increased efficiency and reduced power requirements are desirable.
Summary of the Invention
[0004]
[0004] In the methods, devices, and systems described and claimed below, there are several aspects of the invention that may be embodied separately or together. These aspects may be used alone or in combination with other aspects of the subject matter described herein, and the description of these aspects as a whole is not intended to exclude the separate use of these aspects or the claiming of these aspects separately or in different combinations as set forth in the appended claims.
[0005]
[0005] In one embodiment, a system for removing nitrogen from a natural gas fluid flow includes a feed-flow heat exchanger configured to receive and cool the natural gas fluid flow. A first expansion device is configured to receive the fluid from the feed-flow heat exchanger and expand it. A first feed-flow separation device is configured to receive the expanded fluid from the first expansion device and includes a vapor outlet and a liquid outlet. A first column is in fluid communication with the liquid and vapor outlets of the first feed-flow separation device and is configured to operate at a first operating pressure. The first column includes a first column vapor outlet and a first column liquid outlet, configured so that a first nitrogen-enriched vapor flow exits the first column vapor outlet and a first methane-enriched liquid flow exits the first column liquid outlet. A first compressor is configured to receive and compress the first nitrogen-enriched vapor flow. A first aftercooler is configured to receive the compressed first nitrogen-enriched vapor flow from the first compressor. A second expansion device is configured to receive the fluid from the first aftercooler. The second column is in fluid communication with the second expansion device and is configured to operate at a second operating pressure, which is higher than the first operating pressure. The second column includes a second column vapor outlet and a second column liquid outlet, configured such that a second nitrogen-enriched vapor flow exits the second column vapor outlet and a second methane-enriched liquid flow exits the second column liquid outlet. A feed-flow heat exchanger is in fluid communication with the second column vapor outlet and the first and second column liquid outlets and is configured to heat the nitrogen-enriched and methane-enriched fluids to bring about refrigeration within the feed-flow heat exchanger.
[0006]
[0006] In another embodiment, a method for removing nitrogen from a natural gas fluid feed flow includes the steps of: directing the feed flow into a first column, the first column being operated at a first operating pressure; separating the feed flow in the first column into a first nitrogen-enriched vapor and a first methane-enriched liquid; compressing and cooling the first nitrogen-enriched vapor; directing the compressed and cooled first nitrogen-enriched vapor into a second column, the second column being operated at a second operating pressure higher than the first operating pressure; separating the first nitrogen-enriched vapor in the second column into a second nitrogen-enriched vapor and a second methane-enriched liquid; discharging the second nitrogen-enriched vapor from the second column; and combining the first methane-enriched liquid from the first column and the second methane-enriched liquid from the second column to form a product methane-enriched liquid flow. [Brief explanation of the drawing]
[0007] [Figure 1-1]
[0007] Figure 1 is a schematic diagram of one embodiment of the system of the present disclosure. [Figure 1-2] Figure 1 is a schematic diagram of one embodiment of the system of this disclosure. [Figure 1-3] Figure 1 is a schematic diagram of one embodiment of the system of this disclosure. [Modes for carrying out the invention]
[0008]
[0008] A more detailed description of the systems and methods provided in this disclosure is given below. It should be understood that the following descriptions of specific systems and methods are illustrative and not intended to be exhaustive of all possible variations or applications. Therefore, the scope of this disclosure is not intended to be restrictive and should be understood to include variations or embodiments that a person skilled in the art might conceive of.
[0009]
[0009] It should be noted that in this specification, lines, conduits, pipes, passages, and similar structures, as well as corresponding flows, may be referred to together by the same element numbers shown in the figures.
[0010]
[0010] The term “column” as used below means a distillation, fractionation, or rectification column, including a contact column or zone, which brings a counterflow liquid and a vapor phase into contact, resulting in the separation of a fluid mixture, for example, by bringing the vapor phase and the liquid phase into contact on a series of vertically spaced plates or trays or packaging materials positioned within the column.
[0011]
[0011] Similarly, as used herein and as known in the art, a heat exchanger is a device or area within a device in which indirect heat exchange occurs between two or more flows of different temperatures, or between a flow and the environment. Furthermore, all heat exchangers referenced herein may be incorporated into one or more heat exchanger devices, or each may be an individual heat exchanger device. As used herein, the terms “communication,” “communicating,” and similar terms generally refer to fluid communication unless otherwise indicated. Two fluids in communication may exchange heat when mixed, but such exchange, while possible in a heat exchanger, is not considered to be the same as heat exchange in a heat exchanger.
[0012]
[0012] As used herein, the terms “high,” “middle,” “warm,” “cold,” and similar terms are relative to a comparable flow, as is customary in the art.
[0013]
[0013] Reference numerals introduced herein in relation to the figures in the drawings may be repeated in one or more subsequent figures for a common element or component without further explanation herein, in order to provide context for other features.
[0014]
[0014] In the claims, letters (e.g., a, b, and c) are used to identify the claimed steps. These letters are used to help refer to method steps and are not intended to indicate the order in which the claimed steps are performed, unless such order is specifically given in the claims and only to the extent that it is given.
[0015]
[0015] One embodiment of the nitrogen removal unit (NRU) system and method of the present disclosure, shown in Figure 1, utilizes a two-column system 10 to influence nitrogen-methane separation from the feed flow. The system 10 includes a first column 50 which may operate at about 1.61 MPa (230 psig) to 2.24 MPa (320 psig) and a second column 142 which may operate at about 2.1 MPa (300 psig) to 2.45 MPa (350 psig). By utilizing a two-column system with the first column 50 operating at a relatively low pressure (about 1.61 MPa (230 psig) to 2.24 MPa (320 psig)), it is possible to generate nitrogen-enriched overhead vapor within the column. Compression of the overhead vapor from column 50 provides a high-pressure flow for the final nitrogen-methane separation in the second column 142. Furthermore, operating column 50 at relatively low pressure provides the system and method with low total power consumption, a reduced energy footprint, and overall lower capital expenditure (CAPEX) and operating expenditure (OPEX). Additionally, this allows the system to be smaller, offering packaging advantages.
[0016]
[0016] The supply flow for system 10 may include a natural gas supply. Typically, the natural gas contains nitrogen and methane, and may also contain several other species that normally occur in a natural gas reservoir, such as carbon dioxide and higher-order hydrocarbons having 2–4 carbon atoms. Generally, this flow will be pre-treated to remove higher-order hydrocarbons and natural gas liquids to a practical degree. Simply as an example, the supply flow contains about 4–7 mol% nitrogen and is typically available at about 1.4 MPa (200 psig)–2.03 MPa (290 psig). The NRU system 10 may, simply as an example, produce a final gas product with about 2.0–3.0 mol% nitrogen and nitrogen vapor with about 0.5–2.5 mol% methane, suitable for discharge into the atmosphere.
[0017]
[0017] Referring to Figure 1, the supply flow is received by the supply line 12 and then moves through the compressor 14 and aftercooler heat exchanger 16 where the flow is compressed and cooled. For example, the supply flow may first pass through the compressor 14 and be compressed to about 2.8 MPa (400 psig) to 3.15 MPa (450 psig), and the compressed flow may then pass through the exchanger 16 and be cooled to about 37.8°C (100°F) to 48.9°C (120°F). After compression and cooling, the flow moves through line 18 toward the supply flow heat exchanger 20.
[0018]
[0018] In the embodiments shown, a portion of the NRU supply to be compressed may be refrigerated. For example, a small amount of propane-type refrigeration may be used with respect to a portion of the NRU supply. This would allow for a reduced NRU supply pressure by opening an internal temperature pinch in the NRU inlet heat exchanger. Refrigerating the NRU supply may further reduce system CAPEX and OPEX. This would have particular benefits for systems that already utilize propane-type refrigeration in upstream cryogenic natural gas liquid (NGL) recovery units.
[0019]
[0019] Referring to Figure 1, the compressed and cooled flow is received by a cooling passage 22 in the supply flow heat exchanger 20, where the flow is cooled by indirect heat exchange using the return flow, as described below. As an example, the supply flow heat exchanger 20 (along with the heat exchangers 40, 122, and 176 described herein) may be a brazed aluminum heat exchanger (BAHX) or other heat exchanger types known in the art. This applies to other heat exchangers described below, such as 54, 102, and 132. The cooled flow exits the supply flow heat exchanger 20 via line 25 and moves toward the separation container 30.
[0020]
[0020] The steam in the separation vessel 30 exits the vessel through line 38 and heads toward the first main heat exchanger 40. The steam flow is received by a cooling passage 42 in the first main heat exchanger 40, where it is cooled by indirect heat exchange using a return flow as described below. The cooled flow exits the first heat exchanger 40 through line 44 and passes through expansion valve 46 and line 48 toward column 50. Expansion valve 46 and any other expansion valves described below may be Joule-Thomson (JT) valves or other types of expansion valves known in the art. In the shown embodiment, a portion of the steam flow in line 38 may move toward heat exchanger 54 through line 52. The steam flow may be received by a cooling passage 56 in heat exchanger 54 and exit heat exchanger 54 through line 58. The cooled flow may then pass through expansion valve 60 and enter column 50 as a mixed phase through line 62.
[0021]
[0021] The methane-enriched liquid in the separation container 30 exits the container through line 64 at the bottom of the separation container 30. The liquid flow passes through valve 66 and enters the separation container 70, with its pressure reduced before moving through line 68.
[0022] In the embodiment shown, the separation vessel 70 may be a vessel similar to the separation vessel 30. The vapor in the separation vessel 70 exits through the top of the vessel via line 72. The vapor stream then enters column 50 via line 76. The liquid in the separation vessel 70 exits the vessel via line 78 at the bottom of the separation vessel 70. The liquid in line 78 may be enriched with methane. The liquid stream passes through expansion valve 80 and line 82 and merges into line 208, which will be described in more detail below.
[0023]
[0023] The first column 50 receives flow via lines 48, 62, and 76 at different locations in the column. Column 50 may provide bulk nitrogen separation. In the first column 50, liquid passes downward against the upward flowing vapor to produce an overhead vapor having a nitrogen concentration exceeding that of the feed and a bottom liquid having a methane concentration exceeding that of the feed. For example, column 50 may produce an overhead vapor product stream 96 having about 12 - 24 mol% nitrogen and a bottom liquid stream 123 having about 0.5 - 1.5% nitrogen. The operating pressure of column 50 may be about 1.61 MPa (230 psig) - 2.24 MPa (320 psig). By operating column 50 at this pressure, the bottom liquid may evaporate at the NRU feed pressure without recompression.
[0024]
[0024] As shown in FIG. 1, in the embodiment shown, column 50 may include a reboiler service including line 84. The liquid in column 50 passes through line 84 and line 90 and is received by the heating passage 92 in heat exchanger 54, so that the flow in the cooling passage 56 is cooled. The evaporated flow exits heat exchanger 54 via line 94 and is directed back to column 50. The evaporated flow may then contribute to stripping nitrogen from the descending liquid in column 50.
[0025]
[0025] The methane-enriched liquid exits the bottom of column 50 via line 123. After passing through expansion valve 125, the flow moves through line 127 and merges into line 204.
[0026]
[0026] The nitrogen-enriched vapor exits the top of column 50 via line 96 and is further separated in the second column 142. In some embodiments, a portion of the overhead nitrogen-enriched vapor within column 50 is collected for “low BTU” fuel gas, which can reduce the overall system requirements for nitrogen emissions.
[0027]
[0027] As shown in FIG. 1, the vapor exiting column 50 via line 96 moves towards heat exchanger 102 via line 100. The heating passage 104 within heat exchanger 102 receives the flow. The heated flow exits heat exchanger 102 via line 106 and passes through compressor 108 and aftercooler heat exchanger 110, whereby the flow is compressed and cooled. For example, the nitrogen-enriched high-pressure vapor flow may first pass through compressor 108 and be compressed to about 3.15 MPa (450 psig) to 3.85 MPa (550 psig), and the compressed flow may then pass through aftercooler heat exchanger 110 and be cooled to about 37.8 °C (100 °F) to 48.9 °C (120 °F). After compression and cooling, the flow moves through line 112 towards heat exchanger 102.
[0028]
[0028] The compressed and cooled flow may be received by a cooling passage 118 in the heat exchanger 102, where the flow is cooled by indirect heat exchange using a steam flow moving through a heating passage 104. The cooled flow exits the heat exchanger 102 via line 120 and is led toward the second column 142. Line 120 may branch into two lines 121a and 121b. A portion of the cooled flow moves through line 121a and is received by a cooling passage 124 in the second main heat exchanger 122. The cooled flow exits the second main heat exchanger 122 via line 126, and the flow then passes through an expansion valve 128. After passing through the expansion valve 128, the flow enters the second column 142 via line 130. Another portion of the cooled flow moves through line 121b and is received by a cooling passage 134 in the heat exchanger 132. The cooled flow exits the heat exchanger 132 via line 136, and then the flow passes through the expansion valve 138. After passing through the expansion valve 138, the flow then merges with line 130 via line 140 and enters column 142.
[0029]
[0029] The second column 142 provides the final nitrogen-methane separation. In one embodiment, the second column 142 may be the same as column 50. The second column 142 may produce an overhead vapor product via line 174 having about 0.5 to 2.5 mol% methane and a bottom liquid via line 194 having about 0.5 to 1.5% nitrogen. The operating pressure of the second column 142 may be about 2.1 MPa (300 psig) to 2.45 MPa (350 psig). By operating the second column 142 at this pressure, the overhead vapor may be produced by low-pressure evaporation of a portion of the bottom liquid of the column so as to balance the bottom liquid, and may evaporate at the NRU feed pressure without recompression.
[0030]
[0030] In the embodiment shown, the second column 142 may comprise a reboiler including at least one reboiler line and a heat exchanger 132. In the embodiment shown, the second column 142 may include a second reboiler line that carries the flow received by the heating passage 160 in the heat exchanger 132. The evaporated flow exits the heat exchanger 132 via line 162 and returns to the second column 142.
[0031]
[0031] Furthermore, the second column 142 may include a steam cooling line 164 so that a flux flow is formed. More specifically, a portion of the steam in the second column 142 may pass through the cooling line 164 and be received by a cooling passage 166 in the product flow heat exchanger. The cooled flow then returns to the second column 142 from the cooling passage 166 as a flux flow.
[0032]
[0032] The steam from the second separation column 142 may be collected or discharged into the atmosphere. For example, nitrogen-enriched steam exits the second column 142 at the top of the second column 142 via line 174. In the shown embodiment, the steam may pass through a series of heat exchangers to be heated before the steam is collected or discharged. For example, the steam flow in line 174 may be received by a heating passage 178 in the product flow heat exchanger. After heating, the steam flow exits the product flow heat exchanger, travels through line 180, and is received by a heating passage 182 in the first main heat exchanger 40. The heated flow then exits through line 184 and is received by a heating passage 186 in the heat exchanger 20. The heated steam flow exits the heat exchanger 20 via line 188, passes through valve 190, and is collected or discharged into the atmosphere via line 192.
[0033]
[0033] The methane-enriched liquid exiting the second column 142 via line 194 may be collected as the final product gas. In the shown embodiment, the methane-enriched liquid from the second column 142 is combined with methane-enriched liquid from other parts of the system and collected as the final product gas. For example, the methane-enriched liquid from the second column 142, column 50, and separation vessel 70 may all move toward line 212 and be collected as the final product gas.
[0034]
[0034] More specifically, the methane-enriched liquid exits the second column 142 via line 194. Line 194 may branch into lines 195a and 195b. A portion of the liquid flow travels through line 195a and passes through the expansion valve 196. After passing through valve 196, the flow travels through line 198 and is collected as a product gas. In the shown embodiment, the flow in line 198 is received by a heating passage 202 in the second main heat exchanger 122 to provide cooling within the second main heat exchanger 122. The heated flow exits via line 204 and is received by a heating passage 206 in the first main heat exchanger 40 to provide cooling within the first main heat exchanger 40. The heated flow then exits via line 208 and is received by a heating passage 210 in the heat exchanger 20 to provide cooling within the heat exchanger 20. The heated flow may then exit through line 212 and be collected. The system may include any number of sequential heatings for the product liquid without departing from the scope of this disclosure.
[0035]
[0035] Since low-pressure methane may be produced at approximately 0.028 MPa (4 psig) to 0.07 MPa (10 psig), a portion of the methane-enriched liquid in the second column 142 is compressed and cooled before being collected. For example, the final product gas may be compressed to the NRU feed pressure. As shown in Figure 1, a portion of the liquid flow moves through line 195b and is received by the expansion valve 218. After passing through the expansion valve 218, the flow moves through line 220 and is received by the heating passage 224 in the product flow heat exchanger to provide cooling within the product flow heat exchanger. The heated flow exits the product flow heat exchanger 176 via line 226 and is then received by the heating passage 228 in the first main heat exchanger 40 to provide cooling within the first main heat exchanger 40. The flow then exits line 230 and is received by a heating passage 232 in the heat exchanger 20, providing cooling within the heat exchanger 20. The heated flow exits the heat exchanger 20 via line 234 and passes through a series of compressors 236a, 236b, 236c and aftercooler heat exchangers 238a, 238b, 238c. In one embodiment, the flow first passes through compressor 236a and exchanger 238a, then through compressor 236b and exchanger 238b, and then through compressor 236c and exchanger 238c. The system may compress and cool the product gas by including more or fewer pairs of compressors and exchangers without departing from the scope of the present disclosure. The compressed and cooled flow exiting the compression and cooling stages travels through line 240 and merges into product line 212 for collection.
[0036]
[0036] In one embodiment, one or more of the valves described above may be connected to a separate programmable controller. In another embodiment, the controller is connected to a main programmable controller. In yet another embodiment, the valves included in the system 10 may be opened and closed manually.
[0037]
[0037] There are several embodiments of the subject matter that may be embodied separately or together in the methods, devices, and systems described and claimed below. These embodiments may be used alone or in combination with other embodiments of the subject matter described herein, and the description of these embodiments as a whole is not intended to exclude the use of these embodiments separately or claims of separate or different combinations of such embodiments as set out in the appended claims.
[0038]
[0038] Preferred embodiments of the present invention have been shown and described, but changes and modifications may be made in embodiments without departing from the spirit of the invention, and it will be apparent to those skilled in the art that the scope of the present invention is defined by the appended claims.
Claims
1. A system for removing nitrogen from natural gas fluid flows, a. A supply flow heat exchanger configured to receive and cool the natural gas fluid flow, b. A first expansion device configured to receive and expand a fluid from the supply flow heat exchanger, c. A first supply flow separation device configured to receive an expanded fluid from the first expansion device, the first supply flow separation device including a steam outlet and a liquid outlet, d. A first column having fluid communication with the liquid and vapor outlets of the first supply flow separation device and configured to operate at a first operating pressure, comprising a first column vapor outlet and a first column liquid outlet, configured such that a first nitrogen-enriched vapor flow exits the first column vapor outlet and a first methane-enriched liquid flow exits the first column liquid outlet, e. A first compressor configured to receive and compress the first nitrogen-enriched vapor flow, f. A first aftercooler configured to receive the compressed first nitrogen-enriched steam flow from the first compressor, g. A second expansion device configured to receive fluid from the first aftercooler, h. A second column having fluid communication with the second expansion device and configured to operate at a second operating pressure, wherein the second operating pressure is higher than the first operating pressure, and the second column includes a second column vapor outlet and a second column liquid outlet, configured such that a second nitrogen-enriched vapor flow exits the second column vapor outlet and a second methane-enriched liquid flow exits the second column liquid outlet. i. A system in which the feed-flow heat exchanger is in fluid communication with the second column steam outlet and the first and second column liquid outlets, and is configured to heat the nitrogen-enriched fluid and the methane-enriched fluid to bring about refrigeration within the feed-flow heat exchanger.
2. The system according to claim 1, further comprising a supply flow compressor configured to receive and cool the natural gas fluid flow, and a supply flow aftercooler configured to receive and cool the cooled natural gas fluid flow from the supply flow compressor, wherein the supply flow aftercooler is configured to guide the fluid to the supply flow heat exchanger.
3. The system according to claim 1, further comprising a third expansion device and a fourth expansion device, the third expansion device being configured to receive a liquid flow from the liquid outlet of the first supply flow separation device, and further comprising a second supply flow separation device being configured to receive a fluid from the third expansion device, the second supply flow separation device having a liquid outlet and a steam outlet, the liquid outlet of the second supply flow separation device being configured to direct a fluid flow to the supply flow heat exchanger and to bring refrigeration within the supply flow heat exchanger, the steam outlet of the second supply flow separation device being configured to direct steam to the fourth expansion device, and the fourth expansion device being configured to direct a fluid to the first column.
4. The system further comprises a fifth expansion device, a sixth expansion device, and a first column reboiler heat exchanger having a first column reboiler heating passage and a first column reboiler cooling passage. i) The first column reboiler cooling passage has an inlet configured to receive a portion of the steam flow from the steam outlet of the first feed flow separation device, and an outlet configured to guide the cooled fluid flow to the fifth expansion device, the fifth expansion device configured to guide the cooled fluid flow to the first column, ii) The sixth expansion device is configured to receive and expand the first reboiler flow from the first column, iii) The system according to claim 1, wherein the first column reboiler heating passage is configured to receive the expanded first reboiler fluid flow from the sixth expansion device and to heat the expanded first reboiler fluid flow so that refrigeration is provided into the first column reboiler heat exchanger and the heated first reboiler fluid flow is returned to the first column.
5. The system according to claim 1, further comprising a first main heat exchanger, the first main heat exchanger being configured to receive and cool a steam flow from the steam outlet of a first feed-flow expansion device, to guide the cooled fluid flow to the feed-flow expansion device, to receive and heat a methane-enriched liquid flow from a first column liquid outlet and a second column liquid outlet, and a nitrogen-enriched fluid flow from a second column steam outlet, thereby bringing refrigeration within the first main heat exchanger.
6. The system according to claim 5, further comprising a second main heat exchanger, the second main heat exchanger being configured to receive and cool a fluid from the first aftercooler, to guide the fluid to a first expansion valve, and to receive and heat the fluid flow from the first column liquid outlet and the second column liquid outlet to bring about freezing in the first main heat exchanger.
7. The system further comprises a ninth expansion device and a third main heat exchanger, the third main heat exchanger receiving and cooling a flux flow from the second column and returning the cooled flux flow to the second column. The liquid flow is received from the liquid outlet of the second column and cooled, and the cooled liquid flow is guided from the second column to the ninth expansion device. The system according to claim 6, configured to receive and heat a nitrogen-enriched fluid flow from the second column vapor outlet and an expanded methane-enriched fluid flow from the ninth expansion device, thereby bringing about refrigeration in the third main heat exchanger.
8. The system according to claim 7, further comprising a product gas compressor configured to receive heated methane-enriched fluid from the supply flow heat exchanger, and a product gas aftercooler configured to receive and cool compressed methane-enriched fluid from the discharge compressor.
9. The system according to claim 8, wherein the outlet of the product gas aftercooler is configured to guide the fluid to the junction with the first methane enrichment flow exiting the supply flow heat exchanger.
10. The system further comprises a seventh expansion device, an eighth expansion device, and a second column reboiler heat exchanger having a second column reboiler heating passage and a second column reboiler cooling passage. i) The second column reboiler cooling passage has an inlet configured to receive a portion of the fluid flow from the first aftercooler, and an outlet configured to guide the cooled fluid flow to the seventh expansion device, the seventh expansion device configured to guide the cooled fluid flow to the second column, ii) The eighth expansion device is configured to receive and expand the second reboiler flow from the second column, iii) The system according to claim 1, wherein the second column reboiler heating passage is configured to receive the expanded reboiler fluid flow from the eighth expansion device and to heat the expanded reboiler fluid flow so that refrigeration is provided into the second column reboiler heat exchanger and to return the heated second reboiler fluid flow to the first column.
11. The system according to claim 1, wherein the first column is positioned in a first cold box and the second column is positioned in a second cold box.
12. The system according to claim 1, wherein the first operating pressure of the first column is approximately 1.61 MPa (230 psig) to 2.24 MPa (320 psig).
13. The system according to claim 12, wherein the second operating pressure of the second column is approximately 2.1 MPa (300 psig) to 2.45 MPa (350 psig).
14. The system according to claim 1, wherein the second operating pressure of the second column is approximately 2.1 MPa (300 psig) to 2.45 MPa (350 psig).
15. The system according to claim 1, wherein the first nitrogen-enriched flow exiting the supply flow heat exchanger is led to a vent.
16. A method for removing nitrogen from a natural gas fluid supply flow, A step of directing a supply flow to a first column, wherein the first column is operated at a first operating pressure, The steps include separating the supply flow into a first nitrogen-enriched vapor and a first methane-enriched liquid within the first column, The first nitrogen-enriched steam is compressed and cooled, The steps include: introducing the compressed and cooled first nitrogen-enriched vapor into a second column, wherein the second column operates at a second operating pressure higher than the first operating pressure; The steps include separating the first nitrogen-enriched vapor into a second nitrogen-enriched vapor and a second methane-enriched liquid in the second column, The steps include: discharging the second nitrogen-enriched vapor from the second column, A method comprising the steps of combining the first methane-enriched liquid from the first column and the second methane-enriched liquid from the second column, thereby forming a product methane-enriched liquid flow.
17. The method according to claim 16, wherein the first operating pressure is approximately 1.61 MPa (230 psig) to 2.24 MPa (320 psig).
18. The method according to claim 17, wherein the second operating pressure is approximately 2.1 MPa (300 psig) to 2.45 MPa (350 psig).
19. The method according to claim 16, wherein the second operating pressure is approximately 2.1 MPa (300 psig) to 2.45 MPa (350 psig).
20. The method according to claim 16, comprising compressing the supply flow to about 2.8 MPa (400 psig) to 3.15 MPa (450 psig) and cooling the supply flow to about 37.8°C (100°F) to 48.9°C (120°F) before it enters the first column.
21. The method according to claim 16, wherein the supply flow contains about 4 to 7 mol% nitrogen and has a pressure of about 1.4 MPa (200 psig) to 2.03 MPa (290 psig).
22. The method according to claim 16, wherein the first nitrogen-enriched steam contains about 12 to 24 mol% nitrogen, and the first methane-enriched flow contains about 0.5 to 1.5 mol% nitrogen.
23. The method according to claim 16, wherein the first nitrogen-enriched vapor is compressed to about 3.15 MPa (450 psig) to 3.85 MPa (550 psig) and cooled to about 37.8°C (100°F) to 48.9°C (120°F) before being introduced into the second column.
24. The method according to claim 16, wherein the second nitrogen-enriched flow contains about 0.5 to 2.5 mol% methane, and the second methane-enriched liquid contains about 0.5 to 1.5 mol% nitrogen.