A natural gas recovery ethane system and method

Abstract

The application discloses a natural gas ethane recovery system and a recovery method. The natural gas ethane recovery system comprises a natural gas supply device, a first heat exchange device, a demethanizer, a deethanizer, a helium extraction column, a heavy hydrocarbon separator, a gas compressor, a first reflux pipe and a second reflux pipe. The outlet of the natural gas supply device is connected with the inlet of the heavy hydrocarbon separator. The gas phase outlet of the heavy hydrocarbon separator is connected with the inlet of the helium extraction column through the first heat exchange device. The liquid phase outlet of the helium extraction column is connected with the inlet of the demethanizer. The gas phase outlet of the demethanizer is connected with the gas inlet end of the gas compressor through the first heat exchange device. The gas outlet end of the gas compressor is connected with the first reflux pipe. The first reflux pipe is connected with the second reflux pipe through the first heat exchange device. The second reflux pipe is connected with the inlet of the demethanizer. The liquid phase outlet of the demethanizer is connected with the inlet of the deethanizer. The above scheme can solve the problem of low ethane recovery rate.

Description

Technical Field

[0001] This invention relates to the field of ethane recovery technology from natural gas, and more particularly to a system and method for ethane recovery from natural gas. Background Technology

[0002] The ethylene industry is the core of the petrochemical industry, and ethylene production is one of the important indicators of a country's petrochemical development level; therefore, ethylene is a very important strategic resource. Ethane is typically used as the main feedstock for ethylene production through cracking. Ethylene plants using ethane as feedstock have very low construction investment and operating costs.

[0003] The main component of natural gas is alkanes, with methane making up the vast majority, and smaller amounts of ethane, propane, and other components. To maximize the utilization of natural gas, diversify natural gas products, and enhance its economic value, recovering and reusing ethane from natural gas is a good option.

[0004] In related technologies, the recovery of ethane from natural gas mainly adopts a partial dry gas recirculation process. The partial dry gas recirculation process involves condensing and subcooling a portion of the gas phase separated by the heavy hydrocarbon separator and then using it as a reflux into the demethanizer, thereby condensing the ethane flashed out in the demethanizer and thus improving ethane recovery.

[0005] However, in related technologies, the reflux in the demethanizing tower is mainly gas phase with a small amount of liquid phase. Therefore, the gas phase reflux has a poor condensation effect on ethane, resulting in low ethane recovery efficiency. Summary of the Invention

[0006] This invention discloses a natural gas ethane recovery system to solve the problem of low ethane recovery rate in natural gas ethane recovery.

[0007] To solve the above problems, the present invention adopts the following technical solution:

[0008] A natural gas ethane recovery system includes a natural gas supply unit, a first heat exchange unit, a demethanizer, a deethaner, a helium stripper, a heavy hydrocarbon separator, an external gas compressor, a first reflux pipe, and a second reflux pipe.

[0009] The outlet of the natural gas supply device is connected to the inlet of the heavy hydrocarbon separator. The gas phase outlet of the heavy hydrocarbon separator is connected to the inlet of the helium stripping tower through the first heat exchange device. The liquid phase outlet of the helium stripping tower is connected to the inlet of the demethanizing tower. The gas phase outlet of the demethanizing tower is connected to the inlet of the external gas compressor through the first heat exchange device. The outlet of the external gas compressor is connected to the first reflux pipe. The first reflux pipe is connected to the second reflux pipe through the first heat exchange device. The second reflux pipe is connected to the inlet of the demethanizing tower. The liquid phase outlet of the demethanizing tower is connected to the inlet of the deethaner.

[0010] Optionally, the natural gas ethane recovery system further includes a demethanizing reboiler and a helium-extraction reboiler, wherein the helium-extraction reboiler provides heat to the helium-extraction tower; and the demethanizing reboiler provides heat to the demethanizing tower.

[0011] The outlet of the natural gas supply device is connected to the first heat exchange device through the demethanizing reboiler, and the first heat exchange device is connected to the inlet of the heavy hydrocarbon separator through the helium-lifting reboiler.

[0012] Optionally, the demethanizer has a first inlet and a second inlet, the first inlet being connected to the liquid phase outlet of the helium stripping tower, and the second inlet being connected to a second reflux pipe. In the direction from the gas phase outlet to the liquid phase outlet of the demethanizer, the first inlet is located between the second inlet and the gas phase outlet of the demethanizer.

[0013] Optionally, the natural gas ethane recovery system further includes at least one liquid phase extraction pipeline and at least one liquid phase reflux pipeline, wherein at least one liquid phase extraction pipeline and at least one liquid phase reflux pipeline are connected in a one-to-one correspondence. One end of the liquid phase extraction pipeline is connected to the demethanizer, and the other end of the liquid phase extraction pipeline is connected to one end of the liquid phase reflux pipeline through the first heat exchange device. The other end of the liquid phase reflux pipeline is connected to the demethanizer. The connection point between the demethanizer and each liquid phase reflux pipeline is located between the connection point between the corresponding liquid phase extraction pipeline and the demethanizer and the gas phase outlet of the demethanizer.

[0014] Optionally, the natural gas ethane recovery system further includes a first throttling expansion valve, through which the liquid phase outlet of the helium extraction tower is connected to the feed inlet of the demethanizer tower.

[0015] Optionally, the natural gas ethane recovery system further includes a second throttling expansion valve, and the second return pipe is equipped with the second throttling expansion valve.

[0016] Optionally, the natural gas ethane recovery system further includes a second heat exchanger, a first refrigeration unit, and a second refrigeration unit. The second heat exchanger is connected to the de-ethane tower, the second refrigeration unit is used to provide cooling capacity to the second heat exchanger, and the first refrigeration unit is used to provide cooling capacity to the first heat exchanger.

[0017] Optionally, the first refrigeration device includes a first refrigerant compressor, a third throttling expansion valve, and a fourth throttling expansion valve;

[0018] The first heat exchange device is provided with a first heat exchange channel, a second heat exchange channel and a third heat exchange channel;

[0019] The first heat exchange channel is connected to the refrigerant inlet of the first mixed refrigerant compressor; the liquid phase outlet of the first mixed refrigerant compressor is connected to the second heat exchange channel; the second heat exchange channel is connected to the third throttling expansion valve; and the third throttling expansion valve is connected to the first heat exchange channel. The gas phase outlet of the first mixed refrigerant compressor is connected to the third heat exchange channel; the third heat exchange channel is connected to the fourth throttling expansion valve; and the fourth throttling expansion valve is connected to the first heat exchange channel.

[0020] Optionally, the second refrigeration unit includes a second refrigerant compressor, a sixth throttling expansion valve, and a seventh throttling expansion valve;

[0021] The second heat exchange device is provided with a sixth heat exchange channel, a seventh heat exchange channel and an eighth heat exchange channel;

[0022] The seventh heat exchange channel is connected to the refrigerant inlet of the second mixed refrigerant compressor; the liquid phase outlet of the second mixed refrigerant compressor is connected to the sixth heat exchange channel; the sixth heat exchange channel is connected to the sixth throttling expansion valve; and the sixth throttling expansion valve is connected to the seventh heat exchange channel. The gas phase outlet of the second mixed refrigerant compressor is connected to the eighth heat exchange channel; the eighth heat exchange channel is connected to the seventh throttling expansion valve; and the seventh throttling expansion valve is connected to the seventh heat exchange channel.

[0023] Optionally, the natural gas ethane recovery system further includes an ethane collection tank, an eighth throttling expansion valve, a first pipeline, a second pipeline, and a third pipeline. The second heat exchange device is provided with a ninth heat exchange channel and a tenth heat exchange channel. The gas phase outlet of the de-ethane tower is connected to the tenth heat exchange channel through the first pipeline. The tenth heat exchange channel is connected to the feed inlet of the de-ethane tower through the second pipeline. The second pipeline is connected to the ninth heat exchange channel through the third pipeline. The ninth heat exchange channel is connected to the feed inlet of the ethane collection tank through the eighth throttling expansion valve.

[0024] A method for recovering ethane, the method being applied to the aforementioned natural gas ethane recovery system, the method comprising:

[0025] The natural gas supply unit feeds natural gas into a heavy hydrocarbon separator for separation to obtain a first gas phase and a first liquid phase;

[0026] The first gas phase is passed through a first heat exchanger and then fed into a helium extraction tower, where the helium extraction tower separates the first gas phase to obtain a second liquid phase and a second gas phase.

[0027] The second liquid phase is fed into a demethanizer, which separates the second liquid phase to obtain a third liquid phase and a third gas phase.

[0028] The third gas phase is fed into the external gas compressor after heat exchange through the first heat exchange device to obtain the fourth gas phase. Part of the fourth gas phase is fed into the demethanizer after heat exchange through the first heat exchange device; the third liquid phase is fed into the deethanizer.

[0029] The technical solution adopted in this invention can achieve the following beneficial effects:

[0030] In the natural gas ethane recovery system disclosed in this invention, the gas phase separated by the heavy hydrocarbon separator enters the helium stripping tower after heat exchange in the first heat exchanger. The liquid phase separated in the helium stripping tower is then fed into the demethanizer tower through its liquid phase outlet. The gas phase separated in the demethanizer tower, after heat exchange in the first heat exchanger, is then partially returned to the demethanizer tower by a portion of the gas pressurized by the external gas compressor. At this point, one stream of return to the demethanizer tower is the liquid phase fed into the helium stripping tower, and the other stream is the dry gas pressurized by the external gas compressor. Compared to related technologies, the solution in this application allows for a larger contact area between the liquid phase separated in the helium stripping tower and the ethane flash vapor in the demethanizer tower, resulting in better condensation and thus improving the ethane recovery rate. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 This is a schematic diagram of the structure of the natural gas ethane recovery system disclosed in an embodiment of the present invention;

[0033] Figure 2 This is a flowchart of an ethane recovery method disclosed in an embodiment of the present invention.

[0034] Explanation of reference numerals in the attached figures:

[0035] 100-Natural gas decarbonization unit, 101-Absorber tower, 102-Subcooler, 103-Regeneration tower, 104-Acid gas separator, 105-Purified gas separator, 110-Tail gas compressor,

[0036] 200-Natural Gas Dehydration and Mercury Removal Unit

[0037] 310 - First heat exchanger, 311 - First heat exchange channel, 312 - Second heat exchange channel, 313 - Third heat exchange channel, 314 - Fourth heat exchange channel, 315 - Fifth heat exchange channel, 320 - Second heat exchanger, 321 - Sixth heat exchange channel, 322 - Seventh heat exchange channel, 323 - Eighth heat exchange channel, 324 - Ninth heat exchange channel, 325 - Tenth heat exchange channel

[0038] 400 - Demethanizer, 410 - Demethanizer reboiler, 420 - First feed inlet, 430 - Second feed inlet, 440 - External gas compressor, 450 - Liquid phase extraction line, 460 - Liquid phase reflux line, 470 - First throttling expansion valve, 480 - Second throttling expansion valve, 491 - First reflux pipe, 492 - Second reflux pipe

[0039] 500 - Deethaner column, 510 - First pipeline, 520 - Second pipeline, 530 - Third pipeline, 540 - Ethane collection tank, 550 - Eighth throttling expansion valve.

[0040] 600 - Helium extraction tower, 610 - Helium extraction cooler, 620 - Helium extraction separator, 630 - Helium extraction reboiler.

[0041] 700-Heavy Hydrocarbon Separator

[0042] 811-First mixed refrigerant compressor, 812-Third throttling expansion valve, 813-Fourth throttling expansion valve, 814-Methane compressor, 815-Fifth throttling expansion valve, 821-Second mixed refrigerant compressor, 822-Sixth throttling expansion valve, 823-Seventh throttling expansion valve. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0044] The technical solutions disclosed in the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0045] like Figure 1As shown in the figure, an embodiment of the present invention discloses a natural gas ethane recovery system. The disclosed natural gas ethane recovery system includes a natural gas supply device, a first heat exchange device 310, a demethanizer 400, a deethaner 500, a helium stripper 600, a heavy hydrocarbon separator 700, an external gas compressor 440, a first reflux pipe 491, and a second reflux pipe 492.

[0046] A natural gas supply unit provides natural gas to the heavy hydrocarbon separator 700. The outlet of the natural gas supply unit is connected to the inlet of the heavy hydrocarbon separator 700. The gas phase outlet of the heavy hydrocarbon separator 700 is connected to the inlet of the helium stripping tower 600 via a first heat exchanger 310. The liquid phase outlet of the helium stripping tower 600 is connected to the inlet of the demethanizer 400. The gas phase outlet of the demethanizer 400 is connected to the inlet of the external gas compressor 440 via the first heat exchanger 310. The outlet of the external gas compressor 440 is connected to a first reflux pipe 491, which is connected to a second reflux pipe 492 via the first heat exchanger 310. The second reflux pipe 492 is connected to the inlet of the demethanizer 400. The liquid phase outlet of the demethanizer 400 is connected to the inlet of the deethaner 500.

[0047] In the specific process, the natural gas supply unit feeds natural gas into the heavy hydrocarbon separator 700 for separation to obtain a first gas phase and a first liquid phase. The first gas phase includes, but is not limited to, light hydrocarbons such as methane, ethane, and helium, while the first liquid phase includes, but is not limited to, liquid petroleum hydrocarbons such as octane, which are heavy hydrocarbons. The first liquid phase separated by the heavy hydrocarbon separator 700 can be subjected to combustion treatment, or it can be collected. The scheme disclosed in this application is for the recovery of light hydrocarbons such as ethane; therefore, the treatment of heavy hydrocarbons is not limited herein.

[0048] The first gas phase is passed through the first heat exchanger 310 and then introduced into the top of the helium extraction tower 600. The helium extraction tower 600 separates the first gas phase to obtain a second liquid phase and a second gas phase. Since helium is difficult to liquefy, the gas phase separated by the helium extraction tower 600 usually contains a large amount of helium; therefore, the helium in the natural gas is removed by the helium extraction tower 600. The second liquid phase produced in the helium extraction tower 600 contains liquid methane and liquid ethane.

[0049] The second liquid phase is introduced into the top of the demethanizer 400, where it is separated to obtain a third liquid phase and a third gas phase. The demethanizer 400 removes methane from the second liquid phase, resulting in a third liquid phase containing liquid ethane. This third liquid phase is then introduced into the deethanerizer 500 for deethane removal. The third gas phase, after heat exchange in the first heat exchanger 310, is compressed in the external gas compressor 440 to obtain a fourth gas phase. The low-pressure third gas phase is then boosted to a high-pressure fourth gas phase, both of which contain methane. A portion of the fourth gas phase is discharged and collected. The remaining portion is introduced into the first heat exchanger 310 through the first reflux pipe 491, and then back into the demethanizer 400 through the second reflux pipe 492, forming another reflux stream. The third liquid phase is then introduced into the deethaner 500 column for deethane removal.

[0050] Optionally, the demethanizer 400, deethaner 500, helium stripper 600, and heavy hydrocarbon separator 700 can be plate distillation columns or packed distillation columns, and of course, other separation devices are also possible; this document does not impose any limitations. Furthermore, the specific working principles of the demethanizer 400, deethaner 500, helium stripper 600, and heavy hydrocarbon separator 700 are well-known technologies and will not be elaborated upon here. The aforementioned external gas compressor 440 can be a piston compressor, screw compressor, or centrifugal compressor; the specific working principle of the external gas compressor 440 is well-known technology and will not be elaborated upon here.

[0051] Compared with related technologies, the solution in this application introduces a liquid phase separated in the helium stripping tower 600 into the demethanizing tower 400. The contact area between the liquid phase and the ethane flash vapor is larger, resulting in better condensation and thus improving the ethane recovery rate.

[0052] In addition, a portion of the fourth gas phase is fed into the demethanizer 400 after heat exchange through the first heat exchanger 310, forming another reflux. The two refluxes can further improve the reflux effect in the demethanizer 400, thus further improving the ethane recovery rate.

[0053] The scheme disclosed in this application first removes helium, and then performs demethane and deethane removal operations, thereby avoiding the inclusion of some helium in ethane and methane, and improving the purity of methane and ethane.

[0054] In the above embodiments, the natural gas ethane recovery system further includes a demethanizing reboiler 410 and a helium-extraction reboiler 630. Specifically, the demethanizing reboiler 410 can be located at the bottom of the demethanizing tower 400, and the helium-extraction reboiler 630 can be located at the bottom of the helium-extraction tower 600. The helium-extraction reboiler 630 is used to provide heat to the helium-extraction tower 600. The demethanizing reboiler 410 is used to provide heat to the demethanizing tower 400.

[0055] The heat for the helium-boiling reboiler 630 and the demethanizing reboiler 410 can be provided by the first heat exchanger 310, or by a separate heat exchange mechanism. However, this would increase the energy consumption of the natural gas ethane recovery system.

[0056] Based on this, in another optional embodiment, the outlet of the natural gas supply device can be connected to the first heat exchange device 310 through the demethanizer reboiler 410, and the first heat exchange device 310 can be connected to the inlet of the heavy hydrocarbon separator 700 through the helium-lifting reboiler 630.

[0057] The specific process flow is as follows: the natural gas supplied by the natural gas supply unit is first fed into the demethanizer reboiler 410 to provide heat to the demethanizer reboiler 410, and then fed into the helium-extracting reboiler 630 after heat exchange in the first heat exchange device 310 to provide heat to the helium-extracting reboiler 630, and finally fed into the heavy hydrocarbon separator 700.

[0058] In this scheme, the heat of the demethanizing reboiler 410 and the helium-recovering reboiler 630 is provided by natural gas, so there is no need to provide heat through the first heat exchange device 310 or a separate heat exchange mechanism, thereby reducing the energy consumption of the natural gas ethane recovery system.

[0059] In another alternative embodiment, the demethanizer 400 may have a first inlet 420 and a second inlet 430. The first inlet 420 may be connected to the liquid phase outlet of the helium stripping tower 600, and the second inlet 430 may be connected to a second reflux pipe 492. Along the direction from the gas phase outlet to the liquid phase outlet of the demethanizer 400, the first inlet 420 is located between the second inlet 430 and the gas phase outlet of the demethanizer 400. Specifically, the gas phase outlet of the demethanizer 400 is located at the top of the demethanizer 400, and its liquid phase outlet is located at the bottom of the demethanizer 400. The first inlet 420 and the second inlet 430 may be located between the gas phase outlet and the liquid phase outlet of the demethanizer 400, with the first inlet 420 located above the second inlet 430.

[0060] In this scheme, the first feed inlet 420 is located above the second feed inlet 430. The first feed inlet 420 is for the liquid phase, while the second feed inlet 430 is for the gas phase. As the gas phase rises, it can form mixed flow with the liquid phase, thereby further improving the reflux effect in the demethanizer 400.

[0061] To further improve the reflux effect within the demethanizer 400, in another optional embodiment, the natural gas ethane recovery system further includes at least one liquid phase extraction line 450 and at least one liquid phase reflux line 460, with each liquid phase extraction line 450 and the liquid phase reflux line 460 connected in a one-to-one correspondence. One end of the liquid phase extraction line 450 can be connected to the demethanizer 400, and the other end of the liquid phase extraction line 450 can be connected to one end of the liquid phase reflux line 460 via a first heat exchange device 310. The other end of the liquid phase reflux line 460 can be connected to the demethanizer 400. The connection point between the demethanizer 400 and each liquid phase reflux line 460 can be located between the corresponding connection point of the liquid phase extraction line 450 and the demethanizer 400 and the gas phase outlet of the demethanizer 400.

[0062] In this scheme, the liquid phase extraction pipeline 450 extracts part of the liquid phase from the demethanizing unit. After the extracted liquid phase recovers its cooling capacity through the first heat exchanger 310, it is returned to the upper tray at its extraction position through the liquid phase return pipeline 460. This allows for the condensation of the evaporated gas phase, thereby further improving the reflux effect and thus further increasing the ethane recovery rate.

[0063] In another optional embodiment, the natural gas ethane recovery system may further include a first throttling expansion valve 470, through which the liquid phase outlet of the helium stripping tower 600 can be connected to the feed inlet of the demethanizer tower 400. In this scheme, the liquid phase in the helium stripping tower 600 is throttled and depressurized by the first throttling expansion valve 470, causing the high-pressure fluid to expand and depressurize, generating a low temperature to cool the liquid phase entering the demethanizer tower 400, thereby preventing partial vaporization of the liquid phase during transmission and maintaining pressure stability during liquid phase transmission.

[0064] The specific working principle of the throttling expansion valve in the above embodiments is common knowledge and will not be described in detail here.

[0065] In another optional embodiment, the natural gas ethane recovery system may further include a second throttling expansion valve 480, and the second return pipe 492 may be equipped with the second throttling expansion valve 480. In this scheme, a portion of the fourth gas phase, after heat exchange through the first heat exchange device 310, is then throttled and depressurized by the second throttling expansion valve 480, further ensuring that the temperature of the return gas is at a lower level. This allows the return gas to better condense the flash vapor of ethane, thereby further improving the ethane recovery rate.

[0066] To avoid overly complex structures in the heat exchanger of the natural gas ethane recovery system, in another optional embodiment, the natural gas ethane recovery system may further include a second heat exchanger 320, which can be connected to the deethaner 500. In this case, the second heat exchanger 320 can be used to exchange heat with the gas phase of the deethaner 500. In this scheme, the deethaner 500 is equipped with a separate heat exchanger, thereby simplifying the structure of the heat exchanger in the natural gas ethane recovery system and avoiding excessive complexity.

[0067] In the above embodiments, the first heat exchanger 310 and the second heat exchanger 320 can be provided with cooling capacity by the same refrigeration device. In this case, a single refrigeration device is insufficient to meet the cooling capacity requirements of different heat exchangers.

[0068] Based on this, in another optional embodiment, the natural gas ethane recovery system may further include a first refrigeration unit and a second refrigeration unit, wherein the second refrigeration unit can be used to provide cooling capacity to the second heat exchanger 320, and the first refrigeration unit can be used to provide cooling capacity to the first heat exchanger 310.

[0069] In this scheme, the first heat exchange device 310 and the second heat exchange device 320 are equipped with corresponding refrigeration devices, which can meet the different heat exchange requirements of the first heat exchange device 310 and the second heat exchange device 320, thereby further improving the heat exchange effect of the natural gas ethane recovery system.

[0070] In another alternative embodiment, the first refrigeration device may include a first mixed refrigerant compressor 811, a third throttling expansion valve 812, and a fourth throttling expansion valve 813. The first heat exchange device 310 may be provided with a first heat exchange channel 311, a second heat exchange channel 312, and a third heat exchange channel 313.

[0071] The first heat exchange channel 311 is connected to the refrigerant inlet of the first mixed refrigerant compressor 811. The liquid phase outlet of the first mixed refrigerant compressor 811 is connected to the second heat exchange channel 312, and the second heat exchange channel 312 is connected to the third throttling expansion valve 812. The third throttling expansion valve 812 is connected to the first heat exchange channel 311; the gas phase outlet of the first mixed refrigerant compressor 811 is connected to the third heat exchange channel 313, the third heat exchange channel 313 is connected to the fourth throttling expansion valve 813, and the fourth throttling expansion valve 813 is connected to the first heat exchange channel 311.

[0072] The first mixed refrigerant compressor 811 is used to pressurize the refrigerant and also to separate the refrigerant. The refrigerant in the first mixed refrigerant compressor 811 is usually composed of several combinations of methane, nitrogen, ethane, propane, isobutane and isopentane.

[0073] In the specific process, the first refrigerant mixing compressor 811 separates the refrigerant into a gas phase and a liquid phase. The liquid phase separated by the first refrigerant mixing compressor 811 is introduced into the second heat exchange flow through its liquid phase outlet.

[0074] Heat exchange occurs within channel 312, and then the refrigerant is throttled and depressurized through the third throttling expansion valve 812 before being introduced into the first heat exchange channel 311. After heat exchange in the first heat exchange channel 311, the refrigerant returns to the first mixed refrigerant compressor 811.

[0075] The gas phase separated from the first mixed refrigerant compressor 811 is first introduced into the third heat exchange channel 313 for heat exchange, and then after being throttled and depressurized by the fourth throttling expansion valve 813, it is introduced into the first heat exchange channel 311 for heat exchange again. Finally, it returns to the first mixed refrigerant compressor 811 through the refrigerant inlet of the first mixed refrigerant compressor 811 for circulation.

[0076] In this scheme, the first refrigeration unit adopts a two-stage throttling method, which can make full use of the cooling capacity of the refrigerant, thereby reducing the energy consumption of the natural gas ethane recovery system.

[0077] In the above embodiments, the first refrigerant compressor 811 may include a compressor, a cooler, and a separator. The compressor is connected to the separator via the cooler, and the refrigerant is compressed and cooled before being fed into the separator.

[0078] The first mixed refrigerant compressor 811 separates the gas phase and liquid phase. The refrigerant inlet of the first mixed refrigerant compressor 811 is the compressor's feed inlet. The gas phase outlet and liquid phase outlet of the fifth mixed refrigerant compressor 811 are the gas phase outlet and liquid phase outlet of the separator, respectively.

[0079] Export. The specific working principle of the first mixed refrigerant compressor 811 is well-known technology and is not limited in this article.

[0080] In another alternative embodiment, the second refrigeration device may include a second mixed refrigerant compressor 821, a sixth throttling expansion valve 822, and a seventh throttling expansion valve 823. The second heat exchange device 320 may be provided with a sixth heat exchange channel 321, a seventh heat exchange channel 322, and an eighth heat exchange channel 323.

[0081] The seventh heat exchange channel 322 can be connected to the refrigerant inlet of the second mixed refrigerant compressor 821.

[0082] The liquid phase outlet of the second mixed refrigerant compressor 821 is connected to the sixth heat exchange channel 321. The sixth heat exchange channel 321 can be connected to the sixth throttling expansion valve 822, and the sixth throttling expansion valve 822 can be connected to the seventh heat exchange channel 322. The gas phase outlet of the second mixed refrigerant compressor 821 can be connected to the eighth heat exchange channel 323, and the eighth heat exchange channel 323 can be connected to the seventh throttling expansion valve 823. The seventh throttling expansion valve 823 is connected to the seventh heat exchange channel 322.

[0083] The refrigerant in the second mixed refrigerant compressor 821 is typically a combination of several of the following: methane, nitrogen, ethane, propane, isobutane, and isopentane. The structure of the second mixed refrigerant compressor 821 can be the same as that of the first mixed refrigerant compressor 811, so it will not be described in detail here.

[0084] In the specific process, the second refrigerant compressor 821 separates the refrigerant into a gas phase and a liquid phase. The liquid phase separated by the second refrigerant compressor 821 is introduced into the sixth heat exchange channel 321 through its liquid phase outlet for heat exchange. Then, after being throttled and depressurized by the sixth expansion valve 822, it is introduced into the seventh heat exchange channel 322. After heat exchange in the seventh heat exchange channel 322, it returns to the refrigerant inlet of the second refrigerant compressor 821. The gas phase separated by the second refrigerant compressor 821 is first introduced into the eighth heat exchange channel 323 for heat exchange, and then, after being throttled and depressurized by the seventh expansion valve 823, it is introduced into the seventh heat exchange channel 322 for further heat exchange.

[0085] The heat is exchanged and finally returned to the second mixed refrigerant compressor 0821 via the refrigerant inlet of the second mixed refrigerant compressor 821 for circulation.

[0086] In this scheme, the second refrigeration unit adopts a two-stage throttling method, which can make full use of the cooling capacity of the refrigerant, thereby reducing the energy consumption of the natural gas ethane recovery system.

[0087] In the above embodiments, the natural gas ethane recovery system may further include an ethane collection tank 540, containing natural gas.

[0088] The ethane recovery tank can be connected to the gas phase outlet of the de-ethane tower 500 through the second heat exchange device 320. After being subcooled, the gas phase outlet forms liquid ethane, which is then stored in the ethane collection tank 540.

[0089] In another alternative embodiment, the natural gas ethane recovery system may further include an eighth throttling expansion valve 550, a first pipeline 510, a second pipeline 520, and a third pipeline 530. A ninth heat exchange channel 324 and a tenth heat exchange channel 325 may be provided within the second heat exchange unit 320. The gas phase outlet of the ethane stripper 500 may...

[0090] The first pipeline 510 is connected to the tenth heat exchange channel 325. The tenth heat exchange channel 325 is connected to the feed inlet of the deethaner 500 via the second pipeline 520. The second pipeline 520 is connected to the ninth heat exchange channel 324 via the third pipeline 530. The ninth heat exchange channel 324 is connected to the feed inlet of the ethane collection tank 540 via the eighth throttling expansion valve 550.

[0091] In the specific process, the gas phase in the deethaner 500 is introduced into the tenth heat exchange channel 325 through the first pipeline 510. After heat exchange in the tenth heat exchange channel 325, part of the gas phase is returned to the deethaner 500 through the second pipeline 520 to form reflux, and part of the gas phase is introduced into the ninth heat exchange channel 324 through the third pipeline 530.

[0092] After heat exchange, the ethane is introduced into the eighth throttling expansion valve 550. After being throttled and depressurized by the eighth throttling expansion valve 550, liquid ethane is formed and then introduced into the ethane collection device for collection.

[0093] This scheme returns a portion of the gas phase after heat exchange in the ethane stripper 500 to the top of the ethane stripper 500, thus forming a reflux to condense other substances in the ethane, thereby further improving the purity of the ethane.

[0094] Furthermore, the natural gas ethane recovery system may also include an ethane deboiler, which can be located at the bottom of the ethane deboiler 500. Part of the liquid phase in the ethane deboiler 500 returns to the bottom of the ethane deboiler 500 after passing through the ethane deboiler. At this time, the liquid phase separated in the ethane deboiler 500 can provide heat to the ethane deboiler.

[0095] In the above embodiments, the natural gas ethane recovery system may further include a booster pump. The liquid phase outlet of the demethanizer 400 is connected to the feed inlet of the deethaner 500 via the booster pump, thereby improving the liquid phase inflow efficiency and preventing liquid phase reflux.

[0096] In another alternative, the natural gas ethane recovery system may also include a helium cooler 610 and a helium separator 620. The gas phase outlet of the helium tower 600 can be connected to the inlet of the helium separator 620 through the helium cooler 610, and the gas phase outlet of the helium separator 620 can be used to discharge crude helium.

[0097] In the specific process flow, the second gas phase separated from the helium extraction tower 600 contains a large amount of helium. This second gas phase is passed into the helium extraction cooler 610 for deep cooling, thereby condensing the ethane, methane, and other gaseous liquids carried in the helium. After separation by the separator, the separated liquid phase is returned to the top of the helium extraction tower 600 for further distillation. Simultaneously, the refluxed liquid phase forms a backflow, thus improving the reflux effect of the helium extraction tower 600. The gas phase separated by the helium separator 620 is crude helium, which can be passed into a distillation unit to obtain helium with higher purity. This application only relates to the co-production of crude helium; the helium purification and distillation unit is not described in detail here.

[0098] The natural gas ethane recovery system disclosed in this application removes helium before removing ethane and methane. Therefore, the technical solution disclosed in this application can also co-produce helium, thereby improving the utilization rate of natural gas.

[0099] In addition, this application first removes helium to avoid excessive helium in the subsequent methane and ethane, thus improving the purity of methane and ethane.

[0100] In another optional embodiment, the first refrigeration device may further include a methane compressor 814 and a fifth throttling expansion valve 815. The first heat exchange device 310 may also include a fourth heat exchange channel 314 and a fifth heat exchange channel 315. The refrigerant outlet of the methane compressor 814 may be connected to the fourth heat exchange channel 314, the fourth heat exchange channel 314 may be connected to the fifth throttling expansion valve 815, the fifth throttling expansion valve 815 may be connected to a helium-lifting cooler 610, the helium-lifting cooler 610 may be connected to the fifth heat exchange channel 315, and the fifth heat exchange channel 315 may be connected to the refrigerant inlet of the methane compressor 814.

[0101] The methane compressor 814 uses methane as a refrigerant. After compressing the methane, it is introduced into the fourth flow channel for heat exchange through its refrigerant outlet. Then, after being throttled and depressurized by the fifth throttling expansion valve 815, it is introduced into the helium cooling device, thereby providing helium cooling capacity to the helium cooler 610. Finally, it returns to the refrigerant inlet of the methane compressor 814 through the fifth heat exchange flow channel 315.

[0102] In this scheme, the methane refrigerant compressor provides cooling capacity to the helium cooler 610, thereby further optimizing the heat exchange process of the natural gas ethane recovery system and avoiding uneven heat exchange.

[0103] In the above embodiments, the methane compressor 814 may include a methane feed tank, a compressor, and a cooler. The refrigerant inlet of the methane compressor 814 is the feed port of the methane feed tank, and the discharge port of the methane feed tank is connected to the compressor. After the compressor compresses the methane, it passes through the cooler for heat exchange and then enters the fourth heat exchange channel 314.

[0104] To improve the cleanliness of natural gas, the natural gas supply device may include a natural gas decarbonization device 100 and a natural gas dehydration and mercury removal device 200. Natural gas is introduced into the natural gas decarbonization device 100 through a pipeline. After being decarbonized by the natural gas decarbonization device 100, it is discharged through the outlet of the natural gas decarbonization device 100. Then, it enters the natural gas dehydration and mercury removal device 200 through the inlet. After being dehydrated and demercured in the natural gas dehydration and mercury removal device 200, it is discharged through the outlet of the natural gas dehydration and mercury removal device and then enters the heavy hydrocarbon separator 700 through the inlet of the heavy hydrocarbon separator 700.

[0105] In this scheme, natural gas is decarbonized by a natural gas decarbonization unit 100 and dehydrated and demercured by a natural gas dehydration and mercury removal unit 200, thereby removing substances such as carbon dioxide, water vapor and mercury from the natural gas, thus improving the cleanliness of the natural gas.

[0106] In the above embodiments, the natural gas decarbonization device 100 includes, but is not limited to, an absorption tower 101, a subcooler 102, a regeneration tower 103, an acid gas separator 104, and a purified gas separator 105. Specifically, the process flow can be as follows: natural gas is subcooled by the subcooler 102 and then fed to the bottom of the absorption tower 101. After being absorbed by the absorbent in the absorption tower 101, it is discharged from the top of the absorption tower 101. The discharged natural gas then passes through the subcooler 102 again and enters the purified gas separator 105 for purification and separation. The purified natural gas then enters the natural gas dehydration and mercury removal device 200. The absorbent in the absorption tower 101 absorbs carbon dioxide to produce a rich solution with a high carbon dioxide concentration. The rich solution passes through a flash tank and then enters the top of the regeneration tower 103. The rich solution is regenerated in the regeneration tower 103, and after regeneration, it becomes a lean solution, which is then circulated back to the top of the absorption tower 101 for reuse. The acid gas discharged from the top of regeneration tower 103 is introduced into acid gas separator 104. After the acid gas passes through acid gas separator 104 and the condensate is recovered, it is discharged. The condensate separated from acid gas separator 104 is sent back to regeneration tower 103 through a pipeline and a reflux pump to maintain the system solution concentration. The gas phase separated by acid gas separator 104 can be discharged together with the gas compressed by the external gas compressor.

[0107] The working principle of the natural gas decarbonization device 100 in the above embodiments is a well-known technology and will not be described in detail here.

[0108] In another optional embodiment, the natural gas ethane recovery system may further include a tail gas compressor 110. The inlet of the tail gas compressor 110 may be connected to the gas phase outlet of the acid gas separator 104 of the natural gas decarbonization unit 100, and the liquid phase outlet of the tail gas compressor 110 may be connected to the inlet of the acid gas separator 104. The gas phase outlet of the tail gas compressor 110 is used to discharge the compressed gas. In this case, the compressed gas from the tail gas compressor 110 is discharged together with the gas.

[0109] In this scheme, the exhaust gas compressor 110 compresses the acid gas, thereby removing the water vapor from the acid gas, so that the water vapor condenses and the water separated by the exhaust gas compressor 110 can be reintroduced into the acid gas separator 104, thereby reducing the damage to the water in the natural gas decarbonization device 100.

[0110] Optionally, the exhaust compressor 110 can be a piston compressor, screw compressor or centrifugal compressor. The specific working principle of the exhaust compressor 110 is well known technology and will not be described in detail here.

[0111] In the above scheme, the natural gas dehydration and mercury removal device 200 includes, but is not limited to, a drying tank, a mercury removal tank, and a storage tank. The decarbonized natural gas is sequentially fed into the drying tank, mercury removal tank, and other equipment for water and mercury removal operations. The natural gas after dehydration and mercury removal is stored in the storage tank, which is connected to the aforementioned heavy hydrocarbon separator 700. The working principle of the natural gas dehydration and mercury removal device is well-known technology and will not be elaborated upon here.

[0112] In the above embodiments, each material can have a corresponding heat exchange channel when it enters the first heat exchange device 310 for heat exchange, which will not be listed one by one in this article.

[0113] Based on the natural gas ethane recovery system of any of the above embodiments of the present invention, the present invention also discloses an ethane recovery method, which is applied to any of the natural gas ethane recovery systems described above, such as... Figure 2 As shown, the method for recovering ethane includes:

[0114] S100, the natural gas supply device feeds natural gas into the heavy hydrocarbon separator 700 for separation to obtain a first gas phase and a first liquid phase.

[0115] S200: The first gas phase is passed through the first heat exchanger 310 and then introduced into the helium extraction tower 600. The helium extraction tower 600 separates the first gas phase to obtain the second liquid phase and the second gas phase.

[0116] S300, The second liquid phase is introduced into the demethanizer 400, and the demethanizer 400 separates the introduced second liquid phase to obtain the third liquid phase and the third gas phase;

[0117] S400 and the third gas phase are fed into the external gas compressor 440 after heat exchange in the first heat exchange device 310 to obtain the fourth gas phase. Part of the fourth gas phase is fed into the demethanizer 400 after heat exchange in the first heat exchange device 310. The third liquid phase is fed into the deethanizer 500.

[0118] Compared with related technologies, the solution in this application introduces a liquid phase separated in the helium stripping tower 600 into the demethanizing tower 400. The contact area between the liquid phase and the ethane flash vapor is larger, resulting in better condensation and thus improving the ethane recovery rate.

[0119] In addition, a portion of the fourth gas phase is fed into the demethanizer 400 after heat exchange through the first heat exchanger 310, forming another reflux. The two refluxes can further improve the reflux effect in the demethanizer 400, thus further improving the ethane recovery rate.

[0120] The scheme disclosed in this application first removes helium, and then performs demethane and deethane removal operations, thereby avoiding the inclusion of some helium in ethane and methane, and improving the purity of methane and ethane.

[0121] like Figure 1As shown, this application discloses a specific process flow. The natural gas after dehydration and mercury removal is first used as a heat source at the bottom of the demethanizer 400. After exchanging heat with the reboiler of the demethanizer 400, its temperature is reduced to 25-32°C. It then enters the first heat exchange device 310, is cooled to -50°C, and enters the helium reboiler 630 at the bottom of the helium stripping tower 600. It serves as a heat source for the helium reboiler 630, heating the temperature at the bottom of the helium stripping tower 600 from -91°C to -88°C. At the same time, the temperature of the stream is reduced to -63°C, and it enters the heavy hydrocarbon separator 700. Natural gas from the top of the heavy hydrocarbon separator 700 is cooled to -105°C by the first heat exchanger 310 and then enters the helium stripping tower 600. After rectification in the helium stripping tower 600, the gaseous phase at the top of the tower enters the helium stripping cooler 610 at the top of the helium stripping tower 600, where it is cooled to -142°C by methane refrigerant before being separated in the helium stripping separator 620 at the top of the helium stripping tower 600. The liquid phase at the bottom of the helium stripping separator 620 is refluxed back into the helium stripping tower 600. The crude helium separated from the top of the helium stripping separator 620 is reheated to room temperature and then sent to the helium purification unit to extract high-purity helium. The natural gas condensate at the bottom of the helium stripping tower 600 is depressurized to 1.9–2.6 MPaG and enters the top of the demethanizer tower 400. Natural gas from the top of the demethanizer 400 is reheated to ambient temperature by the first heat exchanger 310 and then compressed by the external gas compressor 440 to 4.5–6.0 MPaG. Simultaneously, a portion of dry gas is separated and cooled to -106°C by the first heat exchanger 310, then depressurized to 1.9–2.6 MPaG by the throttling expansion valve before entering the upper part of the demethanizer 400. Ethane-rich liquid from the bottom of the demethanizer 400 is pressurized to 2.2–2.9 MPaG by a booster pump before entering the deethanizer 500. The deethaner 500 is equipped with a deethaner reboiler. Natural gas condensate is produced at the bottom of the deethaner 500. Ethane gas at the top of the deethaner 500 is cooled to -7°C by the second heat exchanger 320 and then split into two streams. One stream returns to the top of the deethaner 500 as reflux, while the other stream is further cooled to -100°C by the second heat exchanger 320 and then throttled by the expansion valve before being sent to the ethane collection tank 540 for storage. The operating pressure of the demethanizer 400 can be 1.7–2.6 MPaG, the top temperature can be -110°C, and the bottom temperature can be -5°C. The operating pressure of the deethaner 500 is 2.2–2.9 MPaG, the top temperature is -3°C, and the bottom temperature can be 67°C.

[0122] The above embodiments of the present invention focus on describing the differences between the various embodiments. As long as the different optimization features between the various embodiments are not contradictory, they can be combined to form a better embodiment. For the sake of brevity, they will not be described in detail here.

[0123] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A natural gas recovery ethane system characterized by, It includes a natural gas supply unit, a first heat exchange unit (310), a demethanizer (400), a deethanizer (500), a helium stripper (600), a heavy hydrocarbon separator (700), an external gas compressor (440), a first reflux pipe (491), and a second reflux pipe (492); The outlet of the natural gas supply device is connected to the inlet of the heavy hydrocarbon separator (700). The gas phase outlet of the heavy hydrocarbon separator (700) is connected to the inlet of the helium stripping tower (600) through the first heat exchange device (310). The demethanizer (400) has a first inlet (420) and a second inlet (430). The first inlet (420) is connected to the liquid phase outlet of the helium stripping tower (600). The gas phase outlet of the demethanizer (400) is connected to the inlet of the external gas compressor (440) through the first heat exchange device (310). The outlet of the external gas compressor (440) is connected to the first reflux pipe (491). The first reflux pipe (491) is connected to the second reflux pipe (492) through the first heat exchange device (310). The second inlet (430) is connected to the second reflux pipe (492). The second reflux pipe (492) is connected to the demethanizer (400), and is used to supply pressurized dry gas to the demethanizer (400). The liquid outlet of the demethanizer (400) is connected to the feed inlet of the deethaner (500). In the direction from the gas outlet to the liquid outlet of the demethanizer (400), the first feed inlet (420) is located between the second feed inlet (430) and the gas outlet of the demethanizer (400). The demethanizer (400), the deethaner (500), and the helium stripper (600) are plate distillation columns or packed distillation columns. The gas phase outlet of the demethanizer (400) is located at the top of the demethanizer (400), and its liquid phase outlet is located at the bottom of the demethanizer (400). The first feed inlet (420) is located above the second feed inlet (430). During the process of the gas phase rising, it can form a mixed flow with the liquid phase.

2. The natural gas recovery ethane system of claim 1, wherein, The natural gas ethane recovery system also includes a demethanizing reboiler (410) and a helium-extracting reboiler (630), the helium-extracting reboiler (630) being used to provide heat to the helium-extracting tower (600); the demethanizing reboiler (410) being used to provide heat to the demethanizing tower (400); The outlet of the natural gas supply device is connected to the first heat exchange device (310) through the demethanizer reboiler (410), and the first heat exchange device (310) is connected to the inlet of the heavy hydrocarbon separator (700) through the helium-lifting reboiler (630).

3. The natural gas ethane recovery system according to claim 1, characterized in that, The natural gas ethane recovery system further includes at least one liquid phase extraction pipeline (450) and at least one liquid phase reflux pipeline (460). At least one liquid phase extraction pipeline (450) and at least one liquid phase reflux pipeline (460) are connected in a one-to-one correspondence. One end of the liquid phase extraction pipeline (450) is connected to the demethanizer (400), and the other end of the liquid phase extraction pipeline (450) is connected to one end of the liquid phase reflux pipeline (460) through the first heat exchange device (310). The other end of the liquid phase reflux pipeline (460) is connected to the demethanizer (400). The connection point between the demethanizer (400) and each liquid phase reflux pipeline (460) is located between the connection point of the corresponding liquid phase extraction pipeline (450) and the demethanizer (400) and the gas phase outlet of the demethanizer (400).

4. The natural gas ethane recovery system according to claim 1, characterized in that, The natural gas ethane recovery system also includes a first throttling expansion valve (470), and the liquid phase outlet of the helium extraction tower (600) is connected to the feed inlet of the demethanizer tower (400) through the first throttling expansion valve (470).

5. The natural gas ethane recovery system according to claim 1, characterized in that, The natural gas ethane recovery system also includes a second throttling expansion valve (480), and the second return pipe (492) is provided with the second throttling expansion valve (480).

6. The natural gas ethane recovery system according to claim 1, characterized in that, The natural gas ethane recovery system also includes a second heat exchange device (320), a first refrigeration device, and a second refrigeration device. The second heat exchange device (320) is connected to the de-ethane tower (500). The second refrigeration device is used to provide cooling capacity to the second heat exchange device (320), and the first refrigeration device is used to provide cooling capacity to the first heat exchange device (310).

7. The natural gas ethane recovery system according to claim 6, characterized in that, The first refrigeration device includes a first mixed refrigerant compressor (811), a third throttling expansion valve (812), and a fourth throttling expansion valve (813). The first heat exchange device (310) is provided with a first heat exchange channel (311), a second heat exchange channel (312) and a third heat exchange channel (313). The first heat exchange channel (311) is connected to the refrigerant inlet of the first mixed refrigerant compressor (811), the liquid phase outlet of the first mixed refrigerant compressor (811) is connected to the second heat exchange channel (312), the second heat exchange channel (312) is connected to the third throttling expansion valve (812), and the third throttling expansion valve (812) is connected to the first heat exchange channel (311); the gas phase outlet of the first mixed refrigerant compressor is connected to the third heat exchange channel (313), the third heat exchange channel (313) is connected to the fourth throttling expansion valve (813), and the fourth throttling expansion valve (813) is connected to the first heat exchange channel (311).

8. The natural gas ethane recovery system according to claim 6, characterized in that, The second refrigeration unit includes a second mixed refrigerant compressor (821), a sixth throttling expansion valve (822), and a seventh throttling expansion valve (823). The second heat exchange device (320) is provided with a sixth heat exchange channel (321), a seventh heat exchange channel (322) and an eighth heat exchange channel (323). The seventh heat exchange channel (322) is connected to the refrigerant inlet of the second mixed refrigerant compressor (821), the liquid phase outlet of the second mixed refrigerant compressor (821) is connected to the sixth heat exchange channel (321), the sixth heat exchange channel (321) is connected to the sixth throttling expansion valve (822), and the sixth throttling expansion valve (822) is connected to the seventh heat exchange channel (322); the gas phase outlet of the second mixed refrigerant compressor (821) is connected to the eighth heat exchange channel (323), the eighth heat exchange channel (323) is connected to the seventh throttling expansion valve (823), and the seventh throttling expansion valve (823) is connected to the seventh heat exchange channel (322).

9. The natural gas ethane recovery system according to claim 6, characterized in that, The natural gas ethane recovery system also includes an ethane collection tank (540), an eighth throttling expansion valve (550), a first pipeline (510), a second pipeline (520), and a third pipeline (530). The second heat exchange device (320) is provided with a ninth heat exchange channel (324) and a tenth heat exchange channel (325). The gas phase outlet of the de-ethane tower (500) is connected to the tenth heat exchange channel (325) through the first pipeline (510). The tenth heat exchange channel (325) is connected to the feed inlet of the de-ethane tower (500) through the second pipeline (520). The second pipeline (520) is connected to the ninth heat exchange channel (324) through the third pipeline (530). The ninth heat exchange channel (324) is connected to the feed inlet of the ethane collection tank (540) through the eighth throttling expansion valve (550).

10. A method for recovering ethane, characterized in that, The recovery method is applied to the natural gas ethane recovery system according to any one of claims 1 to 9, and the recovery method comprises: The natural gas supply unit feeds natural gas into a heavy hydrocarbon separator (700) for separation to obtain a first gas phase and a first liquid phase; The first gas phase is passed through the first heat exchanger (310) and then introduced into the helium extraction tower (600). The helium extraction tower (600) separates the first gas phase to obtain the second liquid phase and the second gas phase. The second liquid phase is fed into a demethanizer (400), which separates the second liquid phase to obtain a third liquid phase and a third gas phase. The third gas phase is fed into the external gas compressor (440) after heat exchange through the first heat exchange device (310) for compression to obtain the fourth gas phase. Part of the fourth gas phase is fed into the demethanizer (400) after heat exchange through the first heat exchange device (310); the third liquid phase is fed into the deethanizer (500).

Images