Integrated system for capturing carbon dioxide in flue gas by membrane method

By combining membrane separation and PSA technology into an integrated system, the high cost and high energy consumption problems of low-concentration carbon dioxide capture are solved, and efficient CO2 recovery and concentration increase are achieved, adapting to flue gases of different concentrations and meeting the requirements of the liquefaction process.

CN223366600UActive Publication Date: 2025-09-23DALIAN EUROFILM IND
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Patent Information

Application Number
CN202422841231.7
Authority / Receiving Office
CN · China
Patent Type
Utility models(China)
Current Assignee / Owner
Filing Date
2024-11-21
Publication Date
2025-09-23
Estimated Expiration
2034-11-21

AI Technical Summary

Technical Problem

Existing technologies have problems with large investment and high energy consumption when capturing low-concentration carbon dioxide, especially when the carbon dioxide concentration in flue gas is low. Membrane separation technology requires a multi-stage process, which increases costs. Chemical absorption and pressure swing adsorption methods are not efficient in low-concentration environments.

Method used

An integrated system that uses membrane method to capture carbon dioxide in flue gas, combining membrane separation technology with PSA technology, first increases the CO2 concentration through the integration of a one-stage two-stage membrane combination and a PSA unit, and then performs pressure swing adsorption, using the CO2 selective permeation membrane and PSA unit to improve the CO2 recovery rate and concentration.

Benefits of technology

It achieves efficient capture of carbon dioxide in low-concentration flue gas, with a CO2 recovery rate of no less than 90% and a concentration of 95%, reducing energy consumption and investment costs, adapting to raw gas of different concentrations, and producing high-concentration CO2 products.

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Abstract

The utility model discloses an integrated system for capturing carbon dioxide in flue gas by a membrane method. The integrated system comprises a first compression unit, a first membrane separator, a second membrane separator, a second compression unit, a third compression unit, a PSA (Pressure Swing Adsorption) unit and a fourth compression unit, a feed gas pipeline is connected with a first compression unit, the first compression unit is connected with a gas inlet of a first membrane separator, an interception side outlet of the first membrane separator is connected with a gas inlet of a second membrane separator, an interception side outlet of the second membrane separator is connected with an emptying pipeline, and a permeation side outlet of the second membrane separator is connected with a second compression unit. The second compression unit is connected with a feed gas pipeline; a permeation side outlet of the first membrane separator is connected with a third compression unit, and the third compression unit is connected with an inlet end of a PSA unit; the tail gas outlet end of the PSA unit is connected with an eleventh pipeline, the desorbed gas outlet end of the PSA unit is connected with a fourth compression unit, the fourth compression unit is connected into the third compression unit through a thirteenth pipeline with a valve, and the thirteenth pipeline can be connected with downstream equipment needing CO2 through a fourteenth pipeline with a valve; cO2 selective permeable membranes are arranged in the first membrane separator and the second membrane separator.
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Description

Technical Field

[0001] The utility model relates to the technical field of gas separation, in particular to an integrated system for capturing carbon dioxide in flue gas using a membrane method. Background Art

[0002] Carbon capture technology refers to a range of techniques and methods used to capture carbon dioxide (CO2) from industrial emissions or the atmosphere. These technologies are of great significance in mitigating global climate change and promoting greenhouse gas emissions reduction. Specifically, CO2 capture technology is a key step in achieving carbon capture and storage (CCS). It aims to separate and purify CO2 contained in industrial exhaust or the atmosphere for subsequent transportation, utilization, or storage.

[0003] The lower the concentration of carbon dioxide, the more difficult it is to capture. Taking flue gas as an example, the concentration of carbon dioxide in the flue gas of coal-fired power plants is usually between 12% and 15%. The flue gas flow is large, the CO2 partial pressure is low, the composition is complex, and it contains SO2 and NO. x The CO2 concentration in flue gas from gas-fired power plants is lower, at approximately 3% to 4%, and the oxygen concentration is higher, at approximately 13% to 18%. These characteristics place even greater demands on the innovative development and cost control of CO2 capture technology.

[0004] Currently, widely used carbon dioxide capture and recovery technologies include chemical absorption, pressure swing adsorption, and membrane separation technology. Chemical absorption has problems such as high energy consumption, susceptibility to corrosion of equipment, and easy degradation of absorbents. Pressure swing adsorption is more suitable for scenarios with higher CO2 concentrations. When used in environments with lower CO2 concentrations, its investment cost and operating energy consumption increase significantly, and some pollutants in the flue gas may have an adverse effect on the performance and selectivity of the adsorbent. Membrane separation technology is limited by the permeability selectivity of current membrane materials. If a higher CO2 capture concentration is to be achieved, the partial pressure difference in the membrane separation process needs to be greatly increased. If the CO2 concentration to be produced exceeds 95%, a multi-stage membrane separation process must be adopted, which will lead to a significant increase in the investment cost and operating energy consumption of the membrane.

[0005] It is not difficult to see that for the capture and recovery of low-concentration CO2 in flue gas, a single technology has its shortcomings, with problems such as large investment and high energy consumption. In order to effectively reduce system investment and operating costs, it is urgent to develop more economical and efficient carbon dioxide capture technology. Summary of the Invention

[0006] The utility model provides an integrated system for capturing carbon dioxide in flue gas using a membrane method, so as to overcome the above problems.

[0007] In order to achieve the above purpose, the technical solution of the utility model is:

[0008] An integrated system for capturing carbon dioxide from flue gas using a membrane method, comprising a first compression unit, a first membrane separator, a second membrane separator, a second compression unit, a third compression unit, a PSA unit, and a fourth compression unit;

[0009] The raw gas pipeline is connected to the first compression unit, the first compression unit is connected to the air inlet of the first membrane separator, the retentate side outlet of the first membrane separator is connected to the air inlet of the second membrane separator, the retentate side outlet of the second membrane separator is connected to the exhaust pipeline, the permeate side outlet of the second membrane separator is connected to the second compression unit, and the second compression unit is connected to the raw gas pipeline;

[0010] The permeate side outlet of the first membrane separator is connected to the third compression unit, and the third compression unit is connected to the inlet end of the PSA unit;

[0011] The tail gas outlet of the PSA unit is connected to the eleventh pipeline, the desorption gas outlet of the PSA unit is connected to the fourth compression unit, the fourth compression unit is connected to the third compression unit through the thirteenth pipeline with a valve, and the thirteenth pipeline can be connected to the downstream equipment requiring CO2 through the fourteenth pipeline with a valve;

[0012] The first membrane separator and the second membrane separator are both provided with a CO2 selective permeation membrane.

[0013] Furthermore, the first compression unit includes a first blower and a first gas-liquid separator;

[0014] The raw gas pipeline is connected to the inlet of the first blower, the outlet of the first blower is connected to the air inlet of the first gas-liquid separator, and the air outlet of the first gas-liquid separator is connected to the air inlet of the first membrane separator.

[0015] Furthermore, the second compression unit includes a first vacuum pump and a first cooler;

[0016] The permeate side outlet of the second membrane separator is connected to the air inlet of the first vacuum pump, and the air outlet of the first vacuum pump is connected to the raw gas pipeline through a pipeline provided with a first cooler and then connected to the first compression unit.

[0017] Furthermore, the third compression unit includes a second vacuum pump, a second cooler and a second gas-liquid separator;

[0018] The permeate side outlet of the first membrane separator is connected to the air inlet of the second vacuum pump through the seventh pipeline, the air outlet of the second vacuum pump is connected to the inlet of the second cooler, the outlet of the second cooler is connected to the air inlet of the second gas-liquid separator, and the air outlet of the second gas-liquid separator is connected to the inlet end of the PSA unit.

[0019] Furthermore, the fourth compression unit is a third vacuum pump, the analytical gas outlet of the PSA unit is connected to the air inlet of the third vacuum pump, and the air outlet of the third vacuum pump is connected to the third compression unit through a thirteenth pipeline with a valve.

[0020] Furthermore, the analytical gas outlet of the PSA unit is connected to the fourth compression unit via a twelfth pipeline, and a carbon dioxide detector is provided on the twelfth pipeline.

[0021] Furthermore, it also includes a first discharge pipeline, which is connected to the discharge port of the first gas-liquid separator.

[0022] Furthermore, it also includes a second discharge pipeline, one end of the second discharge pipeline is connected to the discharge port of the second gas-liquid separator, and the other end of the second discharge pipeline is connected to the first discharge pipeline.

[0023] Beneficial effects:

[0024] The utility model provides an integrated system for capturing carbon dioxide in flue gas by membrane method. By combining membrane separation technology with PSA technology, membrane separation is first used to increase the CO2 concentration, and then pressure swing adsorption is performed, thereby reducing the energy consumption in the CO2 purification process. A first-stage two-stage membrane combination is realized by a first membrane separator and a second membrane separator, and is integrated with a PSA unit to prepare a gas with a CO2 concentration higher than 95%, thereby meeting the needs of a subsequent liquefaction process. By redirecting the initial analysis gas of the PSA to the first membrane separator to increase the CO2 recovery rate, a separation target of a CO2 recovery rate of not less than 90% is achieved, and the CO2 content in the PSA analysis gas can be increased to 95%. The utility model has good adaptability to raw gases of different concentrations and can produce high-concentration CO2 products. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0026] Figure 1 This is a schematic structural diagram of an integrated system for capturing carbon dioxide in flue gas using a membrane method disclosed in the utility model.

[0027] In the picture:

[0028] 110. First blower;

[0029] 120. First gas-liquid separator;

[0030] 130. First membrane separator;

[0031] 140. Second membrane separator;

[0032] 150. First vacuum pump;

[0033] 160, first cooler;

[0034] 170, second vacuum pump;

[0035] 180, second cooler;

[0036] 190. Second gas-liquid separator;

[0037] 200, PSA unit;

[0038] 210, third vacuum pump;

[0039] 10. Raw gas pipeline; 11. First pipeline; 12. Second pipeline; 13. Third pipeline; 14. Fourth pipeline; 15. Fifth pipeline; 16. Exhaust pipeline; 17. Seventh pipeline; 18. Eighth pipeline; 19. Ninth pipeline; 20. Tenth pipeline; 21. Eleventh pipeline; 22. Twelfth pipeline; 23. Thirteenth pipeline; 24. Fourteenth pipeline;

[0040] 50. First discharge pipeline; 51. Second discharge pipeline. DETAILED DESCRIPTION

[0041] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0042] This embodiment provides an integrated system for capturing carbon dioxide from flue gas using a membrane method. Figure 1 As shown, it includes a first compression unit, a first membrane separator 130, a second membrane separator 140, a second compression unit, a third compression unit, a PSA unit 200 and a fourth compression unit;

[0043] In this embodiment, the first compression unit includes a first blower 110 and a first gas-liquid separator 120, the second compression unit includes a first vacuum pump 150 and a first cooler 160, the third compression unit includes a second vacuum pump 170, a second cooler 180 and a second gas-liquid separator 190, and the fourth compression unit is a third vacuum pump 210;

[0044] The raw gas pipeline 10 is connected to the inlet of the first blower 110, the outlet of the first blower 110 is connected to the air inlet of the first gas-liquid separator 120 through the first pipeline 11, and the air outlet of the first gas-liquid separator 120 is connected to the air inlet of the first membrane separator 130 through the second pipeline 12;

[0045] The retentate-side outlet of the first membrane separator 130 is connected to the air inlet of the second membrane separator 140 via the third pipeline 13. The retentate-side outlet of the second membrane separator 140 is connected to the exhaust pipeline 16. The permeate-side outlet of the second membrane separator 140 is connected to the air inlet of the first vacuum pump 150 via the fourth pipeline 14. The air outlet of the first vacuum pump 150 is connected to the air inlet of the first blower 110 via the fifth pipeline 15 provided with the first cooler 160 and connected to the raw gas pipeline 10. The gas at the outlet of the first vacuum pump 150 is relatively hot and is connected to the first cooler 160 via the fifth pipeline 15 to reduce the gas temperature to room temperature.

[0046] The permeate side outlet of the first membrane separator 130 is connected to the air inlet of the second vacuum pump 170 through the seventh pipeline 17, the air outlet of the second vacuum pump 170 is connected to the inlet of the second cooler 180 through the eighth pipeline 18, and the outlet of the second cooler 180 is connected to the air inlet of the second gas-liquid separator 190 through the ninth pipeline 19. The gas temperature at the outlet of the second vacuum pump 170 is relatively high, and is connected to the second cooler 180 through the eighth pipeline 18 to reduce the gas temperature to room temperature. The air outlet of the second gas-liquid separator 190 is connected to the inlet end of the PSA unit 200 through the tenth pipeline 20. The PSA unit is a prior art and includes a plurality of adsorption towers each containing an adsorbent that preferentially adsorbs CO2.

[0047] The tail gas outlet end of the PSA unit 200 is connected to the eleventh pipeline 21, and the desorption gas outlet end of the PSA unit 200 is connected to the air inlet of the third vacuum pump 210 through the twelfth pipeline 22. The twelfth pipeline 22 is provided with a carbon dioxide detector. The air outlet of the third vacuum pump 210 is connected to the eighth pipeline 18 between the air outlet of the second vacuum pump 170 and the air inlet of the second gas-liquid separator 190 through the thirteenth pipeline 23 with a valve. The thirteenth pipeline 23 can be connected to a downstream device requiring CO2 through a fourteenth pipeline 24 with a valve. In this embodiment, the downstream device is a CO2 liquefaction device.

[0048] The first membrane separator 130 and the second membrane separator 140 are both provided with a CO 2 selective permeation membrane, and the CO 2 selective permeation membrane can preferentially permeate the CO 2 gas component.

[0049] In a specific embodiment, Figure 1As shown, the first discharge pipeline 50 is further included. The first discharge pipeline 50 is connected to the discharge port of the first gas-liquid separator 120 to discharge the condensate generated by condensation of the first gas-liquid separator 120.

[0050] In a specific embodiment, Figure 1 As shown, it also includes a second discharge pipeline 51, one end of which is connected to the discharge port of the second gas-liquid separator 190, and the other end of the second discharge pipeline 51 is connected to the first discharge pipeline 50, so as to discharge the condensate generated by the condensation of the second gas-liquid separator 190 and the first gas-liquid separator 120 in a centralized manner.

[0051] Flue gas is pre-treated to remove solid particles, primary SO2 and NO x After the acidic gas is extracted, it enters the integrated system for capturing carbon dioxide in flue gas by membrane method through the raw gas pipeline 10. After being pressurized by the first blower 110, it enters the first gas-liquid separator 120 through the first pipeline 11 to remove possible entrained solid particles and droplets. Then, it enters the first membrane separator 130 through the second pipeline 12. The first membrane separator 130 has a built-in CO2 selective permeable membrane that preferentially transmits the CO2 gas component.

[0052] After separation in the first membrane separator 130, the retentate gas enters the second membrane separator 140 through the third pipeline 13. The second membrane separator 140 has a built-in CO2 selective permeation membrane that preferentially transmits the CO2 gas component. The permeate gas from the second membrane separator 140 is enriched in CO2 and enters the first vacuum pump 150 and the first cooler 160 through the fourth pipeline 14. Then, it returns to the inlet of the first blower 110 through the fifth pipeline 15, thereby improving the CO2 recovery rate. The retentate gas from the second membrane separator 140 is discharged through the exhaust pipeline 16.

[0053] The permeate gas separated by the first membrane separator 130 can increase the concentration of CO2 to more than 40% (V), and then enters the second vacuum pump 170 through the seventh pipeline 17. The second vacuum pump 170 provides the driving force for the membrane separation process. The gas temperature at the outlet of the second vacuum pump 170 is relatively high. It is connected to the second cooler 180 through the eighth pipeline 18 to reduce the gas temperature to room temperature, and then enters the second gas-liquid separator 190 through the ninth pipeline 19. The condensate generated by the second gas-liquid separator 190 is discharged after merging with the condensate generated by the first gas-liquid separator 120 through the second discharge pipeline 51. The gas passing through the second gas-liquid separator 190 enters the PSA unit 200 through the tenth pipeline 20. The tail gas generated after passing through the PSA unit is discharged through the eleventh pipeline 21.

[0054] A carbon dioxide detector is provided on the twelfth pipeline 22. The decomposed gas from the PSA unit enters the third vacuum pump 210 via the twelfth pipeline 22. Since the concentration of CO2 in the decomposed gas obtained in the initial stage of the PSA unit is relatively low, the valve on the thirteenth pipeline 23 is first opened to allow the decomposed gas to return to the inlet of the second cooler 180 via the thirteenth pipeline 23 to ensure the recovery rate of CO2. When the carbon dioxide detector detects that the concentration of CO2 in the decomposed gas reaches 95% (V) or more, the valve on the thirteenth pipeline 23 is closed and the valve on the fourteenth pipeline 24 is opened to allow the decomposed gas to be transported to the downstream CO2 liquefaction device via the fourteenth pipeline 24.

[0055] To better illustrate the effect of the integrated system for capturing carbon dioxide from flue gas using a membrane method disclosed in the present invention, the following process flow is described in detail:

[0056] The raw gas is flue gas, and the gas volume is 500Nm 3 / h, which is composed as follows:

[0057] Components <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[O2]]> <![CDATA[H2O]]> Composition (vol%) 15.00 75.00 5.00 5.00

[0058] After one cycle, part of the gas returns to the raw gas pipeline 10 from the permeate side outlet of the second membrane separator 140 and re-enters the first membrane separator 130. The gas volume entering the first membrane separator 130 is 532.04Nm 3 / h, which is composed as follows:

[0059] Components <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[O2]]> <![CDATA[H2O]]> Composition (vol%) 15.88 73.98 5.18 4.96

[0060] Among them, the gas volume discharged from the first membrane separator 130 to the second membrane separator 140 is 340.80Nm 3 / h, which is composed as follows:

[0061] Components <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[O2]]> <![CDATA[H2O]]> Composition (vol%) 1.55 94.17 4.06 0.22

[0062] Among them, the gas volume discharged from the first membrane separator 130 into the second vacuum pump 170 is 191.25Nm 3 / h, which is composed as follows:

[0063] Components <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[O2]]> <![CDATA[H2O]]> Composition (vol%) 41.41 38.00 7.19 13.40

[0064] The gas volume discharged from the second membrane separator 140 into the first vacuum pump 150 is 19.81 Nm 3 / h, which is composed as follows:

[0065] Components <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[O2]]> <![CDATA[H2O]]> Composition (vol%) 9.76 78.58 10.10 1.56

[0066] Among them, the gas volume discharged into the exhaust pipeline 16 through the second membrane separator 140 is 320.98Nm 3 / h, which is composed as follows:

[0067] Components <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[O2]]> <![CDATA[H2O]]> Composition (vol%) 1.04 95.14 3.68 0.14

[0068] This embodiment provides an integrated system for capturing carbon dioxide from flue gas using a membrane method. The system combines low-pressure membrane separation technology with low-pressure PSA technology. Membrane separation is first used to increase the CO2 concentration, and then pressure swing adsorption is performed, thereby reducing energy consumption in the CO2 purification process. A first-stage two-stage membrane combination is realized through the first membrane separator 130 and the second membrane separator 140, and is integrated with the PSA unit 200 to produce a gas with a CO2 concentration higher than 95%, thereby meeting the requirements of the subsequent liquefaction process. By redirecting the initial analysis gas of the PSA to the first membrane separator 130 to improve the CO2 recovery rate, a separation target of a CO2 recovery rate of not less than 90% is achieved, and the CO2 content in the PSA analysis gas can be increased to 95%, avoiding the traditional replacement process. The system has good adaptability to raw gases of different concentrations, can produce high-concentration CO2 products, and has a high degree of reliability.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An integrated system for capturing carbon dioxide from flue gas using a membrane method, characterized in that: The invention comprises a first compression unit, a first membrane separator (130), a second membrane separator (140), a second compression unit, a third compression unit, a PSA unit (200) and a fourth compression unit; The raw gas pipeline (10) is connected to the first compression unit, the first compression unit is connected to the air inlet of the first membrane separator (130), the interception side outlet of the first membrane separator (130) is connected to the air inlet of the second membrane separator (140), the interception side outlet of the second membrane separator (140) is connected to the emptying pipeline (16), the permeation side outlet of the second membrane separator (140) is connected to the second compression unit, and the second compression unit is connected to the raw gas pipeline (10); The permeate side outlet of the first membrane separator (130) is connected to the third compression unit, and the third compression unit is connected to the inlet end of the PSA unit (200); The tail gas outlet of the PSA unit (200) is connected to an eleventh pipeline (21), the desorption gas outlet of the PSA unit (200) is connected to a fourth compression unit, the fourth compression unit is connected to the third compression unit via a thirteenth pipeline (23) with a valve, and the thirteenth pipeline (23) can be connected to a downstream device requiring CO2 via a fourteenth pipeline (24) with a valve; The first membrane separator (130) and the second membrane separator (140) are both provided with a CO2 selective permeation membrane.

2. The integrated system for capturing carbon dioxide from flue gas by membrane method according to claim 1, characterized in that: The first compression unit includes a first blower (110) and a first gas-liquid separator (120); The raw gas pipeline (10) is connected to the inlet of the first blower (110), the outlet of the first blower (110) is connected to the air inlet of the first gas-liquid separator (120), and the air outlet of the first gas-liquid separator (120) is connected to the air inlet of the first membrane separator (130).

3. The integrated system for capturing carbon dioxide from flue gas by membrane method according to claim 1, characterized in that: The second compression unit includes a first vacuum pump (150) and a first cooler (160); The permeate side outlet of the second membrane separator (140) is connected to the air inlet of the first vacuum pump (150), and the air outlet of the first vacuum pump (150) is connected to the raw gas pipeline (10) through a pipeline provided with a first cooler (160) and then connected to the first compression unit.

4. The integrated system for capturing carbon dioxide from flue gas by membrane method according to claim 2, characterized in that: The third compression unit includes a second vacuum pump (170), a second cooler (180) and a second gas-liquid separator (190); The permeate side outlet of the first membrane separator (130) is connected to the air inlet of the second vacuum pump (170) through the seventh pipeline (17), the air outlet of the second vacuum pump (170) is connected to the inlet of the second cooler (180), the outlet of the second cooler (180) is connected to the air inlet of the second gas-liquid separator (190), and the air outlet of the second gas-liquid separator (190) is connected to the inlet end of the PSA unit (200).

5. The integrated system for capturing carbon dioxide from flue gas by membrane method according to claim 1, characterized in that: The fourth compression unit is a third vacuum pump (210), the analytical gas outlet of the PSA unit (200) is connected to the air inlet of the third vacuum pump (210), and the air outlet of the third vacuum pump (210) is connected to the third compression unit through a thirteenth pipeline (23) with a valve.

6. The integrated system for capturing carbon dioxide from flue gas by membrane method according to claim 1, characterized in that: The analytical gas outlet of the PSA unit (200) is connected to the fourth compression unit via a twelfth pipeline (22), and a carbon dioxide detector is provided on the twelfth pipeline (22).

7. The integrated system for capturing carbon dioxide from flue gas by membrane method according to claim 4, characterized in that: It also includes a first discharge pipeline (50), wherein the first discharge pipeline (50) is connected to the liquid discharge port of the first gas-liquid separator (120).

8. The integrated system for capturing carbon dioxide from flue gas using a membrane method according to claim 7, characterized in that: It also includes a second discharge pipeline (51), one end of which is connected to the liquid discharge port of the second gas-liquid separator (190), and the other end of which is connected to the first discharge pipeline (50).