Membrane tower coupled decarburization system

Abstract

This invention provides a membrane-coupling decarbonization system, comprising a cold box, a pretreatment unit, a flash tank, a distillation column, a bottom reboiler, a top condenser, a top reflux tank, a carbon dioxide subcooler, a membrane separator, a throttling device, a first carbon dioxide compressor, a second carbon dioxide compressor, and a carbon dioxide expander. It is used to decarbonize associated gas or natural gas from oil fields, and to separately export the separated natural gas and high-purity carbon dioxide. The membrane-coupling decarbonization system provided by this invention utilizes the liquid carbon dioxide separated within the distillation column itself. After expansion and cooling by the carbon dioxide expander, the carbon dioxide enters the top condenser for evaporation. The cooling energy released during evaporation is directly supplied to the top condenser, achieving the effect of completely eliminating the need for external refrigeration units and external refrigerants in the top condensation stage of the distillation column.

Description

Technical Field

[0001] This invention relates to the field of natural gas purification and carbon capture technology, and in particular to a membrane tower coupled decarbonization system. Background Technology

[0002] Associated gas or natural gas from oil fields often contains high concentrations of carbon dioxide and heavy hydrocarbon components, requiring decarbonization and carbon capture purification to meet pipeline transportation requirements and CCUS application needs. Currently, carbon capture and purification processes for such associated gas mainly include amine absorption, membrane separation, cryogenic distillation, and combinations of these methods. Among these, the membrane-distillation coupling process, combining the preliminary concentration advantages of membrane separation with the high-purity separation characteristics of cryogenic distillation, offers higher processing efficiency and is gradually becoming the mainstream application solution in the industry.

[0003] For associated gas or natural gas from oil fields containing high CO2 and heavy hydrocarbons, existing carbon capture and purification processes mostly adopt a coupled model of "membrane separation pretreatment + cryogenic distillation purification," with the core objective of achieving associated gas decarbonization and CO2 capture and purification. However, this model has several technical shortcomings in practical applications, especially in terms of insufficient cold source supply, making it difficult to adapt to the actual application needs of offshore and onshore oil and gas fields.

[0004] For example, a membrane-coupling decarbonization system is disclosed in the prior art, which uses a membrane separation unit coupled with a cryogenic distillation column to achieve natural gas decarbonization and CO2 purification. The main drawback of this technology is that the condensation at the top of the distillation column must rely on an external refrigerant for cooling, requiring a separate refrigeration circuit (such as an external refrigeration unit), resulting in a complex system structure, large equipment footprint, high initial investment, and the operating energy consumption of the refrigeration unit significantly increases the overall energy consumption of carbon capture.

[0005] In summary, the current carbon capture and purification processes for associated gas or natural gas from oil fields with high CO2 and heavy hydrocarbon content generally suffer from a key technical bottleneck due to the unreasonable cold source supply method: the condensation at the top of the distillation column must rely on external refrigeration units or external refrigerants, making it impossible to achieve self-cooling or cold energy recovery and utilization. This results in a complex system structure, large footprint, and high operating energy consumption, which does not conform to the development direction of cost reduction and efficiency improvement of CCUS technology.

[0006] Therefore, there is an urgent need to develop a high-efficiency and energy-saving carbon capture and purification device and process that can solve the above-mentioned cold source supply defects, adapt to the processing of associated gas or natural gas in oil fields with high CO2 content and heavy hydrocarbons, achieve cost reduction and efficiency improvement in the carbon capture process, and meet the practical application needs of offshore and onshore oil and gas exploration. Summary of the Invention

[0007] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a membrane tower coupled decarbonization system, which aims to solve the problem that in the existing membrane-distillation coupled carbon capture process for associated gas or natural gas from oil fields with high carbon dioxide content and heavy hydrocarbons, the condensation at the top of the distillation tower depends on an external refrigeration unit, and self-cooling or cold energy recovery cannot be achieved, resulting in a complex system and high energy consumption.

[0008] This invention provides a membrane tower decarbonization system, including a cold box, a pretreatment unit, a flash tank, a distillation column, a bottom reboiler, a top condenser, a top reflux tank, a carbon dioxide subcooler, a membrane separator, a throttling device, a first carbon dioxide compressor, a second carbon dioxide compressor, and a carbon dioxide expander. The inlet of the pretreatment unit is connected to the raw gas source and is used to dehydrate and remove mercury from the raw gas supplied by the raw gas source to obtain pretreated gas. The raw gas is associated gas or natural gas from oil fields with high carbon dioxide and heavy hydrocarbon content. The pretreated gas is cooled by the cold box and then enters the reboiler at the bottom of the tower. The reboiler is heated and cooled, and then the gas returns to the cold box for further cooling before entering the flash tank for flash treatment. The flash vapor phase enters the cold box, providing cooling for the cold box, and then enters the membrane separator for decarbonization. The flash liquid phase is throttled and cooled by the throttling device before entering the distillation column. The liquid carbon dioxide drawn from the bottom of the distillation column is cooled by the subcooler and then enters the carbon dioxide expander for further expansion and cooling before entering the top condenser to provide cooling for the condensation of the gas phase components at the top of the distillation column before entering the downstream user end. The gas phase component drawn from the top of the distillation column is cooled by heat exchange with the liquid carbon dioxide drawn from the bottom of the distillation column in the top condenser and then enters the top reflux tank. The gas phase in the top reflux tank passes through the subcooler and enters the cold box to release cold energy and increase temperature. Then it is compressed by the first carbon dioxide compressor and enters the membrane separator. The natural gas separated by the membrane separator enters the downstream user end, and the carbon dioxide separated by the membrane separator is compressed by the second carbon dioxide compressor, cooled by the cold box, and then enters the distillation column.

[0009] According to the membrane tower coupled decarbonization system provided by the present invention, the throttling device is a two-phase expander, which is used to perform work on an external generator.

[0010] The membrane tower coupled decarbonization system provided by the present invention further includes a heavy hydrocarbon separation tank and a carbon dioxide liquefaction pipeline. The carbon dioxide, which provides cooling for the condensation of the gas phase components at the top of the distillation tower, enters the heavy hydrocarbon separation tank to remove heavy hydrocarbons. The carbon dioxide with separated heavy hydrocarbon components is liquefied through the carbon dioxide liquefaction pipeline and then enters the downstream user end.

[0011] According to the membrane tower coupled decarbonization system provided by the present invention, the liquefaction pipeline includes a third carbon dioxide compressor, a water cooler, a carbon dioxide condenser, and a second pressurizing pump. The carbon dioxide gas separated by the heavy hydrocarbon separator is pressurized by the third carbon dioxide compressor and then enters the water cooler for cooling. It then enters the carbon dioxide condenser and exchanges heat with the liquid carbon dioxide from the carbon dioxide subcooler. Finally, it enters the downstream user end together with the liquid carbon dioxide from the carbon dioxide subcooler.

[0012] According to the membrane tower coupled decarbonization system provided by the present invention, the pretreatment unit includes a molecular sieve adsorption tank and a mercury removal reactor connected in series. The upstream end of the molecular sieve adsorption tank is connected to the raw material gas source for dehydrating the raw material gas, and the downstream end of the mercury removal reactor is connected to the cold box for removing mercury from the dehydrated raw material gas.

[0013] According to the membrane tower coupled decarbonization system provided by the present invention, the molecular sieve adsorption tank includes two, which are connected in parallel between the raw gas source and the upstream end of the mercury removal reactor, and the two molecular sieve adsorption tanks work alternately.

[0014] The present invention has the following advantages due to the adoption of the above technical solutions: The membrane tower coupled decarbonization system provided by this invention utilizes the liquid carbon dioxide separated by the distillation tower itself. After being expanded and cooled by a carbon dioxide expander, the carbon dioxide enters the top condenser for evaporation. The cooling energy released during the evaporation process is directly supplied to the top condenser, realizing that the top condensation stage of the distillation tower does not require external refrigeration units or external refrigerants. This fundamentally eliminates the costs of purchasing, transporting, storing, and replenishing external refrigerants for the distillation system, reduces the operational burden of refrigerant replenishment on offshore platforms, lowers the safety hazards of refrigerant leakage and replacement, simplifies the distillation unit process, reduces the footprint and maintenance workload of related equipment, and achieves efficient self-cooling operation of the distillation system. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the membrane tower coupled decarbonization system provided by the present invention.

[0017] Figure label: 110: Molecular sieve adsorption tank; 120: Mercury removal reactor; 200: Cold box; 300: Flash tank; 410: Distillation column; 420: Bottom reboiler; 430: Top condenser; 440: Top reflux tank; 500: Subcooler; 600: Membrane separator; 700: Two-phase expander; 800: First carbon dioxide compressor; 900: Second carbon dioxide compressor; 1000: Carbon dioxide expander; 1100: Heavy hydrocarbon separator; 1210: Third carbon dioxide compressor; 1220: Water cooler; 1230: Carbon dioxide condenser; 1240: Second booster pump; 1300: First booster pump. Detailed Implementation

[0018] 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 with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0019] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0021] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0023] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0024] This invention provides a membrane-coupling decarbonization system, comprising a cold box, a pretreatment unit, a flash tank, a distillation column, a bottom reboiler, a top condenser, a top reflux tank, a carbon dioxide subcooler, a membrane separator, a throttling device, a first carbon dioxide compressor, a second carbon dioxide compressor, and a carbon dioxide expander. It is used to decarbonize associated gas or natural gas from oil fields, and to separately export the separated natural gas and high-purity carbon dioxide. The membrane-coupling decarbonization system provided by this invention utilizes the liquid carbon dioxide separated within the distillation column itself. After expansion and cooling by the carbon dioxide expander, the carbon dioxide enters the top condenser for evaporation. The cooling energy released during evaporation is directly supplied to the top condenser, achieving the effect of completely eliminating the need for external refrigeration units and external refrigerants in the top condensation stage of the distillation column.

[0025] The following is combined Figure 1 The membrane tower coupled decarbonization system of the present invention is described.

[0026] An embodiment of the present invention provides a membrane tower coupled decarbonization system, including a cold box 200, a pretreatment unit, a flash tank 300, a distillation column 410, a bottom reboiler 420, a top condenser 430, a top reflux tank 440, a subcooler 500, a membrane separator 600, a throttling device, a first carbon dioxide compressor 800, a second carbon dioxide compressor 900, and a carbon dioxide expander 1000.

[0027] The raw gas from the upstream raw gas source first enters the pretreatment unit for dehydration and mercury removal to form pretreated gas. The raw gas is associated gas or natural gas from oil fields with high carbon dioxide and heavy hydrocarbon content.

[0028] Subsequently, the pretreated gas enters the cold box 200 for a first cooling process, specifically by exchanging heat with the refrigerant inside the cold box 200 to lower its temperature. The cooled pretreated gas then enters the reboiler 420 at the bottom of the tower to provide it with heat, and then returns to the cold box 200 for a second cooling process. After cooling, it enters the flash tank 300 for flash evaporation.

[0029] The gas phase with high carbon dioxide content obtained after flash evaporation enters the cold box 200, where the cold box 200 recovers the cold energy, and then enters the membrane separator 600 for decarbonization treatment. The separated low carbon dioxide gas is then transported to the downstream user end.

[0030] The liquid phase with high carbon dioxide content obtained after flash evaporation is cooled by throttling and then enters distillation column 410 to participate in the subsequent distillation and purification process.

[0031] The liquid carbon dioxide separated at the bottom of the distillation column 410 is partially extracted and sent to the carbon dioxide expander 1000 for expansion and cooling. The cooled carbon dioxide enters the top condenser 430 for evaporation and heat absorption, providing cooling capacity for the top condenser 430. The vapor fraction after evaporation is 98%~99%. After providing cooling capacity, it enters the downstream user end.

[0032] The cold energy released during the evaporation process is directly supplied to the top condenser 430, providing a cold source for the condensation of the gaseous components at the top of the distillation column 410. This enables the distillation column 410 to operate under its own cooling system, completely eliminating the distillation column 410's dependence on external refrigerants and external refrigeration units. This reduces the cost and safety risks of transporting and storing external refrigerants on offshore platforms, while also simplifying the system process and reducing the equipment footprint.

[0033] The vapor phase drawn from the top of distillation column 410 enters the top condenser 430, where it absorbs the cooling energy released by the evaporation of liquid carbon dioxide and then enters the top reflux tank 440. The vapor phase separated from the top reflux tank 440 passes through the subcooler 500 and then enters the cold box 200 to release its cooling energy and be heated. It is then compressed by the first carbon dioxide compressor 800 and combined with the flash vapor obtained from the flash evaporation to enter the membrane separator 600 for decarbonization treatment.

[0034] The low-carbon dioxide gas separated from the membrane separator 600 is transported to the downstream user end. The separated carbon dioxide gas is compressed by the second carbon dioxide compressor 900 and cooled by the cold box 200 before returning to the distillation column 410 to continue natural gas decarbonization and carbon dioxide purification.

[0035] The membrane tower coupled decarbonization system provided by this invention utilizes the liquid carbon dioxide separated by the distillation tower 410 itself. After being expanded and cooled by the carbon dioxide expander 1000, the carbon dioxide enters the top condenser 430 to evaporate and release cold energy. The released cold energy is directly supplied to the top condenser 430, realizing that the top condensation stage of the distillation tower 410 does not require an external refrigeration unit or external refrigerant. This fundamentally eliminates the costs of purchasing, transporting, storing, and replenishing external refrigerants for the distillation system, reduces the operational burden of refrigerant replenishment on offshore platforms, reduces the safety hazards of refrigerant leakage and replacement, simplifies the distillation unit process, reduces the footprint and maintenance workload of related equipment, and achieves efficient self-cooling operation of the distillation system.

[0036] In some embodiments, the aforementioned throttling device can be a two-phase expander 700. Liquid material from the flash tank 300 enters the two-phase expander 700, undergoes expansion, cooling, and depressurization, and then generates electricity. The generated electricity is directly supplied to the power-consuming equipment of the carbon capture system itself, achieving partial energy self-sufficiency. Simultaneously, the two-phase expansion process significantly reduces the temperature of the material entering the distillation column 410, further optimizing the distillation separation effect and reducing system energy consumption.

[0037] The membrane tower coupled decarbonization system provided by this invention uses a two-phase expander 700 in both key components, replacing the traditional expansion valve, thus achieving dual technical effects: Firstly, in the liquid phase treatment stage after the flash evaporation of the raw gas, the two-phase expander 700 expands, cools, and depressurizes the liquid material. On the one hand, it generates electricity externally, and the generated electricity can supply the internal electrical equipment of the system, realizing energy recovery and partial self-sufficiency, and reducing the overall energy consumption of the system. On the other hand, it can significantly reduce the temperature of the material entering the distillation column 410, thereby reducing the cooling demand of the top of the distillation column 410 and further optimizing the energy consumption of distillation separation.

[0038] Secondly, in the self-expansion refrigeration stage of distillation column 410, the two-phase expander 700 expands and cools the liquid carbon dioxide extracted from distillation column 410. Compared with traditional expansion valves, it can cool the liquid carbon dioxide to a lower temperature, and release more cooling capacity after entering the top condenser 430, which fully meets the cooling capacity requirements of the top condenser 430, ensuring the stable and reliable self-refrigeration operation of distillation column 410, while further improving the efficiency of cooling capacity utilization and reducing energy waste.

[0039] In some embodiments, the system further includes a heavy hydrocarbon separator 1100 and a carbon dioxide liquefaction pipeline. The two-phase flow after evaporation in the top condenser 430 enters the heavy hydrocarbon separator 1100, where the entrained heavy hydrocarbon components are separated to prevent heavy hydrocarbons from mixing with the carbon dioxide product and affecting its purity. The carbon dioxide gas phase after heavy hydrocarbon separation is liquefied in the carbon dioxide liquefaction pipeline and then transported to the downstream user.

[0040] Specifically, the carbon dioxide liquefaction pipeline includes a third carbon dioxide compressor 1210, a water cooler 1220, a carbon dioxide condenser 1230, and a second pressurizing pump 1240. The gaseous carbon dioxide first enters the third carbon dioxide compressor 1210 for compression, then undergoes water cooling in the water cooler 1220, and then enters the first heat exchange channel of the carbon dioxide condenser 1230. Simultaneously, liquid carbon dioxide drawn from the distillation column 410 is pressurized by the first pressurizing pump 1300 and enters the second heat exchange channel of the carbon dioxide condenser 1230. The liquid carbon dioxide in the second heat exchange channel cools the gaseous carbon dioxide in the first heat exchange channel, turning it into liquid carbon dioxide. The liquefied carbon dioxide is then pressurized by the second pressurizing pump 1240 and merges with the liquid carbon dioxide in the second heat exchange channel, becoming the final carbon dioxide product that is then sent out.

[0041] The membrane tower coupled decarbonization system provided by this invention partially vaporizes the liquid carbon dioxide extracted from the distillation tower 410 and, in conjunction with the heavy hydrocarbon separator 1100, effectively removes heavy hydrocarbon components, achieving heavy hydrocarbon separation. This not only stably obtains carbon dioxide products with a purity of over 99%, significantly improving product purity, but also eliminates the need to drastically increase the reflux ratio of the distillation tower 410, effectively reducing the reboiling and condensation loads of the distillation tower 410, thus reducing the energy consumption of the distillation system. This solves the problem of high energy consumption in traditional processes due to the lack of heavy hydrocarbon removal methods and the need to increase the distillation load to ensure purity.

[0042] In some embodiments, the pretreatment unit includes a molecular sieve adsorption tank 110 and a mercury removal reactor 120. The upstream end of the molecular sieve adsorption tank 110 is connected to the raw gas source, and the downstream end is connected to the upstream end of the mercury removal reactor 120. The downstream end of the mercury removal reactor is connected to a cold box 200. The molecular sieve adsorption tank 110 is used to dehydrate the raw gas, and the mercury removal reactor 120 is used to remove mercury from the dehydrated raw gas.

[0043] Furthermore, two molecular sieve adsorption tanks 110 can be provided, connected in parallel between the raw gas source and the upstream end of the mercury removal reactor. Under normal operating conditions, the two molecular sieve adsorption tanks 110 work alternately, with one adsorbing while the other regenerates.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A membrane tower coupled decarbonization system, characterized in that, It includes a cold box (200), a pretreatment unit, a flash tank (300), a distillation column (410), a bottom reboiler (420), a top condenser (430), a top reflux tank (440), a carbon dioxide subcooler (500), a membrane separator (600), a throttling device, a first carbon dioxide compressor (800), a second carbon dioxide compressor (900), and a carbon dioxide expander (1000). The inlet of the pretreatment unit is connected to the raw gas source and is used to dehydrate and remove mercury from the raw gas supplied by the raw gas source to obtain pretreated gas. The raw gas is associated gas or natural gas from oil fields with high carbon dioxide and heavy hydrocarbon content. The pretreated gas is cooled by the cold box (200) and then enters the bottom reboiler (420). The bottom reboiler (420) is heated and cooled, and then returns to the cold box (200) to be cooled again before entering the flash tank (300) for flash treatment. The gas phase after flash evaporation enters the cold box (200), which provides cooling capacity to the cold box (200) and then enters the membrane separator (600) for decarbonization. The liquid phase after flash evaporation is throttled and cooled by the throttling device and then enters the distillation column (410). The liquid carbon dioxide drawn from the bottom of the distillation column (410) is cooled by the subcooler (500) and then enters the carbon dioxide expander (1000) for further expansion and cooling before entering the top condenser (430) to provide cooling for the condensation of the gas phase components at the top of the distillation column (410) before entering the downstream user end. The gas phase component drawn from the top of the distillation column (410) is cooled by heat exchange with the liquid carbon dioxide drawn from the bottom of the distillation column (410) in the top condenser (430) and then enters the top reflux tank (440). The gas phase in the top reflux tank (440) passes through the subcooler (500) and then enters the cold box (200) to release cold energy and increase temperature. Then it is compressed by the first carbon dioxide compressor (800) and enters the membrane separator (600). The natural gas separated by the membrane separator (600) enters the downstream user end, and the carbon dioxide separated by the membrane separator (600) is compressed by the second carbon dioxide compressor (900), cooled by the cold box (200), and then enters the distillation column (410).

2. The membrane tower coupled decarbonization system according to claim 1, characterized in that, The throttling device is a two-phase expander (700), which is used to perform work on the outward generator.

3. The membrane tower coupled decarbonization system according to claim 1, characterized in that, It also includes a heavy hydrocarbon separator (1100) and a carbon dioxide liquefaction pipeline. The carbon dioxide, which provides cooling for the condensation of the gas phase components at the top of the distillation column (410), enters the heavy hydrocarbon separator (1100) to remove heavy hydrocarbons. The carbon dioxide separated from the heavy hydrocarbon components is liquefied through the carbon dioxide liquefaction pipeline and then enters the downstream user end.

4. The membrane tower coupled decarbonization system according to claim 3, characterized in that, The liquefaction pipeline includes a third carbon dioxide compressor (1210), a water cooler (1220), a carbon dioxide condenser (1230), and a second pressurizing pump (1240). The carbon dioxide gas separated by the heavy hydrocarbon separator (1100) is pressurized by the third carbon dioxide compressor (1210) and then enters the water cooler (1220) for cooling. It then enters the carbon dioxide condenser (1230) to exchange heat with the liquid carbon dioxide from the carbon dioxide subcooler (500). Finally, it enters the downstream user end together with the liquid carbon dioxide from the carbon dioxide subcooler (500).

5. The membrane tower coupled decarbonization system according to claim 1, characterized in that, The pretreatment unit includes a molecular sieve adsorption tank (110) and a mercury removal reactor (120) connected in series. The upstream end of the molecular sieve adsorption tank (110) is connected to the raw material gas source for dehydrating the raw material gas. The downstream end of the mercury removal reactor (120) is connected to the cold box (200) for removing mercury from the dehydrated raw material gas.

6. The membrane tower coupled decarbonization system according to claim 5, characterized in that, The molecular sieve adsorption tank (110) includes two, which are connected in parallel between the raw material gas source and the upstream end of the mercury removal reactor (120), and the two molecular sieve adsorption tanks (110) work alternately.

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