A carbon capture system using purified flue gas expansion refrigeration coupled with compressed flue gas energy storage

Abstract

The application discloses a carbon capture system adopting purified flue gas expansion refrigeration coupled with compressed flue gas energy storage, wherein a dehumidification filter device is sequentially connected with a primary compressor and a heat exchange channel No.1 of an inter-stage heat exchanger, and then is divided into two paths through a third switch valve, one path is sequentially connected with a medium-pressure gas storage tank and a valve, and then is merged with the other path, and then is sequentially connected with a secondary compressor, a liquefied heat exchanger No.1 heat exchange channel and a gas-liquid separator; a liquid phase outlet of the gas-liquid separator is connected with a liquid CO2 storage tank, a gas phase outlet is divided into two paths, one path is sequentially connected with a first flow control valve, a primary expander, a liquefied heat exchanger No.2 heat exchange channel, a secondary expander and a liquefied heat exchanger No.3 heat exchange channel, and then is connected to a first switch valve; the other path is sequentially connected with a second flow control valve and a high-pressure gas storage tank, and then is connected to the first switch valve; after being merged into one path, the path is sequentially connected with a heat exchange channel No.2 of the inter-stage heat exchanger, a second switch valve and a release energy expander. The application improves the comprehensive utilization efficiency of cold and heat of the system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of compressed energy storage and CO2 capture, and particularly relates to a carbon capture system adopting purified flue gas expansion refrigeration coupled with compressed flue gas energy storage. BACKGROUND

[0002] At present, the intermittence, volatility and uncertainty of renewable energy can affect the safe operation of the power grid system, and under this background, energy storage technology has attracted more and more attention.

[0003] Energy storage technologies mainly include compressed gas energy storage, pumped hydro energy storage, flywheel energy storage, electromagnetic energy storage, electrochemical energy storage, etc. Among them, compressed gas energy storage has the advantages of low construction cost, long operation life, less site restriction, large capacity, etc., and has good application prospects in dealing with the intermittent energy supply of renewable energy and power grid peak regulation. The gas source of compressed gas energy storage is extensive, which can be air, carbon dioxide, industrial waste gas, etc. In the energy storage mode, the gas source is pressurized by multiple stages of compressor and stored in the high-pressure gas storage tank; in the energy release mode, the high-pressure gas is expanded to realize the energy output to the outside. The cooling after gas compression and the heating before expansion help to improve the energy storage efficiency of the system, prevent liquid expansion, and improve the efficiency and operation safety of the system. At present, the huge energy consumption generated in the inter-stage cooling of the compressor and the inter-stage heating of the expander has become the main factor limiting the compressed gas energy storage, and scholars have carried out researches on the comprehensive utilization of cold and heat in the gas heating and cooling links in the compressed energy storage process.

[0004] In view of the greenhouse effect problem caused by fossil energy, a variety of carbon dioxide capture technologies have been developed at present, including chemical absorption method represented by amine carbon capture, physical adsorption method, membrane separation method, low-temperature liquefaction method, etc. The low-temperature liquefaction method is to change the gaseous carbon dioxide into liquid by compression and condensation to achieve separation. This technology has high extraction purity and no secondary pollution, and the liquid capture form is convenient for later storage and transportation. However, the huge energy consumption in the compression link limits the further development of this technology.

[0005] Combining compressed flue gas energy storage with low-temperature liquefied carbon capture technology is expected to provide a competitive industrial flue gas carbon capture scheme, which can solve the power peak regulation and realize the liquid capture of carbon dioxide in waste gas at the same time.

[0006] A system and method for flue gas compression energy storage coupled with carbon capture are disclosed in Chinese Patent Publication No. CN 114777419 A. In this system, flue gas is compressed to a high-pressure state through three stages, and after passing through a refrigeration device, it enters a gas-liquid separator to achieve liquefied carbon dioxide capture. Heat exchangers are provided between the compressors and between the expanders, and a circulating system is formed by a heat exchange medium to achieve comprehensive utilization of cold and heat. However, this system requires the additional introduction of a refrigeration device, increasing the initial investment in equipment and the land occupied by the system. Moreover, due to the large time interval between energy storage and release, the use of circulating media for post-compressor cooling and pre-expander heating requires high insulation performance of the pipelines and heat exchange medium storage tanks. Additionally, there is a temperature difference between the high-temperature gas and the heat exchange medium, and between the heat exchange medium and the low-temperature gas, reducing the efficiency of the comprehensive utilization of cold and heat in the system.

[0007] In summary, the prior art combines compressed flue gas energy storage with liquefied carbon dioxide capture and explores system design. However, the current coupled system still faces the following problems: the liquefied carbon dioxide separation process requires the additional introduction of a refrigeration system, increasing the initial investment in equipment and the land occupied by the system. To improve the energy storage efficiency of the system and prevent the expander from working with liquid, the energy storage gas needs to be cooled and heated in stages, which will result in a large energy consumption from external cold and heat sources. Due to the time interval between energy storage and release, the use of circulating heat exchange media requires high insulation performance of the pipelines and heat exchange medium storage tanks. Additionally, there is a temperature difference between the high-temperature gas and the heat exchange medium, and between the heat exchange medium and the low-temperature gas, reducing the efficiency of the comprehensive utilization of cold and heat in the system. SUMMARY

[0008] The present application provides a carbon capture system that couples purified flue gas expansion refrigeration with compressed flue gas energy storage. The system uses purified flue gas after carbon dioxide removal for two-stage expansion to produce a refrigeration effect, achieving carbon dioxide liquefaction capture without the need for additional refrigeration systems. The system utilizes liquefied heat exchangers and inter-stage heat exchangers for comprehensive utilization of cold and heat. In the energy release mode, the system uses medium-pressure flue gas to directly heat the expanded gas without the need for additional heat exchange media, reducing the insulation performance requirements of the pipelines and medium-pressure gas storage tanks.

[0009] A carbon capture system that couples purified flue gas expansion refrigeration with compressed flue gas energy storage includes a dehumidification and filtration device, a primary compressor, an inter-stage heat exchanger, a secondary compressor, a liquefied heat exchanger, a gas-liquid separator, a liquid CO2 storage tank, a primary expander, a secondary expander, a high-pressure gas storage tank, an energy release expander, and a medium-pressure gas storage tank.

[0010] The dehumidification filtering device is sequentially connected with the first-stage compressor, the first heat passage of the inter-stage heat exchanger, and is divided into two pipelines through the third switch valve, one of which is sequentially connected with the medium-pressure gas storage tank and the valve and is merged with the other pipeline, and the merged pipeline is sequentially connected with the second-stage compressor, the first heat passage of the liquefaction heat exchanger, the feed inlet of the gas-liquid separator.

[0011] The liquid-phase outlet of the gas-liquid separator is connected with the liquid CO2 storage tank; the gas-phase outlet of the gas-liquid separator is divided into two pipelines, one of which is sequentially connected with the first flow control valve, the first-stage expander, the second heat passage of the liquefaction heat exchanger, the second-stage expander, the third heat passage of the liquefaction heat exchanger and is connected to the first switch valve; the other pipeline is sequentially connected with the second flow control valve and the high-pressure gas storage tank and is connected to the first switch valve; the two pipelines are merged into one pipeline through the first switch valve and are sequentially connected with the second heat passage of the inter-stage heat exchanger and the second switch valve, and the outlet of the second switch valve is connected with the atmosphere or the energy-releasing expander.

[0012] The flow distribution of the compressed gas is controlled through the first flow control valve and the second flow control valve; the switching between the energy storage mode and the energy releasing mode is realized through the control of the first switch valve, the second switch valve and the third switch valve.

[0013] Further, the first-stage expander and the second-stage expander use the purified flue gas from which CO2 is removed through the gas-liquid separator as the working medium, the purified flue gas is expanded to cool after passing through the first-stage expander and provides cold energy for the second heat passage of the liquefaction heat exchanger; the heated purified flue gas continues to expand to cool in the second-stage expander and provides cold energy for the third heat passage of the liquefaction heat exchanger; the high-pressure flue gas is liquefied through the first heat passage of the liquefaction heat exchanger by using the refrigeration effect generated by the expansion of the high-pressure gas.

[0014] Further, in the energy storage mode, the first switch valve is connected with the gas path of the outlet of the third heat passage of the liquefaction heat exchanger, the second switch valve is connected with the atmosphere, and the third switch valve is connected with the gas inlet of the second-stage compression stage; the valve is opened, and after the flue gas stored in the medium-pressure gas storage tank enters the second-stage compressor, the valve is closed.

[0015] Further, in the energy releasing mode, the first switch valve is connected with the outlet of the high-pressure gas storage tank, the second switch valve is connected with the inlet of the energy-releasing expander, and the third switch valve is connected with the inlet of the medium-pressure gas storage tank, and the valve is closed.

[0016] Further, in the energy releasing mode, the first-stage compressor remains in the running state, the compressed high-temperature gas is used as the heat source of the high-pressure expansion gas, and the heat exchange is performed in the inter-stage heat exchanger; the cooled medium-pressure gas is stored in the medium-pressure gas storage tank.

[0017] Further, the compressed gas amount handled by the primary compressor in the energy releasing mode can be adjusted according to the demand for the net energy output.

[0018] Further, the first flow control valve and the second flow control valve realize reasonable distribution of the flow of the refrigeration flue gas and the energy storage flue gas by controlling the valve opening degree according to the cold demand of the liquefaction heat exchange and the work demand of the expansion energy release.

[0019] Optionally, the primary compressor, the secondary compressor, the primary expander, the secondary expander and the energy releasing expander are coaxial or different in shaft according to the operation condition and the equipment layout.

[0020] Optionally, the liquefaction heat exchanger is a plate-fin type, a coiled tube type or a shell-and-tube type heat exchanger.

[0021] Optionally, the first switch valve, the second switch valve and the third switch valve are electromagnetic switch valves or manual switch valves.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. The present application uses the purified flue gas after removal of carbon dioxide to expand and refrigerate, provides cold for the high-pressure flue gas, realizes carbon dioxide liquefaction capture, and the energy released in the expansion process can be directly output to the outside or input into the system again as stored energy, so that compared with the current coupling system, no additional refrigeration device needs to be introduced, the initial investment and land occupation demand of the equipment are reduced.

[0024] 2. The present application uses a three-stream type liquefaction heat exchanger to couple the expansion refrigeration and the carbon dioxide capture, uses the high-temperature and high-pressure flue gas as the heating source of the expanded gas, and introduces the gas after expansion heat exchange into the inter-stage heat exchanger as the cold source of the compressed gas, so that the comprehensive utilization of cold and heat of the system is realized.

[0025] 3. The present application uses the medium-pressure flue gas to directly heat the high-pressure gas to be expanded in the energy releasing mode, compared with the current system using a circulating heat exchange medium, overcomes the high heat preservation performance requirement of the system due to the time span of energy storage and energy release, reduces the investment, and at the same time reduces the number of heat exchange equipment, so that the structure is compact and the operation is flexible. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a whole structure schematic diagram of a carbon capture system using purified flue gas expansion refrigeration coupled with compressed flue gas energy storage according to the present application;

[0027] Figure 2 It is a connection schematic diagram of the system in the energy storage working mode according to the embodiment of the present application;

[0028] Figure 3 It is a connection schematic diagram of the system in the energy releasing working mode according to the embodiment of the present application.

[0029] In the diagram: 1. Dehumidification filter; 2. Primary compressor; 3. Interstage heat exchanger; 4. Secondary compressor; 5. Liquefaction heat exchanger; 6. Gas-liquid separator; 7. Liquid CO2 storage tank; 8-a. First flow control valve; 8-b. Second flow control valve; 9. Primary expander; 10. Secondary expander; 11. High-pressure gas storage tank; 12-a. First switching valve; 12-b. Second switching valve; 12-c. Third switching valve; 13. Energy release expander; 14. Medium-pressure gas storage tank; 15. Valve. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0031] like Figure 1 As shown, a carbon capture system employing purified flue gas expansion and refrigeration coupled with compressed flue gas energy storage includes: a dehumidification and filtration module, a compression energy storage module, an interstage heat exchange module, a liquefaction capture module, an expansion refrigeration module, and an expansion energy release module. The modules are interconnected, and the flow distribution of compressed gas is controlled by a flow control valve, while a switching valve corresponds to the switching between two operating modes.

[0032] The dehumidification and filtration module includes a dehumidification and filtration device 1, which is connected to the air inlet of the primary compressor 2.

[0033] The compressed energy storage module includes a primary compressor 2, a secondary compressor 4, a high-pressure gas storage tank 11, a medium-pressure gas storage tank 14, and a valve 15. The exhaust port of the primary compressor 2 is connected to the interstage heat exchanger 3; the inlet of the secondary compressor 4 is connected to the third switching valve 12-c or valve 15, and the exhaust port is connected to the first heat exchange channel of the liquefaction heat exchanger 5; the high-pressure gas storage tank 11 controls the flow of high-pressure gas through the second flow control valve 8-b and the first switching valve 12-a set before and after; the inlet of the medium-pressure gas storage tank 14 is connected to the third switching valve 12-c; and valve 15 connects the medium-pressure gas storage tank 14 and the secondary compressor 4.

[0034] The liquefaction capture module includes a liquefaction heat exchanger 5, a gas-liquid separator 6, a liquid CO2 storage tank 7, a first flow control valve 8-a, and a second flow control valve 8-b. The first heat exchange channel of the liquefaction heat exchanger 5 is connected to the exhaust port of the secondary compressor 4 and the inlet of the gas-liquid separator 6, respectively. The second heat exchange channel is connected to the exhaust port of the primary expander 9 and the inlet of the secondary expander 10, respectively. The third heat exchange channel is connected to the exhaust port of the secondary expander 10 and the first switching valve 12-a, respectively. The liquid phase outlet of the gas-liquid separator 6 is connected to the liquid CO2 storage tank 7, and the gas phase outlet is connected to the first flow control valve 8-a and the second flow control valve 8-b.

[0035] The expansion refrigeration module comprises a primary expander 9 and a secondary expander 10, the gas inlet of the primary expander 9 is connected with the gas phase outlet of the gas-liquid separator 6 through a first flow control valve 8-a, and the purified flue gas after CO2 removal is expanded twice to be cooled, and then the cooled purified flue gas is sent into the liquefaction heat exchanger 5 to exchange heat with the incoming high-temperature and high-pressure flue gas.

[0036] The inter-stage heat exchange module comprises an inter-stage heat exchanger 3, a first switching valve 12-a, a second switching valve 12-b and a third switching valve 12-c, the ① heat exchange flow channel of the inter-stage heat exchanger 3 is connected with the gas outlet of the primary compressor 2 and the inlet of the third switching valve 12-c respectively, the inlet and outlet of the ② heat exchange flow channel are connected with the first switching valve 12-a and the second switching valve 12-b respectively, the first switching valve 12-a is connected with the high-pressure gas storage tank 11 or the ③ heat exchange flow channel of the liquefaction heat exchanger 5, the second switching valve 12-b is connected with the external atmosphere or the energy release expander 13, and the third switching valve 12-c is connected with the secondary expander 4 or the medium-pressure gas storage tank 15.

[0037] The expansion energy release module comprises the energy release expander 13, the flue gas stored in the high-pressure gas storage tank 11 is connected through the first switching valve 12-a and the second switching valve 12-b, and then introduced into the inter-stage heat exchanger 3 of the two-stage compressor to complete the energy release to the external atmosphere.

[0038] In the application, the primary expander 9 and the secondary expander 10 use the purified flue gas after CO2 removal as the working medium, the refrigeration effect generated by the high-pressure gas expansion is used to realize the liquefaction capture of CO2 in the high-pressure flue gas, and the expansion work can be directly output to the outside or input into the system again as stored energy.

[0039] The expansion refrigeration module comprises two-stage expansion, the purified flue gas is heated in the ② heat exchange flow channel of the liquefaction heat exchanger 5 after passing through the primary expander 9, the heated purified flue gas continues to expand in the secondary expander 10 to generate the refrigeration effect and do work to the outside.

[0040] The liquefaction heat exchanger 5 is a three-stream heat exchanger, the expanded cold fluid exchanges heat with the incoming high-temperature and high-pressure compressed flue gas to realize the liquefaction separation of CO2.

[0041] When the system is in the energy storage mode, the first switching valve 12-a is connected with the outlet gas path of the ③ heat exchange flow channel of the liquefaction heat exchanger 5, the second switching valve 12-b is connected with the external atmosphere, the third switching valve 12-c is connected with the gas inlet of the secondary compressor 4, and the valve 15 is opened; after the flue gas stored in the medium-pressure gas storage tank 14 is completely introduced into the secondary compressor 4, the valve 15 is closed, and the remaining valves remain unchanged.

[0042] When the system is in the energy release working mode, the first switching valve 12-a is connected to the outlet of the high-pressure gas storage tank 11, the second switching valve 12-b is connected to the inlet of the energy release expander 13, the third switching valve 12-c is connected to the inlet of the medium-pressure gas storage tank 14, and valve 15 is closed.

[0043] In energy release mode, the first-stage compressor 2 remains operational. The compressed high-temperature gas serves as a heat source for the high-pressure expansion gas, undergoing heat exchange in the interstage heat exchanger 3. The cooled medium-pressure gas is stored in the medium-pressure gas storage tank 14. The amount of compressed gas processed by the first-stage compressor 2 in energy release mode can be adjusted according to the net energy demand for external output.

[0044] The first flow control valve 8-a and the second flow control valve 8-b can achieve a reasonable distribution of the flow rates of refrigeration flue gas and energy storage flue gas by controlling the valve opening according to the cooling capacity required for liquefaction heat exchange and the power required for expansion energy release.

[0045] A connection diagram of the system in energy storage mode in this embodiment of the invention is shown below. Figure 2 As shown, the working process is as follows:

[0046] (1) The flue gas passes through the dehumidification filter 1 to remove moisture and dust impurities before entering the compression energy storage module.

[0047] (2) The pretreated flue gas enters the first-stage compressor 2 and is compressed to a medium-pressure state. It is cooled in the interstage heat exchanger 3. The third switching valve 12-c connects the first heat exchange channel of the interstage heat exchanger 3 with the air inlet of the second-stage compressor 4. The flue gas is further compressed to a high-pressure state in the second-stage compressor 4.

[0048] (3) Open valve 15. In the energy release mode, the flue gas stored in the medium-pressure gas storage tank 14 in advance is sent to the secondary compressor 4 together with the incoming flue gas to be further compressed to a high pressure state. After all the flue gas stored in the medium-pressure gas storage tank 14 has been sent to the secondary compressor 4, close valve 15.

[0049] (4) The high-pressure flue gas enters the No. 1 heat exchange channel of the liquefaction heat exchanger 5 and exchanges heat with the low-temperature gas in the No. 2 and No. 3 heat exchange channels of the liquefaction heat exchanger 5 to realize the liquefaction and capture of carbon dioxide in the flue gas components; the flue gas after heat exchange enters the gas-liquid separator 6 to realize the gas-liquid separation of liquid carbon dioxide product and purified flue gas; the captured carbon dioxide is sent to the liquid CO2 storage tank 7.

[0050] (5) The purified flue gas flows out from the gas phase outlet of the gas-liquid separator 6 and is distributed by the first flow control valve 8-a and the second flow control valve 8-b. The purified flue gas flowing through the first flow control valve 8-a is used for expansion refrigeration to provide cooling for the liquefaction process. The purified flue gas flowing through the second flow control valve 8-b is sent to the high-pressure gas storage tank 11 for storage and standby.

[0051] (6) The purified flue gas for expansion refrigeration flows into the first expander 9, the No. 2 heat exchange channel of the liquefaction heat exchanger 5, the second expander 10, and the No. 3 heat exchange channel of the liquefaction heat exchanger 5 in sequence. The high-temperature gas in the No. 1 heat exchange channel is used as a heat source of the expansion gas, and the external energy output is increased under the condition that the initial and final pressures are constant. Meanwhile, the expander is prevented from working with liquid, and the expansion work can be directly output to the outside or input into the system as stored energy.

[0052] (7) The first switching valve 12-a connects the No. 3 heat exchange channel of the liquefaction heat exchanger 5 and the No. 2 heat exchange channel of the inter-stage heat exchanger 3, and the purified flue gas expanded to the normal pressure is sent into the inter-stage heat exchanger 3 to cool the incoming medium-pressure flue gas as a cold source. The outlet of the second switching valve 12-b is connected to the external environment, and the purified flue gas is directly discharged after heat exchange. The system completes the storage of input energy and the liquefaction capture of carbon dioxide.

[0053] The connection diagram of the system in the energy release mode in the embodiment of the present application is shown in FIG. 2, and the working process is as follows: Figure 3

[0054] (1) The flue gas passes through the dehumidification and filtration device 1 to remove water and dust impurities, and enters the compression energy storage module.

[0055] (2) The pretreated flue gas enters the first compressor 2 to be compressed to a medium-pressure state, and is cooled in the inter-stage heat exchanger 3. The first switching valve 12-a connects the No. 1 heat exchange channel of the inter-stage heat exchanger 3 and the medium-pressure gas storage tank 14, and the valve 15 is kept closed. The flue gas is stored in the medium-pressure gas storage tank 14. In the energy release mode, the compressed gas amount processed by the first compressor 2 can be adjusted according to the demand for the net energy output to the outside.

[0056] (3) The first switching valve 12-a connects the high-pressure gas storage tank 11 and the No. 2 heat exchange channel of the inter-stage heat exchanger 3, and the purified flue gas is heated by the high-temperature exhaust gas of the first compressor 2, and the inter-stage cooling of the compressed gas is realized.

[0057] (4) The outlet of the second switching valve 12-b is connected to the energy release expander 13, and the heated purified flue gas is further expanded to the normal pressure to complete the energy output to the outside.

[0058] The technical solutions and beneficial effects of the present application are described in detail in the above embodiments, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the present application. Any modification, supplement and equivalent replacement made within the principle range of the present application should be included in the protection range of the present application.​

Claims

1. A carbon capture system using purified flue gas expansion refrigeration coupled with compressed flue gas energy storage, characterized in that, The device comprises a dehumidification filter device (1), a primary compressor (2), an inter-stage heat exchanger (3), a secondary compressor (4), a liquefaction heat exchanger (5), a gas-liquid separator (6), a liquid CO2 storage tank (7), a primary expander (9), a secondary expander (10), a high-pressure gas storage tank (11), an energy-releasing expander (13), and a medium-pressure gas storage tank (14). The dehumidification filter device (1) is sequentially connected to the primary compressor (2) and the ① heat exchange channel of the inter-stage heat exchanger (3), and then is divided into two pipelines by the third switch valve (12-c), one of which is sequentially connected to the medium-pressure gas storage tank (14) and the valve (15) and then is combined with the other pipeline, and the combined pipeline is sequentially connected to the secondary compressor (4), the ① heat exchange channel of the liquefaction heat exchanger (5), and the feed inlet of the gas-liquid separator (6). The liquid phase outlet of the gas-liquid separator (6) is connected to the liquid CO2 storage tank (7), and the gas phase outlet of the gas-liquid separator (6) is divided into two pipelines, one of which is sequentially connected to the first flow control valve (8-a), the primary expander (9), the ② heat exchange channel of the liquefaction heat exchanger (5), the secondary expander (10), and the ③ heat exchange channel of the liquefaction heat exchanger (5), and then is connected to the first switch valve (12-a), and the other pipeline is sequentially connected to the second flow control valve (8-b) and the high-pressure gas storage tank (11), and then is connected to the first switch valve (12-a); the two pipelines are combined into one pipeline after passing through the first switch valve (12-a), and are sequentially connected to the ② heat exchange channel of the inter-stage heat exchanger (3) and the second switch valve (12-b), and the outlet of the second switch valve (12-b) is connected to the atmosphere or the energy-releasing expander (13). The flow distribution of the compressed gas is controlled by the first flow control valve (8-a) and the second flow control valve (8-b), and the switching between the energy storage mode and the energy releasing mode is realized by controlling the first switch valve (12-a), the second switch valve (12-b), and the third switch valve (12-c).

2. The carbon capture system employing purified flue gas expansion refrigeration coupled with compressed flue gas energy storage of claim 1, wherein, The primary expander (9) and the secondary expander (10) use the purified flue gas from which CO2 has been removed by the gas-liquid separator (6) as the working medium, the purified flue gas expands to cool after passing through the primary expander (9) and provides cold energy for the ② heat exchange channel of the liquefaction heat exchanger (5), the heated purified flue gas continues to expand to cool in the secondary expander (10) and provides cold energy for the ③ heat exchange channel of the liquefaction heat exchanger (5), and the high-pressure flue gas is liquefied by the refrigeration effect generated by the expansion of the high-pressure gas in the ① heat exchange channel of the liquefaction heat exchanger (5).

3. The carbon capture system employing purified flue gas expansion refrigeration coupled with compressed flue gas energy storage of claim 1, wherein, In the energy storage mode, the first switch valve (12-a) is connected to the gas path of the outlet of the ③ heat exchange channel of the liquefaction heat exchanger (5), the second switch valve (12-b) is connected to the atmosphere, and the third switch valve (12-c) is connected to the gas inlet of the secondary compressor (4); the valve (15) is opened, and after the flue gas stored in the medium-pressure gas storage tank (14) enters the secondary compressor (4), the valve (15) is closed.

4. The carbon capture system employing purified flue gas expansion refrigeration coupled with compressed flue gas energy storage of claim 1, wherein, In the energy release mode, the first switch valve (12-a) is connected with the outlet of the high-pressure gas tank (11), the second switch valve (12-b) is connected with the inlet of the energy release expander (13), the third switch valve (12-c) is connected with the inlet of the medium-pressure gas tank (14), and the valve (15) is closed.

5. The carbon capture system employing purified flue gas expansion refrigeration coupled with compressed flue gas energy storage of claim 4, wherein, In the energy release mode, the primary compressor (2) keeps running, the compressed high-temperature gas is used as the heat source of the high-pressure expansion gas, and heat exchange is performed in the inter-stage heat exchanger (3), and the cooled medium-pressure gas is stored in the medium-pressure gas tank (14).

6. The carbon capture system employing purified flue gas expansion refrigeration coupled with compressed flue gas energy storage of claim 1, wherein, The first flow control valve (8-a) and the second flow control valve (8-b) realize the flow distribution of the refrigeration flue gas and the energy storage flue gas by controlling the valve opening degree according to the liquefaction heat exchange demand and the expansion energy release demand.

7. The carbon capture system employing purified flue gas expansion refrigeration coupled with compressed flue gas energy storage of claim 1, wherein, The primary compressor (2), the secondary compressor (4), the primary expander (9), the secondary expander (10) and the energy release expander (13) are coaxial or different shafts according to the operation condition and the equipment layout.

8. The carbon capture system employing purified flue gas expansion refrigeration coupled with compressed flue gas energy storage of claim 1, wherein, The liquefaction heat exchanger (5) is a plate-fin type, a coil type or a tube-shell type heat exchanger.

9. The carbon capture system employing purified flue gas expansion refrigeration coupled with compressed flue gas energy storage of claim 1, wherein, The first switch valve (12-a), the second switch valve (12-b) and the third switch valve (12-c) are electromagnetic switch valves or manual switch valves.

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