A phase change flue gas CO2 capture method and system based on absorbent dual solvent circulation

Abstract

This invention relates to the technical field of flue gas carbon dioxide capture, and discloses a phase change flue gas CO2 capture method and system based on a dual-solvent cycle of absorbent. The method includes the following steps: (1) performing liquid-solid phase separation on a mixture of flue gas and absorbent / solvent I to obtain a solid absorbent product and solvent I; (2) mixing the solid absorbent product and solvent II and then performing CO2 desorption to obtain a CO2 product and an absorbent / solvent II mixture; (3) performing liquid-liquid phase separation on the absorbent / solvent II mixture to obtain an absorbent and solvent II; (4) mixing solvent I obtained in step (1) with the absorbent again and repeating step (1) to achieve circulation; mixing solvent II in step (3) with the solid absorbent product again and repeating step (2) to achieve circulation. This invention achieves advantages such as fast CO2 absorption rate, high desorption efficiency, and low carbon capture cost through the dual-solvent cycle system design.

Description

Technical Field

[0001] This invention relates to the technical field of flue gas carbon dioxide capture, and in particular to a phase change flue gas CO2 capture method and system based on a dual solvent cycle absorbent. Background Technology

[0002] Carbon dioxide (CO2) is the largest anthropogenic greenhouse gas emitted by humans, with coal-fired power plants and industrial boilers being the largest sources. Post-combustion CO2 capture is a crucial technological pathway for the low-carbon utilization of fossil fuels. Chemical absorption is currently the mainstream technology widely used for CO2 capture in flue gas after combustion. This technology relies on aqueous absorbent solutions to capture CO2 from flue gas. For example, patent CN1747774B discloses a method for separating and recovering carbon dioxide from byproduct gases generated in steel plants using chemical absorption; patent CN103381330B discloses an absorbent for capturing or separating carbon dioxide, which uses an absorbent solution composed of organic active components such as amines and ionic liquids, along with water, to chemically react with CO2. At high temperatures (approximately 120°C), a reversible reaction occurs, thereby separating CO2 from the flue gas. However, the CO2 absorption rates of the above-mentioned chemical absorption methods are relatively low, and the capture energy consumption and cost are also high.

[0003] For this chemical absorption process, researchers both domestically and internationally have proposed using non-aqueous organic solvents, which can help improve the CO2 absorption rate of the absorbent and reduce the energy consumption of collection. Because organic solvents have advantages such as lower specific heat capacity and lower latent heat of vaporization than water, the application of organic solvent-based absorbents in chemical absorption processes can reduce collection energy consumption. Yuan et al. (DOI:10.1016 / j.ces.2018.02.026) demonstrated through experimental measurements that using NMP organic solvent can increase the CO2 absorption rate of MEA absorbent by 4 times. However, the application of absorbent / organic solvent systems in existing chemical absorption processes also has disadvantages. The system may experience liquid-liquid and liquid-solid phase separation. For example, the invention patent with publication number CN 108079746B discloses an ethanolamine / diethylaminoethanol system, which undergoes liquid-liquid phase separation after absorbing CO2, forming an organic phase and an aqueous phase. The invention patent with publication number CN114870570A discloses a mixed system of N-methyldiethanolamine, piperazine and organic solvent, which spontaneously forms a liquid-solid two-phase system after absorbing CO2 gas.

[0004] The aforementioned absorbent / organic solvent system, when applied to existing chemical absorption processes, suffers from problems such as poor heat transfer performance due to phase separation and high viscosity, and low heat transfer efficiency in high-temperature CO2 desorption towers. Furthermore, it fails to fully leverage the advantages of organic solvents in increasing CO2 absorption rates and reducing energy consumption. Therefore, there is an urgent need to develop a phase-change flue gas CO2 capture system based on an absorbent / organic solvent system. Summary of the Invention

[0005] To address the problems of poor heat exchange performance and low heat transfer efficiency of high-temperature CO2 desorption towers caused by phase separation and high viscosity when using absorbent / organic solvent systems in existing chemical absorption processes, this invention provides a phase change type flue gas CO2 capture method and system based on absorbent dual-solvent circulation. Through the dual-solvent circulation system design, different organic solvents are circulated in the absorption tower and desorption tower, giving full play to the advantages of organic solvents such as fast CO2 absorption rate, high circulation capacity of CO2 enriched phase, and organic solvent purging-assisted CO2 desorption, which helps to reduce carbon capture costs.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a phase change flue gas CO2 capture method based on a dual solvent cycle absorbent, comprising the following steps:

[0008] (1) The flue gas and absorbent / solvent I mixture were subjected to liquid-solid phase separation to obtain solid absorbent product and solvent I;

[0009] (2) After mixing the solid absorbent product and solvent II, an absorbent-CO2 / solvent II mixture is obtained; then CO2 desorption is performed to obtain CO2 product and absorbent / solvent II mixture.

[0010] (3) Perform liquid-liquid phase separation on the absorbent / solvent II mixture to obtain absorbent and solvent II;

[0011] (4) After mixing the solvent I obtained in step (1) with the absorbent in step (3) again, repeat step (1) to achieve the cycle; after mixing the solvent II in step (3) with the solid phase absorbent product obtained in step (1) again, repeat step (2) to achieve the cycle.

[0012] This system fully utilizes the solvent effect. The absorbent, in combination with solvent I, achieves high CO2 absorption capacity and rate, while the absorbent, in combination with solvent II, achieves low regeneration energy consumption and high CO2 desorption rate. This improves the CO2 absorption rate of the absorbent in the absorption tower while reducing the energy load of absorbent regeneration in the CO2 desorption tower. The system can operate continuously, or it can perform CO2 absorption and storage of absorbent products, or CO2 desorption and release of CO2 product gas independently.

[0013] Preferably, the absorbent is one or more of organic amines, amino acid salts, and ionic liquids; solvent I is one or more of 1,2-propanediol, 1,4-butanediol, ethylene glycol, polyethylene glycol, dimethyl sulfoxide, N,N-dimethylacetamide, and water; and solvent II is one of pentane, hexane, cyclohexane, and n-heptane.

[0014] Preferably, the absorbent is one of ethylenediamine, tetramethylenediamine, diethylenetriamine, tetraethylenepentamine, piperazine, 2-amino-2-methyl-1-propanol, potassium taurate, potassium proline, and potassium sarcosinate.

[0015] The relationship between the absorbent and solvent I is relatively close. For the CO2 absorption process, the absorbent and solvent I can preferably be combined as follows: diethylenetriamine and polyethylene glycol-water; ethylenediamine and polyethylene glycol; piperazine and 1,2-propanediol; tetramethylenediamine and 1,4-butanediol; piperazine and N,N-dimethylacetamide; diethylenetriamine and polyethylene glycol; potassium proline and ethylene glycol-water; potassium sarcosinate and 1,4-butanediol-water; etc.

[0016] The correspondence between the absorbent and solvent II is relatively weak. When used in the CO2 desorption process, it mainly relies on the advantages of solvent II, such as low latent heat of vaporization, low viscosity, and purging-assisted desorption. The selection is based on the mutual cooperation between the absorbent and solvent II. Solvent II can be further preferably pentane or hexane.

[0017] Preferably, in step (1), the mass percentage of absorbent and solvent I in the absorbent / solvent I mixture is 10%:90% to 50%:50%; in step (2), the mass percentage of absorbent-CO2 and solvent II in the absorbent-CO2 / solvent II mixture is 50%:50% to 90%:10%, more preferably 80%:20%.

[0018] In the CO2 capture method of this invention, not only does the selection of absorbent and solvent I and solvent II result in better synergy, but the ratio between absorbent and solvent I and solvent II also affects the final CO2 absorption and desorption effect, and affects CO2 capture efficiency and energy consumption.

[0019] Secondly, the present invention also provides a phase change flue gas CO2 capture system based on a dual solvent cycle of absorbent, the system comprising a CO2 absorption tower and a CO2 desorption tower;

[0020] The CO2 absorption tower includes a flue gas inlet, and its top is connected to an absorbent / solvent I mixing device, and its bottom is connected to a liquid-solid phase separator; the liquid-solid phase separator includes a solid absorbent product outlet and a solvent I outlet, the solid absorbent product outlet is connected to an absorbent solid dissolution device, and the solvent I outlet is connected to an absorbent / solvent I mixing device.

[0021] The solvent II inlet of the absorbent solid phase dissolution device is connected to the absorbent / solvent II phase separation device, and its outlet is connected to the CO2 desorption tower; the top of the CO2 desorption tower is connected to the CO2 product gas outlet, and its bottom is connected to the absorbent / solvent II phase separation device; the absorbent outlet of the absorbent / solvent II phase separation device is connected to the absorbent / solvent I mixing device.

[0022] Flue gas and absorbent / solvent I mixture are introduced into the CO2 absorption tower for mixing, and then the mixture is introduced into a liquid-solid phase separator for liquid-solid phase separation to obtain solid absorbent product and solvent I. The solid absorbent product is introduced into the absorbent solid phase dissolution device, and solvent I is introduced into the absorbent / solvent I mixing device.

[0023] The solid-phase absorbent product is mixed with solvent II in an absorbent solid-phase dissolution device. The resulting absorbent-CO2 / solvent II mixture is then passed into a CO2 desorption tower for CO2 desorption, yielding CO2 product gas and the absorbent / solvent II mixture. The absorbent / solvent II mixture is then subjected to liquid-liquid phase separation in an absorbent / solvent II phase separation device. The resulting absorbent is passed into an absorbent / solvent I mixing device, while the resulting solvent II is passed into an absorbent solid-phase dissolution device. This allows for the effective recycling of the absorbent, solvent I, and solvent II, improving recycling efficiency and reducing energy consumption and costs.

[0024] Preferably, the absorbent solid-phase dissolution device and the CO2 desorption tower are equipped with heat exchangers; the heat exchangers are also connected to the absorbent / solvent II phase separation device and the absorbent / solvent I mixing device, respectively.

[0025] Preferably, the solvent II outlet of the absorbent / solvent II phase separation device is connected to the absorbent solid phase dissolution device and the reboiler, respectively; the reboiler is connected to the bottom of the CO2 desorption tower.

[0026] Preferably, a solvent I storage tank is provided between the liquid-solid phase separator and the absorbent / solvent I mixing device; and a solvent II storage tank is provided between the absorbent / solvent II phase separation device and the absorbent solid phase dissolution device.

[0027] Preferably, the operating temperature range of the CO2 absorption tower is 20–60°C; and the operating temperature range of the CO2 desorption tower is 80–130°C.

[0028] Preferably, the operating temperature range of the liquid-solid phase separator is 25–70°C, and the residence time is 0.5–5 min; the operating temperature range of the solid phase dissolution device is 30–80°C; and the heat exchanger has a heat exchange temperature difference range of 2–20°C.

[0029] Preferably, the top of the CO2 desorption tower is connected to condenser II, and the regenerated gas is condensed to obtain CO2 product gas, while the condensate is recycled into the CO2 desorption tower.

[0030] Preferably, the top of the CO2 absorption tower is connected to condenser I, and the condensed absorbent and solvent I mixture is returned to the CO2 absorption tower.

[0031] Preferably, the CO2 absorption tower is a packed tower; the solid-phase dissolution device is a stirred reactor or a static mixing reactor; the reboiler is a falling film reboiler or a thermosiphon reboiler; the absorbent / solvent I mixing device is a stirred reactor or a static mixing reactor; and the heat exchanger is a shell-and-tube type or a plate type.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) By designing a dual solvent circulation system, different organic solvents can circulate in the absorption tower and desorption tower, giving full play to the advantages of organic solvents such as fast CO2 absorption rate, high circulation capacity of CO2 enriched phase, and organic solvent purging to assist CO2 desorption, which is conducive to reducing carbon capture cost.

[0034] (2) This system can operate continuously, or it can be used to absorb and store absorbent products of CO2 or desorb CO2 products of CO2. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process flow of a phase change flue gas CO2 capture system based on a dual solvent cycle absorbent.

[0036] The attached diagram is labeled as follows: 1—Flue gas inlet; 2—CO2 absorption tower; 201—Flue gas outlet of absorption tower; 202—Absorbent liquid outlet of absorption tower; 3—Condenser I; 301—Flue gas after CO2 capture; 302—Absorbent / solvent I condensate; 4—Liquid-solid phase separator; 401—Solid absorbent product; 402—Solvent I; 4A—Solvent I storage tank; 402A—Solvent I entering Solvent I storage tank; 5—Solid phase dissolution device; 501—Absorbent-CO2 / solvent II mixture; 6—Absorbent / solvent I mixing device; 601—Absorbent / solvent I mixture; 7—Heat exchanger; 701—Absorbent after heating. 702—Absorbent after cooling; 8—CO2 desorption tower; 801—Regeneration gas; 802—Absorbent / solvent II mixture after CO2 desorption; 9—Condenser II; 901—CO2 product gas; 902—Absorbent / solvent II condensate; 10—Reboiler; 11—Absorbent / solvent II phase separation device; 11A—Solvent II storage tank; 1101—Solvent II; 1101A—Solvent II entering the Solvent II storage tank; 1101B—Solvent II entering the reboiler; 1101C—Solvent II heated by the reboiler; 1102—Absorbent. Detailed Implementation

[0037] The technical solution of the present invention is illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0038] General Implementation Examples

[0039] A phase change flue gas CO2 capture method based on a dual solvent cycle absorbent includes the following steps:

[0040] (1) The flue gas and absorbent / solvent I mixture are subjected to liquid-solid phase separation, wherein the mass percentage of absorbent and solvent I in the absorbent / solvent I mixture is 10%:90% to 50%:50%, to obtain solid phase absorbent product and solvent I.

[0041] (2) After mixing the solid absorbent product and solvent II, an absorbent-CO2 / solvent II mixture is obtained. The mass percentage of absorbent-CO2 and solvent II in the absorbent-CO2 / solvent II mixture is 50%:50%~90%:10%. Then CO2 desorption is performed to obtain CO2 product and absorbent / solvent II mixture.

[0042] (3) Perform liquid-liquid phase separation on the absorbent / solvent II mixture to obtain absorbent and solvent II;

[0043] (4) After mixing the solvent I obtained in step (1) with the absorbent in step (3) again, repeat step (1) to achieve the cycle; after mixing the solvent II in step (3) with the solid phase absorbent product obtained in step (1) again, repeat step (2) to achieve the cycle.

[0044] The absorbent is one or more of organic amines, amino acid salts, and ionic liquids, preferably one of ethylenediamine, tetramethylenediamine, diethylenetriamine, tetraethylenepentamine, piperazine, 2-amino-2-methyl-1-propanol, potassium taurate, potassium proline, and potassium sarcosinate; solvent I is one or more of 1,2-propanediol, 1,4-butanediol, ethylene glycol, polyethylene glycol, dimethyl sulfoxide, N,N-dimethylacetamide, and water; solvent II is one of pentane, hexane, cyclohexane, and n-heptane.

[0045] A phase change flue gas CO2 capture system based on a dual solvent cycle absorbent:

[0046] The system includes a CO2 absorption tower 2 and a CO2 desorption tower 8. CO2-containing flue gas enters the CO2 absorption tower 2 through the flue gas inlet 1 and mixes with the absorbent / solvent I mixture 601 introduced into the CO2 absorption tower 2 via the absorbent / solvent I mixing device 6. The top of the CO2 absorption tower 2 is connected to a condenser I 3. The flue gas exiting the absorption tower through the flue gas outlet 201 enters the condenser I 3 for condensation, resulting in CO2-captured flue gas 301 and absorbent / solvent I condensate 302. The absorbent / solvent I condensate 302 is then reintroduced into the CO2 absorption tower 2, while the CO2-captured flue gas 301 is discharged.

[0047] The bottom of CO2 absorption tower 2 is connected to liquid-solid separator 4. The absorbent liquid from the absorption tower outlet 202 enters the liquid-solid separator 4 for liquid-solid separation. After liquid-solid separation, solid absorbent product 401 and solvent I 402 are obtained. Solid absorbent product 402 is fed into absorbent solid phase dissolution device 5, and solvent I 402 is fed into solvent I storage tank 4A for storage. Then, solvent I 402A that has entered solvent I storage tank is fed into absorbent / solvent I mixing device 6.

[0048] Solid absorbent product 401 is mixed with solvent II 1101 introduced from absorbent / solvent II phase separation device 11 in absorbent solid dissolution device 5 to obtain absorbent-CO2 / solvent II mixture 501. This mixture is then passed into heat exchanger 7 to obtain heated absorbent-CO2 / solvent II mixture 701, which is then passed into CO2 desorption tower 8 for desorption. After desorption, regeneration gas 801 and absorbent / solvent II mixture 802 after CO2 desorption are obtained. Regeneration gas 801 is passed into condenser II 9 for condensation to obtain CO2 product gas 901 and absorbent / solvent II condensate 902. Absorbent / solvent II condensate 902 is then reintroduced into CO2 desorption tower 8. The absorbent / solvent II mixture 802 after CO2 desorption is introduced from the bottom of the CO2 desorption tower 8 into the absorbent / solvent II phase separation device 11. Liquid-liquid phase separation is carried out in the absorbent / solvent II phase separation device 11 to obtain absorbent 1102 and solvent II 1101. The absorbent 1102 is introduced into the heat exchanger 7 to obtain the cooled absorbent 702, which is then introduced into the absorbent / solvent I mixing device 6 for mixing. Finally, the resulting absorbent / solvent I mixture 601 is introduced back into the CO2 absorption tower 2 to achieve circulation.

[0049] The solvent II1101 obtained in the absorbent / solvent II phase separation device 11 will be divided into two parts. One part, solvent II1101A, will be stored in the solvent II storage tank 11A. The solvent II1101A that has entered the solvent II storage tank will be fed into the absorbent solid phase dissolution device 5 to mix with the solid phase absorbent product 401. The other part, solvent II1101B, will be fed into the reboiler 10 to obtain solvent II1101C heated by the reboiler, which will then be fed into the CO2 desorption tower 8.

[0050] The operating temperature range of the CO2 absorption tower is 20–60℃; the operating temperature range of the CO2 desorption tower is 80–130℃; the operating temperature range of the liquid-solid phase separator is 25–70℃, and the residence time is 0.5–5 min; the operating temperature range of the solid phase dissolution device is 30–80℃; and the heat exchange temperature difference range of the heat exchanger is 2–20℃.

[0051] The CO2 absorption tower is a packed tower; the solid phase dissolution device is either a stirred reactor or a static mixing reactor; the reboiler is either a falling film reboiler or a thermosiphon reboiler; the absorbent / solvent I mixing device is either a stirred reactor or a static mixing reactor; and the heat exchanger is either a shell-and-tube type or a plate type.

[0052] Example 1

[0053] In a phase change flue gas CO2 capture method based on absorbent dual solvent circulation, the absorbent used is diethylenetriamine, solvent I is a mixture of polyethylene glycol and water, and solvent II is pentane.

[0054] like Figure 1 As shown, the system used in the above method includes a CO2 absorption tower 2 and a CO2 desorption tower 8. CO2-containing flue gas enters from the flue gas inlet 1 of the CO2 absorption tower 2 and mixes with the absorbent / solvent I mixture 601 introduced into the CO2 absorption tower 2 via the absorbent / solvent I mixing device 6. The top of the CO2 absorption tower 2 is connected to a condenser I 3. The flue gas exiting from the absorption tower flue gas outlet 201 enters the condenser I 3 for condensation, resulting in CO2-captured flue gas 301 and absorbent / solvent I condensate 302. The absorbent / solvent I condensate 302 is then reintroduced into the CO2 absorption tower 2, while the CO2-captured flue gas 301 is discharged.

[0055] The bottom of CO2 absorption tower 2 is connected to liquid-solid separator 4. The absorbent liquid from the absorption tower outlet 202 enters the liquid-solid separator 4 for liquid-solid separation. After liquid-solid separation, solid absorbent product 401 and solvent I 402 are obtained. Solid absorbent product 402 is fed into absorbent solid phase dissolution device 5, and solvent I 402 is fed into solvent I storage tank 4A for storage. Then, solvent I 402A that has entered solvent I storage tank is fed into absorbent / solvent I mixing device 6.

[0056] Solid absorbent product 401 is mixed with solvent II 1101 introduced from absorbent / solvent II phase separation device 11 in absorbent solid dissolution device 5 to obtain absorbent-CO2 / solvent II mixture 501. This mixture is then passed into heat exchanger 7 to obtain heated absorbent-CO2 / solvent II mixture 701, which is then passed into CO2 desorption tower 8 for desorption. After desorption, regeneration gas 801 and absorbent / solvent II mixture 802 after CO2 desorption are obtained. Regeneration gas 801 is passed into condenser II 9 for condensation to obtain CO2 product gas 901 and absorbent / solvent II condensate 902. Absorbent / solvent II condensate 902 is then reintroduced into CO2 desorption tower 8. The absorbent / solvent II mixture 802 after CO2 desorption is introduced from the bottom of the CO2 desorption tower 8 into the absorbent / solvent II phase separation device 11. Liquid-liquid phase separation is carried out in the absorbent / solvent II phase separation device 11 to obtain absorbent 1102 and solvent II 1101. The absorbent 1102 is introduced into the heat exchanger 7 to obtain the cooled absorbent 702, which is then introduced into the absorbent / solvent I mixing device 6 for mixing. Finally, the resulting absorbent / solvent I mixture 601 is introduced back into the CO2 absorption tower 2 to achieve circulation.

[0057] The solvent II1101 obtained in the absorbent / solvent II phase separation device 11 will be divided into two parts. One part, solvent II1101A, will be stored in the solvent II storage tank 11A. The solvent II1101A that has entered the solvent II storage tank will be fed into the absorbent solid phase dissolution device 5 to mix with the solid phase absorbent product 401. The other part, solvent II1101B, will be fed into the reboiler 10 to obtain solvent II1101C heated by the reboiler, which will then be fed into the CO2 desorption tower 8.

[0058] The CO2 absorption tower 2 operates at 40℃. In the absorbent / solvent I mixture 601, the mass concentration ratio of diethylenetriamine, polyethylene glycol, and water is 30%:60%:10%, and the CO2 absorption capacity is 2.4 mol / L. The liquid-solid phase separator 4 operates at 50℃ with a residence time of 5 min. The solid phase dissolution device 5 operates at 30℃. In the absorbent-CO2 / solvent II mixture 701 after heating, the mass concentration ratio of diethylenetriamine-CO2 and pentane is 50%:50%. The CO2 desorption tower 8 operates at 90℃. The absorbent / solvent II phase separation device 11 operates at 80℃. The heat exchange temperature difference of the heat exchanger 10 is 10℃.

[0059] Example 2

[0060] The difference from Example 1 is that the absorbent used is triethylenetetramine, solvent I is 1,2-propanediol, and solvent II is pentane.

[0061] The CO2 absorption tower 2 operates at 40℃. In the absorbent / solvent I mixture 601, the mass concentration ratio of triethylenetetramine to 1,2-propanediol is 20%:80%, and the CO2 absorption capacity is 1.90 mol / L. The liquid-solid phase separator 4 operates at 50℃ with a residence time of 5 min. The solid phase dissolution device 5 operates at 30℃. In the absorbent-CO2 / solvent II mixture 701 after heating, the mass concentration ratio of triethylenetetramine-CO2 to pentane is 80%:20%. The CO2 desorption tower 8 operates at 87℃. The absorbent / solvent II phase separation device 11 operates at 80℃. The heat exchange temperature difference of the heat exchanger 10 is 10℃.

[0062] Example 3

[0063] The difference from Example 1 is that the absorbent used is potassium proline, solvent I is ethylene glycol and water, and solvent II is hexane.

[0064] The CO2 absorption tower 2 operates at 40℃. In the absorbent / solvent I mixture 601, the mass concentration ratio of potassium proline, ethylene glycol, and water is 30%:60%:10%, and the CO2 absorption capacity is 2.7 mol / L. The liquid-solid phase separator 4 operates at 45℃ with a residence time of 5 min. The solid phase dissolution device 5 operates at 50℃. In the absorbent-CO2 / solvent II mixture 701 after heating, the mass concentration ratio of potassium proline, CO2, and hexane is 70%:30%. The CO2 desorption tower 8 operates at 95℃. The absorbent / solvent II phase separation device 11 operates at 60℃. The heat exchanger 10 has a heat exchange temperature difference of 15℃.

[0065] Comparative Example 1

[0066] A conventional CO2 desorption process was used (using the same CO2 absorption tower and CO2 desorption tower as in Examples 1-3).

[0067] Flue gas is introduced into the CO2 absorption tower, followed by a mixture of absorbent / solvent I for CO2 absorption. The product exiting the CO2 absorption tower is mixed with solvent II and then introduced into a CO2 desorption tower for CO2 desorption. The absorbent / solvent II mixture is heated, and the resulting steam is used to heat the CO2 desorption tower, providing heat for the CO2 desorption process. CO2 product gas is obtained, and the absorbent is separated and returned to the CO2 absorption tower for reuse.

[0068] The absorbent used is monoethanolamine, and solvents I and II are both water. In the absorbent / solvent I mixture, the mass concentration ratio of monoethanolamine to water is 30%:70%. The mass concentration ratio of the product exiting the CO2 absorption tower to solvent II is 70%:30%. No phase separation occurs during either the CO2 absorption or desorption process. The operating temperature of the CO2 absorption tower is 40℃, and the operating temperature of the CO2 desorption tower is 105℃.

[0069] Table 1

[0070]

[0071] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A phase change flue gas CO2 capture method based on a dual-solvent cycle absorbent, characterized in that, The steps include: (1) The flue gas and absorbent / solvent I mixture are subjected to liquid-solid phase separation. The absorbent is one or more of organic amine, amino acid salt, and ionic liquid. The solvent I is one or more of 1,2-propanediol, 1,4-butanediol, ethylene glycol, polyethylene glycol, dimethyl sulfoxide, N,N-dimethylacetamide, and water to obtain solid phase absorbent product and solvent I. (2) After mixing the solid absorbent product and solvent II, solvent II is one of pentane, hexane, cyclohexane and n-heptane to obtain absorbent-CO2 / solvent II mixture; then CO2 desorption is performed to obtain CO2 product and absorbent / solvent II mixture. (3) Perform liquid-liquid phase separation on the absorbent / solvent II mixture to obtain absorbent and solvent II; (4) After mixing the solvent I obtained in step (1) with the absorbent in step (3) again, repeat step (1) to achieve the cycle; after mixing the solvent II in step (3) with the solid absorbent product obtained in step (1) again, repeat step (2) to achieve the cycle.

2. The phase change flue gas CO2 capture method based on dual solvent circulation of absorbent as described in claim 1, characterized in that, The absorbent is one of the following: ethylenediamine, tetramethylenediamine, diethylenetriamine, tetraethylenepentamine, piperazine, 2-amino-2-methyl-1-propanol, potassium taurate, potassium proline, and potassium sarcosinate.

3. The phase change flue gas CO2 capture method based on dual solvent circulation of absorbent as described in claim 2, characterized in that, The combination of absorbent and solvent I is as follows: diethylenetriamine and polyethylene glycol-water, ethylenediamine and polyethylene glycol, piperazine and 1,2-propanediol, tetramethylenediamine and 1,4-butanediol, piperazine and N,N-dimethylacetamide, diethylenetriamine and polyethylene glycol, potassium proline and ethylene glycol-water or potassium sarcosinate and 1,4-butanediol-water.

4. The phase change flue gas CO2 capture method based on dual solvent circulation of absorbent as described in claim 1, characterized in that, Solvent II is one of pentane and hexane.

5. The phase change flue gas CO2 capture method based on dual solvent circulation of absorbent as described in claim 1, characterized in that, In step (1), the mass percentage of absorbent and solvent I in the absorbent / solvent I mixture is 10%:90%~50%:50%; in step (2), the mass percentage of absorbent-CO2 and solvent II in the absorbent-CO2 / solvent II mixture is 50%:50%~90%:10%.

6. A phase change flue gas CO2 capture system based on a dual-solvent absorption agent cycle using the method described in any one of claims 1-5, characterized in that, The system includes a CO2 absorption tower and a CO2 desorption tower; The CO2 absorption tower includes a flue gas inlet, and its top is connected to the absorbent / solvent I mixing device, and its bottom is connected to the liquid-solid phase separator; the liquid-solid phase separator includes a solid absorbent product outlet and a solvent I outlet, the solid absorbent product outlet is connected to the absorbent solid dissolution device, and the solvent I outlet is connected to the absorbent / solvent I mixing device. The solvent II inlet of the absorbent solid-phase dissolution device is connected to the absorbent / solvent II phase separation device, and its outlet is connected to the CO2 desorption tower. The top of the CO2 desorption tower is connected to the CO2 product gas outlet, and its bottom is connected to the absorbent / solvent II phase separation device. The absorbent outlet of the absorbent / solvent II phase separation device is connected to the absorbent / solvent I mixing device. The absorbent solid-phase dissolution device and the CO2 desorption tower are equipped with heat exchangers. The heat exchangers are also connected to the absorbent / solvent II phase separation device and the absorbent / solvent I mixing device, respectively. The solvent II outlet of the absorbent / solvent II phase separation device is connected to the absorbent solid-phase dissolution device and the reboiler, respectively. The reboiler is connected to the bottom of the CO2 desorption tower.

7. The phase change flue gas CO2 capture system based on dual solvent circulation of absorbent as described in claim 6, characterized in that, A solvent I storage tank is also provided between the liquid-solid phase separator and the absorbent / solvent I mixing device; a solvent II storage tank is also provided between the absorbent / solvent II phase separation device and the absorbent solid phase dissolution device.

8. The phase change flue gas CO2 capture system based on dual solvent circulation of absorbent as described in claim 6, characterized in that, The operating temperature range of the CO2 absorption tower is 20~60℃; the operating temperature range of the CO2 desorption tower is 80~130℃.

9. The phase change flue gas CO2 capture system based on dual solvent circulation of absorbent as described in claim 6 or 8, characterized in that, The operating temperature range of the liquid-solid phase separator is 25~70℃, and the residence time is 0.5~5min; the operating temperature range of the solid phase dissolution device is 30~80℃.

10. The phase change flue gas CO2 capture system based on a dual-solvent absorption agent cycle as described in claim 6 or 8, characterized in that, The top of the CO2 desorption tower is connected to condenser II, and the regenerated gas is condensed to obtain CO2 product gas. The condensate is recycled back into the CO2 desorption tower. The top of the CO2 absorption tower is connected to condenser I, and the condensed absorbent and solvent I mixture is sent back to the CO2 absorption tower.

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