Method for capturing carbon dioxide

Abstract

This invention relates to the field of carbon dioxide capture technology and discloses a method for capturing carbon dioxide: 1. Raw gas is introduced from the bottom of an absorption tower and comes into contact with absorbent liquid I fed from the middle of the absorption tower for a first-stage absorption, resulting in a first-stage treated gas and rich liquid I; the first-stage treated gas comes into contact with absorbent liquid II fed from the top of the absorption tower for a second-stage absorption, resulting in a coarsely purified gas and rich liquid II; the concentration of absorbent in absorbent liquid I is lower than that in absorbent liquid II; 2. Rich liquid I is pressurized and then heat-exchanged through a first heat exchanger before being introduced into the middle section of a regeneration tower for a first-stage regeneration, resulting in lean liquid I and a first-stage regeneration gas; 3. Rich liquid II is heat-exchanged sequentially through a second and a third heat exchanger before being introduced into the upper section of the regeneration tower for a second-stage regeneration, resulting in lean liquid II and a second-stage regeneration gas; 4. The second-stage regeneration gas is separated to obtain carbon dioxide. The method provided by this invention can reduce absorbent loss and regeneration energy consumption while ensuring the carbon dioxide capture effect.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture, and more specifically to a method for capturing carbon dioxide. Background Technology

[0002] With the accelerated advancement of carbon emission reduction efforts, the research, development, utilization, and storage (CCUS) technology has received increasing attention from major countries. Since flue gas generated from the combustion of various fossil fuels is one of the main sources of carbon dioxide emissions, carbon dioxide capture technology from flue gas has attracted widespread attention across various industries.

[0003] Currently, chemical absorption is the most mature method in the field of flue gas carbon dioxide capture, but its high capture cost limits its further promotion. The loss of the absorption solvent and the energy consumption for regeneration are significant components of this cost. Therefore, reducing the loss of the absorption solvent and the energy consumption for regeneration during chemical absorption flue gas carbon capture has become a hot research topic in this field.

[0004] In the chemical absorption method for flue gas carbon capture, degradation is one of the main causes of absorbent solvent loss. Because the absorbent solvents used are generally highly concentrated, oxidative degradation reactions inevitably occur when they come into countercurrent contact with oxygen in the flue gas. Reducing the solvent concentration can effectively control oxidative degradation, but this often affects the carbon capture efficiency of the flue gas and also adversely impacts regeneration energy consumption. Furthermore, high-concentration absorbents, due to their high boiling points, also exacerbate thermal degradation of the system during regeneration.

[0005] CN101524621B discloses a staged absorption and regeneration flue gas decarbonization system, belonging to the field of clean coal technology. The system consists of two main parts: an adsorption system and a regeneration system. The adsorption system includes a rich solution tank, an absorption tower, packing material, a demister, and two lean solution inlets; the regeneration system includes a regeneration tower, a lean solution tank, two accumulation tanks, a demister, a solution boiler, and a regeneration gas cooler. This device employs a novel two-stage absorption and staged regeneration technology, adapting to the absorption characteristics of the absorbent, significantly optimizing the system, reducing regeneration energy and electricity consumption, and is suitable for decarbonization in coal-fired power plants and the chemical industry.

[0006] CN117244383A discloses a carbon dioxide removal system for flue gas, comprising: an absorption system including an absorption tower, the absorption tower having a bottom, a packing section, and a liquid distributor, and a liquid inlet device and a demister at the top; a regeneration system including a regeneration tower, the regeneration tower having a bottom and a reboiler at the bottom, a packing section, a liquid distributor, and a redistributor in the middle, and a liquid inlet device and an acid gas cooler at the top; a heat exchange system; a decarbonizing agent collection system having a bottom, an absorbent tank, a packing washing section, and a liquid distributor in the middle, and a liquid inlet device and a demister at the top; pumps including a variable frequency pump, a liquid booster pump, and a lean liquid pump; and a control system. This invention, by setting up multiple absorption towers and collecting the rich liquid from each tower separately, and by installing a liquid redistributor after the absorption section height exceeds 1 meter, reduces the absorption tower height and improves the contact and reaction effect between the decarbonizing absorbent and carbon dioxide in the flue gas.

[0007] CN217410281U provides a flue gas decarbonization system using an alcohol amine method. The system includes an absorption unit, a heat exchange unit, and a solution regeneration unit connected in sequence. The absorption unit includes an absorption tower, which, from bottom to top, comprises a rich solution zone, a first absorption zone, a first collection zone, a second absorption zone, and a demisting zone. This system utilizes alcohol amine solutions with different regeneration levels in the first and second absorption zones of the absorption tower to perform staged absorption of CO2 in the flue gas. This effectively reduces the circulation volume of the regenerated alcohol amine solution, thereby reducing the energy consumption of the flue gas decarbonization system and making it suitable for large-scale application.

[0008] Although existing patents propose various staged absorption and staged regeneration processes for the chemical absorption method of flue gas carbon dioxide capture, they can only reduce regeneration energy consumption and enhance the absorption process. The concentration of absorbent used is exactly the same, and they cannot reduce absorbent loss. Summary of the Invention

[0009] The purpose of this invention is to solve the problems of high absorbent loss and high regeneration energy consumption in the chemical capture of carbon dioxide, and to provide a carbon dioxide capture method that has the advantages of good carbon dioxide capture effect, low absorbent loss and low energy consumption.

[0010] To achieve the above objectives, the present invention provides a method for capturing carbon dioxide, wherein the method includes the following steps:

[0011] (1) The raw gas containing carbon dioxide is introduced into the absorption tower from the bottom of the absorption tower and comes into contact with the absorbent liquid I fed from the middle of the absorption tower to carry out a first-stage absorption, and a first-stage treated gas and rich liquid I are obtained.

[0012] The first-stage treated gas comes into contact with absorbent liquid II fed from the top of the absorption tower for second-stage absorption, resulting in crude purified gas and rich liquid II; wherein, the concentration of absorbent in absorbent liquid I is lower than the concentration of absorbent in absorbent liquid II; the crude purified gas comes into contact with washing water for washing, resulting in purified gas.

[0013] (2) After the rich liquid I is pressurized and heat-exchanged by the first heat exchanger, it is introduced into the middle section of the regeneration tower for a first-stage regeneration to obtain lean liquid I and a first-stage regeneration gas; wherein, the lean liquid I is returned to step (1) as the absorbent liquid I after being heat-exchanged by the first heat exchanger and the second heat exchanger in sequence.

[0014] (3) The rich liquid II is introduced into the upper section of the regeneration tower after being heat-exchanged by the second heat exchanger and the third heat exchanger in sequence for two-stage regeneration to obtain lean liquid II and two-stage regeneration gas; wherein, the lean liquid II is returned to step (1) as the absorbent liquid II after being heat-exchanged by the third heat exchanger and the first condenser in sequence.

[0015] (4) The two-stage regeneration gas is introduced into the regeneration gas separator for cooling and separation to obtain water and carbon dioxide.

[0016] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0017] 1) The carbon dioxide capture method provided by the present invention uses absorbents with different absorbent concentrations to capture carbon dioxide in raw gas (e.g., flue gas) containing carbon dioxide, and then regenerates and circulates the captured rich liquid. This can effectively reduce the residence time of the absorbent, avoid oxidative degradation and thermal degradation of the absorbent as much as possible, and improve the thermal efficiency of the regeneration process. Thus, while ensuring the carbon dioxide capture effect, the loss of absorbent and regeneration energy consumption are reduced as much as possible.

[0018] 2) The carbon dioxide capture method provided by the present invention uses a low-concentration absorbent to contact the raw gas, which can capture most of the carbon dioxide in the raw gas, helps to inhibit the oxidative degradation of the absorbent, and regenerates this rich liquid separately, which can effectively reduce the regeneration temperature of this rich liquid during regeneration, help to reduce the probability of thermal degradation of the absorbent, and thus reduce the loss of the absorbent.

[0019] 3) The carbon dioxide capture method provided by the present invention uses a high-concentration absorbent to contact the raw gas (i.e., the first-stage processing gas) that has already been in contact with a low-concentration absorbent, which can further improve the carbon dioxide capture effect.

[0020] 4) The carbon dioxide capture method provided by the present invention adopts a two-stage regeneration process in the regeneration tower. The first-stage regeneration gas from the first-stage regeneration process can enter the second-stage regeneration process to play a stripping role, which helps to reduce the energy consumption of the regeneration process. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the carbon dioxide capture method in an embodiment of the present invention;

[0022] Figure 2 This is a process flow diagram of the carbon dioxide capture method in the comparative example of the present invention.

[0023] Explanation of reference numerals in the attached figures

[0024] 1. Pretreatment tower; 2. Pretreatment pump; 3. Pretreatment cooler

[0025] 4. Fan; 5. Absorber tower; 6. Absorbent liquid pump.

[0026] 7. Absorbent II pump; 8. Washing pump; 9. Washing water cooler.

[0027] 10. Rich liquid pump I; 11. First heat exchanger; 12. Regeneration tower

[0028] 13. Second heat exchanger; 14. Rich liquid II pump; 15. Third heat exchanger

[0029] 16, First condenser; 17, Second condenser; 18, Regeneration gas separator

[0030] S101, raw material gas; S102, absorbent liquid I; S103, absorbent liquid II

[0031] S104, purified gas; S105, carbon dioxide; S106, water. Detailed Implementation

[0032] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] This invention provides a method for capturing carbon dioxide, wherein the method includes the following steps:

[0034] (1) The raw gas containing carbon dioxide is introduced into the absorption tower from the bottom of the absorption tower and comes into contact with the absorbent liquid I fed from the middle of the absorption tower to carry out a first-stage absorption, and a first-stage treated gas and rich liquid I are obtained.

[0035] The first-stage treated gas comes into contact with absorbent liquid II fed from the top of the absorption tower for second-stage absorption, resulting in crude purified gas and rich liquid II; wherein, the concentration of absorbent in absorbent liquid I is lower than the concentration of absorbent in absorbent liquid II; the crude purified gas comes into contact with washing water for washing, resulting in purified gas.

[0036] (2) After the rich liquid I is pressurized and heat-exchanged by the first heat exchanger, it is introduced into the middle section of the regeneration tower for a first-stage regeneration to obtain lean liquid I and a first-stage regeneration gas; wherein, the lean liquid I is returned to step (1) as the absorbent liquid I after being heat-exchanged by the first heat exchanger and the second heat exchanger in sequence.

[0037] (3) The rich liquid II is introduced into the upper section of the regeneration tower after being heat-exchanged by the second heat exchanger and the third heat exchanger in sequence for two-stage regeneration to obtain lean liquid II and two-stage regeneration gas; wherein, the lean liquid II is returned to step (1) as the absorbent liquid II after being heat-exchanged by the third heat exchanger and the first condenser in sequence.

[0038] (4) The two-stage regeneration gas is introduced into the regeneration gas separator for cooling and separation to obtain water and carbon dioxide.

[0039] In this invention, the inventors discovered through research that employing a two-stage absorption process in the absorption tower—that is, the feed gas first contacts a low-concentration absorbent liquid I, and then contacts a high-concentration absorbent liquid II—can minimize oxidative and thermal degradation of the absorbent while ensuring effective carbon dioxide capture, significantly reducing absorbent loss. Similarly, employing a two-stage regeneration process in the regeneration tower—that is, regenerating rich liquid I and rich liquid II separately—not only helps to slow down thermal degradation during regeneration but also allows for the comprehensive utilization of the heat from rich liquid I and rich liquid II, further reducing the energy consumption for absorbent regeneration.

[0040] In step (1):

[0041] In a preferred embodiment of the present invention, the carbon dioxide content in the raw material gas is 2-40 v%, preferably 5-20 v%, and more preferably 10-15 v%. The present invention does not specifically limit the type of raw material gas containing carbon dioxide; for example, the raw material gas can be flue gas emitted from industries such as petrochemicals, steel, cement, and power generation.

[0042] In a preferred embodiment of the present invention, before introducing the raw gas into the absorption tower, the raw gas is first introduced into a pretreatment tower to contact with an alkaline solution (an alkaline solution known in the art, such as an aqueous solution of sodium hydroxide and / or sodium carbonate) for impurity removal and cooling. In this invention, the pretreatment tower is used to cool the raw gas to a suitable absorption temperature and further reduce the content of strongly acidic impurities such as SO2, SO3, and NO2 in the raw gas.

[0043] In a preferred embodiment of the present invention, the operating conditions of the pretreatment tower include: a gas-liquid ratio of 100-600:1, preferably 200-400:1; and a feed temperature of alkali solution of 20-60℃, preferably 40-45℃. Unless otherwise specified, in this invention, the gas-liquid ratio refers to the ratio, by volume, between the amount of gas flowing through per unit time and the amount of liquid sprayed per unit time.

[0044] In a preferred embodiment of the present invention, the temperature of the raw gas after treatment by the pretreatment tower is 20-60°C, preferably 30-50°C.

[0045] In a preferred embodiment of the present invention, absorbent I and absorbent II are each an aqueous solution of an absorbent; wherein the absorbent in absorbent I and absorbent II are each selected from organic amines.

[0046] This invention does not specifically limit the organic amines used; any organic amine commonly found in the art can be used in this invention. For example, the organic amine can be one or more of monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), N-methyldiethanolamine (MDEA), diethylenetriamine (DETA), triethylenetetramine (TETA), piperazine, hydroxyethylpiperazine, 2-amino-2-methyl-1-propanol (AMP), diethylaminoethanol, N-ethyldiethanolamine, and 3-diethylamino-1-propanol. More preferably, the absorbent in absorbent liquid I and absorbent liquid II is the same.

[0047] In a preferred embodiment of the present invention, the concentration of the absorbent in the absorbent liquid I is 5-15 wt%, for example, it can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, or any value within any two of the above ranges, preferably 8-12 wt%.

[0048] In a preferred embodiment of the present invention, the operating conditions of the first-stage absorption include: the feed temperature of the absorbent liquid I is 40-70°C, preferably 50-60°C; and the gas-liquid ratio of the first-stage absorption is 200-500:1, preferably 300-400:1.

[0049] In a preferred embodiment of the present invention, the concentration of the absorbent in absorbent liquid I is 10-40 wt% lower than the concentration of the absorbent in absorbent liquid II, for example, 10 wt%, 12.5 wt%, 15 wt%, 17.5 wt%, 20 wt%, 22.5 wt%, 25 wt%, 27.5 wt%, 30 wt%, 32.5 wt%, 35 wt%, 37.5 wt%, 40 wt%, and any value within any two of these ranges, preferably 20-30 wt% lower.

[0050] In this invention, the inventors discovered that a large difference between the concentrations of the absorbent in absorbent liquid I and absorbent liquid II affects the removal efficiency of carbon dioxide from the feed gas; a small difference fails to achieve the effects of multi-stage absorption and regeneration, tending towards single-stage absorption and regeneration. When the concentration difference between the absorbent in absorbent liquid I and absorbent liquid II is within the aforementioned defined range, especially the preferred range, the removal efficiency of carbon dioxide from the feed gas is better, the absorbent loss is smaller, and the reduction in regeneration energy consumption is more significant.

[0051] In a preferred embodiment of the present invention, the concentration of the absorbent in the absorbent liquid II is 25-45 wt%, for example, it can be 25 wt%, 27.5 wt%, 30 wt%, 32.5 wt%, 35 wt%, 37.5 wt%, 40 wt%, 42.5 wt%, 45 wt%, or any value within any two of these ranges, preferably 30-40 wt%.

[0052] In a preferred embodiment of the present invention, the operating conditions for the two-stage absorption include: the feed temperature of the absorbent II is 30-50°C, preferably 35-45°C; and the gas-liquid ratio of the two-stage absorption is 400-800:1, preferably 500-700:1. The amount of gas in the gas-liquid ratio of the two-stage absorption is calculated based on the amount of raw material gas.

[0053] In a preferred embodiment of the present invention, the washing operation conditions include: the feed temperature of the washing liquid is 30-50°C, preferably 35-45°C, and the gas-liquid ratio of the washing section is 200-600:1, preferably 300-500:1.

[0054] In this invention, the amount of gas in the gas-liquid ratio of the washing section is calculated based on the amount of raw material gas. The washing water can further recover the absorbent entrained in the crude purified gas, helping to further reduce absorbent loss.

[0055] In step (2):

[0056] In a preferred embodiment of the present invention, the pressure of the rich liquid I after pressurization is 0.2-0.5 MPa, preferably 0.3-0.4 MPa.

[0057] In a preferred embodiment of the present invention, the temperature of the rich liquid I after pressurization and heat exchange through the first heat exchanger is 85-110°C, preferably 90-105°C.

[0058] In a preferred embodiment of the present invention, the operating conditions for the first stage of regeneration include: a first stage regeneration pressure of 10-200 kPa, preferably 50-100 kPa.

[0059] In a preferred embodiment of the present invention, the temperature of the lean liquid I after heat exchange with the first heat exchanger is 50-80°C, preferably 55-75°C.

[0060] In this invention, lean solution I carries a large amount of heat. By using lean solution I to exchange heat with rich solution I and rich solution II in sequence, rich solution I and rich solution II can be preheated before regeneration, which is beneficial to make full use of the heat in lean solution I and reduce regeneration energy consumption.

[0061] In step (3):

[0062] In a preferred embodiment of the present invention, the temperature of the rich liquid II after heat exchange in the second heat exchanger is 45-75°C, preferably 50-70°C; and the temperature after heat exchange in the third heat exchanger is 80-105°C, preferably 85-100°C.

[0063] In a preferred embodiment of the present invention, the operating conditions for the two-stage regeneration include: the two-stage regeneration pressure is 10-150 kPa, preferably 30-100 kPa.

[0064] In a preferred embodiment of the present invention, the temperature of the lean liquid II after heat exchange with the third heat exchanger is 45-80°C, preferably 50-75°C.

[0065] In step (4):

[0066] In a preferred embodiment of the present invention, the second-stage regeneration gas is condensed to 30-50°C, preferably 35-45°C, by a second condenser before entering the regeneration gas separator.

[0067] In a preferred embodiment of the present invention, the operating conditions of the regenerated gas separator include: a separation temperature of 30-50°C, preferably 35-45°C; and a separation pressure of 5-145 kPa, preferably 40-90 kPa.

[0068] In a preferred embodiment of the present invention, the water is divided into at least part A and part B. Part A is returned to absorbent liquid I in step (1), and part B is returned to absorbent liquid II in step (2). In this invention, adding part A and part B to absorbent liquid I and absorbent liquid II respectively helps to maintain a stable absorbent concentration in the absorbent liquid.

[0069] In a preferred embodiment of the present invention, the mass ratio of part A to part B is 1-5:1, preferably 2-4:1.

[0070] In a preferred embodiment of the present invention, the carbon dioxide capture method operates stably with the following steps:

[0071] (1) The raw gas containing carbon dioxide (S101) enters the pretreatment tower 1 and comes into contact with the alkaline solution pumped in by the pretreatment pump 2 and cooled by the pretreatment cooler 3 to perform pretreatment. After removing the strong acid components in the raw gas and cooling it down, it is taken out from the top of the pretreatment tower 1.

[0072] The raw gas drawn from the top of the pretreatment tower 1 is transported by the blower 4 to the bottom of the absorption tower 5 and enters the absorption tower 5; the absorbent liquid I (S102) is pumped by the absorbent liquid I pump 6 to the second heat exchanger 13 for heat exchange and then enters the absorption tower 5 from the middle. The raw gas and the absorbent liquid I come into contact in the middle and lower part of the absorption tower 5 for a first-stage absorption, resulting in a first-stage treated gas and rich liquid I.

[0073] The first-stage gas enters the upper section of the absorption tower 5 through the gas lift cap. The absorption liquid II (S103) is pumped to the first condenser 16 by the absorption liquid II pump 7 and cooled. It then enters the absorption tower 5 from the top. The first-stage gas and the absorption liquid II come into contact in the middle and upper part of the absorption tower 5 for second-stage absorption, resulting in crude purified gas and rich liquid II.

[0074] The crude purified gas continues to rise and enters the washing section set at the top of the absorption tower 5, where it comes into contact with the washing water pumped in by the water washing pump 8 and cooled by the water washing water cooler 9, and is washed to obtain purified gas (S104). The obtained purified gas is directly discharged.

[0075] (2) Rich liquid I is drawn from the bottom of the absorption tower 5, pressurized by the rich liquid I pump 10, and then enters the first heat exchanger 11 for heat exchange. After heat exchange, it enters the regeneration tower 12 from the middle section for first-stage regeneration to obtain lean liquid I and first-stage regeneration gas. The obtained lean liquid I first enters the first heat exchanger 11, and after heat exchange, it is mixed with absorbent I (S102). It is then pumped into the second heat exchanger 13 by absorbent I pump 6, and after heat exchange, it returns to the middle section of the absorption tower 5 for recycling. The obtained first-stage regeneration gas enters the upper section of the regeneration tower 5 through the gas riser and participates in the subsequent second-stage regeneration.

[0076] (3) Rich liquid II is drawn from the collection plate in the middle section of the absorption tower 5 and enters the second heat exchanger 13. After heat exchange, it is pumped to the third heat exchanger 15 by the rich liquid II pump 14. After heat exchange, it enters the regeneration tower 12 from the upper section of the regeneration tower 12 for two-stage regeneration to obtain lean liquid II and second-stage regeneration gas. The obtained lean liquid II enters the third heat exchanger 15. After heat exchange, it is mixed with absorbent liquid II (S103) and pumped to the first condenser 16 by the absorbent liquid II pump 7. After cooling, it is returned to the upper part of the absorption tower 5 for recycling.

[0077] (4) The second-stage regeneration gas, after being cooled by the second condenser 17, enters the regeneration gas separator 18 for separation, yielding water and carbon dioxide (S105). The obtained carbon dioxide is sent to the subsequent process, while the obtained water is divided into part A and part B. Part A is returned to the section before absorbent liquid I pump 6, and part B is returned to the section before absorbent liquid II pump 7. Figure 1 As shown.

[0078] In this invention, the carbon dioxide capture method employs a multi-stage process in both absorption and regeneration. The absorption process utilizes multiple absorbent solutions with different absorbent concentrations. Preferably, two absorbent solutions with different absorbent concentrations are used for a two-stage absorption and two-stage regeneration process. Specifically, after the feed gas (e.g., flue gas) enters the absorption tower, it is first absorbed in the lower section using a low-concentration absorbent solution (i.e., absorbent solution I), and then enters the upper section of the absorption tower where it is further absorbed using a high-concentration absorbent solution (i.e., absorbent solution II). Finally, after the entrained absorbent is recovered in the washing section at the top of the absorption tower, the gas is discharged from the top of the absorption tower. After absorbing carbon dioxide, the low-concentration absorbent is transformed into a low-concentration rich liquid (i.e., rich liquid I). It is drawn from the bottom of the absorber, pressurized, and the heat of the low-concentration lean liquid (i.e., lean liquid I) is recovered before entering the lower section of the regeneration tower. Heat is provided by the reboiler in the bottom of the regeneration tower to regenerate the low-concentration rich liquid. The regenerated low-concentration lean liquid first recovers heat through the low-concentration lean-rich liquid heat exchanger (i.e., the first heat exchanger), and then exchanges heat with the high-concentration rich liquid (i.e., rich liquid II) (in the second heat exchanger) before entering the lower section of the absorber tower. The high-concentration rich liquid is drawn from the collection tray in the middle section of the absorption tower. It first exchanges heat with the low-concentration lean liquid (in the second heat exchanger), and then recovers the heat of the high-concentration lean liquid through the high-concentration lean-rich liquid heat exchanger (i.e., the third heat exchanger) before entering the upper section of the regeneration tower. It is then regenerated by the gas stripping obtained from the regeneration of the low-concentration rich liquid in the lower section of the regeneration tower. The resulting high-concentration lean liquid (i.e., lean liquid II) first recovers heat through the high-concentration lean-rich liquid heat exchanger, and then cools through the high-concentration lean liquid cooler before entering the upper section of the absorption tower.

[0079] The present invention will be described in detail below through embodiments. The embodiments are described in detail below. Figure 1 The carbon dioxide capture system shown was used. A comparative example was conducted in... Figure 2The carbon dioxide capture system shown is used. The feed gas is flue gas from a coal-fired boiler in a petrochemical industry power plant, with a carbon dioxide content of 12%.

[0080] Example 1

[0081] (1) The raw gas enters the pretreatment tower and comes into contact with the sodium carbonate aqueous solution pumped in by the pretreatment pump and cooled by the pretreatment cooler. The gas-liquid ratio is 300:1 and the sodium carbonate aqueous solution temperature at the tower inlet is 40°C. After removing the strong acid components and cooling down, the gas is taken out from the top of the pretreatment tower.

[0082] The feed gas, at a temperature of 40°C, is drawn from the top of the pretreatment tower and transported by a blower to the bottom of the absorption tower, where it enters the absorption tower. Absorbent liquid I (a 10 wt% MEA aqueous solution) is pumped to the second heat exchanger and then enters the absorption tower from the middle. The feed gas and absorbent liquid I contact each other in the lower middle part of the absorption tower for a first-stage absorption, yielding a first-stage treated gas and rich liquid I. The feed temperature of absorbent liquid I is 50°C, and the gas-liquid ratio for the first-stage absorption is 300:1.

[0083] The first-stage treated gas enters the upper section of the absorption tower through the riser cap. The absorbent liquid II (30wt% MEA aqueous solution) is pumped to the first condenser for cooling and then enters the absorption tower from the top. The first-stage treated gas and absorbent liquid II come into contact in the middle and upper part of the absorption tower for second-stage absorption, resulting in crude purified gas and rich liquid II. The feed temperature of absorbent liquid II is 40℃, and the gas-liquid ratio of the second-stage absorption is 500:1.

[0084] The crude purified gas continues to rise and enters the washing section set at the top of the absorption tower, where it comes into contact with the washing water pumped in by the water washing pump and cooled to 40°C by the water washing water cooler. The washing is carried out under the condition of gas-liquid ratio of 300:1 to obtain purified gas, which is then directly discharged.

[0085] (2) Rich liquid I is drawn from the bottom of the absorption tower, pressurized to 0.3 MPa by the rich liquid I pump, and then enters the first heat exchanger to exchange heat to 90°C. It then enters the regeneration tower from the middle section and undergoes a first-stage regeneration under 60 kPa conditions to obtain lean liquid I and a first-stage regeneration gas. The obtained lean liquid I first enters the first heat exchanger, and after being heated to 75°C, it is mixed with absorbent liquid I. It is then pumped into the second heat exchanger by the absorbent liquid I pump, and after being heated to 50°C, it is returned to the middle section of the absorption tower for recycling. The obtained first-stage regeneration gas enters the upper section of the regeneration tower through the gas riser.

[0086] (3) Rich liquid II is drawn from the collection plate in the middle section of the absorption tower and enters the second heat exchanger. It is heated to 60°C and then pumped to the third heat exchanger by the rich liquid II pump. After being heated to 90°C, it enters the regeneration tower from the upper section of the regeneration tower and undergoes two-stage regeneration under 50 kPa conditions to obtain lean liquid II and second-stage regeneration gas. The obtained lean liquid II enters the third heat exchanger and is heated to 65°C. It is then mixed with absorbent liquid II and pumped to the first condenser by the absorbent liquid II pump. After being cooled to 40°C, it is returned to the upper part of the absorption tower for recycling.

[0087] (4) The second stage regenerated gas is condensed to 40°C by the second condenser and then enters the regenerated gas separator. It is separated under the condition of 45 kPa to obtain water and carbon dioxide. The obtained carbon dioxide is sent to the subsequent process, and the obtained water is divided into part A and part B according to the mass ratio of 80:20. Part A is returned to the front of the absorbent liquid I pump, and part B is returned to the front of the absorbent liquid II pump.

[0088] Example 2

[0089] (1) The raw gas enters the pretreatment tower and comes into contact with the sodium carbonate aqueous solution pumped in by the pretreatment pump and cooled by the pretreatment cooler. The gas-liquid ratio is 250:1 and the sodium carbonate aqueous solution temperature at the tower inlet is 45°C. After removing the strong acid components and cooling down, the gas is taken out from the top of the pretreatment tower.

[0090] The feed gas, at a temperature of 45°C, is drawn from the top of the pretreatment tower and transported by a blower to the bottom of the absorption tower, where it enters the absorption tower. Absorbent liquid I (a 5 wt% MEA aqueous solution) is pumped to the second heat exchanger and then enters the absorption tower from the middle. The feed gas and absorbent liquid I contact each other in the lower middle part of the absorption tower for a first-stage absorption, yielding a first-stage treated gas and rich liquid I. The feed temperature of absorbent liquid I is 60°C, and the gas-liquid ratio for the first-stage absorption is 200:1.

[0091] The first-stage treated gas enters the upper section of the absorption tower through the riser cap. The absorbent liquid II (45wt% MEA aqueous solution) is pumped to the first condenser for cooling and then enters the absorption tower from the top. The first-stage treated gas and absorbent liquid II come into contact in the middle and upper part of the absorption tower for second-stage absorption, resulting in crude purified gas and rich liquid II. The feed temperature of absorbent liquid II is 45℃, and the gas-liquid ratio of the second-stage absorption is 700:1.

[0092] The crude purified gas continues to rise and enters the washing section set at the top of the absorption tower, where it comes into contact with the washing water pumped in by the water washing pump and cooled to 35°C by the water washing water cooler. The washing is carried out under the condition of gas-liquid ratio of 400:1 to obtain purified gas, which is then directly discharged.

[0093] (2) Rich liquid I is drawn from the bottom of the absorption tower, pressurized to 0.35 MPa by the rich liquid I pump, and then enters the first heat exchanger to exchange heat to 98°C. It then enters the regeneration tower from the middle section and undergoes a first-stage regeneration under 60 kPa conditions to obtain lean liquid I and a first-stage regeneration gas. The obtained lean liquid I first enters the first heat exchanger, and after being heated to 75°C, it is mixed with absorbent liquid I. It is then pumped into the second heat exchanger by the absorbent liquid I pump, and after being heated to 60°C, it is returned to the middle section of the absorption tower for recycling. The obtained first-stage regeneration gas enters the upper section of the regeneration tower through the gas riser.

[0094] (3) Rich liquid II is drawn from the collection plate in the middle section of the absorption tower and enters the second heat exchanger. It is heated to 70°C and then pumped to the third heat exchanger by the rich liquid II pump. After being heated to 92°C, it enters the regeneration tower from the upper section of the regeneration tower and undergoes two-stage regeneration under 50 kPa conditions to obtain lean liquid II and second-stage regeneration gas. The obtained lean liquid II enters the third heat exchanger and is heated to 75°C. It is then mixed with absorbent liquid II and pumped to the first condenser by the absorbent liquid II pump. After being cooled to 45°C, it is returned to the upper part of the absorption tower for recycling.

[0095] (4) The second stage regenerated gas is condensed to 40°C by the second condenser and then enters the regenerated gas separator. It is separated under the condition of 45 kPa to obtain water and carbon dioxide. The obtained carbon dioxide is sent to the subsequent process, and the obtained water is divided into part A and part B according to the mass ratio of 75:25. Part A is returned to the front of the absorbent I pump, and part B is returned to the front of the absorbent II pump.

[0096] Example 3

[0097] (1) The raw gas enters the pretreatment tower and comes into contact with the sodium hydroxide aqueous solution pumped in by the pretreatment pump and cooled by the pretreatment cooler. The gas-liquid ratio is 200:1 and the sodium hydroxide aqueous solution enters the tower at 45°C. After removing the strong acid components and cooling down, the gas is taken out from the top of the pretreatment tower.

[0098] The feed gas, at a temperature of 45°C, is drawn from the top of the pretreatment tower and transported by a blower to the bottom of the absorption tower, where it enters the absorption tower. Absorbent liquid I (15 wt% aqueous solution of compound amines, including 6 wt% MEA, 6 wt% MDEA, and 3 wt% AMP) is pumped to the second heat exchanger and then enters the absorption tower from the middle. The feed gas and absorbent liquid I contact each other in the lower middle part of the absorption tower for a first-stage absorption, resulting in a first-stage treated gas and rich liquid I. The feed temperature of absorbent liquid I is 60°C, and the gas-liquid ratio for the first-stage absorption is 500:1.

[0099] The first-stage treated gas enters the upper section of the absorption tower through a riser cap. Absorbent liquid II (25 wt% aqueous solution of compound amines, including 10 wt% MEA, 10 wt% MDEA, and 5 wt% AMP) is pumped to the first condenser for cooling and then enters the absorption tower from the top. The first-stage treated gas and absorbent liquid II contact in the upper middle part of the absorption tower for second-stage absorption, yielding crude purified gas and rich liquid II. The feed temperature of absorbent liquid II is 45℃, and the gas-liquid ratio for the second-stage absorption is 400:1.

[0100] The crude purified gas continues to rise and enters the washing section set at the top of the absorption tower, where it comes into contact with the washing water pumped in by the water washing pump and cooled to 35°C by the water washing water cooler. The washing is carried out under the condition of gas-liquid ratio of 400:1 to obtain purified gas, which is then directly discharged.

[0101] (2) Rich liquid I is drawn from the bottom of the absorption tower, pressurized to 0.3 MPa by the rich liquid I pump, and then enters the first heat exchanger to exchange heat to 94°C. Then it enters the regeneration tower from the middle section and undergoes a first-stage regeneration under 60 kPa conditions to obtain lean liquid I and a first-stage regeneration gas. The obtained lean liquid I first enters the first heat exchanger, and after being heated to 75°C, it is mixed with absorbent liquid I. It is then pumped into the second heat exchanger by the absorbent liquid I pump, and after being heated to 60°C, it is returned to the middle section of the absorption tower for recycling. The obtained first-stage regeneration gas enters the upper section of the regeneration tower through the gas riser.

[0102] (3) Rich liquid II is drawn from the collection plate in the middle section of the absorption tower and enters the second heat exchanger. It is heated to 70°C and then pumped to the third heat exchanger by the rich liquid II pump. After being heated to 88°C, it enters the regeneration tower from the upper section of the regeneration tower and undergoes two-stage regeneration under 50 kPa conditions to obtain lean liquid II and second-stage regeneration gas. The obtained lean liquid II enters the third heat exchanger and is heated to 75°C. It is then mixed with absorbent liquid II and pumped to the first condenser by the absorbent liquid II pump. After being cooled to 45°C, it is returned to the upper part of the absorption tower for recycling.

[0103] (4) The second stage regenerated gas is condensed to 40°C by the second condenser and then enters the regenerated gas separator. It is separated under the condition of 45 kPa to obtain water and carbon dioxide. The obtained carbon dioxide is sent to the subsequent process, and the obtained water is divided into part A and part B according to the mass ratio of 50:50. Part A is returned to the absorbent I pump and part B is returned to the absorbent II pump.

[0104] Example 4

[0105] (1) The raw gas enters the pretreatment tower and comes into contact with the sodium carbonate aqueous solution pumped in by the pretreatment pump and cooled by the pretreatment cooler. The gas-liquid ratio is 350:1 and the sodium carbonate aqueous solution temperature at the tower inlet is 40°C. After removing the strong acid components and cooling down, the gas is taken out from the top of the pretreatment tower.

[0106] The feed gas, at a temperature of 40°C, is drawn from the top of the pretreatment tower and transported by a blower to the bottom of the absorption tower, where it enters the absorption tower. Absorbent liquid I (10 wt% aqueous solution of compound amines, including 4 wt% MEA, 4 wt% MDEA, and 2 wt% AMP) is pumped to the second heat exchanger and then enters the absorption tower from the middle. The feed gas and absorbent liquid I contact each other in the lower middle part of the absorption tower for a first-stage absorption, resulting in a first-stage treated gas and rich liquid I. The feed temperature of absorbent liquid I is 50°C, and the gas-liquid ratio for the first-stage absorption is 350:1.

[0107] The first-stage treated gas enters the upper section of the absorption tower through a riser cap. Absorbent liquid II (35 wt% aqueous solution of compound amines, including 14 wt% MEA, 14 wt% MDEA, and 7 wt% AMP) is pumped to the first condenser for cooling and then enters the absorption tower from the top. The first-stage treated gas and absorbent liquid II contact in the upper middle part of the absorption tower for second-stage absorption, yielding crude purified gas and rich liquid II. The feed temperature of absorbent liquid II is 35℃, and the gas-liquid ratio for the second-stage absorption is 600:1.

[0108] The crude purified gas continues to rise and enters the washing section set at the top of the absorption tower, where it comes into contact with the washing water pumped in by the water washing pump and cooled to 40°C by the water washing water cooler. The washing is carried out under the condition of gas-liquid ratio of 300:1 to obtain purified gas, which is then directly discharged.

[0109] (2) Rich liquid I is drawn from the bottom of the absorption tower, pressurized to 0.35 MPa by the rich liquid I pump, and then enters the first heat exchanger to exchange heat to 98°C. It then enters the regeneration tower from the middle section and undergoes a first-stage regeneration under 70 kPa conditions to obtain lean liquid I and a first-stage regeneration gas. The obtained lean liquid I first enters the first heat exchanger, and after being heated to 65°C, it is mixed with absorbent liquid I. It is then pumped into the second heat exchanger by the absorbent liquid I pump, and after being heated to 50°C, it is returned to the middle section of the absorption tower for recycling. The obtained first-stage regeneration gas enters the upper section of the regeneration tower through the gas riser.

[0110] (3) Rich liquid II is drawn from the collection plate in the middle section of the absorption tower and enters the second heat exchanger. It is heated to 60°C and then pumped to the third heat exchanger by the rich liquid II pump. After being heated to 92°C, it enters the regeneration tower from the upper section of the regeneration tower and undergoes two-stage regeneration under 60 kPa conditions to obtain lean liquid II and second-stage regeneration gas. The obtained lean liquid II enters the third heat exchanger and is heated to 65°C. It is then mixed with absorbent liquid II and pumped to the first condenser by the absorbent liquid II pump. After being cooled to 35°C, it is returned to the upper part of the absorption tower for recycling.

[0111] (4) The second stage regenerated gas is condensed to 40°C by the second condenser and then enters the regenerated gas separator. It is separated under the condition of 55 kPa to obtain water and carbon dioxide. The carbon dioxide is sent to the subsequent process, and the water is divided into part A and part B according to the mass ratio of 75:25. Part A is returned to the front of the absorbent liquid I pump, and part B is returned to the front of the absorbent liquid II pump.

[0112] Example 5

[0113] (1) The raw gas enters the pretreatment tower and comes into contact with the sodium carbonate aqueous solution pumped in by the pretreatment pump and cooled by the pretreatment cooler. The gas-liquid ratio is 400:1 and the sodium carbonate aqueous solution temperature at the tower inlet is 40°C. After removing the strong acid components and cooling down, the gas is taken out from the top of the pretreatment tower.

[0114] The feed gas, at a temperature of 40°C, is drawn from the top of the pretreatment tower and transported by a blower to the bottom of the absorption tower, where it enters the absorption tower. Absorbent liquid I (5 wt% aqueous solution of compound amines, including 2 wt% MEA, 2 wt% MDEA, and 1 wt% AMP) is pumped to the second heat exchanger and then enters the absorption tower from the middle. The feed gas and absorbent liquid I contact each other in the lower middle part of the absorption tower for a first-stage absorption, resulting in a first-stage treated gas and rich liquid I. The feed temperature of absorbent liquid I is 50°C, and the gas-liquid ratio for the first-stage absorption is 200:1.

[0115] The first-stage treated gas enters the upper section of the absorption tower through a riser cap. Absorbent liquid II (45 wt% aqueous solution of compound amines, including 18 wt% MEA, 18 wt% MDEA, and 9 wt% AMP) is pumped to the first condenser for cooling and then enters the absorption tower from the top. The first-stage treated gas and absorbent liquid II contact in the upper middle part of the absorption tower for second-stage absorption, yielding crude purified gas and rich liquid II. The feed temperature of absorbent liquid II is 35℃, and the gas-liquid ratio for the second-stage absorption is 800:1.

[0116] The crude purified gas continues to rise and enters the washing section set at the top of the absorption tower, where it comes into contact with the washing water pumped in by the water washing pump and cooled to 40°C by the water washing water cooler. The washing is carried out under the condition of gas-liquid ratio of 300:1 to obtain purified gas, which is then directly discharged.

[0117] (2) Rich liquid I is drawn from the bottom of the absorption tower, pressurized to 0.3 MPa by the rich liquid I pump, and then enters the first heat exchanger to exchange heat to 100°C. It then enters the regeneration tower from the middle section and undergoes a first-stage regeneration under 90 kPa conditions to obtain lean liquid I and a first-stage regeneration gas. The obtained lean liquid I first enters the first heat exchanger, and after being heated to 65°C, it is mixed with absorbent liquid I. It is then pumped into the second heat exchanger by the absorbent liquid I pump, and after being heated to 50°C, it is returned to the middle section of the absorption tower for recycling. The obtained first-stage regeneration gas enters the upper section of the regeneration tower through the gas riser.

[0118] (3) Rich liquid II is drawn from the collection plate in the middle section of the absorption tower and enters the second heat exchanger. It is heated to 60°C and then pumped to the third heat exchanger by the rich liquid II pump. After being heated to 94°C, it enters the regeneration tower from the upper section of the regeneration tower and undergoes two-stage regeneration under 80 kPa conditions to obtain lean liquid II and second-stage regeneration gas. The obtained lean liquid II enters the third heat exchanger and is heated to 65°C. It is then mixed with absorbent liquid II and pumped to the first condenser by the absorbent liquid II pump. After being cooled to 35°C, it is returned to the upper part of the absorption tower for recycling.

[0119] (4) The second stage regenerated gas is condensed to 40°C by the second condenser and then enters the regenerated gas separator. It is separated under the condition of 75 kPa to obtain water and carbon dioxide. The obtained carbon dioxide is sent to the subsequent process, and the obtained water is divided into part A and part B according to the mass ratio of 83:17. Part A is returned to the front of the absorbent liquid I pump, and part B is returned to the front of the absorbent liquid II pump.

[0120] Comparative Example 1

[0121] (1) The raw gas enters the pretreatment tower and comes into contact with the sodium carbonate aqueous solution pumped in by the pretreatment pump and cooled by the pretreatment cooler. The pretreatment is carried out under the conditions of a gas-liquid ratio of 300 and a sodium carbonate aqueous solution temperature of 40°C. After removing strong acid components and cooling down, the gas is taken out from the top of the pretreatment tower.

[0122] The feed gas, at a temperature of 40°C, is drawn from the top of the pretreatment tower and transported by a blower to the bottom of the absorption tower, where it enters the absorption tower. Absorbent liquid II (30wt% MEA aqueous solution) is pumped to the first condenser for cooling and then enters the absorption tower from the top. The feed gas contacts absorbent liquid II for absorption, resulting in crude purified gas and rich liquid. The feed temperature of absorbent liquid II is 40°C, and the gas-liquid ratio is 300:1.

[0123] The crude purified gas continues to rise and enters the washing section set at the top of the absorption tower, where it comes into contact with the washing water pumped in by the water washing pump and cooled to 40°C by the water washing water cooler. The washing is carried out under the condition of gas-liquid ratio of 300:1 to obtain purified gas, which is then directly discharged.

[0124] Rich liquid is drawn from the bottom of the absorption tower, pressurized to 0.3 MPa by rich liquid pump II, and then enters the first heat exchanger to exchange heat to 95°C. It then enters the regeneration tower from the top and is regenerated under 60 kPa conditions to obtain lean liquid and regeneration gas. The obtained lean liquid enters the first heat exchanger to exchange heat to 60°C, and is then pumped by absorbent liquid pump II to the first condenser. After being cooled to 40°C, it is returned to the upper part of the absorption tower for recycling.

[0125] After being condensed to 40°C by the condenser, the regenerated gas enters the regenerated gas separator, where it is separated under a 45 kPa condition to obtain water and carbon dioxide. The carbon dioxide is sent to the subsequent process, while all the water is returned to the absorbent II pump for recycling.

[0126] Comparative Example 2

[0127] Similar to Comparative Example 1, except that the absorbent was replaced by an equal mass of 30 w% of a complex amine aqueous solution (12 w% MEA, 12 w% MDEA, 6 w% AMP).

[0128] Test Example 1

[0129] The absorbent loss and regeneration energy consumption in Examples 1-5 and the comparative examples were calculated, and the results are shown in Table 1:

[0130] The calculation method for absorbent loss is: absorbent dosage added per hour (kg / h) / CO2 production (t / h). The calculation method for regeneration energy consumption is: reboiler heat load (GJ / h) / CO2 production (t / h).

[0131] Table 1

[0132] <![CDATA[CO2 capture rate]]> <![CDATA[Absorbent loss (kg / tCO2)]]> <![CDATA[Regeneration energy consumption / (GJ / tCO2)]]> Example 1 90.2％ 2.1 3.4 Example 2 90.3％ 1.9 3.7 Example 3 90.1％ 1.1 3.0 Example 4 90.5％ 1.2 2.7 Example 5 90.3％ 1.3 2.9 Comparative Example 1 90.4％ 2.5 4.2 Comparative Example 2 90.6％ 1.5 3.5

[0133] As shown in Table 1, the carbon dioxide capture method provided in this invention has the advantages of low absorbent loss and low regeneration energy consumption, making it suitable for industrial application. By comparing Examples 1 and 2 with Comparative Example 1 and Examples 3-5 with Comparative Example 2, it can be seen that the two-stage absorption and two-stage regeneration operation in this invention can significantly reduce absorbent loss and regeneration energy consumption.

[0134] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for capturing carbon dioxide, characterized in that, The method includes the following steps: (1) The raw gas containing carbon dioxide is introduced into the absorption tower from the bottom of the absorption tower and comes into contact with the absorbent liquid I fed from the middle of the absorption tower to carry out a first-stage absorption, and a first-stage treated gas and rich liquid I are obtained. The first-stage treated gas comes into contact with absorbent liquid II fed from the top of the absorption tower for second-stage absorption, resulting in crude purified gas and rich liquid II; wherein, the concentration of absorbent in absorbent liquid I is lower than the concentration of absorbent in absorbent liquid II; the crude purified gas comes into contact with washing water for washing, resulting in purified gas. (2) After the rich liquid I is pressurized and heat-exchanged by the first heat exchanger, it is introduced into the middle section of the regeneration tower for a first-stage regeneration to obtain lean liquid I and a first-stage regeneration gas; wherein, the lean liquid I is returned to step (1) as the absorbent liquid I after being heat-exchanged by the first heat exchanger and the second heat exchanger in sequence. (3) The rich liquid II is introduced into the upper section of the regeneration tower after being heat-exchanged by the second heat exchanger and the third heat exchanger in sequence for two-stage regeneration to obtain lean liquid II and two-stage regeneration gas; wherein, the lean liquid II is returned to step (1) as the absorbent liquid II after being heat-exchanged by the third heat exchanger and the first condenser in sequence. (4) The two-stage regeneration gas is introduced into the regeneration gas separator for cooling and separation to obtain water and carbon dioxide.

2. The capture method according to claim 1, wherein, The carbon dioxide content in the raw gas is 2-40% v%, preferably 5-20% v%. Preferably, before introducing the raw gas into the absorption tower, the raw gas is first introduced into the pretreatment tower to contact with the alkaline solution for impurity removal and cooling. Preferably, the operating conditions of the pretreatment tower include: a gas-liquid ratio of 100-600:1, preferably 200-400:1; and a feed temperature of alkali solution of 20-60℃, preferably 40-45℃. Preferably, the temperature of the raw gas after treatment in the pretreatment tower is 20-60°C, more preferably 30-50°C.

3. The capture method according to claim 1 or 2, wherein, Absorbent I and Absorbent II are each aqueous solutions of absorbents; wherein the absorbents in Absorbent I and Absorbent II are each selected from organic amines. Preferably, the organic amine is selected from one or more of monoethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, diethylenetriamine, triethylenetetramine, piperazine, hydroxyethylpiperazine, 2-amino-2-methyl-1-propanol, diethylaminoethanol, N-ethyldiethanolamine, and 3-diethylamino-1-propanol; Preferably, the absorbent in absorbent liquid I and absorbent liquid II is the same.

4. The capture method according to any one of claims 1-3, wherein, The concentration of the absorbent in the absorbent liquid I is 5-15 wt%, preferably 8-12 wt%. Preferably, the operating conditions for the first-stage absorption include: the feed temperature of the absorbent liquid I is 40-70℃, preferably 50-60℃; and the gas-liquid ratio of the first-stage absorption is 200-500:1, preferably 300-400:

1.

5. The capture method according to any one of claims 1-4, wherein, The concentration of the absorbent in absorbent solution I is 10-40 wt% lower than the concentration of the absorbent in absorbent solution II, preferably 20-30 wt% lower.

6. The capture method according to any one of claims 1-5, wherein, The concentration of the absorbent in the absorbent liquid II is 25-45 wt%, preferably 30-40 wt%. Preferably, the operating conditions for the two-stage absorption include: the feed temperature of the absorbent liquid II is 30-50℃, preferably 35-45℃; and the gas-liquid ratio of the two-stage absorption is 400-800:1, preferably 500-700:

1.

7. The capture method according to any one of claims 1-6, wherein, The pressure of the rich liquid I after pressurization is 0.2-0.5 MPa, preferably 0.3-0.4 MPa; Preferably, the temperature of the rich liquid I after pressurization and heat exchange in the first heat exchanger is 85-110℃, more preferably 90-105℃; Preferably, the operating conditions for the first-stage regeneration include: a first-stage regeneration pressure of 10-200 kPa, preferably 50-100 kPa; Preferably, the temperature of the lean liquid I after heat exchange with the first heat exchanger is 50-80℃, more preferably 55-75℃.

8. The capture method according to any one of claims 1-7, wherein, The temperature of the rich liquid II after heat exchange in the second heat exchanger is 45-75℃, preferably 50-70℃; the temperature after heat exchange in the third heat exchanger is 80-105℃, preferably 85-100℃. Preferably, the operating conditions for the two-stage regeneration include: a two-stage regeneration pressure of 10-150 kPa, preferably 30-100 kPa; Preferably, the temperature of the lean liquid II after heat exchange with the third heat exchanger is 45-80℃, more preferably 50-75℃.

9. The capture method according to any one of claims 1-8, wherein, The operating conditions of the regenerated gas separator include: separation temperature of 30-50℃, preferably 35-45℃, and separation pressure of 5-145kPa, preferably 40-90kPa.

10. The capture method according to any one of claims 1-9, wherein, The condensate obtained from the regenerated gas separator is divided into at least part A and part B. Part A is returned to the absorbent liquid I in step (1), and part B is returned to the absorbent liquid II in step (2). Preferably, the mass ratio of part A to part B is 1-5:1, more preferably 2-4:1.

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