A carbon dioxide absorption system and method based on multiple absorbents

Abstract

This invention belongs to the field of carbon capture technology, specifically relating to a carbon dioxide absorption system and method based on multiple absorbents. The system includes an absorption tower, a lean-rich liquid heat exchanger, a rich liquid heater, and a desorption unit. The desorption unit includes a desorption system and a falling film evaporation system connected in parallel. The desorption system is used to desorb the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system is used to desorb the heated rich liquid with a viscosity ≥30 mPa·s. The lean liquid cooler is used to cool the first heat exchange lean liquid, which is then returned to the absorption tower. This system can effectively achieve simultaneous carbon capture of composite amine absorbents, two-phase absorbents, and ionic liquid absorbents with different viscosities within the carbon dioxide absorption system of this invention. Furthermore, the system has a small footprint and is flexible in operation.

Description

Technical Field

[0001] This invention relates to the field of carbon capture technology, and specifically to a carbon dioxide absorption system and method based on multiple absorbents. Background Technology

[0002] Addressing global climate change hinges on reducing greenhouse gas emissions, particularly carbon dioxide. Among numerous carbon dioxide emission reduction technologies, chemical absorption is currently the most widely used and effective carbon dioxide capture technology. Mixed organic amine absorbents are a relatively mature and widely used type of absorbent, and most existing carbon capture systems are designed and constructed based on composite amine absorption processes. However, due to the inherent properties of organic amines, this type of absorbent suffers from high regeneration energy consumption and high investment costs, limiting its practicality in certain operating environments.

[0003] Compared to traditional compound amine absorption processes, two-phase absorption and ionic liquid absorption processes have advantages in certain application environments. Therefore, two-phase absorption or ionic liquid absorption processes are used in specific environments. However, compound amine absorption is still the dominant absorbent used in industry. To effectively capture carbon dioxide, different absorption processes need to be combined for different application environments. However, there is currently no carbon dioxide absorption system that combines multiple absorbents such as compound amine absorbents, two-phase absorbents, and ionic liquid absorbents. If different absorbents are used simultaneously, multiple absorption and desorption units are required, which have a large footprint and lack operational flexibility. Summary of the Invention

[0004] The purpose of this invention is to address the lack of research in existing technologies on carbon dioxide absorption systems that utilize multiple absorbents, such as composite amines, two-phase absorbents, and ionic liquids, by proposing a carbon dioxide absorption system and method based on multiple absorbents. This system, through the parallel operation of a conventional desorption tower and a falling film evaporation system, can effectively achieve simultaneous carbon capture of composite amine absorbents, two-phase absorbents, and ionic liquid absorbents with different viscosities within the carbon dioxide absorption system described in this invention. Furthermore, this system has a small footprint and is highly flexible in operation.

[0005] To achieve the above objectives, the first aspect of the present invention proposes a carbon dioxide absorption system based on multiple absorbents. This system includes an absorption tower, a lean-rich liquid heat exchanger, a rich liquid heater, and a desorption unit. The desorption unit includes a desorption system and a falling film evaporation system connected in parallel.

[0006] The rich liquid from the absorption tower and the lean liquid from the desorption unit exchange heat in the rich-lean-lean liquid heat exchanger to obtain a first heat exchange rich liquid and a first heat exchange lean liquid.

[0007] The rich liquid heater is used to heat the first heat exchange rich liquid to obtain a heated rich liquid;

[0008] The desorption system is used to desorb the heated rich solution with a viscosity <30 mpa·s, and the falling film evaporation system is used to desorb the heated rich solution with a viscosity ≥30 mpa·s.

[0009] Preferably, the falling film evaporation system includes a falling film desorption tower, an evaporation chamber, a third condenser, a negative pressure storage tank, and a vacuum pump connected in sequence, with the upper part of the falling film desorption tower connected to the rich liquid heater via a connecting pipe. More preferably, a second valve is provided on the connecting pipe between the rich liquid heater and the falling film desorption tower.

[0010] Preferably, the falling film evaporation system further includes a circulation pump, which is connected to the upper and lower parts of the falling film desorption tower, respectively.

[0011] Preferably, the desorption system includes a desorption tower and a second condenser connected to each other, and the rich liquid heater is connected to the desorption tower through a connecting pipe, which is equipped with a first valve.

[0012] Preferably, the lower part of the absorption tower is connected to the lean and rich liquid heat exchanger via a connecting pipe, and a rich liquid pump is installed on the connecting pipe.

[0013] Preferably, the lower part of the desorption tower is connected to the lean and rich liquid heat exchanger via a connecting pipe, and a lean liquid pump is installed on the connecting pipe.

[0014] Preferably, the evaporation chamber is connected to the lean liquid pump.

[0015] Preferably, the system further includes a lean liquid cooler for cooling the first heat exchange lean liquid from the lean-rich liquid heat exchanger and returning the cooled first heat exchange lean liquid to the absorption tower.

[0016] Preferably, a separator is provided at the lower end of the absorption tower; more preferably, the separator is connected to the rich liquid pump.

[0017] Preferably, the separator is connected to the lean liquid cooler via a connecting pipe; more preferably, a light phase pump is provided on the connecting pipe between the separator and the lean liquid cooler.

[0018] Preferably, the upper end of the absorption tower is connected in sequence to a first condenser and a first gas analyzer.

[0019] Preferably, the system further includes a second gas analyzer for analyzing the gas from the vacuum pump and the second condenser.

[0020] A second aspect of this invention provides a carbon dioxide absorption method based on multiple absorbents, implemented in the system described above, comprising:

[0021] Carbon dioxide-containing flue gas is introduced into the absorption tower and comes into contact with the absorbent for carbon dioxide absorption, resulting in a carbon dioxide-rich solution. This rich solution is then transported to a lean-rich solution heat exchanger, where it exchanges heat with the lean solution flowing out of the desorption unit, resulting in a first heat-exchange rich solution and a first heat-exchange lean solution. The first heat-exchange rich solution is then fed into the rich solution heater for heating, resulting in a heated rich solution. When the viscosity of the heated rich solution is <30 MPa·s, it is transported to the desorption tower for desorption. When the viscosity of the heated rich solution is ≥30 MPa·s, it is transported to the falling film evaporation system for desorption, resulting in the lean solution. The first heat-exchange lean solution is then fed into the lean solution cooler for cooling and then returned to the absorption tower.

[0022] Preferably, the flue gas contains 9-13% carbon dioxide, 86-90% nitrogen, 0.085-0.088% carbon monoxide and 0.012-0.015% sulfur dioxide.

[0023] Preferably, the temperature of the flue gas is 30-60°C.

[0024] Preferably, the absorbent is a two-phase absorbent, a complex amine absorbent, or an ionic liquid absorbent.

[0025] Preferably, the viscosity of the two-phase absorbent is 10-15 mPa·s;

[0026] Preferably, the viscosity of the composite amine absorbent is 0.8-10 mPa·s;

[0027] Preferably, the viscosity of the ionic liquid absorbent is 30-100 mPa·s.

[0028] Preferably, the temperature of the first heat exchange rich liquid is 60-90℃.

[0029] Preferably, the temperature of the first heat exchange lean solution is 50-80°C.

[0030] Preferably, the temperature of the heated rich liquid is 100-125°C.

[0031] Preferably, the first heat exchange lean solution is further cooled to 25-40°C.

[0032] According to the carbon dioxide absorption system based on multiple absorbents described in this invention, firstly, flue gas containing a certain concentration of carbon dioxide is contacted and absorbed by absorbents in an absorption tower to obtain a carbon dioxide-rich solution. Then, the rich solution and the lean solution flowing out of the desorption unit exchange heat in a lean-rich solution heat exchanger to obtain a first heat-exchange rich solution and a first heat-exchange lean solution. The first heat-exchange rich solution is further heated to obtain a heated rich solution. When the viscosity of the heated rich solution is <30 mPa·s, the heated rich solution is transported to the desorption tower for desorption. When the viscosity of the heated rich solution is ≥30 mPa·s, the heated rich solution is transported to the falling film evaporation system for desorption. Therefore, the carbon dioxide absorption system based on multiple absorbents of this invention can effectively achieve carbon capture in one system simultaneously using composite amine absorbents, two-phase absorbents, and ionic liquid absorbents with different viscosities, thus eliminating the need to configure different absorption and desorption devices according to different absorbents. This system has the advantages of small footprint and flexible operation. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a carbon dioxide absorption system based on multiple absorbents according to the present invention.

[0034] Explanation of reference numerals in the attached figures

[0035] 1. Absorption tower; 2. Lean and rich liquid heat exchanger; 3. Desorption tower; 4. Falling film desorption tower; 5. Lean liquid cooler; 6. Rich liquid heater; 7. Evaporation chamber; 8. Negative pressure storage tank; 9. Vacuum pump; 10. First condenser; 11. Second condenser; 12. Third condenser; 13. First gas analyzer; 14. Second gas analyzer; 15. Light phase pump; 16. Rich liquid pump; 17. Lean liquid pump; 18. Circulation pump; 19. First valve; 20. Second valve; 21. Desorption system; 22. Separator; 23. Falling film evaporation system. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0037] 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.

[0038] Furthermore, terms such as "upper," "lower," "top," "bottom," "inner," and "outer," indicating orientation or positional relationships, are based on the orientation or relative positional relationships shown in the accompanying drawings. They are merely simplified descriptions for the convenience of describing this application and do not indicate that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0039] The first aspect of this invention proposes a carbon dioxide absorption system based on multiple absorbents, such as... Figure 1 As shown, the system includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, and a desorption unit. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel.

[0040] The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the rich-lean-lean liquid heat exchanger 2 to obtain a first heat exchange rich liquid and a first heat exchange lean liquid.

[0041] The rich liquid heater 6 is used to heat the first heat exchange rich liquid to obtain a heated rich liquid;

[0042] The desorption system 21 is used to desorb the heated rich liquid with a viscosity <30 mpa·s, and the falling film evaporation system 23 is used to desorb the heated rich liquid with a viscosity ≥30 mpa·s.

[0043] In the system described in this invention, in a specific embodiment, the absorption tower 1 can be a conventional packed tower in the art, made of 316L stainless steel. The absorption tower 1 includes a packing section and a demister from bottom to top. A thermocouple is installed at the center of the packing section, and a differential pressure measurement port is reserved. Temperature measuring points are located at the top, middle, and bottom of the absorption tower 1, while pressure measuring points are located at the bottom and top. The packing section has a differential pressure measuring point. In a preferred embodiment, the packing height of the packing section is adjustable to facilitate changing the type of packing. The demister is a wire mesh demister. In a preferred embodiment, it is required that the liquid entering the absorption tower 1 is uniformly distributed across the cross-section of the tower; a spray device or a liquid distributor can be used. In the specific implementation process, flue gas containing carbon dioxide enters from the bottom of the absorption tower 1, and the absorbent enters from the top. The gas and absorbent come into countercurrent contact, and the resulting purified gas escapes from the top of the tower. After the liquid carried by the gas is removed by the condenser at the top of the tower, it is discharged into the vent pipe. The resulting saturated absorbent, i.e., the rich liquid, is stored in the tower tank.

[0044] In the system described in this invention, in a specific embodiment, the lower part of the absorption tower 1 is connected to the lean-rich liquid heat exchanger 2 via a connecting pipe, and a rich liquid pump 16 is installed on the connecting pipe. In the specific implementation process, the rich liquid stored in the absorption tower 1 is transported to the lean-rich liquid heat exchanger 2 by the rich liquid pump 16 for heat exchange to obtain the first heat-exchanged rich liquid.

[0045] In the system described in this invention, in a specific embodiment, the rich liquid heater 6 can be a conventional choice in the art. In the specific implementation process, the first heat exchange rich liquid is delivered to the rich liquid heater 6 for further heating to obtain a heated rich liquid.

[0046] In the system described in this invention, in a specific embodiment, the desorption system 21 includes a desorption tower 3 and a second condenser 11 connected to each other; the rich liquid heater 6 is connected to the upper part of the desorption tower 3 via a connecting pipe, and a first valve 19 is provided on the connecting pipe. In the specific implementation process, when the viscosity of the heated rich liquid from the rich liquid heater 6 is <30 mPa·s, the first valve 19 is opened, and the heated rich liquid in the rich liquid heater 6 is sent into the desorption tower 3 for desorption.

[0047] In the system described in this invention, in a specific embodiment, the desorption tower 3 can be a conventional choice in the art. The desorption tower 3 includes, from top to bottom, a demister, a packing section, and a reboiler. Temperature measuring points are located at the top, middle, and bottom of the desorption tower 3; pressure measuring points are located at the bottom and top; the packing section has a differential pressure measuring point; and a pneumatic pressure regulating valve is installed at the top. The desorption pressure of the desorption tower 3 is controllable, ranging from 0 to 200 kPa. In the desorption tower 3, the heat of desorption is provided through the reboiler, and the desorption temperature is <200°C. In a preferred embodiment, the desorption tower 3 is equipped with a safety valve, and the packing height of the packing section is adjustable for easy replacement of the packing type. In the specific implementation process, the heated rich liquid with a viscosity <30 mPa·s from the rich liquid heater 6 desorbs carbon dioxide in the desorption tower 3. The tower reboiler provides heat source steam. The steam flows upward and the rich liquid flows downward. The gas and liquid contact in countercurrent contact for mass and heat transfer. The rich liquid is desorbed into lean liquid and enters the tower reboiler. It is then returned to the absorption tower 1 for reuse via the lean liquid pump 17. The carbon dioxide and some steam desorbed at the top of the tower are condensed and separated by the top condenser. The low-temperature gas is regenerated under pressure controlled by a pressure regulating valve and then discharged into the vent pipe.

[0048] In the system described in this invention, in a specific embodiment, the lower part of the desorption tower 3 is connected to the lean-rich liquid heat exchanger 2 via a connecting pipe, and a lean liquid pump 17 is installed on the connecting pipe. In the specific implementation process, the lean liquid output from the desorption tower 3 is fed into the lean-rich liquid heat exchanger 2 via the lean liquid pump 17 for heat exchange, resulting in a first heat-exchanged lean liquid. Specifically, the flow rate of the lean liquid should be controlled within a suitable range, which is 20-60 L / h.

[0049] In a specific embodiment of the system described in this invention, the system further includes a lean liquid cooler 5, which can be a conventional choice in the art. In the specific implementation, the first heat exchange lean liquid enters the lean liquid cooler 5 for further cooling, and then returns to the absorption tower 1 for recycling.

[0050] In the system described in this invention, in a specific embodiment, the falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8, and a vacuum pump 9 connected in sequence. The upper part of the falling film desorption tower 4 is connected to the rich liquid heater 6 via a connecting pipe. In a preferred embodiment, a second valve 20 is provided on the connecting pipe between the rich liquid heater 6 and the falling film desorption tower 4. In the specific implementation process, when the viscosity of the heated rich liquid from the rich liquid heater 6 is ≥30 mpa·s, the heated rich liquid enters from the top of the falling film desorption tower 4. The falling film desorption tower 4 provides heat (i.e., desorption power), and the vacuum pump 9 provides a negative pressure desorption environment. The desorption gas and lean liquid generated by desorption enter the evaporation chamber 7 together. The evaporation chamber 7 provides evaporation space for the desorption gas and lean liquid, ensuring a large amount of gas-liquid separation. The separated lean liquid enters the lean liquid pump 17. The separated desorption gas carries a small amount of water and absorbent, and then is condensed in the third condenser 12. The condensed liquid and desorption gas enter the negative pressure storage tank 8 for separation.

[0051] In the system described in this invention, in a specific embodiment, the evaporation chamber 7 is connected to the lean liquid pump 17. During implementation, the lean liquid generated in the evaporation chamber 7 enters the lean-rich liquid heat exchanger 2 via the lean liquid pump 17, where it exchanges heat with the rich liquid from the rich liquid pump 16. Specifically, the flow rate of the lean liquid should be controlled within a suitable range, which is 20-60 L / h.

[0052] In the system described in this invention, in a preferred embodiment, the falling film evaporation system 23 further includes a circulation pump 18, which is connected to the upper and lower parts of the falling film desorption tower 4 respectively. Specifically, the function of the circulation pump 18 is to force circulation to ensure more complete desorption and prevent insufficient desorption in a single cycle.

[0053] In the system described in this invention, in a specific embodiment, the falling film desorption tower 4 is heated by heat transfer oil, with controllable temperature and adjustable vacuum. The falling liquid is required to be evenly distributed. Temperature measuring points and vacuum measuring points are set at the top and bottom of the tower. The desorption pressure of the falling film desorption tower 4 is controllable, and the liquid level can be vacuum-collected and controlled. The desorption pressure range is ≥10 kPa(a), and the desorption temperature is <200℃.

[0054] In the system described in this invention, in a specific embodiment, when the absorbent filled in the absorption tower 1 is a two-phase absorbent, the two-phase absorbent will separate into a light phase and a heavy phase after absorbing the gas. In this document, the light phase refers to an absorbent containing a small amount of carbon dioxide, and the heavy phase refers to an absorbent rich in carbon dioxide. To separate the light and heavy phases, a separator 22 is provided at the lower end of the absorption tower 1. The absorption tower 1 and the separator 22 are detachably connected. Specifically, the separator 22 is made of high borosilicate glass or 316L stainless steel, depending on the liquid level. In a more preferred embodiment, the separator 22 is equipped with an interface adjuster to adjust the separation interface, which is more conducive to phase separation control.

[0055] In the system described in this invention, in a specific embodiment, when the absorbent filled in the absorption tower 1 is a two-phase absorbent, the separator 22 is connected to the rich liquid pump 16. During the specific implementation, the two-phase absorbent absorbs carbon dioxide in the absorption tower 1. The absorbed light phase and the heavy phase are effectively separated in the separator 22. The separated heavy phase enters the rich liquid pump 16 and then the lean-rich liquid heat exchanger 2 for heat exchange, finally entering the desorption unit for desorption.

[0056] In the system described in this invention, in a preferred embodiment, the separator 22 and the lean liquid cooler 5 are connected by a connecting pipe. A light phase pump 15 is installed on the connecting pipe between the separator 22 and the lean liquid cooler 5. Specifically, the light phase pump 15 is detachably connected to the separator 22 and the lean liquid cooler 5. In a specific implementation, the light phase separated in the separator 22 enters the lean liquid cooler 5 through the light phase pump 15 for cooling and is then reused in the absorption tower 1.

[0057] In the system described in this invention, in a specific embodiment, the upper end of the absorption tower 1 is sequentially connected to a first condenser 10 and a first gas analyzer 13. During the specific implementation, the purified gas obtained in the absorption tower 1 escapes from the top of the tower, passes through the top condenser to remove any carried liquid, is analyzed by the first gas analyzer 13, and then is discharged into the vent pipe.

[0058] In a specific embodiment of the system described in this invention, the system further includes a second gas analyzer 14 for analyzing the gas from the vacuum pump 9 and the second condenser 11. In the specific implementation, the pollutant gas and some vapor desorbed at the top of the desorption tower 3 are condensed and separated by the second condenser 11 at the top of the tower. The low-temperature gas has its regeneration pressure controlled by a pressure regulating valve, and is analyzed by the second gas analyzer 14 before being discharged to the vent pipe. The desorbed gas separated in the negative pressure storage tank 8 enters the second gas analyzer 14 through the vacuum pump 9 for gas analysis before being discharged to the vent pipe.

[0059] In the system described in this invention, in a specific embodiment, the cooling water used by the lean liquid cooler 5, the first condenser 10, the second condenser 11 and the third condenser 12 is process water, the process water temperature is 20°C, and the equipment is required to have its own chiller to supply cooling water.

[0060] In the system described in this invention, in a specific embodiment, the system is equipped with corresponding temperature, pressure, differential pressure, liquid level, and gas / liquid flow monitoring, and integrates a control cabinet and monitoring software. In a preferred embodiment, a reliable, high-quality PLC (Programmable Logic Controller) or DCS (Distributed Control System) is used for on-site control. The PLC is required to be an imported brand. The temperature is displayed by the PLC, and the tower temperature can be set and adjusted through a constant temperature circulation system. The entire device exhibits good stability, repeatability, and accuracy in operation. An integrated software control operating system is used, featuring an intuitive interface that is convenient, safe, and stable. A 20% margin is reserved for the number of control points in the control cabinet for future modifications and changes. The control software provides on-site operation with visual and controllable capabilities, remote viewing capabilities, and visual and query capabilities on mobile phones and iPads. The supporting operating platform and monitoring software system includes: one computer workstation with the operating software installed, running Windows 10 or later, and a laser printer.

[0061] In the system described in this invention, in a specific embodiment, the lean liquid and the rich liquid each have a liquid sampling port for collecting lean and rich liquid samples for subsequent load testing.

[0062] According to a first embodiment of the present invention, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger 2 to obtain a first heat-exchange rich liquid and a first heat-exchange lean liquid. The rich liquid heater 6 is used to heat the first heat-exchange rich liquid to obtain a heated rich liquid. The desorption system 21 is used to desorb the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system 23 is used to desorb the heated rich liquid with a viscosity ≥30 mPa·s.

[0063] According to a second embodiment of the present invention, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger 2 to obtain a first heat-exchange rich liquid and a first heat-exchange lean liquid. The rich liquid heater 6 heats the first heat-exchange rich liquid to obtain a heated rich liquid. The desorption system 21 desorbs the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system 23 desorbs the liquid with a viscosity ≥30 mPa·s. The rich liquid is heated to a concentration of mPa·s for desorption; the falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8 and a vacuum pump 9 connected in sequence. The upper part of the falling film desorption tower 4 is connected to the rich liquid heater 6 through a connecting pipe. A second valve 20 is provided on the connecting pipe between the rich liquid heater 6 and the falling film desorption tower 4.

[0064] According to a third embodiment of the present invention, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger 2 to obtain a first heat-exchange rich liquid and a first heat-exchange lean liquid. The rich liquid heater 6 heats the first heat-exchange rich liquid to obtain a heated rich liquid. The desorption system 21 desorbs the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system 23 desorbs the liquid with a viscosity ≥30 mPa·s. The rich liquid is heated to a concentration of mPa·s for desorption; the falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8, and a vacuum pump 9 connected in sequence. The upper part of the falling film desorption tower 4 is connected to the rich liquid heater 6 through a connecting pipe. A second valve 20 is provided on the connecting pipe between the rich liquid heater 6 and the falling film desorption tower 4; the falling film evaporation system 23 also includes a circulation pump 18, which is connected to the upper and lower parts of the falling film desorption tower 4 respectively.

[0065] According to a fourth embodiment of the present invention, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger 2 to obtain a first heat-exchange rich liquid and a first heat-exchange lean liquid. The rich liquid heater 6 heats the first heat-exchange rich liquid to obtain a heated rich liquid. The desorption system 21 desorbs the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system 23 desorbs the liquid with a viscosity ≥30 mPa·s. The rich liquid is heated to a concentration of mPa·s for desorption; the falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8, and a vacuum pump 9 connected in sequence. The upper part of the falling film desorption tower 4 is connected to the rich liquid heater 6 through a connecting pipe. A second valve 20 is provided on the connecting pipe between the rich liquid heater 6 and the falling film desorption tower 4; the falling film evaporation system 23 also includes a circulation pump 18, which is connected to the upper and lower parts of the falling film desorption tower 4 respectively; the desorption system 21 includes a desorption tower 3 and a second condenser 11 connected together. The rich liquid heater 6 is connected to the upper part of the desorption tower 3 through a connecting pipe. A first valve 19 is provided on the connecting pipe.

[0066] According to a fifth embodiment of the present invention, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger 2 to obtain a first heat-exchange rich liquid and a first heat-exchange lean liquid. The rich liquid heater 6 heats the first heat-exchange rich liquid to obtain a heated rich liquid. The desorption system 21 desorbs the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system 23 desorbs the liquid with a viscosity ≥30 mPa·s. The rich liquid is heated to a concentration of mPa·s for desorption; the falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8, and a vacuum pump 9 connected in sequence. The upper part of the falling film desorption tower 4 is connected to the rich liquid heater 6 through a connecting pipe. A second valve 20 is installed on the connecting pipe between the rich liquid heater 6 and the falling film desorption tower 4; the falling film evaporation system 23 also includes a circulation pump 18, which is connected to the upper part of the falling film desorption tower 4 and the... The lower part is connected; the desorption system 21 includes a desorption tower 3 and a second condenser 11 connected together, the rich liquid heater 6 is connected to the upper part of the desorption tower 3 through a connecting pipe, and a first valve 19 is installed on the connecting pipe; the lower part of the absorption tower 1 is connected to the lean and rich liquid heat exchanger 2 through a connecting pipe, and a rich liquid pump 16 is installed on the connecting pipe, and the lower part of the desorption tower 3 is connected to the lean and rich liquid heat exchanger 2 through a connecting pipe, and a lean liquid pump 17 is installed on the connecting pipe.

[0067] According to a sixth embodiment of the present invention, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger 2 to obtain a first heat-exchange rich liquid and a first heat-exchange lean liquid. The rich liquid heater 6 heats the first heat-exchange rich liquid to obtain a heated rich liquid. The desorption system 21 desorbs the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system 23 desorbs the liquid with a viscosity ≥30 mPa·s. The rich liquid is heated to a concentration of mPa·s for desorption; the falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8, and a vacuum pump 9 connected in sequence. The upper part of the falling film desorption tower 4 is connected to the rich liquid heater 6 through a connecting pipe, and a second valve 20 is installed on the connecting pipe between the rich liquid heater 6 and the falling film desorption tower 4; the falling film evaporation system 23 also includes a circulation pump 18, which is connected to the upper and lower parts of the falling film desorption tower 4 respectively; The desorption system 21 includes a desorption tower 3 and a second condenser 11 connected together. The rich liquid heater 6 is connected to the upper part of the desorption tower 3 through a connecting pipe, and a first valve 19 is installed on the connecting pipe. The lower part of the absorption tower 1 is connected to the lean and rich liquid heat exchanger 2 through a connecting pipe, and a rich liquid pump 16 is installed on the connecting pipe. The lower part of the desorption tower 3 is connected to the lean and rich liquid heat exchanger 2 through a connecting pipe, and a lean liquid pump 17 is installed on the connecting pipe. The evaporation chamber 7 is connected to the lean liquid pump 17.

[0068] According to a seventh embodiment of the present invention, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger 2 to obtain a first heat-exchange rich liquid and a first heat-exchange lean liquid. The rich liquid heater 6 heats the first heat-exchange rich liquid to obtain a heated rich liquid. The desorption system 21 desorbs the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system 23 desorbs the liquid with a viscosity ≥30 mPa·s. The rich liquid is heated to a concentration of mPa·s for desorption; the falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8, and a vacuum pump 9 connected in sequence. The upper part of the falling film desorption tower 4 is connected to the rich liquid heater 6 through a connecting pipe. A second valve 20 is installed on the connecting pipe between the rich liquid heater 6 and the falling film desorption tower 4; the falling film evaporation system 23 also includes a circulation pump 18, which is connected to the upper and lower parts of the falling film desorption tower 4 respectively; the desorption system 21 includes a desorption tower 3 and a second condenser 11 connected together, and the rich liquid heater 6... The upper part of the desorption tower 3 is connected to the upper part of the desorption tower 3 via a connecting pipe, on which a first valve 19 is installed; the lower part of the absorption tower 1 is connected to the lean-rich liquid heat exchanger 2 via a connecting pipe, on which a rich liquid pump 16 is installed; the lower part of the desorption tower 3 is connected to the lean-rich liquid heat exchanger 2 via a connecting pipe, on which a lean liquid pump 17 is installed; the evaporation chamber 7 is connected to the lean liquid pump 17; the system also includes a lean liquid cooler 5, used to cool the first heat exchange lean liquid from the lean-rich liquid heat exchanger 2, and return the cooled first heat exchange lean liquid to the absorption tower 1.

[0069] According to an eighth embodiment of the present invention, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The rich liquid from the absorption tower 1 and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger 2 to obtain a first heat-exchange rich liquid and a first heat-exchange lean liquid. The rich liquid heater 6 heats the first heat-exchange rich liquid to obtain a heated rich liquid. The desorption system 21 desorbs the heated rich liquid with a viscosity <30 mPa·s, and the falling film evaporation system 23 desorbs the liquid with a viscosity ≥30 mPa·s. The rich liquid is heated to a concentration of mPa·s for desorption; the falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8, and a vacuum pump 9 connected in sequence. The upper part of the falling film desorption tower 4 is connected to the rich liquid heater 6 through a connecting pipe. A second valve 20 is installed on the connecting pipe between the rich liquid heater 6 and the falling film desorption tower 4; the falling film evaporation system 23 also includes a circulation pump 18, which is connected to the upper and lower parts of the falling film desorption tower 4 respectively; the desorption system 21 includes a desorption tower 3 and a second condenser 11 connected together. The rich liquid heater 6 is connected to the upper part of the desorption tower 3 through a connecting pipe. A first valve 19 is installed on the connecting pipe; the lower part of the absorption tower 1 The system is connected to the rich-lean liquid heat exchanger 2 via a connecting pipe, on which a rich liquid pump 16 is installed. The lower part of the desorption tower 3 is connected to the rich-lean liquid heat exchanger 2 via a connecting pipe, on which a lean liquid pump 17 is installed. The evaporation chamber 7 is connected to the lean liquid pump 17. The system also includes a lean liquid cooler 5, used to cool the first heat exchange lean liquid from the rich-lean liquid heat exchanger 2 and return the cooled first heat exchange lean liquid to the absorption tower 1. A separator 22 is installed at the lower end of the absorption tower 1. The separator 22 is connected to the rich liquid pump 16 and the lean liquid cooler 5 via a connecting pipe. A light phase pump 15 is installed on the connecting pipe between the separator 22 and the lean liquid cooler 5.

[0070] A second aspect of the present invention provides a carbon dioxide absorption method based on multiple absorbents, implemented in the system described above. The method includes: introducing carbon dioxide-containing flue gas into the absorption tower 1 and contacting it with absorbents to absorb carbon dioxide, obtaining a carbon dioxide-rich liquid; then conveying the rich liquid to the lean-rich liquid heat exchanger 2, whereby the rich liquid exchanges heat with the lean liquid flowing out of the desorption unit, obtaining a first heat-exchange rich liquid and a first heat-exchange lean liquid; inputting the first heat-exchange rich liquid into the rich liquid heater 6 for heating, obtaining a heated rich liquid; when the viscosity of the heated rich liquid is <30 mPa·s, conveying the heated rich liquid to the desorption tower 3 for desorption; when the viscosity of the heated rich liquid is ≥30 mPa·s, conveying the heated rich liquid to the falling film evaporation system 23 for desorption, obtaining the lean liquid; inputting the first heat-exchange lean liquid into the lean liquid cooler 5 for cooling, and then returning it to the absorption tower 1.

[0071] In the method described in this invention, in a specific embodiment, the flue gas contains 9-13% carbon dioxide, 86-90% nitrogen, 0.085-0.088% carbon monoxide and 0.012-0.015% sulfur dioxide, with the remaining components being other impurities, including dust, etc.

[0072] In the method described in this invention, in a specific embodiment, the temperature of the flue gas is 30-60°C, for example, it can be 30°C, 45°C, 50°C or 60°C.

[0073] In the method described in this invention, in a specific embodiment, the absorbent filled in the absorption tower 1 can be determined according to the actual situation. Specifically, the absorbent is a two-phase absorbent, a complex amine absorbent, or an ionic liquid absorbent.

[0074] In the method described in this invention, in a specific embodiment, the viscosity of the two-phase absorbent is 10-15 mPa·s; the viscosity of the composite amine absorbent is 0.8-10 mPa·s; and the viscosity of the ionic liquid absorbent is 30-100 mPa·s.

[0075] In the method described in this invention, in specific embodiments, the sources of the two-phase absorbent, the complex amine absorbent, and the ionic liquid absorbent are not limited; they can be purchased or prepared by a certain formula.

[0076] In the method described in this invention, in a specific embodiment, the temperature of the rich liquid flowing out of the absorption tower 1 is 45-55°C.

[0077] In the method described in this invention, in a specific embodiment, the rich liquid undergoes heat exchange in the lean-rich liquid heat exchanger 2, and the temperature is increased from 45-55°C to 60-90°C to obtain the first heat exchange rich liquid, for example, it can be 60°C, 70°C, 80°C or 90°C.

[0078] In the method described in this invention, in a specific embodiment, the temperature of the lean solution output from the desorption unit is 110-120°C.

[0079] In the method described in this invention, in a specific embodiment, the lean liquid undergoes heat exchange in the lean-rich liquid heat exchanger 2, and the temperature is reduced from 110-120℃ to 50-80℃ to obtain the first heat exchange lean liquid, for example, it can be 50℃, 60℃, 70℃ or 80℃.

[0080] In the method described in this invention, in a specific embodiment, the temperature of the heated rich liquid is 100-125°C, for example, it can be 100°C, 110°C, 115°C, 120°C or 125°C.

[0081] In the method described in this invention, in a specific embodiment, the first heat exchange lean liquid is further cooled to 25-40°C in the lean liquid cooler 5, for example, it can be 25°C, 30°C, 35°C or 40°C.

[0082] The following examples further illustrate the carbon dioxide absorption system and method based on multiple absorbents described in this invention. These examples are implemented based on the technical solution of this invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this invention is not limited to the following examples.

[0083] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0084] Example 1

[0085] like Figure 1As shown, the carbon dioxide absorption system based on multiple absorbents includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The lower end of the absorption tower 1 is connected to the lean-rich liquid heat exchanger 2 via a connecting pipe. A rich liquid pump 16 is installed on the connecting pipe, and the rich liquid pump 16 is connected to the rich liquid heater 6. The desorption system 21 includes a desorption tower 3 and a second condenser 11. The rich liquid heater 6 is connected to the desorption tower 3 via a connecting pipe, and a first valve 19 is installed on the connecting pipe. The falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, a third condenser 12, a negative pressure storage tank 8, and a vacuum pump 9 connected in sequence, as well as a circulation pump 18 connected to the falling film desorption tower 4. The falling film desorption tower 4 is connected to the rich liquid heater 6 via a connecting pipe, and a second valve 20 is installed on the connecting pipe; the lower end of the desorption tower 3 is connected to the lean and rich liquid heat exchanger 2 via a connecting pipe, and a lean liquid pump 17 is installed on the connecting pipe, and the evaporation chamber 7 is connected to the lean liquid pump 17; a separator 22 is installed at the lower end of the absorption tower 1, and the separator 22 is connected to the rich liquid pump 16; the separator 22 is connected to the lean liquid cooler 5 via a connecting pipe, and a light phase pump 15 is installed on the connecting pipe between the separator 22 and the lean liquid cooler 5; the upper end of the absorption tower 1 is sequentially connected to the first condenser 10 and the first gas analyzer 13, the second condenser 11 is connected to the second gas analyzer 14, and the vacuum pump 9 is connected to the second gas analyzer 14.

[0086] In this embodiment, flue gas containing 13% carbon dioxide, 86% nitrogen, 0.088% carbon monoxide, and 0.012% sulfur dioxide at a temperature of 45°C enters from the bottom of absorption tower 1. Absorption tower 1 is filled with a two-phase absorbent composed of N,N-diethylethanolamine (DEEA) and 1,4-butanediamine (BDA) (in a 2:1 ratio) with a viscosity of 3 mPa·s (at 40°C). The two-phase absorbent flows downwards from the top of the tower, contacting the flue gas countercurrently to form a light phase and a heavy phase. The purified gas escapes through the top of absorption tower 1, is condensed in the first condenser 10, and its composition is analyzed in the first gas analyzer 13 before being discharged into the vent pipe. The viscosity of the heavy phase is measured to be 4 mPa·s. The light phase and the heavy phase are further separated in the separator 22 at a pressure of mPa·s. The light phase is pumped by the light phase pump 15 into the lean liquid cooler 5, where the temperature is cooled from 60°C to 28°C, and then returned to the absorption tower 1. The heavy phase is pumped by the rich liquid pump 16 into the lean-rich liquid heat exchanger 2 for heat exchange to obtain the first heat exchange rich liquid, where the temperature is increased from 50°C to 90°C. The first heat exchange rich liquid is then fed to the rich liquid heater 6 for heating to obtain the heated rich liquid, where the temperature is increased from 90°C to 125°C. The first valve 19 is opened and the second valve 20 is closed, and the heated rich liquid from the rich liquid heater 6 is heated. The liquid is fed to desorption tower 3 for desorption at a temperature of 120°C, resulting in a lean liquid and desorbed gas at 115°C. The lean liquid flows out from the bottom of desorption tower 3 and passes through lean liquid pump 17 into lean-rich liquid heat exchanger 2 for heat exchange, where its temperature decreases from 115°C to 70°C. It is then further fed to lean liquid cooler 5 for cooling, where its temperature decreases from 70°C to 40°C, and finally returned to absorption tower 1. The desorbed gas escapes from the top of desorption tower 3, is condensed in second condenser 11, and its gas composition is analyzed in second gas analyzer 14 before being discharged into the vent pipe. The gas detected by first gas analyzer 13 contains 0.21% carbon dioxide, and the gas detected by second gas analyzer 14 contains 99.95% carbon dioxide.

[0087] Example 2

[0088] Implemented in accordance with Embodiment 1, except that the separator 22 and light phase pump 15 are removed, and the bottom of the absorption tower 1 is directly connected to the rich liquid pump 16. The system includes an absorption tower 1, a lean-rich liquid heat exchanger 2, a rich liquid heater 6, a desorption unit, and a lean liquid cooler 5. The desorption unit includes a desorption system 21 and a falling film evaporation system 23 connected in parallel. The lower end of the absorption tower 1 is connected to the lean-rich liquid heat exchanger 2 via a connecting pipe, on which the rich liquid pump 16 is installed. The rich liquid pump 16 is connected to the rich liquid heater 6. The desorption system 21 includes a desorption tower 3 and a second condenser 11. The rich liquid heater 6 is connected to the desorption tower 3 via a connecting pipe, on which a first valve 19 is installed. The falling film evaporation system 23 includes a falling film desorption tower 4, an evaporation chamber 7, and a second condenser 11 connected in sequence. The absorption tower 3 consists of a three-phase condenser 12, a negative pressure storage tank 8, and a vacuum pump 9, as well as a circulating pump 18 connected to the falling film desorption tower 4. The falling film desorption tower 4 is connected to the rich liquid heater 6 via a connecting pipe, on which a second valve 20 is installed. The lower end of the desorption tower 3 is connected to the lean and rich liquid heat exchanger 2 via a connecting pipe, on which a lean liquid pump 17 is installed. The evaporation chamber 7 is connected to the lean liquid pump 17. The upper end of the absorption tower 1 is sequentially connected to the first condenser 10 and the first gas analyzer 13, and the second condenser 11 and the second gas analyzer 14 are connected. The vacuum pump 9 is connected to the second gas analyzer 14.

[0089] In this embodiment, flue gas at a temperature of 45°C, containing 12% carbon dioxide, 87% nitrogen, 0.087% carbon monoxide, and 0.013% sulfur dioxide, enters from the bottom of absorption tower 1. Absorption tower 1 is filled with a gas having a viscosity of 80... A four-season ammonium salt-type ionic liquid absorbent with a viscosity of 90 mPa·s is used. The absorbent flows downwards from the top of the tower, counter-currently contacting the flue gas to obtain a rich liquid. The purified gas escapes from the top of the absorption tower 1, is condensed in the first condenser 10, and its composition is analyzed in the first gas analyzer 13 before being discharged into the vent pipe. The viscosity of the rich liquid is measured to be 90 mPa·s. The rich liquid is then pumped by a rich liquid pump 16 into a lean-rich liquid heat exchanger 2 for heat exchange to obtain a first heat-exchange rich liquid, with the temperature increasing from 40°C to 80°C. This first heat-exchange rich liquid is then further fed to a rich liquid heater 6 for heating to obtain a heated rich liquid, with the temperature increasing from 80°C to 125°C. A second valve 20 is opened, and a first valve 19 is closed, allowing the heated rich liquid from the rich liquid heater 6 to be transported to a falling film evaporation system 23 for desorption. The hot rich liquid enters from the top of the falling film desorption tower 4, with a desorption temperature of 120°C. The vacuum pump 9 provides a desorption pressure of 15 kPa(a). The heated rich liquid is continuously circulated in the falling film desorption tower 4 by the circulation pump 18 to improve the desorption efficiency. The lean liquid and desorbed gas produced by desorption enter the evaporation chamber 7 for separation. The separated lean liquid flows out from the bottom of the evaporation chamber 7 and enters the lean-rich liquid heat exchanger 2 through the lean liquid pump 17 for heat exchange, where the temperature is reduced from 110°C to 60°C. Then, it is continued to be transported to the lean liquid cooler 5 for cooling, where the temperature is reduced from 60°C to 28°C. Finally, it is reused in the absorption tower 1. The separated desorbed gas is condensed in the third condenser 12. The condensed liquid and desorbed gas enter the negative pressure storage tank 8 for separation and gas composition analysis in the second gas analyzer 14. Then, it is discharged into the vent pipe. The gas detected by the first gas analyzer 13 contains 0.05% carbon dioxide, and the gas detected by the second gas analyzer 14 contains 99.95% carbon dioxide.

[0090] As can be seen from the above embodiments, the carbon dioxide absorption system based on multiple absorbents of the present invention can effectively achieve carbon capture simultaneously in the carbon dioxide absorption system of the present invention using composite amine absorbents, two-phase absorbents and ionic liquid absorbents with different viscosities. Moreover, the system has a small footprint and is flexible in operation.

[0091] 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 carbon dioxide absorption system based on a plurality of absorbents, characterized by, The system comprises an absorption tower (1), a lean-rich liquid heat exchanger (2), a rich liquid heater (6) and a desorption unit, the desorption unit comprises a desorption system (21) and a falling film evaporation system (23) connected in parallel, Wherein, the rich liquid from the absorption tower (1) and the lean liquid from the desorption unit exchange heat in the lean-rich liquid heat exchanger (2), to obtain first heat-exchanged rich liquid and first heat-exchanged lean liquid; The rich liquid heater (6) is used for heating the first heat-exchanged rich liquid to obtain heated rich liquid; The desorption system (21) is used for desorbing the heated rich liquid with viscosity < 30 mpa·s, and the falling film evaporation system (23) is used for desorbing the heated rich liquid with viscosity ≥ 30 mpa·s.

2. The carbon dioxide absorption system based on multiple absorbents according to claim 1, wherein, The falling film evaporation system (23) comprises a falling film desorption tower (4), an evaporation chamber (7), a third condenser (12), a negative pressure storage tank (8) and a vacuum pump (9) connected in sequence, and the upper part of the falling film desorption tower (4) is connected with the rich liquid heater (6) through a connecting pipeline.

3. The carbon dioxide absorption system based on multiple absorbents according to claim 2, a second valve (20) is arranged on the connecting pipeline of the rich liquid heater (6) and the falling film desorption tower (4).

4. The carbon dioxide absorption system based on multiple absorbents according to claim 3, wherein, The falling film evaporation system (23) further comprises a circulating pump (18), and the circulating pump (18) is connected with the upper part and the lower part of the falling film desorption tower (4) respectively.

5. The carbon dioxide absorption system based on multiple absorbents according to claim 3 or 4, characterized in that, The desorption system (21) comprises a desorption tower (3) and a second condenser (11) connected with each other; The rich liquid heater (6) is connected with the upper part of the desorption tower (3) through a connecting pipeline, and a first valve (19) is arranged on the connecting pipeline.

6. The carbon dioxide absorption system based on multiple absorbents according to claim 5, wherein, The lower part of the absorption tower (1) is connected with the lean-rich liquid heat exchanger (2) through a connecting pipeline, and a rich liquid pump (16) is arranged on the connecting pipeline; The lower part of the desorption tower (3) is connected with the lean-rich liquid heat exchanger (2) through a connecting pipeline, and a lean liquid pump (17) is arranged on the connecting pipeline.

7. The carbon dioxide absorption system based on multiple absorbents according to claim 6, wherein, The evaporation chamber (7) is connected with the lean liquid pump (17).

8. The carbon dioxide absorption system based on multiple absorbents according to claim 6 or 7, characterized in that, The system further comprises a lean liquid cooler (5) for cooling the first heat-exchanged lean liquid from the lean-rich liquid heat exchanger (2) and returning the cooled first heat-exchanged lean liquid to the absorption tower (1).

9. The carbon dioxide absorption system based on multiple absorbents according to claim 8, wherein, The lower end of the absorption tower (1) is provided with a layering device (22).

10. The carbon dioxide absorption system based on multiple absorbents according to claim 9, wherein, The layering device (22) is connected with the rich liquid pump (16).

11. The carbon dioxide absorption system based on multiple absorbents according to claim 10, wherein, The layering device (22) is connected with the lean liquid cooler (5) through a connecting pipeline.

12. The carbon dioxide absorption system based on multiple absorbents according to claim 11, wherein, A light phase pump (15) is arranged on the connecting pipeline of the layering device (22) and the lean liquid cooler (5).

13. The carbon dioxide absorption system based on multiple absorbents according to claim 8, wherein, The upper end of the absorption tower (1) is connected with a first condenser (10) and a first gas analyzer (13) in sequence.

14. The carbon dioxide absorption system based on multiple absorbents according to claim 13, wherein, The system further comprises a second gas analyzer (14) for analyzing the gas from the vacuum pump (9) and the second condenser (11).

15. A method for carbon dioxide absorption based on a plurality of absorbents, which is carried out in the system according to any one of claims 1 to 14, characterized in that, The method comprises: The flue gas containing carbon dioxide is introduced into the absorption tower (1) and contacted with the absorbent to absorb carbon dioxide to obtain rich liquid containing carbon dioxide, and then the rich liquid is transported into the rich-lean liquid heat exchanger (2) to heat exchange the rich liquid with lean liquid out of the desorption unit to obtain first heat exchange rich liquid and first heat exchange lean liquid, the first heat exchange rich liquid is input into the rich liquid heater (6) to heat to obtain heated rich liquid; when the viscosity of the heated rich liquid is < 30 mpa·s, the heated rich liquid is transported into the desorption tower (3) to desorb, when the viscosity of the heated rich liquid is ≥ 30 mpa·s, the heated rich liquid is transported into the falling film evaporation system (23) to desorb to obtain the lean liquid; the first heat exchange lean liquid is input into the lean liquid cooler (5) to cool, and then returned to the absorption tower (1).

16. The method of claim 15, wherein the plurality of absorbents are selected from the group consisting of amines, amine salts, alkanolamines, alkanolamine salts, and mixtures thereof. The flue gas contains 9-13% of carbon dioxide, 86-90% of nitrogen, 0.085-0.088% of carbon monoxide and 0.012-0.015% of sulfur dioxide.

17. The carbon dioxide absorption method based on multiple absorbents according to claim 15 or 16, characterized by, The temperature of the flue gas is 30-60℃.

18. The method of claim 17, wherein the plurality of absorbents are selected from the group consisting of amines, amine salts, amines and amine salts, and mixtures thereof. The absorbent is two-phase absorbent, composite amine absorbent or ionic liquid absorbent.

19. The method of claim 18, wherein the plurality of absorbents are selected from the group consisting of amines, amine salts, amines and amine salts, and mixtures thereof. The viscosity of the two-phase absorbent is 10-15 mpa·s.

20. The method of claim 18, wherein the plurality of absorbents comprises a first absorbent and a second absorbent, and the first absorbent is a solution of potassium carbonate and the second absorbent is a solution of potassium bicarbonate. The viscosity of the composite amine absorbent is 0.8-10 mpa·s.

21. The method of claim 18, wherein the plurality of absorbents comprises a first absorbent and a second absorbent, and the first absorbent is a solution of potassium carbonate and the second absorbent is a solution of potassium bicarbonate. The viscosity of the ionic liquid absorbent is 30-100 mpa·s.

22. The method according to claim 15 or 16, wherein The temperature of the first heat exchange rich liquid is 60-90℃.

23. The method according to claim 15 or 16, wherein The temperature of the first heat exchange lean liquid is 50-80℃.

24. The carbon dioxide absorption method based on multiple absorbents according to claim 15 or 16, characterized by, The temperature of the heated rich liquid is 100-125℃.

25. The method according to claim 15 or 16, wherein The first heat exchange lean liquid is further cooled to 25-40℃.

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