A carbon capture system recovers waste heat from a deabsorber overhead with a cascade heat pump

Abstract

This invention provides a carbon capture system for recovering waste heat from the overhead gas of a desorption tower using a cascade heat pump. The system includes a desorption tower, an absorption tower, a lean-rich liquid heat exchanger, a high-temperature waste heat recovery unit, a second heat exchanger, and a cascade heat pump unit. The invention utilizes circulating water and lean liquid as the working fluids for recovering the high-temperature and low-temperature waste heat from the overhead gas, respectively, effectively recovering and utilizing the waste heat from the desorption tower and reducing energy consumption. By replacing the circulating water medium between the low-temperature waste heat recovery section and the high-temperature waste heat recovery unit with a cascade heat pump unit, the temperature of the low-temperature waste heat can be directly and significantly increased, thereby improving the COP of the low-temperature heat pump. The module for recovering the high-temperature waste heat from the overhead gas (i.e., the high-temperature waste heat recovery unit) is completely independent of the module for recovering the low-temperature waste heat (including the second heat exchanger and the cascade heat pump unit), achieving modular waste heat recovery and improving the flexibility and resilience of the carbon capture system.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture technology, and in particular to a carbon capture system that uses a cascade heat pump to recover waste heat from the top gas of a desorption tower. Background Technology

[0002] Existing carbon capture processes often use absorbents such as ethanolamine (MEA) solutions to absorb CO2, and then use thermal desorption to regenerate the absorbent and generate CO2 products.

[0003] MEA (Metal-on-Anatomical Extraction) is currently the most mature and widely used post-combustion chemical absorption carbon capture technology, and its process flow has become the industry benchmark. Traditional MEA carbon capture systems include... Figure 1 As shown, the absorbent is a lean CO2 solution, which becomes a rich CO2 solution in the absorption tower. The rich solution then passes through a lean-rich solution heat exchanger and enters the desorption tower, where it undergoes thermal desorption to produce CO2 products, simultaneously regenerating the lean CO2 solution. The regenerated lean solution is replenished with water and absorbent before re-entering the absorption tower to complete the cycle. However, the existing carbon capture process still requires relatively high heat and cold consumption, and there is currently no effective solution to recover the recoverable sensible heat and latent heat of phase change in the overhead gas of the desorption tower. In particular, the recovery measures for the low-temperature waste heat of the overhead gas are relatively simple, resulting in weak flexibility and resilience to fluctuations in the overall system.

[0004] Therefore, for carbon capture thermal desorption processes such as MEA, effectively recovering the waste heat from the overhead gas, expanding the means of recovering the low-temperature waste heat from the overhead gas, and improving the system's flexibility and resistance to fluctuations are important requirements for carbon capture processes. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a carbon capture system for recovering waste heat from the top gas of a desorption tower using a cascade heat pump to overcome or at least partially solve the above problems.

[0006] One objective of this invention is to effectively recover and utilize the waste heat from the top gas of the desorption tower, while improving the flexibility and resistance to fluctuations of the entire system.

[0007] A further objective of this invention is to further improve the waste heat recovery efficiency of high-temperature heat pumps and reduce energy consumption.

[0008] Specifically, the present invention provides a carbon capture system for recovering waste heat from the overhead gas of a desorption tower using a cascade heat pump, comprising: Desorption tower, with a top gas outlet; The absorption tower is configured to use an absorbent liquid to absorb carbon dioxide from the gas to be treated, thereby obtaining a rich liquid. A rich-lean-rich liquid heat exchanger is connected between an absorption tower and a desorption tower and is configured to exchange heat between the rich liquid from the absorption tower and the lean liquid from the desorption tower. A high-temperature waste heat recovery unit includes a first heat exchanger and a first waste heat utilization element. The first heat exchanger has a gas inlet and a gas outlet connected to the top gas outlet of the tower, and is configured to allow the waste heat recovery medium flowing through it to exchange heat with the top gas output from the top gas outlet of the tower to recover the waste heat of the top gas. The first waste heat utilization element is connected to the desorption tower and is configured to use the waste heat recovered by the first heat exchanger to heat the rich liquid and / or medium-lean liquid of the desorption tower through heat exchange. The second heat exchanger, located downstream of the gas outlet of the first heat exchanger and connected to the cold lean liquid outlet of the lean-rich liquid heat exchanger, is configured to allow the lean liquid from the lean-rich liquid heat exchanger to exchange heat with the overhead gas after passing through the first heat exchanger in order to recover the waste heat of the overhead gas; and Cascade heat pump unit, comprising: The first heat pump subunit includes a third heat exchanger and a fourth heat exchanger sequentially connected in the first working fluid loop along the flow direction of the first heat pump working fluid. The third heat exchanger is also connected to a second heat exchanger and is configured to allow the first heat pump working fluid flowing through it to exchange heat with the lean liquid after heat exchange from the second heat exchanger, thereby absorbing heat from the lean liquid; and The second heat pump subunit includes a fourth heat exchanger and a second waste heat utilization element sequentially connected in the second working fluid loop along the flow direction of the second heat pump working fluid. The fourth heat exchanger is configured to allow the second heat pump working fluid flowing through it to exchange heat with the first heat pump working fluid from the third heat exchanger to absorb heat from the first heat pump working fluid. The second waste heat utilization element is connected to the desorption tower and is configured to use the second heat pump working fluid after absorbing heat to heat the rich liquid and / or medium-lean liquid of the desorption tower through heat exchange.

[0009] Optionally, the high-temperature waste heat recovery unit includes: The water circulation subunit includes a first heat exchanger and a fifth heat exchanger connected to each other to form a water circulation loop. The first heat exchanger is configured to allow water flowing through it as a waste heat recovery medium to exchange heat with overhead gas, and to output the heat-exchanged water to the fifth heat exchanger; and The third heat pump subunit includes a fifth heat exchanger and a first waste heat utilization element sequentially connected in the third working fluid loop along the flow direction of the third heat pump working fluid. The fifth heat exchanger is configured to allow the third heat pump working fluid flowing through it to exchange heat with water from the first heat exchanger to absorb heat from the water. The first waste heat utilization element is configured to use the heat from the third heat pump working fluid from the fifth heat exchanger to heat the rich liquid and / or lean liquid of the desorption tower.

[0010] Optionally, the third heat pump subunit is a compression heat pump unit, and the third heat pump working fluid that has absorbed heat in the fifth heat exchanger evaporates at least partially into a gaseous state. The third heat pump subunit also includes: A first compressor, connected in the third working fluid loop and located downstream of the fifth heat exchanger and upstream of the first waste heat recovery element, is configured to compress the gaseous third heat pump working fluid; and The first throttling valve, connected in the third working fluid loop and located downstream of the first waste heat utilization element and upstream of the fifth heat exchanger, is configured to depressurize the first heat pump working fluid from the first waste heat utilization element.

[0011] Optionally, the high-temperature waste heat recovery unit is a heat pump unit, and a fourth heat pump working fluid is used as the waste heat recovery medium. The first heat exchanger and the first waste heat utilization element are sequentially connected along the flow direction of the fourth heat pump working fluid to form the fourth working fluid loop.

[0012] Optionally, the high-temperature waste heat recovery unit is a compression heat pump unit, and the fourth heat pump working fluid after heat exchange in the first heat exchanger is at least partially evaporated into a gaseous state. The high-temperature waste heat recovery unit also includes: The second compressor, connected in the fourth working fluid loop and located downstream of the first heat exchanger and upstream of the first waste heat recovery element, is configured to compress the gaseous fourth heat pump working fluid; and The second throttle valve, connected in the fourth working fluid loop and located downstream of the first waste heat utilization element and upstream of the first heat exchanger, is configured to depressurize the fourth heat pump working fluid from the first waste heat utilization element.

[0013] Optionally, the first heat pump subunit is a compression heat pump unit, and the first heat pump working fluid after heat exchange in the third heat exchanger is at least partially evaporated into a gaseous state. The first heat pump subunit also includes: A third compressor, connected in the first working fluid loop and located downstream of the third heat exchanger and upstream of the fourth heat exchanger, is configured to compress the gaseous first heat pump working fluid; and The third throttle valve, connected in the first working fluid loop and located downstream of the fourth heat exchanger and upstream of the third heat exchanger, is configured to depressurize the first heat pump working fluid from the fourth heat exchanger.

[0014] Optionally, the second heat pump subunit is a compression heat pump unit, and the second heat pump working fluid after heat exchange in the fourth heat exchanger evaporates at least partially into a gaseous state. The second heat pump subunit also includes: A fourth compressor, connected in the second working fluid loop and located downstream of the fourth heat exchanger and upstream of the second waste heat recovery element, is configured to compress the gaseous second heat pump working fluid; and The fourth throttle valve, connected in the second working fluid loop and located downstream of the second waste heat utilization element and upstream of the fourth heat exchanger, is configured to depressurize the second heat pump working fluid from the second waste heat utilization element.

[0015] Optionally, both the first waste heat utilization element and the second waste heat utilization element include: A reboiler is connected to the bottom of the desorption tower; and / or Interstage heaters are connected to the middle section of the desorption tower.

[0016] Optionally, the carbon capture system also includes: The first gas-liquid separator is located between the first heat exchanger and the second heat exchanger, and is configured to separate the gas from the overhead gas after passing through the first heat exchanger and output the separated overhead gas to the second heat exchanger. The second gas-liquid separator is connected to the second heat exchanger and is configured to perform gas-liquid separation on the overhead gas after passing through the second heat exchanger. The fifth compressor is connected to the second gas-liquid separator and is configured to compress the gas separated by the second gas-liquid separator; A cooler, connected to the fifth compressor, is configured to cool the compressed gas; A third gas-liquid separator, connected to a cooler, is configured to perform gas-liquid separation on the cooled compressed gas; and The sixth compressor, connected to the third gas-liquid separator, is configured to recompress the separated compressed gas and output it as product gas.

[0017] Optionally, the carbon capture system also includes: The first confluencer is connected to the first gas-liquid separator, the second gas-liquid separator, the third gas-liquid separator, the third heat exchanger, and the absorption tower, respectively. It is configured to mix the liquids separated by the first gas-liquid separator, the second gas-liquid separator, and the third gas-liquid separator with the lean liquid output from the third heat exchanger to form a mixed liquid, and return the mixed liquid to the absorption tower. or A second confluencer, connected between the second and third heat exchangers and to the first and second gas-liquid separators, is configured to mix the lean liquid output from the second heat exchanger with the liquid separated by the first and second gas-liquid separators before outputting it to the third heat exchanger; and The third confluencer is connected to the third gas-liquid separator, the third heat exchanger, and the absorption tower, respectively. It is configured to mix the liquid separated by the third gas-liquid separator with the mixed lean liquid output from the third heat exchanger to form a mixed liquid, and return the mixed liquid to the absorption tower.

[0018] Optionally, the absorbent is an aqueous solution of the absorbent; the absorbent is a homogeneous mixed ligand complex system, including: amine ligands, amino acid ligands, transition metal ions, and activators; The amine-containing ligand is an amino compound capable of forming monodentate, bidentate, or polydentate coordination with metal ions, including chain- or branched alkanolamines, amines, or their derivatives, wherein at least some of the amine-containing ligands have the following structural unit: HO-CR1R2-(CH2). m -CR3R4-NH2, m=1–3; Amino acid ligands include amino acids or their salts, wherein amino acids have dual coordination sites of amino and carboxyl groups; The transition metal ion contains two or more different metal centers, selected from any combination of Cr, Mn, Ni, Cu, Zn, and Co metal ions, with a total concentration of 0.001–1.0 mol / L, and forms the following reversible coordination complex system with an amine-containing ligand: Where n = 1–6, and the coordination constant is in the range of 10. 0 -10 20 They are continuously distributed within a range, thus forming a multi-level coordination energy level structure; The activator is a polyamine compound that promotes CO2 absorption kinetics, with a concentration of 0.05–3.0 mol / L.

[0019] The carbon capture system provided by this invention, which uses a cascade heat pump to recover waste heat from the overhead gas of a desorption tower, employs circulating water and lean liquid as the working fluids for recovering the high-temperature and low-temperature waste heat from the overhead gas, respectively. This effectively recovers and utilizes the waste heat from the overhead gas of the desorption tower, achieving almost 100% heat recovery from the carbon capture system itself and reducing energy consumption by more than 50%. Furthermore, by replacing the circulating water medium between the low-temperature waste heat recovery section and the high-temperature waste heat recovery unit with a cascade heat pump, the temperature of the low-temperature waste heat can be significantly increased, thereby improving the COP (Coefficient of Performance) of the low-temperature heat pump.

[0020] Meanwhile, in the carbon capture system of the present invention, which uses a cascade heat pump to recover waste heat from the top gas of the desorption tower, the module for recovering high-temperature waste heat from the top gas (i.e., the high-temperature waste heat recovery unit) is completely independent of the module for recovering low-temperature waste heat (including the second heat exchanger and the cascade heat pump unit). In other words, modularization of waste heat recovery is achieved. Therefore, the carbon capture system of the present invention has improved flexibility and significantly enhanced resistance to fluctuations under conditions such as renewable energy power supply and variable frequency loads.

[0021] Furthermore, the carbon capture system for recovering waste heat from the top gas of a desorption tower using a cascade heat pump provided by this invention directly recovers the high-temperature waste heat from the top gas using a fourth heat pump working fluid. The entire system no longer requires circulating water as a medium, which further improves the waste heat recovery efficiency and COP of the high-temperature heat pump. Moreover, compared to using circulating water as a heat transfer medium, using a fourth heat pump working fluid to directly recover high-temperature waste heat can increase the high-temperature heat source temperature of the heat pump and allow the heat pump working fluid to have higher operating pressure and temperature, thereby further reducing energy consumption.

[0022] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below.

[0023] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0024] To more clearly illustrate the technical solution of the present invention, some embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that the same reference numerals may indicate the same or similar parts or components in different drawings; the drawings of the present invention are not necessarily drawn to scale. In the drawings: Figure 1 A schematic diagram of a conventional MEA carbon capture process system in the prior art; Figure 2 This is a schematic structural block diagram of a carbon capture system for recovering waste heat from the top gas of a desorption tower using a cascade heat pump, according to an embodiment of the present invention. Figure 3 This is a schematic diagram of a carbon capture system for recovering waste heat from the top gas of a desorption tower using a cascade heat pump, according to another embodiment of the present invention. Figure 4 This is a schematic diagram of a carbon capture system for recovering waste heat from the top gas of a desorption tower using a cascade heat pump, according to another embodiment of the present invention. Detailed Implementation

[0025] Those skilled in the art should understand that the embodiments described below are merely a part of the embodiments of the present invention, and not all of the embodiments of the present invention. These partial embodiments are intended to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by those skilled in the art without creative effort should still fall within the scope of protection of the present invention.

[0026] Furthermore, one or more examples of embodiments of the invention are illustrated in the accompanying drawings. Each example is provided by way of explanation and is not intended to limit the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from the scope or spirit of the invention. For example, features shown or described as part of one embodiment may be used with another embodiment to produce yet another embodiment.

[0027] It should be noted that in the description of this invention, terms such as "center," "upper," "lower," "top," "bottom," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate direction or positional relationships, are based on the direction or positional relationships shown in the accompanying drawings. These are used merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this invention. Furthermore, terms such as "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0028] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection, an indirect connection through intermediate components, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] MEA (Metal-on-Anatomical Extraction) is currently the most mature and widely used post-combustion chemical absorption carbon capture technology. Traditional MEA carbon capture systems include, for example... Figure 1As shown, the CO2-rich solution obtained in the absorber flows out from the bottom outlet of the absorber and enters the lean-rich solution heat exchanger as the RICHOUT stream. It exchanges heat with the CO2-lean solution (LEANOUT) flowing from the bottom of the stripper. After being cooled by the heat exchange, the CO2-lean solution stream S2 mixes with the supplemental absorbent MEAMU to form a mixed stream S5. S5 is then cooled and enters the absorber as the absorbent LEANIN. Simultaneously, the flue gas to be treated enters the absorber from the bottom, is treated by countercurrent contact with the absorbent, and then exits the absorber from the top as the GASOUT stream. The water stream WATEROUT drawn from the middle of the absorber mixes with the supplemental water WATERMU to form stream S1. S1 is cooled, and the resulting water stream WATERIN enters the absorber. The CO2-rich liquid, heated by the lean-rich liquid heat exchanger, is reheated to form a stream called RICHIN, which enters the desorption tower. Thermal desorption occurs within the desorption tower, and the resulting overhead gas is output from the top of the tower. After flash evaporation, CO2 product CO2OUT and condensate COND are obtained. The condensate COND is further separated to obtain streams S7 and S8.

[0030] Figure 1 The paper also presents simulation results for the conventional MEA carbon capture process. The simulation results show that the conventional flue gas carbon capture process requires a total heat consumption of approximately 5.5 GJ / ton of CO2 to the reboiler of the desorber and a cooling capacity of 5-6 GJ / ton of CO2. These cooling capacities are used for the condensation of the overhead gas in the desorber (approximately 110°C → approximately 40°C, accounting for approximately 50% of the total cooling consumption) and the cooling of the lean liquid (from 60°C → 30°C, accounting for approximately 50% of the total cooling consumption), respectively.

[0031] Further simulation using the Aspen Plus process allows for parameter optimization of traditional carbon capture processes through techniques such as rich-liquid diversion and flash regeneration, significantly reducing the required heat and cooling consumption. However, existing carbon capture engineering demonstrations require approximately 3.6–4.0 GJ / ton CO2 for heat, 2.4–4.0 GJ / ton CO2 for cooling, and 70–150 kWh / ton CO2 for electricity.

[0032] Through extensive research, the inventors of this application have innovatively recognized that in traditional carbon capture processes, directly cooling the medium-temperature lean liquid (30-50°C) after passing through a lean-rich liquid heat exchanger at the absorption end before entering the absorption tower wastes 0.5-2.5 GJ / ton of CO2 in heat and generates a corresponding amount of cooling loss. Simultaneously, due to differences in desorption temperature and pressure across different processes, the overhead gas in the desorption tower contains approximately 45%-90% water vapor and 25%-10% non-condensable vapor, of which the high-quality sensible heat and latent heat of phase change from recoverable gaseous water is approximately 1.5-3.5 GJ / ton of CO2. Clearly, the heat and cold in the carbon capture process are mismatched because the heat of reaction from the chemical reaction at the absorption end is difficult to recover from entering the decarbonized flue gas (or air). Furthermore, when the pressure in the desorption tower is between 0.5 bar and 1 bar, the temperature of the overhead gas is between 85°C and 120°C, and this portion of heat has high quality and can be effectively utilized.

[0033] In view of this, the inventors of this application have proposed a technical solution for recovering waste heat from the top gas of a tower. However, the inventors have innovatively recognized that in the solution for recovering the low-temperature waste heat from the top gas of a tower, if the cold source medium needs to be upgraded and then passed through a low-temperature heat pump and a high-temperature heat pump in sequence before it can become usable waste heat, then in this process the high-temperature heat pump will ultimately undertake all the waste heat recovery, which will reduce the flexibility and stability of the entire system.

[0034] To address this, the present invention proposes a two-step decoupled recovery scheme for waste heat from the overhead gas: using a high-temperature heat pump to directly recover the high-grade waste heat from the overhead gas, and using a cascade heat pump to directly upgrade the low-grade waste heat from the overhead gas to a high grade for direct utilization. Specifically, an embodiment of the present invention provides a carbon capture system 100 for recovering waste heat from the overhead gas of a desorption tower using a cascade heat pump.

[0035] Figure 2 This is a schematic structural block diagram of a carbon capture system 100 for recovering waste heat from the overhead gas of a desorption tower using a cascade heat pump, according to an embodiment of the present invention. The heat transfer between the system and the desorption tower 110 is indicated by dashed arrows from the first waste heat recovery element 221 and the second waste heat recovery element 322. See also... Figure 2 As shown, the carbon capture system 100 for recovering waste heat from the top gas of the desorption tower using a cascade heat pump generally includes a desorption tower 110 with a top gas outlet 111, an absorption tower 120, a lean and rich liquid heat exchanger 130, a high-temperature waste heat recovery unit 200, a second heat exchanger 140, and a cascade heat pump unit 300.

[0036] Absorber 120 is configured to absorb carbon dioxide from the gas to be treated using an absorbent to obtain a rich solution. A rich-lean-lean solution heat exchanger 130 is connected between absorber 120 and desorption tower 110. Its cold rich solution inlet, hot rich solution outlet, and hot lean solution inlet are connected to the rich solution outlet of absorber 120, the rich solution inlet of desorption tower 110, and the lean solution outlet of desorption tower 110, respectively. It is configured to allow heat exchange between the rich solution from absorber 120 and the lean solution from desorption tower 110.

[0037] The working principles of the absorption tower 120, the desorption tower 110, and the lean and rich liquid heat exchanger 130 should be known to those skilled in the art. In order not to obscure the focus of the present invention, they will not be specifically described in this application.

[0038] The high-temperature waste heat recovery unit 200 includes a first heat exchanger 211 and a first waste heat utilization element 221. The first heat exchanger 211 has a gas inlet 2111 and a gas outlet 2112 communicating with the top gas outlet 111 of the column, and is configured to allow the waste heat recovery medium flowing through it to exchange heat with the top gas output from the top gas outlet 111 to recover the waste heat of the top gas. The first waste heat utilization element 221 is connected to the desorption column 110 (specifically, it can be thermally connected), and is configured to use the waste heat recovered by the first heat exchanger 211 to heat the rich liquid and / or lean liquid of the desorption column 110 through heat exchange.

[0039] The second heat exchanger 140 is located downstream of the gas outlet 2112 of the first heat exchanger 211 and connected to the cold lean liquid outlet of the lean-rich liquid heat exchanger 130. It is configured to allow the lean liquid from the lean-rich liquid heat exchanger 130 to exchange heat with the overhead gas after passing through the first heat exchanger 211 in order to recover the waste heat of the overhead gas.

[0040] The cascaded heat pump unit 300 includes a coupled first heat pump subunit 310 and a second heat pump subunit 320.

[0041] The first heat pump subunit 310 includes a third heat exchanger 312 and a fourth heat exchanger 313 sequentially connected in the first working fluid loop 311 along the flow direction of the first heat pump working fluid. The third heat exchanger 312 is also connected to the second heat exchanger 140 and is configured to allow the first heat pump working fluid flowing through it to exchange heat with the lean liquid after heat exchange from the second heat exchanger 140, thereby absorbing heat from the lean liquid.

[0042] The second heat pump subunit 320 includes a fourth heat exchanger 313 and a second waste heat utilization element 322 sequentially connected in the second working fluid loop 321 along the flow direction of the second heat pump working fluid. The fourth heat exchanger 313 is configured to allow the second heat pump working fluid flowing through it to exchange heat with the first heat pump working fluid from the third heat exchanger 312 to absorb heat from the first heat pump working fluid. The second waste heat utilization element 322 is connected to the desorption tower 110 (specifically, it may be thermally connected) and is configured to use the heat-absorbed second heat pump working fluid to heat the rich and / or lean solutions of the desorption tower 110 through heat exchange.

[0043] The carbon capture system 100 provided in this embodiment of the invention, which uses a cascade heat pump to recover waste heat from the top gas of a desorption tower, employs circulating water and lean liquor as the working fluids for recovering the high-temperature and low-temperature waste heat from the top gas, respectively. This effectively recovers and utilizes the waste heat from the top gas of the desorption tower 110, achieving almost 100% heat recovery and reducing energy consumption by more than 50%. Furthermore, by replacing the circulating water medium between the low-temperature waste heat recovery section and the high-temperature waste heat recovery unit 200 with a cascade heat pump, the temperature of the low-temperature waste heat can be significantly increased, thereby improving the COP of the low-temperature heat pump.

[0044] Meanwhile, in the carbon capture system 100 of the present invention, which uses a cascade heat pump to recover waste heat from the top gas of the desorption tower, the module for recovering high-temperature waste heat from the top gas (i.e., the high-temperature waste heat recovery unit 200) is completely independent of the module for recovering low-temperature waste heat (including the second heat exchanger 140 and the cascade heat pump unit 300). In other words, modularization of waste heat recovery is achieved. As a result, the carbon capture system 100 of the present invention has improved flexibility and significantly enhanced resistance to fluctuations under conditions such as renewable energy power supply and the need for frequency and load changes.

[0045] Figure 3 This is a schematic diagram of a carbon capture system 100 that recovers waste heat from the overhead gas of a desorption tower using a cascade heat pump, according to another embodiment of the present invention. Figure 4 This is a schematic diagram of a carbon capture system 100 for recovering waste heat from the top gas of a desorption tower using a cascaded heat pump, according to another embodiment of the present invention. The dashed arrows from the first waste heat utilization element 221 and the second waste heat utilization element 322 to the desorption tower 110 indicate the heat transfer between them.

[0046] See Figure 3 As shown, in some optional embodiments, the high-temperature waste heat recovery unit 200 may include a water circulation subunit 210 and a third heat pump subunit 220.

[0047] The water circulation subunit 210 includes a first heat exchanger 211 and a fifth heat exchanger 212 connected to each other to form a water circulation loop 213. The first heat exchanger 211 is configured to allow water flowing through it as a waste heat recovery medium to exchange heat with the overhead air, and to output the heat-exchanged water to the fifth heat exchanger 212.

[0048] The third heat pump subunit 220 includes a fifth heat exchanger 212 and a first waste heat utilization element 221 sequentially connected in the third working fluid loop 222 along the flow direction of the third heat pump working fluid. The fifth heat exchanger 212 is configured to allow the third heat pump working fluid flowing through it to exchange heat with water from the first heat exchanger 211 to absorb heat from the water. The first waste heat utilization element 221 is configured to use the heat from the third heat pump working fluid from the fifth heat exchanger 212 to heat the rich and / or lean liquid in the desorption tower 110.

[0049] In this embodiment, a process of coupling circulating water and a heat pump is used to recover the high-temperature waste heat of the tower top gas, reducing the difficulty of process implementation.

[0050] See also Figure 3 In some further embodiments, the third heat pump subunit 220 may be a compression heat pump unit. The third heat pump working fluid, after absorbing heat in the fifth heat exchanger 212, evaporates at least partially into a gaseous state. The third heat pump subunit 220 may further include: a first compressor 223, connected in the third working fluid loop 222 and located downstream of the fifth heat exchanger 212 and upstream of the first waste heat utilization element 221, configured to compress the gaseous third heat pump working fluid; and a first throttle valve 224, connected in the third working fluid loop 222 and located downstream of the first waste heat utilization element 221 and upstream of the fifth heat exchanger 212, configured to depressurize the first heat pump working fluid from the first waste heat utilization element 221.

[0051] In some optional embodiments, the third heat pump subunit 220 may further include a gas-liquid separator 225 disposed between the fifth heat exchanger 212 and the first compressor 223, for separating the evaporated third heat pump working fluid into gas and liquid phases, and outputting the separated gaseous third heat pump working fluid to the first compressor 223, thereby preventing liquid from entering the first compressor 223 and causing damage to it. This gas-liquid separator may be, for example, a flash tank.

[0052] See Figure 4 As shown, in some alternative embodiments, the high-temperature waste heat recovery unit 200 may be a heat pump unit, and a fourth heat pump working fluid may be used as the waste heat recovery medium. The first heat exchanger 211 and the first waste heat utilization element 221 are sequentially connected along the flow direction of the fourth heat pump working fluid to form a fourth working fluid loop 229.

[0053] See also Figure 4In some further embodiments, the high-temperature waste heat recovery unit 200 is a compression heat pump unit. The fourth heat pump working fluid, after heat exchange within the first heat exchanger 211, evaporates at least partially into a gaseous state. The high-temperature waste heat recovery unit 200 may further include: a second compressor 226 connected in the fourth working fluid loop 229 and located downstream of the first heat exchanger 211 and upstream of the first waste heat utilization element 221, configured to compress the gaseous fourth heat pump working fluid; and a second throttle valve 227 connected in the fourth working fluid loop 229 and located downstream of the first waste heat utilization element 221 and upstream of the first heat exchanger 211, configured to depressurize the fourth heat pump working fluid from the first waste heat utilization element 221.

[0054] In this embodiment, a fourth heat pump working fluid is used to directly recover the high-temperature waste heat from the tower top gas. The entire system no longer requires circulating water as a medium, which further improves the waste heat recovery efficiency and COP of the high-temperature heat pump. Moreover, compared with circulating water as a heat transfer medium, using a fourth heat pump working fluid to directly recover high-temperature waste heat can increase the high-temperature heat source temperature of the heat pump and allow the heat pump working fluid to have higher operating pressure and temperature, thereby further reducing energy consumption.

[0055] In some alternative embodiments, such as Figure 4 As shown, the high-temperature waste heat recovery unit 200 may further include a gas-liquid separator 228 disposed between the first heat exchanger 211 and the second compressor 226, for separating the evaporated fourth heat pump working fluid into gas and liquid components, and outputting the separated gaseous fourth heat pump working fluid to the second compressor 226, thereby preventing liquid from entering the second compressor 226 and causing damage to it. This gas-liquid separator may be, for example, a flash tank.

[0056] See Figure 3 and Figure 4 In some embodiments, the first heat pump subunit 310 may be a compression heat pump unit. The first heat pump working fluid, after heat exchange within the third heat exchanger 312, evaporates at least partially into a gaseous state. The first heat pump subunit 310 may further include: a third compressor 314, connected in the first working fluid loop 311 and located downstream of the third heat exchanger 312 and upstream of the fourth heat exchanger 313, configured to compress the gaseous first heat pump working fluid; and a third throttle valve 315, connected in the first working fluid loop 311 and located downstream of the fourth heat exchanger 313 and upstream of the third heat exchanger 312, configured to depressurize the first heat pump working fluid from the fourth heat exchanger 313.

[0057] In some optional embodiments, the first heat pump subunit 310 may further include a gas-liquid separator 316 disposed between the third heat exchanger 312 and the third compressor 314, for separating the evaporated first heat pump working fluid into gas and liquid phases, and outputting the separated gaseous first heat pump working fluid to the third compressor 314, thereby preventing liquid from entering the third compressor 314 and causing damage to the third compressor 314. This gas-liquid separator may be, for example, a flash tank.

[0058] See also Figure 3 and Figure 4 In some embodiments, the second heat pump subunit 320 may be a compression heat pump unit. The second heat pump working fluid, after heat exchange within the fourth heat exchanger 313, evaporates at least partially into a gaseous state. The second heat pump subunit 320 may further include: a fourth compressor 323, connected in the second working fluid loop 321 and located downstream of the fourth heat exchanger 313 and upstream of the second waste heat utilization element 322, configured to compress the gaseous second heat pump working fluid; and a fourth throttle valve 324, connected in the second working fluid loop 321 and located downstream of the second waste heat utilization element 322 and upstream of the fourth heat exchanger 313, configured to depressurize the second heat pump working fluid from the second waste heat utilization element 322.

[0059] In some optional embodiments, the second heat pump subunit 320 may further include a gas-liquid separator 325 disposed between the fourth heat exchanger 313 and the fourth compressor 323, for separating the evaporated second heat pump working fluid into gas and liquid phases, and outputting the separated gaseous second heat pump working fluid to the fourth compressor 323, thereby preventing liquid from entering the fourth compressor 323 and causing damage to it. This gas-liquid separator may be, for example, a flash tank.

[0060] The first, second, third, and fourth heat pump refrigerants can be commonly used heat pump refrigerants, such as R245fa, as needed. These heat pump refrigerants can be the same or different.

[0061] In some embodiments, the first waste heat utilization element 221 may be a reboiler connected to the bottom of the desorption tower 110 for heating the medium-lean liquor in the desorption tower 110.

[0062] In other embodiments, the first waste heat utilization element 221 may be an interstage heater connected to the middle section of the desorption tower 110 for heating the rich liquid in the desorption tower 110.

[0063] In some other embodiments, the first waste heat utilization element 221 may include a reboiler and an interstage heater.

[0064] Similarly, in some embodiments, the second waste heat utilization element 322 may be a reboiler connected to the bottom of the desorption tower 110 for heating the lean liquor in the desorption tower 110.

[0065] In other embodiments, the second waste heat utilization element 322 may be an interstage heater connected to the middle section of the desorption tower 110 for heating the rich liquid in the desorption tower 110.

[0066] In some other embodiments, the second waste heat utilization element 322 may include a reboiler and an interstage heater.

[0067] See also Figure 3 and Figure 4 In some embodiments, the carbon capture system 100 may further include a first gas-liquid separator 151, which is disposed between the first heat exchanger 211 and the second heat exchanger 140, configured to perform gas-liquid separation on the overhead gas after passing through the first heat exchanger 211, and output the separated overhead gas to the second heat exchanger 140.

[0068] In some embodiments, the carbon capture system 100 may further include: a second gas-liquid separator 152 connected to a second heat exchanger 140 and configured to perform gas-liquid separation on the overhead gas after passing through the second heat exchanger 140; a fifth compressor 153 connected to the second gas-liquid separator 152 and configured to compress the gas separated by the second gas-liquid separator 152; and a cooler 154 connected to the fifth compressor 153 and configured to cool the compressed gas.

[0069] In some embodiments, the carbon capture system 100 may further include: a third gas-liquid separator 155 connected to a cooler 154 and configured to perform gas-liquid separation on the cooled compressed gas; and a sixth compressor 156 connected to the third gas-liquid separator 155 and configured to recompress the separated compressed gas as product gas output.

[0070] See Figure 4 As shown, in some embodiments, the carbon capture system 100 may further include a first confluencer 157, which is connected to the first gas-liquid separator 151, the second gas-liquid separator 152, the third gas-liquid separator 155 and the third heat exchanger 312 respectively, and is configured to mix the liquid separated by the first gas-liquid separator 151, the second gas-liquid separator 152 and the third gas-liquid separator 155 with the lean liquid output from the third heat exchanger 312 to form a mixed liquid.

[0071] Furthermore, the first confluencer 157 can also be connected to the absorption tower 120 and configured to return the mixed liquid to the absorption tower 120.

[0072] See Figure 3As shown, in some other embodiments, the carbon capture system 100 may also include a second combiner 158 and a third combiner 159.

[0073] The second confluencer 158 is connected between the second heat exchanger 140 and the third heat exchanger 312, and is also connected to the first gas-liquid separator 151 and the second gas-liquid separator 152. It is configured to mix the lean liquid output from the second heat exchanger 140 with the liquid separated by the first gas-liquid separator 151 and the second gas-liquid separator 152, and then output the mixture to the third heat exchanger 312.

[0074] The third confluencer 159 is connected to the third gas-liquid separator 155 and the third heat exchanger 312 respectively, and is configured to mix the liquid separated by the third gas-liquid separator 155 with the mixed lean liquid output from the third heat exchanger 312 to form a mixed liquid.

[0075] Furthermore, the third confluencer 159 can also be connected to the absorption tower 120 and configured to return the mixed liquid to the absorption tower 120.

[0076] The absorbent solution is an aqueous solution of the absorbent. In some embodiments, the absorbent is a homogeneous mixed ligand complex system, comprising: an amine-containing ligand, an amino acid ligand, a transition metal ion, and an activator. The amine-containing ligand serves as the first ligand, and the amino acid ligand serves as the second ligand.

[0077] In some optional embodiments, the amine-containing ligand is an amino compound capable of forming monodentate, bidentate, or polydentate coordination with metal ions, including chain or branched alkanolamines, amines, or derivatives thereof, wherein at least a portion of the amine-containing ligand has the structural unit HO-CR1R2-(CH2). m -CR3R4-NH2, m=1–3.

[0078] In some alternative embodiments, the amino acid ligand comprises an amino acid or a salt thereof, wherein the amino acid has a dual coordination site of an amino group and a carboxyl group.

[0079] In some optional embodiments, the transition metal ion comprises two or more different metal centers, selected from any combination of metal ions such as Cr, Mn, Ni, Cu, Zn, and Co, and its total concentration in the homogeneous mixed ligand complex system is 0.001–1.0 mol / L, and it forms the following reversible coordination complex system with the amine-containing ligand: Where n = 1–6, and the coordination constant is in the range of 10. 0 -10 20 They are continuously distributed within a range, thus forming a multi-level coordination energy level structure.

[0080] In some optional embodiments, the activator is a polyamine compound that promotes CO2 absorption kinetics, and its concentration in the homogeneous mixed ligand complex system is 0.05–3.0 mol / L.

[0081] In the absorbent system of the present invention, amine ligands and amino acid ligands form a mixed ligand complex network with dynamic exchange characteristics under the action of transition metal ions. During the CO2 absorption and desorption process, the coordination structure of this complex network undergoes reversible reconstruction, so that the heat of reaction is stored and released at least partly in the form of coordination bond energy, thereby realizing the heat buffering of heat absorption and the energy compensation of heat desorption.

[0082] This absorbent system can achieve CO2 desorption and regeneration in a temperature range of 80-120°C, and compared with the corresponding amine system without metal ions, it exhibits reduced desorption energy consumption or reboiler heat load.

[0083] Transition metal ions regulate the electronic structure and bond energy distribution of amine-containing ligands through coordination-inductive effects, thereby increasing the bond dissociation energy of the α-carbon adjacent to the amine group and inhibiting oxidative degradation through at least one of the following pathways: a) reducing the rate of free radical generation; b) catalyzing the decomposition of peroxy radicals; c) capturing reaction intermediate free radicals to form stable complexes; d) altering the reaction pathway to inhibit the propagation of chain reactions.

[0084] When the absorbent system contains two or more transition metal ions, the bimetallic or multimetallic system can form a synergistic catalytic and energy regulation effect through electronic coupling or redox cycle between different metal centers, thereby simultaneously achieving absorption heat management and anti-degradation performance improvement.

[0085] Those skilled in the art will understand that, in order to promote the circulation of circulating water, waste heat recovery medium and heat pump working fluid, devices such as pumps can be provided to provide circulation driving force in each loop and circuit.

[0086] The following is based on Figure 3 and Figure 4 The carbon capture system 100 shown is a specific embodiment that uses a cascade heat pump to recover waste heat from the top gas of the desorption tower. The technical effect of the technical solution of the present invention is verified through simulation.

[0087] Taking a carbon capture unit with a capacity of 10,000 tons of CO2 / year as an example, since the parameters of the rich liquor correspond to the scale, the simulation starts directly from the rich liquor at the bottom outlet of the absorption tower. The parameters of the low-temperature rich liquor are shown in Table 1 below (corresponding to a carbon load of 0.45 mol / mol).

[0088] Table 1. Rich solution injection conditions for carbon capture process

[0089] Simulation results show that for schemes using circulating water and lean liquid as waste heat recovery working fluids respectively, the COP efficiency of the low-temperature heat pump can reach as high as 6.2, and the cascade heat pump unit 300 can directly raise the low-temperature waste heat of 30℃ to the high-temperature heat of 95℃.

[0090] For schemes that do not use circulating water but instead recover high-temperature and low-temperature waste heat from the overhead gas using a fourth heat pump working fluid and a low-temperature lean liquid respectively, the low-temperature heat pump COP efficiency can reach up to 6.5, and the cascade heat pump unit 300 can directly raise the low-temperature 30℃ waste heat to a high-temperature 95℃. Furthermore, the high-temperature heat pump waste heat recovery efficiency is improved, with the COP increasing to 5.5, and energy consumption only 1.8 GJ / ton CO2. Using the heat pump working fluid to directly recover high-temperature waste heat increases the high-temperature heat source temperature of the heat pump by 10K (from 70K in circulating water to 80K in the overhead gas). Direct heat exchange allows the heat pump working fluid to have higher operating pressure and temperature, thereby reducing energy consumption.

[0091] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0092] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.

Claims

1. A carbon capture system for recovering waste heat from the overhead gas of a desorption tower using a cascade heat pump, comprising: Desorption tower, with a top gas outlet; The absorption tower is configured to use an absorbent liquid to absorb carbon dioxide from the gas to be treated, thereby obtaining a rich liquid. A rich-lean-rich liquid heat exchanger is connected between the absorption tower and the desorption tower and is configured to exchange heat between the rich liquid from the absorption tower and the lean liquid from the desorption tower. A high-temperature waste heat recovery unit includes a first heat exchanger and a first waste heat utilization element. The first heat exchanger has a gas inlet and a gas outlet connected to the top gas outlet of the tower, and is configured to allow the waste heat recovery medium flowing through it to exchange heat with the top gas output from the top gas outlet of the tower to recover the waste heat of the top gas. The first waste heat utilization element is connected to the desorption tower and is configured to use the waste heat recovered by the first heat exchanger to heat the rich liquid and / or lean liquid of the desorption tower through heat exchange. The second heat exchanger is located downstream of the gas outlet of the first heat exchanger and connected to the cold lean liquid outlet of the lean-rich liquid heat exchanger. It is configured to allow the lean liquid from the lean-rich liquid heat exchanger to exchange heat with the overhead gas after passing through the first heat exchanger in order to recover the waste heat of the overhead gas. as well as Cascade heat pump unit, comprising: The first heat pump subunit includes a third heat exchanger and a fourth heat exchanger sequentially connected in the first working fluid loop along the flow direction of the first heat pump working fluid. The third heat exchanger is also connected to the second heat exchanger and is configured to allow the first heat pump working fluid flowing through it to exchange heat with the lean liquid after heat exchange from the second heat exchanger, thereby absorbing heat from the lean liquid. and The second heat pump subunit includes a fourth heat exchanger and a second waste heat utilization element sequentially connected in the second working fluid loop along the flow direction of the second heat pump working fluid. The fourth heat exchanger is configured to allow the second heat pump working fluid flowing through it to exchange heat with the first heat pump working fluid from the third heat exchanger to absorb the heat from the first heat pump working fluid. The second waste heat utilization element is connected to the desorption tower and is configured to use the second heat pump working fluid after absorbing heat to heat the rich liquid and / or lean liquid of the desorption tower through heat exchange.

2. The carbon capture system recovering the heat of the overhead gas of a desorption column with a cascade heat pump according to claim 1, wherein, The high-temperature waste heat recovery unit includes: A water circulation subunit includes a first heat exchanger and a fifth heat exchanger connected to each other to form a water circulation loop. The first heat exchanger is configured to allow water flowing through it as the waste heat recovery medium to exchange heat with the overhead gas, and to output the heat-exchanged water to the fifth heat exchanger. The third heat pump subunit includes the fifth heat exchanger and the first waste heat utilization element, which are sequentially connected in the third working fluid loop along the flow direction of the third heat pump working fluid. The fifth heat exchanger is configured to allow the third heat pump working fluid flowing through it to exchange heat with water from the first heat exchanger to absorb heat from the water. The first waste heat utilization element is configured to use the heat from the third heat pump working fluid from the fifth heat exchanger to heat the rich and / or lean liquid in the desorption tower.

3. The carbon capture system of claim 2, wherein, The third heat pump subunit is a compression heat pump unit, and the third heat pump working fluid that absorbs heat in the fifth heat exchanger evaporates at least partially into a gaseous state. The third heat pump subunit also includes: The first compressor, connected in the third working fluid loop and located downstream of the fifth heat exchanger and upstream of the first waste heat utilization element, is configured to compress the gaseous third heat pump working fluid. as well as A first throttling valve, connected in the third working fluid loop and located downstream of the first waste heat utilization element and upstream of the fifth heat exchanger, is configured to depressurize the first heat pump working fluid from the first waste heat utilization element.

4. The carbon capture system of claim 1, wherein, The high-temperature waste heat recovery unit is a heat pump unit, and the fourth heat pump working fluid is used as the waste heat recovery medium. The first heat exchanger and the first waste heat utilization element are sequentially connected along the flow direction of the fourth heat pump working fluid to form a fourth working fluid loop.

5. The carbon capture system recovering the heat of the overhead gas of a desorption column with a cascade heat pump according to claim 4, wherein, The high-temperature waste heat recovery unit is a compression heat pump unit, and the fourth heat pump working fluid after heat exchange in the first heat exchanger is at least partially evaporated into a gaseous state. The high-temperature waste heat recovery unit also includes: The second compressor, connected in the fourth working fluid loop and located downstream of the first heat exchanger and upstream of the first waste heat utilization element, is configured to compress the gaseous fourth heat pump working fluid. as well as The second throttle valve, connected in the fourth working fluid loop and located downstream of the first waste heat utilization element and upstream of the first heat exchanger, is configured to depressurize the fourth heat pump working fluid from the first waste heat utilization element.

6. The carbon capture system of claim 1, wherein, The first heat pump subunit is a compression heat pump unit, and the first heat pump working fluid after heat exchange in the third heat exchanger evaporates at least partially into a gaseous state. The first heat pump subunit also includes: The third compressor, connected in the first working fluid loop and located downstream of the third heat exchanger and upstream of the fourth heat exchanger, is configured to compress the gaseous first heat pump working fluid. as well as The third throttle valve, connected in the first working fluid loop and located downstream of the fourth heat exchanger and upstream of the third heat exchanger, is configured to depressurize the first heat pump working fluid from the fourth heat exchanger.

7. The carbon capture system of claim 1, wherein, The second heat pump subunit is a compression heat pump unit, and the second heat pump working fluid after heat exchange in the fourth heat exchanger evaporates at least partially into a gaseous state; The second heat pump subunit also includes: The fourth compressor, connected in the second working fluid loop and located downstream of the fourth heat exchanger and upstream of the second waste heat utilization element, is configured to compress the gaseous second heat pump working fluid. as well as A fourth throttle valve, connected in the second working fluid loop and located downstream of the second waste heat utilization element and upstream of the fourth heat exchanger, is configured to depressurize the second heat pump working fluid from the second waste heat utilization element.

8. The carbon capture system recovering the heat of desorption column overhead vapor waste heat with a cascade heat pump of any one of claims 1-7, wherein, Both the first waste heat utilization element and the second waste heat utilization element include: A reboiler is connected to the bottom of the desorption tower; and / or An interstage heater is connected to the middle section of the desorption tower.

9. The carbon capture system for recovering waste heat from the overhead gas of a desorption tower using a cascade heat pump according to any one of claims 1-7, further comprising: A first gas-liquid separator is disposed between the first heat exchanger and the second heat exchanger, and is configured to perform gas-liquid separation on the overhead gas after passing through the first heat exchanger, and output the separated overhead gas to the second heat exchanger. The second gas-liquid separator is connected to the second heat exchanger and is configured to perform gas-liquid separation on the overhead gas after passing through the second heat exchanger. The fifth compressor is connected to the second gas-liquid separator and is configured to compress the gas separated by the second gas-liquid separator; A cooler, connected to the fifth compressor, is configured to cool the compressed gas; The third gas-liquid separator is connected to the cooler and is configured to perform gas-liquid separation on the cooled compressed gas. as well as The sixth compressor is connected to the third gas-liquid separator and is configured to recompress the separated compressed gas and output it as product gas. The carbon capture system further includes: The first confluencer is connected to the first gas-liquid separator, the second gas-liquid separator, the third gas-liquid separator, the third heat exchanger, and the absorption tower, respectively. It is configured to mix the liquids separated by the first gas-liquid separator, the second gas-liquid separator, and the third gas-liquid separator with the lean liquid output from the third heat exchanger to form a mixed liquid, and return the mixed liquid to the absorption tower. or A second confluencer, connected between the second heat exchanger and the third heat exchanger and connected to the first gas-liquid separator and the second gas-liquid separator, is configured to mix the lean liquid output from the second heat exchanger with the liquid separated from the first gas-liquid separator and the second gas-liquid separator before outputting it to the third heat exchanger; and The third confluencer is connected to the third gas-liquid separator, the third heat exchanger, and the absorption tower, respectively, and is configured to mix the liquid separated by the third gas-liquid separator with the mixed lean liquid output from the third heat exchanger to form a mixed liquid, and return the mixed liquid to the absorption tower.

10. The carbon capture system recovering the heat of desorption column overhead vapor waste heat with a cascade heat pump of any one of claims 1-7, wherein, The absorbent solution is an aqueous solution of the absorbent; the absorbent is a homogeneous mixed ligand complex system, comprising: amine ligands, amino acid ligands, transition metal ions, and activators; wherein the amine-containing ligand is an amine group compound capable of forming monodentate, bidentate or polydentate coordination with metal ions, including chain or branched structure of alcohol amine, amine or derivatives thereof, wherein at least part of the amine-containing ligand has the following structural unit: HO-CR1R2-(CH2) m -CR3R4-NH2, m = 1-3; The amino acid ligand comprises an amino acid or a salt thereof, wherein the amino acid has dual coordination sites of amino and carboxyl groups; The transition metal ions comprise two or more different metal centers selected from any combination of Cr, Mn, Ni, Cu, Zn, Co metal ions, with a total concentration of 0.001-1.0 mol / L, and form the following reversible coordination complex system with the amine-containing ligand: wherein n = 1-6, the coordination constant continuously distributes within the range of 10 0 -10 20 , thereby forming a multi-level coordination energy level structure; The activator is a polyamine compound that promotes CO2 absorption kinetics, and its concentration is 0.05–3.0 mol / L.

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