A carbon capture system recovering heat from the overhead of a desorption column with recycle water and lean liquid

Abstract

This invention provides a carbon capture system for recovering waste heat from the overhead gas of a desorption tower using circulating water and lean liquor. The system recovers the waste heat from the overhead gas in two steps using circulating water and a waste heat recovery medium, and gradually improves its thermal quality through two heat pump units. Specifically, high-grade waste heat from the overhead gas is recovered using circulating water and directly supplied to the second heat pump unit (i.e., a high-temperature heat pump). Low-grade waste heat from the overhead gas is recovered using the waste heat recovery medium. This low-grade waste heat is then upgraded by the first heat pump unit (i.e., a low-temperature heat pump) and also supplied to the high-temperature heat pump. The high-temperature heat pump uses the recovered waste heat to heat the rich and / or lean liquor of the desorption tower, thereby effectively recovering and utilizing the waste heat from the overhead gas of the desorption tower, significantly reducing the cooling and heating losses during desorption.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture technology, and in particular to a carbon capture system that recovers waste heat from the top gas of a desorption tower using circulating water and lean liquid. 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 thermal desorption yields 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 a significant amount of recoverable sensible heat and latent heat of phase change in the overhead gas of the desorption tower is wasted.

[0004] Therefore, for carbon capture thermal desorption processes such as MEA, effectively recovering the waste heat from the overhead gas for energy-saving optimization is an important requirement 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 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, thereby greatly reducing the cold and heat consumption during desorption.

[0007] A further objective of the present invention is to reduce the amount of circulating water used and further reduce the total energy consumption of the system.

[0008] Another further objective of this invention is to reduce the energy consumption of the overhead gas compression, improve the heat pump heat exchange efficiency, and increase the amount of waste heat recovery.

[0009] Specifically, the present invention provides a carbon capture system for recovering waste heat from the overhead gas of a desorption tower, comprising: Desorption tower, with a top gas outlet; The waste heat recovery water circulation unit includes a first heat exchanger, a second heat exchanger, a third heat exchanger, a first confluencer, and a splitter forming a first water circulation loop. 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 water 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 water after heat exchange from the first heat exchanger and the water after flowing through the second heat exchanger enter the first confluencer to be merged. The merged water passes through the third heat exchanger and is then divided into two water streams by the splitter. The two water streams enter the first heat exchanger and the second heat exchanger, respectively. The waste heat recovery medium unit includes: a fourth heat exchanger located downstream of the gas outlet of the first heat exchanger and configured to allow the waste heat recovery medium flowing through it to exchange heat with the overhead gas after passing through the first heat exchanger; and a fifth heat exchanger located downstream of the fourth heat exchanger along the flow direction of the waste heat recovery medium. A first heat pump unit includes a second heat exchanger and a fifth heat exchanger sequentially connected in the first working fluid loop along the flow direction of the first heat pump working fluid. The fifth heat exchanger is configured to allow the first heat pump working fluid flowing through it to exchange heat with a waste heat recovery medium after heat exchange from a fourth heat exchanger, thereby absorbing heat from the waste heat recovery medium. The second heat exchanger is configured to allow water flowing through it to exchange heat with the first heat pump working fluid after heat absorption, thereby raising its temperature. The second heat pump unit includes a third heat exchanger and a waste heat utilization element. The third heat exchanger is configured to allow the second heat pump working fluid flowing through it to exchange heat with the combined water from the first confluencer to absorb heat from the water. The waste heat utilization element is connected to the desorption tower and is configured to use the heat from the second heat pump working fluid after absorbing heat to heat the rich and / or lean liquids of the desorption tower through heat exchange.

[0010] Optionally, the carbon capture system also includes: An absorption tower is configured to absorb carbon dioxide from the gas to be treated using an absorbent liquid to obtain a rich liquid; and 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. The fourth heat exchanger is connected to the cold lean liquid outlet of the lean-rich liquid heat exchanger to receive the cold lean liquid from the lean-rich liquid heat exchanger as a waste heat recovery medium.

[0011] Optionally, the carbon capture system also includes: The first gas-liquid separator is located between the first heat exchanger and the fourth heat exchanger. It 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 fourth heat exchanger.

[0012] Optionally, the carbon capture system also includes: The second gas-liquid separator is connected to the fourth heat exchanger and is configured to perform gas-liquid separation on the overhead gas after passing through the fourth heat exchanger. A first compressor is connected to a second gas-liquid separator and is configured to compress the gas separated by the second gas-liquid separator. A cooler, connected to the first 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. The second compressor, connected to the third gas-liquid separator, is configured to recompress the separated compressed gas before outputting it as product gas; and The second confluencer is connected to the first gas-liquid separator, the second gas-liquid separator, the third gas-liquid separator and the fifth heat exchanger respectively, and 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 waste heat recovery medium output from the fifth heat exchanger to form a mixed liquid. The second confluencer is also connected to the absorption tower and is configured to return the mixed liquid to the absorption tower.

[0013] Optionally, the carbon capture system also includes: The third compressor is located between the first gas-liquid separator and the fourth heat exchanger. It is configured to compress the separated overhead gas and output the compressed overhead gas to the fourth heat exchanger.

[0014] Optionally, the carbon capture system also includes: A fourth gas-liquid separator, connected to a fourth heat exchanger, is configured to perform gas-liquid separation on the overhead gas after passing through the fourth heat exchanger; and The fourth compressor, connected to the fourth gas-liquid separator, is configured to compress the gas separated by the fourth gas-liquid separator; The waste heat recovery medium unit also includes: The sixth heat exchanger is located downstream of the fourth heat exchanger and upstream of the fifth heat exchanger along the flow direction of the waste heat recovery medium, and is connected to the fourth compressor. It is configured to allow the waste heat recovery medium flowing through it to exchange heat with the compressed gas from the fourth compressor to absorb the heat of the compressed gas, and to output the waste heat recovery working medium after absorbing heat to the fifth heat exchanger.

[0015] Optionally, the carbon capture system also includes: The fifth gas-liquid separator, connected to the sixth heat exchanger, is configured to perform gas-liquid separation on the compressed gas after it has passed through the sixth heat exchanger; and The fifth compressor, connected to the fifth gas-liquid separator, is configured to recompress the separated compressed gas and output it as product gas. The waste heat recovery medium unit also includes: The third confluencer is located between the sixth and fifth heat exchangers and is connected to the first, fourth, and fifth gas-liquid separators. It is configured to mix the waste heat recovery medium output from the sixth heat exchanger with the liquid separated by the first, fourth, and fifth gas-liquid separators to form a mixed liquid, and output the mixed liquid as the waste heat recovery medium to the fifth heat exchanger. The fifth heat exchanger is also connected to the absorption tower and is configured to return the waste heat recovery medium after passing through the fifth heat exchanger to the absorption tower.

[0016] Optionally, the first heat pump unit is a compression heat pump unit, and the first heat pump working fluid, after absorbing heat in the fifth heat exchanger, evaporates into a gaseous state. The first heat pump unit also includes: A sixth compressor, connected in the first working fluid loop and located downstream of the fifth heat exchanger and upstream of the second heat exchanger, is configured to compress the gaseous first heat pump working fluid; and The first throttling valve, connected in the first working fluid loop and located downstream of the second heat exchanger and upstream of the fifth heat exchanger, is configured to depressurize the first heat pump working fluid from the second heat exchanger.

[0017] Optionally, the second heat pump unit further includes a seventh compressor and a second throttle valve, wherein the third heat exchanger, the seventh compressor, the waste heat utilization element and the second throttle valve are sequentially connected along the flow direction of the second heat pump working fluid to form a second working fluid loop. The waste heat utilization elements 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.

[0018] Optionally, the second heat pump unit also includes an eighth compressor, a seventh heat exchanger, and a third throttle valve; Among them, the third heat exchanger, the eighth compressor, the seventh heat exchanger and the third throttling valve are connected sequentially along the flow direction of the second heat pump working fluid to form the third working fluid loop; The seventh heat exchanger and waste heat recovery element are also connected to form a second water circulation loop; The seventh heat exchanger is configured to allow the water flowing through it to exchange heat with the compressed second heat pump working fluid from the eighth compressor so that at least part of it evaporates into water vapor; The waste heat recovery element is configured to use steam from the seventh heat exchanger to heat the rich and / or lean liquor in the desorption tower. The waste heat utilization elements 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.

[0019] 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.

[0020] The carbon capture system for recovering waste heat from the top gas of a desorption tower provided by this invention utilizes circulating water and a waste heat recovery medium to recover the waste heat from the top gas in two steps, and gradually improves the thermal quality through two heat pump units. Specifically, high-grade waste heat from the top gas is recovered through circulating water and directly supplied to the second heat pump unit (i.e., the high-temperature heat pump); low-grade waste heat from the top gas is recovered through the waste heat recovery medium, and the recovered low-grade waste heat is upgraded by the first heat pump unit (i.e., the low-temperature heat pump) and also supplied to the high-temperature heat pump. The high-temperature heat pump uses the recovered waste heat to heat the rich and / or lean solutions of the desorption tower, thereby effectively recovering and utilizing the waste heat from the top gas of the desorption tower, and greatly reducing the cooling and heating losses during desorption.

[0021] Furthermore, in the carbon capture system for recovering waste heat from the top gas of the desorption tower provided by this invention, lean liquor is used as a low-temperature waste heat recovery medium for recovering low-grade waste heat, thereby significantly reducing the amount of circulating water used. Moreover, since the low-temperature waste heat of the lean liquor after passing through the lean-rich liquor heat exchanger is additionally recovered, the total energy consumption of the system can be further reduced.

[0022] Furthermore, in the carbon capture system for recovering waste heat from the overhead gas of the desorption tower provided by this invention, a compressor is installed between the first heat exchanger for recovering high-grade waste heat and the fourth heat exchanger for recovering low-grade waste heat to improve the quality of the low-grade waste heat. By adding a compression process (which can be simply referred to as interstage compression) to the two-stage heat exchange process, a balance between energy consumption and heat source temperature is achieved. Compared to the process of directly compressing the overhead gas, most of the water in the overhead gas can be condensed through a first-stage heat exchange, reducing the energy consumption of overhead gas compression. Compared to direct heat exchange, the low-temperature waste heat can be upgraded, significantly improving the heat pump heat exchange efficiency and increasing the amount of waste heat recovered.

[0023] 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.

[0024] 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

[0025] 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 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 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 according to another embodiment of the present invention. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] In view of this, the inventors of this application have proposed a technical solution for recovering waste heat from the top gas of a desorption tower using circulating water. To further improve waste heat recovery efficiency and reduce circulating water consumption, embodiments of this invention provide a carbon capture system 100 for recovering waste heat from the top gas of a desorption tower.

[0035] Figure 2 This is a schematic structural block diagram of a carbon capture system 100 for recovering waste heat from the top gas of a desorption tower according to an embodiment of the present invention, wherein the heat transfer between the two is indicated by a dashed arrow from the waste heat recovery element 171 to the desorption tower 110. See also Figure 2 As shown, the carbon capture system 100 for recovering waste heat from the top gas of the desorption tower generally includes a desorption tower 110 with a top gas outlet 111, a waste heat recovery water circulation unit 140, a waste heat recovery medium unit 150, a first heat pump unit 160, and a second heat pump unit 170.

[0036] The waste heat recovery water circulation unit 140 includes a first heat exchanger 142, a second heat exchanger 143, a third heat exchanger 144, a first confluencer 145, and a diverter 146 forming a first water circulation loop 141.

[0037] The first heat exchanger 142 has a gas inlet 1421, a gas outlet 1422, a water inlet, and a water outlet communicating with the top gas outlet 111. The first confluencer 145 has a first inlet, a second inlet, and an outlet, with the first inlet connected to the water outlet of the first heat exchanger 142. The third heat exchanger 144 has a water inlet and a water outlet, with the outlet of the first confluencer 145 connected to the water inlet of the third confluencer 144. The splitter 146 has an inlet, a first outlet, and a second outlet, with the inlet connected to the water outlet of the third heat exchanger 144 and the first outlet connected to the water inlet of the first heat exchanger 142. The second heat exchanger 143 has a water inlet and a water outlet, respectively connected to the second outlet of the splitter 146 and the second inlet of the first confluencer 145.

[0038] The first heat exchanger 142 is configured to allow the water flowing through it to exchange heat with the overhead gas output from the overhead gas outlet 111 to recover the waste heat of the overhead gas. The water after heat exchange from the first heat exchanger 142 and the water after flowing through the second heat exchanger 143 enter the first confluencer 145 to be merged. The merged water passes through the third heat exchanger 144 and is then divided into two streams by the splitter 146. These two streams enter the first heat exchanger 142 and the second heat exchanger 143 respectively.

[0039] The waste heat recovery medium unit 150 includes a fourth heat exchanger 151 and a fifth heat exchanger 152. The fourth heat exchanger 151 is located downstream of the gas outlet 1422 of the first heat exchanger 142 and is configured to allow the waste heat recovery medium flowing through it to exchange heat with the overhead gas after passing through the first heat exchanger 142. The fifth heat exchanger 152 is located downstream of the fourth heat exchanger 151 along the flow direction of the waste heat recovery medium.

[0040] The first heat pump unit 160 includes a second heat exchanger 143 and a fifth heat exchanger 152 sequentially connected in the first working fluid loop 161 along the flow direction of the first heat pump working fluid. The fifth heat exchanger 152 is configured to allow the first heat pump working fluid flowing through it to exchange heat with the waste heat recovery medium after heat exchange from the fourth heat exchanger 151, thereby absorbing the heat from the waste heat recovery medium. The second heat exchanger 143 is configured to allow the water flowing through it to exchange heat with the first heat pump working fluid after heat absorption, thereby raising its temperature; that is, the water is used to further recover the low-grade waste heat after being upgraded by the first heat pump unit 160.

[0041] The second heat pump unit 170 includes a third heat exchanger 144 and a waste heat utilization element 171. The third heat exchanger 144 is configured to allow the second heat pump working fluid flowing through it to exchange heat with the combined water from the first confluencer 145 to absorb heat from the water. The waste heat utilization element 171 is connected to the desorption tower 110 and is configured to use the heat from the second heat pump working fluid after heat absorption to heat the rich and / or lean solutions of the desorption tower 110 through heat exchange.

[0042] In the carbon capture system 100 for recovering waste heat from the top gas of a desorption tower provided in this embodiment of the invention, the waste heat from the top gas is recovered in two steps using circulating water and a waste heat recovery medium, and the thermal quality is gradually improved through two heat pump units. Specifically, the high-grade waste heat from the top gas is recovered through circulating water and directly supplied to the second heat pump unit 170 (i.e., the high-temperature heat pump); the low-grade waste heat from the top gas is recovered through the waste heat recovery medium, and the recovered low-grade waste heat is also supplied to the high-temperature heat pump after being upgraded by the first heat pump unit 160 (i.e., the low-temperature heat pump). The high-temperature heat pump uses the recovered waste heat to heat the rich liquid and / or lean liquid of the desorption tower 110, thereby effectively recovering and utilizing the waste heat from the top gas of the desorption tower 110, and greatly reducing the cooling and heating losses during desorption.

[0043] In practical applications, an appropriate working medium can be used as the waste heat recovery medium as needed. In some embodiments, the waste heat recovery medium can also be circulating water. In this case, the fourth heat exchanger 151 and the fifth heat exchanger 152 can be connected to form a water circulation loop to recover low-grade waste heat.

[0044] In other embodiments, lean liquid may be used as the waste heat recovery medium.

[0045] Figure 3 This is a schematic diagram of a carbon capture system 100 for recovering waste heat from the top gas of a desorption tower 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 according to another embodiment of the present invention, wherein the heat transfer between the waste heat recovery element 171 and the desorption tower 110 is indicated by a dashed arrow. See also Figures 2 to 4 As shown, the carbon capture system 100 also includes an absorption tower 120 and a lean-rich liquid heat exchanger 130. The absorption tower 120 is configured to absorb carbon dioxide from the gas to be treated using an absorbent to obtain a rich liquid. The lean-rich liquid heat exchanger 130 is connected between the absorption tower 120 and the desorption tower 110, with its cold rich liquid inlet, hot rich liquid outlet, and hot lean liquid inlet connected to the rich liquid outlet of the absorption tower 120, the rich liquid inlet of the desorption tower 110, and the lean liquid outlet of the desorption tower 110, respectively, configured to allow heat exchange between the rich liquid from the absorption tower 120 and the lean liquid from the desorption tower 110. The medium inlet of the fourth heat exchanger 151 is connected to the cold lean liquid outlet of the lean-rich liquid heat exchanger 130 to receive the cold lean liquid from the lean-rich liquid heat exchanger 130 as a waste heat recovery medium.

[0046] 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.

[0047] In this embodiment, lean liquor is used as a low-temperature waste heat recovery medium to recover low-grade waste heat, thereby significantly reducing the amount of circulating water used. Moreover, since the low-temperature waste heat of the lean liquor after passing through the lean-rich liquor heat exchanger 130 is additionally recovered (the lean liquor temperature drops from 30°C to about 25°C), the total energy consumption of the system can be further reduced.

[0048] See Figure 3 and Figure 4 In some embodiments, the carbon capture system 100 may further include a first gas-liquid separator 181. The first gas-liquid separator 181 is disposed between the first heat exchanger 142 and the fourth heat exchanger 151, and is configured to perform gas-liquid separation on the overhead gas after passing through the first heat exchanger 142, and output the separated overhead gas to the fourth heat exchanger 151.

[0049] See also Figure 3 In some embodiments, the carbon capture system 100 may further include: a second gas-liquid separator 182 connected to a fourth heat exchanger 151, configured to perform gas-liquid separation on the overhead gas after passing through the fourth heat exchanger 151; a first compressor 183 connected to the second gas-liquid separator 182, configured to compress the gas separated by the second gas-liquid separator 182; a cooler 184 connected to the first compressor 183, configured to cool the compressed gas; a third gas-liquid separator 185 connected to the cooler 184, configured to perform gas-liquid separation on the cooled compressed gas; and a second compressor 186 connected to the third gas-liquid separator 185, configured to further compress the separated compressed gas and output it as product gas (i.e., compressed CO2).

[0050] Optionally, the carbon capture system 100 may also include a cooler connected to the second compressor 186 for cooling the compressed product gas.

[0051] In some embodiments, the carbon capture system 100 may further include a second confluencer 187, which is connected to the first gas-liquid separator 181, the second gas-liquid separator 182, the third gas-liquid separator 185 and the fifth heat exchanger 152 respectively, and is configured to mix the liquid separated by the first gas-liquid separator 181, the second gas-liquid separator 182 and the third gas-liquid separator 185 with the waste heat recovery medium (i.e., lean liquid) output from the fifth heat exchanger 152 to form a mixed liquid.

[0052] In some further embodiments, the second confluencer 187 may also be connected to the absorber 120, specifically, it may be connected to the lean liquid inlet of the absorber 120 and configured to return the mixed liquid to the absorber 120.

[0053] See Figure 4As shown, in some embodiments, the carbon capture system 100 may further include a third compressor 191 disposed between the first gas-liquid separator 181 and the fourth heat exchanger 151, configured to compress the separated overhead gas and output the compressed overhead gas to the fourth heat exchanger 151.

[0054] In this embodiment, a compressor is installed between the first heat exchanger 142, which recovers high-grade waste heat, and the fourth heat exchanger 151, which recovers low-grade waste heat, to improve the quality of the low-grade waste heat. By adding a compression process (which can be simply referred to as interstage compression) to the two-stage heat exchange process, a balance between energy consumption and heat source temperature is achieved. Compared to the process of directly compressing the overhead gas, most of the water in the overhead gas can be condensed through a first-stage heat exchange, reducing the energy consumption of overhead gas compression. Compared to direct heat exchange, the quality of low-temperature waste heat can be improved, significantly increasing the heat pump heat exchange efficiency and the amount of waste heat recovered.

[0055] See also Figure 4 The carbon capture system 100 may further include: a fourth gas-liquid separator 192, connected to a fourth heat exchanger 151, configured to perform gas-liquid separation on the overhead gas after passing through the fourth heat exchanger 151; and a fourth compressor 193, connected to the fourth gas-liquid separator 192, configured to compress the gas separated by the fourth gas-liquid separator 192. The waste heat recovery medium unit 150 may further include a sixth heat exchanger 153. The sixth heat exchanger 153 is located downstream of the fourth heat exchanger 151 and upstream of the fifth heat exchanger 152 along the flow direction of the waste heat recovery medium, and is connected to the fourth compressor 193, configured to allow the waste heat recovery medium flowing through it to exchange heat with the compressed gas from the fourth compressor 193 to absorb the heat from the compressed gas, and to output the heat-absorbed waste heat recovery medium to the fifth heat exchanger 152.

[0056] In this embodiment, the low-grade waste heat of the top gas is upgraded by the fourth compressor 193, and then the upgraded low-grade waste heat is further recovered by the sixth heat exchanger 153, thereby further improving the waste heat recovery efficiency and the amount of waste heat recovered.

[0057] See also Figure 4 In some embodiments, the carbon capture system 100 may further include: a fifth gas-liquid separator 194 connected to a sixth heat exchanger 153, configured to perform gas-liquid separation on the compressed gas after passing through the sixth heat exchanger 153; and a fifth compressor 195 connected to the fifth gas-liquid separator 194, configured to further compress the separated compressed gas and output it as product gas (i.e., compressed CO2).

[0058] In some further embodiments, the waste heat recovery medium unit 150 may also include a third confluencer 154. The third confluencer 154 is disposed between the sixth heat exchanger 153 and the fifth heat exchanger 152, and is connected to the first gas-liquid separator 181, the fourth gas-liquid separator 192, and the fifth gas-liquid separator 194. It is configured to mix the waste heat recovery medium (i.e., lean liquid) output from the sixth heat exchanger 153 with the liquid separated by the first gas-liquid separator 181, the fourth gas-liquid separator 192, and the fifth gas-liquid separator 194 to form a mixed liquid, and output the mixed liquid as the waste heat recovery medium to the fifth heat exchanger 152.

[0059] In some further embodiments, the fifth heat exchanger 152 may also be connected to the absorption tower 120 and configured to return the waste heat recovery medium after passing through the fifth heat exchanger 152 to the absorption tower 120. Specifically, the waste heat recovery medium outlet of the fifth heat exchanger 152 may be connected to the lean liquid inlet of the absorption tower 120, thereby returning the waste heat recovery medium after passing through the fifth heat exchanger 152 to the absorption tower 120 through the lean liquid inlet.

[0060] See Figure 3 and Figure 4 In some embodiments, the first heat pump unit 160 is a compression heat pump unit. The first heat pump working fluid, after absorbing heat in the fifth heat exchanger 152, evaporates at least partially into a gaseous state. The first heat pump unit 160 may further include: a sixth compressor 162, connected in the first working fluid loop 161 and located downstream of the fifth heat exchanger 152 and upstream of the second heat exchanger 143, configured to compress the gaseous first heat pump working fluid; and a first throttle valve 163, connected in the first working fluid loop 161 and located downstream of the second heat exchanger 143 and upstream of the fifth heat exchanger 152, configured to depressurize the first heat pump working fluid from the second heat exchanger 143.

[0061] In some optional embodiments, the first heat pump unit 160 may further include a gas-liquid separator 164 disposed between the fifth heat exchanger 152 and the sixth compressor 162, 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 sixth compressor 162, thereby preventing liquid from entering the sixth compressor 162 and causing damage to it. This gas-liquid separator may be, for example, a flash tank.

[0062] See Figure 3In some embodiments, the second heat pump unit 170 may further include a seventh compressor 172 and a second throttle valve 173. The third heat exchanger 144, the seventh compressor 172, the waste heat utilization element 171, and the second throttle valve 173 are sequentially connected along the flow direction of the second heat pump working fluid to form a second working fluid loop 174. After absorbing heat from the combined water of the first confluencer 145 through the third heat exchanger 144, the second heat pump working fluid evaporates at least partially into a gaseous state and then enters the seventh compressor 172 for compression. The compressed second heat pump working fluid is cooled and undergoes a phase change by heating the rich liquid and / or lean liquid of the desorption tower 110 through the waste heat utilization element 171. After that, it enters the second throttle valve 173 for depressurization and then enters the third heat exchanger 144, thereby forming a working fluid cycle.

[0063] In some optional embodiments, the second heat pump unit 170 may further include a gas-liquid separator 196 disposed between the third heat exchanger 144 and the seventh compressor 172, 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 seventh compressor 172, thereby preventing liquid from entering the seventh compressor 172 and causing damage to it. This gas-liquid separator may be, for example, a flash tank.

[0064] See Figure 4 In some embodiments, the second heat pump unit 170 may further include an eighth compressor 175, a seventh heat exchanger 176, and a third throttle valve 177. The third heat exchanger 144, the eighth compressor 175, the seventh heat exchanger 176, and the third throttle valve 177 are sequentially connected along the flow direction of the second heat pump working fluid to form a third working fluid loop 178. The seventh heat exchanger 176 and the waste heat recovery element 171 are also connected to form a second water circulation loop 179. The seventh heat exchanger 176 is configured to allow water flowing through it to exchange heat with the compressed second heat pump working fluid from the eighth compressor 175 to at least partially evaporate into water vapor. The waste heat recovery element 171 is configured to use the water vapor from the seventh heat exchanger 176 to heat the rich and / or lean liquid of the desorption tower 110.

[0065] Specifically, the second heat pump working fluid absorbs heat from the combined water of the first confluencer 145 through the third heat exchanger 144, at least partially evaporating into a gaseous state, and then enters the eighth compressor 175 for compression. The compressed second heat pump working fluid enters the seventh heat exchanger 176 to heat the water flowing through it, thereby cooling itself and undergoing a phase change. It then enters the third throttling valve 177 to be depressurized, and then enters the third heat exchanger 144, thus forming a working fluid cycle. The water passing through the seventh heat exchanger 176 is heated and at least partially converted into water vapor. It then cools itself and condenses by heating the rich and / or lean liquid of the desorption tower 110 through the waste heat utilization element 171, and then enters the seventh heat exchanger 176 again, thus forming a water cycle.

[0066] In some optional embodiments, the second heat pump unit 170 may further include a gas-liquid separator 197 disposed between the third heat exchanger 144 and the eighth compressor 175, 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 eighth compressor 175, thereby preventing liquid from entering the eighth compressor 175 and causing damage to it. This gas-liquid separator may be, for example, a flash tank.

[0067] In some alternative embodiments, the second heat pump unit 170 may further include a mixer 198 disposed in the second water circulation loop 179 and located downstream of the waste heat recovery element 171 and upstream of the seventh heat exchanger 176. The mixer is used to mix water from the waste heat recovery element 171 with water replenished as needed before outputting it to the seventh heat exchanger 176.

[0068] The first and second heat pump working fluids can be commonly used heat pump working fluids as needed, such as R245fa.

[0069] In some embodiments, the waste heat utilization element 171 may be a reboiler connected to the bottom of the desorption tower 110 for heating the lean liquor in the desorption tower 110.

[0070] In other embodiments, the waste heat utilization element 171 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.

[0071] In some other embodiments, the waste heat recovery element 171 may include a reboiler and an interstage heater.

[0072] By utilizing the recovered waste heat for interstage heating, heat exchange in the rich liquid can be promoted, thereby improving desorption efficiency and increasing CO2 production.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] The following is based on Figure 3 and Figure 4 The carbon capture system 100 for recovering waste heat from the top gas of the desorption tower shown is a specific embodiment. The technical effect of the technical solution of the present invention is verified through simulation.

[0084] 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).

[0085] Table 1. Rich solution injection conditions for carbon capture process

[0086] Simulation results show that the technical solution of the present invention has the following beneficial effects: (1) Desorption achieves full-process electrification, eliminating the need for an external cold source.

[0087] (2) Using lean liquid as the working fluid for low-temperature waste heat recovery significantly reduces the amount of circulating water used.

[0088] (3) The total energy consumption of the system is reduced by about 25%. Due to the additional recovery of the low-temperature waste heat of the lean liquid after passing through the lean-rich liquid heat exchanger 130 (the lean liquid temperature is reduced from 30°C to about 25°C), the energy consumption is reduced to 2.2 GJ / ton CO2.

[0089] (4) Interstage compression achieves a balance between energy consumption and heat source temperature. Compared to the process of directly compressing the overhead gas, about 60% of the water in the overhead gas can be condensed through a first-stage heat exchange, reducing the energy consumption of direct compression of the overhead gas by about 50%. Compared to direct heat exchange, the low-temperature waste heat can be upgraded, significantly improving the heat pump heat exchange efficiency, and the amount of waste heat recovered increases by 50% year-on-year.

[0090] 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.

[0091] 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, comprising: Desorption tower, with a top gas outlet; The waste heat recovery water circulation unit includes a first heat exchanger, a second heat exchanger, a third heat exchanger, a first confluencer, and a splitter forming a first water circulation loop. 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 water flowing through it to exchange heat with the top gas output from the top gas outlet of the tower to recover waste heat from the top gas. The water after heat exchange from the first heat exchanger and the water after flowing through the second heat exchanger enter the first confluencer to be merged. The merged water passes through the third heat exchanger and is then divided into two streams by the splitter. The two streams enter the first heat exchanger and the second heat exchanger, respectively. The waste heat recovery medium unit includes: a fourth heat exchanger located downstream of the gas outlet of the first heat exchanger and configured to allow the waste heat recovery medium flowing through it to exchange heat with the overhead gas after passing through the first heat exchanger; and a fifth heat exchanger located downstream of the fourth heat exchanger along the flow direction of the waste heat recovery medium. A first heat pump unit includes a second heat exchanger and a fifth heat exchanger sequentially connected in a first working fluid loop along the flow direction of the first heat pump working fluid. The fifth heat exchanger is configured to allow the first heat pump working fluid flowing through it to exchange heat with a waste heat recovery medium after heat exchange with the output of the fourth heat exchanger, thereby absorbing heat from the waste heat recovery medium. The second heat exchanger is configured to allow water flowing through it to exchange heat with the first heat pump working fluid after absorbing heat, thereby raising its temperature. The second heat pump unit includes the third heat exchanger and a waste heat utilization element. The third heat exchanger is configured to allow the second heat pump working fluid flowing through it to exchange heat with the combined water from the first confluencer to absorb heat from the water. The waste heat utilization element is connected to the desorption tower and is configured to use the heat from the second heat pump working fluid after absorbing heat to heat the rich and / or lean liquids of the desorption tower through heat exchange.

2. The carbon capture system for recovering waste heat from the top gas of the desorption tower according to claim 1, wherein, The carbon capture system also includes: An absorption tower is configured to absorb carbon dioxide from the gas to be treated using an absorbent liquid to obtain a rich liquid; and 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. The fourth heat exchanger is connected to the cold lean liquid outlet of the lean-rich liquid heat exchanger to receive the cold lean liquid from the lean-rich liquid heat exchanger as the waste heat recovery medium.

3. The carbon capture system for recovering waste heat from the top gas of the desorption tower according to claim 2, wherein, The carbon capture system also includes: A first gas-liquid separator is disposed between the first heat exchanger and the fourth 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 fourth heat exchanger.

4. The carbon capture system for recovering waste heat from the top gas of the desorption tower according to claim 3, wherein, The carbon capture system also includes: The second gas-liquid separator is connected to the fourth heat exchanger and is configured to perform gas-liquid separation on the overhead gas after passing through the fourth heat exchanger. A first compressor is connected to the second gas-liquid separator and configured to compress the gas separated by the second gas-liquid separator; A cooler, connected to the first 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. The second compressor, connected to the third gas-liquid separator, is configured to recompress the separated compressed gas and output it as product gas; and The second confluencer is connected to the first gas-liquid separator, the second gas-liquid separator, the third gas-liquid separator, and the fifth heat exchanger, respectively, and 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 waste heat recovery medium output from the fifth heat exchanger to form a mixed liquid; The second confluencer is also connected to the absorption tower and is configured to return the mixed liquid to the absorption tower.

5. The carbon capture system for recovering waste heat from the top gas of the desorption tower according to claim 3, wherein, The carbon capture system also includes: The third compressor is located between the first gas-liquid separator and the fourth heat exchanger, and is configured to compress the separated overhead gas and output the compressed overhead gas to the fourth heat exchanger. A fourth gas-liquid separator, connected to the fourth heat exchanger, is configured to perform gas-liquid separation on the overhead gas after passing through the fourth heat exchanger; and A fourth compressor, connected to the fourth gas-liquid separator, is configured to compress the gas separated by the fourth gas-liquid separator; The waste heat recovery medium unit also includes: The sixth heat exchanger is located downstream of the fourth heat exchanger and upstream of the fifth heat exchanger along the flow direction of the waste heat recovery medium, and is connected to the fourth compressor. It is configured to allow the waste heat recovery medium flowing through it to exchange heat with the compressed gas from the fourth compressor to absorb the heat of the compressed gas, and to output the waste heat recovery working medium after absorbing heat to the fifth heat exchanger.

6. The carbon capture system for recovering waste heat from the top gas of the desorption tower according to claim 5, wherein, The carbon capture system also includes: A fifth gas-liquid separator, connected to the sixth heat exchanger, is configured to perform gas-liquid separation on the compressed gas after it has passed through the sixth heat exchanger; and The fifth compressor, connected to the fifth gas-liquid separator, is configured to recompress the separated compressed gas and output it as product gas. The waste heat recovery medium unit also includes: The third confluencer is located between the sixth heat exchanger and the fifth heat exchanger, and is connected to the first gas-liquid separator, the fourth gas-liquid separator and the fifth gas-liquid separator. It is configured to mix the waste heat recovery medium output from the sixth heat exchanger with the liquid separated by the first gas-liquid separator, the fourth gas-liquid separator and the fifth gas-liquid separator to form a mixed liquid, and output the mixed liquid as the waste heat recovery medium to the fifth heat exchanger. The fifth heat exchanger is also connected to the absorption tower and is configured to return the waste heat recovery medium after passing through the fifth heat exchanger to the absorption tower.

7. The carbon capture system for recovering waste heat from the overhead gas of a desorption tower according to any one of claims 1-6, wherein, The first heat pump unit is a compression heat pump unit, and the first heat pump working fluid, after absorbing heat in the fifth heat exchanger, evaporates into a gaseous state. The first heat pump unit further includes: A sixth compressor, connected in the first working fluid loop and located downstream of the fifth heat exchanger and upstream of the second heat exchanger, is configured to compress the gaseous first heat pump working fluid; and A first throttling valve, connected in the first working fluid loop and located downstream of the second heat exchanger and upstream of the fifth heat exchanger, is configured to depressurize the first heat pump working fluid from the second heat exchanger.

8. The carbon capture system for recovering waste heat from the overhead gas of a desorption tower according to any one of claims 2-6, wherein, The second heat pump unit further includes a seventh compressor and a second throttle valve, wherein the third heat exchanger, the seventh compressor, the waste heat utilization element and the second throttle valve are sequentially connected along the flow direction of the second heat pump working fluid to form a second working fluid loop; The waste heat utilization element includes: 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 according to any one of claims 2-6, wherein, The second heat pump unit also includes an eighth compressor, a seventh heat exchanger, and a third throttle valve; The third heat exchanger, the eighth compressor, the seventh heat exchanger, and the third throttling valve are sequentially connected along the flow direction of the second heat pump working fluid to form a third working fluid loop. The seventh heat exchanger and the waste heat utilization element are also connected to form a second water circulation loop; The seventh heat exchanger is configured to allow water flowing through it to exchange heat with the compressed second heat pump working fluid from the eighth compressor to at least partially evaporate into water vapor. The waste heat recovery element is configured to use steam from the seventh heat exchanger to heat the rich and / or lean liquor of the desorption tower. The waste heat utilization element includes: 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.

10. The carbon capture system for recovering waste heat from the overhead gas of a desorption tower according to any one of claims 2-6, 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; 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 a portion 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 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 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; 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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