Two-stage recycling water cascade recovery tower top gas waste heat module and carbon dioxide capture system

Abstract

The application provides a two-stage circulating water cascade recovery tower top gas waste heat module and a carbon dioxide capture system. The module comprises a desorption tower, a first-stage water circulating unit, a second-stage water circulating unit and a waste heat upgrading unit. First, high-temperature waste heat of the tower top gas is recovered by a first circulating water flow of the first-stage water circulating unit to preliminarily heat the first circulating water flow, and then low-temperature waste heat of the tower top gas is recovered by a second circulating water flow of the second-stage water circulating unit. The recovered low-temperature waste heat is upgraded by the waste heat upgrading unit, and then exchanges heat with the preliminarily heated first circulating water flow to at least partially convert the first circulating water flow into water vapor, and then the generated water vapor is used to heat rich liquid and / or medium-lean liquid of the desorption tower. Through the cascade heat exchange of the two-stage circulating water, the heat exchange difficulty is greatly reduced, the waste heat recovery efficiency is improved, and the use amount of the circulating water and the working medium is reduced, thereby reducing the engineering operation cost.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture technology, and in particular to a two-stage circulating water cascade recovery tower top gas waste heat module and a carbon dioxide capture system. 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, has low recovery efficiency of sensible heat and latent heat of phase change in the overhead gas of the desorption tower, and requires a large amount of media for waste heat recovery.

[0004] Therefore, for carbon capture thermal desorption processes such as MEA, improving waste heat recovery efficiency and optimizing the amount of medium used are important requirements for carbon capture processes. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a two-stage circulating water cascade recovery tower top gas waste heat module and carbon dioxide capture system to overcome or at least partially solve the above problems.

[0006] One objective of this invention is to reduce the difficulty of heat exchange, improve the efficiency of waste heat recovery, and reduce the amount of circulating water used.

[0007] A further objective of this invention is to improve the thermal quality of the top gas and reduce the difficulty of waste heat recovery.

[0008] In particular, according to one aspect of the present invention, a two-stage circulating water cascade recovery tower top gas waste heat module is provided, comprising: Desorption tower, with a top gas outlet; The first-stage water circulation unit includes a first heat exchanger, a second heat exchanger, and a waste heat recovery element connected sequentially in the first water circulation loop along the water flow direction. The first heat exchanger is also connected to the top gas outlet of the tower and is configured to allow the first circulating water flowing through it to exchange heat with the top gas output from the top gas outlet of the tower in order to recover the waste heat of the top gas to initially heat the first circulating water. The second-stage water circulation unit includes a third heat exchanger and a fourth heat exchanger sequentially connected in the second water circulation loop along the water flow direction. The third heat exchanger is also connected to the first heat exchanger and is configured to receive the overhead gas after passing through the first heat exchanger, and to exchange heat between the second circulating water flowing through it and the overhead gas to recover the waste heat of the overhead gas and output the heated second circulating water to the fourth heat exchanger; and The waste heat upgrading unit includes a fourth heat exchanger, an upgrading unit, and a second heat exchanger connected in sequence. The fourth heat exchanger is configured to exchange heat between the working medium of the waste heat upgrading unit and the heated second circulating water to absorb heat. The upgrading unit is configured to increase the temperature of the working medium after absorbing heat. The second heat exchanger is configured to exchange heat between the heated working medium and the pre-heated first circulating water to convert at least part of the first circulating water into water vapor. The waste heat utilization element is connected to the desorption tower and is configured to heat the rich and / or lean liquids of the desorption tower by heat exchange using a first circulating water flow that is at least partially converted into water vapor.

[0009] Optionally, the waste heat upgrading unit is a heat pump unit, and the working medium is a heat pump working fluid.

[0010] Optionally, the waste heat upgrading unit is a compression heat pump unit, which includes a fourth heat exchanger, a first compressor serving as an upgrader, a second heat exchanger, and a throttling valve sequentially connected in the working fluid loop along the flow direction of the heat pump working fluid; wherein The heat pump working fluid, after absorbing heat in the fourth heat exchanger, evaporates into a gaseous state. The first compressor is configured to compress the gaseous heat pump working fluid; The throttle valve is configured to depressurize the heat pump working fluid from the second heat exchanger.

[0011] Optionally, the two-stage circulating water cascade recovery tower top gas waste heat module also includes: The second compressor is located in the connecting path between the top gas outlet of the tower and the first heat exchanger. It is configured to compress the top gas output from the top gas outlet of the tower and output the compressed top gas to the first heat exchanger.

[0012] Optionally, the waste heat recovery element includes: 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.

[0013] Optionally, the two-stage circulating water cascade recovery tower top gas waste heat module also includes: A gas-liquid separator, connected to a third heat exchanger, is configured to perform gas-liquid separation on the overhead gas after passing through the third heat exchanger.

[0014] According to another aspect of the present invention, a carbon dioxide capture system is also provided, comprising: 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. The aforementioned two-stage circulating water cascade recovery tower top gas waste heat module; 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.

[0015] Optionally, the liquid outlet of the gas-liquid separator is connected to the absorption tower to return the condensate separated by the gas-liquid separator to the absorption tower.

[0016] 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.

[0017] The two-stage circulating water cascade recovery module for top gas waste heat recovery and the carbon dioxide capture system provided by this invention divide the waste heat recovery of the top gas into two steps. First, the high-temperature waste heat of the top gas is recovered using the first circulating water flow of the first-stage water circulation unit to preliminarily heat the first circulating water flow. Then, the low-temperature waste heat of the top gas is recovered using the second circulating water flow of the second-stage water circulation unit. The recovered low-temperature waste heat is then upgraded (temperature increased) by the waste heat upgrading unit and exchanged with the preliminarily heated first circulating water flow to at least partially convert the first circulating water flow into water vapor. The generated water vapor is then used to heat the rich liquid and / or lean liquid in the desorption tower. Through the cascade heat exchange of the two-stage circulating water, the heat exchange difficulty is significantly reduced, and the waste heat recovery efficiency is improved. Moreover, the amount of circulating water and working medium used is reduced, thereby reducing the engineering operating cost.

[0018] Furthermore, in the two-stage circulating water cascade recovery tower top gas waste heat module and carbon dioxide capture system provided by the present invention, a compression heat pump is used as the waste heat upgrading unit, so that desorption does not require an external cold source or an external heat source, realizing full-process electrification.

[0019] Furthermore, the two-stage circulating water cascade recovery tower top gas waste heat module and carbon dioxide capture system provided by the present invention improve the thermal quality of the tower top gas by compression, significantly reducing the difficulty of waste heat recovery and significantly reducing energy consumption.

[0020] 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.

[0021] 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

[0022] 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 A schematic structural block diagram of a two-stage circulating water cascade recovery tower top gas waste heat module according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a two-stage circulating water cascade recovery tower top gas waste heat module according to another embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of a two-stage circulating water cascade recovery tower top gas waste heat module according to another embodiment of the present invention; Figure 5 This is a schematic structural block diagram of a carbon dioxide capture system according to an embodiment of the present invention. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 using circulating water. To further improve waste heat recovery efficiency and reduce circulating water consumption, embodiments of this invention provide a two-stage circulating water cascade recovery module 100 for waste heat from the top gas of a tower.

[0032] Figure 2 This is a schematic structural block diagram of a two-stage circulating water cascade recovery tower top gas waste heat module 100 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 utilization element 124 to the desorption tower 110. See also Figure 2 As shown, the two-stage circulating water cascade recovery tower top gas waste heat module 100 generally includes a desorption tower 110 with a tower top gas outlet 111, a first-stage water circulation unit 120, a second-stage water circulation unit 130, and a waste heat upgrading unit 140.

[0033] The first-stage water circulation unit 120 includes a first heat exchanger 122, a second heat exchanger 123, and a waste heat recovery element 124, which are sequentially connected in the first water circulation loop 121 along the water flow direction. The first heat exchanger 122 is also connected to the top gas outlet 111 and is configured to exchange heat between the first circulating water flowing through it and the top gas output from the top gas outlet 111 to recover the waste heat of the top gas and preliminarily heat the first circulating water.

[0034] The second-stage water circulation unit 130 includes a third heat exchanger 132 and a fourth heat exchanger 133 sequentially connected in the second water circulation loop 131 along the water flow direction. The third heat exchanger 132 is also connected to the first heat exchanger 122 and is configured to receive the overhead gas after passing through the first heat exchanger 122, and to exchange heat between the second circulating water flowing through it and the overhead gas to recover the waste heat of the overhead gas and output the heated second circulating water to the fourth heat exchanger 133.

[0035] The waste heat upgrading unit 140 includes a fourth heat exchanger 133, a heat exchanger 142, and a second heat exchanger 123 connected in sequence. The fourth heat exchanger 133 is configured to exchange heat between the working medium of the waste heat upgrading unit 140 and the heated second circulating water flow to absorb heat. The heat exchanger 142 is configured to increase the temperature of the working medium after heat absorption. The second heat exchanger 123 is configured to exchange heat between the heated working medium and the pre-heated first circulating water flow to at least partially convert the first circulating water flow into water vapor.

[0036] Waste heat utilization element 124 is connected to desorption tower 110 (specifically, it can be thermally connected) and configured to heat the rich and / or lean liquid of desorption tower 110 by heat exchange using a first circulating water flow that is at least partially converted into water vapor.

[0037] The two-stage circulating water cascade recovery module 100 for top gas waste heat recovery provided in this embodiment of the invention divides the waste heat recovery of the top gas into two steps. First, the high-temperature waste heat of the top gas is recovered using the first circulating water flow (also known as high-temperature circulating water) of the first-stage water circulation unit 120 to preliminarily heat the first circulating water flow. Then, the low-temperature waste heat of the top gas is recovered using the second circulating water flow (also known as low-temperature circulating water) of the second-stage water circulation unit 130. The recovered low-temperature waste heat is then upgraded (temperature increased) by the waste heat upgrading unit 140 and exchanged with the preliminarily heated first circulating water flow to convert at least part of the first circulating water flow into water vapor. The generated water vapor is then used to heat the rich liquid and / or lean liquid in the desorption tower 110. Through the cascade heat exchange of the two-stage circulating water, the heat exchange difficulty is significantly reduced, and the waste heat recovery efficiency is improved. Moreover, the amount of circulating water and working medium used is reduced, thereby reducing the engineering operating cost.

[0038] Figure 3 This is a schematic diagram of the structure of a two-stage circulating water cascade recovery tower top gas waste heat module 100 according to another embodiment of the present invention. Figure 4 This is a schematic diagram of the structure of a two-stage circulating water cascade recovery tower top gas waste heat module 100 according to another embodiment of the present invention, wherein the heat transfer between the waste heat utilization element 124 and the desorption tower 110 is indicated by a dashed arrow. Furthermore, to better illustrate other structures associated with the two-stage circulating water cascade recovery tower top gas waste heat module 100, Figure 3 and Figure 4 The image also shows a liquid-rich / liquid-poor heat exchanger 180.

[0039] In some embodiments, the waste heat upgrading unit 140 may be a heat pump unit 140, with the working medium being a heat pump working fluid. Using the heat pump unit 140, low-grade waste heat can be effectively upgraded to high-grade heat, and this is easily implemented.

[0040] See Figure 3 and Figure 4As shown, in some embodiments, the waste heat enhancement unit 140 may be a compression heat pump unit 140, which includes a fourth heat exchanger 133, a first compressor 142 serving as an enhancer 142, a second heat exchanger 123, and a throttling valve 143 sequentially connected in the working fluid loop 141 along the flow direction of the heat pump working fluid. The heat pump working fluid, after absorbing heat in the fourth heat exchanger 133, evaporates into a gaseous state. The first compressor 142 is configured to compress the gaseous heat pump working fluid. The throttling valve 143 is configured to depressurize the heat pump working fluid from the second heat exchanger 123.

[0041] This embodiment uses a compression heat pump as the waste heat upgrading unit, so that desorption does not require an external cold source or an external heat source, thus realizing full-process electrification.

[0042] The heat pump working fluid can be a commonly used heat pump working fluid, such as R245fa, as needed.

[0043] See Figure 4 As shown, in some embodiments, the two-stage circulating water cascade recovery tower top gas waste heat module 100 may further include a second compressor 150. The second compressor 150 is disposed in the communication path between the tower top gas outlet 111 and the first heat exchanger 122, and is configured to compress the tower top gas output from the tower top gas outlet 111 and output the compressed tower top gas to the first heat exchanger 122.

[0044] In this embodiment, the thermal quality of the top gas is improved by compression, which greatly reduces the difficulty of waste heat recovery and significantly reduces energy consumption.

[0045] See Figure 3 and Figure 4 As shown, in some embodiments, the two-stage circulating water cascade recovery tower top gas waste heat module 100 may further include a gas-liquid separator 160. The gas-liquid separator 160 is connected to the third heat exchanger 132 and is configured to perform gas-liquid separation on the tower top gas after passing through the third heat exchanger 132, and output the separated carbon dioxide gas and condensate through its gas outlet 162 and liquid outlet 161, respectively.

[0046] In some embodiments, the waste heat utilization element 124 may be a reboiler connected to the bottom of the desorption tower 110 for heating the medium-lean liquor in the desorption tower 110.

[0047] In other embodiments, the waste heat utilization element 124 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.

[0048] In some other embodiments, the waste heat utilization element 124 may include a reboiler and an interstage heater.

[0049] By utilizing the recovered waste heat for interstage heating, it is possible to promote heat exchange in the rich liquid, improve desorption efficiency, and thus increase CO2 production.

[0050] Those skilled in the art will understand that, in order to promote the circulation of circulating water and heat pump working fluid, devices such as pumps that provide circulation driving force can be provided in the first water circulation loop 121, the working fluid loop 141, and the second water circulation loop 131.

[0051] Based on the same technical concept, embodiments of the present invention also provide a carbon dioxide capture system 200.

[0052] Figure 5 This is a schematic structural block diagram of a carbon dioxide capture system 200 according to an embodiment of the present invention. See also... Figure 5 As shown, the carbon dioxide capture system 200 generally includes: an absorption tower 170, a two-stage circulating water cascade recovery tower top gas waste heat module 100 as described in any of the foregoing embodiments or combinations thereof, and a lean-rich liquid heat exchanger 180. The absorption tower 170 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 180 is connected between the absorption tower 170 and the desorption tower 110, and is configured to exchange heat between the rich liquid from the absorption tower 170 and the lean liquid from the desorption tower 110.

[0053] In some alternative embodiments, the liquid outlet 161 of the gas-liquid separator 160 can be connected to the absorption tower 170 to return the condensate separated by the gas-liquid separator 160 to the absorption tower 170. For example, the separated condensate can be mixed with lean cold liquid and returned to the absorption tower 170 as a regenerated absorbent.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The following is based on Figure 3 and Figure 4 The carbon dioxide capture system 200 with the structure of the two-stage circulating water cascade recovery tower top gas waste heat module 100 shown is a specific embodiment. The technical effect of the technical solution of the present invention is verified by simulation.

[0064] 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 170 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).

[0065] Table 1. Rich solution injection conditions for carbon capture process

[0066] Simulation results show that the technical solution of the present invention has the following beneficial effects: (1) Desorption does not require an external cold source or an external heat source, thus achieving full-process electrification.

[0067] (2) For the uncompressed overhead gas scheme, the heat exchange difficulty is greatly reduced by the two-stage circulating water heat exchange (the heat exchanger terminal difference is greater than 5K), thereby efficiently recovering waste heat. The energy consumption is only 2.5GJ / ton CO2, which is more than 55% lower.

[0068] (3) For the scheme of compressing the overhead gas, the thermal quality of the overhead gas is improved by compression, and the waste heat is recovered through two-stage circulating water. The terminal difference of the first heat exchanger 122, which recovers high-quality waste heat, is greater than 10K, which greatly reduces the difficulty of waste heat recovery. The waste heat of the overhead gas is recovered through two-stage circulating water at high and low temperatures, with a larger terminal difference of the heat exchangers and lower design difficulty. Moreover, the energy consumption is greatly reduced, and the final process heat consumption is only 1.42GJ / tonCO2, which reduces the desorption energy consumption by 74%.

[0069] (4) The consumption of circulating water and heat pump working fluid is very low, at 2.7 and 15.5 ton / hr respectively, resulting in low engineering operating costs.

[0070] (5) Since the waste heat recovery process is carried out under normal pressure, the engineering difficulty and cost are greatly reduced, and the application scenarios are wide.

[0071] 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.

[0072] 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 two-stage circulating water cascade recovery tower top gas waste heat module, comprising: Desorption tower, with a top gas outlet; The first-stage water circulation unit includes a first heat exchanger, a second heat exchanger, and a waste heat recovery element connected sequentially in the first water circulation loop along the water flow direction. The first heat exchanger is also connected to the top gas outlet of the tower and is configured to allow the first circulating water flowing through it to exchange heat with the top gas output from the top gas outlet of the tower in order to recover the waste heat of the top gas to initially heat the first circulating water. The second-stage water circulation unit includes a third heat exchanger and a fourth heat exchanger connected sequentially in the second water circulation loop along the water flow direction. The third heat exchanger is also connected to the first heat exchanger and is configured to receive the top gas after passing through the first heat exchanger, and to exchange heat between the second circulating water flowing through it and the top gas to recover the waste heat of the top gas and output the heated second circulating water to the fourth heat exchanger. as well as The waste heat upgrading unit includes a fourth heat exchanger, an upgrading device, and a second heat exchanger connected in sequence. The fourth heat exchanger is configured to exchange heat between the working medium of the waste heat upgrading unit and the heated second circulating water to absorb heat. The upgrading device is configured to increase the temperature of the working medium after absorbing heat. The second heat exchanger is configured to exchange heat between the heated working medium and the pre-heated first circulating water to convert at least part of the first circulating water into water vapor. The waste heat utilization element is connected to the desorption tower and is configured to heat the rich and / or lean liquids of the desorption tower by heat exchange using the first circulating water flow, which is at least partially converted into water vapor.

2. The two-stage circulating water cascade recovery tower top gas waste heat module according to claim 1, wherein, The waste heat upgrading unit is a heat pump unit, and the working medium is a heat pump working fluid.

3. The two-stage circulating water cascade recovery tower top gas waste heat module according to claim 2, wherein, The waste heat upgrading unit is a compression heat pump unit, which includes a fourth heat exchanger sequentially connected in the working fluid loop along the flow direction of the heat pump working fluid, a first compressor serving as the upgrading unit, a second heat exchanger, and a throttling valve; wherein The heat pump working fluid in the fourth heat exchanger evaporates into a gaseous state after absorbing heat. The first compressor is configured to compress the gaseous heat pump working fluid; The throttling valve is configured to depressurize the heat pump working fluid from the second heat exchanger.

4. The two-stage circulating water cascade recovery tower top gas waste heat module according to any one of claims 1-3 further includes: The second compressor is located in the communication path between the top gas outlet of the tower and the first heat exchanger, and is configured to compress the top gas output from the top gas outlet of the tower and output the compressed top gas to the first heat exchanger.

5. The two-stage circulating water cascade recovery tower top gas waste heat module according to any one of claims 1-3, wherein, The waste heat recovery 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.

6. The two-stage circulating water cascade recovery tower top gas waste heat module according to any one of claims 1-3, further comprising: A gas-liquid separator, connected to the third heat exchanger, is configured to perform gas-liquid separation on the overhead gas after passing through the third heat exchanger.

7. A carbon dioxide capture system, comprising: 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. Two-stage circulating water cascade recovery tower top gas waste heat module according to any one of claims 1-5; as well as 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.

8. The carbon dioxide capture system according to claim 7, wherein, The two-stage circulating water cascade recovery tower top gas waste heat module also includes: A gas-liquid separator, connected to the third heat exchanger, is configured to perform gas-liquid separation on the overhead gas after passing through the third heat exchanger; The liquid outlet of the gas-liquid separator is connected to the absorption tower to return the condensate separated by the gas-liquid separator to the absorption tower.

9. The carbon dioxide capture system according to claim 7 or 8, 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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