System and method for capturing carbon dioxide through cascade amine method

Abstract

The invention relates to a system and a method for capturing carbon dioxide by a cascade amine method. The system comprises a primary absorption tower, a primary desorption tower, a first rich and lean solution heat exchanger, a first barren solution cooler, a secondary absorption tower, a secondary desorption tower, a second rich and lean solution heat exchanger, a second barren solution cooler, a regenerated gas cooler and a gas-liquid separator, through gradient utilization of the amine liquid and arrangement of two-stage CO2 capture, the problem of efficiency exponential attenuation caused by degradation of the amine liquid in long-period operation is effectively solved, the service life of the amine liquid is prolonged, the capture rate of CO2 is improved, meanwhile, regeneration energy consumption is reduced, and the impurity removal effect is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of carbon dioxide capture, and in particular, to a system and method for capturing carbon dioxide using a cascaded amine process. Background Art

[0002] Traditional CO2 capture systems generally utilize a single-stage amine absorption-regeneration process, with a typical architecture consisting of a single absorption tower and a desorption tower circulating system. Specifically, the following are the key features: 1. Single amine circulation mode: Fresh amine (e.g., 30% MEA) is used to directly treat raw flue gas containing high CO2 concentrations (12-15%). During continuous operation, the amine reacts with impurities (SOx / NOx / dust) to form heat-stable salts (HSS), causing absorption efficiency to decline from an initial over 95% to less than 85% after 500 hours of operation. This requires frequent replenishment or replacement of the amine (approximately 2,000 hours). 2. Full thermal regeneration technology: All amines are regenerated using steam heating at 120-150°C, resulting in a regeneration energy consumption of up to 3.0-3.8 GJ / tCO2. High temperatures exacerbate amine degradation, creating a vicious cycle. 3. Impurity treatment defects: Flue gas pretreatment relies on an independent scrubber, but residual impurities still react with the amine solution, and the annual accumulation of HSS reaches 8-12wt%. Additional ion exchange resins or chemical precipitation equipment are required, increasing system complexity and cost.

[0003] Prior art proposals have proposed batch regeneration of amine solutions based on their degradation levels, but this fails to address the degradation of fresh amine solutions caused by premature exposure to high-concentration impurities. Some approaches have attempted to replace thermal regeneration with electrodialysis, but single electrodialysis treatment of high-concentration CO₂-rich solutions results in severe membrane fouling, energy consumption still exceeding 3.0 GJ / tCO₂, shortening membrane replacement cycles and increasing costs. Another related improvement utilizes two absorption towers connected in series, but these share a regeneration unit, resulting in mixed regeneration of fresh and old amine solutions and inability to accurately protect the active amine solution.

[0004] In summary, the existing technology still has the problems of continuous degradation of amine solution leading to exponential decay of absorption efficiency, sharp increase in overall regeneration energy consumption with the deterioration of amine solution, and flue gas impurities (SO x 、NO x , particulate matter) accumulate in the absorbent to form a large amount of heat-stable salt (HSS), and the regeneration of the full amount of amine solution or the regular replacement of new amine solution leads to increased operating costs and other problems. Summary of the Invention

[0005] To address the aforementioned technical issues, the present disclosure provides a system and method for capturing carbon dioxide using a cascaded amine process. This system effectively addresses the exponential efficiency decay caused by amine degradation during long-term operation, while also reducing regeneration energy consumption and improving impurity removal.

[0006] To achieve the above objectives, the present disclosure provides, in a first aspect, a system for capturing carbon dioxide using a cascade amine process, the system comprising a primary absorption tower, a primary desorption tower, a first lean-rich liquid heat exchanger, a first lean liquid cooler, a secondary absorption tower, a secondary desorption tower, a second lean-rich liquid heat exchanger, a second lean liquid cooler, a regenerated gas cooler, and a gas-liquid separator; The first treated gas outlet of the primary absorption tower is connected to the first treated gas inlet of the secondary absorption tower, the first rich liquid outlet of the primary absorption tower is connected to the first rich liquid inlet of the primary desorption tower through the first lean-rich liquid heat exchanger, and the first lean liquid outlet of the primary desorption tower is connected to the first lean liquid inlet of the primary absorption tower through the first lean-rich liquid heat exchanger and the first lean liquid cooler in sequence; The second rich liquid outlet of the secondary absorption tower is connected to the second rich liquid inlet of the secondary desorption tower through the second rich-lean liquid heat exchanger, and the second lean liquid outlet of the secondary desorption tower is connected to the second lean liquid inlet of the secondary absorption tower through the second rich-lean liquid heat exchanger and the second lean liquid cooler in sequence; The first carbon dioxide outlet of the primary desorption tower and the second carbon dioxide outlet of the secondary desorption tower are respectively communicated with the carbon dioxide inlet of the gas-liquid separator through a regeneration gas cooler.

[0007] Optionally, a first rich liquid pump is provided on the pipeline between the first rich liquid outlet of the primary absorption tower and the first lean-rich liquid heat exchanger, and a first lean liquid pump is provided on the pipeline between the first lean liquid outlet of the primary desorption tower and the first lean-rich liquid heat exchanger; A second rich liquid pump is provided on the pipeline between the second rich liquid outlet of the secondary absorption tower and the second lean-rich liquid heat exchanger, and a second lean liquid pump is provided on the pipeline between the second lean liquid outlet of the secondary desorption tower and the second lean-rich liquid heat exchanger; An amine liquid dispensing pipeline is connected between the primary absorption tower and the secondary absorption tower, and a flow control valve and a delivery pump are sequentially arranged on the amine liquid dispensing pipeline along the direction of amine liquid flow; The primary absorption tower is also provided with an inlet for flue gas to be treated, and the secondary absorption tower is also provided with an inlet for fresh amine solution.

[0008] Optionally, the primary absorption tower comprises multiple primary absorption filler layers sequentially spaced from bottom to top, and a first spray layer is provided above each primary absorption filler layer; the primary desorption tower comprises multiple primary desorption filler layers sequentially spaced from bottom to top and a first entrainment separator; The secondary absorption tower includes multiple levels of absorption filler layers spaced apart from bottom to top, and a second spray layer is provided above each secondary absorption filler layer; the secondary desorption tower includes multiple levels of desorption filler layers spaced apart from bottom to top and a second mist separator.

[0009] Optionally, the system further comprises an amine recovery heating device and an electrodialysis device; The recovered amine outlet of the amine recovery and heating device is connected to the recovered amine liquid inlet of the primary desorption tower; a first lean liquid recovery branch is further provided on the pipeline between the first lean liquid outlet of the primary desorption tower and the first lean-rich liquid heat exchanger, and the inlet of the amine recovery and heating device is connected to the outlet of the first lean liquid recovery branch; Preferably, the amine recovery and heating device comprises a falling film evaporator and a flash compressor connected in series; A second lean liquid recovery branch and a second lean liquid regeneration branch are sequentially arranged on the pipeline between the second lean liquid cooler and the second lean liquid inlet of the secondary absorption tower and along the direction of flow of the second lean liquid. The outlet of the second lean liquid recovery branch is connected to the inlet of the electrodialysis device, and the inlet of the second lean liquid regeneration branch is connected to the outlet of the electrodialysis device.

[0010] Optionally, the system further comprises an underground tank and an exhaust gas scrubber; The inlet of the underground tank is connected to the liquid outlet of the gas-liquid separator, and the outlet of the underground tank is connected to the separation liquid inlet of the secondary decomposition tower; The second treated gas outlet of the secondary absorption tower is communicated with the tail gas scrubber inlet.

[0011] Optionally, the system further comprises an intelligent control unit, which comprises a controller, an online conductivity meter, a pH meter and a near-infrared spectrometer; The online conductivity meter, the pH meter and the near-infrared spectrometer are used to monitor the amine solution concentration, degradation products and HSS content in the primary absorption tower and the secondary absorption tower in real time; The controller is respectively connected to the online conductivity meter, the pH meter and the near-infrared spectrometer for signal transmission. The controller is used to control the allocation of the amine solution in the primary absorption tower and the secondary absorption tower based on the real-time monitoring data of the amine solution concentration, degradation products and HSS content from the online conductivity meter, the pH meter and the near-infrared spectrometer.

[0012] A second aspect of the present disclosure provides a method for capturing carbon dioxide using a cascade amine process using the system described in the first aspect, the method comprising: The preheated flue gas to be treated is passed from the bottom of the primary absorption tower into the primary absorption tower and countercurrently contacts with the first amine liquid from the top of the tower to obtain a first treated gas and a first rich liquid; the first rich liquid is passed through a first lean-rich liquid heat exchanger and then into a primary desorption tower for a first desorption treatment to obtain first carbon dioxide and a first lean liquid; a portion of the first lean liquid is passed through the first lean-rich liquid heat exchanger and the first lean liquid cooler in sequence and then returned to the primary absorption tower; The first treated gas is passed from the bottom of the secondary absorption tower into the secondary absorption tower and countercurrently contacts with the second amine liquid from the top of the tower to obtain a second treated gas and a second rich liquid; the second rich liquid is passed through a second lean-rich liquid heat exchanger and then enters a secondary desorption tower for a second desorption treatment to obtain a second carbon dioxide and a second lean liquid; a portion of the second lean liquid is passed through the second lean-rich liquid heat exchanger and the second lean liquid cooler in sequence and then returned to the secondary absorption tower; The first carbon dioxide and the second carbon dioxide are combined and then pass through a regeneration gas cooler and then enter a gas-liquid separator to separate and obtain pure carbon dioxide.

[0013] Optionally, the separated liquid obtained by the gas-liquid separator enters an underground tank for storage and then enters a secondary desorption tower; The second treated gas is discharged after being washed by the tail gas scrubber; Another part of the first lean liquid enters the amine recovery and heating device for amine liquid recovery treatment, so that the recovered amine liquid enters the primary decomposition tower; The amine recovery and heating device comprises a falling film evaporator and a flash compressor connected in series; Preferably, the falling film evaporator has a temperature of 100-120°C, a pressure of 0.04-0.08 MPa, and a residence time of 5-15 min; the flash compressor has a pressure of 0.03-0.08 MPa and a temperature of 90-110°C; Another portion of the second lean liquid enters the electrodialysis device for amine liquid regeneration treatment, so that the regenerated amine liquid enters the secondary absorption tower; Preferably, the operating voltage of the electrodialysis device is 40-60V, and the current density is 200-400A / m 2 .

[0014] Optionally, the first amine liquid is a waste amine liquid with a running time greater than 2000 hours, and the mass concentration of the waste amine liquid is 18-25% by weight; preferably, the first amine liquid is waste monoethanolamine; The second amine liquid is a fresh amine liquid with a running time of less than 500 hours, and the mass concentration of the fresh amine liquid is 20-35% by weight; preferably, the second amine liquid is fresh monoethanolamine.

[0015] Optionally, in the primary absorption tower, the temperature is 40-55°C, the liquid-gas ratio is 1.5-2 L / m 3 In the primary analytical tower, the temperature is 100-108 ° C, the liquid-gas ratio is 1.5-2L / m 3 ; In the secondary absorption tower, the temperature is 40-55°C and the liquid-gas ratio is 2-2.5 L / m 3 In the secondary decomposition tower, the temperature is 100-108 ° C, the liquid-gas ratio is 2-2.5L / m 3 ; The temperature of the preheated flue gas to be treated is 38-43°C.

[0016] Through the above technical solution, the present invention effectively solves the problem of exponential efficiency decay caused by amine liquid degradation during long-term operation through the cascade utilization of amine liquid and the two-stage CO2 capture setting, thereby extending the life of the amine liquid, improving the CO2 capture rate, and at the same time reducing regeneration energy consumption and improving the impurity removal effect.

[0017] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings: Figure 1 It is a structural diagram of the system of embodiment 1 of the present disclosure.

[0019] Figure 2 Schematic diagram of the system structure of Example 1.

[0020] Description of Reference Numerals A primary absorption tower; B secondary absorption tower; R1 primary desorption tower; R2 secondary desorption tower; H1 first lean and rich liquid heat exchanger; H2 second lean and rich liquid heat exchanger; AL first lean liquid cooler; BL second lean liquid cooler; ZL regeneration gas cooler; F gas-liquid separator; AFP first rich liquid pump; APP first lean liquid pump; BFP second rich liquid pump; BPP second lean liquid pump; LKF flow control valve; SP transfer pump; HX1 amine recovery and heating device; ED electrodialysis device; D underground tank; WG tail gas scrubber. DETAILED DESCRIPTION

[0021] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0022] In this disclosure, unless otherwise specified, directional terms such as "top" and "bottom" generally refer to the top and bottom of a device under normal use. "Upstream" and "downstream" refer to the direction of flow of the medium in a pipeline. Terms such as "first" and "second" are used solely to distinguish between different components and do not imply a specific order of connection.

[0023] like Figure 1 As shown, the first aspect of the present disclosure provides a system for capturing carbon dioxide using a cascade amine process, the system comprising a primary absorption tower A, a primary desorption tower R1, a first lean-rich liquid heat exchanger H1, a first lean liquid cooler AL, a secondary absorption tower B, a secondary desorption tower R2, a second lean-rich liquid heat exchanger H2, a second lean liquid cooler BL, a regeneration gas cooler ZL, and a gas-liquid separator F; The first treated gas outlet of the primary absorption tower A is connected to the first treated gas inlet of the secondary absorption tower B, the first rich liquid outlet of the primary absorption tower A is connected to the first rich liquid inlet of the primary decomposition tower R1 through the first lean-rich liquid heat exchanger H1, and the first lean liquid outlet of the primary decomposition tower R1 is connected to the first lean liquid inlet of the primary absorption tower A through the first lean-rich liquid heat exchanger H1 and the first lean liquid cooler AL in sequence; The second rich liquid outlet of the secondary absorption tower B is connected to the second rich liquid inlet of the secondary desorption tower R2 through the second rich-lean liquid heat exchanger H2, and the second lean liquid outlet of the secondary desorption tower R2 is connected to the second lean liquid inlet of the secondary absorption tower B through the second rich-lean liquid heat exchanger H2 and the second lean liquid cooler BL in sequence; The first carbon dioxide outlet of the primary desorption tower R1 and the second carbon dioxide outlet of the secondary desorption tower R2 are respectively connected to the carbon dioxide inlet of the gas-liquid separator F through the regeneration gas cooler ZL.

[0024] The present disclosure can realize the cascade utilization of amine liquid. Specifically, the first cascade utilization: the primary absorption tower A can capture no less than 70% of the CO2 in the flue gas to be treated, preferably 70-80% of the CO2; the second cascade utilization: the secondary absorption tower B can increase the CO2 capture rate to more than 99.5%; through the two-stage CO2 capture setting, the exponential decay problem of efficiency caused by the degradation of amine liquid during long-term operation is effectively solved, and at the same time, the regeneration energy consumption can be reduced and the impurity removal effect can be improved.

[0025] In the present disclosure, the first lean liquid outlet of the primary desorption tower R1 is connected to the first lean liquid inlet of the primary absorption tower A via the first lean-rich liquid heat exchanger H1 and the first lean liquid cooler AL, wherein the first lean-rich liquid heat exchanger H1 is located upstream of the first lean liquid cooler AL along the direction of flow of the first lean liquid. The second lean liquid outlet of the secondary desorption tower R2 is connected to the second lean liquid inlet of the secondary absorption tower B via the second lean-rich liquid heat exchanger H2 and the second lean liquid cooler BL, wherein the second lean-rich liquid heat exchanger H2 is located upstream of the second lean liquid cooler BL along the direction of flow of the second lean liquid.

[0026] In one embodiment of the present disclosure, a first rich liquid pump AFP is provided on the pipeline between the first rich liquid outlet of the primary absorption tower A and the first lean-rich liquid heat exchanger H1; wherein, the pipeline between the first rich liquid outlet of the primary absorption tower A and the first lean-rich liquid heat exchanger H1 refers to the pipeline connecting the first rich liquid outlet of the primary absorption tower A and the first rich liquid inlet of the first lean-rich liquid heat exchanger H1. A first lean liquid pump APP is provided on the pipeline between the first lean liquid outlet of the primary desorption tower R1 and the first lean-rich liquid heat exchanger H1; wherein, the pipeline between the first lean liquid outlet of the primary desorption tower R1 and the first lean-rich liquid heat exchanger H1 refers to the pipeline connecting the first lean liquid outlet of the primary desorption tower R1 and the first lean-rich liquid heat exchanger H1.

[0027] A second rich liquid pump BFP is installed on the pipeline between the second rich liquid outlet of the secondary absorption tower B and the second lean-rich liquid heat exchanger H2; wherein, the pipeline between the second rich liquid outlet of the secondary absorption tower B and the second lean-rich liquid heat exchanger H2 refers to the pipeline connecting the second rich liquid outlet of the secondary absorption tower B and the second lean liquid inlet of the second lean-rich liquid heat exchanger H2. A second lean liquid pump BPP is installed on the pipeline between the second lean liquid outlet of the secondary desorption tower R2 and the second lean-rich liquid heat exchanger H2; wherein, the pipeline between the second lean liquid outlet of the secondary desorption tower R2 and the second lean-rich liquid heat exchanger H2 refers to the pipeline connecting the second lean liquid outlet of the secondary desorption tower R2 and the second lean-rich liquid heat exchanger H2.

[0028] In one embodiment of the present disclosure, an amine liquid dispensing pipeline is connected across the primary absorption tower A and the secondary absorption tower B, and a flow control valve LKF and a delivery pump SP are sequentially provided on the amine liquid dispensing pipeline along the direction of amine liquid flow. In the above embodiment, real-time cross-stage amine liquid dynamic replenishment can be achieved; by cross-stage amine liquid dispensing, the amine concentration in the primary absorption tower A is maintained in the optimized range of 18-25% by weight, and the amine concentration in the secondary absorption tower B is maintained in the optimized range of 20-35% by weight, which can solve the problem of full regeneration or regular replacement of amine liquid and effectively reduce costs. Preferably, the replenishment rate of real-time cross-stage amine liquid dynamic replenishment is 8-12m 3 / h.

[0029] In one embodiment of the present disclosure, a flue gas inlet to be treated (i.e. Figure 1 The flue gas inlet is shown in FIG), which is used to introduce the flue gas to be treated into the primary absorption tower A.

[0030] In one embodiment of the present disclosure, a fresh amine liquid inlet is further provided on the secondary absorption tower B for introducing fresh amine liquid into the secondary absorption tower.

[0031] In one embodiment of the present disclosure, the primary absorption tower A includes multiple primary absorption packing layers spaced sequentially from bottom to top, with a first spray layer disposed above each primary absorption packing layer. In this embodiment, the multiple primary absorption packing layers are preferably 2-4 layers, with the spacing between two adjacent primary packing layers being 1.5-3 meters; and the spacing between each primary packing layer and the first spray layer disposed above it is 0.8-1.5 meters.

[0032] In one embodiment of the present disclosure, the secondary absorption tower B includes a multi-level absorption packing layer arranged in sequence from bottom to top, and a second spray layer is arranged above each layer of the secondary absorption packing layer; in the above embodiment, the multi-level absorption packing layer is preferably 3-5 layers, and the distance between two adjacent levels of the packing layer is 1.2-2.5m; the distance between each level packing layer and the second spray layer arranged above it is 0.8-1.5m.

[0033] In the present disclosure, the first spray layer and the second spray layer can adopt those conventionally adopted by those skilled in the art. Specifically, the first spray layer and the second spray layer can each be independently provided with a plurality of nozzles and liquid distributors to evenly cover the amine liquid on the packing layer, so that it can fully contact with the flue gas to be treated or the first treated gas to ensure the capture rate of carbon dioxide.

[0034] In one embodiment of the present disclosure, the primary desorption tower R1 includes multiple layers of primary desorption packing layers and a first entrainment separator that are sequentially spaced from bottom to top. In the above embodiment, the multiple layers of primary desorption packing layers are preferably 2-4 layers, and the spacing between two adjacent layers of primary desorption packing layers is 1.5-3m. In one embodiment of the present disclosure, the secondary desorption tower R2 includes multiple layers of secondary desorption packing layers and a second entrainment separator that are sequentially spaced from bottom to top. In the above embodiment, the multiple layers of secondary desorption packing layers are preferably 3-5 layers, and the spacing between two adjacent layers of secondary desorption packing layers is 1.2-1.5m.

[0035] In the present disclosure, by providing the first mist separator and the second mist separator, the mist and / or droplets of amine liquid formed by the airflow entrainment can be separated from the gas to avoid being carried into the subsequent system, thereby further ensuring the purity of the carbon dioxide; in addition, the loss of amine liquid caused by the mist and / or droplet-shaped amine liquid being carried into the subsequent system can be avoided, thereby effectively reducing the operating cost.

[0036] In the present disclosure, the inlet for the flue gas to be treated is arranged at the bottom of the primary absorption tower A, and the first treated gas outlet and the first lean liquid inlet are each independently arranged at the top of the primary absorption tower A. The first treated gas inlet of the secondary absorption tower B is arranged at the bottom of the secondary absorption tower B, and the second lean liquid inlet and the fresh amine liquid inlet are each independently arranged at the top of the secondary absorption tower B. This achieves countercurrent contact between the flue gas to be treated and the first lean liquid, and between the first treated gas and the second lean liquid and / or the fresh amine liquid.

[0037] In the present disclosure, the first rich liquid inlet and the first carbon dioxide outlet of the primary desorption tower R1 are each independently provided at the top of the primary desorption tower R1, and the first lean liquid outlet of the primary desorption tower R1 is provided at the bottom of the primary desorption tower R1. The second rich liquid inlet and the second carbon dioxide outlet of the secondary desorption tower R2 are each independently provided at the top of the secondary desorption tower R2, and the second lean liquid outlet of the secondary desorption tower R2 is provided at the bottom of the secondary desorption tower R2. The first rich liquid inlet of the primary desorption tower R1 is connected to the first entrainment separator, and the second rich liquid inlet of the secondary desorption tower R2 is connected to the second entrainment separator.

[0038] In one embodiment of the present disclosure, the system further comprises an amine recovery heating device HX1 and an electrodialysis device ED; The recovered amine outlet of the amine recovery and heating device HX1 is connected to the recovered amine liquid inlet of the primary desorption tower R1. A first lean liquid recovery branch is also provided in the pipeline between the first lean liquid outlet of the primary desorption tower R1 and the first lean-rich liquid heat exchanger H1. The inlet of the amine recovery and heating device HX1 is connected to the outlet of the first lean liquid recovery branch. More specifically, along the direction of flow of the first lean liquid, the first lean liquid recovery branch is located downstream of the first lean liquid pump APP.

[0039] Preferably, the amine recovery and heating device HX1 comprises a falling film evaporator and a flash compressor connected in series. More specifically, the first lean liquid in the first lean liquid recovery branch first enters the falling film evaporator for evaporation and separation of water and amine liquid from the first lean liquid. The evaporated water and amine liquid are then processed by the flash compressor connected in series before entering the primary desorption tower R1. The remaining (unevaporated) waste amine liquid impurities in the falling film evaporator undergo subsequent waste liquid treatment (e.g., incineration). The flash compressor provides a negative pressure environment for the evaporated water and amine liquid obtained by the falling film evaporator, lowering their boiling points. The series connection of the falling film evaporator and flash compressor further efficiently promotes amine liquid recovery and regeneration.

[0040] In one embodiment of the present disclosure, a second lean liquid recovery branch and a second lean liquid regeneration branch are sequentially disposed in the pipeline between the second lean liquid cooler BL and the second lean liquid inlet of the secondary absorption tower B, along the direction of flow of the second lean liquid. The outlet of the second lean liquid recovery branch is connected to the inlet of the electrodialysis device ED, and the inlet of the second lean liquid regeneration branch is connected to the outlet of the electrodialysis device ED. In this embodiment, the provision of the electrodialysis device ED can further improve the purity and regeneration efficiency of the second lean liquid.

[0041] In one embodiment of the present disclosure, the system further comprises an underground tank D and an exhaust gas scrubber WG; The inlet of the underground tank D is connected to the liquid outlet of the gas-liquid separator F, and the outlet of the underground tank D is connected to the separation liquid inlet of the secondary decomposition tower R2; The second treated gas outlet of the secondary absorption tower B is communicated with the inlet of the tail gas scrubber WG.

[0042] In one embodiment of the present disclosure, the system further comprises an intelligent control unit, which comprises a controller, an online conductivity meter, a pH meter and a near-infrared spectrometer; The online conductivity meter, the pH meter and the near-infrared spectrometer are used to monitor the amine solution concentration, degradation products and HSS content in the primary absorption tower A and the secondary absorption tower B in real time; The controller is respectively connected to the online conductivity meter, the pH meter and the near-infrared spectrometer for signal transmission. The controller is used to control the allocation of the amine solution in the primary absorption tower A and the secondary absorption tower B based on the real-time monitoring data of the amine solution concentration, degradation products and HSS content from the online conductivity meter, the pH meter and the near-infrared spectrometer.

[0043] In the present disclosure, multiple online conductivity meters may be provided, for example, two, one connected to primary absorption tower A and the other to secondary absorption tower B. The online conductivity meters can be conventionally used by those skilled in the art, such as industrial-grade contact-type or inductive conductivity sensors (e.g., InPro 7000 series, CLS82D, etc.), with a range of 1-100 mS / cm and temperature compensation. The online conductivity meters are used to monitor the concentration of the amine solution in primary absorption tower A and secondary absorption tower B.

[0044] In the present disclosure, multiple pH meters may be provided, for example, two, one connected to primary absorption tower A and the other to secondary absorption tower B. The pH meters can be conventionally used by those skilled in the art, such as corrosion-resistant industrial online pH sensors (e.g., InPro 4800, CPS71D, etc.), with electrodes made of titanium alloy or Hastelloy and built-in temperature compensation. The pH meters are used to monitor the levels of amine degradation products in primary absorption tower A and secondary absorption tower B.

[0045] In the present disclosure, multiple near-infrared spectrometers may be provided, for example, two, with the probe of one near-infrared spectrometer positioned in primary absorption tower A and the probe of the other near-infrared spectrometer positioned in secondary absorption tower B. The near-infrared spectrometers conventionally used by those skilled in the art may be industrial online spectrometers (e.g., models XDS RapidContent and MATRIX-F), with probes made of Hastelloy or titanium alloy and a spectral range covering 1100-2500 nm. The near-infrared spectrometer is used to detect the HSS content in primary absorption tower A and secondary absorption tower B. Representative amine solution samples must be collected, and the actual HSS concentration is determined through laboratory analysis (e.g., ion chromatography). This is then correlated with the near-infrared spectrum to establish a calibration model.

[0046] According to the present disclosure, by online monitoring of the amine solution concentration, degradation products, and HSS content in the primary absorption tower A and the secondary absorption tower B, the application of the amine solution can be tracked in a timely manner, facilitating precise control of the operation.

[0047] A second aspect of the present disclosure provides a method for capturing carbon dioxide using a cascade amine process using the system described in the first aspect, the method comprising: The preheated flue gas to be treated is passed from the bottom of the primary absorption tower A into the primary absorption tower A and countercurrently contacts with the first amine liquid from the top of the tower to obtain a first treated gas and a first rich liquid. The first rich liquid passes through the first lean-rich liquid heat exchanger H1 and then enters the primary desorption tower R1 for a first desorption treatment to obtain first carbon dioxide and a first lean liquid. A portion of the first lean liquid passes through the first lean-rich liquid heat exchanger H1 and the first lean liquid cooler AL in sequence and then returns to the primary absorption tower A. The first treated gas is passed from the bottom of the secondary absorption tower B into the secondary absorption tower B and countercurrently contacts with the second amine liquid from the top of the tower to obtain a second treated gas and a second rich liquid. The second rich liquid passes through the second lean-rich liquid heat exchanger H2 and then enters the secondary desorption tower R2 for a second desorption treatment to obtain a second carbon dioxide and a second lean liquid. A portion of the second lean liquid passes through the second lean-rich liquid heat exchanger H2 and the second lean liquid cooler BL in sequence and then returns to the secondary absorption tower B. The first carbon dioxide and the second carbon dioxide are combined and then pass through the regeneration gas cooler ZL and then enter the gas-liquid separator F to separate and obtain pure carbon dioxide.

[0048] In the present disclosure, the method captures carbon dioxide from flue gas in a cascaded manner. The first stage captures at least 70% of the CO₂ in the flue gas to be treated, preferably 70-80%. The second stage captures CO₂ and increases the capture rate to over 99.5%. This two-stage CO₂ capture effectively addresses the exponential efficiency decay caused by amine degradation during long-term operation, while reducing regeneration energy consumption and improving impurity removal. Furthermore, during CO₂ capture in the primary absorption tower A and the secondary absorption tower B, countercurrent contact facilitates comprehensive contact between the first amine solution and the preheated flue gas to be treated, and between the second amine solution and the first treated gas, effectively ensuring CO₂ capture.

[0049] In the present disclosure, the first amine liquid from the top of the tower may be referred to as a first lean liquid, and the second amine liquid from the top of the tower may be referred to as a second lean liquid and / or a fresh amine liquid.

[0050] In one embodiment of the present disclosure, the separated liquid obtained by the gas-liquid separator F is stored in an underground tank D and then enters the secondary desorption tower R2. In the above embodiment, the gas-liquid separator F can produce high-concentration carbon dioxide after separation, which is sent to the next-level CO2 product processing unit for use; the separated liquid passes through the underground tank D and then enters the secondary desorption tower R2, realizing the utilization and recycling of the amine liquid and saving energy.

[0051] In the present disclosure, the second treated gas is discharged after being washed by the tail gas scrubber WG; that is, it is discharged into the atmosphere. The tail gas scrubber WG can adopt a conventional device in the field, such as a wet scrubber, to capture droplets of amine liquid aerosol carried by the flue gas. The captured droplets of amine liquid aerosol can be returned to the secondary absorption tower B.

[0052] In the present disclosure, the first lean liquid is divided into two parts. One part passes through the first lean-rich liquid heat exchanger H1 and the first lean liquid cooler AL and then returns to the primary absorption tower A; the other part of the first lean liquid enters the amine recovery and heating device HX1 for amine recovery treatment, so that the recovered amine enters the primary decomposition tower R1. The part of the first lean liquid entering the amine recovery and heating device HX1 accounts for 5-20% of the volume of the circulation volume; the amine recovery and heating device HX1 includes a falling film evaporator and a flash compressor connected in series.

[0053] Furthermore, the second lean liquid is also divided into two parts. One part passes through the second lean-rich liquid heat exchanger H2 and the second lean liquid cooler BL and is directly returned to the secondary absorption tower B; the other part of the second lean liquid enters the electrodialysis device ED for amine liquid regeneration treatment, so that the regenerated amine liquid enters the secondary absorption tower B and enters the electrodialysis device ED. This part of the second lean liquid accounts for 3-10% by volume of the circulation amount.

[0054] In the present disclosure, after the first-stage capture, thermal regeneration treatment is used to degrade the first lean liquid (i.e., amine liquid); after the second-stage capture, an electrodialysis device ED is used to perform electrodialysis thermal coupling regeneration to maintain the activity of the second lean liquid; by using different regeneration devices in the two stages, the problem of optimizing the coupled utilization of the two regeneration technologies in the same system is successfully solved, effectively promoting the regeneration of the amine liquid, extending the service life of the amine liquid, and improving the CO2 capture rate.

[0055] In one embodiment of the present disclosure, the falling film evaporator has a temperature of 120-140°C, a pressure of 0.04-0.08 MPa, and a residence time of 5-15 min; the flash compressor has a pressure of 0.03-0.08 MPa and a temperature of 90-110°C.

[0056] In the present disclosure, the electrodialysis device can be configured as a selective ion exchange membrane group. In one embodiment of the present disclosure, the operating voltage of the electrodialysis device ED is 40-60V, and the current density is 200-400A / m 2 .

[0057] In the present disclosure, in the first-stage capture process, the first amine liquid is waste amine liquid with a running time of more than 2000 hours, and the mass concentration of the waste amine liquid is 18-25% by weight; preferably, the first amine liquid is waste monoethanolamine; in the second-stage capture process, the second amine liquid is fresh amine liquid with a running time of less than 500 hours, and the mass concentration of the fresh amine liquid is 20-35% by weight; preferably, the second amine liquid is fresh monoethanolamine. This arrangement effectively recycles the amine liquid, avoids the waste of amine liquid with a long running time, and reduces overall costs.

[0058] In one embodiment of the present disclosure, in the primary absorption tower A, the temperature is 40-55°C, the liquid-gas ratio is 1.5-2 L / m 3 In the primary analytical tower R1, the temperature is 100-108 ° C, the liquid-gas ratio is 1.5-2L / m 3 ; In the secondary absorption tower B, the temperature is 40-55°C and the liquid-gas ratio is 2-2.5 L / m 3 In the secondary analytical tower R2, the temperature is 100-108 ° C, the liquid-gas ratio is 2-2.5L / m 3 ; The temperature of the preheated flue gas to be treated is 38-43°C.

[0059] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited thereby.

[0060] like Figure 1 As shown, the system includes a primary absorption tower A, a primary desorption tower R1, a first lean-rich liquid heat exchanger H1, a first lean liquid cooler AL, a secondary absorption tower B, a secondary desorption tower R2, a second lean-rich liquid heat exchanger H2, a second lean liquid cooler BL, a regenerated gas cooler ZL and a gas-liquid separator F; The first treated gas outlet of the primary absorption tower A is connected to the first treated gas inlet of the secondary absorption tower B. The first rich liquid outlet of the primary absorption tower A is connected to the first rich liquid inlet of the primary decomposition tower R1 through the first lean-rich liquid heat exchanger H1. The first lean liquid outlet of the primary decomposition tower R1 is connected to the first lean liquid inlet of the primary absorption tower A through the first lean-rich liquid heat exchanger H1 and the first lean liquid cooler AL in sequence. The second rich liquid outlet of the secondary absorption tower B is connected to the second rich liquid inlet of the secondary desorption tower R2 through the second rich and lean liquid heat exchanger H2, and the second lean liquid outlet of the secondary desorption tower R2 is connected to the second lean liquid inlet of the secondary absorption tower B through the second rich and lean liquid heat exchanger H2 and the second lean liquid cooler BL in turn; The first carbon dioxide outlet of the primary desorption tower R1 and the second carbon dioxide outlet of the secondary desorption tower R2 are respectively connected to the carbon dioxide inlet of the gas-liquid separator F through the regeneration gas cooler ZL.

[0061] A first rich liquid pump AFP is provided on the pipeline between the first rich liquid outlet of the primary absorption tower A and the first lean-rich liquid heat exchanger H1, and a first lean liquid pump APP is provided on the pipeline between the first lean liquid outlet of the primary desorption tower R1 and the first lean-rich liquid heat exchanger H1; A second rich liquid pump BFP is provided on the pipeline between the second rich liquid outlet of the secondary absorption tower B and the second lean-rich liquid heat exchanger H2, and a second lean liquid pump BPP is provided on the pipeline between the second lean liquid outlet of the secondary desorption tower R2 and the second lean-rich liquid heat exchanger H2; An amine liquid dispensing pipeline is connected between the primary absorption tower A and the secondary absorption tower B. A flow control valve LKF and a delivery pump SP are sequentially arranged on the amine liquid dispensing pipeline along the direction of amine liquid flow. The primary absorption tower A is also provided with an inlet for flue gas to be treated, and the secondary absorption tower B is also provided with an inlet for fresh amine solution.

[0062] The primary absorption tower A includes multiple primary absorption filler layers sequentially spaced from bottom to top, and a first spray layer is provided above each primary absorption filler layer; the primary desorption tower R1 includes multiple primary desorption filler layers sequentially spaced from bottom to top and a first entrainment separator; The secondary absorption tower B includes a multi-level absorption filler layer spaced from bottom to top, and a second spray layer is arranged above each level absorption filler layer; the secondary desorption tower R2 includes a multi-level desorption filler layer spaced from bottom to top and a second mist separator.

[0063] The system also includes an amine recovery heating unit HX1 and an electrodialysis unit ED; The recovered amine outlet of the amine recovery heating device HX1 is connected to the recovered amine liquid inlet of the primary decomposition tower R1; a first lean liquid recovery branch is also provided on the pipeline between the first lean liquid outlet of the primary decomposition tower R1 and the first lean-rich liquid heat exchanger H1, and the inlet of the amine recovery heating device HX1 is connected to the outlet of the first lean liquid recovery branch; Preferably, the amine recovery heating device HX1 comprises a falling film evaporator and a flash compressor connected in series; A second lean liquid recovery branch and a second lean liquid regeneration branch are sequentially arranged on the pipeline between the second lean liquid cooler BL and the second lean liquid inlet of the secondary absorption tower B and along the direction of flow of the second lean liquid. The outlet of the second lean liquid recovery branch is connected to the inlet of the electrodialysis device ED, and the inlet of the second lean liquid regeneration branch is connected to the outlet of the electrodialysis device ED.

[0064] The system also includes an underground tank D and an exhaust gas scrubber WG; The inlet of the underground tank D is connected to the liquid outlet of the gas-liquid separator F, and the outlet of the underground tank D is connected to the separation liquid inlet of the secondary decomposition tower R2; The second treated gas outlet of the secondary absorption tower B is connected to the inlet of the tail gas scrubber WG.

[0065] The system also includes an intelligent control unit, which includes a controller, an online conductivity meter, a pH meter and a near-infrared spectrometer; Among them, online conductivity meter, pH meter and near-infrared spectrometer are used to monitor the amine solution concentration, degradation products and HSS content in primary absorption tower A and secondary absorption tower B in real time; The controller is respectively connected to the signals of the online conductivity meter, pH meter and near-infrared spectrometer. The controller is used to control the allocation of amine solution in the primary absorption tower A and the secondary absorption tower B according to the real-time monitoring data of the online conductivity meter, pH meter and near-infrared spectrometer on the concentration of amine solution, degradation products and HSS content.

[0066] Example 1 The system disclosed herein is used to capture carbon dioxide using a cascade amine process, and the specific steps are as follows: The primary absorption tower A is heated to 50°C, and the flue gas to be treated, which is preheated to 43°C, is passed from the bottom of the primary absorption tower A into the primary absorption tower A and countercurrently contacts with the waste monoethanolamine (20% by weight) from the top of the tower. The liquid-gas ratio is 1.5 L / m 3 , obtain the first processed gas and the first rich liquid; raise the temperature of the primary analytical tower R1 to 105°C, and allow the first rich liquid to pass through the first lean-rich liquid heat exchanger H1 and then enter the primary analytical tower R1 for the first analytical treatment, with a liquid-gas ratio of 2L / m 3 , obtaining first carbon dioxide and first lean liquid; a portion of the first lean liquid (92 volume %) is sequentially passed through the first lean-rich liquid heat exchanger H1 and the first lean liquid cooler AL and then returned to the primary absorption tower A; another portion of the first lean liquid (8 volume %) enters the amine recovery and heating device HX1 for amine liquid recovery treatment. The amine recovery and heating device HX1 includes a falling film evaporator and a flash compressor connected in series. The falling film evaporator has a temperature of 130°C, a pressure of 0.04 MPa, and a residence time of 20 minutes. The first lean liquid then enters the flash compressor (0.08 MPa, 90°C) for treatment, and then the recovered amine liquid enters the primary desorption tower R1; The temperature of the secondary absorption tower B was raised to 50°C, and the first treated gas was passed from the bottom of the secondary absorption tower B into the secondary absorption tower B to countercurrently contact with the fresh monoethanolamine (30 wt%) from the top of the tower. The liquid-gas ratio was 2 L / m 3 , obtain the second processed gas and the second rich liquid; raise the temperature of the secondary analytical tower R2 to 105 ° C, and let the second rich liquid pass through the second lean and rich liquid heat exchanger H2 and then enter the secondary analytical tower R2 for the second analytical treatment, with a liquid-gas ratio of 2.5L / m 3, obtaining a second carbon dioxide and a second lean liquid; a portion of the second lean liquid (95% by volume) is passed through the second lean-rich liquid heat exchanger H2 and the second lean liquid cooler BL in sequence and then returned to the secondary absorption tower B; another portion of the second lean liquid (5% by volume) enters the electrodialysis device ED for amine solution regeneration treatment. The electrodialysis device is a selective ion exchange membrane group with an operating voltage of 50V and a current density of 300A / m 2 The regenerated amine liquid enters the secondary absorption tower B.

[0067] The first carbon dioxide and the second carbon dioxide are combined and then pass through the regeneration gas cooler ZL and then enter the gas-liquid separator F to separate and obtain pure carbon dioxide.

[0068] The separated liquid obtained by the gas-liquid separator F enters the underground tank D for storage, and then enters the secondary analysis tower R2.

[0069] Comparative Example 1 like Figure 2 As shown, the absorption tower X is heated to 50°C, and the flue gas to be treated, which is preheated to 43°C, is introduced from the bottom of the absorption tower X to react with the amine liquid. The liquid-gas ratio is 4.5L / m 3 , and obtain treated gas and rich liquid; heat the analytical tower Z to 105 ° C, and let the rich liquid pass through the lean and rich liquid heat exchanger H and then enter the analytical tower Z for the first analytical treatment, with a liquid-gas ratio of 5L / m 3 , obtaining carbon dioxide and lean liquid. The carbon dioxide passes through the regeneration gas cooler ZL2 and enters the gas-liquid separator F2, where it is separated to obtain pure carbon dioxide.

[0070] The separated liquid obtained by the gas-liquid separator F2 enters the underground tank D2 for storage, and then enters the analytical tower Z2.

[0071] Indicators such as HSS content, CO2 capture rate, long-term operating cost, regeneration energy consumption, annual amine solution replenishment rate, and equipment maintenance were monitored in real time for Example 1 and Comparative Example 1. The results are shown in Table 1. Regeneration energy consumption mainly refers to the heat used to heat the amine solution in the desorption tower.

[0072] Table 1

[0073] As shown in Table 1, compared with Comparative Example 1, Example 1 effectively reduces system amine loss and degradation. Long-term operation offers low process costs, low amine loss, and low annual replenishment requirements, significantly reducing CO2 capture costs. In Comparative Example 1, amine degradation and loss necessitated frequent amine replacement (annual replenishment rate of 50-70%), and equipment corrosion caused by high HSS content increased maintenance costs. In summary, the disclosed system effectively addresses the exponential efficiency decay caused by amine degradation during long-term operation, while simultaneously reducing regeneration energy consumption and improving impurity removal.

[0074] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0075] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0076] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A system for capturing carbon dioxide using a cascade amine process, characterized in that: The system includes a primary absorption tower (A), a primary desorption tower (R1), a first lean-rich liquid heat exchanger (H1), a first lean liquid cooler (AL), a secondary absorption tower (B), a secondary desorption tower (R2), a second lean-rich liquid heat exchanger (H2), a second lean liquid cooler (BL), a regeneration gas cooler (ZL) and a gas-liquid separator (F); The first treated gas outlet of the primary absorption tower (A) is communicated with the first treated gas inlet of the secondary absorption tower (B); the first rich liquid outlet of the primary absorption tower (A) is communicated with the first rich liquid inlet of the primary desorption tower (R1) via the first rich-lean liquid heat exchanger (H1); the first lean liquid outlet of the primary desorption tower (R1) is communicated with the first lean liquid inlet of the primary absorption tower (A) via the first rich-lean liquid heat exchanger (H1) and the first lean liquid cooler (AL) in sequence; The second rich liquid outlet of the secondary absorption tower (B) is connected to the second rich liquid inlet of the secondary desorption tower (R2) through the second rich-lean liquid heat exchanger (H2), and the second lean liquid outlet of the secondary desorption tower (R2) is connected to the second lean liquid inlet of the secondary absorption tower (B) through the second rich-lean liquid heat exchanger (H2) and the second lean liquid cooler (BL) in sequence; The first carbon dioxide outlet of the primary desorption tower (R1) and the second carbon dioxide outlet of the secondary desorption tower (R2) are respectively connected to the carbon dioxide inlet of the gas-liquid separator (F) through a regeneration gas cooler (ZL).

2. The system according to claim 1, wherein: A first rich liquid pump (AFP) is provided on the pipeline between the first rich liquid outlet of the primary absorption tower (A) and the first lean-rich liquid heat exchanger (H1); a first lean liquid pump (APP) is provided on the pipeline between the first lean liquid outlet of the primary desorption tower (R1) and the first lean-rich liquid heat exchanger (H1); A second rich liquid pump (BFP) is provided on the pipeline between the second rich liquid outlet of the secondary absorption tower (B) and the second rich-lean liquid heat exchanger (H2); a second lean liquid pump (BPP) is provided on the pipeline between the second lean liquid outlet of the secondary desorption tower (R2) and the second rich-lean liquid heat exchanger (H2); An amine liquid dispensing pipeline is connected between the primary absorption tower (A) and the secondary absorption tower (B), and a flow control valve (LKF) and a delivery pump (SP) are sequentially arranged on the amine liquid dispensing pipeline along the direction of amine liquid flow; The primary absorption tower (A) is also provided with an inlet for flue gas to be treated, and the secondary absorption tower (B) is also provided with an inlet for fresh amine solution.

3. The system according to claim 2, wherein: The primary absorption tower (A) comprises multiple primary absorption filler layers sequentially spaced from bottom to top, and a first spray layer is provided above each primary absorption filler layer; the primary desorption tower (R1) comprises multiple primary desorption filler layers sequentially spaced from bottom to top and a first entrainment separator; The secondary absorption tower (B) includes multiple layers of absorption filler layers sequentially spaced from bottom to top, and a second spray layer is provided above each layer of the secondary absorption filler layer; the secondary desorption tower (R2) includes multiple layers of desorption filler layers sequentially spaced from bottom to top and a second entrainment separator.

4. The system according to claim 1, wherein: The system also includes an amine recovery heating device (HX1) and an electrodialysis device (ED); The recovered amine outlet of the amine recovery and heating device (HX1) is connected to the recovered amine liquid inlet of the primary decomposition tower (R1); a first lean liquid recovery branch is further provided on the pipeline between the first lean liquid outlet of the primary decomposition tower (R1) and the first lean-rich liquid heat exchanger (H1), and the inlet of the amine recovery and heating device (HX1) is connected to the outlet of the first lean liquid recovery branch; Preferably, the amine recovery heating device (HX1) comprises a falling film evaporator and a flash compressor connected in series; A second lean liquid recovery branch and a second lean liquid regeneration branch are sequentially arranged on a pipeline between the second lean liquid cooler (BL) and the second lean liquid inlet of the secondary absorption tower (B) and along the direction of flow of the second lean liquid. The outlet of the second lean liquid recovery branch is connected to the inlet of the electrodialysis device (ED), and the inlet of the second lean liquid regeneration branch is connected to the outlet of the electrodialysis device (ED).

5. The system according to claim 1, wherein: The system also includes an underground tank (D) and an exhaust gas scrubber (WG); The inlet of the underground tank (D) is connected to the liquid outlet of the gas-liquid separator (F), and the outlet of the underground tank (D) is connected to the separation liquid inlet of the secondary decomposition tower (R2); The second treated gas outlet of the secondary absorption tower (B) is communicated with the inlet of the tail gas scrubber (WG).

6. The system according to claim 2, wherein: The system also includes an intelligent control unit, which includes a controller, an online conductivity meter, a pH meter and a near-infrared spectrometer; The online conductivity meter, the pH meter and the near-infrared spectrometer are used to monitor the amine solution concentration, degradation products and HSS content in the primary absorption tower (A) and the secondary absorption tower (B) in real time; The controller is respectively connected to the online conductivity meter, the pH meter and the near-infrared spectrometer for signal transmission. The controller is used to control the allocation of the amine solution in the primary absorption tower (A) and the secondary absorption tower (B) based on the real-time monitoring data of the amine solution concentration, degradation products and HSS content obtained by the online conductivity meter, the pH meter and the near-infrared spectrometer.

7. A method for capturing carbon dioxide using a cascade amine process using the system according to any one of claims 1 to 6, characterized in that: The method comprises: The preheated flue gas to be treated is passed from the bottom of the primary absorption tower (A) into the primary absorption tower (A) and countercurrently contacts with the first amine liquid from the top of the tower to obtain a first treated gas and a first rich liquid; the first rich liquid passes through a first lean-rich liquid heat exchanger (H1) and then enters a primary desorption tower (R1) for a first desorption treatment to obtain first carbon dioxide and a first lean liquid; a portion of the first lean liquid passes through the first lean-rich liquid heat exchanger (H1) and a first lean liquid cooler (AL) in sequence and then returns to the primary absorption tower (A); The first treated gas is passed from the bottom of the secondary absorption tower (B) into the secondary absorption tower (B) to countercurrently contact with the second amine liquid from the top of the tower to obtain a second treated gas and a second rich liquid; the second rich liquid is passed through a second lean-rich liquid heat exchanger (H2) and then enters a secondary desorption tower (R2) for a second desorption treatment to obtain a second carbon dioxide and a second lean liquid; a portion of the second lean liquid is passed through the second lean-rich liquid heat exchanger (H2) and the second lean liquid cooler (BL) in sequence and then returned to the secondary absorption tower (B); The first carbon dioxide and the second carbon dioxide are combined and then pass through a regeneration gas cooler (ZL) and then enter a gas-liquid separator (F) to separate and obtain pure carbon dioxide.

8. The method according to claim 7, wherein: The separated liquid obtained from the gas-liquid separator (F) enters the underground tank (D) for storage, and then enters the secondary desorption tower (R2); The second treated gas is discharged after being washed by a tail gas scrubber (WG); Another portion of the first lean liquid enters the amine recovery and heating device (HX1) for amine liquid recovery treatment, so that the recovered amine liquid enters the primary decomposition tower (R1); The amine recovery heating device (HX1) comprises a falling film evaporator and a flash compressor connected in series; Preferably, the falling film evaporator has a temperature of 100-120°C, a pressure of 0.04-0.08 MPa, and a residence time of 5-15 min; the flash compressor has a pressure of 0.03-0.08 MPa and a temperature of 90-110°C; Another portion of the second lean liquid enters the electrodialysis device (ED) for amine solution regeneration treatment, so that the regenerated amine solution enters the secondary absorption tower (B); Preferably, the operating voltage of the electrodialysis device (ED) is 40-60V, and the current density is 200-400A / m 2 .

9. The method according to claim 6, wherein: The first amine liquid is a waste amine liquid with a running time of more than 2000 hours, and the mass concentration of the waste amine liquid is 18-25% by weight; preferably, the first amine liquid is waste monoethanolamine; The second amine liquid is a fresh amine liquid with a running time of less than 500 hours, and the mass concentration of the fresh amine liquid is 20-35% by weight; preferably, the second amine liquid is fresh monoethanolamine.

10. The method according to claim 6, wherein: In the primary absorption tower (A), the temperature is 40-55°C and the liquid-gas ratio is 1.5-2 L / m 3 In the primary analytical tower (R1), the temperature is 100-108°C and the liquid-gas ratio is 1.5-2L / m 3 ; In the secondary absorption tower (B), the temperature is 40-55°C and the liquid-gas ratio is 2-2.5 L / m 3 In the secondary decomposition tower (R2), the temperature is 100-108 ° C, the liquid-gas ratio is 2-2.5L / m 3 ; The temperature of the preheated flue gas to be treated is 38-43°C.

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