A process for recovering carbon dioxide from flue gas

Abstract

This invention provides a process for recovering carbon dioxide from flue gas: After being washed and cooled, the flue gas enters a CO2 absorption tower, where an MEA solution absorbs CO2. The rich solution is heated by a lean-rich solution heat exchanger before entering a regeneration tower. Inside the regeneration tower, the CO2 regeneration gas released from the decomposition of the rich solution is compressed and heated, then introduced as the first heat source into the reboiler of the regeneration tower. After heat exchange and cooling, the CO2 regeneration gas is sent to downstream processes after gas-liquid separation and cooling. The condensate obtained from gas-liquid separation is collected in a circulating water tank. The condensate exchanges heat with the CO2 regeneration gas to be cooled in a circulating cooler and then returns to the circulating water tank. Low-pressure steam in the circulating water tank is extracted using a heat pump, pressurized and heated by a steam ejector, and then introduced as the second heat source into the reboiler of the regeneration tower. This invention constructs a closed-loop energy cycle system of "compression-heat exchange-condensation-heat pump-reheating," realizing the cascade recovery and upgrading utilization of compression heat and latent heat of low-grade steam, thereby improving the overall energy utilization efficiency and operational economy of the process.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide recovery technology, and more specifically to a process for recovering carbon dioxide from flue gas. Background Technology

[0002] As a major greenhouse gas, carbon dioxide (CO2) emission reduction has become a global focus. At the same time, CO2, as a valuable carbon resource, is widely used in fields such as machining, chemical synthesis, oil extraction, food preservation, and chemical synthesis after purification, demonstrating significant environmental and economic value.

[0003] Among numerous flue gas CO2 capture technologies, monoethanolamine (MEA) chemical absorption has become the most widely used process in industry due to its fast absorption rate, good selectivity, and high technological maturity. A typical MEA process includes two core units: absorption and regeneration. In the absorption tower, the MEA aqueous solution comes into countercurrent contact with the flue gas, chemically absorbing CO2 to form a rich solution. The rich solution is heated by a lean-rich solution heat exchanger and then enters the regeneration tower. The heat provided by the reboiler (usually 110~120℃) desorbs the CO2, and the regenerated lean solution is returned to the absorption tower for recycling.

[0004] However, excessively high regeneration energy consumption is the main bottleneck restricting the large-scale application of the MEA method. The regeneration process requires a large amount of low-pressure steam to provide the heat needed for CO2 desorption. The CO2 regeneration gas discharged from the top of the regeneration tower contains considerable latent heat and sensible heat of vaporization. However, in existing technologies, this part of low-grade heat energy is usually directly discharged into the environment through air coolers or water coolers, or recovered by waste heat boilers to generate low-grade steam for other purposes, without achieving energy integration with the regeneration system itself.

[0005] Existing technologies lack effective means for the energy cascade utilization of regenerated gas generated by the regeneration tower and for internal thermal integration within the system. They fail to fully explore the potential of directly using compression heat for regeneration heating and upgrading and reusing the latent heat of water vapor through heat pump technology, resulting in high regeneration steam consumption and limited process economics. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention discloses a process for recovering carbon dioxide from flue gas, which can effectively utilize the heat energy of CO2 regeneration gas discharged from the regeneration tower in a cascade manner, and realize the upgrading and utilization of low-grade heat energy, thereby reducing the overall process energy consumption and improving economic benefits.

[0007] To achieve the above technical objectives, this invention proposes a process for recovering carbon dioxide from flue gas, which includes the following steps: After being washed and cooled, the flue gas enters the CO2 absorption tower, where MEA solution is used to absorb CO2. The rich liquid after CO2 absorption is heated by a lean-rich liquid heat exchanger and then enters the regeneration tower. Inside the regeneration tower, the CO2 regeneration gas released from the decomposition of the rich liquid is compressed and heated, and then introduced into the reboiler of the regeneration tower as the first heat source to heat the regeneration tower. After heat exchange and cooling, the CO2 regeneration gas is sent to the downstream process after gas-liquid separation and cooling. The condensate obtained from gas-liquid separation is collected in a circulating water tank. The condensate is then returned to the circulating water tank after exchanging heat with the CO2 regeneration gas to be cooled in a circulating cooler using a circulation device. Low-pressure steam is extracted from the circulating water tank using a heat pump, and after being pressurized and heated by a steam injector, it is introduced into the reboiler of the regeneration tower as a second heat source to maintain the bottom temperature of the regeneration tower. The condensate after heat exchange is returned to the circulating water tank.

[0008] The above technical solution incorporates multi-stage coupled thermal energy utilization technology. Specifically, the CO2 regenerated gas extracted from the regeneration tower is compressed and heated, then used as a first heat source to heat the regeneration tower and recover the heat of compression. The condensate obtained after the CO2 regenerated gas is cooled by heat exchange is input into the circulating water tank. The condensate in the circulating water tank can exchange heat with the gaseous material obtained by gas-liquid separation to further recover the heat of compression. This achieves the cascade recovery and utilization of the heat of compression, replacing or significantly reducing the consumption of externally supplied steam in the traditional MEA method, and solving the technical problem of high energy consumption in the existing technology. In addition, the above technical solution combines heat pump extraction and steam injection to obtain a second heat source for heating the reboiler of the regeneration tower, constructing a closed-loop energy cycle system of "compression-heat exchange-condensation-heat pump-reheating", improving the overall energy utilization efficiency of the system and realizing the upgrading and utilization of low-grade thermal energy.

[0009] In a further example of the present invention, the CO2 regeneration gas is drawn from the top of the regeneration tower at a temperature of 90~100°C and a pressure of 0~0.01MPa(G). After being compressed to 0.5~1.0MPa(G) by the CO2 regeneration gas compressor, it enters the reboiler of the regeneration tower. The operation is at atmospheric pressure when the gauge pressure is 0.

[0010] In a further example of the invention, the second heat source is used to maintain the temperature at the bottom of the regeneration tower at 105~120°C.

[0011] In a further example of the present invention, the operating temperature of the CO2 absorption tower is 30~60℃ and the operating pressure is 0~0.01MPa(G).

[0012] In a further example of the present invention, the regeneration tower reboiler includes a first regeneration tower reboiler and a second regeneration tower reboiler. The compressed and heated CO2 regeneration gas enters the first regeneration tower reboiler for heat exchange, and the steam discharged from the steam ejector enters the second regeneration tower reboiler for heat exchange.

[0013] In a further example of the present invention, the inlet pressure of the heat pump is -0.5 to -0.2 MPa(G), used to draw low-pressure steam generated by flash evaporation in the circulating water tank; the outlet pressure is 0.2 to 0.3 MPa(G), and the heat pump can be a mechanical vapor recompression heat pump (MVR), which does not require external driving steam; optionally, the compression ratio of the heat pump is 1.5 to 3.0. The operating steam pressure of the steam ejector is 0.5 to 1.0 MPa(G), and the outlet pressure is 0.25 to 0.4 MPa(G); the ejector pressure of the steam ejector is matched with the outlet pressure of the heat pump; optionally, the compression ratio of the steam ejector is 1.2 to 2.0, further pressurizing and heating through the Venturi effect.

[0014] In a further example of the present invention, before entering the CO2 absorption tower, the flue gas first enters a scrubbing tower and comes into countercurrent contact with cooling water to reduce the flue gas temperature to 35~45°C, while simultaneously washing away dust.

[0015] In a further example of the present invention, in the CO2 absorption tower, the unabsorbed tail gas is washed and cooled to a temperature not exceeding 45°C, and then discharged into the atmosphere after being dehydrated by a demister.

[0016] In a further example of the present invention, the rich liquid is heated to 90~100°C by the rich-lean-poor liquid heat exchanger and then enters the upper part of the regeneration tower.

[0017] In the above technical solution, lean liquor is collected from the bottom of the regeneration tower, and the lean liquor is cooled down after exchanging heat with the rich liquor in the lean-rich liquor heat exchanger. In a further example of the present invention, the lean liquor collected from the bottom of the regeneration tower is cooled to no higher than 40°C, for example, 35~40°C, and then enters the upper part of the CO2 absorption tower as an absorbent to absorb the washed and cooled flue gas.

[0018] In a further example of the present invention, the gas-liquid separation and cooling operation includes: the CO2 regenerated gas after heat exchange and cooling first enters the first CO2 separator for gas-liquid separation, the condensate at the bottom of the tank enters the circulating water tank, and the gas phase at the top of the tank enters the circulating cooler and the demineralized water cooler for further cooling to 35~45°C, and then enters the second CO2 separator for further separation. The CO2 gas at the top of the tank enters the downstream CO2 compressor, and the condensate at the bottom of the tank enters the circulating water tank.

[0019] In a further example of the present invention, the downstream process includes: the CO2 gas after passing through the CO2 compressor is cooled by a cryostat and then enters a third CO2 separator; the condensate at the bottom of the tank enters the circulating water tank and / or returns to the CO2 absorption tower; and the gas phase at the top of the tank is input into the subsequent CO2 refining process.

[0020] In a further example of the present invention, the circulating water tank is equipped with a liquid level control system, which discharges part of the condensate outside the system and / or returns it to the CO2 absorption tower when the liquid level reaches a set upper limit.

[0021] Compared with existing technologies, the beneficial effects of this invention are as follows: The carbon dioxide recovery process in flue gas of this invention utilizes the compression heat of CO2 regenerated gas as a first heat source in a cascade manner, and combines it with a heat pump extraction-steam injection system to generate a second heat source, thus constructing a closed-loop energy cycle system of "compression-heat exchange-condensation-heat pump-reheating". This process realizes the cascade recovery and upgraded utilization of compression heat and latent heat of low-grade steam, which can significantly reduce the external steam consumption in the traditional MEA method and improve the overall energy utilization efficiency and operating economy of the process. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A structural diagram of a carbon dioxide recovery process in flue gas according to the present invention is shown.

[0023] The above figures include the following reference numerals: 1-CO2 absorption tower, 2-regeneration tower, 3-washing tower, 41-lean and rich liquid heat exchanger, 42-circulating cooler, 43-first regeneration tower reboiler, 44-second regeneration tower reboiler, 45-deionized water cooler, 46-deep cooler, 47-lean liquid cooler, 5-circulating water tank, 6-heat pump, 7-steam ejector, 81-first CO2 separator, 82-second CO2 separator, 83-third CO2 separator, 91-CO2 regeneration gas compressor, 92-CO2 compressor, 93-booster fan. Detailed Implementation

[0024] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0025] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0026] Furthermore, it should be noted that although the various steps of the preparation method of the present invention are described in a specific order in the description of the present invention, these orders are not restrictive. Without departing from the basic principles of the present invention, those skilled in the art can perform the steps in different orders.

[0027] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "multiple" or "at least one" means two or more.

[0028] All numerical designations, such as pressure, temperature, flow rate, and range, are approximate values. It should be understood that, while not always explicitly stated, all numerical designations are preceded by the term "approximately." It should also be understood that, while not always explicitly stated, the reagents described herein are merely examples, and their equivalents are known in the art.

[0029] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0030] Example 1

[0031] This embodiment discloses a process for recovering carbon dioxide from flue gas. The process includes the following steps: After being washed and cooled, the flue gas enters a CO2 absorption tower 1, where a MEA solution is used to absorb CO2. The rich liquid after CO2 absorption is heated by a lean-rich liquid heat exchanger 41 and then enters a regeneration tower 2. In the regeneration tower 2, the CO2 regeneration gas released by the decomposition of the rich liquid is compressed and heated, and then introduced into the reboiler of the regeneration tower as the first heat source to heat the regeneration tower 2. After the CO2 regeneration gas is cooled by heat exchange, it is sent to the downstream process after gas-liquid separation and cooling. The condensate obtained from gas-liquid separation is collected in a circulating water tank 5. A circulation device (such as a circulating pump) is used to make the condensate exchange heat with the CO2 regeneration gas to be cooled in a circulating cooler 42 and then return it to the circulating water tank 5. A heat pump 6 is used to extract low-pressure steam from the circulating water tank 5. After being pressurized and heated by a steam ejector 7, the steam is introduced into the reboiler of the regeneration tower as the second heat source to maintain the bottom temperature of the regeneration tower 2. The condensate after heat exchange is returned to the circulating water tank 5.

[0032] Furthermore, the concentration of the MEA solution is 8wt%~38wt%, preferably 15wt%~20wt%.

[0033] Furthermore, the CO2 regenerated gas is extracted from the top of regeneration tower 2 at a temperature of 90~100℃ and a pressure of 0~0.01MPa(G). This allows the CO2 regenerated gas to be heated through compression, and this temperature range can be used as a heat source to heat the regenerator of the regeneration tower to a suitable temperature. After being compressed to 0.5~1.0MPa(G) by the CO2 regenerated gas compressor, it enters the regenerator of the regeneration tower. The CO2 regenerated gas compressor compresses the CO2 regenerated gas to a suitable pressure range, which not only meets the gas pressure requirements of downstream CO2 liquefaction, transportation or utilization, but also obtains high-quality heat energy for regeneration heating through the same process. This achieves the synergistic utilization of pressure energy and heat energy, and reduces overall energy consumption.

[0034] Furthermore, the temperature at the bottom of regeneration tower 2 is maintained at 105~120℃ using a second heat source. By controlling the temperature, CO2 in the rich solution is fully desorbed, while ensuring the regeneration quality and circulation absorption capacity of the MEA solution.

[0035] Furthermore, the operating temperature of CO2 absorption tower 1 is 30~60℃, and the operating pressure is 0~0.01MPa(G).

[0036] Furthermore, the reboiler of the regeneration tower includes a first reboiler 43 and a second reboiler 44. The CO2 regeneration gas after compression and heating enters the first reboiler 43 for heat exchange, and the steam discharged from the steam ejector 7 enters the second reboiler 44 for heat exchange. By setting the first reboiler 43 and the second reboiler 44 to utilize compression heat and heat pump steam respectively, the two heat sources can be optimally matched according to their temperature characteristics (compression heat has a high temperature but limited flow, while heat pump steam has a moderate temperature but adjustable flow) to achieve cascaded utilization of energy. At the same time, the two heat sources can serve as backups for each other, improving the reliability and operational flexibility of the system.

[0037] Furthermore, the inlet pressure of heat pump 6 is -0.5 to -0.2 MPa(G), and the outlet pressure is 0.2 to 0.3 MPa(G); the operating steam pressure of steam ejector 7 is 0.5 to 1.0 MPa(G), and the outlet pressure is 0.25 to 0.4 MPa(G). This effectively extracts low-pressure steam from circulating water tank 5 and pressurizes it to the pressure level required for reboiler heating, achieving an economical upgrade from low-grade heat energy to high-grade heat energy. Optionally, the heat pump can be a screw-type steam recompression heat pump, a water source high-temperature steam heat pump, or a steam jet heat pump, preferably a steam compression heat pump. Optionally, the steam ejector can be a non-adjustable steam jet booster or an adjustable steam jet booster, preferably a non-adjustable steam jet booster.

[0038] Furthermore, before entering the CO2 absorption tower 1, the flue gas first enters the scrubbing tower 3 and comes into countercurrent contact with cooling water, reducing the flue gas temperature to 35~45℃ and simultaneously washing away dust. Through the scrubbing in the scrubbing tower 3, the high-temperature flue gas prevents the MEA solution from evaporating, degrading, or deteriorating, and also avoids dust clogging the absorption tower packing or contaminating the MEA solution, thereby extending the absorbent's lifespan and improving CO2 absorption efficiency. Optionally, the operating temperature of the scrubbing tower 3 is 40~120℃; alternatively, the scrubbing water discharged from the bottom of the scrubbing tower 3 is sent to a cooling tower to lower the temperature to approximately 40℃, and the cooled scrubbing water is then recycled back into the scrubbing tower 3 by a circulation device (such as a circulation pump).

[0039] Furthermore, in CO2 absorption tower 1, the unabsorbed tail gas is washed and cooled to no higher than 45°C, and then discharged into the atmosphere after being deliquescent by a demister. By washing, cooling and efficiently demisting the unabsorbed tail gas, the MEA solution droplets entrained in the tail gas can be effectively recovered, which not only reduces absorbent loss and lowers operating costs, but also avoids secondary pollution of the atmospheric environment caused by entrained impurities.

[0040] Furthermore, the rich liquor is heated to 90~100℃ by the lean-rich liquor heat exchanger 41 before entering the upper part of the regeneration tower 2. Heating the rich liquor to a suitable temperature before entering the regeneration tower 2 not only allows the sensible heat of the lean liquor to be recovered through the lean-rich liquor heat exchanger 41 and reduces the heat load of the reboiler at the bottom of the regeneration tower 2, but also ensures that the temperature is close to the temperature inside the regeneration tower 2, which is conducive to the stable desorption of CO2.

[0041] High-temperature lean liquor is collected from the bottom of the regeneration tower and cooled by the lean-rich liquor heat exchanger 41. Further, the lean liquor collected from the bottom of the regeneration tower 2, after being cooled to no higher than 40°C, enters the upper part of the CO2 absorption tower 1; thus, the sensible heat in the lean liquor can be recovered and utilized for preheating the rich liquor, and the lean liquor is controlled at a suitable temperature, improving its efficiency in contacting and absorbing CO2 after entering the CO2 absorption tower 1. Optionally, the lean liquor output from the lean-rich liquor heat exchanger 41 is cooled by the lean liquor cooler 47 before being input into the upper part of the CO2 absorption tower 1, thereby facilitating the control of the temperature of the lean liquor input into the upper part of the CO2 absorption tower 1 and improving process operability.

[0042] Furthermore, the gas-liquid separation and cooling operation includes: the CO2 regenerated gas after heat exchange and cooling first enters the first CO2 separator 81 for gas-liquid separation, the condensate at the bottom of the tank enters the circulating water tank 5, and the gas phase at the top of the tank enters the circulating cooler 42 and the demineralized water cooler 45 for further cooling to 35~45℃, and then enters the second CO2 separator 82 for separation again. The CO2 gas at the top of the tank enters the downstream CO2 compressor 92, and the condensate at the bottom of the tank enters the circulating water tank 5. Through the coupling of two-stage gas-liquid separation and coolers, while fully recovering the condensate and reducing material loss, the water content of the CO2 gas phase is effectively reduced to protect the downstream compressor, and the sensible heat of the regenerated gas is transferred to the condensate to provide a heat source for subsequent extraction by the heat pump 6, promoting the synergistic optimization of efficient gas-liquid separation and energy cascade utilization.

[0043] Furthermore, the downstream process includes: the CO2 gas after passing through the CO2 compressor 92 is cooled by the cryocooler 46 and then enters the third CO2 separator 83. The condensate at the bottom of the separator enters the circulating water tank 5, and the gas phase at the top of the separator is input into the subsequent CO2 refining process. Optionally, the outlet temperature of the cryocooler 46 is approximately 40°C. Further deep cooling separation removes saturated moisture from the compressed CO2 gas, helping to prevent corrosion of downstream refining equipment and icing blockage under low-temperature conditions. The recovered condensate is returned to the circulating water tank 5 and participates in the heat cycle, or is directly used as lean liquid and / or returned to the CO2 absorption tower 1, achieving cascade utilization of system water resources and water balance in process operation.

[0044] Furthermore, the circulating water tank 5 is equipped with a liquid level control system. When its liquid level reaches the set upper limit, part of the condensate is discharged outside the system and / or returned to the CO2 absorption tower 1. Thus, the stability of the steam space at the top of the tank can be regulated by liquid level control to ensure the extraction efficiency of the heat pump 6. At the same time, by returning part of the condensate to the absorption tower to recover the absorbent or discharging it out in a timely manner, the dual optimization of material recovery and system water balance can be achieved.

[0045] Figure 1 An optional structure of the process in this embodiment is shown, including: Scrubber 3 is used for cooling and dust removal of flue gas; the upper part of scrubber 3 is connected to the scrubbing water inlet pipe, and the lower part is connected to the flue gas inlet pipe.

[0046] CO2 absorption tower 1 is connected to the top outlet of scrubbing tower 3 for absorbing CO2 through MEA solution; when CO2 absorption reaches equilibrium, a rich solution is obtained. Optionally, scrubbing tower 3 is connected to CO2 absorption tower 1 via booster fan 93.

[0047] The rich and lean liquid heat exchanger 41 is connected to the rich liquid outlet of the CO2 absorption tower 1; it is used for heat exchange between the rich and lean liquids.

[0048] The regeneration tower 2 is connected to the lean-rich liquid heat exchanger 41 and is used to regenerate the rich liquid and release CO2 regeneration gas to obtain lean liquid. The high-temperature lean liquid collected from the regeneration tower 2 is output from the bottom of the regeneration tower and then exchanges heat with the rich liquid in the lean-rich liquid heat exchanger 41. The regeneration tower 2 is provided with a first regeneration tower reboiler 43 and a second regeneration tower reboiler 44. Optionally, the lean liquid after heat exchange with the lean-rich liquid heat exchanger 41 is input into the lean liquid inlet of the CO2 absorption tower 1 (located in the upper part of the CO2 absorption tower 1). Further optionally, the lean liquid after heat exchange with the lean-rich liquid heat exchanger 41 is cooled by the lean liquid cooler 47 before being input into the upper part of the CO2 absorption tower 1.

[0049] The CO2 regenerated gas compressor is connected to the CO2 regenerated gas outlet of regeneration tower 2 and is used to compress and heat the CO2 regenerated gas. The heated and pressurized CO2 regenerated gas supplies heat to regeneration tower 2 through the first regeneration tower reboiler 43.

[0050] The CO2 regeneration gas, cooled by heat exchange and output from the reboiler 43 of the first regeneration tower, first enters the first CO2 separator 81 for gas-liquid separation in the circulating water tank 5. The condensate at the bottom of the tank enters the circulating cooler 42 and the demineralized water cooler 45 for further cooling to 35~45℃, and then enters the second CO2 separator 82 for further separation. The CO2 gas at the top of the tank enters the downstream CO2 compressor 92, and the condensate at the bottom of the tank enters the circulating water tank 5. The condensate is then returned to the circulating water tank 5 after heat exchange with the CO2 regeneration gas to be cooled in the circulating cooler 42 using a circulation device.

[0051] Heat pump 6 and steam ejector 7 are used to extract low-pressure steam from circulating water tank 5. After being pressurized and heated by steam ejector 7, the steam is introduced into the reboiler of the regeneration tower as a second heat source to maintain the bottom temperature of regeneration tower 2. The condensate after heat exchange is returned to circulating water tank 5.

[0052] Optionally, it also includes a CO2 compressor 92. The CO2 gas output from the top of the second CO2 separator 82 enters the CO2 compressor, and the condensate at the bottom of the tank enters the circulating water tank 5. The CO2 gas after the CO2 compressor is cooled by the cryocooler 46 and then enters the third CO2 separator 83. The condensate at the bottom of the tank enters the circulating water tank 5 or is returned to the upper part of the regeneration tower 2 as lean liquid. The gas phase at the top of the tank is input into the subsequent CO2 refining process.

[0053] Example 2

[0054] Based on the carbon dioxide recovery process in flue gas shown in Example 1, this example proposes a carbon dioxide recovery process in flue gas under specific operating conditions. It should be noted that this example is merely a preferred embodiment and does not limit the scope of protection of the present invention. Specifically: The gas temperature from the flue gas inlet pipe is approximately 140°C. The gas enters the scrubbing tower 3 and comes into countercurrent contact with cooling scrubbing water sprayed from the top of the tower. The gas is cooled and the dust is washed away. The scrubbing water discharged from the bottom of the tower is sent to a cooling tower for further cooling, and then returned to the scrubbing tower 3 for recycling. The water balance can be controlled by using fresh demineralized water. The gas temperature discharged from the top of the scrubbing tower 3 drops to approximately 40°C, and is then pressurized to ~6000 Pa(G) by the booster fan 93 before entering the bottom of the CO2 absorption tower 1.

[0055] In CO2 absorption tower 1, CO2 components in the gas are absorbed by MEA solution. Unabsorbed tail gas is washed and cooled to ≤45°C at the top of the absorption tower, and then discharged directly into the atmosphere after the entrained solution is removed by the high-efficiency demister at the top of the tower. The solution that reaches equilibrium after absorbing CO2 is called rich solution. The rich solution is collected from the bottom of CO2 absorption tower 1 (about 50°C), pressurized, and first enters the lean-rich solution heat exchanger 41 to heat the rich solution to about 99°C, and then enters regeneration tower 2. Finally, it is sprayed into the tower through the top nozzle of regeneration tower 2.

[0056] Inside regeneration tower 2, the rich liquid decomposes to release CO2 regeneration gas. This CO2 regeneration gas, along with a large amount of water vapor and a small amount of MEA vapor, is extracted from the top of the tower at a temperature of approximately 90-100℃ and a pressure of approximately 0.005 MPa(G). It then enters CO2 regeneration gas compressor 91 and is compressed to 0.5-1.0 MPaG (approximately 170℃), before entering the first regeneration tower reboiler 43 to provide a heat source for regeneration tower 2. The cooled CO2 regeneration gas enters the first CO2 separator 81 for gas-liquid separation. The condensate at the bottom of the tank enters the circulating water tank 5, while some of the steam and CO2 (approximately 115℃) at the top of the tank enters the circulating cooler 42 (cooled to approximately 95℃) and the demineralized water cooler 45 for further cooling. After cooling to approximately 40℃, it enters the second CO2 separator 82 for separation. The CO2 gas at the top of the tank enters the CO2 compressor 92, and the condensate at the bottom of the tank enters the circulating water tank 5.

[0057] The lean liquor drawn from the bottom of regeneration tower 2 is pressurized by the lean liquor pump, flows through the lean and rich liquor heat exchanger 41 (cooled to about 60.4°C) and the lean liquor water cooler to be further cooled to ≤40°C, and then sent to the upper part of CO2 absorption tower 1.

[0058] The condensate (approximately 90°C) in the circulating water tank 5 is pressurized by the circulating pump, heated by the circulating cooler 42, and returned to the circulating water tank 5. The steam at the top of the circulating water tank 5 is extracted by the heat pump 6, pressurized and heated by the steam ejector 7, and then enters the reboiler 44 of the second regeneration tower to provide heat to the regeneration tower 2, so as to ensure that the bottom temperature of the regeneration tower 2 is 105~120°C. The cooled condensate is returned to the circulating water tank 5.

[0059] Through the combined heating of the first reboiler 43 and the second reboiler 44 of the regeneration tower 2, 70% to 100% of the heat load of the reboiler in the regeneration tower 2 can be provided by the energy recovered from within the system. When the system load fluctuates or the energy price ratio changes, the proportion of external supplementary steam can be dynamically adjusted within the range of 0 to 30% by adjusting the speed of the heat pump and / or the working steam flow of the steam ejector. Thus, through "dual heat source complementarity", energy cost optimization is achieved under the premise of ensuring system reliability.

[0060] Comparative Example This comparative example uses the same flue gas conditions and treatment scale as Example 1, but the regeneration system adopts the conventional process: the CO2 regeneration gas (95°C, atmospheric pressure) at the top of regeneration tower 2 is directly cooled to 40°C by a cooler and then enters the gas-liquid separation. The gas compressed to 0.6MPa(G) is cooled to 40°C by an aftercooler; the reboiler relies entirely on external 0.3~0.5MPa(G) saturated steam for heating, without the heat pump system 6.

[0061] Calculations show that the regeneration energy consumption of the traditional process is 5.5 GJ / t CO2, while the regeneration energy consumption of the process in Example 1 is reduced to 2.1 GJ / t CO2, achieving an energy saving rate of 62%, which is significantly better than existing technologies. The carbon dioxide recovery process in flue gas of this invention greatly improves the economics of the MEA method for CO2 capture, providing a feasible energy-saving path for large-scale industrial applications. Here, regeneration energy consumption refers to the energy required to desorb and regenerate a unit mass of CO2 (usually measured in tons) from the rich liquid.

[0062] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple improvements can be made without departing from the concept of the present invention, and all such improvements should be considered to fall within the scope of protection of the present invention.

Claims

1. A process for the recovery of carbon dioxide from flue gas, characterized in that, Includes the following steps: After being washed and cooled, the flue gas enters the CO2 absorption tower (1), where the CO2 is absorbed by MEA solution. The rich liquid after CO2 absorption is heated by the lean-rich liquid heat exchanger (41) and then enters the regeneration tower (2). Inside the regeneration tower (2), the CO2 regeneration gas released by the rich liquid decomposition is compressed and heated, and then introduced into the reboiler of the regeneration tower as the first heat source to heat the regeneration tower (2). After heat exchange and cooling, the CO2 regeneration gas is sent to the downstream process after gas-liquid separation and cooling. The condensate obtained from gas-liquid separation is collected in a circulating water tank (5). The condensate is then returned to the circulating water tank (5) after exchanging heat with the CO2 regeneration gas to be cooled in a circulating cooler (42) using a circulation device. The low-pressure steam in the circulating water tank (5) is extracted by the heat pump (6), and after being pressurized and heated by the steam injector (7), it is introduced into the reboiler of the regeneration tower as a second heat source to maintain the bottom temperature of the regeneration tower (2). The condensate after heat exchange is returned to the circulating water tank (5).

2. Process for the recovery of carbon dioxide from flue gases according to claim 1, characterized in that, The CO2 regenerated gas is drawn from the top of the regeneration tower (2) at a temperature of 90~100℃ and a pressure of 0~0.01MPa(G). After being compressed to 0.5~1.0MPa(G) by the CO2 regenerated gas compressor (91), it enters the reboiler of the regeneration tower.

3. The process for the recovery of carbon dioxide from flue gases according to claim 1, characterized in that, The temperature at the bottom of the regeneration tower (2) is maintained at 105~120℃ using the second heat source; And / or, the operating temperature of the CO2 absorption tower (1) is 30~60℃ and the operating pressure is 0~0.01MPa(G).

4. The process for the recovery of carbon dioxide from a flue gas according to claim 1, characterized in that, The regeneration tower reboiler includes a first regeneration tower reboiler (43) and a second regeneration tower reboiler (44). The compressed and heated CO2 regeneration gas enters the first regeneration tower reboiler (43) for heat exchange, and the steam discharged from the steam ejector (7) enters the second regeneration tower reboiler (44) for heat exchange.

5. The carbon dioxide recovery process from flue gas according to claim 1, characterized in that, The inlet pressure of the heat pump (6) is -0.5~-0.2MPa(G), and the outlet pressure is 0.2~0.3MPa(G); the working steam pressure of the steam ejector (7) is 0.5~1.0MPa(G), and the outlet pressure is 0.25~0.4MPa(G).

6. The carbon dioxide recovery process from flue gas according to claim 1, characterized in that, Before entering the CO2 absorption tower (1), the flue gas first enters the scrubbing tower (3) and comes into countercurrent contact with cooling water to reduce the flue gas temperature to 35~45℃, while washing away dust. And / or, in the CO2 absorption tower (1), the unabsorbed tail gas is washed and cooled to no higher than 45°C, and then discharged into the atmosphere after being deliquescent by a demister.

7. The carbon dioxide recovery process from flue gas according to claim 1, characterized in that, The rich liquid is heated to 90~100℃ by the lean-rich liquid heat exchanger (41) and then enters the upper part of the regeneration tower (2); And / or, the lean liquid drawn from the bottom of the regeneration tower (2) is cooled to no higher than 40°C and then enters the upper part of the CO2 absorption tower (1).

8. The carbon dioxide recovery process from flue gas according to claim 1, characterized in that, The gas-liquid separation and cooling operation includes: the CO2 regenerated gas after heat exchange and cooling first enters the first CO2 separator (81) for gas-liquid separation, the condensate at the bottom of the tank enters the circulating water tank (5), the gas phase at the top of the tank enters the circulating cooler (42) and the demineralized water cooler (45) for further cooling to 35~45℃, and then enters the second CO2 separator (82) for separation again, the CO2 gas at the top of the tank enters the downstream CO2 compressor (92), and the condensate at the bottom of the tank enters the circulating water tank (5).

9. The carbon dioxide recovery process from flue gas according to claim 8, characterized in that, The downstream process includes: CO2 gas after passing through the CO2 compressor (92) is cooled by the cryocooler (46) and then enters the third CO2 separator (83); the condensate at the bottom of the tank enters the circulating water tank (5) and / or returns to the CO2 absorption tower (1); and the gas phase at the top of the tank is input into the subsequent CO2 refining process.

10. The carbon dioxide recovery process from flue gas according to any one of claims 1-9, characterized in that, The circulating water tank (5) is equipped with a liquid level control system. When its liquid level reaches the set upper limit, part of the condensate is discharged outside the system and / or returned to the CO2 absorption tower.

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