A system and method for carbon dioxide capture

Abstract

The application discloses a system and method for carbon dioxide capture, and the system comprises a wet desulfurization unit for removing SO2 in flue gas, a cooling unit for removing a large amount of water vapor contained in the flue gas, an adsorption and desorption unit for adsorbing pollutants in the flue gas, and a membrane separation unit for capturing carbon dioxide in the flue gas. The application can deeply remove the pollutants in the flue gas, avoid membrane pollution, maximize the long-time operation of the membrane separation unit and improve the separation efficiency of the membrane; meanwhile, the flue gas temperature at the inlet of the desulfurization unit can be effectively reduced, the vaporization amount of the quenching circulating liquid is reduced, and then the generation amount of soluble salts in the quenching process is reduced, so that the source reduction of the soluble salts is realized.

Description

Technical Field

[0001] This invention relates to carbon dioxide capture, and more specifically to an adsorption-coupled membrane separation method for carbon dioxide capture. Background Technology

[0002] Carbon Dioxide Capture Storage Utilization (CCUS) is a new technology that separates and purifies CO2 generated during industrial production through capture processes, stores it for a long time, or reuses it in new production processes to achieve CO2 recycling and resource utilization.

[0003] Membrane separation technology, which separates CO2 with the aid of membrane materials, features simple equipment, high efficiency and energy saving, easy operation, and environmental friendliness, and has a promising future. However, membrane fouling is a common problem during the separation process, which limits the further development of membrane separation technology. Membrane fouling mainly refers to the deposition of particulate matter on the membrane surface or blockage of membrane pores, causing narrowing of membrane channels, increased filtration resistance, and decreased flux. After prolonged operation, membrane fouling becomes increasingly severe. In severe cases, bridging can occur between filter elements, leading to membrane deformation and damage, and affecting the normal operation of the collection device.

[0004] The main components causing membrane fouling in stationary pollution source exhaust gases are ultrafine dust or soot, soluble salts, and condensable particulate matter. The smaller the particle size of these pollutants, the deeper they penetrate into the respiratory tract. Once in the alveoli, they directly affect lung ventilation, making the body prone to hypoxia. When these pollutants are emitted into the atmosphere, they form colored plumes such as blue or yellow smoke due to Rayleigh scattering. However, existing processes do not adequately address these pollutants, resulting in low or no removal efficiency.

[0005] Taking NaOH wet desulfurization flue gas as an example, filter cartridges or membranes are used to capture particulate matter in the flue gas. The captured particulate matter contains soluble salts such as Na2SO3 and Na2SO4, as well as ammonium salt aerosols and SO3 aerosols, which are condensable particulate matter (CPM) components (including particles with a diameter of less than 0.3 μm). When these components pass through the membrane separation device, they will accumulate on the membrane, affecting the membrane's service life and separation efficiency.

[0006] Existing solutions to membrane fouling include physical cleaning, chemical cleaning, a combination of physical and chemical cleaning, and electro-cleaning. Physical methods are not very effective at cleaning membrane tubing and may require shutdown of the equipment. Chemical methods have strict requirements, as the chemical reagents used may cause irreversible damage to the membrane tubing. Electro-cleaning requires disassembling the membrane tubing for cleaning, which can disrupt the plant's production process. Each of these methods has its own drawbacks in addressing membrane fouling.

[0007] Given the above issues, further improvements are still needed in flue gas carbon capture technology to improve separation efficiency while effectively extending membrane lifespan. Summary of the Invention

[0008] The present invention aims to solve at least one of the above-mentioned technical problems.

[0009] This invention provides a carbon dioxide capture system and method that can deeply remove pollutants from flue gas, avoid membrane fouling, maximize the long-term operation of the membrane separation unit, and improve the membrane separation efficiency. At the same time, it can effectively reduce the flue gas temperature at the inlet of the desulfurization unit, reduce the vaporization of the quenching circulating liquid, and thus reduce the amount of soluble salts generated during the quenching process, thereby achieving source reduction of soluble salts.

[0010] According to a first aspect of the present invention, a carbon dioxide capture system is provided, the system comprising: a wet desulfurization unit for removing SO2 from flue gas. x The unit includes a cooling unit connected to the wet desulfurization unit, used to cool the flue gas after wet desulfurization; an adsorption-desorption unit connected to the cooling unit, used to adsorb pollutants in the flue gas after cooling; and a membrane separation unit connected to the adsorption-desorption unit, used to separate carbon dioxide from the flue gas after purification by the adsorption-desorption unit.

[0011] According to a second aspect of the present invention, the present invention provides a method for carbon dioxide capture, comprising:

[0012] 1) Flue gas enters the wet desulfurization unit to remove SO₂. x ;

[0013] 2) The flue gas after passing through the wet desulfurization unit enters the cooling unit and is cooled to 20-40℃;

[0014] 3) The flue gas cooled by the cooling unit enters the adsorption and desorption unit to adsorb and remove pollutants;

[0015] 4) The flue gas passing through the adsorption and desorption unit enters the membrane separation unit, where carbon dioxide (i.e., permeate gas) is separated.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects:

[0017] (1) The present invention sets up an adsorption and desorption unit before the membrane separation unit. Through the adsorption of the adsorbent, the fine particulate matter in the flue gas that is difficult to effectively capture by existing technologies and is easy to clog the membrane equipment is removed. This ensures that the flue gas entering the membrane separation unit does not contain or contains only a small amount of particulate matter, which can greatly extend the service life of the membrane and effectively improve the separation efficiency of the membrane, thereby increasing the technical competitiveness of membrane separation technology in the field of carbon dioxide capture.

[0018] (2) The present invention sets at least three adsorption and desorption devices in the adsorption and desorption unit, so that they are simultaneously in use, rinsing and drying states, which can ensure that the flue gas continuously enters the adsorption device, and the adsorbent simultaneously carries out the adsorption and desorption process, and synergistically removes particulate matter in the flue gas, thereby improving the adsorption efficiency and meeting the requirements of long-term operation of the factory.

[0019] (3) In this invention, the heat of the flue gas is used for heating during the drying process of the adsorption device, thereby reducing the temperature of the flue gas entering the wet desulfurization unit. When the flue gas enters the wet desulfurization unit, the lower the flue gas temperature, the less the amount of liquid vaporization in the quenching circulation, and the less soluble salt is generated, thereby achieving source reduction of soluble salts, which indirectly improves the adsorption efficiency and membrane lifespan, while reducing the water consumption of the wet desulfurization unit.

[0020] (4) In this invention, a portion of the permeate gas is used as a raw material in the membrane separation unit, which increases the carbon dioxide concentration in the flue gas. The higher the carbon dioxide concentration in the flue gas, the better the membrane separation effect and the higher the separation efficiency. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the carbon dioxide capture system and process flow according to an embodiment of the present invention;

[0022] Figure 1 In the diagram: 1-Wet desulfurization unit; 2-Cooling unit; 3-Adsorption / desorption unit; 3-1 Adsorption device in operation; 3-2 Adsorption device in rinsing state; 3-3 Adsorption device in drying state; 4-Fan; 5-First compressor; 6-Membrane separation device; 7-Vacuum pump; 8-Second compressor; 9-Programmable valve; 10-Membrane separation unit; 11-Flue gas supply pipeline; 12-Circulating water pipeline; 13-Make-up water pipeline; 14-Carbon dioxide; 15-Atmosphere. Arrows indicate material flow direction. Detailed Implementation

[0023] The method of the present invention will be further described in detail below through embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0024] like Figure 1 As shown, this embodiment provides a carbon dioxide capture system, including: a wet desulfurization unit 1, used to remove SO2 from flue gas. x Cooling unit 2, connected to the wet desulfurization unit 1, is used to cool the flue gas after wet desulfurization by the wet desulfurization unit 1; adsorption-desorption unit 3, connected to the cooling unit 2, is used to adsorb pollutants in the flue gas after cooling by the cooling unit 2; membrane separation unit 10, connected to the adsorption-desorption unit 3, is used to separate carbon dioxide 14 from the flue gas after purification by the adsorption-desorption unit 3.

[0025] According to an embodiment of the present invention, the SO x It refers to the general term for sulfur oxides. Specifically, it includes sulfur dioxide (SO2), sulfur trioxide (SO3, sulfuric anhydride), sulfur dioxide (S2O3), and sulfur monoxide (SO).

[0026] According to an embodiment of the present invention, the wet desulfurization unit 1 removes SO2 from the flue gas. x It can prevent SO x This affects the adsorption efficiency of the adsorption-desorption unit. Furthermore, the wet desulfurization unit 1 can simultaneously and initially cool the flue gas to 50-70℃. Studies have found that within this temperature range, the flue gas and absorbent are in full contact, cooling and reaching saturation. While the flue gas is cooling, some sulfur dioxide is absorbed, while some sulfur trioxide and larger particles condense and fall with the water vapor in the flue gas, thus playing a preliminary role in purifying the flue gas.

[0027] According to an embodiment of the present invention, the wet desulfurization unit 1 is a desulfurization tower.

[0028] According to an embodiment of the present invention, the cooling unit 2 cools the flue gas after wet desulfurization to 20-40°C, specifically, for example, 20°C, 25°C, 30°C, 35°C, and 40°C.

[0029] Studies have found that if the temperature of the flue gas after wet desulfurization is reduced to too low a temperature, such as below 20°C, the required flow rate of the cooling medium is too large, resulting in excessive energy consumption and affecting the overall plant efficiency. If the flue gas temperature is too high, some water vapor will enter the adsorption unit, affecting the subsequent adsorption and desorption process. At the same time, impurities such as soluble salts contained in the water vapor may corrode the pipelines and affect the service life of the equipment.

[0030] According to an embodiment of the present invention, the cooling unit 2 can also remove a large amount of water vapor contained in the flue gas, preventing the water vapor from affecting the separation effect of the subsequent membrane separation unit.

[0031] According to an embodiment of the present invention, the cooling unit 2 uses one or more of the following media: air, circulating water, chilled water, brine, ammonia vapor, etc.

[0032] According to an embodiment of the present invention, the cooling unit 2 is one or more of an air cooler, a heat exchanger, a cooling tower, and an industrial chiller.

[0033] The present invention has found that when the cooled flue gas is re-introduced into the adsorption-desorption unit 3, the adsorption efficiency of the adsorption-desorption unit 3 and the service life of the membrane in the membrane separation unit can be significantly improved, while the water consumption of the wet desulfurization unit is reduced.

[0034] According to an embodiment of the present invention, the adsorption-desorption unit 3 can prevent flue gas from directly entering the membrane separation unit 10 and causing membrane fouling, while improving the membrane separation efficiency.

[0035] According to an embodiment of the present invention, the adsorption-desorption unit 3 includes at least three adsorption-desorption devices for adsorbing pollutants such as ultrafine dust or soot, soluble salts, and condensable particulate matter (ammonium salts, sulfates, etc.) from flue gas. In some specific examples, such as Figure 1 As shown, the system includes an adsorption device 3-1 in use, an adsorption device 3-2 in rinsing mode, and an adsorption device 3-3 in drying mode. The three adsorption / desorption devices are in use, rinsing, and drying modes respectively, allowing for continuous treatment of the flue gas.

[0036] According to an embodiment of the present invention, the adsorption and desorption unit 3 is equipped with an adsorbent, preferably one or more of porous materials such as activated carbon, zeolite, mesoporous materials, silica gel and molecular sieves.

[0037] According to an embodiment of the present invention, the adsorption and desorption unit 3 uses fresh water, demineralized water, purified water, etc. as rinsing media to wash away the pollutants adsorbed by the adsorbent, thereby regenerating the adsorbent. The rinsing media is returned to the wet desulfurization unit as its makeup water.

[0038] According to an embodiment of the present invention, the adsorption and desorption unit 3 uses the inlet flue gas of the wet desulfurization unit 1 as a drying medium to remove the moisture contained in the adsorbent, and the flue gas passing through the adsorption and desorption unit is returned to the wet desulfurization unit 1.

[0039] According to an embodiment of the present invention, the membrane separation unit 10 includes a membrane separation device 6.

[0040] According to an embodiment of the present invention, the membrane material in the membrane separation device 6 is one or more of the following: porous ceramic ultrafiltration membrane (pore size range of 3-50 nm), porous ceramic nanofiltration membrane, dense metal material, porous metal material, zeolite membrane, molecular sieve carbon membrane, and glass membrane.

[0041] According to an embodiment of the present invention, the gas trapped by the membrane separation device 6 that does not pass through the membrane separation unit 10 is directly released to the atmosphere or released to the atmosphere after the pressure energy is recovered by the energy recovery device.

[0042] According to an embodiment of the present invention, the carbon dioxide capture system further includes a programmable valve 9, which is disposed on the pipeline between the cooling unit 2 and the adsorption-desorption unit 3, for controlling the direction of flue gas. Specifically, based on time and the state of the adsorbent, the valve is opened and closed by program control to switch the flue gas path, thereby achieving a stable long-term operation of the adsorption-desorption unit 3.

[0043] According to an embodiment of the present invention, the carbon dioxide capture system further includes a first compressor 5, which is disposed between the adsorption / desorption unit 3 and the membrane separation device 6, for increasing the flue gas pressure at the outlet of the adsorption / desorption unit and increasing the flue gas flow rate.

[0044] According to an embodiment of the present invention, the membrane separation unit 10 further includes a vacuum pump 7 and a second compressor 8, which are sequentially arranged after the membrane separation device 6. The vacuum pump 7 is used to increase the vacuum level at the product outlet of the membrane separation unit, thereby increasing the capture rate of carbon dioxide by the membrane separation unit. The second compressor 8 is used to compress the carbon dioxide product.

[0045] According to an embodiment of the present invention, the carbon dioxide capture system further includes a flue gas supply pipeline 11 for supplying flue gas.

[0046] According to an embodiment of the present invention, the carbon dioxide capture system further includes a circulating water supply pipeline 12 for supplying circulating water. In some specific examples, the circulating water supply pipeline supplies circulating water to the adsorption / desorption equipment in use, rinsing, or drying states, respectively.

[0047] According to an embodiment of the present invention, the carbon dioxide capture system further includes a water supply pipeline 13 for spraying and settling the rising flue gas in the wet desulfurization unit (desulfurization tower) to reduce the concentration of particulate matter and the content of soluble salts in the flue gas.

[0048] According to an embodiment of the present invention, the carbon dioxide capture system further includes a fan 4, which is disposed between the flue gas supply pipeline 11 and the adsorption-desorption unit 3, for transporting flue gas.

[0049] According to an embodiment of the present invention, the wet desulfurization unit 1, the cooling unit 2, the adsorption-desorption unit 3, and the membrane separation unit 10 are connected by pipelines. Methods well known in the art can be used.

[0050] This invention provides a method for carbon dioxide capture, comprising: 1) flue gas entering the wet desulfurization unit to remove SO2. x2) The flue gas after passing through the wet desulfurization unit enters the cooling unit and is cooled to 20-40℃ (specifically, 20℃, 25℃, 30℃, 35℃, 40℃); 3) The flue gas after passing through the cooling unit enters the adsorption and desorption unit to adsorb and remove pollutants; 4) The flue gas after passing through the adsorption and desorption unit enters the membrane separation unit to separate carbon dioxide (i.e., permeate gas).

[0051] According to an embodiment of the present invention, the flue gas in step 1) is regenerated flue gas from coal-fired boilers, coal-fired power plants, catalytic cracking catalyst regeneration, process heating furnaces, coking plants, or steel sintering plants, etc., after denitrification treatment. The temperature of the flue gas is typically 180-230℃.

[0052] According to an embodiment of the present invention, in step 1), the temperature of the flue gas after passing through the wet desulfurization unit is reduced to 50-70°C.

[0053] According to an embodiment of the present invention, in the above-described carbon dioxide capture method, step 1) further includes introducing another stream of flue gas into the adsorption and desorption unit 3 to dry the adsorbent, and then into the wet desulfurization unit 1. Specifically, the flue gas is backmixed with the flue gas that directly enters the wet desulfurization unit 1 at the inlet of the wet desulfurization unit 1 before entering the wet desulfurization unit 1. After backmixing, the inlet temperature of the wet desulfurization unit 1 is 150-200°C. The reduced flue gas temperature after backmixing decreases the vaporization amount of the quenching circulating liquid in the desulfurization tower, thereby reducing the amount of soluble salts generated during the quenching process, thus achieving source reduction of soluble salts.

[0054] According to an embodiment of the present invention, the flue gas outlet temperature of the cooling unit 2 is 20-40°C, specifically, for example, 20°C, 25°C, 30°C, 35°C, and 40°C.

[0055] According to an embodiment of the present invention, in step 4), the flue gas passing through the adsorption and desorption unit 3 is pressurized by a compressor before entering the membrane separation unit 10. The outlet pressure of the compressor is 150-500 kPa, preferably 220-400 kPa, and more preferably 300-400 kPa.

[0056] According to an embodiment of the present invention, the pollutants mentioned in step 3) include ultrafine dust or soot, soluble salts, and condensable particulate matter (ammonium salts, sulfates, etc.) in the flue gas.

[0057] According to an embodiment of the present invention, the operating pressure of the membrane separation unit 10 in step 4) is 1.5 bar to 5.0 bar.

[0058] According to an embodiment of the present invention, in the above-described carbon dioxide capture method, step 4) further includes exporting a portion of the separated carbon dioxide as a product; and returning another portion of the separated carbon dioxide to the inlet of the membrane separation unit 10 to increase the carbon dioxide concentration in the flue gas.

[0059] According to an embodiment of the present invention, in step 4), the carbon dioxide concentration in the flue gas of the membrane separation unit 10 is 12-20% (by volume). Studies have shown that the higher the carbon dioxide concentration in the flue gas at this point, the better the membrane separation effect and the higher the separation efficiency.

[0060] According to an embodiment of the present invention, in step 4), the volume ratio between the permeate gas directly exported as carbon dioxide product and the permeate gas returned to the inlet of the membrane separation unit is 2.0-5.0.

[0061] According to embodiments of the present invention, in the above-described carbon dioxide capture method, the flue gas that does not pass through the membrane device is directly discharged into the atmosphere as intercepted gas, or it can be discharged into the atmosphere through an energy recovery device or a nitrogen recovery device.

[0062] In some specific instances, the carbon dioxide capture method includes:

[0063] 1) The first flue gas directly enters the wet desulfurization unit; the second flue gas enters the adsorption and desorption unit to dry the adsorbent, and then backmixes with the first flue gas before entering the wet desulfurization unit; SO₂ is removed in the wet desulfurization unit. x ;

[0064] 2) The flue gas after passing through the wet desulfurization unit enters the cooling unit and is cooled to 20-40℃ (specifically, for example, 20℃, 25℃, 30℃, 35℃, 40℃);

[0065] 3) The flue gas passing through the cooling unit enters the adsorption and desorption unit to adsorb and remove pollutants;

[0066] 4) The flue gas passing through the adsorption and desorption unit enters the membrane separation unit to separate carbon dioxide; a portion of the separated carbon dioxide is exported as a product; and the other portion of the separated carbon dioxide is returned to the inlet of the membrane separation unit to increase the carbon dioxide concentration in the flue gas.

[0067] The following wet desulfurization unit 1 is a desulfurization tower.

[0068] like Figure 1As shown, this embodiment provides a method for carbon dioxide capture. The first flue gas is supplied via flue gas supply pipeline 11 to the lower part of the desulfurization tower. A pipeline from the top of the desulfurization tower connects to cooling unit 2. Cooling unit 2 is connected to programmable valve 9 via a pipeline. The outlet of programmable valve 9 is connected via pipeline to the inlets of adsorption devices 3-1 (in use), 3-2 (in flushing), and 3-3 (in drying). The outlet of adsorption / desorption unit 3 is connected via pipeline to the inlet of first compressor 5. The outlet of first compressor 5 is connected to the inlet of membrane separation device 6. The outlet of membrane separation device 6 on the interception side is directly vented to the atmosphere 15. The outlet of membrane separation device 6 on the permeate side is connected to the inlet of vacuum pump 7. The outlet of vacuum pump 7 is connected to the inlet of second compressor 8. The outlet of second compressor 8 is connected to the carbon dioxide product storage tank. The outlet of second compressor 8 is also connected to the inlet of membrane separation device 6. Circulating water pipeline 12 is connected to the inlets of adsorption devices 3-1 (in use), 3-2 (in flushing), and 3-3 (in drying). Pipelines leading out from the outlets of these adsorption devices are connected to a supplementary... The water pipeline 13 inlet is used to reduce the concentration of particulate matter and soluble salt content in the desulfurization flue gas, and plays a role in spraying and settling the rising flue gas in the tower. The second flue gas is connected to the inlet of the fan 4 through the flue gas supply pipeline 11. The outlet pipeline of the fan 4 is connected to the inlet of the adsorption device 3-1 in operation, the adsorption device 3-2 in flushing, and the adsorption device 3-3 in drying, respectively. The outlet pipeline of the adsorption-desorption unit 3 is connected to the flue gas supply pipeline 11 for backmixing. The temperature of the flue gas after backmixing is reduced, which reduces the quenching circulating liquid in the desulfurization tower. The vaporization rate is increased, thereby reducing the amount of soluble salts generated during rapid cooling, thus achieving source reduction of soluble salts. When the flue gas enters the adsorption-desorption unit 3, the valve before the adsorption device 3-1 in the operating state is opened, while the program-controlled valves before the other two adsorption devices are closed. The adsorption device 3-2 in the flushing state opens the inlet valve of the circulating water pipeline 12 to carry out the desorption process of the adsorbent. The adsorption device 3-3 in the drying state opens the inlet valve of the flue gas heat exchanger to carry out the drying and dehydration process of the adsorbent. The above operations are carried out simultaneously to ensure that the three adsorption devices are in the operating, flushing, and drying states respectively.

[0069] It should be noted that 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 indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0070] Example 1

[0071] like Figure 1As shown, in this embodiment, flue gas with a CO2 content of 12% (by volume) is fed to the desulfurization tower, and the inlet temperature of the flue gas in the desulfurization tower is 180°C. The flue gas undergoes SO2 removal in the desulfurization tower. x After entering the cooling unit 2 to cool down to 30°C, the water vapor in the flue gas is removed. It then enters the adsorption and desorption unit 3 from the cooling unit 2. After being drawn out from the adsorption device 3-1 in use, it enters the first compressor 5, is compressed to 300 kPa, and then enters the membrane separation unit 10.

[0072] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0073] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 80% and the purity of the separated CO2 is 86%.

[0074] Example 2

[0075] like Figure 1 As shown, in this embodiment, flue gas with a CO2 content of 20% (by volume) is fed to the desulfurization tower, and the inlet temperature of the flue gas in the desulfurization tower is 180°C. The flue gas undergoes SO2 removal in the desulfurization tower. x After entering the cooling unit 2 to cool down to 30°C, the water vapor in the flue gas is removed. It then enters the adsorption and desorption unit 3 from the cooling unit 2. After being drawn out from the adsorption device 3-1 in use, it enters the first compressor 5, is compressed to 300 kPa, and then enters the membrane separation unit 10.

[0076] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0077] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 83% and the purity of the separated CO2 is 88%.

[0078] Example 3

[0079] like Figure 1 As shown, in this embodiment, flue gas with a CO2 content of 25% (by volume) is fed to the desulfurization tower, and the inlet temperature of the flue gas in the desulfurization tower is 180°C. The flue gas undergoes SO2 removal in the desulfurization tower. xAfter entering the cooling unit 2 to cool down to 30°C, the water vapor in the flue gas is removed. It then enters the adsorption and desorption unit 3 from the cooling unit 2. After being drawn out from the adsorption device 3-1 in use, it enters the first compressor 5, is compressed to 300 kPa, and then enters the membrane separation unit 10.

[0080] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0081] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 85% and the purity of the separated CO2 is 90%.

[0082] Example 4

[0083] like Figure 1 As shown, in this embodiment, flue gas with a CO2 content of 20% (by volume) is fed to the desulfurization tower, and the inlet temperature of the flue gas in the desulfurization tower is 150°C. The flue gas undergoes SO2 removal in the desulfurization tower. x After entering the cooling unit 2 to cool down to 40°C, the water vapor in the flue gas is removed. It then enters the adsorption and desorption unit 3 from the cooling unit 2. After being drawn out from the adsorption device 3-1 in use, it enters the first compressor 5, is compressed to 400 kPa, and then enters the membrane separation unit 10.

[0084] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0085] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 85% and the purity of the separated CO2 is 90%.

[0086] Example 5

[0087] like Figure 1 As shown, in this embodiment, flue gas with a CO2 content of 20% (by volume) is fed to the desulfurization tower, and the inlet temperature of the flue gas in the desulfurization tower is 180°C. The flue gas undergoes SO2 removal in the desulfurization tower. x After entering the cooling unit 2 to cool down to 40°C, the water vapor in the flue gas is removed. It then enters the adsorption and desorption unit 3 from the cooling unit 2. After being drawn out from the adsorption device 3-1 in use, it enters the first compressor 5, is compressed to 400 kPa, and then enters the membrane separation unit 10.

[0088] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0089] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 80% and the purity of the separated CO2 is 85%.

[0090] Example 6

[0091] like Figure 1 As shown, in this embodiment, flue gas with a CO2 content of 20% (by volume) is fed to the desulfurization tower, and the inlet temperature of the flue gas in the desulfurization tower is 200°C. The flue gas undergoes SO2 removal in the desulfurization tower. x After entering the cooling unit 2 to cool down to 40°C, the water vapor in the flue gas is removed. It then enters the adsorption and desorption unit 3 from the cooling unit 2. After being drawn out from the adsorption device 3-1 in use, it enters the first compressor 5, is compressed to 400 kPa, and then enters the membrane separation unit 10.

[0092] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0093] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 77% and the purity of the separated CO2 is 81%.

[0094] Example 7

[0095] like Figure 1 As shown, in this embodiment, flue gas with a CO2 content of 20% (by volume) is fed to the desulfurization tower, and the inlet temperature of the flue gas in the desulfurization tower is 180°C. The flue gas undergoes SO2 removal in the desulfurization tower. x After entering the cooling unit 2 to cool down to 40°C, the water vapor in the flue gas is removed. It then enters the adsorption and desorption unit 3 from the cooling unit 2. After being drawn out from the adsorption device 3-1 in use, it enters the first compressor 5, is compressed to 350 kPa, and then enters the membrane separation unit 10.

[0096] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0097] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 86% and the purity of the separated CO2 is 91%.

[0098] Table 1. Experimental results of the carbon dioxide capture system of the present invention under different operating conditions in Examples 1-7.

[0099] <![CDATA[CO₂ content in flue gas, %]]> 12 20 25 20 20 20 20 flue gas temperature at the inlet of the desulfurization tower (°C) 180 180 180 150 180 200 180 Cooling temperature ℃ 30 30 30 40 40 40 40 Membrane feed gas pressure kPa 300 300 300 400 400 400 350 <![CDATA[CO₂ capture rate%]]> 80 83 85 85 80 77 86 <![CDATA[CO₂ Purity %]]> 86 88 90 90 85 81 91

[0100] Comparative Example 1

[0101] The main difference between this comparative example and Example 1 is that the carbon dioxide capture system does not employ an adsorption-desorption unit. Instead, flue gas with a CO2 content of 12% (by volume) is transported to the desulfurization tower, and the inlet flue gas temperature of the desulfurization tower is 180°C. SO2 is removed from the flue gas in the desulfurization tower. x After entering the cooling unit 2 to cool down to 30°C, the water vapor in the flue gas is removed. Then, it enters the first compressor 5 from the cooling unit 2, is compressed to 300 kPa, and then directly enters the membrane separation unit 10.

[0102] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0103] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. After the same time as in Example 1, the CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 60% and the purity of the separated CO2 is 65%.

[0104] Comparative Example 2

[0105] The main difference between this comparative example and Example 1 is that the flue gas with a CO2 content of 12% (by volume) is fed into the desulfurization tower, and the inlet flue gas temperature of the desulfurization tower is 180°C. The flue gas undergoes SO2 removal in the desulfurization tower. x After entering the cooling unit 2 to cool down to 30°C, the water vapor in the flue gas is removed. It then enters the adsorption and desorption unit 3 from the cooling unit 2. After being drawn out from the adsorption device 3-1 in use, it enters the first compressor 5, is compressed to 200 kPa, and then enters the membrane separation unit 10.

[0106] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0107] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 70% and the purity of the separated CO2 is 74%.

[0108] The CO2 capture rate and purity in this comparative example are lower than those in Example 1, mainly because the pressure of the flue gas before entering the membrane separation unit is too low and the pressure difference before and after the membrane unit is too small, resulting in a decrease in membrane separation efficiency and thus affecting the purity of CO2 recovery.

[0109] Comparative Example 3

[0110] The main difference between this comparative example and Example 1 is that the carbon dioxide capture system does not use a cooling unit. Flue gas with a CO2 content of 12% (by volume) is transported to the desulfurization tower, and the inlet flue gas temperature is 180°C. After SOx is removed in the desulfurization tower, the flue gas enters the adsorption-desorption unit 3. It is then drawn out from the adsorption device 3-1 (in use) and enters the first compressor 5, where it is compressed to 200 kPa before entering the membrane separation unit 10.

[0111] The gas trapped by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through the energy recovery device.

[0112] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. After the same time as in Example 1, the CO2 content and capture rate of the permeate gas are calculated, and the results show that the CO2 capture rate is 65% and the purity of the separated CO2 is 70%.

[0113] The CO2 capture rate and purity in this comparative example are lower than those in Example 1, mainly because the temperature of the flue gas before entering the adsorption-desorption unit is too high (the temperature is 60°C at this time). The large amount of water vapor in the flue gas affects the adsorption efficiency of the adsorption-desorption unit. The decrease in adsorption efficiency causes the flue gas to carry a small amount of impurities when entering the membrane separation unit, resulting in a decrease in membrane separation efficiency, which in turn affects the purity of CO2 recovery.

[0114] Comparative Example 4

[0115] The main difference between this comparative example and Example 1 is that the flue gas with a CO2 content of 12% (by volume) is fed into the desulfurization tower, and the flue gas temperature at the inlet of the desulfurization tower is 180°C. After SOx is removed in the desulfurization tower, the flue gas enters the cooling unit 2 to be cooled to 30°C, where water vapor is removed. It then enters the adsorption-desorption unit 3 from the cooling unit 2, and is drawn out from the adsorption device 3-1 in use before entering the first compressor 5. After being compressed to 300 kPa, it enters the membrane separation unit 10.

[0116] A side stream is added before the membrane separation unit to introduce different amounts of CO2, ensuring that the CO2 content before entering the membrane separation unit 10 is 15%, 20%, and 25% (volume content), respectively. The gas intercepted by the membrane separation unit 10 is the purified flue gas after carbon capture, which can be directly released into the atmosphere or released into the atmosphere after recovering pressure energy through an energy recovery device.

[0117] The permeate gas from membrane separation unit 10 enters the second compressor 8 after passing through vacuum pump 7. After compression, it enters the CO2 storage tank as a high-concentration CO2 product gas. The CO2 content and capture rate of the permeate gas were calculated, with capture rates of 81%, 82.5%, and 84%, respectively. The purity of the separated CO2 was 87%, 87.5%, and 89%, respectively. This comparative example shows that the higher the carbon dioxide concentration in the flue gas before the membrane separation unit, the better the membrane separation effect and the higher the separation efficiency.

[0118] The above demonstrates that the carbon dioxide capture system and method of this invention are rationally designed and can be used for adsorption-coupled membrane separation in catalytic cracking flue gas. It can meet the capture requirements of different feedstock flue gas, and the process parameters can be adjusted according to the actual industrial process needs to achieve specific capture targets. It has strong application prospects and is expected to promote the application and development of membrane separation methods in some carbon capture fields.

[0119] The technical solutions disclosed in this invention can be implemented by researchers in the art by appropriately modifying the process parameters, based on the content herein. Although the methods of this invention have been described through preferred embodiments, those skilled in the art can obviously modify or recombine the methods described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technology. It should be particularly noted that all similar substitutions and modifications are obvious to those in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A carbon dioxide capture system, characterized in that, The system includes: Wet desulfurization units are used to remove SO2 from flue gas. x ; A cooling unit, connected to the wet desulfurization unit, is used to cool the flue gas after wet desulfurization by the wet desulfurization unit; An adsorption-desorption unit, connected to the cooling unit, is used to adsorb pollutants in the flue gas after it has been cooled by the cooling unit. The adsorption-desorption equipment of the adsorption-desorption unit uses the inlet flue gas of the wet desulfurization unit as a drying medium to remove the moisture contained in the adsorbent. The flue gas after the adsorption-desorption equipment is returned to the wet desulfurization unit. A membrane separation unit, connected to the adsorption-desorption unit, is used to separate carbon dioxide from the flue gas purified by the adsorption-desorption unit.

2. The carbon dioxide capture system according to claim 1, characterized in that, The wet desulfurization unit is a desulfurization tower; and / or, The cooling unit is one or more of the following: air cooler, heat exchanger, cooling tower, and industrial chiller.

3. The carbon dioxide capture system according to claim 1, characterized in that, The adsorption-desorption unit includes at least three adsorption-desorption devices for adsorbing pollutants in flue gas.

4. The carbon dioxide capture system according to claim 3, characterized in that, The three adsorption and desorption devices are respectively in use, rinsing, and drying states.

5. The carbon dioxide capture system according to claim 1, characterized in that, The membrane separation unit includes a membrane separation device.

6. The carbon dioxide capture system according to claim 5, characterized in that, The membrane separation unit also includes a vacuum pump and a second compressor, which are sequentially arranged after the membrane separation device; the vacuum pump is used to increase the vacuum degree of the membrane separation unit product outlet and increase the capture rate of carbon dioxide by the membrane separation unit; the second compressor is used to compress the carbon dioxide product.

7. The carbon dioxide capture system according to claim 1, characterized in that, The carbon dioxide capture system also includes a programmable valve, installed on the pipeline between the cooling unit and the adsorption / desorption unit, for controlling the direction of the flue gas; and / or, The carbon dioxide capture system also includes a first compressor, which is located between the adsorption / desorption unit and the membrane separation device, to increase the flue gas pressure at the outlet of the adsorption / desorption unit and increase the flue gas velocity.

8. The carbon dioxide capture system according to any one of claims 1-7, characterized in that, The carbon dioxide capture system also includes a flue gas supply line for supplying flue gas; and / or, The carbon dioxide capture system also includes a circulating water supply line for supplying circulating water; and / or, The carbon dioxide capture system also includes a water supply line for spraying and settling the rising flue gas in the wet desulfurization unit, reducing the concentration of particulate matter and the content of soluble salts in the flue gas; and / or, The carbon dioxide capture system also includes a fan, which is located between the flue gas supply pipeline and the adsorption / desorption unit, for transporting flue gas.

9. A method for capturing carbon dioxide, characterized in that, Using the carbon dioxide capture system according to any one of claims 1-8, the method comprises: 1) Flue gas enters the wet desulfurization unit to remove SO₂. x Another stream of flue gas is introduced into the adsorption-desorption unit to dry the adsorbent before entering the wet desulfurization unit. 2) The flue gas after passing through the wet desulfurization unit enters the cooling unit and is cooled to 20-40℃; 3) The flue gas cooled by the cooling unit enters the adsorption-desorption unit to adsorb and remove pollutants; 4) The flue gas passing through the adsorption and desorption unit enters the membrane separation unit, where carbon dioxide is separated.

10. The carbon dioxide capture method according to claim 9, characterized in that, Step 1) The temperature of the flue gas after passing through the wet desulfurization unit is reduced to 50-70℃; and / or, Step 1) The flue gas that directly enters the wet desulfurization unit is backmixed at the inlet of the wet desulfurization unit before entering the wet desulfurization unit; The inlet temperature of the wet desulfurization unit after backmixing is 150-200℃; and / or, Step 2) The flue gas after passing through the wet desulfurization unit enters the cooling unit and is cooled to 20°C, 25°C, 30°C, 35°C, or 40°C; and / or, In step 4), the flue gas passing through the adsorption-desorption unit is pressurized by a compressor before entering the membrane separation unit; the compressor outlet pressure is 150-500 kPa; and / or, In step 4), the operating pressure of the membrane separation unit is 1.5 bar to 5.0 bar; and / or, Step 4) further includes exporting a portion of the separated carbon dioxide as a product; returning another portion of the separated carbon dioxide to the inlet of the membrane separation unit to increase the carbon dioxide concentration in the flue gas; optionally, the volume ratio between the permeate gas exported as the carbon dioxide product and the permeate gas returned to the inlet of the membrane separation unit is 2.0-5.0; and / or, In step 4), the carbon dioxide concentration in the flue gas of the membrane separation unit is 12-20%.

11. The method for capturing carbon dioxide according to claim 10, characterized in that, The compressor outlet pressure mentioned in step 4) is 220-400 kPa.

12. The method for capturing carbon dioxide according to claim 10, characterized in that, The compressor outlet pressure mentioned in step 4) is 300-400 kPa.

13. The method for capturing carbon dioxide according to any one of claims 9 to 12, characterized in that, The method includes: 1) The first flue gas directly enters the wet desulfurization unit; the second flue gas enters the adsorption-desorption unit to dry the adsorbent, and then backmixes with the first flue gas before entering the wet desulfurization unit; SO₂ is removed in the wet desulfurization unit. x ; 2) The flue gas after passing through the wet desulfurization unit enters the cooling unit and is cooled to 20-40℃; 3) The flue gas passing through the cooling unit enters the adsorption-desorption unit to adsorb and remove pollutants; 4) The flue gas passing through the adsorption and desorption unit enters the membrane separation unit to separate carbon dioxide; a portion of the separated carbon dioxide is exported as a product; and the other portion of the separated carbon dioxide is returned to the inlet of the membrane separation unit to increase the carbon dioxide concentration in the flue gas.

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