Carbon dioxide trapping method and system coupled with membrane absorption and crystallization

Abstract

The invention relates to the technical field of waste gas treatment and recycling, in particular to a carbon dioxide (CO2) trapping method and system coupled with membrane absorption and crystallization. The method is characterized in that membrane absorption and crystallization are coupled, CO2 in gas is captured by potassium carbonate (K2CO3) absorption liquid to generate potassium bicarbonate (KHCO3), KHCO3 crystals are efficiently extracted by adopting an anti-solvent crystallization technology, pure COgas is separated through high-temperature desorption, a K2CO3 absorbent is regenerated, and meanwhile, an anti-solvent is recycled to realize cyclic utilization. Compared with a traditional tower type CO2 trapping process, the membrane absorption technology used in the method is higher in efficiency, trapping can be achieved at the low temperature and pressure, and the occupied area of equipment is remarkably reduced. In addition, the anti-solvent crystallization process avoids the problems of high energy consumption and low efficiency in KHCO3 separation by a conventional variable-temperature or reactive crystallization method. According to the method, emission reduction and resource utilization of the COgas are achieved, recycling of the K2CO3 absorbent and the anti-solvent is supported, the agent cost of the system and the regeneration energy consumption of the absorbent are remarkably reduced, and good environmental benefits and economic benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of waste gas treatment and resource utilization technology, specifically relating to a carbon dioxide capture method and system that couples membrane absorption and crystallization. Background Technology

[0002] The large-scale emission of carbon dioxide (CO2) from industrial processes significantly exacerbates the greenhouse effect, leading to a series of environmental problems such as global warming and sea-level rise. Capturing, storing, and utilizing this CO2 not only effectively reduces emissions but also offers significant environmental and economic benefits. Chemical absorption is one of the most widely used CO2 capture methods, with commonly used absorbents including organic amines, amino acids, and carbonates. Compared to other absorbents, carbonate absorbents have advantages such as high absorption load, low cost and availability, low toxicity and volatility, and no corrosiveness to equipment. However, their main drawback is the relatively slow CO2 absorption rate.

[0003] In recent years, studies have shown that using a high-concentration potassium carbonate (K2CO3) solution as the absorbent can significantly accelerate the CO2 absorption rate. Furthermore, the potassium bicarbonate (KHCO3) generated during absorption precipitates due to supersaturation, forming KHCO3 crystals. Unlike traditional absorbent regeneration methods, direct crystal regeneration avoids the sensible heat and latent heat of vaporization generated by heating the aqueous solution, thus significantly reducing CO2 regeneration energy consumption. Based on this, Australian researchers developed the UNO MK 3 process (WO 2011 / 130796) and applied it to CO2 capture in power plant flue gas. Chinese patent CN 206853446U also discloses a carbon dioxide absorption and separation device that uses a K2CO3 solution in an absorption tower to absorb CO2, generating a saturated KHCO3 solution, and then precipitating KHCO3 crystals in a cooling crystallization tank. However, traditional tower absorption equipment is prone to problems such as flooding, channeling, and mist entrainment, resulting in low CO2 mass transfer efficiency. Furthermore, although the solubility of KHCO3 is significantly lower than that of K2CO3, it is still as high as 32.4 g / 100 mL H2O at 25°C. Therefore, to simultaneously achieve high absorption efficiency and high crystallization yield, switching between high-temperature absorption and warm crystallization is usually required. However, if the system lacks a sufficient heat source or has low heat exchange efficiency, this process will consume a large amount of energy. Chinese patent CN 116547056A discloses a continuous method and system for preparing sodium bicarbonate crystals, which uses a membrane contactor to concentrate sodium bicarbonate solution to promote crystallization and avoid temperature-changing operation. However, when the solution is supersaturated, crystals are prone to grow or adhere to the membrane surface, leading to a decrease in membrane flux and thus hindering the smooth progress of the concentration process. Summary of the Invention

[0004] This invention provides a carbon dioxide capture method and system that couples membrane absorption and crystallization, which can replace the traditional gas-liquid contact absorption tower in the existing CO2 capture process. It also uses anti-solvent crystallization technology to solve the problems of low KHCO3 crystallization yield and high energy consumption in the existing crystallization process.

[0005] According to a first aspect of the present invention, the present invention provides a carbon dioxide capture method by coupled membrane absorption and crystallization, comprising the following steps: Step 1: High-concentration carbon dioxide (CO2) gas is passed from top to bottom through the tube side of the hollow fiber membrane contactor, while potassium carbonate (K2CO3) absorbent is circulated from bottom to top through the shell side of the hollow fiber membrane contactor to absorb CO2, resulting in low-concentration CO2 gas and saturated potassium bicarbonate (KHCO3) absorbent. The high-concentration CO2 gas has a concentration range of 20%-50% and a flow rate of 10-30 L / h. The K2CO3 absorbent has a mass concentration range of 25%-40%, a flow rate range of 8-15 L / h, and a temperature range of 25℃-40℃. The membrane fibers used in the hollow fiber membrane should be hydrophobic, with a porosity range of 20%-50% and a pore size range of 0.02-0.2 μm. Step 2: Add a certain amount of ethanol to the crystallization tank, and then introduce the KHCO3 saturated absorbent into the crystallization tank to induce antisolvent crystallization and obtain KHCO3 crystals; the volume concentration of ethanol is greater than 95%, and the volume ratio of KHCO3 saturated absorbent to ethanol is in the range of 1:2-1:4; the crystallization temperature in the crystallization tank is controlled in the range of 20℃-30℃. Step 3: The obtained KHCO3 crystals are fed into a CO2 desorption tower for heating and regeneration to obtain solid potassium carbonate. A mixture of CO2 and water vapor is also obtained, which is condensed to obtain pure CO2 gas. Simultaneously, the ethanol-K2CO3-KHCO3 solution after crystal removal is subjected to alcohol-water separation to obtain regenerated ethanol and a K2CO3-KHCO3 solution. The heating and regeneration temperature range for KHCO3 crystals is 120℃-180℃. The ethanol regeneration method is one or more of distillation, pervaporation, and adsorption methods, and the volume concentration of the regenerated ethanol is greater than 95%. Step 4: After cooling, the regenerated K2CO3 solid and the K2CO3-KHCO3 solution after alcohol-water separation are added back to the potassium carbonate absorption tank to realize the recycling of K2CO3 absorbent. The regenerated ethanol is added back to the ethanol storage tank to realize the recycling of antisolvent.

[0006] Preferably, the heat from the regenerated K2CO3 solid and K2CO3-KHCO3 solution in step 4 is recovered by a heat exchanger and used to heat the ethanol-K2CO3-KHCO3 solution in step 3 to recover ethanol.

[0007] According to a second aspect of the present invention, a carbon dioxide capture system coupled with membrane absorption and crystallization is provided, comprising a hollow fiber membrane contactor 11, an absorbent pump 12, a potassium carbonate absorbent storage tank 13, an automatic absorbent monitoring device 14, a one-way valve 15 from the absorbent tank to the crystallization tank, a crystallization tank 21, an automatic ethanol addition control device 22, an ethanol storage tank 23, an ethanol regeneration device 24, a one-way valve 25 for the solid outlet of the crystallization tank, a one-way valve 26 for the liquid outlet of the crystallization tank, a heat exchanger I 27, a heat exchanger II 28, a CO2 desorption tower 31, and a condenser 32.

[0008] In one embodiment, high-concentration CO2 gas enters through the tube-side gas inlet 111 of the hollow fiber membrane contactor 11, flows down through the hollow fiber membrane contactor 11, and then flows out through the tube-side gas outlet 112 to obtain low-concentration CO2 gas. The K2CO3 absorbent in the potassium carbonate absorbent storage tank 13 is introduced from the shell-side liquid inlet 113 of the hollow fiber membrane contactor 11 by the absorbent pump 12, flows from bottom to top through the hollow fiber membrane contactor 11 to absorb CO2, and after absorption, the liquid flows out from the shell-side liquid outlet 114 and is circulated back to the potassium carbonate absorbent storage tank 13. When the automatic monitoring device 14 detects that the potassium carbonate absorption liquid storage tank 13 is saturated with KHCO3, the CO2 membrane absorption process stops. Ethanol in the ethanol storage tank 23 is introduced into the crystallization tank 21 through the ethanol automatic addition control device 22. Then, the one-way valve 15 of the pipe connecting the potassium carbonate absorption liquid storage tank 13 and the crystallization tank 21 is opened. The KHCO3-saturated absorption liquid flows into the crystallization tank 21 and mixes thoroughly with ethanol to undergo anti-solvent crystallization to obtain KHCO3 crystals. After the crystallization process in the crystallization tank 21 reaches a steady state, it is allowed to stand until the KHCO3 crystals are completely precipitated. Then, the one-way valve 25 of the solid pipeline is opened to export the KHCO3 crystals from the crystallization tank 21. After the crystals are completely discharged from the crystallization tank 21, close the one-way valve 25 and open the one-way valve 26 of the liquid pipeline to discharge the ethanol-water mixed solution from the crystallization tank 21 and send it into the ethanol regeneration device 24 to obtain regenerated anhydrous ethanol, which is then added to the ethanol storage tank 23. At the same time, a K2CO3-KHCO3 solution is obtained, which is cooled by heat exchanger I 27 and then added back to the potassium carbonate absorption solution storage tank 13. The heat can be reused for the regeneration of the ethanol-K2CO3-KHCO3 solution. The KHCO3 crystals exported from the crystallization tank 21 are sent to the CO2 desorption tower 31, heated to desorb CO2, and regenerated K2CO3 solid is obtained. The CO2 desorption tower 31 produces pure CO2 gas after the water vapor is removed by the condenser 32. At the same time, the regenerated K2CO3 solid at the bottom of the CO2 desorption tower 31 is cooled by the heat exchanger II 28 and then replenished to the potassium carbonate absorbent storage tank 13 to realize the recycling of K2CO3 absorbent. The heat can be reused for the regeneration of ethanol-K2CO3-KHCO3 solution.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention couples membrane absorption and antisolvent crystallization technologies, and can quickly complete the large-scale crystallization of KHCO3 after achieving efficient CO2 capture, thereby reducing greenhouse gas emissions while obtaining valuable products.

[0010] (2) The present invention uses KHCO3 crystals for regeneration, which avoids the sensible heat and latent heat of vaporization required for regeneration by heating saturated solution, and significantly reduces regeneration energy consumption.

[0011] (3) The present invention uses ethanol as an antisolvent to crystallize KHCO3 and realizes the recycling of ethanol, which improves the crystallization efficiency, greatly reduces the crystallization energy consumption and required reagents, and has certain environmental and economic benefits. Attached Figure Description

[0012] Figure 1 A schematic diagram of a CO2 capture system for coupling membrane absorption and crystallization; Figure 2 This describes the change in CO2 load during the absorption process of the K2CO3 absorbent in Example 1 of the present invention. Figure 3 This shows the change in CO2 content in the gas after membrane absorption in Example 1 of the present invention. Figure 4 The XRD pattern of KHCO3 crystals obtained by antisolvent crystallization in Example 1 of this invention; Figure label: 11-Hollow fiber membrane contactor; 111-Hollow fiber membrane tube-side gas inlet; 112-Hollow fiber membrane tube-side gas outlet; 113-Hollow fiber membrane shell-side liquid inlet; 114-Hollow fiber membrane shell-side liquid outlet; 12-Absorbent pump; 13-Potassium carbonate absorbent storage tank; 14-Absorbent automatic monitoring device; 15-Potassium carbonate absorbent tank to crystallizer check valve; 21-Crystallizer; 22-Ethanol automatic addition control device; 23-Ethanol storage tank; 24-Ethanol regeneration device; 25-Crystallizer solid outlet check valve; 26-Crystallizer liquid outlet check valve; 27-Heat exchanger I; 28-Heat exchanger II; 31-CO2 desorption tower; 32-Condenser. Detailed Implementation

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0014] like Figure 1 As shown, according to one aspect of the present invention, the present invention provides a CO2 capture system coupled with membrane absorption and crystallization, which includes a hollow fiber membrane contactor 11, an absorbent pump 12, a potassium carbonate absorbent storage tank 13, an automatic absorbent monitoring device 14, a one-way valve 15 from the absorbent tank to the crystallization tank, a crystallization tank 21, an automatic ethanol addition control device 22, an ethanol storage tank 23, an ethanol regeneration device 24, a one-way valve 25 for the solid outlet of the crystallization tank, a one-way valve 26 for the liquid outlet of the crystallization tank, a heat exchanger I 27, a heat exchanger II 28, a CO2 desorption tower 31, and a condenser 32.

[0015] The hollow fiber membrane contactor 11 and the crystallization tank 21 will be described in detail below.

[0016] like Figure 1 As shown, CO2-rich gas is introduced through the hollow fiber membrane tube-side gas inlet 111, while simultaneously, the K2CO3 absorbent from the potassium carbonate absorbent storage tank 13 is introduced through the hollow fiber membrane shell-side liquid inlet 113 to absorb CO2 using the absorbent pump 12. The membrane contactor uses hydrophobic and permeable membrane fibers, allowing only gas to pass through. After CO2 removal, the gas exits through the hollow fiber membrane tube-side gas outlet 112. The K2CO3 absorbent, having absorbed CO2, exits through the hollow fiber membrane shell-side liquid outlet 114, returning to the potassium carbonate absorbent storage tank 13, where it is then cycled again by the absorbent pump 12. The K2CO3 in the absorbent is gradually converted to KHCO3 until the automatic absorbent monitoring device 14 detects that the KHCO3 concentration in the absorbent has reached saturation, at which point CO2 membrane absorption stops.

[0017] After membrane absorption stops, a certain amount of ethanol is introduced from the ethanol storage tank 23 into the crystallization tank 21 via the automatic ethanol addition control device 22. The one-way valve 15 from the absorbent tank to the crystallization tank is opened, allowing the KHCO3-saturated absorbent to be introduced into the crystallization tank 21. The absorbent mixes thoroughly with the ethanol, resulting in antisolvent crystallization and obtaining a large amount of KHCO3 crystals. Once the antisolvent crystallization in the crystallization tank 21 reaches a steady state, the tank is allowed to stand to allow the KHCO3 crystals to fully precipitate. The solid outlet one-way valve 25 of the crystallization tank is then opened, sending the KHCO3 crystals to the CO2 desorption tower. After all the crystals have flowed out, the liquid outlet one-way valve 26 of the crystallization tank is opened, sending the ethanol-K2CO3-KHCO3 mixed solution to the ethanol regeneration device 24 for alcohol-water separation. The obtained regenerated ethanol is added to the ethanol storage tank 23 for further antisolvent crystallization, while the K2CO3-KHCO3 aqueous solution after ethanol removal is returned to the potassium carbonate absorbent storage tank 13 for further CO2 membrane absorption. Heat is recovered from the regenerated K2CO3-KHCO3 aqueous solution using heat exchanger I27 and reused for subsequent regeneration of the ethanol-K2CO3-KHCO3 solution.

[0018] CO2 desorption tower 31 regenerates KHCO3 crystals through heating, yielding CO2, water vapor, and solid K2CO3. The solid K2CO3 is cooled via heat exchanger II 28 and then replenished in the potassium carbonate absorbent storage tank 13 for reuse in CO2 membrane absorption. The recovered heat can also be reused for the regeneration of the ethanol-K2CO3-KHCO3 solution. The CO2 and water vapor mixture is dried to obtain pure CO2, which is then stored appropriately for other uses.

[0019] According to another aspect of the present invention, the present invention provides a CO2 capture method by coupling membrane absorption and crystallization, which is implemented using the above-mentioned CO2 capture system by coupling membrane absorption and crystallization, and specifically includes the following steps.

[0020] Step 100: A CO2-rich gas (such as biogas, coal-fired power plant exhaust gas, etc.) is introduced into the tube side of the hollow fiber membrane contactor 11 through the gas inlet 111, flowing from top to bottom through the tube side. Simultaneously, a K2CO3 absorbent is introduced into the shell side of the hollow fiber membrane contactor 11 through the liquid inlet 113, flowing from bottom to top through the shell side. Under the influence of the chemical potential difference across the membrane, CO2 gas molecules selectively permeate through the membrane pores into the K2CO3 absorbent and react to form KHCO3. The relevant chemical equations are shown in Equation 1: K2CO3+ CO2+ H2O → 2KHCO3 (1) The CO2-removed gas flows out from the tube-side gas outlet 112 of the hollow fiber membrane contactor 1. The K2CO3 absorbent flows out from the shell-side liquid outlet 114 of the hollow fiber membrane contactor 11, returning to the potassium carbonate absorbent storage tank 13, and is circulated by the absorbent pump 12. During the CO2 membrane absorption process, the concentrations of K2CO3 and KHCO3 in the absorbent are periodically monitored using an automatic absorbent monitoring device 14. When the KHCO3 concentration reaches saturation, membrane absorption is stopped to prevent membrane crystallization, which would reduce subsequent absorption flux and increase operating costs.

[0021] Step 200: A certain volume of ethanol is introduced into the crystallization tank 21 via the automatic ethanol addition control device 22. Then, the one-way valve 15 from the absorbent tank to the crystallization tank is opened, allowing the KHCO3-saturated absorbent to flow into the crystallization tank 21, inducing antisolvent crystallization. The volume ratio of absorbent to ethanol should be between 1:2 and 1:4. Ethanol and water have strong hydrogen bonding and are miscible in any ratio. During antisolvent crystallization, ethanol molecules have a greater affinity for water molecules, increasing the amount of interaction between them and reducing the number of water molecules interacting with ions. This ultimately reduces the solubility of the electrolyte in the mixed solvent, leading to supersaturation and precipitation. For the K2CO3-KHCO3 ion system, the solubility of K2CO3 is significantly higher than that of KHCO3. Adding the above-mentioned proportion of ethanol can obtain pure KHCO3 crystals, while retaining K2CO3 in the absorbent, thus achieving the separation of K2CO3 and KHCO3.

[0022] Step 300: After the crystallization process reaches a steady state and the crystals have fully precipitated, open the one-way valve 25 at the solid outlet of the crystallization tank, and send the KHCO3 solid into the CO2 desorption tower 31 for heating and regeneration to obtain solid K2CO3, while simultaneously obtaining a mixture of CO2 and water vapor. The relevant chemical equations are shown in Equation 2: 2KHCO3→ K2CO3+ CO2+ H2O (2) The mixture of CO2 and water vapor is condensed in condenser 32 to remove the water vapor, yielding pure CO2 gas, which can be stored appropriately for other uses. After all the crystals have flowed out of crystallization tank 21, the one-way valve 26 at the liquid outlet of the crystallization tank is opened, and the ethanol-K2CO3-KHCO3 mixed solution is sent to ethanol regeneration unit 24 for alcohol-water separation. Since ethanol and K2CO3-KHCO3 aqueous solution have a certain boiling point difference, they can be separated by physicochemical methods such as distillation and pervaporation.

[0023] Step 400: Heat is recovered from the regenerated K₂CO₃-KHCO₃ aqueous solution and solid K₂CO₃ using heat exchangers I 27 and II 28, and used for further regeneration of the ethanol-K₂CO₃-KHCO₃ mixed solution. The cooled solid K₂CO₃ and K₂CO₃-KHCO₃ aqueous solution are replenished back into the potassium carbonate absorbent storage tank 13 for further CO₂ membrane absorption, thus achieving the recycling of the K₂CO₃ absorbent. The separated regenerated ethanol is replenished back into the ethanol storage tank 23 for further antisolvent crystallization.

[0024] In summary, this invention organically combines membrane absorption and antisolvent crystallization, achieving rapid and large-scale crystallization of KHCO3 while efficiently capturing CO2. Compared to absorption tower-type CO2 capture, the large contact area of ​​the hollow fiber membrane enhances CO2 mass transfer while reducing equipment footprint. Compared to traditional temperature-varying crystallization methods, antisolvent crystallization can be carried out at ambient temperatures (20℃-30℃), requiring no external energy input and saving operating costs. The generated KHCO3 crystals can be directly used for CO2 regeneration, avoiding the sensible heat and latent heat of vaporization required for regeneration of saturated solutions, significantly reducing CO2 regeneration energy consumption. Simultaneously, this invention enables the recycling of K2CO3 absorbent and ethanol, reducing the amount of external reagents required for the system. Therefore, this invention can reduce greenhouse gas emissions while obtaining valuable products and reducing energy consumption and reagent costs, demonstrating significant environmental and economic benefits.

[0025] Example 1 The following example, using CO2 capture in simulated biogas, illustrates the implementation process of this invention.

[0026] The simulated biogas composition used was 40% CO2 and 60% CH4. The hollow fiber membrane contactor 11 used contained 850 membrane filaments with a pore size of 0.1 μm, a porosity of 45%, an effective filament length of 27 cm, and a total membrane area of ​​0.36 m². 2 The simulated biogas flow rate was 18 L / h. A 30% K₂CO₃ absorbent solution was used to capture CO₂ at a temperature of 25°C and a flow rate of 10.95 L / h. An automatic absorbent solution monitoring device 14 was used to monitor the concentrations of K₂CO₃ and KHCO₃ in the absorbent solution and convert them into CO₂ load, such as... Figure 2 As shown, the K2CO3 absorbent reached KHCO3 saturation after 2.5 hours of circulating CO2 absorption. The CO2 concentration in the effluent was measured every half hour. Figure 3As shown, the CO2 concentration in the effluent remained below 8%, indicating that the hollow fiber membrane can efficiently capture CO2 at room temperature, and the effluent can be used as vehicle fuel or enter natural gas pipelines. After obtaining a saturated KHCO3 solution, membrane absorption was stopped, and anhydrous ethanol, three times the volume of the absorbent liquid, was introduced into the crystallization tank 21 via the automatic ethanol addition control device 22. The one-way valve 15 from the absorbent tank to the crystallization tank was opened, allowing all the saturated KHCO3 solution to enter the crystallization tank, initiating antisolvent crystallization. After the crystallization process reached a steady state and the crystals had fully precipitated, the one-way valve 25 of the solid outlet of the crystallization tank was opened to collect the KHCO3 crystals and dry them. Calculations showed that the KHCO3 recovery rate was 87.6%, and XRD testing confirmed that the crystals were high-purity potassium bicarbonate. Figure 4 As shown. After solid-liquid separation, the mixed solution exhibited clear stratification, with the upper layer having a volume 6.5 times that of the lower layer. The upper layer was a high-concentration ethanol-water mixture (ethanol concentration > 86%) with extremely low ion content; the lower layer had a lower ethanol content but was rich in ions (K+). + CO3 2- The upper layer of K2CO3-KHCO3 solution is directly returned to the ethanol storage tank 23. A small amount of ethanol is separated from the lower layer solution using distillation (distillation temperature 78℃). The separated ethanol is returned to the ethanol storage tank 23, while the resulting K2CO3-KHCO3 aqueous solution is cooled by heat exchanger I 27 and returned to the potassium carbonate absorbent storage tank 13. The collected heat is used for further distillation and regeneration of the ethanol-K2CO3-KHCO3 mixture. All KHCO3 crystals are sent to the CO2 desorption tower 31, with the desorption temperature set at 150℃. The gas exiting from the top of the desorption tower is dried to obtain pure CO2 gas. The regenerated K2CO3 solid is recovered from the bottom of the tower, cooled by heat exchanger II 28, and returned to the K2CO3 absorbent storage tank 13 for further membrane absorption. The recovered heat is used for further distillation and regeneration of the ethanol-K2CO3-KHCO3 mixture. Theoretical calculations show that if the heat of reaction from CO2 absorption and KHCO3 crystallization is recovered, and a heat exchanger with an efficiency of 75% is used, the theoretical regeneration energy consumption of the entire system for the absorbent and antisolvent is only 3.2 GJ / t CO2, which is less than the regeneration energy consumption of the absorbent in the CO2 absorption process using organic amines (monoethanolamine, diethanolamine, etc.). Since the regenerated ethanol still contains a small amount of water, it needs to be dehydrated periodically to maintain a high antisolvent crystallization efficiency. Highly efficient dehydrating agents include regenerated potassium carbonate solid and 3Å molecular sieves. As can be seen from the above examples, this invention reduces greenhouse gas emissions while obtaining high-value products, and simultaneously achieves reagent recycling within the system, reducing the energy consumption and reagent costs of CO2 capture, thus demonstrating good environmental and economic benefits.

[0027] Although the invention has been described with reference to preferred embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the embodiments can be combined in any manner as long as there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A carbon dioxide capture process coupling membrane absorption with crystallization, characterized in that, The method comprises the following steps: Step 1: high-concentration carbon dioxide (CO2) gas is passed from top to bottom through the tube side of a hollow fiber membrane contactor, and potassium carbonate (K2CO3) absorption liquid is circulated from bottom to top in the shell side of the hollow fiber membrane contactor to absorb CO2, so as to obtain low-concentration CO2 gas and potassium bicarbonate (KHCO3) saturated absorption liquid; the concentration of the high-concentration CO2 gas is 20%-50%, the flow rate is 10-30 L / h; the mass concentration of the K2CO3 absorption liquid is 25%-40%, the flow rate is 8-15 L / h, and the temperature is 25℃-40℃; the hollow fiber membrane should have hydrophobicity, the porosity is 20%-50%, and the pore size is 0.02-0.2 μm; Step 2: a certain amount of ethanol is added to a crystallization tank, and then the KHCO3 saturated absorption liquid is introduced into the crystallization tank to induce anti-solvent crystallization, so as to obtain KHCO3 crystals; the volume concentration of the ethanol is greater than 95%, and the volume ratio of the KHCO3 saturated absorption liquid to the ethanol is 1:2-1:4; the crystallization temperature in the crystallization tank is controlled to be 20℃-30℃; Step 3: the obtained KHCO3 crystals are sent into a CO2 desorption tower for heating and regeneration, so as to obtain solid potassium carbonate, and a mixture of CO2 and water vapor is obtained, and after condensation, pure CO2 gas is obtained, and the ethanol-K2CO3-KHCO3 solution after removing the crystals is subjected to alcohol-water separation, so as to obtain regenerated ethanol and a K2CO3-KHCO3 solution; the heating and regeneration temperature of the KHCO3 crystals is 120℃-180℃; the ethanol regeneration method is one or more of distillation, pervaporation and adsorption, and the volume concentration of the regenerated ethanol is greater than 95% after regeneration; Step 4: the regenerated K2CO3 solid and the K2CO3-KHCO3 solution after alcohol-water separation are cooled and supplemented into a potassium carbonate absorption liquid tank, so as to realize the recycling of the K2CO3 absorption agent, and the regenerated ethanol is supplemented into an ethanol storage tank, so as to realize the recycling of the anti-solvent.

2. A method of capturing carbon dioxide by coupling membrane absorption and crystallization according to claim 1, characterized in that, The heat of the regenerated K2CO3 solid and the K2CO3-KHCO3 solution in step 4 is recovered through a heat exchanger, and is used to heat the ethanol-K2CO3-KHCO3 solution in step 3 to recover ethanol.

3. A carbon dioxide capture system coupled with membrane absorption and crystallization, characterized in that: It comprises: (11) a hollow fiber membrane contactor, (12) an absorption liquid pump, (13) a potassium carbonate absorption liquid storage tank, (14) an absorption liquid automatic monitoring device, (15) an absorption liquid tank to crystallization tank one-way valve, (21) a crystallization tank, (22) an ethanol automatic adding control device, (23) an ethanol storage tank, (24) an ethanol regeneration device, (25) a crystallization tank solid outlet one-way valve, (26) a crystallization tank liquid outlet one-way valve, (27) a heat exchanger I, (28) a heat exchanger II, (31) a CO2 desorption tower, and (32) a condenser. High concentration CO2 gas enters from the shell side liquid inlet (113) of the hollow fiber membrane contactor (11), flows through the hollow fiber membrane contactor (11) from top to bottom, and is discharged from the shell side liquid outlet (114) to obtain low concentration CO2 gas; When the potassium carbonate absorption liquid storage tank (13) is saturated with KHC03, the CO2 membrane absorption process is stopped by the automatic monitoring device (14); The ethanol in the ethanol storage tank (23) is introduced into the crystallization tank (21) by the ethanol automatic addition control device (22), and then the one-way valve (15) of the connecting pipeline between the potassium carbonate absorption liquid storage tank (13) and the crystallization tank (21) is opened, the KHC03-saturated absorption liquid flows into the crystallization tank, and the ethanol is fully mixed to occur anti-solvent crystallization to obtain potassium bicarbonate crystals; After the crystallization process in the crystallization tank (21) reaches a steady state, the KHC03 crystals are completely precipitated by standing, the solid pipeline one-way valve (25) is opened, and the KHC03 crystals are guided out of the crystallization tank (21); After the crystals are completely guided out of the crystallization tank (21), the one-way valve (25) is closed, the liquid pipeline one-way valve (26) is opened, the ethanol-K2CO3-KHC03 mixed solution is guided out of the crystallization tank (21), and is sent into the ethanol regeneration device (24) to obtain regenerated anhydrous ethanol, which is supplemented into the ethanol storage tank (23), and K2CO3-KHC03 solution is obtained, which is cooled by the heat exchanger I (27) and supplemented back into the potassium carbonate absorption liquid storage tank (13), and the heat can be reused for the regeneration of the ethanol-K2CO3-KHC03 solution; The CO2 desorption tower (31) is cooled by the heat exchanger II (28) to obtain pure CO2 gas, and the regenerated K2CO3 solid at the bottom of the CO2 desorption tower (31) is supplemented into the potassium carbonate absorption liquid storage tank (13) again to realize the recycling of the K2CO3 absorbent, and the heat can be reused for the regeneration of the ethanol-K2CO3-KHC03 solution. The KHC03 crystals discharged from the crystallization tank (21) are fed into a CO2 desorption tower (31) to desorb CO2 by heating 2， and obtain regenerated K2CO3 solid; The CO2 desorption tower (31) is cooled by the heat exchanger II (28) to obtain pure CO2 gas, and the regenerated K2CO3 solid at the bottom of the CO2 desorption tower (31) is supplemented into the potassium carbonate absorption liquid storage tank (13) again to realize the recycling of the K2CO3 absorbent, and the heat can be reused for the regeneration of the ethanol-K2CO3-KHC03 solution.

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