Carbon dioxide recovery and purification system and method for lime kiln tail gas based on membrane separation and multi-stage adsorption

Abstract

The application discloses a lime kiln tail gas carbon dioxide recovery and purification system and method based on membrane separation and multistage adsorption, and belongs to the field of industrial gas separation and recovery. The system comprises a pretreatment unit, a membrane separation system, an adsorption purification system, a deep cooling purification system, and a tail gas reflux system. The system and method of the application can increase the carbon dioxide concentration from 12% to 15% to 35% to 50% through membrane separation and pre-enrichment, realize efficient hydrocarbon removal and impurity removal and deep cooling rectification by adopting three-stage pressure swing adsorption combined with temperature swing adsorption, and realize the efficient recovery of carbon dioxide by combining tail gas reflux circulation and reprocessing, so that the carbon dioxide recovery rate can be significantly improved from less than 70% to more than 90%, the product purity can reach more than 99.5%, the energy consumption can be reduced, the service life of the adsorbent can be prolonged, and the system operation stability can be improved, thereby providing an efficient and feasible solution for industrial carbon emission reduction and resource utilization.

Description

Technical Field

[0001] This invention relates to the field of industrial gas separation and recovery, specifically to a process system and method for the efficient capture, enrichment and deep purification of carbon dioxide (CO2) in the tail gas of industrial furnaces such as lime kilns, cement kilns and glass kilns. Background Technology

[0002] Lime (calcium oxide) is an important basic material in national economic construction, widely used in many industries such as steel, metallurgy, construction, chemical industry, agriculture, and environmental protection. However, limestone (mainly composed of calcium carbonate) decomposes during high-temperature calcination, producing a large amount of carbon dioxide.

[0003] Traditional technologies for recovering and purifying carbon dioxide from lime kiln tail gas mainly include physical absorption methods (such as the amine method), chemical absorption methods (such as the potassium carbonate method), physical adsorption methods (such as pressure swing adsorption (PSA) and vacuum pressure swing adsorption (VPSA), membrane separation methods, and cryogenic separation methods. Among these methods, pressure swing adsorption (PSA) technology has been applied to a certain extent in the field of carbon dioxide recovery from industrial tail gas due to its advantages such as simple operation, relatively low energy consumption, and no secondary pollution.

[0004] Currently, a typical carbon dioxide recovery and purification process system for lime kiln tail gas often employs a combination of "two-stage pressure swing adsorption (PSA) + cryogenic liquefaction + gasification" technology. This process typically includes the following main stages:

[0005] 1. Pretreatment stage: The tail gas from the lime kiln first passes through a dust collector to remove dust, then is cooled by a cooler, and finally passes through a gas-liquid separator to remove condensate. Subsequently, the tail gas may be further dehydrated or have small amounts of acidic components removed by a purification tower to protect downstream equipment.

[0006] 2. Pressure Swing Adsorption Stage: The pretreated exhaust gas enters a Pressure Swing Adsorption (PSA) unit. This unit typically consists of multiple adsorption towers filled with specific adsorbents (such as molecular sieves, activated carbon, etc.). By controlling the pressure changes within the adsorption towers (pressure adsorption, depressurization desorption), the selective adsorption capacity of the adsorbent for carbon dioxide is utilized to separate carbon dioxide from other components in the exhaust gas (such as nitrogen and oxygen). Traditional two-stage PSA systems perform two adsorption-desorption cycles to gradually improve the purity of the carbon dioxide.

[0007] 3. Cryogenic Purification Stage: The carbon dioxide gas initially purified by PSA may reach a purity of 90% to 98%, but still contains trace impurities. This gas then enters a cryogenic liquefaction unit, where it is liquefied through deep cooling. The liquid carbon dioxide then undergoes further purification in a distillation column to remove residual non-condensable gases or low-boiling-point impurities, achieving the purity requirements for industrial products (e.g., above 99%).

[0008] 4. Gasification and storage: The final purified liquid carbon dioxide is gasified and sent to the product storage tank for storage.

[0009] Although the aforementioned "two-stage pressure swing adsorption + cryogenic liquefaction" technology has achieved carbon dioxide recovery and utilization to a certain extent, it still faces many challenges and limitations in practical industrial applications. These limitations make it difficult for its recovery efficiency, economic efficiency, and operational stability to meet the increasingly stringent environmental protection and resource utilization requirements. Its core bottlenecks are mainly reflected in the following aspects:

[0010] I. Low and Fluctuating CO2 Concentration in Initial Tail Gas: The initial carbon dioxide concentration in lime kiln tail gas is typically around 12%–15%, and its concentration and flow rate fluctuate significantly due to factors such as kiln operating conditions and fuel type. Such a low and unstable initial concentration poses a significant challenge to the subsequent separation process. Directly treating low-concentration tail gas using adsorption or cryogenic technology requires processing a large volume of gas, resulting in high equipment investment, large adsorbent consumption, and high regeneration energy consumption, thus significantly increasing the unit cost of carbon dioxide recovery. Simultaneously, concentration fluctuations also affect the stable operation and separation efficiency of the separation equipment.

[0011] II. Limited Adsorption and Desorption Efficiency Leading to Low CO2 Recovery Rate: Traditional two-stage pressure swing adsorption (PSA) systems suffer from insufficient adsorption saturation and incomplete desorption when treating low-concentration CO2 tail gas. During the adsorption stage, although the adsorbent has strong selective adsorption capacity for CO2, some CO2 still penetrates the adsorption bed and is discharged along with non-product gas, especially when the adsorbent is about to become saturated. During the desorption stage, particularly when using vacuum desorption, although CO2 desorption can be promoted, the adsorption-desorption isotherm characteristics of the adsorbent make it difficult to completely desorb all adsorbed CO2, resulting in incomplete adsorbent regeneration and affecting the adsorption capacity of the next cycle. More importantly, during the switching, purging, venting, and regeneration operations of the adsorption tower, the PSA system inevitably generates CO2-containing tail gas emissions. The CO2 in these gases is difficult to recover effectively due to its low concentration or incomplete purification, and is directly emitted into the atmosphere, causing significant CO2 loss. In existing technologies, this portion of CO2-containing exhaust gas is usually not further treated, making it difficult to improve the overall CO2 recovery rate, which is usually limited to 60% to 70%.

[0012] III. Adsorbent Lifespan and System Stability: The performance of PSA adsorbents is affected by trace impurities in the exhaust gas (such as water vapor, sulfides, nitrogen oxides, hydrocarbons, etc.). Even after initial purification, these trace impurities may gradually accumulate in the pores of the adsorbent, leading to adsorbent poisoning or performance degradation, thereby shortening the adsorbent's lifespan and increasing replacement frequency and operating costs. Furthermore, frequent adsorption-desorption cycles can also cause a degree of fatigue to the adsorbent's structure, affecting its long-term stability.

[0013] IV. Cryogenic processes are sensitive to impurities and suffer from pre-condensation losses: Cryogenic liquefaction is a crucial step in achieving high-purity CO2 separation. However, even with high purity, the CO2 produced by a PSA system may still contain trace amounts of non-condensable gases (such as nitrogen, oxygen, and methane) and easily condensable hydrocarbons (such as ethylene and acetylene) or sulfides. These impurities may solidify and crystallize at extremely low temperatures, causing blockages in heat exchangers and pipes, severely affecting the stable operation and heat transfer efficiency of cryogenic equipment, and even leading to equipment damage and shutdown. To avoid blockages, additional purification or compromises to operating conditions are sometimes necessary before cryogenic liquefaction, which may result in some CO2 being emitted before condensation, causing additional losses.

[0014] In view of the shortcomings of the existing technology, there is an urgent need in the field for a new carbon dioxide recovery and purification system and method that can effectively solve the problem of low-concentration exhaust gas treatment, significantly improve CO2 recovery rate, ensure high product purity, reduce energy consumption, and improve the long-term operational stability of the system. Summary of the Invention

[0015] To address the technical problems of low recovery rate, high energy consumption, impurity interference, and poor system stability in the existing lime kiln tail gas carbon dioxide recovery and purification process, this invention provides a lime kiln tail gas carbon dioxide recovery and purification system based on membrane separation and multi-stage adsorption. Through integrated innovative technologies, the carbon dioxide recovery rate is significantly increased from the current level (usually below 70%) to over 90%, and the product CO2 purity is increased to over 99.5%. At the same time, energy consumption is optimized, the lifespan of key materials is extended, and the operational reliability of the entire system is greatly enhanced.

[0016] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0017] A carbon dioxide recovery and purification system for lime kiln tail gas based on membrane separation and multi-stage adsorption includes:

[0018] The pretreatment unit is used to remove dust and moisture from the tail gas of the lime kiln and to pre-remove harmful impurities.

[0019] A membrane separation system is connected to the outlet of the pretreatment unit and is used to pre-enrich carbon dioxide in the pretreated exhaust gas, significantly increasing the carbon dioxide concentration.

[0020] An adsorption purification system is connected to the enriched gas outlet of the membrane separation system and is used to perform deep adsorption purification of carbon dioxide gas enriched by membrane separation.

[0021] A cryogenic purification system, connected to the purified gas outlet of the adsorption purification system, is used to liquefy and finally distill the high-purity carbon dioxide gas after adsorption purification to meet the demand for higher purity products; and

[0022] The exhaust gas recirculation system is connected to the exhaust gas emission ends of the membrane separation system and the adsorption purification system, and is also connected to the inlet end of the membrane separation system. It is used to recover the carbon dioxide-containing exhaust gas discharged from the adsorption purification system and send it back to the membrane separation system for reprocessing, thereby maximizing the overall CO2 recovery rate.

[0023] The system also includes a product storage system for storing the final high-purity product CO2, typically configured as a product carbon dioxide tank.

[0024] Specifically, the pretreatment unit is sequentially connected to a dust collector, a primary cooler, a secondary cooler, a gas-liquid separator, and a pre-dehydration purification tower. The dust collector is used to capture solid particles in the exhaust gas; the primary and secondary coolers are connected in series to achieve deep cooling of the exhaust gas and promote water vapor condensation; the gas-liquid separator is used to efficiently separate condensate; the pre-dehydration purification tower is filled with adsorbent or absorbent to remove residual moisture, sulfides, nitrogen oxides, and other acidic gases, ensuring the cleanliness of the gas entering subsequent units and protecting the sensitive membrane components and adsorbent.

[0025] Specifically, the membrane separation system includes a hollow fiber membrane module, a booster fan, and a throttling valve. The hollow fiber membrane module preferably uses a highly selective, high-flux CO2 separation membrane material (such as polyimide, polysulfone, or a mixed matrix membrane), arranged in the form of a hollow fiber membrane, possessing a large specific surface area, effectively achieving selective separation of CO2 from non-condensable gases such as N2 and O2. The booster fan is used to increase the pressure on the feed side of the membrane module, providing the driving force for membrane separation, while the throttling valve is used to precisely control the pressure on the outlet side of the membrane module (permeable side or non-permeable side) to optimize the pressure difference across the membrane, thereby maximizing the CO2 permeation rate and enrichment factor. Through this membrane separation system, the CO2 concentration in lime kiln tail gas can be pre-enriched from 12%–15% to 35%–50%, significantly reducing the load on subsequent adsorption separation and improving overall separation efficiency and economy.

[0026] Specifically, the adsorption and purification system includes: a three-stage pressure swing adsorption tower, a temperature-switching regeneration adsorption tower, and a vacuum pump system; wherein,

[0027] Three-stage Pressure Swing Adsorption (PSA) towers are preferably filled with adsorbents that have high selectivity for CO2, such as high-performance molecular sieves (e.g., 13X molecular sieve, 5A molecular sieve) or modified activated carbon. The three-stage PSA towers employ a stepped pressure adsorption / desorption cycle operation mode, that is, by optimizing the adsorption pressure, desorption pressure, and cycle time of each stage of the PSA tower, CO2 is concentrated and separated in stages. For example, the first stage of PSA is mainly responsible for the initial capture and coarse separation of large quantities of CO2; the second stage performs medium purification of the product from the first stage; and the third stage performs high-purity purification of the product from the second stage to ensure that the final CO2 purity reaches 90%~98%.

[0028] Temperature-switching regeneration adsorption towers (TSA) are used for the deep regeneration of part or all of the adsorbent in an adsorption purification system. This process thoroughly removes residual CO2 and other impurities from the adsorbent, restoring its maximum adsorption capacity and activity. TSA towers introduce an external heat source (such as steam, electric heating, or waste heat) to raise the temperature of the adsorbent bed. Utilizing the characteristic that CO2 adsorption decreases with increasing temperature, complete CO2 desorption is achieved, ensuring long-term efficient operation and extending the adsorbent's lifespan. The combination of a TSA tower and a three-stage pressure swing adsorption (PSA) tower enables even more thorough adsorbent regeneration and the desorption of CO2 with higher purity.

[0029] Vacuum pump system: Connected to the three-stage pressure swing adsorption tower and the temperature-switching regeneration adsorption tower, it is used to perform vacuum operation on the adsorption tower during the desorption and regeneration stages, reduce the pressure inside the tower, promote the efficient desorption of adsorbed gas, ensure the rapid regeneration of the adsorbent, and recover the desorbed CO2 gas to the maximum extent.

[0030] Specifically, the cryogenic purification system includes: a high-efficiency hydrocarbon removal and impurity removal device, a carbon dioxide icing system, a carbon dioxide distillation column, a liquid carbon dioxide buffer tank, and a carbon dioxide vaporizer. Among these,

[0031] High-efficiency hydrocarbon removal and impurity removal unit: Located between the adsorption purification system and the carbon dioxide refrigeration system, this unit is used to deeply remove residual trace hydrocarbons (such as methane, ethane, ethylene, acetylene, etc.), sulfides, nitrogen oxides, and other trace impurities that may solidify or affect product quality under cryogenic conditions from CO2 gas. This unit can employ adsorption (such as special activated carbon, molecular sieves), catalytic oxidation, or a combination of adsorption and condensation technologies. Its main purpose is to protect downstream cryogenic equipment from impurity blockage or corrosion, ensure the stable and efficient operation of the cryogenic unit, and further improve product purity.

[0032] Carbon dioxide ice machine system: It adopts a multi-stage compression refrigeration cycle to cool the high-purity CO2 gas after deep impurity removal to an extremely low temperature (such as -20℃ to -50℃), so that it condenses into liquid CO2.

[0033] Carbon dioxide distillation column: used for precise distillation and separation of liquid CO2. It utilizes the boiling point difference between CO2 and trace inert gases (such as residual N2, O2) or low-boiling impurities, and conducts multiple gas-liquid contacts and mass transfers through the packing or trays inside the column. The inert gases or light components are discharged from the top, and finally, a liquid CO2 product with extremely high purity (≥99.5%) is obtained at the bottom or middle of the column.

[0034] Liquid carbon dioxide buffer tank and carbon dioxide vaporizer: The buffer tank is used to temporarily store high-purity liquid CO2 after distillation to balance supply and demand fluctuations. The vaporizer heats and vaporizes the liquid CO2, converting it into high-pressure gaseous CO2 for subsequent transportation and use.

[0035] Specifically, the exhaust gas recirculation system includes: a low-concentration exhaust gas buffer tank and a recirculation booster fan, wherein,

[0036] Low-concentration exhaust gas buffer tank: Used to collect and balance all low-concentration CO2 exhaust gases discharged from the membrane separation system and adsorption purification system.

[0037] The reflux booster fan pressurizes the exhaust gas collected in the buffer tank and sends it back to the front end of the membrane separation system (i.e., the outlet of the pre-dehydration purification tower), allowing it to re-enter the entire recovery and purification process for treatment. This closed-loop design significantly reduces CO2 emission losses.

[0038] Based on the above system, the present invention also provides a method for high-recovery-rate carbon dioxide recovery and purification of lime kiln tail gas, comprising the following steps:

[0039] S1: Exhaust gas pretreatment and membrane separation pre-enrichment:

[0040] The CO2-containing tail gas (CO2 concentration approximately 12%~15%) generated from the lime kiln is introduced into a dust collector for dust capture. After dust removal, the tail gas undergoes deep cooling in a primary and secondary cooler, followed by condensate separation in a gas-liquid separator. The dehydrated tail gas then enters a pre-dehydration purification tower for further dehydration and removal of trace amounts of sulfides, nitrogen oxides, and other harmful impurities. The purified tail gas is then sent to a membrane separation system, where CO2 is pre-enriched through hollow fiber membrane modules driven by a booster fan, increasing the CO2 concentration to 35%~50%. The lean CO2 gas is then collected in a low-concentration tail gas buffer tank.

[0041] S2: Staged pressure swing adsorption and temperature swing adsorption for deep purification:

[0042] After membrane separation and enrichment, the CO2 gas enters a three-stage pressure swing adsorption (PSA) tower group for stepwise adsorption purification. By precisely controlling the adsorption pressure, desorption pressure, and circulation cycle, CO2 is concentrated in stages, producing CO2 gas with a purity of 90%~98%. Part of the PSA desorbed gas or adsorbent requiring deep regeneration is introduced into a temperature-switching regeneration adsorption tower for complete desorption and regeneration through heating, recovering high-purity CO2. During the desorption stages of PSA and TSA, a vacuum pump system is used to create a vacuum, promoting CO2 desorption efficiency and adsorbent regeneration. All low-concentration CO2 tail gas generated during desorption, purging, and venting processes in the three-stage PSA and temperature-switching regeneration adsorption towers is collected in a low-concentration tail gas buffer tank.

[0043] S3: High-efficiency hydrocarbon removal and cryogenic distillation:

[0044] High-purity CO2 gas (90%~98%) produced from the adsorption purification system enters a high-efficiency hydrocarbon removal and impurity removal unit for deep removal of trace impurities such as hydrocarbons, sulfides, and nitrogen oxides. The purified CO2 gas is then sent to a carbon dioxide refrigeration system for deep cooling and liquefaction, forming liquid CO2. The liquid CO2 then enters a carbon dioxide distillation column for precision distillation, further removing residual inert gases or low-boiling-point impurities, achieving a product CO2 purity of ≥99.5%. The high-purity liquid CO2 after distillation is stored in a liquid carbon dioxide buffer tank and is vaporized via a carbon dioxide vaporizer when needed.

[0045] S4: Exhaust gas recirculation and reuse:

[0046] The CO2-containing exhaust gas collected in the low-concentration exhaust gas buffer tank in steps S1 and S2 is pressurized by a reflux booster fan and sent back to the front end of the membrane separation system in step S1 (i.e., the outlet of the pre-dehydration purification tower) to achieve CO2 recycling and reuse.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) This invention solves the problems of difficult treatment of low-concentration tail gas and tail gas loss in traditional schemes by introducing a membrane separation pre-enrichment and tail gas recirculation system. Membrane separation increases the initial CO2 concentration by 2-3 times, greatly reducing the subsequent adsorption load; tail gas recirculation sends the originally emitted CO2 back to the system for recovery, increasing the overall CO2 recovery rate from the traditional 60%~70% to over 90%, achieving the ultimate utilization of CO2 resources and significantly improving the CO2 recovery rate.

[0049] (2) The present invention adopts a three-stage pressure swing adsorption combined with temperature swing adsorption for deep purification, which is more refined than the existing two-stage PSA; a high-efficiency dehydrocarbon removal and impurity removal device is added before deep cryogenics, which effectively removes trace impurities that affect purity and the operation of deep cryogenic equipment, so that the final product CO2 purity can stably reach more than 99.5%, effectively improving the product CO2 purity.

[0050] (3) This invention uses membrane separation as a pre-enrichment stage, which significantly reduces the processing gas volume of the subsequent adsorption system, thereby reducing the energy consumption for adsorbent regeneration and the power consumption of related equipment. At the same time, the efficient hydrocarbon removal and impurity removal device ensures the heat transfer efficiency and stability of the cryogenic unit, indirectly reducing cryogenic energy consumption. The overall energy consumption (CO2 per unit product) is significantly reduced compared to traditional solutions, resulting in a significant reduction in system energy consumption.

[0051] (4) The deep purification and high-efficiency hydrocarbon removal device of the pretreatment unit designed in this invention effectively protects the membrane module and adsorbent from damage and poisoning by impurities such as dust, moisture, sulfides, and hydrocarbons. Combined with the thorough regeneration function of temperature-changing adsorption, the service life of the adsorbent can be extended by more than 20%.

[0052] (5) The membrane separation pre-enrichment of the present invention reduces the operating condition fluctuation of subsequent units; the high-efficiency dehydrocarbon removal and impurity removal device effectively avoids the risk of cryogenic blockage; the integrated optimization of each module makes the whole system run more smoothly, reduces unplanned downtime, and lowers maintenance costs.

[0053] (6) This invention is not only applicable to CO2 recovery from lime kiln tail gas, but its modular design and optimized separation and purification strategy also make it applicable to the treatment of CO2-containing industrial tail gas from cement kilns, glass kilns and other industries. It has good versatility and promotion prospects. Attached Figure Description

[0054] Figure 1 This is a system flowchart of an embodiment of the present invention.

[0055] In the above figures, the component names corresponding to the reference numerals are as follows:

[0056] 1: Dust collector; 2: Primary cooler; 3: Secondary cooler; 4: Gas-liquid separator; 5: Pre-dehydration purification tower; 6: Membrane separation system; 7-1: First-stage pressure swing adsorption tower; 7-2: Second-stage pressure swing adsorption tower; 7-3: Third-stage pressure swing adsorption tower; 8: Temperature-changing regeneration adsorption tower; 9: Vacuum pump system; 10: High-efficiency hydrocarbon removal and impurity removal device; 11: Carbon dioxide reflux icing system; 12: Carbon dioxide distillation tower; 13: Liquid carbon dioxide buffer tank; 14: Carbon dioxide vaporizer; 15: Low-concentration tail gas buffer tank; 16: Reflux booster fan; 17: Product carbon dioxide tank. Detailed Implementation

[0057] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments. Example

[0058] like Figure 1 As shown, this lime kiln tail gas carbon dioxide recovery and purification system based on membrane separation and multi-stage adsorption includes the following main units and key equipment:

[0059] The pretreatment unit specifically includes, in sequence, a dust collector 1, a primary cooler 2, a secondary cooler 3, a gas-liquid separator 4, and a pre-dehydration purification tower 5. The dust collector 1 is used to capture solid particles in the exhaust gas; it is a bag filter with a designed processing air volume of 50,000 Nm³. 3 / h, with a filtration accuracy of less than 5 microns, ensuring that the dust content in the exhaust gas is below 20mg / Nm³. 3 A primary cooler 2 and a secondary cooler 3 are connected in series to achieve deep cooling of the exhaust gas and promote water vapor condensation. A shell-and-tube heat exchanger is used, with industrial cooling water and chilled water as the cooling medium. The primary cooling reduces the exhaust gas temperature from approximately 180°C to 40°C, and the secondary cooling further reduces it to 10°C to maximize water vapor removal. A gas-liquid separator 4 is used for efficient separation of condensate; a high-efficiency cyclone plate gas-liquid separator is used, achieving a separation efficiency of over 99%, ensuring complete separation of condensate. The pre-dehydration purification tower 5 is filled with adsorbent or absorbent to remove residual moisture, sulfides, nitrogen oxides, and other acidic gases, ensuring the cleanliness of the gas entering subsequent units and protecting the sensitive membrane components and adsorbent; it is filled with activated alumina and a small amount of alkaline desulfurizing agent (such as calcium oxide-modified adsorbent). The towers are designed to operate alternately, with online regeneration (such as hot nitrogen purging regeneration) performed when one tower is saturated, ensuring that the exhaust gas dew point is below -20°C and the hydrogen sulfide and sulfur dioxide contents are both below 1 ppm.

[0060] The membrane separation system 6 specifically includes hollow fiber membrane modules, a booster fan, and a throttling valve. The hollow fiber membrane modules preferably use highly selective, high-flux CO2 separation membrane materials (such as polyimide, polysulfone, or mixed matrix membranes), arranged in the form of hollow fiber membranes. They have a large specific surface area, effectively achieving selective separation of CO2 from non-condensable gases such as N2 and O2. Specifically, a two-stage tandem membrane separation configuration is adopted. The first-stage membrane module is used for initial enrichment, with its feed-side pressure set at 0.8 MPa, the permeate-side (CO2-rich side) pressure set at 0.2 MPa, and the non-permeate-side (CO2-lean side) pressure close to atmospheric pressure. The second-stage membrane module is used to further enrich the CO2-rich permeate gas from the first-stage membrane module, with its feed-side pressure set at 0.6 MPa and the permeate-side pressure set at 0.1 MPa. The booster fan is used to increase the pressure on the feed side of the membrane module, providing the driving force for membrane separation. A multi-stage centrifugal fan with a rated displacement of 15000 Nm³ is selected. 3The purified tail gas is pressurized to 0.8 MPa per hour and used as feed for membrane separation. A throttling valve is installed at the permeate side outlet of the membrane module to precisely control the pressure within the range of 0.05~0.3 MPa, optimizing separation efficiency. This valve is used to precisely control the pressure on the outlet side (permeate side or non-permeate side) of the membrane module to optimize the pressure difference across the membrane, maintaining it at 0.4~0.7 MPa, thereby maximizing the CO2 permeation rate and enrichment factor. Through this membrane separation system, the CO2 concentration in lime kiln tail gas, which was 12%~15%, can be pre-enriched to 35%~50%, significantly reducing the load on subsequent adsorption separation and improving overall separation efficiency and economy.

[0061] The adsorption purification system specifically includes three-stage pressure swing adsorption (PSA) towers 7-1, 7-2, and 7-3, a temperature-switching regeneration adsorption tower 8, and a vacuum pump system 9. The three-stage PSA towers are preferably filled with adsorbents exhibiting high selectivity for CO2, such as high-performance molecular sieves (e.g., 13X molecular sieve, 5A molecular sieve) or modified activated carbon. A three-tower parallel, cyclically switching PSA system is employed. Each tower is filled with approximately 20 tons of high-performance carbon molecular sieve and 13X molecular sieve. The adsorbent ratio is 2:1; the upper 13X molecular sieve adsorbs CO2 and water, while the lower carbon molecular sieve adsorbs N2 and O2. The three-stage PSA towers employ a stepped pressure adsorption / desorption cycle operation mode, that is, by optimizing the adsorption pressure, desorption pressure, and cycle period of each stage of the PSA tower, CO2 is concentrated and separated in stages. For example, the first stage PSA is mainly responsible for the initial capture and coarse separation of large quantities of CO2; the adsorption pressure is 1.0 MPa, the desorption pressure is 0.08 MPa, the adsorption time is 70 seconds, and the desorption time is 75 seconds. The main product CO2 concentration is about 75%. The second stage performs moderate purification of the first stage product; the adsorption pressure is 1.0 MPa, the desorption pressure is 0.06 MPa, the adsorption time is 55 seconds, and the desorption time is 50 seconds. The purified first stage product yields a CO2 concentration of about 92%. The third stage performs high-purity purification of the second stage product to ensure that the final CO2 purity reaches 90%~98%; the adsorption pressure is 0.9 MPa, and a step-down desorption method is used: first, the pressure is reduced to 0.3 MPa and maintained for 10 seconds, then reduced to near vacuum at 0.02 MPa, with a total desorption time of 60 seconds and an adsorption time of 45 seconds. The purified second stage product yields a CO2 concentration of over 98%. PSA Cycle: The various towers are automatically switched between multiple steps, including adsorption, pressure equalization, desorption, purging, and rinsing, via program-controlled valves. Temperature-Switch Regeneration Adsorption Tower 8: Used for deep regeneration of part or all of the adsorbent in the adsorption purification system, to completely remove residual CO2 and other impurities, restoring the adsorbent's maximum adsorption capacity and activity. The TSA tower introduces an external heat source (such as steam, electric heating, or waste heat) to raise the adsorbent bed temperature. Utilizing the characteristic that CO2 adsorption decreases with increasing temperature, complete CO2 desorption is achieved, ensuring long-term efficient operation and extending the adsorbent's service life. The combination of the temperature-switch regeneration adsorption tower and the three-stage pressure swing adsorption tower enables more thorough adsorbent regeneration and higher purity CO2 desorption. Alternating operation of the two towers, filled with specially modified molecular sieves, is employed. Used for periodic (every 24 hours) complete regeneration of the PSA system or treatment of low-purity desorbed gas generated by the PSA system. Adsorption Stage: Atmospheric temperature and pressure adsorption. Regeneration stage: Complete desorption is achieved by heating with steam to 150-200℃, followed by cooling. The heating and cooling time is approximately 2-4 hours.Vacuum pump system 9: Connected to the three-stage pressure swing adsorption tower and the temperature-switching regeneration adsorption tower, it is used to perform vacuuming operations on the adsorption tower during the desorption and regeneration stages, reducing the pressure inside the tower, promoting efficient desorption of the adsorbed gas, ensuring rapid regeneration of the adsorbent, and maximizing the recovery of desorbed CO2 gas. A liquid ring vacuum pump with a vacuuming capacity of 1200m is selected. 3 / h, ensuring that the required vacuum level can be quickly reached and maintained during the PSA and TSA desorption stages, promoting efficient CO2 desorption.

[0062] The cryogenic purification system specifically includes a high-efficiency hydrocarbon removal and impurity removal device 10, a carbon dioxide refrigeration system 11, a carbon dioxide distillation column 12, a liquid carbon dioxide buffer tank 13, and a carbon dioxide vaporizer 14. The high-efficiency hydrocarbon removal and impurity removal device 10 is located between the adsorption purification system and the carbon dioxide refrigeration system. It is used to deeply remove residual trace hydrocarbons (such as methane, ethane, ethylene, acetylene, etc.), sulfides, nitrogen oxides, and other trace impurities that may solidify or affect product quality under cryogenic conditions from CO2 gas. This device can employ adsorption (such as special activated carbon, molecular sieves), catalytic oxidation, or a combination of adsorption and condensation technologies. Its main purpose is to protect subsequent cryogenic equipment from impurity blockage or corrosion, ensure the stable and efficient operation of the cryogenic unit, and further improve product purity. A dual-tower adsorber configuration is used, filled with special activated carbon and high-silica molecular sieves. It is designed for the deep adsorption and removal of trace C1-C4 hydrocarbons (below 1 ppm), sulfides, and nitrogen oxides from the gas. The two towers operate alternately, with one tower adsorbing and the other regenerating (heating + vacuum desorption). Carbon dioxide refrigeration system 11: Employs a multi-stage compression refrigeration cycle to cool high-purity CO2 gas, after deep impurity removal, to extremely low temperatures (e.g., -20℃ to -50℃), condensing it into liquid CO2. A multi-stage compression refrigeration system using ammonia refrigerant is used to cool the CO2 gas to -35℃, liquefying it. Carbon dioxide distillation column 12: Used for precise distillation separation of liquid CO2. Utilizing the boiling point difference between CO2 and trace amounts of inert gases (such as residual N2, O2) or low-boiling-point impurities, multiple gas-liquid contacts and mass transfers occur through the packing or trays within the column. Inert gases or light components are discharged from the top, ultimately yielding a highly pure liquid CO2 product (≥99.5%) at the bottom or middle of the column. A packed column structure is used, 20 meters high and 1 meter in diameter. A top condenser and a bottom reboiler are included. The operating pressure is approximately 2.0 MPa, the top temperature is approximately -30℃, and the bottom temperature is approximately -10℃. This is used for distillation to remove residual inert gases such as N2 and O2, as well as trace low-boiling-point impurities, from liquid CO2, ensuring product purity. Liquid CO2 buffer tank 13 and CO2 vaporizer 14: The buffer tank is used for temporary storage of high-purity liquid CO2 after distillation, balancing supply and demand fluctuations. The vaporizer heats and vaporizes the liquid CO2, converting it into high-pressure gaseous CO2 for subsequent transportation and use. The buffer tank has a volume of 50m³. 3The vaporizer uses a water bath heating vaporizer with a vaporization capacity of 2000 kg / h.

[0063] The exhaust gas recirculation system specifically includes a low-concentration exhaust gas buffer tank 15 and a recirculation booster fan 16. The low-concentration exhaust gas buffer tank 15 is used to collect and balance all low-concentration CO2-containing exhaust gases discharged from the membrane separation system and adsorption purification system. A multi-stage design can be adopted, such as a single-stage buffer tank with a volume of 25m³. 3 The secondary buffer tank, configured with a volume of 15m³, is used to collect the non-permeable side gas of the membrane separation system. 3 This system collects all low-concentration CO2 exhaust gases generated during the desorption, purging, and valve switching stages of the PSA and TSA systems. The gases from different buffer tanks are then mixed via a manifold structure and sent to the return booster blower. The return booster blower 16 pressurizes the exhaust gases collected in the buffer tanks and returns them to the front end of the membrane separation system 6, allowing them to re-enter the entire recovery and purification process for further treatment. This closed-loop design significantly reduces CO2 emission losses. A Roots blower with a flow rate of 5000 Nm³ is selected. 3 / h, pressurize the collected exhaust gas to 0.1MPa and send it back to the front inlet of the membrane separation system 6 (outlet of the pre-dehydration purification tower 5).

[0064] The product storage system includes product CO2 tank 17: capacity 100m³ 3 It is used to store the final high-purity gaseous CO2 product.

[0065] This system processes the tail gas from a lime kiln in a steel plant. The original tail gas flow rate is 40,000 Nm³. 3 / h, CO2 concentration of 13%, temperature of 180℃, dust content of 200mg / Nm 3 .

[0066] Exhaust gas pretreatment and membrane separation pre-enrichment

[0067] The exhaust gas from the lime kiln first enters dust collector 1, which removes more than 99% of the dust, resulting in an exhaust dust content of less than 20 mg / Nm³. 3 .

[0068] After dust removal, the exhaust gas passes through the primary cooler 2 and the secondary cooler 3 in sequence, gradually reducing the temperature from 180℃ to 10℃.

[0069] The cooled exhaust gas enters gas-liquid separator 4, where approximately 10 tons / hour of condensate is separated.

[0070] The dehydrated tail gas enters the pre-dehydration purification tower 5. In this tower, the tail gas passes through an adsorption bed filled with activated alumina and an alkaline desulfurizing agent, undergoing deep dehydration, desulfurization, and denitrification. The purified tail gas has a dew point below -40℃, and both H2S and SO2 contents are less than 0.1ppm. The tower operates with two towers alternating, and regeneration is achieved by purging with heated nitrogen gas, with a regeneration cycle of 8 hours.

[0071] Purified exhaust gas (approximately 35,000 Nm³) 3 The gas (at a CO2 concentration of 13%) is pressurized to 0.8 MPa by a booster fan and enters the first-stage hollow fiber membrane module of membrane separation system 6. In the membrane module, CO2 preferentially permeates and separates from N2 and O2. The gas on the permeate side (CO2-rich side) flows to the second-stage membrane module.

[0072] CO2-rich permeate gas from the first-stage membrane module (approximately 10,000 Nm³) 3 CO2-rich permeate (approximately 38% CO2 per hour) enters the second-stage hollow fiber membrane module for further enrichment. The CO2-rich permeate from the second-stage membrane module (approximately 5000 Nm³ / h) enters the module for further enrichment. 3 A high-concentration enriched gas (approximately 48% CO2 per hour) enters the subsequent adsorption and purification system. The non-permeable side gas of the first-stage membrane module (approximately 25000 Nm³) is also present. 3 / h, CO2 concentration approximately 3%) and the non-permeable side gas of the second-stage membrane module (approximately 5000 Nm³). 3 If the CO2 concentration is approximately 20% (per hour), the gas will be returned to the low-concentration tail gas buffer tank 15 for recovery, thereby improving the total CO2 recovery rate.

[0073] After passing through the membrane separation system, the CO2 concentration in the lime kiln tail gas increased from 13% to approximately 48%.

[0074] Staged pressure swing adsorption and temperature swing adsorption for deep purification

[0075] High concentration of CO2 gas (approximately 5000 Nm³) after membrane separation and enrichment 3 (CO2 concentration 48%) first enters the first stage pressure swing adsorption tower 7-1 for adsorption. The operating pressure is 1.0 MPa and the adsorption time is 75 seconds.

[0076] The non-adsorbed components of the first stage PSA tower (mainly N2, O2, and a small amount of CO2) are collected as part of the PSA tail gas in a low-concentration tail gas buffer tank 15. The adsorbed CO2 is recovered during the desorption stage: desorption is performed at 0.08 MPa for 75 seconds, and the desorbed gas (approximately 2800 Nm³) is recovered. 3 (75% CO2 concentration) enters the second stage pressure swing adsorption tower 7-2.

[0077] The second-stage PSA column further purifies 75% CO2 under an operating pressure of 1.0 MPa and a desorption pressure of 0.05 MPa, with an adsorption time of 55 seconds and a desorption time of 50 seconds. The desorbed gas (approximately 1800 Nm³) 3 (CO2 concentration 92%) enters the third stage pressure swing adsorption tower 7-3.

[0078] The third stage of the PSA column performs purification adsorption at an adsorption pressure of 0.9 MPa for 45 seconds. Stepwise desorption is then performed: first, the pressure is reduced to 0.3 MPa and held for 10 seconds, then reduced to 0.02 MPa (near vacuum) and held for 50 seconds, for a total desorption time of 60 seconds. The final product is CO2 gas with a purity of up to 98.5% (approximately 1500 Nm³). 3 / h), which is sent to the high-efficiency dehydrocarbon removal and impurity removal unit 10.

[0079] All low-concentration tail gases generated during the desorption, purging, and venting processes of the PSA adsorption tower (including non-product gases discharged from the first, second, and third stages of PSA and low-purity CO2 in the initial / final stages of desorption) are collected in the low-concentration tail gas buffer tank 15.

[0080] Every 24 hours, a portion of the adsorbent in the PSA system (or a specific PSA tower) undergoes deep regeneration in the temperature-switching regeneration adsorption tower 8. The temperature-switching adsorption tower first adsorbs low-purity desorbed gas or saturated adsorbent generated by the PSA system, then heats it to 180°C with steam, utilizing the high-temperature desorption characteristics of the adsorbent to completely remove residual CO2 and other impurities, achieving complete activation of the adsorbent. The higher-purity portion of the desorbed CO2 gas can be returned to the PSA system inlet, while the lower-purity portion enters the low-concentration tail gas buffer tank 15.

[0081] The vacuum pump system 9 operates continuously during the desorption phases of PSA and TSA to ensure that the pressure inside the adsorption tower drops rapidly to the set vacuum level, maximizing the desorption efficiency of CO2 and the regeneration quality of the adsorbent.

[0082] High-efficiency hydrocarbon removal and impurity removal and cryogenic distillation

[0083] High-purity CO2 gas (approximately 1500 Nm³) produced from the three-stage pressure swing adsorption tower 3 The gas (CO2 purity 98.5%) first enters the high-efficiency hydrocarbon removal and impurity removal unit 10. Under normal temperature and pressure, this unit, through the adsorption of special activated carbon and high-silica molecular sieves, reduces the hydrocarbon content in the gas to below 0.5 ppm and the sulfide and nitrogen oxide content to below 0.01 ppm, ensuring protection for subsequent cryogenic equipment. This unit also operates with two towers alternating, periodically undergoing heating, desorption, and regeneration.

[0084] After impurity removal, the high-purity CO2 gas enters the carbon dioxide ice machine system 11, where it is cooled to -35°C and condensed into liquid CO2 through a multi-stage compression and expansion refrigeration cycle.

[0085] Liquid CO2 enters carbon dioxide distillation column 12. The internal operating pressure of the distillation column is set to 2.0 MPa, the top temperature is approximately -30°C, and the bottom temperature is approximately -10°C. Through the distillation process, a small amount of inert gases (such as residual N2 and O2) are discharged from the top of the column, and liquid CO2 product with a purity of ≥99.9% is obtained from the bottom or side of the column.

[0086] The high-purity liquid CO2 (approximately 1200 kg / h) after distillation is stored in liquid carbon dioxide buffer tank 13.

[0087] When needed, liquid CO2 is vaporized by carbon dioxide vaporizer 14 and converted into gaseous CO2, which is then stored in product CO2 tank 17.

[0088] Exhaust gas recirculation and reuse

[0089] Throughout the entire operation, all low-concentration CO2 gas (CO2 concentration between 3% and 20%) on the non-permeable side of membrane separation system 6, and all low-concentration CO2 tail gas (CO2 concentration between 5% and 30%) generated in the steps of desorption, purging, pressure equalization, venting, and adsorption bed switching of PSA systems 7-1, 7-2, 7-3 and TSA system 8 are uniformly collected into low-concentration tail gas buffer tank 15.

[0090] When the buffer tank level reaches the set value, the reflux booster fan 16 starts, pressurizing the exhaust gas in the buffer tank to 0.1 MPa and sending it back to the front inlet of the membrane separation system 6 (the outlet of the pre-dehydration purification tower 5). This gas mixes with fresh pretreated exhaust gas and re-enters the membrane separation system for CO2 pre-enrichment and recovery.

[0091] Through this closed-loop design, CO2 that would otherwise be directly emitted can re-enter the entire recycling process, realizing the recycling of CO2 resources and increasing the overall CO2 recovery rate from the original 60%~70% to over 90%.

[0092] Through the above processing steps, this system can achieve the following technical specifications:

[0093] Carbon dioxide recovery rate: Calculations show that the overall system recovery rate can stably reach ≥92% (compared to 60%~70% for traditional solutions). Among them, the recovery rate of the pre-enrichment stage of the membrane separation system is about 90%, and the recovery rate of membrane enriched gas in the PSA+TSA stage can reach 95%. With the contribution of tail gas recirculation, the overall recovery rate is greatly improved.

[0094] Product CO2 purity: The final product CO2 purity can reach ≥99.9% (compared to ≥99% of traditional methods).

[0095] System energy consumption (per unit product): Membrane separation pre-enrichment reduces the subsequent PSA processing volume. Combined with the optimized PSA cycle and complete TSA regeneration, as well as the high-efficiency dehydrocarbon removal and impurity removal device before cryogenic treatment to ensure cryogenic efficiency, the overall energy consumption of CO2 per unit product is significantly reduced by more than 20% compared with the traditional solution.

[0096] Adsorbent lifespan: Membrane separation, as a pre-treatment protection stage, and for deep purification in pre-dehydration purification towers and hydrocarbon removal and impurity removal devices, effectively protects PSA and TSA adsorbents, extending their lifespan by more than 25%.

[0097] System operational stability: The membrane separation system reduces the fluctuation of gas composition entering the adsorption unit; the high-efficiency hydrocarbon removal and impurity removal device effectively avoids blockage and operation interruption of the cryogenic equipment; the optimized matching and automated control between the units enable the entire system to operate stably and continuously for a long time, and significantly reduce the maintenance cycle and failure rate.

[0098] In summary, the innovative advantages of this invention are reflected in the following aspects:

[0099] Deep integration of multiple technologies: It organically combines a variety of advanced technologies such as membrane separation, three-stage PSA, TSA and exhaust gas recirculation to form a highly integrated and optimized CO2 recovery and purification system, rather than simply superimposing them. Each unit complements the other and plays a synergistic role.

[0100] Staged enrichment and purification: Primary enrichment is achieved through membrane separation, followed by deep purification through multi-stage adsorption. CO2 concentration and purification are achieved in stages and gradients, avoiding the bottleneck of single technology for processing low-concentration, high-flow-rate gases.

[0101] Closed-loop recovery concept: The innovative introduction of an exhaust gas recirculation system recycles low-concentration emissions from membrane separation, PSA and TSA processes, reducing CO2 emissions at the source, which is the key to achieving ultra-high recovery rates.

[0102] Impurity depth control: The specially designed high-efficiency hydrocarbon removal and impurity removal device is the key to solving the "pain points" of the cryogenic system, ensuring the long-term stable operation of the cryogenic equipment, and indirectly improving the CO2 recovery rate.

[0103] Intelligent control: The system adopts advanced DCS (Distributed Control System) or PLC (Programmable Logic Controller) for full-process automated control, monitors the temperature, pressure, flow and composition of each unit in real time, and automatically adjusts the operating parameters according to changes in operating conditions to achieve optimized system operation and minimize energy consumption.

[0104] Therefore, the carbon dioxide recovery and purification system and method for lime kiln tail gas based on membrane separation and multi-stage adsorption of the present invention effectively solves the core problems of low recovery rate, high energy consumption, and impurity interference in the prior art through its unique combination of technologies and optimized design. This solution not only significantly improves the CO2 recovery rate and product purity, but also has good economic and environmental benefits, providing strong technical support for the capture and resource utilization of carbon dioxide in the industrial field, and possesses broad prospects for industrial application.

[0105] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any changes made based on the design principles of the present invention, or any non-creative modifications made thereon, shall fall within the scope of protection of the present invention.

Claims

1. A carbon dioxide recovery and purification system for lime kiln tail gas based on membrane separation and multi-stage adsorption, characterized in that, include: The pretreatment unit is used to remove dust and moisture from the tail gas of the lime kiln and to pre-remove harmful impurities. A membrane separation system is connected to the outlet of the pretreatment unit and is used to pre-enrich carbon dioxide in the pretreated exhaust gas. An adsorption purification system is connected to the enriched gas outlet of the membrane separation system and is used to perform deep adsorption purification of carbon dioxide gas enriched by membrane separation. A cryogenic purification system is connected to the purified gas outlet of the adsorption purification system and is used to liquefy and finally distill and purify the high-purity carbon dioxide gas after adsorption purification. as well as The exhaust gas recirculation system is connected to both the exhaust gas discharge end of the membrane separation system and the exhaust gas discharge end of the adsorption purification system, and is also connected to the air inlet of the membrane separation system. It is used to recover the carbon dioxide-containing exhaust gas discharged from the membrane separation system and the adsorption purification system and send it back to the membrane separation system for further processing. The membrane separation system includes: Hollow fiber membrane modules, comprising membrane materials that selectively allow carbon dioxide to permeate; A booster fan is used to increase the pressure on the feed side of the hollow fiber membrane module; and A throttle valve is used to control the pressure on the outlet side of the hollow fiber membrane module; The adsorption purification system includes: A three-stage pressure swing adsorption tower is used to purify carbon dioxide gas enriched by membrane separation through partial pressure step adsorption. A temperature-switching regeneration adsorption tower is used for deep regeneration of the adsorbent in the three-stage pressure swing adsorption tower and for further purification of the low-purity desorbed gas generated by the three-stage pressure swing adsorption tower; and A vacuum pump system is connected to the three-stage pressure swing adsorption tower and the temperature-switching regeneration adsorption tower to provide vacuum during the desorption stage of the three-stage pressure swing adsorption tower and the regeneration stage of the temperature-switching regeneration adsorption tower. The cryogenic purification system includes: A high-efficiency hydrocarbon removal and impurity removal device is installed between the gas outlet of the adsorption and purification system and the gas inlet of the carbon dioxide icing machine system for deep removal of hydrocarbons, sulfides and / or nitrogen oxides from carbon dioxide gas. A carbon dioxide icing system is used to liquefy carbon dioxide gas after it has been dehydrogenated and purified. A carbon dioxide distillation column is used to purify liquid carbon dioxide through distillation. Liquid carbon dioxide buffer tank; and Carbon dioxide vaporizer.

2. The lime kiln tail gas carbon dioxide recovery and purification system based on membrane separation and multi-stage adsorption according to claim 1, characterized in that, The preprocessing unit includes: Dust collectors are used to remove dust from exhaust gases; At least one stage of cooler is used for deep cooling of the exhaust gas after dust removal; A gas-liquid separator is used to separate condensate; and Pre-dehydration purification towers are used to perform deep dehydration and / or removal of sulfides and nitrogen oxides from dehydrated exhaust gases.

3. The lime kiln tail gas carbon dioxide recovery and purification system based on membrane separation and multi-stage adsorption according to claim 1, characterized in that, The hollow fiber membrane module is a membrane module consisting of at least two stages connected in series.

4. The lime kiln tail gas carbon dioxide recovery and purification system based on membrane separation and multi-stage adsorption according to claim 1, characterized in that, The three-stage pressure swing adsorption tower is filled with carbon molecular sieves and 13X molecular sieves.

5. The lime kiln tail gas carbon dioxide recovery and purification system based on membrane separation and multi-stage adsorption according to claim 1, characterized in that, The high-efficiency hydrocarbon removal and impurity removal device adopts activated carbon adsorption, molecular sieve adsorption, or catalytic oxidation technology.

6. The lime kiln tail gas carbon dioxide recovery and purification system based on membrane separation and multi-stage adsorption according to claim 1, characterized in that, The exhaust gas recirculation system includes: A low-concentration exhaust gas buffer tank is used to collect the carbon dioxide-containing exhaust gas discharged from the adsorption and purification system; and A reflux booster fan is used to pressurize the exhaust gas in the low-concentration exhaust gas buffer tank and send it back to the inlet of the membrane separation system.

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