Double-tower carbon capture system based on negative pressure steam purging circulation

Abstract

The invention relates to a double-tower carbon capture system based on negative pressure steam purge cycle, which comprises a desorption unit (1), a gas inlet unit (2), an adsorption tower unit (3), a temperature control unit (4), a negative pressure control unit (5) and a control system (6), the adsorption tower unit (3) comprises a first adsorption tower (A-101) and a second adsorption tower (B-101), the desorption unit (1) comprises a steam generator (ZQ-1), and the steam generator (ZQ-1) comprises a steam generator (ZQ-2). The steam generator (ZQ-1) is connected in parallel with the first adsorption tower (A-101) and the second adsorption tower (B-101) and introduces steam as a purging medium; the gas inlet unit (2), the temperature control unit (4) and the negative pressure control unit (5) are respectively connected in parallel with the first adsorption tower (A-101) and the second adsorption tower (B-101). Compared with the prior art, the process flow and equipment can remarkably enhance the mass transfer efficiency in the adsorption and desorption process, shorten the circulation time and improve the stability of the adsorbent, so that the total energy consumption of the DAC system is effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of atmospheric carbon dioxide capture technology, specifically relating to a device and corresponding process for directly capturing carbon dioxide from ambient air (Direct Air Capture, DAC), and particularly a system and method based on adsorption-desorption cycle and using steam-assisted regeneration to reduce energy consumption. Background Technology

[0002] Direct air capture (DAC) technology is crucial for addressing climate change and achieving negative emissions. However, the main obstacle to its large-scale application lies in its high energy consumption and operating costs. Due to the extremely low CO2 concentration in ambient air (approximately ~420 ppm), capture systems need to process large amounts of gas, resulting in persistently high energy consumption per unit weight of CO2 captured.

[0003] Currently, adsorption, especially temperature-variable vacuum adsorption (TVSA) cycle, is one of the mainstream technologies in the DAC field. Its typical process includes: at near-ambient temperature, ambient air is passed through a bed of solid adsorbent (such as amine-functionalized adsorbent material), where CO2 is selectively adsorbed; after adsorption saturation, the CO2 is desorbed by heating the bed and drawing a vacuum, thereby regenerating the adsorbent and releasing a high-concentration CO2 product gas.

[0004] Although TVSA technology has certain advantages over other methods, its energy consumption remains significant. The main problems include: 1. High desorption energy consumption: To achieve deep desorption, the entire adsorbent bed and device need to be heated, resulting in high thermal energy consumption. At the same time, maintaining a high vacuum environment requires continuous vacuum pump power consumption.

[0005] 2. Slow desorption kinetics: Under simple heating and negative pressure conditions, the mass transfer rate of CO2 desorbing from the adsorption site and diffusing into the main gas flow is slow, which prolongs the desorption cycle and limits the production capacity of the device.

[0006] 3. The contradiction between purity and energy consumption: To improve the purity of CO2 product gas, a higher vacuum or a longer desorption time is often required, which further exacerbates the energy consumption problem.

[0007] Root cause analysis of existing technical problems: The core issue lies in the limited desorption driving force of traditional TVSA cycles. Heating primarily provides the energy to break the chemical bonds between CO2 and the adsorbent, while vacuum is mainly used to reduce the partial pressure of CO2, thereby disrupting the adsorption equilibrium. However, both methods have limited effectiveness in enhancing mass transfer, making the desorption process the "bottleneck" of the entire cycle, resulting in low efficiency and concentrated energy consumption.

[0008] To address the shortcomings of existing technologies, relevant research has proposed several improvement schemes. For example, patent document CN115475482A discloses a system coupling water capture and carbon dioxide capture, which uses a desorption medium for regeneration. However, the introduction of steam may cause condensation on the adsorbent surface, affecting material stability. Patent document CN101745288A discloses a multi-tower vacuum pressure swing temperature adsorption method, but its process involves pressure adsorption and high-temperature desorption, which would result in significant additional energy input in scenarios involving large volumes of gas, such as direct air capture. Patent document CN120344304A and non-patent documents (Bajamundi, CJE; Koponen, J.; Ruuskanen, V.; Elfving, J.; Kosonen, A.; Kauppinen, J.; Ahola, J. Capturing CO2 from Air: Technical Performance and Process Control Improvement. J. CO2 Util. 2019, 30, 232–239. https: / / doi.org / 10.1016 / j.jcou.2019.02.002) both mention the use of steam in the process, but the former focuses on the heat recovery system, while the latter only uses steam as an indirect heat exchange medium. Neither fully utilizes steam to directly participate in and enhance the desorption mass transfer process. Another non-patent literature (Zhu, X.; Ge, T.; Yang, F.; Wang, R. Design of Steam-Assisted Temperature Vacuum-Swing Adsorption Processes for Efficient CO2 Capture from Ambient Air. Renew. Sust. Energ. Rev. 2021, 137, 110651. https: / / doi.org / 10.1016 / j.rser.2020.110651) established a model for steam-assisted temperature-swing vacuum adsorption, but its model is based on fixed inlet conditions and does not fully consider the complex impact of dynamic changes in air composition and state parameters in the actual environment on process operation. It cannot solve the objective fact that the composition and state of ambient air change with time and space in actual operation.

[0009] Therefore, there is an urgent need in this field for a high-efficiency, low-energy direct air capture process that can significantly enhance the mass transfer efficiency of the desorption process, shorten the desorption time, and adapt to fluctuations in environmental conditions, thereby effectively reducing the total energy consumption of the DAC system. Summary of the Invention

[0010] The present invention aims to overcome at least one of the defects of the prior art and provide a dual-tower carbon capture system based on negative pressure steam purging cycle, which significantly enhances the mass transfer efficiency of the adsorption and desorption process, shortens the cycle time, and improves the stability of the adsorbent, thereby effectively reducing the total energy consumption of the DAC system.

[0011] The objective of this invention can be achieved through the following technical solution: a dual-tower carbon capture system with negative pressure steam purging circulation, comprising a desorption unit, an air inlet unit, an adsorption tower unit, a temperature control unit, a negative pressure control unit, and a control system. The adsorption tower unit includes a first adsorption tower and a second adsorption tower. The desorption unit includes a steam generator connected in parallel to the first and second adsorption towers, introducing steam as the purging medium. By introducing a temperature and humidity control unit at the front end of the adsorption tower unit, the incoming air is maintained at the optimal state for adsorbent operation, thereby improving the CO2 capture effect.

[0012] The air intake unit, temperature control unit, and negative pressure control unit are connected in parallel to the first adsorption tower and the second adsorption tower, respectively. The control system controls the pressure and temperature inside the first adsorption tower and the second adsorption tower, as well as the air intake volume and temperature and humidity of the air intake unit.

[0013] Furthermore, the first and second adsorption towers are also connected to nitrogen purging pipelines; switching between air and nitrogen purging adjusts the water vapor content in the desorbed gas while ensuring desorption efficiency, and the nitrogen purging path is the same as the steam purging path.

[0014] Furthermore, the steam generator heats the liquid water under ambient conditions to steam at a pressure of 0.1~0.4MPa and a temperature of 100~140℃, which is then introduced into the first adsorption tower and the second adsorption tower for steam purging.

[0015] Furthermore, the air intake unit includes an air compressor, a drying tube, and an atomizer connected in sequence; ambient air passes through the air compressor, the drying tube, and the atomizer, and the air condition is controlled to be 10~40℃ and 20~70%RH by the temperature control unit in conjunction with the drying tube and the atomizer, before entering the first adsorption tower and the second adsorption tower.

[0016] Furthermore, the first and second adsorption towers are filled with solid adsorbents, and oil bath jackets are arranged around them to control the temperature inside the towers.

[0017] Furthermore, the temperature control unit includes a first circulating oil bath, a second circulating oil bath, a third circulating oil bath, and a fourth circulating water bath, wherein the first circulating oil bath and the second circulating oil bath are respectively connected to the oil bath jackets of the first adsorption tower and the second adsorption tower. The first circulating oil bath cools the first and second adsorption towers. The second circulating oil bath heats the first and second adsorption towers; The third circulating oil bath is connected to the intake unit and controls the air temperature output by the intake unit to be 10~40℃. The fourth circulating water bath is connected to the steam generator to keep the steam warm.

[0018] Furthermore, the negative pressure control unit includes a vacuum pump connected to the outlet pipes of the first adsorption tower and the second adsorption tower, and the outlet pipes are also equipped with a condenser and a drying pipe.

[0019] Furthermore, the vacuum pump is equipped with a pressure stabilizing valve to pump the adsorption tower to 0.01~0.2 bar before desorption; The condenser separates the humid CO2 gas that comes out of the two adsorption towers during the vapor desorption process. The drying tube dehumidifies the separated CO2 gas.

[0020] Furthermore, the control system controls the pressure inside the first and second adsorption towers, and simultaneously controls the temperature of each oil bath and water bath in the temperature control unit, as well as the spray volume of the atomizer in the air intake unit.

[0021] Furthermore, through the coordinated control of temperature, pressure, humidity, and steam flow, fully automatic, multi-mode cyclic operation can be achieved to adapt to different environmental conditions and adsorbent characteristics.

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention introduces steam as the purging medium into the traditional TVSA cycle, significantly enhancing desorption mass transfer efficiency, shortening desorption time, and reducing desorption energy consumption. The condensation heat of the steam can also be used to provide some of the heat energy required for desorption, further improving energy efficiency.

[0023] This invention reduces the energy required for adsorption by pumping the adsorption tower to 0.01~0.2 bar before desorption and preheating the adsorbent using a jacketed oil bath. The process involves steam desorption of the adsorbent at 60°C. Subsequently, steam is introduced while maintaining the same negative pressure inside the adsorption tower. The negative pressure and steam medium promote the desorption kinetics of the adsorbent, significantly improving the desorption effect, shortening the cycle time, and suppressing the condensation of water vapor on the adsorbent surface, thereby greatly extending the adsorbent's lifespan.

[0024] This invention preheats the adsorbent using a jacketed oil bath before desorption, then introduces steam while maintaining negative pressure within the adsorption tower. This direct steam medium promotes the desorption kinetics of the adsorbent, significantly improving its desorption efficiency and shortening the cycle time. The use of an oil bath medium for non-direct contact heating of the adsorbent effectively prevents water vapor from condensing on the adsorbent surface and damaging its structure, thus reducing the system's CO2 capture capacity. Temperature and humidity control of the air before CO2 adsorption ensures the adsorbent operates in an optimal environment, improving its efficiency.

[0025] The air intake unit of this invention includes the function of controlling the temperature and humidity of the incoming air. It can flexibly adjust the state and moisture content of the incoming air for the optimal adsorption conditions of different adsorbents, so that the adsorbent can be maintained to work under the best conditions.

[0026] This invention significantly enhances desorption mass transfer efficiency, shortens desorption time, and reduces desorption energy consumption. The heat of condensation of steam can also be used to provide part of the heat energy required for desorption, further improving energy efficiency. It allows for switching between air / nitrogen purging gases, adjusting the water vapor content in the desorption gas while ensuring desorption efficiency and saving steam consumption. Attached Figure Description

[0027] Figure 1 is a simplified modular diagram of the system of the present invention; Figure 2 is a simplified diagram of the DAC model; Figure 3 is a simplified diagram of the desorption unit model; Figure 4 is a simplified diagram of the intake unit model; Figure 5 is a simplified diagram of the temperature control unit model; Figure 6 is a simplified diagram of the adsorption tower unit model; Figure 7 is a simplified diagram of the negative pressure control unit model; Figure 8 shows the temperature, pressure, and humidity curves inside the three sets of -85kPa, 60°C steam-assisted variable temperature vacuum circulation adsorption towers when the equipment of the present invention is running automatically under no-load conditions (P8 is the pressure inside the adsorption tower, RH2 is the humidity inside the adsorption tower, and T10 is the temperature inside the adsorption tower). Figure 9 shows the CO2 desorption curves under four typical desorption conditions (s-TVSA condition with steam-assisted temperature variable vacuum desorption; N2-TVSA condition with nitrogen-assisted temperature variable vacuum desorption; TVSA condition with temperature variable vacuum desorption; and TCSA condition with nitrogen-assisted temperature variable desorption)). Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0029] Existing temperature-controlled vacuum adsorption (TVSA)-based DAC systems typically rely solely on increasing temperature and decreasing pressure to drive CO2 desorption during the desorption phase. This results in slow desorption rates, high thermal energy consumption, and high vacuum maintenance costs. This invention introduces steam as a purge medium, coupled with a TVSA cycle, to form a novel steam-assisted temperature-controlled vacuum adsorption (S-TVSA) process. This aims to significantly improve desorption mass transfer efficiency, reduce regeneration temperature and vacuum requirements, and thus significantly reduce energy consumption and operating costs per unit of CO2 captured.

[0030] During DAC operation, differences in ambient air temperature and humidity significantly affect the adsorption performance of the adsorbent, resulting in substantial variations in the device's capture efficiency over time and space. This invention addresses this by introducing a temperature and humidity control unit at the front end of the adsorbent, maintaining the incoming airflow at the optimal operating conditions for the adsorbent and thus improving CO2 capture efficiency.

[0031] like Figure 1-2 As shown, the negative pressure steam purging cycle dual-tower carbon capture system of the present invention mainly includes six subsystems: a desorption unit 1, an air inlet unit 2, an adsorption tower unit 3, a temperature control unit 4, a negative pressure control unit 5, and a control system 6. The adsorption tower unit 3 includes a first adsorption tower A-101 and a second adsorption tower B-101. The desorption unit 1, air inlet unit 2, temperature control unit 4, and negative pressure control unit 5 are respectively connected in parallel to the first adsorption tower A-101 and the second adsorption tower B-101. The desorption unit 1 provides steam and nitrogen for desorption. After the air passes through the intake unit 2 and its temperature and humidity are controlled, it enters the first adsorption tower A-101 and the second adsorption tower B-101. The temperature control unit 4 is responsible for controlling the temperature inside the first adsorption tower A-101 and the second adsorption tower B-101. The negative pressure control unit 5 is connected to the separation and collection unit 7. During desorption, the negative pressure control unit 5 is responsible for providing a certain negative pressure inside the first adsorption tower A-101 and the second adsorption tower B-101, and for extracting the desorbed CO2 from the first adsorption tower A-101 and the second adsorption tower B-101 into the separation and collection unit 7. Each connecting pipeline is equipped with multiple valves, temperature and humidity sensors, and pressure sensors, which are connected to the control system 6. This system can monitor the system's operating status, adjust valve openings and closings, and control the set parameters such as temperature, humidity, pressure, and flow rate in the desorption unit 1, the intake unit 2, and the negative pressure control unit 5.

[0032] Specifically, desorption unit 1 includes steam generator ZQ-1, such as... Figure 2-3As shown, steam generator ZQ-1 is connected to a main pipeline. This main pipeline is equipped with valve QV1 (responsible for controlling steam inflow, closed when steam is not in use and open when steam is in use) and valve QV3 (acting as a safety valve for steam venting, closed when steam desorption is needed and open when steam desorption is not needed). A branch pipeline connects the two pipelines in parallel to the first adsorption tower A-101 and the second adsorption tower B-101. The pipeline connecting to the first adsorption tower A-101 is equipped with valve 0104A. Steam generator ZQ-1 is connected to the second adsorption tower B-101... The pipeline is equipped with valve 0203B; valves 0109A and 0208B are respectively installed on the outlet pipelines of the first adsorption tower A-101 and the second adsorption tower B-101; the first adsorption tower A-101 and the second adsorption tower B-101 are also connected to a nitrogen purging pipeline (nitrogen can be used as a backup purging gas, replacing steam or being introduced into the first adsorption tower A-101 and the second adsorption tower B-101 together with steam for desorption), and valve 0102A is installed on this pipeline. By switching between air and nitrogen purging, the water vapor content in the desorbed gas can be adjusted while ensuring desorption efficiency.

[0033] Liquid water under ambient conditions is heated to steam at a pressure of 0.1~0.4 MPa and a temperature of 100~140℃ using steam generator ZQ-1. When steam is not used, it can be directly discharged and collected as liquid water through valves QV1 and QV3. When steam desorption is used, steam enters the first adsorption tower A-101 and the second adsorption tower B-101 through valves 0104A and 0203B, carrying the desorbed CO2 through valves 0109A and 0203B. 8B leaves the adsorption tower; when the steam flows in the pipeline, it is kept warm by the oil bath medium of the temperature control unit 4 (in a preferred embodiment, the fourth circulating water bath HW-4); in addition to steam, the desorption unit 1 can also be purged with nitrogen. The nitrogen gas is introduced through valve 0102A, and after the temperature is controlled by the fourth circulating water bath HW-4, it enters the first adsorption tower A-101 and the second adsorption tower B-101, and then leaves the adsorption tower through valves 0109A and 0208B. The path is the same as the steam path.

[0034] The air intake unit 2: as follows Figure 2 and 4 As shown, it includes an air compressor YSJ-1, a drying pipe GLQ-1, a valve QV-2, and an atomizer JLB-1 connected in sequence, and then connected to the first adsorption tower A-101 and the second adsorption tower B-101 through parallel pipes, and valves 0110A and 0209B are provided on the connecting pipes; Ambient air is compressed by air compressor YSJ-1, passes through drying pipe GLQ-1, valve QV-2, and atomizer JLB-1, and is kept warm by the oil bath medium in the third circulating oil bath HW-3 of temperature control unit 4, resulting in air with a state of 10~40℃ and 20~70%RH. This air then enters the first adsorption tower A-101 and the second adsorption tower B-101 through valves 0110A and 0209B. After passing through the adsorbent in the towers, it leaves the adsorption towers through valves 0103A and 0202B, with the exhaust gas directly discharged into the air. The humidity of the air is controlled collaboratively by drying pipe GLQ-1 for dehumidification and atomizer JLB-1 for humidification. The intake unit is equipped with valve QV-9 to discharge liquid water introduced into the pipeline due to humidification.

[0035] The adsorption tower 3: as follows Figure 6As shown, the first adsorption tower A-101 and the second adsorption tower B-101 are filled with solid adsorbent with a volume of less than 6cm*6cm*25cm for selective adsorption of CO2 in ambient air. The first adsorption tower A-101 and the second adsorption tower B-101 are connected to the air inlet unit 2 through valves 0110A, 0209B, 0103A, and 0202B, respectively, and to the desorption unit 1 through valves 0104A and 0203B, and to the negative pressure control unit 5 through valves 0109A and 0208B. Oil bath jackets (first circulating oil bath HW-1 and second circulating oil bath HW-2) are arranged around the two adsorption towers to achieve temperature control inside the adsorption towers. The temperature of the oil bath is adjusted by the temperature control unit 4. Solid adsorbents are commercially available products (such as Lewatit VP OC 1065, A110 molecular sieve, 5A molecular sieve, amine-based mesoporous materials, etc. Adsorbents can be in powder, granular, honeycomb, or other forms) or products prepared by methods reported in existing technologies, such as PEI-supported mesoporous metal oxides (Reference: Zhu, X.; Ge, T.; Yang, F.; Lyu, M.; Chen, C.; O'Hare, D.; Wang, R. Efficient CO2 Capture from Ambient Air with Amine-Functionalized Mg–Al Mixed Metal Oxides. J. Mater. Chem. A 2020, 8, 16421–16428. https: / / doi.org / 10.1039 / D0TA05079B.), and amine-functionalized honeycomb adsorbents (Reference: Shao, Q.; Gan, Z.; Ge, B.; Liu, X.; Chen, C.; O'Hare, D.; Zhu, X. 3D Printing of Poly(Ethyleneimine)-Functionalized Mg-Al Mixed Metal Oxide Monoliths for Direct Air Capture of CO2. Journal of Energy Chemistry 2024, 96, 491–500. https: / / doi.org / 10.1016 / j.jechem.2024.05.015.), resin materials (see product: https: / / lanxess.com / en-us / products-and-brands / products / l / lewatit--vp-oc-1065), etc.

[0036] The temperature control unit 4: as follows: Figure 2 and 5 As shown, it includes a first circulating oil bath HW-1, a second circulating oil bath HW-2, a third circulating oil bath HW-3, and a fourth circulating water bath HW-4; wherein, the first circulating oil bath HW-1 and the second circulating oil bath HW-2 are respectively connected to the oil bath jackets of the first adsorption tower A-101 and the second adsorption tower B-101. The first circulating oil bath HW-1 provides cold oil to cool the first adsorption tower A-101 and the second adsorption tower B-101; the second circulating oil bath HW-2 provides hot oil to heat the first adsorption tower A-101 and the second adsorption tower B-101; the third circulating oil bath HW-3 is connected to the air inlet unit 2 and provides oil at 10~40℃ to control the air temperature; the fourth circulating water bath HW-4 is connected to the steam generator ZQ-1 and provides water to keep the steam warm; the temperature control unit also includes valves 0105A, 0106A, and 0107A. Valves 0108A, 0204B, 0205B, 0206B, and 0207B control the temperature of the high and low temperature oil bath. Opening valves 0105A and 0108A indicates heating of the first adsorption tower A-101; opening valves 0204B and 0207B indicates heating of the second adsorption tower B-101; opening valves 0106A and 0107A indicates cooling of the first adsorption tower A-101; and opening valves 0205B and 0206B indicates cooling of the second adsorption tower B-101.

[0037] The negative pressure control unit 5: such as Figure 7 As shown, it includes a vacuum pump ZKB-1; the vacuum pump ZKB-1 is connected to the outlet pipes of the first adsorption tower A-101 and the second adsorption tower B-101, and the outlet pipes are also equipped with a condenser FLG-1 and a drying pipe.

[0038] The gas inside the two adsorption towers passes through valves 0109A and 0208B respectively, and is separated into water and CO2 by condenser FLG-1. The gas then passes through a drying tube and is extracted by vacuum pump ZKB-1, which is equipped with a pressure regulating valve to adjust the upstream pressure. The negative pressure control unit 5 is used to extract residual gas from the adsorption towers before and after desorption, and to control the negative pressure environment inside the towers during the desorption stage. The function of condenser FLG-1 is to separate the humid CO2 gas exiting the two adsorption towers during vapor desorption. The cooled liquid water is directly discharged through valve 0210B. The CO2 is further dehumidified through the drying tube to obtain high-purity CO2 gas, which can be collected through valve QV-4. The pressure regulating valve regulates and controls the pressure inside the adsorption towers, with an adjustment range of 0.01~1.0 bar.

[0039] The control system 6 uses a commercially available Mitsubishi GT2715-XTBD control terminal to send and read signals.

[0040] The pressure regulating valve of vacuum pump ZKB-1 is directly adjusted by controlling the PLC panel and program, thereby controlling the pressure inside the first adsorption tower A-101 and the second adsorption tower B-101; the temperature of each oil bath / water bath (first circulating oil bath HW-1, second circulating oil bath HW-2, third circulating oil bath HW-3, and fourth circulating water bath HW-4) in temperature control unit 4 is controlled, thereby controlling the temperature of steam, air, first adsorption tower A-101 and second adsorption tower B-101; the spray volume of atomizer JLB-1 in air intake unit 2 is controlled, thereby controlling the humidity of the air; the control system has a control panel on which the operation of each unit can be controlled; the control system has an automatic operation function, and the opening and closing of each valve can be set on the panel to make each unit operate automatically.

[0041] II. Work Process (Taking the S-TVSA circulation in the first adsorption tower A-101 as an example) 1. Adsorption stage: Set the temperature of the third circulating oil bath HW-3 and the spray flow rate of the atomizer JLB-1 to obtain air under certain conditions (10~40℃, 20~70%RH), and set the air intake flow rate (5~60Nm). 3 After ( / h), open valves 0110A and 0103A to introduce gas into the first adsorption tower A-101, where CO2 is captured by the adsorbent.

[0042] 2. Preheating and vacuuming stage: Close valves 0110A and 0103A, open valves 0109A and 0208B to start vacuum pump ZKB-1, set the negative pressure value, reduce the pressure inside the first adsorption tower A-101 to (0.01~0.10 bar), and extract the residual gas inside the tower; at the same time, set the temperature of the second circulating oil bath HW-2 to preheat the adsorption tower to the target temperature (60~140℃).

[0043] 3. Steam purge and desorption stage: Set the pressure regulator valve to control the pressure inside the tower at 0.2~1.0 bar, and set the steam flow rate (0~20 g / min). Open valves 0104A and 0109A to allow steam to enter the first adsorption tower A-101. The steam, carrying the desorbed CO2, leaves the adsorption tower and enters the condenser FLG-1 to complete gas-liquid separation. The gaseous CO2 is then dehumidified through the drying tube and extracted by the vacuum pump ZKB-1 for final collection. The steam serves both as a heat source to provide some of the heat required for desorption and as a purge medium to reduce the partial pressure of CO2 and accelerate desorption kinetics.

[0044] 4. Cooling and Preparation Stage: Close valves 0104A and 0109A to stop steam supply; set the temperature of the first circulating oil bath HW-1 to cool the first adsorption tower A-101 to near ambient temperature (10~40℃); set the pressure of the pressure regulating valve to reduce the pressure inside the tower to (0.01~0.10 bar), and extract the participating gas from the tower. One cycle is completed.

[0045] The above system can perform fully automatic, multi-mode cyclic operation such as single-tower negative pressure steam purging, double-tower negative pressure steam purging, or single-tower nitrogen-assisted purging, adapting to different environmental conditions and adsorbent characteristics. The following is a description of specific embodiments.

[0046] Example 1 I. Single-tower negative pressure steam purging process control flow Step (1) Adsorption Under conditions of temperature 10~40℃, humidity 20~80%RH, and atmospheric pressure, CO2 in the air was directly adsorbed, with a concentration of approximately 400~1000ppm. In this embodiment, the adsorbent selected was the amine-functionalized hydrotalcite reported in the literature (Zhu, X.; Ge, T.; Yang, F.; Lyu, M.; Chen, C.; O'Hare, D.; Wang, R. Efficient CO2 Capture from Ambient Air with Amine-Functionalized Mg–Al Mixed Metal Oxides. J. Mater.Chem. A 2020, 8 (32), 16421–16428.). The temperatures of the first circulating oil bath HW-1 and the second circulating oil bath HW-2 were set to 10~40℃ as required, maintaining the air and adsorbent temperatures at 10~40℃. The flow rate of the metering pump JLB-1 was set to 0~50mL / min as required, controlling the air humidity to 20~80%RH.

[0047] Operating equipment and valves: Valve 0110A, Valve 0103A, First circulating oil bath HW-1, Second circulating oil bath HW-2; Step (2) Preheating: The temperature of the second circulating oil bath HW-2 is set to 60~80℃, and the adsorbent temperature is indirectly heated to 60~80℃ using the oil bath. At the same time, the pressure regulating valve is set to 0.01~0.2 bar, and the residual gas in the first adsorption tower A-101 is extracted using the vacuum pump ZKB-1.

[0048] Operating equipment and valves: Valve 0109A, Second Circulating Oil Bath HW-2, Vacuum Pump ZKB-1; Step (3) Desorption: Steam is introduced for purging. The pressure regulating valve is set to 0.2 bar. The steam pressure is controlled at 0.2 bar by the vacuum pump ZKB-1 and the pressure regulating valve. The temperature of the fourth circulating water bath HW-4 is set to 60~80℃ to maintain the energy of the negative pressure steam. The steam and the desorbed CO2 will be drawn together to the condenser to complete gas-liquid separation. At the same time, the temperature of the second circulating oil bath HW-2 is maintained at 60~80℃.

[0049] Operating equipment and valves: Valve QV-1, Valve 0104A, Valve 0109A, Second Circulating Oil Bath HW-2, Fourth Circulating Water Bath HW-4, Vacuum Pump ZKB-1; Step (4) Cooling: Stop the steam supply, set the pressure regulating valve to 0.01~0.2 bar, and use vacuum pump ZKB-1 to extract the residual gas in the first adsorption tower A-101. Set the temperature of the first circulating oil bath HW-1 to 10~40℃, and use the oil bath to indirectly cool the temperature of the adsorbent to 10~40℃.

[0050] Operating equipment and valves: Valve 0109A, first circulating oil bath HW-1, vacuum pump ZKB-1; II. Control Flow of Double-Tower Negative Pressure Steam Purging Process Step (1) First adsorption tower A-101, second adsorption tower B-101 First adsorption tower A-101: Under conditions of temperature 10~40℃, humidity 20~80%RH, and atmospheric pressure, it directly adsorbs CO2 from the air, with a concentration of approximately 400~1000ppm. The first circulating oil bath HW-1 and the third circulating oil bath HW-3 are set to a temperature of 10~40℃ as needed, maintaining the air and adsorbent temperatures at 10~40℃. The metering pump JLB-1 is set to a flow rate of 0~50mL / min as needed, controlling the air humidity at 20~80%RH. Second adsorption tower B-101: Steam is introduced for purging. The pressure regulating valve is set to 0.2 bar. The steam pressure is controlled at 0.2 bar by the vacuum pump ZKB-1 and the pressure regulating valve. The temperature of the fourth circulating water bath HW-4 is set to 60~80℃ to maintain the energy of the negative pressure steam. The steam and the desorbed CO2 will be drawn together to the condenser to complete gas-liquid separation. At the same time, the temperature of the second circulating oil bath HW-2 is maintained at 60~80℃.

[0051] Operating equipment and valves: Valve 0110A, Valve 0103A, Valve QV-1, Valve 0202B, Valve 0209B, Valve ZKB-1, and all circulating oil baths.

[0052] Step (2): Preheat the first adsorption tower A-101 and cool the second adsorption tower B-101. First adsorption tower: The second circulating oil bath HW-2 is set at a temperature of 60~80℃ to indirectly heat the adsorbent to 60~80℃. At the same time, a pressure regulating valve is set at 0.01~0.2 bar, and a vacuum pump ZKB-1 is used to extract the residual gas in the adsorption tower.

[0053] Second adsorption tower B-101: Stop the steam supply, set the pressure regulating valve to 0.01~0.2 bar, and use vacuum pump ZKB-1 to extract the residual gas in the adsorption tower. Set the temperature of the first circulating oil bath HW-1 to 10~40℃, and use the oil bath to indirectly cool the adsorbent to 10~40℃.

[0054] Operating equipment and valves: Valve 0109A, Valve 0208B, First circulating oil bath HW-1, Second circulating oil bath HW-2, Vacuum pump ZKB-1; Step (3) First adsorption tower A-101, second adsorption tower B-101 First adsorption tower: Steam is introduced for purging. The pressure regulating valve is set to 0.2 bar. The steam pressure is controlled at 0.2 bar by the vacuum pump ZKB-1 and the pressure regulating valve. The fourth circulating water bath HW-4 is set to a temperature of 60~80℃ to maintain the energy of the negative pressure steam. The steam and the desorbed CO2 will be drawn together to the condenser to complete gas-liquid separation. At the same time, the temperature of the second circulating oil bath HW-2 is maintained at 60~80℃.

[0055] The second adsorption tower directly adsorbs CO2 from the air at a concentration of approximately 400-1000 ppm under conditions of temperature (10-40℃), humidity (20-80%RH), and atmospheric pressure. The first circulating oil bath (HW-1, 3) is set to a temperature of 10-40℃ to maintain the air and adsorbent temperatures within this range. The metering pump (JLB-1) is set to a flow rate of 0-50 mL / min to control the air humidity at 20-80%RH.

[0056] Operating equipment and valves: Valve QV-1, Valve 0104A, Valve 0109A, Valve 0202B, Valve 0209B, all circulating oil baths, vacuum pump ZKB-1; Step (4) Cooling the first adsorption tower and preheating the second adsorption tower. First adsorption tower: Stop the steam supply, set the pressure regulating valve to 0.01~0.2 bar, and use vacuum pump ZKB-1 to extract the residual gas in the adsorption tower. Set the temperature of the first circulating oil bath HW-1 to 10~40℃, and use the oil bath to indirectly cool the adsorbent to 10~40℃.

[0057] Second adsorption tower: The temperature of the second circulating oil bath HW-2 is set at 60~80℃, and the adsorbent is indirectly heated to 60~80℃ using the oil bath. At the same time, the pressure regulating valve is set at 0.01~0.2 bar, and the residual gas in the adsorption tower is extracted using the vacuum pump ZKB-1.

[0058] Operating equipment and valves: Valve 0109A, Valve 0208B, First circulating oil bath HW-1, Second circulating oil bath HW-2, Vacuum pump ZKB-1.

[0059] III. Single-tower nitrogen-assisted purging process control flow Step (1) Adsorption Under conditions of temperature 10~40℃, humidity 20~80%RH, and atmospheric pressure, CO2 in the air is directly adsorbed, with a concentration of approximately 400~1000ppm. The second circulating oil bath (HW-2) and the fourth circulating oil bath (HW-4) are set to temperatures of 10~40℃ as needed to maintain the air and adsorbent temperatures within this range. The metering pump (JLB-1) is set to a flow rate of 0~50mL / min as needed to control the air humidity at 20~80%RH.

[0060] Operating equipment and valves: Valve 0110A, Valve 0103A, First Circulating Oil Bath HW-1, Third Circulating Oil Bath HW-3; Step (2) Preheating: The temperature of the first circulating oil bath HW-1 is set to 60~80℃, and the adsorbent is indirectly heated to 60~80℃ using the oil bath. At the same time, the pressure regulating valve is set to 0.01~0.2 bar, and the residual gas in the adsorption tower is extracted using the vacuum pump ZKB-1.

[0061] Operating equipment and valves: Valve 0109A, Second Circulating Oil Bath HW-2, Vacuum Pump ZKB-1; Step (3) Desorption: Nitrogen gas is introduced for purging. The pressure regulating valve is set to 0.2 bar. The steam pressure is controlled at 0.2 bar by the vacuum pump ZKB-1 and the pressure regulating valve. The temperature of the third circulating oil bath HW-3 is set to 60~80℃ to maintain the energy of the negative pressure steam. The steam and the desorbed CO2 will be drawn together to the condenser to complete gas-liquid separation. At the same time, the temperature of the first circulating oil bath HW-1 is maintained at 60~80℃.

[0062] Operating equipment and valves: Valve 0102A, Valve 0104A, Valve 0109A, Second Circulating Oil Bath HW-2, Fourth Circulating Oil Bath HW-4, Vacuum Pump ZKB-1; Step (4) Cooling: Stop the steam supply, set the pressure regulator valve to 0.01~0.2 bar, and use vacuum pump ZKB-1 to extract the residual gas in the adsorption tower. Set the temperature of the second circulating oil bath HW-2 to 10~40℃, and use the oil bath to indirectly cool the adsorbent to 10~40℃.

[0063] Operating equipment and valves: Valve 0109A, first circulating oil bath HW-1, vacuum pump ZKB-1.

[0064] Figure 8 The above system automatically operates under no-load conditions, and the internal temperature, pressure, and humidity curves of three sets of -85kPa, 60℃ steam-assisted variable temperature vacuum circulation adsorption towers are shown in the figure (P8 in the figure is the pressure inside the adsorption tower, RH2 is the relative humidity inside the adsorption tower, and T10 is the temperature inside the adsorption tower). The figure shows the temperature, pressure, and humidity curves inside the first adsorption tower A-101 under simulated -85 kPa, 60°C steam-assisted variable-temperature vacuum circulation. The circulation process consists of four steps: (1) 30min adsorption: Open valves 0110A and 0103A, and set the air flow rate to 10Nm. 3 / h, first circulating oil bath HW-1 25℃, metering pump JLB-1 10mL / min, to control the air and tower conditions during adsorption at 25±1℃ (T10) and 50±3%RH (RH2). (2) 30min preheating: Open valve 0109A and vacuum pump ZKB-1, set pressure stabilizing valve to 0.15bar and second circulating oil bath HW-2 to 60℃, so as to achieve the preheating of adsorbent to 0.15bar and 60℃, extract residual gas in adsorption tower, and avoid introducing steam to condense on the surface of adsorbent; (3) 30 min desorption: Open valve 0104A, valve 0109A, vacuum pump ZKB-1, set the second circulating oil bath HW-2, the fourth circulating oil bath HW-4 60℃, and the pressure stabilizing valve 0.15 bar, and introduce negative pressure steam to desorb CO2. Control the steam and the state inside the tower during desorption at 0.15±0.02 bar (P8) and 60±1℃ (T10). (4) 30 min cooling: Open valve 0109A and vacuum pump ZKB-1, set the first circulating oil bath HW-1 to 25℃, extract the participating gas in the adsorption tower, let the adsorbent return to 25℃, and prepare to start the next cycle.

[0065] The experiment was repeated three times, from Figure 8As can be seen, during the adsorption stage, the temperature T10 can be controlled between 25±1℃, the humidity is ultimately maintained at 50±3%, and the pressure is at atmospheric pressure. During the preheating stage, the tower temperature T10 can rise from 25℃ to 60℃ within 5 minutes and stabilize at 60±1℃, while the tower pressure P8 drops to the predetermined value within 1 minute and stabilizes at -85±2 kPa. During the desorption stage, after steam is introduced, the tower temperature T10 stabilizes at 60±1℃, and the tower pressure P8 stabilizes at -85±2 kPa. During the cooling stage, the tower temperature T10 can drop from 60℃ to 25℃ within 5 minutes and stabilize at 25±1℃, while the tower pressure P8 is maintained below -80 kPa to fully remove any residual water vapor in the tower. The above three sets of parallel experiments demonstrate the stability and repeatability of the system's automatic cyclic operation.

[0066] Figure 9 The CO2 desorption curves of the above system under four typical desorption conditions are shown (s-TVSA condition with steam-assisted temperature variable vacuum desorption; N2-TVSA condition with nitrogen-assisted temperature variable vacuum desorption; TVSA condition with temperature variable vacuum desorption; and TCSA condition with nitrogen-assisted temperature variable desorption). Should Figure 9 This section compares the desorption kinetics under different desorption conditions. The adsorbent material was amine-functionalized hydrotalcite reported in the literature (Zhu, X.; Ge, T.; Yang, F.; Lyu, M.; Chen, C.; O'Hare, D.; Wang, R. Efficient CO2 Capture from Ambient Air with Amine-Functionalized Mg–Al Mixed Metal Oxides. J. Mater.Chem. A 2020, 8 (32), 16421–16428.). The specific operation is as follows: (1) Place the adsorbent into the adsorption tower; (2) Adsorption: Open valves 0110A and 0103A, set the CO2 gas mixing (400ppm) flow rate to 0.1L / min, and consider the adsorption to be saturated when the CO2 concentration meter reading at the outlet of the adsorption tower shows 90% of the inlet CO2 concentration reading; (3) Desorption: TCSA operating condition: Open valves 0102A, 0104A, and 0109A, set the second circulating oil bath HW-2 and the fourth circulating oil bath HW-4 to 120℃, and introduce 0.1L / min of N2 to desorb CO2; TVSA operating condition: Open valve 0109A and vacuum pump ZKB-1, set the second circulating oil bath HW-2 to 120℃ and the pressure regulating valve to 0.10 bar, and directly desorb CO2; N2-TVSA operating condition: Open valves 0102A, 0104A, 0109A, and vacuum pump ZKB-1; set the second circulating oil bath HW-2 and the fourth circulating oil bath HW-4 to 120℃ and the pressure regulating valve to 0.10 bar; introduce 0.1 L / min of N2 to desorb CO2. s-TVSA operating condition: Open valves QV-1, 0104A, 0109A, and vacuum pump ZKB-1; set the second circulating oil bath HW-2 and the fourth circulating oil bath HW-4 to 120℃ and the pressure regulating valve to 0.10 bar; and introduce 0.1 L / min of water vapor to desorb CO2. (4) Complete the experiment, calculate the flow rate of CO2 at the outlet in the desorption step, and obtain the desorption curve of the adsorbent by combining the adsorbent mass.

[0067] from Figure 9 It can be seen that TVSA can only desorb about 50% of CO2 within 60 minutes. When nitrogen is used as an auxiliary purge gas (N2-TVSA and TCSA), the desorption rate increases significantly, and desorption can be completed in about 30 minutes. When steam is used as the desorption gas (S-TVSA), the desorption rate is further improved, and desorption can be completed within 8 minutes. Simple condensation is then sufficient to complete the separation, yielding high-purity CO2.

[0068] In summary, it can be seen that the present invention has the following significant advantages: 1. Steam-assisted desorption process: Based on the traditional TVSA cycle, steam is introduced as the purging medium, which significantly enhances desorption mass transfer efficiency, shortens desorption time, and reduces desorption energy consumption. The condensation heat of the steam can also be used to provide part of the heat energy required for desorption, further improving energy efficiency.

[0069] 2. Variable operating condition purging strategy (optional): Air / nitrogen or other gas purging can be switched to adjust the water vapor content in the desorbed gas while ensuring desorption efficiency and saving steam consumption.

[0070] 3. Integrated control system: Through multi-variable coordinated control (temperature, pressure, humidity, steam flow), it realizes fully automatic, multi-mode cyclic operation and adapts to different environmental conditions and adsorbent characteristics.

[0071] The above embodiments are intended to illustrate the present invention, not to limit it. Although preferred embodiments have been described in detail, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions without departing from the spirit and scope of the invention, and such modifications and substitutions all fall within the protection scope of the present invention. The above description of the embodiments is to facilitate understanding and use of the invention by those skilled in the art. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A dual-tower carbon capture system with negative pressure steam purging circulation, characterized in that, The dual-tower carbon capture system includes a desorption unit (1), an air inlet unit (2), an adsorption tower unit (3), a temperature control unit (4), a negative pressure control unit (5), and a control system (6). The adsorption tower unit (3) includes a first adsorption tower (A-101) and a second adsorption tower (B-101). The desorption unit (1) includes a steam generator (ZQ-1), which is connected in parallel to the first adsorption tower (A-101) and the second adsorption tower (B-101) to introduce steam as a purging medium. The air intake unit (2), temperature control unit (4), and negative pressure control unit (5) are connected in parallel to the first adsorption tower (A-101) and the second adsorption tower (B-101), respectively. The control system (6) controls the pressure and temperature inside the first adsorption tower (A-101) and the second adsorption tower (B-101), as well as the air intake volume and temperature and humidity of the air intake unit (2).

2. The dual-tower carbon capture system with negative pressure steam purging circulation according to claim 1, characterized in that, The first adsorption tower (A-101) and the second adsorption tower (B-101) are also connected to nitrogen purging pipes; switching between air and nitrogen purging can adjust the water vapor content in the desorbed gas while ensuring desorption efficiency. The nitrogen purging path is the same as the steam purging path.

3. The dual-tower carbon capture system with negative pressure steam purging circulation according to claim 1, characterized in that, The steam generator (ZQ-1) heats liquid water under ambient conditions to steam at a pressure of 0.1~0.4MPa and a temperature of 100~140℃, which is then introduced into the first adsorption tower (A-101) and the second adsorption tower (B-101) for steam purging.

4. The dual-tower carbon capture system with negative pressure steam purging circulation according to claim 1, characterized in that, The air intake unit (2) includes an air compressor (YSJ-1), a drying tube (GLQ-1), and an atomizer (JLB-1) connected in sequence. Ambient air passes through the air compressor (YSJ-1), the drying tube (GLQ-1), and the atomizer (JLB-1). The temperature control unit (4) works with the drying tube (GLQ-1) and the atomizer (JLB-1) to control the air condition to 10~40℃ and 20~70%RH before entering the first adsorption tower (A-101) and the second adsorption tower (B-101).

5. The dual-tower carbon capture system with negative pressure steam purging circulation according to claim 1, characterized in that, The first adsorption tower (A-101) and the second adsorption tower (B-101) are filled with solid adsorbents, and oil bath jackets are arranged around the outside to achieve temperature control inside the towers.

6. The dual-tower carbon capture system with negative pressure steam purging circulation according to claim 1, characterized in that, The temperature control unit (4) includes a first circulating oil bath (HW-1), a second circulating oil bath (HW-2), a third circulating oil bath (HW-3), and a fourth circulating water bath (HW-4), wherein the first circulating oil bath (HW-1) and the second circulating oil bath (HW-2) are respectively connected to the oil bath jackets of the first adsorption tower (A-101) and the second adsorption tower (B-101); The first circulating oil bath (HW-1) cools the first adsorption tower (A-101) and the second adsorption tower (B-101); The second circulating oil bath (HW-2) heats the first adsorption tower (A-101) and the second adsorption tower (B-101); The third circulating oil bath (HW-3) is connected to the intake unit (2) to control the air temperature output by the intake unit (2) to be 10~40℃; The fourth circulating water bath (HW-4) is connected to the steam generator (ZQ-1) to keep the steam warm.

7. The dual-tower carbon capture system with negative pressure steam purging circulation according to claim 1, characterized in that, The negative pressure control unit (5) includes a vacuum pump (ZKB-1), which is connected to the outlet pipes of the first adsorption tower (A-101) and the second adsorption tower (B-101). The outlet pipes are also equipped with a condenser (FLG-1) and a drying pipe.

8. A dual-tower carbon capture system with negative pressure steam purging circulation according to claim 7, characterized in that, The vacuum pump (ZKB-1) is equipped with a pressure regulating valve, which pumps the adsorption tower to 0.01~0.2 bar before desorption. The condenser (FLG-1) separates the humid CO2 gas that comes out of the two adsorption towers during the vapor desorption process. The drying tube dehumidifies the separated CO2 gas.

9. A dual-tower carbon capture system with negative pressure steam purging circulation according to claim 1, characterized in that, The control system (6) controls the pressure inside the first adsorption tower (A-101) and the second adsorption tower (B-101), and at the same time controls the temperature of each oil bath and water bath in the temperature control unit (4), as well as the spray volume of the atomizer (JLB-1) of the air intake unit (2).

10. A dual-tower carbon capture system with negative pressure steam purging circulation according to claim 1, characterized in that, By coordinating the control of temperature, pressure, humidity, and steam flow, fully automatic, multi-mode cyclic operation can be achieved, adapting to different environmental conditions and adsorbent characteristics.

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