A direct air carbon fixation system and method using a composite algae liquid coupled with a variable humidity adsorbent

Abstract

The present invention discloses a direct air carbon fixation system and method using a composite algae liquid coupled with a variable humidity adsorbent, belonging to the field of air capture technology. The system comprises a CO2 adsorption device, a microalgae carbon fixation device, and a solution-microalgae separation device. The present invention captures ultra-low concentrations of carbon dioxide (400 ppm) in the atmosphere using a variable humidity adsorbent, and adsorbs carbon dioxide using a composite algae liquid. Depending on the pH value of the algae liquid, the CO2 adsorption device adopts different adsorption-desorption operation modes, resulting in an adsorbent regeneration rate of >80%. The algae liquid can be recycled through photosynthesis, providing a continuous and stable supply of two carbon sources: carbon-rich algae liquid and high-concentration carbon dioxide gas, thereby achieving direct air carbon dioxide capture and fixation with high efficiency and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of direct air capture of carbon dioxide, and in particular to a direct air carbon fixation system and method using a composite algae liquid coupled with a variable humidity adsorbent. Background Art

[0002] In recent years, researchers have shown increasing interest in carbon dioxide capture, utilization, and storage (CCUS) technologies to address global warming caused by increasing greenhouse gas emissions. Among these technologies, direct air capture (DAC) is considered a key technology for achieving global carbon neutrality due to its ability to process CO2 from air at ultra-low partial pressures and its flexible device deployment.

[0003] However, current DAC technology generally uses variable temperature and variable pressure regeneration technology to achieve regeneration of the adsorbent while desorbing CO2; however, these technologies often have high energy consumption and operating costs. Therefore, variable humidity regeneration technology that does not rely on heat sources has become a highly sought-after direct air carbon dioxide capture technology. This technology uses ambient water vapor (humidity regulation) to achieve adsorption and desorption of CO2 gas. The adsorbent has a strong binding energy with CO2 in a dry state and can directly adsorb CO2 from the air until it reaches adsorption saturation or a certain adsorption amount. Subsequently, a certain amount of water is sprayed on the adsorbent or the relative humidity of the adsorbent surface is increased to reduce the binding energy between CO2 and the adsorbent, and the free energy of water is used to achieve desorption of CO2 and regeneration of the adsorbent.

[0004] Due to their rapid growth, high carbon sequestration efficiency, and good environmental adaptability, microalgae-based CO2 capture and conversion technology is considered a promising technology. It can effectively convert captured CO2, making it useful not only as a biofuel feedstock but also in food, feed, cosmetics, pharmaceuticals, and other fields, producing other high-value products while sequestering carbon. Furthermore, microalgae can utilize nutrients in wastewater, such as nitrogen and phosphorus, for growth, helping to reduce production costs and environmental pollution.

[0005] Due to the low energy consumption of variable humidity adsorption, its adsorption process has been widely studied and optimized. However, the circulation capacity and desorption rate of the adsorbent in variable humidity adsorption are still relatively low, the desorption time is also long, and there is a lot of room for improvement in the kinetics. In the study of Hou et al. (HOU C, KUMAR DR, JIN Y, et al. Porosity and hydrophilicity modulated quaternary ammonium-based sorbents for CO2 capture [J]. Chemical Engineering Journal, 2021, 413.), when moist N2 was purged onto the adsorbent to desorb CO2, the circulation capacity of the adsorbent was only 0.5 mmol / g, the desorption rate was about 50%, and the desorption time was more than 2h. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a direct air carbon fixation system and method of a composite algae liquid coupled with a variable humidity adsorbent, so as to solve the problems in the prior art of using microalgae for variable humidity adsorption, such as low circulation capacity and desorption rate of the adsorbent and long desorption time.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A direct air carbon fixation system with a composite algae liquid coupled with a variable humidity adsorbent, including a CO2 adsorption device;

[0009] One end of the CO2 adsorption device is provided with an air inlet and a liquid inlet, and the other end is provided with a liquid discharge port and a drive device; a rotating shaft is provided inside the CO2 adsorption device, one end of which is connected to the drive device; a plurality of wetting adsorbents are provided on the rotating shaft, and a spray device is provided above the wetting adsorbents. The CO2 adsorption device carries algae liquid, and the liquid level of the algae liquid is higher than the liquid discharge port;

[0010] The discharge port is connected to a microalgae carbon fixation device, the discharge port of the microalgae carbon fixation device is connected to a solution-microalgae separation device, and the discharge port of the solution-microalgae separation device is connected to a spraying device;

[0011] The algae liquid in the microalgae carbon fixation device and the CO2 adsorption device are both compound algae liquids. The compound algae liquid is Na + With K + Compound algae liquid;

[0012] A pH sensor is provided in the microalgae carbon fixation device, and the pH sensor is connected to a computer. The computer can control the opening and closing of the air inlet and the liquid inlet, as well as the start and stop of the spraying device.

[0013] A further improvement of the present invention is:

[0014] Preferably, the pH value of the algae liquid flowing into the liquid inlet or the algae liquid sprayed by the spraying device is 9.5-11.5.

[0015] Preferably, the wettable adsorbent is at least one of a quaternized resin, activated carbon or a metal organic framework.

[0016] Preferably, the wettable adsorbent is a sheet material;

[0017] A plurality of rows of wettable adsorbents are arranged circumferentially along the rotating shaft;

[0018] The sheet-like wettable adsorbents in each column of wettable adsorbents are arranged along the length direction of the rotating shaft.

[0019] Preferably, the flow rate of the algae liquid flowing into the liquid inlet is 0.1 to 2 L / min, and the average residence time of the algae liquid in the CO2 adsorption device is 3 to 10 seconds;

[0020] The flow rate of the algae liquid sprayed by the spraying device is 0.1 to 2 L / min.

[0021] The rotation speed of the shaft is 0.0017~0.033r / min.

[0022] Preferably, the microalgae carbon fixation device is an open photobioreactor for cultivating microalgae.

[0023] Preferably, the pH value of the algae liquid in the microalgae carbon fixation device is 10.5-11.5.

[0024] Preferably, the algae liquid in the microalgae carbon fixation device is a mixture of two or more of Na2CO3, NaHCO3, K2CO3 and KHCO3;

[0025] Na in algae liquid + With K + The molar ratio is 20:1 to 100:1.

[0026] Preferably, the CO2 adsorption device is connected to a vacuum pump, and the vacuum pump is connected to the microalgae carbon fixation device.

[0027] A direct air carbon fixation method based on the above system using a composite algae solution coupled with a variable humidity adsorbent includes the following two adsorption and desorption operation modes:

[0028] Mode 1 is a continuous capture mode. When the pH value of the algae liquid is greater than 10.5, the air inlet is opened, the spray device is closed, and the liquid inlet is used to transport algae liquid to the CO2 adsorption device 2. The algae liquid in the CO2 adsorption device is at a high level. The rotating shaft drives the dry wetting adsorbent to rotate. During the rotation, the wetting adsorbent absorbs CO2 from the air. The dry wetting adsorbent comes into contact with the algae liquid at the bottom of the CO2 adsorption device. The algae liquid absorbs the CO2 in the wetting adsorbent and becomes carbon-rich algae liquid. After the carbon-rich algae liquid is input into the microalgae carbon fixation device, the microalgae in the microalgae carbon fixation device fix the CO2 in the carbon-rich algae liquid through photosynthesis. After the pH value of the algae liquid is measured, it is transported to the solution-microalgae separation device. The solution-microalgae separation device transports the separated carbon-depleted algae liquid to the spray device.

[0029] Mode 2 is the intermittent spraying mode. When the pH of the algae liquid is less than 10.5, in the adsorption stage, the air inlet is opened, the spraying device is closed, and the rotating shaft drives the dry humidifying adsorbent to rotate. The humidifying adsorbent adsorbs CO2 in the air during rotation, and the algae liquid in the CO2 adsorption device is in a high-level state; in the desorption stage, the air inlet is closed, the spraying device is opened, and the spraying device sprays out carbon-depleted algae liquid. After the carbon-depleted algae liquid contacts the humidifying adsorbent, the vacuum pump is started to pass the CO2 desorbed by the adsorbent into the microalgae carbon fixation device in the form of gas.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention discloses a direct air carbon fixation system using a composite algae liquid coupled with a variable-humidity adsorbent. This system comprises an algae liquid disposed at the bottom of a CO2 adsorption device, a variable-humidity adsorbent disposed within the device, a spray device disposed above the variable-humidity adsorbent, and a pH sensor disposed within the microalgae carbon fixation device. The pH sensor collects the different pH values ​​of the algae liquid. The CO2 adsorption device employs different adsorption / desorption methods to enable continuous CO2 adsorption. Furthermore, due to the continuous renewal of the algae liquid in the CO2 adsorption device, the variable-humidity adsorbent and algae liquid in the CO2 adsorption device are always in an adsorption state, thereby improving the circulation capacity and desorption rate of the variable-humidity adsorbent in the CO2 adsorption device. By addressing key issues such as the adsorption process and the composition of the microalgae solution, the present invention studies a coupling system for direct air capture of carbon dioxide using a composite algae liquid with high-efficiency variable-pressure coupling and a microalgae carbon fixation system, enabling low-cost air CO2 capture and conversion.

[0032] The present invention also has the following advantages:

[0033] 1. The present invention realizes efficient ion exchange between algae liquid and variable humidity adsorbent by compounding algae liquid. Compared with the adsorbent desorption by humidity change alone, the Na + With K +The molar ratio shortens the desorption time and ensures the growth of microalgae. The pH value of the algae solution can be easily restored and the adsorbent can be recycled through photosynthesis.

[0034] 2. The present invention uses ultra-low concentrations of carbon dioxide in the atmosphere as a carbon source, determines regeneration performance by detecting the pH of the algae solution, and introduces carbon that cannot be desorbed from the algae solution at a low pH into the algae solution in the form of carbon dioxide gas by increasing the vacuum degree of the CO2 adsorption device. This allows the system to always operate in a high-efficiency range under different conditions. Compared with traditional technical routes that rely on sodium bicarbonate as a carbon source for cultivating microalgae, the system of the present invention has low operating costs and high carbon fixation efficiency.

[0035] 3. The CO2 adsorption device designed in the present invention can determine the growth status of microalgae based on the pH of the algae liquid, change the carbon content of the algae liquid by adjusting the shaft speed, and further regulate the growth indicators of microalgae. It is simple to operate and also realizes the continuous coupling operation of direct air capture of carbon dioxide and microalgae carbon fixation. Through the efficient utilization of the adsorbent, the adsorbent regeneration rate is maintained at >80%.

[0036] The present invention realizes the continuous supply of microalgae carbon source by circulating algae liquid and efficiently desorbing adsorbent, which is suitable for promotion and application to accelerate the realization of carbon neutrality goals. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the coupling of composite algae liquid with direct air capture for efficient humidification regeneration and microalgae carbon sequestration;

[0038] Figure 2 It is a structural schematic diagram of the CO2 adsorption device;

[0039] Figure 3 This is an internal side view of the CO2 adsorption device.

[0040] Among them, 1. air conveying device; 2. CO2 adsorption device; 3. microalgae carbon fixation device; 4. solution-microalgae separation device; 5. humidifying adsorbent; 6. drain port; 7. rotating shaft; 8. exhaust port; 9. liquid inlet; 10. spraying device; 11. air inlet; 12. driving device; 13. vacuum pump. DETAILED DESCRIPTION

[0041] The present invention is described in further detail below with reference to the accompanying drawings:

[0042] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; in addition, unless otherwise expressly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be a communication between the internal parts of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] The present invention discloses a direct air carbon fixation system of a composite algae solution coupled with a variable humidity adsorbent, comprising a fan 1, a CO2 adsorption device 2, a microalgae carbon fixation device 3, a solution-microalgae separation device 4 and a vacuum pump 5.

[0044] The gas output end of the fan 1 is connected to the air inlet 11 of the CO2 adsorption device 2, the discharge port 6 of the CO2 adsorption device 2 is connected to the liquid inlet of the microalgae carbon fixation device 3, the discharge port of the microalgae carbon fixation device 3 is connected to the liquid inlet of the solution-microalgae separation device 4, the discharge port of the solution-microalgae separation device 4 is connected to the liquid inlet 9 of the CO2 adsorption device 2, and the discharge port 6 of the CO2 adsorption device 2 is connected to the liquid inlet of the microalgae carbon fixation device 3.

[0045] The fan 1 is used to send air to the CO2 adsorption device 2. The adsorbent in the CO2 adsorption device 2 captures ultra-low concentration carbon dioxide (400ppm) in the atmosphere, and the clean air after adsorption is discharged into the environment through the exhaust port 8.

[0046] In some embodiments of the present invention, the fan 1 is used to collect and transport the air flow rate that can control the flow into the CO2 adsorption device 2 to be 50-200m 3 / h.

[0047] See also Figure 2, a CO2 adsorption device 2, a built-in humidifying adsorbent 5, a spraying device 10 and a rotating shaft 7, the rotating shaft 7 is connected to an external driving device 12; the spraying device 10 is arranged along the upper end of the interior of the CO2 adsorption device 2, above the humidifying adsorbent 5; an air inlet 11 and a liquid inlet 9 are provided at one end of the interior of the CO2 adsorption device 2, and the air inlet 11 is above the liquid inlet 9; a driving device 12 is provided at one end of the interior of the CO2 adsorption device 2, and the driving device 12 is connected to the power input end of the rotating shaft 7, an exhaust port 8 is provided above the rotating shaft 7, and a liquid discharge port 6 is provided below the rotating shaft 7; the exhaust port 8 is connected to the vacuum pump 13, and the liquid discharge port 6 is connected to the microalgae carbon fixation device 3. The CO2 adsorption device 2 operates as follows: one side of the humidified adsorbent 5 is loaded onto a rotating shaft 7 and rotates with it. Air delivered through an air inlet 11 sweeps through the humidified adsorbent 5 and is then discharged through an exhaust port 8. Algae liquid flowing into the liquid inlet 9 and spraying device 10 is collected at the bottom of the CO2 adsorption device 2 and flows out of the liquid outlet 6 to the microalgae carbon fixation device 3. The pH of the algae liquid flowing into or spraying the CO2 adsorption device 2 is between 9.5 and 11.5.

[0048] In some embodiments of the present invention, see Figure 3 The dehumidifying adsorbent 5 is a sheet material, and the sheet plane of the dehumidifying adsorbent 5 is coplanar with the rotating shaft 7; there are several rows of dehumidifying adsorbents 5 arranged in a circumferential array around the rotating shaft 7, and the dehumidifying adsorbents 5 in each row are arranged in an array along the length direction of the rotating shaft 7.

[0049] In some embodiments of the present invention, the wetting adsorbent 5 in the CO2 adsorption device 2 includes at least one of quaternized resin, activated carbon, and metal organic framework, which has the function of spraying alkaline solution to desorb carbon dioxide.

[0050] In some embodiments of the present invention, the flow rate of the algae liquid flowing into the liquid inlet 9 is 0.1 to 2 L / min, and the average residence time of the algae liquid is 3 to 10 s.

[0051] In some embodiments of the present invention, the flow rate of the algae liquid sprayed by the spraying device 10 is 0.1 to 2 L / min.

[0052] In some embodiments of the present invention, the rotational speed of the shaft 7 in the CO adsorption device 2 is 0.0017 to 0.033 r / min. When the pH of the algae solution is high, indicating rapid carbon source consumption, the shaft rotational speed is increased to increase the carbon source supply. When the pH of the algae solution is low, the shaft rotational speed is decreased to reduce the carbon source supply.

[0053] The microalgae carbon fixation device 3 uses an open photobioreactor to cultivate microalgae. It has a built-in pH sensor connected to a computer and an aeration port at the bottom. The aeration port is connected to the aerator. The light-dark cycle ratio of the microalgae carbon fixation device 3 is 12:12, the light intensity is 6000-10000 lux, and the ambient temperature is 15-30°C. The open photobioreactor cultivates microalgae. Depending on the pH value, the CO3 2- With HCO3 - There is a balance between the two, and microalgae can - The microalgae photosynthesize as a carbon source. As the pH value of the algae liquid gradually increases during photosynthesis, the algae liquid flows to the solution-microalgae separation device 4 for separation. When the CO2 adsorption device adopts the continuous capture mode, the microalgae carbon fixation device only receives the carbon-rich algae liquid as a carbon source. When the CO2 adsorption device adopts the intermittent spray mode, in addition to the carbon-rich algae liquid, high-concentration carbon dioxide desorbed by the adsorbent is pumped to the bottom of the microalgae carbon fixation device 3. It is broken into small bubbles by the aerator and then comes into contact with the algae liquid to replenish carbon consumption. As the pH value of the algae liquid gradually increases during photosynthesis, the algae liquid flows to the solution-microalgae separation device for separation.

[0054] The CO2 desorbed from the adsorbent is passed into the microalgae carbon fixation device 3 in the form of gas, continuously reducing the CO2 content inside the CO2 adsorption device 2, so that the absolute pressure of the CO2 adsorption device 2 is less than 10kPa.

[0055] In some embodiments of the present invention, the algae species used in the microalgae carbon fixation device 3 are one or more of Spirulina, Chlorella, Dunaliella salina, and Nannochloropsis, and the light source of the microalgae carbon fixation device 3 is at least one of artificial light or natural light; the light-dark cycle ratio is 12:12, the light intensity is 8000-10000 lux, the ambient temperature is 25°C, and the pH of the internal algae liquid is 10.5-11.5.

[0056] In some embodiments of the present invention, the culture medium for microalgae is one or a mixture of BG11 medium, BBM medium and Zarrouk medium.

[0057] In some embodiments of the present invention, the recombined algae solution in the microalgae carbon fixation device 3 contains Na + With K + By adding two or more of Na2CO3, NaHCO3, K2CO3 and KHCO3, the Na content of algae solution can be regulated. + With K + The molar ratio of Na in the composite algae solution is 20:1 to 100:1, which can make the adsorbent regeneration rate >80%. + With K +The ratio of is 40:1 to 60:1, the carbonate ion content is 0.010 to 0.100 mol / L, and the average residence time of the algae liquid in the microalgae carbon fixation device 3 is 5 s.

[0058] The solution-microalgae separation device 4 uses centrifugal separation to separate the solution and the microalgae product, and the separated solution flows into the CO2 adsorption device 2. The solution and the microalgae product are separated by centrifugation, and the separated solution flows into the CO2 adsorption device to desorb the adsorbent.

[0059] The second aspect of the present invention discloses a direct air carbon fixation method using a composite algae solution coupled with a wettable adsorbent. The CO2 adsorption device 2 includes an adsorbent 5 and a spray device 10. The adsorbent 5 adsorbs carbon dioxide from the air when dry and desorbs it when wet. Specifically, the CO2 adsorption device 2 operates under two adsorption modes: continuous adsorption and intermittent adsorption, depending on the pH value of the algae solution measured within the microalgae carbon fixation device 3. Specifically, the following adsorption-desorption operating modes are available:

[0060] Mode 1: When the pH of the algae liquid is greater than 10.5, the adsorbent 5 in the CO2 adsorption device 2 rotates with the shaft 7, alternately contacting and immersing the algae liquid at the bottom of the CO2 adsorption device 2. The air inlet 11 is always open, and the spray device 10 is always closed. The algae liquid flows into the CO2 adsorption device 2 from the liquid inlet 9 and is collected at the bottom of the device, keeping the liquid level above the center line of the shaft 7. The algae liquid flows out of the CO2 adsorption device 2 from the liquid outlet 6 and flows into the microalgae carbon fixation device 3. The microalgae carbon fixation device 3 receives the carbon-rich algae liquid flowing out of the CO2 adsorption device 2. The microalgae are then 3- The algae liquid is photosynthesized as a carbon source, and after the pH value is measured, it flows to the solution-microalgae separation device 4 for separation. The solution-microalgae separation device 4 separates CO2 and algae liquid inside it to obtain carbon-depleted algae liquid, and transmits the carbon-depleted algae liquid to the spray device 10 of the CO2 adsorption device 2. The specific adsorption process of this mode is that after the dry adsorbent adsorbs CO2, it contacts the algae liquid with a high liquid level. CO2 is desorbed in the alkaline algae liquid with a higher pH value to generate carbonate and carbonate ions. The desorbed adsorbent rotates above the liquid surface and enters the adsorption state after air drying. The adsorbent continuously performs adsorption and desorption in the CO2 adsorption device 2.

[0061] In mode 2, when the algae solution pH is <10.5, the CO2 adsorption device switches to intermittent spray mode. Liquid inlet 9 remains closed, maintaining the liquid level below the lowest point of the wetting adsorbent 5. To ensure an adsorbent regeneration rate of >80%, the CO2 adsorption device 2 operates in two phases: adsorption and desorption. During the adsorption phase, the air inlet 11 is open, and the spray device 10 is closed. During the desorption phase, the air inlet 11 is closed, the spray device 10 is opened, and the vacuum pump 13 is activated, passing the CO2 desorbed from the adsorbent into the microalgae carbon sequestration device 3 as a gas. During the adsorption phase, no algae solution flows into the adsorption device, and the bottom liquid level remains below the lowest point of the wetting adsorbent. During the desorption phase, the air inlet is closed, and the spray device is opened. Algae solution is sprayed out of the spray device, contacts the adsorbent, and flows to the bottom of the adsorption device.

[0062] It should be understood that in the above process, when the adsorbent saturated with CO2 is sprayed with a neutral aqueous solution, CO2 is mainly released in the form of gas; when the weakly alkaline algae solution is sprayed, part of it is absorbed by the alkaline solution and part is released in the form of gas.

[0063] The algae solution in the algae carbon fixation device 3 is coupled with direct air capture, efficient humidification regeneration and microalgae carbon fixation system. Its principle is to use the algae solution with increased pH value to desorb the humidification adsorbent, and the carbon dioxide adsorbed by the adsorbent is converted to CO3 2- and HCO3 - The microalgae are stored in the form of algae liquid, and the microalgae are stored in the form of HCO3 - The algae solution uses photosynthesis as a carbon source to achieve carbon fixation. When the pH value of the algae solution is less than 10.5, the algae solution desorbs the saturated adsorbent and flows out of the CO2 adsorption device, entering the next air adsorption cycle. The air conveying device is used to blow the adsorbent dry, allowing the adsorbent to adsorb saturated carbon dioxide again, and performing a direct air carbon dioxide capture and algae solution regeneration cycle. When the pH value of the algae solution is greater than 10.5, there is no need for staged adsorption and desorption. The adsorbent can be dried and adsorbed in the space above the centerline of the adsorption device's rotating shaft, and the algae solution can dryly desorb the adsorbent in the space below the centerline of the adsorption device's rotating shaft, thereby achieving continuous capture and fixation of carbon dioxide.

[0064] In a preferred embodiment, the algae liquid culture medium sprayed in the CO2 adsorption device 2 and the carbon fixation device 3 is a mixture of one or both of BG11 culture medium and Zarrouk culture medium, and the Na + With K + The ratio is 40:1~60:1, the carbonate ion content is 0.010~0.100 mol / L, and the average residence time of the algae liquid is 5s.

[0065] The following is further described with reference to specific embodiments.

[0066] Example 1

[0067] The microalgae carbon fixation device uses Chlorella vulgaris, the light source is artificial light, the light-dark cycle ratio is 12:12, the light intensity is 8000 lux, and the ambient temperature is 25°C. The air conveying device passes dry air containing carbon dioxide (400ppm) into the CO2 adsorption device through the air path, and the ventilation volume is 50m 3 / h, the unadsorbed air is discharged from the exhaust port, the shaft speed is 0.0017r / min, the algae solution Na + With K + The molar ratio of is 60:1, the flow rate is 1L / min, the algae liquid level at the bottom of the device is flush with the center line of the rotating shaft, and the adsorbent saturated adsorption capacity is about 0.8mmol / g. The microalgae carbon fixation device receives the carbon-rich algae liquid flowing out of the carbon dioxide adsorption device, and the microalgae is absorbed by HCO3 - The algae solution was photosynthesized as a carbon source. After the pH value was measured, the algae solution was flowed to the solution-microalgae separation device for separation and calculation of the carbon fixation rate. After the system was operated for 24 hours, the pH of the algae solution was stabilized at 10.7-10.8, and the carbon fixation rate could reach 0.06 g·L -1 ·D -1 .

[0068] Example 2

[0069] The difference from Example 1 is that the shaft speed in the CO2 adsorption device is 0.033 r / min. After the system has been running for 24 hours, the pH of the algae liquid is stabilized at 10.2. Then, the operating state of the CO2 adsorption device is changed, and the spray device is turned on to intermittently adsorb carbon dioxide and desorb the algae liquid. The algae liquid flow rate is still 1 L / min, and the algae liquid level at the bottom of the device is always lower than the lowest point of the wet adsorbent. The microalgae carbon fixation device receives the carbon-rich algae liquid flowing out of the carbon dioxide adsorption device. After measuring the pH value, the algae liquid flows to the solution-microalgae separation device for separation and calculation of the carbon fixation rate. After the system has been running for 24 hours, the pH of the algae liquid is stabilized at 10.4-10.5, and the carbon fixation rate can reach 0.09 g·L -1 ·D -1 .

[0070] Example 3

[0071] The difference from Example 1 is that the algae solution Na + With K + The molar ratio of CO2 to CO2 was 75:1, and the CO2 adsorption device continued to operate in continuous adsorption mode with a shaft speed of 0.0017 r / min. After the system operated for 24 hours, the pH of the algae solution stabilized at 10.9-11.0, and the carbon fixation rate reached 0.10 g·L -1 ·D -1 .

[0072] Comparing the experimental results of Examples 1 and 2, it is clear that controlling the shaft speed can affect the adsorbent regeneration rate, and thus the carbon supply of the algae solution. Increasing the carbon supply can promote microalgae photosynthesis and raise the pH of the algae solution to above 10.5. When the pH of the algae solution is less than 10.5, adjusting the adsorption device operating state and using a spray interval can increase the adsorbent regeneration rate, increase the carbon supply of the algae solution, effectively promote microalgae growth, and raise the pH of the algae solution.

[0073] Comparing the experimental results of Example 1 and Example 3, it can be seen that different Na + With K + The ratio of algae solution will affect the regeneration rate of the adsorbent and the growth rate of microalgae. + With K + When the molar ratio is 75:1, the maximum carbon fixation rate of microalgae can reach 0.10 g·L -1 ·D -1 . Na in algae liquid + The increase can effectively improve the desorption kinetics of the adsorbent and promote the desorption equilibrium to be reached faster.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A direct air carbon fixation system with a composite algae liquid coupled with a variable humidity adsorbent, characterized in that: comprising a CO2 adsorption device (2); One end of the CO2 adsorption device (2) is provided with an air inlet (11) and a liquid inlet (9), and the other end is provided with a liquid discharge port (6) and a driving device (12); a rotating shaft (7) is provided inside the CO2 adsorption device (2), and one end of the rotating shaft (7) is connected to the driving device (12); a plurality of wettable adsorbents (5) are provided on the rotating shaft (7), and a spraying device (10) is provided above the wettable adsorbents (5); the CO2 adsorption device (2) carries algae liquid, and the liquid level of the algae liquid is higher than the liquid discharge port (6); The liquid discharge port (6) is connected to the microalgae carbon fixation device (3), the liquid discharge port of the microalgae carbon fixation device (3) is connected to the solution-microalgae separation device (4), and the liquid discharge port of the solution-microalgae separation device (4) is connected to the spraying device (10); The algae liquid in the microalgae carbon fixation device (3) and the CO2 adsorption device (2) are both compound algae liquids, and the compound algae liquid is Na + With K + Compound algae liquid; A pH sensor is provided in the microalgae carbon fixation device (3), and the pH sensor is connected to a computer. The computer can control the opening and closing of the air inlet (11) and the liquid inlet (9), as well as the start and stop of the spray device (10).

2. A direct air carbon fixation system of composite algae liquid coupled with variable humidity adsorbent according to claim 1, characterized in that: The pH value of the algae liquid flowing into the liquid inlet (9) or the algae liquid sprayed by the spraying device (10) is 9.5 to 11.

5.

3. The direct air carbon fixation system of a composite algae liquid coupled with a variable humidity adsorbent according to claim 1, characterized in that: The moisture-changing adsorbent (5) is at least one of quaternized resin, activated carbon or metal organic framework.

4. The direct air carbon fixation system of a composite algae liquid coupled with a variable humidity adsorbent according to claim 1, characterized in that: The dehumidifying adsorbent (5) is a sheet-like material; A plurality of rows of wettable adsorbents (5) are arranged circumferentially along a rotating shaft (7); The sheet-shaped humidifying adsorbents (5) in each column of humidifying adsorbents (5) are arranged in an array along the length direction of the rotating shaft (7).

5. The direct air carbon fixation system of a composite algae liquid coupled with a variable humidity adsorbent according to claim 1, characterized in that: The flow rate of the algae liquid flowing into the liquid inlet (9) is 0.1 to 2 L / min, and the average residence time of the algae liquid in the CO2 adsorption device (2) is 3 to 10 seconds; The flow rate of the algae liquid sprayed by the spraying device (10) is 0.1 to 2 L / min. The rotation speed of the rotating shaft (7) is 0.0017-0.033 r / min.

6. The direct air carbon fixation system of a composite algae liquid coupled with a variable humidity adsorbent according to claim 1, characterized in that: The microalgae carbon fixation device (3) is an open photobioreactor for cultivating microalgae.

7. The direct air carbon fixation system of a composite algae liquid coupled with a variable humidity adsorbent according to claim 1, characterized in that: The pH value of the algae liquid in the microalgae carbon fixation device (3) is 10.5-11.

5.

8. The direct air carbon fixation system of a composite algae liquid coupled with a variable humidity adsorbent according to claim 1, characterized in that: The algae liquid in the microalgae carbon fixation device (3) is a mixture of two or more of Na2CO3, NaHCO3, K2CO3 and KHCO3; Na in algae liquid + With K + The molar ratio is 20:1 to 100:

1.

9. The direct air carbon fixation system of composite algae liquid coupled with variable humidity adsorbent according to claim 1, characterized in that: The CO2 adsorption device (2) is connected to a vacuum pump (13), and the vacuum pump (13) is connected to the microalgae carbon fixation device (3).

10. A direct air carbon fixation method based on the system of claim 1 using a composite algae solution coupled with a humidifying adsorbent, characterized in that: There are two adsorption and desorption operation modes: Mode 1 is a continuous capture mode. When the pH value of the algae liquid is greater than 10.5, the air inlet (11) is opened, the spray device (10) is closed, and the liquid inlet (9) transports the algae liquid to the CO2 adsorption device (2). The algae liquid in the CO2 adsorption device (2) is in a high-level state. The rotating shaft (7) drives the dry humidifying adsorbent (5) to rotate. The humidifying adsorbent (5) absorbs CO2 in the air during the rotation. The dry humidifying adsorbent (5) contacts the algae liquid at the bottom of the CO2 adsorption device (2). The algae liquid absorbs CO2 in the humidifying adsorbent (5) and becomes a carbon-rich algae liquid. After the carbon-rich algae liquid is input into the microalgae carbon fixation device (3), the microalgae in the microalgae carbon fixation device (3) fix the CO2 in the carbon-rich algae liquid through photosynthesis. After the pH value of the algae liquid is measured, it is transported to the solution-microalgae separation device (4). The solution-microalgae separation device (4) transports the separated carbon-poor algae liquid to the spray device (10). Mode 2 is an intermittent spraying mode. When the pH of the algae liquid is less than 10.5, in the adsorption stage, the air inlet (11) is opened, the spraying device (10) is closed, and the rotating shaft (7) drives the dry humidifying adsorbent (5) to rotate. The humidifying adsorbent (5) adsorbs CO2 in the air during the rotation process, and the algae liquid in the CO2 adsorption device (2) is in a high-level state; in the desorption stage, the air inlet (11) is closed, the spraying device (10) is opened, and the spraying device (10) sprays out the carbon-poor algae liquid. After the carbon-poor algae liquid contacts the humidifying adsorbent (5), the vacuum pump (13) is started to pass the CO2 desorbed by the adsorbent into the microalgae carbon fixation device (3) in the form of gas.

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