Direct air carbon sequestration system and method using compound algae liquid coupled with moisture swing adsorbent

Abstract

Provided are a direct air carbon sequestration system and method using a compound algae liquid coupled with a moisture swing adsorbent, relating to the technical field of air capture. The system comprises a CO2 adsorption device (2), a microalgae carbon sequestration device (3), and a solution-microalgae separation device (4). Ultralow-concentration carbon dioxide (400 ppm) in the atmosphere is captured by means of moisture swing adsorbents (5), and the carbon dioxide can be adsorbed by means of a compound algae liquid; on the basis of different pH values of the algae liquid, the CO2 adsorption device (2) uses different adsorption-desorption operating modes, so that the recycling rate of the adsorbents is greater than 80%; the algae liquid can be recycled by means of photosynthesis, and two carbon sources of a carbon-rich algae liquid and a high-concentration carbon dioxide gas are continuously and stably supplied; and therefore, direct air carbon dioxide capture and sequestration are achieved with high efficiency and low costs.

Description

Direct air carbon capture system and method using compounded algae liquid coupled with variable humidity adsorbent TECHNICAL FIELD

[0001] The present application relates to the technical field of direct air carbon capture, and specifically relates to a direct air carbon capture system and method using compounded algae liquid coupled with variable humidity adsorbent. BACKGROUND

[0002] In recent years, in order to cope with the problem of global warming caused by the increase of greenhouse gas emissions, researchers have shown increasing interest in carbon capture, utilization and storage (CCUS) technology. Among these technologies, direct air capture (DAC) is considered one of the key technologies to achieve global carbon neutrality because it can handle CO2 in air at ultra-low partial pressure and the device can be placed flexibly.

[0003] However, the DAC technology currently generally uses temperature and pressure swing regeneration technology to desorb CO2 while regenerating the adsorbent; but these technologies often have high energy consumption and operating costs. Therefore, variable humidity regeneration technology, which does not rely on heat sources, has become a direct air carbon capture technology that has attracted much attention. This technology uses ambient moisture (humidity adjustment) to achieve CO2 adsorption and desorption. The adsorbent has strong binding energy with CO2 in a dry state, and can directly adsorb CO2 from air until it reaches adsorption saturation or a certain adsorption amount. Subsequently, a certain amount of water is sprayed onto the adsorbent or the relative humidity of the adsorbent surface is increased, thereby reducing the binding energy of CO2 and the adsorbent, and using the free energy of water to achieve CO2 desorption and adsorbent regeneration.

[0004] Because microalgae have fast growth rate, high carbon fixation efficiency and good environmental adaptability, using microalgae for CO2 capture and conversion technology is considered a promising technology. It can effectively convert captured CO2, not only as a raw material for biofuels, but also for food, feed, cosmetics, pharmaceuticals and other fields, producing other high-value products while fixing carbon. In addition, microalgae can grow using nutrients such as nitrogen and phosphorus in wastewater, which not only helps to reduce production costs, but also reduces environmental pollution.

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

[0006] SUMMARY

[0007] The purpose of the present application is to overcome the above-mentioned shortcomings of the prior art, and to provide a direct air carbon fixation system and method of complex algae liquid coupled with variable wet adsorbent, to solve the problems of low cycle capacity and desorption rate of the adsorbent and long desorption time when using microalgae for variable wet adsorption in the prior art.

[0008] To achieve the above-mentioned purpose, the following technical solutions are adopted in the present application:

[0009] A direct air carbon fixation system of complex algae liquid coupled with variable wet adsorbent, comprising a CO2 adsorption device;

[0010] 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 outlet and a driving device; a rotating shaft is arranged inside the CO2 adsorption device, one end of the rotating shaft is connected with the driving device; a plurality of variable wet adsorbents are arranged on the rotating shaft, a spraying device is arranged above the variable wet adsorbents, and the algae liquid is carried in the CO2 adsorption device, and the liquid level of the algae liquid is higher than the liquid outlet;

[0011] The liquid outlet of the microalgae carbon fixation device is communicated with a solution-microalgae separation device, and the liquid outlet of the solution-microalgae separation device is communicated with the spraying device;

[0012] The algae liquid in the microalgae carbon fixation device and the CO2 adsorption device is a complex algae liquid, and the complex algae liquid is a complex algae liquid of Na + and K + ;

[0013] A pH sensor is arranged in the microalgae carbon fixation device, and the pH sensor is connected with a computer, and the computer can control the on-off of the air inlet and the liquid inlet, and the start-stop of the spraying device.

[0014] Further improvement of the present application is that:

[0015] Preferably, the pH value of the algal liquid flowing into the liquid inlet or sprayed by the spraying device is 9.5-11.5.

[0016] Preferably, the humidification adsorbent is at least one of quaternary ammonium resin, activated carbon or metal organic framework.

[0017] Preferably, the humidification adsorbent is a sheet material.

[0018] A plurality of columns of humidification adsorbents are arranged along the circumference of the rotating shaft.

[0019] The sheet humidification adsorbents in each column of humidification adsorbents are arranged along the length direction of the rotating shaft.

[0020] Preferably, the flow rate of the algal liquid flowing into the liquid inlet is 0.1-2 L / min, and the average residence time of the algal liquid in the CO2 adsorption device is 3-10 s.

[0021] The flow rate of the algal liquid sprayed by the spraying device is 0.1-2 L / min.

[0022] The rotating speed of the rotating shaft is 0.0017-0.033 r / min.

[0023] Preferably, the microalgal carbon fixation device is an open photobioreactor for culturing microalgae.

[0024] Preferably, the pH value of the algal liquid in the microalgal carbon fixation device is 10.5-11.5.

[0025] Preferably, the algal liquid in the microalgal carbon fixation device is a mixture added with two or more of Na2CO3, NaHCO3, K2CO3 and KHCO3.

[0026] The molar ratio of Na + to K + in the algal liquid is 20:1-100:1.

[0027] Preferably, the CO2 adsorption device is connected with a vacuum pump, and the vacuum pump is connected with the microalgal carbon fixation device.

[0028] A direct air carbon fixation method based on the above system, which couples the compounded algal liquid with the humidification adsorbent, includes the following two adsorption and desorption operation modes:

[0029] Mode 1, for continuous capture mode, when the pH value of the algal liquid is greater than 10.5, the air inlet is opened, the spraying device is closed, the liquid inlet delivers the algal liquid to the CO2 adsorption device 2, and the algal liquid in the CO2 adsorption device is in a high position; the dry wet adsorbent is rotated by the rotating shaft, the wet adsorbent absorbs CO2 in the air during rotation, the dry wet adsorbent contacts the algal liquid at the bottom of the CO2 adsorption device, the algal liquid absorbs CO2 in the wet adsorbent to become carbon-rich algal liquid, the carbon-rich algal liquid is input into the microalgae carbon fixation device, the microalgae in the microalgae carbon fixation device fix CO2 in the carbon-rich algal liquid through photosynthesis, the pH value of the algal liquid is measured, and then the algal liquid is delivered to the solution-microalgae separation device; the solution-microalgae separation device delivers the separated carbon-poor algal liquid to the spraying device;

[0030] Mode 2, for intermittent spraying mode, when the pH value of the algal liquid is less than 10.5, in the adsorption stage, the air inlet is opened, the spraying device is closed, the dry wet adsorbent is rotated by the rotating shaft, and the wet adsorbent absorbs CO2 in the air during rotation; in the desorption stage, the air inlet is closed, the spraying device is opened, the spraying device sprays carbon-poor algal liquid, and the carbon-poor algal liquid contacts the wet adsorbent, and then the vacuum pump is started to desorb CO2 from the adsorbent in the form of gas and input into the microalgae carbon fixation device.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] The present application discloses a kind of direct air carbon fixation systems of compound algal liquid coupling wet adsorbent, the system is provided with algal liquid in the bottom of CO2 adsorption device, is provided with wet adsorbent inside, wet adsorbent is provided with spraying device above, is provided with pH sensor in microalgae carbon fixation device, different pH values of algal liquid are collected by pH sensor, CO2 adsorption device uses different adsorption / desorption mode, so that it can continuously adsorb CO2, and because the algal liquid in CO2 adsorption device is constantly updated, the wet adsorbent and algal liquid in CO2 adsorption device are always in adsorption state, improve the circulation capacity and desorption rate of wet adsorbent in CO2 adsorption device.The present application solves the key problems such as adsorption process and microalgae solution composition, studies the coupling system of compound algal liquid high-efficiency pressure coupling direct air capture carbon dioxide and microalgae carbon fixation system, which can realize low-cost air CO2 capture and conversion.

[0033] The present application also has the following advantages:

[0034] 1、The present application realizes efficient ion exchange of algal liquid and wet adsorbent by compounding algal liquid, compared with only relying on humidity change to desorb adsorbent, the Na + and K +The molar ratio of the two is not only shortened the adsorption time, but also ensures the growth of microalgae, and the pH value of the algal liquid can be easily recovered and the adsorbent can be regenerated through photosynthesis.

[0035] 2、The present application uses ultra-low concentration carbon dioxide in the atmosphere as a carbon source, detects the pH of the algal liquid to judge the regeneration performance, and passes the carbon that cannot be desorbed by the algal liquid when the pH is low in the form of carbon dioxide gas into the algal liquid by increasing the vacuum degree of the CO2 adsorption device, so that the system always runs in the high efficiency interval in different states, compared with the traditional technology route that relies on sodium bicarbonate as a carbon source to culture microalgae, the system has low operation cost and high carbon fixation efficiency.

[0036] 3、The CO2 adsorption device designed in the present application can judge the growth state of microalgae according to the pH of the algal liquid, change the carbon content of the algal liquid by adjusting the rotating speed of the rotating shaft, and further control the growth index of microalgae, which is simple to operate, and realizes the continuous coupling operation of direct air capture of carbon dioxide and microalgae carbon fixation, and maintains the regeneration rate of the adsorbent > 80% through efficient use of the adsorbent.

[0037] The present application realizes the continuous supply of microalgae carbon source by efficient desorption of the adsorbent by circulating the algal liquid, which is suitable for popularization and application, and accelerates the realization of the carbon neutralization target. BRIEF DESCRIPTION OF DRAWINGS

[0038] Fig. 1 is a schematic diagram of coupling direct air capture of complex algal liquid with efficient humidification regeneration and microalgae carbon fixation;

[0039] Fig. 2 is a structural schematic diagram of the CO2 adsorption device;

[0040] Fig. 3 is an internal side view of the CO2 adsorption device.

[0041] Among them, 1, air conveying device; 2, CO2 adsorption device; 3, microalgae carbon fixation device; 4, solution-microalgae separation device; 5, humidified adsorbent; 6, liquid discharge port; 7, rotating shaft; 8, exhaust port; 9, liquid inlet; 10, spraying device; 11, air inlet; 12, driving device; 13, vacuum pump. DETAILED DESCRIPTION

[0042] The present application will be further described in detail below in combination with the drawings:

[0043] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application; the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance; in addition, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0044] The application discloses a kind of compound algal liquid coupling variable wet adsorbent direct air carbon fixation system, including fan 1, CO2 adsorption device 2, microalgae carbon fixation device 3, solution-microalgae separation device 4 and vacuum pump 5.

[0045] The gas output end of fan 1 is connected with the gas inlet 11 of CO2 adsorption device 2, the liquid outlet 6 of CO2 adsorption device 2 is connected with the liquid inlet of microalgae carbon fixation device 3, the liquid outlet of microalgae carbon fixation device 3 is connected with the liquid inlet of solution-microalgae separation device 4, the liquid outlet of solution-microalgae separation device 4 is communicated with the liquid inlet 9 of CO2 adsorption device 2, the liquid outlet 6 of CO2 adsorption device 2 is connected with the liquid inlet of microalgae carbon fixation device 3,

[0046] Fan 1 is used to send air into CO2 adsorption device 2, and ultra-low concentration carbon dioxide (400ppm) in atmosphere is captured by adsorbent in CO2 adsorption device 2, and clean air after adsorption is discharged to environment by exhaust port 8.

[0047] In some embodiments of the application, by fan 1, for collecting and transporting the flow of air flowing into CO2 adsorption device 2 can be controlled to be 50~200m 3 / h.

[0048] Referring to Fig. 2, the CO2 adsorption device 2 is provided with the wetting adsorbent 5, the spraying device 10 and the rotating shaft 7, the rotating shaft 7 is connected with the external driving device 12; the spraying device 10 is arranged at the upper end along the inside of the CO2 adsorption device 2, above the wetting adsorbent 5; one end of the inside of the CO2 adsorption device 2 is provided with the gas inlet 11 and the liquid inlet 9, the gas inlet 11 is above the liquid inlet 9; one end of the inside of the CO2 adsorption device 2 is provided with the driving device 12, the driving device 12 is connected with the power input end of the rotating shaft 7, the upper end of the rotating shaft 7 is provided with the gas outlet 8, and the lower end is provided with the liquid outlet 6; the gas outlet 8 is communicated with the vacuum pump 13, and the liquid outlet 6 is communicated with the microalgae carbon fixation device 3. The working process of the CO2 adsorption device 2 is as follows: one side of the wetting adsorbent 5 is loaded on the rotating shaft 7 and rotates with the rotating shaft 7, the air delivered by the gas inlet 11 blows the wetting adsorbent 5 and then is discharged from the gas outlet 8, and the algal liquid flowing into the CO2 adsorption device 2 from the liquid inlet 9 and the spraying device 10 is collected at the bottom of the CO2 adsorption device 2 and then flows out from the liquid outlet 6 to the microalgae carbon fixation device 3. The pH of the algal liquid flowing into or sprayed by the CO2 adsorption device 2 is 9.5-11.5.

[0049] In some embodiments of the present application, referring to Fig. 3, the wetting adsorbent 5 is a sheet material, the sheet plane of the wetting adsorbent 5 is coplanar with the rotating shaft 7; the rotating shaft 7 is provided with a plurality of columns of wetting adsorbents 5 around the circumference thereof, and each column of wetting adsorbents 5 is arranged along the length direction of the rotating shaft 7.

[0050] In some embodiments of the present application, the wetting adsorbent 5 in the CO2 adsorption device 2 comprises at least one of a quaternary ammonium resin, activated carbon and a metal organic framework, and has the function of desorbing carbon dioxide by spraying alkali solution.

[0051] In some embodiments of the present application, the flow rate of the algal liquid flowing into the liquid inlet 9 is 0.1-2 L / min, and the average residence time of the algal liquid is 3-10 s.

[0052] In some embodiments of the present application, the flow rate of the algal liquid sprayed by the spraying device 10 is 0.1-2 L / min.

[0053] In some embodiments of the present application, the rotating speed of the rotating shaft 7 in the CO2 adsorption device 2 is 0.0017-0.033 r / min. When the pH value of the algal liquid is high, it indicates that the carbon source in the algal liquid is consumed quickly, and thus the rotating speed of the rotating shaft is increased to increase the supply amount of the carbon source; when the pH value of the algal liquid is low, the rotating speed of the rotating shaft is reduced to reduce the supply amount of the carbon source.

[0054] The microalgae carbon fixation device 3 adopts an open type photobioreactor to culture microalgae, is internally connected with a pH sensor and a computer, is provided with an aeration port at the bottom, and the aeration port is connected with an aerator. 2- - The microalgae carbon fixation device 3 adopts an open type photobioreactor to culture microalgae, is internally connected with a pH sensor and a computer, is provided with an aeration port at the bottom, and the aeration port is connected with an aerator. - The microalgae carbon fixation device 3 adopts an open type photobioreactor to culture microalgae, is internally connected with a pH sensor and a computer, is provided with an aeration port at the bottom, and the aeration port is connected with an aerator.

[0055] The microalgae carbon fixation device 3 adopts an open type photobioreactor to culture microalgae, is internally connected with a pH sensor and a computer, is provided with an aeration port at the bottom, and the aeration port is connected with an aerator.

[0056] In some embodiments of the present application, 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 environmental temperature is 25℃, and the internal pH of the algae liquid is 10.5-11.5.

[0057] In some embodiments of the present application, the culture medium of the microalgae is one or a mixture of several of BG11 medium, BBM medium and Zarrouk medium.

[0058] In some embodiments of the present application, the microalgae carbon fixation device 3 contains Na + and K + in the compounded algae liquid, the molar ratio of Na + and K + is 20:1-100:1, and the regeneration rate of the adsorbent is greater than 80%. More preferably, the molar ratio of Na + and K + in the compounded algae liquid is 20:1-100:1.The ratio of the two is 40:1~60:1, the content of carbonate ions is 0.010~0.100 mol / L, and the average residence time of the algal liquid in the microalgae carbon fixation device 3 is 5s.

[0059] The solution-microalgae separation device 4 separates the solution and the microalgae product by centrifugation, and the separated solution flows into the CO2 adsorption device 2. By centrifuging the solution and the microalgae product, the separated solution flows into the CO2 adsorption device to desorb the adsorbent.

[0060] The second aspect of the present application discloses a direct air carbon fixation method for coupling algal liquid and wet adsorbent, the adsorbent 5 in the CO2 adsorption device 2 is combined with the spraying device 10, and the adsorbent 5 adsorbs carbon dioxide in the air when it is dry and desorbs when it is wet. Specifically, the CO2 adsorption device 2 adopts two adsorption working conditions of continuous adsorption and intermittent adsorption according to the measured pH value of the algal liquid in the microalgae carbon fixation device 3, and specifically includes the following two adsorption-desorption operation modes:

[0061] Mode 1: when the pH of the algal liquid is greater than 10.5, the adsorbent 5 in the CO2 adsorption device 2 rotates with the rotating shaft 7, alternately contacts and is immersed in the algal liquid at the bottom of the CO2 adsorption device 2, the air inlet 11 is always open, the spraying device 10 is always closed, the algal liquid flows into the CO2 adsorption device 2 from the liquid inlet 9 and is collected at the bottom of the device, the liquid level is higher than the center line of the rotating shaft 7, the algal 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 algal liquid flowing out of the CO2 adsorption device 2, the microalgae performs photosynthesis by taking HCO3- as carbon source, the algal liquid after pH measurement flows into the solution-microalgae separation device 4 for separation, the solution-microalgae separation device 4 separates CO2 and algal liquid therein to obtain carbon-poor algal liquid, and the carbon-poor algal liquid is transmitted to the spraying device 10 of the CO2 adsorption device 2; the specific adsorption process of this mode is that the dry adsorbent contacts the algal liquid after adsorbing CO2, CO2 is desorbed in the alkaline algal liquid with high pH value to generate carbonate and carbonate, the desorbed adsorbent is rotated above the liquid surface, dried by air and enters the adsorption state, and the adsorbent continuously adsorbs and desorbs in the CO2 adsorption device 2.

[0062] Mode 2, when the pH of the algae liquid is less than 10.5, the CO2 adsorption device is changed to a spraying intermittent mode, the liquid inlet 9 is always closed, and the liquid level is kept below the lowest point of the wetted adsorbent 5. In order to ensure that the regeneration rate of the adsorbent is greater than 80%, the CO2 adsorption device 2 can be divided into two stages of adsorption and desorption. In the adsorption stage, the gas inlet 11 is opened, and the spraying device 10 is closed. In the desorption stage, the gas inlet 11 is closed, and the spraying device 10 is opened. The vacuum pump 13 is started, and the CO2 desorbed from the adsorbent is in the form of gas and is introduced into the microalgae carbon fixation device 3. In the adsorption stage, no algae liquid flows into the adsorption device, and the bottom liquid level is always below the lowest point of the wetted adsorbent. In the desorption stage, the gas inlet is closed, the spraying device is opened, the algae liquid is sprayed from the spraying device and contacts the adsorbent, and flows to the bottom of the adsorption device.

[0063] It should be understood that in the above process, when the saturated adsorbent sprays a neutral aqueous solution, CO2 is mainly released in the form of gas; when the weak alkaline algae liquid is sprayed, part of it is absorbed by the alkaline solution, and part of it is released in the form of gas.

[0064] The compounded algae liquid in the algae carbon fixation device 3 couples the system of high-efficiency wet regeneration by direct air capture and microalgae carbon fixation. The principle is to use the algae liquid with a high pH value to desorb the wet adsorbent. The carbon dioxide adsorbed by the adsorbent is stored in the form of CO3 2- and HCO3 - in the algae liquid. The microalgae performs photosynthesis by taking HCO3 - as a carbon source to achieve the purpose of carbon fixation. When the pH value of the algae liquid is less than 10.5, the algae liquid flows out of the CO2 adsorption device after desorbing the saturated adsorbent, that is, it enters the next air adsorption cycle. The air conveying device is used to blow and dry the adsorbent, so that the adsorbent can adsorb saturated carbon dioxide again, and the cycle of direct air carbon dioxide capture and algae liquid regeneration is realized. When the pH value of the algae liquid is greater than 10.5, adsorption and desorption do not need to be performed in stages. The drying and adsorption of the adsorbent can be realized in the space above the center line of the adsorption device shaft, and the dry desorption of the adsorbent by the algae liquid can be realized in the space below the center line of the adsorption device shaft, thereby realizing continuous capture and fixation of carbon dioxide.

[0065] In a preferred example, the algae liquid sprayed in the CO2 adsorption device 2 and the carbon fixation device 3 is one of BG11 medium and Zarrouk medium or a mixture of the two. The ratio of Na + and K + in the compounded algae liquid is 40:1 to 60:1, the content of carbonate ions is 0.010 to 0.100 mol / L, and the average residence time of the algae liquid is 5 s.

[0066] The above and other embodiments will be further described in conjunction with specific examples.

[0067] Example 1

[0068] 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 environmental temperature is 25℃. The air conveying device passes dry air containing carbon dioxide (400ppm) into the CO2 adsorption device through the gas path, the air flow is 50m 3 / h, the un-adsorbed air is discharged from the exhaust port, the rotating shaft rotating speed is 0.0017r / min, the molar ratio of the compounded algal liquid Na + and K + is 60:1, the flow rate is 1L / min, the algal liquid level at the bottom of the device is flush with the center line of the rotating shaft, and the saturated adsorption capacity of the adsorbent is about 0.8mmol / g. The microalgae carbon fixation device receives the carbon-rich algal liquid flowing out of the carbon dioxide adsorption device, the microalgae performs photosynthesis by taking HCO3- as the carbon source, the algal liquid after pH determination flows to the solution-microalgae separation device for separation and calculation of the carbon fixation rate, after the system runs for 24h, the algal liquid pH is stabilized at 10.7-10.8, and the carbon fixation rate can reach 0.06g·L -1 ·D -1 .

[0069] Example 2

[0070] The difference from Example 1 is that the rotating shaft rotating speed in the CO2 adsorption device is 0.033r / min, after the system runs for 24h, the algal liquid pH is stabilized at 10.2, then the running state of the CO2 adsorption device is changed, the spraying device is turned on, and the intermittent adsorption of carbon dioxide and desorption of the algal liquid is changed, the algal liquid flow rate is still 1L / min, and the algal 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 algal liquid flowing out of the carbon dioxide adsorption device, the algal liquid after pH determination flows to the solution-microalgae separation device for separation and calculation of the carbon fixation rate, after the system runs for 24h, the algal liquid pH is stabilized at 10.4-10.5, and the carbon fixation rate can reach 0.09g·L -1 ·D -1 .

[0071] Example 3

[0072] The difference from Example 1 is that the molar ratio of the compounded algal liquid Na + and K + is 75:1, the CO2 adsorption device still runs in the continuous adsorption mode, and the rotating shaft rotating speed is 0.0017r / min. After the system runs for 24h, the algal liquid pH is stabilized at 10.9-11.0, and the carbon fixation rate can reach 0.10g·L -1 ·D -1 .

[0073] Comparing the experimental results of comparative example 1 and example 2, it can be seen that controlling the rotating speed of the rotating shaft can affect the regeneration rate of the adsorbent, and then affect the carbon supply amount of the algal liquid, and the increase of the carbon supply amount can promote the photosynthesis of the microalgae, so that the pH value of the algal liquid is restored to above 10.5. When the pH value of the algal liquid is less than 10.5, by changing the running state of the adsorption device, the spray gap mode can be used to improve the regeneration rate of the adsorbent, increase the carbon supply amount of the algal liquid, effectively promote the growth of the microalgae, and restore the pH value of the algal liquid.

[0074] Comparing the experimental results of comparative example 1 and example 3, it can be seen that different Na + and K + ratios of the algal liquid can affect the regeneration rate of the adsorbent and the growth rate of the microalgae. When the molar ratio of Na + to K + is 75:1, the maximum carbon fixation rate of the microalgae can reach 0.10 g·L -1 ·D -1 . Increasing the Na + in the algal liquid can effectively improve the desorption kinetics of the adsorbent and promote the desorption equilibrium to be reached faster.

[0075] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A direct air carbon capture system comprising a complexed algal liquid coupled to a variable moisture adsorbent, wherein the system comprises: The CO2 adsorption device (2) is provided with an air inlet (11) and a liquid inlet (9) at one end and a liquid outlet (6) and a driving device (12) at the other end. The CO2 adsorption device (2) is provided with a rotating shaft (7) inside, one end of the rotating shaft (7) is connected with the driving device (12), and a plurality of wetted adsorbents (5) are arranged on the rotating shaft (7), and a spraying device (10) is arranged above the wetted adsorbents (5), and the CO2 adsorption device (2) carries algal liquid, and the liquid level of the algal liquid is higher than the liquid outlet (6). The microalgae carbon fixation device (3) is communicated with the solution-microalgae separation device (4), and the solution-microalgae separation device (4) is communicated with the spraying device (10). The microalgae carbon fixation device (3) and the CO2 adsorption device (2) are both complex algae liquid, and the complex algae liquid is Na + K + complex algae liquid; The microalgae carbon fixation device (3) is provided with a pH sensor, and the pH sensor is connected with a computer, and the computer can control the on-off of the air inlet (11) and the liquid inlet (9), and the start-stop of the spraying device (10).

2. The direct air carbon capture system of claim 1, wherein the system further comprises a carbon capture unit. The pH value of the algal liquid flowing into the liquid inlet (9) or sprayed by the spraying device (10) is 9.5-11.

5.

3. The direct air carbon capture system of claim 1, wherein the system further comprises a carbon capture unit. The wetted adsorbent (5) is at least one of quaternized resin, activated carbon or metal organic framework.

4. The direct air carbon capture system of claim 1, wherein the system further comprises a carbon capture unit. The wetted adsorbent (5) is a sheet material. A plurality of columns of wetted adsorbents (5) are arranged along the circumference of the rotating shaft (7). The sheet-shaped wetted adsorbents (5) in each column of wetted adsorbents (5) are arranged along the length direction of the rotating shaft (7).

5. The direct air carbon capture system of claim 1, wherein the system further comprises a carbon capture unit. The flow rate of the algal liquid flowing into the liquid inlet (9) is 0.1-2 L / min, and the average residence time of the algal liquid in the CO2 adsorption device (2) is 3-10 s. The flow rate of the algal liquid sprayed by the spraying device (10) is 0.1-2 L / min. The rotating speed of the rotating shaft (7) is 0.0017-0.033 r / min.

6. The direct air carbon capture system of claim 1, wherein the system further comprises a carbon capture unit. The microalgae carbon fixation device (3) is an open type photobioreactor for culturing microalgae.

7. The direct air carbon capture system of claim 1, wherein the system further comprises a carbon capture device. The pH value of the algal liquid in the microalgae carbon fixation device (3) is 10.5-11.

5.

8. The direct air carbon capture system of claim 1, wherein the system further comprises a carbon capture device. The algal liquid in the microalgae carbon fixation device (3) is a mixture of two or more of Na2CO3, NaHCO3, K2CO3 and KHCO3. The molar ratio of Na + to K + is 20:1-100:

1.

9. The direct air carbon capture system of claim 1, wherein the system further comprises a chiller configured to cool the air to a temperature of about 0°C to about 10°C. The CO2 adsorption device (2) is communicated with a vacuum pump (13), and the vacuum pump (13) is communicated with the microalgae carbon fixation device (3).

10. A direct air carbon capture method based on the system of claim 1, wherein the method comprises, The following two adsorption and desorption operation modes are included: Mode 1, for continuous capture mode, when the pH of the algal liquid > 10.5, the air inlet (11) is opened, the spraying device (10) is closed, the liquid inlet (9) delivers the algal liquid to the CO2 adsorption device (2), the algal liquid in the CO2 adsorption device (2) is in a high position; the shaft (7) drives the dry wet adsorbent (5) to rotate, the wet adsorbent (5) adsorbs CO2 in the air during rotation, the dry wet adsorbent (5) contacts the algal liquid at the bottom of the CO2 adsorption device (2), the algal liquid absorbs CO2 in the wet adsorbent (5) to become carbon-rich algal liquid, the carbon-rich algal liquid is input into the microalgae carbon fixation device (3), the microalgae in the microalgae carbon fixation device (3) fix CO2 in the carbon-rich algal liquid through photosynthesis, after measuring the pH of the algal liquid, it is delivered to the solution-microalgae separation device (4); the solution-microalgae separation device (4) delivers the separated carbon-poor algal liquid to the spraying device (10); Mode 2, for intermittent spraying mode, when the pH of the algal liquid < 10.5, in the adsorption stage, the air inlet (11) is opened, the spraying device (10) is closed, the shaft (7) drives the dry wet adsorbent (5) to rotate, the wet adsorbent (5) adsorbs CO2 in the air during rotation, the algal liquid in the CO2 adsorption device (2) is in a high position; in the desorption stage, the air inlet (11) is closed, the spraying device (10) is opened, the spraying device (10) sprays carbon-poor algal liquid, after the carbon-poor algal liquid contacts the wet adsorbent (5), the vacuum pump (13) is started to desorb CO2 from the adsorbent in the form of gas into the microalgae carbon fixation device (3).

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