Direct air carbon dioxide capture system and method utilizing lng cold energy

Abstract

The application discloses a direct air carbon dioxide capture and utilization system and method using LNG cold energy, which comprises an LNG gasification cold release device, an air carbon dioxide capture device and a carbon dioxide utilization device; ambient air is cooled and dehumidified by a low-temperature cold energy heat exchanger of the LNG gasification cold release device and then enters the air carbon dioxide capture device; when desorbing carbon dioxide, humid carbon dioxide released by the air carbon dioxide capture device is first cooled and dehydrated by the low-temperature cold energy heat exchanger of the LNG gasification cold release device, and then is cooled and liquefied by the low-temperature cold energy heat exchanger of the LNG gasification cold release device to obtain liquid carbon dioxide product. The application solves the problem that the capture efficiency of the direct air carbon dioxide capture system is easily affected by the humidity of ambient air, and through air cooling and dehumidification, humid carbon dioxide product gas is cooled, dehydrated, liquefied and dry ice is prepared, so that the cycle efficiency of air carbon dioxide capture and the system energy utilization efficiency are effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of greenhouse gas emission reduction technology, specifically a direct air carbon dioxide capture and utilization system and method utilizing LNG cold energy. Background Technology

[0002] Global warming and other climate change issues are serious challenges facing the world today. Studies show that anthropogenic carbon dioxide emissions are the primary cause of global warming. Stationary sources such as large fossil fuel power plants and mobile sources such as transportation account for 60% and 40% of carbon dioxide emissions, respectively. Carbon capture, utilization, and storage (CCUS) are effective means of addressing emissions from stationary sources, while mobile source emissions are characterized by small individual emissions, wide distribution, and large quantities, making them difficult to address at the source. Direct air carbon dioxide capture and utilization (DAC) technology, through engineering solutions, directly captures carbon dioxide from the air, reducing atmospheric carbon dioxide concentration and fundamentally solving the problem of mobile source emission reduction.

[0003] Currently, direct air carbon dioxide capture mainly includes technologies such as alkaline solution absorption and high-temperature regeneration, amine-based material adsorption and medium-temperature regeneration, and quaternary ammonium-based material adsorption and wet regeneration. Technologies involving medium- and high-temperature regeneration processes suffer from high energy consumption. Wet regeneration, however, utilizes water evaporation to drive carbon dioxide release and material regeneration, significantly reducing operating energy consumption and costs. Its independence from high-temperature heat sources greatly enhances its deployment flexibility. However, the carbon dioxide capture capacity of quaternary ammonium-based materials is affected by ambient humidity, decreasing sharply at relative humidity levels above 80%. Since the carbon dioxide concentration in the air is only 0.04%, direct air carbon dioxide capture requires a large volume of air. Adding conventional dehumidification equipment to remove moisture from the air would be extremely expensive. Furthermore, the carbon dioxide product gas produced by wet regeneration contains moisture, and the equipment investment and operating energy consumption for dehydration and subsequent compression into liquid carbon dioxide products are high.

[0004] The vaporization process of liquefied natural gas (LNG) in receiving terminals typically uses seawater or ambient air as a heat source, resulting in a significant waste of cold energy. Currently, the utilization of LNG cold energy is mainly in cryogenic power generation, cryogenic cold storage, and air liquefaction, which suffers from imbalances in the spatial and temporal distribution of LNG cold energy supply and demand, and the lack of cascade utilization also leads to low energy efficiency. Air carbon dioxide capture, on the other hand, requires cold energy but offers high flexibility, allowing the system to be directly constructed within or near the LNG receiving terminal.

[0005] Therefore, providing a direct air carbon dioxide capture and utilization system and method that utilizes LNG cold energy has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, this invention provides a direct air carbon dioxide capture and utilization system utilizing LNG cold energy. This system solves the problem that the capture efficiency of air carbon dioxide capture systems is easily affected by ambient humidity. By cooling and dehumidifying the air, the moist carbon dioxide product gas is cooled, dehydrated, liquefied, and dry ice is produced, effectively improving the cycle efficiency of air carbon dioxide capture and the energy utilization efficiency of the system.

[0007] Therefore, one technical solution adopted by the present invention is: a direct air carbon dioxide capture and utilization system utilizing LNG cold energy, which includes an LNG vaporization and cooling device, an air carbon dioxide capture device, and a carbon dioxide utilization device.

[0008] The LNG vaporization and cooling device includes a cold energy utilization branch and a direct vaporization branch connected in parallel with it; the cold energy utilization branch includes an LNG storage tank, an LNG booster pump, a low-temperature cold energy heat exchanger and a medium-low temperature cold energy heat exchanger connected in sequence.

[0009] The aforementioned air carbon dioxide capture device includes an air fan, an air carbon dioxide collector, and a desorption vacuum pump connected in sequence;

[0010] The air outlet of the air blower is connected to the air inlet of the medium-low temperature cold energy heat exchanger through a pipe, and the air outlet of the medium-low temperature cold energy heat exchanger is connected to the air inlet of the air carbon dioxide trap through a pipe.

[0011] The gas inlet of the desorption vacuum pump is connected to the desorption gas outlet of the air carbon dioxide trap via a pipe; the gas outlet of the desorption vacuum pump is connected to the gas inlet of the medium-low temperature cold energy heat exchanger via a pipe.

[0012] The gas inlet of the carbon dioxide utilization device is connected to the gas outlet of the low-temperature cold energy heat exchanger via a pipeline for producing dry ice.

[0013] LNG is drawn from the LNG storage tank and finally enters the downstream pipeline network for users after the first NG flow control valve. The cooling demand of the direct air carbon dioxide capture unit fluctuates (depending on the ambient temperature and humidity, operating sequence, etc.). Therefore, in order to ensure that all LNG is vaporized, a direct vaporization branch is still needed. The LNG flow ratio of the two branches is adjusted according to the cooling demand of the direct air carbon dioxide capture unit through the first NG flow control valve and the second NG flow control valve.

[0014] LNG booster pumps are used to pressurize and drive the flow of liquefied natural gas. The pumps are always running during system operation.

[0015] Furthermore, the air carbon dioxide trap includes a first air carbon dioxide trap and a second air carbon dioxide trap, which are connected in parallel; the first air carbon dioxide trap is provided with a first sprayer group and a first adsorption module, and the second air carbon dioxide trap is provided with a second sprayer group and a second adsorption module.

[0016] When the first air dioxide collector is in the CO2 collection state, the second air carbon dioxide collector is in the spray and desorption CO2 release state; when the first air dioxide collector ends the collection state and enters the spray and desorption CO2 release stage, the second air carbon dioxide collector simultaneously enters the CO2 collection state, and the two states are interchanged, thus forming a continuous cycle to continuously output CO2.

[0017] The desorption vacuum pump is connected to the desorption gas outlets of the first air carbon dioxide collector and the second air carbon dioxide collector via pipelines, and the pipelines are respectively equipped with a first desorption outlet valve and a second desorption outlet valve.

[0018] Two air carbon dioxide traps are the smallest unit for achieving continuous operation.

[0019] The liquid used for spraying is liquid water. The first adsorption module and the second adsorption module can be composed of polypropylene-based strong base anion exchange membrane, polyvinyl chloride-based strong base anion exchange membrane, polyethersulfone-based strong base anion exchange membrane, polyacetal-based strong base anion exchange membrane, etc., but are not limited to the above.

[0020] Furthermore, the low-temperature cold energy heat exchanger includes a first low-temperature cold energy heat exchanger and a second low-temperature cold energy heat exchanger, which are connected in parallel; the medium-low temperature cold energy heat exchanger includes a first medium-low temperature cold energy heat exchanger and a second medium-low temperature cold energy heat exchanger, which are connected in parallel.

[0021] The gas outlet of the second low-temperature cold energy heat exchanger is connected to the gas inlet of the second low-temperature cold energy heat exchanger via a pipeline, and a carbon dioxide compressor is installed on the pipeline;

[0022] The desorption vacuum pump is connected to the gas inlet of the second low-temperature cold energy heat exchanger.

[0023] By setting up two low-temperature heat exchangers, the energy transfer using low-temperature refrigerant is more efficient and can be adjusted by a low-temperature refrigerant circulation pump. In contrast, directly setting up a single low-temperature heat exchanger (where LNG directly exchanges heat with air) results in lower heat exchange efficiency and is difficult to adjust. The function of the first low-temperature heat exchanger is to transfer the cold energy of LNG to the second low-temperature heat exchanger via low-temperature refrigerant, thus liquefying CO2.

[0024] By installing a medium-low temperature refrigerant heat exchanger, cold energy transfer is achieved using a medium-low temperature refrigerant, resulting in higher energy efficiency. This efficiency can be adjusted via a first and a second medium-low temperature refrigerant circulation pump. The second medium-low temperature refrigerant heat exchanger is used to cool and remove moisture from the desorbed CO2 gas.

[0025] Furthermore, the medium-low temperature cold energy heat exchanger also includes a third medium-low temperature cold energy heat exchanger, and the first, second and third medium-low temperature cold energy heat exchangers are connected in parallel; the third medium-low temperature cold energy heat exchanger is used to cool the air entering the system for dehumidification.

[0026] A low-temperature refrigerant circulation pump is installed on the pipe connecting the refrigerant outlet of the first low-temperature heat exchanger and the refrigerant inlet of the second low-temperature heat exchanger.

[0027] A first medium-low temperature refrigerant circulation pump is installed on the pipe connecting the refrigerant outlet of the first medium-low temperature heat exchanger and the refrigerant inlet of the second medium-low temperature heat exchanger.

[0028] A second low-temperature refrigerant circulation pump is installed on the pipe connecting the refrigerant outlet of the first low-temperature heat exchanger and the refrigerant inlet of the third low-temperature heat exchanger.

[0029] Furthermore, a first NG flow control valve is provided between the LNG storage tank and the LNG booster pump, and a second NG flow control valve is provided on the natural gas outlet pipeline of the first medium-low temperature heat exchanger.

[0030] Furthermore, the direct gasification branch includes an LNG storage tank and an LNG vaporizer assembly connected thereto.

[0031] Furthermore, the air fan is connected to the air inlet of the third medium-low temperature heat exchanger; the air outlet of the third medium-low temperature heat exchanger is connected to the air inlets of the first and second air carbon dioxide traps via pipes, and the pipes are respectively equipped with a first air inlet valve and a second air inlet valve; the air outlet pipes of the first and second air carbon dioxide traps are respectively equipped with a first air outlet valve and a second air outlet valve.

[0032] Furthermore, the carbon dioxide utilization device includes a carbon dioxide compressor, a liquid carbon dioxide storage tank, a dry ice machine, and a dry ice storage tank;

[0033] The gas outlet of the second low-temperature cold energy heat exchanger is connected to a liquid carbon dioxide storage tank via a pipeline, and the pipeline is equipped with an unliquefied gas discharge outlet.

[0034] The liquid carbon dioxide storage tank is connected to the liquid inlet of the dry ice machine via a pipeline, and a liquid carbon dioxide regulating valve is installed on the pipeline. The solid outlet and gas outlet of the dry ice machine are respectively connected to the dry ice storage tank and the carbon dioxide compressor.

[0035] Furthermore, the circulating water inlets of the first and second air carbon dioxide traps are connected to the circulating water pump, and the circulating water outlets of the first and second air carbon dioxide traps are connected to the water storage tank. The first air carbon dioxide trap, the second air carbon dioxide trap, the circulating water pump, and the water storage tank constitute a circulating water loop.

[0036] The condensate outlets of the second and third medium-low temperature heat exchangers and the circulating water inlet of the water storage tank are connected by pipes, and the pipes are equipped with condensate recovery valves and condensate discharge valves; the water storage tank is equipped with a level gauge.

[0037] The present invention also provides a method for direct air carbon dioxide capture and utilization using the above-mentioned LNG cold energy. The humid carbon dioxide released by the air carbon dioxide capture device is first cooled and dehydrated by the medium-low temperature cold energy heat exchanger of the LNG vaporization and cooling device, and then cooled and liquefied by the low temperature cold energy heat exchanger of the LNG vaporization and cooling device to obtain liquid carbon dioxide product; the carbon dioxide utilization device uses liquid carbon dioxide to produce dry ice product.

[0038] Furthermore, the direct air carbon dioxide capture and utilization method utilizing LNG cold energy, which employs the aforementioned direct air carbon dioxide capture and utilization system utilizing LNG cold energy, includes the following steps:

[0039] S1. Start the low-temperature refrigerant circulation pump and the medium-low temperature refrigerant circulation pump on the cold energy utilization branch, and open the NG flow control valve on the cold energy utilization branch.

[0040] S2. Open the air inlet valve and air outlet valve of the air carbon dioxide trap, start the air fan, and the air is dehumidified by exchanging heat with the medium and low temperature refrigerant through the medium and low temperature cold energy heat exchanger. The air is then introduced into the air carbon dioxide trap. The carbon dioxide in the air is fixed by the adsorption module inside the air carbon dioxide trap, and the remaining gas is discharged through the air outlet valve.

[0041] S3. Close the air inlet valve and air outlet valve, open the circulating water inlet valve and circulating water outlet valve of the air carbon dioxide trap, start the circulating water pump and sprayer group, and the water in the storage tank is sprayed into the adsorption module in the air carbon dioxide trap through the circulating water pump and sprayer group, and then discharged into the storage tank through the bottom circulating water outlet and the pipeline for circulation.

[0042] S4. Stop the circulating water pump, close the circulating water inlet valve and the circulating water outlet valve, open the desorption outlet valve of the air carbon dioxide trap, start the desorption vacuum pump and the carbon dioxide compressor. The desorbed gas pumped out by the desorption vacuum pump exchanges heat with the medium and low temperature refrigerant to remove water through the medium and low temperature cold energy heat exchanger. The carbon dioxide is compressed in the carbon dioxide compressor. The high-pressure carbon dioxide is liquefied after exchanging heat with the low temperature refrigerant through the low temperature cold energy heat exchanger and enters the liquid carbon dioxide storage tank.

[0043] S5. Open the liquid carbon dioxide regulating valve, and the liquid carbon dioxide enters the dry ice machine. The produced dry ice enters the dry ice storage tank, and the by-product carbon dioxide gas re-enters the carbon dioxide compressor for compression and liquefaction, thus achieving recycling.

[0044] S6. Repeat operations S2-S4 to form a continuous operation cycle.

[0045] Medium and low temperature refrigerants: R22, R404A, R407C, R410A, R502, etc., but not limited to the above.

[0046] Low-temperature refrigerants: R14, R23, R116, etc., but not limited to the above.

[0047] Furthermore, when the low-temperature cold energy heat exchanger is running, the condensate drain valve located between the low-temperature cold energy heat exchanger and the air carbon dioxide trap is opened to drain the condensate; when the circulating water pump stops running, when the level gauge of the water storage tank shows that the liquid level is lower than the minimum value, the condensate recovery valve located between the low-temperature cold energy heat exchanger and the air carbon dioxide trap is opened and the condensate drain valve is closed to replenish water into the water storage tank; when the level gauge of the water storage tank shows that the liquid level reaches the maximum value, the condensate drain valve is opened and the condensate recovery valve is closed.

[0048] Furthermore, when the demand for dry ice products is low, the flow rate of liquid carbon dioxide entering the dry ice machine can be reduced by adjusting the liquid carbon dioxide regulating valve, thereby reducing the dry ice output; when the demand for dry ice products is high, the flow rate of liquid carbon dioxide can be increased by adjusting the liquid carbon dioxide regulating valve, thereby increasing the dry ice output.

[0049] The beneficial effects of this invention are as follows:

[0050] Air carbon dioxide capture is limited by the chemical properties of materials, and its capture capacity significantly decreases under high ambient humidity. This invention utilizes LNG cold energy to dehumidify the air before carbon dioxide capture, which improves the efficiency of carbon dioxide recycling and significantly enhances the environmental adaptability of the air carbon dioxide capture process. The carbon dioxide product gas regenerated by the carbon dioxide capture system contains a large amount of moisture, which conventional processes require condensers and multi-stage compression equipment for liquefaction. This invention utilizes LNG cold energy in a tiered manner: the medium-low temperature range (-40℃ to -20℃) is used to remove moisture from the product gas, and the low temperature range (-80℃ to -60℃) is used for carbon dioxide liquefaction and dry ice production. Compared to traditional air carbon dioxide capture processes, this significantly reduces the size of the compressor equipment and lowers power consumption. Conventional air carbon dioxide processes suffer from severe desorption of circulating water, requiring regular replenishment. This invention collects a portion of the air condensate from the capture process and the product gas condensate from the regeneration process to supplement the desorption recycling water, effectively saving water and improving the utilization rate of raw material resources. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1This is a structural block diagram of the direct air carbon dioxide capture and utilization system utilizing LNG cold energy according to the present invention. The system comprises: 1. LNG storage tank; 2. LNG vaporizer assembly; 3. LNG booster pump; 4. First low-temperature cold energy heat exchanger; 5. First medium-low temperature cold energy heat exchanger; 6. Low-temperature refrigerant circulation pump; 7. Second low-temperature cold energy heat exchanger; 8. First medium-low temperature refrigerant circulation pump; 9. Second medium-low temperature refrigerant circulation pump; 10. Second medium-low temperature cold energy heat exchanger; 11. Third medium-low temperature cold energy heat exchanger; 12. First NG flow control valve; 13. Second NG flow control valve; 14. Air fan; 15. First air carbon dioxide capture device; 16. Second air carbon dioxide capture device; 17. First sprayer assembly; 18. Second sprayer assembly; 19. First adsorption module. ; 20. Second adsorption module; 21. First air inlet valve; 22. Second air inlet valve; 23. First air outlet valve; 24. Second air outlet valve; 25. Desorption vacuum pump; 26. Carbon dioxide compressor; 27. Liquid carbon dioxide storage tank; 28. Dry ice machine; 29. ​​Dry ice storage tank; 30. First desorption outlet valve; 31. Second desorption outlet valve; 32. Liquid carbon dioxide regulating valve; 33. Circulating water pump; 34. Water storage tank; 35. Level gauge; 36. First circulating water inlet valve; 37. Second circulating water inlet valve; 38. First circulating water outlet valve; 39. Second circulating water outlet valve; 40. Condensate discharge valve; 41. Condensate recovery valve. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In the following examples, LNG stands for Liquefied Natural Gas; NG stands for Natural Gas.

[0055] Example 1

[0056] Please see the appendix Figure 1 This is a schematic diagram of a direct air carbon dioxide capture and utilization system that utilizes the cold energy of LNG. The system includes an LNG vaporization and cooling device, an air carbon dioxide capture device, and a carbon dioxide utilization device.

[0057] The LNG vaporization and cooling device includes a cold energy utilization branch consisting of an LNG storage tank 1, an LNG booster pump 3, a first cryogenic cold energy heat exchanger 4, a second cryogenic cold energy heat exchanger 7, a first medium-low temperature cold energy heat exchanger 5, a second medium-low temperature cold energy heat exchanger 10, and a third medium-low temperature cold energy heat exchanger 11 connected in sequence, and a direct vaporization branch consisting of the LNG storage tank 1 and the LNG vaporizer group 2. In the cold energy utilization branch, a first NG flow control valve 12 is installed between the LNG storage tank 1 and the LNG booster pump 3, and a second NG flow control valve 13 is installed on the natural gas outlet pipeline of the first medium-low temperature cold energy heat exchanger 5. A cryogenic cold energy circulation pump 6 is installed on the pipeline connecting the refrigerant outlet of the first cryogenic cold energy heat exchanger 4 and the refrigerant inlet of the second cryogenic cold energy heat exchanger 7. A first low-temperature refrigerant circulation pump 8 is installed on the pipe connecting the refrigerant outlet of the first low-temperature refrigerant heat exchanger 5 to the refrigerant inlet of the second low-temperature refrigerant heat exchanger 10, and a second low-temperature refrigerant circulation pump 9 is installed on the pipe connecting the refrigerant outlet of the first low-temperature refrigerant heat exchanger 5 to the refrigerant inlet of the third low-temperature refrigerant heat exchanger 11.

[0058] LNG vaporizer group 2 is always running, and its flow rate is adjusted as needed by LNG.

[0059] The air carbon dioxide capture device includes an air fan 14, a first air carbon dioxide collector 15, a second air carbon dioxide collector 16, and a desorption vacuum pump 25 connected in sequence. The air fan is connected to the air inlet of a third medium-low temperature heat exchanger 11. The air inlets of the first air carbon dioxide collector 15 and the second air carbon dioxide collector 16 are respectively connected to the air outlet of the third medium-low temperature heat exchanger 11 via pipes, and the pipes are respectively equipped with a first air inlet valve 21 and a second air inlet valve 22. The first air carbon dioxide collector 15 is equipped with a first sprayer group 17 and a first adsorption module 19, and the second air carbon dioxide collector 16 is equipped with a second sprayer group 18 and a second adsorption module 20. The air outlet pipes of the first air carbon dioxide collector 15 and the second air carbon dioxide collector 16 are respectively equipped with a first air outlet valve 23 and a second air outlet valve 24. The desorbed gas outlets of the first air carbon dioxide trap 15 and the second air carbon dioxide trap 16 are respectively connected to the desorption vacuum pump 25 via pipelines, with a first desorption outlet valve 30 and a second desorption outlet valve 31 respectively installed on the pipelines. The desorption vacuum pump 25 is connected to the gas inlet of the second medium-low temperature heat exchanger 10. The circulating water inlets of the first air carbon dioxide trap 15 and the second air carbon dioxide trap 16 are connected to the circulating water pump 33, and the circulating water outlets of the first air carbon dioxide trap 15 and the second air carbon dioxide trap 16 are connected to the water storage tank 34 to form a circulating water loop. The circulating water inlet of the water storage tank 34 is also connected to the condensate drain outlets of the second medium-low temperature heat exchanger 10 and the third medium-low temperature heat exchanger 11 via pipelines, with a condensate recovery valve 41 and a condensate discharge valve 40 installed on the pipelines. A level gauge 35 is installed inside the water storage tank 34.

[0060] The carbon dioxide utilization device includes a carbon dioxide compressor 26, a liquid carbon dioxide storage tank 27, a dry ice machine 28, and a dry ice storage tank 29 connected in sequence. The carbon dioxide compressor 26 is connected via pipes to the gas outlet of the second medium-low temperature heat exchanger 10 and the gas inlet of the second low-temperature heat exchanger 7. The liquid carbon dioxide storage tank 27 is connected via a pipe to the liquid outlet of the second low-temperature heat exchanger 7, and the pipe is equipped with an unliquefied gas discharge outlet. The liquid carbon dioxide storage tank 27 is connected via a pipe to the liquid inlet of the dry ice machine 28, and the pipe is equipped with a liquid carbon dioxide regulating valve 32. The solid outlet and gas outlet of the dry ice machine 28 are connected to the dry ice storage tank 29 and the carbon dioxide compressor 26, respectively.

[0061] Example 2

[0062] The direct air carbon dioxide capture and utilization system utilizing LNG cold energy described in Example 1, and the method for direct air carbon dioxide capture and utilization utilizing LNG cold energy, include the following steps:

[0063] S1. Start the low-temperature refrigerant circulation pump 6, the first medium-low temperature refrigerant circulation pump 8, and the second medium-low temperature refrigerant circulation pump 9. Open the first NG flow control valve 12 and the second NG flow control valve 13.

[0064] S2. Open the first air inlet valve 21 and the first air outlet valve 23, start the air fan 14, and after the air passes through the third medium and low temperature cold energy heat exchanger 11 and the medium and low temperature refrigerant for heat exchange and dehumidification, it is introduced into the first air carbon dioxide trap 15. The carbon dioxide in the air is fixed by the first adsorption module 19, and the remaining gas is discharged through the first air outlet valve 23.

[0065] S3. Close the first air inlet valve 21 and the first air outlet valve 23, open the first circulating water inlet valve 36 and the first circulating water outlet valve 38, start the circulating water pump 33 and the first sprayer group 17. The water in the storage tank 34 is sprayed to the first adsorption module 19 through the circulating water pump 33 and the first sprayer group 17, and then discharged into the storage tank 34 through the bottom circulating water outlet, the first circulating water outlet valve 38 and the pipeline, and circulates.

[0066] S4. Stop the circulating water pump 33, close the first circulating water inlet valve 36 and the first circulating water outlet valve 38, open the first desorption outlet valve 30, start the desorption vacuum pump 25 and the carbon dioxide compressor 26. After the desorbed gas exchanges heat with the medium and low temperature refrigerant in the second medium and low temperature cold energy heat exchanger 10 to remove water, the carbon dioxide is compressed in the carbon dioxide compressor 26. After the high-pressure carbon dioxide exchanges heat with the low temperature refrigerant in the second low temperature cold energy heat exchanger 7 to liquefy, it enters the liquid carbon dioxide storage tank 27.

[0067] S5. Open the liquid carbon dioxide regulating valve 32, and the liquid carbon dioxide enters the dry ice machine 28. The produced dry ice enters the dry ice storage tank 29, and the by-product carbon dioxide gas re-enters the carbon dioxide compressor 26 for compression, thus achieving recycling.

[0068] S6. While operating steps S3-S4, open the second air inlet valve 22 and the second air outlet valve 24. The cooled and dehumidified air is introduced into the second air carbon dioxide trap 16. The carbon dioxide in the air is fixed by the second adsorption module 20, and the remaining gas is discharged through the second air outlet valve 24.

[0069] S7. Close the second air inlet valve 22 and the second air outlet valve 24, open the second circulating water inlet valve 37 and the second circulating water outlet valve 39, start the circulating water pump 33 and the second sprayer group 18. The water in the storage tank 34 is sprayed to the second adsorption module 20 through the circulating water pump 33 and the second sprayer group 18, and then discharged into the storage tank 34 through the bottom circulating water outlet, the second circulating water outlet valve 39 and the pipeline, and circulates.

[0070] S8. Stop the circulating water pump 33, close the second circulating water inlet valve 37 and the second circulating water outlet valve 39, open the second desorption outlet valve 31, and the desorbed gas exchanges heat with the low-temperature refrigerant and removes water through the second medium-low temperature cold energy heat exchanger 10. The carbon dioxide is compressed in the carbon dioxide compressor 26, and the high-pressure carbon dioxide is liquefied by exchanging heat with the low-temperature refrigerant through the second low temperature cold energy heat exchanger 7 and enters the liquid carbon dioxide storage tank 27.

[0071] S9. While performing steps S7-S8, repeat step S2.

[0072] S10. After completing operation S2, repeat operations S3-S4, and simultaneously repeat operation S6.

[0073] S11. After completing operation S6, repeat operations S7-S8, and at the same time repeat operation S2.

[0074] S12. Repeat the S10-S11 operation to form a continuous operation cycle.

[0075] When the second and third medium-low temperature cold energy heat exchangers 10 and 11 are running, the condensate drain valve 40 is opened to drain the condensate. During periods when the circulating water pump is not running, when the level gauge 35 shows a level below the minimum value, the condensate recovery valve 41 is opened, and the condensate drain valve 40 is closed to replenish water into the storage tank 34. When the level gauge 35 shows a level reaching the maximum value, the condensate drain valve 40 is opened, and the condensate recovery valve 41 is closed.

[0076] When the demand for dry ice products is low, the flow rate of liquid carbon dioxide entering the dry ice machine 28 can be reduced by adjusting the liquid carbon dioxide regulating valve 32 to decrease the dry ice production; when the demand for dry ice products is high, the flow rate of liquid carbon dioxide can be increased by adjusting the liquid carbon dioxide regulating valve 32 to increase the dry ice production.

[0077] When the ambient humidity is low, the air dehumidification capacity is small. The LNG flow rate in the cold energy utilization branch can be reduced by the first NG flow control valve and the second NG flow control valve 13 to ensure the LNG vaporization effect. When the ambient humidity is high, the air dehumidification demand is high. The LNG flow rate in the cold energy utilization branch can be increased by the first NG flow control valve 12 and the second NG flow control valve 13 to ensure the air carbon dioxide capture effect.

Claims

1. A direct air carbon dioxide capture and utilization system utilizing LNG cold energy, characterized in that, This includes LNG vaporization and cooling units, air carbon dioxide capture units, and carbon dioxide utilization units; The LNG vaporization and cooling device includes a cold energy utilization branch and a direct vaporization branch connected in parallel with it; the cold energy utilization branch includes an LNG storage tank (1), an LNG booster pump (3), a low-temperature cold energy heat exchanger and a medium-low temperature cold energy heat exchanger connected in sequence. The air carbon dioxide capture device includes an air fan (14), an air carbon dioxide collector, and a desorption vacuum pump (25) connected in sequence. The air outlet of the air blower (14) is connected to the air inlet of the medium and low temperature cold energy heat exchanger through a pipe, and the air outlet of the medium and low temperature cold energy heat exchanger is connected to the air inlet of the air carbon dioxide trap through a pipe. The gas inlet of the desorption vacuum pump (25) is connected to the desorption gas outlet of the air carbon dioxide trap via a pipe; the gas outlet of the desorption vacuum pump (25) is connected to the gas inlet of the medium and low temperature cold energy heat exchanger via a pipe. The gas inlet of the carbon dioxide utilization device is connected to the gas outlet of the low-temperature cold energy heat exchanger via a pipeline for producing dry ice. The low-temperature cold energy heat exchanger includes a first low-temperature cold energy heat exchanger (4) and a second low-temperature cold energy heat exchanger (7), which are connected in parallel; the medium-low temperature cold energy heat exchanger includes a first medium-low temperature cold energy heat exchanger (5) and a second medium-low temperature cold energy heat exchanger (10), which are connected in parallel. The gas outlet of the second low-temperature cold energy heat exchanger (10) is connected to the gas inlet of the second low-temperature cold energy heat exchanger (7) through a pipeline, and a carbon dioxide compressor (26) is provided on the pipeline. The desorption vacuum pump (25) is connected to the gas inlet of the second medium-low temperature cold energy heat exchanger (10); A first NG flow control valve (12) is provided between the LNG storage tank (1) and the LNG booster pump (3), and a second NG flow control valve (13) is provided on the natural gas outlet pipeline of the first medium and low temperature cold energy heat exchanger (5). And / or, the direct vaporization branch includes an LNG storage tank (1) and an LNG vaporizer assembly (2) connected thereto.

2. The direct air carbon dioxide capture and utilization system utilizing LNG cold energy according to claim 1, characterized in that, The air carbon dioxide trap includes a first air carbon dioxide trap (15) and a second air carbon dioxide trap (16), which are connected in parallel. The first air carbon dioxide trap (15) is provided with a first sprayer group (17) and a first adsorption module (19), and the second air carbon dioxide trap (16) is provided with a second sprayer group (18) and a second adsorption module (20). The desorption vacuum pump (25) is connected to the desorption gas outlets of the first air carbon dioxide trap (15) and the second air carbon dioxide trap (16) through pipelines, and the pipelines are respectively provided with a first desorption outlet valve (30) and a second desorption outlet valve (31).

3. The direct air carbon dioxide capture and utilization system utilizing LNG cold energy according to claim 1, characterized in that, The medium-low temperature cold energy heat exchanger also includes a third medium-low temperature cold energy heat exchanger (11), and the first medium-low temperature cold energy heat exchanger (5), the second medium-low temperature cold energy heat exchanger (10) and the third medium-low temperature cold energy heat exchanger (11) are connected in parallel; A low-temperature refrigerant circulation pump (6) is installed on the pipe connecting the refrigerant outlet of the first low-temperature heat exchanger (4) and the refrigerant inlet of the second low-temperature heat exchanger (7). A first low-temperature refrigerant circulation pump (8) is installed on the pipe connecting the refrigerant outlet of the first low-temperature cold energy heat exchanger (5) and the refrigerant inlet of the second low-temperature cold energy heat exchanger (10). A second low-temperature refrigerant circulation pump (9) is installed on the pipe connecting the refrigerant outlet of the first low-temperature cold energy heat exchanger (5) and the refrigerant inlet of the third low-temperature cold energy heat exchanger (11).

4. The direct air carbon dioxide capture and utilization system utilizing LNG cold energy according to claim 1, characterized in that, The air fan (14) is connected to the air inlet of the third medium-low temperature cold energy heat exchanger (11); the air outlet of the third medium-low temperature cold energy heat exchanger (11) is connected to the air inlet of the first air carbon dioxide trap (15) and the second air carbon dioxide trap (16) respectively through pipes, and the pipes are respectively equipped with a first air inlet valve (21) and a second air inlet valve (22); the air outlet pipes of the first air carbon dioxide trap (15) and the second air carbon dioxide trap (16) are respectively equipped with a first air outlet valve (23) and a second air outlet valve (24).

5. The direct air carbon dioxide capture and utilization system utilizing LNG cold energy according to claim 1, characterized in that, The carbon dioxide utilization device includes a carbon dioxide compressor (26), a liquid carbon dioxide storage tank (27), a dry ice machine (28), and a dry ice storage tank (29). The gas outlet of the second low-temperature cold energy heat exchanger (7) is connected to the liquid carbon dioxide storage tank (27) through a pipeline, and the pipeline is provided with an unliquefied gas discharge outlet; The liquid carbon dioxide storage tank (27) is connected to the liquid inlet of the dry ice machine (28) through a pipeline. A liquid carbon dioxide regulating valve (32) is provided on the pipeline. The solid outlet and gas outlet of the dry ice machine (28) are respectively connected to the dry ice storage tank (29) and the carbon dioxide compressor (26).

6. The direct air carbon dioxide capture and utilization system utilizing LNG cold energy according to claim 1, characterized in that, The circulating water inlets of the first air carbon dioxide trap (15) and the second air carbon dioxide trap (16) are connected to the circulating water pump (33), and the circulating water outlets of the first air carbon dioxide trap (15) and the second air carbon dioxide trap (16) are connected to the water storage tank (34). The first air carbon dioxide trap (15), the second air carbon dioxide trap (16), the circulating water pump (33) and the water storage tank (34) constitute a circulating water loop. The condensate outlet of the second medium-low temperature cold energy heat exchanger (10) and the third medium-low temperature cold energy heat exchanger (11) are connected to the circulating water inlet of the water storage tank (34) by a pipeline. The pipeline is equipped with a condensate recovery valve (41) and a condensate discharge valve (40). The water storage tank (34) is equipped with a level gauge (35).

7. A method for direct air carbon dioxide capture and utilization using LNG cold energy, employing the system described in any one of claims 1-6, characterized in that, The humid carbon dioxide released by the air carbon dioxide capture device is first cooled and dehydrated by the medium-low temperature cold energy heat exchanger of the LNG vaporization and cooling device, and then liquefied by the low temperature cold energy heat exchanger of the LNG vaporization and cooling device to obtain liquid carbon dioxide product; the carbon dioxide utilization device uses liquid carbon dioxide to produce dry ice product.

8. The method according to claim 7, characterized in that, Including the following steps: S1. Start the low-temperature refrigerant circulation pump and the medium-low temperature refrigerant circulation pump on the cold energy utilization branch, and open the NG flow control valve on the cold energy utilization branch. S2. Open the air inlet valve and air outlet valve of the air carbon dioxide trap, start the air fan (14), and after the air passes through the medium and low temperature cold energy heat exchanger and the medium and low temperature refrigerant for heat exchange and dehumidification, it is introduced into the air carbon dioxide trap. The carbon dioxide in the air is fixed by the adsorption module in the air carbon dioxide trap, and the remaining gas is discharged through the air outlet valve. S3. Close the air inlet valve and the air outlet valve, open the circulating water inlet valve and the circulating water outlet valve of the air carbon dioxide trap, start the circulating water pump (33) and the sprayer group, and the water in the storage tank (34) is sprayed into the adsorption module in the air carbon dioxide trap through the circulating water pump (33) and the sprayer group, and then discharged into the storage tank (34) through the pipeline from the bottom circulating water outlet, and circulates. S4. Stop the circulating water pump (33), close the circulating water inlet valve and the circulating water outlet valve, open the desorption outlet valve of the air carbon dioxide trap, start the desorption vacuum pump (25) and the carbon dioxide compressor (26). The desorbed gas pumped out by the desorption vacuum pump (25) is dehydrated by exchanging heat with the medium and low temperature refrigerant through the medium and low temperature cold energy heat exchanger. The carbon dioxide is compressed in the carbon dioxide compressor (26). The high pressure carbon dioxide is liquefied by exchanging heat with the low temperature refrigerant through the low temperature cold energy heat exchanger and then enters the liquid carbon dioxide storage tank (27). S5. Open the liquid carbon dioxide regulating valve (32), the liquid carbon dioxide enters the dry ice machine (28), the produced dry ice enters the dry ice storage tank (29), and the by-product carbon dioxide gas enters the carbon dioxide compressor (26) again for compression, so as to achieve recycling. S6. Repeat operations S2-S4 to form a continuous operation cycle.

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