An air carbon capture method based on electric heating molten salt storage integration

Abstract

The application discloses an air carbon capture method based on electric heating molten salt storage integration, which comprises the following steps: 1) CO2 storage and water vapor heat exchange condensation; 2) heating rich liquid and desorbing CO2; 3) high-temperature lean liquid after desorption is heat-exchanged with low-temperature rich liquid through a heat exchanger, enters a mixing tank and is mixed with an inflow of an absorption liquid pool through stirring blades; 4) the absorption liquid flowing out of the mixing tank is driven into a venturi tower by a pump, is distributed into fine liquid drops by a nozzle and is upward jet flow. The application effectively reduces the regeneration energy consumption through molten salt energy storage, desorption integration design and energy cascade utilization; the air flow is comprehensively driven by jet flow and thermal pressure difference, so that an absorption tower does not need to be additionally provided with a power device, thereby reducing the absorption energy consumption; through the optimization design of the spraying layer and the absorption tower, the gas-liquid interaction is strengthened, the gas-liquid mass transfer is enhanced and the carbon capture efficiency is improved.

Description

Technical Field

[0001] This invention relates to the fields of comprehensive energy utilization and greenhouse gas emission reduction technology, and in particular to an air carbon capture method based on integrated storage and utilization of electrically heated molten salt. Background Technology

[0002] Gases that contribute to the greenhouse effect include carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons, among which CO2 accounts for 77% of total greenhouse gas emissions and is the primary cause of the greenhouse effect.

[0003] Carbon capture and storage (CCUS) technologies are categorized into carbon capture and storage (CCS), carbon capture and utilization (CCU), biomass-coupled carbon capture and storage (BECCS), and direct air capture and storage (DACCS). CCS and CCU technologies were the first to be proposed, primarily focusing on separating and recovering industrial CO2 from the atmosphere and isolating it for long-term use. However, recent climate simulations indicate that without the adoption of carbon-negative technologies such as BECCS and DACCS, it will be impossible to achieve the goal of controlling atmospheric CO2 concentrations below 450 ppm by the end of this century.

[0004] Compared to other CCUS technologies, DACCS research started later and still has significant room for development. Since the CO2 content in the air is only 420 ppm, equivalent to a partial pressure of approximately 42 Pa, physical separation methods such as adsorption and membrane separation are difficult to achieve efficient absorption. Furthermore, air contains various gaseous components, among which O2 and N2 molecules have diameters similar to CO2, resulting in poor selectivity for physical separation methods. Therefore, early DACCS schemes widely adopted chemical absorption methods using alkaline solutions and alkanolamine solutions as absorbents. However, existing chemical absorption separation technologies still have high operating energy consumption, such as the need for absorbent rich solution regeneration and forced airflow, which severely restricts their widespread application. In addition, because the DACCS process involves the utilization of multiple energy sources, some existing DACCS schemes include renewable energy power generation devices and steam turbines, as well as renewable energy heating devices and energy storage devices, greatly increasing system complexity and cost. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide an air carbon capture method based on the integrated storage and utilization of electrically heated molten salt. By optimizing the energy scheduling of storage, transfer and utilization of the electrically heated molten salt system, the operating energy consumption and cost of DACCS technology can be reduced.

[0006] The objective of this invention is achieved as follows: A method for capturing carbon in the air based on an integrated electrically heated molten salt storage system, comprising a carbon dioxide absorption section, a carbon dioxide desorption section, and an energy supply section, specifically including the following steps:

[0007] Step 1) CO2 storage and water vapor heat exchange and condensation: The low-temperature decarbonized rich liquid in the absorbent pool enters the connected U-shaped tube bundle through the liquid inlet chamber at the top of the carbon dioxide storage tank and exchanges heat with the CO2 and H2O gaseous mixture generated by the electrically heated molten salt tank. The temperature of the low-temperature decarbonized rich liquid is raised, and the water vapor is condensed into liquid. The condensed water vapor is transported to the absorbent pool through the drain valve. After the carbon dioxide storage tank reaches a certain pressure, pure CO2 gas is output from the outlet.

[0008] Step 2) Heating the rich solution and desorbing CO2: Driven by a pump, the low-temperature decarbonized rich solution enters the U-shaped tube bundle at the bottom of the electrically heated molten salt tank through the inlet chamber, where it transfers heat with the electrically heated molten salt outside the U-shaped tube bundle. Through convective heat transfer, the low-temperature rich solution is heated to a certain temperature, at which point a large amount of CO2 is desorbed and released. The gas-liquid mixture in the riser tube of the U-shaped tube bundle enters the gas-liquid separation chamber at the top of the electrically heated molten salt tank. The water vapor and CO2 mixture flows out from the gas side outlet at the top of the separation chamber, while the desorbed high-temperature lean solution flows out from the liquid side outlet at the bottom. Under the action of pressure difference, the mixed gas in the electrically heated molten salt tank will automatically flow into the carbon dioxide storage tank without the need for additional power equipment.

[0009] Step 3) The desorbed high-temperature lean solution exchanges heat with the low-temperature rich solution through a heat exchanger, and then enters the mixing tank to be mixed with the incoming flow of the absorbent pool by the stirring blades to form CO2 absorbent.

[0010] Step 4) The absorbent liquid flowing out of the mixing tank is driven by a pump into the Venturi tower, where it is distributed into fine droplets through nozzles and jetted upwards. The Venturi tower includes a converging section, a throat, and a diverging section. A spray layer is provided below the throat. The spray layer is designed to cover an area twice that of the throat. The high-speed droplets generated by the spray layer entrain air and flow upwards. When passing through the throat, the gas accelerates due to the reduced flow area, and the shear force increases, further breaking the droplets and reducing their diameter, thus increasing the gas-liquid mass transfer area. After passing through the throat, the gas velocity slows down, and the droplets begin to flow downwards under gravity, eventually flowing into the absorbent liquid pool. This process generates a significant "wind-pulling effect" due to the gas being heated by the droplets, which enhances the gas flow. Through the combined effect of the droplet jet and the thermal pressure difference, the use of additional power machinery is avoided.

[0011] Step 5) The energy supply section includes the photovoltaic array, mains power and controller; the photovoltaic array provides power; when the photovoltaic array has excess power, the controller switches the line to supply power to the mains grid.

[0012] As a further limitation of the present invention, the temperature of the low-temperature decarbonization rich liquid in step 1) is increased to 65°C~75°C.

[0013] As a further limitation of the present invention, step 2) describes heating the low-temperature rich liquid to a certain temperature of 120°C to 140°C.

[0014] As a further limitation of the present invention, the working pressure of the gas-liquid separation chamber in step 2) is 1.5 bar to 3 bar.

[0015] To increase energy storage density and enhance thermal conductivity, the electrically heated molten salt in step 2) is a ternary composite molten salt.

[0016] As a further limitation of the present invention, the upper gradually expanding part of the Venturi tower in step 4) is provided with a demister to remove small-diameter droplets carried by the air; the lower part of the Venturi tower is provided with a baffle plate to optimize air distribution.

[0017] In order to utilize the residual heat of the absorbent liquid pool to heat the air and enhance the wind-pulling effect, the absorbent liquid pool is covered with a plastic film.

[0018] Compared with existing technologies, the present invention, employing the above technical solution, offers the following advantages: In the carbon dioxide desorption section, the integrated design of the electrically heated molten salt tank and the carbon dioxide storage tank achieves comprehensive functions such as energy storage, heating of the rich liquid, gas-liquid separation, and CO2 storage. The carbon dioxide storage tank utilizes the low-temperature rich liquid for heat exchange with the CO2 and H2O gaseous mixture. On one hand, it recovers some heat energy to raise the temperature of the low-temperature rich liquid, reducing regeneration energy consumption; on the other hand, it condenses water vapor into liquid water to create a low-pressure environment, avoiding the need for other power equipment to extract the mixed gas from the electrically heated molten salt tank, thus reducing operating energy consumption. The electrically heated molten salt tank uses a ternary composite molten salt as the working fluid, which has the advantages of high energy density, high heat capacity, and excellent thermal conductivity. The high integration of molten salt energy storage and the absorbent desorption process helps reduce system construction costs and operating energy consumption. In the rising section of the U-shaped tube, as a large amount of CO2 is desorbed, the internal fluid is a gas-liquid mixture, thus utilizing natural convection to reduce the output energy consumption of the pump in maintaining the working fluid flow. In the gas-liquid separation chamber, the pressure difference with the carbon dioxide storage tank is used to achieve the self-flow of the mixed gas, thus avoiding the need for a power unit.

[0019] In the carbon dioxide absorption section, the structural characteristics of the Venturi tower, along with the spray jet and "wind-pulling" effect, accelerate the flow of air from the environment, fully utilizing the kinetic and thermal energy of the spray droplets. This avoids the need for additional power machinery and reduces system operating energy consumption. The Venturi tower's structural characteristics also mean that the spray coverage only needs to cover the throat area, effectively reducing the spray layer area and preventing air "short-circuiting." The throat's contraction characteristics accelerate the airflow and further break up the droplets, increasing the gas-liquid contact area, which is beneficial for efficient CO2 removal. Finally, the Venturi tower's gradually expanding upper section reduces the outlet airflow velocity, thereby minimizing droplet carryover from the absorption tower.

[0020] In terms of energy supply, a combination of solar photovoltaic power, grid power, and a control and dispatch system is used to achieve a stable and low-cost power supply. Solar photovoltaic power is the primary energy source, and when photovoltaic power generation exceeds system demand, power will be supplied to the grid. At night, off-peak electricity is used directly for energy supply, thus achieving comprehensive utilization of green electricity and off-peak electricity. Furthermore, due to the energy storage characteristics of electrically heated molten salt, the system's energy is mainly supplied by solar energy.

[0021] In summary, this invention can significantly reduce energy consumption, operating costs, and construction costs in the air carbon capture process, and can achieve efficient decarbonization, demonstrating significant application advantages and prospects. Attached Figure Description

[0022] Figure 1 Schematic diagram of the invention.

[0023] The components include: 1. Absorption tank; 2. Gate valve 1; 3. Pump 1; 4. Surface heat exchanger; 5. Regulating valve 1; 6. Check valve 1; 7. Flow meter 1; 8. Carbon dioxide storage tank; 9. Pump 2; 10. Electric heating molten salt tank; 11. Gate valve 2; 12. Steam trap; 13. Gate valve 3; 14. Check valve 2; 15. Regulating valve 2; 16. Pump 3; 17. Flow meter 2; 18. Mixing tank; 19. Flow meter 3; 20. Check valve 3; 21. Regulating valve 3; 22. Pump 4; 23. Pump 5; 24. Venturi tower; 25. Demister; 26. Baffle plate; 27. Spray layer; 28. Plastic film; 29. ​​Human-shaped truss; 30. Water supply tank; 31. Controller; 32. Photovoltaic array; 33. Mains power. Detailed Implementation

[0024] like Figure 1 The method for capturing carbon in the air based on an integrated electrically heated molten salt storage and utilization system includes a carbon dioxide absorption section, a carbon dioxide desorption section, and an energy supply section. Taking a 30wt% MEA aqueous solution as the CO2 absorbent as an example, the specific steps are as follows:

[0025] Step 1) CO2 storage and steam heat exchange and condensation: The operating temperature of the absorbent tank 1 is 30°C~40°C. When the online pH meter detects that the pH of the absorbent tank is 9.7~9.5, the CO2 load of the absorbent is 0.2~0.3 (mol CO2) / (mol MEA). Gate valve 2 is opened, and under the combined action of pump 3, regulating valve 5, and flow meter 7, a certain flow rate of decarbonized rich liquid is delivered to the carbon dioxide storage tank 8. During this process, heat exchanger 4 facilitates heat exchange between the low-temperature decarbonized rich liquid and the high-temperature lean liquid flowing out of the electric heating tank 10, raising the temperature of the low-temperature rich liquid to 45°C~55°C. The carbon dioxide storage tank 8 integrates CO2 storage and heat exchange functions. Its upper spherical cavity is divided into an inlet chamber and an outlet chamber by a partition. The low-temperature decarbonized rich liquid enters through the inlet chamber... The chamber enters a connected U-shaped pipe, where it undergoes sufficient convective heat exchange with the high-temperature CO2 and H2O gaseous mixture flowing out from the electrically heated molten salt tank 10. This raises the temperature of the low-temperature decarbonization rich liquid to 65°C~75°C and causes water vapor to condense into liquid. The condensed water vapor flows back to the absorption liquid pool 1 through the steam trap 12, gate valve 3 13, and check valve 2 14. The rich liquid is then transported to the electrically heated molten salt tank 10 by pump 2 9. Once the carbon dioxide storage tank 8 reaches a certain pressure, pure CO2 gas is output through pipelines or other means.

[0026] Step 2) Heating the rich liquid and desorbing CO2: The spherical chamber above the electrically heated molten salt tank 10 is divided into an inlet chamber and a gas-liquid separation chamber by a partition. The low-temperature decarbonized rich liquid enters the U-shaped tube bundle from the inlet chamber of the electrically heated molten salt tank 10 under the drive of the pump, and transfers heat with the electrically heated molten salt outside the U-shaped tube bundle. Through convective heat transfer, the low-temperature rich liquid is heated to 100°C~120°C. The heating molten salt is a ternary molten salt with a working temperature of 150°C~180°C. At this time, a large amount of CO2 is desorbed and released. The gas-liquid mixture in the riser of the U-shaped tube bundle enters the gas-liquid separation chamber of the electrically heated molten salt tank. The gas flows out from the gas side outlet at the upper end of the separation chamber, and the desorbed high-temperature lean liquid flows out from the liquid side outlet at the lower end. The working pressure of the gas-liquid separation chamber is 1.5 bar~3 bar. The carbon dioxide storage tank 8 is in a vacuum state due to water condensation. Under the action of pressure difference, the mixed gas in the electrically heated molten salt tank will automatically flow into the carbon dioxide storage tank 8.

[0027] Step 3) The desorbed high-temperature lean solution exchanges heat with the low-temperature rich solution through heat exchanger 4, reducing the temperature to 80°C~85°C. It then enters mixing tank 18 and mixes with the incoming flow from absorbent pool 1. Mixing tank 18 is equipped with stirring blades, driven by the liquid flow to enhance the mixing of the two fluids. The temperature of the mixed liquid is 55°C~65°C, and the CO2 load is 0.05~0.1 (molCO2) / (mol MEA).

[0028] Step 4) The absorbent liquid flowing out of the mixing tank 18 is driven by pump 23 into the venturi tower 24, and distributed into fine droplets through the nozzles and jetted upwards; the venturi tower 24 includes a converging section, a throat, and a diverging section; a spray layer 27 is provided 2m below the throat; the coverage area of ​​the spray layer 27 is twice that of the throat; the droplets D generated by the spray layer 27 32 With a diameter of 300-500 mm and a jet velocity of 8-12 m / s, it can entrain air upwards, simultaneously increasing the air temperature through convective heat exchange, achieving a "wind-pulling" effect that further enhances the upward airflow. Upon reaching the throat, the air velocity is further increased due to the contraction of the Venturi throat, strengthening gas-liquid interactions, including enhanced CO2 absorption, enhanced heat exchange, and enhanced force interactions. During this process, the droplets are further broken up, resulting in D... 32 The diameter is reduced to 200-400 mm, thereby increasing the gas-liquid mass transfer area. After passing through the throat, the gas velocity slows down, and the droplets begin to flow downwards under gravity, eventually flowing into the absorbent pool 1. A demister 25 is installed at the upper expanding section of the Venturi tower 24 to remove small-diameter droplets carried by the air. A guide plate 26 is installed at the lower part of the Venturi tower 24 to optimize air distribution. A humanoid truss 29 is constructed below the Venturi tower 24 to support the dynamic and static loads of the Venturi tower. A plastic film 28 is covered above the absorbent pool 1 to prevent debris from falling into the absorbent pool 1 and to utilize the residual heat of the absorbent pool 1 to preheat the air, enhancing the "wind-pulling" effect. The Venturi tower spray arrangement enhances the upward flow of gas, avoiding the use of fans and other power equipment, thus reducing energy consumption. Furthermore, it makes full use of the volume of the Venturi tower 24, causing the droplets to move upwards and then downwards, extending the gas-liquid interaction time.

[0029] Step 5) The energy supply section includes the photovoltaic array, mains power, and controller; the photovoltaic array provides power; when the photovoltaic array has excess power, the controller switches the line to supply power to the mains grid; at night, the system operates using inexpensive off-peak electricity. This achieves low-cost 24-hour operation, avoids the construction costs of other redundant equipment, and the system is simple and easy to control.

[0030] In operation, this invention provides an air carbon capture method based on an integrated electric heating molten salt storage and utilization system. Through the integrated design of molten salt energy storage, desorption, and energy cascade utilization, the regeneration energy consumption is effectively reduced. By using jet and thermal pressure difference to drive air flow, the absorption tower does not require an additional power unit, thus reducing absorption energy consumption. Through the optimized design of the spray layer and absorption tower, the gas-liquid interaction is enhanced, the gas-liquid mass transfer is improved, and the carbon capture efficiency is increased.

[0031] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A method for capturing carbon in the air based on an integrated electrically heated molten salt storage system, comprising a carbon dioxide absorption section, a carbon dioxide desorption section, and an energy supply section, characterized in that, Specifically, the following steps are included: Step 1) CO2 storage and water vapor heat exchange and condensation: The low-temperature decarbonized rich liquid in the absorbent pool enters the connected U-shaped tube bundle through the liquid inlet chamber at the top of the carbon dioxide storage tank and exchanges heat with the CO2 and H2O gaseous mixture generated by the electrically heated molten salt tank. The temperature of the low-temperature decarbonized rich liquid is raised, and the water vapor is condensed into liquid. The condensed water vapor is transported to the absorbent pool through the drain valve. After the carbon dioxide storage tank reaches a certain pressure, pure CO2 gas is output from the outlet. Step 2) Heating the rich solution and desorbing CO2: Driven by a pump, the low-temperature decarbonized rich solution enters the U-shaped tube bundle at the bottom of the electrically heated molten salt tank through the inlet chamber, where it transfers heat with the electrically heated molten salt outside the U-shaped tube bundle. Through convective heat transfer, the low-temperature rich solution is heated to a certain temperature, at which point a large amount of CO2 is desorbed and released. The gas-liquid mixture in the riser tube of the U-shaped tube bundle enters the gas-liquid separation chamber at the top of the electrically heated molten salt tank. The water vapor and CO2 mixture flows out from the gas side outlet at the top of the separation chamber, while the desorbed high-temperature lean solution flows out from the liquid side outlet at the bottom. Under the action of pressure difference, the mixed gas in the electrically heated molten salt tank will automatically flow into the carbon dioxide storage tank without the need for additional power equipment. Step 3) The desorbed high-temperature lean solution exchanges heat with the low-temperature rich solution through a heat exchanger, and then enters the mixing tank to be mixed with the incoming flow of the absorbent pool by the stirring blades to form CO2 absorbent. Step 4) The absorbent liquid flowing out of the mixing tank is driven by a pump into the Venturi tower, and is distributed into fine droplets through nozzles and jetted upwards; the Venturi tower includes a converging section, a throat, and a diverging section; a spray layer is provided below the throat; the spray coverage area of ​​the spray layer is twice that of the throat; the droplets generated by the spray layer entrain air and flow upwards, and when passing through the throat, the droplets are further broken up, resulting in a smaller diameter and an increased gas-liquid mass transfer area; after passing through the throat, the gas flow rate slows down, and at the same time, the droplets begin to flow downwards under the action of gravity, and eventually flow into the absorbent liquid pool; Step 5) The energy supply section includes the photovoltaic array, mains power and controller; the photovoltaic array provides power; when the photovoltaic array has excess power, the controller switches the line to supply power to the mains grid.

2. The air carbon capture method based on integrated electric heating molten salt storage and utilization according to claim 1, characterized in that, The temperature of the low-temperature decarbonization rich liquor in step 1) is increased to 65°C~75°C.

3. The air carbon capture method based on integrated electric heating molten salt storage and utilization according to claim 1, characterized in that, Step 2) describes heating the low-temperature rich liquid to a certain temperature of 120°C~140°C.

4. The air carbon capture method based on electrically heated molten salt storage and utilization as described in claim 1, characterized in that, The working pressure of the gas-liquid separation chamber mentioned in step 2) is 1.5 bar to 3 bar.

5. The air carbon capture method based on integrated electric heating molten salt storage and utilization according to claim 1, characterized in that, The electrically heated molten salt mentioned in step 2) is a ternary composite molten salt.

6. The air carbon capture method based on integrated electric heating molten salt storage and utilization according to claim 1, characterized in that, In step 4), the upper expanding section of the Venturi tower is equipped with a demister to remove small-diameter droplets carried by the air; the lower part of the Venturi tower is equipped with a baffle to optimize air distribution.

7. The air carbon capture method based on integrated electric heating molten salt storage and utilization according to claim 1, characterized in that, The absorbent pool is covered with a plastic film.

Images