Carbon dioxide capture and conversion system and method based on calcium carbonate hydrogenation methanation

Abstract

The invention provides a carbon dioxide capture and conversion system and method based on calcium carbonate hydrogenation methanation, and relates to the technical field of carbon neutralizer.The system comprises a carbon dioxide capture unit, a pressurized feeding system, a reaction unit, a gas-solid separation unit and a methane separation and compression module; green carbon reacts with calcium hydroxide to generate calcium carbonate, green hydrogen and calcium carbonate are pressurized and mixed through a pressurized feeding system and then heated and pressurized in a reaction unit to react to obtain a gas-phase product and calcium hydroxide, and a green methane product is separated from the gas-phase product. Through the carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation, calcium circulation can be realized at a low temperature, so that the utilization rate of calcium can be improved, green carbon capture and resource conversion reaction conditions are optimized, related requirements of equipment are reduced, and the production cost is reduced. Furthermore, the adaptability and the flexibility based on calcium carbonate hydrogenation methanation can be improved.

Description

Technical Field

[0001] This application belongs to the field of carbon neutrality treatment technology, and in particular relates to a carbon dioxide (CO2) capture and conversion system and method based on the hydrogenation and methanation of calcium carbonate (CaCO3). Background Technology

[0002] Global climate change has become a major challenge facing humanity, and reducing atmospheric CO2 concentration is an international consensus. Calcium cycle technology is considered one of the promising carbon capture technologies due to its low adsorbent cost and high CO2 capture efficiency.

[0003] In related technologies, calcium oxide (CaO) can be reacted with CO2 to generate CaCO3 for capture. The CaCO3 is then calcined and decomposed at high temperature (usually >900 degrees Celsius) to regenerate CaO and high-concentration CO2 for storage or utilization.

[0004] However, the extremely high regeneration temperature results in huge energy consumption for calcium cycling and stringent equipment requirements, which severely restricts its industrial application. Summary of the Invention

[0005] This application provides a carbon dioxide capture and conversion system and method based on calcium carbonate hydrogenation and methanation, which solves the problem that the extremely high regeneration temperature leads to huge energy consumption in calcium cycling and demanding equipment requirements, which seriously restricts its industrial application.

[0006] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, embodiments of this application provide a carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation, characterized in that the carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation includes: a carbon dioxide capture unit, a pressurized feeding system, a reaction unit, a gas-solid separation unit, and a methane separation and compression module. The carbon dioxide capture unit is connected to the pressurized feeding system to obtain green carbon, which reacts with calcium hydroxide in the carbon dioxide capture unit to generate calcium carbonate, and the calcium carbonate is delivered to the pressurized feeding system. The green carbon is carbon dioxide captured from the atmosphere. The pressurized feeding system is connected to the reaction unit and is used to mix the pressurized green hydrogen with the calcium carbonate and to deliver the mixed calcium carbonate and green hydrogen to the reaction unit. The green hydrogen is hydrogen produced by waste wind and solar power. The reaction unit is used to heat and pressurize the mixed calcium carbonate and green hydrogen, so that the mixed calcium carbonate and green hydrogen react to obtain gaseous products and calcium hydroxide, and the gaseous products are delivered to the gas-solid separation unit. The gas-solid separation unit is used to separate the gaseous products and the calcium hydroxide to obtain unreacted green hydrogen, green methane and the calcium hydroxide. The methane separation and compression module is connected to the gas-solid separation unit and is used to separate the green methane and unreacted green hydrogen to obtain green methane product, and to deliver the unreacted green hydrogen to the hydrogen compressor of the pressurized feed system.

[0007] Optionally, the pressurized feeding system includes: a hydrogen compressor and a solid feed unit; The hydrogen compressor is used to obtain the green hydrogen and pressurize the green hydrogen to obtain the pressurized green hydrogen; The solid feed unit is connected to the carbon dioxide capture unit and is used to obtain the calcium carbonate in the carbon dioxide capture unit.

[0008] Optionally, the carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation further includes: an adsorbent recycling unit; The adsorbent circulation unit is connected to the carbon dioxide capture unit and the gas-solid separation unit respectively, and is used to deliver the calcium hydroxide separated in the gas-solid separation unit to the carbon dioxide capture unit.

[0009] Optionally, the carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation further includes: a heat energy recovery and management system; The heat recovery and management system includes: a first heat exchanger, a second heat exchanger, and a third heat exchanger; The first heat exchanger is used to absorb the heat generated when the mixed calcium carbonate and green hydrogen react in the reaction unit, and to transfer the heat to the third heat exchanger. The second heat exchanger is used to absorb the heat of the gaseous products in the gas-solid separation unit and transfer the heat to the third heat exchanger. The third heat exchanger is used to provide heat to the pressurized feeding system based on the heat transferred by the first and second heat exchangers, so as to preheat the mixed calcium carbonate and green hydrogen.

[0010] Optionally, the system further includes: an electrolytic cell; The electrolyzer is used to produce green hydrogen through an electrolytic reaction based on the curtailment of wind and solar power, and to transfer the green hydrogen to the hydrogen compressor.

[0011] Optionally, the carbon dioxide capture unit includes a capture inlet and a capture outlet; The capture inlet is used to obtain the raw material gas containing the green carbon, so that the green carbon in the raw material gas reacts with the calcium hydroxide in the carbon dioxide capture unit to obtain the calcium carbonate; The capture outlet is used to discharge gases other than the green carbon from the raw material gas.

[0012] Optionally, the carbon dioxide capture unit is a turbulent bed, moving bed, or fixed bed adsorption device.

[0013] Optionally, the gas-solid separation unit is at least one of a cyclone separator, a ceramic filter, or a bag filter.

[0014] In a second aspect, embodiments of this application provide a carbon dioxide capture and conversion method based on calcium carbonate hydrogenation methanation, characterized in that it is applied to a carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation as described in any of the first aspects, the method comprising: Green carbon is obtained through a carbon dioxide capture unit, which reacts with calcium hydroxide in the carbon dioxide capture unit to generate calcium carbonate. The green carbon is carbon dioxide captured from the atmosphere. The calcium carbonate and green hydrogen are mixed and preheated by a pressurized feeding system to obtain mixed calcium carbonate and green hydrogen, wherein the green hydrogen is hydrogen produced by waste wind and solar power. The mixed calcium carbonate and green hydrogen are heated and pressurized in the reaction unit to cause the mixed calcium carbonate and green hydrogen to react and obtain gaseous products and calcium hydroxide. The gaseous products and calcium hydroxide are separated by the gas-solid separation unit to obtain unreacted green hydrogen, green methane and calcium hydroxide, and the calcium hydroxide is then transported to the carbon dioxide capture unit. The unreacted green hydrogen and green methane are separated by a methane separation and compression module to obtain a green methane product, and the unreacted green hydrogen is then fed into the hydrogen compressor of the pressurized feed system.

[0015] This application provides a carbon dioxide capture and conversion system based on the hydrogenation and methanation of calcium carbonate. The system includes a carbon dioxide capture unit and a reaction unit connected to a pressurized feed system, a gas-solid separation unit connected to the reaction unit, and a methane separation and compression module connected to the gas-solid separation unit. The carbon dioxide capture unit captures green carbon, which reacts with calcium hydroxide to produce calcium carbonate. The pressurized green hydrogen is then mixed with the calcium carbonate via the pressurized feed system. The mixed calcium carbonate and green hydrogen are then heated and pressurized within the reaction unit, causing them to react and produce a gaseous product and the calcium hydroxide. The gas-solid separation unit separates the gaseous product and the calcium hydroxide, yielding unreacted green hydrogen, green methane, and calcium hydroxide. Finally, the methane separation and compression module separates the green methane and the unreacted green hydrogen to obtain a green methane product. The carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation described above can achieve calcium cycling at lower temperatures, thereby improving calcium utilization and reducing equipment requirements, and further enhancing the adaptability and flexibility of calcium carbonate hydrogenation methanation-based systems.

[0016] 1. Break through the energy consumption bottleneck of high temperature (>900℃) in traditional calcium recycling and regeneration, and reduce the regeneration temperature to the medium temperature range (700-800℃).

[0017] 2. Completely solve the thermal management problems of traditional CO2 catalytic hydrogenation reaction, which is characterized by intense exothermic reaction (ΔH = -165 kJ / mol), easy overheating of the bed, and easy deactivation of the catalyst.

[0018] 3. To achieve the capture and conversion of green CO2 directly from low-concentration CO2 sources such as air or industrial exhaust, overcoming its dependence on high-concentration CO2 sources.

[0019] 4. Chemically store intermittent renewable energy (curtailed wind and solar power) in the form of green hydrogen in high-energy-density CH4, simultaneously addressing the issues of green hydrogen consumption, CO2 emission reduction, and the intertemporal and spatial distribution of renewable energy.

[0020] 5. By optimizing system energy integration, the external energy input is significantly reduced, improving the economic efficiency of the entire process. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation proposed in an embodiment of this application; Figure 2 This is a schematic diagram of another carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation proposed in an embodiment of this application. Figure 3This is a schematic diagram of another carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation proposed in an embodiment of this application. Figure 4 This is a schematic diagram of another carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation proposed in an embodiment of this application. Figure 5 This is a schematic flowchart illustrating a carbon dioxide capture and conversion method based on the hydrogenation and methanation of calcium carbonate, provided for an embodiment of this application. Detailed Implementation

[0022] In the following description, specific details such as particular system structures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application can also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known techniques and structures for converting carbon dioxide to methane are omitted so as not to obscure the description of this application with unnecessary detail.

[0023] The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification and appended claims of this application, the singular expressions “a,” “the,” “the,” and “the” are intended to also include expressions such as “one or more,” unless the context clearly indicates otherwise.

[0024] Global climate change has become a major challenge facing humanity, and reducing atmospheric CO2 concentration is an international consensus. Calcium cycle technology is considered one of the promising carbon capture technologies due to its low adsorbent cost and high CO2 capture efficiency. Its basic principle is to utilize the reaction of CaO with CO2 to generate CaCO3 for capture. The CaCO3 is then calcined and decomposed at high temperatures (typically >900℃) to regenerate CaO and high-concentration CO2 for storage or utilization. However, the extremely high regeneration temperature leads to huge energy consumption and demanding equipment requirements in calcium cycle technology, severely restricting its industrial application.

[0025] On the other hand, CO2 catalytic hydrogenation methanation is an effective way to convert CO2 into valuable chemicals (CH4) and achieve anthropogenic carbon cycling. However, it has two major bottlenecks: First, the core reaction is highly exothermic (ΔH = -165 kJ / mol), which can easily cause the catalyst bed to "runaway" and lead to catalyst sintering and deactivation, making reaction heat management difficult; second, it usually requires a high concentration of CO2 source, making it difficult to directly couple to the low-concentration green carbon capture process in the atmosphere.

[0026] Although some studies have attempted to combine the calcium cycle with the hydrogenation process, such as the hydrogenation of CaCO3 to produce CO at intermediate temperature and ambient pressure, this pathway has a low CO yield and is accompanied by a large amount of CO2 directly decomposing and escaping, resulting in incomplete conversion and failing to achieve near-zero CO2 emissions and efficient resource utilization.

[0027] In addition, with the rapid development of renewable energy, the large-scale production of "green hydrogen" by electrolyzing water from renewable energy has become possible. However, hydrogen itself still faces challenges in "consumption" such as high storage and transportation costs and significant safety challenges.

[0028] Therefore, it is of great significance to develop a technology that can couple low-concentration atmospheric green carbon capture, has mild reaction conditions, avoids the risk of catalyst deactivation, and can achieve high CO2 conversion rate and high selectivity to generate energy products.

[0029] This application proposes a carbon dioxide capture and conversion system based on the hydrogenation and methanation of calcium carbonate. It breaks away from the traditional catalytic hydrogenation paradigm by directly hydrogenating CaCO3 to CH4 under specific high pressure and medium temperature conditions, achieving high conversion rate (>98%) and high selectivity (~100%) without a catalyst.

[0030] Moreover, the heat release of this reaction (ΔH = -95 kJ / mol) is much lower than that of the traditional CO2 hydrogenation catalytic reaction, which fundamentally avoids the risk of reactor "runaway temperature". Simple single-stage adiabatic fixed bed reactors can be used, which greatly simplifies the system structure and control.

[0031] In addition, reducing the traditional calcium recycling temperature from >900℃ to around 750℃ significantly reduces energy consumption and equipment requirements.

[0032] In addition, green hydrogen produced from intermittent renewable energy sources can be directly used as a reactant, and low-concentration CO2 that is difficult to utilize can be directly converted into green CH4 that is easy to store and transport, thus perfectly solving the problem of green hydrogen and green carbon consumption.

[0033] Furthermore, the reaction directly produces high-pressure green methane, which can be directly used to produce green liquefied natural gas (LNG) for cross-cycle energy storage, fed into the gas turbine peak-shaving power grid, or transmitted through a rich pipeline network, realizing cross-cycle energy storage and utilization with significant economic benefits.

[0034] See Figure 1 , Figure 1 This is a schematic diagram of a carbon dioxide capture and conversion system based on the hydrogenation and methanation of calcium carbonate proposed in an embodiment of this application. The system may include: a carbon dioxide capture unit 110, a pressurized feeding system 120, a reaction unit 130, a gas-solid separation unit 140, and a methane separation and compression module 150.

[0035] The pressurized feeding system 120 can be connected to the carbon dioxide capture unit 110 and the reaction unit 130 respectively, and the gas-solid separation unit 140 can be connected to the reaction unit 130 and the methane separation and compression module 150 respectively.

[0036] Specifically, the carbon dioxide capture unit 110 can be connected to the pressurized feeding system 120. The carbon dioxide capture unit 110 can capture green carbon, which can then react with pre-set calcium hydroxide within the carbon dioxide capture unit 110 to generate calcium carbonate.

[0037] Green carbon refers to carbon dioxide captured from the atmosphere. For example, carbon dioxide captured from the natural atmosphere can be green carbon, as can carbon dioxide captured from flue gas discharged from factory pipelines. This application does not specifically limit the method of acquiring green carbon.

[0038] Accordingly, after calcium carbonate is generated, it can be fed into the pressurized feed system 120. The pressurized feed system 120 is connected to the reaction unit 130, and can receive the calcium carbonate fed by the carbon dioxide capture unit 110, mix the calcium carbonate with pressurized green hydrogen, and then feed the mixed calcium carbonate and green hydrogen into the reaction unit 130.

[0039] Green hydrogen is hydrogen produced from abandoned wind and solar power.

[0040] Furthermore, during the mixing of calcium carbonate and pressurized green hydrogen, the pressurized feed system 120 can be used to preheat and pressurize the calcium carbonate and pressurized green hydrogen to increase the enthalpy of calcium carbonate and green hydrogen, providing thermodynamic preparation for subsequent reactions and reducing the reaction initiation energy barrier.

[0041] For example, the mixed calcium carbonate and green hydrogen can be pressurized to 10 to 15 MPa by a pressurized feeding system 120, while the heat released by the reaction of calcium carbonate and green hydrogen can be used to heat the mixed calcium carbonate and green hydrogen to 600 to 650°C.

[0042] After heating, pressurizing, and mixing calcium carbonate and pressurized green hydrogen, the mixed calcium carbonate and green hydrogen can be transported to reaction unit 130. Within reaction unit 130, the mixed calcium carbonate and green hydrogen can continue to be heated and pressurized, allowing them to undergo a methanation reaction, producing gaseous products and calcium hydroxide. The gaseous products include green methane, and the calcium hydroxide can be transported to the gas-solid separation unit 140 as a regeneration adsorbent.

[0043] For example, in reaction unit 130, the mixed calcium carbonate and green hydrogen can be heated to 720–780°C and pressurized to 10–15 MPa, causing a methanation reaction. This reaction is a catalytic hydrogenation reaction, following the CaCO3 hydrogenation pathway. Within the thermodynamically favorable range, methane (CH4) and the regenerated adsorbent calcium hydroxide (Ca(OH)2) can be generated. The main reaction is: CaCO3(s) + 4H2(g) → CH4(g) + Ca(OH)2(s) + H2O(g) (ΔH = -95kJ / mol). Here, H2O(g) represents gaseous water, and ΔH represents the heat of reaction.

[0044] Since the gaseous products and calcium hydroxide obtained from the reaction are mixed in the reaction unit 130, they need to be separated by the gas-solid separation unit 140 to obtain unreacted green hydrogen, green methane and calcium hydroxide.

[0045] Subsequently, the methane, unreacted green hydrogen, and water vapor in the gaseous products can be further separated. Through cooling, water separation, and purification, the methane and green hydrogen can be separated, so that the separated green methane can be used to prepare green LNG and other products, while the separated green hydrogen can be transported to the pressurized feed system 120.

[0046] It should be noted that in practical applications, the carbon dioxide capture unit 110 can be a turbulent bed, moving bed or fixed bed adsorption device, while the gas-solid separation unit 140 can be at least one of a cyclone separator, ceramic filter or bag filter. When the gas-solid separation unit 140 includes multiple devices, they can be used in combination. This application embodiment does not specifically limit the carbon dioxide capture unit 110 and the gas-solid separation unit 140.

[0047] In one alternative embodiment, see Figure 2 , Figure 2 This is a schematic diagram of another carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation proposed in an embodiment of this application. The pressurized feeding system 120 may include a hydrogen compressor 121 and a solid feed unit 122.

[0048] The solid feed unit 122 can be connected to the carbon dioxide capture unit 110.

[0049] Specifically, the hydrogen compressor 121 can receive green hydrogen and pressurize it to obtain pressurized green hydrogen. Correspondingly, the solid feed unit 122 can obtain calcium carbonate produced in the carbon dioxide capture unit 110, so that the pressurized green hydrogen can be mixed with calcium carbonate under heating and pressurization in the pressurized feed system 120.

[0050] Further, see Figure 2 The carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation may also include: an electrolyzer 160.

[0051] The electrolyzer 160 can be connected to the hydrogen compressor 121. After the electrolyzer 160 uses surplus wind and solar power to electrolyze water to produce green hydrogen, it can transfer the produced green hydrogen to the hydrogen compressor 121 so that the green hydrogen can be reacted with calcium carbonate to produce green methane. Moreover, the surplus wind and solar power refers to the electricity generated after the wind and solar power is wasted.

[0052] In another alternative embodiment, see Figure 3 , Figure 3 This is a schematic diagram of another carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation proposed in the embodiments of this application. The carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation may further include: an adsorbent circulation unit 170.

[0053] The adsorbent circulation unit 170 can be connected to the carbon dioxide capture unit 110 and the gas-solid separation unit 140, respectively.

[0054] Furthermore, after the reaction between calcium carbonate and green hydrogen is complete, the calcium hydroxide separated in the gas-solid separation unit 140 can be transported to the carbon dioxide capture unit 110 through the adsorbent circulation unit 170, so that the calcium hydroxide can be recycled in the carbon dioxide capture unit 110 to prepare green methane.

[0055] In yet another alternative embodiment, see Figure 4 , Figure 4 This is a schematic diagram of another carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation proposed in this application embodiment. The carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation also includes: a heat energy recovery and management system 180.

[0056] The heat recovery and management system 180 may include a first heat exchanger 181, a second heat exchanger 182, and a third heat exchanger 183.

[0057] Specifically, the first heat exchanger 181 is located near the reaction unit 130 and can absorb the heat generated when the mixed calcium carbonate and green hydrogen react in the reaction unit 130, and transfer the heat to the third heat exchanger 183.

[0058] Similarly, the second heat exchanger 182 is located near the gas-solid separation unit 140 and can absorb the heat of the gas phase products in the gas-solid separation unit 140 and transfer the heat to the third heat exchanger 183.

[0059] Correspondingly, the third heat exchanger 183 can be located near the pressurized feed system 120, so as to provide heat to the pressurized feed system 120 based on the heat transferred by the first heat exchanger 181 and the second heat exchanger 182, thereby preheating the mixed calcium carbonate and green hydrogen.

[0060] In another alternative embodiment, the carbon dioxide capture unit 110 may include a capture inlet and a capture outlet.

[0061] The collection inlet can be connected to the external environment to obtain natural air as feed gas, or it can be connected to the factory pipeline to collect the flue gas discharged from the pipeline. Therefore, the collection inlet can obtain feed gas containing green carbon, which reacts with calcium hydroxide within the carbon dioxide capture unit 110 to produce calcium carbonate. Correspondingly, the collection outlet can discharge gases other than carbon dioxide from the feed gas.

[0062] In summary, the carbon dioxide capture and conversion system based on the hydrogenation and methanation of calcium carbonate provided in this application includes a carbon dioxide capture unit and a reaction unit connected to a pressurized feed system, a gas-solid separation unit connected to the reaction unit, and a methane separation and compression module connected to the gas-solid separation unit. The carbon dioxide capture unit can capture green carbon, which then reacts with calcium hydroxide to produce calcium carbonate. The pressurized green hydrogen is mixed with calcium carbonate through the pressurized feed system. The mixed calcium carbonate and green carbon are then heated and pressurized in the reaction unit, causing them to react and produce a gaseous product and the calcium hydroxide. The gas-solid separation unit then separates the gaseous product and the calcium hydroxide to obtain unreacted green hydrogen, green methane, and calcium hydroxide. Finally, the methane separation and compression module separates the methane and unreacted green hydrogen to obtain a green methane product. The carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation described above can achieve calcium cycling at lower temperatures, thereby improving calcium utilization and reducing equipment requirements, and further enhancing the adaptability and flexibility of calcium carbonate hydrogenation methanation-based systems.

[0063] Specifically, this application proposes a carbon dioxide capture and conversion system based on the hydrogenation and methanation of calcium carbonate. Through a new pathway, CaCO3 can be directly hydrogenated to generate CH4 under specific high pressure and medium temperature conditions, breaking away from the traditional catalytic hydrogenation paradigm and achieving high conversion rate (>98%) and high selectivity (~100%) without a catalyst.

[0064] Moreover, the heat release of this reaction (ΔH = -95 kJ / mol) is much lower than that of the traditional CO2 hydrogenation catalytic reaction, which fundamentally avoids the risk of reactor "runaway temperature". Simple single-stage adiabatic fixed bed reactors can be used, which greatly simplifies the system structure and control.

[0065] In addition, reducing the traditional calcium recycling temperature from >900℃ to around 750℃ significantly reduces energy consumption and equipment requirements.

[0066] In addition, green hydrogen produced from intermittent renewable energy sources can be directly used as a reactant, and low-concentration CO2 that is difficult to utilize can be directly converted into green CH4 that is easy to store and transport, thus perfectly solving the problem of green hydrogen and green carbon consumption.

[0067] Furthermore, the reaction directly produces high-pressure green methane, which can be directly used to prepare LNG for cross-cycle energy storage, fed into the gas turbine peak-shaving power grid, or transmitted to other regions through a rich pipeline network, realizing cross-cycle energy storage and utilization with significant economic benefits.

[0068] Figure 5 This schematic flowchart illustrates a carbon dioxide capture and conversion method based on the hydrogenation and methanation of calcium carbonate, provided as an example and not a limitation. It is applicable to the aforementioned carbon dioxide capture and conversion system based on the hydrogenation and methanation of calcium carbonate. See also... Figure 5 The method includes: Step 501: Obtain green carbon through the carbon dioxide capture unit, and let the green carbon react with the calcium hydroxide in the carbon dioxide capture unit to generate calcium carbonate.

[0069] Green carbon is carbon dioxide captured from the atmosphere.

[0070] Step 502: Mix and preheat calcium carbonate and green hydrogen through a pressurized feeding system to obtain mixed calcium carbonate and green hydrogen.

[0071] Green hydrogen is hydrogen produced from abandoned wind and solar power.

[0072] Step 503: Heat and pressurize the mixed calcium carbonate and green hydrogen in the reaction unit to react the mixed calcium carbonate and green hydrogen to obtain gaseous products and calcium hydroxide.

[0073] Step 504: Separate the gaseous products and calcium hydroxide through the gas-solid separation unit to obtain unreacted green hydrogen, green methane and calcium hydroxide, and then transport calcium hydroxide to the carbon dioxide capture unit.

[0074] Step 505: The unreacted green hydrogen and methane are separated by the methane separation and compression module to obtain green methane product, and the unreacted green hydrogen is sent to the hydrogen compressor.

[0075] Since the above process is similar to that of a carbon dioxide capture and conversion system based on the hydrogenation and methanation of calcium carbonate, it will not be described in detail here.

[0076] The following experiments, conducted using the methods provided in the embodiments of this application, demonstrate four types of experiments based on the hydrogenation and methanation of calcium carbonate, and provide a comparative experiment based on existing technology. These experiments prove that the CaCO3 hydrogenation and methanation reaction proposed in this application significantly reduces the heat release compared to existing methanation reactions, resulting in a smaller temperature rise. This fundamentally reduces the risk of reactor overheating, making it possible to use a simple single-stage adiabatic fixed-bed reactor. The process equipment is simple, and it has high tolerance to impurities in the feed gas. Overall investment and operating costs are expected to be reduced by 20-30%.

[0077] Experiment 1 A Hastelloy C276 high-pressure fixed-bed reactor with an inner diameter of 20 mm was used, equipped with a high-pressure micro-feed pump to deliver simulated CaCO3 slurry and a high-precision hydrogen mass flow controller. The reaction was carried out under the conditions of 11.0 MPa, 750℃, a CaCO3 feed rate of 5 g / min, and an H2 flow rate of 1.5 NL / min (H2 / CaCO3 molar ratio = 4.2). The outlet gas was analyzed by online gas chromatography. After 10 hours of continuous operation, the CaCO3 conversion rate stabilized at 98.5%–99.0%, the CH4 selectivity was >99.5%, and the byproduct CO was below the detection limit. X-ray diffraction (XRD) analysis of the post-reaction solid showed that its main component was Ca(OH)2, confirming the reaction pathway.

[0078] Experiment 2 A laboratory-scale Ca-C dual-cycle system was configured. The CO2 capture unit was a fixed bed filled with Ca(OH)2 powder, through which simulated air (0.04% CO2, 78% nitrogen (N2), 21% oxygen (O2), 0.96% argon (Ar)) was introduced to simulate the capture and conversion process of actual atmospheric green carbon. Low-concentration CO2 was captured at 300℃ to generate CaCO3. The generated CaCO3 was transferred to a high-pressure fixed-bed reactor in the hydrogenation reaction unit. The system was pressurized to 11 MPa and heated to 750℃. Then, high-purity H2 was introduced for the reaction. The products were analyzed by online gas chromatography. The results showed that the conversion rate of CaCO3 reached 98.5%, and the selectivity for CH4 was greater than 99.8%. XRD analysis of the reacted solid showed that the main component was Ca(OH)2. The solid was reused in CO2 capture experiments, and its capture performance did not show significant decline, demonstrating the recyclability of the adsorbent.

[0079] Experiment 3 Design a pilot-scale unit capable of capturing and converting 100 kg of CO2 per hour. A turbulent bed adsorption tower will be used as the CO2 capture unit, processing 2000 Nm³ / h of gas (for 15% concentration flue gas). A single-stage adiabatic fixed-bed reactor will be employed, with a design pressure of 11.5 MPa and a design temperature of 800℃, made of Inconel 625 chromium-nickel-iron alloy. A lock-hopper system will be used to continuously transport solids from the atmospheric pressure capture unit to the high-pressure reaction unit. A coiled-tube heat exchanger will be designed to recover heat from the reaction outlet. This pilot-scale unit will verify the technical and economic indicators of this invention under continuous operation, providing an engineering design basis for the construction of a 10,000-ton-scale industrial demonstration plant.

[0080] Experiment 4 A Ca-C dual-cycle CO2 capture and conversion method based on CaCO3 hydrogenation methanation is designed, comprising a carbonization reactor, a cyclone separator, a fluidized bed high-pressure hydrogenation reactor, and a product separator connected in sequence.

[0081] Flue gas from a power plant with a CO2 concentration of approximately 15% is passed into a carbonization reactor filled with Ca(OH)2 and undergoes a carbonization reaction at 650°C to produce CaCO3. The reacted gas is then discharged after a cyclone separator removes entrained dust, and the collected CaCO3 solids are fed into a pressurized feed system via a solid feed unit. Simultaneously, H2 (purity >99.9%) produced by electrolyzing water from renewable energy sources is introduced into the pressurized feed system. The internal temperature of the reaction unit is controlled at 780°C, and the pressure at 11 MPa. Under these conditions, CaCO3 reacts with H2 to produce CH4, Ca(OH)2, and H2O.

[0082] After the reaction, the gas-solid mixture is discharged and enters the gas-solid separation unit and the methane separation and compression module. The high-purity CH4 gas obtained from the separation is collected as a product, the by-product water is condensed and discharged, and the solid Ca(OH)2 is sent back to the carbon dioxide capture unit to start the next cycle. Testing showed that under these conditions, the conversion rate of CaCO3 reached 98.5%, and the selectivity of CH4 was greater than 99.9%, demonstrating that the system achieves highly efficient CO2 capture and conversion.

[0083] Comparative experiment Compared to traditional catalytic hydrogenation processes: At the same CH4 yield, the exothermic CO2 catalytic hydrogenation reaction in traditional industries is severe, and the relatively low operating temperature of 400℃-500℃ makes effective heat transfer difficult, easily causing catalyst bed temperature runaways of several hundred degrees, leading to catalyst deactivation and posing a significant engineering obstacle. To control temperature stability, traditional processes require complex three-stage adiabatic reactors and interstage cooling systems, with heat exchangers or quench gas injection systems between stages. Furthermore, due to the use of nickel-based catalysts, the sulfur content in the feed gas must be strictly controlled to prevent poisoning. This results in numerous control points, high energy consumption, and significant additional energy losses.

[0084] In summary, the carbon dioxide capture and conversion method based on calcium carbonate hydrogenation methanation provided in this application involves obtaining green carbon through a carbon dioxide capture unit, reacting carbon dioxide with calcium hydroxide to generate calcium carbonate, mixing pressurized green hydrogen with calcium carbonate through a pressurized feeding system, and then heating and pressurizing the mixed calcium carbonate and green hydrogen in a reaction unit to produce gaseous products and calcium hydroxide. The gaseous products and calcium hydroxide are then separated by a gas-solid separation unit to obtain unreacted green hydrogen, green methane, and calcium hydroxide. Finally, methane and unreacted green hydrogen are separated by a methane separation and compression module to obtain methane product. This carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation can achieve calcium recycling at lower temperatures, thereby improving calcium utilization and reducing equipment requirements, thus enhancing the adaptability and flexibility of calcium carbonate hydrogenation methanation.

[0085] Specifically, this application proposes a carbon dioxide capture and conversion system based on the hydrogenation and methanation of calcium carbonate. Through a new pathway, CaCO3 can be directly hydrogenated to generate CH4 under specific high pressure and medium temperature conditions, breaking away from the traditional catalytic hydrogenation paradigm and achieving high conversion rate (>98%) and high selectivity (~100%) without a catalyst.

[0086] Moreover, the heat release of this reaction (ΔH = -95 kJ / mol) is much lower than that of the traditional CO2 hydrogenation catalytic reaction, which fundamentally avoids the risk of reactor "runaway temperature". Simple single-stage adiabatic fixed bed reactors can be used, which greatly simplifies the system structure and control.

[0087] In addition, reducing the traditional calcium recycling temperature from >900℃ to around 750℃ significantly reduces energy consumption and equipment requirements.

[0088] In addition, green hydrogen produced from intermittent renewable energy sources can be directly used as a reactant, and low-concentration CO2 that is difficult to utilize can be directly converted into green CH4 that is easy to store and transport, thus perfectly solving the problem of green hydrogen and green carbon consumption.

[0089] Furthermore, the reaction directly produces high-pressure green methane, which can be directly used to prepare LNG for cross-cycle energy storage, fed into the gas turbine peak-shaving power grid, or transmitted to other regions through a rich pipeline network, realizing cross-cycle energy storage and utilization with significant economic benefits.

[0090] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0091] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0092] In the embodiments provided in this application, it should be understood that the disclosed apparatus / devices and methods can be implemented in other ways. For example, the apparatus / device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0093] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0094] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0095] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0096] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0097] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A carbon dioxide capture and conversion system based on calcium carbonate hydrogenation and methanation, characterized in that, The carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation includes: a carbon dioxide capture unit, a pressurized feeding system, a reaction unit, a gas-solid separation unit, and a methane separation and compression module; The carbon dioxide capture unit is connected to the pressurized feeding system to obtain green carbon, which reacts with calcium hydroxide in the carbon dioxide capture unit to generate calcium carbonate, and the calcium carbonate is delivered to the pressurized feeding system. The green carbon is carbon dioxide captured from the atmosphere. The pressurized feeding system is connected to the reaction unit and is used to mix the pressurized green hydrogen with the calcium carbonate and to deliver the mixed calcium carbonate and green hydrogen to the reaction unit. The green hydrogen is hydrogen produced by waste wind and solar power. The reaction unit is used to heat and pressurize the mixed calcium carbonate and green hydrogen, so that the mixed calcium carbonate and green hydrogen react to obtain gaseous products and calcium hydroxide, and the gaseous products are delivered to the gas-solid separation unit. The gas-solid separation unit is used to separate the gaseous products and the calcium hydroxide to obtain unreacted green hydrogen, green methane and the calcium hydroxide. The methane separation and compression module is connected to the gas-solid separation unit and is used to separate the green methane and unreacted green hydrogen to obtain green methane product, and to deliver the unreacted green hydrogen to the hydrogen compressor of the pressurized feed system.

2. The system according to claim 1, characterized in that, The pressurized feeding system includes: a hydrogen compressor and a solid feed unit; The hydrogen compressor is used to obtain the green hydrogen and pressurize the green hydrogen to obtain the pressurized green hydrogen; The solid feed unit is connected to the carbon dioxide capture unit and is used to obtain the calcium carbonate in the carbon dioxide capture unit.

3. The system according to claim 1, characterized in that, The carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation also includes: an adsorbent recycling unit; The adsorbent circulation unit is connected to the carbon dioxide capture unit and the gas-solid separation unit respectively, and is used to deliver the calcium hydroxide separated in the gas-solid separation unit to the carbon dioxide capture unit.

4. The system according to claim 1, characterized in that, The carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation also includes: a heat energy recovery and management system; The heat recovery and management system includes: a first heat exchanger, a second heat exchanger, and a third heat exchanger; The first heat exchanger is used to absorb the heat generated when the mixed calcium carbonate and green hydrogen react in the reaction unit, and to transfer the heat to the third heat exchanger. The second heat exchanger is used to absorb the heat of the gaseous products in the gas-solid separation unit and transfer the heat to the third heat exchanger. The third heat exchanger is used to provide heat to the pressurized feeding system based on the heat transferred by the first and second heat exchangers, so as to preheat the mixed calcium carbonate and green hydrogen.

5. The system according to claim 1, characterized in that, The system also includes: an electrolytic cell; The electrolyzer is used to produce green hydrogen through an electrolytic reaction based on the curtailment of wind and solar power, and to transfer the green hydrogen to the hydrogen compressor.

6. The system according to any one of claims 1 to 5, characterized in that, The carbon dioxide capture unit includes a capture inlet and a capture outlet; The capture inlet is used to obtain the raw material gas containing the green carbon, so that the green carbon in the raw material gas reacts with the calcium hydroxide in the carbon dioxide capture unit to obtain the calcium carbonate; The capture outlet is used to discharge gases other than the green carbon from the raw material gas.

7. The system according to any one of claims 1 to 5, characterized in that, The carbon dioxide capture unit is a turbulent bed, moving bed, or fixed bed adsorption device.

8. The system according to any one of claims 1 to 5, characterized in that, The gas-solid separation unit is at least one of a cyclone separator, a ceramic filter, or a bag filter.

9. A method for capturing and converting carbon dioxide based on the hydrogenation and methanation of calcium carbonate, characterized in that, The method, applied to the carbon dioxide capture and conversion system based on calcium carbonate hydrogenation methanation as described in any one of claims 1 to 8, comprises: Green carbon is obtained through a carbon dioxide capture unit, which reacts with calcium hydroxide in the carbon dioxide capture unit to generate calcium carbonate. The green carbon is carbon dioxide captured from the atmosphere. The calcium carbonate and green hydrogen are mixed and preheated by a pressurized feeding system to obtain mixed calcium carbonate and green hydrogen, wherein the green hydrogen is hydrogen produced by waste wind and solar power. The mixed calcium carbonate and green hydrogen are heated and pressurized in the reaction unit to cause the mixed calcium carbonate and green hydrogen to react and obtain gaseous products and calcium hydroxide. The gaseous products and calcium hydroxide are separated by the gas-solid separation unit to obtain unreacted green hydrogen, green methane and calcium hydroxide, and the calcium hydroxide is then transported to the carbon dioxide capture unit. The unreacted green hydrogen and green methane are separated by a methane separation and compression module to obtain a green methane product, and the unreacted green hydrogen is then fed into the hydrogen compressor of the pressurized feed system.

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