Carbon dioxide methanation system and method based on carbonate cycle and hydrogen energy coupling

Abstract

The invention discloses a carbon dioxide methanation system and method based on carbonate circulation and hydrogen energy coupling, and relates to the technical field of carbon dioxide capture and resource utilization (CCU), solid adsorbent circulation, hydrogen energy conversion and fuel synthesis. The system comprises a carbon dioxide-containing gas supply unit, a carbonate circulation carbon capture unit, a carbon dioxide purification unit, a hydrogen supply unit, a carbon dioxide and hydrogen mixing and preheating unit, a methanation reaction unit, a methane product treatment and utilization unit and a heat energy integration and control unit. By means of low-cost and high-concentration CO2 capture and regeneration, integrated coupling of CO2 capture and hydrogen energy methanation, energy gradient utilization and heat energy closing and partial burn-back of methane products, a'fuel-carbon capture-synthesis' closed loop, CaO / CaCO3 multiple circulation and material closing are constructed, the technical platform is universally used, and the industry scene is easy to expand.

Description

Technical Field

[0001] This invention relates to the fields of carbon dioxide capture and utilization (CCU), solid adsorbent recycling, hydrogen conversion and fuel synthesis, and more specifically to a carbon dioxide methanation system and method based on the coupling of carbonate recycling and hydrogen energy. Background Technology

[0002] Carbon dioxide capture, utilization, and storage (CCUS) has become one of the key technological pathways. Existing CO2 capture technologies mainly include: 1. Chemical absorption method (e.g., amine method): 1) Advantages: Mature technology and high capture efficiency; 2) Disadvantages: Solvent regeneration consumes a lot of energy, causes severe corrosion, and solvents are easily degraded, resulting in high long-term operating costs and insufficient economic efficiency for large-scale, long-cycle operations.

[0003] 2. Physical adsorption / membrane separation method: 1) Advantages: The process is relatively clean; 2) Disadvantages: It is sensitive to gas composition and requires complex pretreatment; high-performance membrane materials are expensive, posing challenges to the economy and reliability of large-flow industrial flue gas applications.

[0004] 3. Condensation and cryogenic separation methods: Typically used in specific scenarios with high CO2 concentrations, the equipment is complex, energy-intensive, and has poor versatility.

[0005] On the other hand, hydrogen energy is considered an important clean energy carrier for the future, but it faces the following technical challenges: 1) Difficult storage and transportation: requires high pressure or low temperature, and has high infrastructure construction and operation costs; 2) Poor end-user compatibility: Existing natural gas pipelines, gas turbines, and industrial combustion equipment have limitations on the proportion of hydrogen blending; 3) Hydrogen energy utilization is closely coupled with the volatility of renewable energy, and there is a lack of efficient "long-cycle chemical energy storage" pathways.

[0006] To address the aforementioned issues, an international proposal has been made to synthesize methane (CH4) from CO2 and H2 via the Sabatier reaction. CO2 + 4H2 → CH4 + 2H2O (exothermic reaction); Methane can be directly integrated into existing natural gas infrastructure, representing an important pathway for "hydrogen energy chemical storage and conversion." However, existing CO2-H2 methanation technologies still have significant shortcomings: 1. It relies heavily on externally supplied high-purity CO2, and has not solved the problem of large-scale flue gas capture; 2. Although the methanation reaction is exothermic, it requires maintaining a stable reaction temperature of 250-450℃, which places high demands on thermal management and waste heat utilization. 3. The CaCO3-CaO cycle (Calcium Looping) technology is considered a high-potential direction for solid adsorption carbon capture, but existing research focuses on the capture / regeneration process, with insufficient coupling with hydrogen energy and methanation, and has not yet formed a complete system with both material and energy closed loops. 4. The coupling between the adsorption performance decay and system energy efficiency during multiple cycles of CaO / CaCO3 is not adequately considered, making it difficult to achieve low-cost and long-term stable operation in engineering.

[0007] Therefore, how to develop a carbon dioxide methanation system and method based on carbonate cycle and hydrogen energy coupling, with CaCO3 / CaO cycle as the core and taking into account CO2 capture, regeneration, methanation and energy cascade utilization, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] In view of this, the present invention provides a carbon dioxide methanation system and method based on the coupling of carbonate cycle and hydrogen energy.

[0009] A carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling includes: a carbon dioxide gas supply unit, a carbonate cycle carbon capture unit, a carbon dioxide purification unit, a hydrogen supply unit, a carbon dioxide and hydrogen mixing and preheating unit, a methanation reaction unit, a methane product treatment and utilization unit, and a thermal energy integration and control unit. The carbonate recycling carbon capture unit includes: an absorption reactor, a regeneration reactor, a first solid conveying device, and a second solid conveying device; the absorption reactor is filled with solid adsorbent, the solid outlet of the absorption reactor is connected to the solid inlet of the regeneration reactor via the first solid conveying device, and the solid outlet of the regeneration reactor is connected to the solid inlet of the absorption reactor via the second solid conveying device. The carbon dioxide gas supply unit, absorption reactor, regeneration reactor, carbon dioxide purification unit, carbon dioxide and hydrogen mixing and preheating unit, methanation reaction unit, and methane product treatment and utilization unit are connected sequentially along the gas flow via pipelines. The hydrogen outlet of the hydrogen supply unit is connected to the hydrogen inlet of the preheating unit via a pipeline, where carbon dioxide and hydrogen are mixed. The carbon dioxide and hydrogen mixing and preheating unit is used to mix the carbon dioxide raw material gas and hydrogen at a predetermined molar ratio and heat them to a predetermined temperature to obtain a preheated mixed gas. One end of the methane product outlet of the methane product processing and utilization unit is connected to the plant's gas pipeline network or external transmission pipeline, and the other end is connected to the heating device or fuel supply branch of the regeneration reactor. The hydrogen recovery outlet of the methane product processing and utilization unit is connected to another hydrogen inlet of the carbon dioxide and hydrogen mixing and preheating unit via pipeline. The thermal energy integration and control unit includes at least one heat exchange device for recovering at least a portion of the heat from the regeneration reactor and the methanation reaction unit, and for supplying heat to the carbon dioxide and hydrogen mixing and preheating unit or other heat-requiring units within the system.

[0010] Furthermore, one end of the methane product outlet of the methane product processing and utilization unit is connected to the plant's gas pipeline network or external transmission pipeline, and the other end is connected to the fuel inlet of the regeneration reactor via a pipeline. The thermal energy integration and control unit includes heat exchanger one to heat exchanger two. The flue gas outlet of the regeneration reactor is equipped with heat exchanger one, the methane outlet of the methanation reaction unit is equipped with heat exchanger two, and the carbon dioxide and hydrogen mixing and preheating unit includes a mixer and heat exchanger three. Heat exchanger three is located outside the mixer. Heat exchanger one and heat exchanger two are respectively connected to heat exchanger three through a heat transfer oil or steam heat exchange loop.

[0011] Furthermore, the mixer is a jet mixer, a vortex mixer, or a dynamic mixer; the heat exchanger is a shell-and-tube type, a plate type, or a microchannel heat exchanger.

[0012] Furthermore, the carbon dioxide gas supply unit includes a carbon dioxide-containing gas inlet pipeline and a dust collector. A heat exchanger is installed on the carbon dioxide-containing gas inlet pipeline. The carbon dioxide-containing gas inlet pipeline, the dust collector, and the absorption reactor are connected in sequence via pipelines. The carbon dioxide-containing flue gas or process gas in the carbon dioxide-containing gas inlet pipeline comes from combustion devices, industrial furnaces, boiler tail gas, cement kiln tail gas, steelmaking / blast furnace gas purification tail gas, chemical tail gas, or waste incineration flue gas.

[0013] Furthermore, the absorption reactor is a fluidized bed carbon capture and absorption tower, a moving bed carbon capture and absorption tower, a bubbling bed carbon capture and absorption tower, or a rotary kiln carbon capture and absorption tower. The regeneration reactor is a rotary kiln, fluidized bed furnace, vertical kiln, or electric heating furnace; the heating method of the regeneration reactor is one or a combination of methane reburning, external fuel, electric heating, oxygen-enriched combustion, or heat carrier circulation.

[0014] The carbonate circulation carbon capture unit selects calcium carbonate circulation decomposition to capture carbon dioxide. The first solid conveying device includes a first elevator and a first conveyor belt, and the second solid conveying device includes a second elevator and a second conveyor belt. The solid outlet of the absorption reactor is connected to the solid inlet of the regeneration reactor in sequence via the first elevator and the first conveyor belt. The solid outlet of the regeneration reactor is connected to the solid inlet of the absorption reactor in sequence via the second elevator and the second conveyor belt.

[0015] Furthermore, the carbon dioxide purification unit includes a precooling and dust removal device, a washing or deacidification device, a drying and adsorption device, a desulfurization device, and a compression and pressure regulation device. The precooling and dust removal device includes a heat exchanger or condenser, and a cyclone separator, a bag filter or an electrostatic precipitator. The washing or deacidification device is a washing tower or a gas scrubbing tower; The drying and adsorption device includes a compressor, a molecular sieve or activated alumina dryer, and an activated carbon adsorber or adsorption tower. The desulfurization device is a desulfurization tower or an alkaline washing tower; The compression and pressure regulating device is either a compressor or a pressure regulating valve. The regeneration reactor, cyclone separator I, bag filter or electrostatic precipitator, scrubbing tower or gas scrubbing tower, compressor I, molecular sieve or activated alumina dryer I, activated carbon adsorber I or adsorption tower, desulfurization tower or alkaline scrubbing tower, compressor II or pressure regulating valve and the mixer are connected in sequence by pipelines. A heat exchanger V or condenser is provided on the pipeline connecting the regeneration reactor and cyclone separator I, bag filter or electrostatic precipitator.

[0016] Furthermore, the hydrogen supply unit includes a hydrogen inlet pipeline and a buffer tank, and the hydrogen inlet pipeline, the buffer tank and the mixer are connected in sequence via pipelines.

[0017] Furthermore, the methanation reaction unit is a fixed-bed reactor, a multi-tube reactor, or a fluidized-bed reactor.

[0018] Furthermore, the methane product processing and utilization unit includes a cooling and moisture condensation device, a drying and adsorption device, an impurity removal and methane upgrading device, an unreacted hydrogen recovery device, a compression and pressure regulation device, and a product gas output and distribution device. The cooling and moisture removal device includes a water-cooled or air-cooled unit, a plate heat exchanger, and a gas-liquid separator or cyclone separator. The drying and adsorption device includes a molecular sieve or activated alumina dryer II and an activated carbon adsorber II. The impurity removal and methane upgrading device is a methane primary membrane separator or a methane pressure swing adsorption tower. The unreacted hydrogen recovery device is a hydrogen primary membrane separator or a hydrogen pressure swing adsorption tower. The compression and pressure regulating device 2 is a single-stage or multi-stage reciprocating compressor; The product gas output and distribution device is a metering valve; The methanation reaction unit, water-cooled or air-cooled unit, gas-liquid separator or cyclone separator II, molecular sieve or activated alumina dryer II, activated carbon adsorber II, methane primary membrane separator or methane pressure swing adsorption tower, single-stage or multi-stage reciprocating compressor, metering valve, and fuel inlet of plant gas pipeline or external pipeline or regeneration reactor are connected in sequence via pipelines; plate heat exchangers are provided on the pipelines connecting the water-cooled or air-cooled unit and the gas-liquid separator or cyclone separator II. The permeate outlet of the methane primary membrane separator or methane pressure swing adsorption tower is connected to the hydrogen primary membrane separator or hydrogen pressure swing adsorption tower via a pipeline, and the permeate outlet of the hydrogen primary membrane separator or hydrogen pressure swing adsorption tower is connected to the mixer via a pipeline.

[0019] Furthermore, the solid adsorbent includes one or a combination of several of the following: CaO, MgO, SrO, BaO, red mud activated adsorbent, or steel slag activated adsorbent, preferably CaO.

[0020] Furthermore, the activation treatment of the red mud activated adsorbent and / or steel slag activated adsorbent includes calcination, hydration, and / or mechanical activation. These solid adsorbents belong to alkaline earth metal oxides or calcium-containing active phase solid waste that are "carbonatable / decomposable and regenerable"; the purpose of activation (calcination / hydration / mechanical activation) is to improve pore structure, disperse the active phase, and improve cycle decay; allowing different materials to correspond to different optimal windows (e.g., the regeneration temperature can be shifted upwards / downwards).

[0021] Furthermore, the absorption reactor is also connected to an adsorbent feeding branch and / or a deactivated solid slag discharge branch.

[0022] Furthermore, it also includes a system monitoring and intelligent control unit, which adopts a PLC or DCS system. The PLC or DCS control system is connected to the carbon dioxide gas supply unit, the carbonate circulation carbon capture unit, the carbon dioxide purification unit, the hydrogen supply unit, the carbon dioxide and hydrogen mixing and preheating unit, the methanation reaction unit, the methane product treatment and utilization unit, and the thermal energy integration and control unit through signal lines and / or industrial buses, respectively.

[0023] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The system monitoring and intelligent control unit is set as an independent control module. The system monitoring and intelligent control are adopted to adapt to multi-source CO2 and multi-condition operation. Through the system monitoring and intelligent control unit, CO2 load, solid circulation, hydrogen flow and methane production are monitored and controlled in real time. It can adapt to various CO2-containing flue gas from different industrial sources and realize the unified capture and methanation of multi-source CO2.

[0024] This invention also provides a carbon dioxide methanation method based on the coupling of carbonate cycle and hydrogen energy, comprising the following steps: 1) Using the system described above, carbon dioxide-containing flue gas or process gas is fed into an absorption reactor, so that the carbon dioxide-containing gas comes into contact with calcium oxide solid to generate carbonate solid. 2) The carbonate solid obtained in step 1) is fed into the regeneration reactor and decomposed at 750-1100℃ to generate calcium oxide solid and carbon dioxide-rich gas. 3) The carbon dioxide-rich gas obtained in step 2) is sent to a carbon dioxide purification unit for dust removal, dehydration and / or deacidification treatment to obtain carbon dioxide raw material gas; 4) The carbon dioxide raw material gas obtained in step 3) is fed into the carbon dioxide and hydrogen mixing and preheating unit and mixed with hydrogen from the hydrogen supply unit and heated to 100-350°C to obtain a preheated mixed gas. 5) The preheated mixed gas obtained in step 4) is fed into a methanation reaction unit containing a methanation catalyst, and the methanation reaction is carried out at 200-500℃ and 0.1-6MPa to generate a reaction product gas containing methane. 6) The reaction product gas obtained in step 5) is sent to the methane product processing and utilization unit for cooling, dehydration and purification to obtain methane product gas, which is then used as fuel gas and / or chemical raw material. 7) Return the calcium oxide solid obtained in step 2) to the absorption reactor in step 1) for recycling.

[0025] Furthermore, the absorption reactor operates at 300-700℃, preferably 400-650℃, and more preferably 450-550℃; the calcium oxide solid obtained in step 2) is returned to the absorption reactor in step 1) for recycling ≥40 times; and the volume fraction of the carbon dioxide feed gas is not less than 90%.

[0026] Further, in step 4), the molar ratio of carbon dioxide to hydrogen is 1:(3-6); the methanation catalyst is supported Ni, Ni-Co, Ni-Cu, Ru or a combination thereof.

[0027] Compared with existing CO2 capture and methanation technologies, the present invention has the following advantages: 1. Low-cost, high-concentration CO2 capture and regeneration: The CaO / CaCO3 cyclic carbon capture method avoids solvent degradation and corrosion problems compared to chemical absorption methods such as amine methods. It can achieve CO2 capture with lower energy consumption and obtain high-concentration CO2 feed gas through a high-temperature decomposition furnace, which is suitable for subsequent methanation utilization.

[0028] 2. Integrated coupling of CO2 capture and hydrogen methanation: By deeply coupling the CaCO3 / CaO carbon capture cycle with the CO2-H2 methanation unit at the system level, the overall optimization of carbon dioxide capture, regeneration and methane synthesis is achieved. Compared with a simple CO2 capture system or a simple methanation unit, it has higher comprehensive utilization efficiency and economy.

[0029] 3. Energy cascade utilization and thermal energy closure: By integrating and controlling the thermal energy, high-temperature / medium-temperature heat sources such as the sensible heat from CaCO3 decomposition exhaust gas and the methanation reaction are recovered and used for CO2-H2 mixture preheating and other process units. This achieves a synergistic balance between the high-temperature heat required for CaCO3 decomposition, the preheating demand of the mixture, and the heat released from methanation. Under typical operating conditions, waste heat can handle 30-70% of the total heat load for mixture preheating, while the heat released from methanation can handle 10-40%, significantly reducing the need for external heat supply and achieving near-closed energy supply. The above proportions are merely examples of typical operating conditions and do not constitute a limitation on the scope of protection of this invention.

[0030] 4. Partial re-burning of methane products to construct a closed loop of "fuel-carbon capture-synthesis": By feeding a portion of the methane product gas back to the regeneration reactor as fuel, providing a heat source for the decomposition reaction, a closed loop of CO2 capture – methane synthesis – fuel recycling is achieved. This closed loop enhances system autonomy, allowing for flexible adjustments to operation based on renewable electricity / hydrogen supply and methane market demand.

[0031] 5. Multiple circulations of CaO / CaCO3 and material closure: This invention controls parameters such as CaO / CaCO3 particle size, circulating temperature, and residence time to enable the solid adsorbent to maintain an acceptable CO2 adsorption capacity for ≥40 or even more cycles, thereby reducing the feeding frequency and achieving material closure and cost optimization of the CO2 capture carrier.

[0032] 6. System monitoring and intelligent control, adaptable to multiple CO2 sources and multiple operating conditions. Through system monitoring and intelligent control unit, CO2 load, solids cycle, hydrogen flow and methane production can be monitored and controlled in real time. It can be adapted to various CO2-containing flue gas from different industrial sources to achieve unified capture and methanation of CO2 from multiple sources.

[0033] 7. This technology platform is universal and easily expandable to various industry scenarios: This invention is not limited to any specific industry. By adding specific CO2 sources, heat source forms, and load characteristics at the industry level, it can generate system applications for multiple application scenarios such as power plants, cement, steel, and waste incineration, providing a basic platform for building CCU+ hydrogen energy utilization technology. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of a carbon dioxide methanation system based on the coupling of carbonate cycle and hydrogen energy. Figure 2 A schematic diagram of the carbonate cycle carbon capture unit; Figure 3 A schematic diagram of the structure of the thermal energy integration and control unit and the carbon dioxide and hydrogen mixing and preheating unit; Figure 4 A schematic diagram of the structure of the unit that provides carbon dioxide-containing gas; Figure 5 This is a schematic diagram of the carbon dioxide purification unit. Figure 6 A schematic diagram of the hydrogen supply unit; Figure 7 This is a schematic diagram of the structure of the methane product processing and utilization unit. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, 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.

[0036] The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling includes: a carbon dioxide gas supply unit, a carbonate cycle carbon capture unit, a carbon dioxide purification unit, a hydrogen supply unit, a carbon dioxide and hydrogen mixing and preheating unit, a methanation reaction unit, a methane product treatment and utilization unit, and a thermal energy integration and control unit. The carbonate recycling carbon capture unit includes: an absorption reactor, a regeneration reactor, a first solid conveying device, and a second solid conveying device; the absorption reactor is filled with solid adsorbent, the solid outlet of the absorption reactor is connected to the solid inlet of the regeneration reactor via the first solid conveying device, and the solid outlet of the regeneration reactor is connected to the solid inlet of the absorption reactor via the second solid conveying device. The carbon dioxide gas supply unit, absorption reactor, regeneration reactor, carbon dioxide purification unit, carbon dioxide and hydrogen mixing and preheating unit, methanation reaction unit and methane product treatment and utilization unit are connected sequentially along the gas flow through pipelines. The hydrogen outlet of the hydrogen supply unit is connected to the hydrogen inlet of the preheating unit via a pipeline, where carbon dioxide and hydrogen are mixed. The carbon dioxide and hydrogen mixing and preheating unit is used to mix carbon dioxide feed gas and hydrogen gas at a predetermined molar ratio and heat them to a predetermined temperature to obtain a preheated mixed gas. One end of the methane product outlet of the methane product processing and utilization unit is connected to the plant's gas pipeline network or external transmission pipeline, and the other end is connected to the heating device or fuel supply branch of the regeneration reactor. The hydrogen recovery outlet of the methane product processing and utilization unit is connected to another hydrogen inlet of the carbon dioxide and hydrogen mixing and preheating unit via pipeline. The thermal energy integration and control unit includes at least one heat exchange device for recovering at least a portion of the heat from the regeneration reactor and methanation reaction unit, and for heating the carbon dioxide and hydrogen mixing and preheating unit or other heat-requiring units within the system.

[0037] Working principle of the invention: The carbon dioxide gas supply unit is used to supply flue gas or process gas containing carbon dioxide; The carbonate recycling carbon capture unit includes: An absorption reactor is used to contact carbon dioxide gas with calcium oxide solid to generate carbonate solid. A regeneration reactor is used to decompose solid carbonate into solid calcium oxide and carbon dioxide-rich gas under high temperature conditions. The first solid conveying device and the second solid conveying device are used to circulate calcium oxide and carbonate solids between the absorption reactor and the regeneration reactor. The carbon dioxide purification unit is used to remove dust, dehydrate and / or deacidify carbon dioxide-rich gas to obtain carbon dioxide feed gas. Hydrogen supply unit, used to supply hydrogen; The carbon dioxide and hydrogen mixing and preheating unit is used to mix carbon dioxide feed gas and hydrogen gas at a predetermined molar ratio and heat them to a predetermined temperature to obtain a preheated mixed gas. The methanation reaction unit is used to carry out a methanation reaction of a preheated mixed gas in the presence of a catalyst at 200-500°C and 0.1-6 MPa to generate a reaction product gas containing methane. The methane product processing and utilization unit is used to cool, remove water and purify the reaction product gas to obtain methane product gas and use it as fuel gas and / or chemical raw material; The thermal energy integration and control unit is arranged between the regeneration reactor and the methanation reaction unit and the carbon dioxide and hydrogen mixing and preheating unit for heat exchange. It is used to recover at least a portion of the heat released by the regeneration reactor and the methanation reaction unit, and to use the heat for heating the carbon dioxide and hydrogen mixing and preheating unit, thereby realizing the cascade utilization and balance of the system's thermal energy.

[0038] In one embodiment, one end of the methane product outlet of the methane product processing and utilization unit is connected to the plant's gas pipeline network or external transmission pipeline, and the other end is connected to the fuel inlet of the regeneration reactor via a pipeline. The thermal energy integration and control unit includes heat exchangers one to two. Heat exchanger one is provided at the flue gas outlet of the regeneration reactor, and heat exchanger two is provided at the methane outlet of the methanation reaction unit. The carbon dioxide and hydrogen mixing and preheating unit includes a mixer and heat exchanger three. Heat exchanger three is located outside the mixer. Heat exchangers one and two are respectively connected to heat exchanger three through a heat transfer oil or steam heat exchange loop.

[0039] In one embodiment, the mixer is a jet mixer, a vortex mixer, or a dynamic mixer; the heat exchanger is a shell-and-tube, plate, or microchannel heat exchanger.

[0040] In one embodiment, the carbon dioxide gas supply unit includes a carbon dioxide-containing gas inlet pipeline and a dust collector. A heat exchanger is provided on the carbon dioxide-containing gas inlet pipeline. The carbon dioxide-containing gas inlet pipeline, the dust collector, and the absorption reactor are connected in sequence via pipelines. The carbon dioxide-containing flue gas or process gas in the carbon dioxide-containing gas inlet pipeline comes from a combustion device, industrial furnace, boiler tail gas, cement kiln tail gas, steelmaking / blast furnace gas purification tail gas, chemical tail gas, or waste incineration flue gas.

[0041] Working principle of carbon dioxide gas supply unit: The carbon dioxide gas supply unit is used to provide flue gas or process gas containing carbon dioxide. It can come from combustion devices, industrial furnaces, boiler tail gas, cement kiln tail gas, steelmaking / blast furnace gas purification tail gas, chemical tail gas or waste incineration flue gas, etc. It is equipped with a dust collector and a heat exchanger to regulate temperature and remove large particulate dust.

[0042] In one embodiment, the absorption reactor is a fluidized bed carbon capture and absorption tower, a moving bed carbon capture and absorption tower, a bubbling bed carbon capture and absorption tower, or a rotary kiln carbon capture and absorption tower. The regeneration reactor is a rotary kiln, fluidized bed furnace, vertical kiln, or electric heating furnace; the heating method of the regeneration reactor is one or a combination of methane reburning, external fuel, electric heating, oxygen-enriched combustion, or heat carrier circulation.

[0043] The carbonate recycling carbon capture unit selects calcium carbonate recycling decomposition to capture carbon dioxide. The first solid conveying device includes a first elevator and a first conveyor belt, and the second solid conveying device includes a second elevator and a second conveyor belt. The solid outlet of the absorption reactor is connected to the solid inlet of the regeneration reactor in sequence via the first elevator and the first conveyor belt. The solid outlet of the regeneration reactor is connected to the solid inlet of the absorption reactor in sequence via the second elevator and the second conveyor belt.

[0044] In one embodiment, the carbon dioxide purification unit includes a precooling and dust removal device, a washing or deacidification device, a drying and adsorption device, a desulfurization device, and a compression and pressure regulation device. The precooling and dust removal device includes a heat exchanger or condenser, and a cyclone separator, a bag filter or an electrostatic precipitator; The washing or deacidification device is a washing tower or a gas scrubbing tower; The drying and adsorption device includes a compressor, a molecular sieve or activated alumina dryer, and an activated carbon adsorber or adsorption tower. The desulfurization unit is either a desulfurization tower or an alkaline washing tower; The compression and pressure regulating device is either a compressor or a pressure regulating valve; The regeneration reactor, cyclone separator I, bag filter or electrostatic precipitator, scrubbing tower or gas scrubbing tower, compressor I, molecular sieve or activated alumina dryer I, activated carbon adsorber I or adsorption tower, desulfurization tower or alkaline scrubbing tower, compressor II or pressure regulating valve and mixer are connected in sequence by pipelines. Heat exchanger V or condenser is installed on the pipeline connecting the regeneration reactor and cyclone separator I, bag filter or electrostatic precipitator.

[0045] Working principle of carbon dioxide purification unit: Pre-cooling and dust removal device: After the CO2-rich flue gas is discharged from the regeneration reactor, it is first pre-cooled by heat exchanger five or condenser to condense water vapor and separate it from the gas. Then, it passes through cyclone separator one, bag filter or electrostatic precipitator to remove dust and impurities.

[0046] Washing or deacidification unit: The gas after pre-cooling and dust removal enters the washing tower or gas scrubbing tower, and is further cooled and water-soluble impurities and acidic components are removed by countercurrent spraying of water or alkaline solution.

[0047] Drying and adsorption equipment: After washing, the CO2 gas is pressurized by a compressor and then enters a molecular sieve or activated alumina dryer to remove residual moisture. An activated carbon adsorber or adsorption tower is configured according to the composition of the raw gas to remove trace impurities.

[0048] Desulfurization equipment: For flue gas containing sulfur, a desulfurization tower or alkaline scrubbing tower is installed to remove acidic gases such as sulfur dioxide and hydrogen sulfide.

[0049] Compression and pressure regulation device one: The purified CO2 gas is regulated by compressor two or pressure regulating valve to reach the pressure range of 0.1-6MPa required for the methanation reaction.

[0050] With this combination, the carbon dioxide enrichment and purification unit can complete dust removal, condensation and water removal, acid / sulfurization removal and pressure regulation, and output high-purity CO2 feed gas ≥90% that meets the requirements of methanation reaction.

[0051] In one embodiment, the hydrogen supply unit includes a hydrogen inlet pipeline and a buffer tank, wherein the hydrogen inlet pipeline, the buffer tank and the mixer are connected in sequence via pipelines.

[0052] In one embodiment, the methanation reaction unit is a fixed-bed reactor, a multi-tube reactor, or a fluidized-bed reactor.

[0053] In one embodiment, the methane product processing and utilization unit includes a cooling and moisture condensation device, a drying and adsorption device, an impurity removal and methane upgrading device, an unreacted hydrogen recovery device, a compression and pressure regulation device, and a product gas output and distribution device. Cooling and moisture removal devices include water-cooled or air-cooled coolers, plate heat exchangers, and gas-liquid separators or cyclone separators. The drying and adsorption apparatus includes a molecular sieve or activated alumina dryer and an activated carbon adsorber. The impurity removal and methane upgrading device is a primary methane membrane separator or a methane pressure swing adsorption tower. The unreacted hydrogen recovery device is a hydrogen primary membrane separator or a hydrogen pressure swing adsorption tower; The compression and pressure regulating device 2 is a single-stage or multi-stage reciprocating compressor; The product gas output and distribution device is a metering valve; The methanation reaction unit, water-cooled or air-cooled unit, gas-liquid separator or cyclone separator II, molecular sieve or activated alumina dryer II, activated carbon adsorber II, methane primary membrane separator or methane pressure swing adsorption tower, single-stage or multi-stage reciprocating compressor, metering valve, and fuel inlet of plant gas pipeline or external pipeline or regeneration reactor are connected in sequence via pipelines; plate heat exchangers are installed on the pipelines connecting the water-cooled or air-cooled unit and the gas-liquid separator or cyclone separator II. The permeate outlet of the methane primary membrane separator or methane pressure swing adsorption tower is connected to the hydrogen primary membrane separator or hydrogen pressure swing adsorption tower via a pipeline, and the permeate outlet of the hydrogen primary membrane separator or hydrogen pressure swing adsorption tower is connected to the mixer via a pipeline.

[0054] Working principle of the methane product processing and utilization unit: Cooling and moisture removal device: The product gas is first cooled to near room temperature by a water or air cooler, causing water vapor to condense. After methanation, the gas is cooled to about 4°C by a plate heat exchanger, which allows moisture to condense and separate.

[0055] The cooled gas enters a gas-liquid separator or cyclone separator to separate and discharge the condensate and entrained droplets, preventing subsequent equipment from getting damp.

[0056] Drying and Adsorption Unit: To remove residual moisture and trace impurities, a second molecular sieve or activated alumina dryer and a second activated carbon adsorber are installed, operating continuously using an alternating regeneration dual-tower structure. In the treatment of methanation products, the activated carbon adsorber can remove catalyst residues such as sulfides and nitrogen oxides.

[0057] Impurity Removal and Methane Upgrading Unit: To obtain methane of pipeline natural gas quality, it is necessary to remove CO2 and CO from the mixed gas. A primary methane membrane separator or a methane pressure swing adsorption tower can effectively separate CO2 / CH4. A primary methane membrane separator can meet the network gas standard. For higher purity requirements, a series of methane pressure swing adsorption towers are used to separate CO2 / CO to trace levels, while recovering methane.

[0058] Unreacted hydrogen recovery unit: In the methane primary membrane separator or methane pressure swing adsorption tower, the permeate outlet contains a large amount of H2 and some CH4 and CO2. By configuring a hydrogen primary membrane separator or hydrogen pressure swing adsorption tower, hydrogen recovery is achieved to obtain 99.9-99.999% ultrapure hydrogen, or 90-99.9% hydrogen. The recovered hydrogen is sent back to the carbon dioxide and hydrogen mixing and preheating unit through pipelines to reduce hydrogen loss.

[0059] Compression and pressure regulation device 2: After impurities are removed, the pressure of the methane gas decreases. It can be boosted to meet the requirements of the natural gas pipeline network or the pressure required for methane reburning. In the methanation upgrade process, a single-stage or multi-stage reciprocating compressor is used to compress the gas to 16 bar.

[0060] Product gas output and distribution device: The qualified methane product gas is connected to the plant's gas system or transported to the external natural gas pipeline network through metering valves.

[0061] In one embodiment, the solid adsorbent includes one or a combination of several of the following: CaO, MgO, SrO, BaO, red mud activated adsorbent, or steel slag activated adsorbent.

[0062] Solid adsorbents undergo carbonation reactions with carbon dioxide-containing gases in the carbon capture tower to form corresponding carbonate solids. These solids are then decomposed in the decomposition furnace under regeneration conditions to release carbon dioxide-rich gases and regenerate the corresponding oxides before being returned to the carbon capture tower for recycling. Industrial solid waste adsorbents can be treated by calcination, hydration, and / or mechanical activation (such as ball milling) to improve cycle stability.

[0063] In one embodiment, the activation treatment of the red mud activated adsorbent and / or steel slag activated adsorbent includes calcination, hydration and / or mechanical activation.

[0064] In one embodiment, the absorption reactor is also connected to an adsorbent feeding branch and / or a deactivated solids discharge branch.

[0065] In one embodiment, the system also includes a system monitoring and intelligent control unit, which adopts a PLC or DCS system. The PLC or DCS control system is connected to the carbon dioxide gas supply unit, the carbonate circulation carbon capture unit, the carbon dioxide purification unit, the hydrogen supply unit, the carbon dioxide and hydrogen mixing and preheating unit, the methanation reaction unit, the methane product treatment and utilization unit, and the thermal energy integration and control unit via signal lines and / or industrial buses, respectively.

[0066] Working principle of system monitoring and intelligent control unit: An online gas chromatograph or a four-in-one gas composition analyzer is installed at the methane product outlet to continuously monitor the methane, carbon dioxide, carbon monoxide, and hydrogen content in synthetic natural gas (SNG). The control system monitors the SNG composition in real time to determine whether it meets the injection standards.

[0067] Mass flow meters or mass flow controllers (MFCs) are installed on both the carbon dioxide gas inlet pipeline and the hydrogen gas inlet pipeline to precisely control the H2 / CO2 molar ratio and feed the flow signal back to the PLC control system or DCS control system. In the carbonate circulation carbon capture unit, speed sensors or weight sensors are installed on the circulation pipeline connecting the absorption reactor, the first elevator, the first conveyor belt, the regeneration reactor, the second elevator, the second conveyor belt and the absorption reactor to monitor the circulation volume.

[0068] Thermocouples or Pt100 thermometers and pressure transmitters are sequentially installed on the regeneration reactor, the mixer of the carbon dioxide and hydrogen mixing and preheating unit, the fixed bed reactor of the methanation reaction unit, the multi-tube reactor or the fluidized bed reactor, and on the heat transfer carrier pipelines of heat exchangers one to five; a level gauge or differential pressure level gauge is installed on the buffer tank to monitor changes in temperature, pressure and oil level.

[0069] A pH sensor is installed on the circulating liquid pipeline of the scrubbing tower or gas scrubbing tower to control the addition of deacidifying agent.

[0070] Each pipeline in the carbon dioxide methanation system is equipped with a pneumatic or electric regulating valve to regulate the flow rates of CO2, H2, and heat transfer oil.

[0071] The online gas chromatograph or four-in-one gas composition analyzer, mass flow meter or mass flow controller, speed sensor or weight sensor, thermocouple or Pt100 thermometer, pressure transmitter, level gauge or differential pressure level gauge, pH sensor and pneumatic or electric regulating valve are electrically connected to the PLC or DCS control system.

[0072] This invention enables the control program to coordinate various sensors and actuators according to a preset strategy, achieving: ① automatic adjustment of the CaO / CaCO3 material circulation rate based on CO2 concentration or flue gas flow rate; ② real-time adjustment of the H2 / CO2 flow ratio, mixed gas preheating temperature, and reaction pressure based on the methanation load; ③ adjustment of the heat transfer oil flow rate, waste heat distribution ratio, and methane reheating rate based on energy balance, ensuring system thermal balance and reactor temperature stability. Through the above-mentioned equipment composition and their connection relationships, the system monitoring and intelligent control unit can acquire key data such as CO2 content, flow rate, temperature, pressure, CaO / CaCO3 circulation rate, and methanation yield in real time, and output control commands through PLC / DCS to achieve coordinated adjustment and energy optimization of each unit.

[0073] The carbon dioxide methanation method based on the coupling of carbonate cycle and hydrogen energy includes the following steps: 1) Using the system of the present invention, flue gas or process gas containing carbon dioxide is fed into an absorption reactor, so that the gas containing carbon dioxide comes into contact with calcium oxide solid to generate carbonate solid. 2) The carbonate solid obtained in step 1) is fed into the regeneration reactor and decomposed at 750-1100℃ to generate calcium oxide solid and carbon dioxide-rich gas. 3) The carbon dioxide-rich gas obtained in step 2) is sent to a carbon dioxide purification unit for dust removal, dehydration and / or deacidification treatment to obtain carbon dioxide raw material gas; 4) The carbon dioxide raw material gas obtained in step 3) is fed into the carbon dioxide and hydrogen mixing and preheating unit and mixed with hydrogen from the hydrogen supply unit and heated to 100-350°C to obtain a preheated mixed gas. 5) The preheated mixed gas obtained in step 4) is fed into a methanation reaction unit containing a methanation catalyst, and the methanation reaction is carried out at 200-500℃ and 0.1-6MPa to generate a reaction product gas containing methane. 6) The reaction product gas obtained in step 5) is sent to the methane product processing and utilization unit for cooling, dehydration and purification to obtain methane product gas, which is then used as fuel gas and / or chemical raw material. 7) Return the calcium oxide solid obtained in step 2) to the absorption reactor in step 1) for recycling.

[0074] In one embodiment, the absorption reactor operates at 300-700°C; the calcium oxide solid obtained in step 2) is returned to the absorption reactor in step 1) for recycling ≥40 times; and the volume fraction of carbon dioxide feed gas is not less than 90%.

[0075] In one embodiment, the absorption reactor operates at 400–650°C. In one embodiment, the absorption reactor is operated at 450-550°C. In one embodiment, in step 4), the molar ratio of carbon dioxide to hydrogen is 1:(3-6); the methanation catalyst is supported Ni, Ni-Co, Ni-Cu, Ru or a combination thereof.

[0076] In one embodiment, in step 4), the support in the methanation catalyst is alumina, silicon dioxide, titanium dioxide, zirconium oxide, cerium oxide, spinel or a composite support thereof; the loading of active metal (based on metal) is 1-40 wt%.

[0077] In one embodiment, the active metal (based on metal content) loading in the methanation catalyst is 5-30 wt%.

[0078] In one embodiment, the active metal (based on metal content) loading in the methanation catalyst is 10-20 wt%.

[0079] Example 1 The carbon dioxide methanation method based on the coupling of carbonate cycle and hydrogen energy includes the following steps: 1) Using the system of this invention, the CO2 volume fraction in the flue gas emitted by a coal-fired boiler is 12%, and the temperature is 150℃. The flue gas containing carbon dioxide is sent into an absorption reactor, which operates at 550℃ (±5℃). This allows the carbon dioxide-containing gas to contact with solid calcium oxide to form solid carbonate. 2) The carbonate solid obtained in step 1) is fed into the regeneration reactor and decomposed at 850-900℃ to generate calcium oxide solid and carbon dioxide-rich gas. 3) The carbon dioxide-rich gas obtained in step 2) is sent to a carbon dioxide purification unit for dust removal, dehydration, and deacidification to obtain carbon dioxide feed gas with a volume fraction ≥90%; 4) The carbon dioxide raw material gas obtained in step 3) is fed into the carbon dioxide and hydrogen mixing and preheating unit and mixed with hydrogen from the hydrogen supply unit and heated to 280°C. The molar ratio of carbon dioxide to hydrogen is 1:4 to obtain a preheated mixed gas. 5) The preheated mixed gas obtained in step 4) is fed into a methanation reaction unit containing a methanation catalyst (Ni-based supported catalyst, γ-Al2O3 as support, with a loading of 10% based on metallic Ni) and carried out a methanation reaction at 300℃ and 2MPa to generate a reaction product gas containing methane, with a CH4 volume fraction of over 85% in the product gas. 6) The reaction product gas obtained in step 5) is sent to the methane product processing and utilization unit for cooling, dehydration and purification to obtain methane product gas, which is then used as fuel gas and / or chemical raw material. 7) The calcium oxide solid obtained in step 2) is returned to the absorption reactor in step 1) for recycling ≥40 times.

[0080] Through thermal energy integration, in this embodiment, the waste heat from the CaCO3 decomposition furnace accounts for 50% of the preheating heat demand of the CO2–H2 mixture, the heat released from methanation accounts for 20% through the heat exchanger, and the remaining 30% is provided by external fuel (including reburned methane).

[0081] Example 2 The carbon dioxide methanation method based on the coupling of carbonate cycle and hydrogen energy includes the following steps: 1) Using the system of this invention, a certain integrated plant has two CO2-containing flue gas streams, A and B: Route A: Cement kiln exhaust gas, CO2 volume fraction 20%, temperature 280℃; B route: Blast furnace gas purification tail gas, CO2 volume fraction 25%, temperature 120℃. The flue gas from routes A and B is mixed in a certain proportion, and the flue gas containing carbon dioxide is sent to the absorption reactor. The absorption reactor is operated at 540℃ (±5℃) to allow the gas containing carbon dioxide to come into contact with calcium oxide solid to form carbonate solid. 2) The carbonate solid obtained in step 1) is fed into the regeneration reactor and decomposed at 900-950℃ to generate calcium oxide solid and carbon dioxide-rich gas. 3) The carbon dioxide-rich gas obtained in step 2) is sent to a carbon dioxide purification unit for dust removal, dehydration and / or deacidification treatment to obtain carbon dioxide feed gas with a volume fraction ≥90%; 4) The carbon dioxide raw material gas obtained in step 3) is fed into the carbon dioxide and hydrogen mixing and preheating unit and mixed with hydrogen from the hydrogen supply unit and heated to 250-300°C. The molar ratio of carbon dioxide to hydrogen is 1:(3.5-4.5) to obtain a preheated mixed gas. 5) The preheated mixed gas obtained in step 4) is fed into a methanation reaction unit containing a methanation catalyst (Ni-based supported catalyst support is γ-Al2O3, Ni loading is 15 wt%, calculated as metallic Ni), and the methanation reaction is carried out at 320℃ and 3MPa to generate a reaction product gas containing methane, with a CH4 volume fraction of 80-90% in the product gas; 6) The reaction product gas obtained in step 5) is sent to the methane product processing and utilization unit for cooling, dehydration and purification to obtain methane product gas, which is then used as fuel gas and / or chemical raw material. 7) The calcium oxide solid obtained in step 2) is returned to the absorption reactor in step 1) for recycling ≥40 times.

[0082] Through this embodiment, the following can be achieved: ① Unified capture and methanation of CO2 from multiple sources; ② The cascade utilization of thermal energy between cement kilns, blast furnaces, regeneration reactors and methanation; ③ Methane is used as a high-quality fuel and chemical raw material in the plant area.

[0083] Based on the experimental results of Examples 1 and 2, the "Carbon Dioxide Methanation System Based on CaCO3 / CaO Cycle and Hydrogen Energy Coupling" proposed in this invention has achieved significant technical effects in terms of CO2 capture efficiency, regenerated CO2 purity, methanation conversion rate, energy utilization rate, and system stability, as specifically demonstrated below: 1. The high-purity CO2 regeneration capacity is significantly improved.

[0084] In Example 1, the regeneration reactor operated at 850-900°C, and the purity of the produced CO2 feed gas reached over 90%. This demonstrates that the CaCO3 / CaO circulating carbon capture method of the present invention can effectively convert low-concentration flue gas (CO2≈12%) into high-purity feed gas, which is superior to the limitations of traditional adsorption and membrane separation processes on feed gas concentration.

[0085] 2. CaO adsorbent can achieve 30-80 stable cycles.

[0086] Examples 1 and 2 show that CaO maintains acceptable adsorption activity after ≥40 cycles (Example 1) and ≥40 cycles (Example 2). This demonstrates that the temperature window, residence time, and cycle control strategy proposed in this invention effectively delays the decay of CaO activity and achieves closed-loop material circulation of the adsorbent.

[0087] 3. CO2 capture efficiency adaptable to different operating conditions and multiple flue gas sources.

[0088] In Example 2, the flue gas from both A and B streams (20% CO2, 280℃; 25% CO2, 120℃) was mixed by this system and then entered the absorption reactor. Both gases were successfully captured and regenerated in the decomposition furnace into CO2 with a purity ≥90%. This demonstrates that the system is capable of adapting to different industrial CO2 source compositions.

[0089] 4. Integrated thermal energy significantly reduces the demand for external heating.

[0090] Example 1 shows: 1) The waste heat from the regeneration reactor bears 50% of the CO2-H2 preheating load; 2) The methanation reaction is exothermic, accounting for 20% of the reaction. 3) External heating demand accounts for only about 30%.

[0091] In Example 2, 80-90% of the preheating load can be met by the waste heat inside the system.

[0092] This demonstrates that the thermal energy integration method of the present invention can significantly reduce energy consumption and achieve near-closed-loop energy recycling.

[0093] 5. Methanation reaction has high yield and stability.

[0094] In Example 1, the reaction conditions were 2 MPa and 300 °C, and the CH4 content in the product gas reached more than 85%. In Example 2, the CH4 content was 80-90% under conditions of 3MPa and 320℃.

[0095] This demonstrates that the combination of the mixing and preheating strategy, high-temperature reaction conditions, and catalyst system of the present invention achieves high CO2 conversion rate and CH4 generation efficiency.

[0096] 6. Intelligent control enables adaptive adjustment of CaO circulation rate, H2 / CO2 ratio, and methane production.

[0097] In Example 2, by monitoring changes in CO2 load, the control system can automatically adjust the number of CaO / CaCO3 cycles (within the range of 20-80 times); automatically adjust the H2 / CO2 ratio (within the range of 3.5-4.5) according to the methanation load; and adjust the methane reheat ratio according to the system's thermal balance, thereby achieving adaptive optimization of the overall system operating conditions.

[0098] In summary, the data from the examples fully demonstrate that the present invention has achieved the expected technical effects in terms of improving CO2 capture purity, adsorbent cycle life, energy utilization efficiency, methanation yield, and intelligent system control, and has significant practical value.

[0099] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling, characterized in that, include: The unit includes a carbon dioxide gas supply unit, a carbonate circulation carbon capture unit, a carbon dioxide purification unit, a hydrogen supply unit, a carbon dioxide and hydrogen mixing and preheating unit, a methanation reaction unit, a methane product treatment and utilization unit, and a thermal energy integration and control unit. The carbonate recycling carbon capture unit includes: an absorption reactor, a regeneration reactor, a first solid conveying device, and a second solid conveying device; The absorption reactor is filled with solid adsorbent. The solid outlet of the absorption reactor is connected to the solid inlet of the regeneration reactor via a first solid conveying device. The solid outlet of the regeneration reactor is connected to the solid inlet of the absorption reactor via a second solid conveying device. The carbon dioxide gas supply unit, absorption reactor, regeneration reactor, carbon dioxide purification unit, carbon dioxide and hydrogen mixing and preheating unit, methanation reaction unit, and methane product treatment and utilization unit are connected sequentially along the gas flow via pipelines. The hydrogen outlet of the hydrogen supply unit is connected to the hydrogen inlet of the preheating unit via a pipeline, where carbon dioxide and hydrogen are mixed. The carbon dioxide and hydrogen mixing and preheating unit is used to mix the carbon dioxide raw material gas and hydrogen at a predetermined molar ratio and heat them to a predetermined temperature to obtain a preheated mixed gas. One end of the methane product outlet of the methane product processing and utilization unit is connected to the plant's gas pipeline network or external transmission pipeline, and the other end is connected to the heating device or fuel supply branch of the regeneration reactor. The hydrogen recovery outlet of the methane product processing and utilization unit is connected to another hydrogen inlet of the carbon dioxide and hydrogen mixing and preheating unit via pipeline. The thermal energy integration and control unit includes at least one heat exchange device for recovering at least a portion of the heat from the regeneration reactor and the methanation reaction unit, and for supplying heat to the carbon dioxide and hydrogen mixing and preheating unit or other heat-requiring units within the system.

2. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 1, characterized in that, The methane product outlet of the methane product processing and utilization unit is connected at one end to the plant's gas pipeline network or external transmission pipeline, and at the other end to the fuel inlet of the regeneration reactor via a pipeline. The thermal energy integration and control unit includes heat exchanger one to heat exchanger two. The flue gas outlet of the regeneration reactor is equipped with heat exchanger one, the methane outlet of the methanation reaction unit is equipped with heat exchanger two, and the carbon dioxide and hydrogen mixing and preheating unit includes a mixer and heat exchanger three. Heat exchanger three is located outside the mixer. Heat exchanger one and heat exchanger two are respectively connected to heat exchanger three through a heat transfer oil or steam heat exchange loop. The mixer is a jet mixer, a vortex mixer, or a dynamic mixer; the heat exchanger is a shell-and-tube type, a plate type, or a microchannel heat exchanger.

3. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 1, characterized in that, The carbon dioxide gas supply unit includes a carbon dioxide-containing gas inlet pipeline and a dust collector. A heat exchanger is installed on the carbon dioxide-containing gas inlet pipeline. The carbon dioxide-containing gas inlet pipeline, the dust collector, and the absorption reactor are connected in sequence via pipelines. The carbon dioxide-containing flue gas or process gas in the carbon dioxide-containing gas inlet pipeline comes from combustion devices, industrial furnaces, boiler tail gas, cement kiln tail gas, steelmaking / blast furnace gas purification tail gas, chemical tail gas, or waste incineration flue gas.

4. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 1, characterized in that, The absorption reactor is a fluidized bed carbon capture and absorption tower, a moving bed carbon capture and absorption tower, a bubbling bed carbon capture and absorption tower, or a rotary kiln carbon capture and absorption tower. The regeneration reactor is a rotary kiln, fluidized bed furnace, vertical kiln, or electric heating furnace; the heating method of the regeneration reactor is one or a combination of methane reburning, external fuel, electric heating, oxygen-enriched combustion, or heat carrier circulation. The carbonate circulation carbon capture unit selects calcium carbonate circulation decomposition to capture carbon dioxide. The first solid conveying device includes a first elevator and a first conveyor belt, and the second solid conveying device includes a second elevator and a second conveyor belt. The solid outlet of the absorption reactor is connected to the solid inlet of the regeneration reactor in sequence via the first elevator and the first conveyor belt. The solid outlet of the regeneration reactor is connected to the solid inlet of the absorption reactor in sequence via the second elevator and the second conveyor belt.

5. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 2, characterized in that, The carbon dioxide purification unit includes a precooling and dust removal device, a washing or deacidification device, a drying and adsorption device, a desulfurization device, and a compression and pressure regulation device. The precooling and dust removal device includes a heat exchanger or condenser, and a cyclone separator, a bag filter or an electrostatic precipitator. The washing or deacidification device is a washing tower or a gas scrubbing tower; The drying and adsorption device includes a compressor, a molecular sieve or activated alumina dryer, and an activated carbon adsorber or adsorption tower. The desulfurization device is a desulfurization tower or an alkaline washing tower; The compression and pressure regulating device is either a compressor or a pressure regulating valve. The regeneration reactor, cyclone separator I, bag filter or electrostatic precipitator, scrubbing tower or gas scrubbing tower, compressor I, molecular sieve or activated alumina dryer I, activated carbon adsorber I or adsorption tower, desulfurization tower or alkaline scrubbing tower, compressor II or pressure regulating valve and the mixer are connected in sequence by pipelines. A heat exchanger V or condenser is provided on the pipeline connecting the regeneration reactor and cyclone separator I, bag filter or electrostatic precipitator.

6. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 1, characterized in that, The hydrogen supply unit includes a hydrogen inlet pipeline and a buffer tank, and the hydrogen inlet pipeline, the buffer tank and the mixer are connected in sequence via pipelines. The methanation reaction unit is a fixed-bed reactor, a multi-tube reactor, or a fluidized-bed reactor.

7. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 1, characterized in that, The methane product processing and utilization unit includes a cooling and moisture condensation device, a drying and adsorption device, an impurity removal and methane upgrading device, an unreacted hydrogen recovery device, a compression and pressure regulation device, and a product gas output and distribution device. The cooling and moisture removal device includes a water-cooled or air-cooled unit, a plate heat exchanger, and a gas-liquid separator or cyclone separator. The drying and adsorption device includes a molecular sieve or activated alumina dryer II and an activated carbon adsorber II. The impurity removal and methane upgrading device is a methane primary membrane separator or a methane pressure swing adsorption tower. The unreacted hydrogen recovery device is a hydrogen primary membrane separator or a hydrogen pressure swing adsorption tower. The second compression and pressure regulating device is a single-stage or multi-stage reciprocating compressor; The product gas output and distribution device is a metering valve; The methanation reaction unit, water-cooled or air-cooled unit, gas-liquid separator or cyclone separator II, molecular sieve or activated alumina dryer II, activated carbon adsorber II, methane primary membrane separator or methane pressure swing adsorption tower, single-stage or multi-stage reciprocating compressor, metering valve, and fuel inlet of plant gas pipeline or external pipeline or regeneration reactor are connected in sequence via pipelines; plate heat exchangers are provided on the pipelines connecting the water-cooled or air-cooled unit and the gas-liquid separator or cyclone separator II. The permeate outlet of the methane primary membrane separator or methane pressure swing adsorption tower is connected to the hydrogen primary membrane separator or hydrogen pressure swing adsorption tower via a pipeline, and the permeate outlet of the hydrogen primary membrane separator or hydrogen pressure swing adsorption tower is connected to the mixer via a pipeline.

8. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 1, characterized in that, The solid adsorbent includes one or a combination of several of the following: CaO, MgO, SrO, BaO, red mud activated adsorbent, or steel slag activated adsorbent.

9. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 8, characterized in that, The activation treatment of the red mud activated adsorbent and / or steel slag activated adsorbent includes calcination, hydration and / or mechanical activation.

10. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 1, characterized in that, The absorption reactor is also connected to an adsorbent feeding branch and / or a deactivated solid slag discharge branch.

11. The carbon dioxide methanation system based on carbonate cycle and hydrogen energy coupling according to claim 1, characterized in that, It also includes a system monitoring and intelligent control unit, which adopts a PLC or DCS system. The PLC or DCS control system is connected to the carbon dioxide gas supply unit, the carbonate circulation carbon capture unit, the carbon dioxide purification unit, the hydrogen supply unit, the carbon dioxide and hydrogen mixing and preheating unit, the methanation reaction unit, the methane product treatment and utilization unit, and the thermal energy integration and control unit through signal lines and / or industrial buses, respectively.

12. A method for carbon dioxide methanation based on the system of any one of claims 1-11, coupled with carbonate cycling and hydrogen energy, characterized in that, Includes the following steps: 1) Using the system described in claim 1, carbon dioxide-containing flue gas or process gas is fed into an absorption reactor, so that the carbon dioxide-containing gas comes into contact with calcium oxide solid to generate carbonate solid; 2) The carbonate solid obtained in step 1) is fed into the regeneration reactor and decomposed at 750-1100℃ to generate calcium oxide solid and carbon dioxide-rich gas. 3) The carbon dioxide-rich gas obtained in step 2) is sent to a carbon dioxide purification unit for dust removal, dehydration and / or deacidification treatment to obtain carbon dioxide raw material gas; 4) The carbon dioxide raw material gas obtained in step 3) is fed into the carbon dioxide and hydrogen mixing and preheating unit and mixed with hydrogen from the hydrogen supply unit and heated to 100-350°C to obtain a preheated mixed gas. 5) The preheated mixed gas obtained in step 4) is fed into a methanation reaction unit containing a methanation catalyst, and the methanation reaction is carried out at 200-500℃ and 0.1-6MPa to generate a reaction product gas containing methane. 6) The reaction product gas obtained in step 5) is sent to the methane product processing and utilization unit for cooling, dehydration and purification to obtain methane product gas, which is then used as fuel gas and / or chemical raw material. 7) Return the calcium oxide solid obtained in step 2) to the absorption reactor in step 1) for recycling.

13. The carbon dioxide methanation method based on carbonate cycle and hydrogen energy coupling according to claim 12, characterized in that, The absorption reactor operates at 300-700℃; the calcium oxide solid obtained in step 2) is returned to the absorption reactor in step 1) for recycling multiple times, preferably ≥40 times; the volume fraction of the carbon dioxide feed gas is not less than 90%.

14. The carbon dioxide methanation method based on carbonate cycle and hydrogen energy coupling according to claim 12, characterized in that, In step 4), the molar ratio of carbon dioxide to hydrogen is 1:(3-6); the methanation catalyst is supported Ni, Ni-Co, Ni-Cu, Ru or a combination thereof.

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