A CO2 capture-methanation system and method based on catalyst coupled with waste heat

Abstract

This invention belongs to the technical field of CO2 capture and resource utilization in coal-fired power plants, and relates to a CO2 capture-methanation system and method based on catalyst-coupled waste heat. It includes: a CO2 capture unit, comprising a fixed-bed adsorption tower and an adsorbent regeneration device, the fixed-bed adsorption tower being connected to the adsorbent regeneration device; a catalytic methanation unit, comprising a fixed-bed reactor, the fixed-bed reactor being connected to the adsorbent regeneration device; a waste heat utilization unit, comprising a heat exchanger and a heat transfer oil circulation system, the cold-side outlet of the heat exchanger being connected to the heat transfer oil circulation system, the heat transfer oil circulation system being connected to both the adsorbent regeneration device and the fixed-bed reactor; and a solid waste backfilling unit, comprising a mineralization reaction tank, the mineralization reaction tank being connected to the fixed-bed reactor and the adsorbent regeneration device. This invention achieves synergy between CO2 capture, conversion, waste heat utilization, and solid waste backfilling, improving the system's economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of CO2 capture and resource utilization technology in coal-fired power plants, and relates to a CO2 capture-methanation system and method based on catalyst coupling waste heat. Background Technology

[0002] As a significant source of carbon emissions, coal-fired power plants currently rely primarily on geological sequestration for CO2 treatment. While this method enables large-scale CO2 sequestration, its resource utilization rate is less than 5%, and the sequestration cost is high, making it difficult to establish a sustainable carbon cycle model. Regarding CO2 resource utilization, CO2 methanation technology can convert CO2 into high-value methane fuel, showing broad application prospects. However, existing CO2 methanation technologies still face two major technical bottlenecks: First, the catalyst system is highly dependent on precious metals (such as Ru, Rh, etc.) or high-purity supports (such as Al2O3, SiO2, etc.), resulting in high material costs. While single Ni-based catalysts are relatively inexpensive, they are prone to rapid activity decay due to carbon buildup during the reaction, with catalyst lifespans generally less than 500 hours, severely impacting system stability and economic efficiency. Second, in existing processes, both the adsorbent regeneration process of the CO2 capture unit and the methanation reaction process consume large amounts of external electricity or steam, resulting in high overall system energy consumption and making it difficult to meet the demands of large-scale industrial applications.

[0003] Meanwhile, coal-fired power plants generate a large amount of solid waste and waste heat resources during operation. Statistics show that only about 40% of fly ash from coal-fired power plants is used for low-value-added applications such as building material production, while the majority is disposed of through stockpiling, which not only occupies a large amount of land resources but also easily causes environmental problems such as dust and groundwater pollution. Furthermore, the flue gas emitted from the tail-end flue of power plant boilers typically has a temperature of 200-300℃ and contains a large amount of waste heat; however, the current recovery and utilization rate of this waste heat is less than 30%, resulting in significant energy waste. Summary of the Invention To address the problems in the existing technology, this invention provides a CO2 capture-methanation system and method based on catalyst coupling waste heat, which realizes the synergy of CO2 capture, conversion, waste heat utilization and solid waste backfilling, and improves the economic and environmental benefits of the system.

[0004] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a CO2 capture-methanation system based on catalyst coupled with waste heat, comprising: The CO2 capture unit includes a fixed-bed adsorption tower and an adsorbent regeneration device, wherein the outlet of the fixed-bed adsorption tower is connected to the inlet of the adsorbent regeneration device. A catalytic methanation unit, the catalytic methanation unit including a fixed-bed reactor, the inlet of the fixed-bed reactor being connected to the outlet of the adsorbent regeneration device; The waste heat utilization unit includes a heat exchanger and a heat transfer oil circulation system. The cold side outlet of the heat exchanger is connected to the inlet of the heat transfer oil circulation system. The outlet of the heat transfer oil circulation system is connected to the heat medium inlet of the adsorbent regeneration device and the heat medium inlet of the fixed bed reactor, respectively. A solid waste backfilling unit, comprising a mineralization reaction tank, wherein the inlet of the mineralization reaction tank is connected to the catalyst outlet of the fixed bed reactor, and the air inlet of the mineralization reaction tank is connected to the air outlet of the adsorbent regeneration device.

[0005] Preferably, the fixed-bed adsorption tower includes an adsorption tower shell and an adsorption bed; the adsorption bed is disposed inside the adsorption tower shell; the top outlet of the adsorption tower shell is connected to the inlet of the adsorbent regeneration device.

[0006] Preferably, the adsorption bed is filled with a fly ash-derived adsorbent; the fly ash-derived adsorbent includes a microwave-activated coal fly ash carrier and zinc oxide loaded on the surface of the coal fly ash carrier.

[0007] Preferably, the CO2 capture unit further includes a CO2 buffer tank and a purity detector; the outlet of the adsorbent regeneration device is connected to the inlet of the CO2 buffer tank; the outlet of the CO2 buffer tank is connected to the inlet of the purity detector; and the outlet of the purity detector is connected to the inlet of the fixed-bed reactor.

[0008] Preferably, the fixed-bed reactor includes a reactor shell, a catalyst bed, and a heating jacket; the catalyst bed is disposed inside the reactor shell; the heating jacket is fitted onto the outer wall of the reactor shell; the heat medium inlet of the heating jacket is connected to the outlet of the heat transfer oil circulation system; and the air inlet of the reactor shell is connected to the air outlet of the adsorbent regeneration device.

[0009] Preferably, the catalyst bed is filled with a fly ash-derived Ni-Mn bimetallic catalyst; the fly ash-derived Ni-Mn bimetallic catalyst includes a microwave-activated coal fly ash support and nickel and manganese supported on the surface of the coal fly ash support; the nickel and the manganese are mutually doped on the surface of the coal fly ash support.

[0010] Preferably, the heat transfer oil circulation system includes a heat transfer oil pump, a first regulating valve, and a second regulating valve; the cold side outlet of the heat exchanger is connected to the inlet of the heat transfer oil pump; the outlet of the heat transfer oil pump is connected to the inlet of the first regulating valve and the inlet of the second regulating valve, respectively; the outlet of the first regulating valve is connected to the heat medium inlet of the adsorbent regeneration device; and the outlet of the second regulating valve is connected to the heat medium inlet of the fixed bed reactor.

[0011] Preferably, the solid waste backfilling unit further includes a slurry preparation device; the slurry preparation device includes a mixing tank, a fly ash hopper, and a water replenishment device; the outlet of the fly ash hopper is connected to the inlet of the mixing tank; the water replenishment device is connected to the inlet of the mixing tank; and the outlet of the mixing tank is connected to the inlet of the mineralization reaction tank.

[0012] Preferably, it further includes a central control module; the central control module includes a controller, a first temperature sensor, a second temperature sensor, a first pressure sensor, a second pressure sensor, a gas composition sensor, and a flow sensor; the first temperature sensor and the first pressure sensor are installed on the inlet pipe of the fixed bed adsorption tower; the second temperature sensor and the second pressure sensor are installed on the inlet pipe of the fixed bed reactor; the gas composition sensor is installed on the connecting pipe between the adsorbent regeneration device and the fixed bed reactor; the flow sensor is installed on the outlet pipe of the heat transfer oil circulation system; the catalytic methanation unit further includes a feed valve, which is installed on the inlet pipe of the fixed bed reactor; The first temperature sensor, the second temperature sensor, the first pressure sensor, the second pressure sensor, the gas composition sensor, and the flow sensor are respectively connected to the signal input terminal of the controller; the feed valve is connected to the signal output terminal of the controller.

[0013] Secondly, the present invention provides a CO2 capture-methanation system based on catalyst coupling waste heat, comprising the following steps: The flue gas to be treated is fed into the fixed bed adsorption tower, and the purified flue gas is discharged after adsorption; the adsorbent in the fixed bed adsorption tower after adsorption saturation is transported to the adsorbent regeneration device. The waste heat utilization unit is started, the heat exchanger recovers external waste heat and heats the heat transfer oil, and the heat transfer oil is transported to the adsorbent regeneration device and the fixed bed reactor through the heat transfer oil circulation system to heat and regenerate the adsorbent in the adsorbent regeneration device, and at the same time preheat the fixed bed reactor. The CO2 gas released during the regeneration process of the adsorbent regeneration device is transported to the inlet of the fixed bed reactor through the outlet. Hydrogen gas is introduced into the fixed-bed reactor, and the hydrogen gas reacts with CO2 in the presence of a catalyst to produce methane. The catalyst, after its activity has degraded in the fixed-bed reactor, is transported to the feed inlet of the mineralization reaction tank through the catalyst outlet, and a portion of the CO2 gas output from the outlet of the adsorbent regeneration device is introduced into the inlet of the mineralization reaction tank to carry out the mineralization reaction.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The CO2 capture unit uses a fixed-bed adsorption tower to capture CO2 from flue gas. After adsorption saturation, the adsorbent is regenerated in an adsorbent regeneration unit, releasing high-concentration CO2 to provide feedstock for the downstream catalytic methanation unit. The catalytic methanation unit converts CO2 into methane via a fixed-bed reactor, realizing the fuel utilization of carbon resources. The waste heat utilization unit recovers external waste heat through a heat exchanger and uses a heat transfer oil circulation system to transfer the heat to the adsorbent regeneration unit and the fixed-bed reactor, providing the necessary thermal energy for adsorbent regeneration and methanation reactions, significantly reducing the system's dependence on external energy sources. The solid waste backfilling unit receives spent catalyst and some CO2 in a mineralization reaction tank, converting solid waste into backfill material and solidifying CO2, achieving resource-based disposal of waste. This invention achieves synergy between CO2 capture, conversion, waste heat utilization, and solid waste backfilling, improving the system's economic and environmental benefits. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of a CO2 capture-methanation system based on catalyst coupling waste heat according to the present invention; Figure 2 This is a flowchart of the method of the present invention.

[0017] The system includes: 1. CO2 capture unit; 2. Catalytic methanation unit; 3. Waste heat utilization unit; and 4. Solid waste backfilling unit. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0022] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply refers to its direction relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0023] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or a simple connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] The present invention will now be described in further detail with reference to the accompanying drawings: The first objective of this invention is to provide a CO2 capture-methanation system based on catalyst coupling with waste heat, such as... Figure 1 As shown, it includes: CO2 capture unit 1, the CO2 capture unit 1 includes a fixed bed adsorption tower and an adsorbent regeneration device, the outlet of the fixed bed adsorption tower is connected to the inlet of the adsorbent regeneration device. Catalytic methanation unit 2, the catalytic methanation unit 2 includes a fixed bed reactor, the inlet of the fixed bed reactor is connected to the outlet of the adsorbent regeneration device; Waste heat utilization unit 3 includes a heat exchanger and a heat transfer oil circulation system. The cold side outlet of the heat exchanger is connected to the inlet of the heat transfer oil circulation system. The outlet of the heat transfer oil circulation system is connected to the heat medium inlet of the adsorbent regeneration device and the heat medium inlet of the fixed bed reactor, respectively. Solid waste backfilling unit 4 includes a mineralization reaction tank. The inlet of the mineralization reaction tank is connected to the catalyst outlet of the fixed bed reactor, and the air inlet of the mineralization reaction tank is connected to the air outlet of the adsorbent regeneration device.

[0025] Specifically, CO2 capture unit 1 uses a fixed-bed adsorption tower to selectively adsorb CO2 from the flue gas of a coal-fired power plant. After saturation, the adsorbent is regenerated by a thermal regeneration device to release high-concentration CO2, ensuring continuous and stable operation of the capture and regeneration process. The fixed-bed reactor in catalytic methanation unit 2 receives CO2 from the regeneration device and reacts with externally supplied hydrogen under the action of a catalyst to produce high-purity methane product gas, realizing the resource conversion of CO2. Waste heat utilization unit 3 recovers low-grade waste heat from the flue gas at the tail end of the power plant boiler through a heat exchanger, and then circulates it through a heat transfer oil system. Heat is delivered in stages to the adsorbent regeneration unit and the fixed-bed reactor, providing the necessary heat for the thermal regeneration and methanation reactions of the adsorbent, thereby replacing or significantly reducing external energy input and substantially lowering the system's operating energy consumption. The solid waste backfilling unit 4 introduces the degraded catalyst from the catalytic methanation unit 2 into a mineralization reactor, mixes it with fly ash slurry generated by the power plant, and introduces some of the remaining CO2 flowing out of the system. Under normal temperature and pressure, a carbonate mineralization reaction generates a filling paste with compressive strength, which can be used for backfilling coal mine goaf areas, achieving resource-based disposal of solid waste and deep solidification of CO2. On the one hand, this system uses waste heat from the power plant to replace external heat sources, significantly reducing the energy costs of CO2 capture and methanation processes and improving the system's economic efficiency. On the other hand, the system co-processes and transforms fly ash and degraded catalyst—two types of solid waste—within the system into backfillable materials, achieving near-zero emissions of solid waste and additional CO2 mineralization and sequestration, thus creating synergistic benefits in carbon reduction, waste heat utilization, and solid waste resource utilization.

[0026] For example, the fixed-bed adsorption tower includes an adsorption tower shell and an adsorption bed; the adsorption bed is disposed inside the adsorption tower shell; the adsorption bed is supported by multiple layers of sieve plates or grids and filled with fly ash-derived adsorbent in a layered or integral filling manner; the lower part of the adsorption tower shell is provided with a flue gas inlet and a gas distributor, so that the incoming flue gas passes through the adsorption bed from bottom to top after being evenly distributed, and fully contacts the adsorbent to achieve selective capture of CO2; the top outlet of the adsorption tower shell is connected to the inlet of the adsorbent regeneration device through a pipeline, so as to switch the gas path after adsorption saturation and introduce the regeneration medium or desorption gas into the adsorption bed for thermal regeneration.

[0027] The fly ash-derived adsorbent includes a microwave-activated coal fly ash carrier and zinc oxide loaded on the surface of the coal fly ash carrier. Coal fly ash, a porous mineral material rich in aluminosilicates, is activated by microwave radiation. Utilizing the selective heating and rapid temperature rise characteristics of microwaves, moisture and volatiles within the fly ash particles rapidly escape, forming numerous micropores and mesopores on the particle surface and within the particles. This significantly increases the specific surface area and pore volume. Simultaneously, the microwave field induces lattice distortion or partial amorphization of quartz, mullite, and other crystalline phases in the fly ash, exposing more surface-active sites such as silanol and aluminol hydroxyl groups. This provides a highly dispersed carrier framework for zinc oxide loading. Zinc oxide, as an active component for medium-temperature CO2 adsorption, is uniformly loaded onto the surface and pores of the activated fly ash through equal-volume or excessive impregnation methods. During subsequent calcination, highly dispersed nano-sized ZnO particles are formed. These particles enhance loading stability through chemical bonds such as Zn-O-Si and Zn-O-Al with the fly ash carrier, preventing agglomeration of active components during high-temperature regeneration.

[0028] For example, the preparation method of fly ash-derived adsorbent includes: selecting fly ash from a coal-fired power plant (SiO2 content 55%, Al2O3 content 25%), grinding it to a particle size ≤100μm, placing it in a microwave reactor, setting the power to 600W, and activating it for 12min; weighing 100g of activated fly ash, adding 50mL of impregnation solution containing Zn(NO3)2 (ZnO loading 6%), and impregnating it for 12h using the equal volume impregnation method; placing the impregnated sample in a forced-air drying oven, drying it at 110℃ for 6h, then placing it in a muffle furnace, calcining it at 500℃ for 3h, and cooling it to room temperature to obtain the fly ash-derived adsorbent.

[0029] On the one hand, using fly ash generated by the power plant itself as an adsorbent carrier, replacing traditional commercial carriers such as high-purity alumina and molecular sieves, significantly reduces the cost of adsorbent raw materials while achieving high-value utilization of fly ash. On the other hand, microwave activation has advantages over traditional thermal activation, including shorter processing time, lower energy consumption, and stronger control over pore structure. It can optimize the pore structure according to the characteristics of fly ash raw materials, enabling the adsorbent to maintain a high adsorption capacity and selectivity for CO2 under low-temperature adsorption conditions of 30~80℃, and achieve rapid regeneration of the adsorbent at a regeneration temperature of 150~200℃, which is highly matched with the temperature range of waste heat from the power plant, reducing regeneration energy consumption. In addition, after ZnO is loaded onto the activated fly ash carrier, the inherent alkali metal oxides (such as CaO and MgO) in the fly ash form a composite adsorption system with ZnO, which produces a synergistic chemical adsorption effect on CO2, further improving the adsorption efficiency and cycle stability. This allows the adsorbent to maintain stable capture performance after multiple adsorption-regeneration cycles, thus providing low-cost, high-efficiency, and long-life adsorbent material support for the entire CO2 capture-methanation system.

[0030] For example, the CO2 capture unit 1 further includes a CO2 buffer tank and a purity detector; the outlet of the adsorbent regeneration device is connected to the inlet of the CO2 buffer tank; the outlet of the CO2 buffer tank is connected to the inlet of the purity detector; and the outlet of the purity detector is connected to the inlet of the fixed-bed reactor. Since the CO2 gas released during the thermal regeneration process of the adsorbent regeneration device is not a stable and continuous flow, its flow rate and pressure fluctuate with the regeneration process. If directly fed into the catalytic methanation unit 2, it can easily lead to unstable reactor inlet pressure and space velocity fluctuations, thereby affecting the conversion efficiency and product quality of the methanation reaction. Therefore, a CO2 buffer tank is connected in series between the regeneration device and the reactor. Utilizing the gas storage and pressure stabilization functions of the buffer tank, the intermittent and fluctuating desorbed gas is converted into a continuous and stable gas source output. Simultaneously, the volume buffering effect of the tank eliminates gas pulse phenomena, providing stable feeding conditions for subsequent processes. The purity detector installed after the buffer tank can monitor the CO2 gas before it enters the reactor in real time online, ensuring that its purity meets the requirements of the methanation reaction for the raw material gas. Once the purity is detected to be lower than the set threshold, the system can automatically switch the gas path to return or vent the unqualified gas, so as to avoid impurities entering the catalyst bed and causing catalyst poisoning or side reactions.

[0031] For example, the fixed-bed reactor includes a reactor shell, a catalyst bed, and a heating jacket. The catalyst bed is located inside the reactor shell and is supported by multiple layers of sieves or grids. Fly ash-derived Ni-Mn bimetallic catalyst is packed in stages to ensure uniform gas flow distribution and that the bed pressure drop is controlled within a reasonable range. The heating jacket is fitted onto the outer wall of the reactor shell. The heat transfer medium inlet of the heating jacket is connected to the outlet of the heat transfer oil circulation system, using heat transfer oil as the heat transfer medium to indirectly heat the reactor. The heating jacket can adopt a segmented structure, with multiple independent temperature control zones set along the reactor axis to match the temperature distribution requirements at different locations in the bed during the methanation reaction, avoiding local overheating due to exothermic reactions that could accelerate catalyst carbonization or sintering. The gas inlet of the reactor shell is connected to the gas outlet of the adsorbent regeneration device. The feed gas (a mixture of CO2 and H2 at a stoichiometric ratio of 4:1) is preheated before entering the catalyst bed, where the methanation reaction occurs under operating conditions of 300-400℃ and 1.0-2.0MPa.

[0032] The fly ash-derived Ni-Mn bimetallic catalyst comprises a microwave-activated coal fly ash support and nickel and manganese loaded on the surface of the coal fly ash support; the nickel and manganese are mutually doped on the surface of the coal fly ash support. Nickel and manganese salts are simultaneously loaded onto the activated fly ash surface using an equal-volume co-impregnation method. Utilizing the uniform mixing of the two metal ions in the impregnation solution and the synergistic adsorption of functional groups on the support surface, nickel and manganese form highly dispersed alloy or composite oxide phases during subsequent calcination and reduction. These phases interpenetrate and are in close contact at the nanoscale, avoiding the segregation and isolated agglomeration problems common in single nickel-based catalysts. This catalyst uses fly ash from power plants as a carrier instead of traditional high-purity alumina or molecular sieves, significantly reducing the catalyst preparation cost and enabling high-value utilization of solid waste. Secondly, the introduction of manganese can inhibit the migration and sintering of nickel grains under high-temperature reaction conditions through a dual mechanism of geometric isolation effect and electronic modulation effect. At the same time, manganese preferentially interacts with carbon precursors that may be generated in the reaction system, slowing down the carbon formation rate on the nickel surface, thereby maintaining high activity stability during continuous operation and significantly extending the service life of the catalyst. In addition, the mutual doping distribution of nickel and manganese forms a tight interfacial structure, which promotes the synergistic activation of CO2 and H2 at bimetallic active sites in the methanation reaction, improving the reaction rate and selectivity. This allows for the maintenance of high CO2 conversion efficiency with low dependence on precious metals, providing a high-performance, low-cost core catalytic material guarantee for the long-term stable operation of the system.

[0033] For example, the preparation method of fly ash-derived Ni-Mn bimetallic catalyst includes: selecting fly ash from a coal-fired power plant (SiO2 content 55%, Al2O3 content 25%), grinding it to a particle size ≤100μm, placing it in a microwave reactor, setting the power to 600W, and activating it for 12min; weighing 100g of the activated fly ash, adding a mixed impregnation solution containing Ni(NO3)2 and Mn(NO3)2 (Ni loading 12%, Mn loading 3%), and impregnating it with an equal volume for 12h; drying it at 110℃ for 6h, and then calcining it in a muffle furnace at 450℃ for 4h; placing the calcined sample in a hydrogen atmosphere, reducing it at 400℃ for 2h, and cooling it to room temperature to obtain the fly ash-derived Ni-Mn bimetallic catalyst.

[0034] For example, the heat transfer oil circulation system includes a heat transfer oil pump, a first regulating valve, and a second regulating valve; the cold-side outlet of the heat exchanger is connected to the inlet of the heat transfer oil pump; the outlet of the heat transfer oil pump is connected to the inlet of the first regulating valve and the inlet of the second regulating valve, respectively; the outlet of the first regulating valve is connected to the heat medium inlet of the adsorbent regeneration device; and the outlet of the second regulating valve is connected to the heat medium inlet of the fixed-bed reactor. The heat transfer oil pump, as the circulation power source, pressurizes and transports the high-temperature heat transfer oil, after absorbing waste heat in the heat exchanger, to each heat-using unit. Since the adsorbent regeneration device and the fixed-bed reactor require different heat medium temperatures (the former requires 150~200℃ for medium-temperature regeneration of the adsorbent, while the latter requires 300~400℃ to meet the activation energy requirements of the methanation reaction), the traditional method of series heating via a single pipeline cannot simultaneously meet the heat demands of two temperature levels and would result in energy waste. To this end, a first regulating valve and a second regulating valve are installed in parallel at the outlet of the heat transfer oil pump. Heat is supplied to the adsorbent regeneration device and the fixed bed reactor through two independent branch pipelines. The first regulating valve can adjust its opening according to the real-time temperature feedback of the adsorbent regeneration device to control the flow rate of the heat medium entering the regeneration device to maintain a stable regeneration temperature. The second regulating valve independently adjusts the heat supply to the reactor according to the bed temperature of the fixed bed reactor to ensure that the methanation reaction operates stably within the optimal temperature range.

[0035] For example, the solid waste backfilling unit 4 further includes a slurry preparation device; the slurry preparation device includes a mixing tank, a fly ash hopper, and a water replenishment device; the outlet of the fly ash hopper is connected to the inlet of the mixing tank for quantitatively conveying fly ash generated by the power plant into the mixing tank; the water replenishment device is connected to the inlet of the mixing tank for adjusting the solid content and fluidity of the slurry; the outlet of the mixing tank is connected to the inlet of the mineralization reaction tank for sending the uniformly mixed fly ash slurry into the mineralization reaction tank to carry out a mineralization reaction with the depleted catalyst and residual CO2.

[0036] For example, the system of the present invention further includes a central control module; the central control module includes a controller, a first temperature sensor, a second temperature sensor, a first pressure sensor, a second pressure sensor, a gas composition sensor, and a flow sensor; the first temperature sensor and the first pressure sensor are installed on the inlet pipe of the fixed bed adsorption tower to monitor the temperature and pressure of the flue gas entering the adsorption tower in real time, ensuring that the adsorption conditions are maintained within a suitable range of 30~80℃ and atmospheric pressure, and avoiding excessively high flue gas temperature or pressure fluctuations from affecting the adsorption efficiency; the second temperature sensor and the second pressure sensor are installed on the inlet pipe of the fixed bed reactor. The gas composition sensor is used to monitor the temperature and pressure of the feed gas entering the reactor, providing real-time operating condition feedback for the methanation reaction. It is installed on the connecting pipeline between the adsorbent regeneration device and the fixed-bed reactor to monitor the purity of the CO2 gas released during regeneration online, ensuring that the CO2 purity entering the reactor meets the process requirement of ≥99%. The flow sensor is installed on the outlet pipeline of the heat transfer oil circulation system to monitor the flow rate of heat transfer oil delivered to each heat-using unit, providing data support for precise control of waste heat distribution. The catalytic methanation unit 2 also includes a feed valve, which is installed on the inlet pipeline of the fixed-bed reactor. The first temperature sensor, the second temperature sensor, the first pressure sensor, the second pressure sensor, the gas composition sensor, and the flow sensor are all connected to the signal input terminal of the controller; the feed valve, the first regulating valve, and the second regulating valve are all connected to the signal output terminal of the controller. Based on the temperature, pressure, gas purity, and flow data collected by the sensors, and combined with preset process parameter thresholds, the controller automatically calculates and outputs control commands: when the gas composition sensor detects that the CO2 purity is lower than the set threshold, the controller automatically closes the feed valve and switches the gas path to prevent substandard gas from entering the reactor and causing catalyst poisoning; when the second temperature sensor reports that the reactor inlet temperature deviates from the optimal reaction range, the controller adjusts the opening of the second regulating valve to change the flow rate of the heat transfer oil, achieving precise control of the reaction temperature; when the first temperature sensor or the first pressure sensor detects abnormal operating conditions at the adsorption tower inlet, the controller can coordinate with the preceding flue gas pretreatment system for adjustment to ensure the stable operation of the adsorption unit.

[0037] A second objective of this invention is to provide a CO2 capture-methanation system based on catalyst-coupled waste heat, such as... Figure 2 As shown, it includes the following steps: The flue gas to be treated is fed into the fixed bed adsorption tower, and the purified flue gas is discharged after adsorption; the adsorbent in the fixed bed adsorption tower after adsorption saturation is transported to the adsorbent regeneration device. Start the waste heat utilization unit 3. The heat exchanger recovers external waste heat and heats the heat transfer oil. The heat transfer oil is then transported to the adsorbent regeneration device and the fixed bed reactor through the heat transfer oil circulation system. The adsorbent in the adsorbent regeneration device is heated and regenerated, and the fixed bed reactor is preheated at the same time. The CO2 gas released during the regeneration process of the adsorbent regeneration device is transported to the inlet of the fixed bed reactor through the outlet. Hydrogen gas is introduced into the fixed-bed reactor, and the hydrogen gas reacts with CO2 in the presence of a catalyst to produce methane. The catalyst, after its activity has degraded in the fixed-bed reactor, is transported to the feed inlet of the mineralization reaction tank through the catalyst outlet, and a portion of the CO2 gas output from the outlet of the adsorbent regeneration device is introduced into the inlet of the mineralization reaction tank to carry out the mineralization reaction.

[0038] Specifically, the flue gas from a coal-fired power plant, after dust removal and desulfurization pretreatment, is first introduced into a fixed-bed adsorption tower and subjected to an adsorption at 30-80°C and a space velocity of 500-1000 h⁻¹. -1 Under normal operating conditions, fly ash-derived ZnO-based adsorbents are used to selectively adsorb CO2 from flue gas. After purification, the CO2 concentration in the flue gas is reduced to below 500 ppm and then directly emitted. When the adsorbent reaches saturation, the system switches to regeneration mode. Start the waste heat utilization unit 3. The waste heat of the flue gas at 200~300℃ is recovered by the finned waste heat exchanger installed at the tail flue of the power plant boiler to heat the heat transfer oil. The heat transfer oil is divided into two paths through the circulation system. One path is to adjust the temperature to 150~200℃ and send it to the adsorbent regeneration device to thermally regenerate the saturated adsorbent, so that it desorbs and releases high-purity CO2. The desorbed adsorbent is recycled. The other path heats the heat transfer oil to 300~400℃ and sends it to the heating jacket of the fixed bed reactor to preheat the reactor and provide the heat required for the methanation reaction. The CO2 gas released from the regeneration unit is pressure-stabilized by a buffer tank and monitored online by a purity detector to ensure that the purity is ≥99% before being sent to the inlet of the fixed-bed reactor. At the same time, hydrogen gas is introduced into the reactor at a molar ratio of H2 to CO2 of 4:1. Under the action of a fly ash-derived Ni-Mn bimetallic catalyst, a methanation reaction occurs at 300~400℃ and 1.0~2.0MPa to produce methane. After the reaction mixture is condensed and dehydrated, methane product gas with a purity of ≥98% is obtained. It can be directly connected to the gas boiler of a power plant for combustion and power generation or purified and used as urban gas transmission. When the catalyst activity decay rate in the fixed-bed reactor is ≥50%, the spent catalyst is discharged and transported to the mineralization reaction tank. At the same time, a portion of the CO2 output from the outlet of the regeneration unit (approximately 10%~15% of the total CO2 processing capacity of the system) is introduced into the mineralization reaction tank. It reacts with the spent catalyst and fly ash slurry (adjusted to pH 8~10) that have been pre-mixed in the slurry preparation device at a mass ratio of 1:5~1:10 at room temperature and pressure for 24~48 hours. This allows CO2 to combine with calcium and magnesium ions in the slurry to form carbonates. The slurry is then solidified into a filling paste with a compressive strength ≥3MPa for use in backfilling coal mine goaf areas. During the above operation, the central control module collects data from each unit in real time through temperature, pressure, gas composition, and flow sensors located at the air inlet of the adsorption tower, the air inlet of the reactor, the pipeline between the regeneration unit and the reactor, and the heat transfer oil outlet pipeline. When the CO2 purity is detected to be lower than 99%, the reactor feed valve is automatically closed. When the reactor temperature deviates from the set value, the opening of the first regulating valve and the second regulating valve in the heat transfer oil circulation system is automatically adjusted to accurately control the temperature. The operating parameters of the adsorption tower and the reactor are dynamically adjusted according to the power plant load changes to ensure stable operation of the system under variable operating conditions with flue gas volume fluctuations of ±30%.

[0039] This method utilizes the waste heat from coal-fired power plant flue gas in a cascade manner for adsorbent regeneration and methanation reactions, replacing traditional external electric heating or steam heating, thereby reducing the system's external energy consumption by more than 50%. Adsorbents and catalysts are prepared using fly ash from power plants, reducing material costs by 40% to 60%. Simultaneously, the co-mineralization of exhausted catalysts and fly ash achieves zero solid waste emissions. The Mn-doped Ni-based catalyst exhibits significantly improved resistance to carbon deposition, achieving a continuous operating life of over 1000 hours. Combined with intelligent regulation by the central control module, the CO2 conversion efficiency is maintained above 95%, and the methane purity is not less than 98%.

[0040] Example Start the waste heat utilization unit 3, connect the heat exchanger to the tail flue of the power plant boiler, recover the waste heat of the flue gas at about 250°C to heat the heat transfer oil, and adjust the temperature of the heat transfer oil to 180°C and 350°C respectively through the first regulating valve and the second regulating valve of the heat transfer oil circulation system. The heat transfer oil is then delivered to the heat medium inlet of the adsorbent regeneration device and the heating jacket of the fixed bed reactor to preheat the adsorbent regeneration device. At the same time, the fixed bed reactor is preheated to the temperature range required for the reaction. The preheating time is 30 minutes.

[0041] The CO2 capture unit 1 is started, and the flue gas from the coal-fired power plant (with a CO2 concentration of 12%, and other components mainly consisting of N2, O2, and a small amount of water vapor) after dust removal and desulfurization pretreatment is introduced into the fixed-bed adsorption tower. The adsorption temperature is set at 50℃ and the flue gas space velocity is set at 800 h⁻¹. -1In the adsorption tower, flue gas flows from bottom to top through the adsorption bed, making full contact with the fly ash-derived adsorbent to achieve selective CO2 adsorption. Online monitoring shows that the CO2 concentration in the purified flue gas discharged after adsorption is reduced to below 1.2%, with a CO2 adsorption efficiency of over 90%. The purified flue gas meets emission standards and can be directly discharged into the atmosphere.

[0042] After 8 hours of continuous adsorption, the fly ash-derived adsorbent in the adsorption bed reached adsorption saturation. The system automatically switched to regeneration mode, closed the flue gas inlet valve, and maintained the temperature of the heat transfer oil in the adsorbent regeneration unit at 180℃ for thermal regeneration of the adsorbent, which lasted for 2 hours. During the regeneration process, the CO2 adsorbed by the adsorbent was desorbed and released. After being transported to a CO2 buffer tank for pressure stabilization, the CO2 was tested by a purity detector. The test results showed that the purity of the desorbed CO2 reached 99.5%, meeting the requirements for feed gas in the catalytic methanation reaction.

[0043] Catalytic methanation unit 2 is started, where 99.5% pure CO2 is mixed with externally supplied hydrogen at a molar ratio of 4:1. After preheating, the mixture is introduced into a fixed-bed reactor. The reactor temperature is set at 350℃ and the reaction pressure at 1.5MPa. The feed gas undergoes methanation under the action of a fly ash-derived Ni-Mn bimetallic catalyst, producing methane and a small amount of byproducts. After the reaction, the mixed gas is condensed and dehydrated to remove moisture. Online monitoring shows that the methane purity reaches 98.5% and the CO2 conversion efficiency reaches 96%. The resulting methane product gas is fed into a power plant's gas-fired boiler for combustion and power generation.

[0044] The solid waste backfilling unit 4 was started. The deactivated catalyst, whose activity had decreased after a period of operation in the fixed-bed reactor, was discharged and fed into the mixing tank of the slurry preparation device at a mass ratio of 1:8 with the fly ash produced by the coal-fired power plant. An appropriate amount of deionized water was added through a water replenishment device to adjust the pH of the slurry to 9. After thorough mixing, the slurry was transported to the mineralization reaction tank. Simultaneously, a portion of the CO2 output from the adsorbent regeneration device (approximately 12% of the total CO2 processing capacity of the system) was introduced into the mineralization reaction tank. The mineralization reaction temperature was controlled at room temperature and the pressure at atmospheric pressure, and the reaction was carried out for 36 hours. After the reaction, the generated filling paste was sampled and tested. The compressive strength reached 3.5 MPa, and the CO2 mineralization rate reached 32%. This filling paste was directly used for backfilling of the goaf areas of surrounding coal mines, achieving both solid waste resource utilization and additional CO2 mineralization and sequestration.

[0045] Performance test results: After 1000 hours of continuous operation, the CO2 conversion efficiency remained at 95%~96%, and the methane purity remained stable at over 98%; the catalyst activity decay rate was 45%, and no obvious carbon deposition was observed; the external energy consumption of the system was reduced by 52% compared to the traditional electric heating system; the system can dispose of 1000 tons of fly ash and consume 5000 tons of CO2 annually, generating an additional economic benefit of approximately 1.2 million yuan.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A CO2 capture-methanation system based on catalyst coupled with waste heat, characterized in that, include: CO2 capture unit (1), the CO2 capture unit (1) includes a fixed bed adsorption tower and an adsorbent regeneration device, the outlet of the fixed bed adsorption tower is connected to the inlet of the adsorbent regeneration device. Catalytic methanation unit (2), the catalytic methanation unit (2) includes a fixed bed reactor, the inlet of the fixed bed reactor is connected to the outlet of the adsorbent regeneration device; Waste heat utilization unit (3), the waste heat utilization unit (3) includes a heat exchanger and a heat transfer oil circulation system, the cold side outlet of the heat exchanger is connected to the inlet of the heat transfer oil circulation system, and the outlet of the heat transfer oil circulation system is connected to the heat medium inlet of the adsorbent regeneration device and the heat medium inlet of the fixed bed reactor respectively. Solid waste backfilling unit (4), the solid waste backfilling unit (4) includes a mineralization reaction tank, the inlet of the mineralization reaction tank is connected to the catalyst outlet of the fixed bed reactor, and the air inlet of the mineralization reaction tank is connected to the air outlet of the adsorbent regeneration device.

2. The CO2 capture-methanation system based on catalyst coupling waste heat according to claim 1, characterized in that, The fixed-bed adsorption tower includes an adsorption tower shell and an adsorption bed; the adsorption bed is disposed inside the adsorption tower shell; the top outlet of the adsorption tower shell is connected to the inlet of the adsorbent regeneration device.

3. The CO2 capture-methanation system based on catalyst coupling waste heat according to claim 2, characterized in that, The adsorption bed is filled with fly ash-derived adsorbent; the fly ash-derived adsorbent includes a microwave-activated coal fly ash carrier and zinc oxide loaded on the surface of the coal fly ash carrier.

4. The CO2 capture-methanation system based on catalyst coupling waste heat according to claim 1, characterized in that, The CO2 capture unit (1) further includes a CO2 buffer tank and a purity detector; the outlet of the adsorbent regeneration device is connected to the inlet of the CO2 buffer tank; the outlet of the CO2 buffer tank is connected to the inlet of the purity detector; and the outlet of the purity detector is connected to the inlet of the fixed bed reactor.

5. The CO2 capture-methanation system based on catalyst coupling waste heat according to claim 1, characterized in that, The fixed-bed reactor includes a reactor shell, a catalyst bed, and a heating jacket; the catalyst bed is disposed inside the reactor shell; the heating jacket is fitted onto the outer wall of the reactor shell; the heat medium inlet of the heating jacket is connected to the outlet of the heat transfer oil circulation system; and the air inlet of the reactor shell is connected to the air outlet of the adsorbent regeneration device.

6. The CO2 capture-methanation system based on catalyst coupling waste heat according to claim 5, characterized in that, The catalyst bed is filled with fly ash-derived Ni-Mn bimetallic catalyst; the fly ash-derived Ni-Mn bimetallic catalyst includes a microwave-activated coal fly ash support and nickel and manganese supported on the surface of the coal fly ash support; the nickel and manganese are mutually doped on the surface of the coal fly ash support.

7. The CO2 capture-methanation system based on catalyst coupling waste heat according to claim 1, characterized in that, The heat transfer oil circulation system includes a heat transfer oil pump, a first regulating valve, and a second regulating valve; the cold side outlet of the heat exchanger is connected to the inlet of the heat transfer oil pump; the outlet of the heat transfer oil pump is connected to the inlet of the first regulating valve and the inlet of the second regulating valve, respectively; the outlet of the first regulating valve is connected to the heat medium inlet of the adsorbent regeneration device; and the outlet of the second regulating valve is connected to the heat medium inlet of the fixed bed reactor.

8. The CO2 capture-methanation system based on catalyst coupling waste heat according to claim 1, characterized in that, The solid waste backfilling unit (4) also includes a slurry preparation device; the slurry preparation device includes a mixing tank, a fly ash hopper and a water replenishment device; the outlet of the fly ash hopper is connected to the inlet of the mixing tank; the water replenishment device is connected to the inlet of the mixing tank; the outlet of the mixing tank is connected to the inlet of the mineralization reaction tank.

9. A CO2 capture-methanation system based on catalyst coupling waste heat according to claim 1, characterized in that, It also includes a central control module; the central control module includes a controller, a first temperature sensor, a second temperature sensor, a first pressure sensor, a second pressure sensor, a gas composition sensor, and a flow sensor; the first temperature sensor and the first pressure sensor are installed on the inlet pipe of the fixed bed adsorption tower; the second temperature sensor and the second pressure sensor are installed on the inlet pipe of the fixed bed reactor; the gas composition sensor is installed on the connecting pipe between the adsorbent regeneration device and the fixed bed reactor; the flow sensor is installed on the outlet pipe of the heat transfer oil circulation system; the catalytic methanation unit (2) also includes a feed valve, which is installed on the inlet pipe of the fixed bed reactor; The first temperature sensor, the second temperature sensor, the first pressure sensor, the second pressure sensor, the gas composition sensor, and the flow sensor are respectively connected to the signal input terminal of the controller; the feed valve is connected to the signal output terminal of the controller.

10. A CO2 capture-methanation system based on catalyst coupling waste heat according to any one of claims 1 to 9, characterized in that, Includes the following steps: The flue gas to be treated is fed into the fixed bed adsorption tower, and the purified flue gas is discharged after adsorption; the adsorbent in the fixed bed adsorption tower after adsorption saturation is transported to the adsorbent regeneration device. Start the waste heat utilization unit (3), the heat exchanger recovers external waste heat and heats the heat transfer oil, and the heat transfer oil is transported to the adsorbent regeneration device and the fixed bed reactor through the heat transfer oil circulation system to heat and regenerate the adsorbent in the adsorbent regeneration device, and at the same time preheat the fixed bed reactor. The CO2 gas released during the regeneration process of the adsorbent regeneration device is transported to the inlet of the fixed bed reactor through the outlet. Hydrogen gas is introduced into the fixed-bed reactor, and the hydrogen gas reacts with CO2 in the presence of a catalyst to produce methane. The catalyst, after its activity has degraded in the fixed-bed reactor, is transported to the feed inlet of the mineralization reaction tank through the catalyst outlet, and a portion of the CO2 gas output from the outlet of the adsorbent regeneration device is introduced into the inlet of the mineralization reaction tank to carry out the mineralization reaction.

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