An energy-saving system for producing green methane by hydrogenation of carbon dioxide

Abstract

This utility model relates to an energy-saving system for the preparation of green methane by carbon dioxide hydrogenation, comprising: a feed gas preheater connected to a carbon dioxide main pipe and a first methanation reactor, wherein all CO2 is fed into the inlet of the first methanation reactor after passing through the feed gas preheater; the hydrogen main pipe is divided into multiple branches, and the green hydrogen feedstock is preheated by the green hydrogen feed preheater and then fed into each stage of the hydrogen branch pipe, and the green hydrogen feedstock is diverted into each stage of the methanation reactor (except the final stage); the high-temperature condensate from the gas-liquid separator outlet is fed into the carbon dioxide main pipe as a heat transfer medium to control the temperature rise of the methanation reaction. Compared with the prior art, this utility model mixes the high-temperature condensate with the feed gas in the carbon dioxide main pipe, reduces the partial pressure of water, and recovers the low-grade waste heat at the outlet of the methanation reactor through the feed gas preheater. By diverting the hydrogen and adding the high-temperature condensate heat transfer medium, the temperature rise of the methanation reaction is reduced, the methanation reaction process is improved, the heat utilization rate is high, and the number of reaction stages is reduced.

Description

Technical Field

[0001] This utility model relates to the field of carbon dioxide resource utilization and application technology, and in particular to an energy-saving system for producing green methane by hydrogenation of carbon dioxide. Background Technology

[0002] With the booming global economy, the extensive exploitation and use of fossil fuels has led to excessive emissions of greenhouse gases, primarily carbon dioxide, into the Earth's atmosphere, causing a series of severe environmental problems such as global warming. Therefore, carbon capture, utilization, and storage (CCUS) has become a crucial link in solving environmental problems and has attracted widespread attention. Currently, CCUS technology has been deployed on a large scale, with many coal-fired power plants and other enterprises building CO2 capture facilities. However, a thorny issue remains: if the captured CO2 cannot be utilized for high-value purposes, on the one hand, the cost of CCUS projects will remain high, making large-scale promotion difficult; on the other hand, if large amounts of captured CO2 are not properly disposed of, the emission reduction effect will be significantly reduced.

[0003] Meanwhile, with the rapid development of the new energy industry, the installed capacity of renewable energy sources such as photovoltaics and wind power continues to climb. However, due to limitations in energy storage technology, grid regulation capabilities, and geographical distribution, the phenomenon of curtailment of solar and wind power still exists. Curtailed renewable energy can be converted into green hydrogen through water electrolysis, providing a new method for the storage and conversion of renewable energy. However, green hydrogen, when existing alone, has certain limitations in application scenarios and storage and transportation, necessitating the search for more effective utilization pathways.

[0004] Utilizing carbon capture CO2 and green hydrogen to produce methane presents an excellent solution to the aforementioned problems. From an emissions reduction perspective, this provides an efficient outlet for captured CO2, converting CO2 that might otherwise be released back into the atmosphere into stable methane, achieving true carbon reduction. From an energy utilization perspective, on the one hand, it successfully realizes the reaction of abandoned renewable energy with CO2 through green hydrogen as an intermediate step to produce methane, achieving cross-form energy storage and conversion, greatly improving energy efficiency; on the other hand, methane, as a high-quality clean energy source, can be widely used in heating, power generation, and chemical raw materials, effectively supplementing energy supply and reducing dependence on traditional fossil fuels, thus promoting a cleaner and more sustainable energy structure.

[0005] The hydrogenation of carbon dioxide to produce methane is a strongly exothermic reaction, and the specific equation is as follows:

[0006] CO2+H2→CH4+2H2O△H=-165.51kJ / mol

[0007] The release of heat is a chemical energy loss in the conversion of hydrogen into synthetic natural gas. The key issue in developing this route is to recover and convert it into other usable energy sources to compensate for the chemical energy loss.

[0008] Patent CN220969064U discloses a production system for the Sabatier reaction of carbon dioxide hydrogenation methanation. In this system, H2 is split into four streams from the main pipe and diverted to corresponding reactors through different branch pipes. A five-stage methanation reactor is also included. A portion of the product gas is circulated through a compressor to the inlet of the first-stage methanation reactor to dilute the feed gas and control the temperature rise of the methanation reaction. Patent CN209098535U discloses a carbon dioxide recovery and utilization system from power plant flue gas. High-purity CO2 product gas obtained after purification is thoroughly mixed with high-purity hydrogen gas from an electrolysis unit through a gas mixer before entering the reactor for complete reaction to generate methane gas. During the reaction, excess CO2 gas is maintained to ensure complete hydrogen reaction, thereby controlling the reaction temperature. Patent CN116966741A discloses an integrated reaction device for carbon dioxide capture and hydrogenation to methane. In this method, the absorbent that has absorbed carbon dioxide in the absorption tower is desorbed in the integrated desorption and hydrogenation tower after passing through a heat exchanger. The liquid separated by the gas-liquid separator exchanges heat with the absorbent that has absorbed carbon dioxide flowing out of the absorption tower through a heat exchanger to achieve heat recovery. The gas separated in the gas-liquid separator is mixed with hydrogen and then enters the integrated desorption and hydrogenation tower and the hydrogenation reaction tower. This device reasonably couples CO2 capture and hydrogenation to methane, but the equipment needs to be equipped with a matching hydrogenation reaction tower to control the feed flow rate in order to control the desorption temperature and reaction temperature.

[0009] The aforementioned prior art has solved its respective technical problem, but the disclosed prior art still has the following drawbacks:

[0010] For temperature control using product gas recirculation, a recirculation gas compressor is required in the process, increasing compressor investment and power consumption, and posing significant operational risks. While temperature control using external diluents and quenchers, such as CO2, can avoid the use of a recirculation gas compressor, the large amount of diluent added throughout the entire process necessitates a separation device or facility at the outlet of the final methanation reactor. Due to limitations in heat transfer temperature difference, a significant portion of this low-temperature waste heat cannot be effectively recovered, resulting in low waste heat recovery rate and low by-product steam output in the methanation unit.

[0011] Therefore, there is an urgent need for an energy-saving system for the production of green methane by carbon dioxide hydrogenation with high waste heat recovery rate. Utility Model Content

[0012] The purpose of this invention is to address the shortcomings of the existing technology by providing an energy-saving system for the hydrogenation of carbon dioxide to produce green methane. This system mixes high-temperature condensate with the feed gas in the carbon dioxide main pipe, reducing the partial pressure of water. Then, the low-grade waste heat from the intermediate methanation reactor outlet is further recovered through the feed gas preheater. By splitting the hydrogen flow and adding a heat-transfer medium from the high-temperature condensate, the temperature rise of the methanation reaction is reduced, the methanation process is improved, and the system achieves high heat utilization, fewer reactor stages, and lower equipment operating and investment costs.

[0013] The objective of this utility model can be achieved through the following technical solutions:

[0014] The purpose of this invention is to provide an energy-saving system for the preparation of green methane by carbon dioxide hydrogenation. The system includes a carbon dioxide main pipe, a green hydrogen feed assembly, a feed gas mixture feed pipeline, a feed gas preheater, a first methanation reactor, an intermediate methanation reactor, a gas-liquid separator I, a high-temperature condensate main pipe, a final-stage methanation reactor, and a gas-liquid separator II. The carbon dioxide main pipe, the green hydrogen feed assembly, and the high-temperature condensate main pipe are respectively connected to the feed gas mixture feed pipeline. The green hydrogen feed assembly is respectively connected to the inlets of the first methanation reactor and the intermediate methanation reactor. The feed gas mixture feed pipeline is connected to the inlet of the feed gas preheater. The outlet of the feed gas preheater is connected to the inlet of the first methanation reactor. The system is as follows: The first methanation reactor and the intermediate methanation reactor are connected sequentially; the outlet of the intermediate methanation reactor is connected to the inlet of gas-liquid separator I via a feed gas preheater; gas-liquid separator I is connected to the final-stage methanation reactor and the high-temperature condensate main pipe; the gas phase outlet of gas-liquid separator I is connected to the final-stage methanation reactor; the liquid phase outlet of gas-liquid separator I is connected to the high-temperature condensate main pipe; the outlet of the final-stage methanation reactor is connected to the inlet of gas-liquid separator II; the green hydrogen feed assembly includes a green hydrogen feed preheater, which is located between the outlet of the final-stage methanation reactor and the inlet of gas-liquid separator II; gas-liquid separator II is used to obtain methane products.

[0015] Furthermore, the green hydrogen feed assembly is used to introduce raw material green hydrogen, and the green hydrogen feed assembly also includes a green hydrogen feed pipe, a first green hydrogen inlet branch, and an intermediate green hydrogen inlet branch; the green hydrogen feed pipe is connected to the inlet of the green hydrogen feed preheater; the outlet of the green hydrogen feed preheater is connected to the first green hydrogen inlet branch and the intermediate green hydrogen inlet branch respectively; the first green hydrogen inlet branch is connected to the raw material mixed gas feed pipe; and the intermediate green hydrogen inlet branch is connected to the inlet of the intermediate methanation reactor.

[0016] Furthermore, both the first green hydrogen inlet branch and the intermediate green hydrogen inlet branch are equipped with green hydrogen flow control mechanisms; the green hydrogen flow control mechanisms are used to control the green hydrogen feed flow rate in stages and to control the reaction progress in the first methanation reactor and the intermediate methanation reactor.

[0017] Furthermore, a waste heat boiler is provided between the outlet of the first methanation reactor and the inlet of the intermediate methanation reactor.

[0018] Furthermore, the third methanation reactor is connected in sequence to the third methanation reactor outlet cooler and gas-liquid separator I after recovering waste heat through the feed gas preheater; a waste heat boiler is provided between the outlet of the feed gas preheater and the inlet of the gas-liquid separator I; a preheater is provided between the gas phase outlet of the gas-liquid separator I and the inlet of the final methanation reactor.

[0019] Furthermore, the outlet of the final-stage methanation reactor is preheated with raw material gas H2 via a green hydrogen feed preheater, and then enters gas-liquid separator II via a cooler; a cooler is provided between the outlet of the green hydrogen feed preheater and the inlet of gas-liquid separator II.

[0020] Furthermore, the intermediate methanation reactor includes a second methanation reactor and a third methanation reactor; the outlet of the first methanation reactor is connected to the inlet of the second methanation reactor; the outlet of the second methanation reactor is connected to the inlet of the third methanation reactor; and the outlet of the third methanation reactor is connected to the inlet of the gas-liquid separator I through a feed gas preheater.

[0021] Furthermore, the intermediate green hydrogen inlet branch includes a second green hydrogen inlet branch and a third green hydrogen inlet branch. The second green hydrogen inlet branch is connected to the inlet of the second methanation reactor, and the third green hydrogen inlet branch is connected to the inlet of the third methanation reactor.

[0022] Furthermore, the first methanation reactor, the second methanation reactor, and the third methanation reactor are fixed-bed adiabatic reactors.

[0023] Furthermore, the final-stage methanation reactor is an isothermal reactor.

[0024] Furthermore, both the raw gas feed preheater and the green hydrogen feed preheater are heat exchangers.

[0025] Furthermore, a waste heat boiler is provided between the outlet of the first methanation reactor and the inlet of the second methanation reactor; a waste heat boiler is also provided between the outlet of the second methanation reactor and the inlet of the third methanation reactor.

[0026] Furthermore, the system also includes a steam drum, a boiler water inlet pipe, and a steam outlet pipe; the steam drum is used to generate steam using the heat generated by the final stage isothermal methanation reaction in the final stage methanation reactor; the steam drum is connected to the final stage methanation reactor and forms a heat exchange loop; the boiler water inlet pipe and the steam outlet pipe are respectively connected to the steam drum; the boiler water inlet pipe is used to introduce boiler water into the steam drum; the steam outlet pipe is used to discharge steam from the steam drum.

[0027] Furthermore, the system also includes a pressure control mechanism; the pressure control mechanism is connected to the steam discharge pipe; the pressure control mechanism is used to control the flow rate of steam discharge and maintain the pressure inside the steam drum.

[0028] Furthermore, the system also includes a temperature control mechanism; the temperature control mechanism is connected to the high-temperature condensate main pipe; the temperature control mechanism is used to control the outlet temperature of the first methanation reactor by controlling the flow rate of the high-temperature condensate.

[0029] Furthermore, a condensate circulation pump is connected to the high-temperature condensate main pipe.

[0030] Furthermore, the gas-liquid separator II is provided with a liquid phase outlet, which is used to discharge condensate; the gas phase outlet of the gas-liquid separator II is connected to a gas phase outlet pipe II for obtaining methane product.

[0031] Furthermore, the energy-saving system for producing green methane by carbon dioxide hydrogenation includes: a feed gas preheater connected to the carbon dioxide main pipe and the first methanation reactor; all carbon dioxide feedstock is fed into the inlet of the first methanation reactor after passing through the feed gas preheater; the hydrogen main pipe is divided into three branches; the green hydrogen feedstock is preheated by the green hydrogen feed preheater and then fed into the first, second, and third hydrogen branches respectively; the green hydrogen feedstock is diverted through each branch into the first, second, and third methanation reactors (except the final stage), and the methanation reaction process is controlled by the H2 diversion flow rate; the high-temperature condensate from the gas-liquid separator outlet is fed into the carbon dioxide main pipe as a heat transfer medium to control the temperature rise of the methanation reaction. Compared with the prior art, the energy-saving system of this utility model mixes the high-temperature condensate with the feed gas in the carbon dioxide main pipe, reducing the partial pressure of water, and then further recovers the low-grade waste heat from the outlet of the third methanation reactor through the feed gas preheater. By diverting hydrogen and adding a high-temperature condensate heat transfer medium, the temperature rise of the methanation reaction is reduced, the methanation reaction process is improved, the heat utilization rate is high, the number of reaction stages is small, and the equipment operating cost and investment cost are low.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The energy-saving system for preparing green methane by carbon dioxide hydrogenation provided by this utility model mixes the high-temperature condensate (high-temperature condensate) with the raw material gas in the carbon dioxide main pipe, which reduces the partial pressure of water. Then, the low-grade waste heat at the outlet of the intermediate methanation reactor is further recovered through the raw material gas feed preheater. By splitting the hydrogen and adding the heat transfer medium of the high-temperature condensate, the temperature rise of the methanation reaction is reduced, the methanation reaction process is improved, the heat utilization rate is high, the number of reactor stages is small, and the equipment operating cost and investment cost are low.

[0034] (2) The energy-saving system for producing green methane by carbon dioxide hydrogenation provided by this utility model controls the reaction process through H2 diversion and utilizes the recovered high-temperature condensate (high-temperature condensate) for re-vaporization temperature control, making operation and temperature control simple. The system also utilizes a waste heat boiler to recover the reaction heat from the methanation reactors (first and second stage methanation reactors) and uses heat exchangers (raw material gas feed preheater and green hydrogen feed preheater) to recover the outlet reaction heat from the methanation reactors (third stage and final stage methanation reactors) to preheat the raw material gas, achieving full utilization of heat. The entire system is more flexible in operation, has improved operational reliability, and is simple in design. Attached Figure Description

[0035] Figure 1 A schematic diagram of the energy-saving system for preparing green methane by hydrogenation of carbon dioxide according to this invention.

[0036] The numbers in the diagram are as follows:

[0037] 1-Carbon dioxide main pipe; 2-Feed gas mixture feed pipe; 3-Feed gas feed preheater; 4-Feed gas preheating pipe; 5-First methanation reactor; 6-Bottom discharge pipe of the first methanation reactor; 7-First waste heat boiler; 8-First methanation conveying pipe; 9-Second feed collection pipe; 10-Second methanation reactor; 11-Bottom discharge pipe of the second methanation reactor; 12-Second waste heat boiler; 13-Second methanation conveying pipe; 14-Third feed collection pipe; 15-The 16-Third-stage methanation reactor; 17-Third-stage methanation reactor bottom discharge pipe; 18-Third-stage methanation reactor outlet cooler; 19-Third-stage methanation reactor outlet waste heat pipe II; 20-Gas-liquid separator I; 21-Final stage reactor feed pipe; 22-Final stage reactor feed preheater; 23-Final stage reactor preheating pipe; 24-Final stage methanation reactor; 25-Final stage methanation reactor bottom discharge pipe I; 26-Green hydrogen feed preheater Equipment; 27- Bottom discharge pipe II of the final stage methanation reactor; 28- Cooler; 29- Final stage methanation conveying pipe; 30- Gas-liquid separator II; 31- Gas phase outlet pipe II; 32- Liquid phase outlet of gas-liquid separator II; 33- Green hydrogen feed pipe; 34- Green hydrogen preheating pipe I; 35- Third hydrogen branch pipe I; 36- Third hydrogen branch pipe II; 37- Green hydrogen flow control mechanism III; 38- Green hydrogen preheating pipe II; 39- Second hydrogen branch pipe I; 40- Second hydrogen branch pipe II; 4 1-Green hydrogen flow control mechanism II; 42-First hydrogen branch pipe I; 43-First hydrogen branch pipe II; 44-Green hydrogen flow control mechanism I; 45-High-temperature condensate pipe I; 46-Condensate circulation pump; 47-High-temperature condensate pipe II; 48-High-temperature condensate pipe III; 49-Boiler water inlet pipe; 50-Steam drum; 51-Pressure control mechanism; 52-Steam outlet pipe II; 53-Steam outlet pipe I; 54-Heat exchange pipe I; 55-Heat exchange pipe II; 56-Temperature control mechanism. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Any component models, material names, connection structures, control methods, etc., not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0039] The embodiments described in this application are only a part of the embodiments of this utility model and cannot represent all embodiments. Other embodiments obtained by those skilled in the art without creative effort on this application should fall within the protection scope of this utility model.

[0040] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0041] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0042] In the following embodiments, green hydrogen is directly produced through renewable energy power generation such as solar and wind power, and the production process generates virtually no greenhouse gases. The raw material CO2 is obtained through carbon capture or other technological means.

[0043] Example 1

[0044] like Figure 1 As shown, this embodiment provides an energy-saving system for producing green methane by hydrogenation of carbon dioxide. The system includes a carbon dioxide main pipe 1, a green hydrogen feed assembly, a raw material mixed gas feed pipe 2, a raw material gas feed preheater 3, a first methanation reactor 5, a first waste heat boiler 7, a second methanation reactor 10, a second waste heat boiler 12, a third methanation reactor 15, a gas-liquid separator I20, a high-temperature condensate main pipe, a final stage reactor feed preheater 22, a final stage methanation reactor 24, and a gas-liquid separator II30.

[0045] The green hydrogen feed assembly is used to introduce raw material green hydrogen. The green hydrogen feed assembly includes a green hydrogen feed preheater 26, a green hydrogen feed pipe 33, a green hydrogen preheating pipe I34, a green hydrogen preheating pipe II38, a first green hydrogen inlet branch, a second green hydrogen inlet branch, and a third green hydrogen inlet branch. The green hydrogen feed preheater 26 is located between the outlet of the final-stage methanation reactor 24 and the inlet of the gas-liquid separator II30. The first green hydrogen inlet branch includes a first hydrogen branch pipe I42 and a first hydrogen branch pipe II43 connected in sequence. The second green hydrogen inlet branch includes a second hydrogen branch pipe I39 and a second hydrogen branch pipe II40 connected in sequence. The third green hydrogen inlet branch includes a third hydrogen branch pipe I35 and a third hydrogen branch pipe II36 connected in sequence. The green hydrogen feed pipe 33 is connected to the inlet of the green hydrogen feed preheater 26; the outlet of the green hydrogen feed preheater 26 is connected to the green hydrogen preheating pipe I34; the green hydrogen preheating pipe I34 is connected to the green hydrogen preheating pipe II38 and the third hydrogen branch pipe I35 of the third green hydrogen inlet branch; the green hydrogen preheating pipe II38 is connected to the first hydrogen branch pipe I42 of the first green hydrogen inlet branch and the second hydrogen branch pipe I39 of the second green hydrogen inlet branch; the first hydrogen branch pipe II43 of the first green hydrogen inlet branch is connected to the raw material mixed gas feed pipe 2; the second hydrogen branch pipe II40 of the second green hydrogen inlet branch is connected to the inlet of the second methanation reactor 10; the third hydrogen branch pipe II36 of the third green hydrogen inlet branch is connected to the inlet of the third methanation reactor 15.

[0046] The carbon dioxide main pipe 1, the first hydrogen branch pipe II43 of the first green hydrogen inlet branch, and the high-temperature condensate main pipe are respectively connected to the raw material mixed gas feed pipe 2.

[0047] The raw material mixed gas feed pipe 2 is connected to the inlet of the raw material gas feed preheater 3;

[0048] The outlet of the feed gas preheater 3 is connected to the inlet of the first methanation reactor 5 via a feed gas preheating pipe 4; the outlet of the first methanation reactor 5 is connected to the inlet of the second methanation reactor 10 via a first methanation reactor bottom discharge pipe 6, a first waste heat boiler 7, a first methanation conveying pipe 8, and a second feed collection pipe 9 connected in sequence. The second hydrogen branch pipe II40 is connected to the second feed collection pipe 9.

[0049] The outlet of the second methanation reactor 10 and the inlet of the third methanation reactor 15 are connected in sequence via the bottom discharge pipe 11 of the second methanation reactor, the second waste heat boiler 12, the second methanation conveying pipe 13, and the third feed collection pipe 14. The third hydrogen branch pipe II36 is connected to the third feed collection pipe 14.

[0050] The outlet of the third methanation reactor 15 is connected to the inlet of the feed gas preheater 3 through the bottom discharge pipe 16 of the third methanation reactor.

[0051] The outlet of the feed gas preheater 3 and the inlet of the gas-liquid separator I20 are connected in sequence through the waste heat pipe I17 of the third methanation reactor, the outlet cooler 18 of the third methanation reactor, and the waste heat pipe II19 of the third methanation reactor. The outlet gas of the third methanation reactor 15 recovers waste heat through the feed gas preheater 3 and then passes through the outlet cooler 18 of the third methanation reactor and the gas-liquid separator I20 in sequence. The recovered waste heat can preheat the gas in the feed gas inlet pipe 2.

[0052] The high-temperature condensate main pipe includes high-temperature condensate pipe I45, high-temperature condensate pipe II47, and high-temperature condensate pipe III48; a condensate circulation pump 46 is connected to the high-temperature condensate main pipe; the inlet of the condensate circulation pump 46 is connected to the high-temperature condensate pipe I45, and the outlet of the condensate circulation pump 46 is connected to the high-temperature condensate pipe II47; the high-temperature condensate pipe II47 is connected to the high-temperature condensate pipe III48; and the high-temperature condensate pipe III48 is connected to the raw material mixed gas feed pipe 2.

[0053] The gas-liquid separator I20 is connected to the final-stage methanation reactor 24 and the high-temperature condensate main pipe, respectively; the gas phase outlet of the gas-liquid separator I20 is connected to the inlet of the final-stage methanation reactor 24 through the final-stage reactor feed pipe 21, the final-stage reactor feed preheater 22, and the final-stage reactor preheating pipe 23 connected in sequence.

[0054] The liquid phase outlet of the gas-liquid separator I20 is connected to the high-temperature condensate pipe I45 of the high-temperature condensate main pipe.

[0055] The outlet of the final-stage methanation reactor 24 is connected to the inlet of the gas-liquid separator II 30 via a series of sequentially connected components: the bottom discharge pipe I 25 of the final-stage methanation reactor, the green hydrogen feed preheater 26, the bottom discharge pipe II 27 of the final-stage methanation reactor, the cooler 28, and the final-stage methanation conveying pipe 29. The outlet of the final-stage methanation reactor 24 is connected to the inlet of the green hydrogen feed preheater 26 via the bottom discharge pipe I 25 of the final-stage methanation reactor. The outlet of the green hydrogen feed preheater 26 is connected to the inlet of the cooler 28 via the bottom discharge pipe II 27 of the final-stage methanation reactor. The outlet of the cooler 28 is connected to the inlet of the gas-liquid separator II 30 via the final-stage methanation conveying pipe 29. The outlet gas of the final stage methanation reactor 24 is preheated by the green hydrogen feed preheater 26 to the feed gas H2 from the green hydrogen feed pipeline 33. After that, the outlet gas is further cooled by the cooler 28 and then enters the gas-liquid separator II 30. The feed gas H2 in the green hydrogen feed pipeline 33 is preheated by the green hydrogen feed preheater 26 and then enters the green hydrogen preheating pipeline I 34.

[0056] The gas-liquid separator II30 is used to obtain methane products.

[0057] The gas-liquid separator II30 is provided with a liquid phase outlet 32, which is used to discharge condensate; the gas phase outlet of the gas-liquid separator II30 is connected to a gas phase outlet pipe II31 for obtaining methane product.

[0058] The third methanation reactor 15 is connected to the third methanation reactor outlet cooler 18 and gas-liquid separator I20 in sequence after the waste heat is recovered by the feed gas preheater 3; the outlet of the final methanation reactor 24 is preheated by the feed gas H2 through the green hydrogen feed preheater 26, and then enters the gas-liquid separator II30 through the cooler 28.

[0059] The system also includes a steam drum 50, a boiler water inlet pipe 49, and a steam exhaust pipe;

[0060] The steam drum 50 is used to generate steam using the heat generated by the final isothermal methanation reaction in the final-stage methanation reactor 24. The steam drum 50 is connected to the shell side of the final-stage methanation reactor 24 through heat exchange pipes I54 and II55, forming a heat exchange loop. The outlet of the steam drum 50 is connected to the inlet of the shell side of the final-stage methanation reactor 24 through heat exchange pipe I54, and the inlet of the steam drum 50 is connected to the outlet of the shell side of the final-stage methanation reactor 24 through heat exchange pipe II55.

[0061] The boiler water inlet pipe 49 is connected to the steam drum 50; the outlet of the steam drum 50 is connected to a steam discharge pipe; the steam discharge pipe includes a steam outlet pipe I53 and a steam outlet pipe II52 connected in sequence; the steam outlet pipe I53 is connected to the outlet of the steam drum 50, and the steam outlet pipe II52 is connected to the steam outlet pipe I53.

[0062] The boiler water inlet pipe 49 is used to introduce boiler water into the steam drum 50; the steam outlet pipe is used to discharge steam from the steam drum 50.

[0063] The first methanation reactor 5, the second methanation reactor 10, and the third methanation reactor 15 are fixed-bed adiabatic reactors.

[0064] The final-stage methanation reactor 24 is an isothermal reactor.

[0065] Both the raw gas feed preheater 3 and the green hydrogen feed preheater 26 are heat exchangers.

[0066] The gases in the feed gas pipeline 2 and feed gas preheating pipeline 4 are both feed gas mixtures; the gases in the bottom discharge pipeline 6 of the first methanation reactor, the first methanation conveying pipeline 8, the bottom discharge pipeline 11 of the second methanation reactor, the second methanation conveying pipeline 13, the third feed collection pipeline 14, the bottom discharge pipeline 16 of the third methanation reactor, the waste heat pipeline II19 of the third methanation reactor, the bottom discharge pipeline I25 of the final methanation reactor, the bottom discharge pipeline II27 of the final methanation reactor, and the final methanation conveying pipeline 29 are all methanation reaction product gases; the gases in the green hydrogen feed pipeline 33, the green hydrogen preheating pipeline I34, the third hydrogen branch pipeline II36, the green hydrogen preheating pipeline II38, the second hydrogen branch pipeline II40, and the first hydrogen branch pipeline I42 are all hydrogen (H2); the liquids in the high-temperature condensate pipeline I45 and the high-temperature condensate pipeline II47 are all high-temperature condensate.

[0067] Example 2

[0068] like Figure 1 As shown, this embodiment provides an energy-saving system for producing green methane by hydrogenation of carbon dioxide. Based on Embodiment 1, this embodiment further includes the following settings:

[0069] The system also includes a pressure control mechanism 51; the pressure control mechanism 51 is connected to the steam discharge pipe; the pressure control mechanism 51 is used to control the flow rate of steam discharge and maintain the pressure inside the steam drum 50. The pressure control mechanism 51 includes a fifth valve and a pressure detector; the fifth valve is located between the steam outlet pipe II 52 and the steam outlet pipe I 53; the pressure detector is connected to the steam drum 50 and is used to detect the pressure of the steam drum 50; the opening degree of the fifth valve is adjusted according to the pressure of the steam drum 50 detected by the pressure detector.

[0070] The high-temperature condensate main pipe is equipped with a temperature control interlock. In the three-stage methanation reactors connected in series, namely the first methanation reactor 5, the second methanation reactor 10, and the third methanation reactor 15, the reaction degree in the first methanation reactor 5 is the largest, and therefore the temperature rises the most drastically. By controlling the flow rate of water vapor entering the first methanation reactor 5 after entering the raw material mixture feed pipe 2, and by injecting high-temperature condensate into the CO2 and H2 mixture to reduce the gas phase partial pressure of water, the temperature of the gas outlet of the first methanation reactor 5 is controlled, thereby controlling the temperature of the entire methanation reactor within a suitable range.

[0071] The temperature control mechanism 56 is used to control the outlet temperature of the first methanation reactor 5 by controlling the flow rate of the high-temperature condensate; the high-temperature condensate main pipe is connected to the temperature control mechanism 56; the temperature control mechanism 56 includes a fourth valve and a temperature detector; the fourth valve is located between the high-temperature condensate pipe II 47 and the high-temperature condensate pipe III 48; the temperature detector is connected to the bottom discharge pipe 6 of the first methanation reactor and is used to detect the temperature of the bottom discharge pipe 6 of the first methanation reactor; the opening degree of the fourth valve is adjusted according to the temperature of the bottom discharge pipe 6 of the first methanation reactor detected by the temperature detector.

[0072] The first, second, and third green hydrogen inlet branches are equipped with flow control interlocks to control the green hydrogen feed flow rate in stages and control the reaction progress in each methanation reactor.

[0073] The first, second, and third green hydrogen inlet branches are each equipped with a green hydrogen flow control mechanism; the green hydrogen flow control mechanism is used to control the green hydrogen feed flow rate in stages and to control the reaction progress in the first methanation reactor 5, the second methanation reactor 10, and the third methanation reactor 15.

[0074] A green hydrogen flow control mechanism I44 is provided between the first hydrogen branch pipe I42 and the first hydrogen branch pipe II43; the green hydrogen flow control mechanism I44 includes a first valve and a first flow meter; the first valve is located between the first hydrogen branch pipe I42 and the first hydrogen branch pipe II43; the first flow meter is connected to the first hydrogen branch pipe I42, and the first hydrogen branch pipe I42 is the measuring point location of the first flow meter, used to detect the flow rate of the first hydrogen branch pipe I42; the opening degree of the first valve is adjusted according to the flow rate of the first hydrogen branch pipe I42 detected by the first flow meter.

[0075] A green hydrogen flow control mechanism II41 is provided between the second hydrogen branch I39 and the second hydrogen branch II40; the green hydrogen flow control mechanism II41 includes a second valve and a second flow meter; the second valve is located between the second hydrogen branch I39 and the second hydrogen branch II40; the second flow meter is connected to the second hydrogen branch I39, and the second hydrogen branch I39 is the measuring point location of the second flow meter, used to detect the flow rate of the second hydrogen branch I39; the opening degree of the second valve is adjusted according to the flow rate of the second hydrogen branch I39 detected by the second flow meter.

[0076] A green hydrogen flow control mechanism Ⅲ37 is provided between the third hydrogen branch pipe I35 and the third hydrogen branch pipe II36. The green hydrogen flow control mechanism Ⅲ37 includes a third valve and a third flow meter. The second valve is located between the third hydrogen branch pipe I35 and the third hydrogen branch pipe II36. The third flow meter is connected to the third hydrogen branch pipe I35. The green hydrogen feed pipe Ⅲ42 is the measuring point of the third flow meter, used to detect the flow rate of the third hydrogen branch pipe I35. The opening degree of the third valve is adjusted according to the flow rate of the third hydrogen branch pipe I35 detected by the third flow meter.

[0077] Example 3

[0078] like Figure 1 As shown, this embodiment provides an energy-saving system for producing green methane by hydrogenation of carbon dioxide. Based on Embodiment 2, this embodiment further includes the following settings:

[0079] The energy-saving system for producing green methane by carbon dioxide hydrogenation includes a controller, which can be a mainstream microcontroller or a processor based on x86, ARM, or RISC-V architecture.

[0080] The first flow meter is communicatively connected to the controller, and the controller is communicatively connected to the first valve. The controller controls the opening degree of the first valve based on the flow rate of the first hydrogen branch pipe I42 detected by the first flow meter.

[0081] The second flow meter is communicatively connected to the controller, and the controller is communicatively connected to the second valve. The controller controls the opening degree of the second valve based on the flow rate of the second hydrogen branch pipe I39 detected by the second flow meter.

[0082] The third flow meter is communicatively connected to the controller, and the controller is communicatively connected to the third valve. The controller controls the opening degree of the third valve based on the flow rate of the third hydrogen branch I35 detected by the third flow meter.

[0083] The temperature detector is communicatively connected to the controller, and the controller is communicatively connected to the fourth valve. The controller controls the opening degree of the fourth valve based on the temperature of the discharge pipe 6 at the bottom of the first methanation reactor detected by the temperature detector.

[0084] The pressure detector is communicatively connected to the controller, and the controller is communicatively connected to the fifth valve. The controller controls the opening degree of the fifth valve based on the pressure of the steam drum 50 detected by the pressure detector.

[0085] The communication connection can be wired or wireless.

[0086] This invention utilizes three stages of adiabatic methanation reactors, connected in series with a final stage isothermal methanation reactor. Hydrogen is introduced in stages, with H2 being diverted to the first three stages. High-temperature condensate is injected into a CO2 and H2 mixture to reduce the partial pressure of water in the gas phase. The condensate is then recovered via a heat exchanger, vaporized, and fed into the inlet of the first-stage methanation reactor. This process controls the bed temperature and methanation reaction progress of each stage of the reactor. The heat generated by the final isothermal methanation reaction is fed into a steam drum to produce steam. The final reactor outlet passes through a green hydrogen feed preheater, cooler, and gas-liquid separator to obtain high-purity methane.

[0087] The above description of the embodiments is provided to enable those skilled in the art to understand and use the utility model. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present utility model is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present utility model without departing from its scope should be within the protection scope of the present utility model.

Claims

1. An energy-saving system for preparing green methane by carbon dioxide hydrogenation, characterized in that, The system includes a carbon dioxide main pipe (1), a green hydrogen feed assembly, a raw material mixed gas feed pipe (2), a raw material gas feed preheater (3), a first methanation reactor (5), an intermediate methanation reactor, a gas-liquid separator I (20), a high-temperature condensate main pipe, a final stage methanation reactor (24), and a gas-liquid separator II (30). The carbon dioxide main pipe (1), the green hydrogen feed assembly, and the high-temperature condensate main pipe are respectively connected to the raw material mixed gas feed pipe (2); The green hydrogen feed assembly is connected to the first methanation reactor (5) and the intermediate methanation reactor, respectively. The raw material mixed gas feed pipe (2) is connected to the raw material gas feed preheater (3); The feed gas preheater (3) is connected to the first methanation reactor (5); The first methanation reactor (5) and the intermediate methanation reactor are connected in sequence; The intermediate methanation reactor and the gas-liquid separator I (20) are connected via a feed gas preheater (3); The gas-liquid separator I (20) is connected to the final stage methanation reactor (24) and the high-temperature condensate main pipe, respectively; The final stage methanation reactor (24) is connected to the gas-liquid separator II (30); The green hydrogen feed assembly includes a green hydrogen feed preheater (26), which is located between the final methanation reactor (24) and the gas-liquid separator II (30). The gas-liquid separator II (30) is used to obtain methane products.

2. The energy saving system for producing green methane by carbon dioxide hydrogenation according to claim 1, characterized in that, The green hydrogen feed assembly is used to introduce raw material green hydrogen. The green hydrogen feed assembly also includes a green hydrogen feed pipe (33), a first green hydrogen inlet branch, and an intermediate green hydrogen inlet branch. The green hydrogen feed pipe (33) is connected to the green hydrogen feed preheater (26); The green hydrogen feed preheater (26) is connected to the first green hydrogen inlet branch and the intermediate green hydrogen inlet branch respectively; The first green hydrogen inlet branch is connected to the raw material mixed gas feed pipe (2); The intermediate green hydrogen inlet branch is connected to the intermediate methanation reactor.

3. The energy saving system for producing green methane by carbon dioxide hydrogenation according to claim 2, characterized in that, Both the first green hydrogen inlet branch and the intermediate green hydrogen inlet branch are equipped with green hydrogen flow control mechanisms. The green hydrogen flow control mechanism is used to control the green hydrogen feed flow rate in stages and to control the reaction progress in the first methanation reactor (5) and the intermediate methanation reactor.

4. The energy-saving system for producing green methane by carbon dioxide hydrogenation according to claim 1, characterized in that, A waste heat boiler is provided between the first methanation reactor (5) and the intermediate methanation reactor; A waste heat boiler is provided between the raw gas feed preheater (3) and the gas-liquid separator I (20); A preheater is provided between the gas phase outlet of the gas-liquid separator I (20) and the final methanation reactor (24); A cooler (28) is provided between the green hydrogen feed preheater (26) and the gas-liquid separator II (30).

5. The energy saving system for producing green methane by carbon dioxide hydrogenation according to claim 1, characterized in that, The intermediate methanation reactor includes a second methanation reactor (10) and a third methanation reactor (15); The first methanation reactor (5) is connected to the second methanation reactor (10); The second methanation reactor (10) is connected to the third methanation reactor (15); The third methanation reactor (15) is connected to the gas-liquid separator I (20) via the feed gas preheater (3).

6. The energy saving system for producing green methane by carbon dioxide hydrogenation according to claim 5, characterized in that, A waste heat boiler is provided between the first methanation reactor (5) and the second methanation reactor (10); A waste heat boiler is provided between the second methanation reactor (10) and the third methanation reactor (15).

7. The energy saving system for producing green methane by carbon dioxide hydrogenation according to claim 1, characterized in that, The system also includes a steam drum (50), a boiler water inlet pipe (49), and a steam outlet pipe; The steam drum (50) is connected to the final methanation reactor (24) and forms a heat exchange loop; The boiler water inlet pipe (49) and steam outlet pipe are respectively connected to the steam drum (50); The boiler water inlet pipe (49) is used to introduce boiler water into the steam drum (50); The steam discharge pipe is used to discharge water vapor from the steam drum (50).

8. The energy saving system for producing green methane by carbon dioxide hydrogenation according to claim 7, characterized in that, The system also includes a pressure control mechanism (51); The pressure control mechanism (51) is connected to the steam discharge pipe; The pressure control mechanism (51) is used to control the flow rate of steam discharge and maintain the pressure inside the steam drum (50).

9. The energy saving system for producing green methane by carbon dioxide hydrogenation according to claim 1, characterized in that, The system also includes a temperature control mechanism (56); The temperature control mechanism (56) is connected to the high-temperature condensate main pipe; The temperature control mechanism (56) is used to control the outlet temperature of the first methanation reactor (5) by controlling the flow rate of the high-temperature condensate.

10. The energy saving system for producing green methane by carbon dioxide hydrogenation according to claim 1, characterized in that, A condensate circulation pump (46) is connected to the high-temperature condensate main pipe; The gas-liquid separator II (30) is provided with a gas-liquid separator II liquid phase outlet (32), which is used to discharge condensate; The gas phase outlet of the gas-liquid separator II (30) is connected to a gas phase outlet pipe II (31) for obtaining methane products.

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