A shunt type carbon dioxide energy storage coupling methanol synthesis system and operation method

Abstract

The present application relates to carbon dioxide energy storage and methanol synthesis technical field, especially in a kind of shunt type carbon dioxide energy storage coupling methanol synthesis system and operating method, the carbon dioxide obtained by carbon capture is introduced into liquid carbon dioxide energy storage release unit, make it serve as energy storage circulating medium and methanol synthesis carbon source, carbon dioxide shunt device is set on the graded expansion path, and the carbon dioxide after expansion is divided into circulation branch and synthesis branch;Carbon dioxide in circulation branch continues to expand and work after returning energy storage cycle, carbon dioxide in synthesis branch is mixed with hydrogen obtained by photovoltaic hydrogen production after raw gas pressure regulating mixing unit, and is used for methanol synthesis, system is preheated for electrolytic water hydrogen production by waste heat recovery, and carbon capture regeneration process is heated, energy management unit is used to coordinate photovoltaic power generation, energy storage release, hydrogen production, carbon dioxide shunt and methanol synthesis process, improve carbon dioxide comprehensive utilization rate, energy utilization efficiency and system operating stability.

Description

Technical Field

[0001] This invention relates to the fields of carbon dioxide energy storage and methanol synthesis technology, and in particular to a split-type carbon dioxide energy storage coupled methanol synthesis system and its operation method. Background Technology

[0002] Liquid carbon dioxide (CO2) energy storage technology uses CO2 as the energy storage medium. When there is surplus electricity, it stores energy through compression, cooling, and condensation processes. When there is insufficient electricity, it releases energy to generate electricity through pressurization, heating, and expansion. It features high energy density, low dependence on geographical conditions, and easy coupling with carbon capture processes. In existing CO2 energy storage systems, CO2 is typically used primarily as a circulating working fluid, returning to the storage cycle after energy release, thus not fully utilizing its resource attributes as a chemical feedstock. Photovoltaic PEM (Polymerized Electrolytic Milling) water electrolysis for hydrogen production offers advantages such as fast response, wide load adjustment range, and high hydrogen purity. However, fluctuations in photovoltaic output can affect the continuity and stability of the hydrogen production process. Liquid CO2 energy storage can store energy when there is surplus photovoltaic power and release it to generate electricity when photovoltaic power is insufficient. Furthermore, the heat generated during compression and heat exchange can be used for preheating or maintaining the temperature of the feed water in the PEM water electrolysis hydrogen production process, thereby improving the system's energy utilization level. Synthesizing methanol from CO2 and hydrogen produced from renewable energy sources is an important pathway to realize the resource utilization of CO2. However, existing carbon capture, carbon dioxide storage, photovoltaic hydrogen production, and methanol synthesis systems are mostly set up relatively independently, with insufficient coupling of material and energy flows between the systems, such as the coupling system and working method of carbon dioxide storage and green hydrogen to methanol proposed in application number 202511911667.1. If the low-pressure carbon dioxide after the carbon dioxide storage system has completed its expansion is used for methanol synthesis, it usually needs to be repressurized; if a large amount of carbon dioxide is directly extracted from the energy storage cycle for methanol synthesis, it may cause insufficient working fluid in the cycle, affecting the continuous operation of the energy storage system.

[0003] Therefore, it is necessary to propose a system and operation method that can synergistically couple carbon capture, liquid carbon dioxide energy storage, photovoltaic hydrogen production and methanol synthesis, so as to achieve the goal of using some carbon dioxide with suitable pressure as a carbon source for methanol synthesis while maintaining the carbon dioxide energy storage cycle, and maintaining the balance of the working fluid in the cycle through carbon capture replenishment, thereby improving the renewable energy absorption capacity, carbon dioxide resource utilization level and the overall energy utilization efficiency of the system. Summary of the Invention

[0004] The main objective of this invention is to provide a split-flow carbon dioxide energy storage coupled methanol synthesis system and its operation method. This system and operation method can solve the problems of insufficient coupling between existing carbon capture, liquid carbon dioxide energy storage, photovoltaic hydrogen production and methanol synthesis systems, as well as the single utilization mode of carbon dioxide energy storage cycle working fluid.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A split-flow carbon dioxide energy storage coupled methanol synthesis system includes a carbon capture unit, a liquid carbon dioxide energy storage and release unit, a photovoltaic PEM hydrogen production unit, a solar thermal storage unit, a methanol synthesis unit, a waste heat recovery unit, and an energy management unit. The carbon capture unit is used to capture carbon dioxide, and the carbon dioxide outlet of the carbon capture unit is connected to the liquid carbon dioxide energy storage and release unit for supplying the captured carbon dioxide to the liquid carbon dioxide energy storage and release unit. The photovoltaic PEM hydrogen production unit includes a photovoltaic power generation device and a PEM electrolyzer. The photovoltaic power generation device is electrically connected to the PEM electrolyzer and the liquid carbon dioxide energy storage and release unit, respectively, for supplying power to the PEM electrolyzer, and supplying power to the liquid carbon dioxide energy storage and release unit when the photovoltaic power generation exceeds the power demand of the PEM electrolyzer. The liquid carbon dioxide energy storage and release unit is used to compress, cool, condense and store carbon dioxide in the energy storage state, and to make the stored carbon dioxide perform work to output electrical energy through pressurization, heat exchange and heating, and at least one stage of expansion in the energy release state. The output electrical energy is used to supplement the power demand of the PEM electrolyzer or to supply power to the outside. The liquid carbon dioxide energy storage and release unit is provided with a carbon dioxide diversion device on the energy release expansion path. The carbon dioxide diversion device is used to divide the carbon dioxide after at least one stage of expansion into a first part of carbon dioxide entering the circulation branch and a second part of carbon dioxide entering the synthesis branch. The circulation branch is connected to the subsequent expansion device and low-pressure side of the liquid carbon dioxide energy storage and release unit, so as to allow the first part of carbon dioxide entering the circulation branch to continue to expand and do work, and return to the liquid carbon dioxide energy storage and release unit after temperature adjustment, so as to maintain the carbon dioxide energy storage cycle. The synthesis branch is connected to the feed gas pressure regulating and mixing unit of the methanol synthesis unit, and is used to transport the second part of carbon dioxide entering the synthesis branch to the feed gas pressure regulating and mixing unit; the feed gas pressure regulating and mixing unit is used to treat the second part of carbon dioxide by at least one of purification, pressure regulation, temperature regulation and flow metering, and mix the treated second part of carbon dioxide with hydrogen. The PEM electrolyzer is used to electrolyze water to produce hydrogen using the electrical energy provided by the photovoltaic power generation device and the electrical energy released by the liquid carbon dioxide energy storage and release unit. The hydrogen outlet of the PEM electrolyzer is directly or via a hydrogen storage device connected to the feed gas pressure regulating and mixing unit to transport the hydrogen generated by water electrolysis to the feed gas pressure regulating and mixing unit, so that the second part of carbon dioxide and hydrogen are mixed and then enter the methanol synthesis unit, where they react to produce methanol under the action of a catalyst. The carbon capture unit is also used to replenish the liquid carbon dioxide energy storage and release unit with carbon dioxide according to the amount of carbon dioxide consumed by the methanol synthesis unit. The solar thermal storage unit is connected to the liquid carbon dioxide energy storage and release unit, and is used to provide heat for heating before carbon dioxide expansion and interstage reheating during the energy release process. The waste heat recovery unit is connected to the liquid carbon dioxide energy storage and release unit, the photovoltaic PEM hydrogen production unit and the carbon capture unit respectively. It is used to recover the heat released during the operation of the liquid carbon dioxide energy storage and release unit and to use the recovered heat for at least one of the following: carbon dioxide preheating in the energy release stage, preheating or temperature maintenance of the electrolytic water in the PEM electrolyzer, and regeneration of the absorbent in the carbon capture unit. The energy management unit is connected to the photovoltaic power generation device, the liquid carbon dioxide energy storage and release unit, the carbon dioxide diversion device, the PEM electrolyzer, the carbon capture unit, the solar thermal storage unit, the waste heat recovery unit, and the methanol synthesis unit, respectively, and is used to coordinate the photovoltaic power generation, carbon dioxide energy storage and release, solar heating, waste heat recovery, carbon dioxide diversion, carbon dioxide replenishment, photovoltaic hydrogen production, and methanol synthesis processes.

[0006] The liquid carbon dioxide energy storage and release unit includes a compression device, a cooling device, a condensation device, a carbon dioxide storage tank, a carbon dioxide pump, a heating device, and an expansion device. In energy storage mode, carbon dioxide is compressed by the compression device, cooled by the cooling device, and condensed by the condensation device before entering the carbon dioxide storage tank for storage. In the energy-released state, the carbon dioxide in the carbon dioxide storage tank is pressurized by the carbon dioxide pump, heated by the heating device, and then enters the expansion device to expand and do work; The carbon dioxide diversion device is located at at least one expansion outlet of the expansion device.

[0007] The liquid carbon dioxide energy storage and release unit includes a low-pressure tank, compressor I, heat exchanger I, compressor II, heat exchanger II, condenser, high-pressure tank, carbon dioxide pump, preheater, heat exchanger III, turbine I, carbon dioxide diversion device, heat exchanger IV, turbine II, and cooler; The low-pressure tank, compressor I, heat exchanger I, compressor II, heat exchanger II, condenser and high-pressure tank are connected in sequence to complete the buffering, multi-stage compression, cooling, condensation and storage of carbon dioxide; The high-pressure tank, the carbon dioxide pump, the preheater, the heat exchanger III, and the turbine I are connected in sequence to complete the pressurization, preheating, preheating before expansion, and first-stage expansion of carbon dioxide. The carbon dioxide diversion device is located on the outlet side of turbine I and is connected to the circulation branch and the synthesis branch respectively; The circulation branch is connected in sequence to the heat exchanger IV, the turbine II, the cooler and the low-pressure tank, so that the first part of carbon dioxide returns to the low-pressure tank after interstage reheating, secondary expansion and cooling; The water-side inlet of the cooler is connected to the cooler inlet pipeline, and the water-side outlet of the cooler is connected to the reboiler in the carbon capture unit through the cooler-to-reboiler hot water supply pipeline, which is used to transfer the heat released by carbon dioxide after secondary expansion to the reboiler. The synthesis branch is connected to the feed gas pressure regulating and mixing unit of the methanol synthesis unit, and is used to transport the second part of carbon dioxide to the feed gas pressure regulating and mixing unit.

[0008] The carbon dioxide diversion device includes a diversion interface and flow regulating valves respectively installed on the circulation branch and the synthesis branch, used to adjust the ratio of carbon dioxide flow entering the circulation branch and the synthesis branch according to at least one of the methanol synthesis load of the methanol synthesis unit, the system hydrogen storage, the energy storage status of the liquid carbon dioxide energy storage and release unit, and the system power demand.

[0009] The solar thermal storage unit is connected to heat exchanger III and heat exchanger IV respectively, and is used to provide pre-expansion heating for carbon dioxide entering turbine I during the energy release stage, and to provide interstage reheat for carbon dioxide entering turbine II.

[0010] The solar thermal storage unit includes a solar collector, a hot oil tank, and a cold oil tank; The solar collector is connected to the hot oil tank and is used to heat the heat transfer oil and transport the heated high-temperature heat transfer oil to the hot oil tank. The hot oil tank is connected to the heat transfer oil inlets of heat exchanger III and heat exchanger IV respectively, and is used to supply high-temperature heat transfer oil to heat exchanger III and heat exchanger IV; The heat transfer oil outlets of heat exchanger III and heat exchanger IV are connected to the cold oil tank, and the cold oil tank is connected to the solar collector to form a heat transfer oil circulation.

[0011] The waste heat recovery unit includes a hot water storage tank, a cold water storage tank, a PEM water supply tank, and a water circulation pipeline; The cold water storage tank is connected to the water-side inlet of heat exchanger I and heat exchanger II respectively, and the water-side outlet of heat exchanger I and heat exchanger II is connected to the hot water storage tank, which is used to recover the heat released during the compression and cooling of carbon dioxide. The hot water storage tank is connected to the water-side inlet of the preheater, and the water-side outlet of the preheater is connected to the cold water storage tank to form a waste heat recovery water circulation. The water-side inlet of the condenser is connected to the cold water storage tank, and the water-side outlet of the condenser is connected to the PEM water supply tank, which is used to use the recovered condensation heat for preheating the electrolytic water of the PEM electrolyzer. The water-side inlet of the cooler is connected to the water supply pipeline, and the water-side outlet of the cooler is connected to the reboiler, which is used to transfer the heat released by carbon dioxide after secondary expansion to the reboiler.

[0012] The photovoltaic PEM hydrogen production unit includes a photovoltaic power generation device, a PEM electrolyzer, an oxygen storage tank, and a hydrogen storage tank. The photovoltaic power generation device is electrically connected to the PEM electrolyzer and the liquid carbon dioxide energy storage and release unit, respectively. The PEM electrolyzer is used to electrolyze water to produce hydrogen using the electrical energy provided by the photovoltaic power generation device and the electrical energy released by the liquid carbon dioxide energy storage and release unit. The hydrogen outlet of the PEM electrolyzer is connected to the hydrogen storage tank, which is connected to the feed gas pressure regulating and mixing unit to provide hydrogen to the methanol synthesis unit. The oxygen outlet of the PEM electrolyzer is connected to the oxygen storage tank; The PEM water supply tank is connected to the PEM electrolysis cell and is used to supply electrolysis water to the PEM electrolysis cell.

[0013] The methanol synthesis unit includes a feed gas pressure regulating and mixing unit, a methanol reactor, a separator, a methanol storage tank, and a water storage tank; The raw material gas pressure regulating and mixing unit is connected to the synthesis branch and the hydrogen storage tank respectively, and is used to receive the second part of carbon dioxide delivered by the synthesis branch and the hydrogen delivered by the hydrogen storage tank, and to perform at least one of the following treatments on the second part of carbon dioxide and hydrogen: purification, pressure regulation, temperature regulation, flow metering and mixing. The feed gas pressure regulating and mixing unit is connected to the methanol reactor; The methanol reactor is used to hydrogenate carbon dioxide and hydrogen after they have been treated by the feed gas pressure regulating and mixing unit under the action of a catalyst, to produce methanol and water. The methanol reactor is connected to the separator; The separator is used to separate the reaction products output from the methanol reactor; The separator is connected to the methanol storage tank and the water storage tank respectively, and is used to transport the separated methanol to the methanol storage tank and the separated water to the water storage tank.

[0014] The methanol synthesis unit also includes an unreacted gas circulation pipeline, which is used to return the unreacted carbon dioxide and hydrogen separated by the separator to the feed gas pressure regulating and mixing unit.

[0015] The energy management unit is configured as follows: When the photovoltaic power generation of the photovoltaic power generation device is greater than the set power requirement of the PEM electrolyzer, the photovoltaic power generation device is controlled to prioritize power supply to the PEM electrolyzer, and the remaining electrical energy is input into the liquid carbon dioxide energy storage and release unit for energy storage. When the photovoltaic power generation of the photovoltaic power generation device is lower than the minimum operating power requirement of the PEM electrolyzer, or when the system has an external power supply requirement, the liquid carbon dioxide energy storage and release unit is controlled to release energy and generate electricity. Based on at least one of the following: the energy storage status of the liquid carbon dioxide energy storage and release unit, the system power shortage, the available hydrogen reserves of the photovoltaic PEM hydrogen production unit, and the methanol synthesis load of the methanol synthesis unit, the carbon dioxide diversion device is controlled to adjust the carbon dioxide diversion ratio between the circulation branch and the synthesis branch. When the carbon dioxide demand of the methanol synthesis unit increases and the hydrogen storage in the hydrogen storage tank meets the preset conditions, the carbon dioxide diversion device is controlled to increase the carbon dioxide flow rate into the synthesis branch. When the system power shortage increases, the demand for energy release and power generation increases, or the hydrogen storage in the hydrogen storage tank is lower than the preset condition, the carbon dioxide diversion device is controlled to increase the flow rate of carbon dioxide entering the circulation branch. Based on the amount of carbon dioxide consumed by the methanol synthesis unit and the amount of carbon dioxide working fluid in the liquid carbon dioxide energy storage and release unit, the carbon capture unit is controlled to replenish carbon dioxide to the liquid carbon dioxide energy storage and release unit so that the amount of carbon dioxide working fluid in the liquid carbon dioxide energy storage and release unit is maintained within a preset range.

[0016] The carbon dioxide in the liquid carbon dioxide energy storage and release unit is in a gaseous or gas-liquid equilibrium state in the low-pressure tank, and in a liquid, near-critical, or high-pressure dense phase state in the high-pressure tank.

[0017] A method for operating a split-flow carbon dioxide energy storage coupled methanol synthesis system includes the following steps: S1. Carbon dioxide is captured from a carbon dioxide-containing gas source through a carbon capture unit, and the captured carbon dioxide is transported to a liquid carbon dioxide energy storage and release unit after being treated by at least one of purification, drying, compression and buffering. S2. Power is supplied to the PEM electrolyzer by the electrical energy released by the photovoltaic power generation device or the liquid carbon dioxide energy storage and release unit, so that the PEM electrolyzer can electrolyze water to produce hydrogen, and the hydrogen is stored in a hydrogen storage tank. S3. When the photovoltaic power generation of the photovoltaic power generation device is higher than the set power requirement of the PEM electrolyzer, the remaining photovoltaic power after meeting the hydrogen production requirements is input into the liquid carbon dioxide energy storage and release unit, so that the carbon dioxide is compressed, cooled and condensed from the low-pressure tank through compressor I, heat exchanger I, compressor II, heat exchanger II and condenser in sequence, and stored in the high-pressure tank. S4. Water from the cold water storage tank enters heat exchanger I and heat exchanger II to recover the heat released during the compression and cooling of carbon dioxide. The water after absorbing heat is stored in the hot water storage tank to preheat the carbon dioxide after it has been pressurized by the carbon dioxide pump during the energy release stage. Water from the cold water storage tank enters the condenser to recover the heat released during the condensation of carbon dioxide. The water after absorbing heat is then transported to the PEM water supply tank to provide preheated electrolysis water to the PEM electrolyzer. S5. When the photovoltaic power generation of the photovoltaic power generation device is lower than the minimum operating power requirement of the PEM electrolyzer, or when the system needs to output electrical energy, the carbon dioxide in the high-pressure tank is pressurized, preheated and heated before expansion by the carbon dioxide pump, preheater and heat exchanger III in sequence, and then enters turbine I for first-stage expansion to do work, and the output electrical energy is used to supplement the power demand of the PEM electrolyzer or to supply power to the outside. S6. The carbon dioxide after the first stage expansion of the turbine I is transported to the carbon dioxide splitting device, and the carbon dioxide splitting device divides the carbon dioxide into a first part of carbon dioxide that enters the circulation branch and a second part of carbon dioxide that enters the synthesis branch. S7. The first part of carbon dioxide is sequentially reheated through heat exchanger IV, expanded in turbine II to do work, and cooled by cooler before returning to the low-pressure tank to maintain the carbon dioxide energy storage cycle. S8. Water is introduced into the cooler through the cooler inlet pipe to absorb the heat released by carbon dioxide after the secondary expansion, and is then transported to the reboiler via the hot water supply pipe from the cooler to the reboiler to provide at least part of the heat for the absorbent regeneration process of the carbon capture unit. S9. The second part of carbon dioxide is transported to the raw material gas pressure regulating and mixing unit via the synthesis branch carbon dioxide pipeline, and the hydrogen in the hydrogen storage tank is transported to the raw material gas pressure regulating and mixing unit via the hydrogen to methanol synthesis pipeline. The raw material gas pressure regulating and mixing unit performs at least one of the following treatments on the second part of carbon dioxide and hydrogen: purification, pressure regulation, temperature regulation, flow metering, and mixing. The treated mixed raw material gas is then transported to the methanol reactor. S10. The second part of carbon dioxide and hydrogen are reacted in the methanol reactor under the action of a catalyst to produce methanol and water. The reaction products are separated by a separator. The separated methanol is transported to a methanol storage tank, the separated water is transported to a water storage tank, and the unreacted carbon dioxide and hydrogen are recycled back to the raw material gas pressure regulating and mixing unit. S11. Based on the amount of carbon dioxide consumed during methanol synthesis, control the carbon capture unit to replenish carbon dioxide to the liquid carbon dioxide energy storage and release unit, and adjust the flow ratio between the first part of carbon dioxide entering the circulation branch and the second part of carbon dioxide entering the synthesis branch based on at least one of the photovoltaic power generation, liquid carbon dioxide energy storage status, system power shortage, hydrogen storage in the hydrogen storage tank, and methanol synthesis load of the methanol synthesis unit.

[0018] The beneficial effects of this invention are as follows: The split-flow carbon dioxide energy storage coupled methanol synthesis system and operating method of this invention have the following technical features and advantages in practical use: 1. This invention directly introduces carbon dioxide obtained from carbon capture into a liquid carbon dioxide energy storage and release unit, so that carbon dioxide serves as both an energy storage cycle working fluid and a carbon source for methanol synthesis. This achieves the synergistic utilization of captured carbon dioxide in the energy storage, energy release, and chemical conversion processes, thereby improving the comprehensive utilization value of carbon dioxide. At the same time, this invention sets up a carbon dioxide diversion device on the staged expansion path of the liquid carbon dioxide energy storage and release unit. The carbon dioxide diversion device divides the carbon dioxide after at least one stage of expansion into a circulation branch and a synthesis branch, and adjusts the carbon dioxide flow ratio of the two branches. This allows a portion of the carbon dioxide to continue expanding and doing work and return to the energy storage cycle, while the other portion of the carbon dioxide is transported to the feed gas pressure regulating and mixing unit for conditioning via the synthesis branch, thus taking into account both the energy storage cycle and the supply of feedstock for methanol synthesis. 2. This invention extracts carbon dioxide for methanol synthesis from an intermediate pressure stage, maintaining a certain pressure. This reduces the energy consumption required to expand all the carbon dioxide to a low pressure and then recompress it to the methanol synthesis pressure, thus improving the coupling efficiency between carbon dioxide energy storage and methanol synthesis. The carbon capture unit replenishes the carbon dioxide consumed during methanol synthesis, and the replenishment amount is adjusted according to the methanol synthesis load and the carbon dioxide inventory in the energy storage system, thereby maintaining the working fluid balance in the liquid carbon dioxide energy storage cycle and improving the system's continuous operation capability and material balance stability. This invention combines liquid carbon dioxide energy storage with photovoltaic hydrogen production. When photovoltaic power generation is surplus, surplus electricity is used for carbon dioxide energy storage. When photovoltaic power generation is insufficient or at night, the liquid carbon dioxide energy storage release unit generates electricity to supplement the power demand of the PEM electrolyzer, thereby reducing the impact of photovoltaic output fluctuations on the photovoltaic hydrogen production process and improving the continuity and stability of photovoltaic hydrogen production. 3. This invention utilizes the heat generated during the energy storage and release process of liquid carbon dioxide in a graded manner through a waste heat recovery unit. Specifically, the heat of compression generated during the compression and cooling of carbon dioxide is used for preheating carbon dioxide in the energy release stage, the heat released during the condensation of carbon dioxide is used for preheating water for PEM electrolysis, and the waste heat from the cooling of carbon dioxide after secondary expansion is used for regeneration of the absorbent liquid in the reboiler of the carbon capture unit. This reduces the dependence of the energy storage, energy release, hydrogen production, and carbon capture processes on external heat sources and improves the overall energy utilization efficiency of the system. 4. This invention utilizes a solar thermal storage unit to provide heat for preheating and interstage reheating of carbon dioxide before expansion, thereby increasing the turbine inlet temperature and expansion work capacity. Simultaneously, a feed gas pressure regulating and mixing unit is used to purify, regulate the pressure and temperature of carbon dioxide and hydrogen, measure their flow rate, and mix them to meet the feed conditions required for methanol synthesis, thereby improving the operational compatibility between energy storage and release and methanol synthesis. 5. This invention coordinates and controls the processes of photovoltaic power generation, carbon dioxide energy storage and release, carbon dioxide diversion, carbon capture and replenishment, photovoltaic hydrogen production and methanol synthesis through an energy management unit, so as to realize the synergistic utilization of electrical energy, thermal energy, hydrogen energy and carbon resources, improve the renewable energy absorption capacity, system operation flexibility and comprehensive energy utilization efficiency, and can be applied to scenarios such as coal-fired power plants, gas-fired power plants, steel plants, cement plants, chemical industrial parks and renewable energy hydrogen production bases. Attached Figure Description

[0019] Figure 1 This is an overall flow chart of a split-type carbon dioxide energy storage coupled methanol synthesis system and its operation method according to the present invention; The diagram is labeled as follows: 100—Carbon capture unit; 101—Absorber; 102—Rich solution storage tank; 103—Lean solution storage tank; 104—Absorbent heat exchanger; 105—Regeneration tower; 106—Reboiler; 107—Carbon dioxide pre-compressor; 200—Liquid carbon dioxide energy storage and release unit; 201—Low-pressure tank; 202—Compressor I; 203—Heat exchanger I; 204—Compressor II; 205—Heat exchanger II; 206—Condenser; 207—High-pressure tank; 208—Carbon dioxide pump; 209—Preheater; 210—Heat exchanger III; 211—Turbine I; 212—Carbon dioxide diversion device; 213—Heat exchanger IV; 214—Turbine II; 215—Cooler; 300—Photovoltaic PEM hydrogen production unit. ; 301—Photovoltaic power generation device; 302—PEM electrolyzer; 303—Oxygen storage tank; 304—Hydrogen storage tank; 400—Solar thermal storage unit; 401—Solar collector; 402—Hot oil tank; 403—Cold oil tank; 500—Methanol synthesis unit; 501—Raw gas pressure regulating and mixing unit; 502—Methanol reactor; 503—Separator; 504—Methanol storage tank; 505—Water storage tank; 600—Waste heat recovery unit; 601—Hot water storage tank; 602—Cold water storage tank; 603—PEM water supply tank; 700—Energy management unit; 1—Industrial flue gas pipeline; 2—Rich absorbent output pipeline; 3—Rich absorbent before heat exchange pipeline; 4—Rich absorbent after heat exchange pipeline; 5—Reboiler to regeneration tower pipeline; 6—Reboiler reflux line; 7—Reflux heat exchange post-line; 8—Lean absorbent reflux line; 9—Regeneration tower bottom liquid phase line; 10—Regenerated carbon dioxide output line; 11—Compressed carbon dioxide to low-pressure tank line; 12—Low-pressure carbon dioxide output line; 13—First-stage compressed carbon dioxide line; 14—First-stage cooled carbon dioxide line; 15—Second-stage compressed carbon dioxide line; 16—Second-stage cooled carbon dioxide line; 17—Condensed carbon dioxide line; 18—High-pressure carbon dioxide output line; 19—Pump post-carbon dioxide line; 20—Preheated carbon dioxide line; 21—First-stage heated carbon dioxide line; 22—First-stage expanded carbon dioxide line; 23—Circulation branch carbon dioxide line; 24— 25—Carbon dioxide pipeline after reheating; 26—Carbon dioxide pipeline after secondary expansion; 27—Carbon dioxide reflux pipeline after cooling; 28—Carbon dioxide pipeline for synthesis branch; 29—Methanol synthesis mixed feedstock gas pipeline; 30—Methanol reaction product pipeline; 31—Water product pipeline; 32—Hydrogen output pipeline; 33—Hydrogen to methanol synthesis pipeline; 34—Oxygen output pipeline; 35—Unreacted gas circulation pipeline; W1—Hot water output pipeline for heat exchanger I; W2—Hot water inlet pipeline for hot water storage tank; W3—Hot water output pipeline for heat exchanger II; W4—Hot water supply pipeline from hot water storage tank to preheater; W5—Return water pipeline from preheater to cold water storage tank; W6—Cold water main outlet pipeline for cold water storage tank; W7—Water supply pipeline from cold water storage tank to heat exchanger II;W8—Water supply line from cold water storage tank to heat exchanger I; W9—Water supply line from cold water storage tank to condenser; W10—Hot water supply line from condenser to PEM water supply tank; W11—Water supply line from PEM water supply tank to PEM electrolyzer; W12—Cooler inlet line; W13—Hot water supply line from cooler to reboiler; O1—Line from solar collector to hot oil tank; O2—High-temperature heat transfer oil outlet main pipe from hot oil tank; O3—Oil supply line from hot oil tank to heat exchanger IV; O4—Oil supply line from hot oil tank to heat exchanger III; O5—Low-temperature heat transfer oil return line from heat exchanger IV; O6—Low-temperature heat transfer oil return line from heat exchanger III; O7—Low-temperature heat transfer oil return main pipe from cold oil tank; O8—Oil supply line from cold oil tank to solar collector. Detailed Implementation

[0020] Specific Embodiment 1: To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that: In the present invention, unless otherwise specified, all embodiments and preferred methods mentioned herein can be combined to form new technical solutions. In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions. The "scope" disclosed in the present invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively. Unless otherwise stated, the technical and scientific terms used herein have the same meaning as those skilled in the art.

[0021] As per the instruction manual Figure 1 As shown, the present invention provides a split-flow carbon dioxide energy storage coupled methanol synthesis system, which includes a carbon capture unit 100, a liquid carbon dioxide energy storage and release unit 200, a photovoltaic PEM hydrogen production unit 300, a solar thermal energy storage unit 400, a methanol synthesis unit 500, a waste heat recovery unit 600, and an energy management unit 700.

[0022] The carbon capture unit 100 is used to capture carbon dioxide from industrial flue gas, combustion exhaust gas or other carbon dioxide-containing gas sources, and to transport the captured carbon dioxide to the liquid carbon dioxide energy storage and release unit 200.

[0023] The liquid carbon dioxide energy storage and release unit 200 is used to compress, cool, condense, and store carbon dioxide during the energy storage stage, and to output electrical energy during the energy release stage by pressurizing, preheating, solar heating, and multi-stage expansion of the stored high-pressure carbon dioxide. A carbon dioxide diversion device 212 is provided on the staged expansion path of the liquid carbon dioxide energy storage and release unit 200. The carbon dioxide diversion device 212 is used to divide the carbon dioxide after the first stage of expansion into a circulation branch and a synthesis branch, and to regulate the flow ratio of carbon dioxide entering the two branches. The first portion of carbon dioxide entering the circulation branch continues to expand and return to the low-pressure tank 201, while the second portion of carbon dioxide entering the synthesis branch is transported to the feed gas pressure regulating and mixing unit 501 of the methanol synthesis unit 500.

[0024] The photovoltaic PEM hydrogen production unit 300 is used to produce hydrogen by electrolyzing water using the photovoltaic power output from the photovoltaic power generation device 301 and the electrical energy released by the liquid carbon dioxide energy storage and release unit 200.

[0025] The solar thermal storage unit 400 is used to provide heat for the preheating of carbon dioxide before expansion and the interstage reheating process of the liquid carbon dioxide energy storage and release unit 200.

[0026] The methanol synthesis unit 500 receives the second portion of carbon dioxide transported by the synthesis branch and the hydrogen produced by the photovoltaic PEM hydrogen production unit 300 through the feed gas pressure regulating and mixing unit 501. The feed gas pressure regulating and mixing unit 501 includes a purification device, a pressure regulating device, a temperature regulating device, and a flow metering device respectively installed on the carbon dioxide inlet pipeline and the hydrogen inlet pipeline, and a mixing device and a buffer device installed on the mixing pipeline after the carbon dioxide and hydrogen are combined. The purification device removes moisture, absorbent entrainment, and other impurities that affect the methanol synthesis reaction from the carbon dioxide and hydrogen. The pressure regulating device regulates the pressure of the carbon dioxide and hydrogen through a regulating valve or a pressurizing device. The temperature regulating device regulates the temperature of the carbon dioxide and hydrogen through a heat exchanger or a heater. The flow metering device detects the flow rate of the carbon dioxide and hydrogen and adjusts the supply flow rate of the carbon dioxide and hydrogen through a flow regulating valve based on the detection result. The mixing device thoroughly mixes the pressure- and temperature-regulated carbon dioxide and hydrogen. The buffer device stabilizes the pressure and flow rate of the mixed feed gas. The treated carbon dioxide and hydrogen are mixed in the proportion required for the methanol synthesis reaction and transported to the methanol reactor 502 through the methanol synthesis mixed feed gas pipeline 28.

[0027] The waste heat recovery unit 600 is used to recover the heat released during the compression, cooling, condensation and expansion and cooling of carbon dioxide, and to use the recovered heat for carbon dioxide preheating, PEM electrolysis water preheating and carbon capture unit 100 absorbent regeneration.

[0028] The energy management unit 700 is used to collect real-time power generation of the photovoltaic power generation device 301, operating power demand of the PEM electrolyzer 302, energy storage status of the liquid carbon dioxide energy storage and release unit 200, hydrogen storage capacity of the hydrogen storage tank 304, methanol synthesis load of the methanol synthesis unit 500, and diversion status of the carbon dioxide diversion device 212, and generates corresponding control signals based on the above operating parameters to coordinate and control the photovoltaic power generation device 301, liquid carbon dioxide energy storage and release unit 200, PEM electrolyzer 302, carbon dioxide diversion device 212, carbon capture unit 100, and methanol synthesis unit 500; when the photovoltaic power generation is greater than that of the PEM electrolyzer 302... When the set power demand is met, the photovoltaic power generation device 301 is controlled to prioritize power supply to the PEM electrolyzer 302, and the remaining electrical energy is used for energy storage in the liquid carbon dioxide energy storage and release unit 200. When the photovoltaic power generation is lower than the minimum operating power demand of the PEM electrolyzer 302 or when there is an external power supply demand for the system, the liquid carbon dioxide energy storage and release unit 200 is controlled to release energy and generate electricity. Based on at least one parameter among the energy storage status of the liquid carbon dioxide energy storage and release unit 200, the system power gap, hydrogen storage, and methanol synthesis load, the carbon dioxide diversion device 212 is controlled to adjust the carbon dioxide flow rate entering the circulation branch and the synthesis branch, thereby coordinating the carbon dioxide energy storage cycle, photovoltaic hydrogen production, and methanol synthesis process.

[0029] The operation method of the split-flow carbon dioxide energy storage coupled methanol synthesis system of the present invention is as follows: 1. Carbon capture process Specifically, industrial flue gas enters the absorption tower 101 via industrial flue gas pipeline 1, and comes into countercurrent contact with lean absorbent from lean liquid storage tank 103 within the absorption tower 101. Carbon dioxide in the industrial flue gas is absorbed by the absorbent to form rich absorbent, which then enters the rich absorbent storage tank 102 via rich absorbent output pipeline 2.

[0030] The rich absorbent in the rich absorbent storage tank 102 enters the absorbent heat exchanger 104 via the rich absorbent heat exchanger pre-heat exchanger pipeline 3, where it exchanges heat with the lean absorbent from the reboiler 106. After being heated by the heat exchange, the rich absorbent enters the regeneration tower 105 via the rich absorbent heat exchanger post-heat exchanger pipeline 4.

[0031] Inside the regeneration tower 105, the rich absorbent undergoes desorption and releases high-concentration carbon dioxide under the heat provided by the reboiler 106. The liquid phase at the bottom of the regeneration tower 105 enters the reboiler 106 through the bottom liquid phase pipeline 9. After being heated by the reboiler 106, it returns to the regeneration tower 105 through the reboiler-to-regeneration tower pipeline 5. Another portion is transported to the absorbent heat exchanger 104 through the reboiler reflux pipeline 6 to exchange heat with the rich absorbent, thereby recovering the waste heat of the lean absorbent and preheating the rich absorbent.

[0032] At least a portion of the heat required by reboiler 106 comes from the residual heat after the secondary expansion of the liquid carbon dioxide storage and release unit 200. External supply water or circulating water enters cooler 215 via cooler inlet line W12, where it absorbs the heat released by the carbon dioxide after the secondary expansion. The water, heated by the heat absorption, is then transported to reboiler 106 via cooler to reboiler hot water supply line W13 to provide some heat for the absorbent regeneration process.

[0033] The lean absorbent after analysis enters the absorbent heat exchanger 104 via the reboiler reflux line 6, where it exchanges heat with the rich absorbent to cool down. After cooling, the lean absorbent enters the lean liquid storage tank 103 via the reflux heat exchange line 7, and then returns to the absorption tower 101 via the lean absorbent reflux line 8, thus forming an absorbent circulation.

[0034] The high-concentration carbon dioxide output from the top of regeneration tower 105 enters the carbon dioxide pre-compressor 107 for preliminary compression via regenerated carbon dioxide output pipeline 10. The compressed carbon dioxide then enters the low-pressure tank 201 via compressed carbon dioxide to low-pressure tank pipeline 11.

[0035] Based on the composition of the carbon dioxide gas source and the requirements of methanol synthesis raw materials, the carbon dioxide output from the regeneration tower 105 can also be treated for impurity removal, purification and drying before entering the low-pressure tank 201, so as to reduce the impact of moisture, absorbent entrainment and other impurities on the liquid carbon dioxide energy storage cycle and methanol synthesis process.

[0036] 2. Carbon dioxide energy storage process The low-pressure tank 201 is used to receive carbon dioxide delivered by the carbon capture unit 100 and carbon dioxide returned by the circulation branch, and to buffer and stabilize the carbon dioxide to provide a stable carbon dioxide working medium to the liquid carbon dioxide energy storage and release unit 200.

[0037] During the energy storage phase, carbon dioxide in low-pressure tank 201 enters compressor I 202 via low-pressure carbon dioxide output line 12 for primary compression. The primary compressed carbon dioxide then enters heat exchanger I 203 via primary compression line 13 for cooling. The cooled carbon dioxide then enters compressor II 204 via primary cooling line 14 for secondary compression. The secondary compressed carbon dioxide then enters heat exchanger II 205 via secondary compression line 15 for further cooling. The carbon dioxide cooled by heat exchanger II 205 then enters condenser 206 via secondary cooling line 16.

[0038] Carbon dioxide further releases heat in condenser 206 and condenses or transforms into a high-pressure dense phase suitable for storage. The carbon dioxide processed by condenser 206 enters high-pressure tank 207 for storage via condensed carbon dioxide pipeline 17, thus completing the carbon dioxide energy storage process. In this embodiment, low-pressure tank 201 is used to store carbon dioxide in a gaseous or gas-liquid equilibrium state, while high-pressure tank 207 is used to store carbon dioxide in a liquid, near-critical, or high-pressure dense phase state.

[0039] 3. Compression heat recovery process The waste heat recovery unit 600 includes a hot water storage tank 601, a cold water storage tank 602, a PEM supply tank 603, and corresponding water circulation pipelines. During the carbon dioxide energy storage process, the high-temperature carbon dioxide at the outlet of compressor I 202 releases compression heat in heat exchanger I 203, and the high-temperature carbon dioxide at the outlet of compressor II 204 releases compression heat in heat exchanger II 205.

[0040] The low-temperature water in cold water storage tank 602 is output through the cold water storage tank outlet manifold W6. The low-temperature water output from the cold water storage tank outlet manifold W6 flows through the cold water storage tank to heat exchanger II supply line W7 and the cold water storage tank to heat exchanger I supply line W8, respectively, into heat exchangers II 205 and I 203. The low-temperature water entering heat exchanger I 203 exchanges heat with the high-temperature carbon dioxide after primary compression and absorbs the heat released by the carbon dioxide after primary compression. The water after heat absorption is then transported to the hot water junction point via the hot water output line W1 of heat exchanger I. The low-temperature water entering heat exchanger II 205 exchanges heat with the high-temperature carbon dioxide after secondary compression and absorbs the heat released by the carbon dioxide after secondary compression. The water after heat absorption is then transported to the hot water junction point via the hot water output line W3 of heat exchanger II. After the hot water from heat exchangers I 203 and II 205 is combined, it enters the hot water storage tank 601 for storage via the hot water storage tank inlet line W2. Through the aforementioned water circulation, the heat of carbon dioxide compression recovered in heat exchangers I 203 and II 205 is stored in hot water storage tank 601 as hot water for use in subsequent carbon dioxide preheating processes.

[0041] 4. Carbon dioxide preheating and hot water circulation process When the liquid carbon dioxide energy storage and release unit 200 enters the energy release state, the high-temperature water in the hot water storage tank 601 enters the preheater 209 via the hot water supply pipeline W4 from the hot water storage tank to the preheater.

[0042] In preheater 209, high-temperature water exchanges heat with carbon dioxide pressurized by carbon dioxide pump 208, transferring the recovered heat of compression to the carbon dioxide, thus preheating the carbon dioxide before it enters the solar heating process. The water, cooled by heat exchange in preheater 209, returns to cold water storage tank 602 via the return water pipeline W5 from the preheater to the cold water storage tank. Thus, a waste heat recovery water cycle is formed between cold water storage tank 602, heat exchangers I 203 and II 205, hot water storage tank 601, and preheater 209, realizing the recovery of carbon dioxide compression heat during the energy storage stage and its reuse during the energy release stage.

[0043] 5. Condensation heat recovery and PEM water supply process The low-temperature water in the cold water storage tank 602 can also enter the condenser 206 via the condenser water supply pipeline W9. In the condenser 206, the low-temperature water exchanges heat with the carbon dioxide after secondary cooling, absorbing the heat released by the carbon dioxide during further cooling and condensation.

[0044] After absorbing the heat of condensation, the water is transported via the condenser to the PEM supply water tank 603 through the hot water supply pipeline W10. The PEM supply water tank 603 stores the electrolysis water preheated by waste heat and provides buffering and regulation of the water flow rate and temperature. The preheated water in the PEM supply water tank 603 is then transported to the PEM electrolyzer 302 via the PEM supply water tank to the PEM electrolyzer supply water pipeline W11, serving as the electrolysis water for the PEM electrolyzer 302. By recovering the heat of carbon dioxide condensation in the condenser 206 to preheat the electrolysis water, the external heat required for heating the inlet water of the PEM electrolyzer 302 can be reduced, improving the overall energy utilization efficiency of the system.

[0045] 6. Photovoltaic PEM hydrogen production process The photovoltaic PEM hydrogen production unit 300 includes a photovoltaic power generation device 301, a PEM electrolyzer 302, an oxygen storage tank 303, and a hydrogen storage tank 304.

[0046] The electricity generated by the photovoltaic power generation device 301 is preferentially supplied to the PEM electrolyzer 302 to drive the PEM electrolyzer 302 to produce hydrogen through water electrolysis. Preheated water in the PEM water supply tank 603 enters the PEM electrolyzer 302 via the PEM water supply tank to the PEM electrolyzer water supply pipeline W11. Under the action of DC power, the water undergoes an electrolysis reaction in the PEM electrolyzer 302 to produce hydrogen and oxygen.

[0047] Hydrogen produced by PEM electrolyzer 302 enters hydrogen storage tank 304 via hydrogen output pipeline 32. Hydrogen storage tank 304 is used to stabilize hydrogen supply and to deliver hydrogen to feed gas pressure regulating and mixing unit 501 according to the operating load of methanol synthesis unit 500.

[0048] The oxygen produced by the PEM electrolyzer 302 is stored in the oxygen storage tank 303 via the oxygen output pipeline 34. The oxygen can be exported as a byproduct or used in other industrial processes.

[0049] When the power output of the photovoltaic power generation device 301 is higher than the set hydrogen production power of the PEM electrolyzer 302, the photovoltaic power generation device 301 prioritizes meeting the power demand of the PEM electrolyzer 302. The remaining photovoltaic power is used to drive the compressor I 202, compressor II 204 and other electrical equipment in the liquid carbon dioxide energy storage and release unit 200, so that the liquid carbon dioxide energy storage and release unit 200 enters the energy storage state.

[0050] When the power generation of the photovoltaic power generation device 301 is lower than the minimum operating power requirement of the PEM electrolyzer 302, or when there is an external power supply requirement for the system, the liquid carbon dioxide energy storage and release unit 200 enters the energy release state and outputs electrical energy through the expansion of turbine I 211 and turbine II 214 to supplement the power demand of the PEM electrolyzer 302 or to supply power to the outside.

[0051] 7. Carbon dioxide energy release process During the energy release phase, the high-pressure carbon dioxide in the high-pressure tank 207 enters the carbon dioxide pump 208 via the high-pressure carbon dioxide output pipeline 18. After being pressurized by the carbon dioxide pump 208, the carbon dioxide enters the preheater 209 via the post-pump carbon dioxide pipeline 19. In the preheater 209, the pressurized carbon dioxide absorbs the heat of compression stored in the hot water storage tank 601 and is preheated.

[0052] Preheated carbon dioxide enters heat exchanger III 210 via preheated carbon dioxide pipeline 20. In heat exchanger III 210, the carbon dioxide absorbs heat from the solar thermal storage unit 400 and is heated to a suitable turbine inlet temperature. The heated carbon dioxide from heat exchanger III 210 then enters turbine I 211 via primary heating carbon dioxide pipeline 21 for first-stage expansion and work. The mechanical energy output from turbine I 211 can be converted into electrical energy by a generator, which is used to supplement the power demand of the PEM electrolyzer 302 or to supply power to external systems.

[0053] 8. Carbon dioxide diversion and circulation branch process The carbon dioxide from the outlet of turbine I 211 is expanded in the first stage and then enters the carbon dioxide diversion device 212 via the carbon dioxide pipeline 22.

[0054] The carbon dioxide diversion device 212 includes a diversion interface and flow regulating valves respectively installed on the circulation branch and the synthesis branch. Based on the liquid carbon dioxide storage status, system power demand, hydrogen reserves, and methanol synthesis load, the carbon dioxide diversion device 212 distributes the expanded carbon dioxide to the circulation branch and the synthesis branch, and regulates the flow ratio of carbon dioxide entering the two branches.

[0055] The first portion of carbon dioxide entering the circulation branch enters heat exchanger IV 213 via circulation branch carbon dioxide pipeline 23. In heat exchanger IV 213, the first portion of carbon dioxide absorbs heat provided by solar thermal storage unit 400 and undergoes interstage reheating. The carbon dioxide reheated by heat exchanger IV 213 enters turbine II 214 via reheated carbon dioxide pipeline 24 to continue expanding and doing work.

[0056] The carbon dioxide from the outlet of turbine II 214 undergoes secondary expansion and then enters cooler 215 via carbon dioxide line 25. In cooler 215, the expanded carbon dioxide exchanges heat with water supplied via cooler inlet line W12. After being cooled by cooler 215, the carbon dioxide returns to low-pressure tank 201 via cooled carbon dioxide return line 26 to maintain the liquid carbon dioxide energy storage cycle.

[0057] Water that has absorbed the waste heat of carbon dioxide in cooler 215 is transported to reboiler 106 via hot water supply line W13 from cooler to reboiler, providing some heat for the regeneration process of absorbent in carbon capture unit 100.

[0058] 9. Solar thermal storage process The solar thermal storage unit 400 includes a solar collector 401, a hot oil tank 402, and a cold oil tank 403. The solar collector 401 absorbs solar radiation and heats the thermal oil or other heat storage medium. The high-temperature thermal oil heated by the solar collector 401 enters the hot oil tank 402 for storage via the solar collector-to-hot oil tank pipeline O1. When the liquid carbon dioxide energy storage and release unit 200 enters the energy release state, the high-temperature thermal oil in the hot oil tank 402 is output via the high-temperature thermal oil output main pipe O2.

[0059] The high-temperature heat transfer oil output from the hot oil tank's high-temperature heat transfer oil outlet main pipe O2 is divided into two paths. One path goes through the hot oil tank to the heat exchanger IV supply line O3 and enters the heat exchanger IV 213, which is used to provide interstage reheat for the carbon dioxide after the first-stage expansion; the other path goes through the hot oil tank to the heat exchanger III supply line O4 and enters the heat exchanger III 210, which is used to provide pre-expansion heating for the carbon dioxide before it enters the turbine I 211.

[0060] After releasing heat and cooling down in heat exchanger IV 213, the high-temperature heat transfer oil enters the low-temperature heat transfer oil return main O7 to the cold oil tank through the low-temperature heat transfer oil return line O5 of heat exchanger IV. After releasing heat and cooling down in heat exchanger III 210, the high-temperature heat transfer oil enters the low-temperature heat transfer oil return main O7 to the cold oil tank through the low-temperature heat transfer oil return line O6 of heat exchanger III.

[0061] The low-temperature heat transfer oil from heat exchangers III210 and IV213 converges and then flows into cold oil tank 403 via the cold oil return main O7. The low-temperature heat transfer oil in cold oil tank 403 is then transported to solar collector 401 via the solar collector oil supply pipeline O8, where it reabsorbs solar radiation heat, thus forming a heat transfer oil circulation.

[0062] 10. Synthesis branch and feed gas conditioning process The second portion of carbon dioxide entering the synthesis branch enters the feed gas pressure regulating mixing unit 501 via the synthesis branch carbon dioxide pipeline 27. Since this second portion of carbon dioxide is drawn from the intermediate pressure position after the first-stage expansion in turbine I 211, it retains a certain pressure. Compared to fully expanding the carbon dioxide to a low pressure before using it for methanol synthesis, drawing the carbon dioxide from the intermediate pressure position reduces the energy consumption required to recompress the carbon dioxide to the methanol synthesis pressure.

[0063] Hydrogen in hydrogen storage tank 304 enters the feed gas pressure regulating and mixing unit 501 via hydrogen-to-methanol synthesis pipeline 33. The feed gas pressure regulating and mixing unit 501 purifies, regulates the pressure and temperature, measures the flow rate and performs necessary buffering treatments on the second part of carbon dioxide and hydrogen, and mixes the carbon dioxide and hydrogen in the proportion required for methanol synthesis.

[0064] Preferably, the supply ratio of carbon dioxide and hydrogen is adjusted according to the stoichiometric relationship of the methanol synthesis reaction and the amount of unreacted gas circulating, so that the mixed feed gas meets the pressure, temperature and composition conditions required by the methanol reactor 502.

[0065] 11. Methanol Synthesis and Product Separation Process The methanol synthesis unit 500 includes a feed gas pressure regulating and mixing unit 501, a methanol reactor 502, a separator 503, a methanol storage tank 504, and a water storage tank 505. The mixed feed gas, after being processed by the feed gas pressure regulating and mixing unit 501, enters the methanol reactor 502 through the methanol synthesis mixed feed gas pipeline 28. In the methanol reactor 502, carbon dioxide and hydrogen undergo a hydrogenation reaction under the action of a methanol synthesis catalyst to produce methanol and water. The methanol reactor 502 is a fixed-bed reactor or a tubular fixed-bed reactor capable of accommodating the methanol synthesis catalyst and ensuring sufficient contact between the mixed feed gas and the catalyst. When a fixed-bed reactor is selected, it is a cylindrical pressure vessel with an internal catalyst bed filled with a copper-based methanol synthesis catalyst. The fixed-bed reactor has a feed gas inlet distributor at the top and a product outlet at the bottom. The fixed-bed reactor is equipped with an external heating / cooling jacket or internal heat exchange tubes to control the reaction temperature. When a tubular fixed-bed reactor is selected, the reactor includes a shell and multiple reaction tubes disposed within the shell. The reaction tubes are filled with catalyst, and a heat exchange medium (such as heat transfer oil or boiling water) is circulated through the shell side for heat transfer and temperature control, enabling a continuous heat exchange-reaction process. The mixed feed gas enters the methanol reactor 502 via the methanol synthesis mixed feed gas pipeline 28, passes through the catalyst bed, and is discharged via the methanol reaction product pipeline 29. The reaction temperature, reaction pressure, and processing capacity of the methanol reactor 502 are set according to the catalyst used and the methanol synthesis load.

[0066] The reaction products output from methanol reactor 502 enter separator 503 via methanol reaction product pipeline 29. Separator 503 separates methanol, water, and unreacted carbon dioxide and hydrogen through condensation, gas-liquid separation, or other separation methods. The separated methanol enters methanol storage tank 504 via methanol product pipeline 30, and the separated water enters water storage tank 505 via water product pipeline 31. The unreacted carbon dioxide and hydrogen separated by separator 503 can be returned to feed gas pressure regulating and mixing unit 501 through unreacted gas circulation pipeline 35 to improve the utilization rate of carbon dioxide and hydrogen.

[0067] 12. Carbon dioxide replenishment process The second portion of carbon dioxide entering the synthesis branch is consumed during methanol synthesis, so the carbon capture unit 100 is used to replenish the liquid carbon dioxide storage and release unit 200 with a corresponding mass of carbon dioxide.

[0068] The energy management unit 700 determines the amount of carbon dioxide that the carbon capture unit 100 replenishes to the low-pressure tank 201 based on the amount of carbon dioxide consumed by the methanol synthesis unit 500 within a preset control cycle, the diversion ratio of the carbon dioxide diversion device 212, the amount of carbon dioxide stored in the low-pressure tank 201, and the amount of carbon dioxide stored in the high-pressure tank 207.

[0069] In one operating mode, the amount of carbon dioxide replenished to the liquid carbon dioxide energy storage cycle within a preset control period matches the amount of carbon dioxide actually consumed during methanol synthesis.

[0070] In another operating mode, the energy management unit 700 controls the carbon dioxide replenishment amount based on the total carbon dioxide storage in the low-pressure tank 201 and the high-pressure tank 207, so that the carbon dioxide working fluid storage in the liquid carbon dioxide energy storage cycle is kept within a preset range.

[0071] 13. Energy Management Process The energy management unit 700 is communicatively connected to the carbon capture unit 100, the liquid carbon dioxide energy storage and release unit 200, the photovoltaic PEM hydrogen production unit 300, the solar thermal storage unit 400, the methanol synthesis unit 500, the waste heat recovery unit 600, and the carbon dioxide diversion device 212.

[0072] The energy management unit 700 is used to obtain the photovoltaic power generation, the operating power of the PEM electrolyzer 302, the pressure and carbon dioxide inventory of the low-pressure tank 201, the pressure and carbon dioxide inventory of the high-pressure tank 207, the hydrogen inventory of the hydrogen storage tank 304, the temperature and heat storage of the hot water storage tank 601, the temperature of the cold water storage tank 602, the water volume and temperature of the PEM water supply tank 603, the heat storage status of the solar thermal storage unit 400, and the operating load of the methanol synthesis unit 500.

[0073] When the power output of the photovoltaic power generation device 301 exceeds the set power requirement of the PEM electrolyzer 302, the energy management unit 700 controls the photovoltaic power generation device 301 to prioritize power supply to the PEM electrolyzer 302, and inputs the remaining photovoltaic power after meeting the hydrogen production requirements into the liquid carbon dioxide energy storage and release unit 200, so that the compressor I 202 and compressor II 204 can run to complete carbon dioxide energy storage.

[0074] When the power generation of the photovoltaic power generation device 301 is lower than the minimum operating power requirement of the PEM electrolyzer 302, or when there is an external power supply requirement for the system, the energy management unit 700 controls the liquid carbon dioxide energy storage and release unit 200 to enter the energy release state, so that the carbon dioxide in the high-pressure tank 207 is pressurized, preheated, heated and expanded to do work through the carbon dioxide pump 208, preheater 209, heat exchanger III 210 and turbine I 211 in sequence.

[0075] The energy management unit 700 controls the carbon dioxide diversion device 212 to adjust the carbon dioxide flow ratio between the circulation branch and the synthesis branch based on the system power shortage, the liquid carbon dioxide storage status, the hydrogen storage in the hydrogen storage tank 304, and the methanol synthesis load of the methanol synthesis unit 500. When the carbon dioxide demand of the methanol synthesis unit 500 increases and the hydrogen storage in the hydrogen storage tank 304 meets the preset conditions, the energy management unit 700 controls the carbon dioxide diversion device 212 to increase the carbon dioxide flow rate entering the synthesis branch.

[0076] When the system power shortage increases, the demand for energy release and power generation increases, or the hydrogen storage in the hydrogen storage tank 304 is lower than the preset conditions, the energy management unit 700 controls the carbon dioxide diversion device 212 to increase the flow of carbon dioxide into the circulation branch, so that more carbon dioxide can continue to perform interstage reheating and secondary expansion work through heat exchanger IV 213 and turbine II 214.

[0077] The energy management unit 700 also controls the carbon capture unit 100 to replenish carbon dioxide to the liquid carbon dioxide energy storage and release unit 200 based on the amount of carbon dioxide consumed during the methanol synthesis process and the amount of carbon dioxide stored in the low-pressure tank 201 and the high-pressure tank 207, so as to maintain the working fluid balance in the carbon dioxide energy storage cycle.

[0078] In addition, the energy management unit 700 can coordinate the waste heat recovery water circulation, PEM electrolysis water supply, and solar thermal oil circulation based on the temperature of the hot water storage tank 601, the temperature of the cold water storage tank 602, the water volume and temperature of the PEM supply tank 603, and the thermal storage status of the solar thermal storage unit 400.

[0079] Through the above-described operation, this invention enables the captured carbon dioxide to serve both as the working fluid for liquid carbon dioxide energy storage and as a carbon source for methanol synthesis. By employing intermediate pressure diversion, reflux, and carbon capture replenishment, material coordination between the liquid carbon dioxide energy storage cycle and the methanol synthesis process is achieved. Simultaneously, this invention achieves synergistic utilization of electrical energy, thermal energy, hydrogen energy, and carbon resources through the synergistic coupling of subsystems including carbon capture, liquid carbon dioxide energy storage and release, photovoltaic hydrogen production, solar thermal storage, waste heat recovery, and methanol synthesis. This improves the capacity for renewable energy absorption, the level of carbon dioxide resource utilization, and the overall energy efficiency of the system. The basic principles, main features, and advantages of this invention have been shown and described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A split-flow carbon dioxide energy storage coupled methanol synthesis system, characterized in that, It includes a carbon capture unit (100), a liquid carbon dioxide energy storage and release unit (200), a photovoltaic PEM hydrogen production unit (300), a solar thermal storage unit (400), a methanol synthesis unit (500), a waste heat recovery unit (600), and an energy management unit (700). The carbon capture unit (100) is used to capture carbon dioxide. The carbon dioxide outlet of the carbon capture unit (100) is connected to the liquid carbon dioxide energy storage and release unit (200) for supplying the captured carbon dioxide to the liquid carbon dioxide energy storage and release unit (200). The photovoltaic PEM hydrogen production unit (300) includes a photovoltaic power generation device (301), a PEM electrolyzer (302), an oxygen storage tank (303), and a hydrogen storage tank (304). The photovoltaic power generation device (301) is electrically connected to the PEM electrolyzer (302) and the liquid carbon dioxide energy storage and release unit (200) respectively, and is used to supply power to the PEM electrolyzer (302). When the photovoltaic power generation exceeds the power demand of the PEM electrolyzer (302), it supplies power to the liquid carbon dioxide energy storage and release unit (200). The liquid carbon dioxide energy storage and release unit (200) is used to compress, cool, condense and store carbon dioxide in the energy storage state, and to make the stored carbon dioxide perform work to output electrical energy through pressurization, heat exchange and heating, and at least one stage of expansion in the energy release state. The output electrical energy is used to supplement the power demand of the PEM electrolyzer (302) or to supply power to the outside. The liquid carbon dioxide energy storage and release unit (200) is provided with a carbon dioxide diversion device (212) on the energy release expansion path to divide the carbon dioxide after at least one stage of expansion into a first part of carbon dioxide entering the circulation branch and a second part of carbon dioxide entering the synthesis branch. The circulation branch is connected to the subsequent expansion device and low-pressure side of the liquid carbon dioxide energy storage and release unit (200) to allow the first part of carbon dioxide entering the circulation branch to continue to expand and do work, and return to the liquid carbon dioxide energy storage and release unit (200) after temperature adjustment, so as to maintain the carbon dioxide energy storage cycle. The synthesis branch is connected to the feed gas pressure regulating and mixing unit (501) of the methanol synthesis unit (500) and is used to transport the second part of carbon dioxide entering the synthesis branch to the feed gas pressure regulating and mixing unit (501); the feed gas pressure regulating and mixing unit (501) is used to treat the second part of carbon dioxide by at least one of purification, pressure regulation, temperature regulation and flow metering, and mix the treated second part of carbon dioxide with hydrogen. The PEM electrolyzer (302) is used to electrolyze water to produce hydrogen using the electrical energy provided by the photovoltaic power generation device (301) and the electrical energy released by the liquid carbon dioxide energy storage and release unit (200). The hydrogen outlet of the PEM electrolyzer (302) is directly or via a hydrogen storage device connected to the raw material gas pressure regulating and mixing unit (501) to transport the hydrogen generated by water electrolysis to the raw material gas pressure regulating and mixing unit (501), so that the second part of carbon dioxide and hydrogen are mixed and then enter the methanol synthesis unit (500), and react to generate methanol under the action of a catalyst. The carbon dioxide diversion device (212) includes a diversion interface and flow regulating valves respectively disposed on the circulation branch and the synthesis branch, for adjusting the carbon dioxide flow ratio entering the circulation branch and the synthesis branch according to at least one of the methanol synthesis load of the methanol synthesis unit (500), the system hydrogen storage, the energy storage status of the liquid carbon dioxide energy storage and release unit (200) and the system power demand. When the carbon dioxide demand of the methanol synthesis unit (500) increases and the hydrogen storage in the hydrogen storage tank (304) meets the preset conditions, the carbon dioxide diversion device (212) is controlled to increase the carbon dioxide flow rate entering the synthesis branch; when the system power shortage increases, the demand for energy release power generation increases, or the hydrogen storage in the hydrogen storage tank (304) is lower than the preset conditions, the carbon dioxide diversion device (212) is controlled to increase the carbon dioxide flow rate entering the circulation branch. The carbon capture unit (100) is also used to replenish carbon dioxide to the liquid carbon dioxide storage and release unit (200) according to the amount of carbon dioxide consumed by the methanol synthesis unit (500); Based on the amount of carbon dioxide consumed by the methanol synthesis unit (500) and the amount of carbon dioxide working fluid in the liquid carbon dioxide energy storage and release unit (200), the carbon capture unit (100) is controlled to replenish carbon dioxide to the liquid carbon dioxide energy storage and release unit (200) so that the amount of carbon dioxide working fluid in the liquid carbon dioxide energy storage and release unit (200) is maintained within a preset range. The solar thermal storage unit (400) is connected to the liquid carbon dioxide energy storage and release unit (200) and is used to provide heat for heating carbon dioxide before expansion and interstage reheating during the energy release process. The waste heat recovery unit (600) is connected to the liquid carbon dioxide energy storage and release unit (200), the photovoltaic PEM hydrogen production unit (300), and the carbon capture unit (100) respectively. It is used to recover the heat released during the operation of the liquid carbon dioxide energy storage and release unit (200) and to use the recovered heat for at least one of the following: carbon dioxide preheating in the energy release stage, preheating or temperature maintenance of the electrolytic water in the PEM electrolyzer (302), and regeneration of the absorbent in the carbon capture unit (100). The energy management unit (700) is connected to the photovoltaic power generation device (301), the liquid carbon dioxide energy storage and release unit (200), the carbon dioxide diversion device (212), the PEM electrolyzer (302), the carbon capture unit (100), the solar thermal storage unit (400), the waste heat recovery unit (600), and the methanol synthesis unit (500) respectively, and is used to coordinate the photovoltaic power generation, carbon dioxide energy storage and release, solar heating, waste heat recovery, carbon dioxide diversion, carbon dioxide replenishment, photovoltaic hydrogen production, and methanol synthesis processes.

2. The split-flow carbon dioxide energy storage coupled methanol synthesis system according to claim 1, characterized in that, The liquid carbon dioxide energy storage and release unit (200) includes a low-pressure tank (201), compressor I (202), heat exchanger I (203), compressor II (204), heat exchanger II (205), condenser (206), high-pressure tank (207), carbon dioxide pump (208), preheater (209), heat exchanger III (210), turbine I (211), carbon dioxide diversion device (212), heat exchanger IV (213), turbine II (214), and cooler (215). The low-pressure tank (201), the compressor I (202), the heat exchanger I (203), the compressor II (204), the heat exchanger II (205), the condenser (206), and the high-pressure tank (207) are connected in sequence to perform buffering, multi-stage compression, cooling, condensation, and storage of carbon dioxide. The high-pressure tank (207), the carbon dioxide pump (208), the preheater (209), the heat exchanger III (210), and the turbine I (211) are connected in sequence to complete the pressurization, preheating, preheating before expansion, and first-stage expansion of carbon dioxide. The carbon dioxide diversion device (212) is located on the outlet side of the turbine I (211) and is connected to the circulation branch and the synthesis branch respectively; The circulation branch is connected in sequence to the heat exchanger IV (213), the turbine II (214), the cooler (215) and the low-pressure tank (201) to allow the first part of carbon dioxide to return to the low-pressure tank (201) after interstage reheating, secondary expansion and cooling. The water-side inlet of the cooler (215) is connected to the cooler inlet pipeline (W12), and the water-side outlet of the cooler (215) is connected to the reboiler (106) in the carbon capture unit (100) through the cooler to reboiler hot water supply pipeline (W13) to transfer the heat released by carbon dioxide after secondary expansion to the reboiler (106). The synthesis branch is connected to the feed gas pressure regulating and mixing unit (501) of the methanol synthesis unit (500) and is used to transport the second part of carbon dioxide to the feed gas pressure regulating and mixing unit (501).

3. The split-flow carbon dioxide energy storage coupled methanol synthesis system according to claim 2, characterized in that, The solar thermal storage unit (400) is connected to the heat exchanger III (210) and the heat exchanger IV (213) respectively, and is used to provide pre-expansion heating for carbon dioxide entering the turbine I (211) during the energy release phase, and to provide interstage reheat for carbon dioxide entering the turbine II (214).

4. The split-flow carbon dioxide energy storage coupled methanol synthesis system according to claim 3, characterized in that, The solar thermal storage unit (400) includes a solar collector (401), a hot oil tank (402), and a cold oil tank (403). The solar collector (401) is connected to the hot oil tank (402) and is used to heat the heat transfer oil and transport the heated high-temperature heat transfer oil to the hot oil tank (402). The hot oil tank (402) is connected to the heat transfer oil inlets of heat exchanger III (210) and heat exchanger IV (213) respectively, and is used to supply high temperature heat transfer oil to heat exchanger III (210) and heat exchanger IV (213); The heat transfer oil outlets of heat exchanger III (210) and heat exchanger IV (213) are connected to the cold oil tank (403), and the cold oil tank (403) is connected to the solar collector (401) to form a heat transfer oil circulation.

5. A split-flow carbon dioxide energy storage coupled methanol synthesis system according to claim 4, characterized in that, The waste heat recovery unit (600) includes a hot water storage tank (601), a cold water storage tank (602), a PEM water supply tank (603), and a water circulation pipeline; The cold water storage tank (602) is connected to the water-side inlet of heat exchanger I (203) and heat exchanger II (205) respectively, and the water-side outlet of heat exchanger I (203) and heat exchanger II (205) is connected to the hot water storage tank (601) for recovering the heat released during the compression and cooling of carbon dioxide. The hot water storage tank (601) is connected to the water-side inlet of the preheater (209), and the water-side outlet of the preheater (209) is connected to the cold water storage tank (602) to form a waste heat recovery water circulation. The water-side inlet of the condenser (206) is connected to the cold water storage tank (602), and the water-side outlet of the condenser (206) is connected to the PEM water supply tank (603), which is used to use the recovered condensation heat to preheat the electrolytic water of the PEM electrolyzer (302). The water-side inlet of the cooler (215) is connected to the water supply pipeline, and the water-side outlet of the cooler (215) is connected to the reboiler (106) to transfer the heat released by the carbon dioxide after the secondary expansion to the reboiler (106).

6. A split-flow carbon dioxide energy storage coupled methanol synthesis system according to claim 5, characterized in that, The photovoltaic PEM hydrogen production unit (300) includes a photovoltaic power generation device (301), a PEM electrolyzer (302), an oxygen storage tank (303), and a hydrogen storage tank (304). The photovoltaic power generation device (301) is electrically connected to the PEM electrolyzer (302) and the liquid carbon dioxide energy storage and release unit (200), respectively; The PEM electrolyzer (302) is used to electrolyze water to produce hydrogen using the electrical energy provided by the photovoltaic power generation device (301) and the electrical energy released by the liquid carbon dioxide energy storage and release unit (200). The hydrogen outlet of the PEM electrolyzer (302) is connected to the hydrogen storage tank (304), and the hydrogen storage tank (304) is connected to the feed gas pressure regulating and mixing unit (501) for supplying hydrogen to the methanol synthesis unit (500). The oxygen outlet of the PEM electrolyzer (302) is connected to the oxygen storage tank (303); The PEM water supply tank (603) is connected to the PEM electrolyzer (302) and is used to provide electrolysis water to the PEM electrolyzer (302).

7. A split-flow carbon dioxide energy storage coupled methanol synthesis system according to claim 6, characterized in that, The methanol synthesis unit (500) includes a feed gas pressure regulating and mixing unit (501), a methanol reactor (502), a separator (503), a methanol storage tank (504), and a water storage tank (505). The raw material gas pressure regulating and mixing unit (501) is connected to the synthesis branch and the hydrogen storage tank (304) respectively, and is used to receive the second part of carbon dioxide delivered by the synthesis branch and the hydrogen delivered by the hydrogen storage tank (304), and to perform at least one of the following treatments on the second part of carbon dioxide and hydrogen: purification, pressure regulation, temperature regulation, flow metering and mixing. The raw material gas pressure regulating and mixing unit (501) is connected to the methanol reactor (502); The methanol reactor (502) is used to hydrogenate carbon dioxide and hydrogen after they have been treated by the feed gas pressure regulating and mixing unit (501) under the action of a catalyst to produce methanol and water; The methanol reactor (502) is connected to the separator (503); The separator (503) is used to separate the reaction products output from the methanol reactor (502); The separator (503) is connected to the methanol storage tank (504) and the water storage tank (505) respectively, and is used to transport the separated methanol to the methanol storage tank (504) and the separated water to the water storage tank (505). The methanol synthesis unit (500) also includes an unreacted gas circulation line (35) for returning unreacted carbon dioxide and hydrogen separated by the separator (503) to the feed gas pressure regulating and mixing unit (501).

8. A split-flow carbon dioxide energy storage coupled methanol synthesis system according to claim 7, characterized in that, The energy management unit (700) is configured to: When the photovoltaic power generation of the photovoltaic power generation device (301) is greater than the set power requirement of the PEM electrolyzer (302), the photovoltaic power generation device (301) is controlled to supply power to the PEM electrolyzer (302) first, and the remaining electrical energy is input into the liquid carbon dioxide energy storage and release unit (200) for energy storage. When the photovoltaic power generation of the photovoltaic power generation device (301) is lower than the minimum operating power requirement of the PEM electrolyzer (302), or when there is an external power supply requirement for the system, the liquid carbon dioxide energy storage and release unit (200) is controlled to release energy and generate electricity. Based on at least one of the following: the energy storage status of the liquid carbon dioxide energy storage and release unit (200), the system power shortage, the available hydrogen storage of the photovoltaic PEM hydrogen production unit (300), and the methanol synthesis load of the methanol synthesis unit (500), the carbon dioxide diversion device (212) is controlled to adjust the carbon dioxide diversion ratio between the circulation branch and the synthesis branch.

9. The operation method of the split-flow carbon dioxide energy storage coupled methanol synthesis system as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Carbon dioxide is captured from a carbon dioxide-containing gas source through a carbon capture unit (100), and the captured carbon dioxide is transported to a liquid carbon dioxide energy storage and release unit (200) after being treated by at least one of purification, drying, compression and buffering. S2. Power is supplied to the PEM electrolyzer (302) by the electrical energy released by the photovoltaic power generation device (301) or the liquid carbon dioxide energy storage and release unit (200), so that the PEM electrolyzer (302) electrolyzes water to produce hydrogen, and the hydrogen is stored in the hydrogen storage tank (304). S3. When the photovoltaic power generation of the photovoltaic power generation device (301) is higher than the set power requirement of the PEM electrolyzer (302), the remaining photovoltaic power after meeting the hydrogen production requirements will be input into the liquid carbon dioxide energy storage and release unit (200), so that the carbon dioxide will be compressed, cooled and condensed from the low-pressure tank (201) through the compressor I (202), heat exchanger I (203), compressor II (204), heat exchanger II (205) and condenser (206), and stored in the high-pressure tank (207); S4. Water from the cold water storage tank (602) is introduced into heat exchanger I (203) and heat exchanger II (205) to recover the heat released during the compression and cooling of carbon dioxide, and the water after absorbing heat is stored in the hot water storage tank (601) to preheat the carbon dioxide after it has been pressurized by the carbon dioxide pump (208) through the preheater (209) during the energy release stage; water from the cold water storage tank (602) is introduced into the condenser (206) to recover the heat released during the condensation of carbon dioxide, and the water after absorbing heat is transported to the PEM water supply tank (603) to provide preheated electrolysis water to the PEM electrolyzer (302); S5. When the photovoltaic power generation of the photovoltaic power generation device (301) is lower than the minimum operating power requirement of the PEM electrolyzer (302), or when the system needs to output electrical energy, the carbon dioxide in the high-pressure tank (207) is pressurized, preheated and heated before expansion by the carbon dioxide pump (208), preheater (209) and heat exchanger III (210) in sequence, and then enters turbine I (211) to perform first-stage expansion and work, and the output electrical energy is used to supplement the power demand of the PEM electrolyzer (302) or to supply power to the outside. S6. The carbon dioxide after primary expansion by the turbine I (211) is transported to the carbon dioxide splitting device (212), and the carbon dioxide is divided into a first part of carbon dioxide entering the circulation branch and a second part of carbon dioxide entering the synthesis branch by the carbon dioxide splitting device (212). S7. The first part of carbon dioxide is reheated between stages by heat exchanger IV (213), expanded in two stages by turbine II (214) to do work, and cooled by cooler (215) before returning to the low-pressure tank (201) to maintain the carbon dioxide energy storage cycle. S8. Water is introduced into the cooler (215) through the cooler inlet line (W12) to absorb the heat released by carbon dioxide after secondary expansion, and is then transported to the reboiler (106) through the cooler to reboiler hot water supply line (W13) to provide at least part of the heat for the absorbent regeneration process of the carbon capture unit (100). S9. The second part of carbon dioxide is transported to the raw material gas pressure regulating and mixing unit (501) via the synthesis branch carbon dioxide pipeline (27), and the hydrogen in the hydrogen storage tank (304) is transported to the raw material gas pressure regulating and mixing unit (501) via the hydrogen to methanol synthesis pipeline (33). The raw material gas pressure regulating and mixing unit (501) performs at least one of the following treatments on the second part of carbon dioxide and hydrogen: purification, pressure regulation, temperature regulation, flow metering and mixing, and then transports the treated mixed raw material gas to the methanol reactor (502). S10. The second part of carbon dioxide and hydrogen are reacted in the methanol reactor (502) under the action of a catalyst to produce methanol and water. The reaction products are separated by a separator (503). The separated methanol is transported to a methanol storage tank (504), the separated water is transported to a water storage tank (505), and the unreacted carbon dioxide and hydrogen are recycled back to the raw material gas pressure regulating and mixing unit (501). S11. Based on the amount of carbon dioxide consumed during methanol synthesis, control the carbon capture unit (100) to replenish carbon dioxide to the liquid carbon dioxide energy storage and release unit (200), and adjust the flow ratio between the first part of carbon dioxide entering the circulation branch and the second part of carbon dioxide entering the synthesis branch according to at least one of the photovoltaic power generation, liquid carbon dioxide energy storage status, system power shortage, hydrogen storage in hydrogen storage tank (304) and methanol synthesis load of methanol synthesis unit (500).

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