Method and system for capturing carbon dioxide and method for synchronously capturing high-purity hydrogen and carbon dioxide

Abstract

The invention discloses a method and a system for capturing carbon dioxide and a method for synchronously capturing high-purity hydrogen and carbon dioxide, and the method for capturing carbon dioxide comprises the following steps: I, introducing raw material gas into an absorption rotating packed bed to form a rich solution, and discharging decarburized tail gas; iI, the rich solution exchanges heat and enters a desorption rotating packed bed to be desorbed, primary low-pressure carbon dioxide gas is formed, and the barren solution is recycled; iII, compressing and cooling the primary low-pressure carbon dioxide gas, and enabling the gas to enter a two-stage flash tank to realize gas-liquid separation; iV, high-purity liquid-phase carbon dioxide is compressed and subjected to heat exchange, and liquid electronic-grade high-purity carbon dioxide is prepared; and V, the gas-phase carbon dioxide and low-pressure carbon dioxide entering subsequently are converged, the step III and the step IV are repeated, and in the synchronous capturing method of the high-purity hydrogen and the carbon dioxide, decarburized tail gas is conveyed to a hydrogen production unit for preparing the high-purity hydrogen. According to the invention, the low-pressure and low-concentration feed gas can be processed into various high-purity carbon dioxide products and hydrogen products at the same time, and the occupied space and the cost are low.

Description

Technical Field

[0001] The present invention relates to the field of carbon dioxide capture and hydrogen capture, and in particular to a carbon dioxide capture method and system and a method for synchronously capturing high-purity hydrogen and carbon dioxide. Background Art

[0002] High-purity carbon dioxide is widely used as a standard substance, protective atmosphere, and working medium in scientific research and production such as medicine, food, gas chromatography, extraction, electric vacuum technology, laser, nuclear technology, metallurgy, energy, and chemical engineering. Electronic-grade carbon dioxide is weakly acidic. High-purity carbon dioxide is dissolved in deionized water. It can clean particles and oil stains remaining on the surface of silicon wafers and remove static electricity without secondary pollution. Electronic-grade high-purity carbon dioxide has a strong application scenario in the cleaning and drying process of semiconductors. With the rapid development of the semiconductor industry, the demand for electronic-grade high-purity carbon dioxide is expected to continue to rise. Therefore, it is urgent to provide an efficient and low-cost preparation method for electronic-grade high-purity carbon dioxide products.

[0003] Existing carbon capture technology uses a cryogenic distillation production process. Through raw material pretreatment, purification, and cryogenic distillation, a food-grade liquid carbon dioxide product with a purity of more than 99.9 vol% can usually be extracted. The carbon dioxide gas source used in this type of process is usually a high-pressure and high-concentration (>60 vol%) gas source, which generally comes from coal-to-syngas, natural gas reforming hydrogen production, petrochemical industry tail gas, etc.; For example, the invention patent with authorization announcement number CN104654739B provides a device and method for producing food-grade liquid carbon dioxide by double-tower distillation purification, including an air intake buffer tank outlet connected to the inlet of a four-stage compressor of raw gas, the outlet of the four-stage compressor of raw gas is connected to a two-stage distillation tower, and the gas phase outlet at the top of the two-stage distillation tower is connected to a tower top condenser The output liquid of the condenser is connected to the liquid phase inlet at the top of the distillation tower, and the liquid flowing out of the liquid phase outlet at the bottom of the distillation tower is output as a liquid phase carbon dioxide product through heat exchange. It has the advantages of simple process flow and stable operation, and can prepare a carbon dioxide product with a concentration of 99.99vol%. The purity of the electronic-grade carbon dioxide product must reach at least 5N level (99.999%). In order to further improve the purity of the product, the invention patent with publication number CN113277511A provides a production process for purifying synthesis gas to prepare electronic-grade high-purity carbon dioxide. Combined with wet decarbonization and cryogenic distillation process, an electronic-grade carbon dioxide product with a concentration of 99.999% is prepared. However, the high-purity carbon dioxide extraction of this process still cannot get rid of the cryogenic distillation separation process. Since the principle of cryogenic distillation separation is to utilize the different boiling points of various gas components in the raw gas, and to liquefy and purify the components to be separated step by step along the distillation tower by means of high-pressure cryogenics, the closer the boiling points of the gas components are, or the gas components contain components with extremely low boiling points, such as nitrogen, oxygen, hydrogen, etc., the more fillers or plates the distillation tower needs, the higher its operating pressure needs to be, and the lower the cryogenic temperature needs to be, so as to achieve the purpose of graded liquefaction and purification. More fillers / plates mean greater fixed asset investment, and higher pressure and lower temperature mean higher operating costs, all of which will increase the cost of gas separation. Therefore, this type of process is affected by cost and scale and has great limitations.

[0004] However, the content of low-boiling components (nitrogen, oxygen, hydrogen, etc.) in low-pressure (usually atmospheric pressure) and low-concentration carbon dioxide gas sources (3vol%-60vol%) is 40vol%-97vol%, which is much higher than the content of the same gas in high-pressure and high-concentration carbon dioxide gas sources (<40vol%). If carbon dioxide is to be purified from such gas sources, in addition to additional pressure to reach the appropriate operating pressure, greater cooling energy consumption is required to liquefy the low-boiling components. The food-grade carbon dioxide obtained in this way is not cost-competitive, which not only limits its potential for sales as a commodity, but also limits its possibility of being used as a raw material to prepare electronic-grade high-purity carbon dioxide.

[0005] In addition, the applicant found that in some specific hydrogen production processes, such as the off-gas of methanol cracking hydrogen production equipment and the tail gas of the biological industry, the content of carbon dioxide and hydrogen is relatively high. According to the changes in process conditions and operating parameters, the volume fractions of hydrogen and carbon dioxide in these industrial waste gases are usually close to 50%, and other impurities include trace amounts of water vapor and carbon monoxide. In some industrial waste gases, the content of hydrogen is even higher than that of carbon dioxide. Hydrogen is a very important raw material for petrochemicals, coal chemicals, and fine chemicals. With the rapid development of the petrochemical industry and the petrochemical industry with three major synthetic materials as the core, the demand for hydrogen has risen sharply. Many industries, such as organic synthesis, metallurgy, and electronics, have huge demands for high-purity hydrogen. However, since this type of industrial waste gas is usually a normal pressure gas source, in the existing technology, the commonly used membrane separation and pressure swing adsorption hydrogen extraction processes all require the raw gas to be compressed and pressurized for pretreatment, and then the pressurized raw gas is subjected to membrane separation or multiple pressure adjustment treatments, and the hydrogen is purified by the driving force of the pressure difference. However, this type of compression method has extremely high energy consumption and the cost of the hydrogen extraction process is relatively high. Therefore, at present, this type of hydrogen-rich exhaust gas is directly discharged into the atmosphere, which not only wastes potential hydrogen resources but also is not conducive to environmental protection.

[0006] Therefore, for this type of industrial waste gas rich in both hydrogen and carbon dioxide, it is necessary to provide a method for simultaneously recovering hydrogen and carbon dioxide. Summary of the invention

[0007] Therefore, in order to solve the above problems, the present invention provides a carbon dioxide capture method, system and a method for synchronously capturing high-purity hydrogen and carbon dioxide.

[0008] The present invention is achieved through the following technical solutions: A method for capturing carbon dioxide comprises the following steps: Ⅰ: The raw gas containing carbon dioxide is passed into the absorption rotating packed bed, so that the raw gas contacts with the special absorbent in the absorption rotating packed bed under the action of centrifugal force, so that the special absorbent absorbs the carbon dioxide in the raw gas to form a rich liquid, and the decarbonized tail gas is discharged; II: The rich liquid formed in step I is heated through a lean-rich liquid heat exchanger to form a hot rich liquid, and enters a desorption rotating packed bed for desorption. The absorbent regeneration energy is introduced into the desorption rotating packed bed to separate the carbon dioxide in the rich liquid from the absorbent. The separated carbon dioxide is dehydrated to form a primary low-pressure carbon dioxide gas of ≥99.9%. The separated absorbent lean liquid re-enters the lean-rich liquid heat exchanger for heat exchange, and forms a cold lean liquid after heat exchange, and re-flows into the absorption rotating packed bed for recycling as an absorbent; III: The primary low-pressure carbon dioxide gas obtained in step II is compressed and cooled, and then enters a two-stage flash tank in sequence to separate the gas-liquid phase, and forms high-purity liquid carbon dioxide and gaseous carbon dioxide after separation; IV: compressing and heat exchanging the high-purity liquid carbon dioxide obtained in step III to obtain a liquid electronic grade high-purity carbon dioxide product; V: The gaseous carbon dioxide obtained in step III is combined with the low-pressure carbon dioxide gas that enters subsequently, and steps III and IV are repeated.

[0009] Preferably, the method further comprises step III': compressing and cooling the primary low-pressure carbon dioxide gas obtained in step II to prepare a food-grade liquid carbon dioxide product; The step III' is carried out simultaneously with the step III, wherein a part of the primary low-pressure carbon dioxide gas obtained in the step II enters the food-grade extraction unit and is directly made into a food-grade liquid carbon dioxide product after the step III', and the other part enters the electronic-grade extraction unit and is processed through the steps III to V to make a liquid electronic-grade high-purity carbon dioxide product.

[0010] Preferably, step III also includes: the primary low-pressure carbon dioxide gas passes through a first flash tank for a first gas-liquid two-phase separation, and outputs gaseous carbon dioxide and liquid carbon dioxide, wherein the liquid carbon dioxide passes through a pressure reducing valve and then enters a second flash tank for a second gas-liquid two-phase separation, and after separation, high-purity liquid carbon dioxide and gaseous carbon dioxide are formed, and the high-purity liquid carbon dioxide is subjected to the operation of step IV, and the gaseous carbon dioxide obtained by the two gas-liquid two-phase separations is mixed through a mixing valve and then subjected to the operation of step V.

[0011] Preferably, the special absorbent is a ternary system absorbent consisting of a main absorbent, an organic solvent and water, wherein the main absorbent is piperazine, accounting for 30wt%-50wt% of the total mass percentage; the organic solvent is an organic polar solvent that can dissolve piperazine, does not react with piperazine and is miscible with water, accounting for 0.1wt%-50wt% of the total mass percentage; and the remaining components are water.

[0012] Preferably, the "raw gas containing carbon dioxide" in step I is a carbon dioxide gas source at normal pressure and with a concentration of 3 vol%-60 vol%, including but not limited to the purge gas from a methanol cracking hydrogen purification device.

[0013] A method for synchronously capturing high-purity hydrogen and carbon dioxide comprises the following steps: S1: introducing a raw gas containing hydrogen and carbon dioxide into an absorption rotating packed bed, so that the raw gas contacts with a special absorbent in the absorption rotating packed bed under the action of centrifugal force, so that the special absorbent absorbs carbon dioxide in the raw gas to form a rich liquid, and the decarbonized hydrogen-rich tail gas is transported to a hydrogen production unit; S2: The rich liquid formed in step S1 is heated through a lean-rich liquid heat exchanger to form a hot rich liquid, and enters a desorption rotating packed bed for desorption. The absorbent regeneration energy is introduced into the desorption rotating packed bed to separate the carbon dioxide in the rich liquid from the absorbent. The separated carbon dioxide is dehydrated to form a primary low-pressure carbon dioxide gas of ≥99.9%. The separated absorbent lean liquid re-enters the lean-rich liquid heat exchanger for heat exchange, and forms a cold lean liquid after heat exchange, and re-flows into the absorption rotating packed bed for recycling as an absorbent; S3: After the primary low-pressure carbon dioxide gas obtained in step S2 is compressed and cooled, it enters the two-stage flash tank in sequence to achieve gas-liquid two-phase separation, and after separation, high-purity liquid carbon dioxide and gaseous carbon dioxide are formed; S4: compressing and heat exchanging the high-purity liquid carbon dioxide obtained in step S3 to obtain a liquid electronic grade high-purity carbon dioxide product; S5: the gaseous carbon dioxide obtained in step S3 is combined with the low-pressure carbon dioxide gas that enters subsequently, and steps S3 and S4 are repeated; The method further comprises step S2': compressing, cooling and purifying the decarbonized hydrogen-rich tail gas transported to the hydrogen production unit to remove trace impurities in the decarbonized hydrogen-rich tail gas to produce a high-purity hydrogen product; step S2' is performed simultaneously with step S2.

[0014] A carbon dioxide capture system, including: a low-pressure purification unit and an electronic-grade extraction unit; The low-pressure purification unit is used to extract a primary low-pressure carbon dioxide product, including an absorption rotating packed bed for absorbing carbon dioxide, a desorption rotating packed bed for desorbing carbon dioxide, and a lean-rich liquid heat exchanger arranged between the absorption rotating packed bed and the desorption rotating packed bed, the absorption rotating packed bed includes a raw gas inlet and a decarbonization tail gas outlet, and the absorption rotating packed bed contains a special absorbent, the desorption rotating packed bed includes a regeneration energy inlet and a primary low-pressure carbon dioxide gas outlet, and the solution between the absorption rotating packed bed and the desorption rotating packed bed is heat exchanged through the lean-rich liquid heat exchanger; The electronic-grade extraction unit includes a heat exchange device and a cooling device. The output channel of the cooling device is connected to a two-stage flash evaporation device, and the gas phase outlets of the two-stage flash evaporation devices converge and circulate into the heat exchange device. The liquid phase outlet of the second-stage flash evaporation device is connected to a compression device, and the compression device is connected to the electronic-grade liquid carbon dioxide outlet.

[0015] Preferably, the electronic-grade extraction unit includes a first compressor connected to the outlet of the low-pressure purification unit, the outlet of the first compressor is connected to the first inlet of the first heat exchanger, the first outlet of the first heat exchanger is connected to the first inlet of the second heat exchanger, the first outlet of the second heat exchanger is connected to the inlet of the first cooling device, the outlet of the first cooling device is connected to the inlet of the first flash tank, the first outlet of the first flash tank is connected to the inlet of the second flash tank, the second outlet of the first flash tank and the first outlet of the second flash tank are merged through a mixing valve, and the merged gas path is connected to the second inlet of the first heat exchanger, the second outlet of the second flash tank is connected to the inlet of the first pressurizing device, the outlet of the first pressurizing device is connected to the second inlet of the second heat exchanger, the second heat exchanger is also provided with an electronic-grade liquid carbon dioxide outlet, and a pressure reducing valve is provided between the two-stage flash devices.

[0016] Preferably, it also includes a food-grade extraction unit that is synchronously arranged with the electronic-grade extraction unit, and the food-grade extraction unit includes a second compressor connected to the second outlet of the first heat exchanger, the outlet of the second compressor is connected to the inlet of a second cooling device, the outlet of the second cooling device is connected to the inlet of a second pressurizing device, and the outlet of the second pressurizing device outputs food-grade liquid carbon dioxide.

[0017] Preferably, the special absorbent is a ternary system absorbent composed of a main absorbent, an organic solvent and water, wherein the main absorbent is piperazine, accounting for 30wt%-50wt% of the total mass percentage; the organic solvent is an organic polar solvent that can dissolve piperazine, does not react with piperazine and is miscible with water, accounting for 0.1wt%-50wt% of the total mass percentage; and the remaining components are water.

[0018] The beneficial effects of the technical solution of the present invention are mainly reflected in: 1. A two-stage rotating packed bed is used to complete the initial purification of low-concentration carbon dioxide gas source (3vol%-60vol%). The source range of the raw gas is wide and the cost is low. Without the need for deep-cold distillation process, ≥99.9% of primary low-pressure carbon dioxide gas can be obtained. Subsequently, through further purification, electronic grade high-purity carbon dioxide products can be obtained. Among them, the rotating packed bed is a device that uses centrifugal action to enhance the gas-liquid mass transfer process. Under the action of centrifugal force, the liquid flows out from the rotating packed bed through the packing to the outside, so that efficient countercurrent contact occurs between the gas and the liquid. In the high-speed rotating annular rotator, the strong centrifugal force is used to make the gas-liquid film thinner, the mass transfer resistance is reduced, and the mass transfer rate and processing capacity of the equipment are enhanced. At the same time, the rotating packed bed has the characteristics of high efficiency and low cost compared with the tower equipment. Therefore, the use of a rotating packed bed can effectively reduce the cost of carbon capture, improve the carbon capture efficiency, and reduce the floor space, so as to minimize the time and cost of on-site installation.

[0019] 2. After using a rotating packed bed to purify carbon dioxide to low-pressure carbon dioxide of ≥99.9vol%, it can be further processed into electronic-grade high-purity carbon dioxide products through a refining process. The refining process only uses a two-stage flash evaporation device instead of a traditional distillation tower. This not only reduces capital investment and operating costs, but its modular installation method also further enhances the flexibility of carbon capture and expands product categories. It can produce food-grade (≥99.9vol%) carbon dioxide products and electronic-grade (≥99.9996vol%) carbon dioxide products at the same time.

[0020] 3. A pressure reducing valve is provided between the two-stage flash evaporation devices to reduce the pressure at the liquid phase inlet of the second-stage flash evaporation device, thereby reducing the liquid temperature, and then achieving gas-liquid phase equilibrium between the components in the original liquid phase, so that more non-carbon dioxide components flash into the gas phase, and further separate the gas-liquid phases through the second-stage flash evaporation device, thereby achieving the purpose of further purifying carbon dioxide.

[0021] 4. The absorption rotating packed bed uses a special absorbent, with piperazine (PZ) as the main agent, which has high absorption speed, high absorption capacity, high thermal stability and high anti-oxidation stability. By adjusting the ratio of organic solvent and water in the high concentration piperazine solution, the solid (H+PZCOO - ∙H 2 O) precipitation, ensuring that the solid precipitated in the solution is always within the solubility range of the solution, thereby avoiding precipitation of the solution, changing the gas-liquid phase equilibrium in the piperazine-water-carbon dioxide system, expanding the upper limit of the operation of enriching carbon dioxide, and making the special absorbent used in the present invention have a higher carbon dioxide circulation absorption capacity than the existing chemical absorbent.

[0022] 5. Aiming at the off-gas of methanol cracking hydrogen production unit with high content of carbon dioxide and hydrogen and the tail gas of biological industry, we provide the preparation process of high-purity carbon dioxide product and high-purity hydrogen product at the same time. On the one hand, the preparation of high-purity hydrogen and carbon dioxide can be carried out simultaneously. The special absorbent in the absorption rotating packed bed contacts the raw gas under the action of centrifugal force, which can realize the efficient decarbonization of the raw gas, purify the hydrogen while extracting carbon dioxide, and then obtain high-purity (≥99vol%) hydrogen product by simple compression and cooling to remove trace impurities, thereby improving the recovery efficiency and reducing the energy consumption of hydrogen production. On the other hand, it can effectively utilize hydrogen resources and reduce waste gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic flow diagram of the carbon dioxide capture method; Figure 2 It is a working schematic diagram of the low-pressure purification unit; Figure 3 It is a working schematic diagram of the electronic grade extraction unit and the food grade extraction unit; Figure 4 This is a comparison chart of experimental data of carbon dioxide absorption of the special absorbent used in the present invention and the existing absorbent; Figure 5 This is a comparison chart of experimental data of carbon dioxide velocity of the special absorbent used in the present invention and the existing absorbent; Figure 6 It is a schematic flow diagram of a method for simultaneous capture of high-purity hydrogen and carbon dioxide. DETAILED DESCRIPTION

[0024] In order to make the purpose, advantages and features of the present invention more clearly and in detail, the following preferred embodiments are used for illustration and explanation. The embodiments are only typical examples of the application of the technical solution of the present invention. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection claimed by the present invention.

[0025] It is also stated that in the description of the scheme, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying the order of importance, or implicitly indicating the number of technical features shown. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0026] The present invention discloses a method for capturing carbon dioxide, such as Figure 1-Figure 3 As shown, the following steps are included: Ⅰ: If Figure 2 As shown, the raw gas containing carbon dioxide is introduced into the absorption rotating packed bed 1, so that the raw gas contacts with the special absorbent in the absorption rotating packed bed 1 under the action of centrifugal force, so that the special absorbent absorbs the carbon dioxide in the raw gas to form a rich liquid, and the decarbonized tail gas is discharged; Among them, after the raw gas enters the absorption rotating packed bed 1, according to the gas-liquid flow ratio, the gas and the special absorbent can contact in a forward, reverse, or cross-current manner, and the carbon dioxide in the gas is selectively absorbed by the special absorbent to form a rich liquid. In a preferred embodiment, when the absorption rotating packed bed 1 is started, the special absorbent flows out from the rotating packed bed through the packing under the action of centrifugal force, and the raw gas is continuously input into the absorption rotating packed bed 1, so that efficient countercurrent contact occurs between the gas and the liquid. In the high-speed rotating annular rotator, the strong centrifugal force is used to make the gas-liquid film thinner, reduce the mass transfer resistance, and enhance the mass transfer rate and processing capacity of the equipment.

[0027] According to the hydrogen content in the exhaust gas after decarbonization, it can be decided whether the exhaust gas after decarbonization is directly discharged or reused as fuel in the process flow. When the exhaust gas after decarbonization needs to be reused as fuel, a tail gas storage device can be connected to the exhaust gas outlet of the absorption rotating packed bed 1, or a hydrogen purification device can be further set up, which will not be elaborated here.

[0028] In some embodiments, the special absorbent can be organic amines and their mixtures, ionic liquids, mixtures of organic amines and ionic liquids, etc. In one embodiment, the special absorbent is a ternary system absorbent composed of a main absorbent, an organic solvent and water, wherein the main absorbent is piperazine, accounting for 30wt%-50wt% of the total mass percentage; the organic solvent is an organic polar solvent that can dissolve piperazine, does not react with piperazine and is miscible with water, accounting for 0.1wt%-50wt% of the total mass percentage; the remaining components are water.

[0029] In a preferred embodiment, the organic solvent is an organic polar solvent that can dissolve piperazine, does not react with piperazine and is miscible with water, has a melting point of ≤28°C, a boiling point of ≥150°C, and accounts for 5wt%-10wt% of the total mass percentage; the remaining components are all water; the organic solvent is dimethylformamide or cyclopentane sulfone, and under the condition of temperature ≤25°C, when the carbon dioxide loading of the absorbent reaches 0.1 mol CO2 / mol basic group, the absorbent remains in liquid state, and a mixed gas containing carbon dioxide is contacted with the carbon dioxide absorbent, and the carbon dioxide absorbent absorbs carbon dioxide to form a rich amine liquid, and the rich amine liquid is converted into a lean amine liquid after the carbon dioxide in the rich amine liquid is extracted by high-temperature regeneration, and the lean amine liquid is repeatedly used as an absorbent.

[0030] like Figure 4 , Figure 5 As shown, two kinds of special absorbents with different proportions, high-concentration piperazine aqueous solution, and the commonly used amine absorbent representative (ethanolamine) and composite amine absorbent representative (piperazine / N-methyldiethanolamine) in the prior art were used for carbon dioxide absorption comparison experiment and absorption kinetics comparison experiment. Among them, high-concentration piperazine (concentration of 40wt%) has obviously better carbon dioxide absorption performance than the amine absorbent representative (ethanolamine) and composite amine absorbent representative (piperazine / N-methyldiethanolamine) in the experiment. However, high-concentration piperazine aqueous solution has certain defects: when piperazine, water and carbon dioxide come into contact, as carbon dioxide is absorbed, when the water content in the absorbent is high, hydrogen ions (H + ) and bicarbonate (HCO 3 - ) increases, bicarbonate reacts with piperazine to generate piperazine carbamate (PZCOO -) and water, while the protonated piperazine carbamate reacts with water to form a solid precipitate H + PZCOO - ∙H 2 O; such as Figure 4 , Figure 5 As shown in the figure, in the case of adding two organic solvents with different ratios, the performance of the special absorbent of the present invention is significantly improved compared with the high concentration piperazine aqueous solution. This is because the organic solvent in the special absorbent of the present invention has a good solubility for piperazine and its solid precipitate. At the same time, the solid precipitate H can be further reduced by replacing part of the water with the organic solvent. + PZCOO - ∙H 2 O generation, thus further improving the carbon dioxide absorption and regeneration effects compared to conventional high-concentration piperazine aqueous solutions. Figure 4 , Figure 5 The organic solvent used in the experiment is sulfolane, which has a sulfonyl group and two double bonds between sulfur and oxygen. The sulfur-oxygen double bond is a strong polar bond, which makes sulfolane very soluble in water. Among them, the applicant learned through experiments that the carbon dioxide absorbent obtained by using 30wt%-50wt% piperazine, 0.1wt%-50wt% dimethylformamide and the balance of water has a carbon dioxide content of 0.1mol CO2 / mol alkaline group at room temperature (25°C), which is more than 50% lower than the 0.25mol CO2 / mol alkaline group of the high concentration piperazine solvent; and the carbon dioxide absorbent obtained by using 30wt%-50wt% piperazine, 0.1wt%-50wt% sulfolane and the balance of water only needs to load 0.1molCO2 / mol alkaline group of carbon dioxide to remain in liquid state below 0°C, so in these two embodiments, under the condition of temperature ≤25°C, when the carbon dioxide loading of the absorbent reaches 0.1mol When the absorbent is mol CO2 / mol basic group, the absorbent remains in liquid state.

[0031] like Figure 2 As shown, II: the rich liquid formed in step I is heated by the lean-rich liquid heat exchanger to form a hot rich liquid, and enters the desorption rotating packed bed 2 for desorption, and the absorbent regeneration energy is introduced into the desorption rotating packed bed 2 to separate the carbon dioxide in the rich liquid from the absorbent, and the separated carbon dioxide is dehydrated to form a primary low-pressure carbon dioxide gas of ≥99.9%, and the separated absorbent lean liquid re-enters the lean-rich liquid heat exchanger for heat exchange, and forms a cold lean liquid after heat exchange, and re-flows into the absorption rotating packed bed 1 as an absorbent for recycling; In some embodiments, step II usually uses steam as the energy for desorption of the absorbent. By inputting high-temperature steam into the desorption rotating packed bed 2, the chemical reaction between carbon dioxide and the absorbent is reversed, and the carbon dioxide is desorbed from the absorbent and output through the gas phase channel of the desorption rotating packed bed 2. The water is then removed through a condenser to obtain a gaseous carbon dioxide product with a concentration of ≥99.9 vol%. The rich liquid output from step I passes through a lean-rich liquid heat exchanger to form a hot rich liquid, and enters the desorption rotating packed bed 2 to desorb carbon dioxide. After the desorption is completed, the lean liquid is cooled to a cold lean liquid through the lean-rich liquid heat exchanger, and enters the absorption rotating packed bed 1 as an absorbent again, completing a cycle of absorption and desorption.

[0032] like Figure 1 , Figure 3 As shown, III: the primary low-pressure carbon dioxide gas obtained in step II is compressed and cooled, and then enters a two-stage flash tank in sequence to achieve gas-liquid two-phase separation, and after separation, high-purity liquid carbon dioxide and gaseous carbon dioxide are formed.

[0033] Specifically, due to the low internal pressure of the flash tank, the primary low-pressure carbon dioxide gas enters the flash tank after being compressed and cooled, causing some light components to vaporize instantly. Among them, the gas with lower density naturally rises to the top of the flash tank due to buoyancy, while the liquid or droplets with higher density settle to the bottom of the flash tank due to gravity, thereby achieving gas-liquid two-phase separation.

[0034] IV: After the high-purity liquid carbon dioxide obtained in step III is compressed and heat-exchanged, a liquid electronic-grade high-purity carbon dioxide product is obtained. The purity of the electronic-grade liquid carbon dioxide product can reach more than 99.9996 vol%, which fully meets the demand for electronic-grade high-purity carbon dioxide products.

[0035] V: The gaseous carbon dioxide obtained in step III is combined with the low-pressure carbon dioxide gas that enters subsequently, and steps III and IV are repeated; Wherein, step V refers to combining the gaseous carbon dioxide obtained in step III with the subsequently entering low-pressure carbon dioxide gas as the raw material for the next purification.

[0036] In some embodiments, step III' is also included: the primary low-pressure carbon dioxide gas obtained in step II is compressed and cooled to produce a food-grade liquid carbon dioxide product; step III' is performed simultaneously with step III. In this embodiment, a part of the primary low-pressure carbon dioxide gas obtained in step II enters the food-grade extraction unit, and is directly produced into a food-grade liquid carbon dioxide product after step III', and the other part enters the electronic-grade extraction unit and is processed through steps III to V to produce a liquid electronic-grade high-purity carbon dioxide product. Therefore, carbon dioxide products of different purities can be obtained simultaneously, thereby achieving flexibility in carbon dioxide processing and improving the utilization rate of carbon dioxide.

[0037] In some embodiments, step III also includes: the primary low-pressure carbon dioxide gas passes through the first flash tank 7 for a first gas-liquid two-phase separation, and outputs gaseous carbon dioxide and liquid carbon dioxide, wherein the liquid carbon dioxide is reduced in pressure by the pressure reducing valve and enters the second flash tank 8 for a second gas-liquid two-phase separation, and high-purity liquid carbon dioxide and gaseous carbon dioxide are formed after separation, and the high-purity liquid carbon dioxide is subjected to the operation of step IV, and the gaseous carbon dioxide obtained by the two gas-liquid two-phase separations is mixed through the mixing valve 9 and then subjected to the operation of step V, and the pressure of the liquid at the inlet of the second flash tank 8 is reduced by the pressure reducing valve, thereby reducing its temperature, and then achieving gas-liquid phase equilibrium of the components in the original liquid phase, so that more non-carbon dioxide components flash into the gas phase, and then the gas-liquid two phases are separated by the second flash tank 8 to achieve the purpose of further purifying the carbon dioxide.

[0038] In some embodiments, the "raw gas containing carbon dioxide" in step I is a carbon dioxide gas source at normal pressure and a concentration of 3 vol%-60 vol%, including the relaxation gas of a methanol cracking hydrogen purification device. In other embodiments, the "raw gas containing carbon dioxide" in step I can also use a high-concentration carbon dioxide gas source, which will not be elaborated here.

[0039] like Figure 6 As shown, for industrial waste gas generated by a specific hydrogen production process, such as the off-gas of a methanol cracking hydrogen production device and the tail gas of the biological industry, which contains a large amount of hydrogen and carbon dioxide, especially a low-pressure (usually normal pressure) hydrogen and carbon dioxide gas source (hydrogen and carbon dioxide volume fractions are each about 50%), the present invention also discloses a method for synchronously capturing high-purity hydrogen and carbon dioxide, comprising the following steps: S1: introducing a raw gas containing hydrogen and carbon dioxide into an absorption rotating packed bed, so that the raw gas contacts with a special absorbent in the absorption rotating packed bed under the action of centrifugal force, so that the special absorbent absorbs carbon dioxide in the raw gas to form a rich liquid, and the decarbonized hydrogen-rich tail gas is transported to a hydrogen production unit; S2: The rich liquid formed in step S1 is heated through a lean-rich liquid heat exchanger to form a hot rich liquid, and enters a desorption rotating packed bed for desorption. The absorbent regeneration energy is introduced into the desorption rotating packed bed to separate the carbon dioxide in the rich liquid from the absorbent. The separated carbon dioxide is dehydrated to form a primary low-pressure carbon dioxide gas of ≥99.9%. The separated absorbent lean liquid re-enters the lean-rich liquid heat exchanger for heat exchange, and forms a cold lean liquid after heat exchange, and re-flows into the absorption rotating packed bed for recycling as an absorbent; S3: After the primary low-pressure carbon dioxide gas obtained in step S2 is compressed and cooled, it enters the two-stage flash tank in sequence to achieve gas-liquid two-phase separation, and after separation, high-purity liquid carbon dioxide and gaseous carbon dioxide are formed; S4: compressing and heat exchanging the high-purity liquid carbon dioxide obtained in step S3 to obtain a liquid electronic grade high-purity carbon dioxide product; S5: the gaseous carbon dioxide obtained in step S3 is combined with the low-pressure carbon dioxide gas that enters subsequently, and steps S3 and S4 are repeated; The process further comprises step S2': compressing, cooling and purifying the decarbonized hydrogen-rich tail gas delivered to the hydrogen production unit, removing trace amounts of water and impurities such as carbon dioxide in the decarbonized hydrogen-rich tail gas, and producing a high-purity hydrogen product; in one embodiment, "compressing, cooling and purifying the decarbonized hydrogen-rich tail gas delivered to the hydrogen production unit" means: compressing and cooling the decarbonized hydrogen-rich tail gas until part of the gas is liquefied; then further cooling the gas to a temperature close to the liquefaction temperature, so that other gases (such as nitrogen, methane, carbon monoxide, water vapor, etc.) except hydrogen are liquefied, while hydrogen remains in a gaseous state due to its low boiling point, thereby achieving hydrogenation through gas-liquid separation. Purification of gas; in addition, the decarbonized hydrogen-rich tail gas can also be brought into contact with the tower plate or filler, so that the volatile hydrogen in the liquid phase is gradually enriched in the gas phase, and the non-volatile components are enriched in the liquid phase, so as to achieve the separation of hydrogen and obtain high-purity hydrogen; since the raw gas contains hydrogen and carbon dioxide as the main components, and the raw gas is decarbonized after passing through the absorption rotating packed bed, there are only trace amounts of impurity gases in the decarbonized tail gas in addition to hydrogen, and these impurity gases can be separated from hydrogen after compression, cooling and low-temperature distillation purification, so as to achieve the purification of high-purity hydrogen and finally obtain a high-purity hydrogen product (≥99vol%).

[0040] The step S2' is performed synchronously with the step S2.

[0041] In the method for simultaneous capture of high-purity hydrogen and carbon dioxide, the method for capturing carbon dioxide can refer to the corresponding steps in the above-mentioned method for capturing carbon dioxide, wherein the special absorbent can adopt the ternary system absorbent composed of the main absorbent, organic solvent and water as described above, and can also adopt other organic amines and their mixed liquids, ionic liquids, mixed liquids of organic amines and ionic liquids, etc.

[0042] The present invention also discloses a carbon dioxide capture system, comprising: a low-pressure purification unit and an electronic-grade extraction unit; The low-pressure purification unit is used to extract a primary low-pressure carbon dioxide product, including an absorption rotating packed bed 1 for absorbing carbon dioxide, a desorption rotating packed bed 2 for desorbing carbon dioxide, and a lean-rich liquid heat exchanger arranged between the absorption rotating packed bed 1 and the desorption rotating packed bed 2, wherein the absorption rotating packed bed 1 includes a raw gas inlet and a decarbonized tail gas outlet, and the absorption rotating packed bed 1 contains a special absorbent, and the desorption rotating packed bed 2 includes a regeneration energy inlet and a primary low-pressure carbon dioxide gas outlet, and the solution between the absorption rotating packed bed 1 and the desorption rotating packed bed 2 is heat exchanged through the lean-rich liquid heat exchanger; The electronic-grade extraction unit includes a heat exchange device and a cooling device. The output channel of the cooling device is connected to a two-stage flash evaporation device, and the gas phase outlets of the two-stage flash evaporation devices converge and circulate into the heat exchange device. The liquid phase outlet of the second-stage flash evaporation device is connected to a compression device, and the compression device is connected to the electronic-grade liquid carbon dioxide outlet. In a preferred embodiment, a pressure reducing valve is provided between the two-stage flash evaporation devices.

[0043] In some embodiments, the decarbonized tail gas output port of the absorption rotating packed bed 1 is also connected to a hydrogen production unit for synchronously extracting hydrogen from the decarbonized tail gas, and is suitable for situations where the raw gas contains a large amount of hydrogen and carbon dioxide, such as the off-gas from a methanol cracking hydrogen production device and the tail gas from the biological industry, etc. The hydrogen production unit includes a compression device, a cooling device and a purification device; in one embodiment, the compression device may use a compressor, and the cooling device may use a condenser. At the same time, since the boiling point of hydrogen is extremely low (-252.8°C) and the boiling points of other gases are relatively high, they are easy to separate. Therefore, the purification device uses a low-temperature distillation device, and through the different boiling points between the gases, the trace impurity gases (such as nitrogen, methane, carbon monoxide, water vapor, etc.) other than hydrogen in the decarbonized tail gas are separated during the cooling process, thereby achieving the extraction of high-purity hydrogen; first, the decarbonized tail gas passes through the compression device and the cooling device After that, it is compressed and cooled to a low temperature to liquefy part of the gas in preparation for subsequent separation; then, a low-temperature distillation device is used to further cool the gas to a temperature close to the liquefaction temperature, so that other gases (such as nitrogen, methane, etc.) except hydrogen are liquefied, while hydrogen remains in a gaseous state due to its low boiling point; in the distillation tower, the gas-liquid mixture can also contact with the tower plate or filler, so that the volatile hydrogen in the liquid phase is gradually enriched to the gas phase, and the non-volatile components are enriched to the liquid phase, so as to achieve the separation of hydrogen and obtain high-purity hydrogen. Since hydrogen and carbon dioxide are the main components in the raw gas, and the raw gas is decarbonized after passing through the absorption rotating packed bed 1, there are only trace amounts of impurity gases in the decarbonized tail gas except hydrogen, and these impurity gases can be separated from hydrogen after compression, cooling and low-temperature distillation purification, so as to achieve the purification of high-purity hydrogen; the purified hydrogen product can also be compressed and stored for subsequent use.

[0044] like Figure 3As shown, in some embodiments, the electronic-grade extraction unit includes a first compressor 3 connected to the outlet of the low-pressure purification unit, the outlet of the first compressor 3 is connected to the first inlet of the first heat exchanger 4, the first outlet of the first heat exchanger 4 is connected to the first inlet of the second heat exchanger 5, the first outlet of the second heat exchanger 5 is connected to the inlet of the first cooling device 6, the outlet of the first cooling device 6 is connected to the inlet of the first flash tank 7, the first outlet of the first flash tank 7 is connected to the inlet of the second flash tank 8, the second outlet of the first flash tank 7 and the first outlet of the second flash tank 8 are merged through a mixing valve 9, and the merged gas path is connected to the second inlet of the first heat exchanger 4, the second outlet of the second flash tank 8 is connected to the inlet of the first pressurizing device 10, the outlet of the first pressurizing device 10 is connected to the second inlet of the second heat exchanger 5, and the second heat exchanger 5 is also provided with an electronic-grade liquid carbon dioxide outlet.

[0045] Figure 3 S1 in Figure 2 The gaseous carbon dioxide product with a volume of ≥99.9 vol% outputted from the desorption rotating packed bed 2 is compressed by the first compressor 3 to form S2. After S2 is inputted into the first heat exchanger 4 for heat exchange, a part of it forms S14 and enters the second heat exchanger 5. After further heat exchange, S14 forms gas S9, which is then cooled by the first cooling device 6 to form liquid S3. After S3 is inputted into the first flash tank 7, a part of it forms gas S4 and the other part forms liquid S5. After being depressurized by the pressure reducing valve, it becomes liquid S6, which is then outputted into the second flash tank 8. The second flash tank 8 outputs gas S7 and liquid S8 at the same time. Among them, gas S4 and gas S7 converge through the mixing valve 9 and flow into the first heat exchanger 4 again, while liquid S8 is compressed by the first pressurizing device 10 to form S12. Finally, liquid electronic grade high-purity carbon dioxide S10 is outputted after heat exchange by the second heat exchanger 5.

[0046] like Figure 1 , Figure 3 As shown, in some embodiments, a food-grade extraction unit is also included that is synchronously arranged with the electronic-grade extraction unit, and the food-grade extraction unit includes a second compressor 11 connected to the second outlet of the first heat exchanger 4, the outlet of the second compressor 11 is connected to the inlet of a second cooling device 12, the outlet of the second cooling device 12 is connected to the inlet of a second pressurizing device 13, and the outlet of the second pressurizing device 13 outputs food-grade liquid carbon dioxide.

[0047] Figure 3In the process, after the first heat exchanger 4 exchanges heat with S2, another part forms gas S13, which is compressed by the second compression device to form high-pressure gas S15, and then cooled by the second cooling device 12 until liquid S16 is formed, and finally processed by the second pressurizing device 13 to output food-grade carbon dioxide S17.

[0048] In some embodiments, the first cooling device 6 and the second cooling device 12 are both condensers, and the first pressurizing device 10 and the second pressurizing device 13 are both liquid pumps.

[0049] In one embodiment, the special absorbent is a ternary system absorbent composed of a main absorbent, an organic solvent and water, wherein the main absorbent is piperazine, accounting for 30wt%-50wt% of the total mass percentage; the organic solvent is an organic polar solvent that can dissolve piperazine, does not react with piperazine and is miscible with water, accounting for 0.1wt%-50wt% of the total mass percentage; the remaining components are water, such as Figure 4 , Figure 5 As shown in the figure, high concentration piperazine has better carbon dioxide absorption performance than common amine and complex amine absorbents. However, high concentration piperazine aqueous solution has certain defects: when piperazine, water and carbon dioxide come into contact, as carbon dioxide is absorbed, the hydrogen ion (H + ) and bicarbonate (HCO 3 - ) increases, bicarbonate reacts with piperazine to generate piperazine carbamate (PZCOO - ) and water, while the protonated piperazine carbamate reacts with water to form a solid precipitate H + PZCOO - ∙H 2 O; such as Figure 4 , Figure 5 As shown in the figure, in the case of adding two organic solvents with different ratios, the performance of the special absorbent of the present invention is significantly improved compared with the high concentration piperazine aqueous solution. This is because the organic solvent in the special absorbent of the present invention has a good solubility for piperazine and its solid precipitate. At the same time, the solid precipitate H can be further reduced by replacing part of the water with the organic solvent. + PZCOO - ∙H 2 O generation, thus further improving the carbon dioxide absorption and regeneration effects compared to conventional high-concentration piperazine aqueous solutions. Figure 4 , Figure 5 The organic solvent used in the experiment was sulfolane.

[0050] There are many implementation methods of the present invention, and all technical solutions formed by equivalent transformation or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for capturing carbon dioxide, characterized in that: The steps include: Ⅰ: The raw gas containing carbon dioxide is passed into the absorption rotating packed bed, so that the raw gas contacts with the special absorbent in the absorption rotating packed bed under the action of centrifugal force, so that the special absorbent absorbs the carbon dioxide in the raw gas to form a rich liquid, and the decarbonized tail gas is discharged; II: The rich liquid formed in step I is heated through a lean-rich liquid heat exchanger to form a hot rich liquid, and enters a desorption rotating packed bed for desorption. The absorbent regeneration energy is introduced into the desorption rotating packed bed to separate the carbon dioxide in the rich liquid from the absorbent. The separated carbon dioxide is dehydrated to form a primary low-pressure carbon dioxide gas of ≥99.9%. The separated absorbent lean liquid re-enters the lean-rich liquid heat exchanger for heat exchange, and forms a cold lean liquid after heat exchange, and re-flows into the absorption rotating packed bed for recycling as an absorbent; III: The primary low-pressure carbon dioxide gas obtained in step II is compressed and cooled, and then enters a two-stage flash tank in sequence to separate the gas-liquid phase, and forms high-purity liquid carbon dioxide and gaseous carbon dioxide after separation; IV: compressing and heat exchanging the high-purity liquid carbon dioxide obtained in step III to obtain a liquid electronic grade high-purity carbon dioxide product; V: The gaseous carbon dioxide obtained in step III is combined with the low-pressure carbon dioxide gas that enters subsequently, and steps III and IV are repeated.

2. The method for capturing carbon dioxide according to claim 1, characterized in that: The step also includes step III': compressing and cooling the primary low-pressure carbon dioxide gas obtained in step II to produce a food-grade liquid carbon dioxide product; The step III' is carried out simultaneously with the step III, wherein a part of the primary low-pressure carbon dioxide gas obtained in the step II enters the food-grade extraction unit and is directly made into a food-grade liquid carbon dioxide product after the step III', and the other part enters the electronic-grade extraction unit and is processed through the steps III to V to make a liquid electronic-grade high-purity carbon dioxide product.

3. The carbon dioxide capture method according to claim 1, characterized in that: Step III also includes: the primary low-pressure carbon dioxide gas passes through the first flash tank for the first gas-liquid two-phase separation, and outputs gaseous carbon dioxide and liquid carbon dioxide, wherein the liquid carbon dioxide is reduced in pressure by the pressure reducing valve and then enters the second flash tank for the second gas-liquid two-phase separation, and after separation, high-purity liquid carbon dioxide and gaseous carbon dioxide are formed, and the high-purity liquid carbon dioxide is subjected to the operation of step IV, and the gaseous carbon dioxide obtained by the two gas-liquid two-phase separations is mixed through a mixing valve and then subjected to the operation of step V.

4. The carbon dioxide capture method according to claim 1, characterized in that: The special absorbent is a ternary system absorbent composed of a main absorbent, an organic solvent and water, wherein the main absorbent is piperazine, accounting for 30wt%-50wt% of the total mass percentage; the organic solvent is an organic polar solvent that can dissolve piperazine, does not react with piperazine and is miscible with water, accounting for 0.1wt%-50wt% of the total mass percentage; the remaining components are water.

5. The carbon dioxide capture method according to claim 1, characterized in that: The "raw gas containing carbon dioxide" in step I is a carbon dioxide gas source at normal pressure and a concentration of 3 vol%-60 vol%, including but not limited to the purge gas from a methanol cracking hydrogen purification device.

6. A method for synchronously capturing high-purity hydrogen and carbon dioxide, characterized in that: The steps include: S1: introducing a raw gas containing hydrogen and carbon dioxide into an absorption rotating packed bed, so that the raw gas contacts with a special absorbent in the absorption rotating packed bed under the action of centrifugal force, so that the special absorbent absorbs carbon dioxide in the raw gas to form a rich liquid, and the decarbonized hydrogen-rich tail gas is transported to a hydrogen production unit; S2: The rich liquid formed in step S1 is heated through a lean-rich liquid heat exchanger to form a hot rich liquid, and enters a desorption rotating packed bed for desorption. The absorbent regeneration energy is introduced into the desorption rotating packed bed to separate the carbon dioxide in the rich liquid from the absorbent. The separated carbon dioxide is dehydrated to form a primary low-pressure carbon dioxide gas of ≥99.9%. The separated absorbent lean liquid re-enters the lean-rich liquid heat exchanger for heat exchange, and forms a cold lean liquid after heat exchange, and re-flows into the absorption rotating packed bed for recycling as an absorbent; S3: After the primary low-pressure carbon dioxide gas obtained in step S2 is compressed and cooled, it enters the two-stage flash tank in sequence to achieve gas-liquid two-phase separation, and after separation, high-purity liquid carbon dioxide and gaseous carbon dioxide are formed; S4: compressing and heat exchanging the high-purity liquid carbon dioxide obtained in step S3 to obtain a liquid electronic grade high-purity carbon dioxide product; S5: the gaseous carbon dioxide obtained in step S3 is combined with the low-pressure carbon dioxide gas that enters subsequently, and steps S3 and S4 are repeated; The method further comprises step S2': compressing, cooling and purifying the decarbonized hydrogen-rich tail gas transported to the hydrogen production unit to remove trace impurities in the decarbonized hydrogen-rich tail gas to produce a high-purity hydrogen product; step S2' is performed simultaneously with step S2.

7. A carbon dioxide capture system, characterized in that: include: Low-pressure purification units and electronic-grade extraction units; The low-pressure purification unit is used to extract a primary low-pressure carbon dioxide product, including an absorption rotating packed bed for absorbing carbon dioxide, a desorption rotating packed bed for desorbing carbon dioxide, and a lean-rich liquid heat exchanger arranged between the absorption rotating packed bed and the desorption rotating packed bed, the absorption rotating packed bed includes a raw gas inlet and a decarbonization tail gas outlet, and the absorption rotating packed bed contains a special absorbent, the desorption rotating packed bed includes a regeneration energy inlet and a primary low-pressure carbon dioxide gas outlet, and the solution between the absorption rotating packed bed and the desorption rotating packed bed is heat exchanged through the lean-rich liquid heat exchanger; The electronic-grade extraction unit includes a heat exchange device and a cooling device. The output channel of the cooling device is connected to a two-stage flash evaporation device, and the gas phase outlets of the two-stage flash evaporation devices converge and circulate into the heat exchange device. The liquid phase outlet of the second-stage flash evaporation device is connected to a compression device, and the compression device is connected to the electronic-grade liquid carbon dioxide outlet.

8. The carbon dioxide capture system according to claim 7, characterized in that: The electronic-grade extraction unit comprises a first compressor connected to the outlet of the low-pressure purification unit, the outlet of the first compressor is connected to the first inlet of the first heat exchanger, the first outlet of the first heat exchanger is connected to the first inlet of the second heat exchanger, the first outlet of the second heat exchanger is connected to the inlet of the first cooling device, the outlet of the first cooling device is connected to the inlet of the first flash tank, the first outlet of the first flash tank is connected to the inlet of the second flash tank, the second outlet of the first flash tank and the first outlet of the second flash tank are merged through a mixing valve, and the merged gas path is connected to the second inlet of the first heat exchanger, the second outlet of the second flash tank is connected to the inlet of the first pressurizing device, the outlet of the first pressurizing device is connected to the second inlet of the second heat exchanger, the second heat exchanger is also provided with an electronic-grade liquid carbon dioxide outlet, and a pressure reducing valve is provided between the two-stage flash devices.

9. The carbon dioxide capture system according to claim 8, characterized in that: It also includes a food-grade extraction unit that is synchronously arranged with the electronic-grade extraction unit, and the food-grade extraction unit includes a second compressor connected to the second outlet of the first heat exchanger, the outlet of the second compressor is connected to the inlet of a second cooling device, the outlet of the second cooling device is connected to the inlet of a second pressurizing device, and the outlet of the second pressurizing device outputs food-grade liquid carbon dioxide.

10. The carbon dioxide capture system according to claim 7, characterized in that: The special absorbent is a ternary system absorbent composed of a main absorbent, an organic solvent and water, wherein the main absorbent is piperazine, accounting for 30wt%-50wt% of the total mass percentage; the organic solvent is an organic polar solvent that can dissolve piperazine, does not react with piperazine and is miscible with water, accounting for 0.1wt%-50wt% of the total mass percentage; the remaining components are water.

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