System and method for purifying pollutants in flue gas and capturing carbon dioxide

Abstract

The present invention discloses a system and method for purifying pollutants in flue gas and capturing carbon dioxide, wherein the system comprises: a sulfur dioxide and nitrogen monoxide separation unit, whose input end is connected to a flexible peak-shaving coal-fired power unit, for separating sulfur dioxide and nitrogen monoxide gases from the flue gas generated by the unit, and outputting the remaining flue gas; a nitrogen dioxide separation unit, whose input end is connected to the output end of the sulfur dioxide and nitrogen monoxide separation unit, for separating nitrogen dioxide gas from the output flue gas, and outputting the remaining flue gas; a carbon dioxide purification unit, whose input end is connected to the output end of the nitrogen dioxide separation unit, for purifying the output flue gas to obtain a mixed gas containing carbon dioxide; a capture unit, whose input end is connected to the output end of the carbon dioxide purification unit, for extracting the mixed gas containing carbon dioxide to obtain carbon dioxide gas, and discharging the remaining flue gas. The system can remove pollutants and carbon dioxide.

Description

Technical Field

[0001] The present invention relates to the field of flue gas purification, and in particular to a system and method for purifying pollutants in flue gas and capturing carbon dioxide. Background Art

[0002] In recent years, my country has begun to vigorously develop new energy power generation represented by wind power and photovoltaic power. However, these power sources are unstable, random and volatile, which brings challenges to the flexible peak-shaving of the power grid. Therefore, traditional thermal power units are in urgent need of flexible peak-shaving transformation and vigorously improve the flexibility of coal-fired power units. Coal-fired power units need fossil fuels such as coal and natural gas as fuel supply. The combustion of fossil fuels will produce flue gas pollutants (mainly SO2 and NO x ) and CO2 emissions. In order to ensure the net zero emission of pollutants and carbon dioxide from the flexible peak-shaving coal-fired power units, in the existing technology, desulfurization is carried out first, then denitrification, and finally carbon dioxide is removed; desulfurization requires the addition of some reducing catalysts (such as limestone and calcium oxide), and then denitrification also requires the addition of some reducing catalysts (such as urea), and finally a catalyst is added to remove carbon dioxide. The process is relatively complicated, the catalyst cannot be reused, the cost is relatively high, and the removed carbon dioxide is directly discharged, wasting resources.

[0003] With regard to the existing technology of removing pollutants and carbon dioxide by adding catalysts, the process is complex, the cost is high, and the removed carbon dioxide is directly discharged, which wastes resources. No effective solution has been proposed so far. Summary of the invention

[0004] The embodiment of the present invention provides a system and method for purifying pollutants in flue gas and capturing carbon dioxide to solve the problem that in the prior art, pollutants and carbon dioxide are removed by adding catalysts, the process is complex and costly, and the removed carbon dioxide is directly discharged, wasting resources.

[0005] To achieve the above-mentioned purpose, on the one hand, the present invention provides a system for purifying pollutants in flue gas and capturing carbon dioxide, wherein the pollutants include: sulfur dioxide, nitric oxide, and nitrogen dioxide; the system includes: a sulfur dioxide and nitric oxide separation unit, whose input end is connected to the flexible peak-shaving coal-fired power unit, for separating sulfur dioxide and nitric oxide gases in the flue gas generated by the flexible peak-shaving coal-fired power unit, and outputting the remaining flue gas; a nitrogen dioxide separation unit, wherein the input end of the nitrogen dioxide separation unit is connected to the output end of the sulfur dioxide and nitric oxide separation unit, for separating nitrogen dioxide gas in the flue gas output from the sulfur dioxide and nitric oxide separation unit, and outputting the remaining flue gas; a carbon dioxide purification unit, wherein the input end of the carbon dioxide purification unit is connected to the output end of the nitrogen dioxide separation unit, for purifying the flue gas output from the nitrogen dioxide separation unit to obtain a mixed gas containing carbon dioxide; a capture unit, wherein the input end of the capture unit is connected to the output end of the carbon dioxide purification unit, for extracting the mixed gas containing carbon dioxide to obtain carbon dioxide gas, and discharging the remaining flue gas.

[0006] Optionally, the capture unit includes: an absorption tower, the input end of the absorption tower is connected to the output end of the carbon dioxide purification unit, and is used to absorb the mixed gas containing carbon dioxide to generate a liquid rich in carbon dioxide, and output it from its first output end, and discharge the remaining flue gas from its second output end; a lean-rich liquid heat exchanger, the input end of the lean-rich liquid heat exchanger is connected to the first output end of the absorption tower, and is used to heat the output carbon dioxide-rich liquid and output the heated liquid; a regeneration tower, the input end of the regeneration tower is connected to the output end of the lean-rich liquid heat exchanger, and is used to desorb the output heated liquid to regenerate the carbon dioxide gas therein.

[0007] Optionally, the sulfur dioxide and nitrogen monoxide separation unit comprises: a molecular sieve membrane having a selective catalytic effect on sulfur dioxide and nitrogen monoxide gases; the pore size of the molecular sieve membrane having a selective catalytic effect on sulfur dioxide and nitrogen monoxide gases is 2.8 to 3.17 angstroms.

[0008] Optionally, the nitrogen dioxide separation unit comprises: a molecular sieve membrane having a selective catalytic effect on nitrogen dioxide gas; the pore size of the molecular sieve membrane having a selective catalytic effect on nitrogen dioxide gas is 3.3 angstroms.

[0009] Optionally, the carbon dioxide purification unit includes: a graphene inorganic membrane, which is used to perform a first purification on the flue gas output from the nitrogen dioxide separation unit to obtain a first mixed gas containing carbon dioxide; and the channel of the graphene inorganic membrane is 3.3 to 3.6 angstroms.

[0010] Optionally, the carbon dioxide purification unit also includes: a first separation membrane, the input end of the first separation membrane is connected to the output end of the graphene inorganic membrane, and is used to purify the first mixed gas containing carbon dioxide for a second time to obtain a second mixed gas containing carbon dioxide; a second separation membrane, the input end of the second separation membrane is connected to the output end of the first separation membrane, and is used to purify the second mixed gas containing carbon dioxide for a third time to obtain the mixed gas containing carbon dioxide.

[0011] Optionally, it also includes: a first gas storage tank, a second gas storage tank, and a third gas storage tank.

[0012] Optionally, the input end of the first gas storage tank is connected to the output end of the sulfur dioxide and nitrogen monoxide separation unit; the input end of the second gas storage tank is connected to the output end of the nitrogen dioxide separation unit; and the third gas storage tank is arranged between the first separation membrane and the second separation membrane.

[0013] On the other hand, the present invention provides a method for purifying pollutants in flue gas and capturing carbon dioxide. The method adopts the above-mentioned system for purifying pollutants in flue gas and capturing carbon dioxide, and includes the following steps: S101, inputting the flue gas generated by the flexible peak-shaving coal-fired power unit into a sulfur dioxide and nitric oxide separation unit to separate the sulfur dioxide and nitric oxide gases in the flue gas, and outputting the remaining flue gas; S102, separating the nitrogen dioxide gas in the flue gas output from the sulfur dioxide and nitric oxide separation unit through a nitrogen dioxide separation unit, and outputting the remaining flue gas; S103, purifying the flue gas output from the nitrogen dioxide separation unit through a carbon dioxide purification unit to obtain a mixed gas containing carbon dioxide; S104, extracting the mixed gas containing carbon dioxide through a capture unit to obtain carbon dioxide gas, and discharging the remaining flue gas.

[0014] Beneficial effects of the present invention:

[0015] The present invention provides a system and method for purifying pollutants in flue gas and capturing carbon dioxide. The system can quickly remove sulfur dioxide, nitrogen monoxide, nitrogen dioxide and carbon dioxide by designing a sulfur dioxide and nitrogen monoxide separation unit, a nitrogen dioxide separation unit and a carbon dioxide purification unit to replace the catalyst in the prior art, simplifying the process; and can be reused without using a large amount of catalyst, saving costs. The removed carbon dioxide is captured and purified by the capture unit instead of being directly discharged and wasted, making full use of resources.

[0016] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are specifically cited below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is a structural schematic diagram of a system for purifying pollutants in flue gas and capturing carbon dioxide;

[0019] Figure 2 The present invention is a flow chart of a method for purifying pollutants in flue gas and capturing carbon dioxide.

[0020] Explanation of symbols:

[0021] Sulfur dioxide and nitrogen monoxide separation unit-1, nitrogen dioxide separation unit-2, carbon dioxide purification unit-3, absorption tower-4, lean and rich liquid heat exchanger-5, regeneration tower-6, first gas storage tank-7, second gas storage tank-8, third gas storage tank-9, flexible peak-shaving coal-fired power unit-10, first output terminal-41, second output terminal-42. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] In order to ensure the net zero emission of pollutants and carbon dioxide from the flexible peak-shaving coal-fired power units, in the existing technology, desulfurization is first carried out, then denitrification, and finally carbon dioxide is removed; desulfurization requires the addition of some reducing catalysts (such as limestone and calcium oxide), and then denitrification also requires the addition of some reducing catalysts (such as urea), and finally the addition of catalysts to remove carbon dioxide. The process is relatively complicated, the catalyst cannot be reused, the cost is relatively high, and the removed carbon dioxide is directly discharged, wasting resources.

[0024] Therefore, the present invention provides a system for purifying pollutants in flue gas and capturing carbon dioxide. Figure 1 is a schematic diagram of the structure of a system for purifying pollutants in flue gas and capturing carbon dioxide provided by an embodiment of the present invention, such as Figure 1 As shown, the pollutants are mainly sulfur dioxide SO2 and nitrogen oxides NO x , NOx It is mainly nitrogen dioxide NO2 and nitric oxide NO, in addition there are small amounts of nitrogen pentoxide N2O5, nitrogen trioxide N2O3 and nitrous oxide N2O, but they are extremely unstable and will turn into NO2 or NO when exposed to light or heat.

[0025] The system includes:

[0026] A sulfur dioxide and nitrogen monoxide separation unit 1, whose input end is connected to the flexible peak-shaving coal-fired power unit, is used to separate sulfur dioxide and nitrogen monoxide gases in the flue gas generated by the flexible peak-shaving coal-fired power unit and output the remaining flue gas;

[0027] Specifically, the sulfur dioxide and nitrogen monoxide separation unit 1 comprises: a molecular sieve membrane having a selective catalytic effect on sulfur dioxide and nitrogen monoxide gases; the pore size of the molecular sieve membrane is 2.8 to 3.17 angstroms.

[0028] The kinetic diameter of the sulfur dioxide gas is 2.8 angstroms, and the kinetic diameter of the nitrogen monoxide gas is 3.17 angstroms; the pore size of the metal ion modified molecular sieve membrane that has a selective catalytic effect on sulfur dioxide and nitrogen monoxide gases is 2.8 to 3.17 angstroms, so it can just separate the sulfur dioxide and nitrogen monoxide gases in the flue gas.

[0029] A nitrogen dioxide separation unit 2, wherein the input end of the nitrogen dioxide separation unit 2 is connected to the output end of the sulfur dioxide and nitrogen monoxide separation unit 1, and is used to separate the nitrogen dioxide gas from the flue gas output from the sulfur dioxide and nitrogen monoxide separation unit 1, and output the remaining flue gas;

[0030] Specifically, the nitrogen dioxide separation unit 2 comprises: a molecular sieve membrane having a selective catalytic effect on nitrogen dioxide gas; the pore size of the molecular sieve membrane is 3.3 angstroms.

[0031] The kinetic diameter of the nitrogen dioxide gas is 3.3 angstroms, and the kinetic diameter of the carbon dioxide gas is 3.3 angstroms. The metal ion modified molecular sieve membrane that has a selective catalytic effect on nitrogen dioxide gas has a pore size of 3.3 angstroms and only has a selective catalytic effect on nitrogen dioxide gas, so it can just separate the nitrogen dioxide gas from the remaining flue gas.

[0032] a carbon dioxide purification unit 3, wherein the input end of the carbon dioxide purification unit 3 is connected to the output end of the nitrogen dioxide separation unit 2, and is used to purify the flue gas output from the nitrogen dioxide separation unit 2 to obtain a mixed gas containing carbon dioxide;

[0033] Specifically, the carbon dioxide purification unit 3 includes: a graphene inorganic membrane, which is used to purify the flue gas output from the nitrogen dioxide separation unit 2 for the first time to obtain a first mixed gas containing carbon dioxide; the channel of the graphene inorganic membrane is 3.3 to 3.6 angstroms.

[0034] After the pollutants (SO2, NO and NO2) are removed, the flue gas enters the carbon dioxide purification unit 3. Since the content of water and other substances in the flue gas is relatively high, the present invention proposes to use a graphene inorganic membrane with good flue gas tolerance to purify the carbon dioxide in the flue gas. Since the kinetic diameter of carbon dioxide is 3.3 angstroms, and the kinetic diameter of nitrogen in the flue gas is 3.64 angstroms, the channel of the graphene inorganic membrane is 3.3 to 3.6 angstroms, so the graphene inorganic membrane can be used to selectively separate the carbon dioxide gas to obtain a first mixed gas containing carbon dioxide; at this time, the concentration of carbon dioxide is relatively low, so it is necessary to purify it twice through a two-stage membrane process to raise the concentration of carbon dioxide to more than 40 vol%. The two-stage membranes are: a first separation membrane and a second separation membrane;

[0035] The input end of the first separation membrane is connected to the output end of the graphene inorganic membrane, and is used to purify the first mixed gas containing carbon dioxide for a second time to obtain a second mixed gas containing carbon dioxide;

[0036] The input end of the second separation membrane is connected to the output end of the first separation membrane, and is used to purify the second mixed gas containing carbon dioxide for a third time to obtain the mixed gas containing carbon dioxide.

[0037] The concentration of carbon dioxide in the mixed gas containing carbon dioxide obtained after passing through the first separation membrane and the second separation membrane can reach 40 vol% or more.

[0038] A capture unit, the input end of which is connected to the output end of the carbon dioxide purification unit 3, is used to extract the mixed gas containing carbon dioxide to obtain carbon dioxide gas, and discharge the remaining flue gas.

[0039] After passing through the carbon dioxide purification unit 3, the pollutants in the flue gas have been basically removed and the carbon dioxide content in the flue gas has reached more than 40 vol%, so it is suitable to adopt chemical absorption method for efficient capture and regeneration (that is, the mixed gas containing carbon dioxide is extracted through the capture unit to obtain carbon dioxide gas).

[0040] Specifically, the capture unit includes:

[0041] An absorption tower 4, wherein the input end of the absorption tower 4 is connected to the output end of the carbon dioxide purification unit, and is used to absorb the mixed gas containing carbon dioxide, generate a liquid rich in carbon dioxide, and output it from its first output end, and discharge the remaining flue gas from its second output end;

[0042] A lean-rich liquid heat exchanger 5, wherein the input end of the lean-rich liquid heat exchanger 5 is connected to the first output end of the absorption tower 4, and is used to heat the output carbon dioxide-rich liquid and output the heated liquid;

[0043] The regeneration tower 6 has an input end connected to the output end of the lean-rich liquid heat exchanger 5 and is used to desorb the output heated liquid to regenerate the carbon dioxide gas therein.

[0044] In the present invention, by increasing the carbon dioxide content in the flue gas, the capture efficiency and rate of the capture unit for carbon dioxide in the flue gas can be increased, the size of equipment such as the absorption tower 4 can be reduced, the investment cost can be reduced, and the capture and operation costs can also be reduced.

[0045] In an optional embodiment, the flue gas pollutant purification and carbon dioxide capture system further includes: a first gas storage tank, a second gas storage tank, and a third gas storage tank.

[0046] Specifically, the input end of the first gas storage tank is connected to the output end of the sulfur dioxide and nitric oxide separation unit 1, and is used to store the flue gas output from the sulfur dioxide and nitric oxide separation unit 1; the input end of the second gas storage tank is connected to the output end of the nitrogen dioxide separation unit 2, and is used to store the flue gas output from the nitrogen dioxide separation unit 2; the third gas storage tank is arranged between the first separation membrane and the second separation membrane, and is used to store the second mixed gas containing carbon dioxide obtained after purification by the first separation membrane.

[0047] Since the load of the flexible peak-shaving coal-fired power unit changes greatly and at a fast rate, the flue gas flow rate generated by it changes rapidly. Therefore, the sulfur dioxide and nitric oxide membrane separation unit is equipped with a first gas storage tank, the nitrogen dioxide separation unit 2 is equipped with a second gas storage tank, and the carbon dioxide purification unit 3 is equipped with a third gas storage tank to store the input flue gas with a fast flow rate change rate and output the flue gas stably as required. This setting can well adapt to the flue gas with a fast flow rate change rate, thereby reducing the impact of the rapidly changing flue gas flow on the capture unit and ensuring the stability of the mixed gas containing carbon dioxide at the input end of the capture unit.

[0048] Figure 2A method for purifying pollutants in flue gas and capturing carbon dioxide is provided in an embodiment of the present invention. The method adopts the above-mentioned system for purifying pollutants in flue gas and capturing carbon dioxide, and comprises the following steps:

[0049] S101, inputting the flue gas generated by the flexible peak-shaving coal-fired power unit into the sulfur dioxide and nitrogen monoxide separation unit 1 to separate the sulfur dioxide and nitrogen monoxide gases in the flue gas, and outputting the remaining flue gas;

[0050] Specifically, the sulfur dioxide and nitrogen monoxide separation unit 1 comprises: a molecular sieve membrane having a selective catalytic effect on sulfur dioxide and nitrogen monoxide gases; the pore size of the molecular sieve membrane is 2.8 to 3.17 angstroms.

[0051] The kinetic diameter of the sulfur dioxide gas is 2.8 angstroms, and the kinetic diameter of the nitrogen monoxide gas is 3.17 angstroms; the pore size of the metal ion modified molecular sieve membrane that has a selective catalytic effect on sulfur dioxide and nitrogen monoxide gases is 2.8 to 3.17 angstroms, so it can just separate the sulfur dioxide and nitrogen monoxide gases in the flue gas.

[0052] S102, separating the nitrogen dioxide gas in the flue gas outputted from the sulfur dioxide and nitrogen monoxide separation unit 1 through the nitrogen dioxide separation unit 2, and outputting the remaining flue gas;

[0053] Specifically, the nitrogen dioxide separation unit 2 comprises: a molecular sieve membrane having a selective catalytic effect on nitrogen dioxide gas; the pore size of the molecular sieve membrane is 3.3 angstroms.

[0054] The kinetic diameter of the nitrogen dioxide gas is 3.3 angstroms, and the kinetic diameter of the carbon dioxide gas is 3.3 angstroms. The metal ion modified molecular sieve membrane that has a selective catalytic effect on nitrogen dioxide gas has a pore size of 3.3 angstroms and only has a selective catalytic effect on nitrogen dioxide gas, so it can just separate the nitrogen dioxide gas from the remaining flue gas.

[0055] S103, purifying the flue gas output from the nitrogen dioxide separation unit 2 through the carbon dioxide purification unit 3 to obtain a mixed gas containing carbon dioxide;

[0056] Specifically, the carbon dioxide purification unit 3 includes: a graphene inorganic membrane, which is used to purify the flue gas output from the nitrogen dioxide separation unit 2 for the first time to obtain a first mixed gas containing carbon dioxide; the channel of the graphene inorganic membrane is 3.3 to 3.6 angstroms.

[0057] After the pollutants (SO2, NO and NO2) are removed, the flue gas enters the carbon dioxide purification unit 3. Since the content of water and other substances in the flue gas is relatively high, the present invention proposes to use a graphene inorganic membrane with good flue gas tolerance to purify the carbon dioxide in the flue gas. Since the kinetic diameter of carbon dioxide is 3.3 angstroms, and the kinetic diameter of nitrogen in the flue gas is 3.64 angstroms, the channel of the graphene inorganic membrane is 3.3 to 3.6 angstroms, so the graphene inorganic membrane can be used to selectively separate the carbon dioxide gas to obtain a first mixed gas containing carbon dioxide; at this time, the concentration of carbon dioxide is relatively low, so it is necessary to purify it twice through a two-stage membrane process to raise the concentration of carbon dioxide to more than 40 vol%. The two-stage membranes are: a first separation membrane and a second separation membrane;

[0058] The input end of the first separation membrane is connected to the output end of the graphene inorganic membrane, and is used to purify the first mixed gas containing carbon dioxide for a second time to obtain a second mixed gas containing carbon dioxide;

[0059] The input end of the second separation membrane is connected to the output end of the first separation membrane, and is used to purify the second mixed gas containing carbon dioxide for a third time to obtain the mixed gas containing carbon dioxide.

[0060] The concentration of carbon dioxide in the mixed gas containing carbon dioxide obtained after passing through the first separation membrane and the second separation membrane can reach 40 vol% or more.

[0061] S104, extracting the mixed gas containing carbon dioxide through a capture unit to obtain carbon dioxide gas, and discharging the remaining flue gas.

[0062] After passing through the carbon dioxide purification unit 3, the pollutants in the flue gas have been basically removed and the carbon dioxide content in the flue gas has reached more than 40 vol%, so it is suitable to adopt chemical absorption method for efficient capture and regeneration (that is, the mixed gas containing carbon dioxide is extracted through the capture unit to obtain carbon dioxide gas).

[0063] Beneficial effects of the present invention:

[0064] The present invention provides a system and method for purifying pollutants in flue gas and capturing carbon dioxide. The system replaces the catalyst in the prior art by designing a sulfur dioxide and nitrogen monoxide separation unit 1, a nitrogen dioxide separation unit 2, and a carbon dioxide purification unit 3, which can quickly remove sulfur dioxide, nitrogen monoxide, nitrogen dioxide and carbon dioxide, simplify the process, and can be reused without using a large amount of catalyst, saving costs. The removed carbon dioxide is captured and purified by the capture unit, rather than being directly discharged and wasted, making full use of resources.

[0065] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0066] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0067] These computer program instructions may also be stored in a computer readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0068] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0069] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A system for purifying pollutants in flue gas and capturing carbon dioxide, wherein the pollutants include: Sulfur dioxide, nitric oxide, nitrogen dioxide; characterized in that the system comprises: A sulfur dioxide and nitrogen monoxide separation unit, whose input end is connected to the flexible peak-shaving coal-fired power unit, is used to separate sulfur dioxide and nitrogen monoxide gases in the flue gas generated by the flexible peak-shaving coal-fired power unit and output the remaining flue gas; A nitrogen dioxide separation unit, the input end of which is connected to the output end of the sulfur dioxide and nitrogen monoxide separation unit, and is used to separate the nitrogen dioxide gas from the flue gas output from the sulfur dioxide and nitrogen monoxide separation unit, and output the remaining flue gas; a carbon dioxide purification unit, the input end of which is connected to the output end of the nitrogen dioxide separation unit, and is used to purify the flue gas output from the nitrogen dioxide separation unit to obtain a mixed gas containing carbon dioxide; A capture unit, the input end of which is connected to the output end of the carbon dioxide purification unit, for extracting the mixed gas containing carbon dioxide to obtain carbon dioxide gas and discharging the remaining flue gas; The capture unit comprises: an absorption tower, wherein the input end of the absorption tower is connected to the output end of the carbon dioxide purification unit, and is used to absorb the mixed gas containing carbon dioxide, generate a liquid rich in carbon dioxide, and output it from its first output end, and discharge the remaining flue gas from its second output end; A lean-rich liquid heat exchanger, wherein the input end of the lean-rich liquid heat exchanger is connected to the first output end of the absorption tower, and is used to heat the output carbon dioxide-rich liquid and output the heated liquid; A regeneration tower, the input end of which is connected to the output end of the lean-rich liquid heat exchanger, and is used to desorb the output heated liquid to regenerate the carbon dioxide gas therein; The sulfur dioxide and nitrogen monoxide separation unit comprises: a molecular sieve membrane having a selective catalytic effect on sulfur dioxide and nitrogen monoxide gas; the pore size of the molecular sieve membrane having a selective catalytic effect on sulfur dioxide and nitrogen monoxide gas is 2.8 to 3.17 angstroms; The nitrogen dioxide separation unit comprises: a molecular sieve membrane having a selective catalytic effect on nitrogen dioxide gas; the pore size of the molecular sieve membrane having a selective catalytic effect on nitrogen dioxide gas is 3.3 angstroms; The carbon dioxide purification unit comprises: a graphene inorganic membrane, which is used to purify the flue gas output from the nitrogen dioxide separation unit for the first time to obtain a first mixed gas containing carbon dioxide; the channel of the graphene inorganic membrane is 3.3-3.6 angstroms.

2. The system according to claim 1, characterized in that: The carbon dioxide purification unit further includes: a first separation membrane, the input end of the first separation membrane is connected to the output end of the graphene inorganic membrane, and is used to purify the first mixed gas containing carbon dioxide for a second time to obtain a second mixed gas containing carbon dioxide; A second separation membrane, wherein the input end of the second separation membrane is connected to the output end of the first separation membrane, is used for purifying the second mixed gas containing carbon dioxide for a third time to obtain the mixed gas containing carbon dioxide.

3. The system according to claim 2, characterized in that Also includes: The first gas storage tank, the second gas storage tank, and the third gas storage tank.

4. The system according to claim 3, characterized in that: The input end of the first gas storage tank is connected to the output end of the sulfur dioxide and nitrogen monoxide separation unit; the input end of the second gas storage tank is connected to the output end of the nitrogen dioxide separation unit; and the third gas storage tank is arranged between the first separation membrane and the second separation membrane.

5. A method for purifying pollutants in flue gas and capturing carbon dioxide, characterized in that: The system for purifying pollutants in flue gas and capturing carbon dioxide according to any one of claims 1 to 4 comprises the following steps: S101, inputting the flue gas generated by the flexible peak-shaving coal-fired power unit into a sulfur dioxide and nitrogen monoxide separation unit to separate sulfur dioxide and nitrogen monoxide gases in the flue gas, and outputting the remaining flue gas; S102, separating the nitrogen dioxide gas in the flue gas output from the sulfur dioxide and nitrogen monoxide separation unit through a nitrogen dioxide separation unit, and outputting the remaining flue gas; S103, purifying the flue gas output from the nitrogen dioxide separation unit through a carbon dioxide purification unit to obtain a mixed gas containing carbon dioxide; S104, extracting the mixed gas containing carbon dioxide through a capture unit to obtain carbon dioxide gas, and discharging the remaining flue gas.

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