Method for simultaneously preparing carbon dioxide and nitrogen by using flue gas

Abstract

The invention relates to a method for simultaneously preparing high-purity carbon dioxide and nitrogen by using flue gas, which is characterized in that flue gas is used as a raw material, and the high-purity carbon dioxide and nitrogen are economically and conveniently obtained by dedusting, removing impurities such as oxygen, hydrocarbon, hydrogen, CO and the like and reasonably utilizing heat of purification treatment. Belongs to the technical field of carbon capture, waste gas treatment and resource utilization. The method mainly comprises the following six parts: fine removal and dust removal, heat exchange and low-pressure steam production, pretreatment, carbon-nitrogen separation, high-purity nitrogen production and high-purity carbon dioxide production. A mature organic amine method is used for carbon-nitrogen separation, a PSA method is used for high-purity nitrogen refining, and a low-temperature liquefaction method is used for liquid carbon dioxide. On the whole, high-purity carbon dioxide and nitrogen which can be used for chemical synthesis and industrial utilization are obtained through deep impurity removal of flue gas, reasonable configuration of the technological process and comprehensive utilization of heat generated by deoxidation, and 0.3 MPa saturated steam lt is supplemented by a carbon-nitrogen separation unit; 0.9 ton / tCO2, and the loss of the organic amine sold in the market is 1t; and 0.5 kg / t of CO2.

Description

Technical Field

[0001] The present invention relates to a method for simultaneously preparing high-purity carbon dioxide and nitrogen using flue gas. Specifically, flue gas is used as a raw material, dust is removed and impurities such as oxygen, hydrocarbons, hydrogen, CO, etc. are removed, and the heat of the purification process is reasonably utilized to obtain high-purity carbon dioxide and nitrogen in an economical and convenient manner. The method belongs to the technical field of carbon capture, waste gas treatment and resource utilization. Background Art

[0002] In the current global carbon neutrality context, carbon dioxide capture, utilization and storage (CCUS) has become an inevitable technical path to address climate change and achieve carbon neutrality. Flue gas is one of the main sources of carbon dioxide emissions, especially fixed emission sources of flue gas such as coal-fired boilers and gas boilers in power plants. In addition to carbon dioxide (CO2) with a volume fraction of 6% to 15%, flue gas also contains nitrogen with a volume fraction of 60% to 75%. After the flue gas is separated from CO2 by carbon capture technology, the gas is usually discharged into the atmosphere, resulting in a high concentration of nitrogen with a volume fraction of 80% to 95% not being utilized. Nitrogen has a wide range of uses in many industries such as chemical industry and metallurgy, while conventional nitrogen is separated from the air by air separation or other nitrogen production devices. Therefore, the high-concentration nitrogen after flue gas carbon capture is directly discharged into the atmosphere, which to a certain extent causes the underutilization of resources.

[0003] The industry has also noticed that the nitrogen in the exhaust gas after the current flue gas carbon capture is not utilized, and there are a few reports on its utilization. CN114852973A, CN202122516807.9, etc. all proposed methods for obtaining CO2 and nitrogen by flue gas separation. The purity of the nitrogen separated from the flue gas proposed in these patents is limited, and other impurities are not considered for removal, which is limited to general use; at the same time, the configuration of the process flow is also relatively crude, and the process energy utilization needs to be improved.

[0004] The organic amine method is the most mature flue gas carbon capture technology at present, but this technology has high regeneration heat consumption in the carbon capture process and requires a large amount of low-pressure saturated steam. At the same time, organic amines are easily affected by the high concentration of oxygen in the flue gas, which promotes the oxidative degradation of organic amines, resulting in a large loss of organic amines, leading to a higher subsequent waste liquid treatment volume and disposal costs.

[0005] Therefore, in order to more deeply implement the capture and utilization of carbon dioxide in flue gas, it is necessary to make more improvements and enhancements in the scope and depth of flue gas pretreatment, energy utilization of implementation plans, reduction of material consumption, and reduction of waste disposal. Summary of the invention

[0006] The present invention aims to provide a method for simultaneously obtaining high-purity carbon dioxide and nitrogen from flue gas, specifically from the perspectives of deep impurity removal of flue gas, reasonable configuration of process flow and comprehensive utilization of heat, so as to obtain high-purity carbon dioxide and nitrogen that can be used for chemical synthesis and industrial utilization, while reducing external regeneration heat, reducing solvent loss and waste liquid treatment volume of organic amine carbon capture.

[0007] The technical solution of the present invention is as follows: a method for simultaneously preparing carbon dioxide and nitrogen from flue gas, using flue gas as a raw material, removing impurities through purification treatment, and utilizing the heat of the purification process to obtain high-purity carbon dioxide and nitrogen, characterized in that the method comprises six units: a fine dust removal unit (100), a heat exchange and low-pressure steam production unit (201-204), a pretreatment unit (301-302), a carbon-nitrogen separation unit (400), a high-purity nitrogen production unit (501-503), and a high-purity carbon dioxide production unit (601-603). The specific method is as follows: the flue gas passes through the fine dust removal unit 100, where the fine dust removal flue gas is obtained without cooling; the fine dust removal flue gas enters the 201 heat exchange unit, and exchanges heat with the high temperature pre-treated hot flue gas from the subsequent 202 low-pressure steam production unit; the fine dust removal flue gas is heated and enters the pretreatment units 301 and 302 in sequence, and the 301 unit is finely desulfurized, dearsenicized and denitrified, and the hydrocarbons in the flue gas are converted into CO2 and H2 in the 302 unit. The high-temperature flue gas from unit 302 enters the low-pressure steam production unit 202, where low-pressure saturated steam is produced and used in the subsequent carbon-nitrogen separation 400; the higher-temperature flue gas from unit 202 is preheated to the flue gas after deep dust removal in unit 201, preheated to boiler water in unit 203, and rapidly cooled in unit 204 to obtain the flue gas at the feed temperature required for carbon-nitrogen separation; the flue gas enters the carbon-nitrogen separation unit 400, where CO2 and nitrogen in the flue gas are separated to obtain crude nitrogen and crude CO2, respectively, and then The carbon-nitrogen separation unit 400 uses the low-pressure saturated steam produced by the unit 202. The insufficient low-pressure steam is supplemented by the low-pressure saturated steam of the factory. At the same time, part of the condensate of the low-pressure steam returns to the unit 202, and the lost condensate is supplemented by boiler water. The crude nitrogen is compressed by 501, dehydrated by 502, and purified by 503 to obtain high-purity nitrogen. The crude carbon dioxide is compressed by 601, dehydrated by 602, and liquefied by 603 to obtain high-purity liquid CO2, or the crude carbon dioxide is compressed and directly injected into the storage point without liquefaction in 603.

[0008] Furthermore, the 50-100°C flue gas passes through the fine dust removal unit 100, where the dust content is less than 10 mg / Nm3 without cooling and passing through the electrostatic precipitator and ceramic membrane. 3 The fine dust removal flue gas.

[0009] Furthermore, the finely dedusted flue gas enters the 201 heat exchange unit, and exchanges heat with the higher temperature pre-treated hot flue gas coming out of the subsequent 202 low-pressure saturated steam production unit, raising the temperature to 70~130℃.

[0010] Furthermore, the pretreatment unit 301 removes SO X , arsenides, SOx, NOx.

[0011] Furthermore, the flue gas from unit 301 enters the pre-treatment unit 302, where the O 2、 Hydrocarbon, CO, H2 components are preferably converted using catalytic oxidation method.

[0012] Furthermore, according to the O2 content in the flue gas, carbon is converted into CO2 and hydrogen is converted into water during complete reaction, and natural gas or factory waste gas or vent gas containing H2, CO and hydrocarbons is added to consume all the O2 in the flue gas.

[0013] Furthermore, heat is extracted from the high-temperature flue gas to produce 0.3 MPa low-pressure saturated steam in the low-pressure saturated steam production unit 202 .

[0014] Furthermore, the higher temperature flue gas coming out of unit 202 recovers part of the heat in unit 201 and then enters unit 203, where the waste heat is further used to preheat the boiler water required for the low-pressure steam production unit, and then enters the quenching unit to cool the flue gas to 40~50℃, obtaining the flue gas at the feed temperature required for carbon-nitrogen separation.

[0015] Furthermore, the carbon-nitrogen separation adopts the organic amine method, and the crude nitrogen with a volume fraction of >99% (dry basis) is obtained from the absorption tower, and the crude CO2 with a volume fraction of >99% (dry basis) is obtained from the regeneration tower, and regenerated using the low-pressure saturated steam produced by the 202 unit. The 400 carbon-nitrogen separation unit supplements 0.3MPa saturated steam <0.9 tons / tCO2, and the loss of commercially available organic amines is <0.3kg / tCO2.

[0016] Furthermore, the crude nitrogen is compressed, dehydrated and purified to obtain high-purity nitrogen of 99.9% to 99.999%. The dehydration is carried out by molecular sieve method or TEG method. When the dew point is <-15°C, the TEG method is preferred.

[0017] Furthermore, the crude CO2 is compressed, dehydrated and liquefied at low temperature to obtain liquid CO2. The dehydration adopts the molecular sieve method and the liquefaction adopts the low temperature liquefaction method. The compression pressure is preferably 2.2~2.6MPa, the refrigerant is preferably R507 and R717, and the refrigerant temperature is -25~-35℃.

[0018] Furthermore, the crude CO2 is compressed and dehydrated to obtain CO2 with a purity of 99.0~99.9%. The dehydration is carried out by molecular sieve method or TEG method. When the dew point is <-10℃, TEG method is preferred for dehydration.

[0019] Furthermore, the high-temperature flue gas from unit 302 can also be directly sent to the reboiler of the regeneration tower of unit 400 for use, depending on the processing capacity, oxygen content in the flue gas and on-site equipment layout.

[0020] Beneficial effect: The method proposed by the present invention for simultaneously obtaining high-purity carbon dioxide and nitrogen from flue gas can reasonably utilize the higher concentration of nitrogen after flue gas carbon capture to produce high-purity nitrogen.

[0021] The present invention has the following obvious beneficial effects: Control the concentration of solid particles in the flue gas, remove oxygen and residual SOx, NOx, hydrocarbons, CO, H2 and other components in the flue gas, and obtain high-purity carbon dioxide and nitrogen, which can be used for chemical synthesis or other purposes; The heat source of low-pressure saturated steam is generated by using oxygen in flue gas and residual H2, hydrocarbons, CO and supplementary hydrocarbons, H2, CO, etc., and the amount of steam required for external regeneration is reduced when mature organic amine absorption is used in the carbon-nitrogen separation process; It removes oxygen from flue gas, reduces the loss of organic amines during carbon-nitrogen separation by organic amine method, reduces the amount and cost of waste liquid disposal of degradation products, and reduces the corrosion tendency of the system.

[0022] In general, the present invention economically solves the unfavorable factors of high regeneration energy consumption and large organic amine degradation loss that plague the organic amine carbon capture process, while obtaining high-purity carbon dioxide and nitrogen, achieving waste-free utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a schematic flow chart of a method for simultaneously obtaining high-purity carbon dioxide and nitrogen from flue gas according to an embodiment of the present invention.

[0024] In the figure, the unit modules are: 100-fine dust removal; 201-heat exchange; 202-production of low-pressure saturated steam; 203-boiler water preheating; 204-quenching; 301-desulfurization, dearsenicization and denitrification; 302-deoxygenation, hydrocarbons, CO, H2; 400-carbon and nitrogen separation; 501-crude nitrogen compression; 502-crude nitrogen dehydration; 503-crude nitrogen purification; 601-CO2 compression; 602-CO2 dehydration; 603-CO2 liquefaction.

[0025] Logistics: 1: Flue gas; 2: Hot flue gas after pretreatment; 3: Cold flue gas after pretreatment; 4: Crude nitrogen; 5: Crude CO2; 6: Refined nitrogen; 7: Liquefied CO2; 8: Low-pressure saturated steam; 9: Condensate; 10: Boiler make-up water; 11: Make-up fuel gas or waste gas or purge gas containing hydrocarbons, H2, CO. Implementation

[0026] In combination with the technical solution of the present invention, the present invention is further described below through implementation examples and drawings, but they do not limit the protection scope of the present invention. (The percentage of gas in the embodiments is by volume). Example

[0027] The method for obtaining high-purity carbon dioxide and nitrogen from various flue gases mainly includes the following six parts: a fine dust removal unit (100), a heat exchange and low-pressure steam production unit (201-204), a pretreatment unit (301-302), a carbon-nitrogen separation unit (400), a high-purity nitrogen production unit (501-503), and a high-purity carbon dioxide production unit (601-603).

[0028] Combined with Figure 1 The specific implementation is as follows: 50~100℃ flue gas 1 passes through the fine dust removal unit 100, where it is not cooled down, passes through the electrostatic precipitator and the ceramic membrane to obtain a dust content of <10mg / Nm 3 The refined dedusting flue gas enters the 201 heat exchange unit, and exchanges heat with the high-temperature pre-treated hot flue gas from the subsequent 202 production of low-pressure steam. After the temperature is raised to 70~130℃, it enters the refined desulfurization, dearsenicization and denitrification unit 301. In the 301 unit, SO is removed by graded adsorbents. X, arsenide and other impurities, and then enter the 302 unit, where the O2 in the flue gas is used to remove hydrocarbons, CO, and H2 through catalytic methods, and the residual hydrocarbons, H2 and CO in the flue gas react with the O2 in the flue gas to completely convert hydrocarbons into CO2 and water, H2 into water, and CO into CO2. At the same time, according to the O2 content in the flue gas and the residual amount of hydrocarbons, H2, and CO2, natural gas or factory waste gas or vent gas containing H2, CO, and hydrocarbons are appropriately added to basically consume the O2 in the flue gas. The high-temperature flue gas treated from the 302 unit enters the low-pressure saturated steam production unit 202, where 0.3MPa saturated steam 8 is obtained and used for subsequent carbon-nitrogen separation 400. The higher temperature flue gas coming out of the 202 unit recovers part of the heat through 201 and enters the 203 unit, where the waste heat is further used to preheat the boiler water 10 required for the low-pressure steam production unit, and then enters the quenching unit 204, where the flue gas is cooled to 40~50℃ to obtain flue gas 3 with a suitable temperature for the feed temperature required for carbon-nitrogen separation. After the pre-processing, the flue gas 3 is composed of CO2, nitrogen and saturated water, and basically does not contain other trace impurities. Flue gas 3 enters the carbon-nitrogen separation unit 400, where CO2 and nitrogen in the flue gas are separated by organic amine chemical absorption method to obtain nitrogen crude product 4 and CO2 crude product 5 respectively. The low-pressure saturated steam generated by the 202 unit is used in the carbon-nitrogen separation 400 unit, and the insufficient low-pressure steam is supplemented by the low-pressure saturated steam of the factory. At the same time, part of the condensate 9 of the low-pressure steam returns to the 202 unit, and the lost condensate is supplemented by the boiler water supply 10. Crude nitrogen 4 is compressed in 501, dehydrated in 502, and purified in 503 to obtain refined nitrogen with a purity of more than 99.9%, which is used as a raw material for chemical synthesis. The purification accuracy of crude nitrogen 4 in 503 can be flexibly changed according to needs, and the product purity can be from 99% to 99.999%. At the same time, the purified tail gas can be directly discharged, such as PSA analytical gas. Crude carbon dioxide 5 is compressed in 601, dehydrated in 602, and liquefied in 603 to obtain liquid CO2 for EOR oil recovery, chemical reaction and other applications. Crude carbon dioxide 5 can also be compressed as needed and injected directly into the storage point without liquefaction 603. Dehydration and drying 501 and 601 can be flexibly adjusted according to the requirements of water content or dew point in subsequent applications. According to the needs, the CO2 liquefaction process is recommended to use the low-temperature liquefaction method, that is, first compress CO2 to 2.2~2.6MPa, and then liquefy at -25~-35℃, and the refrigerant is preferably R507 and R717.

[0029] The high-temperature flue gas from unit 302 can also be directly sent to the reboiler of the regeneration tower of unit 400 for use, depending on the processing capacity and on-site equipment layout.

[0030] Embodiment 1: The flue gas from coal-fired power plants after desulfurization at 60°C has the following volume fractions: CO2 11.5%, N2 66.8%, O2 6.4%, H2O 15.2%, other trace components CO 300ppmv, SO2<50mg / Nm 3 、NO x <50mg / Nm 3 、Particulate matter <30mg / Nm 3 .

[0031] After 100 units of ceramic membrane filtration, particulate matter <5mg / Nm 3 ; After heat exchange in unit 201, the flue gas is heated to 85°C and then enters unit 301, where it undergoes fine desulfurization and arsenic removal to obtain SO2<1mg / Nm 3 、NO x <5mg / Nm 3 In order to pre-treat the flue gas, a fine desulfurizer, a dearsenicizer, and a denitrifier with CaO, CuO, etc. as effective substances are used in combination in Unit 301.

[0032] When passing through unit 302, natural gas is added to make the oxygen react completely according to the oxygen content and flow rate in the flue gas. Under the conditions of this raw flue gas, the methane added is about 0.0295Nm 3 / Raw flue gas per unit volume flow. The high-temperature flue gas obtained after deoxygenation is used to produce 0.3MPa low-pressure saturated steam. The higher-temperature flue gas after producing saturated steam goes to unit 201 to preheat the flue gas and to unit 203 to preheat the boiler water, and finally is rapidly cooled from 90℃ to 50℃ in unit 204.

[0033] After pretreatment at 50℃, it enters the 400 carbon-nitrogen separation unit, where a composite amine solvent is used to absorb CO2, and crude nitrogen is obtained from the top of the absorption tower. The carbon capture rate is controlled to 100%, and crude CO2 is obtained from the top of the regeneration tower, supplemented with 0.3MPa saturated steam 0.85 tons / tCO2. The loss of the 400 carbon-nitrogen separation unit using commercially available MA organic amine is 0.15kg / tCO2. The crude nitrogen is compressed to 0.6MPa, dehydrated to a dew point of -10℃ by TEG, and purified to 99.99% by four-tower PSA. The crude CO2 is compressed to 0.6MPa, dehydrated by molecular sieve, and compressed to 2.5MPa again. R507 at -30℃ is used as a refrigerant to obtain a liquid carbon dioxide product.

[0034] Embodiment 2:

[0035] The flue gas from coal-fired power plants after desulfurization at 80°C has the following volume fractions: CO2 7.4%, N2 44.4%, O2 3.1%, H2O 45.1%, and other trace components: CO 45ppmv, SO2<50mg / Nm3 、NO x <50mg / Nm 3 、Particulate matter <30mg / Nm 3 .

[0036] After 100 units of ceramic membrane filtration, particulate matter <5mg / Nm 3 ; After heat exchange in unit 201, the flue gas is heated to 100°C and then enters unit 301, where it undergoes fine desulfurization and dearsenicization to obtain SO2<1mg / Nm 3 、NO x <5mg / Nm 3 In order to pre-treat the flue gas, a fine desulfurizer, a dearsenicizer, and a denitrifier with CaO, CuO, etc. as effective substances are used in combination in Unit 301.

[0037] When passing through unit 302, natural gas is added to make the oxygen react completely according to the oxygen content and flow rate in the flue gas. Under the conditions of this raw flue gas, the methane added is about 0.0147Nm 3 / Raw flue gas per unit volume flow. The high-temperature flue gas obtained after deoxygenation is used to produce 0.3MPa low-pressure saturated steam. The higher-temperature flue gas after producing saturated steam goes to unit 201 to preheat the flue gas and to unit 203 to preheat the boiler water, and finally is rapidly cooled from 90℃ to 50℃ in unit 204.

[0038] After pretreatment at 50℃, it enters the 400 carbon-nitrogen separation unit, where a composite amine solvent is used to absorb CO2, and crude nitrogen is obtained from the top of the absorption tower. The carbon capture rate is controlled to 100%, and crude CO2 is obtained from the top of the regeneration tower, supplemented with 0.3MPa saturated steam 0.78 tons / tCO2. The loss of the 400 carbon-nitrogen separation unit using commercially available MA organic amine is 0.15kg / tCO2. The crude nitrogen is compressed to 0.6MPa, dehydrated to a dew point of -10℃ by TEG, and purified to 99.99% by four-tower PSA. The crude CO2 is compressed to 0.6MPa, dehydrated by molecular sieve, and compressed to 2.5MPa again. R507 at -30℃ is used as a refrigerant to obtain a liquid carbon dioxide product.

[0039] Embodiment 3: The flue gas from the gas power plant after desulfurization at 60℃ has the following volume fractions: CO28.6%, N2 69.1%, O2 7.5%, H2O 14.8%, other trace components CO 240ppmv, SO2<50mg / Nm 3 、NO x <50mg / Nm 3 、Particulate matter <20mg / Nm 3 .

[0040] After 100 units of ceramic membrane filtration, particulate matter <3mg / Nm 3 ; After heat exchange in unit 201, the flue gas is heated to 93°C and enters unit 301, where it undergoes fine desulfurization and dearsenicization to obtain SO2<1mg / Nm 3 、NO x <5mg / Nm 3 In order to pre-treat the flue gas, a fine desulfurizer, a dearsenicizer, and a denitrifier with CaO, CuO, etc. as effective substances are used in combination in Unit 301.

[0041] When passing through unit 302, natural gas is added to make the oxygen react completely according to the oxygen content and flow rate in the flue gas. Under the conditions of this raw flue gas, the methane added is about 0.0356Nm 3 / Raw flue gas per unit volume flow. The high-temperature flue gas obtained after deoxygenation is used to produce 0.3MPa low-pressure saturated steam. The higher-temperature flue gas after producing saturated steam goes to unit 201 to preheat the flue gas and to unit 203 to preheat the boiler water, and finally is rapidly cooled from 90℃ to 50℃ in unit 204.

[0042] After pretreatment at 50℃, it enters the 400 carbon-nitrogen separation unit, where a composite amine solvent is used to absorb CO2, and crude nitrogen is obtained from the top of the absorption tower. The carbon capture rate is controlled to 100%, and crude CO2 is obtained from the top of the regeneration tower, supplemented with 0.3MPa saturated steam 0.81 tons / tCO2. The loss of the 400 carbon-nitrogen separation unit using commercially available MA organic amine is 0.17kg / tCO2. The crude nitrogen is compressed to 0.6MPa, dehydrated to a dew point of -10℃ by TEG, and purified to 99.99% by four-tower PSA. The crude CO2 is compressed to 0.6MPa, dehydrated by molecular sieve, and compressed to 2.5MPa again. R507 at -30℃ is used as a refrigerant to obtain a liquid carbon dioxide product.

[0043] It can be seen from the above embodiments that the method of use of the present invention can ensure that high-purity carbon dioxide and nitrogen are obtained from coal-fired and gas-fired flue gas, while reducing the external supply of low-pressure saturated steam (conventional supplementary steam>1.0 ton / tCO2). In addition, there is basically no oxygen in the flue gas, and the degradation of organic amines caused by oxygen will also become very weak, which is much lower than the conventional organic amine consumption of 1kg / tCO2, thereby reducing the consumption of organic amines and the resulting waste liquid disposal problems.

Claims

1. A method for simultaneously producing carbon dioxide and nitrogen from flue gas, using flue gas as raw material, removing impurities through purification treatment, and using the heat generated during the purification process to obtain high-purity carbon dioxide and nitrogen, characterized in that The method comprises six units: a fine dust removal unit (100), a heat exchange and low-pressure steam production unit (201-204), a pretreatment unit (301-302), a carbon-nitrogen separation unit (400), a high-purity nitrogen production unit (501-503), and a high-purity carbon dioxide production unit (601-603). The specific method is as follows: the flue gas passes through the fine dust removal unit 100, and the fine dust removal flue gas is obtained without cooling; the fine dust removal flue gas enters the 201 heat exchange unit, and exchanges heat with the hot flue gas with a higher temperature from the subsequent 202 low-pressure steam production unit; the fine dust removal flue gas is heated and enters the pretreatment units 301 and 302 in sequence, and the fine desulfurization, dearsenicization and denitrification are carried out in the 301 unit, and the hydrocarbons in the flue gas are converted into CO2, water and H2 in the 302 unit. The high-temperature flue gas from unit 302 enters the low-pressure steam production unit 202, where saturated steam is produced for subsequent carbon-nitrogen separation 400; the higher-temperature flue gas from unit 202 is sent to unit 201 for preheating flue gas, unit 203 for preheating boiler water, and unit 204 for rapid cooling to obtain flue gas at the feed temperature required for carbon-nitrogen separation; The flue gas enters the carbon-nitrogen separation unit 400, and the CO2 and nitrogen in the flue gas are separated to obtain crude nitrogen and crude CO2 respectively. The low-pressure saturated steam produced by the 202 unit is used in the carbon-nitrogen separation unit 400, and the insufficient low-pressure steam is supplemented by the low-pressure saturated steam of the factory. At the same time, part of the condensate of the low-pressure steam returns to the 202 unit, and the lost condensate is supplemented by boiler water; the crude nitrogen is compressed by 501, dehydrated by 502, and purified by 503 to obtain high-purity nitrogen; the crude carbon dioxide is compressed by 601, dehydrated by 602, and liquefied by 603 to obtain high-purity liquid CO2, or the crude carbon dioxide is compressed and directly injected into the storage point without liquefaction 603.

2. The method according to claim 1, characterized in that The flue gas at 50~100℃ passes through the fine dust removal unit 100, where the dust content is less than 10mg / Nm3 without cooling and passing through the electrostatic precipitator and ceramic membrane. 3 The fine dust removal flue gas.

3. The method according to claim 1 or 2, characterized in that The finely dedusted flue gas enters the 201 heat exchange unit and exchanges heat with the higher temperature pre-treated hot flue gas coming out of the subsequent 202 low-pressure saturated steam production unit, and is heated to 70~130℃.

4. The method according to claim 1, characterized in that The pretreatment unit 301 removes SO through graded adsorbents. X , arsenides, SOx, NOx.

5. The method according to claim 1 or 4, characterized in that The flue gas from unit 301 enters the pretreatment unit 302, where the O 2、 Hydrocarbon, CO, H2 components are converted into hydrocarbons, CO, and H2 using catalytic oxidation.

6. The method according to claim 5, characterized in that According to the O2 content in the flue gas, when the reaction is complete, the carbon element is converted into CO2 and the hydrogen element is converted into water. Natural gas or factory waste gas or exhaust gas containing H2, CO, and hydrocarbons is added to consume all the O2 in the flue gas.

7. The method according to claim 1, 5 or 6, characterized in that The heat in the high-temperature flue gas is extracted to produce 0.3 MPa low-pressure saturated steam in the low-pressure steam production unit 202.

8. The method according to claim 1 or 7, characterized in that The higher temperature flue gas coming out of unit 202 goes to unit 201 to recover part of the heat and then enters unit 203, where the waste heat is further used to preheat the boiler water required for the low-pressure steam production unit. The flue gas then enters unit 204 to cool down to 40~50℃, obtaining the flue gas at the feed temperature required for carbon-nitrogen separation.

9. The method according to claim 1, characterized in that The carbon-nitrogen separation adopts the organic amine method, and the crude nitrogen with a volume fraction of >99% (dry basis) is obtained from the absorption tower, and the crude CO2 with a volume fraction of >99% (dry basis) is obtained from the regeneration tower. The low-pressure saturated steam produced by the 202 unit is used for regeneration, and the 400 carbon-nitrogen separation unit supplements 0.3MPa saturated steam <0.9 tons / tCO2. The loss of commercially available organic amines is <0.3kg / tCO2.

10. The method according to claim 1 or 9, characterized in that The crude nitrogen is compressed, dehydrated and purified to obtain high-purity nitrogen of 99.9%~99.999%. The molecular sieve method or TEG method is used for dehydration. When the dew point is <-15℃, the TEG method is used for dehydration.

11. The method according to claim 1 or 9, characterized in that Liquid CO2 is obtained after compression, dehydration and low-temperature liquefaction of crude CO2. The molecular sieve method is used for dehydration and the low-temperature liquefaction method is used for liquefaction. The compression pressure is 2.2~2.6MPa, the refrigerant is R507 and R717, and the refrigerant temperature is -25~-35℃.

12. The method according to claim 1 or 9, characterized in that The crude CO2 is compressed and dehydrated to obtain CO2 with a purity of 99.0~99.9%. The molecular sieve method or TEG method is used for dehydration. When the dew point is <-10℃, the TEG method is used for dehydration.

Images