A flue gas carbon dioxide capture method and capture system

Abstract

The present application relates to a kind of flue gas carbon dioxide capture method and system, the method comprises the following steps: flue gas is passed into first pressure swing adsorption column and is carried out first pressure swing adsorption processing, obtains primary decarbonization gas and primary carbon dioxide concentration gas;The primary carbon dioxide concentration gas is passed into second pressure swing adsorption column and is carried out second pressure swing adsorption processing, obtains secondary decarbonization gas and secondary carbon dioxide concentration gas;Membrane concentration separation is carried out to the secondary decarbonization gas, obtains non-permeation gas and membrane separation carbon dioxide concentration gas;Wherein, the first pressure swing adsorption column is filled with first pressure swing adsorbent, and the second pressure swing adsorption column is filled with second pressure swing adsorbent;The first pressure swing adsorbent and the second pressure swing adsorbent are modified carbon hydrophobic adsorbent.The flue gas is carried out first pressure swing adsorption, and the primary concentration gas obtained is carried out second pressure swing adsorption again, and the decarbonization gas of second pressure swing adsorption is further carried out membrane concentration separation, improves CO2 capture rate.

Description

Technical Field

[0001] This invention belongs to the field of energy, specifically relating to a method and system for capturing carbon dioxide from flue gas. Background Technology

[0002] The large-scale combustion and use of fossil fuels has led to a rapid increase in atmospheric CO2 concentration, exacerbating the greenhouse effect. Currently, atmospheric CO2 concentration has exceeded 400 ppm, with coal-fired power generation accounting for the largest proportion, approximately 40% of the total, and thus having the greatest potential to contribute to carbon dioxide emission reduction.

[0003] As the upstream link of CCUS (Capture, Utilization and Storage of Carbon Dioxide), CO2 capture accounts for more than 70% of the cost of the entire CCUS technology chain. It is the biggest bottleneck currently restricting the large-scale demonstration and application of CCUS technology. Therefore, developing efficient and low-cost CO2 capture technology is conducive to accelerating the overall progress of CCUS technology.

[0004] Currently, solvent-based CO2 capture is mainly used in China. While solvent-based capture technology has its own advantages and is relatively mature, it suffers from high energy consumption, severe equipment corrosion, and amine escape, posing a certain risk of secondary environmental pollution. Furthermore, the potential for further technological advancement is diminishing. In contrast, adsorption and membrane separation methods do not rely on chemical reactions or corrosive solvents, offering greater potential for energy and overall cost reduction.

[0005] CN103071364A discloses a system and method for multi-stage capture of carbon dioxide from flue gas. The carbon dioxide capture system includes at least two sets of pressure swing adsorption (PSA) devices, each containing at least one adsorption bed. The adsorbent material in the first-stage PSA device is a hydrophobic adsorbent, while the adsorbent materials in the adsorption beds of subsequent PSA devices are carbon dioxide adsorbent materials. In the first stage, using a hydrophobic adsorbent material, 12% CO2 can be concentrated to a concentration of 40-60%, with a CO2 recovery rate exceeding 90%. After the first stage, most water vapor directly penetrates the adsorption bed and is removed. In subsequent stages, 13X zeolite molecular sieve is used as the adsorbent, which can purify 40-60% CO2 to a concentration of over 95%.

[0006] CN103055659A discloses a system and method for capturing carbon dioxide in flue gas. The carbon dioxide capture system includes a multilayer pressure swing adsorption (PSA) device. The PSA device contains at least one adsorption bed, and each adsorption bed contains at least one water vapor adsorption layer and at least one carbon dioxide adsorption layer. The water vapor adsorption layer is below the carbon dioxide adsorption layer, so that the flue gas first passes through the water vapor adsorption layer and then through the carbon dioxide adsorption layer, thereby removing water vapor from the flue gas while separating carbon dioxide from the flue gas.

[0007] CN108452644A discloses a carbon dioxide membrane capture coupled with nitrogen preparation process for a coal-fired power plant, comprising a carbon dioxide membrane capture module, a nitrogen enrichment module, and a nitrogen preparation module. The carbon dioxide membrane capture module captures carbon dioxide from flue gas, and the high-pressure retrieval gas from the first-stage membrane module is used as the nitrogen source. In the nitrogen enrichment module, most of the oxygen and a small amount of carbon dioxide components in the flue gas are separated from the nitrogen by the membrane module. High-purity nitrogen is then prepared in the nitrogen preparation module using pressure swing adsorption (PSA) technology, utilizing the retrieval gas containing a high concentration and high partial pressure of nitrogen.

[0008] However, existing technologies still suffer from insufficient CO2 capture rates in flue gas. Summary of the Invention

[0009] The purpose of this invention is to improve the CO2 capture rate in flue gas.

[0010] To achieve the above objectives, a first aspect of the present invention provides a method for capturing carbon dioxide in flue gas, the method comprising the following steps:

[0011] The flue gas is fed into the first pressure swing adsorption tower for first pressure swing adsorption treatment to obtain primary decarbonized gas and primary carbon dioxide concentrated gas.

[0012] The primary carbon dioxide concentrate is passed into a second pressure swing adsorption tower for second pressure swing adsorption treatment to obtain secondary decarbonized gas and secondary carbon dioxide concentrate.

[0013] The secondary decarbonized gas is concentrated and separated by membrane to obtain non-permeable gas and membrane-separated carbon dioxide concentrated gas;

[0014] The first pressure swing adsorption tower is filled with a first pressure swing adsorbent, and the second pressure swing adsorption tower is filled with a second pressure swing adsorbent; the first pressure swing adsorbent and the second pressure swing adsorbent are modified carbonaceous hydrophobic adsorbents.

[0015] Optionally, the first pressure swing adsorption process sequentially includes first adsorption, first equalization, first desorption, and first flushing and pressurization; the conditions for the first adsorption include: an adsorption temperature of 30-50℃ and an adsorption pressure of 10-25 kPaG; the vacuum degree of the first desorption is 15-30 kPaA; preferably, the volume fraction of carbon dioxide in the primary decarbonization gas is 1-3 vol%, and the volume fraction of carbon dioxide in the primary carbon dioxide concentrate gas is 45-65 vol%.

[0016] Optionally, the second pressure swing adsorption process sequentially includes a second adsorption, a second pressure equalization, a second desorption, and a second flushing pressurization; the conditions for the second adsorption include: an adsorption temperature of 30-50℃ and an adsorption pressure of 10-25 kPaG; the vacuum degree for the second desorption is 15-30 kPaA; preferably, the volume fraction of carbon dioxide in the secondary decarbonization gas is 20-30 vol%; and the volume fraction of carbon dioxide in the secondary carbon dioxide concentrate gas is 95-97 vol%.

[0017] Optionally, the first pressure swing adsorbent and the second pressure swing adsorbent are each independently selected from one or more of modified coal-based activated carbon, modified liquefaction residue-based, and modified carbon molecular sieve.

[0018] Optionally, a membrane concentrator is used to concentrate and separate the secondary decarbonized gas. The membrane material installed in the membrane concentrator is a hollow fiber membrane, a spiral wound membrane, or a sheet membrane. Preferably, the membrane material is selected from one or more of polydimethylsiloxane (PDMS), polyvinylamine (PVAm), and polyimide (PI).

[0019] Optionally, the membrane concentration separation conditions include: a separation temperature of 30-50℃ and a separation pressure of 100-200 kPaG; preferably, the volume fraction of carbon dioxide in the membrane-separated carbon dioxide concentrate is 55-65 vol%; and the volume fraction of carbon dioxide in the non-permeable gas is 1-4 vol%.

[0020] Optionally, the method further includes the following steps: pressurizing the primary carbon dioxide concentrate before introducing it into the second pressure swing adsorption tower, and cooling the pressurized primary carbon dioxide concentrate to the adsorption temperature; and / or pressurizing the secondary decarbonization gas before performing membrane concentration separation, and cooling the pressurized secondary decarbonization gas to the membrane concentration separation temperature; preferably, the pressure of the pressurized primary carbon dioxide concentrate is 10-25 kPaG; preferably, the pressure of the pressurized secondary decarbonization gas is 100-200 kPaG.

[0021] Optionally, the method further includes the following steps: mixing the membrane-separated carbon dioxide concentrate with the primary carbon dioxide concentrate and returning the mixture to the second pressure swing adsorption separator; the volume ratio of the primary carbon dioxide concentrate to the membrane-separated carbon dioxide concentrate is 1:(0.2-0.3).

[0022] Optionally, the method further includes: compressing the flue gas to 10-25 kPaG before introducing it into the first pressure swing adsorption separator; and cooling the compressed flue gas to 30-50°C; preferably, the volume fraction of carbon dioxide in the flue gas is 12-15 vol%; preferably, the flow rate of the flue gas is 6000-600000 Nm³. 3 / h.

[0023] A second aspect of the present invention provides a flue gas carbon dioxide capture system, comprising a first pressure swing adsorption (PSA) tower, a second PSA tower, and a membrane concentrator; wherein the first PSA tower is provided with a flue gas inlet, a primary decarbonization gas outlet, and a primary carbon dioxide concentrate outlet; the flue gas inlet is connected to a flue gas treatment device for pressurizing and cooling the flue gas, the primary decarbonization gas outlet is connected to a primary decarbonization gas buffer tank, and the primary carbon dioxide concentrate outlet is connected to a first vacuum desorption device and a primary concentrate buffer tank; the second PSA tower is provided with a primary carbon dioxide concentrate inlet and a secondary decarbonization gas outlet. The membrane separator includes a primary carbon dioxide concentrate inlet, a non-permeable gas outlet, and a membrane separation carbon dioxide concentrate outlet. The primary carbon dioxide concentrate inlet is connected to a primary carbon dioxide concentrate treatment device for pressurizing and cooling the primary carbon dioxide concentrate. The secondary decarbonized gas outlet is connected to a secondary decarbonized gas buffer tank, and the secondary carbon dioxide concentrate outlet is connected to a second vacuum desorption device.

[0024] Through the above technical solution, the present invention couples pressure swing adsorption and membrane separation, performs primary pressure swing adsorption on flue gas with low CO2 concentration, performs secondary pressure swing adsorption on the resulting primary concentrated gas, and further concentrates and separates the decarbonized gas from the secondary pressure swing adsorption through membrane, thereby further improving the CO2 capture rate.

[0025] The pressure swing adsorption tower provided by this invention uses a hydrophobic adsorbent in its adsorption bed. The desorbed gas does not need to be separated into CO2 and water vapor. Therefore, CO2 and H2O can be effectively separated. There is no need to set up equipment for impurity removal, purification, pressurization and drying, which reduces the investment in the equipment and the energy consumption for CO2 capture.

[0026] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0027] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0028] Figure 1 This is a flowchart of the first pressure swing adsorption (PSA) portion of a method provided in some embodiments of the present invention.

[0029] Figure 2 The flowcharts are for the second pressure swing adsorption section and the membrane concentration and separation section in the method provided in some embodiments of the present invention.

[0030] Explanation of reference numerals in the attached figures:

[0031] 101. Pipeline; 102. Raw material buffer tank; 103. Pipeline

[0032] 104. First booster fan; 105. Pipeline; 106. First cooler

[0033] 107. Pipeline; 108. First buffer tank; 109. Pipeline

[0034] 110. Pipeline; 111. First Pressure Swing Adsorption Tower; 112. First Stage Decarbonization Gas Buffer Tank

[0035] 113. Pipeline 114. Pipeline 115. Condensate pump

[0036] 116. Pipeline; 117. Condensate tank; 118. First vacuum buffer tank

[0037] 119. First vacuum pump; 120. Pipeline; 121. First-stage concentrated gas buffer tank

[0038] 201. Pipeline; 202. Second booster fan; 203. Pipeline

[0039] 204. Second cooler; 205. Pipeline; 206. Second buffer tank

[0040] 207. Second vacuum buffer tank; 208. Second vacuum pump; 209. Piping

[0041] 210. Second pressure swing adsorption tower; 211. Secondary decarbonization gas buffer tank; 301. Pipelines

[0042] 302, Compressor; 303, Pipeline; 304, Tertiary Cooler

[0043] 305. Pipeline; 306. Membrane concentrator; 307. Pipeline

[0044] 308, Third Vacuum Pump 309 Pipeline Detailed Implementation

[0045] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0046] A first aspect of the present invention provides a method for capturing carbon dioxide in flue gas, the method comprising the following steps:

[0047] The flue gas is fed into the first pressure swing adsorption tower for first pressure swing adsorption treatment to obtain primary decarbonized gas and primary carbon dioxide concentrated gas.

[0048] The primary carbon dioxide concentrate is passed into a second pressure swing adsorption tower for second pressure swing adsorption treatment to obtain secondary decarbonized gas and secondary carbon dioxide concentrate.

[0049] The secondary decarbonized gas is concentrated and separated by membrane to obtain non-permeable gas and membrane-separated carbon dioxide concentrated gas; wherein, the first pressure swing adsorption tower is filled with a first pressure swing adsorbent and the second pressure swing adsorption tower is filled with a second pressure swing adsorbent; the first pressure swing adsorbent and the second pressure swing adsorbent are modified carbonaceous hydrophobic adsorbents.

[0050] Unlike conventional membrane separation methods, this invention couples pressure swing adsorption (PSA) and membrane separation. Low CO2 concentration flue gas undergoes primary PSA, the resulting primary concentrated gas undergoes secondary PSA, and the decarbonized gas from secondary PSA is further concentrated and separated by membrane, thereby further improving the CO2 capture rate.

[0051] Because the adsorption bed of the pressure swing adsorption tower uses a hydrophobic adsorbent, the desorbed gas does not need to be separated into CO2 and water vapor, and the adsorption of H2 and N2 is poor. Therefore, CO2 can be effectively separated from H2, N2 and H2O, eliminating the need for equipment such as impurity removal, pressurization and drying, thus reducing the investment in the equipment and the energy consumption for CO2 capture.

[0052] Pressure swing adsorption (PSA) gas separation technology utilizes the characteristic that the adsorption capacity of a gas on an adsorbent changes with its partial pressure. It adsorbs under higher pressure, while weakly adsorbed components are directly output through the adsorption bed. Then, by reducing the partial pressure of the adsorbed components in the adsorption bed (such as by evacuating the vacuum), the adsorbed components are desorbed from the adsorbent, and the adsorbent is regenerated.

[0053] In some embodiments, the first pressure swing adsorption process sequentially includes first adsorption, first equalization, first desorption, and first flushing and pressurization.

[0054] Specifically, the conditions for the first adsorption include: an adsorption temperature of 30-50℃ and an adsorption pressure of 10-25 kPaG; and a vacuum degree of 15-30 kPaA for the first desorption. The flue gas with a low carbon dioxide concentration undergoes the first adsorption and first desorption to obtain a primary decarbonized gas and a primary carbon dioxide concentrated gas. Specifically, the volume fraction of carbon dioxide in the primary decarbonized gas is 1-3 vol%, and the volume fraction of carbon dioxide in the primary carbon dioxide concentrated gas is 45-65 vol%.

[0055] The second pressure swing adsorption (PSA) process sequentially includes a second adsorption, a second pressure equalization, a second desorption, and a second flushing and pressurization. Specifically, the first and second pressure equalization refer to the process where, during the PSA process, the adsorption beds requiring depressurization and desorption pressurize different adsorption beds requiring pressurization. The pressure of the adsorption beds requiring desorption and depressurization decreases, while the pressure of the adsorption beds requiring pressurization increases, thereby enabling the gas discharged from the adsorption beds to be effectively utilized.

[0056] The principles of the first flush pressurization and the second flush pressurization are the same as above. Preferably, the gas used in the equalization and flush pressurization process can be product gas or intermediate gas at different pressures within the reaction system. For example, the carbon dioxide concentrate gas from membrane separation itself has a certain pressure, and utilizing it can reduce energy consumption to a certain extent.

[0057] The conditions for the second adsorption include: an adsorption temperature of 30-50℃ and an adsorption pressure of 10-25 kPaG; and a vacuum degree of 15-30 kPaA for the second desorption. The primary carbon dioxide concentrate undergoes the second adsorption and second desorption to obtain a secondary decarbonized gas and a secondary carbon dioxide concentrate. Specifically, the volume fraction of carbon dioxide in the secondary decarbonized gas is 20-30 vol%; and the volume fraction of carbon dioxide in the secondary carbon dioxide concentrate is 95-97 vol%.

[0058] In this invention, during pressure swing adsorption, flue gas with low CO2 concentration undergoes micro-positive pressure adsorption and vacuum desorption, which reduces regeneration energy consumption, increases the CO2 concentration in the product gas and the CO2 capture rate of the flue gas, and the CO2 capture rate can reach more than 90%. It can also be operated continuously, quickly and efficiently.

[0059] Preferably, the first pressure swing adsorbent and the second pressure swing adsorbent are each independently selected from one or more of modified coal-based activated carbon, modified liquefaction residue-based adsorbent, and modified carbon molecular sieve. The materials of the first pressure swing adsorbent and the second pressure swing adsorbent can be the same or different.

[0060] The secondary decarbonized gas is concentrated and separated using a membrane concentrator. The membrane material installed in the membrane concentrator is a hollow fiber membrane, a spiral wound membrane, or a sheet membrane. The specific membrane material can be one commonly used in the art. Preferably, the membrane material is selected from one or more of polydimethylsiloxane (PDMS), polyvinylamine (PVAm), and polyimide (PI).

[0061] The membrane concentration and separation conditions include: a separation temperature of 30-50℃ and a separation pressure of 100-200 kPaG; a carbon dioxide volume fraction of 55-65 vol% in the membrane-separated carbon dioxide concentrate; and a carbon dioxide volume fraction of 1-4 vol% in the non-permeable gas.

[0062] The method further includes the following steps: before introducing the primary carbon dioxide concentrate into the second pressure swing adsorption tower, pressurizing the primary carbon dioxide concentrate to provide pressure conditions for carbon dioxide pressure swing adsorption, and cooling the pressurized primary carbon dioxide concentrate to the adsorption temperature.

[0063] Before membrane concentration and separation, the secondary decarbonized gas is pressurized to provide sufficient pressure for membrane separation, thereby promoting the permeation of more carbon dioxide through the membrane material. Cooling the pressurized secondary decarbonized gas to the membrane concentration and separation temperature helps to fully utilize the separation function of the membrane material and improve operational stability. Preferably, the pressure of the pressurized primary carbon dioxide concentrate is 10-25 kPaG; the pressure of the pressurized secondary decarbonized gas is 100-200 kPaG.

[0064] The method further includes the following steps: mixing the membrane-separated carbon dioxide concentrate with the primary carbon dioxide concentrate and then returning the mixture to the second pressure swing adsorption separator; the volume ratio of the primary carbon dioxide concentrate to the membrane-separated carbon dioxide concentrate is 1:(0.2-0.3). Returning the membrane-separated carbon dioxide concentrate to the second pressure swing adsorption separator after mixing with the primary carbon dioxide concentrate avoids the increased energy consumption for capture caused by the circulation of low-concentration tail gas within the system.

[0065] The method further includes: compressing the flue gas to 10-25 kPaG before introducing it into the first pressure swing adsorption separator to provide pressure conditions for the first pressure swing adsorption of the flue gas; and cooling the compressed flue gas to 30-50°C. Preferably, the volume fraction of carbon dioxide in the flue gas is 12-15 vol%; preferably, the flow rate of the flue gas is 6000-600000 Nm³. 3 / h.

[0066] A second aspect of the present invention provides a flue gas carbon dioxide capture system, such as Figure 1 As shown, the flue gas carbon dioxide capture system provided by the present invention includes a first pressure swing adsorption (PSA) tower 111, a second PSA tower 210, and a membrane concentrator 306. The first PSA tower 111 and the second PSA tower 210 are filled with a hydrophobic adsorbent, specifically activated carbon. The membrane material installed in the membrane concentrator 306 can be a hollow fiber membrane, a spiral wound membrane, or a plate membrane. Specifically, the membrane material can be polydimethylsiloxane (PDMS), polyvinylamine (PVAm), or polyimide (PI), or other membrane materials commonly used in the art.

[0067] The first pressure swing adsorption tower 111 is provided with a flue gas inlet, a primary decarbonization gas outlet, and a primary carbon dioxide concentrate gas outlet. Specifically, the flue gas inlet is connected to a flue gas treatment device for pressurizing and cooling the flue gas. Preferably, the flue gas treatment device includes a first booster fan 104 and a first cooler 106 connected in sequence. After the flue gas is pressurized by the first booster fan 104, its temperature increases. The pressurized flue gas is then passed into the first cooler 106 and cooled by circulating water to a suitable adsorption temperature.

[0068] Since the flue gas contains water and impurities, in a preferred embodiment of the present invention, before compressing the flue gas, it is first passed through pipeline 101 into the raw material buffer tank 102 for gas-liquid separation to remove the water entrained in the flue gas. Preferably, before passing the cooled flue gas into the first pressure swing adsorption tower 111, the cooled flue gas can also be passed into the first buffer tank 108 for gas-liquid separation to further remove the water in the compressed flue gas, and the gas phase is passed through pipeline 110 into the first pressure swing adsorption tower 111 for first pressure swing adsorption separation.

[0069] Specifically, the number of first pressure swing adsorption (PSA) towers is 4-8, depending on factors such as flue gas flow rate. The operation process of first PSA separation includes: adsorption, pressure equalization, vacuum desorption, and flushing pressurization.

[0070] The primary decarbonization gas contains a large amount of N2 and a small amount of O2 and H2O. The primary decarbonization gas outlet is connected to a primary decarbonization gas buffer tank 112 to perform gas-liquid separation on the primary decarbonization gas. The gas phase is discharged into the power plant chimney through pipeline 113 as tail gas.

[0071] The primary carbon dioxide concentrate outlet is connected to a first vacuum desorption device and a primary concentrate buffer tank. Specifically, the first vacuum desorption device includes a first vacuum pump 119 and a first vacuum buffer tank 118. Under the suction action of the first vacuum pump 119, the primary carbon dioxide concentrate enters the primary concentrate buffer tank 121 through the first vacuum buffer tank 118.

[0072] The second pressure swing adsorption tower is equipped with a primary carbon dioxide concentrate inlet, a secondary decarbonized gas outlet, and a secondary carbon dioxide concentrate outlet. The primary carbon dioxide concentrate inlet is connected to a primary carbon dioxide concentrate treatment device for pressurizing and cooling the primary carbon dioxide concentrate. Specifically, the primary carbon dioxide concentrate treatment device includes a second booster fan 202 and a second cooler 204 connected in sequence. The primary carbon dioxide concentrate in the primary concentrate buffer tank 121 is pressurized by the second booster fan 202, and the temperature rises. The pressurized primary carbon dioxide concentrate is then passed into the second cooler 204 and cooled by circulating water to a suitable adsorption temperature.

[0073] Preferably, before the cooled primary carbon dioxide concentrate is introduced into the second pressure swing adsorption tower 210, the cooled primary carbon dioxide concentrate can also be introduced into the second buffer tank 206 for gas-liquid separation to further remove moisture from the compressed primary carbon dioxide concentrate, and the gas phase is introduced into the second pressure swing adsorption tower 210 for second pressure swing adsorption separation.

[0074] Specifically, the number of second pressure swing adsorption towers is 4-8, and the operation process of the second pressure swing adsorption separation includes: adsorption, pressure equalization, vacuum desorption and rinsing pressurization.

[0075] The outlet of the secondary decarbonization gas of the second pressure swing adsorption tower 210 is connected to a secondary decarbonization gas buffer tank 211. The secondary decarbonization gas contains a large amount of N2, a small amount of O2 and other components, and the CO2 content in the secondary decarbonization gas is about 20 vol%, which is higher than the CO2 content in the raw flue gas, allowing for further CO2 recovery.

[0076] The outlet of the secondary carbon dioxide concentrate in the second pressure swing adsorption tower 210 is connected to a second vacuum desorption device, which includes a second vacuum pump 208 and a second vacuum buffer tank 207. Under the suction action of the second vacuum pump 208, the secondary carbon dioxide concentrate enters the second vacuum buffer tank 207, and the CO2 content in the secondary carbon dioxide concentrate is concentrated to more than 95 vol%. It is then discharged from the system as CO2 product gas through pipeline 209.

[0077] The membrane concentrator 306 is provided with a secondary decarbonization gas inlet, a non-permeate gas outlet, and a membrane separation carbon dioxide concentrate gas outlet. The secondary decarbonization gas inlet is connected to a secondary decarbonization gas treatment device for pressurizing and cooling the secondary decarbonization gas. Specifically, the secondary decarbonization gas treatment device includes a third pressurizing device and a third cooler 304 connected in sequence. The third pressurizing device can be a compressor 302. After being pressurized by the compressor 302, the temperature of the secondary decarbonization gas increases. The pressurized secondary decarbonization gas is then passed into the third cooler 304 and cooled by circulating water to a suitable adsorption temperature.

[0078] The cooled secondary decarbonized gas enters the membrane concentrator 306. CO2 diffuses through the membrane pores to the other side as the membrane-separated carbon dioxide concentrate, which has a CO2 content of 55-60 vol%. The outlet of the membrane-separated carbon dioxide concentrate is connected to a third vacuum pump 308. The membrane-separated carbon dioxide concentrate is drawn out by the third vacuum pump 308 and then returns to the inlet of the second booster fan 202. The non-permeable gas on the membrane cut-off side is discharged as tail gas through pipeline 307 into the power plant chimney for emission.

[0079] In some specific embodiments of the present invention, the condensate separated from the raw material buffer tank 102, the first buffer tank 108, the primary decarbonization gas buffer tank 112, and the second buffer tank 206 can be sent to the condensate pool 117. After being pressurized by the condensate pump 115, the condensate is sent to the power plant desulfurization tower as makeup water.

[0080] In some specific embodiments of the present invention, the membrane-separated carbon dioxide concentrate gas is mixed with the primary carbon dioxide concentrate gas via pipeline 309 and then fed into the second pressure swing adsorption tower 210 for second pressure swing adsorption separation.

[0081] Specifically, carbon dioxide detectors are installed on the flue gas inlet pipeline, the outlet pipeline of the primary decarbonization gas buffer tank 112, the outlet pipeline of the first vacuum pump 115, the inlet pipeline of the second booster fan 202, the outlet pipeline of the second vacuum pump 208, the outlet pipeline of the secondary decarbonization gas buffer tank 211, the product gas outlet pipeline of the membrane separator concentrator 307, and the outlet pipeline of the third vacuum pump 308 to detect the carbon dioxide content.

[0082] The present invention will be further described in detail below through examples.

[0083] Example 1

[0084] Taking low-concentration desulfurized power plant flue gas as an example, the present invention is used. Figure 1 and Figure 2 The flue gas carbon dioxide capture system shown captures low concentrations of CO2 in power plant flue gas. The effectiveness of the system in treating CO2 is evaluated.

[0085] 10000Nm 3 The flue gas from the power plant, after low-concentration desulfurization at 0.5 kPaG and 55℃ with a CO2 content of 14.17 vol%, enters the raw material buffer tank for vapor-liquid separation to remove entrained moisture. The gas phase is then pressurized to 20 kPaG by the first booster fan, and the flue gas temperature rises to 74.6℃. The pressurized flue gas 104 enters the first cooler and is cooled to 40℃ by circulating water.

[0086] After cooling, the flue gas enters the first buffer tank for vapor-liquid separation to further remove moisture. The gas phase then enters the first pressure swing adsorption (PSA) tower, which is filled with a modified carbonaceous hydrophobic adsorbent. There are six PSA towers in total. The operation of the first PSA tower includes steps such as adsorption, pressure drop equalization, vacuum desorption, and flushing and pressurization. The first adsorbent in the first PSA tower is modified liquefied residue-based activated carbon. The temperature of the first PSA treatment is 40℃, and the pressure is 15 kPaG.

[0087] The primary decarbonization gas contains 1.5 vol% CO2, 84.5 vol% N2, 7.2 vol% O2, and 6.5 vol% H2O. It enters the primary decarbonization gas buffer tank for vapor-liquid separation, and the gas phase is discharged as tail gas into the power plant chimney.

[0088] Under the suction of the first vacuum pump, the minimum desorption working pressure is 20 kPaA. The concentrated CO2 gas with a CO2 content of 49.7 vol% enters the first-stage concentrated gas buffer tank through the first vacuum buffer tank. The condensate separated from the raw material buffer tank, the first buffer tank, and the first-stage decarbonization gas buffer tank enters the condensate pool. After being pressurized by the condensate pump, the condensate is sent to the power plant desulfurization tower as makeup water, with a discharge condensate flow rate of 822.6 kg / h.

[0089] The primary CO2 concentrate is mixed with the membrane-separated CO2 concentrate, with the primary CO2 concentrate accounting for 20% of the mixture. The mixture is pressurized to 20 kPaG by a booster fan, and the temperature rises to 58.4℃. The pressurized mixture then enters a second cooler and is cooled to 40℃ by circulating water. The cooled mixture then enters a second buffer tank for vapor-liquid separation to further remove moisture. The gas phase then enters a second pressure swing adsorption (PSA) tower, which is filled with a modified carbonaceous hydrophobic adsorbent. There are six second PSA towers. The operation of the second PSA tower includes steps such as adsorption, pressure equalization, vacuum desorption, and flushing and pressurization. The second adsorbent in the second PSA tower is a modified carbon molecular sieve; the temperature of the second PSA treatment is 40℃, and the pressure is 18 kPaG.

[0090] Under the suction of the second vacuum pump, the minimum working pressure for desorption is 20 kPaA. The CO2 product gas, which is concentrated to 95.69 vol%, enters the second vacuum buffer tank and is then discharged from the CO2 capture system by the second vacuum pump into the downstream unit. The CO2 capture rate is 90.3%.

[0091] The secondary decarbonized gas discharged from the second pressure swing adsorption tower contains 69.7 vol% N2, 5.9 vol% O2, and 2.8 vol% H2O, with a higher CO2 content than the feed gas (21.4 vol%). It enters the secondary decarbonized gas buffer tank and is pressurized to 150 kPaG by a compressor. The pressurized gas is then cooled to 40°C by circulating water in a third cooler. The cooled gas enters a membrane concentrator using a hollow fiber polyethyleneamine membrane. The membrane separation process is carried out at 40°C and 145 kPaG. CO2 diffuses through the membrane pores to the other side as permeate gas, i.e., membrane-separated carbon dioxide concentrate, with a CO2 content of 57.3 vol%. This permeate gas is then pumped out by a vacuum pump and returned to the inlet of the booster fan. The non-permeate gas on the membrane cutoff side is discharged as tail gas through the exhaust system into the power plant chimney.

[0092] The energy consumption for CO2 capture is 1.72 GJ / tCO2.

[0093] The material balance results are shown in Table 1.

[0094] Table 1

[0095]

[0096] As shown in Table 1, when power plant flue gas with a flow rate of 519.6 kmol / h and a CO2 content of 14.17 vol% is treated using the method of this invention, after the first pressure swing adsorption separation treatment, the flow rate of the primary decarbonized gas is 336.3 kmol / h, and the CO2 content is reduced to 1.53 vol%, while the CO2 content in the primary carbon dioxide concentrate is 49.71 vol%. After the primary concentrate is treated by the second pressure swing adsorption separation treatment, the CO2 content in the secondary carbon dioxide concentrate is 95.69 vol%, which is used as the CO2 product gas. After the secondary decarbonized gas is treated by the membrane separator concentrator, the CO2 content in the membrane-separated carbon dioxide concentrate increases from 21.41 vol% to 57.25 vol%, while the CO2 content in the non-permeable gas decreases to 2.92 vol%.

[0097] Example 2

[0098] The method for capturing CO2 in power plant flue gas in this embodiment is the same as in Embodiment 1, except that: the flue gas is pressurized to 30 kPaG by a first booster fan, and the mixture of primary CO2 concentrate and membrane-separated CO2 concentrate is pressurized to 30 kPaG by a second booster fan. After capture treatment, the CO2 removal rate is 90.3%, and the product gas concentration is 95.69 vol%.

[0099] The energy consumption for CO2 capture is 1.90 GJ / tCO2.

[0100] As can be seen from the above embodiments, the CO2 capture method provided by this invention can meet the capture requirements of CO2-containing gases. Utilizing a pressure swing adsorption-membrane separation coupled process, the CO2 capture rate can reach over 90%, making it a novel and highly efficient carbon capture method. This process can simultaneously improve the CO2 concentration in the product gas and the CO2 capture rate in the flue gas, while effectively reducing regeneration energy consumption. This invention is continuous, fast, efficient, and simple to operate.

[0101] Comparative Example 1

[0102] The method for capturing CO2 in flue gas from a comparative power plant is the same as in Example 1, except that: the flue gas is pressurized to 20 kPaG by a first booster fan, a first pressure swing adsorption tower is filled with molecular sieve adsorbent, the mixture of primary CO2 concentrate and membrane-separated CO2 concentrate is pressurized to 20 kPaG by a booster fan, a second pressure swing adsorption tower is filled with molecular sieve adsorbent, and a freeze-drying dehydration and pressure swing adsorption dehydration unit needs to be added before the first pressure swing adsorption tower. The dehydration and purification requires the consumption of electricity and low-carbon steam.

[0103] After the flue gas is captured, the CO2 removal rate is 89.5%, and the product gas concentration is 95.52 vol%. The energy consumption for CO2 capture is 1.96 GJ / tCO2.

[0104] Comparative Example 2

[0105] The method for capturing CO2 in the flue gas of this comparative power plant was based on existing literature (DOI: 10.1016 / j.memsci.2021.119137). CO2-containing flue gas (CO2 concentration of 14 vol%) was captured using membrane separation. The membrane concentrator was a two-stage pressurized membrane pilot plant. The inlet temperature and pressure of the simulated flue gas were 4.6 bar and 29 °C, respectively. The membrane separator was a polyethyleneamine spiral membrane reactor. After capture treatment, the CO2 removal rate of the simulated flue gas was 61.3%, and the product gas concentration was 78.5 vol%. The unit energy consumption was approximately 809 kWh / tCO2, or 7.45 GJ / tCO2.

[0106] As can be seen from the above embodiments and comparative examples, compared with existing multi-stage pressure swing adsorption and separate membrane concentration methods for CO2 separation, the CO2 capture method provided by this invention can meet the capture requirements of CO2-containing gases. Utilizing a pressure swing adsorption-membrane separation coupled process to capture CO2, the capture rate can reach over 90%, making it a novel and highly efficient carbon capture method. This process can simultaneously improve the CO2 product gas concentration and the CO2 capture rate in flue gas, while effectively reducing regeneration energy consumption. This invention is continuous, fast, efficient, and simple to operate.

[0107] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0108] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0109] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for capturing carbon dioxide from flue gas, characterized in that, The method includes the following steps: The flue gas is fed into the first pressure swing adsorption tower for first pressure swing adsorption treatment to obtain primary decarbonized gas and primary carbon dioxide concentrated gas. The primary carbon dioxide concentrate is passed into a second pressure swing adsorption tower for second pressure swing adsorption treatment to obtain secondary decarbonized gas and secondary carbon dioxide concentrate. The secondary decarbonized gas is concentrated and separated by membrane to obtain non-permeable gas and membrane-separated carbon dioxide concentrated gas; Wherein, the first pressure swing adsorption tower is filled with a first pressure swing adsorbent, and the second pressure swing adsorption tower is filled with a second pressure swing adsorbent; the first pressure swing adsorbent and the second pressure swing adsorbent are modified carbonaceous hydrophobic adsorbents; the first pressure swing adsorbent and the second pressure swing adsorbent are each independently selected from one or more of modified coal-based activated carbon, modified liquefaction residue-based activated carbon, and modified carbon molecular sieves; The method further includes the following step: mixing the membrane-separated carbon dioxide concentrate with the primary carbon dioxide concentrate and then returning the mixture to the second pressure swing adsorption tower; The volume ratio of the primary carbon dioxide concentrate to the membrane-separated carbon dioxide concentrate is 1:(0.2-0.3).

2. The method according to claim 1, wherein, The first pressure swing adsorption process includes, in sequence, first adsorption, first equalization, first desorption, and first flushing and pressurization. The conditions for the first adsorption include: an adsorption temperature of 30-50 °C and an adsorption pressure of 10-25 kPaG; The vacuum degree of the first desorption is 15-30 kPaA; The volume fraction of carbon dioxide in the primary decarbonization gas is 1-3 vol%, and the volume fraction of carbon dioxide in the primary carbon dioxide concentrate gas is 45-65 vol%.

3. The method according to claim 1, wherein, The second pressure swing adsorption process includes, in sequence, a second adsorption, a second equalization, a second desorption, and a second flushing and pressurization. The conditions for the second adsorption include: an adsorption temperature of 30-50 °C and an adsorption pressure of 10-25 kPaG; The vacuum degree of the second desorption is 15-30 kPaA; The volume fraction of carbon dioxide in the secondary decarbonization gas is 20-30 vol; the volume fraction of carbon dioxide in the secondary carbon dioxide concentrate gas is 95-97 vol.

4. The method according to claim 1, wherein, The secondary decarbonized gas is concentrated and separated using a membrane concentrator, wherein the membrane material installed in the membrane concentrator is a hollow fiber membrane, a spiral wound membrane, or a plate membrane. The membrane material is selected from one or more of polydimethylsiloxane, polyethyleneamine, and polyimide.

5. The method according to claim 1, wherein, The conditions for membrane concentration and separation include: a separation temperature of 30-50℃ and a separation pressure of 100-200 kPaG; The volume fraction of carbon dioxide in the membrane-separated carbon dioxide concentrate is 55-65 vol; the volume fraction of carbon dioxide in the non-permeable gas is 1-4 vol.

6. The method according to claim 1, wherein, The method further includes the following steps: Before the primary carbon dioxide concentrate is introduced into the second pressure swing adsorption tower, the primary carbon dioxide concentrate is pressurized and then cooled to the adsorption temperature; and / or Before the secondary decarbonized gas is concentrated and separated by membrane, the secondary decarbonized gas is pressurized and then cooled to the membrane concentration and separation temperature. The pressure of the first-stage carbon dioxide concentrate after pressurization is 10-25 kPaG; The pressure of the secondary decarbonization gas after pressurization is 100-200 kPaG.

7. The method according to claim 1, wherein, The method further includes: compressing the flue gas to 10-25 kPaG before introducing the flue gas into the first pressure swing adsorption tower; and cooling the compressed flue gas to 30-50 °C. The volume fraction of carbon dioxide in the flue gas is 12-15 vol%. The flow rate of the flue gas is 6000-600000 Nm. 3 / h.

8. A flue gas carbon dioxide capture system, characterized in that, The system includes a first pressure swing adsorption tower, a second pressure swing adsorption tower, and a membrane concentrator; The first pressure swing adsorption tower is provided with a flue gas inlet, a primary decarbonization gas outlet and a primary carbon dioxide concentrate gas outlet; the flue gas inlet is connected to a flue gas treatment device for pressurizing and cooling the flue gas, the primary decarbonization gas outlet is connected to a primary decarbonization gas buffer tank, and the primary carbon dioxide concentrate gas outlet is connected to a first vacuum desorption device and a primary concentrate gas buffer tank. The second pressure swing adsorption tower is provided with a primary carbon dioxide concentrate inlet, a secondary decarbonization gas outlet and a secondary carbon dioxide concentrate outlet; the primary carbon dioxide concentrate inlet is connected to a primary carbon dioxide concentrate treatment device for pressurizing and cooling the primary carbon dioxide concentrate, the secondary decarbonization gas outlet is connected to a secondary decarbonization gas buffer tank, and the secondary carbon dioxide concentrate outlet is connected to a second vacuum desorption device. The membrane concentrator is equipped with a secondary decarbonization gas inlet, a non-permeable gas outlet, and a membrane separation carbon dioxide concentrate gas outlet; the secondary decarbonization gas inlet is connected to a secondary decarbonization gas treatment device for pressurizing and cooling the secondary decarbonization gas, and the membrane separation carbon dioxide concentrate gas outlet is connected to a vacuum device. The membrane-separated carbon dioxide concentrate is mixed with the primary carbon dioxide concentrate via a pipeline and then fed into the second pressure swing adsorption tower for second pressure swing adsorption separation.

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