System and method for capturing carbon dioxide in flue gas of gas power plant

Abstract

The invention discloses a gas power plant flue gas carbon dioxide trapping system and method, and belongs to the technical field of gas power plant flue gas treatment. The carbon dioxide trapping system comprises a flue gas pretreatment unit, a membrane enrichment unit, a graded absorption unit, a desorption regeneration unit and an energy collaboration unit. Wherein the membrane enrichment unit is used for pre-enriching low-concentration CO2 flue gas of the flue gas of the gas power plant, so that the load of the subsequent chemical absorption unit and the solvent regeneration energy consumption are remarkably reduced; the graded absorption unit adopts two sections of absorption towers for graded chemical absorption, so that the CO2 absorption effect and efficiency are greatly improved; the desorption and regeneration unit is used for desorbing the enriched liquid absorbed by the graded absorption unit and regenerating the absorbent, and recycling the regenerated absorbent, so that the production cost is greatly reduced, and the energy collaboration unit is used for collecting and utilizing cold energy and heat energy in the flue gas production process of the gas power plant. Compared with an existing carbon dioxide capturing system and method, the system and the method have the advantages of high efficiency, low energy consumption and long-period stable operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flue gas treatment of gas power plants, and particularly relates to a flue gas carbon dioxide capture system and method of a gas power plant. BACKGROUND

[0002] The energy structure is accelerating the transformation to clean and low carbon. Gas power plants play an increasingly important role in the power system due to their high efficiency, flexible start-stop and lower pollutant emissions, and become an important means to replace traditional coal-fired power plants. However, gas power plants are not zero-carbon energy, and the flue gas generated by their combustion still contains a considerable concentration of carbon dioxide, but the concentration is much lower than that of coal-fired power plants. However, in order to control the global temperature rise within the specified target, it is considered indispensable to implement carbon dioxide capture, utilization and storage for gas power plants.

[0003] The most mature and commercialized carbon dioxide capture technology in flue gas at present includes membrane separation method and chemical absorption method. Among them, the membrane separation method uses the different permeation rates of different gases in the membrane material to realize separation, and has the advantages of simplicity and low energy consumption. However, when applied to low-concentration (3-5%) CO2 separation, traditional polymer membranes (such as polyimide) have the problems of insufficient selectivity (CO2 / N2<50) under normal pressure and low-concentration CO2 conditions, and the membrane plasticization failure caused by the wide temperature fluctuation range (50-150℃) of gas power plant flue gas, short service life of the membrane (usually less than 1 year) and the like. Although the use of zeolite membranes in traditional carbon dioxide gas separation membranes can improve the selectivity of carbon dioxide, the cost is high and the durability is low due to the easy dust blockage. Patent application No. CN202410644855.1 discloses a cross-linked polymer membrane, which uses high-temperature cross-linking (>100℃) to improve the stability of the membrane, but additional energy consumption is increased. The chemical absorption method usually uses an alcohol amine aqueous solution as an absorbent, among which MEA (ethanol amine) reacts fastest with CO2 and is thus used most. However, when it is directly used to treat low-concentration CO2 flue gas, the regeneration energy consumption of the absorbent (such as MEA) is high (up to 3.8-4.2 GJ / tCO2), accounting for more than 70% of the total system energy consumption, resulting in high operation cost.

[0004] In recent years, some researches have begun to explore the process of coupling membrane separation as a pretreatment unit with chemical absorption, aiming to preliminarily enrich CO2 by using membrane method to reduce the load of the subsequent absorption tower and the regeneration energy consumption. However, the existing coupling schemes still have obvious shortcomings: (1) the membrane material is not suitable: the inherent selectivity and stability problems have not been solved, and the enrichment effect is limited. (2) low system integration: the energy flow of the entire coupling system has not been deeply optimized. (3) simple control strategy: the existing system lacks intelligent dynamic control strategies to cope with the fluctuation of flue gas working conditions, and it is difficult to make the membrane unit and the absorption unit always work at the optimal efficiency point.

[0005] Therefore, the application provides a flue gas CO2 capture system and method for gas power plants, which is efficient, low in energy consumption and stable in long-period operation, to solve the above problems. SUMMARY

[0006] To solve the technical problems in the background art, the main purpose of the application is to provide a flue gas CO2 capture system and method for gas power plants, which effectively couples the advantages of membrane separation and chemical absorption technology, and integrates energy co-utilization, so as to realize an efficient, low-energy-consumption and long-period-stable CO2 capture system and method.

[0007] To achieve the above purpose, the application provides a flue gas CO2 capture system for gas power plants, which comprises a flue gas pretreatment unit, a membrane enrichment unit, a staged absorption unit, a desorption regeneration unit and an energy co-utilization unit. The flue gas pretreatment unit is used for flue gas cooling and dust removal, and is provided with a flue gas inlet and a pretreated flue gas outlet, wherein the flue gas inlet is connected with the outlet of a gas boiler of the gas power plant. The membrane enrichment unit is filled with a CO2 separation membrane, and is provided with an enrichment unit inlet and a permeate gas outlet, wherein the enrichment unit inlet is connected with the pretreated flue gas outlet. The staged absorption unit comprises an absorption tower, which comprises an upper-stage absorption tower, a lower-stage absorption tower and a gas-liquid redistributor arranged between the upper-stage absorption tower and the lower-stage absorption tower, wherein the lower-stage absorption tower is provided with an absorption tower gas inlet, a first rich liquid outlet and a first regenerated lean liquid backflow port, and the upper-stage absorption tower is provided with a clean flue gas outlet, a second rich liquid outlet and a second regenerated lean liquid backflow port, wherein the absorption tower gas inlet is connected with the permeate gas outlet to receive the enriched CO2 flue gas. The desorption regeneration unit is used for heating and desorbing the first rich liquid and the second rich liquid in the staged absorption unit to obtain product gaseous CO2, the first regenerated lean liquid and the second regenerated lean liquid, and the first regenerated lean liquid and the second regenerated lean liquid are backflowed to the staged absorption unit for recycling. The energy co-utilization unit comprises a heat source subsystem and a cold source subsystem, wherein the heat source subsystem is used for providing desorption heat energy to the desorption regeneration unit, and the cold source subsystem is coupled with a liquefied natural gas gasification device of the gas power plant to recycle liquefied natural gas cold energy.

[0008] Further, the flue gas CO2 capture system for gas power plants further comprises an intelligent control system, which is configured to: adjust the vacuum degree of the permeation side of the membrane enrichment unit in real time based on the fluctuation of the flue gas flow of the gas power plant processed by the CO2 capture system. Based on the carbon dioxide concentration at the membrane enrichment unit outlet, the circulation flow rate of the absorption liquid in the staged absorption unit is optimized in real time.

[0009] Further, the desorption regeneration unit comprises a first group of multi-stage heat exchangers, a second group of multi-stage heat exchangers, a solar reboiler, a desorption tower and a lean liquid cooler, the first group of multi-stage heat exchangers is connected with the first rich liquid outlet, the second group of heat exchangers is connected with the second rich liquid outlet, the inlet end of the desorption tower is connected with the solar reboiler, and the outlet end is connected with the lean liquid cooler, the lean liquid cooler is used for cooling the first regenerated lean liquid and the second regenerated lean liquid, and the solar reboiler is connected with a heat source subsystem.

[0010] Further, the carbon dioxide separation membrane filled in the membrane enrichment unit is a composite membrane with a gradient pore structure, which comprises a surface dense layer, a transition layer and a large-pore support layer from top to bottom; the surface dense layer is an ethylenediamine cross-linked bromomethylated self-microporous polymer with a pore size less than 1 nm; the transition layer is a functionalized polyimide with a gradient pore structure and a pore size of 10-20 nm; and the large-pore support layer is a polysulfone porous base film with a pore size greater than 50 nm.

[0011] Further, the thickness of the surface dense layer is 0.1-1 μm, the thickness of the transition layer is 3-10 μm, and the thickness of the large-pore support layer is 50-150 μm.

[0012] Further, the methyldiethanolamine absorption liquid with a mass concentration of 10-20 wt% is introduced into the lower-stage absorption tower, and the pentaethylenehexamine absorption liquid with a mass concentration of 25-35 wt% is introduced into the upper-stage absorption tower.

[0013] Further, the heat source subsystem comprises a solar heat collector, a molten salt heat storage tank and a gas turbine exhaust steam pipeline, the output end of the solar heat collector is connected with the input end of the molten salt heat storage tank and the solar reboiler respectively, and the molten salt heat storage tank is connected with the gas turbine exhaust steam pipeline in parallel through a temperature control valve.

[0014] Further, the cold source subsystem comprises a primary cold energy utilization pipeline and a secondary cold energy utilization pipeline, the outlet of the primary cold energy utilization pipeline is connected with the product gaseous carbon dioxide outlet of the desorption regeneration unit for liquefying the gaseous carbon dioxide, and the outlet of the secondary cold energy utilization pipeline is connected with the absorption tower gas inlet of the staged absorption unit for cooling the absorption tower inlet flue gas.

[0015] In another aspect of the present application, a flue gas carbon dioxide capture method for a gas power plant is provided, which is realized by using the above-mentioned carbon dioxide capture system and comprises the following steps: Preprocessing: the flue gas at the outlet of the gas boiler is introduced into a flue gas preprocessing unit for cooling and dust removal preprocessing to obtain preprocessed flue gas; Membrane enrichment: the pretreated flue gas enters the enrichment unit of the membrane enrichment unit from the enrichment unit inlet, and after membrane enrichment, the flue gas with increased carbon dioxide concentration flows out from the permeate gas outlet; Fractional absorption: the flue gas from the permeate gas outlet enters the lower section absorption tower from the absorption tower gas inlet of the fractional absorption unit for pre-absorption to obtain first rich liquid and first absorbed flue gas, and the pre-absorbed flue gas enters the upper section absorption tower through the gas-liquid redistributor for deep absorption to obtain clean flue gas and second rich liquid; Desorption regeneration: the first rich liquid and the second rich liquid are introduced into the desorption regeneration unit for heating desorption to obtain gaseous carbon dioxide, first regenerated lean liquid and second regenerated lean liquid, and the gaseous carbon dioxide is liquefied to obtain liquid carbon dioxide, the first regenerated lean liquid is returned to the first regenerated lean liquid return port of the lower section absorption tower for recycling, and the second regenerated lean liquid is returned to the second regenerated lean liquid return port of the upper section absorption tower for recycling; Energy synergy: the energy synergy unit is used to provide heat energy in the heating desorption process, and to provide cold energy for the gaseous carbon dioxide liquefaction process and the cooling of the absorption tower inlet flue gas.

[0016] Further, the method further comprises an intelligent control step: The intelligent control system monitors the amount of pretreated flue gas introduced into the membrane enrichment unit, and adjusts the vacuum degree of the permeation side of the membrane enrichment unit in real time when the amount of flue gas exceeds the preset value, and the negative pressure of the permeation side is increased by 0.01-0.05 MPa when the amount of flue gas exceeds the preset value by 5-15%. The intelligent control system also monitors the carbon dioxide concentration in the permeate gas at the outlet of the membrane enrichment unit in real time, and adjusts the circulation flow rate of the absorption liquid in the upper section absorption tower according to the carbon dioxide concentration in the permeate gas.

[0017] Further, in the fractional absorption process, the liquid-gas ratio in the lower section absorption tower is 1.0-2.0 L / Nm 3 , and the mass concentration of the methyldiethanolamine absorption liquid is 10-20 wt%, and the liquid-gas ratio in the upper section absorption tower is 1.5-2.5 L / Nm 3 , and the mass concentration of the pentaethylenehexamine absorption liquid is 25-35 wt%.

[0018] Compared with the prior art, the present application has the following beneficial effects: The gas power plant flue gas carbon dioxide capture system provided by the application integrates chemical absorption and membrane separation to capture carbon dioxide in flue gas, and comprises five modules, wherein the flue gas pretreatment unit is used for flue gas cooling and dust removal to ensure that the subsequent units can stably and efficiently operate; the membrane enrichment unit is used for pre-enrichment of low-concentration CO2 flue gas of the gas power plant flue gas, thereby significantly reducing the load of the subsequent chemical absorption unit and the solvent regeneration energy consumption; the staged absorption unit adopts two-stage absorption towers for staged chemical absorption, thereby greatly improving the CO2 absorption effect and efficiency; the desorption regeneration unit desorbs the enrichment liquid absorbed by the staged absorption unit and regenerates the absorbent, and the regenerated absorbent is reused, thereby greatly reducing the production cost. In addition, the energy collaborative unit and the intelligent control system are constructed in the system, the energy collaborative unit collects and utilizes the cold energy and the heat energy in the flue gas production process of the gas power plant, and the intelligent control system is used for dynamic regulation and control of the absorbent flow and the membrane pressure difference. In summary, the carbon dioxide capture system has the advantages of high efficiency, low energy consumption and long-period stable operation compared with the existing carbon dioxide capture system. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The structure schematic diagram of the gas power plant flue gas carbon dioxide capture system in an embodiment of the application is shown. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0021] It should be noted that the ethylenediamine crosslinking bromomethylation self-porous polymer of the application is a self-porous polymer (PIMs) that is modified by bromomethylation chemistry to impart reactivity using ethylenediamine as a crosslinking agent. It provides active sites by introducing bromomethyl (-CH2Br) functional groups on the rigid twisted backbone of PIMs, using a crosslinking agent. Self-porous polymer (PIMs): the molecular chain of the polymer cannot be tightly packed due to its rigid structure and twisted conformation, and naturally forms nanoscale micropores (pore size is usually less than 2 nm) when packed in solid state, and the specific surface area can reach more than 800 m² / g.

[0022] To achieve the above-mentioned purpose, the first aspect of the embodiments of the application provides a gas power plant flue gas carbon dioxide capture system, as shown in the figure, the system comprises a flue gas pretreatment unit, a membrane enrichment unit, a staged absorption unit, a desorption regeneration unit and an energy collaborative unit. Figure 1 The system comprises a flue gas pretreatment unit, a membrane enrichment unit, a staged absorption unit, a desorption regeneration unit and an energy collaborative unit. The flue gas pre-treatment unit is used for flue gas cooling and dust removal, and is provided with a flue gas inlet and a pre-treated flue gas outlet, wherein the flue gas inlet is connected with the outlet of the gas boiler of the gas power plant. The membrane enrichment unit is filled with a carbon dioxide separation membrane, and is provided with an enrichment unit inlet and a permeated gas outlet, wherein the enrichment unit inlet is connected with the pre-treated flue gas outlet. The staged absorption unit comprises an absorption tower, wherein the absorption tower comprises an upper-stage absorption tower, a lower-stage absorption tower and a gas-liquid redistributor arranged between the upper-stage absorption tower and the lower-stage absorption tower, the lower-stage absorption tower is provided with an absorption tower gas inlet, a first rich liquid outlet and a first regenerated lean liquid backflow port, and the upper-stage absorption tower is provided with a clean flue gas outlet, a second rich liquid outlet and a second regenerated lean liquid backflow port, wherein the absorption tower gas inlet is connected with the permeated gas outlet to receive the enriched carbon dioxide flue gas. The desorption and regeneration unit is used for heating and desorbing the first rich liquid and the second rich liquid in the staged absorption unit to obtain product gaseous carbon dioxide, the first regenerated lean liquid and the second regenerated lean liquid, and the first regenerated lean liquid and the second regenerated lean liquid are backflowed to the staged absorption unit for recycling. The energy coordination unit comprises a heat source subsystem and a cold source subsystem, wherein the heat source subsystem is used for providing desorption heat energy to the desorption and regeneration unit, and the cold source subsystem is coupled with the liquefied natural gas gasification device of the gas power plant and is used for recycling the cold energy of the liquefied natural gas.

[0023] The flue gas carbon dioxide capture system of the gas power plant provided by the application comprehensively adopts the chemical absorption and membrane separation methods to capture carbon dioxide in flue gas, and comprises five modules, wherein the flue gas pre-treatment unit is used for flue gas cooling and dust removal to ensure that the subsequent units can stably and efficiently operate; the membrane enrichment unit is used for pre-enriching the low-concentration (3-5%) CO2 flue gas of the flue gas of the gas power plant, thereby significantly reducing the load of the subsequent chemical absorption unit and the solvent regeneration energy consumption; the staged absorption unit adopts two-stage absorption towers for staged chemical absorption, thereby greatly improving the CO2 absorption effect and efficiency; the desorption and regeneration unit desorbs the enriched liquid absorbed by the staged absorption unit and regenerates the absorption agent, and the regenerated absorption agent is reused, thereby greatly reducing the production cost, and in addition, the energy coordination unit is constructed in the system to collect and utilize the cold energy and heat energy in the flue gas production process of the gas power plant.

[0024] In a preferred embodiment of the present invention, the flue gas carbon dioxide capture system for gas-fired power plants further includes an intelligent control system. The intelligent control system is configured to: adjust the vacuum level on the permeate side of the membrane enrichment unit in real time based on fluctuations in the flue gas flow rate processed by the carbon dioxide capture system; and optimize the circulation flow rate of the absorbent in the staged absorption unit in real time based on the carbon dioxide concentration at the outlet of the membrane enrichment unit. By sensing the system status in real time and dynamically optimizing key operating parameters (such as membrane-side pressure difference and absorbent circulation volume) through the intelligent control system, the system always operates under optimal conditions, further improving the system's efficiency and stability.

[0025] In a preferred embodiment of the present invention, the desorption regeneration unit includes a first set of multi-stage heat exchangers, a second set of multi-stage heat exchangers, a solar reboiler, a desorption tower, and a lean liquid cooler. The first set of multi-stage heat exchangers is connected to the outlet of the first rich liquid for preheating the first rich liquid, and the second set of heat exchangers is connected to the outlet of the second rich liquid for preheating the second rich liquid. The inlet end of the desorption tower is connected to the solar reboiler, and the outlet end is connected to the lean liquid cooler. The lean liquid cooler is used to cool the first regenerated lean liquid and the second regenerated lean liquid. The solar reboiler is connected to the heat source subsystem.

[0026] This invention utilizes a first set of multi-stage heat exchangers and a second set of multi-stage heat exchangers in the upper and lower sections of the absorption tower, which are configured according to a graded absorption unit. These first and second sets of heat exchangers are used to preheat the first and second rich solutions, which have absorbed high concentrations of CO2, in the upper and lower sections of the absorption tower, respectively. A solar-powered reboiler provides a heat source for the desorption tower to perform desorption. Exemplarily, the desorption process of the desorption regeneration unit is as follows: the first / second rich solution is sequentially heated by a first-stage heat exchanger (using the waste heat from the flue gas at the outlet of the gas-fired boiler to preheat to 90°C to obtain the first / second lean-rich solution) → the first / second lean-rich solution is heated by a second-stage heat exchanger (using the waste heat from the lean solution to preheat to 100°C) → the solar-powered reboiler provides a heat source for the desorption tower to desorb the first / second lean-rich solution (desorption at 120°C) → the lean solution cooler cools the regenerated first / second regenerated lean solution after desorption (using the cold energy of LNG (liquefied natural gas) to cool it to 40°C).

[0027] In a preferred embodiment of the present invention, the flue gas pretreatment unit includes a vortex cooling dust collector for cooling and dust removal. During the cooling and dust removal process: the tangential inlet velocity of the vortex cooling dust collector is 18~22m / s, the inclination angle of the spiral guide plate is 40~45°, and the induced draft fan pressure is 0.12~0.15MPa, achieving a dust removal rate of >95% through centrifugal sedimentation; by countercurrent contact with the boiler outlet flue gas at 35~45℃ atomized cooling water, the flue gas temperature is stabilized at 60±5℃.

[0028] In a preferred embodiment of the present invention, the carbon dioxide separation membrane filled in the membrane enrichment unit is a composite membrane comprising, from top to bottom, a dense surface layer, a transition layer, and a macroporous support layer; the dense surface layer is an ethylenediamine crosslinked bromomethylated self-contained microporous polymer with a pore size less than 1 nm; the transition layer is a functionalized polyimide with a gradient pore structure and a pore size of 10-20 nm; and the macroporous support layer is a polysulfone porous base membrane with a pore size greater than 50 nm. The functionalized polyimide refers to a polyimide main chain or side chain that has been chemically modified to introduce crosslinking sites (such as bromomethyl, alkynyl, amino, etc.). This polymer possesses good mechanical strength, thermal stability, and chemical stability, providing a solid foundation for constructing a stable gradient pore structure and an ideal platform for realizing Hoffmann alkylation or other chemical reactions.

[0029] Existing traditional membrane materials exhibit insufficient CO2 selectivity and are prone to plasticization failure under normal pressure and low CO2 concentration conditions. This invention addresses this issue by designing a three-layer composite membrane. The dense surface layer is a microporous polymer cross-linked with ethylenediamine, serving as the selective separation layer. The rigid, positively charged quaternary ammonium salt network formed by the ethylenediamine cross-linking inhibits polymer chain movement, and the swelling stress generated by CO2 dissolution conversely enhances mechanical strength. Furthermore, the specific interaction between the quaternary ammonium salt and CO2 effectively improves the CO2 selectivity in flue gas (CO2 / N2 greater than 150). The transition layer, a functionalized polyimide with a gradient pore structure, buffers swelling stress and inhibits plastic deformation, while the polysulfone porous base membrane reduces mass transfer resistance. Through the synergistic effect between the layers, this invention effectively improves the plasticity resistance and CO2 selectivity of the carbon dioxide separation membrane. More preferably, the thickness of the dense surface layer is 0.1–1 μm, the thickness of the transition layer is 3–10 μm, and the thickness of the macroporous support layer is 50–150 μm.

[0030] The specific preparation method of the ethylenediamine crosslinked bromomethylated self-porous polymer is as follows: dissolve bromomethylated PIM in a solvent (such as chloroform) to obtain a mixture, add ethylenediamine (the amount of ethylenediamine added accounts for 5~10wt% of the total membrane solution mass) to the mixture to obtain a membrane solution, carry out the crosslinking reaction at 50~80℃ for 3~6h, and then form the ethylenediamine crosslinked bromomethylated self-porous polymer by the scraping method.

[0031] In a preferred embodiment of the present invention, the lower section of the absorption tower in the graded absorption unit is filled with structured packing (such as 3m high 250Y type structured packing) and 10-20wt% methyl diethanolamine (MDEA) absorbent is introduced, while the upper section of the absorption tower is filled with packing (such as 4.5m high wire mesh packing) and 25-35wt% pentaethylenehexamine (PEHA) absorbent is introduced.

[0032] In the staged absorption unit of this invention, the absorption tower employs MDEA and PEHA for staged absorption. The lower stage uses MDEA to neutralize acidic gases and perform pre-absorption, protecting the main absorbent in the upper stage; the upper stage uses PEHA for deep absorption. This combination fully utilizes the characteristics of different amine agents (MDEA's high stability and PEHA's high absorption efficiency), significantly reducing amine agent loss and degradation.

[0033] In a preferred embodiment of the present invention, the gas-liquid redistributor is a conical gas-liquid redistributor with an opening ratio of 35-45%, an inclination angle of 10-20°, and a polytetrafluoroethylene coating on its surface. Installing a gas-liquid redistributor inside the absorption tower effectively prevents amine liquid cross-flow, ensuring uniform distribution and contact efficiency of the gas and liquid phases.

[0034] In a preferred embodiment of the present invention, the heat source subsystem includes a solar collector, a molten salt storage tank, and a gas turbine exhaust steam pipeline. The output end of the solar collector is connected in parallel with the input end of the molten salt storage tank, and the molten salt storage tank is connected in parallel with the gas turbine exhaust steam pipeline via a temperature control valve. The cold source subsystem includes a primary cold energy utilization pipeline and a secondary cold energy utilization pipeline. The outlet of the primary cold energy utilization pipeline is connected to the product gaseous carbon dioxide outlet of the desorption regeneration unit for liquefying gaseous carbon dioxide. The outlet of the secondary cold energy utilization pipeline is connected to the inlet of the absorption tower of the staged absorption unit for cooling the flue gas at the inlet of the absorption tower.

[0035] The molten salt thermal storage tank in the heat source subsystem of this invention can store the daytime surplus solar energy from the solar collector and the waste heat generated by the exhaust steam from the gas turbine. For example, when the solar irradiance is >800W / m²... 2 At that time, the solar collector directly supplies energy to the reboiler, with a solar irradiance of <200W / m². 2 When necessary, start the molten salt heat storage tank (NaNO3-KNO3) for supplemental heating.

[0036] LNG (liquefied natural gas) has a storage temperature of -162°C under normal pressure and requires a large amount of heat (approximately 830 kJ / kg) to vaporize. CO2 has a critical temperature of 31°C and requires high-pressure cryogenic cooling (typically below -50°C) for liquefaction. The initial stage cold energy of LNG (-160°C) perfectly meets this requirement. However, traditional gas-fired power plants directly use seawater or air to vaporize LNG, resulting in wasted cold energy. This invention utilizes a primary cold energy utilization pipeline to supply LNG cold energy to a heat exchanger to cool and liquefy the captured CO2 gas. Compared to traditional compression refrigeration for CO2 liquefaction (energy consumption approximately 0.8 kWh / kg), LNG cold energy liquefaction energy consumption can be reduced to 0.15 kWh / kg. In gas-fired power plants, when the propane refrigeration cycle cools the inlet flue gas of the absorption tower to 40°C and the LNG vaporizes to around -40°C, the cold energy grade is still significantly lower than the ambient temperature. This portion of cold energy is converted into medium-temperature cold energy through a propane refrigeration cycle (working fluid boiling point -42℃). This cold energy is then supplied to the flue gas at the inlet of the absorption tower through a secondary cold energy utilization pipeline to cool the flue gas at the inlet of the absorption tower. This can reduce the flue gas temperature from 50~150℃ to 35~45℃, thereby improving the CO2 capture efficiency of the subsequent chemical absorbent (the absorption rate increases by 15~20% for every 10℃ decrease in temperature).

[0037] A second aspect of the present invention provides a method for capturing carbon dioxide from flue gas in a gas-fired power plant, which employs the aforementioned carbon dioxide capture system. The method includes the following steps: Pretreatment: The flue gas from the gas boiler outlet is passed into the flue gas pretreatment unit for cooling and dust removal pretreatment to obtain pretreated flue gas; Membrane enrichment: The pretreated flue gas enters from the inlet of the enrichment unit of the membrane enrichment unit. After membrane enrichment, the flue gas with increased carbon dioxide concentration flows out from the permeate outlet. Staged absorption: The flue gas from the permeate outlet enters the lower absorption tower through the inlet of the absorption tower of the staged absorption unit for pre-absorption to obtain the first rich liquid and the flue gas after the first absorption. The pre-absorbed flue gas is then passed through the gas-liquid redistributor into the upper absorption tower for deep absorption to obtain the clean flue gas and the second rich liquid. Desorption and regeneration: The first rich liquid and the second rich liquid are passed into the desorption and regeneration unit for heating and desorption to obtain gaseous carbon dioxide, the first regeneration lean liquid and the second regeneration lean liquid. The gaseous carbon dioxide is then liquefied to obtain liquid carbon dioxide. The first regeneration lean liquid is returned to the first regeneration lean liquid return port of the lower absorption tower for recycling, and the second regeneration lean liquid is returned to the second regeneration lean liquid return port of the upper absorption tower for recycling. Energy Coordination: The energy coordination unit provides thermal energy during the heating and desorption process, and provides cold energy for the gaseous carbon dioxide liquefaction process and the flue gas at the inlet of the absorption tower.

[0038] In a preferred embodiment of the present invention, before the staged absorption step, the flue gas at the permeate outlet is cooled to reduce the flue gas temperature at the permeate outlet to 35~45°C.

[0039] In a preferred embodiment of the present invention, the method further includes an intelligent control step: the intelligent control system monitors the amount of pretreated flue gas introduced into the membrane enrichment unit, and adjusts the vacuum degree on the permeate side of the membrane enrichment unit in real time when the amount of flue gas exceeds a preset value. When the amount of flue gas exceeds the preset value by 5 to 15%, the negative pressure on the permeate side increases by 0.01 to 0.05 MPa. The intelligent control system also monitors the carbon dioxide concentration in the permeate gas at the outlet of the membrane enrichment unit in real time, and adjusts the circulation flow rate of the absorbent in the upper absorption tower according to the carbon dioxide concentration in the permeate gas.

[0040] Further, adjusting the circulating flow rate of the absorbent in the upper absorption tower according to the carbon dioxide concentration in the permeate includes: (1) setting the initial circulating flow rate of the absorbent in the upper absorption tower as Q0; (2) adjusting the coefficient k in real time according to the CO2 concentration in the permeate at the outlet of the membrane enrichment unit; (3) according to... After the formula is determined and adjusted, the circulation flow rate of the absorbent in the upper section of the absorber tower is determined. .

[0041] In a preferred embodiment of the present invention, during the staged absorption process, a liquid-to-gas ratio of 1.0~2.0 L / Nm³ is used in the lower absorption tower. 3 Pre-absorption was performed using a methyldiethanolamine absorbent solution with a mass concentration of 10-20 wt%, with a liquid ratio of 1.5-2.5 L / Nm³ in the upper absorption tower. 3 Deep absorption was performed using a pentaethylenehexamine absorbent solution with a mass concentration of 25-35 wt%.

[0042] Example A method for capturing carbon dioxide from flue gas in a gas-fired power plant, using the aforementioned carbon dioxide capture system, includes the following steps: Step S1, Pretreatment: The flue gas from the gas boiler outlet (120~150℃, CO2 mass concentration of 5%) is passed into the flue gas pretreatment unit for cooling and dust removal pretreatment to obtain pretreated flue gas (temperature of 60±5℃).

[0043] Step S2, Membrane enrichment: The pretreated flue gas is drawn from the membrane enrichment unit (filled with a carbon dioxide separation membrane, with a membrane area of ​​6000 m²). 2 The filling density is 800m³. 2 / m 3 From top to bottom, it consists of a dense surface layer, a transition layer, and a macroporous support layer; the dense surface layer is an ethylenediamine cross-linked bromomethylated self-contained microporous polymer with a pore size of less than 1 nm and a cross-linking density of 8.2 × 10⁻⁶. - 4mol / cm 3 The CO2 concentration in the enrichment unit is as follows: The first layer is a functionalized polyimide with a gradient pore structure and a thickness of 0.3 μm; the second layer is a polysulfone porous base membrane with a pore size greater than 50 nm and a thickness of 100 μm. After enrichment by the membrane (vacuum on the permeate side is -0.07 MPa), the flue gas with increased carbon dioxide concentration flows out from the permeate outlet. The CO2 concentration in the membrane enrichment unit changes from 5% at the inlet to 18% at the outlet of the polysulfone porous base membrane, then to 32% at the outlet of the functionalized polyimide with a gradient pore structure, and finally to 42% at the outlet of the ethylenediamine crosslinked bromomethylated self-porous polymer.

[0044] Step S3, staged absorption: The flue gas from the permeate outlet enters the lower absorption tower through the inlet of the absorption tower in the staged absorption unit for pre-absorption to obtain the first rich liquid and the flue gas after the first absorption. The pre-absorbed flue gas is then passed through a gas-liquid redistributor into the upper absorption tower for deep absorption to obtain the clean flue gas and the second rich liquid. The lower absorption tower is filled with 3m high 250Y type structured packing and 15wt% MDEA solution is introduced, with a liquid-to-gas ratio of 1.5L / Nm³. The upper section is filled with 4.5m high wire mesh packing and 30wt% PEHA solution is introduced, with a liquid-to-gas ratio of 2.0L / Nm³. A conical gas-liquid redistributor (40% porosity, 15° inclination, 80μm PTFE coating thickness) is installed between the two layers.

[0045] Step S4, Desorption and Regeneration: The first and second rich solutions are fed into the desorption and regeneration unit for heating and desorption, including: the first / second rich solutions are sequentially heated to 90°C by a primary heat exchanger → the first / second lean-rich solutions are heated to 100°C by a secondary heat exchanger → a solar reboiler provides a heat source for the desorption tower to desorb the first / second lean-rich solutions to obtain gaseous carbon dioxide and the first / second regenerated lean solutions, with a desorption temperature of 120°C → a lean solution cooler cools the desorbed regenerated first / second regenerated lean solutions to 40°C, and then liquefies the gaseous carbon dioxide to obtain liquid carbon dioxide. The cooled first regenerated lean solution is returned to the first regenerated lean solution return port of the lower absorption tower for recycling, and the cooled second regenerated lean solution is returned to the second regenerated lean solution return port of the upper absorption tower for recycling; the energy coordination unit provides heat energy during the heating and desorption process and cold energy for the gaseous carbon dioxide liquefaction process.

[0046] Step S5, Intelligent Control: The intelligent control system monitors the amount of pretreated flue gas introduced into the membrane enrichment unit. When the amount of flue gas exceeds the preset value, the vacuum degree on the permeate side of the membrane enrichment unit is adjusted in real time. Specifically, when the amount of flue gas exceeds the preset value by 10%, the negative pressure on the permeate side is increased by 0.01 MPa. The intelligent control system monitors the carbon dioxide concentration in the permeate gas at the outlet of the membrane enrichment unit in real time, and adjusts the circulation flow rate of the absorbent in the upper absorption tower according to the carbon dioxide concentration in the permeate gas. In this embodiment, the basic flow rate Q0 of the PEHA solution in the upper absorption tower is 10.2 m³ / h, and then... The operational logic adjusts the flow rate of the PEHA solution. (Where, the value of k ranges as follows: when the CO2 concentration in the permeate gas at the outlet of the membrane enrichment unit is less than 30%, k=1.0; when the concentration is 30~45%, k=1.4; when the concentration is greater than 45%, k=1.6).

[0047] The above embodiments are merely illustrative of implementation methods of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. The present invention can also be implemented in other specific ways or forms without departing from the spirit or essential characteristics of the present invention. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of the present invention should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A carbon dioxide capture system for flue gas from a gas-fired power plant, characterized in that, The system includes a flue gas pretreatment unit, a membrane enrichment unit, a graded absorption unit, a desorption and regeneration unit, and an energy synergy unit. The flue gas pretreatment unit is used to cool and remove dust from the flue gas, and is equipped with a flue gas inlet and a pretreated flue gas outlet. The flue gas inlet is connected to the outlet of the gas boiler of the gas-fired power plant. The membrane enrichment unit is filled with a carbon dioxide separation membrane and is provided with an enrichment unit inlet and a permeate outlet. The enrichment unit inlet is connected to the pretreated flue gas outlet. The staged absorption unit includes an absorption tower, which includes an upper absorption tower, a lower absorption tower, and a gas-liquid redistributor disposed between the upper and lower absorption towers. The lower absorption tower is provided with an absorption tower inlet, a first rich liquid outlet, and a first regenerated lean liquid return outlet. The upper absorption tower is provided with a clean flue gas outlet, a second rich liquid outlet, and a second regenerated lean liquid return outlet. The absorption tower inlet is connected to the permeate outlet to receive the enriched carbon dioxide flue gas. The desorption and regeneration unit is used to heat and desorb the first rich liquid and the second rich liquid in the graded absorption unit to obtain product gaseous carbon dioxide, the first regenerated lean liquid and the second regenerated lean liquid, and to return the first regenerated lean liquid and the second regenerated lean liquid to the graded absorption unit for recycling. The energy coordination unit includes a heat source subsystem and a cold source subsystem. The heat source subsystem is used to provide desorption heat energy to the desorption regeneration unit, and the cold source subsystem is coupled to the liquefied natural gas gasification unit of the gas-fired power plant for recovering and utilizing the cold energy of liquefied natural gas.

2. The flue gas carbon dioxide capture system for gas-fired power plants according to claim 1, characterized in that, The flue gas carbon dioxide capture system for the gas-fired power plant also includes an intelligent control system, which is configured as follows: Based on the fluctuations in the flue gas flow rate of the gas-fired power plant processed by the carbon dioxide capture system, the vacuum level on the permeate side of the membrane enrichment unit is adjusted in real time. Based on the carbon dioxide concentration at the outlet of the membrane enrichment unit, the circulation flow rate of the absorbent in the graded absorption unit is optimized in real time.

3. The flue gas carbon dioxide capture system for gas-fired power plants according to claim 1, characterized in that, The desorption regeneration unit includes a first set of multi-stage heat exchangers, a second set of multi-stage heat exchangers, a solar reboiler, a desorption tower, and a lean liquid cooler. The first set of multi-stage heat exchangers is connected to the first rich liquid outlet, and the second set of heat exchangers is connected to the second rich liquid outlet. The inlet end of the desorption tower is connected to the solar reboiler, and the outlet end is connected to the lean liquid cooler. The lean liquid cooler is used to cool the first regenerated lean liquid and the second regenerated lean liquid. The solar reboiler is connected to the heat source subsystem.

4. The flue gas carbon dioxide capture system for gas-fired power plants according to claim 1, characterized in that, The carbon dioxide separation membrane filled in the membrane enrichment unit is a composite membrane with a gradient pore structure, which includes a surface dense layer, a transition layer and a macroporous support layer from top to bottom; the surface dense layer is an ethylenediamine crosslinked bromomethylated self-microporous polymer with a pore size of less than 1 nm; the transition layer is a functionalized polyimide with a gradient pore structure and a pore size of 10~20 nm; and the macroporous support layer is a polysulfone porous base membrane with a pore size of greater than 50 nm.

5. The flue gas carbon dioxide capture system for gas-fired power plants according to claim 4, characterized in that, The thickness of the surface dense layer is 0.1~1μm, the thickness of the transition layer is 3~10μm, and the thickness of the macroporous support layer is 50~150μm.

6. The flue gas carbon dioxide capture system for gas-fired power plants according to claim 1, characterized in that, The lower absorption tower is filled with a methyldiethanolamine absorbent solution with a mass concentration of 10-20 wt%, and the upper absorption tower is filled with a pentaethylenehexamine absorbent solution with a mass concentration of 25-35 wt%.

7. The flue gas carbon dioxide capture system for gas-fired power plants according to claim 1, characterized in that, The heat source subsystem includes a solar collector, a molten salt heat storage tank, and a gas turbine exhaust steam pipeline. The output end of the solar collector is connected to the input end of the molten salt heat storage tank and a solar reboiler, respectively. The molten salt heat storage tank is connected in parallel to the gas turbine exhaust steam pipeline via a temperature control valve. The cold source subsystem includes a primary cold energy utilization pipeline and a secondary cold energy utilization pipeline. The outlet of the primary cold energy utilization pipeline is connected to the product gaseous carbon dioxide outlet of the desorption and regeneration unit for liquefying gaseous carbon dioxide. The outlet of the secondary cold energy utilization pipeline is connected to the inlet of the absorption tower of the staged absorption unit for cooling the flue gas at the absorption tower inlet.

8. A method for capturing carbon dioxide from flue gas in a gas-fired power plant, implemented using a carbon dioxide capture system as described in any one of claims 1 to 7, characterized in that, The method includes the following steps: Pretreatment: The flue gas from the gas boiler outlet is passed into the flue gas pretreatment unit for cooling and dust removal pretreatment to obtain pretreated flue gas; Membrane enrichment: The pretreated flue gas enters from the inlet of the enrichment unit of the membrane enrichment unit. After membrane enrichment, the flue gas with increased carbon dioxide concentration flows out from the permeate outlet. Staged absorption: The flue gas from the permeate outlet enters the lower absorption tower through the inlet of the absorption tower of the staged absorption unit for pre-absorption to obtain the first rich liquid and the flue gas after the first absorption. The pre-absorbed flue gas is then passed through the gas-liquid redistributor into the upper absorption tower for deep absorption to obtain the clean flue gas and the second rich liquid. Desorption and regeneration: The first rich liquid and the second rich liquid are passed into the desorption and regeneration unit for heating and desorption to obtain gaseous carbon dioxide, the first regeneration lean liquid and the second regeneration lean liquid. The gaseous carbon dioxide is then liquefied to obtain liquid carbon dioxide. The first regeneration lean liquid is returned to the first regeneration lean liquid return port of the lower absorption tower for recycling, and the second regeneration lean liquid is returned to the second regeneration lean liquid return port of the upper absorption tower for recycling. Energy Coordination: The energy coordination unit provides thermal energy during the heating and desorption process and provides cold energy for the gaseous carbon dioxide liquefaction process and the flue gas at the inlet of the absorption tower.

9. The method for capturing carbon dioxide from flue gas in a gas-fired power plant according to claim 8, characterized in that, The method also includes an intelligent control step: The intelligent control system monitors the amount of pretreated flue gas introduced into the membrane enrichment unit. When the amount of flue gas exceeds a preset value, the vacuum degree on the permeate side of the membrane enrichment unit is adjusted in real time. When the amount of flue gas exceeds the preset value by 5 to 15%, the negative pressure on the permeate side is increased by 0.01 to 0.05 MPa. The intelligent control system also monitors the carbon dioxide concentration in the permeate gas at the outlet of the membrane enrichment unit in real time and adjusts the circulation flow rate of the absorbent in the upper absorption tower according to the carbon dioxide concentration in the permeate gas.

10. The method for capturing carbon dioxide from flue gas in a gas-fired power plant according to claim 8, characterized in that, In the staged absorption process, a liquid-to-gas ratio of 1.0~2.0 L / Nm³ is used in the lower absorption tower. 3 Pre-absorption was performed using a methyldiethanolamine absorbent solution with a mass concentration of 10-20 wt%, with a liquid ratio of 1.5-2.5 L / Nm³ in the upper absorption tower. 3 Deep absorption was performed using a pentaethylenehexamine absorbent solution with a mass concentration of 25-35 wt%.

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