A flue gas carbon dioxide capture system and method for a gas-fired power plant

Abstract

The application discloses a kind of carbon dioxide capture system and method of gas power plant flue gas, belong to gas power plant flue gas processing technical field.The carbon dioxide capture system includes flue gas pretreatment unit, membrane enrichment unit, hierarchical absorption unit, desorption regeneration unit, energy collaborative unit.The membrane enrichment unit is used to the low concentration CO2 flue gas of gas power plant flue gas is pre-enriched, significantly reduce the load and solvent regeneration energy consumption of subsequent chemical absorption unit;Hierarchical absorption unit uses two-stage absorption tower and carries out hierarchical chemical absorption, greatly improves CO2 absorption effect and efficiency;Desorption regeneration unit desorbs and absorbs the rich liquid absorbed by hierarchical absorption unit, and the regenerated absorbent is recycled, greatly reduces production cost, energy collaborative unit carries out collection and utilization to the cold energy and heat energy of gas power plant flue gas production process, compared with existing carbon dioxide capture system and method has the advantages of high efficiency, low energy consumption, long-period stable operation.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment technology for gas-fired power plants, and particularly to a carbon dioxide capture system and method for flue gas from gas-fired power plants. Background Technology

[0002] The energy structure is rapidly transitioning towards cleaner and lower-carbon energy. Gas-fired power plants, with their high efficiency, flexible start-up and shutdown, and lower pollutant emissions, are playing an increasingly important role in the power system and have become a crucial alternative to traditional coal-fired power plants. However, gas-fired power plants are not zero-carbon energy sources; the flue gas produced still contains a considerable concentration of carbon dioxide, although far lower than that of coal-fired power plants. Nevertheless, implementing carbon dioxide capture, utilization, and storage (CO2 capture, utilization, and storage) for gas-fired power plants is considered indispensable to controlling global warming within established targets.

[0003] Currently, the most mature and commercially viable technologies for capturing carbon dioxide from flue gas include membrane separation and chemical absorption. Membrane separation utilizes the different permeation rates of different gases within a membrane material to achieve separation, offering advantages such as simplicity and low energy consumption. However, when applied to the separation of low-concentration (3-5%) CO2, traditional polymer membranes (such as polyimide) suffer from insufficient selectivity (CO2 / N2 < 50) under normal pressure and low-concentration CO2 conditions. Furthermore, the wide temperature fluctuation range (50-150℃) of flue gas from gas-fired power plants easily leads to membrane plasticization failure, resulting in short membrane lifespan (typically less than one year). While zeolite membranes, used in traditional carbon dioxide gas separation, can improve carbon dioxide selectivity, they are expensive, easily clogged by dust, and have low durability. Patent application CN202410644855.1 discloses a cross-linked polymer membrane that uses high-temperature cross-linking (>100℃) to improve membrane stability, but this additionally increases energy consumption. Chemical absorption typically uses aqueous solutions of ethanolamines as absorbents, with MEA (ethanolamine) reacting fastest with CO2 and therefore being the most widely used. However, when directly treating low-concentration CO2 flue gas, the regeneration energy consumption of absorbents (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 excessively high operating costs.

[0004] In recent years, research has begun to explore the coupling of membrane separation as a pretreatment unit with chemical absorption, aiming to use membrane methods to initially enrich CO2 in order to reduce the load and regeneration energy consumption of subsequent absorption towers. However, existing coupling schemes still have obvious shortcomings: (1) Incompatible membrane materials: their 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: existing systems lack intelligent dynamic control strategies to cope with flue gas operating conditions, making it difficult to ensure that the membrane unit and the absorption unit always work together at the optimal efficiency point.

[0005] Therefore, this invention proposes a high-efficiency, low-energy-consumption, long-term stable operation flue gas carbon dioxide capture system and method for gas-fired power plants to solve the above problems. Summary of the Invention

[0006] To address the technical problems raised in the background, the main objective of this invention is to provide a CO2 capture system and method for flue gas from gas-fired power plants, which effectively couples the advantages of membrane separation and chemical absorption technologies, while integrating energy synergistic utilization, thereby achieving a high-efficiency, low-energy-consumption, and long-cycle stable CO2 capture system and method.

[0007] To achieve the above objectives, the present invention provides a flue gas carbon dioxide capture system for gas-fired power plants, the system comprising a flue gas pretreatment unit, a membrane enrichment unit, a staged absorption unit, a desorption and regeneration unit, and an energy synergy unit.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] Furthermore, the flue gas carbon dioxide capture system of the gas-fired power plant also includes an intelligent control system, which is configured as follows:

[0014] 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.

[0015] 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.

[0016] Furthermore, 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, 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.

[0017] Furthermore, 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.

[0018] Furthermore, 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.

[0019] Furthermore, a methyldiethanolamine absorbent with a mass concentration of 10-20 wt% is introduced into the lower absorption tower, and a pentaethylenehexamine absorbent with a mass concentration of 25-35 wt% is introduced into the upper absorption tower.

[0020] Furthermore, 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 the solar reboiler, respectively. The molten salt heat storage tank is connected in parallel to the gas turbine exhaust steam pipeline through a temperature control valve.

[0021] Furthermore, 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 absorption tower inlet of the staged absorption unit for cooling the flue gas at the absorption tower inlet.

[0022] In another aspect, 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 and includes the following steps:

[0023] 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;

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Furthermore, the method also includes an intelligent control step:

[0029] 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.

[0030] 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.

[0031] Furthermore, in the staged absorption process, a liquid-to-gas ratio of 1.0~2.0 L / Nm³ is adopted in the lower stage 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%.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The carbon dioxide capture system for gas-fired power plant flue gas provided by this invention integrates chemical absorption and membrane separation to capture carbon dioxide from flue gas. It comprises five main modules: a flue gas pretreatment unit for cooling and dust removal, ensuring stable and efficient operation of subsequent units; a membrane enrichment unit for pre-enriching low-concentration CO2 in the flue gas, significantly reducing the load on subsequent chemical absorption units and solvent regeneration energy consumption; a staged absorption unit using two-stage absorption towers for staged chemical absorption, greatly improving CO2 absorption effect and efficiency; and a desorption and regeneration unit for desorbing the enriched liquid absorbed by the staged absorption unit and regenerating the absorbent, reusing the regenerated absorbent, significantly reducing production costs. Furthermore, the system includes an energy coordination unit and an intelligent control system. The energy coordination unit collects and utilizes cold and heat energy from the flue gas production process of the gas-fired power plant, while the intelligent control system dynamically regulates the absorbent flow rate and membrane pressure difference. In summary, the carbon dioxide capture system of this invention has advantages over existing carbon dioxide capture systems, including high efficiency, low energy consumption, and long-term stable operation. Attached Figure Description

[0034] Figure 1 A schematic diagram of a gas-fired power plant flue gas carbon dioxide capture system according to one embodiment of the present invention is shown. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] It should be noted that the ethylenediamine-crosslinked bromomethylated self-porous polymer of the present invention is a self-porous polymer (PIMs) that utilizes ethylenediamine as a crosslinking agent and is chemically modified by bromomethylation to impart reactivity. It achieves this by introducing bromomethyl (-CH2Br) functional groups onto the rigid, twisted backbone of the PIMs to provide active sites, utilizing the crosslinking agent. Self-porous polymers (PIMs): Due to their rigid structure and twisted conformation, the polymer molecular chains cannot be tightly packed, naturally forming nanoscale micropores (pore size typically less than 2 nm) during solid-state packing, with a specific surface area reaching over 800 m² / g.

[0037] To achieve the above objectives, a first aspect of the present invention provides a flue gas carbon dioxide capture system for gas-fired power plants, such as... Figure 1As shown, the system includes a flue gas pretreatment unit, a membrane enrichment unit, a staged absorption unit, a desorption and regeneration unit, and an energy synergy unit.

[0038] The flue gas pretreatment unit is used to cool and remove dust from the flue gas. It 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-fired boiler in the gas-fired power plant.

[0039] The membrane enrichment unit is filled with a carbon dioxide separation membrane and is equipped with an enrichment unit inlet and a permeate outlet. The enrichment unit inlet is connected to the pretreated flue gas outlet.

[0040] 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.

[0041] 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.

[0042] The energy coordinating 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 to recover and utilize the cold energy of liquefied natural gas.

[0043] The carbon dioxide capture system for gas-fired power plant flue gas provided by this invention integrates chemical absorption and membrane separation to capture carbon dioxide from flue gas. It comprises five main modules: a flue gas pretreatment unit for cooling and dust removal, ensuring stable and efficient operation of subsequent units; a membrane enrichment unit for pre-enriching low-concentration (3-5%) CO2 flue gas, significantly reducing the load on subsequent chemical absorption units and solvent regeneration energy consumption; a staged absorption unit using two-stage absorption towers for staged chemical absorption, greatly improving CO2 absorption effect and efficiency; and a desorption and regeneration unit for desorption and absorbent regeneration of the enriched liquid absorbed by the staged absorption unit, reusing the regenerated absorbent to significantly reduce production costs. Furthermore, an energy synergy unit is incorporated into the system to collect and utilize the cold and heat energy generated during the flue gas production process of the gas-fired power plant. In summary, the carbon dioxide capture system of this invention has advantages over existing carbon dioxide capture systems, including high efficiency, low energy consumption, and long-term stable operation.

[0044] 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.

[0045] 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.

[0046] 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).

[0047] 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℃.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] In a preferred embodiment of the present invention, 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 in parallel with the input end of the molten salt heat storage tank, and the molten salt heat storage tank is connected in parallel with the gas turbine exhaust steam pipeline through 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.

[0055] 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.

[0056] 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).

[0057] 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:

[0058] 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;

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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. .

[0066] 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%.

[0067] Example

[0068] 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:

[0069] 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℃).

[0070] 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. - 4 mol / 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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).

[0075] 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 flue gas carbon dioxide capture system for a gas-fired power plant, characterized by, The system comprises a flue gas pretreatment unit, a membrane enrichment unit, a staged absorption unit, a desorption regeneration unit and an energy synergy unit; The flue gas pretreatment unit is used for cooling and dust removal of flue gas, 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 a 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 permeate gas outlet, wherein the enrichment unit inlet is connected with the pretreated flue gas outlet; the carbon dioxide separation membrane is a composite membrane with a gradient pore structure, and comprises a surface dense layer, a transition layer and a macroporous 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 macroporous support layer is a polysulfone porous base film with a pore size greater than 50 nm; 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; 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; 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; the absorption tower gas inlet is connected with the permeate gas outlet to receive the enriched carbon dioxide flue gas; the lower-stage absorption tower is filled with a methyldiethanolamine absorption liquid with a mass concentration of 10-20 wt%; and the upper-stage absorption tower is filled with a pentaethylenehexamine absorption liquid with a mass concentration of 25-35 wt%. 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 carbon dioxide, first regenerated lean liquid and 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 synergy unit comprises a heat source subsystem and a cold source subsystem; 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 and is used for recycling liquefied natural gas cold energy. The flue gas carbon dioxide capture system of the gas power plant further comprises an intelligent control system, which is configured to: based on the fluctuation of the flue gas flow of the gas power plant processed by the carbon dioxide capture system, adjust the vacuum degree of the permeation side of the membrane enrichment unit in real time; and based on the carbon dioxide concentration at the outlet of the membrane enrichment unit, optimize the circulation flow of the absorption liquid in the staged absorption unit in real time.

2. A flue gas CO2 capture system for a gas-fired power plant according to claim 1, characterised in that, 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 multi-stage 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 the heat source subsystem.

3. The flue gas CO2 capture system of a gas-fired power plant according to claim 1, characterized in that, 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 macroporous support layer is 50-150 μm.

4. The flue gas CO2 capture system of a gas-fired power plant according to claim 1, characterized in that, 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 a 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; 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 gaseous carbon dioxide; 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.

5. A method for capturing carbon dioxide from flue gas of a gas-fired power plant, implemented using a carbon dioxide capture system according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: Preprocessing: passing the flue gas at the outlet of the gas boiler into a flue gas preprocessing unit for cooling and dust removal preprocessing to obtain preprocessed flue gas; Membrane enrichment: passing the preprocessed flue gas into the enrichment unit inlet of the membrane enrichment unit, and after membrane enrichment, the flue gas with increased carbon dioxide concentration flows out from the permeated gas outlet; Staged absorption: passing the flue gas at the permeated gas outlet into the lower-stage absorption tower at the absorption tower gas inlet of the staged absorption unit for preabsorption to obtain first rich liquid and first absorbed flue gas, and passing the preabsorbed flue gas into the upper-stage absorption tower through a gas-liquid redistributor for deep absorption to obtain clean flue gas and second rich liquid; Desorption regeneration: passing the first rich liquid and the second rich liquid into the desorption regeneration unit for heating desorption to obtain gaseous carbon dioxide, first regenerated lean liquid and second regenerated lean liquid, liquefying the gaseous carbon dioxide to obtain liquid carbon dioxide, recycling the first regenerated lean liquid to the first regenerated lean liquid return inlet of the lower-stage absorption tower, and recycling the second regenerated lean liquid to the second regenerated lean liquid return inlet of the upper-stage absorption tower; Energy synergy: using the energy synergy unit 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; Intelligent control: the intelligent control system monitors the amount of preprocessed flue gas passed into the membrane enrichment unit, and adjusts the vacuum degree of the permeation side of the membrane enrichment unit in real time when the flue gas amount exceeds the preset value, and the vacuum degree of the permeation side is increased by 0.01-0.05 MPa when the flue gas amount exceeds the preset value by 5-15%; The intelligent control system also monitors the carbon dioxide concentration in the permeated 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-stage absorption tower according to the carbon dioxide concentration content in the permeated gas.

6. The flue gas CO2 capture method of a gas power plant according to claim 5, characterized by, In the fractional absorption process, the liquid-gas ratio is 1.0-2.0 L / Nm 3 in the lower absorption tower, the mass concentration of the methyldiethanolamine absorbent is 10-20 wt% for pre-absorption, the liquid-gas ratio is 1.5-2.5 L / Nm 3 in the upper absorption tower, the mass concentration of the pentaethylenehexamine absorbent is 25-35 wt% for deep absorption.

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