Carbon dioxide capture system

Abstract

The present invention relates to a carbon dioxide capture system capable of capturing high-concentration carbon dioxide from exhaust gases of carbon emission sources by means of a simple structure. The carbon dioxide capture system according to the present invention comprises: a room-temperature separation membrane for primarily capturing carbon dioxide in exhaust gases transferred from carbon emission sources generating the exhaust gases containing carbon dioxide; a membrane contactor for capturing carbon dioxide by means of a mechanism different from the room-temperature separation membrane and secondarily capturing carbon dioxide in the residual exhaust gases from which carbon dioxide has been primarily separated and removed by the room-temperature separation membrane; and a mixer for generating high-concentration carbon dioxide by mixing the carbon dioxide separated by the room-temperature separation membrane and the carbon dioxide separated by the membrane contactor.

Description

carbon dioxide capture system

[0001] The present invention relates to a carbon dioxide capture system capable of capturing high concentrations of carbon dioxide from exhaust gas from a carbon emission source with a simple structure.

[0002] With the growing interest in carbon capture along with blue hydrogen production to achieve carbon neutrality, various carbon capture storage (CCS) technologies are being utilized.

[0003] Representative CCS technologies for capturing carbon dioxide from flue gas after combustion include wet methods, dry methods, and membrane methods.

[0004] The wet method captures carbon dioxide using amines, and the dry method captures carbon dioxide using solid absorbents, and their operating mechanisms are similar.

[0005] Wet and dry methods can capture high concentrations of carbon dioxide, but because the absorption towers are tall and require large areas, they are not economically feasible for use in small and medium-sized carbon emission sources.

[0006] In particular, the wet method offers the advantages of high mass transfer rates and a large gas-liquid contact area, as carbon dioxide is dispersed in the absorbent liquid in the absorption tower. However, the absorption tower may be designed to be excessively large, and there are problems such as overflow and drift of the absorbent liquid. Furthermore, the amine absorbent used in the absorption tower may leak, requiring attention to the health and safety of local residents and environmental pollution.

[0007] Meanwhile, membrane separation methods utilize membranes that selectively capture carbon dioxide. Because they do not use any chemicals, membrane separation methods are more environmentally friendly than wet and dry methods. Unlike wet methods, they do not require a phase change in the fluid, allowing for compactness. Furthermore, they are easy to install, operate, and maintain, making them economical for small- and medium-sized carbon emissions.

[0008] However, the membrane method has the disadvantage of relatively low capture efficiency as it cannot capture carbon dioxide densely.

[0009] The average concentration of carbon dioxide emitted from the combustion of hydrocarbon fuels at small and medium-sized carbon sources is known to be approximately 13% to 20%. Considering the concentration of carbon dioxide emitted from these sources and the construction infrastructure, a smaller capture facility footprint is advantageous, making membrane technology more advantageous than wet or dry methods.

[0010] Low-temperature membranes, which operate in low-temperature environments, have the advantage of higher capture efficiency than ambient-temperature membranes, which operate in room temperature environments. Therefore, technologies that utilize low-temperature membranes to recover the heat of vaporization from liquefied natural gas fuels could be considered. However, this technology is limited to carbon emissions sources where liquefied natural gas is available.

[0011] In order to increase the carbon dioxide capture efficiency using the membrane method, one can consider using a high-performance membrane with good materials and characteristics, such as a low-temperature membrane, but designing the capture process advantageously is also an important consideration.

[0012] For example, when capturing high-concentration carbon dioxide emitted from a carbon emission source using a room-temperature separation membrane, high purity and high recovery rate cannot be achieved with just a single-stage separation membrane process, and at least three or more stages of separation membranes are required.

[0013] Multi-stage membrane separation requires additional equipment such as a compressor and a pressure reducing pump in addition to the membrane at each stage, and also requires the installation of piping to connect each equipment, which increases costs and complicates the process equipment.

[0014] In addition, as the number of separation membranes and additional facilities increases due to the increase in the number of stages, the flow rate of carbon dioxide flowing into the capture process must be large to be efficient, so it may not be suitable for application to small and medium-sized carbon emission sources.

[0015] The present invention aims to solve the above-described problems, and also to provide a carbon dioxide capture system that can be applied to small and medium-sized systems, can capture high concentrations of carbon dioxide, has a simple structure, and is economical and safe.

[0016] According to one aspect of the present invention for achieving the above-described object, a carbon dioxide capture system is provided, comprising: a room temperature separation membrane for primarily capturing carbon dioxide in exhaust gas transported from a carbon emission source generating exhaust gas containing carbon dioxide; a membrane contactor for secondarily capturing carbon dioxide in residual exhaust gas from which carbon dioxide has been primarily separated and removed by the room temperature separation membrane, while capturing carbon dioxide by a mechanism different from that of the room temperature separation membrane; and a mixer for mixing carbon dioxide separated by the room temperature separation membrane and carbon dioxide separated by the membrane contactor to produce high-concentration carbon dioxide.

[0017] Preferably, the system may further include a carbon dioxide liquefaction unit for liquefying high-concentration carbon dioxide generated in the mixer.

[0018] Preferably, the system may further include a recirculation line for resupplying uncondensed carbon dioxide that has not been liquefied in the carbon dioxide liquefaction unit to the room temperature separation membrane to increase the pressure at the inlet through which the exhaust gas is injected into the room temperature separation membrane.

[0019] Preferably, the room temperature separation membrane may include: a separation membrane that operates at room temperature and selectively allows carbon dioxide to pass through; an injection portion for introducing the exhaust gas into one side of the separation membrane; a permeation portion for discharging high-concentration carbon dioxide that has passed through the separation membrane from the other side of the separation membrane; and a residual portion for discharging residual exhaust gas composed of remaining components that have not passed through the separation membrane and supplying the discharged gas to the membrane contactor.

[0020] Preferably, the membrane contactor may include a gas phase portion through which residual exhaust gas transferred from the room temperature separation membrane flows; a liquid phase portion through which an absorbent flows; and one or more contact membranes that mediate contact between the absorbent and the residual exhaust gas while separating the liquid phase and the gas phase.

[0021] Preferably, the membrane contactor may further include a gas phase inlet for introducing the residual exhaust gas into the gas phase; a gas phase discharge for discharging the venting gas from which carbon dioxide has been removed by the absorbent from the gas phase; a liquid phase inlet for introducing a lean absorbent into the liquid phase; a liquid phase discharge for discharging a rich absorbent in which carbon dioxide has been dissolved from the liquid phase; a gas flow rate control unit provided in at least one of the gas phase inlet and the gas phase discharge units and capable of controlling the flow of the gas; and a liquid flow rate control unit provided in at least one of the liquid phase inlet and the liquid discharge units and capable of controlling the flow of the liquid.

[0022] Preferably, the capacity of the membrane contactor can be controlled by controlling at least one of the gas flow rate control unit and the liquid flow rate control unit.

[0023] The carbon dioxide capture system according to the present invention, because it requires a small area, can be used in small and medium-sized facilities with limited land area, such as power plants or process plants where processes that emit a lot of carbon are performed.

[0024] In addition, by arranging room temperature separation membranes and membrane contactors with different carbon dioxide capture mechanisms in series, the advantages of each capture device can be combined while the disadvantages of each method can be compensated for to create a synergistic effect.

[0025] In addition, by combining a room-temperature separation membrane and a membrane contactor, a carbon dioxide capture process that can be operated at room temperature, has a simple configuration, and is efficient can be configured, and there are no restrictions on its application.

[0026] In addition, by utilizing a room-temperature separation membrane, it is possible to capture high concentrations of carbon dioxide by complementing the shortcomings of existing room-temperature separation membranes.

[0027] FIG. 1 is a schematic diagram illustrating a carbon dioxide capture system according to one embodiment of the present invention.

[0028] In order to fully understand the operational advantages of the present invention and the purpose achieved by the practice of the present invention, reference should be made to the attached drawings illustrating preferred embodiments of the present invention and the contents described in the attached drawings.

[0029] Hereinafter, the configuration and operation of a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Here, when adding reference symbols to components in each drawing, it should be noted that identical components are indicated with the same symbols as much as possible even if they are shown in different drawings.

[0030]

[0031] Hereinafter, a carbon dioxide capture system according to one embodiment of the present invention will be described with reference to FIG. 1.

[0032] Referring to FIG. 1, a carbon dioxide capture system according to one embodiment of the present invention may include an exhaust gas line (FL) connected to a carbon emission source (not shown) that generates exhaust gas containing carbon dioxide and for transporting exhaust gas from the carbon emission source, a room temperature separation membrane (100) that primarily captures carbon dioxide in the exhaust gas introduced through the exhaust gas line (FL), and a membrane contactor (200) that secondarily captures carbon dioxide in the residual exhaust gas from which carbon dioxide is primarily separated and removed in the room temperature separation membrane (100).

[0033] The temperature and concentration of the exhaust gas flowing into the room temperature separation membrane (100) through the exhaust gas line (FL) of the present embodiment are not limited, and the temperature may be, for example, room temperature.

[0034] In addition, the carbon emission source of this embodiment can be applied to any plant that generates exhaust gas as a mixed gas containing carbon dioxide, such as a natural gas or biogas purification plant, a hydrogen production plant, a fuel cell power generation plant, or a traditional carbon emission source such as a thermal power plant, a petrochemical plant, or a steel plant, regardless of its size, purpose, or industry.

[0035] The room temperature separation membrane (100) of the present embodiment may include a separation membrane (not shown) that operates at room temperature and selectively allows carbon dioxide to pass through, an injection portion (not shown) that is connected to an exhaust gas line (FL) and allows exhaust gas transported through the exhaust gas line (FL) to flow into one side of the separation membrane, a permeate portion (not shown) that allows carbon dioxide that has passed through the separation membrane to be discharged from the other side of the separation membrane, and a retentate portion (not shown) that allows residual exhaust gas, which is a mixed gas containing the remaining components that have not passed through the separation membrane, to be discharged.

[0036] The gas discharged through the permeation section can be pure carbon dioxide or high-concentration carbon dioxide, and can be transported to a carbon dioxide demand source through the high-concentration carbon dioxide line (CL1).

[0037] Additionally, the residual exhaust gas emitted through the residual portion may be a low-concentration carbon dioxide-containing mixed gas containing trace amounts of carbon dioxide and nitrogen, etc.

[0038] According to this embodiment, the residual exhaust gas generated when carbon dioxide is separated in the room temperature separation membrane (100) is transferred to the membrane contactor (200) through a low concentration carbon dioxide line (CL2) connected from the residual portion of the room temperature separation membrane (100) to the membrane contactor (200).

[0039] The membrane contactor (200) of the present embodiment may include a gas phase section (not shown) in which residual exhaust gas transferred from the residual portion of the room temperature separation membrane (100) flows, a liquid phase section (not shown) in which an absorbent flows, and a contact membrane (not shown) that mediates contact between the absorbent and the residual exhaust gas while separating the liquid phase and the gas phase.

[0040] In the membrane contactor (200), a liquid absorbent flowing on one side of the contact membrane and carbon dioxide in the gaseous residual exhaust gas flowing on the other side of the contact membrane chemically react to cause mass transfer, so that carbon dioxide can be dissolved in the liquid absorbent.

[0041] The membrane contactor (200) may be provided with one or more contact membranes, and a liquid phase may be provided on one side and a gas phase on the other side based on one contact membrane, and adjacent contact membranes may share a gas phase or a liquid phase.

[0042] By evenly distributing one or more contact films within the membrane contactor (200), the material transfer area and permeation performance can be improved, thereby increasing the carbon dioxide capture efficiency.

[0043] The absorbent flowing in the liquid phase may be a liquid substance that selectively absorbs and separates carbon dioxide from the residual exhaust gas. For example, the absorbent may be pure water, sodium hydroxide (NaOH), a carbonate-based, or an amine-based carbon dioxide absorbent.

[0044] In addition, the membrane contactor (200) may further include a gaseous inlet (not shown) for introducing residual exhaust gas into a gaseous portion, a gaseous discharge portion (not shown) for discharging the remaining residual exhaust gas from which carbon dioxide has been removed by an absorbent, i.e., venting gas, from the gaseous portion, a liquid inlet portion (not shown) for introducing lean absorbent into a liquid portion, and a liquid discharge portion (not shown) for discharging rich absorbent with carbon dioxide dissolved therein from the liquid portion.

[0045] At least one of the gas inlet and gas outlet of the present embodiment may be provided with a gas flow control unit (not shown) capable of controlling the flow of gas.

[0046] Additionally, at least one of the liquid inlet and the liquid outlet may be provided with a liquid flow control unit (not shown) capable of controlling the flow of the liquid.

[0047] According to this embodiment, the flow, such as the flow rate or pressure, of the fluid flowing into the membrane contactor (200) or the fluid discharged from the membrane contactor (200) can be independently controlled using the gas flow rate control unit and the liquid flow rate control unit, so that the separation process can be stably performed even at a flow rate higher or lower than that of the fluid that is restricted to prevent overflow or drift in a conventional absorption tower, and it is also easy to control the capture capacity.

[0048] In addition, in order to ensure that the flow directions of the residual exhaust gas and the absorbent within the membrane contactor (200) are countercurrent, the liquid inlet may be provided on one side of the membrane contactor (200), and the gas inlet may be provided on the other side of the membrane contactor (200).

[0049] The gaseous inlet is connected to the low-concentration carbon dioxide line (CL2), and the residual exhaust gas, which is a mixed gas containing low-concentration carbon dioxide discharged through the residual portion of the room-temperature separation membrane (100), can be introduced into the gaseous inlet of the membrane contactor (200) through the low-concentration carbon dioxide line (CL2).

[0050] The capacity of the membrane contactor (200) of the present embodiment can be determined according to the permeability of the room temperature separation membrane (100), such as the separation factor.

[0051] Additionally, according to the present embodiment, a vent line (VL) connected from the gas discharge portion of the membrane contactor (200) may be further included so that the venting gas can be discharged into the atmosphere from the gas discharge portion. The venting gas may be a nitrogen-rich gas.

[0052] The gas emitted through the gas discharge unit can be pure carbon dioxide or high-concentration carbon dioxide, and can be transported to a carbon dioxide demand source through the residual carbon dioxide line (CL3).

[0053] Although not shown in the drawing, the membrane contactor (200) according to the present embodiment may further include an absorbent regeneration unit (not shown) that separates carbon dioxide dissolved in the rich absorbent discharged from the liquid discharge unit and regenerates the absorbent, thereby generating a lean absorbent.

[0054] Carbon dioxide separated from the rich absorbent in the absorbent regeneration unit can be supplied to a carbon dioxide demand source through the residual carbon dioxide line (CL3).

[0055] Additionally, the lean absorbent generated in the absorbent regeneration unit can be recycled to the liquid inlet of the membrane contactor (200).

[0056] The carbon dioxide demand source of the present embodiment may include at least one of a mixer (300) that mixes carbon dioxide transferred from a room temperature separation membrane (100) through a high concentration carbon dioxide line (CL1) and carbon dioxide transferred from a membrane contactor (200) through a residual carbon dioxide line (CL3), and a carbon dioxide liquefaction unit (400) that liquefies gaseous carbon dioxide captured in the room temperature separation membrane (100) and the membrane contactor (200).

[0057] When the carbon dioxide demand source includes both a mixer (300) and a carbon dioxide liquefaction unit (400), carbon dioxide mixed in the mixer (300) can be transported to the carbon dioxide liquefaction unit (400) through a carbon dioxide liquefaction line (CL4) connected from the mixer (300) to the carbon dioxide liquefaction unit (400).

[0058] Additionally, the liquid carbon dioxide generated in the carbon dioxide liquefaction unit (400) may be transported to a liquid carbon dioxide demand source or stored in a carbon dioxide storage unit (not shown).

[0059] According to the present embodiment, a recirculation line (RL) may be further included to re-supply uncondensed gas in a non-liquefied gaseous state from the carbon dioxide liquefaction unit (400) to the injection unit of the room temperature separation membrane (100).

[0060] The concentration of carbon dioxide obtained from the permeation portion of the room temperature separation membrane (100) may vary depending on the concentration and pressure of carbon dioxide in the exhaust gas flowing in through the injection portion.

[0061] According to this embodiment, by providing a recirculation line (RL) to re-supply uncondensed carbon dioxide to the inlet of the room temperature separation membrane (100), the concentration and pressure of carbon dioxide in the inlet can be increased, thereby increasing the carbon dioxide capture efficiency in the room temperature separation membrane (100).

[0062] When capturing carbon dioxide in exhaust gas having the same carbon dioxide concentration, if a recirculation line (RL) is provided according to one embodiment of the present invention to re-supply uncondensed carbon dioxide to the inlet of a room-temperature separation membrane (100), the carbon dioxide concentration and pressure of the fluid introduced into the room-temperature separation membrane (100) increase, so that the carbon dioxide capture rate in the exhaust gas reaches 90% or more, but if the recirculation line (RL) is not provided and uncondensed carbon dioxide is not recirculated to the room-temperature separation membrane (100), the carbon dioxide capture rate in the exhaust gas is only about 70%.

[0063]

[0064] The room temperature separation membrane (100) does not involve a phase change, so it can save energy and increase throughput compared to other existing separation processes. In addition, it has the advantage of being easy and simple to operate and can increase selectivity, but it has the disadvantage of having lower permeability and separation coefficient compared to other existing separation processes. On the other hand, the membrane contactor (200) operates with a mechanism similar to an absorption tower, so it can capture carbon dioxide more densely than a separation membrane, but it has a larger surface area for mass transfer than an absorption tower and no drift phenomenon, so the carbon dioxide absorption rate is higher.

[0065] According to this embodiment, carbon dioxide in the exhaust gas is first captured by using a room temperature separation membrane (100) operable at room temperature, about 50 to 70% of the carbon dioxide is captured, and then carbon dioxide in the remaining exhaust gas is captured more densely from the room temperature separation membrane (100) by using a membrane contactor (200), and carbon dioxide obtained from the permeation portion of the room temperature separation membrane (100) and the gaseous discharge portion of the membrane contactor (200), i.e., the permeation portion, is mixed to obtain high concentration carbon dioxide.

[0066] Since high-concentration carbon dioxide obtained from the permeation portion of the room-temperature separation membrane (100) and the permeation portion of the membrane contactor (200) is mixed and supplied to the carbon dioxide liquefaction portion (400), the liquefaction efficiency can be increased, and thus the system can be operated economically even if an expensive carbon dioxide liquefaction portion (400) is provided.

[0067] In addition, the carbon dioxide capture system according to the present embodiment can be utilized not only for carbon dioxide but also for acid gas removal processes such as SOx, depending on which material the membrane having selectivity for is used for.

[0068] When a carbon dioxide capture system according to this embodiment is applied, energy consumption and required area can be reduced compared to existing carbon dioxide capture processes, while separation efficiency can be improved.

[0069]

[0070] It is obvious to those skilled in the art that the present invention is not limited to the above embodiments, and that various modifications or variations can be made without departing from the technical spirit of the present invention.

[0071] [Explanation of symbols]

[0072] 100: Room temperature separation membrane

[0073] 200: Membrane contactor

[0074] 300: Mixer

[0075] 400: Carbon dioxide liquefaction unit

[0076] FL: exhaust gas line

[0077] CL1: High-concentration carbon dioxide line

[0078] CL2: Low concentration carbon dioxide line

[0079] CL3: Residual carbon dioxide line

[0080] CL4: Carbon dioxide liquefaction line

[0081] RL: Recirculation line

[0082] VL: Ventline

Claims

1. A room temperature separation membrane that primarily captures carbon dioxide in exhaust gas transported from a carbon emission source that generates exhaust gas containing carbon dioxide; A membrane contactor that captures carbon dioxide by a mechanism different from the above-mentioned room-temperature separation membrane and secondarily captures carbon dioxide from the residual exhaust gas from which carbon dioxide has been first separated and removed by the above-mentioned room-temperature separation membrane; and A carbon dioxide capture system comprising a mixer that mixes carbon dioxide separated from the room temperature separation membrane and carbon dioxide separated from the membrane contactor to produce high concentration carbon dioxide.

2. In claim 1, A carbon dioxide capture system further comprising a carbon dioxide liquefaction unit for liquefying high-concentration carbon dioxide generated in the above mixer.

3. In claim 2, A carbon dioxide capture system further comprising a recirculation line for resupplying uncondensed carbon dioxide that has not been liquefied in the carbon dioxide liquefaction unit to the room temperature separation membrane to increase the pressure at the inlet through which the exhaust gas is injected into the room temperature separation membrane.

4. In claim 1, The above room temperature separation membrane is, A membrane that operates at room temperature and selectively allows carbon dioxide to pass through; An injection unit for introducing the exhaust gas into one side of the separation membrane; A permeation section for discharging high-concentration carbon dioxide that has passed through the separation membrane from the other side of the separation membrane; and A carbon dioxide capture system, comprising a residual portion for discharging residual exhaust gas consisting of remaining components that did not pass through the separation membrane and supplying the residual exhaust gas to the membrane contactor.

5. In claim 1, The above membrane contactor, A gas phase in which residual exhaust gas transferred from the above-mentioned room temperature separation membrane flows; A liquid portion in which the absorbent flows; and A carbon dioxide capture system comprising one or more contact membranes that mediate contact between an absorbent and residual exhaust gas while separating the liquid and gas phases.

6. In claim 5, The above membrane contactor, A gaseous inlet section that introduces the above residual exhaust gas into the gaseous section; A gaseous discharge unit that discharges venting gas from which carbon dioxide has been removed by the above absorbent from the gaseous unit; A liquid inlet for introducing a lean absorbent into the liquid portion; A liquid discharge section for discharging a carbon dioxide-dissolved rich absorbent from a liquid section; A gas flow control unit provided in at least one of the gas inlet and gas outlet to control the flow of gas; and A carbon dioxide capture system further comprising a liquid flow control unit provided in at least one of a liquid inlet and a liquid outlet to control the flow of a liquid phase.

7. In claim 6, A carbon dioxide capture system that controls the capacity of the membrane contactor by controlling at least one of the gas flow control unit and the liquid flow control unit.

Images