Carbon dioxide capture system

Abstract

Disclosed herein is a carbon dioxide capture system capable of capturing high-concentration carbon dioxide in flue gas emitted from a carbon emission source using a simple structure. The carbon dioxide capture system includes: a normal temperature membrane configured to perform primary capture of carbon dioxide in flue gas transferred from a carbon emission source generating carbon dioxide-containing flue gas; the membrane contactor is configured to perform secondary capture on carbon dioxide in residual flue gas after primary separation and carbon dioxide removal of the normal-temperature membrane, and the membrane contactor captures carbon dioxide through a mechanism different from that of the normal-temperature membrane; and a mixer configured to mix the carbon dioxide separated by the normal-temperature membrane with the carbon dioxide separated by the membrane contactor to generate high-concentration carbon dioxide.

Description

Technical Field

[0001] This invention relates to a carbon dioxide capture system that can capture high concentrations of carbon dioxide from flue gas emitted from carbon emission sources using a simple structure. Background Technology

[0002] As the world strives to achieve carbon neutrality, there is growing interest in carbon dioxide capture and blue hydrogen production, which has spurred the use of various carbon capture and storage (CCS) technologies.

[0003] CCS technology is used to capture carbon dioxide from flue gas produced by fuel combustion, and typically includes wet absorption, dry absorption and membrane methods.

[0004] Wet absorption uses amines to capture carbon dioxide, while dry absorption uses solid absorbents. These two methods have similar operating mechanisms.

[0005] Although wet and dry absorption methods can capture high concentrations of carbon dioxide, they are not economically feasible for small and medium-sized carbon emission sites due to their large footprint and the need for tall absorption towers.

[0006] In particular, wet absorption offers high mass transfer rates and a large gas-liquid contact area because carbon dioxide is dispersed in the absorbent within the absorption tower. However, wet absorption has several drawbacks: the absorption tower can be very large, and operational problems such as flooding or channeling of the absorbent may occur. Furthermore, due to the risk of amine leakage from the absorbent used in the absorption tower, local health and safety, as well as potential environmental pollution, must be carefully considered.

[0007] Membrane technology utilizes membranes to selectively capture carbon dioxide. Furthermore, it does not use any chemicals, making it more environmentally friendly than wet and dry absorption methods. In addition, membrane technology does not require a phase change of the fluid, unlike wet absorption, allowing for compact system design and offering economic advantages for small to medium-sized carbon emission sources due to its ease of installation, operation, and maintenance.

[0008] However, membrane methods have the disadvantage of relatively low capture efficiency due to their lack of ability to completely capture carbon dioxide.

[0009] The known average concentration of carbon dioxide in flue gas from the combustion of hydrocarbon fuels at small- to medium-sized carbon emission sources ranges from approximately 13% to 20%. Considering the CO2 concentrations and infrastructure limitations at small- to medium-sized emission sites, facilities used for capture processes must have a small footprint. Therefore, membrane methods are superior to either wet or dry absorption methods. Summary of the Invention

[0010] Technical problems to be solved

[0011] Since cryogenic membranes operating in low-temperature environments have higher capture efficiency than ambient-temperature membranes operating at room temperature, the technology of utilizing cryogenic membranes by recovering the latent heat of vaporization from liquefied natural gas (LNG) fuel can be considered. However, this technology is limited to applications that utilize carbon emission sources that use LNG.

[0012] While using high-performance membranes with good material properties, such as cryogenic membranes, may be an option for improving carbon dioxide capture efficiency using membrane methods, the design of an efficient capture process is also an important consideration.

[0013] For example, in order to capture high concentrations of carbon dioxide emitted from carbon emission sources using ambient temperature membranes, a multi-stage membrane process consisting of at least three stages is required, because a single-stage membrane process alone is insufficient to achieve high-purity and high-recovery carbon dioxide recovery.

[0014] Multistage membrane systems require additional equipment at each stage, such as compressors and vacuum pumps, as well as separation membranes and piping for connecting these devices, which leads to problems such as increased costs and increased process design complexity.

[0015] Furthermore, as the number of stages increases, leading to an increase in the number of separation membranes and additional devices, higher carbon dioxide flow rates are required into the capture process to improve efficiency. Therefore, such multi-stage membrane systems may not be suitable for use at small to medium-sized carbon emission sources.

[0016] To address these problems in the field, the present invention provides an economical and safe carbon dioxide capture system suitable for small and medium-sized carbon emission sources, capable of capturing high concentrations of carbon dioxide, and with a simple structure.

[0017] Technical solution

[0018] According to one aspect of the invention, a carbon dioxide capture system includes: an ambient temperature membrane configured to primary capture carbon dioxide from flue gas transferred from a carbon emission source that generates carbon dioxide-containing flue gas; a membrane contactor configured to secondary capture carbon dioxide from residual flue gas remaining after primary separation and removal of carbon dioxide by the ambient temperature membrane, the membrane contactor capturing carbon dioxide through a mechanism different from that of the ambient temperature membrane; and a mixer configured to mix carbon dioxide separated by the ambient temperature membrane with carbon dioxide separated by the membrane contactor to generate a high concentration of carbon dioxide.

[0019] Preferably, the carbon dioxide capture system further includes a carbon dioxide liquefaction device configured to liquefy the high concentration of carbon dioxide generated by the mixer.

[0020] Preferably, the carbon dioxide capture system further includes a recirculation line through which uncondensed carbon dioxide that has not been liquefied in the carbon dioxide liquefaction unit is supplied back to the ambient temperature membrane to increase the pressure at the inlet of the flue gas introduced into the ambient temperature membrane.

[0021] Preferably, the ambient temperature membrane includes: a separation membrane that operates at ambient temperature and allows selective permeation of carbon dioxide; an inlet through which flue gas is introduced into one side of the separation membrane; a permeate outlet disposed on the other side of the separation membrane and allowing high concentrations of carbon dioxide that have passed through the separation membrane to be discharged therethrough; and a retentate outlet through which residual flue gas consisting of other components that have not passed through the separation membrane is discharged to be supplied to the membrane contactor.

[0022] Preferably, the membrane contactor includes: a gas phase channel through which residual flue gas transferred from the ambient temperature membrane flows; a liquid phase channel through which absorbent flows; and at least one contact membrane that mediates contact between the absorbent and the residual flue gas while separating the liquid phase channel and the gas phase channel from each other.

[0023] Preferably, the membrane contactor further includes: a gas phase inlet through which residual flue gas is introduced into a gas phase channel; a gas phase outlet through which exhaust gas generated by removing carbon dioxide from the residual flue gas by the absorbent is discharged from the gas phase channel; a liquid phase inlet through which lean absorbent is introduced into a liquid phase channel; a liquid phase outlet through which rich absorbent containing dissolved carbon dioxide is discharged from the liquid phase channel; a gas flow regulating unit disposed at least one of the gas phase inlet and the gas phase outlet to regulate the gas flow rate; and a liquid flow regulating unit disposed at least one of the liquid phase inlet and the liquid outlet to regulate the liquid flow rate.

[0024] Preferably, the capacity of the membrane contactor is adjusted by controlling at least one of the gas flow regulating unit and the liquid flow regulating unit.

[0025] Beneficial effects

[0026] The carbon dioxide capture system according to the invention requires only a small footprint, and therefore can be used even for small to medium-sized carbon emission sources with limited available space, such as power plants or process facilities that carry out carbon-intensive processes.

[0027] Furthermore, by arranging ambient temperature membranes and membrane contactors utilizing different carbon dioxide capture mechanisms in series, the carbon dioxide capture system benefits from the advantages of both capture devices while compensating for the disadvantages of each method, thus generating a synergistic effect.

[0028] Furthermore, by combining the ambient temperature membrane with the membrane contactor, the carbon dioxide capture system can be built into a highly efficient carbon dioxide capture process that operates at ambient temperature, with simple configuration and no restrictions on the application site.

[0029] In addition, while utilizing ambient temperature membranes, the carbon dioxide capture system can compensate for the shortcomings of ambient temperature membranes, thereby enabling the capture of high concentrations of carbon dioxide. Attached Figure Description

[0030] Figure 1 This is a schematic block diagram of a carbon dioxide capture system according to an embodiment of the present invention. Detailed Implementation

[0031] To fully understand the operational advantages of the present invention and the objectives achieved by implementing the present invention, reference should be made to the accompanying drawings, which illustrate preferred embodiments of the invention and their description.

[0032] The features and effects of exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that throughout the specification and drawings, the same components will be indicated by the same reference numerals.

[0033] The following will refer to Figure 1 A carbon dioxide capture system according to an embodiment of the present invention is described.

[0034] refer to Figure 1 According to one embodiment of the present invention, a carbon dioxide capture system may include: a flue gas line (FL) connected to a carbon emission source (not shown) that generates carbon dioxide-containing flue gas to transfer the flue gas from the carbon emission source; an ambient temperature membrane (100) configured to primary capture carbon dioxide in the flue gas introduced through the flue gas line (FL); and a membrane contactor (200) configured to secondary capture carbon dioxide from the residual flue gas remaining after the primary separation and removal of carbon dioxide by the ambient temperature membrane (100).

[0035] Although the temperature and concentration of the flue gas introduced into the ambient temperature membrane (100) through the flue gas line (FL) according to this embodiment are not limited, the flue gas can be, for example, at ambient temperature.

[0036] Carbon emission sources according to this embodiment may include not only traditional heavy carbon emission sources, such as thermal power plants, petrochemical plants and steel plants, but also any plant that produces flue gas as a mixture of gases containing carbon dioxide, such as natural gas or biogas refineries, hydrogen production plants and fuel cell power plants, regardless of their size, purpose or industry.

[0037] The ambient temperature membrane (100) according to this embodiment may include: a separation membrane (not shown) that operates at ambient temperature and allows selective permeation of carbon dioxide; an inlet (not shown) connected to a flue gas line (FL) and allowing flue gas transferred through the flue gas line (FL) to be introduced through it to one side of the separation membrane; a permeate outlet (not shown) disposed on the other side of the membrane and allowing carbon dioxide that has passed through the separation membrane to be discharged through it; and a retentate outlet (not shown) that allows residual flue gas, i.e., a mixture of components that have not passed through the separation membrane, to be discharged through it.

[0038] The gas emitted through the permeation outlet is pure carbon dioxide or high-concentration carbon dioxide, and can be transferred to carbon dioxide demand sites through the high-concentration carbon dioxide pipeline (CL1).

[0039] The residual flue gas emitted through the retrieval liquid outlet can be a mixture of gases containing low concentrations of carbon dioxide, and may contain trace amounts of carbon dioxide, nitrogen, etc.

[0040] According to this embodiment, the residual flue gas generated by separating carbon dioxide by the ambient temperature membrane (100) is transferred to the membrane contactor (200) through a low-concentration carbon dioxide pipeline (CL2) connected to the retentate outlet of the ambient temperature membrane (100) to the membrane contactor (200).

[0041] The membrane contactor (200) according to this embodiment may include: a gas phase channel (not shown) through which residual flue gas transferred from the retentate outlet of the ambient temperature membrane (100) flows; a liquid phase channel (not shown) through which absorbent flows; and a contact membrane (not shown) mediating contact between the absorbent and the residual flue gas while separating the liquid phase channel and the gas phase channel from each other.

[0042] In the membrane contactor (200), mass transfer occurs between the liquid absorbent flowing on one side of the contact membrane and the carbon dioxide contained in the gaseous residual flue gas flowing on the other side of the contact membrane through a chemical reaction therebetween, thereby allowing the carbon dioxide to dissolve in the liquid absorbent.

[0043] The membrane contactor (200) may include one or more contact membranes, wherein liquid phase channels and gas phase channels may be arranged on opposite sides of each contact membrane, and adjacent contact membranes may share a gas phase channel or a liquid phase channel.

[0044] The uniform distribution of one or more contact membranes within the membrane contactor (200) enhances the mass transfer area and permeation performance, thereby allowing for more efficient carbon dioxide capture.

[0045] The absorbent flowing through the liquid phase channel can be a liquid substance that selectively absorbs and separates carbon dioxide from residual flue gas. For example, the absorbent may include pure water, sodium hydroxide (NaOH), and carbonate-based or amine-based carbon dioxide absorption solutions.

[0046] The membrane contactor (200) may further include: a gas phase inlet (not shown) through which residual flue gas is introduced into a gas phase passage; a gas phase outlet (not shown) through which residual flue gas remaining after carbon dioxide removal by the absorbent, i.e., exhaust gas, is discharged from the gas phase passage; a liquid phase inlet (not shown) through which lean absorbent is introduced into a liquid phase passage; and a liquid phase outlet (not shown) through which rich absorbent containing dissolved carbon dioxide is discharged from the liquid phase passage.

[0047] At least one of the gas phase inlet and gas phase outlet according to this embodiment may be provided with a gas flow rate regulating unit (not shown), configured to regulate the gas flow rate.

[0048] In addition, at least one of the liquid phase inlet and liquid phase outlet may be provided with a liquid flow rate regulating unit (not shown), configured to regulate the liquid flow rate.

[0049] According to this embodiment, since the flow rate (flow rate or pressure) of the fluid introduced into the membrane contactor (200) or discharged from the membrane contactor (200) can be independently controlled by the gas flow rate regulating unit and the liquid flow rate regulating unit, the separation process can be carried out stably even at fluid flow rates that are higher or lower than those that are typically limited in absorption towers to prevent flooding or channeling, while also facilitating the adjustment of capture capacity.

[0050] In addition, to ensure that the residual flue gas and absorbent flow in the membrane contactor (200) in a countercurrent direction, the liquid phase inlet can be arranged on one side of the membrane contactor (200) and the gas phase inlet can be arranged on the other side of the membrane contactor (200).

[0051] The gas phase inlet is connected to the low-concentration carbon dioxide line (CL2), so that the residual flue gas discharged through the retentate outlet of the ambient temperature membrane (100), i.e., the mixed gas containing low-concentration carbon dioxide, can be introduced into the gas phase inlet of the membrane contactor (200) through the low-concentration carbon dioxide line (CL2).

[0052] The capability of the membrane contactor (200) according to this embodiment can be determined based on the permeation performance of the ambient temperature membrane (100), such as the separation factor.

[0053] The carbon dioxide capture system according to this embodiment may further include an exhaust line (VL) extending from the gas phase outlet of the membrane contactor (200) to allow exhaust gas to be discharged from the gas phase outlet into the atmosphere. The exhaust gas may be a nitrogen-rich gas.

[0054] The liquid discharged through the liquid phase outlet is pure carbon dioxide or high-concentration carbon dioxide, which can be transferred to the carbon dioxide demand site through the residual carbon dioxide pipeline (CL3).

[0055] Although not shown in the figure, the membrane contactor (200) according to this embodiment may further include: an absorbent recovery unit (not shown) configured to recover the absorbent by separating carbon dioxide dissolved in the rich absorbent discharged from the liquid phase outlet to produce a lean absorbent.

[0056] Carbon dioxide separated from the rich absorbent by the absorbent recovery unit can be supplied to carbon dioxide demand sites via the residual carbon dioxide pipeline (CL3).

[0057] The lean absorbent generated by the absorbent recovery unit can be recycled to the liquid phase inlet of the membrane contactor (200).

[0058] According to this embodiment, a carbon dioxide demand location may include at least one of the following: a mixer (300) configured to mix carbon dioxide transferred from the ambient temperature membrane (100) via a high-concentration carbon dioxide line (CL1) with carbon dioxide transferred from the membrane contactor (200) via a residual carbon dioxide line (CL3); and a carbon dioxide liquefaction device (400) configured to liquefy gaseous carbon dioxide captured by the ambient temperature membrane (100) and the membrane contactor (200).

[0059] When the carbon dioxide demand site includes both a mixer (300) and a carbon dioxide liquefaction unit (400), the carbon dioxide mixed in the mixer (300) can be transferred to the carbon dioxide liquefaction unit (400) via a carbon dioxide liquefaction line (CL4) connecting the mixer (300) to the carbon dioxide liquefaction unit (400).

[0060] Furthermore, the liquid carbon dioxide generated in the carbon dioxide liquefaction unit (400) can be transferred to the location where liquid carbon dioxide is needed, or can be stored in a carbon dioxide storage unit (not shown).

[0061] According to this embodiment, the carbon dioxide capture system may further include a recirculation line (RL) through which unliquefied, non-condensable gaseous carbon dioxide in the carbon dioxide liquefaction unit (400) is supplied back to the inlet of the ambient temperature membrane (100).

[0062] The carbon dioxide concentration obtained from the permeate outlet of the ambient temperature membrane (100) can vary depending on the carbon dioxide concentration and pressure of the flue gas introduced through the inlet.

[0063] According to this embodiment, since a recirculation line (RL) is provided to supply non-condensable carbon dioxide back to the inlet of the ambient temperature membrane (100), the carbon dioxide concentration and pressure at the inlet can be increased, thereby allowing the ambient temperature membrane (100) to capture carbon dioxide more effectively.

[0064] When capturing carbon dioxide from flue gas with the same initial carbon dioxide concentration, installing a recirculation line (RL) to supply non-condensable carbon dioxide back to the inlet of the ambient temperature membrane (100) significantly increases the carbon dioxide concentration and pressure of the fluid introduced into the ambient temperature membrane (100), thereby ensuring a carbon dioxide capture rate of 90% or higher. Conversely, without a recirculation line (RL) to recirculate non-condensable carbon dioxide to the ambient temperature membrane (100), the carbon dioxide capture rate from the flue gas remains at a much lower level, only about 70%.

[0065] Ambient temperature membranes (100) do not involve phase change, thus ensuring high energy savings and high throughput compared to other typical separation processes. Furthermore, ambient temperature membranes allow for easy and simple operation and offer enhanced selectivity. However, ambient temperature membranes exhibit lower permeability and lower separation factor compared to other typical separation processes. In contrast, membrane contactors (200) operate through a mechanism similar to absorption towers, thus enabling more efficient carbon dioxide capture than separation membranes and providing higher carbon dioxide absorption rates than absorption towers due to their larger mass transfer surface area and the absence of channeling effects.

[0066] According to this embodiment, carbon dioxide in the flue gas is first primary captured using an ambient temperature membrane (100) operating at ambient temperature with a capture rate of about 50% to about 70%. Then, a membrane contactor (200) is used to more thoroughly capture the carbon dioxide in the residual flue gas from the ambient temperature membrane (100). Subsequently, the carbon dioxide obtained from the permeate outlet of the ambient temperature membrane (100) is mixed with the carbon dioxide obtained from the gas phase outlet (permeate outlet) of the membrane contactor (200) to obtain a high concentration of carbon dioxide.

[0067] Furthermore, according to this embodiment, high-concentration carbon dioxide obtained by mixing carbon dioxide from the permeate portion of the ambient temperature membrane (100) with carbon dioxide from the permeate portion of the membrane contactor (200) is supplied to the carbon dioxide liquefaction unit (400) to ensure more efficient liquefaction, thereby allowing the carbon dioxide capture system to operate economically despite the cost of the carbon dioxide liquefaction unit (400).

[0068] Furthermore, the carbon dioxide capture system according to this embodiment can not only be used for carbon dioxide capture, but also for acid gas removal processes, such as SOx removal, by employing membranes that are selective for specific substances.

[0069] Compared to typical carbon dioxide capture processes, the carbon dioxide capture system of this embodiment can reduce energy consumption and required floor space while improving separation efficiency.

[0070] While some embodiments have been described, it will be apparent to those skilled in the art that these embodiments are given by way of illustration only, and various modifications, variations, alterations and equivalent embodiments may be made without departing from the spirit and scope of the invention.

[0071] [Icon Symbol Explanation]

[0072] 100: normal temperature film

[0073] 200: Membrane contactor

[0074] 300: Mixer

[0075] 400: Carbon dioxide liquefaction unit

[0076] FL: Flue gas pipeline

[0077] CL1: High-concentration carbon dioxide pipeline

[0078] CL2: Low-concentration carbon dioxide pipeline

[0079] CL3: Residual carbon dioxide pipeline

[0080] CL4: Carbon dioxide liquefaction pipeline

[0081] RL: Recirculation Pipeline

[0082] VL: Exhaust line

Claims

1. A carbon dioxide capture system, comprising: A room-temperature membrane is configured for primary capture of carbon dioxide from flue gas that has been transferred from a carbon emission source that produces flue gas containing carbon dioxide. A membrane contactor is configured to secondary capture carbon dioxide in residual flue gas remaining after the carbon dioxide has been separated and removed by the ambient temperature membrane in the first stage. The membrane contactor captures carbon dioxide through a different mechanism than the ambient temperature membrane. as well as A mixer configured to mix carbon dioxide separated by the ambient temperature membrane with carbon dioxide separated by the membrane contactor to generate a high concentration of carbon dioxide.

2. The carbon dioxide capture system according to claim 1, further comprising: A carbon dioxide liquefaction device configured to liquefy the high-concentration carbon dioxide generated by the mixer.

3. The carbon dioxide capture system according to claim 2, further comprising: A recirculation line supplies unliquefied, non-condensable carbon dioxide from the carbon dioxide liquefaction unit back to the ambient temperature membrane, thereby increasing the pressure at the inlet of the flue gas introduced into the ambient temperature membrane.

4. The carbon dioxide capture system according to claim 1, wherein the ambient temperature membrane comprises: A separation membrane that operates at room temperature and allows selective permeation of carbon dioxide; An inlet through which the flue gas is introduced into one side of the separation membrane; A permeation outlet is located on the other side of the separation membrane and allows high concentrations of carbon dioxide that have passed through the separation membrane to be emitted through it. as well as The retentate outlet is through which residual flue gas, consisting of other components that have not passed through the separation membrane, is discharged to supply the membrane contactor.

5. The carbon dioxide capture system according to claim 1, wherein the membrane contactor comprises: A gas phase channel through which the residual flue gas transferred from the ambient temperature membrane flows; A liquid phase channel through which the absorbent flows; as well as At least one contact membrane mediates the contact between the absorbent and the residual flue gas while separating the liquid phase channel and the gas phase channel from each other.

6. The carbon dioxide capture system according to claim 5, wherein the membrane contactor further comprises: A gas phase inlet is used to introduce the residual flue gas into the gas phase channel; A gas phase outlet is provided through which exhaust gas generated by the removal of carbon dioxide from the residual flue gas by the absorbent is discharged from the gas phase channel. A liquid phase inlet is used to introduce lean absorbent into the liquid phase channel; A liquid phase outlet through which an absorbent rich in dissolved carbon dioxide is discharged from the liquid phase channel; A gas flow regulating unit is provided at least one of the gas phase inlet and the gas phase outlet to regulate the gas flow rate; as well as A liquid flow rate regulating unit is disposed at at least one of the liquid phase inlet and the liquid phase outlet to regulate the liquid flow rate.

7. The carbon dioxide capture system according to claim 6, wherein the capacity of the membrane contactor is adjusted by controlling at least one of the gas flow regulating unit and the liquid flow regulating unit.

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