Membrane-based integrated optimized level box liquid solvent carbon capture system for combustion post-emissions

Abstract

A post-combustion CO2 capture process designed with thin-walled, interconnected chambers for low pressure direct contact cooling and membrane-based absorption steps. An amine / water blend is used as solvent to optimize the membrane-based absorption capture step and allow for a membrane-based high pressure solvent regeneration step to reduce transport compression. The combination of membranes and amine / water blend reduces the number of process steps required and also lightens the construction (and cost) by modularity, reduced footprint, reduced pump head, and shared internal walls and thinner construction materials.

Description

Technical Field

[0001] The present invention relates to systems for carbon capture, and more specifically, systems for capturing carbon from post-combustion emissions. Technical Background

[0002] Carbon capture from high-pressure combustion exhaust streams is well-established. For low-pressure exhaust streams, such as internal combustion engines powering treatment equipment using natural gas and / or diesel, limited economically viable commercial applications for carbon capture are available. However, several commercial applications for carbon capture from burning coal have been implemented. In all these cases, the cost of carbon capture remains a challenge, even with an increasing carbon tax. This proposed new concept, a membrane-based horizontal box-type liquid solvent carbon capture system, reduces the cost of carbon capture from low-pressure streams by eliminating / minimizing the need for washing steps and solvent recovery, in addition to reducing the size of both the carbon capture and solvent regeneration steps, while incorporating methods and equipment that require only thin-walled containers for the carbon capture steps, and reducing the number of container walls by sharing walls between processes. By applying this new concept, the cost of carbon capture processes will become more competitive in the context of Canada's upcoming carbon tax (after 2030).

[0003] US Patent 9291083 teaches a membrane separation system for reducing the emission of target gases (e.g., sulfur oxides, nitrogen oxides, and carbon oxides) from combustion exhaust gases from sources such as marine engines. The membrane separation system comprises an absorption system containing a semi-permeable hollow fiber membrane through which a liquid absorbent is circulated. Exhaust gases contact the outer surface of the membrane, and the target gases selectively permeate the membrane walls and are absorbed by the liquid carrier within the pores, thereby being removed from the exhaust gas stream. The invention disclosed in US Patent 9291083 does not include embodiments in which a solvent is present on the outer surface of the membrane walls and a gas is present inside the membrane. While US Patent 9291083 does not disclose combining multiple processes into a single container and discloses membranes made of ceramic materials, this invention uses hydrophobic plastics as hollow fiber membranes to absorb the key driving force for CO2 transport across the membrane barrier.

[0004] US6156096A discloses a method for separating at least one gaseous component from a feed containing a gas mixture using a liquid film barrier and a purge fluid. The method includes: selecting a purge gas or a purge liquid film; and providing a processing zone in a processing chamber having a plurality of hydrophobic microporous hollow fibers, the processing chamber having: opposing end walls containing ports, said ports including a feed inlet and a membrane inlet and a purge outlet at one end, and a purge inlet, a feed outlet, and a membrane outlet at the opposite end; and a plurality of hydrophobic elongated microporous hollow fibers extending between the feed and purge inlet ports and the feed and purge outlet ports, respectively, and arranged to allow the feed gas and purge fluid to flow countercurrently through them.

[0005] US20070214957A1 discloses a method for separating CO2 from a CO2-rich liquid, comprising the step of contacting the liquid with a membrane based on trimethylsilyl-substituted polyacetylene under elevated pressure, such that the pressure difference across the membrane is at least 1 bar, and at least a portion of the CO2 is transferred from the liquid through the membrane.

[0006] US7537200B2 discloses a method and apparatus for controlling the dissolved gas content of an aqueous liquid containing dissolved gases by providing a hydrophobic microporous hollow fiber membrane. The method provides a stable interface between an aqueous liquid phase containing dissolved gases on one side of the membrane and a gas phase on the other side of the membrane under equilibrium conditions. It controls the pressures of the aqueous and gas phases such that, during operation, the gas phase pressure reaches but does not exceed the aqueous phase pressure. The gas and liquid phases flow through the membrane to provide simultaneous mass transfer of a first gas in the gas phase into the liquid phase and a second gas dissolved in the aqueous liquid into the gas phase. This results in an increase in the gas content of the first gas in the aqueous phase, a decrease in the gas content of the second gas in the gas phase, and a change in the total dissolved gas pressure (TG) of the aqueous phase.

[0007] US20120055385A1 discloses a method for separating gases, comprising the steps of: (i) passing a CO2-containing waste gas stream through a first membrane separation system to generate a pre-concentrated gas stream and a retentate stream containing at least carbon dioxide; and (ii) directing the pre-concentrated gas stream to at least one purification step to generate a purified CO2 stream; wherein the sulfur-containing gas (SO2) x The CO stream is also substantially separated from the waste gas stream into a pre-concentrated gas stream via a first membrane separation step, and the purified CO stream is substantially free of nitrogen.

[0008] U.S. Patent No. 8,313,557 B2 discloses a system for recovering CO2 from seawater and / or bicarbonate aqueous solutions, comprising: a permeable membrane comprising multiple layers; and a solution containing seawater, an aqueous bicarbonate solution, or both, wherein the solution is under a pressure greater than 100 psig; wherein the solution contains CO2 bound in the ionic form of bicarbonate and carbonate, and wherein these ions dissociate and release CO2; and wherein gaseous CO2 and the dissociated CO2 diffuse from the solution through the membrane.

[0009] US Patent 7938887 discloses various piperazine-aqueous blends for capturing CO2 from various gas streams. The patent teaches piperazine concentrations ranging from, for example, 25.6 wt% to 63.0 wt% (4 mol PZ / kg H2O to 20 mol PZ / kg H2O) and CO2-lean loadings in the range of 0.3 mol CO2 / mol solvent to 0.9 mol CO2 / mol solvent.

[0010] Given the existing technology, there remains a need for improved methods for carbon capture, particularly post-combustion emissions.

[0011] An improved method and apparatus for capturing carbon dioxide from post-combustion exhaust gases (e.g., engine exhaust gases) using hydrophobic plastic membranes has been developed. This new invention introduces hot exhaust gases through a pipe into a series of rectangular, horizontally connected, vertical membrane contactor containers / cylinders containing hydrophobic hollow fiber membranes. First, the engine exhaust gases are cooled in an inner chamber using a mass and heat transfer arrangement by direct countercurrent water spraying. If desired, solvents such as NaOH or KOH can be sprayed in the same chamber to remove any contaminants, such as SOx, that may be present in the engine exhaust gases. The cooled exhaust gases are then guided through internal channels to a second inner chamber containing a hydrophobic hollow fiber membrane. The cooled exhaust gases pass through the interior of the hollow fiber membrane, while the liquid solvent passes through the outer side of the membrane at a higher pressure than the gas on the inner side, where the gas occupies the pores within the fiber membrane. CO2 in the membrane pores is attracted by the solvent, and the absorption force causes CO2 to move across the membrane barrier into the solvent.

[0012] Due to the short gas residence time (<1.5 seconds), the contact between the solvent and the remaining waste gas components is minimal, thus preserving the solvent's activity and minimizing its degradation, thereby eliminating the need for or requiring a small solvent recovery unit. The CO2-reduced post-absorption waste gas stream can then be directly guided to the atmosphere without water washing or with minimal water washing (which typically captures any solvent entrained in such waste gas streams), as there is no or negligible solvent loss into the waste gas during membrane operation. The CO2-rich liquid solvent is heated and guided to a regeneration step, which also includes a membrane, to separate the vaporized CO2 from the liquid solvent. The solvent with the reduced CO2 content is then guided back to the membrane CO2 capture step. The choice of solvent (ideally a blend of amine and water) allows regeneration to be carried out at elevated pressures, and the vaporized CO2 also exits at elevated pressures. The elevated pressures reduce the need for overall CO2 compression for transportation purposes, further reducing the overall cost of the carbon capture process.

[0013] It should be understood that other aspects of the invention will become apparent to those skilled in the art from the following detailed description, in which various embodiments of the invention are shown and described by way of example. It will be appreciated that the invention can have other different embodiments, and that certain details thereof can be modified in many other ways, all without departing from the spirit and scope of the invention. Therefore, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. Summary of the Invention

[0014] According to one aspect of the present invention, a method for capturing carbon dioxide from post-combustion exhaust gases is provided, such a method comprising steps such as the following:

[0015] a) The first step consists of the following:

[0016] i. Direct contact cooling of the exhaust gas after combustion; and

[0017] ii. Condensation and removal in the first chamber;

[0018] b) In the second step, carbon dioxide is captured by liquid solvent absorption in a series of vertical membrane contactor containers / tubes containing hydrophobic hollow fiber membranes in the second chamber; and

[0019] c) The third step is to regenerate the solvent by removing carbon dioxide from the liquid solvent. The third step includes, but is not limited to, a membrane that separates vaporized CO2 from the liquid solvent at a pressure range of 110 kPag to 600 kPag, and other solvent regeneration.

[0020] d) Optionally, the recycled solvent is recovered.

[0021] According to a preferred embodiment of the invention, the second chamber includes a membrane for the absorption of the liquid solvent; wherein the membrane has a sufficiently large cross-sectional area and pore openings to reduce the pressure drop from the solvent side of the membrane to the exhaust gas side of the membrane to a level where the membrane can perform mass transfer without generating additional power.

[0022] Preferably, the membrane is hydrophobic.

[0023] According to a preferred embodiment of the invention, the membrane is made into hollow fibers.

[0024] According to a preferred embodiment of the present invention, the membrane is constructed of plastic or ceramic.

[0025] According to a preferred embodiment of the invention, the membrane provides transmembrane transport driven by absorption.

[0026] According to a preferred embodiment of the present invention, the pressure on the solvent side of the membrane is greater than the pressure on the waste gas side of the membrane to prevent physical transport of waste gas across the membrane.

[0027] According to a preferred embodiment of the invention, at least two thin-walled containers are used for the direct contact cooling and liquid solvent absorption steps.

[0028] According to one aspect of the invention, the CO2 absorption solvent comprises a mass transfer solvent adapted to the short mass transfer time in the membrane.

[0029] According to a preferred embodiment of the invention, the mass transfer solvent comprises at least 15% alkanolamine, which is composed of primary and secondary amines.

[0030] According to a preferred embodiment of the present invention, the primary amine is a monoethanolamine.

[0031] According to a preferred embodiment of the present invention, the alkanolamine is selected from: N-methylmonoethanolamine, N-ethylmonoethanolamine, piperazine, diethanolamine, diisopropanolamine, and combinations thereof.

[0032] According to a preferred embodiment of the present invention, the CO2 recovery rate achieved by the combination of membrane and absorbent solvent is greater than or equal to 90%.

[0033] According to a preferred embodiment of the present invention, the purity of the CO2 product is greater than or equal to 90%.

[0034] According to a preferred embodiment of the invention, the membrane operates at a maximum of 600 kPa, reducing the CO2 product compression stage by at least one stage, preferably two stages.

[0035] According to a preferred embodiment of the invention, the membrane operates in the solvent regeneration system at up to 600 kPag, thereby reducing the CO2 product compression stages by at least 2 stages.

[0036] According to one embodiment of the invention, one of the absorption or regeneration steps is performed using a standard mass transfer device, while the other step uses a membrane.

[0037] According to a preferred embodiment of the invention, a combination of at least one of a reboiler and a preheater is used to generate heat to support the desorption of CO2 from the solvent in the membrane.

[0038] According to a preferred embodiment of the invention, the removal of vaporized water from the CO2 product stream occurs in a vessel having multiple heat transfer steps.

[0039] According to a preferred embodiment of the invention, a container having multiple heat transfer steps is directly connected to the membrane in step 3 of claim 1, or it is a separate container.

[0040] According to a preferred embodiment of the invention, the thin-walled container for CO2 absorption includes a louvered structure so that ambient air can cool the membrane for CO2 absorption.

[0041] According to a preferred embodiment of the invention, the CO2 regeneration membrane can be placed in a horizontal position, a vertical position, or at any angle in between.

[0042] According to a preferred embodiment of the invention, the waste gas and solvent can flow on either side of the membrane, and can flow upward or downward in a countercurrent or cocurrent manner during the CO2 absorption step.

[0043] Preferably, it is not necessary to add caustic alkali to the direct contact cooler.

[0044] Preferably, when using a contactor diaphragm, water washing is not required.

[0045] Preferably, no recovery device is required to extend the lifespan of the CO2 liquid solvent. Attached Figure Description

[0046] The specific implementation method will be better understood with reference to the following figures:

[0047] Figure 1 A general embodiment of a liquid absorbent-based carbon capture process using a membrane contactor is shown;

[0048] Figure 2 An embodiment of a horizontally integrated liquid absorbent-based carbon capture system using a membrane contactor absorption unit is shown;

[0049] Figure 3 This illustrates the contact between exhaust gas and liquid solvent molecules when the membrane is used to enable CO2 capture with liquid solvent pressure; and

[0050] Figure 4 a to Figure 4 c illustrates three feasible implementations of a liquid solvent regeneration process in which membranes are used instead of amine towers with trays / packing to separate vaporized CO2 from the liquid solvent. Detailed Implementation

[0051] The following description and the embodiments described therein are provided by way of example illustrating one or more specific embodiments of the principles of the invention. In the following description of the invention, examples and specific details are provided for illustrative purposes and not for limitation, in order to provide a thorough understanding of the invention. It will be readily understood by those skilled in the art that well-known methods, procedures, and / or components will not be described in order to focus on the invention. Therefore, in some cases, certain structures and techniques have not been described or shown in detail so as not to obscure the invention.

[0052] Figure 1A typical carbon capture process is illustrated, where stream 5 is the feed from any hydrocarbon post-combustion exhaust gas processed in unit 10. The liquid absorbent that preferentially absorbs carbon dioxide (CO2) can be any liquid or combination of liquids blended with water, such as primary amines (e.g., MEA, MDEA, DEA), carbonates (e.g., potassium), propylene glycol (2-amino-2-methylpropane-1-ol, 2-amino-2-methyl-1,3-propanediol), and / or secondary amines, if desired. Unit 10 preferentially captures carbon dioxide at low pressure (<101 kPag) and low temperature (<60°C), where stream 15 exits as a carbon dioxide-depleted vapor stream. Unit 10 can be an absorber tower, a rotating packed bed, or a membrane with mass transfer internals. Stream 25 exits unit 10 as a carbon dioxide-rich liquid absorbent stream. Stream 25 is conveyed to unit 200 to remove CO2 from the liquid absorbent. Unit 200 operates at elevated temperatures (>50°C) and pressures (110 kPag to 600 kPag), reducing the size of downstream CO2 compression equipment. Stream 45 exits unit 200 as a CO2-rich vapor stream. Stream 55 is regenerated liquid absorbent, which returns to unit 10 to capture more CO2. Stream 35 is a makeup stream used to replenish any liquid absorbent lost during the process, such as the liquid absorbent lost in stream 45. Unit 200 can be a conventional tower for regenerating the liquid absorbent to separate CO2 from it, or a rotating packed bed or membrane can be used to reduce the overall size of unit 200.

[0053] In a preferred embodiment, such as Figure 2 As shown, process 10 comprises only two steps in a single container to capture CO2: a direct contact cooler chamber 100 and a membrane-based CO2 capture chamber 600. Stream 5 is fed into process 10 near the bottom of chamber 100 and is typically at a temperature higher than the optimal liquid absorption temperature (i.e., <40°C) (>50°C). Stream 5 contains oxygen, nitrogen, carbon dioxide, carbon monoxide, water, unconverted methane, and other trace hydrocarbon combustion products. Stream 515 enters chamber 100 near the top of the container and consists of cooler water. Chamber 100 acts as a direct contact cooler. Water at a reduced temperature (ideally reduced to 17°C) is directed through distribution device 110 to countercurrently contact the upward-flowing vapor stream in mass transfer and heat transfer device 120. Mass transfer and heat transfer device 120 is preferably structured packing for high vapor and low liquid rates (<50 m³ / s). 3 / m 2The steam stream (with a flow rate of approximately 100 m³ / h) offers optimal mass and heat transfer, making it easier to install in a box / rectangular arrangement than a circular container. Other equivalent mass and heat transfer devices could be trays or random packing. Cooled water reduces the temperature of the steam stream (~25°C) to the point where some of the water vapor condenses. Cooling water and condensate from the steam stream are collected at the bottom of chamber 100 and exit via stream 155. Any excess water is removed via stream 175, where the remaining water enters heat exchanger unit 500 (a water-containing container or reservoir) for further cooling and reuse. A portion of the water in unit 500 moves via stream 505 to pump 550 and becomes stream 515 (the water fed into chamber 100).

[0054] The upward-flowing vapor exiting the mass and heat transfer unit 120 passes through the demister 140 via stream 185 to reach the blower or fan 190. Depending on space constraints and total capital cost, the blower can be located within its own chamber within the vessel, or it can be placed on top of or around the vessel. If a blower is required, the pressure increase can be from 10 kPa to 40 kPa to force the exhaust gas through chamber 600 and into the atmosphere. The lower the pressure increase, the lower the power load required to operate the blower, and therefore the lower the parasitic CO2 load that needs to be captured in the carbon capture unit. The pressurized and cooled exhaust gas enters the membrane chamber 600 via stream 195. Chambers 100 and 600 share a common wall 130, which reduces the amount of material required to manufacture the entire device. Furthermore, no internal flow paths and ducts are required to transport the exhaust gas between chambers, which reduces the pressure drop that the blower 190 needs to overcome. The membrane 620 is supported by an inner wall 630, which also serves as a support for the entire vessel 600. The membrane can be set long enough in the horizontal direction to achieve the necessary CO2 absorption, thus keeping the container height in process 10 below transport restriction thresholds and thresholds that would lead to increased material thickness. Furthermore, the contact height between the liquid / vapor and the membrane allows for shorter chambers in the range of 4 to 6 meters, compared to common absorption towers (20 m to 30 m and above). Advantageously, container 10 can be box-shaped or circular, with the walls of the container and chambers made of a combination of materials and thicknesses that only require support for structures up to 6 m in length, complying with road transport restrictions in Western Canada. The walls can be made of stainless steel, carbon steel, plastic, or wood, or a combination thereof. Internal supports can serve as baffles for two purposes—reducing the amount of material and floor space required to meet process requirements. The integrated design also reduces pressure drop, which lowers the power required to operate the unit, equivalent to producing less CO2.

[0055] The exhaust gas flows downward through membrane chamber 620, then changes direction upward and exits as lean gas in stream 15. This change of direction allows liquid to fall from the vapor stream and collect in a reservoir at the bottom of chamber 600. A demister 670 is optional if further removal of entrained liquid is required before the lean exhaust gas is sent to the atmosphere in stream 15. The lean solvent (a CO2-absorbing solvent with low CO2 content) enters membrane 620 from the bottom in stream 55 and is distributed via a manifold. In another embodiment, the exhaust gas is directed upward through membrane chamber 620, while the CO2-absorbing solvent in stream 55 is directed downward through membrane 620 to facilitate CO2 absorption. In another embodiment, the exhaust gas may flow in a cross-flow pattern with the solvent flowing in membrane 620. The choice of flow direction for the exhaust gas and solvent is based on a trade-off between pressure drop and capital costs. The lean solvent collects CO2, producing a rich solvent stream 255, which is returned to unit 20 via pump 260 and stream 275 for regeneration. The CO2 product from unit 20 exits via stream 45. A bottom reservoir in container 600 collects any small volume of liquid solvent that has passed through the membrane. This liquid is collected as stream 635 and pumped through stream 645 via pump 640 for reuse in the process. In this setup, a water washing setup is optional. A recirculation line (stream 256 branching off from the rich solvent stream 255) may be present to divert a portion of stream 255 to the lean solvent stream 55 to create a combined stream 56. The recirculation line can be used as a means to improve mass transfer and performance with increased solvent flow to capture more CO2 from the exhaust gas.

[0056] To improve CO2 recovery, container 600 may be equipped with (not shown) movable / controllable louvers / panels / or valves on the chamber walls to allow ambient air to flow through the chamber in a cross-flow manner. The louvers can be adjusted to regulate airflow and thus regulate the temperature within the chamber, thereby improving CO2 recovery.

[0057] In one embodiment, membrane 620 includes a housing or cylinder 622 containing a hydrophobic membrane 625, wherein exhaust gas flow 195 flows on the inner side of the hydrophobic membrane and solvent flow 55 flows on the outer side of the hydrophobic membrane 625. In another embodiment, exhaust gas flow 195 may flow on the outer side of the hydrophobic membrane and solvent flow 55 may flow on the inner side of the membrane. The choice of which side of the hydrophobic hollow fiber membrane the solvent and exhaust gas flow on, respectively, is based on a trade-off between pressure drop and capital cost. Figure 3As shown, CO2 in the exhaust gas stream is attracted by the solvent and passes through the membrane barrier of the hydrophobic membrane 625 into the liquid solvent stream 55. The CO2 contactor membrane in unit 600 operates at a higher pressure on the solvent side to reduce solvent exposure to oxygen and oxidizing molecules in the exhaust gas, minimizing solvent degradation, which means no energy-intensive recovery unit is required. The higher solvent-side pressure also prevents any non-CO2 molecules from entering and passing through the membrane. As the solvent enters and exits the membrane housing, CO2 is attracted by the solvent and diffuses through the membrane pores. This hydrophobic membrane, together with the solvent and its higher pressure, acts as a unique barrier and separation device. Only gas molecules attracted by the solvent are absorbed into the membrane pores and carried away by the solvent as it enters, passes through the pores, and exits the membrane housing. Pressure is controlled at the membrane interface to limit solvent breakthrough, the pressure at which this breakthrough occurs is defined as the breakthrough pressure. The membrane is hydrophobic enough to repel water in the solvent, reducing the tendency for water / solvent blends to pass through the membrane. Amines have a strong attraction to water, forming hydrogen bonds, which makes amines soluble in water, where amines tend to remain in water rather than passing through the membrane barrier alone. Because little or no solvent permeates the membrane, the conventional water washing steps required in typical contactors to prevent amines in exhaust gases from being released into the atmosphere are scaled down or eliminated altogether. The solvents consist of mass transfer solvents compatible with the short mass transfer times in the membrane.

[0058] Solvents with rapid mass transfer are compatible with the short mass transfer time in membranes; for example, primary and secondary amines are best suited to match the short contact time of the membrane to achieve recovery rates higher than 90%, and CO2 recovery rates higher than 95% can be achieved. Depending on the CO2 concentration in the exhaust gas, the operating conditions of the CO2 contactor, and the solvent loading, the mass transfer coefficient (KGA) of various amine-water blends is around 1.7 kmol / (m²). 2 (hours kPa) to 1.8 Kmol / (m 2 The mass transfer coefficient of the amine-water blend ranges from 3.5 kmol / (m²h / kPa) to 4 kmol / (m²h / kPa). When combined with hydrophobic plastic membranes for CO2 recovery, the higher amine mass transfer coefficient makes it a preferred solvent.

[0059] Alkyl-linked secondary alkanolamines constitute another class of candidate amines with good gas purification potential. These sterically hindered amines offer high CO2 absorption capacity and reaction rates. Furthermore, even at high amine concentrations, they are more corrosion-resistant than MEAs, and their regeneration energy requirements are lower than those of MEAs and many other amine blends, thus allowing more waste heat to be used for power generation.

[0060] In a preferred embodiment Figure 4 a to Figure 4c illustrates a liquid solvent regeneration process 200, in which a membrane 220 is used to separate vaporized CO2 from a liquid solvent, preferably an amine / water blend. The membrane 220 replaces a typical amine column with trays / packing to separate vaporized CO2 from the liquid solvent. The height of the mass transfer zone in the membrane arrangement is less than that required for a typical amine column, allowing for less material to be constructed, saving on manufacturing, civil engineering, and construction costs. Figure 4 a to Figure 4 c illustrates three feasible implementations of a liquid solvent regeneration process in which membranes are used instead of amine towers with trays / packing to separate vaporized CO2 from the liquid solvent.

[0061] like Figure 4 As shown in Figure a, the rich amine 275 from chamber 600 is warmed in a cross-heat exchange involving one or more heat exchangers 210a, 210b, which may be shell-and-tube, spiral, plate-and-frame, or similar types. Stream 275 may have filters (not shown) on the entire stream or a portion of the stream to remove any solids or precipitates from vessel 10. The warmed rich amine stream 215 undergoes some vaporization, primarily CO2, which vaporizes and enters the membrane shell 220 as a two-phase stream. The higher operating pressure on the membrane shell side forces the vaporized CO2 and water (steam) through pores and into the hollow fiber membrane, separating them from the remaining liquid solvent. The remaining liquid solvent exits the membrane as stream 222 and enters reboiler 235, which, in a preferred embodiment, may be a kettle type, in which the liquid solvent is further heated to vaporize more CO2 and water. The vaporized CO2 and steam exit the reboiler as stream 237 and enter the membrane vessel on the vapor side of the hollow fiber membrane, merging with the first portion of vaporized CO2 and steam in stream 215. The combined CO2 vapor and steam exit the membrane as stream 239. The remaining liquid solvent in reboiler 230, with a reduced CO2 content and referred to as lean, exits the reboiler as stream 235, where it is cooled in cross heat exchanger 210b. It becomes stream 55 (lean liquid solvent) for reuse in the absorption process in chamber 600. Stream 55 can also pass through a separator and an additional cooler (neither shown) to adjust the solvent to meet the desired absorption operating conditions of the absorption process. Absorption is improved at temperatures lower than those of the regeneration step.

[0062] For the regeneration step, amine / water blends containing 15% to 40% wt% amine (preferably secondary amine) exhibit higher degradation temperatures than typical amine MEAs (~120°C) and other amines, in addition to a faster mass transfer rate. Regeneration can occur at higher pressures ranging from 300 kPa to 650 kPa within the higher degradation temperature range of 130°C to 150°C. All separated CO2 and vapor exit the membrane as stream 239 under elevated pressure and are cooled in cross-heat exchanger 210a. Cooling is used to condense the vapor into water for reuse in the system and to purify the CO2 to above 90% and 95% to meet downstream requirements. Stream 245 exits heat exchanger 210a and can proceed to additional cooler 240 and separator 250 for further condensation of the vapor into water and separation from the CO2 vapor, further purifying the CO2 to up to or above 99% wt%. A cooling medium (e.g., water) enters stream 292 and exits as a warmer stream 293, cooling the now two-phase CO2 / water stream 245, and exits cooler 240 as stream 246. CO2 exits separator 250 as stream 45 for further transport and / or processing. Stream 45 is close to 500 kPa and up to 650 kPa, thus reducing the need for further compression during transport and storage or processing, lowering the overall cost of the process. The condensed and collected water in separator 250 exits as stream 265 and can be returned to solvent stream 55 for continued use.

[0063] The membrane regeneration step is effective in separating CO2 from the liquid solvent and can reduce the CO2 content to below 0.4 mol CO2 / mol solvent, and even to 0.2 mol CO2 / mol solvent, to prepare a lean solvent for absorption. With less CO2 in the solvent, more CO2 can be absorbed in membrane chamber 600, reducing the total amount of liquid solvent that needs to be recycled, which lowers the system's power requirements.

[0064] Figure 4b illustrates another embodiment of the solvent regeneration process using membrane 200. Rich amine 275 from chamber 600 is heated in a cross-heat exchange involving one or more heat exchangers 210a, 210b, which can be shell-and-tube, spiral, plate-and-frame, or similar types. Flow 275 may have filters (not shown) on the entire flow or a portion of the flow to remove any solids or precipitates from vessel 10. The heated rich amine flow 215 is directed to heater 290, which can be an in-line heater, shell-and-tube, spiral, plate-and-frame, or similar type, to provide some vaporization, so that flow 295 mainly contains vaporized CO2 and water (steam). Flow 295 enters the membrane shell 220 as a two-phase flow. The higher operating pressure on the membrane shell side forces the vaporized CO2 and water (steam) through the pores of the hollow fiber membrane and separates them from the remaining liquid solvent. Then, water (steam) in the hollow fiber tubes vaporizes CO2 from the solvent at the membrane shell 220. The combined CO2 vapor and steam exit the membrane as stream 239. The remaining liquid solvent, with a reduced CO2 content and referred to as semi-lean, exits membrane 220 as stream 235, where it is cooled in cross-heat exchanger 210b. It becomes stream 55 (semi-lean liquid solvent) for reuse in the absorption process in chamber 600. Stream 55 can also pass through a separator and an additional cooler (neither shown) to adjust the solvent to meet the desired absorption operating conditions for the absorption process. Absorption is improved at temperatures lower than those of the regeneration step.

[0065] For the regeneration step, an amine / water blend containing 15% to 40% amine exhibits a higher degradation temperature than typical amines (~120°C) and other amines, in addition to a faster mass transfer rate. Regeneration can occur at higher pressures ranging from 300 kPa to 650 kPa within a degradation temperature range of 130°C to 150°C. All separated CO2 and vapor exit the membrane as stream 239 under increased pressure and are cooled in cross-heat exchanger 210a. Cooling is used to condense the vapor into water for reuse in the system and to purify the CO2 to above 90%, preferably above 95%, to meet downstream requirements. Stream 245 exits heat exchanger 210a and can proceed to additional cooler 240 and separator 250 for further condensation of the vapor into water and separation from the CO2 vapor, further purifying the CO2 to up to and above 99% by weight. A cooling medium (e.g., water) enters stream 292 and exits as a warmer stream 293, cooling the now two-phase CO2 / water stream 245, and exits cooler 240 as stream 246. CO2 exits separator 250 as stream 45 for further transport and / or processing. Stream 45 is close to 500 kPa and can be as high as 650 kPa, thus reducing the need for further compression during transport and storage or processing, lowering the overall cost of the process. The condensed and collected water in separator 250 exits as stream 265 and can be returned to solvent stream 55 for continued use.

[0066] Figure 4 c illustrates another embodiment of the solvent regeneration process step using membrane 200. (See also...) Figure 4In step b, the rich amine 275 from chamber 600 is warmed in a cross-heat exchange involving one or more heat exchangers 210a and a heat exchanger 201c located inside container 300, which can be shell-and-tube, spiral, plate and frame, or similar types. Container 300 combines multiple heat transfer steps into one container, saving capital costs. Stream 275 may have filters (not shown) on the entire stream or a portion of the stream to remove any solids or precipitates from container 10. The warmed rich amine stream 215 then enters heater 290, which can be an in-line heater, shell-and-tube, spiral, plate and frame, or similar type, to provide a certain amount of vaporization, forming stream 295 primarily consisting of vaporized CO2 and water (steam). Stream 295 enters the membrane shell 220 as a two-phase flow. The higher operating pressure on the membrane shell side forces the vaporized CO2 and water (steam) through the pores of the hollow fiber membrane and separates them from the remaining liquid solvent. Then, water (steam) in the hollow fiber tubes vaporizes CO2 from the solvent at the membrane shell 220. The combined CO2 vapor and steam exit the membrane as stream 239. The remaining liquid solvent, with a reduced CO2 content and referred to as semi-lean, exits membrane 220 as stream 235, where it is cooled in cross heat exchanger 210b. It becomes stream 55 (semi-lean liquid solvent) for reuse in the absorption process in chamber 600. Stream 55 can also pass through a separator and an additional cooler (neither shown) to adjust the solvent to meet the desired absorption operating conditions for the absorption process. Absorption is improved at temperatures lower than those of the regeneration step.

[0067] For the regeneration step, amine / water blends containing 15% to 40% amine by weight exhibit higher degradation temperatures than typical amines (~120°C) and other amines, in addition to a faster mass transfer rate. Regeneration can occur at higher pressures in the range of 300 kPa to 650 kPa within a degradation temperature range of 130°C to 150°C. All separated CO2 and vapor exit the membrane as stream 239 under increased pressure and enter vessel 300 for cooling to condense the vapor in the CO2 / vapor mixture. Cooling is used to condense the vapor into water for reuse in the system and to purify CO2 to above 90% and 95% to meet downstream requirements. The internal vapor stream in vessel 300 is first cooled by an internal heat exchanger 210c and then further cooled by an additional cooling step shown as a heat transfer device 310. 310 is shown as a direct contact cooler that uses water from stream 305 to spray onto the packing and / or trays to cool the upward-flowing vapor and condense more water. The collected water is discharged from the tower as stream 315 for reuse in the process. Unit 310 can also be an indirect heat exchanger using tubes or plates for heat transfer. Cooled vapor, now primarily containing CO2 with a purity higher than 99% by weight, exits vessel 300 as stream 45 for further transport and / or processing. Stream 45 is close to 500 kPa and can reach up to 650 kPa, thus reducing the need for further compression during transport and storage or processing, lowering the overall cost of the process. The condensed and collected water at the bottom of vessel 300 exits as stream 315 and can be returned to the process via stream 55 or others for continued use.

[0068] In a preferred embodiment, the combination of a fast-mass-transfer amine / water blend solvent and a membrane limits the contact and contact time between the secondary amine and the exhaust gas components (e.g., oxygen-based components), which could lead to solvent degradation under prolonged contact conditions, but still allows for desired CO2 capture. Therefore, various common mitigation steps can be avoided, reducing power requirements and the overall cost of the process. Reliability is also improved. In this preferred embodiment, caustic alkali (NaOH) treatment in direct contact coolers, or similar steps for selective catalytic reduction or reduction of NOx and SOx in exhaust gas, typically included in post-combustion carbon capture designs, can be avoided. Furthermore, liquid solvent recovery is not required, whether by conventional thermal, ion exchange, or electrodialysis methods, as the formation of soluble thermally stable salts in the solvent is not a problem for post-combustion exhaust gases originating from natural gas combustion. Additionally, with pressure controlled within the membrane, solvent leakage and entrainment into the exhaust gas are effectively eliminated, thus eliminating the need for the typically required water scrubbing system before exhaust gas is released into the atmosphere.

[0069] In another implementation scheme, Figure 4 a, Figure 4 b and Figure 4 The membrane 220 for CO2 regeneration shown horizontally in c can also be arranged vertically to save floor space and facilitate integration with container 250 or 300.

[0070] In another preferred embodiment, in the presence of high levels of pollutants, the design includes the treatment of NOx and SOx; water washing to suppress solvent emissions into the atmosphere; and solvent recovery as a precaution, wherein the entire process still does not require additional power to operate the CO2 capture and transport steps.

[0071] The examples and corresponding diagrams used in this article are for illustrative purposes only. The principles discussed in this article can be implemented in other systems and devices. Different configurations and terminology may be used without departing from the principles expressed herein. For example, steps, devices, components, and modules may be added, deleted, modified, or rearranged without departing from these principles.

[0072] Unless the context explicitly requires otherwise, throughout the specification and claims, "comprising," "including," etc., shall be interpreted in a inclusive sense, as opposed to exclusive or exhaustive meaning; that is, in the sense of "including but not limited to." The words "in this document," "above," "below," and similar expressions, when used to describe this specification, shall refer to the specification as a whole, and not to any particular part thereof. When referring to a list of two or more items, "or" encompasses all of the following interpretations: any item in the list, all items in the list, and any combination of items in the list. The singular form also includes the meaning of any appropriate plural form.

[0073] When a component is mentioned above, unless otherwise stated, the mention of a component shall be interpreted as including any component that performs the function of the component (i.e., functionally equivalent) as an equivalent of the component, including components that are not structurally or compositionally equivalent to the disclosed structure or composition, wherein the disclosed structure or composition performs the function in the exemplary embodiments shown in this invention.

[0074] For illustrative purposes, specific examples of compositions, systems, methods, and apparatus are described herein. These are merely examples. In practice, various changes, modifications, additions, omissions, and arrangements can be made. The invention includes variations regarding the compositions, processes, or uses that will be apparent to those skilled in the art, including variations obtained by: replacing features or elements with equivalent features or elements; combining and matching features or elements from different examples; combining features or elements from examples as described herein with features or elements from other technologies; omitting or combining features or elements from the examples.

[0075] Therefore, the appended and introduced claims are intended to be interpreted to include all such modifications, arrangements, additions, omissions, and sub-combinations that can be reasonably inferred. The scope of the claims should not be limited to the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the specification as a whole.

Claims

1. A method for capturing carbon dioxide from post-combustion exhaust gases, the method comprising steps such as: a) The first step consists of the following: i. Direct contact cooling of the exhaust gas after combustion; and ii. Condensation and removal in the first chamber; b) The second step involves capturing carbon dioxide in the second chamber via absorption by a liquid solvent; and c) The third step is to regenerate the solvent by removing carbon dioxide from the liquid solvent; d) Optionally, the recycled solvent may be recovered.

2. The method of claim 1, wherein the second chamber comprises a membrane for the absorption of the liquid solvent; wherein the membrane has a sufficiently large cross-sectional area and pore openings to reduce the pressure drop from the solvent side of the membrane to the exhaust gas side of the membrane to a level where the membrane can perform mass transfer without generating additional power.

3. The method of claim 2, wherein the membrane is hydrophobic.

4. The method according to claim 2 or 3, wherein the membrane is made of hollow fibers.

5. The method according to any one of claims 2 to 4, wherein the membrane is constructed of plastic or ceramic.

6. The method according to any one of claims 2 to 5, wherein the membrane provides absorption-derived transport across the membrane.

7. The method according to any one of claims 2 to 6, wherein the pressure on the solvent side of the membrane is greater than the pressure on the waste gas side of the membrane to prevent physical transport of waste gas across the membrane.

8. The method according to any one of claims 1 to 7, wherein the direct contact cooling step and the liquid solvent absorption step are performed using at least two thin-walled containers.

9. The method according to any one of claims 1 to 8, wherein the CO2 absorption solvent comprises a mass transfer solvent adapted to the short mass transfer time in the membrane.

10. The method of claim 9, wherein the mass transfer solvent comprises at least 15% by weight of an amine.

11. The method of claim 10, wherein the primary amine is a monoethanolamine.

12. The method of claim 11, wherein the alkanolamine is selected from: N-methylmonoethanolamine, N-ethylmonoethanolamine, piperazine, diethanolamine, diisopropanolamine, and combinations thereof.

13. The method according to any one of claims 1 to 12, wherein the CO2 recovery rate achieved by the combination of the membrane and the absorption solvent is greater than or equal to 90%.

14. The method according to any one of claims 1 to 13, wherein the purity of the CO2 product is greater than or equal to 90%.

15. The method according to any one of claims 2 to 14, wherein the membrane in step 3 of claim 1 is operated at a maximum of 600 kPa, reducing the CO2 product compression stage by at least one stage, preferably two stages.

16. The method according to any one of claims 2 to 15, wherein the membrane in step 2 of claim 1 is operated at up to 600 kPag, reducing the CO2 product compression levels by at least 2 levels.

17. The method according to any one of claims 2 to 16, wherein the regeneration step 3 of claim 1 is performed using a standard mass transfer device.

18. The method of claim 1, wherein the second chamber comprises a standard mass transfer device for the absorption of the liquid solvent, and the membrane is used for the regeneration of the solvent in step 3.

19. The method of claim 18, wherein a combination of at least one of a reboiler and a preheater is used to generate heat to support the desorption of CO2 from the solvent in the membrane.

20. The method of claim 18, wherein a preheater is used to generate heat to support the desorption of CO2 from the solvent in the membrane.

21. The method according to any one of claims 1 to 20, wherein the removal of vaporized water from the CO2 product stream is carried out in a vessel having multiple heat transfer steps.

22. The method of claim 21, wherein the container having multiple heat transfer steps is directly connected to the membrane in step 3 of claim 1, or is a separate container.

23. The method according to any one of claims 1 to 22, wherein the thin-walled container for CO2 absorption includes a louvered structure so that ambient air can cool the membrane for CO2 absorption.

24. The method according to any one of claims 1 to 23, wherein the CO2 regenerated membrane may be placed in a horizontal position, a vertical position, or at any angle in between.

25. The method according to any one of claims 1 to 24, wherein the waste gas and the solvent can travel on either side of the membrane and can travel upward or downward in a countercurrent or cocurrent manner during the CO2 absorption step.

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