Carbon dioxide phase change absorbent absorption system and process

Abstract

The invention discloses a carbon dioxide phase change absorbent absorption system and process, and belongs to the technical field of carbon dioxide capture. The absorption system comprises an absorption tower internally provided with an absorption area and a phase splitting area from top to bottom, a tube plate type phase splitter assembly is arranged at the upper part of the phase splitting area, and an accommodating space for accommodating a light phase and a heavy phase is arranged at the lower part of the phase splitting area; the tube plate type phase splitter assembly comprises a liquid phase distributor, a baffling tube plate, a liquid collecting tank and a downcomer which are sequentially arranged in the phase splitting area from top to bottom; when the equivalent diameter of the baffling tube plate is DN6-DN20, the baffling tube plate is subjected to sand blasting treatment; when the equivalent diameter of the baffle tube plate is DN20-DN50, the baffle tube plate is filled with a polypropylene (PP) silk screen; after the phase change absorbent absorbs carbon dioxide and separates phases, the upper liquid phase is a rich phase, the lower liquid phase is a lean phase, the density difference of the two phases is 0.03-0.05 g / cm < 3 >, and the viscosity difference is 7-15 mPas. The invention further discloses a carbon dioxide phase change absorbent absorption process adopting the system. The method has excellent liquid-liquid separation and mixing performance, and is simple in process flow and low in equipment investment.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide capture technology, specifically relating to a carbon dioxide phase change absorbent absorption system and process. Background Technology

[0002] Carbon dioxide (CO2) capture, utilization, and storage (CO2) is one of the key technological pathways for addressing global climate change and achieving carbon emission reduction targets. Among numerous CO2 capture technologies, chemical absorption is widely used in process industries such as power generation, steel, and cement due to its advantages of large absorption capacity and high gas separation efficiency. However, traditional chemical absorption has a significant technical bottleneck: the regeneration and desorption process of the absorbent consumes a large amount of heat energy, resulting in high operating costs for the entire CO2 capture process and hindering its large-scale commercial application. To overcome this bottleneck, the development of novel phase change absorbents and their supporting processes has become an important research direction in recent years. After absorbing CO2, phase change absorbents spontaneously separate into two phases (usually a CO2-enriched phase and a CO2-depleted phase), requiring only the smaller enriched phase to be regenerated, thus potentially significantly reducing regeneration energy consumption and improving overall capture efficiency.

[0003] Therefore, several patent solutions involving CO2 capture systems and methods using phase change absorbers have emerged in the existing technology. For example, patent CN109092020A, "Carbon Dioxide Capture System Applicable to Phase Change Absorbers," uses a phase change absorber containing nanoparticles and is equipped with components such as an interstage separator and a cooler. Patent CN110960956A, "A Method and System for Absorbing CO2 from Flue Gas Using Phase Change Absorbers," discloses a method for continuing to absorb CO2 from flue gas using a phase-separated rich liquid phase. Patent CN116747677A, "A Continuous Device and Method for Capturing CO2 in a Liquid-Liquid-Solid Three-Phase System," focuses on a continuous device for processing liquid-liquid-solid three-phase systems. Other patents, such as CN117959925A, CN116371152A, CN102500195A, CN114832584A, and CN118698303A, have optimized the capture system from different perspectives. Their technical solutions generally involve absorption towers, phase separators (such as gravity phase separators, centrifugal phase separators, coalescing devices, etc.), regeneration towers, as well as various heat exchangers, storage tanks, and control systems.

[0004] Although the aforementioned existing technologies have made positive progress in reducing energy consumption by introducing phase change absorbers and optimizing system configuration, they still have some common or inherent drawbacks: 1. The contradiction between phase separation efficiency and energy consumption: Most systems rely on gravity sedimentation for phase separation, which takes a long time and requires large equipment. While centrifugal separation and other enhancement methods can accelerate phase separation, they introduce additional electrical energy consumption, which partially offsets the energy-saving effect of phase change absorbents.

[0005] 2. High system complexity and cost: In order to optimize phase separation and thermal integration, existing technical solutions often require the setting of multi-stage separators, multiple storage tanks, complex heat exchange networks, and supporting pumps, valves and control systems (such as CN117959925A involving two-stage phase separation and amine escape control, and CN116371152A containing four heat exchangers), resulting in complex system structure, large footprint, and increased initial investment and maintenance costs.

[0006] 3. Challenges in Process Continuity and Stability: Instability or incomplete phase separation in the phase separation process directly affects the quality of the lean solution and subsequent absorption efficiency. In some schemes (such as CN110960956A), the lean solution is directly circulated; if phase separation is incomplete, it may lead to a decrease in mass transfer efficiency within the absorption tower. How to achieve efficient and stable phase separation processes and continuous and stable system operation remains an urgent problem to be solved.

[0007] Therefore, the current state of the technology indicates an urgent need to develop a novel CO2 capture system and method that can fully utilize the low-energy potential of phase change absorbers while further addressing the aforementioned shortcomings. The key technical problem this invention aims to solve is: how to design a CO2 capture system and method based on phase change absorbers that features high phase separation efficiency, simplified system configuration, further reduced energy consumption, and stable continuous operation. This has become a technical problem urgently needing to be solved by those skilled in the art. Summary of the Invention

[0008] One of the objectives of this invention is to provide a carbon dioxide phase change absorbent absorption system that combines excellent liquid-liquid separation and mixing performance with the advantages of simple process flow and low equipment investment.

[0009] The second objective of this invention is to provide a carbon dioxide phase change absorbent absorption process, which is based on the above-mentioned system.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention discloses a carbon dioxide phase change absorbent absorption system, which includes an absorption tower connected to a raw material gas delivery pipe and an absorbent delivery pipe. The absorption tower is provided with an absorption zone and a phase separation zone from top to bottom. The upper part of the phase separation zone is equipped with a tube sheet type phase separator assembly, and the lower part is provided with a receiving space for accommodating the light phase and the heavy phase. The tube sheet type phase separator assembly includes a liquid phase distributor, a baffle tube sheet, a liquid collection tank and a downcomer arranged sequentially from top to bottom in the phase separation zone; The equivalent diameter of the baffle plate is DN6~DN50; when the equivalent diameter of the baffle plate is DN6~DN20, it is sandblasted; when the equivalent diameter of the baffle plate is DN20~DN50, it is filled with polypropylene PP wire mesh. After the phase change absorbent absorbs carbon dioxide and separates into two phases, the upper liquid phase is the rich phase and the lower liquid phase is the poor phase, with a density difference of 0.03~0.05 g / cm³. 3 The viscosity difference is 7~15 mPas.

[0011] In some embodiments of the present invention, an overflow plate is provided in the liquid collection tank, and the top end of the downcomer is connected to the lower part of the side wall or the bottom of the liquid collection tank. Preferably, the top height of the downcomer is 40-60% of the liquid level in the bottom of the absorber. In some embodiments of the present invention, the absorber is provided with a light phase outlet and a heavy phase outlet, the light phase outlet being connected to a light phase conveying pipe and the heavy phase outlet being connected to a heavy phase conveying pipe; Preferably, the system further includes a heat exchanger, a pipe mixer, and a regenerated light phase delivery pipe; The heat exchanger has a first flow channel and a second flow channel that are isolated from each other; the pipeline of the light phase delivery pipe passes through the first flow channel of the heat exchanger; the pipeline of the regenerated light phase delivery pipe passes through the second flow channel of the heat exchanger and is connected to the inlet of the pipe mixer. The heavy phase delivery pipe is connected to the inlet of the pipeline mixer; the outlet of the pipeline mixer is connected to the absorbent delivery pipe.

[0012] Preferably, the pipe mixer is an SV type static pipe mixer.

[0013] In this invention, the phase change absorbent is uniformly distributed on a baffle plate via a liquid phase distributor. Subsequently, it falls step-by-step along the baffle plate under gravity. During this process, based on the principle of inertial separation, the lighter and heavier phases are efficiently separated under gravity by utilizing the viscosity difference between the two phases. The separated liquid phase eventually flows into a collection tank and then into the bottom of the absorption tower.

[0014] The phase change absorbent used in this invention consists of 30-35 wt% N-methyldiethanolamine, 5-10 wt% diethylenetriamine, 40-50 wt% sulfolane, and 10-25 wt% water, with a liquid-to-top volume ratio of 40%-60%. This invention sets the height of the downcomer top to 40%-60% of the bottom liquid level to match the volume ratio of the upper and lower liquid phases after the absorbent separates. This design achieves two key effects simultaneously: first, it ensures that the downcomer inlet is always effectively sealed by the lower liquid phase, forming a reliable liquid seal; second, it prevents excessive intake of the upper liquid phase or entrained gas phase. Therefore, it fundamentally avoids flow short-circuiting and decreased mass transfer efficiency caused by improper downcomer height. This height range is a key design parameter for ensuring the stability of the phase interface and efficient process operation within the bottom of the tower.

[0015] In this invention, after the absorbent phase is separated, the CO2-rich light phase is output through a light phase delivery pipe and sent to regeneration. This is fundamentally different from the conventional design where CO2 is enriched in the heavy phase. Since the light phase typically has lower viscosity and better flowability, it not only significantly reduces pipeline transport resistance and the energy consumption of the regeneration unit, but also, because the light phase carries less of the heavy components such as absorbent, it helps reduce the amount of absorbent sent to the regeneration unit and lowers the risk of system blockage, thereby comprehensively improving operational stability.

[0016] The second aspect of this invention discloses a carbon dioxide phase change absorbent absorption process, which employs the above-mentioned system and includes the following steps: S1. The phase change absorbent absorbs carbon dioxide in the absorption tower; the phase change absorbent is composed of N-methyldiethanolamine, diethylenetriamine, sulfolane, and water; S2. The phase change absorbent undergoes liquid-liquid phase separation in the absorption tower. It flows through the tube sheet phase separator assembly by gravity, forming a light phase and a heavy phase at the bottom of the absorption tower, thus achieving liquid-liquid phase separation. S3. The light phase and the heavy phase flow out of the absorption tower respectively; the light phase flows through the heat exchanger, exchanges heat with the regenerated light phase and is then sent to the regeneration unit; the regenerated light phase is cooled by the heat exchanger and then sent to the pipeline mixer; in the pipeline mixer, the regenerated light phase and the heavy phase are mixed and then enter the absorption tower for CO2 absorption.

[0017] In some embodiments of the present invention, the phase change absorbent is composed of: 30-35 wt% N-methyldiethanolamine, 5-10 wt% diethylenetriamine, 40-50 wt% sulfolane, and 10-25 wt% water.

[0018] In some embodiments of the present invention, the phase change absorbent is composed of: 32 wt% N-methyldiethanolamine, 8 wt% diethylenetriamine, 40 wt% sulfolane and 20 wt% water.

[0019] In some embodiments of the present invention, the heavy phase content in the light phase formed at the bottom of the absorption tower is ≤2%; Preferably, the light phase at the bottom of the absorber is a CO2-enriched phase with a viscosity of 10-20 mPas and a density of 1.14-1.20 g / cm³. 3 ; In some embodiments of the present invention, the heavy phase at the bottom of the absorber is a CO2-lean liquid phase with a viscosity of 3-5 mPas and a density of 1.18-1.22 g / cm³. 3 .

[0020] In some embodiments of the present invention, the density difference between the heavy phase and the regenerated light phase is ≤0.1 g / cm³. 3 Viscosity difference ≤ 3 mPas.

[0021] Compared with the prior art, the present invention has the following beneficial effects: This invention addresses the carbon capture process using phase change absorbers, providing a carbon dioxide phase change absorber absorption system and process. Its core lies in utilizing a proprietary phase change absorber, combined with the synergistic effect of a tube sheet phase separator assembly and a pipeline mixer, to create a technical solution with a simple process flow, streamlined equipment, and significant savings in floor space and investment. The advantages and working principle of this invention are mainly reflected in the following three aspects: (1) Proprietary phase change absorbent: The main component is N-methyldiethanolamine, which has the characteristics of low regeneration energy consumption and can significantly reduce CO2 desorption energy consumption; at the same time, sulfolane is added, which has low vapor pressure and is not easily volatilized, which can effectively reduce absorbent loss. After absorbing CO2, the system automatically separates into two phases: the light phase is the CO2 enriched phase and the heavy phase is the CO2 lean liquid phase.

[0022] (2) High-efficiency separation achieved by the tube sheet phase separator assembly: In view of the characteristics that both the light and heavy phases have high viscosity and small density difference after absorption, this assembly is based on the principle of inertial separation and utilizes the viscosity difference between the two phases to achieve high-efficiency separation under the action of gravity. Compared with traditional static phase separators and centrifugal separation equipment, this assembly does not require external power or change of flow direction, and can achieve priority passage of the heavy phase (low viscosity and low resistance) and delayed passage of the light phase (high viscosity), thereby effectively reducing the back mixing problem of the light and heavy phases in the absorber.

[0023] (3) The pipeline mixer achieves efficient mixing: The pipeline mixer of the present invention is used to replace the traditional mixing tank. It has a compact structure and a small footprint. It can efficiently mix the heavy phase with similar viscosity and density and the regenerated light phase.

[0024] In summary, this invention fully utilizes the characteristics of proprietary phase change absorbents that form a light phase with high viscosity and a large viscosity difference but a small density difference after absorbing CO2. By using a tube sheet-type phase separator assembly and a pipeline mixer, the challenges of separating and mixing high-viscosity, similar-density liquids are respectively solved. The entire process is simple, and the equipment configuration is streamlined, offering significant advantages in terms of saving space and investment. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the system structure of the present invention; Figure 2 This is a schematic diagram of the structure of the tube sheet type phase splitter assembly of the present invention. Figure 3 This is a comparison diagram of the phase separation results of the phase change absorbent of the present invention; Figure 4 This is a state diagram of the phase change absorbent of the present invention flowing through a tube sheet type phase separator assembly with an equivalent diameter of DN10 under gravity only after absorbing CO2. Figure 5 This is a schematic diagram of the carbon capture process of the phase change absorbent in Comparative Example 2.

[0026] The corresponding names of the attached figures are: 1-raw material gas conveying pipe, 2-absorption tower, 3-absorbent conveying pipe, 4-tube sheet type phase separator assembly, 4A-microchannel assembly, 5-light phase pump, 6-heavy phase pump, 7-light phase conveying pipe, 8-heavy phase conveying pipe, 9-regenerated light phase conveying pipe, 10-heat exchanger, 11-pipeline mixer, 12-booster pump. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] A carbon dioxide phase change absorbent absorption system includes an absorption tower 2, which is connected to a raw gas conveying pipe 1 and an absorbent conveying pipe 3. The absorption tower 2 is provided with an absorption zone and a phase separation zone from top to bottom. The upper part of the phase separation zone is provided with a tube sheet type phase separator assembly 4, and the lower part is provided with a receiving space for accommodating the light phase and the heavy phase. The tube sheet type phase separator assembly 4 includes a liquid phase distributor 41, a baffle tube sheet 42, a liquid collection tank 43, and a downcomer 45 arranged sequentially from top to bottom in the phase separation zone; The equivalent diameter of the baffle plate 42 is DN6~DN50; when the equivalent diameter of the baffle plate 42 is DN6~DN20, it is sandblasted; when the equivalent diameter of the baffle plate 42 is DN20~DN50, its interior is filled with polypropylene PP wire mesh. After the phase change absorber absorbs carbon dioxide and separates into two phases, the upper liquid phase is the rich phase and the lower liquid phase is the poor phase, with a density difference of 0.03~0.05 g / cm³. 3 The viscosity difference is 7~15 mPas.

[0029] An overflow plate 44 is provided inside the liquid collection tank 43, and the top end of the downcomer 45 is connected to the lower part of the side wall or the bottom of the liquid collection tank 43. The top height of the downcomer 45 is 40-60% of the bottom liquid level of the absorber 2.

[0030] The absorption tower 2 is provided with a light phase outlet and a heavy phase outlet. The light phase outlet is connected to a light phase conveying pipe 7, and a light phase pump 5 is installed on the light phase conveying pipe 7. The heavy phase outlet is connected to a heavy phase conveying pipe 8, and a heavy phase pump 6 is installed on the heavy phase conveying pipe 8.

[0031] The system also includes a heat exchanger 10, a pipe mixer 13, and a regenerated light phase delivery pipe 9; the heat exchanger 10 has a first flow channel and a second flow channel that are isolated from each other; the pipe of the light phase delivery pipe 7 passes through the first flow channel of the heat exchanger 10; the pipe of the regenerated light phase delivery pipe 9 passes through the second flow channel of the heat exchanger 10 and is connected to the inlet of the pipe mixer 11. The heavy phase delivery pipe 8 is connected to the inlet of the pipeline mixer 11; the outlet of the pipeline mixer 13 is connected to the absorbent delivery pipe 3.

[0032] The pipe mixer is an SV type static pipe mixer.

[0033] A carbon dioxide phase change absorbent absorption process, which employs the above-mentioned system, includes the following steps: S1. A phase change absorbent absorbs carbon dioxide in an absorption tower; the phase change absorbent is composed of N-methyldiethanolamine, diethylenetriamine, sulfolane, and water; S2. The phase change absorbent undergoes liquid-liquid phase separation in the absorption tower. It flows through the tube sheet phase separator assembly by gravity, forming a light phase and a heavy phase at the bottom of the absorption tower, thus achieving liquid-liquid phase separation. S3. The light phase and the heavy phase flow out of the absorption tower respectively; the light phase flows through the heat exchanger, exchanges heat with the regenerated light phase and is then sent to the regeneration unit; the regenerated light phase is cooled by the heat exchanger and then sent to the pipeline mixer; in the pipeline mixer, the regenerated light phase and the heavy phase are mixed and then enter the absorption tower for CO2 absorption.

[0034] The phase change absorbent is composed of: 30-35 wt% N-methyldiethanolamine, 5-10 wt% diethylenetriamine, 40-50 wt% sulfolane, and 10-25 wt% water.

[0035] Preferably, the phase change absorbent is composed of: 32 wt% N-methyldiethanolamine, 8 wt% diethylenetriamine, 40 wt% sulfolane and 20 wt% water.

[0036] The heavy phase content in the light phase formed at the bottom of the absorption tower is ≤2%. The light phase at the bottom of the absorption tower is a CO2-enriched phase with a viscosity of 10–20 mPas and a density of 1.14–1.20 g / cm³. 3 ; The heavy phase at the bottom of the absorber is a CO2-lean liquid phase with a viscosity of 3–5 mPas and a density of 1.18–1.22 g / cm³. 3 .

[0037] The density difference between the heavy phase and the regenerated light phase is ≤0.1 g / cm³. 3 Viscosity difference ≤ 3 mPas.

[0038] Example 1 As attached Figures 1-2 As shown in the figure, this embodiment discloses the carbon dioxide phase change absorbent absorption system of the present invention. The system includes an absorption tower 2, which is connected to a raw material gas conveying pipe 1 and an absorbent conveying pipe 3. The absorption tower 2 is provided with an absorption zone and a phase separation zone from top to bottom. The upper part of the phase separation zone is provided with a tube sheet type phase separator assembly 4, and the lower part is provided with a receiving space for accommodating the light phase and the heavy phase. The tube sheet type phase separator assembly 4 includes a liquid phase distributor 41, a baffle tube sheet 42, a liquid collection tank 43, and a downcomer 45 arranged sequentially from top to bottom in the phase separation zone.

[0039] An overflow plate 44 is provided inside the liquid collection tank 43, and the top end of the downcomer 45 is connected to the lower part of the side wall or the bottom of the liquid collection tank 43. The top height of downcomer 45 is 40-60% of the bottom liquid level of absorber 2; The equivalent diameter of the baffle plate 42 is DN6~DN50; when the equivalent diameter of the baffle plate 42 is DN6~DN20, it is sandblasted; when the equivalent diameter is DN20~DN50, it is filled with polypropylene PP wire mesh.

[0040] The absorption tower 2 is provided with a light phase outlet and a heavy phase outlet. The light phase outlet is connected to a light phase conveying pipe 7, and a light phase pump 5 is installed on the light phase conveying pipe 7. The heavy phase outlet is connected to a heavy phase conveying pipe 8, and a heavy phase pump 6 is installed on the heavy phase conveying pipe 8.

[0041] The system also includes a heat exchanger 10, a pipe mixer 13, and a regenerated light phase delivery pipe 9; the heat exchanger 10 has a first flow channel and a second flow channel that are isolated from each other; the pipe of the light phase delivery pipe 7 passes through the first flow channel of the heat exchanger 10; the pipe of the regenerated light phase delivery pipe 9 passes through the second flow channel of the heat exchanger 10 and is connected to the inlet of the pipe mixer 11. The heavy phase delivery pipe 8 is connected to the inlet of the pipeline mixer 11; the outlet of the pipeline mixer 13 is connected to the absorbent delivery pipe 3.

[0042] The pipe mixer is an SV type static pipe mixer.

[0043] Example 2 This embodiment discloses a carbon dioxide phase change absorbent absorption process, which uses the absorption system of Example 1.

[0044] The phase change absorbent in this embodiment is composed of: 32 wt% N-methyldiethanolamine, 8 wt% diethylenetriamine, 40 wt% sulfolane, and 20 wt% water.

[0045] The specific process steps in this embodiment are as follows: S1. The phase change absorbent absorbs carbon dioxide inside the absorption tower; S2. The phase change absorbent undergoes liquid-liquid phase separation in the absorption tower. It flows under gravity through a tube sheet phase separator assembly composed of a sandblasted equivalent diameter DN10 baffle plate, forming a light phase and a heavy phase at the bottom of the absorption tower. The structure of the tube sheet phase separator assembly is as follows: Figure 2 As shown.

[0046] The top height of the downcomer is ~50% of the liquid level in the bottom of absorber tower 2; The light phase at the bottom of the absorber is a CO2-enriched phase with a viscosity of 12.5 mPas and a density of 1.16 g / cm³. 3 The heavy phase is a CO2-lean liquid phase with a viscosity of 4.3 mPas and a density of 1.20; the density difference between the light and heavy phases is 0.04 g / cm³. 3 The viscosity difference between the light and heavy phases is 8.2 mPas; the light phase at the bottom of the absorption tower contains 1 vol% of the heavy phase, thus achieving liquid-liquid phase separation.

[0047] S3. The light phase is pumped to the heat exchanger, where it exchanges heat with the regenerated light phase and is then sent to the regeneration unit; After being cooled by a heat exchanger, the regenerated light phase has a viscosity of 6.5 mPas and a density of 1.10 g / cm³. 3 It is sent to the pipeline mixer; Within the SV-type static pipeline mixer, the heavy phase, pumped by a heavy phase pump, is efficiently mixed with the regenerated light phase before entering the absorption tower for CO2 absorption. The density difference between the heavy phase and the regenerated light phase is 0.1 g / cm³. 3 The viscosity difference is 2.2 mPas.

[0048] The phase change absorbent of this embodiment was applied to the CO2 capture process of flue gas with a CO2 content of 15%, and the results of the comparison of the characteristics of the above absorbents are shown in Table 1: Table 1 Comparison of Phase Change Absorber Properties

[0049] As shown in Table 1, the carbon dioxide phase change absorbent system of this invention has the following characteristics: the light phase is the enriched phase, the heavy phase is the lean liquid phase, the density difference between the two phases is small, and the viscosity difference is 8.2 mPa·s. This type of system is not suitable for static separation or centrifugal separation. (See attached table.) Figure 3 As shown in the left figure, without phase separation treatment by the tube sheet phase separator assembly, the absorbed system is difficult to achieve clear separation.

[0050] Therefore, the process of this invention employs a tube sheet-type phase separator assembly composed of a sandblasted equivalent diameter DN10 baffle plate, achieving highly efficient liquid-liquid separation. In this tube sheet structure, the influence of viscosity on fluid flow behavior is effectively amplified. Because the lighter phase has higher viscosity and flow resistance, its passage time is correspondingly delayed; while the heavier phase has lower viscosity and lower resistance, thus passing preferentially, thereby effectively reducing backmixing within the absorber reboiler. Figure 3 As shown in the right figure, after the tube sheet phase separator assembly composed of a DN10 equivalent diameter baffle plate treated with sandblasting is processed, the phase change absorbent of the present invention can quickly achieve clear separation of the enriched phase and the liquid phase.

[0051] And as attached Figure 4 As shown, the carbon dioxide phase change absorbent of this invention, under gravity alone, flows through a tube sheet phase separator assembly with an equivalent diameter of DN10, and the absorbent is clearly separated into a heavy phase and a light phase fluid. More importantly, as the flow length within the tube increases, the interface between the two phases becomes increasingly clear and stable, evolving from initial formation to continuous development. This experimental phenomenon directly confirms the effectiveness of the phase separator assembly design, demonstrating that it can achieve efficient and thorough gravity phase separation under simple conditions without the need for external power.

[0052] The tube sheet phase separator assembly used in this invention can effectively promote the separation of liquid-liquid systems with small density differences and large viscosity differences, overcome the problem of low efficiency of conventional separation methods, and achieve efficient and rapid separation of enriched phase and lean liquid phase.

[0053] Furthermore, the heavy phase pumped by the heavy phase pump can be mixed with the regenerated light phase in an SV-type static pipeline mixer. The entire process is simple, requires few equipment, and has the combined advantages of small footprint and low investment cost.

[0054] Example 3 This embodiment discloses a carbon dioxide phase change absorbent absorption process, which uses the absorption system of Example 1.

[0055] The phase change absorbent in this embodiment is composed of: 30 wt% N-methyldiethanolamine, 10 wt% diethylenetriamine, 45 wt% sulfolane, and 15 wt% water.

[0056] The specific process steps in this embodiment are as follows: S1. The phase change absorbent absorbs carbon dioxide inside the absorption tower; S2. The phase change absorbent undergoes liquid-liquid phase separation in the absorption tower, and flows by gravity through a tube sheet type phase separator assembly composed of a tube sheet with an equivalent diameter of DN40 filled with polypropylene (PP) wire mesh; a light phase and a heavy phase are formed at the bottom of the absorption tower.

[0057] The light phase at the bottom of the absorber is a CO2-enriched phase with a viscosity of 16.5 mPas and a density of 1.18 g / cm³. 3 The heavy phase is a CO2-lean liquid phase with a viscosity of 4.8 mPas and a density of 1.21; the density difference between the light and heavy phases is 0.03 g / cm³. 3 The viscosity difference between the light and heavy phases is 11.7 mPas; the light phase at the bottom of the absorption tower contains 1.5% heavy phase, thus achieving liquid-liquid phase separation.

[0058] S3. The light phase is pumped to a heat exchanger, where it exchanges heat with the regenerated light phase before being sent to the regeneration unit. After being cooled by the heat exchanger, the regenerated light phase has a viscosity of 7.6 mPas and a density of 1.14 g / cm³. 3 It is sent to the pipeline mixer.

[0059] In the SV-type static pipeline mixer, the heavy phase pumped by the heavy phase pump is efficiently mixed with the regenerated light phase before entering the absorption tower for CO2 absorption. The density difference between the heavy phase and the regenerated light phase is 0.07 g / cm³. 3 The viscosity difference is 2.8 mPas.

[0060] This invention employs a carbon dioxide phase change absorbent absorption process. This process is suitable for phase change absorbents where the light phase is enriched, the heavy phase is lean, and the density difference between the light and heavy phases is small (11.7 mPas), making static separation and centrifugal separation unsuitable. For absorbents with high viscosity differences, polypropylene (PP) mesh is packed into a DN40 equivalent diameter tube sheet, utilizing droplet coalescence and viscosity difference to achieve efficient liquid-liquid separation. The light phase, with its high viscosity, high resistance, and delayed passage, flows later, while the heavy phase, with its low viscosity and low resistance, passes preferentially, reducing backmixing in the absorber bottom. The heavy phase pumped by the heavy phase pump and the regenerated light phase can be mixed using an SV-type static pipeline mixer. The process is simple, requires fewer equipment, and saves space and investment.

[0061] Comparative Example 1 This comparative example uses the dynamic phase separation carbon dioxide capture system from the patent "Dynamic Phase Separation Carbon Dioxide Capture System and Method Based on Phase Change Absorber" (publication number CN 118698303 A). The structural composition of this system is shown in the appendix to the patent. Figure 1 As shown, it is a system comprising an absorption tower, a coalescing device, a centrifugal phase separator, a mixing tank, and a desorption tower.

[0062] One carbon dioxide capture method in this comparative example includes the following steps: Flue gas is conveyed to an absorption tower, and a phase change absorbent is introduced into the absorption tower; in the absorption tower, the phase change absorbent absorbs carbon dioxide in the flue gas and generates a mixed absorbent liquid. The agglomeration product obtained after the mixed absorbent is processed by the agglomeration device is transported to the centrifugal phase separator, and the agglomeration product is separated by the centrifugal phase separator to obtain a rich phase solution and a poor phase solution. The lean phase solution is transported to a mixing tank, and the rich phase solution is transported to a desorption tower via a heat exchanger for desorption treatment to obtain a regenerated absorbent; The regenerated absorbent is transported via the heat exchanger to the mixing tank and mixed with the lean phase solution to obtain a mixed absorbent. Optionally, the mixed absorbent is conveyed to an absorption tower for absorbing carbon dioxide from flue gas.

[0063] The carbon dioxide capture process using the system in this comparative example differs from that in Example 2 in the following ways: The absorbents have different characteristics: In this comparative example, the absorbent forms two phases after phase separation, with the upper phase being a lean phase with relatively low viscosity and the lower phase being a rich phase with relatively high viscosity; while in Example 2, the upper liquid phase is a rich phase with high viscosity and the lower liquid phase is a lean phase with low viscosity; the two have opposite phase distributions.

[0064] The principles of liquid-liquid phase separation differ: Example 2 uses a combination of a coalescing device and a centrifugal phase separator, primarily utilizing density difference and centrifugal force for liquid-liquid separation; Example 2, considering the small density difference and large viscosity difference between the upper and lower phases of the absorbent, utilizes viscous force, achieving liquid-liquid phase separation by allowing the absorbent to flow solely under gravity through a tube sheet type phase separator composed of tube sheets with equivalent diameters of DN6~DN50. The two separation mechanisms are different.

[0065] The liquid-liquid mixing devices differ; this comparative example uses a mixing tank with mechanical stirring for liquid-liquid mixing, while Example 2 uses an SV-type static pipeline mixer. This is because the density difference between the two phases to be mixed is 0.1 g / cm³. 3 With a viscosity difference of 2.2 mPas, both are relatively small, making it suitable for mixing in SV-type static pipeline mixers, thus achieving a more compact structure and a smaller footprint.

[0066] In summary, Embodiment 2 of the present invention demonstrates significant advantages in terms of process flow and equipment selection. Its absorbent's "rich at the top, poor at the bottom" phase separation characteristic is more conducive to the efficient collection and treatment of the rich phase. Simultaneously, the system employs a static pipeline mixer, requiring no external power, resulting in lower energy consumption and a smaller footprint, demonstrating its comprehensive superiority in terms of equipment investment, operational efficiency, and spatial layout. Therefore, Embodiment 2 represents a more efficient, compact, and economical carbon dioxide capture process route.

[0067] Comparative Example 2 As attached Figure 5 As shown, this comparative example discloses a carbon dioxide phase change absorption process that uses a microchannel component 4A to replace the tube sheet phase separator component 4 in this invention. This comparative example achieves liquid-liquid separation by adding an absorbent booster pump 12 to the system and utilizing the inertial force, viscous force, and surface tension difference generated by the absorbent at high flow rates within the microchannels.

[0068] However, compared to the process in Embodiment 2 of this invention, although the viscosity difference of the system itself meets the separation requirements, the comparative example still requires an additional booster pump 12 to provide driving force due to the smaller size of the microchannels, resulting in a more complex system structure and increased operating energy consumption. Furthermore, limited by the physical structure of the microchannels, its processing capacity is low, making it difficult to meet the needs of large-scale industrial applications.

[0069] The significant advantages of the technical approach of this invention are fully demonstrated by comparing it with the comparative example. The comparative example requires the introduction of microchannel components and additional pressurization equipment to achieve liquid-liquid separation, which not only increases system complexity and energy consumption but also limits throughput. In contrast, this invention innovatively utilizes the physical properties of the absorbent itself to achieve separation, fundamentally avoiding the aforementioned problems and forming an advanced process with a simpler structure, lower energy consumption, and greater potential for large-scale application.

[0070] In summary, the results from the embodiments of this invention show that after capturing CO2 using a dedicated phase change absorbent, the carbon dioxide phase change absorbent absorption process of this invention separates the system into two phases: a light phase, which is the CO2-enriched phase, and a heavy phase, which is the CO2-lean liquid phase. Both phases have high viscosity and exhibit a significant viscosity difference and a small density difference. Based on these fluid characteristics, and combining a tube sheet phase separator and a pipeline mixer, the process of this invention can achieve efficient liquid-liquid separation and mixing. The overall process is simple, requires few equipment, saves floor space, and reduces investment costs. Therefore, the carbon dioxide phase change absorption process of this invention has the potential for widespread application in actual production and is expected to generate good social and economic benefits.

[0071] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit the invention, nor are they intended to limit the scope of the patent. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but which still solve the same technical problem as the present invention, should be included within the scope of protection of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the scope of patent protection of the present invention.

Claims

1. A carbon dioxide phase change absorbent absorption system, characterized in that, It includes an absorption tower (2), which is connected to a raw material gas conveying pipe (1) and an absorbent conveying pipe (3). The absorption tower (2) is provided with an absorption zone and a phase separation zone from top to bottom. The upper part of the phase separation zone is provided with a tube sheet type phase separator assembly (4), and the lower part is provided with a receiving space for accommodating the light phase and the heavy phase; The tube sheet type phase separator assembly (4) includes a liquid phase distributor (41), a baffle tube sheet (42), a liquid collection tank (43) and a downcomer (45) arranged sequentially from top to bottom in the phase separation zone. The equivalent diameter of the baffle plate (42) is DN6~DN50; when the equivalent diameter of the baffle plate (42) is DN6~DN20, it is sandblasted; when the equivalent diameter of the baffle plate (42) is DN20~DN50, it is filled with polypropylene PP wire mesh. After the phase change absorber absorbs carbon dioxide and separates into two phases, the upper liquid phase is the rich phase and the lower liquid phase is the poor phase, with a density difference of 0.03~0.05 g / cm³. 3 The viscosity difference is 7~15 mPas.

2. The carbon dioxide phase change absorbent absorption system according to claim 1, characterized in that, An overflow plate (44) is provided inside the liquid collection tank (43), and the top of the downcomer (45) is connected to the lower part of the side wall or the bottom of the liquid collection tank (43). Preferably, the top height of the downcomer (45) is 40-60% of the bottom liquid level of the absorber (2).

3. The carbon dioxide phase change absorbent absorption system according to claim 1, characterized in that, The absorption tower (2) is provided with a light phase outlet and a heavy phase outlet. The light phase outlet is connected to a light phase conveying pipe (7), and the heavy phase outlet is connected to a heavy phase conveying pipe (8). Preferably, the system further includes a heat exchanger (10), a pipe mixer (13), and a regenerated light phase delivery pipe (9). The heat exchanger (10) has a first flow channel and a second flow channel that are isolated from each other; the pipeline of the light phase conveying pipe (7) passes through the first flow channel of the heat exchanger (10); the pipeline of the regenerated light phase conveying pipe (9) passes through the second flow channel of the heat exchanger (10) and is connected to the inlet of the pipe mixer (11). The heavy phase delivery pipe (8) is connected to the inlet of the pipeline mixer (11); the outlet of the pipeline mixer (13) is connected to the absorbent delivery pipe (3).

4. A carbon dioxide phase change absorbent absorption process, characterized in that, The process is carried out using the system described in any one of claims 1-3, and includes the following steps: S1. A phase change absorbent absorbs carbon dioxide in an absorption tower; the phase change absorbent is composed of N-methyldiethanolamine, diethylenetriamine, sulfolane, and water; S2. The phase change absorbent undergoes liquid-liquid phase separation in the absorption tower. It flows through the tube sheet phase separator assembly by gravity, forming a light phase and a heavy phase at the bottom of the absorption tower, thus achieving liquid-liquid phase separation. S3. The light phase and the heavy phase flow out of the absorption tower separately; the light phase flows through the heat exchanger, exchanges heat with the regenerated light phase and is then sent to the regeneration unit; the regenerated light phase is cooled by the heat exchanger and then sent to the pipeline mixer; in the pipeline mixer, the regenerated light phase and the heavy phase are mixed and then enter the absorption tower for CO2 absorption. Preferably, the pipe mixer is an SV type static pipe mixer.

5. The carbon dioxide phase change absorbent absorption process according to claim 4, characterized in that, The phase change absorbent is composed of: 30-35 wt% N-methyldiethanolamine, 5-10 wt% diethylenetriamine, 40-50 wt% sulfolane, and 10-25 wt% water.

6. The carbon dioxide phase change absorbent absorption process according to claim 5, characterized in that, The phase change absorbent is composed of: 32 wt% N-methyldiethanolamine, 8 wt% diethylenetriamine, 40 wt% sulfolane and 20 wt% water.

7. The carbon dioxide phase change absorbent absorption process according to claim 4, characterized in that, The heavy phase content in the light phase at the bottom of the absorption tower is ≤2%. Preferably, the light phase at the bottom of the absorber is a CO2-enriched phase with a viscosity of 10-20 mPas and a density of 1.14-1.20 g / cm³. 3 .

8. The carbon dioxide phase change absorbent absorption process according to claim 4, characterized in that, The heavy phase at the bottom of the absorber is a CO2-lean liquid phase with a viscosity of 3–5 mPas and a density of 1.18–1.22 g / cm³. 3 .

9. The carbon dioxide phase change absorbent absorption process according to claim 4, characterized in that, The density difference between the heavy phase and the regenerated light phase is ≤0.1 g / cm³. 3 Viscosity difference ≤ 3 mPas.

Images