Carbon capture waste heat recycling system based on bilateral direct expansion heat exchange

Abstract

The invention relates to the technical field of carbon dioxide recovery, and discloses a carbon capture waste heat recycling system based on double-side direct expansion heat exchange, which comprises an absorption tower, a desorption tower and a high-temperature heat pump loop, a first heat exchange unit is arranged in the absorption tower, and the first heat exchange unit comprises a finned tube type heat exchanger and is used for recovering flue gas waste heat; a second heat exchange unit is arranged in the desorption tower, and the second heat exchange unit comprises a spraying type heat exchanger and is used for providing heat for pregnant solution desorption; a refrigerant channel of the high-temperature heat pump loop is sequentially connected with the first heat exchange unit and the second heat exchange unit, so that an energy utilization system for transferring flue gas waste heat to a desorption tower is formed, an energy flowing path in the carbon capture system is reconstructed, the core pain point of high energy consumption is solved from the source, and the energy utilization efficiency of the carbon capture system is improved. And multiple beneficial effects of energy conservation, efficiency improvement, cost reduction and simplification are achieved.

Description

Technical Field

[0001] This invention belongs to the field of flue gas carbon dioxide recovery technology, and particularly relates to a carbon capture waste heat recovery and utilization system based on double-sided direct expansion heat exchange. Background Technology

[0002] To achieve the goals of "carbon peaking" and "carbon neutrality," carbon dioxide capture, utilization, and storage (CVS) technologies have become indispensable key pathways. In my country's energy structure, coal-fired power plants are one of the main sources of carbon dioxide emissions, accounting for approximately 40% to 50% of the country's total emissions. Against this backdrop, implementing efficient and economical carbon capture technologies in power plants is of great significance. Currently, chemical absorption methods, represented by the amine method, are widely used due to their high technological maturity and stable capture efficiency. This technology achieves the absorption and separation of carbon dioxide through a reversible chemical reaction between an amine solution and carbon dioxide in flue gas.

[0003] While the amine process boasts high efficiency and maturity in carbon dioxide capture, it suffers from significant energy consumption bottlenecks. For example, the rich liquor after carbon dioxide absorption requires regeneration in a desorption tower through heating, a process typically consuming substantial amounts of thermal energy, usually supplied by an external steam system. This results in persistently high energy consumption for the carbon capture system, severely hindering its large-scale commercial application. However, researchers are exploring methods to reduce regeneration energy consumption and improve overall energy efficiency by modifying the amine solution formulation and introducing catalysts. Simultaneously, the flue gas at the front end of the carbon capture system contains a large amount of unutilized low-temperature waste heat, including sensible heat and considerable latent heat of condensation from water vapor.

[0004] In existing technologies, the recovery of such waste heat mostly adopts indirect heat exchange methods using circulating water as the intermediate working fluid. This technical approach has inherent drawbacks: First, due to the addition of an intermediate heat exchange link, there is heat transfer temperature difference loss, resulting in low overall heat exchange efficiency; second, the system requires additional heat exchangers, water pumps, and water tanks, making the system complex, requiring a large area, and incurring high initial investment; third, acidic components and dust in the flue gas can easily cause corrosion and ash accumulation in the heat exchange equipment, affecting the long-term stability and energy efficiency of the system.

[0005] Therefore, there is an urgent need to develop a new system that can directly and efficiently recover waste heat from flue gas and apply this heat directly to the desorption and regeneration process. This direct recovery technology can overcome the limitations of traditional indirect heat exchange, significantly reduce energy consumption in the carbon capture process, and thus promote the large-scale application of carbon capture technology. Summary of the Invention

[0006] In view of the above-mentioned problems of the existing technology, the present invention solves the problem of how to efficiently recover the waste heat of flue gas generated in the carbon capture process and directly use it for the desorption process, so as to significantly reduce the overall energy consumption of the carbon capture system, while overcoming the problems of large heat exchange temperature difference, low efficiency and system complexity of the existing indirect heat exchange technology.

[0007] This invention provides a carbon capture waste heat recovery and utilization system based on double-sided direct expansion heat exchange, comprising: an absorption tower, a desorption tower, and a high-temperature heat pump circuit; the absorption tower is provided with a first heat exchange unit, which includes a finned tube heat exchanger for recovering waste heat from flue gas; the desorption tower is provided with a second heat exchange unit, which includes a spray heat exchanger for providing heat for rich liquid desorption; the refrigerant channel of the high-temperature heat pump circuit is sequentially connected to the first heat exchange unit and the second heat exchange unit, constituting an energy utilization system that transfers waste heat from flue gas to the desorption tower.

[0008] Optionally, the fins of the finned tube heat exchanger in the first heat exchange unit are spirally wound onto the heat exchange tubes, and the finned heat exchange tubes are arranged in a tube-and-shell configuration. This increases the residence time of the refrigerant in the heat exchange tubes, ensuring sufficient heat exchange with the flue gas.

[0009] Optionally, the fins of the finned tube heat exchanger have an open structure to enhance heat transfer performance and also have the functions of guiding flow and preventing dust accumulation.

[0010] Optionally, the spray heat exchanger of the second heat exchange unit includes a rich liquid spray device and a heat exchange tube bundle through which the refrigerant flows. The rich liquid spray device sprays rich liquid onto the outer surface of the heat exchange tube bundle to reduce the thermal resistance of the liquid boundary layer and enhance heat transfer.

[0011] Optionally, the high-temperature heat pump circuit includes a compressor, a refrigerant channel of the second heat exchange unit, a first throttling device, and a refrigerant channel of the first heat exchange unit connected in sequence through pipelines, forming a thermodynamic cycle that elevates a low-temperature heat source to a high-temperature heat source.

[0012] Optionally, the high-temperature heat pump circuit includes an economizer and a make-up gas circuit. The economizer is connected in series in the pipeline between the refrigerant outlet of the second heat exchange unit and the first throttling device. The make-up gas circuit, through the second throttling device, has its inlet connected to the main refrigerant pipeline before the economizer, and its outlet connected to the make-up gas channel inlet of the economizer. The outlet of this make-up gas channel is connected to the intermediate make-up gas port of the compressor. Experimental studies show that the application of make-up gas technology can effectively increase the heating capacity of the high-temperature heat pump and improve its heating performance.

[0013] Optionally, in a high-temperature heat pump system, an integrated optimization strategy, including the installation of a high-efficiency unit located on the pipeline between the refrigerant outlet and the compressor inlet of the first heat exchange unit, is adopted to achieve efficient energy utilization, thereby significantly improving the overall performance of the system.

[0014] Optionally, it also includes a lean-rich liquid heat exchanger, whose hot-side inlet is connected to the lean liquid outlet of the desorption tower, its hot-side outlet is connected to the lean liquid inlet of the absorption tower, its cold-side inlet is connected to the rich liquid outlet of the absorption tower, and its cold-side outlet is connected to the rich liquid inlet of the desorption tower, for recovering the heat of the lean liquid and reducing the system energy consumption.

[0015] Optionally, the absorption tower shell is further provided with an interstage cooler, the cooling channel of which runs through the shell of the absorption tower and is located in the middle of the shell, in order to improve the absorption capacity of the absorption tower.

[0016] Optionally, the heat exchange tubes in the second heat exchange unit are fixed by a support plate to ensure the structural stability of the heat exchange tube bundle.

[0017] This disclosure provides a carbon capture and waste heat recovery system based on double-sided direct expansion heat exchange, the advantages of which are: The waste heat recovery and utilization system disclosed herein constructs a brand-new energy internal circulation mode through the synergy of "double-sided direct expansion heat exchange" and "high-temperature heat pump cycle", thereby achieving a fundamental reduction in the energy consumption of the carbon capture system.

[0018] Its working principle is as follows: Inside the absorption tower, the system uses a first heat exchange unit to directly exchange heat between the low-temperature refrigerant and the flue gas, efficiently recovering low-grade waste heat from the flue gas. Subsequently, the high-temperature heat pump circuit, acting as the energy enhancement hub of the entire system, enhances the quality of the recovered low-temperature heat energy. Finally, in the second heat exchange unit inside the desorption tower, the enhanced high-temperature heat energy is directly transferred to the rich liquid to drive the carbon dioxide desorption process.

[0019] Based on the core architecture of a "high-temperature heat pump loop" connecting the heat exchange units on both sides, active matching of energy quality is achieved, reducing system energy consumption. The essence of this solution is to treat the previously discarded low-temperature flue gas waste heat as a resource, and through the high-temperature heat pump loop as the core energy hub, precisely enhance its quality and apply it to the desorption stage, which has the highest energy consumption within the system. By adopting heat pump technology, we have changed the past linear energy consumption model where the desorption process relied entirely on external fresh steam, constructing an internal energy closed loop that "recovers, enhances, and reuses" waste heat, thereby significantly reducing the consumption of external energy and operating costs.

[0020] By eliminating intermediate heat exchange stages, energy utilization efficiency is fundamentally improved. Traditional technologies use circulating water or other media for indirect heat exchange, resulting in heat transfer losses due to multiple heat exchange processes and temperature differences. This invention eliminates intermediate media by employing a refrigerant for direct phase change heat exchange, thereby significantly improving the efficiency of energy recovery and utilization. Compared to traditional technologies, this design reduces heat transfer stages and irreversible losses, ensuring that the heat recovered from the flue gas can be transferred to the desorption tower more efficiently and directly, thus achieving a significant improvement in the overall thermal utilization efficiency of the system.

[0021] This has promoted the integration and simplification of the system architecture. The technical solution integrates equipment functions, providing natural architectural support for "integrating flue gas heat recovery and carbon dioxide absorption processes into one unit." This integrated design reduces the number of devices, floor space, and initial investment, simplifies connection piping and control logic, and lowers system complexity and operation and maintenance costs.

[0022] In summary, the core architecture defined in this disclosure, consisting of "the first heat exchange unit of the absorption tower + the second heat exchange unit of the desorption tower + the high-temperature heat pump loop," reconstructs the energy flow path in the carbon capture system, fundamentally solving the core pain point of high energy consumption and generating multiple beneficial effects such as energy saving, efficiency improvement, cost reduction, and simplification.

[0023] It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative only, and are not intended to limit the invention.

[0024] The overview of various implementations or examples of the technology described in this invention is not a complete disclosure of the full scope or all features of the disclosed technology. Attached Figure Description

[0025] In drawings that are not necessarily drawn to scale, the same reference numerals may describe similar parts in different views. The same reference numerals with or without letter suffixes may indicate different instances of similar parts. The drawings generally illustrate various embodiments by way of example rather than limitation and, together with the description and claims, serve to explain embodiments of the invention. Where appropriate, the same reference numerals are used in all drawings to refer to the same or similar parts. Such embodiments are illustrative and not intended to be exhaustive or exclusive embodiments of the apparatus or method.

[0026] Figure 1 This is a schematic diagram of a carbon capture and waste heat recovery system based on double-sided direct expansion heat exchange according to the present invention. Figure 2 This is a schematic diagram of a first heat exchange unit according to the present invention; Figure 3 This is a schematic diagram of another first heat exchange unit of the present invention; Figure 4 This is a schematic diagram of another first heat exchange unit of the present invention; Figure 5 This is a schematic diagram of another first heat exchange unit of the present invention; Figure 6 This is a schematic diagram of a second heat exchange unit according to the present invention; Figure 7 This is a schematic diagram of another second heat exchange unit according to the present invention.

[0027] Figure label: 1. Exhaust fan; 2. Absorption tower; 21. Refrigerant inlet; 22. Finned heat exchange tube; 221. First heat exchange tube; 222. Fin; 223. Fin opening; 23. Refrigerant separator; 3. Rich liquid pump; 4. Lean and rich liquid heat exchanger; 5. Desorption tower; 51. Rich liquid spray pipe main; 52. Spray head; 53. Second heat exchange tube; 54. Heat exchange tube support plate; 6. Gas-liquid separator; 7. Lean liquid pump; 8. Lean liquid cooler; 9. Interstage cooler; 10. Tail gas scrubbing pump; 11. Scrubber cooler; 12. High-efficiency unit; 13. Compressor; 14. Economizer; 15. First expansion valve; 16. Second expansion valve; 17. First heat exchange unit; 18. Second heat exchange unit. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0030] To keep the following description of the embodiments of the present invention clear and concise, detailed descriptions of known functions and known components are omitted.

[0031] Combination Figure 1 As shown, the present invention provides a carbon capture waste heat recovery and utilization system based on double-sided direct expansion heat exchange, comprising: an absorption tower 2, a desorption tower 5, and a high-temperature heat pump circuit; the absorption tower 2 is provided with a first heat exchange unit 17, which adopts a finned tube heat exchanger to recover waste heat from flue gas; the desorption tower 5 is provided with a second heat exchange unit 18, which adopts a spray heat exchanger to provide heat for rich liquid desorption; the refrigerant channel of the high-temperature heat pump circuit is sequentially connected to the first heat exchange unit 17 and the second heat exchange unit 18, constituting an energy utilization system that directionally transfers waste heat from flue gas to the desorption tower 5.

[0032] It should be noted that the high-temperature heat pump circuit described in this application implicitly includes "core components necessary for achieving heat circulation and quality improvement". Whether it is a single-stage compression system or a composite compression system with an economizer 14 and an intermediate air inlet, as long as it can form a pumping circuit for heat from the absorption side to the desorption side, it falls within the scope of the high-temperature heat pump circuit defined by this invention.

[0033] This system employs a dual-sided direct expansion heat exchange design, allowing the refrigerant to absorb waste heat from the flue gas in the first heat exchange unit 17 and then directly release heat into the second heat exchange unit 18, significantly improving heat transfer efficiency. Finned tube heat exchangers enhance heat transfer performance on the flue gas side, while spray heat exchangers improve the uniformity of heating of the rich liquid within the desorption tower 5. The high-temperature heat pump circuit operates stably, enabling the cascade utilization of energy in the carbon capture process without additional high-grade energy consumption, thus reducing overall energy consumption. This structure simplifies the traditional heat exchange process, reduces intermediate heat exchange losses, and provides a highly efficient and energy-saving technological path for industrial flue gas carbon capture. By optimizing the matching relationship between refrigerant flow rate and heat exchange area, the system can maintain efficient operation under varying conditions; and by dynamically adjusting the compressor 13 frequency and circulating working fluid charge based on the flue gas temperature fluctuation characteristics, the stability of waste heat recovery is further improved.

[0034] As a preferred embodiment, the spray-type heat exchanger adopts a multi-stage liquid distribution structure to ensure that the rich liquid fully contacts the heat transfer surface within the tower to enhance desorption efficiency. This design is suitable for high-emission scenarios such as coal-fired power plants and steel kilns, and has broad application value under the background of carbon peaking targets. During system operation, flue gas enters from the bottom of the absorption tower 2 and comes into countercurrent contact with the lean liquid flowing from top to bottom to complete carbon dioxide absorption; the absorbed rich liquid is discharged from the bottom of the tower and sent to the desorption tower 5 by the rich liquid pump 3, where it efficiently transfers heat in the spray-type structure of the second heat exchange unit 18, promoting the release of carbon dioxide.

[0035] The released lean liquid is cooled and returned to absorber 2 for recycling, while the desorbed high-concentration carbon dioxide is sent to the downstream storage or resource utilization. The system monitors flue gas flow and temperature changes in real time and automatically adjusts the operating parameters of the heat pump loop to ensure dynamic matching of energy supply and demand. Under typical operating conditions, it significantly improves the economics of carbon capture.

[0036] Optionally, the fins of the finned tube heat exchanger of the first heat exchange unit 17 are spirally wound on the heat exchange tubes, and the finned heat exchange tubes are arranged in a tube-and-shell manner, which can increase the residence time of the refrigerant in the heat exchange tubes and ensure sufficient heat exchange with the flue gas.

[0037] Understandably, the spiral-wound finned tube arrangement can effectively alleviate the problem of ash accumulation on the flue gas side and improve long-term operational stability. By rationally designing the tube spacing and fin density, an optimal balance can be achieved between pressure drop and heat exchange efficiency. This structure is particularly suitable for low-temperature, high-humidity flue gas environments, avoiding condensation corrosion caused by excessively low local temperatures; the use of corrosion-resistant alloy tubing can further extend equipment life. In actual deployment, the system can be modularly configured according to the characteristics of different emission sources, improving adaptability and scalability.

[0038] Optionally, the fins 222 of the finned tube heat exchanger adopt an open design, which creates a turbulent flow state by breaking the heat transfer boundary layer between the fluid in the flow channel and the wall, thereby improving the heat transfer capacity and also having the functions of guiding flow and preventing dust accumulation.

[0039] Understandably, the perforated structure effectively disrupts boundary layer development, improves the heat transfer coefficient on the flue gas side, and guides accumulated ash out with the airflow to reduce the risk of blockage. Under high dust concentration conditions, this design can reduce maintenance frequency and operating resistance. After optimizing the perforation size and distribution density through numerical simulation, a balance can be achieved between flow uniformity and structural strength.

[0040] Optionally, the spray heat exchanger of the second heat exchange unit 18 includes a rich liquid spray device and a heat exchange tube bundle. The rich liquid spray device sprays rich liquid onto the outer surface of the heat exchange tube bundle, thereby reducing boundary layer thermal resistance and enhancing heat transfer by forming a dynamically renewed liquid film.

[0041] It should be noted that the spray design, by uniformly covering the outer surface of the heat exchange tube bundle with a liquid film, forms a continuously renewing heat transfer interface, which can effectively reduce liquid-side thermal resistance and improve overall heat exchange efficiency. The liquid film is constantly replaced under the influence of gravity and airflow disturbance, suppressing local overheating or dry-wall phenomena and ensuring a stable and efficient desorption process. The spray density and flow rate can be dynamically adjusted according to the load to optimize energy consumption matching. This structure also has self-cleaning properties to reduce the risk of scaling. Combined with an intelligent control system, the coordinated regulation of temperature, flow rate, and spray pressure ensures efficient system operation under varying conditions. Actual operating data shows that this spray structure can maintain a uniform liquid film distribution even under high load conditions, making it particularly suitable for high-boiling-point, high-viscosity rich liquid systems.

[0042] Optionally, the high-temperature heat pump circuit includes a compressor 13, a refrigerant passage of a second heat exchange unit 18, a first throttling device, and a refrigerant passage of a first heat exchange unit 17 connected in sequence through pipelines, forming a closed thermodynamic cycle that elevates a low-temperature heat source to a high-temperature heat source.

[0043] Understandably, the high-temperature heat pump circuit uses compressor 13 to drive the refrigerant to circulate in a closed-loop system, achieving a reverse heat transfer from low-temperature flue gas to the high-temperature desorption process. After absorbing waste heat from the flue gas in the first heat exchange unit 17, the refrigerant undergoes a phase change and evaporates. It is then pressurized and heated by compressor 13, releasing high-temperature heat to the rich liquid in the second heat exchange unit 18 to drive CO2 desorption. Subsequently, it is depressurized and cooled by the first throttling device to complete the cycle. This system utilizes low-grade waste heat, significantly reducing external energy consumption. Through variable frequency control of compressor 13 and multi-stage spray control, it can adapt to fluctuations in flue gas flow and temperature, ensuring efficient and stable operation of the heat pump.

[0044] Optionally, the high-temperature heat pump circuit further includes an economizer 14 and a gas replenishment circuit; the economizer 14 is connected in series in the pipeline between the refrigerant outlet of the second heat exchange unit 18 and the first throttling device; the gas replenishment circuit includes a second throttling device, whose inlet is connected to the main refrigerant pipeline before the economizer 14, and whose outlet is connected to the gas replenishment channel inlet of the economizer 14. The gas replenishment channel outlet is connected to the intermediate gas replenishment port of the compressor 13 to broaden the operating temperature range of the heat pump and improve the system performance coefficient.

[0045] Understandably, the economizer 14 achieves superheating through internal heat exchange of the working fluid, increasing the refrigerant circulation volume and the system's heating capacity. The supplementary gas circuit introduces a portion of the high-pressure refrigerant into the intermediate stage of compressor 13 after throttling, enhancing the isentropic efficiency of the compression process and improving the system's operational stability under large temperature difference conditions. This design significantly improves the adaptability of the high-temperature heat pump under variable load conditions, especially suitable for scenarios with large fluctuations in flue gas waste heat. By implementing a real-time optimized control strategy, the system can automatically adjust the supplementary gas pressure and spray coordination parameters according to different environmental and load conditions, ensuring that the heat pump's COP (coefficient of performance) remains within the high-efficiency range, thereby significantly improving the efficiency of waste heat recovery. In practical applications, this high-temperature heat pump system combines a flue gas temperature prediction model with a feedforward control algorithm to dynamically adjust the compressor 13 frequency, spray density, and supplementary gas flow rate, achieving precise matching of energy supply and demand. By integrating an intelligent sensor network and edge computing module, the system possesses self-diagnostic and adaptive capabilities, effectively responding to operating condition disturbances and extending equipment lifespan. Under typical operating conditions, the system dynamically optimizes compressor speed and spray liquid distribution by real-time monitoring of flue gas temperature, flow rate, and lean refrigerant regeneration requirements, based on advanced control algorithms and sensor technology, ensuring that the heat pump always operates in its high-efficiency range. Combining historical data and machine learning algorithms, the control system can predict load change trends and adjust the timing of the gas injection circuit activation and throttling opening in advance, reducing energy waste. Simultaneously, the economizer 14 and the gas injection circuit work together to maintain high refrigerant circulation efficiency even under large temperature differences, effectively preventing a sudden drop in compressor 13's energy efficiency.

[0046] Optionally, the high-temperature heat pump circuit further includes a high-efficiency unit 12, which is installed on the pipeline between the refrigerant outlet of the first heat exchange unit 17 and the inlet of the compressor 13, for optimizing energy utilization and improving system performance.

[0047] Understandably, the high-efficiency unit 12 recovers the low-temperature heat energy of the refrigerant before throttling, further enhancing the refrigerant superheat, improving the operating conditions of the compressor 13, and reducing power consumption. Its synergistic effect with the economizer 14 and the gas injection circuit forms a multi-stage energy recovery mechanism, significantly improving system stability and energy efficiency under high-temperature heating conditions. Combined with intelligent control strategies, the high-efficiency unit 12 can dynamically adjust the heat exchange intensity based on real-time operating parameters, ensuring the system maintains optimal performance under varying operating conditions. In scenarios involving deep waste heat recovery from flue gas, the high-efficiency unit 12 reduces fluctuations in refrigerant superheat at the compressor 13 inlet by enhancing the refrigerant preheating process. Simultaneously, the high-efficiency unit 12, in synergistic regulation with the spray-type heat exchanger, reduces the heat exchange differential and improves system response speed. Under conditions of frequent start-stop cycles and large heat source fluctuations, it enhances the operational stability of the compressor 13.

[0048] Optionally, it also includes a lean-rich liquid heat exchanger 4, whose hot-side inlet is connected to the lean liquid outlet of the desorption tower 5 and the hot-side outlet is connected to the lean liquid inlet of the absorption tower 2; the cold-side inlet is connected to the rich liquid outlet of the absorption tower 2 and the cold-side outlet is connected to the rich liquid inlet of the desorption tower 5, for recovering the heat of the lean liquid to reduce the system energy consumption.

[0049] Understandably, the lean-rich liquid heat exchanger 4 effectively recovers the waste heat from the lean liquid discharged from the desorption tower 5, reducing the external heat energy input required for the desorption process. This heat exchange mechanism not only improves the thermal efficiency of solution circulation but also mitigates the impact of load fluctuations in the regeneration heat source. Combined with the system's intelligent control strategy, the flow distribution can be dynamically adjusted according to the temperature difference between the lean and rich liquids, optimizing heat exchange matching. Simultaneously, the introduction of the lean-rich liquid heat exchanger 4 effectively balances the heat distribution during absorption and desorption. Furthermore, combined with real-time monitoring and adaptive control, load changes can be dynamically matched, reducing system heat loss.

[0050] Optionally, the absorption tower 2 shell is also provided with an interstage cooler 9, the cooling channel of which runs through the absorption tower 2 shell and is located in the middle of the shell, in order to improve the absorption capacity of the absorption tower 2.

[0051] It is understood that the interstage cooler 9 disclosed in this invention effectively reduces the temperature rise of the solution during absorption by introducing low-temperature cooling energy in the middle of the absorption tower 2, thereby reducing the accumulation of thermal resistance and improving the absorption efficiency of the absorbent for refrigerant vapor, alleviating the problem of absorption capacity attenuation caused by temperature rise. Under high-load conditions, it also reduces irreversible losses in the absorption process. The interstage cooler 9 is deeply coupled with the solution circulation path to achieve segmented temperature-controlled absorption, effectively avoiding solution performance degradation caused by localized overheating.

[0052] Optionally, the heat exchange tubes in the second heat exchange unit 18 are supported and fixed by the heat exchange tube support plate 54 to ensure the structural stability of the heat exchange tube bundle.

[0053] Understandably, the heat exchanger tube support plate 54 is made of corrosion-resistant alloy material, possessing excellent creep and fatigue resistance, enabling long-term stable operation in high-temperature and high-humidity environments. The support plate structure is optimized for fluid dynamics, effectively reducing solution flow resistance while preventing tube bundle vibration and wear caused by turbulent impact. The spacing between the support plates is precisely calculated based on the heat exchanger tube diameter and flow length, ensuring free expansion and contraction of the heat exchanger tubes under thermal expansion and contraction conditions, avoiding weld cracking or support failure due to stress concentration. Its modular layout facilitates on-site installation and subsequent maintenance, significantly improving the overall reliability and operability of the heat exchanger. The support plate surface is equipped with an anti-corrosion coating and flow guide grooves, further enhancing corrosion resistance and heat exchange uniformity.

[0054] In summary, this disclosure employs high-temperature heat pump technology for waste heat recovery and utilization. Within the heat exchange unit of absorption tower 2, the high-temperature heat pump refrigerant exchanges heat with the flue gas, effectively recovering the sensible heat and water vapor condensation heat from the flue gas. This recovered waste heat serves as the low-temperature heat source for the high-temperature heat pump unit, and through the energy boosting of the heat pump, the temperature of the refrigerant is increased. Subsequently, within the heat exchange unit of desorption tower 5, the rich liquid is heated, providing the necessary high-temperature heat source for carbon dioxide desorption. This process not only improves energy utilization efficiency but also significantly reduces energy consumption. For example, a certain thermal power plant, through the application of heat pump condensation heat recovery technology, saves 90 million kilowatt-hours of energy annually and reduces carbon dioxide emissions by 22,000 tons, demonstrating significant social and economic benefits.

[0055] As an example, such as Figure 1 As shown, the flue gas heat recovery tower and absorption tower 2 are combined into one unit, employing a double-sided direct expansion heat exchange process. On the flue gas waste heat recovery side, a spiral wound tube finned heat exchange technology is used. Flue gas flows from bottom to top through horizontally arranged heat exchange tubes via induced draft fan 1. The low-temperature refrigerant undergoes sufficient heat exchange with the flue gas on the tube side, changing from a liquid to a gaseous state. On the carbon dioxide desorption side, a double-sided phase change spray heat exchange technology is used. The rich liquid flows from top to bottom through the heat exchange tubes via spraying. The high-temperature refrigerant directly exchanges heat with the rich liquid on the tube side, then cools and condenses. The carbon dioxide in the rich liquid absorbs heat and desorbs. No intermediate heat exchange medium is added on either the energy recovery side or the demand side, thereby effectively improving heat exchange efficiency.

[0056] In flue gas heat recovery towers, heat is recovered through direct heat exchange between flue gas and refrigerant. Due to the large flow rate of flue gas and the presence of both sensible and latent heat, sufficient heat exchange between the flue gas and refrigerant is crucial to ensure effective heat recovery. Studies of the flow and heat transfer characteristics of flue gas heat exchangers show that heat exchange efficiency can be optimized and energy consumption reduced through simulation and data analysis. Furthermore, analysis of the refrigerant's heat transfer performance under low-temperature conditions indicates that factors such as refrigerant type, flow rate, and physical properties significantly affect heat exchange efficiency. Simultaneously, water vapor in the flue gas condenses into liquid water after releasing latent heat, and the flue gas inevitably contains slight solid impurities. This necessitates that the heat exchange structure possess high heat exchange efficiency, good hydrophobicity, and strong anti-ash accumulation capabilities. This solution employs spiral wound tube finned heat exchange technology. Compared to traditional heat exchangers commonly used for air-refrigerant heat exchange, under the same heat exchange load, it effectively increases the residence time of the refrigerant in the heat exchange tubes, ensuring sufficient heat exchange between the refrigerant and flue gas. Fin 222 features an open-pore design, allowing for continuous airflow and frequent secondary flow, which disrupts the development of the thermal and flow boundary layers, thereby enhancing heat transfer performance. Furthermore, the open-pore fin 222 also improves fluid throughput, reduces flow pressure drop, and serves both as a flow guide and prevents dust accumulation.

[0057] The fins 222 are treated with an anti-corrosion and hydrophobic coating to effectively prevent condensate film buildup and enhance hydrophobic flow capacity. The flue gas side heat exchange surface is arranged at an angle, utilizing gravity to achieve ash self-cleaning and reduce the risk of ash accumulation and blockage. The entire heat exchange module can be disassembled and maintained online, ensuring long-term operational stability. After absorbing heat and vaporizing in the absorption tower 2, the refrigerant enters the high-temperature heat pump compressor 13, where it is compressed into a high-temperature, high-pressure gaseous state. It then enters the heat exchange unit in the desorption tower 5 as a heat source to release heat, enabling efficient desorption of carbon dioxide from the rich liquid. The condensed liquid refrigerant is depressurized and cooled by a throttling device before re-entering the flue gas heat recovery tower to absorb waste heat, completing the cycle. The system utilizes a complete direct expansion heat exchange path for the heat medium to achieve synergistic optimization of deep recovery of flue gas waste heat and carbon dioxide desorption energy consumption, significantly improving overall energy efficiency.

[0058] As another example, a workflow for a carbon capture waste heat recovery and utilization system based on a high-temperature steam heat pump is provided.

[0059] Flue gas system flow: The desulfurized flue gas is conveyed to the absorption tower 2 by the induced draft fan 1, where it exchanges heat with a low-temperature refrigerant in the heat exchange unit of the absorption tower 2 to achieve cooling. The water vapor content in the cooled flue gas is significantly reduced, releasing a large amount of latent heat of vaporization. The refrigerant absorbs the sensible heat of the flue gas and the latent heat of vaporization of the water vapor. Simultaneously, the absorption tower 2 uses a novel absorbent to absorb carbon dioxide from the flue gas. To improve absorption efficiency, an interstage cooling process is implemented, using an interstage cooler 9 to cool the absorbent liquid in the middle of the absorption tower 2. The decarbonized tail gas is discharged after washing, and the tail gas washing liquid is circulated through the tail gas washing pump 10 and cooled by the washing liquid cooler 11.

[0060] Rich liquid system process: After absorbing carbon dioxide in absorption tower 2, the absorbent is transformed into rich liquid. It is then pumped out by rich liquid pump 3 and divided into two paths: one path directly enters desorption tower 5 for desorption; the other path passes through lean-rich liquid heat exchanger 4 to exchange heat with lean liquid before entering desorption tower 5. In the heat exchange unit of desorption tower 5, the rich liquid is sprayed onto the surface of the heat exchange tubes, exchanging heat with the high-temperature refrigerant. After heating, carbon dioxide is desorbed, and the desorbed rich liquid becomes lean liquid, flowing out from the bottom of desorption tower 5.

[0061] Lean liquor system process: The lean liquor flowing out from the bottom of the desorption tower 5 releases heat to the rich liquor through the lean-rich liquor heat exchanger 4, and then enters the absorption tower 2 to absorb carbon dioxide in the flue gas again, transforming into rich liquor and flowing out from the bottom of the absorption tower 2.

[0062] Carbon dioxide capture process: The carbon dioxide desorbed in desorption tower 5, along with water vapor, is discharged from the top of the tower. After separation and cooling by gas-liquid separator 6, moisture is removed, resulting in carbon dioxide product gas with a purity exceeding 99.5%, meeting industrial-grade standards. Subsequently, this product gas enters subsequent stages such as compression for further processing and purification to meet more stringent application requirements, such as food-grade applications.

[0063] Refrigerant Flow: The refrigerant of the high-temperature heat pump absorbs heat from the flue gas in the heat exchange unit of absorption tower 2, evaporates into a low-pressure gaseous state, enters the high-efficiency unit 12 to exchange heat with the high-pressure refrigerant, and after further superheating, enters the compressor 13. After compression and enthalpy increase, it becomes a high-temperature, high-pressure gas, releases heat in the heat exchange unit of desorption tower 5, heats the rich liquid, and provides energy for carbon dioxide desorption. The refrigerant after releasing heat enters the economizer 14 to exchange heat with the refrigerant in the make-up gas loop. The refrigerant after heat exchange is divided into two paths: the main path refrigerant enters the high-efficiency unit 12 to release heat, and then enters the absorption tower 2 after throttling and depressurization through the second expansion valve 16, completing the cycle; the refrigerant in the make-up gas loop enters the economizer 14 to absorb heat after throttling and depressurization through the first expansion valve 15, becomes superheated vapor, and then enters the compressor 13. Adding a make-up gas loop to the system can effectively widen the operating temperature range of the heat pump, and adding a high-efficiency unit 12 can achieve optimized energy utilization and improve system performance.

[0064] As another example, the arrangement and structure of the finned tubes in the heat exchange unit of absorption tower 2 are as follows: Figure 2 As shown, the low-temperature refrigerant enters the refrigerant distribution device 23 through the refrigerant inlet 21 and flows evenly into each finned heat exchange tube to exchange heat with the flue gas. The flue gas flows through the outside of the finned tubes, exchanging heat with the outer wall of the heat exchange tubes and the fins 222. The flue gas flow direction is perpendicular to the refrigerant flow direction. The finned tubes are arranged in an equilateral triangle, and the fins 222 are spirally welded to the heat exchange tubes, with circular holes on the fins 222. The circular holes effectively disrupt the development of the boundary layer on the surface of the fins 222, enhance the turbulence on the flue gas side, and significantly improve the heat transfer efficiency. After the refrigerant completes evaporation and heat absorption in the finned heat exchange tubes, it is collected by the refrigerant collection device and flows out from the refrigerant outlet, returning to the high-temperature heat pump system. This structural design takes into account both heat transfer enhancement and pressure drop control, ensuring that a suitable temperature gradient is maintained in the absorption tower 2, creating favorable conditions for the efficient absorption of carbon dioxide. At the same time, the equilateral triangle arrangement of the finned tubes effectively optimizes the flow path of the flue gas, reduces flow resistance, avoids the formation of local dead zones, and further improves the heat exchange uniformity. The spiral-welded fins 222, combined with the circular hole structure, enhance mechanical strength while promoting airflow turbulence and strengthening convective heat transfer. This design, in conjunction with the high-efficiency unit 12 and the make-up gas circuit, enables the heat pump system to maintain a high energy efficiency ratio under varying operating conditions, significantly reducing regeneration energy consumption and providing key technical support for the energy-saving operation of carbon capture systems.

[0065] This solution employs spiral-wound finned heat exchange technology. Compared to traditional heat exchangers commonly used for air-refrigerant heat exchange, this technology effectively extends the residence time of the refrigerant in the heat exchange tubes under the same heat exchange load, ensuring sufficient heat exchange between the refrigerant and flue gas. The perforated structure of fin 222 not only enhances heat transfer performance but also serves as a flow guide and prevents ash accumulation. Flue gas flows vertically through the finned heat exchange tubes, resulting in a more rational flue gas flow field distribution and allowing for full contact and heat exchange with the finned tubes, thereby effectively improving heat exchange efficiency.

[0066] As another example, in the heat exchange unit 5 of the desorption tower, the arrangement and structure of the heat exchange tubes and spray tubes are as follows: Figure 3 As shown, the rich liquid first enters the rich liquid spray pipe main 51, and then is evenly sprayed onto the surface of the heat exchange tubes through the nozzles 52, where it exchanges heat with the high-temperature refrigerant inside the heat exchange tubes. During this process, the rich liquid absorbs heat, and carbon dioxide is desorbed, thus transforming into a lean liquid. Simultaneously, the high-temperature gaseous refrigerant inside the heat exchange tubes condenses into a low-temperature liquid state after releasing heat. The heat exchange tubes are arranged in an equilateral triangle pattern, while the heat exchange tube support plate 54 plays a crucial supporting role.

[0067] When the rich liquid is sprayed onto the surface of the heat exchange tube, it contacts the surface in the form of small droplets or thin films. This not only significantly increases the contact area but also accelerates the surface renewal rate, effectively reducing the thermal resistance of the liquid boundary layer in traditional immersion heat exchange. In addition, the disturbance effect generated when the droplets impact the tube wall further improves the heat transfer efficiency between the inside and outside of the tube.

[0068] The foregoing description and accompanying drawings fully illustrate embodiments of the present disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included or substituted for parts and features of other embodiments. Embodiments of the present disclosure are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A carbon capture and waste heat recovery system based on double-sided direct expansion heat exchange, characterized in that, include: Absorption tower (2), desorption tower (5) and high-temperature heat pump circuit; The absorption tower (2) is provided with a first heat exchange unit (17), which includes a finned tube heat exchanger for recovering waste heat from flue gas. The desorption tower (5) is provided with a second heat exchange unit (18), which includes a spray heat exchanger for providing heat for the desorption of rich liquid. The refrigerant channel of the high-temperature heat pump circuit is sequentially connected to the first heat exchange unit (17) and the second heat exchange unit (18), forming an energy utilization system that transfers the waste heat of flue gas to the desorption tower.

2. The carbon capture and waste heat recovery system according to claim 1, characterized in that, The fins of the finned tube heat exchanger of the first heat exchange unit (17) are spirally wound on the heat exchange tube, and the finned heat exchange tube is arranged in a tube-and-shell manner.

3. The carbon capture and waste heat recovery system according to claim 2, characterized in that, The fins (222) of the finned tube heat exchanger have an open structure.

4. The carbon capture and waste heat recovery system according to claim 1, characterized in that, The second heat exchange unit (18) includes a rich liquid spray device and a heat exchange tube bundle through which the refrigerant flows. The rich liquid spray device sprays rich liquid onto the outer surface of the heat exchange tube bundle to reduce the thermal resistance of the liquid boundary layer and enhance heat transfer.

5. The carbon capture and waste heat recovery system according to claim 1, characterized in that, The high-temperature heat pump circuit includes a compressor (13), a refrigerant passage of the second heat exchange unit (18), a first throttling device, and a refrigerant passage of the first heat exchange unit (17) connected in sequence through pipelines, forming a thermodynamic cycle that elevates a low-temperature heat source to a high-temperature heat source.

6. The carbon capture and waste heat recovery system according to claim 5, characterized in that, The high-temperature heat pump circuit also includes an economizer (14) and a gas supply circuit; The economizer (14) is connected in series on the pipeline between the refrigerant outlet of the second heat exchange unit (18) and the first throttling device; The gas replenishment circuit includes a second throttling device (15), whose inlet is connected to the main refrigerant pipeline before the economizer (14), and whose outlet is connected to the gas replenishment channel inlet of the economizer (14). The gas replenishment channel outlet is connected to the intermediate gas replenishment port of the compressor (13) to broaden the operating temperature range of the heat pump and improve system performance.

7. The carbon capture and waste heat recovery system according to claim 6, characterized in that, The high-temperature heat pump circuit also includes a high-efficiency unit (12), which is installed on the pipeline between the refrigerant outlet of the first heat exchange unit (17) and the inlet of the compressor (13).

8. The carbon capture and waste heat recovery system according to claim 1, characterized in that, It also includes a lean-rich liquid heat exchanger (4), whose hot-side inlet is connected to the lean liquid outlet of the desorption tower (5), the hot-side outlet is connected to the lean liquid inlet of the absorption tower (2), the cold-side inlet is connected to the rich liquid outlet of the absorption tower (2), and the cold-side outlet is connected to the rich liquid inlet of the desorption tower (5), for recovering the heat of the lean liquid.

9. The carbon capture and waste heat recovery system according to claim 1, characterized in that, An interstage cooler (9) is also provided on the shell of the absorption tower (2). The cooling channel of the interstage cooler (9) runs through the shell of the absorption tower (2) and is located in the middle of the shell, which is used to improve the absorption capacity of the absorption tower.

10. The carbon capture and waste heat recovery system according to claim 4, characterized in that, The heat exchange tubes in the second heat exchange unit (18) are supported and fixed by the heat exchange tube support plate (54).

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